engleski

Foraminiferal record of the Pliocene transgressive succession in some north Adriatic off-shore wells

By the means of the micropaleontological analyses of the sediments from exploration wells in the north part of Adriatic Sea, the Pliocene transgressive succession has been evidenced. Wet-sieving and hand-picking were performed to separate fossils from clasts. Three groups of exploration wells, which were tested, are located west and south-west from Zadar. 1. Koraljka-1, Ksenija-1 and Ksenija-3 2. Kruna-1, Kristina-1 and Kornati more-4 3. Ines-1, Irma-1 and Irma-2 The Pliocene clastic sediments, consist of clayey marl, silt and sand intercalations, overlie different levels of the Miocene sediments. The relation to the base depends to paleorelief and marine sedimentation did not started at the same time.The ticknesses of the sediments are unequal because of same reason.The most complete successsion has been found in the Koraljka-1 well and it seems that the sedimentation was continuous because at the top of the Miocene gypsum has been recorded (MILETIĆ & BAJRAKTAREVIĆ, 1995). The begining of the Pliocene transgressive succesion over the Miocene sedimentary rocks coincides with the first appearance of planktonic foraminifera Globorotalia margaritae BOLLI & BERMUDEZ ( BERGGREN et al. 1995) and the abundance of glauconitic material in alternating layers of marls and poorly consolidated clayey siltites and sandstones (MILETIĆ et al., 1995 ; MILETIĆ & LUGOVIĆ, 1996 ; 2000).The Pliocene transgression was very rapid and the population of planktonic foraminifera from the Atlantic ocean spread of all over the area (HAQ & BOERSMA, 1978 ; ZACHARIASSE et al., 1989). Very important index fossils from the lower to uper Pliocene were found: Sphaeroidinellopsis seminulina (SCHWAGER), Globorotalia margaritae BOLLI & BERMUDEZ, Globorotalia puncticulata (DESHAYES), Globorotalia bononiensis DONDI, Globorotalia aemiliana COLALONGO & SARTONI, Globorotalia crassaformis (GALLOWAY & WISSLER), Globorotalia inflata D&#900 ; ORBIGNY, Globigerinoides ruber D&#900 ; ORBIGNY, Globigerinoides conglobatus (D&#900 ; ORBIGNY), Globigerinoides trilobus (REUSS), Globigerinoides elongatus (D&#900 ; ORBIGNY) Globigerinoides obliquus extremus BOLLI & BERMUDEZ et ctr. In the begining there were no benthic foraminifera because the environment has been changed very fast. The repopulation of benthic foraminifera has been able after the ecological conditions came enough stabile. The populaton of benthic foraminifera during the Pliocene became more abundant and many of important fossils were found: Uvigerina rutila COSHMAN & TODD, Uvigerina peregrina CUSHMAN, Cibicidoides ungerianus (D&#900 ; ORBIGNY), Cibicidoides robertsonianus (BRADY), Cibicidoides kullenbergi (PARKER), Siphonina planoconvexa (SILVESTRI), Cassidulina crassa D&#900 ; ORBIGNY, Cassidulina neocarinata THALMANN, Anomalinoides ornatus (COSTA), Anomalinoides helicinus COSTA, Melonis padanum PERCONIG Heterolepa floridana (CUSHMAN), Planulina ariminensis D&#900 ; ORBIGNY, et. ctr. This kind of marine sedimentation in inner to middle shelf environment during the Pliocene is equal as the sedimentation in the other part of Mediterranean (IACCARINO, 1985). Recent exploration has shown that the paleontological studies and biofacies analyses of the rock material from the drilled wells may yield reliable results in biostratigraphical classification of the investigated sediments. Besides, these results have a direct aplication to structural and tectonical interpretation of the sediments from drilled wells.

Adriatic off-shore; transgressive succesion; Pliocene; foraminifers

nije evidentirano