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Tectonophysics 410 (

Late Pliocene–Quaternary tectonics in the frontal part of the SE

Carpathians: Insights from tectonic geomorphology

Diana Necea a,*, W. Fielitz a, L. Matenco b

a Geological Institute, University of Karlsruhe, Kaiserstr. 12, D-76131, Karlsruhe, Germanyb Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands

Received 13 April 2004; received in revised form 14 March 2005; accepted 25 May 2005

Available online 21 October 2005

Abstract

The Romanian East Carpathians display large-scale heterogeneities along the mountain belt, unusual foredeep geometries,

significant post-collisional and neotectonic activity, and major variations in topography, mostly developed in the aftermath of late

Miocene (Sarmatian; ~11 Ma) subduction/underthrusting and continental collision between the East European/Scythian/Moesian

foreland and the inner Carpathians Tisza-Dacia unit. In particular, the SE corner of the arcuate orogenic belt represents the place of

still active large-scale differential vertical movements between the uplifting mountain chain and the subsiding Focsani foredeep

basin. In this key area, we have analysed the configuration of the present day landforms and the drainage patterns in order to

quantify the amplitude, timing and kinematics of these post-collisional late Pliocene–Quaternary vertical movements. A river

network is incising in the upstream a high topography consisting of the external Carpathians nappes and the Pliocene–Lower

Pleistocene sediments of the foreland. Further eastwards in the downstream, this network is cross-cutting a low topography

consisting of the Middle Pleistocene–Holocene sediments of the foreland. Geological observations and well-preserved geomorphic

features demonstrate a complex succession of geological structures. The late Pliocene–Holocene tectonic evolution is generally

characterised by coeval uplift in the mountain chain and subsidence in the foreland. At a more detailed scale, these vertical

movements took place in pulses of accelerated motion, with laterally variable amplitude both in space and in time. After a first late

Pliocene uplifting period, subsidence took place during the Earliest Pleistocene resulting in a basal Quaternary unconformity. This

was followed by two, quantifiable periods of increased uplift, which affected the studied area at the transition between the

Carpathians orogen and the Focsani foreland basin in the late Early Pleistocene and the late Middle to late Pleistocene. Both large-

scale deformation events affected the western Focsani basin flank, tilting the entire structure with ~98 during the late Early

Pleistocene and uplifted it as a block during the early Late Pleistocene. The late Early Pleistocene tilting resulted in ~750 m uplift

near the frontal monocline and by extrapolation in a presumed 3000 m uplift near the central parts of the Carpathians. The late

Middle to late Pleistocene cumulative uplift reaches ~250 m and correlates with a contemporaneous progradation of the uplifted

areas towards the Focsani Basin. The uplifting events are separated by a second Quaternary unconformity. On the whole, the late

Pliocene–Quaternary evolution of the Carpathians orogen/Focsani basin structure indicate large-scale differential uplift during the

latest stages of a continuous post-collisional orogenic evolution.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Quaternary; Tectonic geomorphology; Fluvial terraces; Uplift; Focsani basin; East Romanian Carpathians

0040-1951/$ - s

doi:10.1016/j.tec

* Correspondi

E-mail addr

(L. Matenco).

2005) 137–156

ee front matter D 2005 Elsevier B.V. All rights reserved.

to.2005.05.047

ng author. Fax: +49 721 608 2138.

esses: necea_diana@yahoo.com (D. Necea), Werner.Fielitz@bio-geo.uni-karlsruhe.de (W. Fielitz), liviu.matenco@falw.vu.nl

D. Necea et al. / Tectonophysics 410 (2005) 137–156138

1. Introduction

The Carpathians orogenic system (Fig. 1a) repre-

sents the ideal site for studying processes linked to

lateral variations in continental collision mode, forma-

tion of arcuate orogens and oroclinal bending, unusual

foredeep development, and most interesting, large-scale

post-collisional deformations and differential vertical

motions along the orogen. The interaction of foreland

platform units with the Carpathians during the Alpine

deformation had a major impact on the geometries and

mechanics of the fold and thrust belt (e.g. Matenco and

Bertotti, 2000; Cloetingh et al., 2004; Tarapoanca et al.,

2003). Most of the recent year studies have been ded-

icated either to the Miocene evolution of the thrust belt

or to the unusual Vrancea seismic zone, which is char-

acterized by the largest strain concentration in Europe

(2�10�7 year�1; Wenzel et al., 1999), and its impact

into the Carpathians tectonic models (Sandulescu,

1988; Hauser et al., 2001; Sperner et al., 2001; Cloe-

tingh et al., 2004; Landes et al., 2004). In this respect,

tectonic geomorphology is a prime method to give

insights on the recent, last phases of orogenic deforma-

tion, which is the result of the uninterrupted interaction

between tectonic processes that tend to build up topog-

raphy and counteracting surface processes (e.g. Bur-

bank et al., 1996; Keller and Pinter, 1996; Burbank and

Anderson, 2001). Ongoing tectonic deformation sus-

tains these geomorphological features, whereas de-

creasing deformation or its cessation leads to their

rapid deterioration by weathering and erosion. In this

context, large-scale differential vertical motions have

been suggested for the late stage evolution of the SE

Carpathians and the adjacent Focsani basin (e.g., Ta-

rapoanca et al., 2003; Bocin et al., 2005—this volume).

However, no geomorphological studies have yet been

applied to quantify these movements and test the re-

gional post-collisional Pliocene–Quaternary evolution-

ary models.

Basin evolution studies demonstrated late Miocene

to Quaternary differential large-scale vertical move-

ments between the actively subsiding Focsani foredeep

basin (Fig. 1b; e.g. Matenco et al., 2003a; Bertotti et al.,

2003; Tarapoanca et al., 2003) and the uplifting adja-

cent orogen (e.g. Sanders et al., 1999). Recent studies

have demonstrated that the foreland zone is character-

ized by an abnormal disposition of the foredeep strata

as well as by large-scale normal faulting, both taking

place during the nappe emplacement and, more inter-

esting, during the post-collisional (post 11 Ma) defor-

mation phase (e.g. Bertotti et al., 2003; Tarapoanca et

al., 2003) and references therein). Apatite fission track

data (Sanders et al., 1999) suggest up to 5 km uplift and

subsequent erosion of the central-northern parts of the

East Carpathians, which took place during the main

Late Miocene collisional event. In contrast, in the SE

Carpathians bend area, e.g., south of the Trotus fault

(Fig. 1b), the main uplift largely postdates the colli-

sional event, and 2–3 km of uplift and erosion being

recorded during the Pliocene–Quaternary (Sanders et

al., 1999).

In this study, we use a detailed geomorphological

analysis on selected key areas in the paired SE Car-

pathians uplifting orogen/subsiding Focsani foreland

basin in order to characterize the tectonic evolution

and to quantify the amplitude of the Pliocene–Quater-

nary deformations (Fig. 1b). Preliminary studies (e.g.

