HR: 0800h
AN: OS51B-1303    [Abstracts]
TI: Uppermost Pleistocene Sea-Level Transgression across a Last Glacial Maximum Mixed Carbonate/Siliciclastic Coastline, Modern Gulf of Papua Shelf Break in the Northern Ashmore Trough
AU: * Mallarino, G
EM: gianni@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Francis, J M
EM: jfrancis@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Droxler, A W
EM: andre@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Opdyke, B N
EM: bno@ems.anu.edu.au
AF: Department of Earth and Marine Sciences, The Australian National University, Linneaus Way, Canberra, ACT 0200 Australia
AU: Bentley, S J
EM: sjb@lsu.edu
AF: Coastal Studies Institute, Department of Oceanography and Coastal Sciences, LSU, 302 Howe-Russell Geosciences Complex , Baton Rouge, LA 70803 United States
AU: Dickens, G R
EM: jerry@rice.edu
AF: Earth Science Department, MS-126, Rice University, P.O. Box 1892, Houston, TX 77251 United States
AU: Peterson, L C
EM: lpeterson@rsmas.miami.edu
AF: RSMAS, MGG, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AB: This research focuses on the analyses of an 8.5 m-long piston core, MV26-0403-73JPC, recovered during a Spring 2004 R/V Melville cruise, in the Gulf of Papua. The core was taken at 138 m of water depth on the modern shelf break of the northern Ashmore Trough. Sediments in the core represent a deepening upward sequence deposited in a mixed carbonate/siliciclastic setting during the time interval from 17,680 $\pm$ 370 to 10,980 $\pm$ 360 calendar years BP based on six calibrated $^{14}$C dates. Four main units are identified based upon the downcore sedimentologic, mineralogic, and micropaleontologic variations. The lowermost Unit D (8.5 to 6.0 mbsf) is approximately 17.5-17 cal. kyr BP in age and consists of a fining upward sequence ranging from bioclastic gravel with abundant ooids to fine sand with other coated grains, bioclasts, and angular quartz grains. The carbonate content of Unit D average 80% whereas the $<$ 63 $\mu$m fraction is rich in quartz. The benthic foraminiferal assemblage is dominated by {\it Calcarina} spp. indicative of a shallow water open marine environment. The overlying Unit C, (6.5 to 3.0 mbsf) consists of silty sand with increased quartz and lower carbonate contents (15%-40%). The age of the top is approximately 16.5 cal. kyr BP. Unit B (3.0 to 0.5 mbsf), which spans the interval up to 12 cal. kyr BP, records an important transition marked by the disappearance of coated grains, an increase of the silt-mud fraction, and the appearance of planktonic foraminifers. The uppermost 0.5 m, Unit A, mostly indurated and ranging in age from 12 to 11 cal. kyr BP, consists of bioclastic packstone-wackestone with {\it Halimeda} segments, red algae, more abundant planktonic foraminifers, and quartz grains. The carbonate content increases to 75% and high-Mg calcite and quartz are the main components of the fine fraction. Calcarinids become a minor component among the benthic foraminifers whereas {\it Amphistegina} spp. (flattened form) dominates, pointing to an outer shelf depositional setting. These observations indicate that the coastline reached the present-day shelf break during the LGM and that the sediments record two distinct pulses of sea-level rise. The first pulse, occurring between 16.5 and 12 cal. Kyr BP and probably representing MWP 1A, corresponds to a backstepping of the shoreline and the first major reflooding of the modern outer shelf, with the shoreface deposits of Unit C overlain by the inner shelf sediments of Unit B. The second melt water pulse (MWP 1B) is recorded in this core ca. 11 cal. kyr BP as a deepening of depositional facies to the outer shelf deposits of Unit A. Holocene sediments have been bypassing the shelf edge at this location.
DE: 4219 Continental shelf processes
DE: 4556 Sea level variations
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting