Bivalves and brachiopods in the Carboniferous- Early Permian of Argentine Precordillera: Diversification and faunal turnover in Southwestern Gondwana

Andrea

Description

Diversification patterns and faunistic turnovers of bivalves and brachiopods through the Carboniferous- Early Permian interval in the central western Argentinean basins are analyzed and compared with the global events proposed in former studies. This study reveals a generalized increase of bivalves, at familiar and generic levels, through three time intervals, i.e., Early Carboniferous (Tournasian-Visean), Late Carboniferous (Bashkirian-Kasimovian) and Early Permian (Asselian-Sakmarian), while the brachiopod diversity seems to remain stable from the Late Carboniferous to the Early Permian. The trends recognized in the faunistic diversity appear to be closely related to the palaeoclimatic, palaeogeographic and palaeotectonic evolution at the Southwestern Gondwana margin. Highly stressing environmental changes in the Early Carboniferous, resulting fundamentally from the development of glacial conditions, may account for the lowest faunistic diversity recorded. Particular stress conditions, such as the nutrient availability, temperature and oxygen level, would have mainly affected the brachiopod faunas that evidence the lowest diversity recognized in the interval studied. At the Visean-Serpukovian boundary, the Late Palaeozoic marine record of the Precordillera shows a major break linked to a globally recognized glacial maximum, whereas an important faunistic turnover is mainly identified in the brachiopod faunas at the beginning of the Late Carboniferous. The more stable, less stressing environmental situation developed during the Late Carboniferous-Early Permian postorogenic sedimentation is also reflected by the different faunal assemblages studied. The Late Carboniferous was characterized by postglacial transgressions. During this time local rebound, a continuous increase of the diversity and an important faunal turnover, which mainly affected the brachiopod faunas, were recorded. These faunal trends may be related to the Early Permian climatic amelioration that affected the central western Argentinian basins. The subsequent Permian transgressive events, which produced new areas of potential spreading for the benthic fauna, allowed its increase and diversification, much better reflected by the bivalve assemblages.

