Diagnostic Tidal Indicators from Intracratonic Playa Lake

Bruce Ainsworth¹, Carmen Krapf¹, Stephen Hasiotis², Tobias Payenberg¹, Kathryn Amos¹, Boyan Vakarelov¹, Marianne Sandstrom¹, and Simon Lang^3
1Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia
²Department of Geology and Natural History Museum and Biodiversity Research Center, University of Kansas, Lawrence, KS
³Woodside Energy Ltd, Perth, WA, Australia

This study of a modern-day, dryland terminal splay complex (TSC) from Lake Eyre, central Australia, indicates that sedimentary and biogenic structures previously considered indicative of marine tidal depositional environments are also generated in an intracratonic playa lake setting. Paired mud drapes (bundles) on cross-beds, cross-bedding reactivation surfaces, lateral bundle thickness variations, herringbone cross-bedding, flaser, wavy, and lenticular bedding, and desiccation cracks were observed in shallow excavation pits on the Kalaweerina Creek TSC. Fluctuations in flow velocity and direction required to generate these “tidal” sedimentary structures are attributed to daily changes in wind direction and velocity causing current reversals in the shallow lake here termed “wind tides”, along with longer period wind velocity and discharge variations in the feeder river system. Cross sections through vertical spider burrows and ant nests that crosscut “tidal” sedimentary structures can be easily mistaken for Skolithos,Gyrolithes, Rhizocorallium and Chondrites which are mostly found in shallow marine environments. These observations suggest that interpretations of similar ancient deposits may require re-evaluation and alternative depositional environments should be considered when interpreting strata containing these classic marine tidal indicators.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery