HR: 1340h
AN: PP13A-0578    [Abstracts]
TI: Relationship Between Holocene Sediment Accumulation and Lake-Volume Change in a Small Coastal Lake in Southwestern Australia
AU: * Telles, F
EM: astrobiology@sbcglobal.net
AF: Department of Geological Sciences California State University, Northridge, 18111 Nordhoff St, Northridge, CA 91330-8266 United States
AU: Pedone, V
EM: vicki.pedone@csun.edu
AF: Department of Geological Sciences California State University, Northridge, 18111 Nordhoff St, Northridge, CA 91330-8266 United States
AU: George, A
EM: ageorge@segs.uwa.edu.au
AF: School of Earth & Geographical Sciences The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 Australia
AB: Change in lithology in a 180-cm-long lake-center core from Lake Thetis, Western Australia serves as a proxy for change in lake volume during the Holocene. Lake Thetis is located on the coastal plain 245 km north of Perth, 1.25 km inland from the Indian Ocean. It occupies a sinkhole in middle Holocene limestone. The 300-m-diameter, steep-sided, ~2-m-deep lake has a 5-m-wide marginal terrace covered by relict and living stromatolites and a bottom covered by a thick, red-purple microbial mat. Lake elevation is not monitored, but changes noted over a 25-year period of up to 0.5 m have alternately exposed and submerged the stromatolite terrace. No hydrological study has been done to determine if the lake has a subterranean connection to the sea. Limited measurements of salinity and pH are similar to or greater than those of seawater. The laminated sediment from the core is divided into three intervals based on texture. From 0 to 45 cm, the core consists of uncompacted, red-purple, organic-rich muddy sand. Very fine-grained carbonate sand forms 50% of the sediment. This interval also contains five, lighter-colored bands, where carbonate sand forms up to 90% of the sediment. From 45 to 130 cm, the core consists of laminated red-brown, muddy, very fine sand and light-red-brown, slightly muddy medium- to fine-grained sand. The frequency of medium- to fine-grained sand layers decreases, but the layer thickness increases, upward. Carbonate grains in the thickest layers are coated with iron-oxide minerals. From 130 to 180 cm, the core consists of alternating red-brown mud, light-gray-purple mud, sandy mud, and muddy very fine sand. The carbonate sand is mostly derived from erosion of the stromatolite terrace, with minor eolian contribution from coastal-plain dunes. Therefore, the mud-dominated basal unit accumulated during a time of high lake elevation, when stromatolites were submerged and actively forming. The middle sand-dominated interval accumulated during a time of low lake elevation, when the emergent stromatolite terrace was actively eroding. The layers containing oxide-coated grains might have formed during periods of prolonged exposure. The uppermost interval accumulated under conditions similar to the modern, where lake elevation varies slightly about the slope break of the terrace. Significant climate and sea-level changes have occurred in this area since the middle Holocene, but current data are insufficient to determine which might be the dominant driver of volume change in Lake Thetis.
DE: 1815 Erosion and sedimentation
DE: 1845 Limnology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting