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Kaolinite peaks in early Toarcian profiles from the Polish Basin-an inferred record of global warming

Brański P.

Geological Quarterly

2010

Vol. 54, No 1

15-24

In lower Toarcian clay deposits (Ciechocinek Fm., VIII depositional sequence of the Lower Jurassic) from three boreholes from the Polish Basin, illite-dominated sedimentation representing the lower part of studied interval was interrupted by enhanced kaolinite input. Levels of high kaolinite/illite ratio at the VIIIb/VIIIc parasequence boundary suggest strong continental weathering in a humid-subtropical to tropical climate related to the phase of the early Toarcian global warming recorded at the top of the tenuicostatum Zone and correlated with isotope curves from a number of European sections. Kaolinite enrichment may be locally enhanced by reworking ofpre-Jurassic kaolinitic rocks and differential settling. Diagenetic processes were not sufficient enough to transform the initial kaolinite,but may have altered smectite and mixed-layers into illite and/or chlorite.