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The Guaymas Basin, in the central Gulf of California, is a marginal ocean basin characterized by active seafloor spreading and high sedimentation rates. It has been the focus of two drilling expeditions, Deep Sea Drilling Project (DSDP) Leg 64 and International Ocean Discovery Program (IODP) Expedition 385. Expedition 385 recovered over 4 km of middle Pleistocene to Holocene core at eight drill sites, providing only simplistic stratigraphic columns that were broadly divided into as many as four lithostratigraphic subunits largely based on diagenetic modifications of sediments (authigenic carbonate and silica). For this study, shipboard sedimentologic descriptions of these subunits were used to create new, more detailed lithostratigraphic columns at an approximately decimeter (core) scale for correlation purposes and sedimentary interpretation. This was accomplished through examination of slabbed core images, visual core description sheets, and a shipboard lithologic database. The new columns provide more detailed downhole variability in lithology. The lithologic classification scheme for Expedition 385 was then integrated with that of sites previously drilled during Leg 64 to translate published visual core descriptions so as to uniformly generate comparable stratigraphic columns for both sets of drill holes. These newly compiled and tabulated data provide a more detailed picture of stratigraphic variation of lithology on a core by core basis across the basin.
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This content will become publicly available on January 10, 2026
Data report: petrography of volcaniclastic intervals in IODP Expedition 385 cores from Guaymas Basin, Gulf of California
The Guaymas Basin is a 6 Ma transtensional ocean basin located in the central Gulf of California characterized by active seafloor spreading, off-axis magmatism, and high biogenic and terrigenous sedimentation rates. Sparse volcaniclastic intervals were identified by shipboard scientists in Quaternary sedimentary cores recovered during International Ocean Discovery Program (IODP) Expedition 385. Shipboard visual core descriptions and smear slide analyses were used to identify 57 volcaniclastic intervals, which were then sampled and analyzed macroscopically and microscopically. Petrographic modal analyses were conducted on a subset of 36 thin sections with a total of 300 points counted per thin section. A grain classification scheme was developed from published literature to characterize the compositional and textural variability of volcanic grains in cores from across the basin. Point count percentages reveal that vitric volcanic lithic fragments, particularly brown glass shards, are the dominant clast type observed at all drill sites, whereas crystal-bearing volcanic lithic fragments and mineral grains comprise a minor percentage of the total points counted. The vitric fragments also exhibit a wide range of shard vesicularity and morphologies. This data report presents a petrographic analysis of volcaniclastic deposits recovered during Expedition 385 to elucidate on the modal and spatial distribution of volcanic material in the Guaymas Basin.
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- PAR ID:
- 10572655
- Publisher / Repository:
- International Ocean Discovery Program
- Date Published:
- Journal Name:
- Proceedings of the International Ocean Discovery Program Expedition reports
- Volume:
- 385
- Issue:
- 206
- ISSN:
- 2377-3189
- ISBN:
- 978-1-954252-77-6
- Subject(s) / Keyword(s):
- International Ocean Discovery Program IODP JOIDES Resolution Expedition 385 Guaymas Basin Tectonics and Biosphere Site U1545 Site U1546 Site U1547 Site U1548 Site U1549 Site U1550 volcaniclastic petrography volcanism
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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