Expanding the spectrum of shallow-marine mixed carbonate-siliciclastic systems: processes, facies distribution and depositional controls of a siliciclastic-dominaterd example

SCHWARZ, E.; VEIGA, G.D.; ÁLVAREZ TRENTINI, G., ISLA, M. Y SPALLETTI, L.A.

SEDIMENTOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2018 vol. 65 p. 1558 - 1589

0037-0746

Most of the present knowledge of shallow-marine, mixed carbonate?siliciclasticsystems relies on examples from the carbonate-dominated end of thecarbonate?siliciclastic spectrum. This contribution provides a detailed reconstruction of a siliciclastic-dominated mixed system (Pilmatue Member of the Agrio Formation, Neuquen Basin, Argentina) that explores the variability ofdepositional models and resulting stratigraphic units within these systems.The Pilmatue Member regressive system comprises a storm-dominated,shoreface to basinal setting with three subparallel zones: a distal mixedzone, a middle siliciclastic zone and a proximal mixed zone. In the latter, asignificant proportion of ooids and bioclasts were mixed with terrigenoussediment, supplied mostly via along-shore currents. Storm-generated flowswere the primary processes exporting fine sand and mud to the middle zone,but were ineffective to remove coarser sediment. The distal zone receivedlow volumes of siliciclastic mud, which mixed with planktonic-derived carbonatematerial. Successive events of shoreline progradation and retrogradationof the Pilmatue system generated up to 17 parasequences, which are bounded by shell beds associated with transgressive surfaces. The facies distributionand resulting genetic units of this siliciclastic-dominated mixed system are markedly different to the ones observed in present and ancient carbonate-dominated mixed systems, but they show strong similarities with the products of storm-dominated, pure siliciclastic shoreface?shelf systems.Basin-scale depositional controls, such as arid climatic conditions and shallow epeiric seas might aid in the development of mixed systems across the full spectrum (i.e. from carbonate-dominated to siliciclastic-dominated end members), but the interplay of processes supplying sand to the system, as well as processes transporting sediment across the marine environment, are key controls in shaping the tridimensional facies distribution and the genetic units of siliciclastic-dominated mixed systems. Thus, the identification of different combinations of basin-scale factors and depositional processes is key for a better prediction of conventional and unconventional reservoirs within mixed, carbonate?siliciclastic successions worldwide.