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doi:10.2204/iodp.proc.344.204.2016

Introduction

Integrated Ocean Drilling Program (IODP) Expedition 344 drilled five sites located offshore the Osa Peninsula, Costa Rica, where the incoming Cocos Ridge has lifted the seismogenic zone to within reach of scientific drilling (see the “Expedition 344 summary” chapter [Harris et al., 2013]). The location of Site U1381 is ~4.5 km seaward of the deformation front offshore Osa Peninsula and Caño Island; Sites U1413, U1380, and U1412 are in the upper, middle, and base slope of the Costa Rica margin, respectively; and Site U1414 is on the flank of the subducting aseismic Cocos Ridge (see the “Expedition 344 summary” chapter [Harris et al., 2013]). Among the five sites, we selected Sites U1380, U1412, U1413, and U1414 to investigate the elemental and isotopic composition (total carbon [TC], total nitrogen [TN], total sulfur [TS], δ¹³C_org, and δ¹⁵N_org) and Rock-Eval pyrolysis of sediment at erosional subduction zones. Based on lithostratigraphic units defined during the expedition, Site U1380 is divided into three units (Unit I and Subunits IIA and IIB), Sites U1412 and U1413 are divided into three units (Units I, II, and III), and Site U1414 is divided into five units (Subunits IA, IB, IIA, and IIB and Unit III) (see the “Expedition 344 summary” chapter [Harris et al., 2013]). Correlation of elements and organic matter in bulk sediment with lithostratigraphic units can be useful for documenting the depositional environment and origin of organic matter. Hence, this study reports several geochemical results on bulk sediment from offshore the Osa Peninsula.

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