Nielsen-05-JSAES-The Triassic Santa Juana Formation at the lower Biobı´o River, South central Chile

ati

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Institut fur geologische Wissenschaften, Fachrichtung Palaontologie, Freie Universitat Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany

were classified as the Santa Juana Formation by Ferraris previously described by Steinmann (1921) and Tavera

Journal of South American Earth SE-mail address: [email protected] 15 June 2005

Abstract

A sequence of Triassic rocks is exposed near the town of Concepcion, Chile. These clastic strata are interpreted as the deposits of rivers,

lakes, playas, and alluvial fans. The deposits comprise conglomerates, arkosic sandstones, and sand-, silt- and mudstones. Four facies

associations comprising eight sedimentary facies can be distinguished. Plant fossils from the sedimentary sequence of the Santa Juana

Formation indicate a Carnian age. The flora includes ferns (Gleichenites, Cladophlebis, Dictyophyllum, Thaumatopteris, Asterotheca,

Saportaea) and seed ferns (Kurtziana, Antevsia, Dicroidium), ginkgophytes (Sphenobaiera), cycads (Pseudoctenis), conifers (Heidiphyllum,

Telemachus, Rissikia), and gymnosperms of uncertain affinities (Linguifolium, Gontriglossa). Two new species are presented: Pseudoctenis

santajuanensis and Gontriglossa reinerae.

q 2005 Elsevier Ltd. All rights reserved.

Keywords: Chile; Flora; Sedimentology; South America; Triassic

Resumen

En las proximidades de la ciudad de Concepcion, Chile, se exponen una secuencia de rocas Triasicos. Estas capas clasticas son

interpretadas como depositos de ros, lagos, lagos efimeros (playa-lakes), y abanicos aluviales. Esta secuencia comprende fanglomerados,

areniscas arcosicas, areniscas, lutitas y arcillolitas. Pueden ser distinguidas cuatro asociaciones de facies que incluyen ocho facies

sedimentarias. En la Formacion Santa Juana se describen restos de plantas, las quales indican una edad Carnico para esta secuencia. Como

elementos florales se pueden distinguir helechos (Gleichenites, Cladophlebis, Dictyophyllum, Thaumatopteris, Asterotheca, Saportaea) y

helechos con semillas (Kurtziana, Antevsia, Dicroidium), ginkgophitas (Sphenobaiera), cicadeas (Pseudoctenis), conferas (Heidiphyllum,

Telemachus, Rissikia), y algunos gimnospermas de atribucion incierta (Linguifolium, Gontriglossa). Se describen dos nuevas especies:

Pseudoctenis santajuanensis y Gontriglossa reinerae.

q 2005 Elsevier Ltd. All rights reserved.

1. Introduction

This paper presents sedimentologic, stratigraphic, and

fossil data for a sequence of Triassic rocks exposed in the

Chilean Coastal Cordillera along the lower Biobo River

west of the town of Concepcion, Chile (Fig. 1). These rocks

for all Triassic deposits in the area surrounding the village

of Santa Juana (Fig. 1). The clastic rocks of the Santa Juana

Formation (Ferraris, 1981) were dated as Late Triassic in

age by Steinmann (1921) and Jaworski (1922) on the basis

of fossil plants and marine invertebrates. Newly collected

plant fossils necessitate a reinvestigation of the floraThe Triassic Santa Juana Form

south ce

Sven Non at the lower Biobo River,

al Chile

ielsen

ciences 19 (2005) 547562

www.elsevier.com/locate/jsamesin a NW-SEtrending basin formed during the initial

breakup of Gondwana and the beginning of the Mesozoic

subduction along its western margin, possibly directly

related to the Gastre fault system (Rapela and Pankhurst,

1992). The Santa Juana Basin is one of a series of other0895-9811/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jsames.2005.06.002(1981), but no clear definition of the formation was

provided. Here, the name Santa Juana Formation is used

Jerez (1960).

The rocks of the Santa Juana Formation were deposited

ricanS.N. Nielsen / Journal of South Ame548Triassic basins in Chile (Charrier, 1979) and Argentina

(Uliana and Biddle, 1988) that are generally thought to be

rift related (Suarez and Bell, 1992). During deposition,

highlands surrounding the basin consisted of Paleozoic

metasediments in the north and northwest and granitoid

rocks of the southern Coastal Batholith in the remaining

parts. The Santa Juana Formation unconformably overlies

these crystalline basement rocks (Gonzalez-Bonorino and

Aguirre, 1970). Consequently, in the north and northwest of

the basin, coarse conglomerates consisting of mainly

metamorphic rocks occur at the base, and granitoid debris

is prominent in the basal part of the central and southern

area. Higher in the sequence, as well as basinward, the

formation becomes progressively finer grained. Dominated

by rivers and lakes, terrestrial sedimentation was interrupted

by at least one short marine ingression. However, this

ingression is recognizable not by sedimentological changes

but solely through the occurrence of marine fossils.

In the study area, gentle folding and intense faulting of

the Santa Juana Formation, together with the scarcity of

stratigraphically valuable fossils and lack of marker

horizons, make stratigraphic correlations among the isolated

outcrops extremely difficult. The few reported volcanic

rocks (Bruggen, 1934; Abad and Figueroa, 2003) and

anthracite seams (Alfaro and Helle, 2000) have not proven

Fig. 1. Geological setting and location of the study area wEarth Sciences 19 (2005) 547562to be of stratigraphic value because of their weathering and

alteration. These same stratigraphic and structural complex-

ities prevent any definitive thickness estimates for the

formation, though such estimates in the literature range

from 300350 m (Felsch, 1913) to 10,00011,000 m

(Tavera Jerez, 1960).

2. Previous models

The first stratigraphical model, provided by Tavera Jerez

(1960), distinguished the following three members in the

eastern part of the Santa Juana Formation, from base to top:

(1) the Quilacoya Member or lower continental section, (2)

the Unihue Member or marine section, and (3) the

Talcamavida-Gomero Member or upper limnic member.

The Quilacoya Member contains carbon seams, plant

remains, and freshwater bivalves. It shows no marine

influence, and its thickness has been estimated as 1500 m.

The Unihue Member contains marine mollusks, mainly the

bivalve Halobia, and has an estimated thickness of 2500

3000 m. The Talcamavida-Gomero Member contains plant

remains, freshwater bivalves, and conchostracans and has an

estimated thickness of 30003500 m. The western part of the

formation is composed of approximately 3000 m of

ith localities of vertical profiles and the found flora.

g allu

arine

ricanconglomerates (Tavera Jerez, 1960). The ages of the three

members are given as possibly Early Carnian for the

Quilacoya Member, Carnian for the Unihue Member, and

Norian-Rhaetian for the Talcamavida-Gomero Member

(Tavera Jerez, 1960).

Cucurella (1978), measuring the uranium, copper, lead,

and zinc contents in these sediments, basically used

Taveras model and placed conglomerates as a fourth

member at the base of the unit. The thickness of the

conglomerates (member 1) is given as 200 m, member 2 is a

250 m thick continental succession, member 3 comprises

400 m of shallow marine rocks, and member 4 is constituted

by approximately 500 m of coarse-grained delta deposits

(Cucurella, 1978).

During fieldwork in 1997, sedimentological studies led to

Fig. 2. Generalized facies distribution of the Santa Juana Formation includin

association, facies 3 and 4), lakes (third facies association, facies 57), and m

Not to scale.

S.N. Nielsen / Journal of South Amea facies model that is not consistent with this lithostrati-

graphic model. Previous models therefore are here regarded

as too simple for the complex history of the Santa Juana

Basin. Similar successions of facies have been observed in

areas that belong to different members in Tavera Jerezs

(1960) and Cucurellas (1978) models. Features such as

grain size vary laterally and are related to transport

mechanisms and the relative distance of source rocks rather

than capable of distinguishing lithological units. At this

stage, it is preferred to distinguish only those sedimentary

facies in the Santa Juana Formation and to compile a still

generalized model of facies development for the basin

(Fig. 2) rather than present a stratigraphic model based on

assumptions but lacking any real stratigraphic data.

3. Sedimentary facies

3.1. Facies 1: granitoid debris

Facies 1 consists mainly of coarse quartz grains derived

from the granitoid basement. The amount of othercomponents that compose the fine-grained matrix varies

considerably. For the study area, the base of the sedimentary

cover on the granitoid basement (Fig. 3A) is difficult to

define because the transition from unweathered to

weathered granitoid basement and to unstratified granitoid

debris seems gradational. Upward in the section and

basinward, stratification becomes recognizable, and the

portion of finer-grained material increases. A transition to

facies 4, which sometimes occurs through facies 2 and/or

facies 3, takes place in a general fining- and thinning-

upward tendency. Even in coarse granitoid debris, fossilized

tree trunks up to 2 m long indicate colonization by

arboraceous plants. In finer-grained granitoid debris,

unidentifiable plant remains are common.vial fan (first facies association, facies 1 and 2), alluvial plain (second facies

deposits (fourth facies association, facies 8). AD refer to sections in Fig. 3.

Earth Sciences 19 (2005) 547562 5493.2. Facies 2: conglomerates and arkosic sandstones

The sedimentary strata overlying Paleozoic metamorphic

rocks are composed of conglomerates and arkosic sand-

stones, with bed thicknesses of several meters (Fig. 3B).

Beds with erosive bases are rare.

The weathered sediments have a yellowish to red color.

Scanning electron microscopy (SEM) examinations

revealed a high portion of unweathered idiomorphic

feldspar. The conglomerates are poorly sorted, with

predominantly angular to subrounded clasts that vary in

size from 2 to more than 20 cm. Most conglomerates are

supported by a heterogeneous sandy matrix. Only a few

clast-supported beds have been observed. Dominant large-

scale sedimentary features are continuous, and parallel

bedding planes are defined by color and grain-size

variations. Internally, the beds tend to be structureless,

chaotic, and disorganized. No bioturbation was observed.

Above the conglomerates and arkosic sandstones, finer-

grained sandstones, siltstones, and mudstones (facies

Fig. 3. Selected lithosections from different localities (see Fig. 1, Table 2). For facies classification of A, B, and D, see Table 1. (A) Section near Quilacoya showing contact zone between granitoid basement and

sedimentary cover. (B) Section near Patagual showing basal part of sedimentary cover on metamorphic shales. (C) Section at the railway between Gomero and Buenuraqui. (D) Section near Santa Juana

illustrating black shale-sandstone alternation.

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3 and 4) become dominant, and plant debris becomes

common (mainly Heidiphyllum). This tendency of fining-

and thinning-upward beds corresponds to that of facies 1.

