Annales Societatis Geologorum Poloniae (2001), vol. 71: 43-51.
UPPER JURASSIC CHALKY LIMESTONES IN THE ZAKRZÓWEK HORST, KRAKÓW, KRAKÓW-WIELUŃ UPLAND (SOUTH POLAND)
Marcin KRAJEWSKI
University o f M ining and Metallurgy; Faculty o f Geology, Geophysics and Ernvironmental Protection, al. M ickiewicza 30; 30-059 Kraków, Poland; e-mail: kramar@ geolog.geol.agh.edu.pl
Krajewski, M., 2001. U pper Jurassic chalky limestones in the Zakrzów ek Horst, Kraków, K raków -W ieluń Upland (South Poland). Annales Societatis Geologorum Poloniae, 71: 43-51.
Abstract: Chalky lim estones in the Zakrzów ek H orst were laid down in sm all sponge-m icrobolite biostrom es that provided stable foundation for the growth o f extensive sponge- "Tubiphytes ” biostrom es form ing the nodular limestones in the Zakrzów ek area. The am m onites occurred in chalky limestones indicate that the studied deposits belong to the youngest palaentologically docum ented U pper Jurassic lim estones in the K raków area (Planula zone). The vertical succession o f fauna and facies characteristics indicate progressive shallow ing o f the environm ent at the end Oxfordian, from deeper shelf to shallow er water.
K ey words: Carbonate buildups, m icrofacies, background sedimentation rate, U pper Jurassic, K raków, Southern Poland.
M anuscript received 28 F e b m a iy 2000, accepted 27 M arch 2001
INTRODUCTION
Chalky limestones are present in the Kraków Upland in only a few outcrops within the small tectonic element - the Zakrzówek Horst (Figs 1, 2). The rare occurrence o f these limestones in the Kraków area is in clear contrast with the other areas o f occurrence o f Upper Jurassic rocks in Poland, where the chalky limestones are one o f the dominant litho
logical varieties.
This paper presents the description o f the lithology, fa
cies and microfacies variation o f the chalky limestones and their adjacent sediments. A n attempt is also presented at the interpretation o f the depositional environment o f the chalky limestones.
GEOLOGICAL BACKGROUND
The studied area lies in the southern part o f the K raków -W ieluń Upland and from tectonic point o f view it is a fragment o f the Carpathian Foredeep (Rutkowski, 1993). Characteristic for the area are numerous horsts built mainly o f M esozoic rocks and surrounded by a system o f faults; tectonic grabens are filled with M iocene clays (Fig.
1). The main faults in the Zakrzówek Horst are oriented SW -N E and N W -SE and have vertical displacements o f ca.
200 m (Rutkowski, 1993). Besides the main faults the pres
ent author found smaller ones near Twardowski Rocks and Księża Hill; their amplitudes are from a few to nearly
twenty metres (they are not shown in Figs 1, 2). Individual blocks between the faults are inclined at various angles, forming fault benches. So in the area o f Twardowski Rocks the strata are inclined 3-5°, in the quarries Zakrzówek and Kapelanka they are nearly horizontal, while at K sięża Hill, they dip at 20° SE (Gradziński, 1972). Moreover, Creta
ceous abrasion surface and small tectonic grabens filled with Cretaceous marls are locally present.
The Zakrzówek Horst is built mainly o f Oxfordian limestones which are up to 225 m thick. The limestones be
long to the bedded facies (Dżułyński, 1952; Gradziński, 1972) and they include numerous nodules and flat lenses of chert. Four main lithological types may be distinguished in the exposed bedded limestones: micritic, chalky, nodular and dolomite-bearing granular ones; all these types form distinctive horizons in vertical sequence and their total thickness is ca. 40 m (Fig. 3). A part o f the limestones was subject to early diagenetic dolomitization (Łaptaś, 1974) and to epigenetic silicification (M atyszkiewicz, 1987).
Chalky limestones are a subordinate lithological variety in the Kraków area, they belong to the facies variety o f the bedded limestones, hence they are scarcely reported in pub
lications (Krobicki, 1984; Matyszkiewicz, 1987, 1993).
