Sequence stratigraphy of a tidally-dominated carbonate-siliciclastic ramp; the Tithonian-early Berriasian of the Southern Neuquén Basin, Argentina

SPALLETTI, L.; FRANZESE, J.; MATHEOS, S.; SCHWARZ, E.

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Lugar: Londres; Año: 2000 vol. 157 p. 433 - 446

0016-7649

Abstract: The Tithonian-Berriasian Vaca Muerta, Carrín Curá and Picún Leufú formations in the southern Neuquén Basin were deposited on a tidally-dominated, mixed carbonate-siliciclastic ramp. Basinal, outer, middle, shallow and back ramp facies associations are recognised and a sequence stratigraphic analysis reveals that the ramp record consists of three shallowing upwards sequences (Ti1, Ti2 and Ti3) within a lower order progradational cycle. A higher order of cyclicity is superimposed onto the middle (Ti2) sequence. The majority of the ramp facies belong to the transgressive and highstand systems tracts; however, at the base of Ti2, a lowstand systems tract is defined, characterised by a basal unconformity and an abrupt basinward shift of the shallow marine lithofacies. Transgressive systems tracts were characterised by slow sedimentation rates and rapid sea-level rises that affected carbonate productivity. Highstand systems tracts show the greatest carbonate productivity and an increased progradation rate on account of a reduction in accommodation space generation. Palaeogeography played a major role in the development of the depositional systems. Partial isolation from the Pacific Ocean reflecting the growth of the Andean magmatic arc and geographic restriction due to tectonic inversion in the central area of the basin resulted in a meso-macrotidal regime that produced a tidally-dominated sedimentary record in the shallow and back ramp environments. Coeval anoxic conditions in the central part of the Neuquén Basin favoured distal ramp and basinal black shale deposition in the studied area during episodes of relative sea-level rise.