Neogene paleoceanography of Western Australia : rivers, winds, ocean currents and latitudinal controls over sedimentation

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2020-05-08

Authors

Tagliaro, Gabriel

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Abstract

During the Neogene period, between 23 and 2.58 million years ago, dramatic changes in tectonic and climatic patterns affected ocean currents, sea level, and sedimentation on the continents and in the oceans. A global warm period in the early Miocene ended when ice-sheet expansion on the Antarctic continent lowered global temperatures in the middle and late Miocene. Global temperatures rebounded during the Pliocene, succeeded by a return to cooling conditions in the Pleistocene. These Neogene climatic events are important because they represent some of the best past analogues to modern and future climate change. The study of Neogene sedimentary archives therefore constitutes a research opportunity to elucidate the effects that warming climates will have on Earth’s oceans and atmosphere. The Australian continent was particularly affected by the Neogene reorganization of climate and tectonics as the northward movement of the Australian plate shifted the continent to warmer sub-tropical climates.

This work reconstructs the paleoceanography and paleoclimate evolution of the Western Australian margin during the Neogene, based on detailed examination of sedimentary archives drilled by the International Ocean Discovery Program (IODP) between 2015 and 2017. Together, these cores form a latitudinal transect of Western Australia and represent the most complete Neogene stratigraphic record in the Southeast Indian Ocean. Results indicate that sedimentation patterns in both shallow and deep-water areas adapted to the displacement of the continent towards lower latitudes and were highly vulnerable to changes in Antarctic climate throughout the period. Biological productivity and aeolian input increased in the Subantarctic Ocean during the early Miocene warming as the Southern Westerlies amplified under warmer temperatures (Chapter 3). In the late Miocene, the continued opening of the Southern Ocean and the transition to colder Antarctic temperatures was accompanied by intensification of deep ocean circulation that formed extensive contourite drifts and ferromanganese crusts in the deep sea (Chapter 4). On the Northwest Shelf, a middle Miocene arid sabkha environment transitioned to a humid environment that accompanied early Pliocene warming, forming a perennial deltaic environment resulting from the southward displacement of Intertropical Convergence Zone towards northern Australia (Chapter 2). The data and interpretations presented in this dissertation shed light on the environmental impacts of changing temperatures on continental margins and on paleoenvironmental sensitivity to atmospheric CO2 forcing.

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