Abstract
AbstractUnderstanding the composition of clay-rich sediments and their transportation into proximal marine basins allows us to better decipher hydroclimatic changes before and within the Palaeocene–Eocene Thermal Maximum (PETM). Only a limited number of such studies exists from the North Sea Basin, which was proximal to the volcanic activity and early rifting hypothesized to have triggered the PETM. The present study examines core material from well 22/10a-4, UK North Sea, as it exhibits an exceptionally expanded and almost stratigraphically complete fine-grained sedimentary sequence suitable for high-resolution analysis.QuantitativeNewmod-for-Windows™-modelled clay mineral assemblages, rather than traditional semi-quantitative estimates, are dominated by smectite-rich, interlayered illite-smectite that probably developed from volcanogenic deposits on continental landmasses. Soil development before the PETM is consistent with the existence of a seasonal tropical climate with a prolonged dry season. A striking rise and fall of kaolinite content within the PETM onset, prior to the principal carbon-isotope excursion, is reported here. This variation is interpreted as a signal of an enhanced hydrologic cycle producing an increase in erosionally derived kaolinite, followed by a dampening of this detrital source as sea-levels rose. Global variations in PETM kaolinite concentrations are consistent with a latitudinal shift in patterns of precipitation in models of global warming.
Highlights
GEOLOGICAL SETTINGThe North Sea Basin first developed as an extensional basin through rifting along the axes of the Central, Viking and Witch Ground grabens during the Late Permian/ Triassic (Glennie, 1986) (Fig. 1)
Quantitative Newmod-for-WindowsTM-modelled clay mineral assemblages, rather than traditional semi-quantitative estimates, are dominated by smectite-rich, interlayered illite-smectite that probably developed from volcanogenic deposits on continental landmasses
As kaolinite may have taken 1–2 My to form during the peak warmth and CO2-rich atmospheric conditions of the Cretaceous (Thiry, 2000), some authors have questioned whether its appearance during the Palaeocene–Eocene Thermal Maximum (PETM) signifies concomitant warming and precipitation (e.g. Gawenda et al, 1999), but instead points to seasonal erosion of pre-existing deposits during the PETM (e.g. Thiry, 2000; Berggren et al, 2012; John et al, 2012)
Summary
The North Sea Basin first developed as an extensional basin through rifting along the axes of the Central, Viking and Witch Ground grabens during the Late Permian/ Triassic (Glennie, 1986) (Fig. 1). The provenance of the sediment, including clay minerals, supplied to the North Sea Basin has varied over time as tectonics have exposed different land areas and drainage patterns have changed. Late Palaeocene regional uplift, associated with the proto-Iceland mantle plume in the North Atlantic (Knox, 1996), led to a sea-level fall of the order of 100 m and the basin becoming more restricted. This drop in sea level produced a lithological change from pale greyish green, waxy bioturbated claystones to medium to dark-grey laminated mudstone and demarcation of the boundary between the lower Lista and upper Sele formations (Figs 2 and 3). Clay mineral assemblage and oxygen-isotope records from the New Jersey margin (John et al, 2012) suggests that the onset preceded the PETM by 20–200 ky, and is supported by further data from Spitsbergen (Harding et al, 2011). Sluijs et al (2008) suggested the thermal expansion of seawater, melting from small-scale Antarctic alpine glaciers and/or a decrease in oceanbasin volume (caused by tectonics/volcanism associated with the North Atlantic Igneous Province, NAIP) as possible mechanisms for the pre-CIE sea-level rise
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