Fielitz and Seghedi, 2005—this volume; Leever et al.,

2003) indicated the Putna valley (Fig. 1b) and the

surrounding river systems as a key area for recording

large differential vertical movements. The well-exposed

continuous profile covers the area from the western

flank of the Focsani basin in the east to the inner part

of the Moldavidian flysch nappes to the west. Using

detailed, local digital elevation models (DEM), geolog-

ic and geomorphological mapping of the Pleistocene–

Holocene river terraces and other Upper Pliocene–Qua-

ternary deposits, as well as additional geologic and

structural field observations, we try to derive the main

neotectonic deformation stages and to characterize their

amplitude, geometry and kinematics. In order to derive

the amplitude of these vertical movements, we have

focused on areas presently displaying the largest uplift.

These observations were furthermore correlated with

published structural data from the East Carpathians

and the Focsani basin.

2. Orogen and foredeep evolution

The East Carpathians are part of the Alpine–Car-

pathians orogenic belt. In this area, the Outer Car-

pathians or Moldavides (senso Sandulescu, 1984)

represents a thin-skinned unit, made up of a complex

nappe pile, emplaced over the slightly deformed fore-

land during the Miocene deformations (20–11 Ma,

Sandulescu, 1984, 1988; Ellouz et al., 1994; Morley,

1996; Badescu, 1998; Zweigel et al., 1998; Matenco

and Bertotti, 2000; Fig. 1b). The emplacement of the

nappes took place in response to late subduction/under-

thrusting and continental collision between the stable

East European/Scythian/Moesian foreland units and the

inner Carpathians Getic/Bucovinian (or Middle

Dacides, Sandulescu, 1988) crustal fragment (Radu-

lescu and Sandulescu, 1973; Constantinescu and

Fig. 1. (a) Digital elevationmodel of the Eastern Alps–Carpathians–Dinarides–Balkans region. Rectangle delimits the study area in the bending area of

the East Romanian Carpathians and dashed parallelogram corresponds to the seismic Vrancea area. (b) Geological map of the study area with themajor

rivers network. Rectangle shows the location of Fig. 3, where A–A’ profile corresponds to the whole Putna river from the source to the mouth (Fig. 5a).

D. Necea et al. / Tectonophysics 410 (2005) 137–156 139

Enescu, 1984; Sandulescu, 1984; Gırbacea and Frisch,

1998; Sperner et al., 2001; Fig. 1a).

2.1. External SE Carpathians nappes

The study area is located north of the East Car-

pathians bending area in Romania and comprises the

most external nappes (Tarcau, Marginal Folds and Sub-

carpathian nappes) and the adjacent foreland (Fig. 1b).

The Tarcau and the Marginal Folds nappes (Dumi-

trescu, 1952) are generally composed of Cretaceous

marine fine clastics (shales and marls), followed by a

mainly turbiditic succession of Senonian to Upper Ol-

igocene in age and the Lower Miocene salt formation.

D. Necea et al. / Tectonophysics 410 (2005) 137–156140

The frontal unit, the Subcarpathian nappe (Sandulescu,

1984) is mainly formed by deeply buried Eocene to

Oligocene clastics, overlain by Miocene molasse-type

sediments interlayered with two evaporitic levels of

Burdigalian and Badenian age (Sandulescu, 1984; for

comparison of local and international stages see Fig. 2).

The emplacement of these nappes started in the late

Early Miocene (late Burdigalian–Badenian) and contin-

ued until the late Miocene (Sarmatian–Meotian; 12–9

Ma) climax of deformation (Sandulescu, 1988; Ellouz

et al., 1994; Zweigel et al., 1998; Matenco and Bertotti,

Fig. 2. Time correlation table, stratigraphic column and tectonic evolution sc

bending area of Romania (modified after Dumitrescu et al., 1970; Sandules

absolute ages are taken from Haq et al. (1987); Rogl (1996); Gradstein et al.

Romanian interval are taken from the magnetostratigraphic results of Vasilie

detailed display of the stratigraphic column.

2000; Matenco et al., 2003a). During the later defor-

mation event the frontal Subcarpathian nappe was

thrusted eastward over the foreland platforms (Matenco

and Bertotti, 2000). The late Pliocene (Romanian) to

Early Pleistocene contractional deformation in the fore-

land reaches as far as the Pericarpathians Front (Hippo-

lyte and Sandulescu, 1996; Hippolyte et al., 1999;

Matenco and Bertotti, 2000; Stefanescu et al., 2000;

Fig. 1b). Apatite fission-track data show that uplift and

exhumation of the East Carpathians started in the late

Badenian–Sarmatian (15–11 Ma) in the central-north-

heme of the Upper Pliocene–Quaternary strata in the East Carpathians

cu, 1984). Time correlation table between Tethys and Paratethys and

(2004); Pillans and Naish (2004). Italic absolute ages in the Meotian–

v et al. (2004). Note the change in time scaling at 13 and 2 Ma, for a

D. Necea et al. / Tectonophysics 410 (2005) 137–156 141

ern parts of the East Carpathians, while in the East

Carpathians bend zone this event started in the Pliocene

(7–2 Ma; Sanders et al., 1999). Ongoing tectonic ac-

tivity in the East Carpathians is also indicated by ver-

tical crustal movements as revealed by geodetic

measurements (Popescu and Dragoescu, 1986; Zugra-

vescu and Polonic, 1997; Radulescu et al., 1998; Zugra-

vescu et al., 1998; van der Hoeven et al., 2004) and

seismic activity (Oncescu et al., 1998).

2.2. SE Carpathians foreland

The Carpathians foreland is composed of a puzzle

of Precambrian stable units with a relatively unde-

formed Paleozoic–Mesozoic autochthonous platform

cover belonging to the Moesian Platform to the

south and the East-European/Scythian Platforms to

the north (Fig. 1a; Sandulescu, 1984; Sandulescu

and Visarion, 1988; Visarion et al., 1988; Tari et al.,

1997 and references therein). Their contrasting geom-

etries and mechanical behaviour influence the style

and kinematics of nappe emplacement (Matenco and

Bertotti, 2000; Tarapoanca et al., 2003). Particularly,

during the Middle Miocene (Badenian) an extensional

event affected the Moesian sector, causing normal

faulting in the upper crust (Tarapoanca et al., 2003)

and a significant re-heating of the mantle and lower

crust. As a result, the Moesian sector has large varia-

tions in underthrusting/subduction characteristics lead-

ing to significant late stage post-collisional vertical

movements in the upper crust (Cloetingh et al.,

2004). The Neogene flexure of the East Carpathians

foreland underneath the nappe pile lead to the forma-

tion of a foredeep basin, whose Badenian–Quaternary

sediments reach 13 km in the central area of the

Focsani basin (Fig. 1a; Matenco and Bertotti, 2000;

Matenco et al., 2003a; Tarapoanca et al., 2003). The

eastern, external flank displays characteristic wedge-

shape bodies of a typical foredeep basin (Dicea,

1995). In contrast, the western flank displays changing

styles of basin geometry along the orogen. North of

the Trotus fault, in the area of the East-European/

Scythian stable units (Fig. 1), strata dip westward

continuing the wedge-foreland-type of geometry.

