Cenomanian–Turonian oceanic anoxic event (OAE2) imprint on the northwestern part of the Adriatic Carbonate Platform and a coeval intra-platform basin (Istria and Premuda Island, Croatia)

Determining of an oceanic anoxic event and paleoenvironmental conditions of the Gulneri Formation Kirkuk Oilfield, Northern Iraq

“…The higher temperature at sample G2 from the Gulneri Formation coincides with the lowest value of δ 18 O.…”

“…According to VPDB, the isotope ratios measured for NBS18 (δ 13 C = -5.00, δ 18 O = -22.96‰) and NBS19 (δ 13 C = 1.95, δ 18 O = -2.20‰) international calcite standards were used to calibrate the measured isotope ratios. For both δ 13 C and δ 18 O values.…”

“…Limestone and calcareous shale samples of the Cenomenian-Turonian sequences were studied. A distinction was made between marine water and fresh water from the Z values calculated by the isotopes (δ 18 O) and (δ 13 C) through the equation proposed by (Keith and Weber, 1964): Z=a(δ 13 C+50) +b(δ 18 O+50) whereas: a= 2.048, b= 0.498, δ 18 O: oxygen isotopes of limestone (vPDB), δ 13 C: isotopic composition of carbon in limestone (vPDB). Samples with a Z value higher than 120 will be classified as marine, Z value lower than 120 are freshwater limestone.…”

“…The temperature of water during deposition of the limestone rocks was deduced using the isotopes (δ 18 6).…”

“…The positive δ 13 C shift, which has been observed in the Gulneri Formation, suggests that the main palaeoceanographic characteristics associated with OAE2 include increased productivity of marine surface waters and greater preservation and burial of organic matter. The δ 18 O fluctuation around the Cenomanian -Turonian boundary is attributed to the difference in δ 18 O in ocean water due to temperature change and/or influx of freshwater. The most noticeable feature comprises variable readings up until the carbon peak connected to a negative excursion for oxygen and subsequent recovery to values as high as -4.2.…”