Facies 2 is interpreted as alluvial fan deposits. The poorly

sorted and poorly rounded coarse-grained sediments

indicate a short transport distance and therefore were

deposited relatively proximal to the basin margin. The

character of these sediments seems to indicate arid or

semiarid climate conditions, but the occurrence of few coal

seams suggests occasional deposition during more humid

intervals.

where few distinct sedimentary structures, mostly parallel

bedding and occasionally ripple marks, are preserved. Some

conglomerates with well-rounded, well-sorted clasts of

predominantly metamorphic origin occur. On the basis of

the occurrence of ripple marks and well-rounded conglom-

erates, as well as the relationship with other facies,

deposition is interpreted to have taken place near the shores

of lakes or river banks or on inactive, muddy, vegetated

overbank areas between sandy river channels.

3.5. Facies 5: black shales

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562 5513.3. Facies 3: sandstones and siltstones

Facies 3 consists mainly of yellowish to red, weathering,

interbedded sandstones and siltstones. Red-brown staining

is interpreted as due to oxidation of pyrite contained in

carbonaceous plant debris (Bell and Suarez, 1995). Some

siltstone layers are cross-laminated, whereas some sand-

stone bedding surfaces contain asymmetrical current ripple

marks. Root traces are also common. A rich flora was found

in silty layers near Patagual (upper part of Fig. 3B).

Steinkerns of freshwater bivalves, probably of the family

Unionidae, and plant remains occur at the railway cut near

Buenuraqui (Fig. 3C). At this location, the rocks are less

weathered and dark gray in color. Frequent fining-upward

cycles and occasional normally graded sandstones were also

observed in this section, as well as lenticular beds

interpreted as channel fills. This outcrop shows gentle

folding and normal faults with dislocation rates of less than

5 m.

The facies assemblage and upward-fining cycles

(Fig. 3C) indicate distal rivers and alluvial plain deposits.

The repeated succession of structures like ripple marks, root

horizons, and layers with plant debris (Fig. 3B, upper part)

suggests deposition in floodplain lakes that were later

colonized by rooting plants.

3.4. Facies 4: siltstones and mudstones

Facies 4 comprises silt- and mudstones that contain a rich

flora. A diverse association of ferns and gymnosperms was

recovered mainly from outcrops at the Cerro Calquinhue,Fig. 4. (1) Conchostraca indet., height of photo 8The soft, easily weathered nature of these rocks results in

poor natural exposures. Only one good section is available

near the village of Santa Juana (Fig. 3D), where a bypass

cuts these mudstones. However, some small outcrops also

exist on both banks of the Biobo River. On some surfaces,

conchostracans (Estheria forbesii Jones 1862 of Tavera

Jerez, 1960; Fig. 4(1)) are very abundant, and isolated plant

fragments and insect remains occur. The shales are rich in

organic carbon and partially bioturbated. These deposits

suggest accumulation in the subaquatic part of a fan delta or

talus deposits with occasional turbidity currents (facies 6).

Finely laminated black shales are interpreted as the product

of settling from suspension in relatively deep water, as

indicated by facies 6. However, some of the black shales

may have been deposited in abandoned channels or lakes,

leading to the still conditions preferred by conchostracans.

Assignment to one of the two rather different environmental

settings is based on the association with facies 6 (deeper

water) or the occurrence of conchostracans (still shallow

water).

3.6. Facies 6: sandstones and siltstones

The coarse- to fine-grained sandstones representing

facies 6 usually occur alternating with the black shales of

facies 5 (Fig. 3D). Sedimentary structures like slumping,

fining-upward sequences, and reworked shale intraclasts are

common. These sandstones are interpreted as lacustrine

turbidites. Occasionally, load structures and flame structures

are present at contact planes with intercalated black shales

of facies 5. These structures, together with slumping, mightmm. (23) Halobia sp., scale bar 10 mm.

possibly driftwood have been recorded. Near the village of

d,

to

to

Fl Sand, silt, mud

Massive Backswamp or abandoned channel

deposits

Massive, roots, bioturbation Root bed, incipient soil

ricanSanta Juana, this facies is exposed at both banks of the

Biobo River. Locally the massive sandstones have a dark

gray color and are rich in organic carbon. Some finer layers

contain unidentifiable plant remains. These massivebe related to earthquake-induced liquefaction rather than

load-related fluid loss, but no unequivocal structures have

been observed.

3.7. Facies 7: massive sandstones

Facies 7 comprises massive sandstones with rare

intercalations of well-rounded conglomerates. The massive

sandstones contain sedimentary structures such as channel

fills, slumping, fining-upward sequences, convolution,

reworked shale intraclasts, and load casts. A few trunks of

Fsm Silt, mud

Fr Mud, siltTable 1

Facies classification (from Miall, 1996)

Facies code Facies

Gmm Matrix supporte

massive gravel

Sr Sand, very fine

coarse

Sh Sand, very fine

coarse, may be

pebbly

Sm Sand, fine to

coarse

S.N. Nielsen / Journal of South Ame552sandstones are interpreted as mass-flow deposits. On top

of these deposits, rivers cut channels and deposited

conglomerates. The erosive nature is indicated by reworked

finer sediment, such as shale intraclasts. However, the base

of this facies was not found, so an interpretation of the place

of deposition is not currently possible.

