Lower Cretaceous limestones from the northern part of Padurea Craiului (Osoiu Hill and Subpiatra sections): biostratigraphy and preliminary data on microbial structures

Abstract

ABSTRACT. Two sections have been measured within the Lower Cretaceous deposits from the northern part of Pădurea Craiului: Osoiu Hill section and Subpiatră section. Thin sections representing more than 180 samples allowed us to present some results on the biostratigraphy, facies succession and the role of microbial structures in the genesis of these limestones. The Osoiu Hill section is dominated by fenestral limestones formed in the intertidal or in the shallow subtidal zone. Their formation is dominantly related to microbial mats. Based on foraminiferal assemblages we attribute a Lower Barremian age to these limestones. The succession in the Subpiatra section is dominated by shallow facies with rudists, corals and Bacinella. These limestones contain Mesorbitolina texana a foraminifer which indicate Gargasian age. A more dense spectrum of microbial structures characterize this section: thrombolitic crusts, Bacinella-Lithocodium type structures, cryptic carbonate marine veneers and rivulariacean-like cyanobacteria. The microbial structures played an important role in the genesis of carbonate sediments and their lithification in the two sections.