Meter-scale cycles as a proxy for the evolution of the Apulian Carbonate Platform during the late Cretaceous (Llogara Pass, Albania)

Abstract

Sedimentological investigations have revealed ten facies in Upper Cretaceous platform carbonates (1220 m thick) at Llogara Pass in southern Albania that can be grouped into four facies associations. These reflect specific environmental conditions, ranging from intertidal to subtidal. The facies form small-scale patterns attesting to high-frequency/low-amplitude cyclicity characteristic of relative sea-level fluctuations. Meter-scale cycles have been classified into six distinct types and characterized on the basis of diagnostic surfaces, diagenetic features, and reservoir properties. A closer look at diagenetic and petrophysical features revealed a drastic porosity reduction at each cycle top (i.e., cycle boundary). This underlines a strong interconnection of facies types and reservoir properties at the cycle scale, thus impacting the whole carbonate succession. The cycle stacking pattern is a reflection of the sedimentary evolution during the late Cretaceous in this southern part of the Apulian Platform. (1) Meter-scale peritidal cycles suggest that the Cenomanian was characterized by stable shallow-water conditions. (2) Thick stromatolitic-dominated cycles typify Turonian deposits. Although the nature of the deposits indicates inner platform conditions, the long-term hiatus documented from Italy (Turonian bauxites) is not evidenced in Llogara. (3) The thin (a few tens of meters) Coniacian–Santonian interval suggests the onset of a significant tectonic control over the sedimentary dynamics, likely accompanied by morphological changes on the Apulian Platform and an emergence of rudist-dominated cycles. (4) Peritidal-subtidal cycles persist during the Campanian, accompanied by a broad development of rudist organisms that evidence significant and repeated relative sea-level rise. These data allow refinement of the general sedimentological evolution during the late Cretaceous on the Apulian Platform.