These papers, dealing with outcrops situated within the Zakrzówek Horst, are dedicated to other topics, hence they do not include a thorough discussion o f the origin and depo
sitional environment o f the chalky limestones. The most complete description o f these outcrops is included in the pa
per by Krobicki (1984) who found that the chalky lime-
44
M. KRAJEW SKIFig. 1. Geological structure o f the studied area (after R ut
kowski, 1993, simplified)
Fig. 2. Location sketch o f the study area (names o f exposures after Szelerewicz & Górny, 1986 and Król & Barabasz, 1997)
stones occur as lenses 4.0-4.5 m thick and ca. 4 m long.
They are embedded in hard and compact bedded limestones.
They include rich fauna, mostly sponges. Numerous are also brachipods, small ammonites, casts o f pelecypods, crabs and gastropods. The bedding partly disappears within the lenses due to the nodular nature o f the limestone. Bedding is marked by horizons o f chert nodules and flat lenses. Kro- bicki (1984) distinguished three horizons o f the chalky limestones in his generalised profile and described their li- thology only in the lowest horizon. The two lowest horizons lie at the altitudes 168 and 190 m above sea level (calculated from an unpublished profile by M. Krobicki, 1984). They were exposed in the Zakrzówek Quarry which is now aban
doned and its lower part is now flooded, together with the exposures o f the two lowest horizons o f the chalky lime
stones. The highest o f the three horizons lies at an altitude o f 210-220 m and this is described here.
B H I2 O E34 E35
Fig. 3. Synthetic section o f the sediments in the Zakrzówek Horst (without the older sediments, now under water). 1 - chalky limestones; 2 - nodular limestones; 3 - dolomites; 4 - granular limestones; 5 - micritic limestones
Matyszkiewicz (1987, 1993) in short comments on the chalky limestones from Zakrzówek points to the chaotic ar
rangement o f cherts, as contrasted with their arrangement in parallel horizons in the bedded limestones. This author also suggests that the chalky limestones could correspond to lo
cal inhomogenities on the basin bottom, possibly related to the dense colonisation by benthos.
METHODS AND TERMINOLOGY
This study included field w ork and observation o f thin sections under a polarising microscope. The field work in
cluded detailed mesoscopic study, vertically and laterally, o f the chalky limestones and the compact limestones near the Jasna nad W isłą Cave (Jasna Cave in short; name after Szelerewicz & Górny, 1986; Figs 2, 4), in Ostatnia C liff (Figs 2, 5; name after Król & Barabasz, 1997) and the Zakrzówek Quarry (Fig. 2). The observations were also car
UPPER JU RASSIC CHA LKY LIM ESTONES
45
Fig. 4. Jasna Cave. The entrance is situated in chalky lime
stones passing upwards to nodular limestones; the white line shows chalky/nodular limestones boundary
ried out within the m assif in numerous caves whose total length attains ca. 1 km (A. Górny pers. commun., 1999).
Because o f the monotonous lithology o f the chalky lime
stones and the difficult access to the outcrops, the detailed descriptions are provided only for the exposure in the Jasna Cave and in Ostatnia Cliff. A tentative name “chalky lime
stone horizon” has been accepted for the chalky limestones and other sediments at the same stratigraphical level. A total o f 130 samples were collected and thin sections for micro
scopic study were made o f them. The other parts o f the stud
ied outcrops were studied in detail mesoscopically. The study included also the limestones directly below and above the chalky limestones horizon. During the laboratory study, microfacies types were described according to the classifi
cation and terminology by W right (1992) which in turn is based on that by Dunham (1962) and its later modification (Embry & Klovan, 1972).
CHALKY LIMESTONES
A total o f eight exposures o f chalky limestones have been found; four in the western, northwestern and southern walls o f abandoned and partly drowned Zakrzówek Quarry (Fig. 2), three in abandoned Kapelanka Quarry in its frag
ment known as Ostatnia Ścianka (Figs 2, 5) and one at the entrance to the Jasna Cave (Figs 2, 4). All outcrops are situ
ated at similar altitudes (210-220 m) and they make up the highest horizon o f the chalky limestones.
Jasna Cave
The cave is situated in the Twardowski Rocks park, in a wall o f an old quarry facing the Vistula River (Figs 2, 4).
