Organic geochemistry of ODP Leg 104 holes

The Leg 104 organic geochemistry program consisted of monitoring (a) hydrocarbon gases, (b) organic and inorganic carbon, and (c) parameters resulting from Rock-Eval pyrolysis at three sites on the Voring Plateau. The results amplify some of those obtained earlier on Deep Sea Drilling Project (DSDP) Leg 38. In a regional sense there is an inverse correlation between amounts of hydrocarbon gas and organic carbon. For example, significant concentrations of methane are present only at Site 644 in the inner part of the plateau where organic carbon contents are always less than 1%; in contrast, at Site 642 on the outer plateau, methane concentrations are very low (ppm range) whereas amounts of organic carbon approach 2%. Only at Site 644 are the environmental conditions such that methanogenesis is an active diagenetic process. Because of the importance of routine gas analyses to the Ocean Drilling Program (ODP), a procedure was devised to improve the use of Vacutainers for collection of gas samples. Comparison of methods for determining organic carbon showed that at Sites 643 and 644 Rock-Eval TOC could be used as a measure of organic carbon, but not at Site 642. Although no liquid or solid hydrocarbons were encountered at any of the sites, a catalog of potential organic geochemical contaminants was developed in anticipation of such a discovery.

Cenozoic ostracoda of ODP Leg 104 holes

Ostracodes are less common than might be normally expected at Sites 642, 643, and 644, perhaps pointing to the fact that the marine habitat below the overlying Pleistocene ice covers was a severe environment. This explanation, however, would not apply to the Pliocene and Miocene deposits from which ostracodes are just as poorly represented. In the latter case the Iceland-Faeroe Ridge might still have acted as a submerged barrier that did not allow an open ocean circulation of bottom waters. Thus the barrier presumably prevented an exchange of cold subarctic bottom water with that of the open Atlantic and therefore benthic deep-sea migration from the south was impeded. Some Quaternary species are, for the first time, recorded to extend to the Pliocene and/or Miocene.