Sedimentary environments of the Middle Jurassic epicontinental deposits from the central part of the Polish Basin (Kuiavian Region)

• Autorzy: Feldman-Olszewska A.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

The Polish Basin was the eastern part of the Jurassic European epicontinental basin. The zone of maximum thickness of the Middle Jurassic deposits runs along the so called Mid-Polish Trough which extends from the West Pomerania (NW) to the Holy Cross Mountains (SE), generally along the Teisseyre-Tornquist Zone. The complete litological profile of the Middle Jurassic deposits exceeds 1100 m in the depocentre of the Mid-Polish Trough (in the Kuiavian Region). Sediments are represented by sandstones, mudstones, heteroliths and claystones with intercalations of siderites, dolomites and coquina beds. Subordinately, crinoidal limestones, arenaceous limestones, gaizes and oolitic ironstones occur. Sedimentological studies were based on investigation of cores from ten deep boreholes. Nineteen lithofacies were distinguished: black shales, massive mudstones, bioturbated mudstones, lenticular bedded mudstones, heteroliths, wavy bedded sandstones, flaser bedded sandstones, sandstones with clay drapes, structureless sandstones (massive and bioturbated), parallel bedded sandstones, cross bedded sandstones, HCS (hummocky cross stratification) cross bedded sandstones, ripple bedded sandstones, herringbone cross bedded sandstones, chamosite sandstones, calcareous sandstones and arenaceous limestones, crinoidal limestones, conglomerates, condensed bed. Additionally, 15 ichnogenera of trace fossils: Asterosoma isp., Bergaueria isp., Chondrites isp., Diplocraterion isp., Gyrochorte isp., Lockeia isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rosselia isp., Skolithos isp., (?)Spongeliomorpha isp., Teichichnus isp., Terebellina isp. and Thalassinoides isp. were recognized in the Middle Jurassic deposits of Kuiavian Region. They point to sedimentation in the transition zone - foreshore environments. Based on the geochemical and palaeoecological investigations, four biofacies connected with different oxygenation of the bottom waters during sedimentation of the black shales have been proposed. The Upper Aalenian - Lower Bajocian deposits represent clayey sedimentation which occurred in dysoxic to anoxic environment. On the other hand, the Upper Bajocian - Lower Bathonian deposits represent dysoxic to oxic conditions. Sedimentation of the Middle Jurassic deposits in the central part of the Polish Basin took place in the shallow epicontinental sea, in environment spanning offshore to foreshore zones of a shallow siliciclastic shelf. Precise sedimentological studies point that the Middle Jurassic succession can be divided into 8 transgressive-regressive cycles. The oldest (Lower Aalenian) one begins with estuarine/foreshore sediments, sharply covered with offshore black shale facies. The Upper Aalenian, Bajocian and Lower Bathonian cycles are built of the transgressive offshore black shales and progradational regressive successions composed of mudstones and heteroliths and topped by shallow or middle shoreface sandstones. The Middle and Upper Bathonian cycles begin with transition zone sediments or lower shoreface deposits. The uppermost part of these cycles are built of sandstones and limestones representing the upper shoreface, foreshore and lagoon environments. The transgressive part of the last (Callovian) cycle is documented by carbonate-siliciclastic shoreface deposits which pass upwards into limestones of the Upper Jurassic. At the boundary between the Middle and the Upper Jurassic a condensed bed occurs.

Słowa kluczowe

EN

Middle Jurassic; sedimentary environments; offshore; shoreface; foreshore; black shales; heteroliths; sandstones; trace fossils

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 86--86

Twórcy

autor

Feldman-Olszewska A.

• Polish Geological Institute, ul. Rakowiecka 4, PL-00975 Warszawa, Poland,