Portail de Conférences / Conference Portal, JK2018

Font Size: 
Uppermost Jurassic-Lowermost Cretaceous microfossils from Piatra Craiului (Southern Carpathians, Romania) and the Jurassic-Cretaceous transition in the eastern part of the Getic Carbonate Platform
Cristian Victor Mircescu, Ioan I. Bucur

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-07 09:20 AM – 09:40 AM
Last modified: 2018-11-24

Abstract


The Piatra Craiului Massif is located in the eastern part of Southern Carpathians (Romania). It borders on the west the Dămbovicioara zone, and belongs to the eastern part of the so-called Getic Carbonate Platform, a system of carbonate platforms covering the Getic Nappe of the Southern Carpathians.

Within the sedimentary succession in Piatra Craiului three lithostratigraphic intervals can be identified: (I) a lower unit consisting of coral-microbial boundstones and coarse, poorly sorted rudstones; (II) a middle unit made up of coarse bioclastic grainstones, and (III) an upper unit consisting of peloidal packstone-wackestone and cyanobacteria-bearing mudstone (peritidal limestones).

The micropaleontological assemblages also permit biostratigraphic separatation of three intervals which cannot be superposed on the lithostratigraphic ones.

The biostratigraphical interval A consists of encrusting organisms (Crescentiella morronensis, Koskinobulina socialis, Lithocodium aggregatum and bacinellid structures, Perturbatacrusta leini, Radiomura cautica). Corals are commonly encrusted by bacinellid-Lithocodium. Microfossils are represented by dasycladalean algae (Campbeliella striata, Clypeina sulcata, Neoteutloporella socialis, Petrascula bursiformis, Salpingoporella pygmea, Salpingoporella annulata, Steinmaniporella kapelensis) and foraminifera (Bramkampella arabica, Everticyclammina praekelleri, Labirynthina mirabilis, Neokilianina rahonensis, Mohlerina basiliensis, Parurgonina caelinensis, Redmondoides lugeoni). This biostratigraphic interval corresponds to lithostratigraphic intervals I and II, the micropaleontological assemblages pointing to a Kimmeridgian-early Tithonian age.

The next biostratigraphic interval (B) contains the algae Clypeina parasolkani, Clypeina sulcata, Salpingoporella annulata, Selliporella neocomiensis, and the foraminifera Anchispirocyclina lusitanica, Pseudocyclammina lituus, Pseudotextulariella courtionensis and Rectocyclammina chouberti. It corresponds to the lower part of lithostratigraphic interval III, and indicate a late Tithonian-early Berriasian age.

The biostratigraphic interval C corresponds to the upper part of the lithostratigraphic interval III and contains, mainly in its uppermost part, the algae Salpingoporella praturloni and Pseudocymopolia pluricellata, and the foraminifera Coscinoconus cherchiae, C. campanellus, Everticyclammina kelleri, Haplophragmoides joukowskyi, Montsalevia salevensis, Moulladella jourdanensis, Nautiloculina broennimanni, Orbitolinidae div. sp. indet., Pfenderina cf. neocomiensis, Protopeneroplis ultragranulata, Pseudocyclammina lituus, and Scythiolina div. sp. This interval is considered of late Berriasian-earliest Valanginian in age.

The entire carbonate succession from Piatra Craiului is a prograding, shallowing upward megasequence. The identified microfossil assemblages permit separatation into three biostratigraphic intervals, but the repartition of the microfossils do not trace exactly any boundary between stages, either Kimmeridgian-Tithonian, or Tithonian-Berriasian, or Berriasian-Valanginian. More detailed studies within the Dâmbovicioara area could maybe permit a better understanding of the Jurassic-Cretaceous transition in this area.