--> Evolution of Clastic Facies Studies in the Guaymas Basin

AAPG Pacific Section Convention, 2020 Vision: Producing the Future:

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Evolution of Clastic Facies Studies in the Guaymas Basin


Over the last 60 years there have been several concerted efforts to define marine clastic sediment types and their distributions in the Guaymas Basin, Gulf of California. The first, an AAPG Memoir 3 paper by van Andel (1964), characterized the compositional variation and distribution of sandy surface sediments in the Guaymas Basin, providing basic information on grain size, heavy mineral composition, and general modal mineralogy. In 1979, Guaymas Basin sediments were cored during Deep Sea Drilling Project Leg 64 at two sites on the Sonoran shelf/slope (479, 480) and three sites on the basin floor in or near the rift grabens (477, 478, 481). The post-cruise study by Einsele and Kelts (1982) provided insight on the types of sandy gravity-flow deposits in the basin as defined by their grain-size and structural characteristics. They estimated that as much as 60% of the sedimentary section recovered from the basin subseafloor is redeposited material and outlined the characteristics of several types of “mud turbidites”. The provenance of sandy gravity-flow deposits was later studied by Marsaglia (1991) who proposed various sources (Sonora River, Yaqui River and Baja California drainages). Leg 64 was also noteworthy in that the hydraulic piston-coring tool, now in standard use in deep-sea drilling, was first successfully tested at Site 481, providing pristine, undeformed core records of unconsolidated finely-laminated diatomaceous sediments. The fluvial vs. eolian origin of the muddy laminae in these diatomaceous sediments was addressed in AAPG Memoir 47 by Baumgartner et al. (1991), who favored an eolian origin based on surface core studies in the Guaymas Basin and discharge records of Sonoran rivers. Recently, interest in the Guaymas Basin has been renewed owing to the combination of shallow igneous, hydrothermal and microbiological processes in this young ocean basin. Cores recovered at eight additional locations in the Guaymas Basin in 2019 on International Ocean Discovery Program Expedition 385 complement the preceding surface sediment and drilling results, providing a broader view of clastic sediment distribution and characteristics across the basin. Study of these cores has just begun. As a preview of more detailed studies to come, we illustrate the nature of some of the recovered clastic laminae/beds using core and petrographic images.