Revised chrono and lithostratigraphy for the Oligocene-Miocene Patagoniense marine deposits in Patagonia: Implications for stratigraphic cycles, paleogeography, and major drivers

Abstract

Richly fossiliferous upper Oligocene to lower Miocene Patagoniense marine deposits constitute a conspicuous feature of the sedimentary record of most basins in Patagonia. Patagoniense meaning and subdivisions have been confusing, and correlation and elucidation of factors controlling sedimentation in a region as extensive as Patagonia are still highly debated. Our revision of the distribution, correlation, stratigraphic arrangement, and timing of deposition, allows redefining the Patagoniense as a succession of widely distributed marine sediments accumulated in Patagonia from ~25 to 15 Ma, showing different timing of accumulation for each basin. It can also be conceived as a higher rank stratigraphic cycle of relative sea-level fluctuation, which comprises two medium rank stratigraphic cycles spanning 2–4 Myr each, in turn enclosing several lower rank cycles of less than 1 Myr. The late Oligocene (~25-23 Ma) medium rank cycle shows deposits restricted mostly to the coastal area of Tierra del Fuego and Santa Cruz provinces in the Austral-Magallanes Basin, which respond to a combination of global sea-level fluctuations and flexural subsidence. The overlying early Miocene (~22-15 Ma) medium rank cycle comprises sediments deposited over extensive areas of Patagonia with a maximum flooding at 20-19 Ma suggesting, in addition to tectonic subsidence in the Austral-Magallanes Basin, regional long-wavelength subsidence and a global sea level component for this episode. The timing and thickness of the regressive part of this cycle show differences for each basin, suggesting the action of local sedimentary controls such as differential rates of sediment supply. Further geochronological and stratigraphic studies are necessary, especially for the northern exposures, which will allow improving time-constrained paleogeographic reconstructions.