An integrated analysis of an orogen–sedimentary basin pair

ABSTRACT

The integration of restored basin geome-try and internal features of syntectonic units (e.g., stratal architecture, thickness, sand-stone composition) with fl exural modeling of the lithosphere constrains the evolution of a basin and its fl exural history related to orogenic growth (spatial/temporal load-ing confi guration). Using this approach, we determined the Maastrichtian-Cenozoic polyphase growth of the Eastern Cordillera of Colombia, an inverted Mesozoic exten-sional basin. The record of this growth occurs in an Andean (post–middle Miocene) thrust belt (the Eastern Cordillera) and in adjacent foreland basins, such as the Llanos Basin to the east. This approach permitted the identifi -cation of fi ve tectono-stratigraphic sequences in the foreland basin and fi ve phases of short-ening for the Eastern Cordillera. Thermo-chronological and geochronological data support the spatial and temporal evolution of the orogen–foreland basin pair.

Tectono-stratigraphic sequences were

identifi ed in two restored cross sections, one located at a salient and the other in a recess on the eastern fl ank of the Eastern Cordil-lera. The lower two sequences correspond to late Maastrichtian–Paleocene fl exural events and record the eastward migration of both tectonic loading and depositional zero in the Llanos Basin. These sequences consist of amalgamated quartzarenites that abruptly grade upward to organic-rich fi ne-grained beds and, to the top, light-colored mud-stones interbedded with litharenites in iso-lated channels. Amalgamated conglomeratic quartzose sandstones of the third sequence record ~15 m.y. of slow subsidence in the Lla-nos Basin and Llanos foothills during early to middle Eocene time, while shortening was taking place farther west in the Magdalena Valley. The fourth sequence, of late Eocene–middle Miocene age, records a new episode of eastward migration of tectonic loads and depositional zero in the Llanos Basin. This sequence begins with deposition of thick fi ne-grained strata to the west, whereas to the east, in the Llanos basin, amalgamated quartzarenites unconformably overlie Cre-taceous and older rocks (former forebulge). Apatite fi ssion tracks in the axial zone of the Eastern Cordillera, growth strata in the

Llanos foothills, and synextensional strata on the forebulge of the Llanos Basin constrain deformation patterns for this time. The post–middle Miocene Andean event initiated with regional fl ooding of the foreland basin in response the widening of tectonic load-ing, after which the foredeep was fi lled with coarse-grained alluvial and fl uvial detritus derived from the Eastern Cordillera.

The geometry of tectonic loads, con-strained by fl exural models, reveals short-ening events of greater magnitude for the uppermost two sequences than for pre–mid-dle Eocene sequences. Tectonic loads for the late Maastrichtian–middle Eocene phases of shortening were less than 3 km high and 100 km wide. For the late Eocene–middle Miocene phase, tectonic loads changed south-ward from 6 km to less than 4 km, and loads were wider to the north. The strong Andean inversion formed today’s Eastern Cordillera structural confi guration and had equivalent tectonic loads of 10–11 km.

Integrated analysis is necessary in poly-phase orogenic belts to defi ne the spatial and temporal variation of tectonic load and fore-land basin confi gurations and to serve studies that seek to quantify exhumation and three-dimensional analyses of thrust belts. For the

For permission to copy, contact [email protected]© 2008 Geological Society of America

1171

An integrated analysis of an orogen–sedimentary basin pair: Latest Cretaceous–Cenozoic evolution of the linked Eastern Cordillera orogen

and the Llanos foreland basin of Colombia

German Bayona†

Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA, and Corporación Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia

Martin CortésCorporacón Geológica ARES, Calle 57 No. 24-11 of 202, Bogotá, Colombia

Carlos JaramilloSmithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA

German OjedaInstituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia

John Jairo Aristizabal§

Ecopetrol S.A., Calle 37 No. 8-43, Bogotá, Colombia

Andres Reyes-HarkerInstituto Colombiano del Petróleo, AA 41815, Km 7 to Piedecuesta, Bucaramanga, Colombia

GSA Bulletin; September/October 2008; v. 120; no. 9/10; p. 1171–1197; doi: 10.1130/B26187.1; 15 fi gures; Data Repository item 2008078.

†E-mail: [email protected] §Present address: REPSOLYP, Calle 71A No. 5-38,

Bogotá, Colombia.

Bayona et al.

1172 Geological Society of America Bulletin, September/October 2008

Eastern Cordillera, thermochronological sampling must span the width of the Eastern Cordillera rather than be concentrated in a single range.

Keywords: foreland basin, Cenozoic stratigra-phy, basin inversion, orogenic belts, Cenozoic tectonics, Llanos Basin, Colombia.

INTRODUCTION

Integrative research on syntectonic sedimen-tary basins should include different types of data sets (sedimentology, stratal architecture, prove-nance, subsidence) and needs to consider kine-matic constraints from the adjacent mountain belts. Tectonic activity, weathering processes, and isostatic readjustment of the crust delimit uplifted blocks and so determine the nature of crustal loads adjacent to a basin. On the other hand, syntectonic sedimentary basins include the most complete record of the evolution of those uplifted blocks. Initiation of deformation in a formerly tectonically quiet (e.g., passive mar-gin) and nearly fl at (e.g., coastal plain) region affects depositional and paleoecological sys-tems, provenance, and paleocurrent indicators, as well as climate variables (e.g., precipitation). The rearrangement of these variables infl uences the tectonic evolution of both mountain ranges (e.g., climatic control of critical wedge in the central Andes; Horton, 1999) and adjacent sedi-mentary basins (e.g., change in fl uvial patterns of the Amazon Basin by uplift of the Andes; e.g., Hoorn et al., 1995).

The kinematic evolution of an orogen affects both the geometry and fi lling patterns of syntec-tonic sedimentary basins. In orogen and fore-land basin systems, estimates of spatial and tem-poral variations of crustal thickening commonly rely on studies of orogenic belt deformation in conjunction with proximal-to-distal synoro-genic stratigraphic and compositional analyses (e.g., Horton et al., 2001; Liu et al., 2005) of the foreland basin. Geodynamic models of fore-land basins have been essential in defi ning the spatial and temporal variation of tectonic load geometries, since there is a primary relationship among tectonic loading, strength of the litho-sphere, and basin geometry (e.g., Jordan, 1981; Cardozo and Jordan, 2001).

Integrated orogen and foreland basin analy-sis of the type presented here is an essential approach to understanding of polyphase thrust-belt systems and deciphering deformation phases. Investigations in the central (e.g., Horton et al., 2001) and northern Andes (e.g., Gómez et al., 2005a) indicate that pre-Neogene deforma-tion played an important role in the tectonic evo-lution of the Andes, which are believed to have

risen strongly in the late Neogene. Therefore, studies of shortening in the Eastern Cordillera of Colombia, a mountain range of the northern Andes, must consider temporal and spatial vari-ations of crustal shortening that resulted from pre-Neogene phases of deformation.

This paper presents a kinematic evolution and quantifi cation of tectonic loading of a polyphase-deformed orogenic belt (Eastern Cordillera) adjacent to a nonmarine foreland basin (Llanos Basin). We integrate provenance, sedimentol-ogy, stratal patterns, biostratigraphy, subsidence, structural, and geodynamic analyses with pub-lished thermochronological and geochronologi-cal data in order to (1) investigate how crustal thickening (i.e., tectonic loading) affected the latest Cretaceous–Paleogene evolution of the Llanos foreland basin, and (2) identify struc-tures in the Eastern Cordillera that might have been active at each phase of deformation. Our results suggest that the present topography of the Eastern Cordillera does not refl ect the com-plex earlier evolution of the northern Andes but rather provides a record only of the last phase of deformation. Therefore, integrated analysis of the adjacent Llanos foreland basin is necessary to investigate the previous deformation events, which are masked by the last phase.

TECTONIC FRAMEWORK OF THE COLOMBIAN ANDES AND EVIDENCES OF PRE-NEOGENE DEFORMATION

Regional Tectonic Setting of the Eastern Cordillera

Three major orogenic belts are the result of the complex interaction of the Nazca, Carib-bean, and South America plates since the Late Cretaceous: the Western Cordillera, the Central Cordillera, and the Eastern Cordillera. The East-ern Cordillera bifurcates to the north into the Santander massif–Perija Range (MS-PR) and the Merida Andes (MA) (Fig. 1). The Eastern Cordillera is interpreted as a wide Cretaceous extensional basin that was formed during at least two stretching events (Sarmiento-Rojas et al., 2006) and that was tectonically inverted dur-ing the Cenozoic (Colleta et al., 1990; Dengo and Covey, 1993; Cooper et al., 1995; Mora et al., 2006). However, basement and sedimentary rocks exposed in the Eastern Cordillera and adjacent basins indicate that this complex region has been the scene of polyphase tectonics since Precambrian time (see Etayo-Serna et al. [1983] and Cediel et al. [2003] for details).

The eastern fl ank of the Eastern Cordillera of Colombia (Fig. 1) exposes contrasting structural styles between highly deformed rocks along an east-verging fold-and-thrust belt and the less-

deformed Llanos foreland basin. Reactivated Mesozoic normal faults, such as the Guaicar-amo fault system in the central Llanos foothills, have been considered to be the major boundary of those structural styles. Models of inversion tectonics have been created for the southern seg-ment of the Eastern Cordillera and Llanos foot-hills (Casero et al., 1997; Rowan and Linares, 2000; Branquet et al., 2002; Restrepo-Pace et al., 2004; Toro et al., 2004; Cortés et al., 2006a; Mora et al., 2006), in the central segment of the Eastern Cordillera and Llanos foothills (Colleta et al., 1990; Dengo and Covey, 1993; Cooper et al., 1995; Cazier et al., 1995; Roeder and Cham-berlain, 1995; Rathke and Coral, 1997; Fajardo-Peña, 1998; Taboada et al., 2000; Sarmiento-Rojas, 2001; Rochat et al., 2003; Toro et al., 2004; Martinez, 2006; Mora et al., 2006), and in the northern segment of the Eastern Cordillera and Llanos foothills (Chigne et al., 1997; Corre-dor, 2003; Villamil et al., 2004). Although struc-tural models differ both in the angle and depth of detachment of the Guaicaramo fault system and in fault involvement of crystalline base-ment to the east, structural restorations from the axial zone of the Eastern Cordillera and Llanos Basin are similar (Fig. 1C). Proposed structural models do not show a relationship between the amount of shortening and fl exural deformation in the adjacent basin, and they differ in (1) the amount of shortening of the Eastern Cordil-lera, mainly from the axial zone to the western boundary of the Eastern Cordillera (Fig. 1C), (2) the geometry of fold structures at depth, and (3) the position and confi guration of Mesozoic eastern and western rift shoulders.

As an alternative method to validate the short-ening estimated in our cross sections, we used the fl exural geometry of synorogenic Paleogene to Neogene foreland basins, growth-strata pat-terns, and crosscutting relationships of hanging-wall and footwall structures on the eastern fl ank of the Eastern Cordillera and Llanos foothills to better constrain the kinematic evolution of the eastern fl ank of the Eastern Cordillera.

Evidence of Pre-Neogene Deformation

Paleobotanical, thermochronological, and geochronological data indicate that surface and rock uplift, as well as rock deformation, have occurred at different times but primarily in the late Neogene. Paleobotanical data indi-cate a change in fl ora from lowland associa-tions to Andean-type forests (Helmens, 1990) in the last 5 m.y., but the timing of this change ranges between 3 and 6 Ma (Helmens and Van der Hammen, 1994; Hooghiemstra and Van der Hammen, 1998). Zircon fi ssion-track ages support earlier uplift in the Central Cordillera

An integrated analysis of an orogen–sedimentary basin pair

Geological Society of America Bulletin, September/October 2008 1173

711 10

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Dengo and Covey, 1993

Cooper et al., 1995

TOP OF CRETACEOUS

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regional pin lineC 333 km

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Present erosion profile

RESTORED WIDTH OF THE PRESENT EASTERN CORDILLERA = 287.5 km

RESTORED WIDTH OF THE PRESENT EASTERN CORDILLERA = 218.2 km

CC restored MV

CCrestored MV

Restored trace of thrust faults

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NORTHERN LLANOSNORTHERN CROSS SECTION (Fig. 3A)

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Lower Cretaceous sedimentary rocks

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Triassic-Jurassic volcanic andsedimentary rocks

Paleozoic

Precambrian basement

Figure 1. (A) Regional tectonic setting of the northern Andes of Colombia. (B) Geologic map of the Eastern Cordillera of Colombia (modi-fi ed from Cediel and Cáceres, 1988) showing the location of the northern and central cross sections (see Fig. 3) and stratigraphic control along the southern stratigraphic cross section (for details, see Bayona et al., 2006). (C) Restored cross sections showing different interpreta-tions of the restored position and geometry of major structures of the Eastern Cordillera. The restored distance between a regional pin line in the Llanos Basin and the Soapaga-Pesca fault (western boundary of our study area) is similar between these two interpretations (differ-ence = 6 km). In contrast, the restored width of the western fl ank of the Eastern Cordillera differs by 75 km.

