MOLAR TOOTH STRUCTURES OF THE NEOARCHEAN MONTEVILLE FORMATION, TRANSVAAL SUPERGROUP, SOUTH AFRICA. II: A WAVE-INDUCED FLUID FLOW MODEL

Abstract

Sedimentological, morphological, and geochemical characteristics of molar tooth (MT) structures in the ca 2·6Ga Monteville Formation suggest a new fluid flow model for MT formation: (i) intercalated shales and carbonate sands were deposited near to above storm wave base; (ii) sediments cracked, forming an interconnected network of MT cracks that were also open to pores in sand lenses; (iii) storm waves pumped sea water into open MT crack networks, causing rapid microcrystalline carbonate nucleation, Ostwald ripening of nuclei, and growth of granular carbonate cores; some of these cores were transported by water flowing through the cracks; (iv) unfilled MT cracks collapsed, and filled MT ribbons deformed plastically as host sediments compacted and dewatered; (v) carbonate cores were overgrown by polygonal rims; and (vi) MT structures deformed brittlely with additional compaction and produced pebbly lags if reworked. MT cracks may have formed by multiple mechanisms; however, expansion of gas from organic decay and sediment heaving due to wave loading best explain MT crack morphology and are most consistent with the fluid flow model for MT CaCO3 presented here. © 2006 The Authors. Journal compilation © 2006 International Association of Sedimentologists.