Tim Hicks¹, Jim Benson², Simon C. Lang³

(1) Santos Ltd, Brisbane, Australia
(2) Santos Ltd, Adelaide, Australia
(3) University of Adelaide, Adelaide, Australia

ABSTRACT: Sedimentology and facies architecture of the Neales River lacustrine delta, Lake Eyre basin, South Australia

Lacustrine delta form important reservoirs in fluvial-lacustrine basins, and as part of a program to understand reservoir geometry of lacustrine deltas in the Permian intracratonic Cooper Basin, a detailed geomorphological, sedimentological and stratigraphic study was conducted on the Neales River lacustrine delta in the Lake Eyre Basin, South Australia. The delta enters the western margin of Lake Eyre, and represents the late Holocene lacustrine "lowstand" delta, that forms part of a larger fan delta system. The ephemeral nature of the delta provides three-dimensional exposure of distributaries and thin mouth bars, which are dominated by crevasse splay processes. Coring, augering, trenching and interpretation of air photographs has helped determine vital statistics regarding facies, width/thickness ratios, bifurcation frequency and other relationships useful for predicting likely reservoir geometry and facies development in lacustrine delta. Although some aspects are exclusive to ephemeral systems, many relationships are relevent to other deltas dominated by crevasse splay processes. The delta is a fluvially-dominated braided delta, and the modern system is up to 5m thick at its proximal apex. Sedimentation is controlled by flash flooding, which occur episodically every few years. High energy bedload traction transport dominates, producing coarse-grained, cross-bedded distributary channel fill (W/T ratios from 40 to 80), sandy crevasse splay lobes dominated by parallel lamination, pseudo-HCS, and climbing ripples. Extensive, but thin sheetflood mouth bars form the delta front, prograding onto a dark brown or bluish lacustrine prodelta clay. These data can be used as an analogue for reservoir modeling, and have proved useful in intracratonic fluvial-lacustrine Cooper Basin of central Australia.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado