Sedimentological study of the upper Jurassic sequence of limestone in the pui zone (Romania)

Abstract

In the points Fundătura and Ciclovina, situated northward of the Pui zone (southern Carpathians, Fig.1), we collected two sections of lithological samples from the Lower Jurassic sequence. Thin-sections effected on these samples formed the subject of a study, the results of which are presented in this paper. The lithological sequence of the Upper Jurassic includes, above the Dogger Formations the following sedimentary terms ( Boldor and Stilla, 1967): 1. (1) Lower?-Middle Callovian, represented by gritty, spathic limestones with abundant siliceous accidents, disposed non-uniformly in the rock mass. 2. (2) Upper Callovian-Lower Oxfordian, composed of marly limestones and fine limestones with Kosmoceras duncani Sow. and Euaspidoceras cf. perarmatum Sow. 3. (3) Upper Oxfordian-Kimmeridgian-Tithonian, comprised in a packet of generally fine, sub-lithographic limestones, with siliceous accidents disposed according to the stratification. In the upper third of this sequence of rosy siliceous limestones, there are distinguished alternances of nodulous limestones. Macrofaunally, the deposits are characterized by the presence of the forms Perisphinctes, Belemnites, Aptychus. Representing a new, transgressive, cycle of sedimentation, there are deposited massive reef limestones with Requienia ammonia Goldf., referred to the Lower Cretaceous in urgonian facies. The section of samples for thin sections included in the Fundătura sector only the upper part of the Malm (Kimmeridgian-Tithonian) deposits, and is concluded by several limestone beds of Early Cretaceous age. Notable in this point is the Fundătura fault which breaks up the Jurassic sequence towards the bottom, and puts it into tectonic contact with the reef limestones of the Lower Cretaceous. In the Ciclovina point, sampling began in the last beds of the Upper Callovian-Lower Oxfordian deposits, continued with the Upper Oxfordian-Kimmeridgian-Tithonian packet of limestones with silica, and comprised also, in its upper part, the first limestone beds of Early Cretaceous age.