The exposed chalky limestones form a lens within hard, bedded limestones. The height and width o f the lens are from a few to nearly twenty metres and its precise boundary is difficult to delineate. Laterally, the chalky limestones pass gradually into the harder, bedded limestones. They are light cream in colour; they smear fingers when touched. The bedding surfaces are not as distinct as in typical bedded
Fig. 5. Ostatnia Cliff. Lenses o f chalky limestones are present in the central part and they pass upwards to nodular limestones; the white line shows chalky/nodular lim estones boundary
limestones; they locally disappear and are marked only by the arrangement o f cherts. Some o f the cherts are arranged chaotically. M ost o f them do not exceed 8 cm in diameter.
Their nuclei often include fragments o f sponges and brachiopods. Fauna is abundant, represented mainly by sponges, brachiopods, gastropods, ammonites (see also sec
tion Stratigraphy) and belemnites. Among the brachipods the most common are Dictyothyropsis cf. loricata, Sellithy- ris sp., Lacunosella cracoviensis (Quenstedt) and Septali- phoria cf. astieriana (d’Orbigny), (M. Krobicki, pers. com
mun., 1999; cf. M uller et al., 2000). The interiors o f some brachiopod shells are not completely filled w ith sediment.
Sponges occur in life position as well as redeposited. In the lower and middle parts o f the lens they are hexactinellids with widely varying forms - from calices to narrow tubes.
The sponge diameters vary from 2 to 10 cm.
M icrofacies in the lower parts o f the lens are bound- stone and wackestone (Figs 6, 7). The boundstone is com
posed o f numerous pure clotted thrombolite (cf. Schmid, 1996; Leinfelder et al., 1996) encrusted with abundant ser- pules. Numerous growth voids and burrows are present, geopetally filled w ith internal sediment composed exclu
sively o f peloids. The voids are less than 3 mm across. Frag
ments o f siliceous sponges and echinoderm plates are also present.
W ackestone and boundstone (Figs 6, 7) predominate in the middle part o f the lens. They are strongly differentiated and are mainly pure leiolite, layered leiolite (term after Braga et al., 1995; cf. Leinfelder et al., 1996; Riding, 2000) and micritic stromatolites, developed on sponge surfaces and poorly structured thrombolites. Fragments o f siliceous sponges encrusted with serpules are also common.
In the upper parts o f the lens, hexactinellids spoges are partly replaced by lithistids sponges, densely packed in sediment. They are accompanied by nektonic fauna, mainly ammonites and belemnite fragments. The ammonites in
clude specimens 4 -1 2 cm in diameter, preserved complete or in large fragments, many o f them incompletely filled with sediment. The fossils do not display important deform a
tions. All fossils are strongly lithified and em bedded in soft sediment. The degree o f compactness o f the sediments and
46
M. KRA JEW SKIFig. 6. Thrombolitic boundstone; chalky limestones, Jasna Cave
Fig. 7. Boundstone. Siliceous sponge overgrown with microbo- lites; chalky limestones, Jasna Cave
the abundance and diversity o f fauna increase from the as
sumed centre o f the lens towards its margins.
M icrobolites are less common in the upper part o f the lens and these are mainly single pure leiolites on sponge outer surfaces. The sediment is mainly bafflestone-bound- stone and wackestone-floatstone, less commonly packstone.
The main components are fragments o f calcareous and sili
ceous sponges and “Tubiphytes ” morronensis (cf. Schmid, 1995,1996) who are up to 0.8 mm across. The other compo
nents include gastropods, echinoderms, brachiopods, Tere- bella lapilloides and numerous unidentifiable bioclasts.
Ostatnia Cliff
This exposure is situated at the western end o f the aban
doned quarry Kapelanka (Figs 2, 5). Ostatnia C liff is 20 m high and 35 m long. The chalky limestones are exposed here in yellowish lenses a few metres thick and long. They are best visible in places from w hich rocks have fallen recently.
In other places the chalky limestones are similar at surface to the typical hard, bedded limestones and only when struck with ham m er they disintegrate into soft debris. They smear fingers upon touching, but are somewhat harder then the chalky limestones from the Jasna Cave. They include cherts
Fig. 8. Boundstone-bafflestone, locally w ackestone. A frag
m ent o f siliceous sponge w ith num erous leiolites; nodular lim e
stones, O statnia C liff
Fig. 9. Boundstone micritic stromatolites. Zakrzów ek Quarry
only sporadically, and these do not exceed 6 cm in size.
Fauna is frequent but less diversified than in the Jasna Cave.
Among the mesoscopically discernible faunal com po
nents, the m ost common are lithistid sponges, less common are hexactinellide sponges, brachiopods (mainly terebratu- lids).
The microfacies is mostly wackestone and bafflestone- boundstone. The lower parts o f the lenses contain numerous poorly structured thrombolites and single pure leiolites on surfaces o f numerous tuberoids built o f fragmented sili
ceous sponges. The upper parts o f the lenses include numer
ous “Tubiphytes ” morronensis w ith diameters o f 0.8 mm and calcareous sponges, while the numbers o f leiolites and thrombolites decrease.
ENCOMPASSING SEDIMENTS OF THE CHALKY LIMESTONES
In the exposures in the Jasna Cave and in Ostatnia C liff the chalky limestones pass laterally into compact bedded limestones (Figs 4, 5) whose microfacies is wackestone.
Fauna includes small bioclasts o f undeterm ined nature and fragments o f echinoderms, brachiopods and “Tubiphytes ”
U PPER JU RASSIC CHA LKY LIM ESTONES
47
Fig. 10. W ackestone - floatstone w ith “Tubiphytes ” m orronen
sis; K sięża H ill
Fig. 11. W ackestone - floatstone w ith Lithocodium aggregatum ; Księża Hill
morronensis embedded in micritic matrix. “Tubiphytes ” morronensis occur as branching and ovate forms, 0.5-0.8 mm across. Common are siliceous sponges up to 15 cm across and poorly structured thrombolites binding the sedi
ment.
Below the chalky limestones horizon lies a horizon o f micritic limestones with scarce fauna (cf. Peszat, 1991).
They are more compact than the sediment in the chalky limestone horizon. The dom inant microfacies is wacke
stone, sporadically mudstone built o f predominant peloids, few tuberoids and less numerous boundstones, those built mainly micritic stromatolites, forming flat and dome-like forms, and o f few layered leiolites.
The micritic limestones are overlain with the described chalky limestone horizon. The proportion o f microbolites in the sediment increases in the transitional zone between the two horizons. These are m ainly poorly structured throm bo
lites, less commonly micritic stromatolites. The chalky limestone horizon is 7 m thick on average and it is distin
guished by the abundance o f benthic and nektonic fauna.
The horizon includes the chalky limestone lenses described above. The chalky limestone lenses usually pass upwards into nodular limestones (Figs 3, 8), sponge-microbolite and sponge- "Tubiphytes ” morronensis, build mostly o f sili-
Fig. 13. Floatstone - w ackestone w ith scleractinian coral (frag
m ent o f colony? pers. commun. E. M orycowa, B. K ołodziej, 2001); K sięża Hill
ceous and calcareous lithistid sponges successively over
grown upwards. M icrofacies o f the nodular limestones are mostly boundstone-bafflestone and wackestone and in most parts have the same lithology as the chalky limestones.
These limestones include common peloidal stromatolites and less common micritic ones w hich include small growth voids and poorly structured thrombolites. Common are “Tu
biphytes ” morronensis 1 mm across and Terebella lapilloi- des,brachiopods (mostly terebratulids) and numerous uni
dentifiable bioclasts.
Above the horizon o f nodular limestone lies a horizon built mainly o f stromatolites (Fig. 9) which is ca. 1 m thick in Zakrzówek Quarry. M esoscopically these are hard lim e
stones w ith conchoidal fracture, resembling micritic lim e
stones. The forms and internal structures o f these strom ato
lites differ from those described earlier from Zakrzówek. In Fig. 12. N odular biostrom es w ith colum nar stromatolites. K sięża Hill
48 M. KRA JEW SKI
Fig. 14. Ammonites collected in the Jasna Cave and used for biostratigraphy. A, B - Idoceras (Subnebrodites) sp., C - Idoceras (Subne- broidites) proteron N itzopoulos, D - O rthosphinctes sp. (imprint); (personal com m unication by B. A. M atyja, 1999). All specim ens in natural size
the Zakrzówek quarry these are micritic stromatolites with darker and lighter bands. The stromatolites are up to 10 cm thick and extend laterally up to several tens o f centimetres.