South of the Trotus fault, strata dip eastwards, reach-

ing a subvertical position near the contact with the

orogen, e.g. with the Subcarpathian nappe.

The sedimentary infill of the Focsani basin began

in the Middle Miocene (Badenian), when subsidence

started as a result of local extension (Tarapoanca et al.,

2003) or as a result of Middle Miocene thrust loading

(Matenco et al., 2003a). Large subsidence was

recorded during the late Miocene (Sarmatian) in the

Focsani basin, further continued in the Meotian. The

late Sarmatian–Meotian subsidence is coeval with the

large-scale eastward motion of the East Carpathians

and emplacement of the Subcarpathian nappe (Sarma-

tian thrusting) on the East-European foreland base-

ment. The total amount of shortening reaches 160

km (Roure et al., 1993; Ellouz et al., 1994; Morley,

1996), coeval with the accumulation of 3000 to 6000

m of molasse sediments (Dicea, 1995). The frontal

thrust is exposed in the areas north of the Trotus fault

and is deeply buried southwards to present depths up

to 6–8 km (e.g. Dicea, 1996). Starting with the latest

Miocene (Meotian–Pontian), the entire Carpathians

system and its foreland started to behave as a single

block (Horvath and Cloetingh, 1996). During this time

interval, the area south of the Trotus fault including

the Focsani basin and extending as far south and

westwards as the Balkans and their South Carpathians

connection, is defined as the Dacic basin (Jipa, 1997).

Decreased subsidence continued during latest Miocene

(Meotian) and accelerated again during late Pliocene

(Romanian)–Pleistocene time in the Focsani basin,

where 2–3 km of sediments were deposited in a

lacustrine to continental fluvial environment (Jipa,

1997; Tarapoanca et al., 2003). These deposits include

more than 2 km of Quaternary clastic sediments, as

indicated by recent shallow seismic profiling (Leever

et al., 2003). Accumulation of these Upper Pliocene

(Romanian)–Pleistocene sediments is coeval with the

latest contractional out-of-sequence bWallachianQphase (senso Sandulescu, 1988), which formed E–W

to NE–SW out-of-sequence trending thrusts and folds

located in a restricted area south of the Ramnicu Sarat

valley (Fig. 1b), the southernmost part of the East

Carpathians (Hippolyte and Sandulescu, 1996; Hippo-

lyte et al., 1999; Matenco and Bertotti, 2000). How-

ever, deposition in the Focsani basin does not reflect

this late stage of thrusting, because the direction of the

contraction is not compatible with the N–S trending

geometry of the Focsani basin. Nevertheless, the

Upper Miocene–Pliocene strata have been tilted up

to a subvertical position near the contact with the

exposed main frontal thrust of the Subcarpathian

nappe and the dip gradually decreases to subhorizontal

in the Holocene sediments towards the central part of

the basin.

2.3. Drainage network

The regional river drainage network consists of E-,

SE- and S-flowing rivers, which cross-cut the East and

D. Necea et al. / Tectonophysics 410 (2005) 137–156142

South Carpathians radiating towards the foreland. The

network has been modified by the late Pliocene–Qua-

ternary folding, thrusting and monoclinal tilting near

the Pericarpathians orogenic front and the western flank

of the Focsani basin, associated with out-of-sequence,

high angle basement faults. The latter apparently trun-

cate both the external thin-skinned units and the under-

lying stable platform of the East Carpathians foreland

(Landes et al., 2004; Bocin et al., 2005—this volume;

Fielitz and Seghedi, 2005—this volume). Surface trans-

port models based on present-day sediment load mea-

surements in the major rivers of the Carpathians and its

vicinity have demonstrated a strong discrepancy be-

tween the erosion-sedimentation balance north and

south of the Trotus/Peceneaga–Camena fault system

(Garcia-Castellanos, 2002; Cloetingh et al., 2003; Fig.

1b). Furthermore, geomorphological analysis demon-

strates equilibrated longitudinal river profiles north of

the Trotus fault, reflecting no younger deformations

than late Miocene (Sarmatian), while southwards, the

fluvial systems show young, still unequilibrated pro-

files, reflecting late Pliocene–Pleistocene deformations

(Radoane et al., 2003). As a result, the areas south of

the Trotus fault have large variations in geomorphic

features (terrace levels, river types, sources, variability

of stream traces) in direct relationship with the still

active vertical movements.

3. Methods of data analysis and river terraces

configurations

In order to investigate the geomorphological evolu-

tion of the SE Carpathians bend area and its adjacent

foreland, transect digital topographic models were

extracted near the Putna valley from digitizing

1 :25,000 topographic maps. From these, a medium

resolution digital elevation model (DEM) was

extracted, covering a surface of 120�40 km (Figs. 3

and 4). Its main geological boundaries are the Trotus

fault to the north, the Peceneaga–Camena fault system

to the east, and the frontal thrusts of the Marginal Folds

and Tarcau nappes to the west. The elevations range

from ~1.800 m in the west (Tarcau nappe near Tulnici)

to 20 m in the southeast (near the Siret–Barlad river

confluence). Locally slope grids with higher resolution

have been calculated from more detailed 1 :10,000

topographic maps for the reaches of the Putna river,

where small-scale river terraces have been mapped. The

DEM served to calculate the absolute elevations for all

terrace levels except for the lower, 1-, 2-, 5- and 10-m

levels, whose precise altitudes have been measured in

the field using local leveling. Terrace elevation in this

paper refers always to the vertical distance calculated

between the terrace surface and the level of the actual

active river channel.

The prime target was the Putna valley, but neighbour-

ing river networks (e.g. Milcov, Susi_a, Fig. 1b) were

also studied. Detailed geomorphological mapping was

carried out between Vitanesti to 50 km east of Tulnici

(Figs. 3 and 4). The field campaigns served to recognize

the types, geometry and relative ages of the fluvial

terraces and other alluvial deposits and their relationship

with the actively uplifting/subsiding basement. This

allowed to determine locations, elevations and number

of river terraces levels, and petrographic composition of

their sedimentary cover. Along the Putna river, a longi-

tudinal profile was zoomed in between the Tulnici and

Vitanesti localities, with individual terrace levels being

projected perpendicularly to the actual river channel (B–

B’ in Figs. 3 and 5a and b). Distances and altitudes of

each terrace segment were also plotted in the longitudi-

nal profile, the individual stream terraces being subse-

quently correlated to determine their extent, amount and

direction of tilting (Fig. 5b).

Stream patterns are very sensitive to active tectonic

movements, being dependent on the type and the

relative direction of deformed structures (e.g.,

Schumm et al., 2000). In general, the river response

to uplift is reflected in two types of stream terraces,

which have been recognized in the study area: degra-

dational (strath-terraces) and aggradational (fill-ter-

races) terraces. According to Burbank and Anderson

(2001), the strath-terraces are created when a river is

incising into the bedrock, typically within or immedi-

ately adjacent to tectonically active areas of mountain

chains (Fig. 6). The fill-terraces appear where the

riverbed is filled with alluvial sediments and the

river is subsequently incising into this filling, leaving

an aggradational abandoned surface at a higher level.

The strath-terrace deposits cover mostly planar to

slightly undulating bedrock surfaces and are composed

of gravels and sand with frequent channel structures,

similarly with the fill terraces. Stream terraces can be

paired or unpaired. The paired ones are formed as a

result of episodic vertical incision of the river channel

into the valley fill, which implies a regional develop-

ment and longer-term stable events (Merritts et al.,

1994). Unpaired strath-terraces are formed in response

to coeval continuous vertical incision and lateral ero-

sion of the river, controlled by episodic tectonic uplifts

(e.g., Merritts et al., 1994).

The ages of the Upper Pliocene–Quaternary deposits

and especially of the geomorphic markers used in this

paper are taken from the published geological maps of

Fig. 3. Regional digital elevation model (DEM) of the study area shows the main valleys and their surroundings with the main Carpathians nappes and Pliocene to Quaternary strata. Notice the late

Pliocene/Earliest Pleistocene unconformity, the late Early Pleistocene N–S trending frontal uplift of the Lower Pleistocene strata and their E (south and centre) to SE (north) change of dipping, which

influence the hydrographic network. The rectangle represents the enlargement shown in Fig. 4 and B–B’ is the approximate location of the Tulnici–Vitanesti cross-section (terrace occurrence) along

the Putna valley thalweg from Fig. 5b.

D.Necea

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410(2005)137–156

143

Fig. 4. Enlargement of the regional digital elevation model (DEM) from Fig. 3 in the central Putna valley area. Superimposed are the river terraces T1–T11 mapped in the field. Notice the highest

level T1 placed at 250 m above the riverbed, which forms the top of an isolated table-like hill and the most wide-spread level T5. Profiles I–VII correspond to Figs. 7a–c (Photographs) and 8a–d

(Cross-sections).

D.Necea

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410(2005)137–156

144

Fig. 5. (a) Longitudinal topographical profile along the Putna river thalweg from source to mouth (for location see Fig. 1b; �100vertical exaggeration). (b) Enlargement of the longitudinal profile

showing the Neogene–Quaternary geology between Tulnici and Vitanesti area including all mapped river terraces and terrace correlations (for location see Figs. 3 and 4; �15vertical exaggeration).

The frontal East Carpathians nappes emplaced in late Miocene (Sarmatian; ~11 Ma) time are covered by Pliocene to Holocene sedimentary successions from the western flank of the Focsani

foredeep basin. These deposits have a general eastward tilt toward the basin centre (outside of section) and are the site of two main Quaternary unconformities, which document complex uplift and

subsidence mechanisms in the East Carpathians/Focsani basin area.

D.Necea

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410(2005)137–156

145

Fig. 6. Schematic profile across a river valley showing a complex sequence of aggradational and degradational surfaces (after Burbank and

Anderson, 2001).

D. Necea et al. / Tectonophysics 410 (2005) 137–156146

the study area (Dumitrescu et al., 1970; Saulea et al.,

1968). No absolute dating of the Quaternary deposits

was possible during this work, but ongoing research is

presently using the optically stimulated luminescence

method to derive these absolute ages.

4. Late pliocene (Romanian) to Holocene geology

and geomorphology

4.1. River drainage system

Two different regional hydrographic domains have

been distinguished on the basis of the geometry of the

drainage network, located roughly to the south and to

the north of the Putna valley. The Milcov and Putna

rivers belong to the southern domain, where the flow is

generally oriented eastwards cross-cutting the Car-

pathians inner nappes and further the Pliocene and

Lower Pleistocene sedimentary succession of the Foc-

sani basin (Figs. 3 and 4). The rivers are oriented nearly

perpendicular to the strike of the tectonic structures

(e.g., the front of the Subcarpathian nappe), the cuesta

of the Lower Pleistocene deposits forming local drain-

age divides (Figs. 3 and 4). Eastwards of the outcrop-

ping Lower Pleistocene strata, the general drainage

changes to the SE as long as the rivers cut the Middle

Pleistocene–Lower Holocene deposits, then turn to the

SSE in the Upper Holocene deposits, close to the

junction with the Siret river (Figs. 1 and 3). The north-

ern domain between the Putna and Siret rivers (e.g.

Susi_a and Zabrau_ rivers) is mainly characterized by a

river network being drained to the SE to SSE up to the

junction with the NNW–SSE oriented Siret river, which

is flowing near the active, SSE-trending Peceneaga–

Camena fault system (Figs. 3 and 4; Matenco et al.,

2003b).

4.2. Late Pliocene (Romanian)–early Pleistocene

The western part of the study area is represented by

the Marginal Folds and Subcarpathian nappes, emplaced

during the main Sarmatian thrusting event (~11 Ma),

characterized by N–S striking folds and thrusts (Fig. 3).

The sediments incorporated into the thrusted nappes are

largely exposed along the main rivers and crop out along

the Putna valley from west of Tulnici to Valea Sarii.

Geomorphologically, the Tarcau and Marginal Folds

nappes are characterized by high topographic elevations

with values up to 1800 m (Fig. 3). Eastwards, the

Subcarpathian nappe exhibits clearly lower elevations

with average values between 400 and 700 m. However,

a clear higher topography of up to nearly 1000 m is

observed along its frontal sole thrust.

East of the frontal nappe thrust, the sedimentary

succession consists of Upper Miocene–Pliocene depos-

its, made up of a wide range of cyclic succession of

sandstones, marls and claystones (Fig. 2; see also Vasi-

liev et al., 2004). The upper deposits have a final basin

fill character, with fine-grained turbiditic-type of suc-

cessions, passing from lacustrine to continental envir-

onments (Jipa, 1997). These N–S oriented deposits

have been tilted westwards up to a subvertical position

(e.g., 858 in Sarmatian) near the contact with the ex-

posed frontal thrust of the Subcarpathian nappe. The

dip decreases gradually eastwards to 15–208 in the

Upper Pliocene (Romanian) deposits (Figs. 3, 5a and

7a). The layers are apparently truncated by an angular

unconformity and covered by Lower Pleistocene depos-

its (Fig. 7a). This reflects the first major uplifting period

of the western Focsani basin flank, which took place in

the late Pliocene.

