A new coral reef province in the Gulf of Carpentaria, Australia: Colonisation, growth and submergence during the early Holocene Peter T. Harris a, ⁎, Andrew D. Heap a , John F. Marshall a , Malcolm McCulloch b a Marine and Coastal Environment Group, Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia b Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia article info abstract Article history: Received 25 November 2007 Received in revised form 24 January 2008 Accepted 5 February 2008 Multibeam sonar mapping, drill cores and underwater video data have confirmed the existence of a previously unknown coral reef province in the Gulf of Carpentaria, Australia. Seven reefs, comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region. U/Th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10.5 kyr BP, making them the oldest Holocene reefs known in Australia. Reef growth persisted for ~ 2.0 kyr but it had ceased at most locations by ~ 7.0 kyr BP. Measurements of reef growth rates (0.95 to 4 m kyr - 1 ), indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise (N 10 m kyr - 1 ), which is consistent with a “give up” reef growth history. Core samples from reef platforms demonstrate that Pleistocene limestone is exposed at depths of 27 and 30 m below present mean sea level. These depths represent regionally significant phases of reef growth during a prolonged sea level still stand. We conclude that the reefs are therefore mostly relict features, whose major phase of growth and development relates to an earlier, pre-Holocene sea level still stand. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. Keywords: coral reefs U/Th dating sea level Quarternary reef growth Holocene 1. Introduction Most of our knowledge of the distribution of coral reefs has been discerned from nautical charts, aerial photographs and satellite images. Our picture of the global distribution of coral reefs is incomplete because the distribution of coral reefs in turbid water, or with surfaces below the limits of remote optical detection, is unknown. Submerged coral reefs not detectable using remote optical techniques occur not only in locations adjacent to charted reefs but also, as the present study demonstrates, in places where they were previously thought not to exist. In Australia, coral reefs of the Great Barrier Reef (including Torres Strait) and Ningaloo Reef provinces are very well studied (Veron, 2000), and their growth histories and character are well established (e.g., Woodroffe et al., 2000; Collins et al., 2002; Hopley et al., 2007). Smaller reef complexes such as the Houtman–Abrolhos Reefs in Western Australia (Collins et al., 1996; Wyrwoll et al., 2006), Sahul Banks and Ashmore and Cartier Reefs in the Timor Sea (Heyward et al., 1997), Lord Howe Island, Middleton and Elizabeth Reefs in the Tasman Sea (Woodroffe et al., 2004, 2005), and Cocos–Keeling and Christmas Islands in the Indian Ocean (e.g., Woodroffe et al., 1991, 1994) have received less treatment but their post-glacial history is still reasonably well known. Until our study, few modern coral reefs had been do- cumented in Australia outside of these regions. Identification of submerged coral reefs at locations around Australia outside of the known reef provinces has been made possible through the utilisation of multibeam sonar. In 2003, three prominent seabed features in the southern Gulf of Carpentaria, denoted on nautical charts as shallow banks, were mapped with multibeam sonar. The results revealed previously unknown submerged coral reefs (sensu Macintyre, 1972) located at around 18–30 m water depth (Harris et al., 2004). The submerged coral reefs exhibited classic reef geomorphology, and extensive surfaces showed that they mostly formed when sea level was ~30 m below its present position. Sparker seismic profiles showed that the coral limestone bioherms were underlain by an acoustic basement with positive relief (Harris et al., 2004). A series of 3–4 lateral ridges on the reef margins indicated that coral growth and deposition of carbonate was associated with repeated submergence, most likely throughout the Quaternary. A live specimen of Turbinaria (plate coral) was recovered from one location and underwater video footage showed that live hard corals also occurred at seven other locations. The fact that these submerged reefs support live hard corals is evidence for a “give-up” growth history (cf., Neumann and Macintyre, 1985) relative to sea level rise. A “give-up” growth history involves slow reef growth following submergence of the reef pedestal during transgression, followed by limited to zero growth under present high sea level conditions. The existence of three submerged reefs in the southern Gulf of Car- pentaria raises several questions, namely: how many other submerged Marine Geology 251 (2008) 85–97 ⁎ Corresponding author. Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia. Tel.: +61 2 6249 9611; fax: +61 2 6249 9920. E-mail addresses: Peter.Harris@ga.gov.au, pharris@aapt.net.au (P.T. Harris). 0025-3227/$ – see front matter. Crown Copyright © 2008 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2008.02.010 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo