Nowe dane na temat stratygrafii pogranicza jury i kredy w Polsce centralnej (Kujawy)

Abstract

Konfrontacja najnowszych wyników badań stratygraficzno-paleontologicznych pogranicza jury i kredy medyterańskiej oraz borealnej narzuciła konieczność ponownej analizy mikro- i makrofauny górnego wołgu i riazania w Polsce oraz modyfikacji podziałów stratygraficznych tych jednostek. W świetle powtórnie przeanalizowanych amonitów, morski riazań Kujaw został podzielony na warstwy z Riazanites, Himalayites i Picteticeras oraz warstwy z Surites, Euthymiceras i Neocosmoceras.

NEW VIEWS ON STRATIGRAPHY OF THE JURASSIC-CRETACEOUS BOUNDARY IN CENTRAL POLAND (KUJAWY)

Comparison of the latest results from stratigraphical-palaeontologic and palaeogeographic investigations on the boundary of Jurassic and Mediterranean and Boreal Cratceous caused the necessity of reiterated analysis of micro·and macrofauna of Upper Volgian and Riasanian and modification of stratigraphic division of these units in Poland.

Microfauna, specially ostracods were examinated reiteratedly by J. Sztejn, and macrofauna, particularly Ammonites describes mainly by S. Marek and A. Raczyńska (S. Marek, 1961. 1967; A. Raczyńska, 1967. 1971) were analysed reiteratedly by M. Rajska (S. Marek et al., 1984). A part of collection of the Riasanian Ammonites in Kujawy was analysed by international team of scientifics during the Ammonite Colloquium held in the Caucasus (Elbrus) in 1987 as the meeting of the Working Group on the Jurassic-Cretaceous Boundary attached to lUGS.

The Purbeck fades deposits, occurring over the Middle Volgian beds with Virgatites virgatus (Michalski) and covered by deposits with Riasanites rjasanensis (Nikitin), were divided into 6 ostracod zones (from F to A).

The deposits representing English formation of Lulworth (A.A. Morter, 1984) were correlated with the Cypridea dunkeri Zone (Zones F. E and D) and the Cypridea granulosa Zone (Zones C, B and A). Zones F, E and D represents the brakish and hyperhaline environment. Zones C and B - the brakish and fresh water and Zone A - the marine-brakish environment. The ostracod Zone A characterizing the first Berriasian sea of Tethys is at last partly age homologue of the jacobil grandis and occitanica Zones in south-eastern France, the jacobi and andrussowi Zones in south-eastern Spain and the jacobi and occitanica Zones in the Crimea and Caucasus. It may not be expelled the supposition that the Ostracod Zone A is also coeval with the lower zones of boreal Berriasian, e.i. the runctoni Zone in England and the sibericus/maynci Zones in Ural, Siberia and Caucasus.

The marine Riasanian in Kujawy, with beds of Riasanites, Himalayites and Picteticeras (in the bonom) and with Surites, Euthymiceras and Neocosmoceras (in the top) correlates best with the boissieri Zone, particularly with the paramimounum/picteti Subzones in the Mediterranean Province. with the euthymi and rjasanesis Zones in the Submediterranean Province and with the rjasanensis and spasskensis Zones of the subareaI Riasanian in the Russian Platform. Correlation with typical profiles of boreal Berriasian is susceptible or various interpretations. The beds of Riasanites, Himalayites and Picteticers may correlate under some corrections with a wide spread kochi Zone.

In the Riasanian Ammonites complex in Kujawy, besides species of Riasanites, dominates the Mediterranean species or Himalayites, Berriasella (Picteticeras), Beriassella (Beriasella). Pseudosubplanites (HegaratelIa), Neocosmoceras and Euthymiceras. The boreal Ammonites are represented by a few species reckoned to Surites, Surites (Caseyiceras) and Subcraspedites (Borealites). Ammonite fauna is of submediterranean type - which means domination of the Tethys influence. Probably there also existed the complex migration ways of Ammonites from the Atlantic (already open then).