Holocene coral reef growth and sea level in a macrotidal, high turbidity setting: Cockatoo Island, Kimberley Bioregion, northwest Australia Tubagus Solihuddin a,d, ⁎, Lindsay.B. Collins a,d , David Blakeway b , Michael J. O' Leary c,d a Department of Applied Geology, Curtin University, Bentley, WA 6102, Australia b Fathom 5 Marine Research, 17 Staines Street, Lathlain, WA 6100, Australia c Department of Environment and Agriculture, Curtin University, Bentley, WA 6102, Australia d The Western Australian Marine Science Institution, Floreat 6014, Australia abstract article info Article history: Received 9 September 2014 Received in revised form 6 November 2014 Accepted 18 November 2014 Available online 25 November 2014 Keywords: Acropora Porites Reef geomorphology Holocene reef growth Sea-level change Accretion rate The inshore Kimberley Bioregion of northwest Australia is a macrotidal, low wave energy, frequent cyclones, and high turbidity setting with abundant fringing coral reefs. Here we describe the Holocene development of a shel- tered fringing reef at Cockatoo Island in the Kimberley, using data from reef cross-sections subaerially exposed in an iron ore mining pit, seismic profiles across the adjacent contemporary reef, and GIS and ground truth mapping of contemporary reef habitats. Subsidence since the Last Interglacial has provided accommodation for ~ 13–20 m of Holocene reef accretion upon an older, probably Last Interglacial, reef. In the pit cross-sections, the reef initi- ated at ~9000 cal y BP and accreted in a catch-up mode, reaching sea level at ~3000 cal y BP, and reef accretion rates varied from 26.8 mm/year to 0.8 mm/year, averaging ~ 2 mm/year. The catch-up interpretation is supported by the predominance of branching Acropora throughout the Holocene section and the absence of contemporary intertidal indicators such as Porites cylindrica and Millepora intricata. This pattern differs from the otherwise similar mud-rich but mostly microtidal inshore fringing reefs of the Great Barrier Reef, which initiated in the late Holocene on shallow substrates under a stable sea level. The study provides the first Holocene reef growth history for an inshore Kimberley reef within a biodiversity “hotspot”. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Kimberley coast is a remote sparsely populated and poorly stud- ied region located in the NW of Western Australia. However, the discov- ery of a major hydrocarbon province in the offshore Browse Basin, and an increase in petroleum exploration in the region, has led to a height- ened awareness of the region's rich biodiversity (Collins, 2002; Chin et al., 2008; Collins et al., 2011). While the presence of coral reefs have been broadly documented, occurring as fringing reefs in coastal settings, platform reefs in mid-ramp settings and atoll-like reefs along the shelf margin (Wilson et al., 2011), there have been few investigations into their biogeography, diversity and developmental history. Coral reefs are particularly ubiquitous to the complex drowned landscape of the Kimberley coast, which provides abundant Proterozoic deformed rocky substrate for fringing reef development. These inshore fringing reefs occur in sheltered and exposed settings and endure in seemingly extreme environment conditions including: high turbidity and sediment input, elevated water temperatures (av. 28.5 °C), a 10 m macrotidal range, significant subaerial exposure during low tides, and frequent cyclones. Despite these extreme conditions, the coral biodiversity in the Kimberley is far richer than that of the inner GBR fringing reefs and a little richer than those of the Pilbara to the south (Wilson, 2013). Critically, our understanding of the development of the Kimberley reefs still remains a gap in our knowledge. For example it is not known whether reefs are thin veneers over rock platforms or significant long-lived accretionary structures. Additionally, the linkages between present reef geomorphology, Holocene sea level rise, reef growth histo- ry, and coastal processes have been recognized (e.g. Wilson, 2013) but are yet to be explored in any detail. Despite this lack of knowledge, Kimberley reefs have been identified as having international signifi- cance and are in need of comprehensive study (Chin et al., 2008; Wilson, 2013). This study will for the first time investigate the Holocene develop- ment and evolution of an inshore Kimberley coral reef located at Cock- atoo Island (Fig. 1). Cockatoo is unique in that iron ore mining on the Island has exposed a complete vertical section of the inner part of a Ho- locene fringing reef. This has allowed for detailed stratigraphic, palaeoecological and geochronological analysis spanning the entire reef growth history, thus enabling an investigation into how these reefs were able to persist under extreme environmental conditions as well as respond to Holocene sea level change. The addition of seismic re- connaissance data has allowed for the broader reef architecture and structure to be assessed. Lastly this study develops a Holocene reef Marine Geology 359 (2015) 50–60 ⁎ Corresponding author at: Department of Applied Geology, Curtin University, Bentley, WA 6102, Australia. Tel.: +61 8 9266 3710. E-mail address: tubagus.solihuddin@postgrad.curtin.edu.au (T. Solihuddin). http://dx.doi.org/10.1016/j.margeo.2014.11.011 0025-3227/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo