BIOSTRATIGRAPHICAL STUDY OF LOWER CRETACEOUS KA [ AJINA RIVER BEDS AND ITS IMPORTANCE FOR GEOLOGY OF NE SERBIA by

This article presents results of detailed palynological study in the Lower Cretaceous Ka{ajina River Beds (Kloko~evac, NE Serbia) and its importance for the geology of NE Serbia. On the basis of the biostratigraphic analysis of fossil spores, pollen grains and dinoflagellates, investigated beds are most probably of Lower Cretaceous age (mainly Valanginian‡Hauterivian). The paleoecological results suggest humid and subtropical conditions in the hinterland.


INTRODUCTION
A set of particular rock beds lie by the Sinaia Beds of the South Carpathians and northeastern Serbia, known as the Azuga Beds in Romania (Codarcea et al., 1961) and as the Ka{ajina River Beds in Serbia (Grubi}, 1962; Fig. 1).In lower part of geological column are dark tabular to thin ‡bedded siltstones with numerous manganese concretions, and topped by red and green shales, usually rich in silica.These shales locally contain the diabase lenses and their tuffs; in Romania, the schistose serpentinite tectonic lenses occur.This part of the column contains also cross ‡laminated silicified limestones, greenish and grayish marls and silicified limestones, laminated grayish marls and fine ‡grained micaceous sandstones.These rocks in alternations, however, do not have the features of sequences characteristic for the flysch.The Ka{ajina River Beds of northeastern Serbia are always found beneath the earliest Sinaia Flysch (Grubi} et al., 1997); this position is not quite evident in the Romanian South Carpathians where, deformed by folding and imbrication, these beds apparently occur in lower and middle parts of the Sinaia Beds (Codarcea et al., 1961).
Using aptychus remains, the Azuga Beds of Romania are dated Tithonian (Staniou, 1978).All efforts to find the characteristic fossils in these beds, since 1957, in NE Serbia, have failed and only some undeterminable radiolarians were found so far.
However, a rich paleopalynological association has been found recently in Serbia, a preliminary study of which is reported by the authors of this contribution (Grubi} et al., 1998).
The Ka{ajina River Beds of NE Serbia form thin, partly discontinuous zones in the Kosovica subzone, and in eastern and western Miro~ Zones.Incidentally, fossil material has been found only in from which samples for micropaleontological study were collected, is located in a Kloko~evac ‡Negotin road cutting at the foot of Kolje hill (Figs. 2, 3).
On the basis of the biostratigraphic analysis of fossil spores, pollen grains and dinoflagellates, investigated beds are most probably of Lower Cretaceous age (mainly Valanginian ‡Hauterivian).The paleoecological results sugest humid and subtropical conditions in the hinterland.

Methods and aims
The palynomorphs was observed on isolated kerogen concentrate from different rock samples with the classical 30% HCl, (removal of carbonate) and 38% HF (removal of silicate) treatments.Therefore HCl was used in order to disolve the silicia gel forming during the HF silicate reaction.The total residue was submitted by separation (ZnCl 2 ; d=1.9 ‡2.0 g/cm 3 ).Occasionally separated kerogen concentrate was also submitted to conditional acetolysis and oxidation (NaCl+HNO 3 ; KClO 3 +HNO 3 ; staining efect on exines; Ercegovac, 1990).Some of the most significant and good preserved palynomorph are illustrated on the Plates I ‡IV.General characters of presented palynomorph association can be described as follows:

BIOSTRATIGRAPHIC CHARACTER OF PALYNOMORPH ASSOCIATIONS
Trilete levigate spores as Cyathidites and Deltoidosporites (fam.Cyatheaceae and Dicksoniaceae) in the investigated samples are sporadic.The same refers to species of the genera Todisporites, Matonisporites and Osmundacidites, indicating a notable reduction in Jurassic floral elements (pteridophyte spores).A particularity of the association is the presence of Cingutriletes and Converrucosisporites-type spores, and of concave spores (Concavisporites variverrucatus) that are common in Upper Jurassic of England and Scotland (Couper, 1958).Spores of Contignisporites-type -common elements of the Upper Jurassic microflora -are found sporadically.
Few Trilites spores are found in samples from the Ka{ajina River Beds. Döring (1966) mentions their relatively common presence in Lower Cretaceous rocks of Germany (Wealden).
Palynomorph associations changed much in composition during the Valanginian: Classopollis ‡like pollen was much reduced; representatives of Platysacus and spores of Rogalskaisporites disappeared.The species Appendicisporites jansonii, A. tricornitatus and others are found at the base of Valanginian unit.The appearance of Pilosisporites verus and P. trichopapillosus spores (Lygodium) is also associated with the Valanginian.Note that the these spores are not found in the Ka{ajina River Beds sediments.
Relatively frequent in the association are the canaliculate species Cicatricosisporites subrotundus, C. angustus, C. australiensis, C. brevilaesuratus, C. cf. dorogensis, C. cf. claricanalis, C. cf. venustus and Appendicisporites tricornitatus, A. tricuspidatus, A. cf. problematicus, A. potomaceous, whose incidence is significant in Lower Cretaceous of Europe and Russia. Vakhrameev & Doludenko (1976) believe that the Berriasian was characterized by the occurrence of striate (canaliculate) spores of the type Cicatricosisporites, whereas in the Indo ‡European paleofloral province the genus Appendicisporites occurs in the Lower Cretaceous (Valanginian).Pocock (1967Pocock ( , 1980) ) studies sedimentary rocks at the Jurassic ‡Cretaceous boundary and interprets the appearance of Cicatricosisporites and Arcellites as an indication of the Lower Cretaceous.
Monosulcate pollen grains of Ginkgoales, Cycadales and Bennettitales are quite infrequent in the presented association.The lack of bisaccate pollen of Pinaceae and Podocarpaceae families can be explained by genetic conditions of these sediments; developed hill vegetation probably did not exist within the reach of the depositional area.The above stated also refers to the genera Araucariacites, Callialapollenites, and Classopollis.The scarcity of the Classopollis ‡type pollen may be explained by the conditions of sedimentation (where xeromorphic vegetation such as Brachyphyllum and Pagiophyllum might have existed at some distance from the coast).
A relatively frequent presence was noted in the examined samples of the Dinoflagellatae algal group.Most of the dinoflagellates remains are poorly preserved.
Dinoflagellate remains in palynomorph associations from the Ka{ajina River Beds have certain biostratigraphical value.Gonyaulacysta, Lanterna and other genera characteristic of Oxfordian and Kimmeridgian, and partly Tithonian, have not been identified.A marine depositional environment is characterized by the relatively common presence of the so ‡called palynoforaminifera and microforaminifera with chitinous linings (Scytinascia; Deák 1964).These remains are often found in sedimentary units of the Jurassic and the Lower Cretaceous, but their biostratigraphical importance is not great.
The Jurassic ‡Cretaceous sedimentation break is not found in several regions of Europe (England, France, etc.;Hughes, 1973), where many palynomorphs characterizing sedimentary rocks of the latest Jurassic are also contained in Lower Cretaceous formations.They are Cicatricosisporites dorogensis, Pilosisporites trichopapilosus, Cingulatisporites valdensis and others.
Transitional systems between the Tithonian and the Berriasian in many regions of Russia are characterised by spores of Cicatricosisporites ‡type.Tithonian, Berriasian, and Valanginian rock units also contain leiotrilete spores (Cyathidites minor, C. junctus, Lygodiumsporites subsimplex, Klukisporites pseudoreticulatus, Gleicheniidites sp. and others concave spores).Still predominant in the Valanginian is pollen of Classopollis, and there are many occurrences of Cicatricosisporites and Appendicisporites species, and species of Gleicheniidites senonicus, Trilobosporites bernissartensis and Cyathidites minor (Vakhrameev & Doludenko, 1976).The genus Appendicisporites is found in Valanginian rocks of the Indo ‡European paleofloral region.
The Jurassic ‡Cretaceous boundary on the continental shelf of the Netherlands, defined on palynomorphs (Burger, 1966;Herngreen et al., 1980) An abundant association of palynomorphs in Lower Cretaceous sedimentary rocks of northwestern Dnieper ‡Donets region, Russia, is reported by Voronova (1984).The Valanginian complex is much diverse, characterized dominantly by spores of the family Schizaceae (Anemia, Lygodium, etc. by about 70%) and Gleicheniaceae (20 ‡30%), and scarce families Dicksoniaceae, Matoniaceae (less than 4%).Pollen grains of conifers (Protoconiferae, Pinaceae, Bennettitaceae, and Ginkoaceae) are comparatively common, and those of Classopollis ‡type are much scarcer, like in the palynomorph association of the Ka{ajina river sediments.Voronova (1984) suggests that the Hauterivian ‡Barremian system of the mentioned sedimentary rocks is very similar to the Valanginian system.Climatic changes reduced Bennettite ‡ and Ginko ‡phytes, and consequently affected the character of the palynomorph association.However, the described system is characterized by the predominance of Gleicheniaceae spores (60%) and the sporadic presence of Anemia, Lygodium, Cibotium, Pelletieria and Dicksonia.These terrestrial ferns, highly prolific in spores, populated largely tropical and subtropical regions.Also sparse are typical representatives of Jurassic flora (Bennettitaceae, Cycadaceae, Gingkoaceae and Araucariaceae).The increased density of Taxodiceae and Cupressaceae pollen and the few occurrences of angiosperm are characteristic of Aptian rock complexes.This floral composition of the vegetation suggests warm and wet climate of the Dnieper and Donets regions in the Lower Cretaceous; the climate was more moderate in the end of the epoch, as evinced by Albian palynologic systems.
A palynomorph association, dated Valanginian ‡Hauterivian, from Lower Cretaceous rocks of Stara Planina (Rsovci; Ercegovac & An|elkovi}, 1972) indicates mesophilic character of the flora that existed in the region.The spore and pollen association still includes some elements of Upper Jurassic flora (spores of the fern Coniopteris and pollen of primitive conifers of Palaeoconiferae group), and floral elements of the early Lower Cretaceous (Schizacaea, Gleicheniaceae and others).This palynological material from Rsovci section ("Viso~ica Region" of Lower Cretaceous bathyal formation on Stara Planina) is well correlated with microflora from the Ka{ajina River Beds.
Published information on changes in the composition of palynomorph associations at the Jurassic ‡Cretaceous boundary is the following: The same refers to species of the genera Todisporites, Matonisporites, and Osmundacidites, indicating a notable reduction in Jurassic floral elements (pteridophyte spores).A particularity of the association is the presence of Cingutriletes and Converrucosisporites ‡type spores, and of concave spores (Concavisporites variverrucatus) which are common in Upper Jurassic of England and Scotland (Couper, 1958).Spores of Contignisporites ‡type -common elements of the Upper Jurassic microflora -are found sporadically.
Sedimentary systems of the Upper Jurassic (mostly Tithonian) in most of the localities over the world contain dinoflagellates, dominantly Scriniodinium luridum, Gonyaulacysta jurassica, Pareodinium ceratophora and others (England;Batten, 1973).However, the species G. jurassica and P. ceratophora are scarce in lowermost parts of the Lower Cretaceous unit.Late in the Tithonian, phytoplankton content is much lower than in the Kimmeridgian, while spores and pollen of terrestrial plants are higher.Valanginian sedimentary rocks often contain marine phytoplankton of Gardodinium and Cyclonephelium genera.