Above the “stromatolite” horizon, there appear numer
ous horizons o f grainstones (packstone-grainstone-rud- stone) which in some parts were partly or even completely dolomitized. The sediments between the grainstones are de
veloped as wackestones and floatstones with numerous
“Tubiphytes" m orronensis up to 1.2 mm across (Fig. 10), Lithocodium aggregation (Fig. 11; cf. Schmid & Leinfelder, 1996; Kołodziej, 1997), calcareous sponges, agglutinating and peloidal stromatolites. The stromatolites have columnar forms, up to 5 cm across and up to 15 cm high (Fig. 12).
Scleractinian corals (Fig. 13; fragment o f colony?; E. Mory- cowa, B. Kołodziej, pers. commun., 2001) occur sporadi
cally.
The same sediments at Księża Hill include forms re
sembling erosional channels filled w ith grainstones (rud- stone-grainstone), built mainly o f ooids and oncoids o f II and IV type (cf. Dahanayake, 1977) and intraclasts, often
with graded bedding. The grainstones are in places bound by single pure leiolites.
STRATIGRAPHY
Biostratigraphic attribution o f the studied deposits was established on the base o f ammonites collected in the Jasna Cave, i.e. in the lower part o f the Zakrzowek Horst section (Fig. 3), ca. 190-200 m above the base o f the Oxfordian.
Twenty fragments o f ammonites were collected, o f which four were determined as Orthosphinctes sp., Idoceras (Sub
nebrodites) proteron Nitzopoulos and two as Idoceras (Sub
nebrodites) sp. (Fig. 14). They indicate that the studied de
posits belong to the Planula zone, Planula subzone, proteron horizon (B. A. Matyja, pers. commun., 1999), hence these are the youngest palaeontologically documented Upper Ju
rassic deposits in the Krakow area. Taking into account the minimal sedimentation rate o f the chalky limestones and the stratigraphical condensation o f the Upper Jurassic deposits
U PPER JU RASSIC CHA LKY LIM ESTONES
49
in the Kraków area, relative to the areas o f the Upland situ
ated farther to the north, it seems likely that the deposits in the middle and upper parts o f the Zakrzówek section belong to still younger zones o f the Upper Jurassic (Krajewski &
Bajda, in press; cf. Matyszkiewicz, 1997)1.
DEPOSITIONAL ENVIRONMENT
The chalky limestones differ markedly from the sur
rounding typical compact bedded limestones. The differ
ences consist mainly in greater diversity o f benthic and nek- tonic fauna and lower compactness in the chalky lime
stones.
The described lenses o f chalky limestones were laid down as small sponge-microbolite biostromes (cf. Lein- felder et al., 1996) passing upwards into sponge biostromes (autoparabiostrome - autobiostrome; cf. Kershow, 1994;
Figs 3, 4, 5) with numerous “Tubiphytes” morronensis and microbolites, forming nodular limestones in the area o f Zakrzówek.
The environment o f deposition o f the sponge-micro
bolite biostromes remains open to discussion. The sponge- microbolite bioconstruction are usually related to deep shelf environment with minimal rate o f deposition, variable or small supply o f nutrients in the marginal parts o f the so called “reef window” (Leinfelder et al., 1996; Leinfelder &
Nose, 1999). The main components o f sediments at Zakrzó
wek are thrombolites, subordinate are stromatolites and leiolites, siliceous and calcareous sponges and “Tubi
phytes ” m orronensis.
The chalky limestones include a broad variety o f sponges. Their frequency and diversity are at maximum in the central parts o f the chalky lenses. Hexactinellids domi
nate in the lower parts o f the lenses, gradually replaced up
wards by lithistids. Calcareous sponges appear in great numbers in the upper parts. The studies in other areas indi
cate that such a sequence reflects a shallowing trend (cf.
Trammer, 1982, 1989; Leinfelder et al., 1993, 1994, 1996;
Keupp et al., 1996). The depositional environment o f the buildups made up o f hexactinellids and lithistids with thrombolites was one o f lower shelf, ca. 100 m deep (cf.
Pratt, 1995; Leinfelder et al., 1994, 1996) or deeper (cf. Pis- era, 1998).