Subsequent Earliest Pleistocene subsidence in the

Focsani basin is characterized by rapid deposition of

Fig. 7. Field views of late Pliocene to Holocene structures in the Putna valley area of the East Carpathians. (a) An angular unconformity is evident

between the 208 dipping Upper Pliocene (Romanian) and the 98 dipping Lower Pleistocene strata. A slightly eastward tilted Upper Pleistocene

strath-terrace (T5) and a Holocene fill-terrace (T10) can also be seen, which are unconformable to the Lower Pleistocene strata. View corresponds to

profile I in Fig. 4 near Vitanesti. (b) In the background the Lower Pleistocene strata are uplifted more than 750 m (Odobesti Hill) and dip 98 ENE-ward toward the Focsani foredeep basin (plain in the right background). Background view corresponds to profile II in Fig. 4. In front of the

Odobesti Hill the unpaired strath-terrace level T5 documents ongoing uplift (see also Fig. 5b). Holocene fill-terraces (T10) can be found near the

incised Putna river. (c) In the background Middle–Upper Pleistocene strath-terraces (T1, T3, T5, and T8) and in the foreground a Holocene fill-

terrace (T10) can be seen. View corresponds to profile IV in Fig. 4 near Tulnici.

D. Necea et al. / Tectonophysics 410 (2005) 137–156 147

400–500 m thick coarse-grained, only slightly consol-

idated sandy gravels/conglomerates and thinner inter-

bedded clays of the Candesti Formation (Dumitrescu et

al., 1970; Fig. 2). The conglomerates are well exposed

along the main rivers, especially on their northern

banks, where 140–150 m thicknesses can be observed

in the outcrops. The gravels have elements of 2 to 20

cm in size and consist of Mesozoic and Paleogene rocks

D. Necea et al. / Tectonophysics 410 (2005) 137–156148

from the adjacent Carpathians nappes cropping out

upstream. These deposits indicate a surprisingly high

energy of the source area. They are laterally continuous

and can be regionally correlated to large areas in the

Dacic foreland basin, probably deposited in a subaerial

fluvial environment in general and as shallow lacustrine

deposits in the Focsani Basin in particular. The unusual

coarse-grained character of these deposits, not present

for instance in the earlier peak collisional syntectonic

sediments, must have another control than only tecton-

ic. It could possibly be of climatic origin due to the

onset of the Pleistocene cold weather conditions leading

to increased physical weathering and a poor vegetation-

al cover.

Geomorphologically, the Lower Pleistocene deposits

can be easily recognized because of their higher topog-

Fig. 8. Topographic cross-sections derived from the DEM—data along the P

the Lower Pleistocene strata (profile III in Fig. 4; no vertical exaggeration), (

V in Fig. 4; �10vertical exaggeration), (c) Holocene fill-terrace T10 (profile

Upper Pleistocene terrace T5 north of N Odobesti Hill area, which is locate

exaggeration).

raphy relative to the surrounding deposits (Fig. 3).

Their maximum elevation of ~1000 m is reached on

top of the Odobesti Hill between Putna and Milcov

valleys (Figs. 3 and 7b). Elsewhere, lower elevations

of near 600 m are observed, in agreement with the

lower strata dip (Fig. 3).

The Lower Pleistocene conglomerates dip was mea-

sured in the outcrops or extrapolated from the DEM.

The latter was favored by the continuity up to few

kilometers of the outcrops, the strata being either par-

allel to the denudation surface on its top or at a minor

angle to its Upper Quaternary overlying cover (mostly

loess). Herewith, a direct or a minimum dip angle for

the bedding could be determined. Cross-section (Fig.

8a) and direct field measurements indicate a ~98 ENE-ward dip of the Lower Pleistocene conglomerates be-

utna valleys show: (a) more than 750 m uplift and 98 ENE-ward tilt of

b) b18 eastward tilt of the Upper Pleistocene strath-terraces T5 (profile

VI in Fig. 4; �10vertical exaggeration), (d) Strong asymmetry of the

d at the cut-bank side of the river (profile VII in Fig. 4; �10vertical

D. Necea et al. / Tectonophysics 410 (2005) 137–156 149

tween Milcov and Putna valleys (Fig. 3). South of the

Milcov valley, the dip direction is oriented more to the

east and the inclination decreases to 2–48. In a similar

way, north of the Putna valley, the inclination decreases

to 2–48 and the strike of these deposits changes to the

SE (Figs. 3 and 7a). Here, the reduced inclination is

also observed in a significant broadening of the out-

cropping areas of these Lower Pleistocene deposits

(Fig. 1). This overall pattern is the result of the northern

periclinal closure of the Focsani syncline-like basin.

4.3. Middle–late Pleistocene

The Middle to Upper Pleistocene sedimentary se-

quence is dominated mostly by the aeolian deposition

of thick loess, which overlain regionally earlier con-

glomeratic deposits and locally older river terrace

deposits.

4.3.1. Regional loess deposition

Thick primary accumulations of Middle–late Pleis-

tocene loess (Dumitrescu et al., 1970) with grey and

brownish paleosol horizons reach up to 50 m thickness

on the eastern flank and maximal 20 m on the western

flank of the Focsani Basin. The loess increases in

thickness from the longitude of Tulnici towards the

foreland, which strongly suggests an eastern source

area. Internal loess markers suggest a regional 2–48inclination, dipping eastwards south of the Putna valley

and SE-wards north of it. A minor unconformity exists

on top of the somewhat steeper dipping Candesti con-

glomerates (98) between the Putna and Milcov valleys.

In both cases, the palaeorelief carpeted by these dust

accumulations must have been very gentle.

4.3.2. Middle–upper Pleistocene terraces

The river adjustments to the active uplift on the

western Focsani basin flank are reflected in the forma-

tion of numerous levels of river terraces. The timing

relationship between these terraces and the regional

loess deposition is not entirely clear. Only one level

of fluvial terrace (T5) is conformably covered by 2–5 m

of loess, suggesting a syn- and post-depositional char-

acter of this level in respect to the loess deposition. The

Middle Pleistocene–Holocene terraces are composed

mainly by gravels and sands; the petrographic compo-

sition of the terrace clasts consisting either of mature

siliceous sandstone (Kliwa sandstone) or radiolarites

characteristic of the Tarcau and Marginal Folds nappes.

Also common are breccias, micro- and macro-conglom-

erates with green schists from the Marginal Folds nappe

and red to green marls from the Subcarpathian nappe

(see also Sandulescu et al., 1981). This composition

indicates the western neighbouring Carpathians nappe

pile, reflecting a short distance between the actively

uplifting source area and the depositional place. Eleven

main terrace levels have been mapped parallel to the

main rivers (from south to north the Milcov, Putna,

Zabala, Naruja and Susi_a). In this paper the main

focus is on the Putna valley because it shows an almost

complete terraces succession (ten levels, Fig. 3). From

the longitudinal profile of the Putna river (Fig. 5a) the

section between Tulnici and Vitanesti has been enlarged

for this study (profile B–B’ in Fig. 5b). It shows the

individual terrace levels, plotted at their elevation above

the active base-level (actual riverbed), their spatial cor-

relation, and the relationship between the terrace levels,

the actual channel bed and the incised bedrocks.

