late paleozoic stratigraphic framework in bolivia

E. Díaz-Martínez e I. Rábano (Eds.), 4th European Meeting on the Palaeontology and Stratigraphy of Latin America Cuadernos del Museo Geominero, nº 8. Instituto Geológico y Minero de España, Madrid, 2007. ISBN 978-84-7840-707-1 © Instituto Geológico y Minero de España

LATE PALEOZOIC STRATIGRAPHIC FRAMEWORK IN BOLIVIA: CONSTRAINTS FROM THE WARM WATER CUEVO MEGASEQUENCE G. Grader1, E. Díaz-Martínez2, V. Davydov3, I. Montañez4, J. Tait5 and P. Isaacson6 1 Washington 2

State University, USA. [email protected] Geological Survey of Spain (IGME), Madrid, Spain. 3 Boise State University, Idaho, USA. 4 University of California, Davis, USA. 5 University of Edinburgh, Scotland. 6 University of Idaho, USA.

Keywords: Carboniferous, Permian, paleoclimate, Bolivia. INTRODUCTION North to south Carboniferous and Permian stratigraphic correlation across Andean Bolivia involve the perennial problem of lateral facies changes from marine to continental units. Compounding this problem are questions of warm water (Titicaca Group) versus cold water (Macharetí/Mandiyutí groups) depositional systems with different and poorly calibrated biochronostratigraphic zones. The mid-Carboniferous is an especially interesting transitional period in Bolivia as there was both carbonate sedimentation to the north, and arguably ice centers to the south. In northern Bolivia, the Early Pennsylvanian Copacabana depositional system of the lower Titicaca Group is time-transgressive over ~40 my and is comprised of the Yaurichambi, Tarma and Copacabana formations (Díaz-Martínez, 1999). Based on well dated cosmopolitan marine organisms, accumulation of these sediments began during the Bashkirian (Early Pennsylvanian) and fit well into regional stratigraphic schemes developed by Sempere (1995) and Díaz-Martínez (1996). As pointed out by Díaz-Martínez (2002), the character and timing of these warmer water depositional environments do not fit many larger scaled Late Paleozoic central Andean and western Gondwanan chronostratigraphies and paleogeographies. This paper updates the regional context of the stratigraphic framework developed by Grader et al. (2003) and discusses new efforts to understand this part of Gondwana/Pangea. SHARP CARBONIFEROUS PALEOCLIMATIC GRADIENT OR REVISED LATE PALEOZOIC GLACIATION? Warm water, intermediate to low latitude, typically “Pangean” successions of the upper Carboniferous and Permian (Titicaca Group) contrast with higher latitude, cold water, “Gondwanan” successions of the lower Carboniferous (Ambo, Macharetí, and Mandiyutí groups; Fig. 1). Previous global compilations of paleogeographic/climatic reconstructions of the Pennsylvanian-Permian have portrayed coeval timing for

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G. Grader, E. Díaz-Martínez, V. Davydov, I. Montañez, J. Tait and P. Isaacson

