A MIDDLE MIOCENE PALEOCEANOGRAPHIC EVENT IN SOUTHERN AUSTRALIA

The Monterey Formation crops out near Monterey along the coastal regions of California and its equivalents are found all around the North Pacific region. The large amounts of organic carbon sequestration in these sediments were the main cause of positive excursion in the DIC (DIC=Dissolved Inorganic Carbon) carbon isotope values. In fact, the initial carbon isotope enrichment resulted in a rapid extraction of organic carbon from the ocean-atmosphere system and deposition in the form of organic-rich sediments on continental shelves, resulting in rocks such as the Monterey Formation.

The purpose of this study is to present geochemical and sedimentological evidence indicating the influence of the Monterey Excursion within the Oligo-Miocene sediments of the Murray Basin along the continental margin of southern Australia.

The high carbon isotope values of the Cadell Marl of the Murray Basin at 16 Ma, which are contemporary with global high carbon isotope values in other parts of the world's oceans, demonstrate the influence of the Monterey Excursion on the carbon isotope compositions of different biogenic carbonates. This observation indicates that the latest Early Miocene (16 Ma) was the period of heaviest carbon isotope values in most of the Cenozoic, even heavier than present day values. Therefore, carbon isotope positive excursions in diverse fossils of the Cadell Marl represents a general correlation with carbon isotope records of the Monterey Formation and deep-sea benthic records, which is also concomitant with the global organic-rich depositional regime of the Early to Middle Miocene. The transfer from the almost ice-free world prior to Middle Miocene time to a glaciated world of the Late Miocene to Holocene is clearly reflected in the carbon and oxygen isotopes of the studied Tertiary sediments.