Microbolites are common in the limestones in Zakrzówek Horst. However, they are not very useful for in
terpretation o f depositional environment. Microbolites could form at various depths, levels o f water energy, salini
ties and degrees o f aeration. The studied sediments com
monly include thrombolites and micritic stromatolites which indicate a low-energy environment with low sedi
mentation rate (cf. Keupp et a l , 1993; Leinfelder et al., 1993, 1996; Schmid, 1995, 1996; Dupraz & Strasser, 1999;
1 A fter final preparation o f the present paper an amm onite Picto- nia albinea Oppel was found at the chalky/nodular limestones boundary (cf. Figs 3, 4), w hich indicates the low erm ost Platy- nota zone (lowermost K im m erydgian; G. Schweigert, pers.
comm un., 2001). The am m onite w ill be discussed in the next publication.
Leinfelder & Schmid, 2000; Riding, 2000).
“Tubiphytes” morronensis are common in the Zakrzó
wek area in the middle and upper parts o f the section. They occur in various forms, mostly ovate, less commonly bran
ching, depending on the firmness o f substratum (cf. Schmid, 1995). The diameter o f the outer tests o f “Tubiphytes ” mor
ronensis increase in thickness upwards in the section. This indicates changes in availability o f light, related to either shallowing or decreasing turbidity (cf. Leinfelder et al., 1996; Krajewski, 2000). In the case o f the limestones ob
served at Zakrzówek both factors seem important. In the up
per parts o f the section “Tubiphytes ” morronensis often oc
cur together w ith Terebella lapilloides in the Terebella-
"Tubiphytes ” association, widely described in the literature (cf. Leinfelder et al., 1993, 1996; Schmid, 1995, 1996; Du
praz & Strasser, 1999). According to them, the occurrence o f this community in shallow w ater setting indicates poor oxygenation. The depth o f deposition o f this association was probable several tens o f metres (cf. Leinfelder et al., 1993, 1994, 1996) in a high mesotrophic environm ent (cf.
Dupraz & Strasser, 1999). In the uppermost parts o f the sec
tion at Zakrzówek “Tubiphytes” morronensis often occur together with Lithocodium aggregatum and the thickness o f the “Tubiphytes ” morronensis outer walls attains 1.2 mm, indicating low mesotrophic or oligotrophic environment o f a few to less than twenty metres deep (cf. Schmid, 1995;
Leinfelder et al., 1996; Schmid & Leinfelder, 1996; Dupraz
& Strasser, 1999; Krajewski, 2000).
CONCLUSION
The basic components and their succession indicate that in the initial stage o f formation o f the sponge-microbolite biostromes (chalky limestones), the depth was about 100 m or more, and that at the end o f their deposition the depth could be o f a few tens o f metres. The sediments found higher in the section could be laid down in an even shal
lower environment.
The occurrence o f relatively infirm sponge-microbolite biostromes (chalky limestones) beneath similar in structure but more compact sponge biostromes with numerous “Tu
biphytes” morronensis and microbiolites (nodular lime
stones) reflects a change in depositional environment. The sponge-microbolite biostromes formed on deep shelf, below the storm wave base in a low-energy environment. Sponges growing loose in sediment (cf. Trammer, 1985) did not de
velop a rigid framework typical o f carbonate buildups in the Kraków area (M atyszkiewicz & Krajewski, 1996; M atysz
kiewicz, 1997), but only an initially lithified construction.
On the other hand, the sponges in the biostromes w ith “Tu
biphytes” morronensis, growing in a shallower environ
ment, were overgrowing one another and formed a structure resistant to erosion.
Acknowledgements
The author thanks J. M atyszkiew icz and G. Haczewski for critical rem arks on the earlier drafts o f this paper, anonym ous R e
view er and B. Kołodziej for theirs suggestions, B. A. M atyja for
50
M. KRAJEW SKIdeterm ination o f the am m onites, M. G radziński and A. G órny for discussion, M. Krobicki for providing access to his M aster thesis and for discussion, E. M orycow a and B. Kołodziej for determina- toion o f the coral and M. K uśm ierek and T. Bartuś for assistance in material collection. This w ork w as funded as AGH project 11.140.54.
