T191 Recent Advances and New Voices in Marine and Coastal Geoscience (Posters)

Tuesday, 24 September 2024
8:00 AM - 5:30 PM
Hall D

COMPOSITION OF MARSILI BASIN MEGABEDS AND MODELING POTENTIAL ORIGIN FROM CAMPANIAN IGNIMBRITE SUPER ERUPTION

Paper number: T191-2
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

  • Faye Higgins Presenting Author
    The Ohio State University, Columbus, OH

Abstract

High resolution subbottom profiler data acquired within the Marsili Basin, Tyrrhenian Sea, unveiled the presence of four widespread sedimentary units, referred to as megabeds, within the upper 70 m of sediments. Megabeds, characterized by their meter-scale thickness, extensive coverage, and acoustically transparent facies, are common in marine basins of tectonically active regions worldwide, and are associated with geohazard events. The Marsili Megabeds are hypothesized to be related to mega-volcanic eruptions from the Phlegrean Fields of Italy including the 39.8 ka Campanian Ignimbrite (CI), and 14.5 ka Neapolitan Yellow Tuff (NYT) super-eruptions. The subbottom profiles intersect with Ocean Drilling Program Leg 107 Site 650, where 600 m of core was acquired in 1986 but without aid of high-resolution profiles. This presents the opportunity to correlate seismic profiles with sediment cores, thereby enhancing our comprehension of megabed structure and depositional mechanisms.

The upper sediment layers of the Marsili Basin are characterized by a succession of calcareous muds interbedded with turbidites. Megabed three, with a maximum thickness of 18.4 m covering an area >1,016 km2 of particular interest. Through age estimations and examination of sedimentological structure, megabed three is hypothesized as the deposit of a subaqueous debris flow triggered by the CI super-eruption. Re-descriptions and XRF elemental scans were conducted on the top 100 m of sediment cores 107-650A-001H to 011H. The base of megabed three consists of planar-bedded medium-to-fine sands rich in Si, Fe, and K, transitioning into a convoluted, unsorted mixture of silty-sandy mud containing pebbles up to 2 centimeters in diameter, then grading back into Ca-rich clay. We then conducted numerical debris flow simulations to test the hypothesis of a debris flow as the transport mechanism for Megabed 3. Simulations revealed that the runout distances of subaqueous debris flows cannot reasonably extend to Site 650, suggesting an improbable scenario for sediment deposition at this location by debris flow. Consequently, megabed three most likely represents the product of a turbidity current as supported by the new core descriptions. Convoluted and other structures affecting bedding can be related to fluid expulsion (and/or drilling disturbance) as identified on subbottom profiler data.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405137

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