Hyperpycnal-flow deposits in Oligocene-Miocene clinothems of the Austral Basin, Tierra del Fuego, Argentina.

J. J. PONCE; E. B. OLIVERO; D. R. MARTINIONI

AAPG Argentina 2008 Hedberg Research Conference, Sediment Transfer from Shelf to Deepwater - Revisiting the Delivery Mechanisms. Conference Field Trip Guidebook.

Laboratorio de Geología Andina (CADIC-CONICET) - American Association of Petroleum Geologists (AAPG)

Lugar: Ushuaia; Año: 2008; p. 25 - 48

ABSTRACT:   The Upper Oligocene-Miocene deposits of the foreland Austral Basin of Tierra del Fuego accumulated just in front of the adjacent fold and thrust belt. They represent the youngest foredeep fill that consists of a more than 600 m thick, superbly exposed, sub-horizontal, clastic succession. It comprises five depositional sequences (SI-SV), bounded by unconformities (dI-dV). The basal sequence (SI) includes two members: A, mudstone dominated, deposited by cohesive flows; and B, glauconite-rich, sandstone dominated, deposited by episodic turbidity currents. The remaining sequences (SII-SV) are composed of complex arrangements of fine conglomerates, coarse- to fine-grained sandstones, and mudstones that were deposited mainly by hyperpycnal flows. The basal unconformities of the SI to SIV involve minor hiatuses, while that of the SV is a major order unconformity. These foredeep depositional sequences constitute clinothems that developed in accordance with two types of clinoform geometries. Type a clinoforms present a wedge shaped geometry and characterize the foredeep infill during the compressional tectonic regime. Regarding this clinoform type, SI is situated closer to the orogen and shows variations in the bedding dip with development of internal unconformities. SII to SIV are situated towards the foreland and are characterized by subhorizontal conformable beds of large lateral extension. Type b clinoforms, with sigmoidal geometry, show a clear northeast progradation related to a progressive foredeep fill under tectonic quiescence. This clinoform type characterizes the deposits in SV. The recognition of hyperpycnites and different types of clinoform geometries in these sequences incorporates new concepts in reservoir prospects, which are critical for the evaluation of the petroleum system in the Austral Basin.