23-25 September 2013
GEOMAR East shore
Europe/Berlin timezone
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Mass-transported deposit deduced from the benthic foraminifera stratigraphy at Site U1413: IODP Exp. 344 (CRISP2), Costa Rica subduction margin

Presented by Ms. Hitomi UCHIMURA on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session


IODP Exp.344 (Costa Rica Seismogenesis Project: CRISP 2) is designed to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones and drilled five sites off the western coast of Costa Rica around the southern end of the Middle America Trench, where the oceanic Cocos Plate is subsiding beneath the Carrbbean Plate. Main objective of this study in the Site U1413 is to understand the tectonic-induced submergence/ uplifting history or paleoslope instabilities in the upper slope area. Benthic foraminifera (BF) are a useful tool to estimate the past bottom-ocean environment. Based on benthic foraminiferal biostratigraphy of U1413, we have recognized the following four biozones for the sequence of past 2 million years and identified plausible slump mass came from the shallower-water environment: Zone I: Hole C, Cores 42R-18R - Characterized by dominant Uvigerina peregrina and Gyloidina altiformis, which are accompanied by Nonion sp. A (Group A) Zone II: Hole C, Cores 14R-2R, Hole A, Core 25X-18X - Dominated by Epistominella smithi, and accompanied by Chilostomella oolina (Group B) ZoneⅢ: Hole A, Cores 17H-11H - Characterized by Brizalina spp. (Group C) Zone Ⅳ: Hole A, Core10H-1H - Characterized by Angulogerina angulosa, Cassidulina tumida, and Uvigerina excellence (Group D) The BF divided into Group A (Zone I) is distributed on the lower continental slope in the modern equatorial Pacific. (Smith, 1963, 1964). Group B in Zone II is reported mainly from the lower to middle slope environment of the Pacific. Group C in Zone Ⅲ is estimated to be distributed in the upper slope. Group D in Zone Ⅳ lives in the upper to middle slope as well as the drill site. On the other hand, some shelf species such as Brizalina bicostata, Cibicorbis inflatus and Uvigerina incilis (Group E) occur throughout the sequence of the hole. Those species are, however, considered to be reworked specimens from shallower environment, because they co-occurred with deeper water species as Groups A to D, and because a similar occurrence has been reported in the Peru-Chile Trench area by Ingle and Kolpack (1980). In Zone III, another species group composed of Brizalina spp., (Group C), which is distributed mainly in the upper slope areas in the modern oceans. Because Group C is not accompanied by Group D or other deeper-water species, the interval of Cores 17H-11H in Hole A apparently correspond to the upper continental slope, at least shallower than the depth of Group D. Also, the tests of Brizalina spp. are well-preserved in contrast to the co-occurred Group E. These results imply that Zone III is allocated Mass transported sediments, like a slump. This interpretation has been also supported by geochemical and logging data. The slump mass has been inferred at the interval between 45-150 mbsf based on the irregular profiles for organic matters and a fold structure plausibly formed by slumping. The slump mass might reflects the active subsidence due to tectonic erosion or passage of subducting seamount at the plate interface. <References> Smith, P., 1963, Geological survey professional paper, 429-A Smith, P., 1964, Geological survey professional paper, 429-B Ingle and Kolpack, 1980, micropaleontology, vol. 26, no.2, pp. 113-150, pls. 1-9 Expedition 344 Scientists, 2013. Costa Rica Seismogenesis Project, Program A Stage 2 (CRISP-A2): sampling and quantifying lithologic inputs and fluid inputs and outputs of the seismogenic zone. IODP Prel. Rept., 344. doi:10.2204/iodp.pr.344.2013


Location: GEOMAR East shore
Address: Wischhofstr. 1-3 / D-24148 Kiel
Room: Lithothek

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