GPR Facies Architecture of Dryland Fluvial Reservoir Analogues, Neales River and Umbum Creek, Lake Eyre, Australia

Ian A. Moffat¹, Mark Reilly², Carmen Krapf¹, Simon Lang¹, and Tobias Payenberg^2
1 University of Adelaide, Adelaide, Australia
² Australian School of Petroleum, University of Adelaide, Adelaide, Australia

Ground Penetrating Radar (GPR) successfully imaged key surfaces and internal facies architecture of dryland fluvial reservoir analogues from the northwestern side of Lake Eyre, in arid central Australia. At Umbum Creek, numerous regularly spaced, reconnaissance 2D strike lines ~1.5km apart were acquired across a shallow incised valley fill using a Pulse Ekko IV system (200 MHz). The data shows inclined lateral-downstream accretion and erosion surfaces, filled with cross-bedded, parallel-bedded and cut-and-fill facies within mainly coarse-grained sandy low sinuosity fluvial convex bar and channel fill, with lesser splays and very-fined grained floodplain sediments. The sediments infill a shallow incised valley (<5m deep, 2-4km wide, >10km long) cut into relict, gypsum-cemented fluvial and aeolian sediments. The valley ends in a lobate terminal splay and distributary complex constructed over the saline playa (>5km radius). High resolution data was acquired by a Mala X3M system (250 and 500 MHz) providing detailed images of internal channel barform geometry, and inset floodplain sediments, especially within small GPR grids over selected areas within the valley fill. A 3D grid (~100m x100m) was also acquired behind cliff exposures of Late Quaternary sediments along the Neales River, 50km to the north. This highlighted channelised (~3-5m deep, ~200m wide) distributary channel fill of a relict terminal splay complex, complete with complex, low angle lateral accretion surfaces produced by alternate bars. The cliff outcrops are mainly fine-grained gypsum-cemented sands with parallel-lamination and climbing ripples, cut into relict lacustrine and playa lake shale and associated shoreline and lake plain and floodplain sediments.