LATE PALEOZOIC PALEOCLIMATE SUCCESSION IN BOLIVIA

Late Paleozoic depositional systems of western Bolivia show two trends - a Gondwanan trend and a Pangean trend, the latter being similar to depositional style in North America. The Gondwanan trend consists of coldwater siliciclastics with glacially-influenced deposition spanning the Late Devonian to Pennsylvanian(?). The Pangean trend closely followed with warm water Permo-Carboniferous carbonates, evaporites, and Upper Permian restricted marine deposits and red beds.

The vertical succession of carbonates with North American faunal affinities over cold water, glacigene deposits is sharp (at least in the Titicaca area). As a mid-Carboniferous hiatus separates these deposits, the succession may be simply explained by paleolatitudinal rotation of Gondwana or by cool water carbonate models. In fact, Permian warming trends in Bolivia seem to inversely mirror cooling conditions and climatic deterioration in NW Pangea. However what is not easily explained is the apparent lateral continuity of Gondwanan and Pangean trends across the Bolivian Cordillera: Gondwanan glacigene deposits in southern Bolivia are thick, sand-prone deposits with diamictites. Palynology suggests these deposits extend into the Pennsylvanian; similar glacially-influenced deposits of Lower Permian age are also reported from Paraguay and Argentina. Conversely, some of the foram- and conodont-dated Pangean carbonates have recently been re-assigned earliest Pennsylvanian ages and Permian carbonates are clearly sub-tropical and reach SE Bolivia. This has led to problems in paleoclimatic interpretation.

The succession of Gondwanan to Pangean paleoclimates in Late Paleozoic Bolivia require steep climate gradients, rapid paleolatitudinal shift and gyrate about litho/bio-stratigraphic debate. Perhaps Late Paleozoic climatic belts were capable of exceptional expansions? The issue is simplified here to point out that the proverbial Late Carboniferous ice sheet could not have extended into Bolivia during Late Carboniferous / Permian time. Glacially-influenced clastic Mississippian / Pennsylvanian(?) deposits in Bolivia exist either adjacent to or simply underlie warm water carbonate deposits. Previous interpretations of temperate mountain glaciers between the Paraná and Subandean basin are also part of the solution for paleoclimatic reconstruction.