Depositional environments and foramiferal assemblages in sediments of the Mirna River delta

Foraminiferska analiza provedena je na šest jezgri duljine od 7,5 do 13 m izvađenih iz deltne ravnice rijeke Mirne. Za mikropaleontološku analizu primijenjen je FOBIMO protokol. U svim jezgrama određeni su apsolutni broj foraminifera, relativni postotak i indeksi bioraznolikosti (Shannonov, indeks dominacije, Simpsonov, Berger-Parkerov i Fisher α). Najplići dijelovi jezgara ne sadrže foraminifere. Najdominantnije vrste u dubljim intervalima pripadaju rodovima Ammonia, Haynesina i Porosononion. U dubljim intervalima, smanjuje se njihova zastupljenost i pojavljuju se jedinke roda Elphidium te miliolida. Povećanjem dubine, marinski utjecaj u jezgrama se povećava i indeksi bioraznolikosti pokazuju sve manju dominaciju pojedinih rodova. Prema zastupljenosti navedenih rodova i varijacija u indeksima bioraznolikosti, prepoznati su slijedeći taložni okoliši: aluvijalni okoliši, brakični okoliši (močvare/lagune), unutrašnji estuariji, središnji i vanjski estuariji. Promjena vertikalnih taložnih okoliša zbog horizontalnog pomaka rijeke ukazuje na progradaciju tijekom holocena.Foraminiferal analysis was carried out on six cores down to the depth from 7.5 to 13 m. from the Mirna River deltaic plain. FOBIMO protocol was used for micropaleontological analysis. For all cores absolute abundance, relative abundance and biodiversity indices (Shannon, Dominance, Simpson, Berger-Parker and Fisher's alpha) were calculated. Foraminifera in the shallowest intervals are completely lacking. In the deeper intervals dominant species belong to Ammonia, Haynesina and Porosononion genus. In deeper intervals, their abundance is reduced and individuals belonging to Elphidium genus and miliolids start to appear. Marine influence became more pronounced with depth and biodiversity indices have shown a decreasing dominance of certain genera. According to the abundance of said genera and variation of biodiversity indices, the following depositional environments were suggested: alluvial environments, brackish environments (marshes/lagoons), inner estuaries, central and outer estuaries. Changes in vertical depositional environments caused by horizontal river movement indicate progradation during Holocene