Mesozoic Dasycladaceae from Romania: Distribution and biostratigraphical importance

Abstract

Dasycladaceae are important indexfossils in Mesozoic shallow-water limestones of Romania. A critical survey of the dasycladacean associations known from the Romanian Middle and Upper Triassic and from the Upper Jurassic-Lower Cretaceous is given. Triassic Dasycladaceae are known from the Apuseni Mountains (Padurea Craiului Mountains and Vascau Plateau). Eastern Carpathians (Rarau, Persani and Brasov), Southern Carpathians (Resita-Moldova Noua Zone), and Northern Dobrogea (Tulcea Zone). A biostratigraphical zonation is possible in the Upper Pelsonian and Lower Illyrian, as well as in the Upper Illyrian and Ladinian and Lower Carnian. No algae are known from the Middle Illyrian. The best information on the sequence of the coenozones can be taken from the sections in the Padurea Craiului Mountains (Fig. 2). A facies model of the Triassic Bihor carbonate platform (Fig. 4) shows a shifting of the facies zones during the Lower and Middle Triassic from continental and supratidal to intertidal and subtidal environments, which are characterized by shallow lagoons with various dasycladacean assemblages and small patch reefs built by sphinctozoan sponges on the inner slope of the lagoons. Upper Jurassic and Lower Cretaceous Dasycladaceae are known from the Eastern and Southern Carpathians, from the Apuseni Mountains, the Moesian Platform, and from the Southern Dobrogea. Several assemblage zones, defined by dasycladacean algae and foraminifera, characterize the Tithonian to Lower Aptian time intervall in the Eastern Carpathians (see Fig. 8). In the Southern Carpathians Dasycladaceae are known from the Tithonian to the Upper Aptian except from the Hauterivian. In the Apuseni Mountains Valanginian and Hauterivian dasyclads are lacking because of the discordant superposition of Tithonian reef limestones by Barremian and Aptian limestones. The Tithonian, Necomian and the Barremian to Lower Aptian is known from wells in the eastern part of the Moesian platform. Berriasian to Lower Aptian algal zones have been recognized in Southern Dobrogea.