COMPARISON OF THE NEOGENE PRODUCTIVE SERIES, AZERBAIJAN WITH THE MODERN EPHEMERAL FLUVIAL SYSTEMS AROUND LAKE EYRE, AUSTRALIA

Clare E.Davies¹, Simon C. Lang², Tobias H.D. Payenberg², Mark R.W. Reilly², Jochen Kassan^2,3, 
and Stephen J.Vincent^1
1 CASP, University of Cambridge, UK
² Australian School of Petroleum (ASP) and Australian Petroleum Cooperative Research Centre (APCRC), University of Adelaide, Adelaide, SA 5005, Australia
³ Whistler Research Pty Ltd, Whistler Court, Greenbank, QLD 4124, Australia

The Neogene Productive Series sediments in Azerbaijan are the focus of active exploration in the South Caspian Basin. Outcrop equivalents to offshore reservoirs occur on the Apsheron Peninsula and in the Kura Basin, therefore a full understanding of the depositional environment has a direct application for understanding the reservoir geometries and continuity. The sedimentology of outcrops in Azerbaijan helps address crucial exploration and production issues, for example, how extensive were lacustrine influences at different times and so are fluvial, deltaic or lacustrine models most applicable for reservoir architecture.

The Productive Series outcrops are interpreted to record a range of depositional environments from fluvial to lacustrine. Sediments are dominated by fluvially derived, channelised and amalgamated high net to gross sand bodies interbedded with heterolithics deposited on the desiccating floodplain, probably from overbank flows and ephemeral ponds. These interpreted depositional environments from Azerbaijan are thought to be similar in depositional setting to the Neales and Umbum river systems located around the margin of Lake Eyre, Central Australia.

A comparison of Azerbaijan outcrops with the modern ephemeral fluvial systems of Lake Eyre indicate many similarities including the change from high to low net to gross depending on the mix of sediments and/or the role of variable accommodation. Data from the Lake Eyre analogues indicates that the amalgamated high net to gross sand sheets may result from sandy bedload rivers and associated frontal splay complexes (i.e. Umbum Creek style), whereas the heterolithic strata may represent either mixed-load frontal splay complexes and narrow distributaries (i.e. Neales River style) or floodplain deposits typical of both the Neales and Umbum systems.

A key difference between the South Caspian Basin and the Lake Eyre Basin is accommodation rate, which has an important influence on preservation potential. The South Caspian Basin, during Productive Series deposition, subsided several orders of magnitude faster than the Lake Eyre system. The surficial morphology of the Lake Eyre systems may be more easily preserved (and hence useful) compared to its long term stratigraphy, because aeolian deflation may result in substantial cannibalisation of the terminal splays/deltas, leading to coarse-grained, high net to gross sand sheets abruptly overlying playa lake or floodplain successions.