The Geomorphology and Sediments of Cockburn Sound
The Geomorphology and Sediments of Cockburn Sound
The Geomorphology and Sediments of Cockburn Sound
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<strong>The</strong> <strong>Geomorphology</strong> <strong>and</strong> <strong>Sediments</strong> <strong>of</strong> <strong>Cockburn</strong> <strong>Sound</strong><br />
Introduction<br />
<strong>Cockburn</strong> <strong>Sound</strong> is a key study site for the Coastal CRC Coastal Water Habitat Mapping (CWHM)<br />
Project. At this site, benthic habitats have been mapped at a range <strong>of</strong> scales <strong>and</strong> levels <strong>of</strong> detail using<br />
a suite <strong>of</strong> acoustic <strong>and</strong> video techniques. <strong>The</strong> focus <strong>of</strong> the Coastal <strong>Geomorphology</strong> subproject in<br />
<strong>Cockburn</strong> <strong>Sound</strong> is to examine the geomorphology <strong>of</strong> the sea bed, the spatial distribution <strong>of</strong> the<br />
various sediment types <strong>and</strong> the geomorphic evolution <strong>of</strong> this basin. <strong>The</strong>se new geological data will<br />
be used to ground-truth acoustic data collected in <strong>Cockburn</strong> <strong>Sound</strong>, such as the multibeam<br />
backscatter data collected using the Coastal CRC’s Reson 8125 Seabat system. This study will also<br />
provide a better underst<strong>and</strong>ing <strong>of</strong> the physical controls on the distribution <strong>of</strong> benthic habitats in the<br />
sound <strong>and</strong> substrate data that can be incorporated into a benthic habitat classification scheme.<br />
Several environmental surveys on the carbonate s<strong>and</strong> resources <strong>of</strong> Parmelia <strong>and</strong> Success Banks have<br />
been conducted over the last two decades. However, relatively little attention has been paid to the<br />
broader nature <strong>of</strong> the sediments <strong>and</strong> stratigraphy <strong>of</strong> <strong>Cockburn</strong> <strong>Sound</strong>, particularly in the deeper<br />
central basin. <strong>The</strong>refore, another focus <strong>of</strong> this study is to provide a more detailed level <strong>of</strong> knowledge<br />
<strong>of</strong> the benthic environments <strong>and</strong> sediment fill in the deeper reaches <strong>of</strong> the sound, <strong>and</strong> a linkage <strong>of</strong><br />
these to more thoroughly studied shallow habitats.<br />
AIMS<br />
This report examines the geomorphology <strong>and</strong> sediments <strong>of</strong> <strong>Cockburn</strong> <strong>Sound</strong> through the analysis <strong>of</strong><br />
a suite <strong>of</strong> sediment grab samples <strong>and</strong> vibracores as well as existing data in published reports <strong>and</strong><br />
scientific papers. <strong>The</strong> specific aims <strong>of</strong> this study are to: 1) Characterise the surface <strong>and</strong> sub-surface<br />
sediments <strong>and</strong> geochemistry <strong>of</strong> <strong>Cockburn</strong> <strong>Sound</strong> from a representative set <strong>of</strong> sediment grab samples<br />
<strong>and</strong> vibracores; <strong>and</strong> 2) Develop a conceptual model <strong>of</strong> the recent evolution <strong>of</strong> <strong>Cockburn</strong> <strong>Sound</strong><br />
(spanning the Late Pleistocene <strong>and</strong> Holocene), based on the new <strong>and</strong> existing data. Importantly,<br />
these geological data are required to enable better interpretation <strong>of</strong> acoustic sub-bottom pr<strong>of</strong>iles <strong>and</strong><br />
multibeam sonar datasets that have or will be collected in <strong>Cockburn</strong> <strong>Sound</strong> as part <strong>of</strong> the Coastal<br />
CRC’s CHWM Project.<br />
STUDY PARTICIPANTS AND COLLABORATION<br />
<strong>The</strong> field survey <strong>and</strong> sample analysis was undertaken by Darren Skene, David Ryan <strong>and</strong> Brendan<br />
Brooke (Geoscience Australia (GA)). Assistance in the field was provided by the crew <strong>of</strong> the vessel<br />
FP Response, Jamie Strickl<strong>and</strong> (Fremantle Ports) <strong>and</strong> Mark Small (Fremantle Ports), Lee Woolhouse<br />
(hydrographic surveyor, Fremantle Ports) <strong>and</strong> Rob McCauley (Curtin University <strong>of</strong> Technology).<br />
Lynda Radke (GA) undertook the analysis <strong>of</strong> the surface sediment geochemical data <strong>and</strong> Jodie Smith<br />
(GA) interpreted the vibracore geochemical data <strong>and</strong> completed the editing <strong>and</strong> formatting <strong>of</strong> the<br />
report. Helen Bostock (GA) assisted with editing the report. Laboratory analyses at GA were<br />
undertaken by Alex McLachlan, Neal Ramsey <strong>and</strong> Richard Brown (sedimentology) <strong>and</strong> Bill Pappas,<br />
John Pike <strong>and</strong> Liz Webber (geochemistry).<br />
REGIONAL SETTING<br />
<strong>Cockburn</strong> <strong>Sound</strong> is an elongate, shallow, partially enclosed coastal basin with an area <strong>of</strong><br />
approximately 124 km 2 , located immediately south <strong>of</strong> Fremantle, Western Australia (Fig. 1). <strong>The</strong><br />
sound is approximately 22 km long <strong>and</strong> ranges from 15 km wide in the north to 9 km wide in the<br />
south <strong>and</strong> sits between the mainl<strong>and</strong> <strong>and</strong> a remnant Pleistocene dune ridge that forms Garden Isl<strong>and</strong>.<br />
This relatively quiescent coastal water body has contrasting shoreline environments with heavy<br />
industry along much <strong>of</strong> its eastern coast whereas the western shoreline <strong>of</strong> Garden Isl<strong>and</strong>, apart from<br />
the naval base at Careening Bay, is largely undeveloped.<br />
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