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Recent oceanographic exploration in the northeast Atlantic has discovered widespread and diverse coral ecosystems in deepwater environments of the several provinces. The Belgica mound province in Porcupine Seabight is one of them and has 47 exposed mounds (De Mol et al., 2007), of which Challenger Mound (Site U1317) was drilled during Integrated Ocean Drilling Program (IODP) Expedition 307 in May 2005. In order to link the mound sediments to the regional stratigraphic framework, two additional sites were selected: Site U1316 at the foot of the mound and Site U1318 upslope from the mound.

Miocene–Pleistocene sediments were recovered from three holes at Site U1318 (51°26.16′N, 11°33.0′W; 423 m water depth) and were divided into three lithologic units at two distinct unconformable horizons. In the deepest hole (U1318B), the uppermost lithologic Unit 1, consisting of 74.5 m thick silty clay, was divided into three subunits (1A, 1B, and 1C) based on relative dominance of laminated/​bioturbated textures. The underlying 8 m thick Unit 2 consists of medium–fine sand interbedded with silty clay layers and contains a 10–20 cm thick oyster bed. The lowermost Unit 3 is composed of 155 m thick siltstone that was divided into three subunits (3A, 3B, and 3C) (see the “Site U1318” chapter).

The age of these units were first evaluated shipboard using calcareous nannofossil biostratigraphy, which assigned Units 1 and 2 to the late middle Pleistocene–late Pleistocene Emiliana huxleyi Zone (<0.26 Ma) and the early Pleistocene (small Gephyrocapsa Zone), respectively. 87Sr/86Sr ratios of the molluscan skeletons evaluated the age of Unit 2 (early Pleistocene) and Unit 3 (Pliocene–middle Miocene) (Kano et al., 2007). The age model of Unit 3 was later refined by dinoflagellate cyst biostratigraphy (Louwye et al., 2008), indicating that the top of the unit is late Serravallian (~12.0 Ma).

Because Site U1318 is upslope from Challenger Mound, it involves sedimentological information on the shelf slope where deepwater coral mounds are developed. We focused on the carbonate fraction, for which potential sources are calcareous nannofossils, benthic foraminifers, planktonic foraminifers, and Cretaceous chalk from ice-rafted transportation. These sources have different carbon and oxygen isotopic values. We report carbon and oxygen isotopic compositions of the bulk sediments from Hole U1318B in order to provide some information on the sediment sources to the upslope site of Challenger Mound.