engleski

Foraminiferal distribution in Holocene sediment core from Raša River mouth (Croatia)

The core of 136 cm length was taken, at station 44° 57' 02 N, 14° 03' 66 E, at the depth of 40 m in Raša River mouth. The aim was to investigate changes in foraminiferal associations along the sediment core, in order to study the evolution of environmental conditions during Holocene. The detailed description of the core is given in the abstract Bogner et al. (this volume). For this purpose subsamples were taken at intervals of 4 cm. The analyses were done from the fraction larger than 63 &micro ; m on the aliquots containing about 300 foraminiferal specimens. Multivariate cluster analysis of foraminiferal associations of the subsamples split them into three groups. The first cluster (0-48 cm) is characterized by co-dominance of Textularia agglutinans, Ammonia beccarii and Cribroelphidium decipiens. The highest diversity of foraminiferal assemblage (Fisher index 7.5 < a < 12.2), its composition and sedimentary features are associated with near-marine to slightly reduced salinity and low sedimentation rates. The second cluster (48&#8211 ; 120 cm) contains a foraminiferal fauna consisting of dominant A. inflata and lesser abundances of A. tepida, C. decipiens, and Haynesina depressula. Estuarine infaunal foraminiferal fauna, diversity between 2.2 < a < 9.7, suggests very variable salinity, temperature, and changes in substrate type. The third cluster (120-136 cm) contains negligible number of foraminifera specimens, suggesting non marine origin. This part of the core is separated from the upper part by the thin peat layer dated to 9994 &plusmn ; 195 yBP. There is an overall trend in increasing species diversity during Holocene from brackish, estuarine (Shannon-Wiener index H(S)= 0.8 &#8211 ; 1.7) to saline, normal marine (H(S)= 1.2 - 2.9) settings. This study supports earlier conclusions that salinity is one of the most influential factors in foraminiferal distribution in karstic estuarine system.

foraminifera; Holocen; Raša River estuary

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