Evidence for changes in Mesozoic and Cenozoic oceanic circulation on the south-western continental margin of Ireland: DSDP/IPOD Leg 80

Abstract

Summary A transect of four coreholes, drilled by the Glomar Challenger across the Irish continental margin at the Goban Spur, evidences a dynamic palaeoceanographic regime during the late Mesozoic and Cenozoic. Shallow marine waters invaded the rift-stage grabens of the Goban Spur in the early Barremian. Thereafter, the margin subsided rapidly, producing a pelagic depositional regime by late Barremian time. Deep marine conditions were maintained as sea-floor spreading began in the early Albian, and chiefly pelagic deposition continued to the present. Among a series of significant post-rift oceanographic changes, one of the most notable is the familiar fluctuation of oxic and anoxic sea-floor environments during the Cenomanian and Turonian. Another marked change took place during the late Palaeocene, when cooler, oxygen-rich, northern bottom waters reached the Goban Spur as a consequence of rifting and sea-floor spreading between Greenland, Rockall Plateau, and Norway. Later during the Cenozoic, the initial production of Antarctic bottom water, several accelerations of polar icecap growth, and fluctuating eustatic sea-level produced a variety of circulatory shifts on the Goban Spur. A particularly significant sedimentological consequence of these interacting processes was the widespread creation of numerous erosional and non-depositional unconformities.

Further evidence for the development of photic-zone euxinic conditions during Mesozoic oceanic anoxic events

“…no carbonate (de Graciansky et al 1986b). It is thought to have been deposited at a depth of c. 1300 m (de Graciansky et al 1986a).…”

“…Deep Sea Drilling Project (DSDP) Sites 367 and 368 are located on the Cape Verde Basin (Leg 41, Site 367, Core 18) and Cape Verde Rise (Leg 41, Site 368), situated off the coasts of Senegal and Gambia, respectively. Geochemical data on these cores have been extensively published(Brumsack & Thurow 1986;de Graciansky et al 1986b;Herbin et al 1986) and indicate that C/T boundary intervals from both cores are characterized by high TOC contents and hydrogen indices. From Site 367, core 18, two samples were analysed: Section 2, interval 91-95 cm (sample 367-2); and Section 3, interval 91-95 cm (sample 367-3).…”