CONCLUSION
On the basis of geological and palynological investigations of the Ka{ajina River Beds (Kloko~evac; NE Serbia), the conclusions are following: The microfloral character of the obtained palynoassociation in Ka{ajina River Beds allows some new consideration in relation to Jurassic ‡Cretaceous boundary in NE Serbia.By the available biostratigraphical data Lower Cretaceous of this sediments was more precise determined.
From these sediments, relatively abundant but rather uniform association of spores, pollen and marine phytoplanktonic remains are obtained.Palynospectres are dominated by Cicatricosisporites, Appendicisporites, Trilites, Foveosporites and Cornutisporites (Welwitchiapites).Rarely, there are also spores of Cyathidites, Matonisporites, Deltoidospora, Biretisporites, Converrucosisporites, Trilobosporites and Cooksonites.Concave spores with pilose appendices, usually very characteristic for the Lower Cretaceous sediments of Europe and Canada, were not identified in the palynofacies of the Ka{ajina River Beds.Especially important characteristic of palynospectres is rare presence of primitive Coniferae pollen grains of Classopollis, Caytonipollenites, Alisporites, Callialasporites and Sphaeripollenites ‡type.The forms of Monosulcites, Ginkgocycadophytus, Alisporites and Podocarpidites are more often present.The remains of dinoflagelates (Cleistosphaeridium, Peridinium, Gonyaulacysta, Pareodinia, Fromea, Ctenidodinium, Tenua, Systematophora, Scriniodinium, and others) are present in significant amounts, with a dominance of Lower Cretaceous forms over Upper Jurassic (Kimmeridgian) ones.
Microscopic examination of organic facies and palynofacies suggests that the preservation state of deposited organic matter in this samples is significantly methamorphosed.
The lithofacial and metamorphic appearances of the Ka{ajina River Beds and the contents of manganese concretions, diabase, and serpentinite, and particularly the complete lack of carbonate ‡shelled fossils are unequivocal indications that these beds are typical "schistes lustres" formed on the deep oceanic floor, below CCD level.
The Valanginian ‡Hauterivian age of the Ka{ajina River Beds has an important geological implication.It definitely corroborates the presence of Lower Cretaceous Sinaia Flysch type and Azuga Beds type their tectonic recurrence and the abnormal positionthrust over the Miro~ parachton, as seen in the Veliki Greben regional section in the Kloko~evac river (Figs. 2, 3) N ., 1967: The microflora of the Albian "Green sands" in the Moesic Platform (Rumania).‡ Rev.