The Northwest Shelf of Australia (NWS) is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the NWS. X-ray diffraction (XRD) derived mineral data is used to delineate the carbonate mineralogy of the different sedimentary facies occurring in core. It is further utilized to assess the influence of terrigenous influx into the shallow-marine system. Bioclastic sediments, which formed during interglacials, are characterized by comparatively high amounts of siliciclastics and calcitic carbonates. Siliciclastics are thought to reflect the humid climate and associated fluvial influx present during interglacials. Needle mudstones and ooid/peloid packstones, which formed during arid glacials, are characterized by an aragonitic mineralogy with little siliciclastics. These findings indicate that the mineralogy of the Quaternary NWS changes cyclically in response to high-frequency glacioeustatic variations in sea level and climate.

Mineralogy was determined on 118 samples using a Siemens D5000 x-ray diffractometer (Bruker (Siemens), Billerica, MA, USA). The measurements of the powdered samples were conducted over an angle field of 66° (4°-70°) with a step size of 4*10-3° per second. Standard Rietveld refinement using the software Profex (ver. 4.0.2) achieved identification and quantification of different mineral phases.