The Late Carboniferous Glacial to Postglacial Transition:

PAZOS, P. J.

GONDWANA RESEARCH

Elsevier

Año: 2002 vol. 5 p. 467 - 487

1342-937X

Namurian-early Westphalian glacial-postglacial deposits have been documented in the Paganzo Basin, Argentina,but integrated sequence stratigraphic and sedimentological analyses of the glacial-postglacial transition are rare. In theCuesta de Huaco section the glacial-postglacial transition encompasses the lower sequence of the existing schemes.Glacioeustatic changes in sea-level controlled the architecture and vertical arrangement of facies. The basal sequenceboundary is coeval with the onset of glaciation when sea level fell, contemporaneous with glacial erosion and bypass ofsediment. The upper sequence boundary is a high-frequency sequence boundary. The basal deposits are interpreted asan early transgressive systems tract (ETST) initiated during glacial retreat. The interval fines upward, contains currentreworked diamictites, conglomerates and sandstones deposited in a subglacial to proglacial environment (Facies 1-11)and ice-rafted glaciomarine rhythmites (Facies 111). Postglacial brackish-marine black shales (Facies IVI represent thelate transgressive systems tract (LTST). Micritic-limestone beds were deposited during a period of sediment starvationcoeval with the maximum marine inundation in the basin (MFZ). It marks a turnaround in the stacking pattern thatbecame coarsening and thickening upward during the overlying highstand systems tract (HST). It consists of finegrainedturbidites (Facies V) and classical turbidites with wave reworked beds at the top (Facies VI) deposited in ashallow deltaic systems. Intervening postglacial brackish deposits contain an ichnofauna dominated by trackways ofarthropods and minor grazing traces, preserved in bedding planes, that resemble nonmarine ichnocoenoses and differfrom the archetypal brackish ichnofaunas, even when palynological data support the saline-depleted environment.