U twory jurajskie wschodniej części Podlasia

Abstract

Utwory jurajskie wschodniej części obniżenia podlaskie, reprezentowane są przez klastyczne i węglanowe osady batonu i keloweju oraz węglanowe osady dolne., i środkowego oksfordu. Prom jurajski rozpoczyna bądź transgresywny zlepieniec kwarcowy, bądź też piaskowiec gruboziarnisty. Na granicy jury środkowej i górnej w wielu otworach zanotowano występowanie warstwy bulastej, zawierającej amonity keloweju i dolnego oksfordu. Wyższe od środkowego oksfordu ogniwa jury na omawianym obszarze nie występują. Na erozyjnej powierzchni formacji koralowcowej leży alb środkowy.

JURASSIC ROCKS IN EASTERN PODLASIE

Jurassic rocks rest on the Triassic in western part of the Bielsk Podlaski region and on various links of the Paleozoic in the eastern. Jurassic transgression comprised this area in the Bathonian. Jurassic section usually begins with transgressive conglomerate or conglomeratic sandstone with fauna represented by pseudomonotids and other bivalves, overlain by chlorite sandstones, siltstones or clay shales with remains of bivalves and assemblage of Bathonian ostracodes and foraminifers. The sea retreated in the Early Callovian to come back in the Late Callovian. The Upper Callovian is represented by rocks with characteristic oolitic structure and Callovian foraminifer assemblage: Nodular layer with ammonites of the Kosmoceras and Quenstedtoceras zones originated in the latest Callovian and earliest Oxfordian.The Middle Jurassic is from 0 to 40 m thick and most probably it does not pass beyond the state boundary in this area. The extent of Upper Jurassic rocks is somewhat greater as they occur in a belt about 80 km wide in part of the westem Byelorussia, adjoining Poland Lower part of the Upper Jurassic is represented by organodetrital spongy limestones with cherts, identical as those from the margins of the Góry Świętokrzyskie Mts and a larger part of the Polish Lowlands, and differentiated here as the Kraśnik Formation. Lower parts of that Formation are characterized by the presence of Lower Oxfordian ammonites ofl the genera Quenstedtoceras and Cardiocerar as well as typical foraminifers. Overlaying rocks yield generically identifiable brachiopods and bivalves and fairly rich foraminifer assemblage but not ammonites. The Kraśnik Formation is overlain by the Coral Formation. Coral limestones forming the latter display near-red structures. They yield numerous colonial and solitary corals and accompanying bryozoans, serpulids, thin-shelled bivalves and brachiopods. Top surface of rocks of that Formation is erosional and overlain by Cretaceous rocks. At present, Upper Jurassic is 60 to 125 m thick in this area.

The character of fauna shows that the Bielsk Podlaski region, similarly as the major part of the Polish Lowlands, belonged to the Boreal zoogeographic province.