Chemostratigraphy of the Sherbrook Supersequence – 13 wells from the offshore Otway Basin

Abstract

An elemental chemostratigraphic study of the offshore Otway Basin has been undertaken as part of a collaboration between Chemostrat and Geoscience Australia, the main aim of which is to better constrain the sequence boundaries of, and within, the Sherbrook Supersequence. This study includes the elemental analysis of 1185 cuttings samples from the Sherbrook Supersequence (and overlying stratigraphy) in 13 offshore wells. Sampling of cuttings was particularly challenging as many of the targeted wells have a paucity of material available for destructive analysis. Inductively Coupled Plasma-Optical Emission Spectrometry and Mass Spectrometry (ICP-OES and MS) analysis was undertaken to establish a regional elemental chemostratigraphic framework of the Sherbrook Supersequence. The resultant framework comprises two chemostratigraphic sequences, seven chemostratigraphic packages and eighteen chemostratigraphic units. While the analysis could not clearly distinguish the base of the Sherbrook Supersequence it has provided valuable insight into correlations between wells, within the Sherbrook and overlying Wangerrip supersequences. Importantly it has confirmed that in the offshore part of the basin sedimentary processes and inputs remain unchanged from the Shipwreck to the Sherbrook (Turonian–Maastrichtian).