A Time-Slice of the Lake Eyre Basin: Towards Better Facies Models

Abstract

Understanding the processes governing sediment distribution is important for predicting reservoir, seal, and migration pathway properties. Cross-discipline collaborations across geomorphology and sedimentology can develop process-based facies models which are adaptable to project-specific contexts (tectonic, climatic, provenance). Examples are given from Australia's Lake Eyre Basin, a presently underutilised modern analogue for fluvial processes in a dryland setting. The Lake Eyre Basin (LEB) catchment is arid to semi-arid, with extremely variable flow regimes. Drainage is centripetal towards Lake Eyre. The LEB is a continent-scale Australian intracratonic sag that overlies the Eromanga, Pedirka, Cooper, and Galilee Basins. Sediments have been accumulating since the Palaeocene; in the LEB's centre and inner north-west, where synsedimentary domal uplift and trough subsidence occurs, the Cainozoic attains thicknesses of 200->300 m. At the field and reservoir scale, the LEB hosts a variety of dissimilar river types, including anabranching and single-thread channels of low to high sinuosity, floodplains of sand or of mud, and bedloads of mud aggregates, sand or gravel. Within the rivers, there are a variety of landform suites related to flows moving from constricted to unconstricted settings. As geomorphic entities, they include 1) valleys with channel-floodplain suites, 2) floodouts (transition from channelized to unchannelised flow down-valley) and 3) distributary channel systems. As sedimentary packages, some will form valley- or basin-fill, and some will be low-angle alluvial fans. Few have been investigated from a sedimentologic viewpoint; others are better known from the geomorphic literature; many are undescribed. Their individual characteristics relate to differences in fluvial processes, sediment provenance, local base level, and post-pluvial history. Differences are expressed in different channel planform and bedload (sand body distribution and connectivity) and floodplain composition and creation (seal and migration barrier qualities). We will present examples from a range of these, in this initial collaboration between a basin-scale process geomorphologist and a reservoir-scale focused process sedimentologist, in the anticipation that this will enable the depositional systems within this large dryland basin to be explored in a new and useful light.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015