172 Paleoclimatology/Paleoceanography (Posters)

Tuesday, 11 October 2011
9:00 AM - 6:00 PM
Hall C

MULTIPLE PALEOCLIMATE PROXIES FROM EOCENE – HOLOCENE LAKE, EOLIAN, AND PALEOSOL FACIES IN WESTERN AUSTRALIA CORES: PRELIMINARY RESULTS

Paper number: 172-5
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Yilgarn Craton of Western Australia hosts ephemeral acid saline lakes, sandflats, mudflats, dunes, ephemeral channels, and desert soils. Modern sediments, lakes, and groundwaters are influenced by arid climate, weather events, and host rock weathering. Sedimentology, mineralogy, and palynology of three cores near Norseman, lead to preliminary interpretations of paleoclimate trends that may have been a driving force in the evolution of acid brines. The deepest of the three cores, LA2-09, is ~60 meters deep, late Eocene in age at the base, and includes coal, muds, sands, and bedded gypsum. Lithofacies include perennial freshwater and saline lakes, ephemeral saline lakes, sandflats, mudflats, root- and fungi-bearing paleosols, and crack-rich paleosols. Nearby cores LA1-09 and CB1-09 also contain eolian facies. Displacive halite and gypsum, and iron oxide, jarosite, alunite, gypsum, and kaolinite/halloysite cements suggest shallow acid saline groundwaters.

Paleoclimate proxies indicate relative humidity and aridity. Abundant organic matter and root- and fungi-bearing paleosols suggest relatively wet climate. Crack-rich paleosols, displacive evaporites, and suspected Dunaliella? algae in gypsum beds indicate relatively dry climate. Increased evaporation promotes pH decrease, so the acid mineral assemblage may also suggest aridity. Physical reworking, low organic content of some sediments, and differences in regional palynological zonations make dating much of the cores challenging. Deposition was not continuous and much of the Oligocene and probably Miocene appear to be missing. Regardless, preliminary observations suggest a general drying trend from the late Eocene until Holocene, with higher-resolution fluctuations in aridity. Early humid climates likely promoted chemical weathering. Later arid climates may have increased salinity and decreased pH, making extremely acid saline brines. This provides clues to how environmental change, water chemistry and atmospheric factors are related.