Processing results from drill hole VNIIO-1988-Sht-01 on the shelf of the Barents Sea (Report 6404, Murmansk)

Interareal correlation has been carried out; composition of the deposits has been determined; sections recovered by marine drilling have been compared; reconstructed paleogeographic conditions confirm previous views on Jurassic and Cretaceous sedimentation in the area: 1. Determinate changes of continental and shallow marine mainly sandy Middle Jurassic deposits by sandy-clayey marine ones to the north and west occur. This indicates similar direction of clastic material migration and converse direction of Jurassic marine transgressions. 2. Increase of sand contents in the deposits also to the east and to the southeast indicates an important source of clastic material. It can result from incipience and development of the epiplatform orogen of Novaya Zemlya - Pai-Khoi in the Late Triassic - Early Jurassic. 3. Compositional and facial changes as well as changes in thicknesses of some Early Cretaceous lithologic-stratigraphic complexes indicate fast change of terrigenous material transport from the north to the south - south-east in the Late Valanginian - Hauterivian. Besides within the South Barents Sea region up to the Shtokman area there occurs weak variability in lithologic parameters of Neocomian avandeltaic deposits and turbidites composed of clays, claystones, and clayey siltstones. Correlation of drilling sections from the Shtokman area and from the South Basin of the Barents Sea together with paleotectonic analysis result to the conclusion about significant structure-forming movements in the Late Jurassic - Early Neocomian. During this time there occurred maximal growth of the Shtokman structure and likely of many other structures belonging to the South Basin of the Barents Sea.

(Table T1) Composition of clay minerals from ODP Leg 204 sediments

This report describes the results of semiquantitative analysis of clay mineral composition by X-ray diffraction. The samples consist of hemipelagic mud and mudstone cored from Hydrate Ridge during Leg 204 of the Ocean Drilling Program. We analyzed oriented aggregates of the clay-sized fractions (<2 µm) to estimate relative percentages of smectite, illite, and chlorite (+ kaolinite). For the most part, stratigraphic variations in clay mineral composition are modest and there are no significant differences among the seven sites that were included in the study. On average, early Pleistocene to Holocene trench slope and slope basin deposits contain 29% smectite, 31% illite, and 40% chlorite (+ kaolinite). Late Pliocene to early Pleistocene strata from the underlying accretionary prism contain moderately larger proportions of smectite with average values of 38% smectite, 27% illite, and 35% chlorite (+ kaolinite). There is no evidence of clay mineral diagenesis at the depths sampled. The expandability of smectite is, on average, equal to 64%, and there are no systematic variations in expandability as a function of burial depth or depositional age. The absence of clay mineral diagenesis is consistent with the relatively shallow sample depths and corresponding maximum temperatures of only 24°-33°C.