Shelf Reservoirs Produced by Combined Gravity Flow and Storm Deposits: Analogous Model from The Portezuelo Del Tontal Formation (Late Ordovician, Precordillera Argentina, Argentina)

BASILICI, GIORGIO; PERALTA, SILVIO H; FINNEY, STANNEY

Barcelona, España

Conferencia; Annual Meeting American Association of Petroleum Geologist (AAPG); 2003

American Association of Petroleum Geologist

Shelf Reservoirs Produced by Combined Gravity Flow and Storm Deposits: Analogous Model from The Portezuelo Del Tontal Formation (Late Ordovician, Precordillera Argentina, Argentina) We presented an analogous reservoir model made up by sandstones with features between sediment gravity flow and storm influenced deposits. This forms a succession of interlayered sandstone and rare shale, called Portezuelo del Tontal Formation (PTF), about 2000 m thick, 100 km long and 25 km wide. Similar sandstone successions are interpreted as deposited by "wave-modified turbidity currents" in shoreline to shelf environments. Since the similarity with sediment gravity flows is very high, it is necessary differentiate these deposits from deep-water systems to reconstruct the geometry and the sequential organisation of the sandstone reservoirs. A 110 m thick section, at the upper part of the PTF, is monotonously made up of sandstone depositional events and thin rare shale strata. Most sandstone strata are identified as a bed-event composed of two parts, representing the combination of two-phase of sedimentation.The lower part of the strata is formed by massive, medium grain-sized sandstone, showing sole marks, traction carpet and floating pelitic clast; it corresponds to the deposition of a concentrated density flows produced by a geostrophic current storm-derived. Very fine grain-sized sandstone, HCS structures and climbing ripples, produced as traction and settling processes of the finest grains by storm wave action, form the upper part. Storm waves generated gravity flows in shoreface and proximal shelf and after reworked and/or deposited on previous deposits. They produced tabular sandstone beds, up to 4 m thick, very continuous laterally, whose interconnection degree is controlled by the frequency and strength of storm mechanisms.