Anatomy of a mixed marine/non-marine lowstand wedge in a ramp setting. The record of a Barremian/Aptian complex relative sea-level fall in Central Neuquén Basin, Argentina

VEIGA, G.D.; HOWELL, J.A.; STRÖMBÄCK, A.

The Neuquén Basin: a case study in sequence stratigraphy and basin dynamics

Geological Society

Lugar: London; Año: 2005; p. 139 - 162

Abstract: During the Cretaceous, western Argentina was occupied by the Neuque´n Basin, aback-arc–foreland basin that was open through the proto-Andes to the Pacific Ocean in thewest. The Neuque´n Basin contains a thick succession of sediments that include the offshoremarine deposits of the Agrio Formation. These deposits represent a time when the arc was anisland chain and the Neuque´n Basin was freely connected to the Pacific. This offshoremarine succession is punctuated by two intervals of arid continental deposits that representmajor, second-order, relative falls in sea level. In both of these cases there is no evidence oftectonic uplift or angular truncation along a basal bounding unconformity. The upper of thetwo lowstand wedges is characterized by a complex arragement of shallow-marine andcontinental deposits. Shallow-marine deposits sharply overlying offshore shales andcapped by a master sequence boundary are interpreted as falling-stage deposits recordinga complex relative sea-level fall. On top of a regional erosion surface, a drying-upwardssuccession of fluvial–aeolian deposits is developed, recording a fully non-marine stage inthe evolution of the basin. These deposits are overlain by a marginal marine evaporitesuccession. The absence of a return to fully open-marine conditions is attributed to upliftin the Andes and marks the transition of the Neuque´n Basin from a back-arc to a forelandsystem. This succession has important implications for the basin’s evolution and in thetiming of the uplift of the Andes, is a very spectacular example of a lowstand wedge andis also a major hydrocarbon reservoir.