the deposition of both these facies in partly connected, regionally adjacent basins (e.g., Francis, 1994; Williams, 1995). However, this was strongly challenged by Díaz-Martínez (2002), using multiple lines of evidence, including well established dates for Copacabana Formation carbonates, revised older ages for taxa and/or biozones from Australia, and criticism of awkward and incongruent paleogeographic models. Díaz-Martínez (2002) argued to restrict all glacigene or cold water deposits in Bolivia to the Mississippian period, suggesting a revised older age for the main Late Paleozoic glaciation in South America. Rainfall belts and phytogeographic migrations changed both spatially and temporally across this active margin (Iannuzzi and Rösler, 2000) and paleolatitudes for western Bolivia declined relatively steadily: 50°S in Late Devonian, 36°S in Early Carboniferous, 38°S in Late Carboniferous, 25°S in Early Permian, and 19°S in Late Permian, according to Tait et al. (2000) and Rakotosolofo et al. (2006). Could strong regional climate gradients allow different facies assemblages to accumulate in close proximity? This important suggestion by Sempere (1995) is reconsidered here. A MIXED COLD AND WARM WATER MID-CARBONIFEROUS DEPOSITIONAL SYSTEM? Depositional history of the Titicaca Group comprises part of a central Andean Late Paleozoic to Triassic marine through regressive red bed megasequence (Cuevo Supersequence; Sempere, 1995). PennsylvanianPermian mixed carbonate and siliciclastic environments of the Yaurichambi and Copacabana formations closely followed cool water Gondwanan facies in vertical succession and were deposited within seaways behind a western marginal arc. The Copacabana depositional system is ~30 to 400 m thick in the Cordillera Oriental and Altiplano of Bolivia, although coeval strata in Peruvian depocenters are ~2000+ m thick. Facies mainly consist of lithic and arkosic siliciclastics, volcaniclastics and deposited in transitional environments with subaqueous or intraformational evaporites, shallow water to deeper marine shales, and initially very restricted marine carbonate environments. These deposits were strongly influenced by regional tectonics (development of sub-basins and active inversion), glacioeustasy, and episodic volcanism (sediment supply), and presently are thought to have occurred in semi-arid climates. Ash dating and proxies for climate change and within these deposits and those of the underlying Siripaca Formation are presently under study, and such data will be very important for facies and paleoclimate relationships in southern Bolivia (also under new study). THE MISSISSIPPIAN-PENNSYLVANIAN TRANSITION The Mississippian-Pennsylvanian transition in central and northern Bolivia and Peruvian depocenters is mostly disconformable to angular, strongly erosional, and time-transgressive (Laubacher, 1977; Dalmayrac et al., 1980; Sempere, 1995; Díaz-Martínez, 1996, 1999; Grader, 2003). However, recent field work suggests that some Mississippian-Pennsylvanian boundary sections near Lake Titicaca may be conformable and are associated with both evaporites and microkarst. Deposition above the mid-Carboniferous boundary at Siripaca and Yaurichambi near Lake Titicaca area is thought to have occurred at different times, although both locations are associated with evaporite solution collapse features within the Yaurichambi Formation. Initial general interpretations of the transition between Siripaca and Yaurichambi formation indicate significant short term climate changes linked to Gondwana glaciation. In southern Bolivia there are also significant facies changes in this mid-Carboniferous interval from partly glacigene units to eolian units (i.e., Cangapi Formation – originally part of the Mandiyutí Group), but 182

LATE PALEOZOIC STRATIGRAPHIC FRAMEWORK IN BOLIVIA: CONSTRAINTS FROM THE WARM WATER CUEVO MEGASEQUENCE

Figure 1. Chronostratigraphy of the Titicaca Group/Cuevo Supersequence. Geology is summarized after Grader et al. (2003) and references therein.

presently there is no obvious or widely agreed upon mid-Carboniferous unconformity (i.e. Villamontes/Cuevo sequence transition; Fig. 1). The Famennian to Viséan Macharetí Group and the redder, more sandy Serpukhovian and younger(?) Mandiyutí Group in southern Bolivia offer a problematic juxtaposition of taxa, facies, paleo-tectonics and climate-proxies that have yet to be resolved (see also Sempere 1995; Nava 1999). Traditionally, these rocks were included within the upper Carboniferous (i.e., Pennsylvanian), but this stratigraphic arrangement is sedimentologically and climatically improbable (DíazMartínez et al., 1999; 2000, 2002). YAURICHAMBI FORMATION RELATIONSHIP TO SIRIPACA FM IN WESTERN BOLIVIA The mid-Carboniferous (Serpukhovian to Bashkirian/Moscovian) transition within the stratigraphic succession in parts of Peru, the Lake Titicaca area and Eastern Cordillera of Bolivia is sharp. This is the unconformity between the upper Ambo Group and basal Titicaca Group marking the transition from the Villamontes to the Cuevo Supersequences (Fig. 1; see also Fig. 7 and caveats in Sempere, 1995). Bashkirian to Early Permian rocks with endemic and North American faunal affinities (Yaurichambi and Copacabana formations) overlie Viséan to Serpukhovian plant-, coal- and paleosol-bearing delta plain mudstones and channeled sandstones of the Siripaca Formation. The Siripaca Formation discontinuously overlies latest Devonian to Mississippian cold water deltaic and marine units with Gondwanan faunal and floral affinities (Díaz-Martínez, 1991; Iannuzzi et al., 1998). Facies indicate humid, seasonal climates and macrofloras 183


