Title of Dissertation: A PETROLOGIC, GEOCHEMICAL AND OSMIUM ISOTOPIC STUDY OF SELECTED PRECAMBRIAN KOMATIITES Amitava Gangopadhyay, Ph. D., 2004 Dissertation Directed By: Professor Richard J. Walker, Department of Geology The major and trace elements, and Re-Os isotope systematics of the ca. 2.7Ga komatiites from the Alexo and Dundonald Beach areas in the Abitibi greenstone belt, Canada, and ca...

A previously published hydrothermal brine-river water mixing model driven by ocean crust production suggests that the molar Mg/Ca ratio of seawater (mMg/Ca(sw)) has varied significantly (approximately 1.0-5.2) over Precambrian time, resulting in six intervals of aragonite-favouring seas (mMg/Ca(sw) > 2) and five intervals of calcite-favouring seas (mMg/Ca(sw) < 2) since the Late Archaean. To ev...

Willis, K.M., Stern, R.J. and Clauer, N., 1988. Age and geochemistry of Late Precambrian sediments of the Hammamat Series from the Northeastern Desert of Egypt. Precambrian Res., 42: 173-187. Late Precambrian crustal evolution in the Northeastern Desert of Egypt culminated in a major episode of strong extension, accompanied by bimodal igneous activity and deposition of clastic sediments in rest...

Some Precambrian trace fossils have been presented as evidence for the early origin of bilaterians; the recent finding that large amoeboid protists leave macroscopic traces at the bottom of the deep ocean questions the metazoan nature of early trace fossils, stressing the importance of single-cell organisms in Precambrian biota.

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