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S tre sz c z e n ie
GÓRNOJURAJSKIE WAPIENIE KREDOWATE ZRĘBU ZAKRZÓWKA W KRAKOWIE, WYŻYNA
KRAKOWSKO-WIELUŃSKA, POŁUDNIOWA POLSKA
Marcin Krajewski
W p racy p rzed staw io n o w y n ik i b ad ań g ó m o ju ra jsk ich w a pien i k red o w aty ch zręb u Z a k rz ó w k a (Fig. 1, 2, 3). S zczeg ó ło w e b a d an ia m ak ro sk o p o w e, m ik ro fa cja ln e o b jęły d w a stanow iska.
P ierw sze stan o w isk o zn ajd u je się w otw o rze Jask in i Jasnej nad W is łą (w sk ró cie Jasnej; F ig. 2, 4). D ru g ie sta n o w isk o zn ajd u je się w e frag m en cie ściany o n a zw ie O sta tn ia Ś cian k a (Fig. 2, 5). B ad a
n ia p rz ep ro w a d z o n e zo stały ró w n ie ż w o sad ach są siad u jący ch z w ap ien iam i kredow atym i.
S traty g rafia zo stała u sta lo n a n a p o d staw ie a m o n itó w z eb ra n y ch w niższej części p ro filu Z a k rz ó w k a (Fig. 3) w ja s k in i Jasnej w sk azu jący ch n a p rzy n ależn o ść w a p ien i k re d o w aty c h do p o z io m u P lan u la, p o d p o z io m u P la n u la h o ry zo n tu P roteron (Fig. 14; inf.
u stn a B. A. M aty ja, 1999).
W Jask in i Jasnej (Fig. 2, 4 ) o d słan iające się w a p ien ie kredo- w ate tw o rz ą so czew k ę w ś ró d tw a rd y ch ty p o w y ch w ap ien i uław i- conych. L iczn ie w y stęp u je fau n a, g łó w n ie gąbki, ram ien io n o g i, ślim aki, o raz a m o n ity i b elem n ity . W d o ln y ch i śro d k o w y ch p a r
tiach w ap ien i k red o w aty ch o b se rw u je się H e x ac tin ellid a w y k a zu ją c e d u że zró żn ico w an ie w m o rfo lo g ii od form w k ształcie k ie li
ch ó w d o fo rm w k ształcie w ą sk ic h rurek. W w y ższy ch p artiach so czew k i H ex actin ellid a z a stęp o w an e s ą p rz ez L ith istid a. W sz y st
k ie sk am ien iało ści s ą silnie z lity fik o w an e i tk w ią w m ięk k im kre- d o w aty m o sadzie.
P o d w z g lęd e m m ik ro fa cja ln y m d o ln e p artie so cz ew k i w y k ształco n e s ą ja k o b io lity ty (b o u n d sto n e ) o raz w aki (w ackestone).
W śro d k o w y ch partiach so c z ew k i d o m in u ją w ak i (w ack esto n e) o raz b io lity ty (boun d sto n e; F ig. 6, 7). W g ó rn y ch p a rtiac h so czew k i o sa d w y k ształco n y je s t g łó w n ie ja k o b io lity t ( bafflestone- b o u n d sto n e) o raz w aki (w ack esto n e-flo atsto n e), rzadziej ja k o
m ik ry to w y z ia m it (packstone).
N a O statniej Ś cian ce (Fig. 2, 5) najczęściej o b serw u je się gąbki z ro d z aju L ith istid a rzadziej H ex actin ellid a, ra m ien io n o g i głó w n ie tereb ratu le. P od w zg lęd em m ik ro facjaln y m w y k szta łco n e s ą ja k o w ak i (w ack esto n e), o raz b io lity ty (b a fflesto n e-b o u n d - stone).
