Genetic sequence stratigraphy of cool water slope carbonates (Pleistocene Eucla Shelf, southern Australia)

Abstract

The south Australian Eucla Shelf belongs to the world's largest cool-water carbonate sedimentary system. During the Pleistocene, it exported large amounts of sediment to the shelf edge and upper slope resulting in an expanded sedimentary wedge. Wedge-internal clinoforming seismic reflectors suggest a stacking of the deposits into genetic sequences. High-resolution stable oxygen and carbon isotope, point counting, grain size, and carbonate mineralogical XRD analyses were carried out to characterize these genetic sequences along a dip-parallel transect of three ODP Leg 182 drill holes located between the shelf edge and upper slope. Oxygen and carbon isotope fluctuations show that the genetic sequences formed as a response to sea level fluctuations. Within the genetic sequences, facies differentiation and sediment volume partitioning occur along the transect. Lowstand deposits are fine grained and contain more sponge spicules and micrite. Highstand deposits are coarse grained with tunicate spicules, brown bioclasts, as well as bryozoan and corallinacean debris. Boundaries separating highstand and lowstand deposits are triggered by sea level fall, and are expressed as abrupt grain size changes or as turning points in grain-size trends. Analyzed components vary in abundance along the transect. Genetic sequences show dip-parallel variations in thickness combined with changing relative proportions of lowstand versus highstand deposits.