Bayona et al.


(around the Campanian-Maastrichtian bound-ary; Toro, 1999; Gómez et al., 2005a) than in the Santander massif–Perija Range and Merida Andes (near the Cretaceous-Tertiary [KT] boundary; Shagam et al., 1984; Kohn et al., 1984). Apatite fi ssion-track ages (AFTA) indicate a northward exhumation that began in the Oligocene in the Floresta (22.3 ± 4 Ma) and southern Santander (30.8 ± 5.8 Ma) mas-sifs (Toro, 1990), then moved to the central and northern Santander massif in the Miocene and Miocene-Pliocene, respectively (Shagam et al., 1984). AFTA ages on the western fl ank of the Eastern Cordillera (Gómez et al., 2003) support two phases of cooling, the fi rst between 65 and 30 Ma, which involved the removal of 3–4 km of overlying sedimentary cover, and the second between 10 and 5 Ma, which involved denuda-tion of 3 km of sedimentary cover. AFTA results on the eastern fl ank of the Eastern Cordillera (Hossack et al., 1999) require exhumation along the Chameza fault at 25 Ma and exhumation in the foothills between 3 and 15 Ma. AFTA data from the Garzon and Quetame massifs indicate younger phases of deformation, ranging from 12 to 3 Ma (Van der Wiel, 1991). The genera-tion of an orographic barrier at ca. 6–3 Ma trig-gered rapid denudation and shortening rates of the eastern fl ank of the Eastern Cordillera (Mora et al., 2005). Reported geochronological data from green muscovite crystallized on emerald-bearing vein wall rocks (Ar/Ar and K/Ar) indi-cate a fi rst extensional event at 65 ± 3 Ma on the eastern fl ank and a compressional event on the western fl ank between 32 and 38 Ma (Branquet et al., 1999).

A regional shift from marine to continental depositional environments at the end of the Cre-taceous was coeval with accretion of oceanic terranes west of the Romeral fault system (e.g., Etayo-Serna et al., 1983; McCourt et al., 1984). Mechanisms driving this shift have been inter-preted as eustasy and tectonism (Villamil, 1999) or increasing rate of sediment supply associated with exhumation and denudation of the Central Cordillera (Gómez et al., 2005a). Interpreted Paleocene basin geometry varies from a single and continuous foreland basin (Cooper et al., 1995; Villamil, 1999; Gómez et al., 2005a) to a continuous negative fl exural basin with appar-ent absence of bounding thrusts (Pindell et al., 2005) to a foreland basin disrupted by uplifts along the axial zone of the basin (Fabre 1981, 1987; Sarmiento-Rojas, 2001; Pardo, 2004), the western border of the basin (Bayona et al., 2003; Restrepo-Pace et al., 2004, Cortés et al., 2006a), or at both borders of the basin (Fajardo-Peña, 1998; Villamil, 1999). The integration of basin geometry, provenance, paleocurrent, sub-sidence, and geodynamics analyses allows us to

identify the location of loads that affected the geometry of the Paleocene foreland basin in the Llanos foothills and Llanos Basin.

Angular unconformities and growth-strata pat-terns of Paleogene beds place constraints on our ability to defi ne phases of deformation. A highly variable angular unconformity between lower-to-middle Eocene strata resting upon Paleocene or older units has been well documented in the subsurface of the Magdalena Valley (Vil-lamil et al., 1995; George et al., 1997; Pindell et al., 1998; Gómez et al., 2003, 2005b) and in outcrops (Restrepo-Pace et al., 2004). In the Magdalena Valley, structures beneath the uncon-formity have been interpreted as high-angle strike-slip faults (Pindell et al., 1998; Gómez et al., 2005b). Strata overlying this unconformity show a wedge of divergent growth strata of mid-dle Eocene–lower Miocene age in the southern middle Magdalena Valley (Gómez et al., 2003) and upper Oligocene–middle Miocene age in the northern Magdalena Valley (Gómez et al., 2005b). In the axial zone of the Eastern Cor-dillera, the structure of the eastern fl ank of the Usme syncline (south of Bogotá in Fig. 1B) has been interpreted as a progressive unconformity that has been growing since the late Paleocene (Julivert, 1963). In the northern Llanos foothills and Llanos Basin, Corredor (2003) and Cortés et al. (2006b) reported growth-strata patterns in Oligocene-Miocene strata. In the central Llanos foothills, Rathke and Coral (1997) and Martinez (2006) suggested the incipient development of broad fault-related anticlines and synorogenic deposition during the Oligocene. Adjacent to leading structures of the Llanos foothills (e.g., Cusiana fault in Fig. 1), however, seismic refl ec-tors of Oligocene and Miocene strata are paral-lel and generally isopachous (Toro et al., 2004). Parra et al. (2005) interpreted the westward coarsening and thickening of the Oligocene clastic wedge across a 20-km-wide syncline as the result of fl exural subsidence related to the uplift of the Quetame massif.

STRUCTURE OF THE EASTERN FLANK OF THE EASTERN CORDILLERA

In order to better understand the regional geometry and lateral variations along the eastern fold-and-thrust belt of the Eastern Cordillera, two regional balanced cross sections extending from the axial zone of the Eastern Cordillera to the Llanos Basin were constructed in areas where the geometry of the Guaicaramo fault sys-tem, the internal structural confi guration of the Eastern Cordillera, and the Cretaceous-Ceno-zoic stratigraphy differ (Figs. 1 and 2). Local cross sections were studied to the north and south of these regional cross sections in order to

confi rm and provide control on the lateral conti-nuity and consistency of the regional structural models. Surface mapping, seismic-refl ection profi les, gravity data, and well data constrain the construction of balanced cross sections. Strati-graphic thickness and units for each thrust sheet were provided from the tectono-stratigraphic analysis carried out along these regional cross sections (see next section).

Structure of the Northern Cross Section

This cross section (Fig. 3A) traverses a base-ment structural high, named the Pamplona indenter by Boinet et al. (1985), which is bor-dered by the northwest-striking Chucarima fault, north-striking Labateca and Chinacota reverse faults, and northeast-striking right-lat-eral Bocono fault. This cross section, located at the recess of the Guaicaramo fault system (the Guaicaramo fault system is displaced to the west to become the Cobugon fault), starts at the western fl ank of the Santander massif, passes through the northern Llanos foothills, and ends at the Caño Limon oil fi eld in the northern Lla-nos Basin (Figs. 1 and 3A). The trace of this cross section is far from the transverse bound-aries of the Pamplona indenter and at the place where deformation is mostly plane strain.

Structural domains in the Eastern Cordillera and Llanos foothills of the northern cross sec-tion involve basement rocks. These domains end southward at the northwest-striking Chu-carima fault system. The latter structure places a >3-km-thick succession of lower Cretaceous rocks (Fabre, 1987) in the upthrown block over NNW-striking folds involving upper Cretaceous and Paleogene strata in the downthrown block. In the latter block, the maximum thickness of the lower Cretaceous rocks is 1.2 km (Fig. 2). South of the Chucarima fault, structural domains are more similar to those described for the central cross section.

Structural balance of the northern cross sec-tion indicates a total shortening of 30.5 km (Fig. 3A). Major basement-involved faults form the boundaries between structural domains. The west-dipping basement-involved faults trans-lated displacement and strain eastward through an imbricated fold-and-thrust belt. The major displacements occurred along faults exposed toward the hinterland, where the Santander mas-sif is exposed (domains DN1&2, Fig. 3A). Out-of-sequence deformation along the Cobugon and Samore faults is inferred from the crosscut-ting relation between fault surfaces and footwall structures (domain DN3). A late Oligocene–early Miocene phase of east-verging deforma-tion is constrained by growth-strata patterns identifi ed in the syncline bounded by the Samore



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Bayona et al.


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gina

l len

gth,

L0

= 1

20.9

km

Def

orm

ed le

ngth

, L1

= 9

0.4

km

L0

= 1

30.1

km

L1=

87.

1 km

Bojaba F.

DN

1D

N2

DN

3D

N4

DC

1D

C2

DC

3D

C5

DC

4

DN

1; D

C1

Stru

ctur

al d

omai

ns

Va

G1&

2

A B Fig

ure

3. (A

) Nor

ther

n an

d (B

) cen

tral

bal

ance

d an

d re

stor

ed c

ross

sec

tion

s sh

owin

g m

ajor

str

uctu

res

and

stru

ctur

al d

omai

ns. T

he a

mou

nt o

f res

tora

tion

for

the

east

ern

fl ank

of

the

Eas

tern

Cor

dille

ra a

long

the

cen

tral

cro

ss s

ecti

on (

Fig

. 3B

) ha

s si

mila

r re

sult

s to

tho

se s

how

n in

Fig

ure

1C (

129

km);

how

ever

, the

str

uctu

ral g

eom

etry

is m

ore

sim

ilar

to th

e C

oope

r et

al.

(199

5) in

terp

reta

tion

. Str

uctu

re o

f the

bas

emen

t in

the

Lla

nos

Bas

in fo

r th

e ce

ntra

l cro

ss s

ecti

on w

as m

odifi

ed fr

om G

eoco

nsul

t-P

ange

a (2

003)

. A c

ompl

ete

list

of r

efer

ence

s fo

r su

rfac

e an

d su

bsur

face

dat

a is

in C

orte

s et

al.

(200

6).



fault (Cortés et al., 2006b) (Fig. 4A). Two con-trasting structural styles are well defi ned in both extremes of the northern Llanos Basin (domain DN4). In the western extreme, strata are folded in a compressive anticline structure (well A1&3 in Fig. 3A), and upper Oligocene–lower Mio-cene strata thin at the crest of the fold, suggest-ing a growth structure (Fig. 4B). At the eastern side (well CL1 in Fig. 3A), synfaulting upper Oligocene–lower Miocene strata document normal faulting (Fig. 4C). This is interpreted as fl exural deformation associated with a forebulge (Cortés et al., 2006b).

The recess geometry of the frontal thrust belt north of the transversal Chucarima fault sug-gests that: (1) the Chucarima fault, a transverse fault, was an E-W transfer fault system in a N-S system of normal faults during Mesozoic rifting phases; and (2) the recess and salient geometries of the frontal thrust belt across the Chucarima transverse fault are controlled by a lateral change

of thickness of lower Cretaceous strata. The lat-eral changes in structural and stratigraphic pat-terns across the Chucarima fault, as described here, defi ne the Chucarima transverse zone. Similar relationships between curved geometry of orogenic belts and basin geometry bounded by transverse structures have been documented in other regions (Macedo and Marshak, 1999).

Structure of the Central Cross Section

This section traverses the area where the Guaicaramo fault system has its easternmost advance into the foreland basin, defi ning a salient geometry of the thrust belt. At this lati-tude, the Eastern Cordillera reaches its maxi-mum width in a NW-SE direction. This cross section starts at the hanging-wall block of the east-verging Pesca fault, the southern equivalent to the basement-rooted Soapaga fault system to the north (Fig. 1). This cross section passes

through the Llanos foothills with no exposures of basement blocks and reaches the Llanos Basin (Fig. 3B). Farther south along the Llanos foothills, the Quetame massif plunges north-ward at the same latitude where other folds plunge, and the Guaicaramo fault system is dis-placed to the west to become the Servita fault. The alignment of these elements corresponds to the Sabanalarga transverse zone; structures that strike parallel to this transverse zone show evidence of reactivation (Mora et al., 2006). We interpret this transverse zone as a buried E-W transfer fault system composed of Mesozoic normal faults, as suggested by Sarmiento-Rojas et al. (2006) in this area and farther south in a system named the Nazareth transfer zone.

Although basement rocks are not exposed along the eastern fl ank of the Eastern Cordil-lera between the Chucarima and Sabanalarga transverse zones, we interpret basement-rooted faults as the boundaries of structural domains in

upper Oligocene-lower Miocenestrata (middle Carbonera Fm.)

2 km

1 s

5 km

Top Carbonera Fm.

Top CretaceousTop Paleocene

Top Carbonera Fm.

Top CretaceousTop Paleocene

Wel

l A1

1 s

Top Carbonera Fm.

NNE SSWNW SE

SWW NEE

Top Cretaceous

A

B

C

1 s

5 km

Samore F.

Figure 4. Evidence of faulting during deposition of upper Oligocene–lower Miocene Carbonera strata (thick black line) in the northern cross section (see Fig. 3A for location of seismic lines). From west to east: (A) Depth-migrated seismic line across the western fl ank of a hanging-wall syncline showing growth-strata patterns; arrows indicate the onlap relation of strata. (B) Left: time-migrated seismic line showing lateral thickness change across an anticline structure in the western Llanos Basin. Right: line fl attened to the top of the Carbonera Formation showing the thinning of strata at the axial zone of the anticline. (C) Time-migrated seismic line showing thickening of the Car-bonera Formation across extensional structures in the Llanos Basin.

Bayona et al.


the Eastern Cordillera and Llanos foothills. Pre-Mesozoic metamorphic and sedimentary rocks exposed in the Floresta massif in the axial zone of the Eastern Cordillera and the Quetame mas-sif to the south of the Sabanalarga transverse zone support this assumption. These basement-rooted faults (domains DC1&2, Fig. 3B) are interpreted as reactivated normal faults because of the contrasting stratigraphic thickness variations of Paleozoic-Mesozoic successions between structural blocks (Mora et al., 2006; Kammer and Sanchez, 2006). The Llanos foot-hills area includes the east-verging Guaicaramo fault system, overturned Neogene beds in the adjacent syncline, and low-angle thrust faults at the leading edge of the deformation front. The Guaicaramo fault system includes a symmetri-cal syncline in the hanging wall and offsets an asymmetrical overturned anticline-syncline pair (domain DC3). To the east, Ordovician, upper Cretaceous, and Cenozoic strata are involved in east-verging low-angle thrust fault systems (domain DC4; Martinez, 2006). These faults deform the eastern fl ank of wide and laterally continuous synclines; both frontal faults and synclines form an en echelon array along the eastern boundary of the Llanos foothills. In the Llanos Basin (domain DC5), upper Creta-ceous and Cenozoic rocks dip gently westward and overlie Paleozoic and basement crystalline rocks. Basement structures locally offset the sedimentary wedge.

The total shortening estimated for this cross section is 43 km (Fig. 3B). Basement-involved structures transfer displacement at shallow depths into a dominantly east-verging fold-and-thrust belt with décollement surfaces at several levels within Cretaceous and Oligocene rocks (Figs. 2 and 3B). West-verging fault systems in the axial zone of the Eastern Cordillera are interpreted as back thrusts that deform the foot-wall block of the Pesca fault (domain DC1). The east-verging basement-cored anticline-syncline pair in the Llanos foothills is interpreted as an overturned and displaced fault-propagation fold because: (1) beds in the hanging wall and foot-wall blocks of the Guaicaramo fault system are overturned and have high-angle dip, and (2) the Guaicaramo fault system displaced overturned beds of the eastern fl ank of the anticline. Kine-matic modeling of similar structures (Narr and Suppe, 1994) indicates that basement-involved structures within the anticline forelimb contrib-ute to the formation of asymmetrical overturned synclines in the front. As the anticline devel-oped, deformation played a more important role in controlling the location and architecture of synorogenic Cenozoic deposition eastward of the Guaicaramo fault system. As shortening increased, the asymmetrical fault-propagation

fold broke along the major fault system, and the hanging wall overrode the overturned fl ank of the asymmetrical syncline. Seismic refl ec-tors of upper Oligocene and Miocene strata do not show growth-strata patterns above the uppermost detachment level (Toro et al., 2004); however, this detachment level cut off structures involving Paleogene strata, suggesting incipi-ent deformation beginning in the Oligocene in the Llanos foothills (Rathke and Coral, 1997; Martinez, 2006). In addition, out-of-sequence reactivation is inferred from offset of fold axes across the east-verging Chameza fault and from the irregular hanging-wall and footwall cutoff patterns of the Guaicaramo fault system.

Two other styles of deformation are inter-preted for the Llanos foothills (domain DC4, Fig. 3B). The fi rst style is observed on the west-ern segment, where fold geometry is related to a ramp-fl at geometry of the basement-rooted Yopal fault and where there is an upper décol-lement surface in upper Eocene rocks. The other style is interpreted on the eastern seg-ment, where fold geometry is associated with the propagation of the east-verging Cusiana fault system, which has a décollement surface in Ordovician sedimentary rocks and breaks to the surface along the frontal limb of the syncline. The latter style is complex at depth due to (1) an out-of-sequence west-verging fault system that offset the east-verging fold-and-thrust system (Martinez, 2006), and (2) the subsequent trun-cation of footwall structures by the east-verging Yopal fault.

MAASTRICHTIAN–PLIOCENE TECTONO-STRATIGRAPHIC SEQUENCES

A tectono-stratigraphic sequence in a foreland basin is a rock unit genetically related to one tec-tonic loading event, and it may be constrained by the internal architecture of foredeep strata (Flemings and Jordan, 1990) and lateral migra-tion of foreland basin depozones (DeCelles and Giles, 1996). In a nonmarine siliciclastic tropical foreland basin (i.e., the Llanos Basin), a tectono-stratigraphic sequence is bounded at the base by fi ne-grained strata in the axial fore-deep (high tectonic subsidence and low infl ux of detritus from the forebulge or orogen) and amalgamated sandstones in the distal foredeep (subsidence decreasing toward the forebulge). In the proximal and axial zone of the foredeep, the tectono-stratigraphic sequence consists of muddy sandstones, sandstones, and conglom-erates showing an upsection increase of lithic content supplied from the orogen coincident with decreasing accommodation space. If the forebulge is exposed, a correlative unconformity

is the equivalent record of foredeep strata. As the paired load (sedimentary and tectonic) and fl exural wave advance cratonward, dark-col-ored mudstones of the axial foredeep migrate cratonward, while deposition of amalgamated sandstones takes place on the former forebulge. If new tectonic loading breaks back within the hinterland or the tectonic loading confi gura-tion changes abruptly, the foreland geometry will change, and a new tectono-stratigraphic sequence will be formed.

The Maastrichtian-Pliocene stratigraphic suc-cession can be divided into fi ve tectono-strati-graphic sequences (Figs. 5 and 6), the chrono-logical intervals of which are constrained by palynological data (see methods in Jaramillo et al., 2006a, 2006b). Palynological age determina-tions have the following resolution: 1–2 m.y. for the Maastrichtian-Paleocene, 5–10 m.y. for the Eocene, 3 m.y. for the Oligocene, and 1–2 m.y. for the early and middle Miocene. In this sec-tion, we focus on lateral and vertical changes of lithofacies associations and key sedimento-logical data for Maastrichtian–middle Miocene tectono-stratigraphic sequences, and we present a brief description of the middle Miocene–Plio-cene sequence. Lithostratigraphic units of the Llanos foothills area are indicated in the head-ers for each tectono-stratigraphic sequence, and equivalent lithostratigraphic units are indicated in Figures 5 and 6.

Tectono-Stratigraphic Sequence One (Upper Maastrichtian to Lower Lower Paleocene; Upper Guadalupe-Guaduas Formations and Equivalent Strata)

A regional shift from marginal to coastal fl uvial depositional environments is recorded in this sequence. A brief description of this shift is presented from east to west. In the cen-tral Llanos foothills, Guerrero and Sarmiento (1996) reported a 150-m-thick coarsening-upward succession from medium-grained to conglomeratic sandstones with cross-beds and reworked bivalves, oysters, and corals (Fig. 5). Bioturbation is observed both in sandstone and black mudstone beds. These Maastrichtian con-glomeratic sandstones have been reported up to 200 km farther north along the Llanos foothills (e.g., Colmenares, 1993; Arango, 1996), and fi ne-grained interbeds show recovery of pollen and dinofl agellate cysts that indicate a Maas-trichtian age (Bayona et al., 2006). In the north-ern Llanos foothills, fi ne-grained siliciclastic successions and thin carbonate interbeds domi-nate (Royero, 2001; Geoestratos-Dunia, 2003). A 30–40-m-thick succession of Maastrichtian carbonaceous mudstones overlies the conglom-eratic sandstones (Fig. 5, section TN).



10 k

m

200

m

UPP

ER P

ALEO

CEN

E

MAASTRICHTIA

N

50%

0In

terv

al w

ith p

alyn

olog

ical

sam

plin

g. P

erce

ntag

e of

mar

ine

infl

u-en

ce is

indi

cate

d w

ith b

ars

at e

ach

spec

ific

dep

th

50%

0

Tec

tono

-str

atig

raph

ic f

orel

and

sequ

ence

s

CA

MPA

NIA

N

UP

PE

RPA

LE

OC

EN

EMAASTRICHTIAN

Con

cent

raci

on F

m.

Con

cent

raci

on F

m.

Upp

er S

ocha

Fm

.

Low

er S

ocha

Fm

.

basa

l san

dsto

ne

lower La Paz Fm. LisamaFm.

upper La Paz Fm.Esmeraldas Fm.C

eL

GL

CL

MC

-BA

TN

La

NM

Lla

nos

foot

hills

Lla

nos

Bas

in

50%

050

%0

50%

00

50%

50%

0

axia

l EC

80 k

m16

0 km

LO

WE

RPA

LE

OC

EN

E

Wes

tern

fla

nk E

C.

CAMPANIAN

LOWER PA

LEOCENE

UPPER PALEOCENE

CAMPANIAN

LOWER-MIDDLEEOCENEUPPER

EOCENE

UPPER EOCENE

UPPER EOCENE

LO

WE

R O

LIG

OC

EN

E

UPPERPA

LEOCENE

LO

WE

R O

LIG

OC

EN

E

ZO

NE

OF

CR

UST

AL

TH

ICK

EN

ING

(3

km)

DU

RIN

G T

HE

MA

AST

RIC

HT

IAN

AREA OF CRUSTALTHICKENING (2.5 km)DURING THE LATE PALEO-CENE

3a 2

1

3b1

1

2

3a

3a

3b

3b

AREA OF CRUSTALTHICKENING DURINGTHE LATE PALEOCENE

Mad

gale

naVa

lley

ZONE OF CRUSTALTHICKENING (1.5 km)DURING THE EOCENE

Gua

duas

Fm

.

Upp

er G

uada

lupe

Fm

.

Low

erE

OC

EN

E

LOWER-MIDDLE EOCENE

LOWER-MIDDLE EOCENE

Pica

cho

Fm.

4aC

once

ntra

cion

Fm

.

axia

l zon

e of

the

Eas

tern

Cor

dille

ra (

EC

) un

itsFo

othi

lls u

nits

Car

bone

ra F

m.

uppe

r M

irad

or F

m.

Cue

rvos

Fm

.

Bar

co F

m.

Gua

duas

Fm

.U

pper

Gua

dalu

pe F

m.

low

er M

irad

or F

m.

Car

bone

ra F

m.

Low

er P

aleo

-ce

ne?

LO

WE

R P

AL

EO

-C

EN

E ?

3a 23b4a4a

LO

WE

R O

LIG

OC

EN

E

AREA OF CRUSTALTHICKENING (1 km) DUR-ING THE EOCENE

sequ

ence

bou

ndar

yin

ferr

ed s

eque

nce

boun

dary

24a

Lla

nos

units

Cue

rvos

Fm

(on

ly to

the

wes

t).

Bar

co F

m.

No

reco

rd

No

reco

rd

No

reco

rd

No

reco

rd

Fig

ure

5. S

trat

igra

phic

cor

rela

tion

of

Maa

stri

chti

an t

o up

perm

ost

Eoc

ene

stra

ta a

mon

g th

e ax

ial z

one

of t

he

Eas

tern

Cor

dille

ra (

sect

ion

La)

, L

lano

s fo

othi

lls (

sect

ion

TN

, w

ell

C-B

A),

and

the

Lla

nos

Bas

in (

wel

ls L

M,

LC

, LG

, Ce)

. Gra

in-s

ize

profi

les

of s

ecti

ons

and

gam

ma-

ray

curv

es o

f w

ells

are

plo

tted

tw

ice

by r

ever

sing

the

sc

ale,

giv

ing

a un

ifor

m d

ispl

ay o

f gr

ain-

size

pat

tern

s. T

his

fi gur

e sh

ows

the

wes

twar

d th

icke

ning

of

tect

ono-

stra

tigr

aphi

c se

quen

ces

one

to t

hree

and

the

low

er p

art

of t

ecto

no-s

trat

igra

phic

seq

uenc

e fo

ur (

nam

ed 4

a; s

ee

text

for

desc

ript

ion

of e

ach

tect

ono-

stra

tigr

aphi

c se

quen

ce).

A p

arti

al s

ecti

on o

f the

wes

tern

fl an

k of

the

Eas

tern

C

ordi

llera

(sec

tion

NM

) is

show

n to

illu

stra

te th

e w

estw

ard

coar

seni

ng o

f Eoc

ene

stra

ta. P

alin

spas

tic

dist

ance

s ar

e in

dica

ted

for

sect

ions

wes

t of

sec

tion

TN

; th

e ho

rizo

ntal

sca

le i

s fo

r se

ctio

ns e

astw

ard

of T

N. S

ourc

es f

or

cons

truc

tion

of c

ompo

site

str

atig

raph

ic s

ecti

ons

and

ages

are

: NM

(Jar

amill

o, 1

999;

Par

do-T

ruji

llo e

t al.,

200

3;

Góm

ez e

t al.,

200

5b);

La

(Yep

es, 2

001;

Par

do, 2

004;

this

stu

dy);

TN

(Gue

rrer

o an

d Sa

rmie

nto,

199

6; J

aram

illo,

19

99;

Jara

mill

o an

d D

ilche

r, 2

001;

and

ref

eren

ces

cite

d in

Bay

ona

et a

l., 2

006)

.

Bayona et al.


10 k

m

200

m

LP

Ce

LG

LC

LM

C-B

AT

N

UP

PE

R O

LIG

OC

EN

EU

PP

ER

OL

IGO

CE

NE

CA

MPA

NIA

N

UPPER PALEOCENE

LO

WE

R M

IOC

EN

E

Lla

nos

foot

hills

Lla

nos

Bas

in

50%

0

50%

0

50%

050

%0

050

%

050

%0

50%

axia

l EC

50%

0

La no record of upper

Oligocene biozone

80 k

m

Car

bone

ra F

m.

UPP

ER

EO

CE

NE

Mid

-OL

IGO

CE

NE

LO

WE

R O

LIG

O

LO

WE

R M

IOC

EN

E

LO

WE

R O

LIG

OC

EN

E

CENE

UPP

ER

PA

LE

OC

EN

E

Car

bone

ra F

m. (

basa

l san

dsto

ne)

3a3b4a

UPPER EOCENE

LO

WE

RE

OC

EN

E

LOWER-MIDDLE EOCENE

4bLOWER-MIDDLEEOCENE

3a3b4a

ZONE OF CRUSTALTHICKENING (3 km)OLIGOCENE

ZONE OF CRUSTALTHICKENING (4 km)OLIGOCENE-LOWERMIOCENE

50%

0In

terv

al w

ith p

alyn

olog

ical

sam

plin

g. P

erce

ntag

e of

mar

ine

infl

u-en

ce is

indi

cate

d w

ith b

ars

at e

ach

spec

ific

dep

th

Con

cent

raci

on F

m.

Con

cent

raci

on F

m.

3a3bPi

cach

o Fm

.

4aC

once

ntra

cion

Fm

.

axia

l zon

e of

the

Eas

tern

Cor

dille

ra (

EC

) un

itsFo

othi

lls u

nits

Car

bone

ra F

m.

uppe

r M

irad

or F

m.

low

er M

irad

or F

m.

Car

bone

ra F

m.

sequ

ence

bou

ndar

yin

ferr

ed s

eque

nce

boun

dary

4b4c5

4c 4b

4b4c5

Lla

nos

units

part

ial r

ecor

d of

Con

cent

raci

on F

m.

Car

bone

ra F

m.

AREA OF CRUSTALTHICKENING (1 km) DUR-ING THE EOCENE

Car

bone

ra F

m.

Car

bone

ra F

m.

Leo

n Fm

.L

eon

Fm.

3735

m38

11 m

3110

m25

15 m

1997

m

Tec

tono

-str

atig

raph

ic f

orel

and

sequ

ence

s

MID

DL

E M

IOC

EN

E

MID

DL

E M

IOC

EN

E

5

No

reco

rd

No

reco

rdG

uaya

bo F

m.

Gua

yabo

Fm

.

No

reco

rd

No

reco

rd

No

reco

rd

2835

m14

00 m

ZO

NE

OF

CR

UST

AL

TH

ICK

EN

NIN

G (

10 k

m)-

pos

t MID

DL

EM

IOC

EN

E

tota

l thi

ckne

ss o

fse

quen

ce 5

(fr

omFa

jard

o et

al.,

2000

)

Fig

ure

6. S

trat

igra

phic

cor

rela

tion

of E

ocen

e to

mid

dle

Mio

cene

str

ata

amon

g th

e ax

ial z

one

of th

e E

aste

rn C

ordi

llera

(sec

tion

La)

, Lla

nos

foot

hills

(sec

tion

T

N, w

ell C

-BA

), an

d th

e L

lano

s ba

sin

(wel

ls L

M, L

C, L

G, C

e, L

P).

Gra

in-s

ize

profi

les

of s

ecti

ons

and

gam

ma-

ray

curv

es o

f wel

ls a

re p

lott

ed tw

ice

by r

ever

s-in

g th

e sc

ale,

giv

ing

a un

ifor

m d

ispl

ay o

f gr

ain-

size

pat

tern

s. T

his

fi gur

e ill

ustr

ates

tec

tono

-str

atig

raph

ic s

eque

nces

thr

ee a

nd f

our

and

the

low

er p

art

of

sequ

ence

fi ve

. The

abr

upt t

hick

enin

g of

thes

e se

quen

ces

mig

rate

s ea

stw

ard,

rea

chin

g th

e th

icke

st s

ucce

ssio

n of

seq

uenc

e fi v

e in

wel

l LC

(381

1 m

). P

alin

spas

tic

dist

ance

bet

wee

n se

ctio

ns L

a an

d T

N is

indi

cate

d; t

he h

oriz

onta

l sca

le is

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Along the axial zone of the Eastern Cordil-lera, strata of this sequence are represented by fi ne- to medium-grained sandstones with cross-beds and abundant ichnofossils (Perez and Salazar, 1978; Fabre, 1981). These beds are overlain by a unit that consists in the lower half of fi ne-grained strata with abundant coal seams and in the upper half of laminated mud-stones and massive light-colored mudstones (Sarmiento, 1992). The thickness of this unit is variable; there is a 1100 m depocenter near Bogotá, and it thins eastward to less than 450 m and northward to less than 300 m near the Santander massif (Fabre, 1981; Royero, 2001). Maastrichtian–lower Paleocene units in the Magdalena Valley include conglomeratic units derived from the Central Cordillera to the south (Gómez et al., 2003), whereas to the north, carbonate silt and mudstones dominate (Gómez et al., 2005b). Maastrichtian strata are absent in the southern Llanos Basin (Bayona et al., 2006), in the frontal thrust sheets of the cen-tral Llanos foothills and Llanos Basin (Cooper et al., 1995), as well as along the frontal thrust sheets of the western fl ank of the Eastern Cor-dillera (Bayona et al., 2003).

Tectono-Stratigraphic Sequence Two (Upper Lower Paleocene to Upper Paleocene; Barco-Cuervos Formations and Equivalent Strata)

Biostratigraphic data indicate that fi ne-grained strata of this tectono-stratigraphic sequence in the axial zone of the Eastern Cordillera corre-late with aggradational, fi ne-to-coarse-grained quartzarenites in the Llanos Basin (Fig. 5). This succession changes upsection from: (1) cross-bedded, fi ne- to coarse-grained upward-fi ning quartzarenites (Fig. 7A), locally conglomeratic in Cocuy (Fabre, 1981) and section La (Pardo, 2004) (this unit pinches out west of Bogotá; Hoorn, 1988); to (2) interbeds of upward-fi n-ing sandstone and mudstone with bidirectional cross-bedded and bioturbated heterolithic lami-nated sandstone; (3) locally bioturbated dark-gray organic-rich claystone and mudstone with thin coal seams and excellent pollen recovery; and (4) at the top, massive light-colored sandy mudstone with very poor pollen recovery. This uppermost lithology contains isolated sand-stones with upward-fi ning and coarsening grain-size trends with cross-beds, wavy lamina-tion, and ripple cross-lamination (Figs. 7B and 7C). The thickness of this tectono-stratigraphic sequence decreases eastward and northward: in the Bogotá area, it varies from 0.9 to 1.2 km (Hoorn, 1988), in sections La-Cocuy-Va (west-ern end of cross sections in Fig. 1), it ranges from 0.4 to 0.8 km (Fabre, 1981; Pardo, 2004;

Geoestratos-Dunia, 2003), in the Llanos foot-hills, it ranges between 0.6 and 0.2 km, and in the Llanos Basin, it ranges from 0 to 0.2 km (Figs. 1 and 5).

The vertical arrangement of lithofacies and palynofacies has been interpreted as a product of deposition, from base to top, in fl uvial, fl u-vial-estuarine, and coastal-plain systems. Sand-stones indicate fl uvial infl uence in the axial zone of the Eastern Cordillera (Pardo, 2004), whereas they are more tidally infl uenced in the Llanos foothills (Cazier et al., 1995; Reyes, 1996). The fi ne-grained strata accumulated in fl oodplains with increasing estuarine infl uence toward the Llanos foothills. The change from excellent to poor pollen recovery in fi ne-grained units sug-gests that deposition of upper strata took place above the water table (Pardo, 2004). Equivalent strata in the Magdalena Valley consist of 1.2-km-thick organic-rich mudstone interbedded with ripple-laminated and cross-bedded lithic sand-stone that accumulated in fl uvial-deltaic plain environments (Gómez et al., 2005b; section NM in Fig. 5).

Tectono-Stratigraphic Sequence Three (Lower to Middle Eocene; Mirador–Basal Carbonera Formations and Equivalent Strata)

Lithological units of this age are reported only west of the Llanos foothills and consist of two intervals. The lower interval (named 3a in Fig. 5) rests in abrupt contact with strata of sequence two (Fig. 7D) and includes fi ne- to medium-grained and locally conglomeratic quartzarenites beds that internally are mas-sive, cross-bedded, and wavy-laminated to the top (Fig. 7E). The upper interval (named 3b in Fig. 5) has upward-fi ning successions and coal interbeds in the northern Llanos foothills (Reyes, 2004), whereas in the central Llanos foothills, sandstones show a diverse ichnofacies associa-tion (Ophiomorpha, Thalassinoides, Psilonich-nus, and Diplocraterion; Pulham et al., 1997), couplets in foreset laminations, and wavy and fl aser lamination in upper mudstone interbeds (Parra et al., 2005). Dark-colored mudstones with thin coal seams rest conformably on the bioturbated sandstones (Jaramillo, 1999; Jara-millo and Dilcher, 2001). These two intervals are separated by light-gray massive sandy mudstone and locally laminated, organic mudstone with plant remains (Fig. 5); this level is characterized by moderate abundance of marine indicators, including foraminiferal test lining and several dinofl agellate cysts, such as Polysphaeridium subtile, Achomos phaera sp., Spiniferites sp. Cordos phaeridium inodes, and Nematosphae-ropsis (Jaramillo and Dilcher, 2001).

The lower and upper intervals are also pres-ent in the axial zone of the Eastern Cordillera (section La in Fig. 5). The lower interval (3a in Fig. 5) includes cross-bedded, medium- to coarse-grained sandstone and conglomeratic sandstone, which changes upsection to inter-beds of tabular-bedded fi ne-grained sandstone and discontinuous mudstone interbeds (Cés-pedes and Peña, 1995; Pardo, 2004). The upper interval (3b in Fig. 5) includes laminated gray mudstone with some interbeds of sandstone and oolithic sandstone (Reyes and Valentino, 1976). The thickness of this sequence in section La is twice as thick as in the Llanos foothills (Fig. 5). Farther west in the Magdalena Valley, coeval lower and middle Eocene strata are as much as 1 km thick and consist of conglomeratic sand-stone, multistoried cross-bedded sandstone and mudstone (Restrepo-Pace et al., 2004; Pardo-Trujillo et al., 2003; Gómez et al., 2005b).

Sandstones of the lower interval have been interpreted as amalgamated fl uvial channels, whereas sandstones of the upper interval record a stronger infl uence of brackish and marine con-ditions. In the central Llanos foothills, these beds accumulated in mouth-bar and coastal-plain set-tings (Cazier et al., 1995; Fajardo, 1995; Warren and Pulham, 2001), whereas in the northern Lla-nos foothills and axial zone of the Eastern Cor-dillera, they accumulated in a more continental setting (Fajardo-Peña, 1998; Reyes, 2004).