4.3.3. Middle Pleistocene terraces

The oldest unpaired strath-terrace level T1 of pre-

sumed Middle Pleistocene age (Dumitrescu et al., 1970)

appears only in two places. The first place is in the

Tulnici–Barsesti area on the right bank of the Putna

valley, where was uplifted at 159–247 m above the

Putna base level (Figs. 4, 5b and 7c). It is a composite

of 3 different sublevels, the highest one being at ~247

m, the dominant one at 171–188 m and a lower one in

its western prolongation at 159 m above base level.

Geomorphologically, it is different from all other ter-

races, forming the top of an isolated hill with a flat

surface. A few meters thick terrace sediments cover

unconformably the western Subcarpathian nappe

deposits. The unusual isolated table-mountain-like mor-

phology is either a real fluvial terrace, or represents the

last erosional remnant of a small intramontaneous sed-

imentary basin. This hill is located in the centre of a

now deeply eroded, low-topography area northwest of

the Putna/Naruja-river confluence (Fig. 4). A less well

preserved terrace-level T1 can be observed southwest

of the Naruja on the left bank of the Zabala valley at an

altitude of 140–167 m above base level (Fig. 3).

4.3.4. Upper Pleistocene terraces

The following eight strath-terraces of Upper Pleis-

tocene age (T2–T9) are located at 89–130 m (T2), 70

m (T3), 51–60 m (T4), 39–41 m (T5), 28–31 m (T6),

19–21 m (T7), 9–11 m (T8), and 5 m (T9) above the

river base level (Figs. 5 and 7a and c). All these

terraces are unpaired and distributed from the frontal

thrust of the Marginal Folds nappe (Tulnici–Herastrau–

Nereju) in the west to the Middle Pleistocene loess

sequence (Satu Nou–Vitanesti–Brosteni) in the east

(Fig. 3). Level T2 (89–130 m) has been identified

D. Necea et al. / Tectonophysics 410 (2005) 137–156150

only on the left bank of the Zabala valley. Remnants of

level T3 (70 m) appear on the right bank of the Putna

valley northeast of level T1 and another small remnant

near Mera in the Milcov valley. Level T4 (51–60 m) is

widespread particularly in the Zabala and Naruja

valleys from the Putna–Zabala confluence as far

south as Nereju and as far west as Herastrau (Fig. 3).

This level is locally composed of two sublevels at 51

and 60 m. The terrace level T5 (39–41 m) is regionally

also widespread and covers the largest surface of all,

suggesting a period of stability prior to a subsequent

large-scale uplift (Fig. 4). This is the only level where

the top of fluvial sediments is covered by primary

loess, 2–5 m thick and with intercalated grey paleosoil

horizons. The age of this level is uncertain, but corre-

lating the two lower grey paleosoil horizons with the

similar levels from the Mostistea Lake area in the SE

Moesian platform (S2-horizons) would suggest 180–

250 ky as the age of the loess deposits (Panaiotu et al.,

2001 and personal communication). According to these

authors, a possible climatic event is associated with

this regional loess deposition in large areas from the

Transylvania Basin in the west to the Carpathians

foreland in the east.

North of the Odobesti Hill, levels T6–T9 are very

well-preserved and developed only on the left bank of

the Putna river. Remnants of levels T6–T8 (28–31, 19–

21 and 9–11 m) have been identified almost every-

where. Their coarse-grained deposits are partly covered

by reworked loess originating from the higher terrace

level T5. Continued uplifted lead to the formation of the

youngest strath-terrace T9 (5 m), which is easily rec-

ognized in the main valleys. This level is deposited over

an irregular base rock morphology and is composed of

generally well-rounded basal gravels overlain by a

sandy succession with clear paleochannels and with

thicknesses up to 3 m in the Milcov, 1–1.5 m in the

Putna, and 1 m in the Susi_a valley.

The frontal thrusts of the Subcarpathian and Mar-

ginal Folds nappes are sealed by the levels T5, 6, 9 and

levels T3, 5, 8, respectively, suggesting that both thrusts

have not been reactivated since terraces deposition. A

latest Pleistocene to Holocene uplifting period can be

derived from the age of the youngest strath-terrace (e.g.,

level T9). The elevation of all strath-terraces decreases

downstream, intersecting the actual riverbed in the

Vitanesti area. These terraces are apparently parallel

to the actual Putna riverbed. However, their eastern

termination is often eroded, preventing a correct geo-

metrical reconstruction. In addition, an eastward tilting

of levels T1–T8 of ~18 (particularly obvious for T5

north of the Odobesti hill) can be derived from DEM

cross-section (Fig. 8b), longitudinal Putna river profile

(Fig. 5b) and detailed field observations.

The Putna valley displays a dual mode of unpaired

terraces deposition. Between Tulnici and east of Valea

Sarii, sedimentation of level T1 takes place only along

the point bar side of the river. In contrast, broad and

very well developed younger asymmetric terraces are

found only on the cut bank side of the Putna river

particularly north of the Odobesti hill (levels T5–T8;

Figs. 4, 7b and 8d). This effect is furthermore dimin-

ishing northwards, levels older than level T8 are poorly

preserved in the Susi_a valley (Fig. 3). The mechanism

generating this dual deposition is rather difficult to

differentiate. One can speculate that a higher uplift

took place north of the Putna valley than southwards,

superimposed on the first order general ESE-ward tilt-

ing of the coupled external nappes/Focsani basin sys-

tem. This second order effect can be the result of either

a local (fault) structure, otherwise not visible in the

available high-resolution seismic lines (e.g., Cloetingh

et al., 2003), or can be related to a differential uplift

along the northern periclinal closure of the Focsani

basin. Whatever the cause, this differential uplift is

also suggested by the geometry of the small tributaries

on the left bank side of the Putna river, which have an

anomalous south-oriented direction in a 2–4 km wide

corridor north of the Odobesti hill (Fig. 3).

4.4. Holocene

Fill-terraces of presumed Holocene age (Dumitrescu

et al., 1970) are widespread in the Putna and neighbour-

ing valleys (levels T10–T11, Figs. 3, 4 and 8). These

levels cover larger areas and are common in the east,

overlaying the Lower–Middle Pleistocene deposits at 2

and 1 m above the base level (Figs. 5b and 7a–c).

Paired terraces, developed on both sides of the main

rivers, are regionally better preserved, more continuous

and less eroded than the older ones (Fig. 3). These can

be observed as far east as a N–S-running line from

Vitanesti to Brosteni. In the Tulnici–Vitanesti sector

of the Putna valley, these geomorphological features

are parallel to the present-day riverbed (Fig. 5b), no

apparent tilting of the terraces occurred in the Holo-

cene. In contrast with the Upper Pleistocene terraces,

there seem to be no differences in terrace development

during the Holocene between the Putna and Susi_a

valley. In addition, paired terraces exist also in the

Putna valley section north of Odobesti Hill, where the

older terraces were strongly unpaired.

