MIDDLE – UPPER JURASSIC (UPPER CALLOVIAN TO LOWER KIMMERIDGIAN) CARBON ISOTOPE CHEMOSTRATIGRAPHY FROM CENTRAL SAUDI ARABIA

Carbon isotope data (δ¹³C) provide an essential means for correlating and interpreting stratigraphic surfaces within complex carbonate strata and refining paleogeographic reconstructions. Although the main factors that control global carbon isotope signatures of Middle – Upper Jurassic carbonates are well understood, the latitudinal and regional variability are poorly understood. This study presents a new high-resolution carbon isotope record (δ¹³C for both carbonate and organic matter) from Middle – Upper Jurassic carbonates (Hanifa Formation, central Saudi Arabia) to explore the impact of local variations on global chemostratigraphic signals, and implications for developing and testing stratigraphic correlations, architecture, and strata zonation.

Discrete δ¹³C signals of the Hanifa Formation illustrate complex relations between sequence stratigraphic framework and δ¹³C time lines. The Hanifa Formation can be divided into six chronostratigraphic units based on the δ¹³C signals, which are very similar between the updip and downdip sections, but are dissimilar to the units that would be made based on lithological characteristics. Superimposing these chronostratigraphic δ¹³C units onto the sequence stratigraphic framework of the Hanifa Formation suggests missing time in the updip section associated with onlap (becoming younger landward) and downlap surfaces (which becoming older landward). δ¹³C data play important a role in constraining the timing of deposition, and to test and guide sequence stratigraphic interpretation.

The interplay of local and global controls produce distinct δ¹³C signals in geographically disparate locations at regional (platform) to global (ocean) scales. Generally, data suggest three scales of δ¹³C signal variability: local control dominated, local control modified, and global control dominated. We interpret the overall variation in carbon isotope signatures to result from reorganization of Tethys oceanography and climate change, but with local modification due to the burial of organic matter during the upper Callovian to lower Kimmeridgian. The carbon isotopic signatures can provide an independent means for constraining and correlating lithofacies within heterogeneous carbonate reservoirs and provide information important to stratal zonation.