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Traces Associated with Wind-Generated Tidal Deposits Formed from the Kalaweerina Creek Terminal Splay Complex, Lake Eyre Basin, Central Australia: Sedimentary Facies and Trace Associations That Might Sway Ichnologic Interpretations

Hasiotis, Stephen T.1; Ainsworth, Bruce 2; Amos, Kathryn J.2; Vakerelov, Boyan K.2; Payenberg, Tobias 2; Krapf, Carmen B.2; Sandstrom, Marianne 2
1 Department of Geology, University of Kansas, Lawrence, KS.
2 Australian School of Petroleum, University of Australia, Adelaide, SA, Australia.

Sedimentary and biogenic structures considered indicative of marine tidal depositional environments are also generated in the Kalaweerina Creek terminal splay complex (TSC) in the dryland setting of Lake Eyre in central Australia, an intracratonic playa lake environment. Terrestrial organisms produced a variety of traces that crosscut cross-beds with paired mud drapes, cross-bedding reactivation surfaces, herringbone cross-bedding, flaser, wavy, and lenticular bedding, and desiccation cracks. Three morphotypes dominated the TSC sediments, all constructed during subaerial conditions. Vertical to subvertical tubes 0.3-1.0 cm in diameter and 5-30 cm deep, sometimes with a bulbous termination 1.3-1.5 times the tube diameter, are common in tabular and trough cross-stratified beds with mud drapes, and are less common in massive to laminated mud. Tubes are filled with sand, mud, or a combination of interlayered fill. Tubes are constructed and occupied by wolf spiders. Subvertical to subhorizontal, slightly sinuous tubes ~0.05-0.2 cm in diameter branch laterally and downward are common in massive to laminated mud and less common in sandier beds. Tubes do not appear to decrease in diameter even after they branch. Most tubes are filled with mud or sand. Some tubes contain the plant roots, which is unequivocal evidence that they produced them. Mostly elliptical, but some circular, elongate tubes typically with a flattened but sloped base and domal roof are found in both sand- and mud-rich layers and form an interconnected system. Tube diameters range from ~0.5-2 cm with width-to-height ratios of 1-2:1. Tubes form a simple system of subvertical to subhorizontal interconnected tubes up to 40 cm deep. In some systems, the central tube forms a downward spiral with several lateral tubes 5-20 cm long branching from it. Tubes in mud are often lined or filled with sand sourced from the surface or a lower sand bed. Ants construct these tube systems, identified by their presence in the tubes along with their larvae and pupation cocoons. Cross sections through these traces in tidal sedimentary structures are easily mistaken for such trace fossils as Skolithos, Gyrolithes, Rhizocorallium, and Chondrites. Co-occurrence of these traces with sedimentary structures indicative of tidal processes could easily be interpreted as evidence for shallow marine intertidal settings based on their superficial resemblance to traces found in intertidal to subtidal marine environments.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009