Meteoric diagenesis of Upper Cretaceous and Paleocene— Eocene shallow-water carbonates in the Kruja Platform (Albania): geochemical evidence

In the central part of the Kruja Platform (Albania) located in the Apulian passive margin, geochemical analyses (calcimetry, Sr, REE and isotopic, δ 13 C and δ 18 O) coupled with sedimentological and sequence stratigraphic study were carried out on Upper Cretaceous (CsB4, CsB5, CsB6 Biozones) and Paleocene to Middle Eocene shallow- water carbonates that crop out in the Kruje-Dajt massif (L'Escalier section) and Makareshi massif (La Route section). The lower values in Sr contents, the homogeneous δ 18 O values in both sections and the covariance between δ 13 C and δ 18 O values (La Route section) are attributed to diagenesis influence by a meteoric water-buffer system, supported by petrographic observations. Moreover, a new exposure surface during the Late Cretaceous time (between CsB5 and CsB6 Biozones) may be proposed according to the low or negative excursions of Sr values, the negative excursions of isotopic values in both sections and a positive peak of normalized REE values (La Route section). These variations correlate with the geochemical signal reported by the decreasing strontium isotope values of rudist shells in the Island of Brac carbonate platform (Apulia domain) during the late Middle Campanian (77.3 Ma). Also, this continental expo- sure is consistent with the global sea-level fall reported from the Boreal Realm, North Atlantic, and the southern Tethyan margin. This geochemical evidence is a complementary tool for the sedimentological analysis and suggests a maximum regression (a sea-level fall) at the transition between the CsB5 and CsB6 Biozones. The high values of Sr content in Middle Eocene carbonates (L'Escalier section) reflect changes in depositional environment from restricted to open marine conditions. REE values increase through transgressive systems tract, characterized by small increase of detrital input. However, anomalies of certain values in both sections suggest disturbances linked either to the changes in clay input and to diagenetic modifications. Peaks in dolomite content are linked with regressive episodes or tendencies, and dolomitic facies, as indicated by intertidal-supratidal depositional environments.