Print this pageLowstand Linear Siliciclastic Coastal Deposits as Substratum for the Growth of Modern Barrier Reefs (Northern Ashmore Trough, South Shelf Edge of the Gulf of Papua)
Andre W. Droxler1, Gianni Mallarino1, Jason M.
Francis1, Bradley Opdyke2, Gerald Dickens1,
Samuel Bentley3, and Larry Peterson4
1 Rice University, Houston, TX
2 Australian National University, Canberra, Australia
3
Louisiana State University, Baton Rouge, LA
4 University of Miami, Miami,
FL
Modern barrier reefs, often mimicking the morphology of modern siliciclastic coastlines, correspond to late Quaternary thin coralgal deposits covering early Brunhes siliciclastic sediments. Results of a NSF-funded R/V Melville cruise along and across the shelf edge in the Northern Ashmore Trough point out that modern barrier reefs were probably initially established on lowstand linear siliciclastic coastal deposits, such as beach ridges or barrier islands, during the early part of the following transgression.
A continuous 30 to 50 m-high ridge, with linear segments exceeding 10 km in length, closely parallels the shelf edge ranging in water depths from 140 to 120 m. A dredge, only scraping the surface of the ridge, yielded mostly rhodoliths, though the main ridge body probably contains a coral framework to explain its impressive height. An 8.5 m-long piston core, MV26-0403-73JPC, retrieved from one of the passes dissecting the ridge in 138 m of water, recovered coastal deposits on top of which the adjacent ridge grew. The bottom 2/3 of the core, spanning in time from 17.5 to 16.5 calendar ky BP, indicates a mixed carbonate-siliciclastic open marine shoreface environment. The upper third of the core records the major re-flooding of the modern outer shelf during an interval from 16.5 to 11 calendar ky BP, corresponding to the Meltwater Pulse 1A and Younger Dryas when sea level rose from -110 to -60 m and during which the shelf edge ridge grew, keeping up with the sea-level rise. The ridge drowned during the Meltwater Pulse 1B.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005