Informations

• Publié par: erevistas
• Publié le: 01 janvier 2010
• Nombre de lectures: 37
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Geologica Acta, Vol.8, Nº 4, December 2010, 501-517
DOI: 10.1344/105.000001585
Available online at www.geologica-acta.com
Bivalves and brachiopods in the Carboniferous - Early Permian
of Argentine Precordillera: Diversifcation and faunal turnover in
Southwestern Gondwana
1 2
ANDREA FABIANA STERREN and GABRIELA ADRIANA CISTERNA
1 CICTERRA - CIPAL - Universidad Nacional de Córdoba
E-mail: [e-mail]
2 Fundación Miguel Lillo, Área Geología, Instituto de Paleontología, S.M. de Tucumán
E-mail: [e-mail]
ABSTRACT
Diversifcation patterns and faunistic turnovers of bivalves and brachiopods through the Carboniferous - Early
Permian interval in the central western Argentinian basins are analyzed and compared with the global events
proposed in former studies. This study reveals a generalized increase of bivalves, at familiar and generic levels,
through three time intervals, i.e., Early Carboniferous (Tournaisian-Visean), Late Carboniferous (Bashkirian-Kasimo-
vian) and Early Permian (Asselian-Sakmarian), while the brachiopod diversity seems to remain stable from the Late
Carboniferous to the Early Permian. The trends recognized in the faunistic diversity appear to be closely related
to the palaeoclimatic, palaeogeographic and palaeotectonic evolution at the Southwestern Gondwana margin.
Highly stressing environmental changes in the Early Carboniferous, resulting fundamentally from the develop-
ment of glacial conditions, may account for the lowest faunistic diversity recorded. Particular stress conditions,
such as the nutrient availability, temperature and oxygen level, would have mainly affected the brachiopod faunas
that evidence the lowest diversity recognized in the interval studied. At the Visean-Serpukovian boundary, the
Late Palaeozoic marine record of the Precordillera shows a major break linked to a globally recognized glacial
maximum, whereas an important faunistic turnover is mainly identifed in the brachiopod faunas at the beginning
of the Late Carboniferous. The more stable, less stressing environmental situation developed during the Late
Carboniferous-Early Permian postorogenic sedimentation is also refected by the different faunal assemblages
studied. The Late Carboniferous was characterized by postglacial transgressions. During this time local rebound,
a continuous increase of the diversity and an important faunal turnover, which mainly affected the brachiopod
faunas, were recorded. These faunal trends may be related to the Early Permian climatic amelioration that affected
the central western Argentinian basins. The subsequent Permian transgressive events, which produced new areas
of potential spreading for the benthic fauna, allowed its increase and diversifcation, much better refected by the
bivalve assemblages.
KEYWORDS Diversifcation. Faunistic turnover. Bivalves. Brachiopods. Carboniferous-Permian. Argentine Precordillera.
501A.F. STERREN and G.A. CISTERNA Bivalves and brachiopods diversifcation in the Late Paleozoic
INTRODUCTION by diachronic Palaeo-Pacifc transgressive events whose
eastern extension was restricted by an important orogenic
The Late Palaeozoic marine biota from the Gondwa- belt known as the Protoprecordillera (Amos and Rolleri,
nan regions shows a close relationship with the palaeogeo- 1965) or the Acadian Precordillera (Baldis and Chebli,
graphic and palaeoclimatic setting. In these areas, the di- 1969). This north-trending upland would have controlled
versifcation and extinction processes observed in several the sedimentation in these two areas: to the west, the Río
invertebrate groups would have been mainly controlled by Blanco (Amos, 1964) and Calingasta-Uspallata (Amos and
the particular dynamic of the glacial event. Rolleri, 1965) basins, dominated by marine sedimentation
and, to the east the Paganzo basin (Azcuy and Morelli,
The beginning of the massive glaciation time interval has 1970) with continental sedimentation mainly (Figs. 1 and 2
been placed at the Serpukovian age, and the biotic changes and electronic Appendix I available at www.geologica-ac-
related are well documented in the south-western Gondwana ta.com). However, the connection of the western Paganzo
margin where the glaciers were widespread throughout. basin fuvial systems with the Carboniferous sea of the
Río Blanco basin can be explained because the height of
The Argentine Precordillera can be considered a classi- the Protoprecordillera would have decreased to the north
cal study area of the Late Palaeozoic marine fossil assem- (Archangelsky et al., 1987; López Gamundí et al., 1994).
blages in the particular palaeoenvironmental context where
the glaciation was clearly recorded. The frst marine transgressive episode was identifed in
two localities of the Río Blanco basin (Fig. 2): to the north
The general aim of this paper is the study of the distri-
bution of bivalves and brachiopods through the Carbonif-
erous-Permian interval in the central western Argentinian
basins (Río Blanco, Calingasta-Uspallata and western Pa-
ganzo basins) and to analyse its relationship with the pal-
aeogeographic and palaeoclimatic scenario.
Bivalves and brachiopods are abundant and impor-
tant components in the Late Palaeozoic marine faunas of
Argentina, and these groups have been the object of nu-
merous taxonomy studies in recent years. The distribution
analysis of these groups allows researchers to recognize
diversifcation patterns and faunistic turnovers from the
Early Carboniferous to the early Permian.
The global diversity study in the marine invertebrate
faunas from the late Early Carboniferous to Early Permian
(Early Sakmarian) allows for the recognition of the slug-
gish diversifcation and low taxonomic rates of evolution -
ary turnover (Powell, 2005). This interval of time with
relatively stable diversity is known as the “late Palaeozoic
ice age” (LPIA) (Stanley and Powell, 2003). Similar pat-
terns, which appear to be relatively infuenced by the local
conditions, are observed in the fossil assemblages consid-
ered in this paper.
GEOLOGICAL AND PALAEOBIOLOGICAL SETTING
FIGURE 1 A) Maps showing the location of the study area and the
paleogeography of the Paganzo, Río Blanco and Calingasta-Uspallata
basins in western Argentina. B) Generalized geographic map showing The Late Palaeozoic geological record in central-
the locations of outcrops sampled in these basins. RP: Río del Peñón western Argentina shows a complex history of interac-
Formation, J: Jagué Formation, QL: Quebrada Larga Formation, Ml: Mal-
tion among tectonism, sea-level changes and climatic imán Formation, T: Tupe Formation, G: Guandacol AN: Agua
Negra LC: La Capilla Formation, DS: Del Salto Formation, conditions (Limarino et al., 2006). Carboniferous-earliest
CT: Ciénaga Larga del Tontal HV: Hoyada Verde Permian marine sediments of the Precordillera appear
EP: El Paso Formation, P: Pituil Formation; Mj: Majaditas Formation, L:
disconnected, showing an irregular pattern along western Leoncito A: Ansilta Formation, Y: Yalguaraz AJ:
Agua del Jagüel Formation, SE: Santa Elena Formation.Argentinian basins. This region was affected several times
502Geologica Acta, 8(4), 501-517 (2010)
DOI: 10.1344/105.000001585A.F. STERREN and G.A. CISTERNA Bivalves and brachiopods diversifcation in the Late Paleozoic
FIGURE 2 Chronostratigraphic chart of the formations studied in this paper. Invertebrate zones: P-A= Protocanites-Azurduya; A-T/M-R= Aseptella-
Tuberculatella/Micraphelia-Rhipidomella; T-S= Tivertonia-Streptorhynchus, C= Costatumulus. Triangles indicate diamictitic horizons. Time scale after
Gradstein et al. (2004). See explanation of the stratigraphy and general characteristics of these units these units in APPENDIX I in the electronic version
of this paper available at www.geologica-acta.com.
(Bolsón de Jagüel Area, La Rioja province), marine sedi- sode: the typical Levipustula Fauna, included in the Levi-
ments with invertebrate faunas were included in the Jag- pustula levis Zone (Serpukhovian-Bashkirian, Taboada,
üel Formation (Fauqué and Limarino, 1991), and to the 1997), recognized in different stratigraphical sections (i.e.,
south (Malimán Area, San Juan province), in the Malimán Hoyada Verde, La Capilla, Leoncito, Yalguaraz, etc., Fig. 2),
Formation (Scalabrini Ortiz, 1972), the lower part of the and a younger fauna that integrates the Balakhonia per-
Angualasto Group (Limarino and Cesari, 1993). Early egrina-Geniculifera tenuiscostata Zone, considered to be
Carboniferous marine fauna from these units integrate the Moscovian-Kasimovian (Taboada, 1997), identifed funda-
Protocanites scalabrinii-Azurduya chavelensis Zone (Sab- mentally in the Pituil Formation (Taboada, 1997) and the
attini et al., 2001), characterized by the brachiopods Az- upper part of the Ansilta Formation (Harrington, 1971).
urduya chavelensis (Amos), Azurduya cingolanii Cisterna The Levipustula Fauna is a relatively diversifed fossil as-
and Isaacson, Chilenochonetes? sp., Pseudosyringothyris? semblage distinguished by the brachiopod species Levipus-
sp. and the bivalves Palaeoneilo subquadratum González, tula levis Maxwell, Costuloplica leoncitensis (Harrington),
Malimania tri