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.