3.8. Facies 8: marine siltstones

Facies 8 contains siltstones superficially indistinguish-

able from those of facies 4 or 6. The abundant marine

bivalve Halobia (Fig. 4(23)) indicates a marine environ-

ment (e.g., Campbell, 1994). Bioturbation led to knobby

surfaces. Other marine fossils could not be found. However,

Jaworski (1922) and Tavera Jerez (1960) reported ammo-

noids (Arcestes, Trachyceras?), bivalves (Palaeoneilo,

Lima, Myoconcha, Phaenodesmia, Myophoria), and a

gastropod (Turbo). No section was measured due to the

small scale of the outcrops.3.9. Facies associations

The sedimentary rocks of the Santa Juana Formation

have been subdivided into eight facies (Fig. 2) grouped into

four facies associations (Fig. 3, Table 1). The first facies

association comprises granitoid debris (facies 1) and alter-

nating conglomerates and arkosic sandstones (facies 2).

These two facies are interpreted as deposits of alluvial fans.

The second facies association contains sandstones to

siltstones (facies 3) and siltstones to mudstones (facies 4),

interpreted as alluvial deposits. The third facies association

comprises black shales containing conchostracans (facies 5,

Fig. 4(1)) alternating with sand- to siltstones (facies 6) and

locally massive sandstones (facies 7). These deposits are

interpreted as accumulating in a sublacustrine setting with

occasional turbidity currents and mass flows. The fourth

facies association consists of marine mudstones, sandstones,Sedimentary structures Interpretation

Weak grading Plastic debris flow (high-strength,

viscous)

Ripple cross-lamination Ripples (lower flow regime)

Horizontal lamination parting or

streaming lineation

Plane-bed flow (critical flow)

Massive, or faint lamination Sediment-gravity flow deposits

Fine lamination, very small ripples Overbank, abandoned channel, or

waning flood deposits

Earth Sciences 19 (2005) 547562and bioturbated siltstones (facies 8) that contain the

abundant bivalve Halobia sp. (Fig. 4(23)).

4. The paleoflora

Descriptions of fossil plant remains from the Santa Juana

Formation, mostly without figures, have been published by

Steinmann (1921) and Tavera Jerez (1960). The flora of the

Santa Juana Formation is a typical Gondwana Upper

Triassic Dicroidium flora, similar to the Molteno flora of

southern Africa (Anderson and Anderson, 1983, 1984,

1989). However, in contrast to the Molteno flora, the Santa

Juana flora is dominated by Heidiphyllum and Pseudoctenis

with Dicroidium as a subordinate component.

Locality 1 (Fig. 1, Table 2) comprises two outcrops at the

Cerro Calquinhue that were cut by a forest road. The

sediments have been deposited by rivers in an alluvial plain

(facies 4). Locality 2 (Fig. 1, Table 2) is located along

Table 2

Coordinates of vertical profiles and flora. Map: data taken from map, GPS: measured by GPS

Section near Quilacoya (Fig. 3A) S37803 0/W073857 0 (Map)Section near Patagual (Fig. 3B) S37801,3070/W073801,3030 (GPS)Section between Gomero and Buenuraqui (Fig. 3C) S37812,1380/W072847,6650 (GPS)Section near Santa Juana (Fig. 3D) S37810,2700/W072857,4060 (GPS)Locality 1 at the Cerro Calquinhue S37805,5950/W072853,5340 (GPS)Locality 2 between Quilacoya and Chillancito S37804,7100/W072856,3280 (GPS)Locality 3 near Patagual S37801,50/W073801,5 0 (Map)

Fig. 5. (1) Gleichenites sp., Cp 1299. (2) Dictyophyllum fuenzalidai Herbst (2000), Cp 1277. (3) Thaumatopteris rothii Frenguelli 1941, Cp 1284. (4)

Cladophlebis sp., Cp 1270. (5) Dictyophyllum tenuifolium (Stipanicic and Menendez 1949) Bonetti and Herbst 1964, Cp 1291. (6) Asterotheca fuchsii

(Schimper ex Zeiller 1875) Herbst 1998, Cp 1282. (7) Saportaea dichotoma (Frenguelli, 1942) Stipanicic and Bonetti (1965), Cp 1297. Scale bar for all figures

is 10 mm.

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562 553

Fig. 6. (1) Kurtziana cacheutensis (Kurtz 1921) Frenguelli 1941, Cp 1287. (2) Antevsia (?) sp., UdeC. (3) Dicroidium crassinervis (Geinitz 1876) Anderson and

Anderson (1983) forma trilobitum (Johnston 1886) Anderson and Anderson (1983), Cp 1285. (4) Dicroidium odontopteroides (Morris 1845) Gothan 1912

forma lineatum (Tenison-Woods 1883) Anderson and Anderson (1983), UdeC. (5) Dicroidium elongatum (Carruthers 1872) Archangelsky 1968 forma

remotipinnulum Anderson and Anderson (1983), Cp 1298. (6) Seed of Dicroidium, UdeC. (7) Dicroidium elongatum (Carruthers 1872) Archangelsky 1968

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562554

the road from Quilacoya to Chillancito, where the marine

facies (facies 8) is exposed in a small outcrop. Locality 3

Todites, sporangia of the Osmundaceae must be present.

Remarks: Steinmann (1921) reported Cladophlebis

to one of these species; a more precise identification is not

possible due to the fragmentary nature of the material.

nobai

0) An

3

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562 555roessertii (Presl 1838) Saporta 1873 (ZGleichenitesroessertii (Presl 1838) Kryshtofovich 1912) and Cladoph-

lebis australis (Morris 1845) Halle 1913 from the Santa

Juana Formation. The specimen figured cannot be attributed

subsp. argentinum (Kurtz 1921) Anderson and Anderson (1983) or Sphe

Gontriglossa reinerae sp. nov. (8) Sphenobaiera africana (Baldoni 198Cladophlebis sp.

