The Exmouth Plateau is a very large marginal plateau containing 10 km of Phanerozoic sediments and is underlain by continental crust that was stretched and thinned, probably in the Late Permian. For much of the Mesozoic it was part of the northern shore of eastern Gondwana and the southern shore of Tethys, and a large part of the Phanerozoic sequence consists of Triassic fluviodeltaic sediments. Late Triassic to Late Jurassic rifting caused block-faulting, and several large grabens have a thick fill of Jurassic shallow-marine carbonates and coal-measure sequences. A major post-rift unconformity, of a minimum Callovian-Oxfordian age, is commonly directly overlain at the Valanginian breakup unconformity by Neocomian transgressive marine sediments, whose character is controlled by the breakup history of the plateau margins. A microcontinent broke away from the northern margin in the Late Jurassic, leaving behind the oceanic crust of the Argo Abyssal Plain. Greater India broke away from the northwestern and southwestern margins of the plateau in the late Valanginian, leaving behind the oceanic crust of the Gascoyne and Cuvier abyssal plains. After breakup, the Exmouth Plateau was surrounded by abyssal plains on three sides, so terrigenous input greatly decreased. As the plateau sank, shallow-marine Early Cretaceous sedimentation gave way slowly to bathyal carbonate sedimentation. Slow sedimentation rates resulted in a Cretaceous-Cenozoic sequence above the post-rift unconformity that is very thin by global standards, so that the plateau is an ideal area to study the pre-rift and rift sequences by geophysical methods, dredging, and drilling. The plateau has been extensively studied by academia, government agencies, and the petroleum industry, and has a vast open file and proprietary data set. In 1988, the Ocean Drilling Program drilled at six sites on the plateau during Leg 122 and two sites on the adjacent abyssal plains during Leg 123, designed to address the geological history of this continental margin, as an exemplar for other, more heavily sedimented margins. The six Exmouth Plateau holes cored a total of 3370 m of Upper Triassic, Cretaceous, and Cenozoic strata, with excellent recovery in all but Upper Triassic carbonates. This paper introduces the results contained in 55 papers included in this volume, covering most aspects of passive margin evolution and paleoenvironment, biostratigraphy, magnetostratigraphy, chemostratigraphy, sequence stratigraphy, rift tectonics, eustatic sea-level fluctuations, cyclic sedimentation, and orbital forcing. This paper also outlines the paleogeographic development of the region from Late Triassic to Albian times.

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A grid of seismic reflection data was used to develop a seismic stratigraphic framework for the Site 766 area. Five seismic sequences were defined and correlated directly with the lithologic units drilled at Site 766. The results of the seismic stratigraphic analysis were used to summarize the geologic history of the site area plus discuss some of the more important regional relationships in the vicinity of the site area. A contour map on acoustic (volcanic) basement plus the wedge-shaped, onlap-fill geometry of the overlying Valanginian-Hauterivian (VH) sandstone/siltstone sequence suggest initial deposition in a deep-water (800-1000 m), asymmetrical rift basin along the western Exmouth Plateau. Although intruded by oceanic volcanics, basement below the site area may be a narrow zone of thin, rifted continental crust rather than true oceanic crust. The VH unit sediments were derived from shallow-water shelves and volcanic landmasses on the thermally uplifted adjacent plateau and possibly were fed into the basin through canyon systems to the south. During the Barremian (BA sequence) the site area and adjacent margins began to subside rapidly after the emplacement of oceanic crust in the Cuvier and Gascoyne basins, and only distal hemipelagic muds were deposited. From Aptian through Cenomanian time (AC sequence) the area continued to subside and received mainly pelagic sediments in a deep-water, open marine setting. Starved, open-marine conditions continued throughout the Late Cretaceous (UK sequence) and the Cenozoic (CZ sequence), with the final disappearance of clay taking place in the Campanian. Strong deep-sea current systems periodically swept the margin throughout the Cretaceous and Cenozoic, as indicated by the overall abbreviated sedimentary section drilled and the numerous erosional unconformities seen on the seismic sections.