New observations on the sediments of “Jama Formation”, Northwestern Ecuador.

A preliminary geologic and paleontological survey on Jama Formation is here presented. The formation is extended from Punta Cabuya to Punta Alcatraz in the central-norther part of coastal Ecuador. The section, about 100 m thick, is mainly constituted by marine sands and fluvial conglomerates in the lower part and by inner shelf mud in the upper part. It can be subdivided in eight depositional sequences bounded by ravimement surfaces. Two bulk samples for paleontological studies have been collected. Mollusks taxa are more than 130 and 32 fish otolith taxa have been found. The mollusks and fish otoliths contents suggest a depositional environment ascrivable to the inner infralittoral domain with depth approssimatively ranging from 0-20/30m. In conclusion the sedimentary succession represents a composite depositional sequence, the origin of which was composed by tectonics and glacial sea-level fluctuations.