L ateraln ie w a p ien ie kred o w ate p rz e c h o d z ą p ły n n ie w zw ięzłe w ap ien ie u ław ico n e (Fig. 4, 5). K u g órze n ajczęściej so czew k i w a p ien i k red o w aty ch ja k i inne w ap ien ie z teg o p o z io m u z astę p o w a n e s ą p rzez g ru z ło w ate w ap ien ie g ą b k o w o -tu b ip h y teso w e z b u d o w an e g łó w n ie z g ąb ek k rzem io n k o w y ch i w ap ien n y ch L ith istid a (b o u n d sto n e - b afflesto n e - w ack esto n e; F ig. 8) i w w ię k sz o ści p a r
tii w y k a z u ją p o d o b n e w y k ształcen ie stru k tu raln e ja k w a p ie n ie k re do w ate. P onad w ap ien iam i g ru zło w aty m i w y stęp u je p o z io m z b u d o w a n y g łó w n ie ze stro m ato litó w (Fig. 9) o raz p o z io m z ia m itó w (p ack sto n e -g rain sto n e - ru dstone; F ig. 3), k tó re w p e w n y c h p a r
tiach u leg ły częścio w ej b ą d ź całkow itej d o lo m ity zacji. P o m ięd z y zia m itam i o sa d y w y k szta łco n e są ja k o w aki (w a c k e sto n e -flo a t
stone) z “Tubiphytes ” morronensis i Lithocodium aggregatum (cf.
S chm id, 1995; S ch m id & L ein feld e r, 1996; K oło d ziej, 1997; Fig.
10,11).
N a p o d sta w ie p rz ep ro w a d z o n y ch b ad a ń stw ierd zo n o , iż o p i
sy w an e so czew k i w ap ien i k re d o w aty ch s ą to niew ielk ie b io stro m y g ą b k o w o -m ik ro b o lito w e (por. L ein feld e r et al., 1996) p rz e c h o dzące k u g ó rze w b io stro m y (por. K ersh o w , 1994; F ig. 3) g ąb k o w e z liczn y m i “Tubiphytes ” morronensis i m ik ro b o litam i tw o rzący m i w rejo n ie Z ak rz ó w k a w ap ien ie gru zło w ate.
D y sk u sy jn y m p ro b lem em je s t śro d o w isk o sed y m en tacji bio s- trom g ąb k o w o -m ik ro b ialn y ch i b io stro m g ą b k o w y ch z “Tubi
phytes ” morronensis w k tó ry c h g łó w n y m i k o m p o n en tam i s ą tro m - bo lity , rzadziej stro m ato lity i leiolity, g ąbki k rzem io n k o w e o raz w a p ien n e i “Tubiphytes" morronensis. B io rąc p o d u w a g ę sukcesję fauny o raz n ie w ie lk ą m iąż szo ść w a p ien i k red o w aty ch , m o żn a stw ierd zić, iż śro d o w isk o sed y m en tacji w a p ie n i u leg a ło zm ian o m , któ re b y ły zw iązan e ze sp ły can iem z b io rn ik a n a p rz eło m ie Oks
fo rd u i kim ery d u . P o d staw o w e k o m p o n en ty i ich następ stw o w sk azu je iż, w p o czątk o w ej fazie tw o rzen ia się w a p ien i k re d o w a ty ch g łęb o k o ść w y n o siła o k oło 100 m lub głębiej, a p o d koniec ich sed y m en tacji m o g ła w y n o sić o k o ło k ilk u d ziesięciu m etrów .
R ó żn ice w z w ięzło ści po d o b n ie w y k szta łc o n y ch k red o w aty ch b io stro m g ą b k o w o -m ik ro b o lito w y ch i g ąb k o w y ch b io stro m gruz- ło w a ty c h z “T ubiphytes’’ m orronensis p ra w d o p o d o b n ie m o g ą o d z w iercie d lać zm ian ę w aru n k ó w śro d o w isk o w y ch . B io stro m y k red o w ate ro z w ija ły się w g łęb szy m szelfie p oniżej sztorm ow ej p o d sta w y fa lo w an ia w śro d o w isk u sp o k o jn y m . G ąbki tk w iąc w stanie lu źn y m z ag łęb io n e w o sad zie (por. T ram m er, 1985) nie ro zw in ęły sztyw nej ko n stru k cji typow ej d la b u d o w li w ę g la n o w y ch a je d y n ie k o n stru k cję in icjaln ie zlity fik o w an ą. N a to m iast g ąbki b io stro m g ru zło w aty ch ro z w ijające się w śro d o w isk u p ły t
szym n arasta ły ko lejn o na sobie i tw o rzy ły z w ię z łą k o nstrukcję.
