Akademik Veri Yönetim Sistemi
10th ISC – International Symposium on the Cretaceous, Vienna, Avusturya, 21 - 26 Ağustos 2017, ss.17
A 748 m thick stratigraphical section was measured along the Upper Jurassic – Lower
Cretaceous carbonate sequence exposed in a tectonic klippe of the Sakarya Zone
(Pontides), north of Sivrihisar. According to the biozonation and microfacies types, two
coeval but dissimiliar rock successions, separated by a thrust fault, have been detected. The
lower succession displays a slope to basin facies and consists of the Kimmeridgian–
Berriasian Yosunlukbayırı Formation and the overlying Valanginian Soğukçam Limestone.
The deposits of this succession are characterized by the continuous pelagic background
sedimentation with taxa including calpionelldis, Saccocoma, calcareous dinocysts and
aptychi, intercalated with the calciturbidites containing platform derived clasts (benthic
foraminifera, microencrusters, worm tubes etc.). The succession commences with pelagic
deposits characterized by toe-of-slope type facies. There is an important increase in the
amount of platform-derived clasts in the Tithonian, reflecting a calciturbiditic – slope type
deposition in the succession. Latest Tithonian onward the background pelagic conditions
dominate the deposition.
This facies evolution resulted in intervals dominated by neritic or pelagic taxa or
characterized by mixed fauna. This types of bio-association gave rise to a composite
biozonation that is based on both pelagic and benthic taxa, providing the link between slope
and platform successions. This biozonation consists of the following biozones: Globuligerina
oxfordiana–Mohlerina basiliensis Zone (Kimmeridgian), Saccocoma Zone (Lower
Tithonian), Protopeneroplis ultragranulata Zone (Upper Tithonian), Crassicollaria
(massutiana subzone) Zone (uppermost Tithonian), Calpionella (alpina, Remaniella, elliptica
subzones) Zone (Lower Berriasian), Calpionellopsis (simplex, oblonga subzones) Zone
(Upper Berriasian) and Calpionellites (darderi subzone) Zone (Lower Valanginian).
Calciturbiditic deposits of the P. ultragranulata Zone are followed by pelagic deposits of the
massutiana subzone in the latest Tithonian. The Jurassic-Cretaceous boundary is located
at the base of the overlying alpina subzone defined by the acme of Calpionella alpina. The
other observed calpionellid bioevents around the J-K boundary are the stepwise last
occurences of Crassicollaria intermedia (below the boundary), Calpionella elliptalpina (at the
boundary) and Crassicollaria brevis (at the boundary) and the marked decrease in the
abundance of Calpionella grandalpina across the Tithonian-Berriasian boundary.