Total organic carbon, lithology and alkylthiophenes in immature sediments (Table 1)

A series of novel long-chain 3,4-dialkylthiophenes (C36-C54) was identified in a number of sediments ranging from Pleistocene to Cretaceous. The identifications were based on mass spectral characterisation, desulphurisation and mass spectral data of synthesised model compounds. These organic sulphur compounds are probably formed by sulphur incorporation into mid-chain dimethylalkadienes with two methylenic double bonds. These putative precursor lipids are unprecedented and may be considered rather unusual. The distribution of 3,4-dialkylthiophenes in sediments varies considerably with the depositional palaeoenvironment, indicating that these compounds have a potential as molecular markers reflecting changes in palaeoenvironment.

(Table 1) Counts and ratios of microfossils at DSDP Hole 64-480

We examined the relative abundance of various components in the coarse fraction (> 150 µm) from a selected portion of the DSDP Site 480 piston core. The components consist mainly of diatoms, radiolarians, benthic and planktonic foraminifers with minor amounts of sponge spicules, terrigenous material, volcanic glass(?), dehydrated gypsum crystals, and spines of unknown biological origin. The examination shows that the siliceous organisms abound in the laminated sediments and that the calcareous organisms are more abundant in the nonlaminated sediments. Seasonal upwelling is responsible for the deposition of laminated sediments. The upwelling creates a strong oxygen-minimum zone, restricting the occurrence of burrowing benthic organisms and benthic foraminifers.