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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 42 (1972)No. 4. (December), Pages 889-898

Paleo-climatic Events Indicated by Mineralogical Changes in Deep-sea Sediments

Marian B. Jacobs, James D. Hays

ABSTRACT

Clay mineral analysis of 12 deep-sea sediment cores raised from the equatorial Pacific Ocean show that from 11 m.y. B.P. (Middle Miocene) to 3.0 m.y. B.P. (Middle Pliocene) the sediments are characterized by an abundance of montmorillonite, 80% and more; 10 to 15% illite; and about 5% kaolinite and chlorite combined. During the last 3 m.y. the abundance of montmorillonite decreases, reaching a concentration of 50% to 60% near the top of the Brunhes. During this same interval, illite abundance increases to 25% to 35% at the top of the Brunhes, with kaolinite and chlorite increasing in a similar manner to 10% to 15%.

It is suggested that the apparent decrease of montmorillonite in the Pleistocene is a dilution effect, the result of an influx of other clay minerals, illite and chlorite, from increased weathering, surface run-off, and wind activity with the intensification of continental glaciation. Crystallinity measurements on the illite (001) peak of the < 2µ sediment size fraction, observed increases in quartz and other detrital minerals in the 2-20µ size fraction, and an increase in the sedimentation rate measured for the Brunhes normal epoch provide supporting evidence of increased continental erosion with the advent of worldwide climatic cooling. Increased quantities of fine grained minerals were released during the major periods of continental glaciation to produce an imprint n oceanic sedimentation.


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