Ostracoda in five sediment cores from the Laptev and Kara seas

Fossil ostracods were investigated in five AMS14C-dated cores from different parts of the Laptev and Kara seas. Three cores from the Laptev Sea shelf are located in river paleovalleys, and one core originates from the western continental slope. The core from the Kara Sea was obtained in the eastern shelf region. Six fossil assemblages were distinguished: estuarine (1), inner-shelf (2), middle-shelf (3), outer-shelf (4), Pre-Holocene upper continental slope (5), and Holocene upper continental slope (6). They show that during the Postglacial sea-level rise there was a transition from estuarine brackish-water environment to modern marine conditions. Assemblages 1-3 are present in the eastern Laptev Sea with the oldest ostracod-bearing samples aging back to 11.4-11.3 cal.ka. Cores from the western Laptev Sea (12.3 cal.ka, assemblages 1-4) and the Kara Sea (8.1 cal.ka, assemblages 2-4) demonstrate similar pattern in assemblage replacement, but contain a number of relatively deep-water species reflecting stronger influence of open-sea waters. Core from the continental slope, water depth 270 m (~ 17 cal.ka) encompasses assemblages 5 and 6, which are absent in the shelf cores. Assemblage 5 stands out as a specific community dominated by relatively deep-water Arctic and North Atlantic species together with euryhaline ones. The assemblages indicate inflows of Atlantic-derived waters and downslope slides due to the proximity to the paleocoastline. Assemblage (6) is similar to the modern local ostracod assemblage at this site.

Ostracodes in bottom sediments of the Laptev Sea

This work is the first detailed description of the Late Pleistocene-Holocene and Recent Ostracoda of the Laptev Sea. A total of 45 species in 22 genera and 13 families have been identified. All these species are described monographically. Three different ecological assemblages of ostracodes corresponding to different combinations of environmental parameters have been established; they are restricted to three regions of the sea: western-central, eastern, and southern. The recent ostracode assemblages of the Laptev Sea have been compared with those from other Arctic areas and are most similar to those of the Beaufort and Kara seas. Data on recent Ostracoda are used for paleoenvironmental reconstructions on the eastern shelf and western continental slope of the Laptev Sea. For this purpose, ostracodes from five sections obtained from these parts of the sea have been examined. The oldest sediments, which are of Late Pleistocene age (15.8 cal. ka BP), have been recovered in a core from the western continental slope. These yielded five ostracode assemblages, which correspond to different paleoenvironments and replaced each other in the course of the rapid postglacial sea-level rise, thus showing variations in the Atlantic water inflow from the west and freshwater discharge from the subaerially exposed shelf. On the outer shelf of the eastern part of the sea, the rapid sea-level rise in the Early Holocene (lowermost dating 11.3 cal. ka BP) led to a rapid transition from assemblages of brackish-water nearshore environments to those of modernlike normal marine environments; modern environments were established about 8.2 cal. ka ago. Since core sections from the inner shelf correspond to the time when the level of the sea had already reached its modern values, changes in taxonomic composition of ostracode assemblages primarily mirror variations in river runoff.

Mesozoic radiolarians of ODP Holes 129-800A and 129-801B

Rich radiolarian faunas were obtained continuously from Middle Jurassic to Lower Cretaceous radiolarite sequences at Sites 800 and 801, drilled during Ocean Drilling Program Leg 129 in the western Pacific. Occurrences of 90 taxa are presented in tables for these sites. Seven radiolarian zones, Dibolachras tytthopora, Cecrops septemporatus, Pseudodictyomitra carpatica, Pseudodictyomitra primitiva, Cinguloturris carpatica, Stylocapsa spiralis, and Tricolocapsa conexa in descending order, were recognized in this interval. The radiolarite sequences of Sites 800 and 801 encompass approximately the Berriasian to Hauterivian (or to Barremian) and the Bathonian/Callovian to Valanginian ages, respectively. At Site 801, a hiatus of early Oxfordian was identified.