Late Paleozoic carbonates and coeval glacial deposits in Bolivia: correlations across a significant paleoclimatic gradient

ISAACSON, P.; DI PASQUO, M.M.; GRADER, G.; ANDERSON, H.

Banff

Conferencia; AAPG/SEPM HEDBERG RESEARCH CONFERENCE; 2014

American Association Petroleum Geology

P.E. Isaacson, M. di Pasquo, G. Grader, H. Anderson, 2014. Late Paleozoic carbonates and coeval glacial deposits in Bolivia: correlations across a significant paleoclimatic gradient. AAPG/SEPM HEDBERG RESEARCH CONFERENCE ?Latitudinal Controls on Stratigraphic Models and Sedimentary Concepts? (28/10-01/10-2014, Banff, Alberta, Canada), Extended abstracts (4 pages). SEPM - Society for Sedimentary Geology 4111 S. Darlington Suite # 100 Tulsa, OK 74135 U.S.A. Formatted by SEPM Introduction In Bolivia there are contrasting paleoclimates from west and north (?northwestern?) to south in coeval Carboniferous depositional systems. In the northwest is the Pangean trend, and in the south is the Gondwanan trend. A Late Devonian glacially-derived rock assemblage is followed by warm water Pennsylvanian and Permian sequences in the Pangean trend. The southern Gondwanan succession consists of Late Devonian through Pennsylvanian cold water siliciclastics with glacially influenced deposition. Here Permian tilloids are also known, with large-scale, down-slope remobilization of siliciclastics and repetitive, thick mud/sand sequences of very different ages that confuse time-slice paleogeographic models. Whereas northwestern and southern Devonian through (limited) Mississippian strata share Gondwanan fauna and are comparable in overall character, a juxtaposition of facies and a sharp climatic gradient in western South America is established by the earliest Pennsylvanian. The Pangean trend in northwestern Bolivia and Perú continues with warm water Pennsylvanian and Permian carbonates, evaporites and mixed siliciclastics of a semi-arid, open seaway association (Copacabana Formation). This unit onlaps from the north, reaching central Bolivia by the Early Permian (early Cisuralian). Regionally the warm Pangean pattern continues into the younger and more restricted overlying Cirsuralian and younger Permian and Triassic rocks characterized by restricted marine deposits of both humid and arid association (including red beds). What makes the Copacabana Formation so enigmatic is 1) its autochthonous succession over cold water, glacigene deposits of the Late Devonian and Mississippian (Figure 1), and 2) its apparent coeval deposition with Pennsylvanian (and Permian) glacial diamictites. Although the former can be attributed to paleolatitudinal shift, or ?clockwise? rotation of Gondwana, what is not easily explained (and much discussed) is the autothonous continuity of northeastern and central Bolivian carbonate deposits of the northern Perú-Bolivia basin with southern Pennsylvanian and Permian glacigene deposits, which accumulated in the Chaco-Tarija basins. Given that these cold and warm water deposits were coeval in time this means there were severe climate gradients within Bolivia beginning in Pennsylvanian time. Western Gondwana records steady progression from mid- (~50oS, Late Devonian) to lower latitudes (< 40oS) by Pennsylvanian time. Glacial deposits migrate away from the northwest. By Early Pennsylvanian (Bashkirian) time carbonates, evaporites and siliciclastics were deposited in NW Bolivia. In central Bolivia, Mississippian diamictites, undated Pennsylvanian siliciclastics, Copacabana lithofacies, and also carbonates of the Vitiacua Formation are vertically stacked at a few locations.