B050-0007
Misplaced Miocene: high-resolution radiolarian biostratigraphy at DSDP’s Site 504

Thursday, 10 December 2020
Poster
Amanda Florea, Western Washington University, Bellingham, WA, United States; Whatcom Community College, Bellingham, WA, United States, Sarah Kachovich, JOIDES Resolution Science Operator, IODP, College Station, TX, United States, Kaatje van der Hoeven Kraft, Whatcom Community College, Department of Sciences, Bellingham, WA, United States and Camilo Ponton, Western Washington University, Bellingham, United States
Abstract:
The palaeontological record is known to be incomplete. Revision and correlation of older drilled sites’ stratigraphy is an ongoing process, as new information and measurements cause continual refinement of fossil datums and the Geological Time Scale. Restrictions in the palaeontological record, such as preservation and quantity of sampling, along with the frequency of specimens, confidence of taxonomic identification, local environmental factors on the stratigraphic range of taxa, and evolutionary and extinction chronology of species in different oceans still cause uncertainties of the biochronological framework.

The focus of this study was to recalibrate historical fossil data, while adding a new higher-resolution radiolarian biostratigraphy to the overlying sediment of the cores from Hole 504, which was originally collected in 1979 on Deep Sea Drilling Program, Leg 69. More famously known is Site 504’s third hole, 504B, which has been progressively deepened and studied by the drilling program nine times (DSDP Legs 69, 70, 83, 92, ODP Legs 111, 137, 140, 148 and IODP Expedition 385-T). Hole 504 consists of clay bearing siliceous nannofossils until ~142 mbsf, beyond this depth, samples transition into siliceous nannofossil bearing chalk, which overlays basement material. Investigations of radiolarian biostratigraphy were carried out on 19 m intervals along the 224 m sedimentary package, for a total of 16 samples. The sampling was higher between Cores 45–48, in an attempt to better constrain the Miocene-Pliocene boundary.

Samples from Cores 1–45 were processed onboard the JOIDES Resolution as part of a student research project for the JR Academy during Expedition 385-T. Post cruise, samples from Cores 45–48 were processed at Whatcom Community College. In this study we integrate a comprehensive biostratigraphy for diatoms, nannofossils, radiolarians and silicoflagellates, where all biohorizons and biozones were modified, where necessary, according to the latest Geological Time Scale. Our results show that new radiolarian datums have allowed us to better place the Miocene-Pliocene boundary. With the majority of studies at Site 504 predominantly focused on the hard rock, it is also important to seek a complete understanding of the overlying sediments to best interpret the complete story.

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