All Pleistocene and Holocene terraces are uncon-

formable to the Lower Pleistocene tilted Candesti con-

D. Necea et al. / Tectonophysics 410 (2005) 137–156 151

glomerates as shown by their different dips and relative

geometry (Figs. 5b and 7a). The terraces extend grad-

ually in time to areas in the east dominated earlier by

the subsidence of the Focsani basin, possibly as a result

of an eastward migration of the main bulk of uplift

during the late Pleistocene–Holocene.

5. Discussion

The geological structures along the studied Putna and

neighbourhood valleys are critical in quantifying the

Fig. 9. Tectonic evolution of the study area during the late Pliocene to Holoce

detailed post-collisional tectonic movements using geo-

morphological markers (Fig. 9). Uplifting and exhuma-

tion of the East Carpathians started in the late Badenian–

Sarmatian (15–11Ma; Sanders et al., 1999) and is coeval

with increased subsidence recorded in the Focsani basin

(Matenco and Bertotti, 2000). Erosion continued in the

Pliocene due to the cessation of plate convergence and

isostatic uplift of the region (Sanders et al., 1999). Dur-

ing the Pontian–Dacian times, lacustrine replaced brack-

ish sedimentation in the whole Dacic Basin (Carpathians

foreland including the Focsani basin).

ne time span as deduced from the observations presented in this paper.

D. Necea et al. / Tectonophysics 410 (2005) 137–156152

The Dacian–Romanian (Pliocene) is a period of

significant changes in the geological evolution of the

Focsani basin (Matenco et al., 2003a; Bertotti et al.,

2003; Tarapoanca et al., 2003), marking the transition

from regional subsidence to the present-day vertical

movements, differentiating the foredeep basin flanks.

Beginning with the Dacian, the lacustrine sedimenta-

tion in the Carpathians foreland was replaced by fluvial

sedimentation (Jipa, 1995, 1997) in the entire Dacic

basin, excepting the Focsani basin, where lacustrine

sedimentation took place until the Lower Pleistocene,

the basin being progressively filled. Despite the high

error bars in the rate estimates, it appears that the

sediment influx (0.9 mm/year; Vasiliev et al., 2004),

sustained by high erosion rates in the mountain chain

(1.0 mm/year; Sanders et al., 1999), exceeded the sub-

sidence in the foreland (0.8 mm/year; Tarapoanca et al.,

2003). The western Focsani basin flank, including the

Carpathians orogen, started to uplift at the same time

with the subsidence in the foreland basin centre (Tara-

poanca et al., 2003), causing the high erosion rates and

resulting in N–S trending steep east-dipping structures

(see Figs. 3, 4, 5b, 8a and 9a). At the same time the

regional drainage network originating during the late

Miocene (Sarmatian) collision event (Fielitz and

Seghedi, 2005—this volume) was modified by this

deformation, resulting a local drainage divide near the

frontal thrust of the Subcarpathian nappe (Figs. 3 and

4). This divide might have represented the now deeply

eroded cuesta of the steeply dipping basal Pliocene

beds in the Putna and neighbouring areas, whose actual

dip was increased by ~108 because of the subsequent

deformations (Figs. 3 and 5b).

During the Earliest Pleistocene, the uplift decelerat-

ed, but subsidence increased and the whole widening

Dacic basin was filled with 400 to 500 m of subaerial

fluvial conglomeratic sediments (Candesti Formation;

Jipa, 1997) covering unconformably the inclined Plio-

cene beds (Figs. 5b, 7a and 9b).

During the late Early Pleistocene, renewed acceler-

ated uplift of at least ~750 m in the Odobesti Hill area

above the actual Putna and Milcov river beds (Fig. 7b)

affected again the western flank of the Focsani basin,

coeval with the ongoing strong subsidence in the basin

centre (Bertotti et al., 2003; Tarapoanca et al., 2003).

This event is responsible for the monoclinal structure of

the Lower Pleistocene Candesti Formation developed

over more than 60 km between the Trotus valley in the

north and the Ramnicu Sarat area in the south (Fig. 1b),

reaching maximum values of ~98 ENE-ward tilting

between the Putna and Milcov valleys (Figs. 3, 4, 5b,

7a and b, 8a and 9c). Extrapolation of this tilting to the

west without modification would result in an uplift of

~1600 m near Valea Sarii, ~3600 m near Tulnici and

~6000 m near the source area of the Putna river (loca-

tion of the main Carpathians drainage divide; see Figs.

1b and 3 for locations). The latter value is questionable,

because the large-scale structure is not simply a tilted

monoclinal block, but has an N–S trending anticlinal

geometry with decreasing inclinations westwards. The

uplift values are further decreasing westwards until the

Targu Secuiesc and Brasov basins, where the uplift is

coeval with up to 500 m of ongoing Quaternary subsi-

dence (Ghenea et al., 1971; Visarion and Rotaru, 1988).

The uplift extrapolations can be compared with fission-

track results obtained in the core of the large-scale

antiformal structure, projected from regions outside of

the study area (north of the Trotus and south of the

Ramnicu Sarat valleys) to the upper reaches of the

Putna valley. These data indicate an exhumation of up

to 3000 m in the East Carpathians for the Pliocene time

interval (7–2 Ma; Sanders et al., 1999), which agrees

well with the order of magnitude of our data, particu-

larly for the large-scale antiformal geometry assumed.

Thus, we can explain the observed exhumation alone

by this Early Pleistocene uplift. Furthermore, it is pos-

sible to calculate minimum uplift rates for the ~750 m

uplift of the Lower Pleistocene deposits near the frontal

monocline. For the Early Pleistocene a minimum uplift

rate of 0.75 mm/year is obtained (~1 Ma; 1.806–0.781

Ma, Gradstein et al., 2004). The late Early Pleistocene

tilting caused the formation of a local drainage divide

running along the cuesta of the uplifted conglomerates

(Figs. 3 and 4). Small W–E oriented tributaries can be

observed running eastward parallel to the dip of the

NNW–SSE striking monocline, leading to the forma-

tion of 30–40 m deep incised valleys.

A decrease in the dip to 48 SE-ward inclined Lower

Pleistocene deposits in the Susi_a and Zabrau_ river areas

represents probably the northern periclinal closure of the

Focsani basin (Figs. 1b, 3 and 9c). The same decrease in

dip, combined with a similar reduction observed in the

Lower Pleistocene beds south of the Milcov valley, can

also be alternatively associated with the western neigh-

bouring periclinal closure of the dome-shaped uplift,

formed as a late stage out-of-sequence basement thrust-

ing into the nappe pile (Landes et al., 2004; Bocin et al.,

2005—this volume; Fielitz and Seghedi, 2005—this

volume). Its centre corresponds to the Vrancea tectonic

half-window, west of Tulnici (Fig. 1b), which expose

deeper structural levels of the Marginal Folds nappe

beneath the overthrusted Tarcau unit.

