Table 3+4. Strontium isotope ratios of Cainozoic samples from the Utsira region

This study is based on biostratigraphic analysis of Upper Cenozoic strata in eight exploration and production wells from the Tampen area (Snorre and Visund fields), and one well from the Troll field. Dating of the units is based primarily on planktonic and bcnthic foraminifera. Eleven fossil assemblages have been defined in sediments from the Lower Oligocene to the Pleistocene. In addition, strontium isotope, lithologic and petrophysical log analyses have been performed, and the studied wells have been correlated along regional 2-D and 3-D seismic lines. In the Troll area the Pleistocene rests unconformably on the Lower Oligocene. The upper part of the Upper Oligocene is absent in all the Tampen wells. In the Visund area (block 34/8) there is a hiatus of more than 2 m.y. between Oligocene and Lower Miocene strata, and in the Snorre area (blocks 34/4 and 34/7) there is a hiatus of more than 18 m.y. between Oligocene and Upper Miocene deposits. The Neogene section has been subdivided into five major lithologic units. In the Visund area, a Lower Miocene unit (1) of predominantly fine-grained, silty sediments has been identified. A major hiatus separates this unit from the overlying Utsira Formation (2), which in the northern North Sea comprises a thick lower part composed of quartzose sand and a thinner upper part of glauconitic sand. The main sands of the Utsira Formation are not present in any of the studied wells, but preliminary results from well 35/11-1 indicate a Late Miocene to possible latest Middle Miocene age for this unit. The glauconitic part of the Utsira Formation (Late Miocene to earliest Early Pliocene in age) overlies the Oligocene strata in the Snorre area and the Lower Miocene deposits in the Visund area. To the east it may drape over the main Utsira Formation sands or partly interfinger with these. It is overlain by a basal upper Pliocene unit (3) consisting of gravity flow deposits. Cores from this unit exhibit ice- rafted pebbles and have a glacio-marine affinity. A thick complex of Upper Pliocene prograding wedges (4) downlap the basal Pliocene unit in the Tampen area and the Utsira Formation in the eastern part of the basin. It is unconformably overlain by a Pleistocene unit at the top (5). An important feature of the Neogene succession is a large incised valley/canyon system which developed in a north-westerly direction from block 35/8 (off Sognefjorden) to about 62ºN. This erosive system cuts into the basal Upper Pliocene unit in block 34/3 and is thus much younger than has been previously suggested

Table 1-8. Strontium isotopic ratios of samples from 8 wells from the Southern Viking Graben

Based on an extensive study of biostratigraphic and strontium isotopic data from wells in the southern Viking Graben and eastern flank of the Utsira High we present an improved chronology of the post-Eocene section of the northern North Sea. Emphasis has been placed on the sandy Utsira and Skade formations. Detailed analyses of foraminiferal and Bolboforma fossil assemblages supported by strontium isotopic data from six exploration and two production wells suggest that the Skade sands were deposited mainly during the Early Miocene whereas the Utsira sands were deposited during the Late Miocene and Early Pliocene. All biostratigraphic data are presented in range charts and have been integrated with wireline log and seismic data. Strontium isotope stratigraphy has been used as an additional dating tool and has proved powerful in the sandy sections. This work also demonstrates a need for an update or modification of the lithostratigraphic nomenclature of the post-Eocene succession in the Norwegian North Sea, and a proposal for a revision is presented

Measurement and Modelling of Pm Sorption onto TiO2 and goethite

The sorption of Pm (1 x 10(-9) M) onto TiO2 and goethite has been studied as a function of pH and Ionic strength (0.01, 0.1 M NaClO4) at ambient temperature under N-2 atmosphere. For both minerals studied there is no effect of the different ionic strengths and the sorption (log K-a vs. pH) increases with a slope of similar to2. At the same pH sorption is lower on the more positively (or less negatively) charged goethite (pH(pzc) = 8.4) than on the TiO2 (pH(pzc) = 6.2). A comparison to other trivalent cations sorbed on different substrates (made by extracting values from %-sorbed curves and calculating these to K-a) indicate a similar pH-dependence. The results have been fitted using a 1-pK basic Stern model with FITEQL [1]. An a priori restriction was that only one sorption reaction stoichiometry at a time was to be used to keep the number of parameters as small as possible. Outersphere and mono-, bi- and tri-dentate inner-sphere complexes were fitted. For each fit the value of the capacitance was varied to find the value that provided the best fit. Two different site densities were used: 1 site/nm(2) and 2.31 sites/nm(2). For the low site density the reaction which provides the best tit was: drop SOH0.5- + Pm+3 drop SOHPm2.5+for both minerals. At the high site density the same reaction fits for TiO2 while there are several reactions that are equivalent in the fit for goethite

Measurement and Modelling of Pm Sorption onto TiO2 and goethite

The sorption of Pm (1 x 10(-9) M) onto TiO2 and goethite has been studied as a function of pH and Ionic strength (0.01, 0.1 M NaClO4) at ambient temperature under N-2 atmosphere. For both minerals studied there is no effect of the different ionic strengths and the sorption (log K-a vs. pH) increases with a slope of similar to2. At the same pH sorption is lower on the more positively (or less negatively) charged goethite (pH(pzc) = 8.4) than on the TiO2 (pH(pzc) = 6.2). A comparison to other trivalent cations sorbed on different substrates (made by extracting values from %-sorbed curves and calculating these to K-a) indicate a similar pH-dependence. The results have been fitted using a 1-pK basic Stern model with FITEQL [1]. An a priori restriction was that only one sorption reaction stoichiometry at a time was to be used to keep the number of parameters as small as possible. Outersphere and mono-, bi- and tri-dentate inner-sphere complexes were fitted. For each fit the value of the capacitance was varied to find the value that provided the best fit. Two different site densities were used: 1 site/nm(2) and 2.31 sites/nm(2). For the low site density the reaction which provides the best tit was: drop SOH0.5- + Pm+3 drop SOHPm2.5+for both minerals. At the high site density the same reaction fits for TiO2 while there are several reactions that are equivalent in the fit for goethite