Tectono-Stratigraphic Sequence Four (Upper Eocene to Middle Miocene; Carbonera Formation and Equivalent Strata)

Lowermost strata of tectono-stratigraphic sequence four vary laterally from fi ne-grained deposits in the axial zone of the Eastern Cordil-lera, Llanos foothills, and northern Llanos Basin to amalgamated sandstones in the central Llanos Basin (intervals 4a and 4b in Fig. 6). Fine-grained strata include laminated dark-gray mudstone with thin seams of coal and bioturbated fi ne-grained sandstone (Mora and Parra, 2004) in the Llanos foothills and dark-colored mudstone rest-ing upon the unconformity in the northern Lla-nos Basin. Amalgamated to upward-fi ning suc-cessions of fi ne- to coarse-grained sandstone and conglomeratic sandstone show an onlap relation with the unconformity in the central and south-ern Llanos Basin (Bayona et al., 2006).

Strata overlying these lowermost beds have a more uniform upward-coarsening grain-size trend in the axial Eastern Cordillera, Llanos foot-hills, and Llanos Basin (interval 4b in Fig. 6). An upward-coarsening succession includes laminated mudstone with mollusks (Parra et al., 2005) and marine- to brackish-water indicators at the base (Fig. 6), which grade to tabular

Bayona et al.


Qpf

Qm

0.5 mm

Lm

Qm

Pgl

QpQc

0.25 mm

Qm— monocrystalline quartzQp— polycrystalline quartz

Qc— cryptocrystalline quartz (chert)

Lm— metamorphic lithic fragment

Pgl— plagioclase fragment

Qpf— foliated polycrystalline quartz

A

B

C

D

E

F

G

Figure 7. (A–B) Abrupt change in sandstone composition within tectono-stratigraphic sequence two in Cocuy area (northern area, Fig. 1). (A) Quartzarenite of the lower upper Paleocene Barco Formation. (B) Sublitharenite of the middle upper Paleocene Cuervos Formation. (C–G) Outcrops around section TN (central cross section). (C) Sets of planar cross-bedding in the upper Paleocene Cuervos Formation; lithic fragments are concentrated along the cross-beds. (D) Topographic contrast at the contact between Cuervos (valley) and Mirador Forma-tions (scarp). (E) Amalgamated channels of the Mirador Formation with thin mudstones interbeds (tectono-stratigraphic sequence three). (F) Coarsening-upward succession at the top of the Carbonera Formation (tectono-stratigraphic sequence four), which is coeval with depo-sition of shale of the Leon Formation in the Llanos Basin (Parra et al., 2005). (G) Mottled reddish mudstones (paleosols) interbedded with sandstones of the Guayabo Formation (tectono-stratigraphic sequence fi ve).



and wavy laminated, locally bioturbated, fi ne-grained sandstone. In the central Llanos foot-hills, these successions include coal seams, feld-spar-bearing fi ne-grained muddy sandstone, and locally conglomeratic cross-bedded sandstone (Parra et al., 2005). Upward-coarsening suc-cessions dominate in the Llanos foothills, with some incursions of brackish waters (Figs. 6 and 7F), whereas in the Llanos Basin, upward-fi ning trends are more common toward the top of this sequence (interval 4c in Fig. 6).

The northward and eastward lateral change of depositional patterns supports an interpreta-tion of an eastward-prograding fl uvial-deltaic plain developing into a coastal plain (or savan-nas) and a coeval lacustrine-lagoonal deposi-tional system to the east (Mora and Parra, 2004; Bayona et al., 2006). In the Llanos Basin, the abrupt change in lithological associations of the lowermost beds has been interpreted as a change from channel-fi ll processes in fl uvial systems to transgressive tidal fl ats and delta bays with minor brackish-water infl uence changing upsec-tion to a lacustrine environment (Fajardo et al., 2000). The lacustrine system interfi ngers on the east with a fl uvial system draining the Guyana craton and on the west with prograding del-taic systems. Strata at the top of this sequence record fl uvial systems across the Llanos Basin (interval 4c in Fig. 6).

Tectono-Stratigraphic Sequence Five (Middle Miocene to Pliocene; Leon and Guayabo Formations)

The uppermost tectono-stratigraphic sequence consists of two lithological units that are recorded partly in the Llanos foothills and occupy most of the Llanos Basin. The lower unit consists of dark-colored laminated mudstone and shale with an isolated record of mollusks and foraminifera (Bayona et al., 2006; Fig. 6). This unit is slightly younger westward, as shown in the southern Lla-nos Basin (Bayona et al., 2006), and sandstone interbeds increase northward and westward (Cooper et al., 1995; Fajardo et al., 2000). In the Llanos foothills, this unit consists of wavy laminated, bioturbated, and varicolored mud-stone interbedded with tabular-bedded, biotur-bated quartzarenite (Geoestratos-Dunia, 2003). The upper unit includes varicolored mudstone, lithic-bearing sandstone, and conglomerate, and the coarser lithologies dominate toward the top (Fig. 7G). The maximum recorded thickness is in the Llanos Basin (in well LC in Fig. 6), and not in the Llanos foothills, as in sequence four. The stratigraphic position of the upper unit indicates a post–middle Miocene age.

These units represent the onset of coarse-grained fl uvial systems covering the Llanos

foothills and Llanos Basin. The lower unit doc-uments westward fl ooding of a broad fl uvial-deltaic system followed by regional onset and establishment of lacustrine-lagoonal environ-ments (Hoorn, 1994), but with less brackish-water infl uence than that reported in Eocene strata. In contrast, the upper unit represents the eastward advance of a coarse clastic wedge accumulated in fl uvial and alluvial-fan systems.

PROVENANCE AND PALEOCURRENTS

Sandstone composition in a tropical nonma-rine foreland basin, such as the Llanos Basin and restored eastern fl ank of the Eastern Cor-dillera since the latest Cretaceous, is controlled mainly by chemical weathering and compo-sition of source areas. Late Paleocene paleo-climate conditions (mean annual temperature = 23.8 ± 2.1 ºC, mean annual precipitation = 3.4 m/yr; Herrera, 2004) and number of mor-phospecies (Jaramillo et al., 2006a) were simi-lar to the present tropical rain forest. Changes in composition of modern fl uvial sands in the Ven-ezuela Llanos Basin indicate that unstable lithic fragments are not preserved more than 200 km from the Andes of Merida (the source area), and sands with more than 25% of lithic fragments lie mostly within 100 km of the Andes (Johnsson et al., 1991). We consider these distances to be the maximum possible for source areas for the Paleocene basin, bearing in mind that tropical climatic conditions controlled chemical weath-ering processes in source and basin areas.

Integration of paleocurrent indicators and sandstone composition from Paleogene rocks in the axial zone of the Eastern Cordillera, Lla-nos foothills, and Llanos Basin indicates a shift in provenance since the Paleocene (Fig. 8; see Data Repository for a complete list of references and evaluation of data1). Maastrichtian to lower Paleocene sandstones of tectono-stratigraphic sequence one contain predominantly quartz fragments and minor feldspars (Fig. 8A) in the Llanos Basin, indicating sediment supply from the Guyana craton. Supply of detritus from the craton is additionally supported by the regional westward migration of the Maastrichtian clastic wedge (Diaz, 1994). In the Bogotá region, sand-stone of the upper Guaduas Formation (lower Paleocene) contains unstable siltstone, mud-stone (10%), and chert (7%) grains, along with phyllite and trace amounts of feldspar grains, suggesting uplift of nearby blocks (Sarmiento, 1992; Torres, 2003).

Sandstones of sublitharenite and litharenite composition in tectono-stratigraphic sequence two contain polycrystalline quartz and unstable lithic fragments (Fig. 7B), which constitute up to 33% of the framework grains, and some feld-spars. Reported lithic grain types include silt-stone, chert, gneiss, schist, phyllite and igneous rock fragments. In addition, paleocurrent data indicate a shift to northward directions and an increasing variability of paleocurrent directions at the end of the Paleocene (Figs. 8B and 8C). Provenance and paleocurrent data suggest expo-sure of basement rocks, such as the Floresta and Santander massifs (Vasquez, 1983; Mesa, 1997), that controlled drainage patterns within the axial zone of the Eastern Cordillera during deposition of tectono-stratigraphic sequence two.

The abrupt change from upper Paleocene litharenites (tectono-stratigraphic sequence two) to lower-middle Eocene quartzarenites and sublitharenites (tectono-stratigraphic sequence three) with feldspars in the clay fraction (Bena-vides, 2004) coincides with a change in stacking pattern of sandstone beds from isolated chan-nel beds within mudstone at the top of tectono-stratigraphic sequence two to multistoried chan-nel beds in tectono-stratigraphic sequence three (Fig. 5). Paleocurrent data indicate a high dis-persion pattern, as would be expected in mature (>10 m.y.) fl uvial systems located in areas of slow subsidence. Supply of detritus from nearby uplifted blocks is supported by the presence of Cretaceous foraminifera fragments in the matrix of conglomerates (Céspedes and Peña, 1995) and lithic clasts composed of chert, claystone, siltstone, gneiss, schist, and igneous rock frag-ments (Mesa, 1997, 2004).

The dominance of quartzose sandstones persists in tectono-stratigraphic sequence four. However, the presence of sublitharenite and subarkose, as well as conglomerate beds con-taining clasts of chert and Cretaceous fossilifer-ous limestones, documents the preservation of unstable lithic fragments supplied from uplifted blocks within the Eastern Cordillera.

The dominance of quartzose sandstone com-position in Paleogene sandstones in the Llanos Basin suggests that the continuing supply of detritus from the Guyana craton was mixed with chemically stable fragments derived from the Eastern Cordillera. However, this pre-Miocene pattern in the Llanos Basin contrasts with sub-litharenites and litharenites in tectono-strati-graphic sequence fi ve (Moreno and Velasquez, 1993), which were derived from the Eastern Cordillera. Palynological samples from fi ne-grained strata of tectono-stratigraphic sequence fi ve contain pollen, as well as dinofl agellate and foraminifera fragments, of Paleocene and older age (Milton Rueda and Vladimir Torres, 2006,

1GSA Data Repository item 2008078, references and evaluation of petrographic and provenance data, is available at www.geosociety.org/pubs/ft2008.htm. Requests may also be sent to [email protected].

Bayona et al.


CE

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Maastrichtian-early early Paleocene (upper Guadalupe Group -lower Guaduas Formation; Sequence One)

Late early Paleocene-early late Paleocene (upper Guaduas, Cacho,Lower Socha and Barco formations; lower Sequence Two)

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Figure 8. Paleogene palinspastic maps of the inverted Eastern Cordillera (EC) and adjacent Llanos Basin (see details in Fig. 10) showing changes in sandstone composition and paleocurrents for tectono-stratigraphic sequences one to four (see Data Repository for complete list of references [see text footnote 1]). (A) Palinspastic distance between Central Cordillera (CC) and Llanos foothills ranges from 335 to 355 km (Colleta et al., 1990; Cooper et al., 1995; Taboada et al., 2000) to 440–460 km (Dengo and Covey, 1993; Roeder and Chamberlain, 1995); the shorter distance is shown for parts B to E. Source areas in the restored Eastern Cordillera need to be considered to explain the presence of litharenites. See discussion in the text about provenance and paleocurrent data for evidence that supports the interpretation of block uplifts within the Eastern Cordillera.



personal commun.) and document unroofi ng of the Eastern Cordillera.

ONE-DIMENSIONAL BACKSTRIPPING AND TWO-DIMENSIONAL FLEXURAL SUBSIDENCE ANALYSIS

A comparison of one-dimensional (1D) tec-tonic subsidence profi les from sections in the axial Eastern Cordillera, Llanos foothills, and Llanos Basin guided selection of time intervals of comparable tectonic subsidence signatures (Fig. 9). Additionally, 1D backstripping tech-niques were used to decompact the measured stratigraphic thickness of each section, follow-ing the methods and assumptions specifi ed in Watts and Ryan (1976) and Allen and Allen (1992). The Late Cretaceous–Cenozoic fi rst-order sea-level curve of Haq et al. (1987) was used for eustasy correction of 1D tectonic sub-sidence.