The uplift of the western flank of the Focsani basin

continued during the Middle– late Pleistocene as docu-

D. Necea et al. / Tectonophysics 410 (2005) 137–156 153

mented by the 9 levels of strath-terraces typical for

tectonically active areas of mountain chains (Burbank

and Anderson, 2001). The oldest unpaired strath-terrace

level T1 of presumed Middle Pleistocene age (Dumi-

trescu et al., 1970) documents ~250 m uplift above the

Putna base level in the hinterland (Figs. 4, 5b, and 7c).

Starting with the early Late Pleistocene the amplitude

of the uplifting area increased, affecting both the orogen

and the foreland. Its eastward extension covered grad-

ually areas dominated earlier by subsidence and accu-

mulation of the Middle Pleistocene loess deposits (Fig.

9d), resulting in a second angular unconformity (Fig.

9e). During this time period, the terrace level T5 repre-

sents a particularly wide-spread event, suggesting a

major period of stability followed by a renewed large-

scale uplifting period. A regional climatic event took

place covering the top of level T5 with 2–5 m of loess

during the late Middle Pleistocene (~180–250 ky). A

decreased amount of uplift took place probably north-

wards, along the strike of the orogen, because terraces

are absent or not well developed in the Susi_a and

Zabrau_ area. Because the terraces are roughly parallel

(up to 18 tilting) to the actual riverbed, the regional

uplift seems to be uniform across the strike of the

orogen (Fig. 9e).

Tentative uplift rates for different fluvial terraces can

be also estimated. If the above assumed age for the

terrace level T5 is correct, 40 m uplift took place during

the last ~200 ky and an uplift rate of 0.2 mm/year was

computed. The highest terrace T1 (~250 m) has a

probable Middle Pleistocene age (Dumitrescu et al.,

1970), which corresponds to 781–126 ky (Gradstein

et al., 2004). This results in maximal ~580 ky between

levels T1 to T5, corresponding to a ~210 m differential

uplift with a minimum uplift rate of 0.4 mm/year. A

general pattern of decreasing uplifts rates from Early to

late Pleistocene seems therefore coherent, being corre-

lated with a coeval progradation of the uplifted areas

towards the Focsani Basin. However, one should note

the very poorly constrained ages of the Quaternary

deposits.

This large-scale pattern continued during the Holo-

cene, uplifting with a few meters the paired fill-terraces.

This can be either a regional uplift, larger than the study

area, or a climatic driven event. The terrace geometries

suggest that the deformation zone between Putna and

Susi_a rivers became tectonically inactive. Ongoing

deformation is inferred by repeated leveling measure-

ments in the central Putna valley indicating actively

uplifting areas (2–5 mm/year) in the vicinity of subsid-

ing foreland blocks (3 mm/year; Popescu and Dra-

goescu, 1986; Zugravescu and Polonic, 1997). The

overall differential vertical movements are confirmed

also by recent GPS studies, which indicate a largely

subsiding area (3 mm/year) spatially juxtaposed over

the Focsani basin centre situated in the vicinity of an

asymmetric uplift zone over the external SE Car-

pathians nappe (van der Hoeven et al., 2004).

The equal large-scale amplitude of the coeval uplift

in the Carpathians as described in this study and sub-

sidence in the foreland and its characteristic ~80 km

wavelength could suggest rather a crustal scale folding

mechanism (lithospheric buckling, senso Cloetingh et

al., 1999) induced by an intraplate compressional stress

field (see the comparative study analysis of Bertotti et

al., 2003). This late-stage tectonic event followed the

collision, taking place during the late Miocene (Sarma-

tian), locked down the orogen–foreland system and

further deformation affected the area as a single block

(e.g. Horvath and Cloetingh, 1996; Matenco and Ber-

totti, 2000). Additional mechanisms like the out-of-

sequence thrusting of the crystalline basement at

depth into the nappe stack, is suggested by tomographic

modeling in the Vrancea area (Landes et al., 2004;

Fielitz and Seghedi, 2005—this volume) and possibly

related to the observed late Early Pleistocene localized

uplift, which can enhance or cause the recent uplift of

parts of the SE Carpathians. However, because the

Miocene nappe thrusts were sealed by the Middle to

Upper Pleistocene terrace deposits, no near surface

reactivation of the nappe structures took place in the

study area.

6. Conclusion

After a late Pliocene uplifting period, subsidence

took place during the Earliest Pleistocene, recognized

in a basal Quaternary unconformity. This was followed

by two coupled quantifiable periods of increased uplift,

which affected the studied area at the transition between

the Carpathians orogen and the Focsani foreland basin,

during the late Early Pleistocene and the late Middle to

late Pleistocene. Both large-scale deformation events

uplifted the western Focsani basin flank, tilting the

entire structure with ~98 relative to the Lower Pleisto-

cene deposits and respectively uplifted it as a block

relative to the lower Upper Pleistocene terraces. The

late Early Pleistocene tilting resulted in a ~750 m uplift

above the actual Putna and Milcov beds near the frontal

monocline and by extrapolation in a 3000 m or higher

uplift near the central parts of the Carpathians, which

fits well with exhumation values deduced from the

published fission track data north and south of the

study area. The late Middle to late Pleistocene cumu-

D. Necea et al. / Tectonophysics 410 (2005) 137–156154

lative uplift reaches ~250 m above the actual Putna bed.

Both deformation events are separated by a second

Quaternary unconformity. Tentative calculations seem

to demonstrate a trend for decreasing uplifts and uplift

rates from Early to late Pleistocene, compatible with a

contemporaneous progradation of the uplifted areas

towards the Focsani Basin.

Acknowledgements

The project represents a collaboration between the

University of Karlsruhe, Germany and the University

of Bucharest, Romania and was funded through

Deutsche Forschungsgemeinschaft (German Research

Foundation) by providing the funding for the Sonder-

forschungsbereich 461 (CRC 461) at the University of

Karlsruhe, Germany: QStrong Earthquakes—A Chal-

lenge for Geosciences and Civil EngineeringQ, whichis greatly acknowledged. We thank Prof. C. Dinu

(University of Bucharest) for the detailed guidance,

discussions and suggestions in the project. The sec-

ond author also wants to thank D. Badescu (Univer-

sity of Bucharest) and M. Melinte (Geoecomar,

Bucharest), who contributed to the development of

this paper with their discussions and the introduction

to the Romanian geology. The third author developed

his work for this publication in the Netherlands Re-

search Centre for Integrated Solid Earth Sciences. We

also thank C. Panaiotu, B. Szekely, and an anony-

mous reviewer for their careful and constructive

reviews, which significantly improved the submitted

manuscript.

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