(Fig. 5(4))

Material examined: Cp 1270, Cp 1271.

Locality: 2.

Description: Terminal part of pinna, 60 mm long and

15 mm wide.

Systematic position: Cladophlebis is regarded as belong-

ing to the Osmundales.(Fig. 1, Table 2) is situated along the road from the Biobo

River to Coronel near the village of Patagual. Similar to

locality 1, the exposed sediments have been deposited by

rivers in an alluvial plain (facies 3).

4.1. Material

Material is stored at the following sites: (Cp) Geolo-

gisch-Palaontologisches Institut und Museum, Abteilung

Palaobotanik, Westfalische Wilhelms-Universitat Munster,

Germany; (UdeC) Santa Juana Collection, Departamento

Ciencias de la Tierra, Universidad de Concepcion, Chile.

UdeC specimens are not numbered.

4.2. Ferns

Gleichenites sp.

(Fig. 5(1))

Material examined: Cp 1299.

Locality: 1.

Description: Axis 62 mm long. Pinnae 5060 mm long.

Central vein of pinnules 5 mm long.

Stratigraphic range: Triassic-Middle Jurassic.

Distribution: Gleichenites is known worldwide.

Systematic position: Gleicheniaceae.

Remarks: This specimen shows similarities with Gleiche-

nites gallegoii Herbst, 1996 from Argentina and Gleichenites

sp. from the Santa Juana Formation (Herbst, 1996). It is

believed to represent a new species because of its differing

pinnule margins. However, characters are too few to allow a

satisfactory diagnosis. Similarities exist with the genus

Todites, especially Todites goeppertiana (Munster 1846)

Krasser 1922, as figured by Harris (1931, Fig. 6C/D) from

eastern Greenland. However, to prove its position relative toPseudoctenis santajuanensis sp. nov. (9) Apical portion of frond, Cp 1300. (101Dictyophyllum fuenzalidai Herbst (2000)

(Fig. 5(2))


Locality: 1.

Description: Specimen, 63 mm long showing an axis

with lateral veins positioned at distances of 11 mm.

Distribution: Chile.

Systematic position: Dipteridaceae.

Remarks: Steinmann (1921) and Tavera Jerez (1960)

reported Clathropteris platyphylla (Goeppert 1842) Brong-

niart 1849 from the Santa Juana Formation, which seems

very similar. However, though the venation is not clear, it is

regarded as Dictyophyllum fuenzalidai Herbst (2000), as

described from near Copiapo (Herbst, 2000).

Dictyophyllum tenuifolium (Stipanicic and Menendez

1949) Bonetti and Herbst 1964

(Fig. 5(5))

Material examined: Cp 1290, Cp 1291, Cp 1292.

Locality: 1.

Description: Frond fragment 120 mm long and 30 mm

wide. Axis of specimen 105 mm long.

Stratigraphic range: Carnian.

Distribution: Argentina.


Remarks: This species shows similarities to Dictyophyl-

lum ellenbergii Greber 1960 (see Fabre and Greber, 1960;

Anderson and Anderson, 1983) from the Molteno For-

mation, southern Africa.

Thaumatopteris rothii Frenguelli 1941

(Fig. 5(3))


Locality: 1.

Description: Specimen with 75 mm long axis. Pinnae

approx. 70 mm long and 13 mm wide. Venation is poorly

preserved.

Stratigraphic range: Late TriassicEarly Liassic.

Distribution: Chile, Argentina.


Remarks: Herbst (1992) regards Thaumatopteris as a

subgenus of Dictyophyllum. Because venation is poorly

preserved, the identification remains uncertain.

Asterotheca fuchsii (Schimper ex Zeiller 1875) Herbst

1998

(Fig. 5(6))


Locality: 1.

Description: Frond fragment approximately 43 mm long

and 28 mm wide. Fragment shows second- and third-order

era pontifolia Anderson and Anderson (1989), Cp 1295, on holotype of

derson and Anderson (1989), Cp 1298, same slab as Fig. 6(5). (911)1) Holotype, Cp1301. Scale bar for all figures is 10 mm.

Stratigraphic range: LadinianNorian.

ricanKurtziana cacheutensis (Kurtz 1921) Frenguelli 1941

(Fig. 6(1))


Locality: 1.

Description: Frond 80 mm!18 mm. Tip and basemissing. Venation usually twice forking.

Stratigraphic range: Late Triassic.

Distribution: Argentina, Southern Africa.

Systematic position: This species is regarded as a

peltasperm (Anderson et al., 1998) or a cycad (Ganuza

et al., 1998).

Antevsia (?) sp.

(Fig. 6(2))

Material examined: UdeC.

Locality: 2.

Description: Maximum width of specimen 15 mm.

Stratigraphic range: Because Antevsia is the male

fructification of the peltasperms, an occurrence from Late

Permian to Late Triassic is presumed.

Systematic position: Peltaspermaceae.

Remarks: This specimen is on the back side of a slab with

Dicroidium odontopteroides.

Dicroidium crassinervis (Geinitz 1876) Anderson and

Anderson (1983)

forma trilobitum (Johnston 1886) Anderson andpinnules. Third-order pinnules (4 mm long and 2 mm wide)

have well-rounded tips with a marked midrib.

Stratigraphic range: Triassic.

Distribution: Chile, Argentina, Australia.

