Carbonate Geochemistry as a Tool for Sequence Stratigraphy Analysis: The Early Cretaceous (Aptian) Carbonate Systems from the Western Maestrat Basin (Spain)

The carbon and oxygen isotope composition of an Aptian platform carbonate succession from the western Maestrat Basin (Spain) have been linked to the attributes of its well-defined sequence stratigraphy framework. The selected section is biostratigraphically well-constrained and exceptionally preserves the stratal stacking patterns and the facies variation and architecture, which allowed a previous identification of five systems tracts, from two depositional sequences, and their key bounding surfaces. Our results show that both isotope proxies exhibit similar geochemical trends, which are largely correlatable with the sea-level variation and the associated system tract. Those systems tracts associated with a relative sea level high (transgressive and highstand intervals) exhibit the more positive δ13C and less negative δ18O values, up to +5.1 and -1.8‰, respectively, being the highstand the one that exhibits the most homogeneous values. In contrast, the systems tracts associated with a relative sea-level low (regressive and lowstand intervals) have wide-ranging isotope values with δ13C values ranging from +0.5 to +4.5‰ and δ18O values from -6.1 to -3.5‰. This range defines a trend of decreasing δ18O and δ13C values towards the sequence boundary, which being characterized by a marked negative carbon and oxygen isotope excursion, represents the lowest point of the relative sea level. Due to the well exposure of the studied outcrops and the good correlation between the stable isotopes and the sea-level fluctuation, the results presented here may be useful for other platform carbonate systems with poor exposure conditions that often show ambiguous evidence of sea-level fluctuations.