LATE PLEISTOCENE PALAEO-ENVIRONMENTAL HISTORY FROM THE GULF OF CARPENTARIA, AUSTRALIA: INTERPRETATION BASED ON FORAMINIFERA, OSTRACODA AND CHARALES

The Gulf of Carpentaria, located in tropical Australia, is an epicontinental sea with maximum water depth of 70 m. The connection with the Pacific Ocean by Torres Strait is only 12 m deep, while the connection with the Indian Ocean to the West by Arafura Sill is 53 m deep. During low sea levels a palaeo-lake called ‘Lake Carpentaria’ developed in the basin. Six sediment cores spanning the last 125 ka (Last Interglacial) where collected, and two non-marine/marine transitions have been identified. A multi-proxy approach based on microfossils and geochemistry is under development to produce the palaeoclimatic reconstruction of the area. The upper six metres of the two longest cores (MD-31 and MD-32) have been analysed. The age spans between the last regression (~ 75 ka) up to the last transgression (~ 9.7 ka), including the Last Glacial Maximum time (~ 20 ka). The foraminifers, ostracods and charophytes are studied, and the environmental reconstruction of the ‘Lake Carpentaria’ is discussed in relation with fluctuations in sea level and monsoon input. Core MD-31 located in the west of the basin, has a higher topographic position, changing from saline lake to freshwater lake to saline lake to a time of highly saline events within dry periods. Core MD-32, collected towards the east, and deeper part of the basin, have a nice sequence of facies from estuarine environment to a saline lake to a freshwater lake. Euryhaline taxa such as Ammonia sp., Leptocythere sp., Cyprideis sp. and Pistocythereis sp., were replaced by an association of Ammonia sp., Helenina sp., Cyprideis sp., and Ilyocypris sp., indicating lower salinity. The disconnection of the lake from the ocean, and increasing freshwater input, produced a change in the biota to taxa of fresher-water affiliation as Ammonia tepida, Ilyocypris sp., Cyprinotus sp., Cypretta sp., Darwinula sp., together with charophytes Chara vulgaris, C. zeylanica and Lychnothamnus barbatus. Lamprothamniumsp., a euryhaline genus, is present in only one level, indicating fluctuating environment. After the last transgression, the assemblages changed to a highly diverse fauna of marine foraminifers and ostracods (including several species of Textularia, Bolivina, Asterorotalia, Pararotalia, Ammonia, Neonesida, Paranesidea, Cyteroptheron Echinocythereis).