across Gondwana at this time, representing frost-free warm temperatures (Iannuzzi and Pfefferkorn, 2002). The Siripaca Formation only occurs at a few sections within the Titicaca subbasin and is thicker and more diverse with lateral volcanic facies in Peru (Zapata et al., 2002). It is regionally cut out or not deposited by a strong mid-Carboniferous unconformity through much of northern and central Bolivia. Only three sections, primarily in northern Bolivia near Lake Titicaca, actually contain Bashkirian fossils (e.g. Millerella-Seminovella), which found with other foraminifera in the absence of the larger fusulinid Profusulinella sp., may be considered Bashkirian (Morrowan). On the other hand, Moscovian (Atokan) conodonts, forams and fusulinids are fairly common (Sakagami et al., 1994; Mamet, 1996; Ottone et al., 1988; Grader et al., 2000). It is difficult to understand how a periodically to permanently warm water sea across much of northern and central Andean and Subandean Bolivia could have tolerated glacigene clastics shed into it from glaciated uplands along the border with Argentina (Díaz-Martínez, 2002). The only possible explanation would be to consider a yet unrecognized physical separation of these basins. Beyond the more local and highly siliciclastic beginnings of estuarine barrier bars, barrier island, and restricted bay facies of the Yaurichambi/Copacabana depositional systems, it is well established that younger and more fossiliferous marine carbonate environments penetrated further and further southward, over eolian and fluvial correlatives (Cangapi Formation). As these transgressions arrived in the Cochabamba and Subandes respectively (by the latest Pennsylvanian and Early Permian), their position correlative with the Cangapi Formation and above the rest of the Macharetí and Mandiyutí Group of the southeast Subandes, makes it highly probable that these depositional systems were never correlatives in time and space (Figs 1 and 2). The start of the Gondwanan/Pangean facies shift and regional change in sedimentation style with mid-Carboniferous hiatus is grossly explained by paleolatitudinal rotation of SW Gondwana (Isaacson and Díaz-Martínez, 1995). Certainly, Permian warming trends in Bolivia seem to inversely mirror cooling conditions and climatic deterioration in NW Pangea (Beauchamp and Desrochers, 1997).

Figure 2. Working chronostratigraphy of the Cuevo Supersequence. Modified after Grader et al. (2003).

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TITICACA GROUP IN NORTHERN AND CENTRAL BOLIVIA–“PANGEAN FACIES” OF THE CUEVO SUPERSEQUENCE The Yaurichambi and Tarma formations of the Cuevo Supersequence are correlative siliciclastic lithosomes that interfinger with dolostone and limestone of the Copacabana Formation (Fig. 1). Abundant heterozoans with upward-increasing populations of photozoans (James, 1997) characterize this heterolithic depositional system. Western volcaniclastic, southeastern, and internal uplifted sources provided abundant siliciclastic material that was reworked on a dynamic back-arc homoclinal ramp. Evaluation of isopachs, paleocurrents, and correlation/timing of sequence stacking patterns have supported the paleogeography presented by Sempere (1995), but with new and somewhat surprising ramp geometries, and stage-bystage paleogeographic maps (although biostratigraphic correlations to southern Bolivia remain obscure). Where not subsequently removed, the uppermost Copacabana Formation occurs below erosional unconformity with the Chutani Formation and is dolomitized and silicified. The Copacabana Coal Member in the Cochabamba area (sensu Chamot, 1965) is a locally occurring sandstone and carbonaceous shale unit with coals and lycophytes that occur with carbonates and increasing volcanic material. The Chutani Formation was locally deposited within early rift environments and is associated regionally with more hyposaline units. Upper Permian fluvial and eolian units, volcaniclastic-influenced restricted environments with Glossopteris record both arid and humid conditions in transitional to continental basins (upper Chutani Formation or San Pablo Formation). Later, these units were much eroded, and large karst sinkholes developed in the Copacabana Formation on uplifted Late Permian through Jurassic rift horsts (see also Sempere et al., 2002). PALEOGEOGRAPHY Like in the Madre de Díos Basin, earliest Pennsylvanian dates and thick sediment accumulation occurred near Lake Titicaca, defining a Pennsylvanian sub-basin (Titicaca Basin). Major differences in initial sediment accumulation and styles of deposition occur on the Copacabana Peninsula (Altiplano area), the Huarina fold and thrust belt, the Cochabamba area, and the southeast Subandes area. Younger strata and different depositional patterns in the Huarina fold and thrust belt indicate that a paleohigh (Huarina High) existed between the northern Altiplano (Titicaca Basin) and the northern Subandes Basin. This transpressional paleohigh explained earlier Mississippian depositional patterns and paleogeography (Díaz-Martínez, 1994, 1999). As Pennsylvanian basins accommodated thick strata, the Huarina High remained exposed. During the Lower Permian, it was submerged, yet thick accumulations of Artinskian shallow water grainstones indicate a persistent sub-aqueous expression of this feature. STRATIGRAPHY The time-transgressive but field-recognizable litho/biofacies of the Copacabana depositional system are differentiated into a localized Bashkirian-Moscovian Lower Copacabana Member, a widespread Kasimovian-to Sakmarian Middle Copacabana Member, and a ubiquitous Late Sakmarian-Artinskian Upper Copacabana Member (Grader, 2003; Fig. 2). The earliest of these deposits (Bashkirian/Atokan) appear in the northern Titicaca and northeastern Subandean basins of Bolivia at about the same time that South America is widely understood to have undergone the first of two major Pennsylvanian glaciations (López185


Gamundí, 1997). Initial Bashkirian carbonates were highly restricted and influenced by coastal plain siliciclastics, volcanic depositional processes and subaqueous evaporites. By Atokan time, marine carbonate ramp environments became better developed and shoreline to distal ramp environments are interbedded at meter to decameter scales throughout the unit. Significant disconformities are present in the Middle member and pending investigation with new ash, fusulinid data and conodont collections. The Upper Copacabana Member has a more slowly changing character, both in shallow and deep-water environments, and reflects a continuum of regional accommodation (tectonic) and global transition from icehouse to greenhouse conditions (i.e., glacio-climatic). Warming-upward climate trends are based mainly on marine limestone paleoecology. This approximately agrees with field work in many other parts of the world and postulation of a major shift in global ocean current circulation (Beauchamp, 2005). A first-order overprint of global to regional tectonics and eustatic sea level change occurs over about five regional transgressive-regressive second-order supersequences, with about twelve 30 to 100 m composite sequences in the Copacabana Formation (Fig. 2). NEW PRELIMINARY FUSULINID OBSERVATIONS AND ADJUSTED CHRONOSTRATIGRAPHY In the late 90s, B. Mamet, V. Davydov and P. Heckel, respectively contributed to determining calcareous foraminifera, fusulinids, and conodonts. These data agreed well with previous biostratigraphic studies (still poorly zoned in Gondwana). Recent review of fusulinids at outcrops near Lake Titicaca and at the Apillapampa Section near Cochabamba will eventually be better integrated with radiogenic dates and new conodont studies (in preparation). New readjustments have been made to the chronostratigraphy published by Grader (2003) showing the significant role of hiatus and missing parts of entire stages, especially during the Late Pennsylvanian, in the up-dip parts of the Bolivia-Peru Basin (Fig. 2). García (1989) originally placed his “T-1” transgression within the Virgilian – we would suggest that it occurs close to the Carboniferous/Permian boundary (now at 298.7Ma; Ramezani et al., 2007). Multiple potential sequence boundaries occur in the Titicaca Basin within this interval, but need more study. CONCLUSIONS 1. Depositional trends of the Peru-Bolivia Basin and northern basins in Brazil were coordinated with common Euramerican Pangean patterns, such as intense Pennsylvanian and Early Permian icehouse cyclicity with significant later changes in environment, loss of productive marine habitat, and overall climate change. Warm-water early Pennsylvanian carbonates with West Texas-Andean and cosmopolitan fauna reflect this Pangean character. They underlie tropical Late Permian /Triassic restricted units and red beds and overlie glacially-influenced coldwater Mississippian deposits of Gondwanan character. 2. The Late Mississippian Siripaca Formation represents an import (interglacial?) warm and humid period that records changing icehouse climates. The unit should have correlative units in the Subandes Basin, many of which are considered glacigene in character and traditionally Pennsylvanian in age. However, most of these units were likely deposited before influx of warm water, fusulinid bearing currents. Copacabana Formation warm-water carbonate ramp deposits in Bolivia occur early in the Pennsylvanian. Authors describing the Gondwanan glacial diamictites of Argentina, Paraguay and southern Bolivia should take them into account when developing South American paleogeography (i.e., Subandean, Chaco, and Tarija basins). 186


3. Did strong climate gradients allow different facies assemblages to accumulate in close proximity? Maybe! Based on new findings in the Ancestral Rocky Mountains (geographical and temporal coexistence of glacigene deposits, loess deposits and carbonates with evaporates in equatorial regions; Soreghan et al., 2002), new ways of thinking about non-Waltherian facies stacking and paleogeographic synthesis should be pursued beyond the schism that separates diverging and preferred paleogeographic reconstructions. Timing of Mississippian and Pennsylvanian glacigene deposits in these basins must be reconciled with depositional environments of the nearby, better-dated Copacabana Formation in order to accurately explain the Late Paleozoic geohistory and paleoclimate of Bolivia. 4. Variations within the three Copacabana members are explained by paleogeographic relief and expected stacking pattern variations on different parts of homoclinal ramps within the larger Bolivian basin. Sequence boundaries in Pennsylvanian and Permian rocks of Bolivia (like elsewhere in Pangea) are excellent proxies for timing of adjacent glaciations elsewhere in South America, but these glaciations may or may not have left a Pennsylvanian record in southern Bolivia. REFERENCES Beauchamp, B. (2005). Early Permian abrupt climate change induced by global shift in thermohaline circulation: drivers and tipping point, GSA Earth System Processes 2, (8–11 august), Abstract. Beauchamp, B. and Desrochers, A. (1997). Permian warm- to very cold-water carbonates and charts in Northwest Pangea. In Cool-water Carbonates, James, N. P. and Clarke, J. A. D. (eds.), SEPM Spec. Pub., 56: 327-348. Chamot, G.A. (1965). Permian section at Apillapampa, Bolivia and its fossil content. Journal of Paleontology, 39 (6): 1221-1124. Dalmayrac, B., Laubacher, G., Marocco, R., Martinez, C., and Tomasi, P. (1980). La chaine hercynienne d’armerique du sud, structure et évolution d’un orogene intracratonique. Geologische Rundschau, 69: 1-21. Díaz-Martínez, E. (1991). Litoestratigrafía del Carbonífero del altiplano de Bolivia. Revista Técnica de YPFB, 12 (2): 295 –302. Díaz-Martínez, E. (1995). Regional Correlations with Late Paleozoic events in Bolivia. 2º Simp. Cronoestratigrafía Cuenca de Paraná, Porto Alegre. Bol. Resumos Expandidos, 245-247. Díaz-Martínez, E. (1996). Síntesis estratigráfica y geodinámica del Carbonífero de Bolivia. Memorias del XII Congreso Geológico de Bolivia, Tarija, Bolivia, 344-367. Díaz-Martínez, E. (1999). Estratigrafía y paleogeografía del Paleozoico superior del norte de los Andes Centrales (Bolivia y sur del Perú). In: J. Macharé, V. Benavides & S. Rosas (eds.), 75 Aniversario Sociedad Geológica del Perú, Volumen Jubilar, 5: 19-26. Díaz-Martínez, E. (2002). Revised older age of Late Paleozoic glaciations in South America. 3rd European meeting on the Paleontology and Stratigraphy of Latin America, Toulouse (France), Extended Abstract, 40-43. Díaz-Martínez, E., Varvrdová, M., Bek, J. and Isaacson, P.E. (1999). Late Devonian (Famennian) glaciation in western Gondwana: evidence from the the Central Andes. Abhandlungen der Geologischen Bundesanstalt, 54: 213-237. García-Duarte, R. (1989). Estratigrafía de detalle del Paleozoico Superior: Formation Copacabana y Mesozoico Inicial: Formaciones Sayari y Ravelo del área oeste de Copacabana. Tesis de Grado, Universidad Mayor de San Andres, La Paz, 89 pp. Grader, G.W., Isaacson, P. E., Rember, B., Mamet, B., Díaz-Martínez, E. and Arispe, O. (2000). Stratigraphy and depositional setting of the Late Paleozoic Copacabana Formation in Bolivia. Zentralblatt Geol. Paläont.Teil I, (7/8): 723-741. Grader, G.W., Isaacson, P.E., Arispe, O., Pope, M. Mamet, B., Davydov, V. and Díaz-Martínez, E. (2003). Back-arc carbonate-siliciclastic sequences of the Pennsylvanian and Permian Copacabana Formation, Titicaca Group, Bolivia. Revista Técnica de Yacimientos Petrolíferos Fiscales Bolivianos, 21: 207-228.

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