Sedimentology and stratigraphy of high-latitude, shelf-edge and slope, 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. The emerging view of the LPIA is that of multiple, small ice sheets that advanced and retreated with alternating glacial and nonglacial cycles across polar and mid-latitude regions of Gondwana. The size, timing, and number of ice sheets are still debated. Much of the near-field record of this ice age is derived from composite records obtained from widely-spaced outcrops across Gondwana with the South Polar record coming mainly from Antarctica, which contains only a Permian record. Therefore, our understanding of the LPIA is incomplete. What is needed is a complete, polar archive from a glaciomarine setting, which preserves a high-fidelity stratal record. The Tepuel Basin (Patagonia, Argentina) is ideal for such a study as it contains a 5000+ m thick Carboniferous to Middle Permian record deposited in a shallow to deep marine, rapidly subsiding, tectonically active basin located within the South Polar Circle throughout much of the LPIA. We studied strata deposited in glacially-influenced outer shelf, shelf-slope break, and basinal slope settings and identified large-scale synsedimentary thrust-faulted diamictites and lonestone-bearing sandstones; coarsening-upward, lonestone-bearing mudstone to wave-rippled cross-laminated successions lacking hummocky cross-stratification; deformed sandstones containing large load structures (T/L= 10x100 m); large (T/L= 10x100 m) slide and slump blocks; and thick (100+ m thick) fossil-bearing mudrock successions. These deposits are interpreted as glacially-shoved ice-proximal deposits; wave-dominated shoreface deposits shielded from winter storms by the occurrence of sea ice; seismically deformed sandstones; mass-transport complexes deposited on the basinal slope; and thick slope and basinal muds. These deposits provide an unparalleled view of a tectonically active basin within the South Polar Circle.