Wiek terygenicznych osadów jurajskich Lubelszczyzny a występowanie niektórych gatunków megaspor

Abstract

Przedstawiono, obserwacje dotyczące występowania kilku gatunków megaspor w terygenicznych osadach jury centralnej i wschodniej Lubelszczyzny. Wskazano na współwystępowanie tych gatunków spor z górnojurajską fauną, co rozszerza zasięg stratygraficzny dotąd dla nich przyjmowany. Nie mogą więc one stanowić obecnie podstawy szczegółowszego podziału stratygraficznego osadów. Omówiono również inne wskaźniki wiekowe terygenicznych osadów zawierających omawiane megaspory.

ON THE AGE OF TERRIGENOUS JURASSIC ROCKS IN THE LUBLIN REGION AND DISTRIBUTION OF SOME MEGASPORE SPECIES

In the Jurassic section of the Lublin region. there are known gray and brittle terrigenous rocks with carbonized flora, rhizoids, coal dust and detritus of mesophytic and Carboniferous coals. The rocks were differentiated as the Zakrzew Formation and dated at the Oxfordian (Figs. 1-6). They yield megaspores hitherto known from the Lower and Middle Jurassic. In the case of the borehole columns Chełm IG 1 and Dorohucza IG 1 (Fig. 2), the records of such megaspores gave the basis for some authors to assign the deposits to the Lias (H. Makowski, 1960; J. Głazek et aI., 1975).

New drillings made in that region, Grabowiec IG 3 and Grabowiec IG 1 (see Fig. 3), cast some light on stratigraphic ranges of several megaspore species. In first of these boreholes, the Jurassic section comprises deposits of the Tyszowce Formation and Ruda Lubycka Formation. In the former, there were recorded Trileites murrayi (H a r r i s) M a r c I n k i e w i c z, Minerisporites richardsoni (M u r r a y) P o t o n i e, Bacutrileites onodios (H a r r i s) M a r c I n k i e w i c z  and fragments of Horstisporites sp. (Tables I-III). The megaspores are accompanied in that formation by gastropods Nerinea acreon d' 0 r b I g n y , Nerinea cf. jeanjeani R o e m e r, Cosmannea cf. desvoidyi (d' 0 r b I g n y), Ptygmatis bruntrutana (T h u r m an n), Isognomon promytiloides A r k e l l, Nerinea sp. and Pseudonerinea sp. (L. Karczewski, 1979) and fairly numerous foraminifers and ostracods Trocholina nodulosa S e i b o I d, Haplophragmoides canui C u s h m a n, Pseudocyclammina jaccardi S c h r o d t; Quinqueloculina jurassica B i e l e c k a  et  S t y k, Cytherella suprajurassica 0 e r t I i and others of minor stratigraphic value (W. Bielecka. 1979a; see also Fig. 3).

In·the borehole column Grabowiec IG 1, the equivalents of rocks of the Tyszowce Formation are those described as the Albertów Formation (Fig. 3). They are represented by gray quartz sandstones very rich in dispersed coal matter, yielding floral remains, rhizoids and traces of activity of benthic burrowers, and displaying thin intercalations of mesophytic coals. The megaspore assemblage recorded here is very close to that from the borehole Grabowiec IG 3 (Fig. 3). In the borehole column Grabowiec IG 1, terrigenous rocks of that formation , rest on micritic and, locally, organodetrital limestones of the Jasieniec Formation, yielding foraminifers and ostracods Pseudocyclammina jaccardi (S c h r o d t), Schuleridea triebeli (S t e g h a us), Protocytheropteron purum (S c h m I d t), Discorbis subspeciosus B o g d a n o v i c h  et  M a k a r i e v a, Verneuilinoides anglicus (C u s h m a n) (see W. Bielecka, 1979b). The foraminifers clearly evidence Oxfordian (Upper Jurassic) age of the limestones. Therefore, they indirectly indicate Oxfordian age of megaspore-bearing rocks of the Albertów Formation.

The data supplied by the two boreholes clearly evidence the occurrence of megaspores hitherto known from the Lower and Middle Jurassic in Upper Jurassic rocks. This makes it possible to state that stratigraphic ranges of the megaspores are markedly broader than previously assumed, comprising the Lower, Middle and Upper Jurassic. The studied megaspore-bearing terrigenous rocks of the Zakrzew, Formation are dated on the basis of foraminifers but the dating is further supported by the results of lithofacies analysis of Jurassic strata in that region.