Late Quaternary Sedimentation and Slope Failure Events on the Costa Rican Margin

The Costa Rican margin is an erosional convergent margin formed by subduction of the Cocos Plate under the Caribbean Plate along the Middle America Trench. The Integrated Ocean Drilling Program (IODP) Expedition 334 was conducted for drilling long sediment cores from the upper Caribbean Plate and the subducting Cocos Plate. Using the first 30 mbsf of the two drill cores retrieved from upper slope (U1379) and middle slope (U1378) of the Costa Rican margin, we attempted to decipher slope failure induced events based on combined geochemical, sedimentological, mineralogical and isotope chemical proxy analyses. The downhole variation data of clay minerals indicates that the source rocks are mainly the young volcanic rocks in central Costa Rica region. Poor crystallinity of clay minerals with fining upward sequence in the middle slope indicates at least two major episodes of slumping/mass deposition from the shallower areas during the glacial period. Major rock forming elements such as SiO2, TiO2, CaO, MgO and Na2O were distinctly different in the cores from upper and middle slopes. C and N isotopes were also found to be different at depths with lithological changes. Our results suggest that slope failure induced events such as turbiditic sedimentation and mass flows mainly during the last glacial period are evident in the Costa Rican margin.