CARBONIFEROUS AND PERMIAN GLACIGENIC AND NON-GLACIAL STRATA OF THE TEPUEL-GENOA BASIN, PATAGONIA, ARGENTINA: A NEAR-CONTINUOUS, DEEP-WATER RECORD OF SOUTH POLAR GONDWANA DURING THE LATE PALEOZOIC ICE AGE

The Pampa de Tepuel and Mojón de Hierro formations constitute a ~5000 m thick, near-continuous Mississippian (late Viséan) to Permian (Sakmarian-early Artinskian) succession that contains at least 6 glacimarine and glacially-influenced marine horizons separated by non-glacial intervals. During the late Paleozoic ice age (LPIA), Patagonia was located within the South Polar circle. Thus, these strata represent the thickest and most complete record of polar conditions during the LPIA.

In our study, we identify 11 facies, which include: 1) wave-rippled and hummocky cross-bedded sandstone; 2) thick fossiliferous mudrock; 3) lonestone-bearing mudrock; 4) sandstone blocks overlying shear planes; 5) deformed sandstone overlying shear planes; 6) thin-bedded sandstone; 7) massive sheet and channel-form sandstone; 8) microbially-mediated sandstone; 9) massive, stratified, and thin-bedded diamictite; 10) graded, reverse-graded, and massive clast-supported sheet and channel-form conglomerate; and 11) deformed conglomerate resting on shear planes. We interpret these units as wave-influenced shelf, neritic, hemipelagic, iceberg-rafted, glaciomarine meltwater plume, mass movement (slides/slumps), turbidite, sandy debris flow, muddy debris flow, and submarine channel deposits. Analysis of grooved and striated surfaces suggests formation of these features as glide planes beneath slide/slump blocks and as iceberg keel marks.

The occurrence of clinoforms suggests deposition near the shelf-slope break and farther basinward. Wave-rippled and hummocky cross-stratified sandstone and mudrock within topset beds and near the top of dipping clinoforms indicate deposition on the outer shelf and upper slope. Thick successions of hemipelagic mudrock, slump/slide blocks, dropstones, diamictites and channelized and sheet turbidites within clinoforms suggest deep-water sedimentation on the slope and on the basin floor. The arrangement of the deposits suggests that during relative sea-level low stands, clastic systems, including glaciers, transited the shelf and shed clastics into the deep basin. Fossil-bearing horizons occur above low-stand deposits and may represent condensed zones that developed during transgression/high-stand and/or the retreat of glaciers and clastics across the shelf.