Two-dimensional (2D) backstripping of the two cross sections was carried out follow-ing the procedures detailed in Watts (2001) to better quantify the subsidence history of the Llanos foothills and Llanos Basin. In order to properly represent the original basin geometry, the positions of each section were plotted in the Paleogene palinspastic map of Sarmiento-Rojas (2001; Fig. 10), which depicts shortening esti-mates for the eastern fl ank of the Eastern Cor-dillera that agree with restorations of our two balanced cross sections. This palinspastic map constrains (1) the most probable position of tectonic loads (areas with no Cenozoic record), (2) areas with growth strata, and (3) areas with intra-Cenozoic angular unconformities. Next, the minimum and maximum 2D basin depths were defi ned for each time interval using the compacted and decompacted thickness, respec-tively, of each section or well. The effect of fl exural subsidence due to sediment loading was calculated after basin geometry was defi ned. The latter exercise permitted calculation of the “observed minimum” and “observed maxi-mum” tectonic fl exural subsidence of the basin for each time interval. In this study, the numeri-cal implementation of Bodine (1981), which allows plates of laterally variable elastic thick-ness to be considered, was applied to model the Llanos foreland basin.

Results of One-Dimensional Backstripping

Breaks between periods of constant sub-sidence rate allow the discrimination of three subsidence events in the Llanos foothills and Llanos foreland basin (Fig. 9); these closely follow the fi ve tectono-stratigraphic sequences defi ned previously. The fi rst subsidence event is

related to increasing subsidence rates in tectono-stratigraphic sequences one and two, the second corresponds to the time interval of tectono-stratigraphic sequence three, and the last regime shows an abrupt increase in subsidence rates in tectono-stratigraphic sequences four and fi ve. The ages of the breaks in the slope of the curve do not overlap for all sections, suggesting that the onset of each event that caused the increase of tectonic subsidence differed across sections in the study area. However, minor differences in the age of those breaks may be due to lack of resolution of biostratigraphic determinations (see bar error for different intervals in Fig. 9).

We interpret all the breaks in the slope of the tectonic subsidence curve as a result of fl exural subsidence related to tectonic and sedimentary loading. Signifi cant differences in the ages of the infl ection points between the northern and central cross sections may record diachronous along-strike tectonic loading. The age differ-ences of infl ection points on curves for the axial zone of the Eastern Cordillera and the Llanos Basin may represent a fl exural response of the lithosphere to foreland-directed migration of tectonic loads.

Results of Two-Dimensional Flexural Backstripping

In this study, we tested two hypotheses of foreland evolution for an 800-km-wide plate. Our fi rst model used a spatially continuous foreland basin with a laterally constant plate fl exural rigidity (Te) for late Maastrichtian, early Paleocene, and late Paleocene time. Our second model considered uplifts of blocks that separated the foreland basin into two main depocenters, the Magdalena and Llanos Basins, on a plate of laterally variable fl exural rigidity (Te). We used data from the Magdalena Valley presented in Pardo-Trujillo et al. (2003) and Gómez et al. (2005a) for section NM, and from Restrepo-Pace et al. (2004) for section RM. Geodynamic modeling of these profi les was extended to include the restored position of the axial Central Cordillera and wells in the distal Llanos Basin (Fig. 10). We focused on the area between the axial zone of the Eastern Cordil-lera and Llanos Basin because the uncertainty of palinspastic restoration increases as we move westward from the axial zone of the Eastern Cordillera to the Magdalena Valley and Central Cordillera (Figs. 1C and 8A).

Model 1: One Basin and Uniform Elastic Thickness

In this hypothesis, the Maastrichtian-Paleo-cene foreland basin was a fl exural response of the lithosphere to loading of the Central Cordil-

lera. The purpose of fl exural modeling was to test whether fl exure of the lithosphere resulting from the weight of the Central Cordillera could reproduce the geometry of the Maastrichtian-Paleocene foreland as far east as the Llanos Basin. Gómez et al. (2005a) were able to obtain a reasonable fi t between the observed and the calculated basin geometry for the Colombian foreland basin using an infi nite plate model, a discrete load confi guration, and a horizontal density contrast between tectonic loads and adjacent sediment fi ll. All model runs reported by Gómez et al. (2005a) were performed on a 35 km Te plate using a thermochronologically constrained history of uplift for the Central Cor-dillera and western fl ank of the Eastern Cordil-lera. We used a tectonic load confi guration simi-lar to the one proposed by Gómez et al. (2005a), but the width of our basin was 40 km narrower (see Figs. 1C and 8A). Our model only consid-ered sections/wells close to the cross sections in order to avoid important changes of thickness of Cenozoic synorogenic strata across these traverse structures, as reported by Parra et al. (2005) and this study.

Model runs using these confi gurations were not able to match the “observed” (i.e., recon-structed) fl exural tectonic subsidence profi le (Fig. 11). One cause of the discrepancy between our results and those of Gómez et al. (2005a) is the restored width of the Eastern Cordillera. Because the basin geometry of Gómez et al. (2005a) is 40 km wider than ours, the additional sedimentary load, 40 km wide and ~1.5 km thick to the west of the axial zone of the Eastern Cordillera, contributed to fl exural subsidence in the Llanos Basin. Because we used a narrower restored basin, both tectonic and sedimentary loading within the restored Eastern Cordillera were required to match the fl exural tectonic sub-sidence in the Llanos Basin (see next section).

Model 2: Interrupted Foreland Basin and Variable Elastic Thickness

The other hypothesis tested in this study was a foreland basin interrupted by tectonic loads in the middle of the basin, which developed on a lithosphere of laterally variable Te. The fl exural strength of the northern Andean lithosphere is known to vary laterally from low values near the axis of the east Andean topography to high val-ues over the Guyana craton, as supported by two-dimensional fl exural models (Ojeda, 2000; Sarm-iento-Rojas, 2001), gravity modeling (Stewart and Watts, 1997), and topography/gravity coher-ence studies (Ojeda and Whitman, 2002).

For each profi le, we applied an estimated Te confi guration that refl ected the lateral variabil-ity in fl exural strength of the lithosphere inher-ited from the complex Phanerozoic tectonics of

Bayona et al.


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Sequence 1

Sequence 1

Figure 9. One-dimensional tectonic subsidence curves for selected sections and wells along the northern and central cross sections. Time inter-vals of the fi ve tectono-stratigraphic sequences are also shown. Cocuy section was modifi ed from Gómez et al. (2005a). Tectono-stratigraphic sequence three records a time interval of very low tectonic subsidence rates, in contrast to Maastrichtian-Paleocene and late Eocene–Pliocene breaks in the slope of the curve. The shape and diachronism of those breaks are interpreted as episodes of fl exural subsidence. See Figure 3 for locations of sections and wells.



1000

000

1100

000

1200

000

1100

000

1300

000

BROKEN PLATE

100

km

LP

CeL

G1&

2L

CLM

C-B

A

La

RM

Medina-Guavio F.

Tesalia-Lengupa F.

Soapaga F.

Cusiana-

Cupiagua F

.

TN

Restored boundary of the Central Cordillera

Prof

ile f

or 2

D g

eody

nam

ic a

naly

sis

poss

ible

loca

tion

of te

cton

ic lo

ads

(no

reco

rd o

f C

enoz

oic

stra

ta)

rest

ored

trac

e of

maj

or f

aults

(se

e Fi

g. 1

)

Labateca F.

NM

Coc

uy

Va

Ju1

Salinas F.

Guica

ramo F.

Nor

ther

n cr

oss

sect

ion

Saba

nala

rga

tran

sver

se z

one

Chinacota F.

1300

000

UN

DE

FOR

ME

D

LL

AN

OS

BA

SIN

Pesca F

.

Bucaramanga F.

Salinas F.

Cha

mez

a F.

Tun

ja

Bog

ota

CENTRAL CORDILLERA

MAGDALENA VALLEY

RE

STO

RE

D

LL

AN

OS

FOO

TH

ILS

RE

STO

RE

D E

AST

ER

N C

OR

DIL

LE

RA

Cen

tral

cro

ss se

ctio

n Cobugon F.

G1&

2

Chu

cari

ma

tran

sver

se

zone

A1&

3

pre-

Eoc

ene

angu

lar

unco

nfor

mity

and

E

ocen

e-M

ioce

ne g

row

th s

trat

a

Olig

ocen

e-lo

wer

Mio

cene

gro

wth

str

ata

CL

1

Romeral paleosuture

MAGDALENA VALLEY

UNDEFORMED

GU

A-1

S-1

Pl-

1

ST-1

5

STO

-2

PR

-1LT

-1

LT-1

wel

l in

the

dist

al L

lano

s ba

sin

proj

ecte

d to

th

e cr

oss

sect

ion

(onl

y fo

r O

ligoc

ene

and

youn

ger

stra

ta; m

odif

ied

from

Faj

ardo

et

al.,

2000

)

tran

sver

se z

one

Fig

ure

10. P

alin

spas

tic

posi

tion

of

sect

ions

and

wel

ls a

nd t

race

of

the

nort

hern

and

cen

tral

cro

ss s

ecti

ons

(ext

ende

d to

the

Cen

tral

Cor

dille

ra)

used

for

tw

o-di

men

sion

al (

2D)

geod

ynam

ic m

odel

ing,

plo

tted

on

the

palin

spas

tic

map

of S

arm

ient

o-R

ojas

(200

1).T

he w

idth

of t

he r

esto

red

Eas

tern

Cor

dille

ra h

ere

is s

imila

r to

the

rest

ored

wid

th p

ropo

sed

by

Col

leta

et a

l. (1

990)

, Coo

per

et a

l. (1

995)

, and

our

res

tore

d cr

oss

sect

ions

sho

wn

in F

igur

e 3.

Pre

sent

pos

itio

ns o

f sec

tion

s/w

ells

are

sho

wn

in F

igur

e 3,

and

pre

sent

trac

es o

f maj

or

faul

ts a

re in

Fig

ure

1. G

row

th s

trat

a, r

epor

ted

angu

lar

unco

nfor

mit

ies,

and

are

as w

ith

no r

ecor

d of

Cen

ozoi

c st

rata

are

als

o in

dica

ted.

Bayona et al.


northern South America (Fig. 12A). The Guy-ana craton is relatively thick, thermally relaxed, and rigid (Te > 50 km; Stewart and Watts, 1997). We assigned a Te in the range of 15–25 km for the lithosphere that underlies the locus of Meso-zoic extension (Sarmiento-Rojas et al., 2006). We regarded the lithosphere under the Central Cordillera as tectonically stable and assigned a Te value of 55 km for the western end of our profi les. Paleosuture zones, such as the Romeral fault system, are zones of plate rupture (zero fl exural strength), or areas of very low fl exural rigidity. We considered the palinspastic position

of Romeral fault system to be the western edge of our broken plate. An older Paleozoic paleo-suture underlying the southern and central Lla-nos foothills (see Cediel et al., 2003) was rep-resented as a laterally variable Te confi guration under the central Llanos foothills.

Results of our second set of models were capable of reproducing the tectonic fl exural subsidence observed in the Llanos foothills and Llanos Basin, and they honor the paleogeogra-phy suggested by stratigraphic and provenance data of our tectono-stratigraphic analyses. Models for the latest Cretaceous–Paleocene are

consistent with early uplift of segments of the axial zone of the Eastern Cordillera. Equivalent tectonic loads (i.e., crustal thickening), rang-ing from 0.5 to 3 km, and synorogenic depo-sition explain the fl exural wavelength and the eastward migration of the fl exural wave, as suggested by the Llanos foreland stratigraphy (Figs. 5, 12B, 12C, and 12D). Tectonic loads on the Santander massif in the northern cross section and west of the Pesca fault on the cen-tral cross section (west of section La) resulted in development of three distinct depocenters, matching the observed tectonic subsidence. For the late Paleocene, a new foreland-breaking deformation front advanced eastward to create widening accommodation space in the Llanos Basin (Fig. 12D). As the basin stratigraphy and geometry indicate, tectonic loads in the north-ern cross section (Santander massif) were wider than in the central cross section.

In the early and middle Eocene, the tectonic load–fl exural wave pair migrated westward (Fig. 12E), explaining the very low subsidence regime in the study area for tectono-stratigraphic sequence three (Fig. 9). Equivalent tectonic loads on the western fl ank of the Eastern Cordil-lera and Magdalena Valley were less than 3 km high on the northern section and less than 2 km high on the central section, with minor loading (<1 km) along the axial zone of the Eastern Cor-dillera and Llanos foothills. In the late Eocene, loads remained largely unchanged except for minor increases in equivalent tectonic loading.

