Sedimentology and Stratigraphy of High-latitude, Glacigenic Deposits from the Late Paleozoic Ice Age in the Tepuel-Genoa Basin, Patagonia, Argentina

Abstract

The Late Paleozoic Ice Age (LPIA) was the longest lived ice age of the Phanerozoic lasting ~87 million years. During this time multiple, small ice sheets advanced and retreated with alternating glacial and nonglacial intervals across Gondwana. Controversy still remains over the size, timing, and number of ice sheets because the traditional view of Gondwana during this time is of a single, large ice sheet that waxed and waned across the supercontinent. Furthermore, high-latitude glacially-influenced basins during the Carboniferous have received limited attention, underscoring the poor understanding of glacial to non-glacial transitions. The Tepuel Basin in Patagonia, Argentina, was located within the south polar circle through much of the LPIA, and contains a near complete sedimentary record of the Carboniferous through the Early Permian due to high subsidence rates in an outer shelf, basin slope, and basin floor setting. The strata within the Pampa de Tepuel contain sandstones, some reworked by waves, mudstone containing fossils and lonestones, conglomerates, and diamictites. Six stratigraphic sections were examined along an outer shelf to basin slope environment and the strata are divided into eight lithofacies associations which are: 1) massive mudrock 2) thin-bedded sandstone and mudstone, 3) deformed and undeformed sediment blocks, 4) thick-bedded wave-rippled sandstone, 5) large-scale loaded sandstone 6) conglomerate and massive sands, 7) two diamictite subfacies, and 8) thrust-faulted, massive, boulder-bearing sandstone. Evidence was found for a glacial advance to the shelf edge, and evidence for seismic activity was seen in large loaded sandstone deposits within the wave-rippled sandstone facies, which are interpreted to be seismites. The sequence stratigraphy of the area suggests that a forced regression occurred, allowing for coarser clastics to be deposited further out in the basin, followed by a rapid transgression. The strata within the study area contain fossils of the Lanipustula Biozone, which is considered to range from Serpukovian to early Moscovian in age. Glaciation was occurring in polar Gondwana at this time, and the glaciation was associated with a drop in sea level. This research aids our understanding of the stratigraphy of high-latitude, glaciomarine shelf systems and in understanding of the late Paleozoic Ice Age.