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

ISBELL, JOHN; GULBRANSON ERIK L; TABOADA ARTURO C; PAGANI MARÍA A; LIMARINO CARLOS O; FRAISER MARGARET L; PAULS KATHRYN N; HENRY LINDSAY C

Alburquerque

Conferencia; The Carboniferous-Permian transition Conference; 2013

New Mexico Natural Museum & Science

The Pampa de Tepuel and Mojón de Hierro formations in the Tepuel-Genoa Basin exposed in the Sierra Tepuel between Tecka and Gobernador Costa, Argentina, constitute an ~5000 m thick, near-continuous Mississippian (late Viséan) to Permian (Sakmarian-early Artinskian) succession that contains at least 6 glacimarine and glaciallyinfluenced marine horizons separated by non-glacial intervals (Taboada et al., 2009; Pagani and Taboada, 2010; Taboada, 2010; Taboada and Pagani, 2010). During much of the Carboniferous and Permian, 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. The Tepuel-Genoa Basin was interpreted by López-Gamundí and Breitkreuz (1997) as a foreland basin, and by Forsythe (1982) and Ramos (2008) as either a forearc or a peripheral foreland basin. Regardless of tectonic scenario, rapid basin subsidence was required to produce such a thick Carboniferous to Permian succession. Dropstone- and fossil-bearing strata of the Pampa de Tepuel and lower portion of the Mojón de Hierro formations were previously interpreted by González-Bonorino (1992) and González and Díaz Saravia (2010) as intercalated glacial and marine strata deposited in subglacial to littoral/near-shore marine environments. The occurrence of striated and grooved surfaces was used as evidence for either terrestrial subglacial conditions or as evidence of grounded ice advance into a shallow glacimarine setting. Conversely, López-Gamundí and Limarino (1984) interpreted strata in the Pampa de Tepuel Formation as submarine debris flow, sandy turbidity current, and hemipelagic deposits. In our ongoing investigation, we identify numerous facies, which include: 1) wave rippled and hummocky cross-stratified sandstone; 2) thick fossil-bearing mudrock; 3) lonestone-bearing mudrock; 4) discontinuous blocks of sandstone overlying shear planes; 5) folded and brecciated 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 (slide blocks and slumps), turbidite/bottom current, sandy debris flow, muddy debris flow, and submarine cannel deposits. Analysis of grooved and striated surfaces within the succession suggests that these features formed as glide planes beneath slide and slump blocks and as iceberg keel marks. Clinoforms occur at the Tepuel Hill Section, suggesting that strata at this site were deposited within the basin near the shelf-slope break. At the same locality, wave rippled and hummocky cross-stratified sandstone and associated mudrock within topset beds and at the top of clinoforms indicate deposition on the outer shelf and upper slope. Thick successions of hemipelagic mudrock, horizons of slump/slide blocks, dropstones, diamictites, and channelized and sheet turbidites within clinoforms suggest deep-water sedimentation on the slope and possibly on the basin floor. The arrangement of the deposits suggests that during relative sea-level lowstands, clastic systems, including glaciers, transited the shelf and shed clastics into the deep basin. Fossil-bearing horizons occur above lowstand deposits and may represent condensed zones that developed during transgression/highstand and/or the retreat of glaciers and clastics across the shelf. The ages of the youngest known glacial deposits in the Tepuel-Genoa Basin are poorly constrained. Fossil floral data suggest deposition during the Late Carboniferous (Cúneo, 1990); whereas, fossil invertebrates suggest an age no younger than middle Artinskian (Taboada et al., 2009; Pagani and Taboada, 2010; Taboada, 2010; Taboada and Pagani, 2010). Plant fossils and deltaic deposits located in the upper Mojón de Hierro and in the Río Genoa formations indicate a shallowing of the basin by the late Early Permian (Andreis and Cúneo, 1989; Cúneo, 1990).