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

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

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

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

0016-7649

The Tithonian Vaca Muerta, Carrín Curá and Picún Leufú formations in the southern Neuquén Basin are interpreted as a tidally-dominated, mixed carbonate-siliciclastic ramp, in which outer, middle, shallow and back ramp facies associations are recognised. Sequence stratigraphic analysis of large-scale exposures reveals that the Tithonian ramp record consists of three shallowing upwards sequences (Ti1, Ti2 and Ti3), within a second 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 by an abrupt basinward shift of the shallow marine lithofacies. Transgressive systems tracts were characterised by a slow sedimentation rate and rapid sea-level rise that partially affected carbonate productivity. Highstand systems tracts show the greatest carbonate productivity and an increased progradation rate, favoured by a significant reduction in accommodation space generation. Sequence stacking in the Tithonian of the Neuquén Basin is the result of both eustatically and tectonically controlled variations in relative sea level. The palaeogeography of the Neuquén Basin played a major role in the development of the depositional systems. Partial isolation from the Pacific Ocean, produced by the growth of the Andean magmatic arc to the west of the basin, favoured anoxic conditions in the basinal settings, as well as a meso-macrotidal regime, that resulted in a tidally-dominated sedimentary record for the middle, shallow and back ramp environments.