Nor

ther

n cr

oss

sect

ion

Equivalent tectonic load observed maximum computed

observed minimum

forebulge produced by tectonic loading

Tectonic subsidenceObserved decompacted thickness(maximum total subsidence)

200 400 600 800

0

2

4

-2(km)

(km)

CC MV EC Ft Llanos

0

La

LP

C-B

A

RM

Cen

tral

cro

ss s

ectio

n

200 400 600 800

0

2

4

-2(km)

(km)

CC MV EC Ft Llanos

0

NM

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

TN

DensitiesMantle = 3300 kg/m3

Tectonic loads = 2700 kg/m3

Sediments = 2400 kg/m3

Elastic thickness = 35 kmE = 70 GPa; v = 0.25;gravity = 9.78 m/s

Lower Paleocene (60-65 Ma)

Figure 11. Two-dimensional model for fl exural tectonic sub-sidence using a constant elastic thickness of the lithosphere (35 km), continuous basin geometry for lower Paleocene strata (60–65 Ma), and an 800-km-wide plate with a broken bound-ary at the restored position of the Romeral paleosuture (see Fig. 1A). Effects of fl exural subsidence by sediment loads have been removed to calculate observed fl exural tectonic subsidence. CC—Central Cordillera; MV—Magdalena Valley; EC—East-ern Cordillera; Ft—Llanos foothills. See Figures 3 and 10 for actual and restored positions of sections and wells, respectively. This model indicates that tectonic loading is required within the restored Eastern Cordillera in order to match the observed tec-tonic subsidence in the Llanos Basin as modeled in Figure 12.

Figure 12. Two-dimensional fl exural model using variable elastic thickness of the litho-sphere (A), interrupted basin geometry since Maastrichtian, and an 800-km-wide plate with a broken boundary at the restored position of the Romeral fault system (see Fig. 1A). Effects of fl exural subsidence by sediment loads have been removed to cal-culate observed fl exural tectonic subsidence in two regional cross sections with different geometry of the Guaicaramo fault system (GFS). CC—Central Cordillera; MV—Magdalena Valley; EC—Eastern Cordillera; Ft—Llanos foothills; SM—Santander massif. See Figures 3 and 10 for actual and restored positions of sections and wells, respectively. Note that tectonic loading in the Central Cor-dillera does not contribute to tectonic subsid-ence in the Llanos Basin (B and C, see also Fig. 11). For simplicity, we only show tectonic subsidence profi les from the axial zone of the Eastern Cordillera to the Llanos Basin. See text for discussion of models.



40

(km)

0 0

40

(km)Mesozoic rift

marginsPaleozoicsuture

Mesozoic rift mar-gins

Nor

ther

n cr

oss

sect

ion

(rec

ess

of t

he G

FS)

Cen

tral

cro

ss s

ecti

on (

salie

nt o

f th

e G

FS)

0 200 400 600 800 (km) 0 200 400 600 800 (km)

A

B

C

E

F

G

Equivalent tectonic load observed maximum computed

observed minimum

forebulge (only by tectonic load)

Tectonic subsidenceObserved decompacted thickness(maximum total subsidence) O(

Densities

Mantle = 3300 kg/m3

Tectonic loads = 2700 kg/m3

Sediments = 2400 kg/m3

Elastic thickness = VariableE = 70 GPa; v = 0.25;gravity = 9.78 m/s2

D

200 400 600 800

0

2

4

-2(km)

(km)CC MV EC Ft Llanos

La

LP

C-B

A

RM

TN

Pl-1

ST

O-2

200 400 600 800

0

2

4

-2(km)


La

RM

LP

C-B

AT

N

Pl-1

ST

O-2

C-B

A

200 400 600 800

0

2

-1(km)

(km)EC Ft Llanos

La

LP

-1

TN

Pl-1

ST

O-2

200 400 600 800

0

2

-1

(km)

(km) EC Ft Llanos

La

LP

C-B

AT

N

Pl-1

ST

O-2

200 400 600 800

0

2

-1

(km)

(km)

EC Ft Llanos

La

LP

C-B

AT

N

Pl-1

ST

O-2

200 400 600 800 (km)

0

2

4

-2

(km)EC Ft Llanos

La

6

8

10

LP

C-B

AT

N

Pl-1

ST

O-2

-4

-6

-8

200 400 600 800

0

2

4

-2(km)


LT-1

NM

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

0

2

-1

(km)

200 400 600 800 (km)

EC Ft Llanos

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

LT-1

200 400 600 800

0

2

-1(km)

(km) EC Ft Llanos

0

LT-1

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

0

0

0

2

4

-2

(km)

200 400 600 800 (km)

Ft Llanos

LT-1

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

400 600 800 (km)200

0

2

4

-2

(km)Llanos

6

8

10

-4

-6

LT-1

Coc

uyVa G

1&2

Ar1

&3

Ju1

CL

1

-8

A

B

C

E

F

G

D

SM

SM

SM

EC

Lateral variation of elastic thick-ness

Tectono-stratigraphic sequence one(late Maastrichtian–early Paleo-cene, 65-70 Ma)

Tectono-stratigraphic sequence two(lower segment) (early to middlePaleocene, 60–65 Ma)

Tectono-stratigraphic sequence two(upper segment) (middle to latePaleocene, 55–60 Ma)

Tectono-stratigraphic sequencethree (early to middle Eocene, 44–55 Ma)

Tectono-stratigraphic sequence four(Oligocene, 24–34 Ma)

Tectono-stratigraphic sequence five (upper Miocene-Pliocene, 0–10 Ma)

Bayona et al.


In Oligocene to early middle Miocene time, tectonic loads consisted of uplift of the Santander massif, the eastern fl ank of the Eastern Cordil-lera, and incipient uplifts in the Llanos foothills. The foreland-breaking advance of tectonic load-ing controlled migration of the fl exural wave as recorded by tectono-stratigraphic sequence four (Figs. 6 and 12F). For the Oligocene, equiva-lent tectonic loads on the northern cross sec-tion ranged between 3 and 5 km and were over 150 km wide, whereas for the central cross sec-tion, the effective tectonic load, 2 km high and less than 100 km wide, was located in structures between the axial zone of the Eastern Cordillera and central Llanos foothills sections (Fig. 12F). In the early-middle Miocene, tectonic loads advanced eastward toward the present western Llanos Basin and appeared to be the dominant loads (equivalent tectonic loads of 4–6 km) in foreland basin formation. As discussed later, differential loading along the Eastern Cordil-lera imparted differences in stratal architecture of Oligocene–middle Miocene strata between the central and northern Llanos foothills. For the central cross section, any loads located west of the axial zone of the Eastern Cordillera dur-ing this time resulted in subtle subsidence of the Llanos Basin, as demonstrated by Figures 11 and 12C. Therefore, we considered only the effects of tectonic loading to the east of the axial zone of the Eastern Cordillera.

For the middle-late Miocene to Pliocene, the model predicts fi rst a period of considerable decrease of effective tectonic loading followed by a strong uplift of the Andes. Accumulation of the Leon Formation occurred in a basin created by 2 km of equivalent tectonic load west of well Ar1–3 in the northern cross section and west of well C-BA in the central cross section. The load confi guration in the late Miocene and Pliocene is consistent with the modern load distribution (Fig. 12G). The coarse-grained Guayabo For-mation was deposited in the Llanos Basin as the Eastern Cordillera (equivalent tectonic load of 10–11 km) was emplaced over the adjacent foreland, loaded the lithosphere, and generated a broad fl exural sag east of the Cordilleran fron-tal fault. The uplift of the Eastern Cordillera pro-vided much of the sediment for infi ll of the sag.

DISCUSSION: LINKAGE BETWEEN THRUSTING AND BASIN EVOLUTION

The integrative approach used in this work predicts the geometry and position of the tec-tonic loads necessary to produce the observed basin geometry at different time intervals. Our results and published thermochronological-geochronological and paleobotanical data (see references in Evidence of Pre-Neogene Defor-

mation section) provide evidence for at least four shortening events in the axial zone and eastern fl ank of the Eastern Cordillera prior to the strong post–middle Miocene Andean defor-mation. These tectonic phases of deformation advanced dominantly eastward from the hinter-land (Figs. 13, 14, and 15), but changes in fl ex-ural subsidence rates and in the relation between hanging-wall and footwall structures document periods of westward migration of deformation and out-of-sequence reactivation, respectively. In our forward kinematic models for the north-ern and central cross sections, we translated the positions of tectonic loads into areas where active basement-involved deformation was tak-ing place.

Kinematics of the Northern Cross Section

The earliest phase of foreland development is recorded in Paleocene strata. Flexural defor-mation may explain: (1) erosion or nondepo-sition of lower Paleocene rocks in the Llanos Basin and erosion of uppermost Cretaceous rocks farther east, (2) eastward migration of the depositional zero in tectono-stratigraphic sequence two (Barco-Cuervos Formations, Figs. 12C, 12D, and 15B), and (3) increased supply of chemically unstable lithic fragments coincident with increased tectonic subsidence rates (Figs. 8, 11, and 15B). Our geodynamic models indicate that uplifted areas were located mainly at the Santander massif (Figs. 12C, 12D, and 15B), a source area for litharenites in the Cocuy and Va sections less than 100 km away. Although reported zircon fi ssion-track ages in the Santander massif suggest exhumation at this time, the data set of Shagam et al. (1984) needs to be reevaluated with new analyses that con-sider analytical and conceptual advances of this technique (Andres Mora, 2007, personal com-mun.). Subsequent, westward migration of tec-tonic loads to the Magdalena Valley in the early Eocene resulted in deposition of amalgamated sandstones of the thin Mirador Formation and basal shale beds of the Carbonera Formation. (Figs. 12E and 13A).

Field evidence supporting shortening during the Oligocene consists of growth strata in broad synclines in the Llanos foothills and adjacent to a fault-related anticline that formed west of the Llanos Basin (Figs. 4, 12F, 13B, and 15C). Localized normal faulting in the eastern Llanos Basin at this time can be explained as fl exural extension at the forebulge, as indicated in our early Oligocene fl exural model (Figs. 12F and 15C). Ages of apatite fi ssion tracks in rocks from the Santander massif (Shagam et al., 1984; Toro, 1990) support this interpretation. New zircon and apatite fi ssion-track analyses should

be conducted in order to test this hypothesis (Andres Mora, 2007, personal commun.).

Out-of-sequence deformation along the Cobugon and Samore faults in the Llanos foot-hills is indicated by the truncation of tight anti-clines involving Paleogene units by both the east-verging Cobugon fault to the west and the west-verging Samore fault to the east (Figs. 3A, 13C, and 13D). East-verging thrust faults bounding eastern structures of the Llanos foot-hills involve upper Miocene–Pliocene strata and locally offset Pliocene strata, suggesting post-Pliocene activity for the last phase (Fig. 13D).

Kinematics of the Central Cross Section

The fi rst shortening recorded in this area occurred during latest Cretaceous to late Paleo-cene time, earlier than in the northern cross sec-tion (Figs. 14A, 14B, and 15A). Loads were less than 3 km high and were located west of the Pesca-Soapaga fault system; they subse-quently advanced eastward to involve rocks of the eastern fl ank of the Eastern Cordillera dur-ing the late Paleocene (Figs. 12B, 12C, and 15B). These pulses explain the eastward thin-ning of Maastrichtian-Paleocene sequences one and two, which are bounded at the base by sandstones and conglomerates and, at the top, by fi ne-grained strata (Fig. 5). Flexural uplift related to the Maastrichtian phase of deforma-tion explains the presence of quartzose sand-stone and conglomerate beds in the Llanos foot-hills (Fig. 15A), which were supplied mainly from uplifted cratonic sources. Flexural exten-sion at the border of the forebulge in the Llanos foothills explains the presence of faults in the Paleocene (65 Ma), as indicated by micas fi lling vein-wall rocks (Fig. 14A). During the Paleo-cene, upper Cretaceous strata were eroded in the eastern Llanos foothills and Llanos Basin, and synorogenic deposition of the Barco-Cuervos succession migrated eastward (Figs. 14B and 15B). Unstable lithic fragments indicate that uplifted areas were less than 100 km from the Llanos foothills, Bogotá, and Tunja areas, and those uplifts controlled the northward dispersal of detritus, as indicated by paleocurrent data (Fig. 15B).

