AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Depositional Environments of the Lake Eyre Basin
(1) Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
(2) Wakelin Associates, Melbourne, VIC, Australia.
This poster presents a review of present understanding of the sedimentology and depositional environments of the Lake Eyre Basin, aspects of which are widely used as a modern analogue for ancient dryland successions and hydrocarbon systems. Due to the basin’s scale and remote location, surprisingly little research has been conducted on the sedimentology of this well-used modern analogue for continental dryland environments. We believe that in many cases, Lake Eyre Basin analogues in use may not be appropriate, due to a lack of understanding of climate, sedimentology and processes operating at these localities. Many environments within the Lake Eyre Basin provide useful analogues that are not being used as widely as they could be. It is hoped that this presentation will increase awareness of the depositional environments and state of knowledge of the sedimentology of the Lake Eyre Basin. To assist with this, we will conclude by presenting a summary of the field observations that have surprised us. Major depositional elements within the basin are ephemeral rivers, dunefields, stony pavements, and playas. Rivers within the Lake Eyre Basin have widely varying sedimentologic characteristics: bedload ranges from cobble to clay particles, planform morphologies include single-channel and highly complex multiple channel (both anabranching and anastomosing), floodplains range from metres to many tens of kilometres wide. Rivers occur within synclinal sub-basins filling with alluvium, and weave a slow and tortuous path through dunefields downstream of anticlines. Some rivers have valley lengths of hundreds to thousands of kilometres, and others terminate via floodouts within the desert. In some rivers, flood events can take several months to travel from the headwaters to the depocentre of the basin, whereas others have a flashy discharge and events can last only a few days. Some examples of surprising field observations are: i) the existence of wind-tide sedimentary structures in playa deposits; ii) that channel bed deposits within a Channel Country location were not distinguishable from levee and floodplain deposits (a regional fluvial seal), iii) the role of tributary asynchronicity in channel placement within the main floodplain, iv) the abundance of flora and fauna, iv) meander-bend deposits that look like scrolled point bars but have a very different sedimentology and process of formation, v) stochastic and non-layered patterns of floodplain sedimentation.