O. Hermelin

Abstract Relative abundance of benthic foraminifera have been analyzed from core V26-145 from the Blake Plateau. The investigated sequence represents the time interval between 1.8 and 4.6 Ma. In order to determine how different sieve sizes influence the relative abundance patterns, three sediment size fractions were studied separately. It becomes difficult to maintain consistent taxonomic concepts in the fraction 63–125 μm, partly because this fraction contains high abundances of juvenile forms. However, the 63–125 μm fraction holds high abundances of the important small speciesEpistominella exigua. Due to these reasons only the two larger fractions (125–250 μm and >250 μm) were considered meaningful to analyze for relative abundance patterns. An analysis of the two larger fractions (>125 μm; >250 μm) shows no consistency in relative abundance patterns. The relative abundance patterns for the 34 most common species in the size fraction >125 μm were analyzed by means of correspondence analysis. Three benthic foraminiferal assemblages (I, II, and III) were recognized and these can be associated with water masses. Assemblage I is associated with the Florida Current and consists of shallow water species (Amphistegina gibbosa, Compressigerina sp. A,Discorbinella biconcavus, Islandiella teretis, Reussella atlantica, andSiphonina pulchra). Assemblage II contains key species for North Atlantic Deep Water (NADW) (Cibicidoides kullenbergi, Epistominella exigua, Globocassidulina subglobosa, Lenticulina peregrina, Oridorsalis umbonatus, andPlanulina wuellerstorfi). The third assemblage (III) contains species associated with the Antilles Current (Bolivina rhomboidalis, Cassidulina obtusa, Cassidulina vortex, andNuttallides umbonifera). The correspondence analysis reveals an alternation in dominance between Assemblage I and Assemblage II prior to 3.3 Ma, suggesting lateral oscillations between the Florida Current and NADW. At about 3.3 Ma Assemblage I disappears and Assemblage III increases in importance, suggesting an increasing influence of the Antilles Current in the upper part of the record.

... 91 (1990) 1-29 1 Elsevier Science Publishers BV, Amsterdam -- Printed in The Netherlands The Importance of the Oxygen Minimum Zone and Sediment Geochemistry in the Distribution of Recent Benthic Foraminifera in the Northwest Indian Ocean JOR HERMELIN1 and GB ...

The impetus for writing this paper has come from many people who have shown an interest in the device we describe; prior to this paper, we had no reference to provide for interested parties. The original device was described in Elmgren (1973) and illustrated in Thomas (1986). These papers are not readily available to many micropaleontologists; hence, we felt the need to redescribe it here with a few modifications. Traditionally, foraminiferal researchers, especially those working in fossil deposits, work on samples that are first processed and then dried. To split these dry samples to aliquots of manageable numbers of foraminifera, they use the well-known “Otto” microsplitter, which provides accurate splits plus or minus 10–20 percent.

During the late early Miocene to early middle Miocene, the Owen Ridge was uplifted to a sufficient height as to be above the realm of turbidite deposition. Monsoonal-induced upwelling appears to have been initiated during the Mio-cene. On the Oman Margin, the effect of upwelling on the microplankton was established by the middle Miocene. How-ever, the effects of upwelling on the Owen Ridge region were not realized until later, in the early late Miocene. A transi-tion in the upwelling regime took place between the Pliocene and Pleistocene. While the Miocene and Pliocene sedi-ments are dominated by the siliceous component, the Pleistocene sediments seem to be dominated by the calcareous component.