Biostratygrafia otwornicowa aalenu i bajosu na Kujawach

Abstract

Opracowano mikrofaunę aalenu i bajosu rejonu Gałkówka, Łęczycy i Gostynina na Kujawach. Wyróżniono 61 gatunków otwornic w tym 2 nowe. Analiza pionowych zasięgów poszczególnych gatunków pozwala na wyraźne wyodrębnienie 2 zespołów otwornicowych: aaleńskiego i górnobajoskiego. W bajosie dolnym zespół otwornic jest ubogi i nieliczny. Wszystkie zbadane gatunki otwornic należą do form bentonicznych. W dolnych partiach profilu przeważają otwornice o skorupkach zlepieńcowatych, a w górnych – wapiennych.FORAMINIFER BIOSTRATIGRAPHY OF THE AALENIAN AND BAJOCIAN IN KUJAWY The paper presents the results of studies on microfauna in lower parts of the Middle Jurassic, i.e. Aalenian and Bajocian. The micropaleontological analyses covered major borehole columns from central part of the Kujawy region (Fig. 1). The microfauna was found to be the richest in the Gałkówek area (Table 1), somewhat less rich in the Łęczyca area (Table 2). and the poorest in thw Gostynin area (Table 3). There were identified 61 foraminifer species, including two new: Pelosina saccula sp. n. and Valvulina calikowskae sp. n. The analysis of stratigraphic ranges of individual foraminifer species from the Aalenian and Bajocian made it possible to differentiate some assemblages of guide and characteristic species for lower members of the Middle Jurassic. Foraminifer assemblages of the Aalenian and Upper Bajocian (Kuiavian) are coherent and highly characteristic whereas the Lower Bajocian assemblage is impoverished in number of individuals and taxa. All the studied foraminifer species are benthic. Foraminifers with agglutinated tests predominate in lower parts of the section and those with calcareous tests - in the upper. The Aalenian is characterized by the presence of Ammodiscus glumaceus G e r k e  et  S o s s i p a t r o v a, Reinholdelfa dreheri (B a r t e n s t e in), Marginulina parasimplex (T e r q u e m), Dentalina subtenuicollis F r a n k e, Verneuilinoides liasinus (T e r q u e m), Astacolus reticulatus (S c h w a g e r), and Astrocolus varians (F r a n k e). Stratigraphically more important foraminifer species of the Upper Bajocian assemblage include Astracolus volubilis D a i n, Epistomina costifera T e r q u e r m, Reinholdella quadrilobata (K a p t a r e n k o-C h e r n o u s o v a), Garantella ornata (H o f k e r), and Planularia eugenii T e r q u e m. Middle and upper parts of the Upper Bajocian are characterized by the presence of Palaeomiliolina rawienis (P a z d r o), Ophthalmidium carinatum P a z d r o, O. carinatum porai P a z d r o. Ammopalmula infrajurensis T e r q u e m, Astacolus kujavianus K o p i k, Planularia polymorpha arachne K o p i k and Ichtyolaria nymha Ko p i k. In the studied area. Lenticulina daphne B i e I e c k a  et  S t y k was found in middle part of the Upper Bajocian only, and Valvulina calikowskae sp. n. and Ammovertella plicata (T e r q u e m) - in upper part of the Upper Bajocian. Some Bathonian foraminifer species were locally found to appear for the first time already in top part of the Upper Bajocian. This is the case of Reinholdella crebra P a z d r o and Palaeomiliolina czestochowiensis (P a z d r o). P a I eo n t o log i c a I  d e s c r i p t I o n sForaminiferidaFamilia Saccamminidae B r a d y, 1884Genus Pelosina Brady, 1879Pelosina saccula sp. n.(Table I, Fig. 4)H o l o t y p u s: Table I. Fig. 4. S t r a t u m  t y p i c u m: Upper Bajocian. L o c u s  t y p i c u s: borehole Gałkówek H6, depth 136.1 m. D e r i v a t I o  n o m i n i s: From Latin saccullus - sack. D i a g n o s i s: Test sack-like in appearance, unichambered. M a t e r i a I: Twelve specimens, usually somewhat squeezed from two sides.D i m e n s i o n s in mm:MUZ IGno. 5706/80/Fno. 5707/80/Fno. (holotype) 5708/80/FLength0.270.390.63Width0.230.340.45Thickness0.100.180.14D e s c r i p t i o n. Test somewhat flattened from two sides, unichambered, more or less ovate in outline, sack-like in shape; upper part slightly protruding. with ending similar to short neck. Aperture ovate: test wall very fine-grained, with siliceous cement. Surface somewhat rough. O c c u r r e n c e: Poland, Kujawy-Aalenian - Upper Bajocian. Familia Ataxophragmiidae S c h w a g e r, 1877Genus Valvulina d' 0 r b i g n y, 1826Valvulina calikowskae sp. n.(Table I, Fig. 20a, b)H o I o t y p us: Table I, Fig. 20a, b. S t r a t u m  t y p i c u m: Upper part of the Upper Bajocian. L o c u s  t y p I c u s: borehole Gałkówek H 23, depth 104.0 m. D e r i v a t i o  n o m i n i s: In honour of geologist Dr. K. Dayczak-Calikowska. D i a g n o s i s: Triserial test, low-conical in shape, with concave ventral surface. Chambers arranged in 3 - 31/2 whorls, each of them consists of three chambers. Sutures distinct at dorsal side, indistinct at the ventral. M a t e r i a I: Thirty specimens, some of which are partly flattened. Dimensions in mm:MUZ IGno. 5738/80/Fno. 5739/80/Fno. (holotype) 5740/80/FLarger diameter0.480.500.54Smaller diameter0.450.480.52Height of cone0.140.210.10D e s c r i p t i o n. Test low-conical in shape, triserial, subcircular in outline. Outer margin sharp. Dorsal side weakly convex, displaying 9 - 11 chambers arranged in 3 -31/2 whorls. Protoculus small, spherical; subsequent chambers initially trapezoidal in shape and later more elongate, with shape close to a section of circle. Spiral sutures depressed; sutures between chambers weakly depressed. Ventral side somewhat concave, with the last three chambers weakly marked and septal suture poorly visible. Aperture located at inner margin of the last chamber, poorly visible. Test wall fine-grained, somewhat rough. O c c u r re n c e: Poland, Kujawy - upper part of the Upper Bajocian.