Systematic position: Asterothecaceae.

Remarks: Even if there are no synangia preserved, this

specimen is regarded as Asterotheca fuchsii because of its

pinnule morphology. However, there is a possibility that this

frond fragment belongs to Cladophlebis (R. Herbst, pers.

comm.)

Saportaea dichotoma (Frenguelli, 1942) Stipanicic and

Bonetti (1965).

(Fig. 5(7))


Locality: 1.

Description: Frond fragment 80 mm long and 80 mm

wide. Lamina deeply segmented. Veins not preserved, only

prominent midrib present.

Stratigraphic range: uppermost Ladinian.

Distribution: Argentina.

Systematic position: Saportaea is regarded as belonging

to the Polypodiales (Anderson and Anderson, 1993).

Remarks: Assignment after the definition provided by

Frenguelli (1942) and Stipanicic and Bonetti (1965) rather

than in the broader sense of Anderson and Anderson (1989).

4.3. Seed ferns

S.N. Nielsen / Journal of South Ame556Anderson (1983)Distribution: Argentina, Southern Africa, Antarctica,

Australia.

Systematic position: Umkomasiaceae.

Dicroidium odontopteroides (Morris 1845) Gothan 1912

forma lineatum (Tenison-Woods 1883) Anderson and

Anderson (1983)

(Fig. 6(4))

Material examined: UdeC.

Locality: 2.

Description: Frond 150 mm long, 40 mm wide.

Stratigraphic range: LadinianCarnian.

Distribution: Argentina, Brazil, Southern Africa, India,

Australia.


Remarks: This specimen has previously been

figured by Bandel et al. (1997, Fig. 2b). It is associated

with marine bivalves (Halobia), Linguifolium, and Antevsia.

Dicroidium elongatum (Carruthers 1872) Archangelsky

1968

forma remotipinnulum Anderson and Anderson (1983)

(Fig. 6(5))


Locality: 1.

Description: Frond forked, approximately 40 mm, pinnae

linear.


Distribution: Southern Africa, Australia, Antarctica.


Remarks: This specimen is located between some

Sphenobaiera africana and is poorly preserved.

Seed of Dicroidium

(Fig. 6(6))


Locality: 1, 3.

Description: Diameter of seed 13 mm.


Remarks: Dicroidium seed similar to that

figured by Anderson and Anderson (1983). This

specimen has previously been figured by Bandel et al.

(1997, Fig. 2c).

4.4. Seed fern or ginkgophyte

Dicroidium elongatum (Carruthers 1872) Archangelsky

1968

subsp. argentinum (Kurtz 1921) Anderson and Anderson(Fig. 6(3))


Locality: 1.

Description: Frond forked, pinnate, medium sized

(100 mm long and 20 mm wide). Three-lobed pinnae.

Earth Sciences 19 (2005) 547562(1983)

Stratigraphic range: AnisianRhetian.

ricanor Sphenobaiera pontifolia Anderson and Anderson

(1989)

(Fig. 6(7))


Locality: 1.

Description: This specimen is approximately 70 mm

long and 10 mm wide.

Stratigraphic range: LadinianCarnian (D. elong. arg.);

LadinianNorian (S. pontifolia).

Distribution: Argentina, Southern Africa, Antarctica

(D. elong. arg.); Argentina, Brazil, Southern Africa,

Antarctica, Australia (S. pontifolia).

Systematic position: Ginkgoopsida.

Remarks: Dicroidium elongatum argentinum and Sphe-

nobaiera pontifolia are indistinguishable without preserved

cuticles (Anderson and Anderson, 1989) or more complete

specimens; therefore, exact determination of this specimen

is impossible.

4.5. Ginkgophytes

Sphenobaiera africana (Baldoni 1980) Anderson and

Anderson (1989)

(Fig. 6(8))


Locality: 1.

Description: The bigger frond is 85 mm to 15 mm.

Lamina fork three to four times into 816 small linear

segments. Base, tips, and venation are not preserved.

Stratigraphic range: Carnian.

Distribution: Argentina, Southern Africa, Australia.

Systematic position: Ginkgoales.

4.6. Cycads

Pseudoctenis santajuanensis sp. nov.

(Fig. 6(911)

Material examined: Cp 1301 (holotype), Cp 1287, Cp

1300, Cp 1302, Cp 1304, Cp 1306, Cp 1307 (paratypes).

Locality: 1.

Diagnosis: Pinnate frond. Pinnae perpendicularly posi-

tioned to the rachis, widely spaced, attached to the upper

surface of the pinna rachis. Pinnae slightly constricted at the

base, widening toward the apex; apex truncate. Pinnae up to

50 mm long and 5 mm wide. Venation dense, up to 25 veins

per 10 mm; veins running more or less parallel, forking once

or twice.

Holotype: Specimen Cp 1301.

Type locality: Cerro Calquinhue, near Quilacoya.

Stratigraphic range: AnisianCarnian.

Systematic position: Cycadales.

Name derivation: After the Santa Juana Formation.

Remarks: This species differs from other species of

Pseudoctenis in having perpendicularly positioned pinnae

with conspicuously constricted bases, in the shape of its

S.N. Nielsen / Journal of South Amepinna apices, and in its size. The most similar species isDistribution: Gondwana.

Systematic position: Voltziaceae.

Telemachus elongatus Anderson (1978)

(Fig. 7(3))


Locality: 1.

Description: Specimen, 40 mm long and 20 mm wide.

