Stratigraphy and Larger Foraminifera of the Middle Eocene to Lower Oligocene Shallow-Marine Units in the Northern and Eastern Parts of the Thrace Basin, NW Turkey

Authors : GYÖRGY LESS, ERCAN ÖZCAN ARAL I OKAY

Pages : 793-845

View : 20 | Download : 10

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :The shallow-marine Eocene Soğucak Limestone and Oligocene Ceylan Formation were studied in the northern and eastern parts of the Thrace Basin with detailed biometric analysis of the full spectrum of larger benthic foraminifera insert ignore into journalissuearticles values(mainly nummulitids and orthophragmines);. This allows us to establish a high-resolution biostratigraphy in the context of the shallow benthic zonation insert ignore into journalissuearticles values(with SBZ zones); of the Tethyan Palaeogene since larger foraminiferal assemblages show a very strong Western Tethyan affinity. Only two species insert ignore into journalissuearticles values(Heterostegina armenica and Orbitoclypeus haynesi); are unknown so far to the west of the Thrace Basin. The age of particular larger foraminiferal sites is determined based on insert ignore into journalissuearticles values(i); the occurrence and developmental stage of different species of Heterostegina insert ignore into journalissuearticles values(H. armenica hacimasliensis n. ssp. is introduced here);, insert ignore into journalissuearticles values(ii); the presence/absence of giant Nummulites, insert ignore into journalissuearticles values(iii); the presence/absence of Spiroclypeus, insert ignore into journalissuearticles values(iv); the developmental stage of reticulate Nummulites, insert ignore into journalissuearticles values(v); the occurrence and developmental stage of orthophragmines, insert ignore into journalissuearticles values(vi); the occurrence of particular Operculina and radiate Nummulites. Six larger foraminiferal horizons could be established. They correspond to insert ignore into journalissuearticles values(i); the vicinity of the early/late Bartonian boundary insert ignore into journalissuearticles values(SBZ 17/18);, insert ignore into journalissuearticles values(ii); the middle late Bartonian insert ignore into journalissuearticles values(SBZ 18B);, insert ignore into journalissuearticles values(iii); the latest Bartonian insert ignore into journalissuearticles values(SBZ 18C);, insert ignore into journalissuearticles values(iv); the early Priabonian insert ignore into journalissuearticles values(SBZ 19);, insert ignore into journalissuearticles values(v); the late Priabonian insert ignore into journalissuearticles values(SBZ 20); and insert ignore into journalissuearticles values(vi); the early Rupelian insert ignore into journalissuearticles values(SBZ 21);. Three main shallow-water depositional environments could be recognized in both the late Bartonian and Priabonian: two of them took place in the middle shelf; one with low and another with high water-energy insert ignore into journalissuearticles values(back-bank and Nummulites-bank facies); whereas the third one refers to the outer shelf insert ignore into journalissuearticles values(fore-bank facies);. Biostratigraphical and palaeoenvironmental observations allow us to reconstruct three subregions in the northern and eastern parts of the Thrace Basin with different depositional histories: insert ignore into journalissuearticles values(i); The eastern part of the territory, with an İstanbul Zone basement was flooded at the beginning of the middle late Bartonian insert ignore into journalissuearticles values(SBZ 18B);, but the carbonate platform was drowned in the latest Bartonian insert ignore into journalissuearticles values(SBZ 18C);. insert ignore into journalissuearticles values(ii); The Çatalca block, lying on the Istranca Massif, formed a palaeohigh in whose peripheries a similar depositional history to for the former sub-region can be reconstructed, although the central part was transgressed only in the late Priabonian and was not drowned at all. insert ignore into journalissuearticles values(iii); The northern margin of the recent Thrace Basin insert ignore into journalissuearticles values(also lying on the Istranca Massif); was flooded only in the latest Bartonian insert ignore into journalissuearticles values(SBZ 18C); or in the early Priabonian insert ignore into journalissuearticles values(SBZ 19); and the Priabonian carbonate platform had only partly and shallowly been drowned. This subregion very probably formed the real northern margin of the whole Thrace Basin in the Palaeogene.
Keywords : Northern and Eastern Thrace, larger benthic foraminifera, biometry, taxonomy, biostratigraphy, Palaeogene, depositional history