Composite Mesozoic Carbon and Oxygen Isotope Signals of Selected Events as Encountered in the Southern Tethyan Margin: an Overview

Several pelagic sections in North-Eastern/Central Tunisia and neighboring basins have recently been the subject of detailed δ13C and δ18O stratigraphy. These studies have been utilized to create a composite Mesozoic (Triassic to Cretaceous) δ13C and δ18O curves, which is useful for high-resolution stratigraphic correlation. The long-term trend of the created composite δ13C and δ18O profiles change on variable time scales (100’s of years), and show the major δ13C positive and negative excursions around the key Mesozoic timelines: the Carnian, Toarcian, Barremian-Aptian, Cenomanian-Turonian, upper Cretaceous and Cretaceous/Paleogene. Short-term fluctuations vary also on time scales of similar magnitudes, and dominated the δ13C signal in the Mid-Cretaceous. Generally, the observed changes in the Carbon-isotopic record have commonly been attributed to changes in the organic carbon flux to the sedimentary reservoir in response to eustatic sea-level change. However, it is also suggested that carbonate production and burial rate may have influenced the δ13C signal. During Triassic and Jurassic, increased inorganic carbon burial led to a shift towards more negative values in the 13C/12C ratio, which is probably linked to the expansion of pelagic carbonate deposits in epicontinental seas (e.g. Carnian and Toarcian carbonate). However, short-term variations in δ13C could either be due to local sea-level changes in the North African epicontinental sea or changes in oceanic 12C storage due to variations in different water properties circulation. In addition, oxygen isotopic data can serve as a useful tool for estimating paleotemperatures in instances where diagenesis is not a hindrance. These data can record changes in paleoclimate associated with cooling or warming during the Mesozoic.