Tectonic impact on the sedimentary magnetic record in active margin settings

Author(s): Riedinger, Natascha; Torres, Marta E.; Solomon, Evan A.
Author Affiliation(s): Primary:
Oklahoma State University, Boone Pickens School of Geology, Stillwater, OK, United States
Other:
Oregon State University, United States
University of Washington, United States
Volume Title: AGU 2017 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2017; American Geophysical Union 2017 fall meeting, New Orleans, LA, Dec. 11-15, 2017. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Here we explore the impact of depositional and tectonic dynamics on sedimentary magnetic signals using samples collected during the Integrated Ocean Drilling Project (IODP) Expedition 334 off Costa Rica. This active margin system displays fast convergence rates, abundant seismicity, and subduction erosion, and thus allows us to study fluid flow responses to rapid episodes of uplift and subsidence in an erosional convergent margin - one of the main goals of the Costa Rica Seismogenesis Project (CRISP). The sediments at the middle slope site (Site U1378; ∼533 m water depth) vary strongly in their magnetic susceptibility and geochemical signals compared to the upper slope site (Site U1379; ∼139 m water depth). The more recent sediments at each site (upper 50 m) clearly show that Site U1378 experienced relative steady state conditions (with respect to pore water geochemistry), while at Site U1379 dynamic conditions lead to non-steady state geochemical profiles - and consequently to a differing magnetic susceptibility profile. These differences are most likely related to changes in methane flux and subsequent shifting of the sulfate-methane transition. Throughout the sediment column at Hole U1379C intervals showing a strong decrease in the magnetic susceptibility can be correlated with specific lithological horizons with abundant carbonate layers. Our data show that these layers are formed diagenetically, based on a depleted carbonate carbon isotope signal (up to -25 ppm) that is consistent with the pore water record. The carbonate layers not only caused a dilution in the magnetic mineral assemblages, but also point to a concurrent alteration process of iron oxides to iron sulfides. This is recorded in the sedimentary record as iron sulfide (pyrite) enrichments and their associated sulfur isotopic signature (δ34S; up to +6.3 ppm). These alterations can be tied to a location fluctuation of the sulfate-methane transition due to changes in the methane flux. The strong difference in the magnetic susceptibility records at the two sites can be linked to in situ diagenesis potentially caused by differences in their histories of subsidence and uplift. This highlights the importance of understanding both the tectonic and digenetic history of sedimentary settings prior the application of proxy tools such as magnetic susceptibility.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Continental margin; Costa Rica Seismogenesis Project; East Pacific; Expedition 334; IODP Site U1378; IODP Site U1379; Integrated Ocean Drilling Program; Magnetic properties; Marine sediments; North Pacific; Northeast Pacific; Pacific Ocean; Sediments; Tectonics
Coordinates: N083532 N083532 W0840438 W0840438
Record ID: 2019060605
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