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Distribution of the planktonic foraminifera species in the Atlantic Ocean sediments in dependence on water temperature (In Russian)



Summary The planktonic foraminifera tests were investigated in 280 samples of surface sediments of the North and Equatorial Atlantic. The dependence of the species di¬stribution on the average annual temperature of the upper water layer was established. The following criteria were used: I.The position of the region of the species highest quantity. 2. The inclination in the quantity changes in proportion with increase or decrease of the water temperature. 3. The temperature limits of the species areals in sediments. The species temperature range was built in which they are ranged from the most cold-water species to the most warm—water one.The studies of left— and right— coi¬ling Globigerina pachyderma and Globorotalia truncatulinoides were made separately. The highest species number occurs in the southern part of the Subtropical zone whe¬re the temperature is 22—23°C. This data may be used for stratigraphical division of cores and palaeoclimatic reconstructions.
... The average percentage was calculated for widely distributed species in every latitudinal belt. Note that, in contrast to this approach, the highest species contents were considered in similar studies on recent planktonic foraminifers (Barash, 1974). The use of average contents in analyzing fossil foraminifers is predetermined by the duration of the studied time intervals (about 1 m.y.), during which significant variations in species contents occur because of the multiple changes in environmental parameters, evolutionary peculiarities of different species, and influence of selective dissolution. ...
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In analysis of the stratigraphic distribution of planktonic foraminifers in the Pliocene–Lower Quaternary sediments of the North Pacific, and research of the space-time distribution dynamics of 60 species at four levels corresponding to the foraminiferal zones N 19, N 20, N 21, and N 22 revealed, significant evolutionary changes at that time were revealed. Twenty-five species became extinct and ten species appeared. Since the early Pliocene, the foraminifer diversity decreased from 53 to 34 species. Three groups of species were revealed: (1) short-lived species; (2) species who reduced and extended distribution areas and abundances, and (3) species whose distribution patterns remained relatively stable. It was shown that the reduction of distribution areas proceeded from the periphery toward the center (i.e., toward the areas with the highest abundances) and, in contrast, distribution areas of the newly appearing and evolving species expanded from their center toward the periphery.
Occurrence conditions and lithological-paleontological characteristics of two diamicton units developed in the southeastern segment of the Barents Sea shelf are considered. It is shown that they are lithologically analogous to the present-day (undoubtedly aqueous) diamicton mud. Correlation between bulk densities of both varieties and consolidation degree (consistency) is described by a single regression equation. We present pieces of evidence contradicting the widespread point of view about the diamicton as a glacial till moving along the seafloor. They are primarily represented by paleontological remains, mainly foraminiferal assemblages. It is shown that dislocations observed in cores and traditionally considered as glaciotectonic movements are confined to fault zones in the acoustic basement and they represent fragments of secondary neotectonic structures. Ridges and hills mapped previously as glacial accumulation morphostructures reflect a relict topography of the recent subaerial shelf development not masked by sedimentation so far.
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