During the early and middle Eocene, tectonic loads were located in the Magdalena Valley, as indicated by the angular unconformity underly-ing Eocene strata and strike-slip deformation. Farther to the east, a period of westward-increas-ing subsidence took place in the axial zone of the Eastern Cordillera (Figs. 11 and 12E). The amalgamation of fl uvial channels of the Mira-dor Formation indicates low rates of subsidence during this episode of deformation (Figs. 4 and 14C). The presence of lithic fragments and



Lower Cretaceous -Jurassic-Triassic

Lower Paleocene -Upper Cretaceous

pre-Mesozoic

Middle Eocene -Paleocene

Middle Miocene -Upper Eocene

Holocene-Middle Miocene

Fault

Contact

Restored fault trace

Well

Outcrop section

A. Late Eocene - Tectono-stratigraphic sequence 4(Deposition of lower Carbonera Fm., 36 Ma)

20 km

B. Middle Miocene - Tectono-stratigraphic sequence 4(Deposition of upper Carbonera Fm., 14 Ma)

D. Present day

C. Latest Miocene - Tectono-stratigraphic sequence 5(Deposition of Guayabo Fm., 5 Ma)

20 km

20 km

20 km

KiW E

nematics of the northern cross section

Va G1&2 A1&3

Lab

atec

a F.

Cob

ugon

F.

Sam

ore

F.

Oligocene growth strata

Va G1&2 A1&3

Lab

atec

a F.

Cob

ugon

F.

Sam

ore

F.

Fig. 4A Fig. 4B

Apatite FT ages (Toro, 1990)

Apatite FT ages (Shagamet al., 1984)

Figure 13. Kinematic forward model for the northern cross section since the middle Eocene. Basin geometry and position of structural activity are constrained by geodynamic modeling, thermochronology, growth structures, and provenance and paleocurrent data. FT—fi ssion track.

Bayona et al.


C. M

iddl

e E

ocen

e -

Tec

tono

-str

atig

raph

ic s

eque

nce

3(D

epos

itio

n of

upp

er M

irad

or F

m.,

39 M

a)

B. L

ates

t P

aleo

cene

- T

ecto

no-s

trat

igra

phic

seq

uenc

e 2

(Dep

osit

ion

of u

pper

Cue

rvos

Fm

., 55

Ma)

D. M

iddl

e M

ioce

ne -

Tec

tono

-str

atig

raph

ic s

eque

nce

4(D

epos

itio

n of

upp

er C

arbo

nera

Fm

., 14

Ma)

20 k

mA

. Lat

est

Cre

tace

ous

- T

ecto

no-s

trat

igra

phic

seq

uenc

e 1

(Dep

osit

ion

of lo

wer

Gua

duas

Fm

., 65

Ma)

E. P

rese

nt d

ay -

Tec

tono

-str

atig

raph

ic s

eque

nce

5

20 k

m

20 k

m

20 k

m

20 k

m

NW

SEK

inem

atic

s of

the

cen

tral

cro

ss s

ecti

on

La

TN

C-B

AL

ML

CL

G1&

2C

eL

PG

u1

Pesca F.

Chameza F.

Guaicaramo F.

Cusiana-Cupiagua F.

Zir

con

FT a

ges

(Sha

gam

et a

l. ,

1984

)M

icas

fill

ing

norm

alfa

ults

(B

ranq

uet e

tal

., 19

99)

-Fo

rebu

lge

Lith

aren

ites;

sou

rce

area

s le

ss th

an 1

00 k

mPa

leor

elie

f co

ntro

lled

nort

hwar

d di

sper

sion

of

detr

itus

Am

alga

mat

ed s

ands

tone

s =

ver

y lo

w s

ubsi

denc

e

Flex

ural

sub

side

nce

caus

es a

brup

t cha

nge

of th

ickn

ess,

inci

pien

t dev

elop

men

t of

stru

ctur

es

Apa

tite

FT a

ges

(Tor

o, 1

990)

Apa

tite

FT a

ges

(Hos

sack

et a

l.,19

99)

Apa

tite

FT a

ges

(Mor

a et

al.,

2005

)

La

TN

C-B

A

Pesca F.

Chameza F.

GuaicaramoF.

LM

LC

LG

1&2

Ce

LP

Gu1

Cusiana-Cupiagua F.

And

ean-

type

pal

eofl

ora

Con

glom

erat

icsa

ndst

ones

Fig

ure

14. K

inem

atic

forw

ard

mod

el fo

r th

e ce

ntra

l cro

ss s

ecti

on s

ince

the

late

Maa

stri

chti

an. B

asin

geo

met

ry a

nd p

osit

ion

of s

truc

tura

l act

ivit

y ar

e co

nstr

aine

d by

geo

dyna

mic

m

odel

ing,

ther

moc

hron

olog

y an

d ge

ochr

onol

ogy

data

, gro

wth

str

uctu

res,

and

pro

vena

nce

and

pale

ocur

rent

dat

a. S

ee e

xpla

nati

on o

f sym

bols

in F

igur

e 13

. FT

—fi s

sion

trac

k.



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Bayona et al.


fragments of Cretaceous foraminifera in the axial zone of the Eastern Cordillera indicates that minor uplifts continued to supply detritus to the adjacent basin.

Late Eocene to middle Miocene shortening emplaced loads less than 4 km high in the area between the axial zone of the Eastern Cordillera and the eastern Llanos foothills (Figs. 12F, 14D, and 15C). Exhumation of this area, bounded by the Chameza fault to the east, is supported by AFTA data. At this time, a fold-and-thrust belt advanced eastward to the present position of the western Llanos foothills (Fig. 15C), and the salient-recess geometry of the thrust belt began to form. Deposition in the eastern Lla-nos foothills was mostly accommodated by increasing fl exural subsidence toward the East-ern Cordillera (Fig. 12F), as indicated by the abrupt change in thickness of Oligocene and lower Miocene strata, and it was less affected by growth of incipient structures. The dominance of sublitharenite and subarkose supports the interpretation that nearby structures in the east-ern Llanos foothills were not exposed to supply detritus to the basin.

Strong basin inversion took place during middle Miocene to Pliocene time and gave rise to today’s Eastern Cordillera structural confi gu-ration (Figs. 12G and 14E). Equivalent tectonic loads along the eastern fl ank of the Eastern Cor-dillera were 10–11 km high, and they advanced eastward to the eastern boundary of the Llanos foothills. The onset of Andean-scale deforma-tion created a regional and nearly simultane-ous fl ooding event that is recorded in most of the sub-Andean foreland basins in the middle Miocene. The rapid uplift and consequent basin fi lling caused abrupt eastward migration of the forebulge and fl uvial-alluvial depositional sys-tems originating from the Eastern Cordillera.

The most active fault during this latter tec-tonic phase was the Guaicaramo fault system, which allowed exhumation of the Quetame massif and basal Cretaceous strata. It was only at this time that strong surface uplift took place between 6 and 3 Ma, as documented by the change of paleobotanical associations and the generation of an orographic barrier that accel-erated deformation on the eastern fl ank of the Eastern Cordillera. Out-of-sequence deforma-tion along the Guaicaramo fault system was coeval with the different phases of exhumation documented by AFTA data for the Garzon and Quetame massifs.

CONCLUSIONS

The integration of palinspastically restored basin geometry and internal features of syntec-tonic units (e.g., stratal architecture, sandstone

composition, etc.), fl exural modeling, and kine-matic constraints of the orogenic belt permits identifi cation of phases of deformation in an orogen–foreland basin system. The current con-fi guration of the Eastern Cordillera and adjacent Llanos Basin of Colombia is the result of the polyphase growth of basement-rooted structures and ensuing foreland basin development. There-fore, a comprehensive analysis of the adjacent foreland basin can be used to defi ne the spatial and temporal patterns of deformation of former events in the evolving Eastern Cordillera.

Five episodes of deformation have been documented from analysis of the sedimentary record in the axial zone and eastern fl ank of the Eastern Cordillera, Llanos foothills, and Llanos Basin. The fi rst three episodes of deformation include shortening during latest Cretaceous to middle Eocene time. During this period, the deformation front fi rst moved eastward from the axial zone to the eastern fl ank of the East-ern Cordillera (tectono-stratigraphic sequences one and two, Figs. 15A and 15B), and then it shifted to the western fl ank of the Eastern Cor-dillera and Magdalena Valley (tectono-strati-graphic sequence three). Flexural deformation induced: (1) erosion of Paleocene–upper Creta-ceous strata in the Llanos foothills and Llanos Basin, (2) westward thickening of unconfor-mity-bounded Maastrichtian- Paleocene syn-tectonic sequences, (3) increased input of lithic fragments in upper Paleocene strata and north-ward dispersal of detritus, (4) amalgamation of fl uvial-to-estuarine channel structures dur-ing the early and middle Eocene, (5) change of subsidence rates in the latest Cretaceous and late Paleocene, and (6) slow tectonic subsid-ence regimes during the early-middle Eocene in the axial Eastern Cordillera and Llanos foothills. These phases of deformation are con-strained in the hinterland by: (1) zircon fi ssion-track data from the Santander massif (Shagam et al., 1984); (2) geochronological data from micas fi lling normal faults associated with fl exural extension during the latest Cretaceous (Branquet et al., 1999); and (3) angular uncon-formities in the Magdalena Valley (Gómez et al., 2003, 2005b). Geodynamic analysis allows us to infer that equivalent tectonic loads for these phases were less that 3 km high, less than 100 km wide, and wider in the northern than in the central part of the study area.

Tectonic loads in the late Eocene–middle Miocene fl exural phase were higher than former episodes of deformation, and they were concen-trated in the axial zone of the Eastern Cordillera, eastern fl ank of the Eastern Cordillera, and to a lesser extent in the Llanos foothills. In the north-ern Llanos foothills, this phase is constrained by the presence of growth strata that bound

basement-rooted structures, whereas in the cen-tral Llanos foothills, it is mainly constrained by the increasing fl exural subsidence toward the Eastern Cordillera and subtle deformation of tectono-stratigraphic sequence four. The fourth tectonic phase was also characterized by east-ward reactivation of tectonic loads and genera-tion of the salient-recess geometry of the thrust belt (Fig. 15C). In the hinterland, this phase is identifi ed by published apatite fi ssion tracks (Shagam et al., 1984; Toro, 1990; Hossack et al., 1999). Geodynamic analyses indicate that tectonic loads were 3–6 km high, 50–100 km wide, and wider in the northern than in the cen-tral cross section.

The last tectonic episode identifi ed in this study encompassed the width of the entire East-ern Cordillera, involved reactivation of basement structures during middle Miocene to Pliocene time, and ultimately defi ned the current confi gu-ration of major structures that bound the Eastern Cordillera, as well as the fl exural geometry of the Llanos Basin. Tectonic loads advanced eastward during at least two periods of out-of-sequence reactivation, as inferred from relations between hanging-wall and footwall structures of the Cha-meza and Guaicaramo faults in the central cross section, and of the Cobugon and Samore faults in the northern cross section. These phases of deformation are further constrained by rock-exhumation (Van der Wiel, 1991; Mora et al., 2005) and surface-uplift (Hooghiemstra and Van der Hammen, 1998) evidence. However, the lack of biostratigraphic constraints in the associ-ated alluvial and fl uvial deposits precludes rec-ognition of individual phases of deformation, similar to those uncovered here for the upper Cretaceous–middle Miocene succession.

The integrative approach used for this research permits identifi cation of the timing of activity on the different structures within the Eastern Cordillera and their effect on the adjacent sedi-mentary basin. This two-dimensional approach should be considered prior to a three-dimen-sional analysis of a thrust belt system in order to constrain the effects of a particular phase of deformation on location of source areas, dis-persal of synorogenic detritus, distribution of depositional systems, and stratal architecture in the basin. In addition, future thermochronologi-cal studies designed to quantify the exhumation of the Eastern Cordillera must encompass the width of the Eastern Cordillera rather than sam-pling a single range.

ACKNOWLEDGMENTS

This research was supported by the Colombian Petroleum Institute, Ecopetrol S.A., the Smithso-nian Paleobiology Endowment Fund, and the Unre-stricted Endowments SI Grants. Thanks are due to



the Biostratigraphic Team at the Colombian Petro-leum Institute, Nestor Gamba, and Johana Pinilla for their collaboration at different stages of this project. We thank Timothy Lawton for a careful review of the manuscript, which, together with the comments of an anonymous reviewer and Associate Editor James Schmitt, improved the content of this paper. Natasha Atkins reviewed the last revised version of the sub-mitted manuscript to improve the fl ow of the English. Bayona acknowledges discussions with Elias Gómez concerning foreland evolution of the Magdalena Val-ley and Llanos Basin, Andres Mora concerning the use of fi ssion-track data and reactivation of Meso-zoic structures, and Cornelius Uba, Mauricio Parra, and Brian Horton concerning evolution of Andean foreland systems.

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An integrated analysis of an orogen–sedimentary basin pair