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Variabilities of Dryland Terminal Splay Complexes: Examples from Western Lake Eyre, Australia

Mark Reilly1, Simon Lang2, John Fisher3, Carmen Krapf2, Tobias Payenberg1, and Jochen Kassan4
1 Australian School of Petroleum, University of Adelaide, Adelaide, Australia
2 University of Adelaide, Adelaide, Australia
3 Royal Holloway University
4 Whistler Research, Brisbane, Australia

A variety of terminal splay complexes can be found along the shoreline of Lake Eyre, Central Australia. Three of those, the Neales, Umbum and Douglas Terminal Splay Complexes (TSC), have been chosen for detailed comparative studies on their facies distribution, element architecture and reservoir geometry.

The modern Neales TSC covers an area of approximately 25 km2 and consists of a fluvial-dominated, high constructive triangular lobate terminal splay. Three active rectilinear avulsion distributary channels (ADCs) dominate the system. The distributary complexes are generally highly constructive lobate terminal splays, with a broad middle-ground bar complex incised by deeper distributary channels.

The Umbum TSC is a radial distributive system covering about 15 km2. It comprises five major erosive ADCs that deposit locally reworked and flood-borne sediment as splays at the end of each channel. Beyond the terminal splay and across the playa floor, suspended fine silts and parallel laminated muds are deposited by a series of braided channels. Following flood events, suspended sediment within ponded water settles out of suspension, forming mud lenses at the base of channels, which are later desiccated.

The approximately 4 km2 Douglas TSC is characterised by two ADCs which terminate basinwards, causing propagation through sheetfloods. With increasing radial distance from the source, the splay shows a decrease in grain size, lithofacies thickness, syn-depositional incisional surfaces and primary sedimentary structures. The exposed surface of the splay is etched by a network of minor distributary channels that are often draped by a thin layer of clay.