Abstract: Upper Paleozoic Deposits of the Chaco-Parana Basin, Argentina, and the Great Gondwana Glaciation

Robert D. Winn Jr., John C. Steinmetz, Hayden C. Tanner

Cores from 5 wells in the Chaco-Parana basin record deposition during late Paleozoic glaciation. The over-600-m-thick, upper Ordonez interval consists of diamictite with lesser amounts of sandstone and shale, and is latest Carboniferous-Early Permian (Potonieisporites-Lundbladispora to Cristatisporites (?)zones), although zone correlation is uncertain. Diamictite units are red to gray, thickly bedded, and unsorted clay-silt-sand mixtures with floating, angular pebbles. Beds are structureless or show soft-sediment shearing. Marine deposition, in places, is indicated by rare marine acritarchs and laminated shale with dropstones. Associated diamictite likely represent marine mudflows. The presence of cross bedding and absence of turbidite features in sandstone and lack of burrowing sugge t that other diamictite represents lodgment tills or subaerial glacial mudflows. Pebble composition of diamictite indicates the source terrane consisted of limestone, granite, gneiss, red shale and sandstone, and volcanic rock in the Sierras Pampeanas and Precordillera region to the west. Upper Ordoflez core becomes redder westward suggesting that coloring is due to exposure and resedimentation of oxidized mud. The upper Ordonez appears to be partly contemporaneous with Paleozoic glacial deposits of the Parana basin in Brazil, but was derived from a different ice center. The overlying Victoriano Rodriguez Formation consists of shale, mudstone, and sandstone that was deposited in fluvial, floodbasin, and shallow to deep marine environments in the Early to Late (?) Permian. Glacial-related strata in the Chaco-Parana and Parana basins are potential hydrocarbon reservoirs. Paleozoic strata are unconformably overlain by Cretaceous rock.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994