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Abstract

Deep-time sea-level oscillations in the Milankovitch-band of orbital cyclicities govern deposition in the pelagic realm mainly by varying siliciclastic input. Pelagic sediments from the Cretaceous greenhouse climate phase provide a valuable archive for sea-level change. Although sea-level variations are of negligible amplitude compared with depositional water-depths, direct physical proxy data are based on higher and coarser siliciclastic input during sea-level lowstand and regressions, and include coarser grain size and grain-size parameters as well as the heavy mineral and clay content. Chemical proxies that relate to siliciclastics are manganese, titanium and zirconium, often normalized v. aluminium. Further proxies provide the ratios of strontium v. calcium, controlled by shelf carbonate erosion, and partly redox-sensitive elements like uranium and thorium. From a mineralogical point of view, the total amount of siliciclastics and their diversity relating to heavy minerals provides sea-level information in hemipelagites, as well as the phyllosilicate content v. biogenic pelagic background deposition of carbonate and siliceous microfossils in pelagites. In addition, measurements of gamma ray emission, linked to U, Th, K content and magnetic susceptibility may relate to sea-level cycles and various other more climate-dependent proxies like oxygen isotopes of fossil calcite and compositional maturity of hemipelagic sediments.

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