--> --> Abstract: Facies and Diagenesis of Older Pleistocene Coral Reefs, Great Barrier Reef, Australia (IODP 325), by Eberhard Gischler, Andre W. Droxler, Jody Webster, and Expedition 325 Scientists; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Facies and Diagenesis of Older Pleistocene Coral Reefs, Great Barrier Reef, Australia (IODP 325)

Eberhard Gischler1; Andre W. Droxler2; Jody Webster3; Expedition 325 Scientists4

(1) Geosciences, Goethe University, Frankfurt, Germany.

(2) Rice University, Houston, TX.

(3) University of Sydney, Sydney, NSW, Australia.

(4) IODP 325, Edinburgh, United Kingdom.

IODP expedition 325 drilled 34 holes along four traverses across the Great Barrier Reef of Australia thereby penetrating some 750 m of reefal deposits of the late Quaternary in water depths ranging from 40-170 m. The expedition took place during 12 February - 1 April and was followed by the onshore science party in Bremen, Germany, during 1-16 July 2010 involving 28 scientists from 9 countries. IODP expedition 325 has three major objectives. They include (1) a reconstruction of deglacial sea level for the period 20-10 kyrs BP with a focus on MWP 1A and 1B events, (2) to use the variability of sea surface temperature and sea-level change on reef growth patterns including drowning, and (3) to quantify paleoclimatic change in high-resolution by sampling skeletons of massive corals during the same time window. According to preliminary age dating, the majority of cores cover the time period of about 25-10 kyrs BP. These late Pleistocene sections appear diagenetically unaltered and comprise coralgal boundstone, coralgal-microbial boundstone, skeletal grainstone and rudstone, and unconsolidated sand. In five cores taken in depths of 40-85 m water depths at three traverses, older Pleistocene (>25 Kyrs BP) reefal deposits were recovered in lower core sections. Lithologies include skeletal grainstone to rudstone, some packstone, coralgal boundstone, and few occurrences of coral-microbial boundstone. Usually, they exhibit clear evidence of diagenetic modification in the meteoric realm, such as caliche phenomena, neomorphism, dissolution vugs, and low magnesium calcite cement growth. Samples are currently being investigated under sedimentologic and diagenetic aspects, and detailed results will be presented at the meeting.