Stratigraphic range: AnisianRhetian.

Distribution: Chile, Southern Africa, New Zealand,

Antarctica.

Systematic position: Voltziaceae.

Remarks: Anderson (1978) and Anderson and Anderson

(1989) proposed that Telemachus as a female cone and

Heidiphyllum leaves are part of the same plant. Even if there

remained some doubt, the coexistence at least 14 localities

worldwide (Axsmith et al., 1998) serves as additional

evidence.

Rissikia media (Tenison-Woods 1883) Townrow 1967

(Fig. 7(4))

Material examined: Cp 1275.P. azcaratei Herbst and Troncoso (2000), from which it

differs by its wider-spaced pinnae and less dense venation

(28 veins per 10 mm in P. azcaratei). Herbst and Troncoso

(2000) mention additional material of P. azcaratei from the

Santa Juana Formation; however, it might prove to belong to

P. santajuanensis.

cf. Pseudoctenis fissa Du Toit 1927

(Fig. 7(1))


Locality: 3.

Description: Fragment of frond 32 mm long, 16 mm

wide. Venation poor, moderately spaced.

Stratigraphic range: AnisianCarnian.

Distribution: Argentina, Southern Africa.

Systematic position: Cycadales.

Remarks: This specimen is placed within P. fissa even if

considerable doubt remains because the tip is unforked,

which seems untypical for P. fissa (see Anderson and

Anderson, 1989). However, there is not sufficient material

available for a safe determination.

4.7. Conifers

Heidiphyllum elongatum (Morris 1845) Retallack 1981

(Fig. 7(2))

Material examined: Cp 1300, Cp 1302, Cp 1303, Cp

1304.

Locality: 1.

Description: Leaf relatively large (170 mm long, 15 mm

wide), narrowly elliptic. Veins well spaced, forking once or

twice.

Earth Sciences 19 (2005) 547562 557Locality: 3.

ricanS.N. Nielsen / Journal of South Ame558Description: Foliage shoot (30 mm long, 7 mm wide).

Pinnae linear.


Distribution: Gondwana.

Systematic position: Podocarpaceae.

4.8. Gymnosperms incertae sedis

Linguifolium steinmannii (Solms-Laubach 1899)

Frenguelli 1941

(Fig. 7(5))


Fig. 7. (1) cf. Pseudoctenis fissa Du Toit 1927, Cp 1274. (2) Heidiphyllum elon

Anderson (1978), Cp 1300. (4) Rissikia media (Tenison-Woods 1883) Townro

Frenguelli 1941, Cp 1288. (69) Gontriglossa reinerae sp. nov. (6) Counterpart of

bar for all figures is 10 mm.Earth Sciences 19 (2005) 547562Locality: 1.

Description: Leaf 75 mm long and 14 mm wide, base

and tip missing. Veins well spaced (12 per 10 mm),

spreading relatively widely from midrib, arching

gently.

Stratigraphic range: LadinianRhetian.

Distribution: Chile, Argentina, Australia, New Zealand.

Systematic position: This species is now regarded as a

ginkgoopsid (Anderson and Anderson, 1993).

Remarks: After recent reports, it seems possible that

Linguifolium also lived in the northern hemisphere (e.g., in

Germany; Kelber, 1998).

gatum (Morris 1845) Retallack 1981, Cp 1302. (3) Telemachus elongatus

w 1967, Cp 1275. (5) Linguifolium steinmannii (Solms-Laubach 1899)

holotype, Cp 1296. (7) Holotype, Cp 1295. (89) Paratype, Cp 1294. Scale

Gontriglossa reinerae sp. nov.

(Fig. 7(69))

Material examined: Cp 1293 (paratype), Cp 1294

(paratype), Cp 1295 (holotype), Cp 1296 (holotype

counterpart).

Locality: 1.

Diagnosis: Leaf relatively large (approx. 150 mm long

and 70 mm wide), presumably elliptical. Base and apex

unknown. Veins frequently anastomosing, arching very

steeply (10208 from midrib).Holotype: Cp 1295, Cp 1296 (counterpart).

Type locality: Cerro Calquinhue, near Quilacoya.


Systematic position: Gontriglossa is regarded as belong-

ing to the Gnetopsida (Anderson et al., 1998).

Name derivation: For my friend and colleague Janet

Zulauf, who at the time of description still held her name of

birth Reiner.

Remarks: Even if its leaf-base and cuticle are unknown,

this species is assigned to the genus Gontriglossa because it

is generally assumed that the Glossopteridales became

extinct at the PermianTriassic boundary.

Discussion: This species is larger than most other species

of Gontriglossa, such as the South African G. verticillata

G. grandis and 20308 in G. nymboidensis and G. laceratabut only 10208 in G. reinerae. In G. nymboidensis andG. lacerata, the veins quickly curve outward, reaching an

angle of 708 to the midrib, whereas the veins in G. reineraeremain always steeper and maintain a maximum angle of

approximately 508 to the midrib.

5. Biogeography and ecology

The flora of the Santa Juana Formation comprises mainly

elements that have a wide distribution in the Late Triassic of

Gondwana (Table 3). Close affinities exist throughout

Gondwana, especially in Argentina, southern Africa,

and Australia, where the flora are best known. Similarly

rich floras probably could be found at other localities; lack

of sampling in other areas appears to be the main reason the

Molteno flora stands out. The nongymnosperms of the

Molteno Formation are currently under revision (Anderson

and Anderson, in prep.), but a comparison is not possible at

the moment.

