Sedimentological and marine eogenetic control on porosity distribution in Upper Cretaceous carbonate turbidites (central Albania)



Results of a detailed petrographic and stable isotope study illustrate that sedimentological differences and eogenetic dissolution/precipitation processes controlled porosity distribution within carbonate turbidites of the Ionian basin (central Albania). Based on lithology characteristics and porosity distribution observed in outcrop, individual turbidite beds can be subdivided into four distinct intervals, i.e. from base to top: (A) a non-porous wackestone/floatstone or packstone followed by (B) porous packstone–grainstone that grades into (C) wackestone and (D) non-porous mudstone with pelagic foraminifera. Wackestone interval C is characterized by an alternation of porous and non-porous laminae. Changes in turbidity current flow regime controlled the initial presence of matrix micrite giving rise to both matrix- and grain-supported lithologies within turbidite sequences. These are non-porous and porous, respectively. Four eogenetic diagenetic processes (dissolution, cementation, neomorphism and compaction) acted shortly after deposition and modified primary porosity characteristics and distribution. Alteration by meteoric water is excluded based on the continuous burial until the Oligocene of the studied deep marine carbonates. Moreover, the stable isotope data with values between −2·1‰ and +0·7‰ for δ18OV-PDB and between +1‰ and +3‰ for δ13CV-PDB, favour alteration by marine-derived pore-waters. Compaction and aggrading neomorphism occurred dominantly in intervals characterized by higher matrix micrite content, i.e. the floatstone base and the wackestone–mudstone upper turbidite part. Framework-stabilizing cementation occurred dominantly in the packstone–grainstone middle part of the turbidite beds. In the latter porous lithologies, matrix micrite was not compacted because of the grain fabric and the framework-stabilizing cements. Here, neomorphism of micrite into microrhombic euhedral calcite occurred and microporosity was preserved.