Abstract

Crusts identified as a stromatolitic mat are described for the first time from a small, tectonically uplifted basin associated with a marine terrace along the central gulf coast of the Baja California peninsula at Punta Chivato. Microscopic analyses of crustal laminae exhibit calcified features directly comparable to microbial processes that precipitate carbonates in modern stromatolites. Floating calcified mats recently described from extremely hypersaline, closed lagoon systems in the northern Gulf of California (Isla Angel de la Guarda) provide the best analog to the Punta Chivato locality. Preservation of the Punta Chivato stromatolites is likely due to the persistence of arid conditions through multiple glacial-interglacial cycles. Comparison with the marine terrace sequence at Punta Chivato implies an age range of 334 ka to 712 ka for the deposit. This study lends support for a dedicated survey of closed lagoons and terraces where microbialites and their fossil stromatolite representatives may be found along the roughly 3000-km length of peninsular gulf shores and related islands.

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