The ecology of Triassic plants has been discussed by

Anderson et al. (1998). While ferns grew in a wide variety

of habitats, other forms lived in more ecologically restricted

Mt

(*)

(*)

(*)

(*)

*

*

*

*

*/* * * *

* * (?) (*) (?) (*)

*

*

*

*

(*)

(*)

ation

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562 559(Thomas) (Anderson and Anderson, 1989) and the

Australian G. moribunda (Johnston) (Holmes, 1992).

Similarly large species are the Australian G. lacerata

(Holmes), G. nymboidensis (Holmes), and G. grandis

(Walkom) (Holmes, 1992), which have a less steep angle

between the midrib and veins. This angle is 65708 in

Table 3

Distribution of the plants found in the Santa Juana Formation

Species Ch Ar Br

Gleichenites sp. (*) (*)

Cladophlebis sp. (*) (*) (*)

Dictyophyllum fuenzalidai *

Dictyophyllum tenuifolium (*) *

Thaumatopteris rothii *

Asterotheca fuchsii * *

Saportaea dichotoma *

Kurtziana cacheutensis * *

Dicroidium crassinervis forma

trilobitum

*

Dicroidium odontopteroides

forma lineatum

*

Dicroidium elongatum remoti-

pinnulum

D. elong. arg. / Sph. pontif. * *

Sphenobaiera Africana (*) * (*)

Pseudoctenis gracipinnata *

Pseudoctenis fissa *

Heidiphyllum elongatum * * (*)

Rissikia media * *

Linguifolium steinmannii * *

Gontriglossa reinerae (?)

Ch: Chile (excluding this work); Ar: Argentina; Br: Brazil; Mt: Molteno FormIndia; Ant: Antarctica. *Occurrence of species; (*) occurrence of genus; (?) supp*

* * * * *

* * (?) *

* * *

(*) (?) (?)

, Southern Africa; Au: East Australia; Ts: Tasmania; NZ: New Zealand; Ind:areas. Heidiphyllum, Rissikia, and Kurtziana preferred wet

areas on floodplains; Pseudoctenis, Saportaea, and

Dicroidium grew in forests to woodlands; Sphenobaiera,

Linguifolium, and Gontriglossa preferred water margins. This

pattern also seems to apply to the Santa Juana Formation. It

is therefore obvious that during the Late Triassic, at least

Au Ts NZ Ind Ant

(*) (*) (*) (*) (*)

(*)

* (*)

(?)

* * *

* * *

* *osed occurrence of genus.

n and

rican Earth Sciences 19 (2005) 547562Table 4

Known stratigraphic range of the found taxa (derived mainly from Anderso

S.N. Nielsen / Journal of South Ame560southern Gondwana had a very homogeneous flora that

reflects environments rather than geographical areas.

6. Stratigraphy

The stratigraphic ranges of several of the plant taxa

encountered (Table 4) are still unsatisfactorily known

because some are only known from a few, poorly dated

localities. Species such as Saportaea dichotoma, Kurtzia

cacheutensis, and Sphenobaiera africana are only known

from one dated locality each, and the presented

stratigraphic range certainly does not represent reality.

Black: range of species, grey: range of genera.Anderson, 1983, 1989)Therefore, no good age assessment based on the paleoflora

can be made for the Santa Juana Formation. However,

regarding the known ranges presented in Table 4, a

Carnian age seems most plausible. The nonmarine

invertebratesbivalves, conchostracans, and insectsdo

not provide good stratigraphical evidence. The marine

bivalve genus Halobia is a good index fossil, but the

material reported here probably represents a new species.

Other marine invertebrates, especially ammonoids, might

give a more exact age than currently is possible. Still,

further work, including palynological investigations and

absolute dating of volcanic rocks, is needed for a good age

assessment.

deposited on an alluvial braidplain that was superimposed

by a large-scale braided river system with lakes, playa lakes,

Hamburg, Germany) is thanked for discussions and

critical reviews of an early draft of the manuscript.

S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562 561Heidi Anderson (Botanical Research Institute, Pretoria,

South Africa) and Rafael Herbst (PRINCEPA-CONICET,

Corrientes, Argentina) made valuable comments on the

determination of the plants. Paulina Vasquez (Institut fur

Angewandte Geowissenschaften, TU Berlin, Germany)

corrected the Spanish abstract. Revisions by Brian Currie

(Department of Geology, Miami University, USA) and

Heidi Anderson significantly improved this work. Field

study was financially supported by the Emmy and Alfred

B. Steffens Memorial Fund of the University of

Hamburg.

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S.N. Nielsen / Journal of South American Earth Sciences 19 (2005) 547562562

The Triassic Santa Juana Formation at the lower Biobo River, south central ChileIntroductionPrevious modelsSedimentary faciesFacies 1: granitoid debrisFacies 2: conglomerates and arkosic sandstonesFacies 3: sandstones and siltstonesFacies 4: siltstones and mudstonesFacies 5: black shalesFacies 6: sandstones and siltstonesFacies 7: massive sandstonesFacies 8: marine siltstonesFacies associations

The paleofloraMaterialFernsSeed fernsSeed fern or ginkgophyteGinkgophytesCycadsConifersGymnosperms incertae sedis

Biogeography and ecologyStratigraphyConclusionsAcknowledgementsReferences

Documents

Nielsen-05-JSAES-The Triassic Santa Juana Formation at the lower Biobı´o River, South central Chile