The Guaymas Basin is an actively spreading oceanic basin in the Gulf of California, northwest Mexico, in which three major sedimentary environments can be established based on their structural position and types of sedimentary sequences. (1) The active rift-valley setting contains a sequence of fine to very fine, poorly sorted, silty sand, interbedded with mass-flow deposits. The latter includes a mixture of terrigenous sediment derived from the mainland and basinal redeposited(?) (diatom-rich) pelagic sediment. The two populations result from the downslope movement of granular solids dispersed in a clay-water fluid; the upper part is muddy and diatomaceous. (2) The basin floor setting is characterized by high sedimentation rates; consequently the frequency of turbidite d position (mainly in the lower part of the stratigraphic column) is higher than in the other two settings. The upper part of the stratigraphic column is lithologically more uniform, and consists of disturbed diatomaceous mud with interbeds of turbidites. (3) The slope setting is a province within the oxygen minimum layer and the sediments consist of varved diatomaceous beds interbedded with graded and cross-laminated turbidites.

The transport and depositional mechanisms within Guaymas Basin are difficult to resolve owing to the diversity of sediments supplied from fluvial, beach, and dune sources bordering the basin and further, to the mixing of these sediments by subaqueous gravity transport into the basin. Turbidites deposited during the Holocene-late Pleistocene period are interbedded with varved diatomaceous ooze, and correlate with interglacial highstands of sea level. The terrigenous particles have surface textures produced by glaciofluvial action, and perhaps are derived from the Colorado River province.

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