Reconstruction of Caspian Sea level changes using magnetic susceptibility during the last millennium

1452-1459Magnetic susceptibility is one of the most important methods for monitoring sediment composition during environmental studies. In this research, to reconstruct the Caspian Sea level changes, magnetic susceptibility variations were used during studies of five sedimentary cores (K1,K3,K5,K7,N1), collected from bottom sediments of Gorgan Bay. Samples were analyzed for grain size, total organic matter, carbonate content and magnetic susceptibility (MS). The results showed a close relationship between particle size distribution and MS magnitude due to variation in terrestrial influx, which is caused by sea-level fluctuations in different times. This process increases with particle size and magnitude of MS simultaneously with sea level fall and decreases during sea level rise. Moreover, no relationship between magnitude of MS and carbonate content was observed. Using magnetic susceptibility curves with other data, such as geological and historical, it can be concluded that these data are suitable for the reconstruction of marine environments, especially in the near shore coastal area

Planktonic foraminiferal turnover across the Cenomanian – Turonian boundary (OAE2) in the northeast of the Tethys realm, Kopet-Dagh Basin

Two Late Cenomanian – Early Turonian (C–T) intervals of the eastern part of the Kopet-Dagh basin, NE Iran have been investigated to evaluate the response of planktonic foraminifera to the geological event OAE2. The Gharesu and Taherabad sections with the thicknesses of 30 m and 22.5 m are composed of shale and marl interbedded with glauconitic sandstone. Three biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica were recognized based on study of planktonic foraminifera, in these sections. We observed the patterns of planktonic foraminiferal assemblage changes around the C–T boundary and divided this succession into several successive intervals. This study confirms that OAE2 was a long term event. A gradual perturbation in the study successions starts in the interval 1 with low abundance and diversity of planktonic foraminifera. An enhanced oxygen minimum zone (OMZ) occurs in the interval 3 which coincides with a temporary absence of planktonic foraminifera and sedimentation of framboidal pyrite. High diversity of planktonic foraminifera and appearance of new genera in the interval 5 indicate return of normal conditions to the basin. A significant short-term sea surface temperature cooling is also indicated by planktonic foraminiferal turnover and carbonate contents in the interval 2 which is comparable with other parts of the Tethys Ocean, Boreal sea and Atlantic region