Emerging polar view of the late Paleozoic ice age as interpreted from deep-water, distal, glacimarine deposits in the Tepuel-Genoa Basin, Patagonia, Argentina.

ISBELL, JOHN; TABOADA ARTURO C; KOCH ZELINDA J; LIMARINO CARLOS O; FRAISER MARGARET L; PAGANI MARÍA A; GULBRANSON ERIK L; CICCIOLI PATRICIA L; DINEEN, ASHLEY

Perth

Congreso; XVII International Congress on the Carboniferous and Permian; 2011

Geological Survey of Western Australia

The Pampa de Tepuel and Mojon de Hierro formations in the Tepuel-Genoa Basin of Patagonia constitutes a ~4000 m thick glacially influenced Mississippian (Tournasian) to Permian (Artinskian) succession. During much of the late Paleozoic, Patagonia was located near or within the South Polar circle. Thus, these strata represent the thickest and most complete record of polar conditions for the late Paleozoic ice age (LPIA). Recent paleomagnetic interpretations by Ramos (2008) and Rapalini et al. (2010) suggests that Patagonia was a separate crustal block during much of the Paleozoic and that it collided with Gondwana during the latest Pennsylvanian and Early Permian. In these scenarios, the Tepuel-Genoa Basin was interpreted by López Gamundi and Breitkreuz (1997) as a foreland basin and by Forsythe (1982) and Ramos (2008) as either a forearc or a peripheral foreland basin.  Although problems occur using these tectonic scenarios to classify sediment within the basin, rapid basin subsidence was required to produce such a thick Carboniferous to Permian succession.  Strata of the  Pampa de Tepuel and lower portion of the Mojon de Hierro formations consist of thick mudrocks; discontinuous blocks of sandstone; folded sandstones; lonestone-bearing shales/rhythmites; thin bedded sandstones; massive sandstones; massive, stratified, and thin bedded diamictites; and graded- and reverse-graded, clast-supported conglomerates. These units are here interpreted as hemipelagic, mass movement (slide blocks and slumps), iceberg rafted, turbidite/bottom current, sandy debris flow, muddy debris flow, meltwater plume, and grounding line fan deposits. Analysis of grooved, striated, and polished surfaces within the Pampa de Tepuel Formation suggest formation as iceberg keel marks, slide block glide planes, and due to Cenozoic tectonism. Horizons of slump/slide blocks dropstones and diamictites interspersed with thick successions of hemipelagic deposits suggest that sedimentation occurred primarily in deep water beyond the basin’s shelf-slope break and that possible relative sea-level low stands allowed clastic systems, including glaciers to shed clastics into the deep basin. Fossil-bearing horizons occur above “low-stand” deposits and may represent condensed zones that developed following “high-stand” retreat of glaciers and clastics “shoreward.”  Plant fossils high in the Mojon de Hierro Formation indicate shallowing of the basin later in the Permian.