GEOLOGICA BALCANICA, 24, 6, Sofia, Decemb., 1994, p. 3-22
Cretaceous/Tertiary boundary in the area of Bjala, eastern Bulgaria - biostratigraphical results
Marin /. Ivanov, Kristalina H. Stoykova
Geological Institute of Bulgarian Academy of Sciences, 11 IS Sofia
(Received 12. 09. 199-1: accepted .?.1. 09. 1994)
Maptm JJ. Hawwa, Kpw:mu.ll/Ha X. CmoiiK06a - FpaHllt{a .lu',tfna.zcoi'Cll 11 paiioue i'. DR.za, Bocmo'l- 1taJl Eo.uapuR- 6uocmpamu,'pacpu'leCKIIC pe3_tf.1bmatnol. fpaHHUa Alea.'naJieoreH ycraHOJl.'lena n Henepe pbiBHOH Ce.'(!DieHTaUHOH!!Ol! llOCJJei(OBaTe .~bHOCTII B OKpeCHOCTI! f. DHJia, Ha 6epery Llcpnoro MOpH. 06Ha)Kei!Hb!H HHTepsa.~ OTHOCHTCH K DCJICHCKOH CBHTe, KOTOJJ
In trod uct ion
~he Cretaceous/Tertiary boundary and its related biological events has, for a long time, been a subject of discussion. The discovery of the geochemical anomaly in the boundary bed (A 1 v are z et a!., 1980) started a rejuvenated phase of discussions
3 in which a large variety of specialists hnve taken pnrt. This interest has fu eled inve stigations aimed at finding and analysing complete, uninterrupted sections across the KIT boundary interval. The KI T boundary in Bulgaria has not been studied so far in terms of event stra tigraph y. Th erefore, we have addressed the foiiO\ving in our stud y: - finding complete sections of uninterrupted sedimentation between the Cre- taceous and Teriiarv: - establishing the position of the Ki T boundary; - studying, in detail, the nannofoss il assemblages; - observing the succession of macro- and nan nofossils across the bound <1ry. Region al geological and stratigr<1phical features of Cretaceous and Tertiary in Bulgaria indicated the East Balkan region to be the most promising area to investi gate. S t o y k o v a, I v a n o v (1992) gave a detailed chronology of the investiga tions, which . between 1991- 1993 have been partly c .Methods The precise lo c<1 tion of the KIT boundary was established by using calcareous nanno fossil biostratigraphy. Sample density differed between the section investigated. The lower horizon of the boundary clay bed was designa ted 0 m. Within the boundary in terval (-0,1 m to -j0,25 m) samples were taken at every 1-2 em; from-1m to -0,1 111 and from + 0,25 rn to + 4 m samp les were taken at every 20 em; elsewhere, samples were taken at every 0,5-1 m. Smear slides, mounted with Canada balsam , were pre pared. Leitz Orthoplan Pol and Jcnapold light microscopes (1200 X magnification) were used for determination of the nannofoss i I taxa. Geological seW ng The sections around the town of Bjala lie within the Luda Kam cia zone, a partly ex ternal zone of the East Balkan, situated between the Sredna Gora zone and the Bal kan- Fore Balkan zone (Z . I v a n ov, 1983 , 1988) (Fig. lA) . The Luda Kamcia zone comprises Late Alpine sinclinorium, complicated by inner nappes and reverse · faults. Palaeogeographically, the zone was a \\·ell differentiated ba sin (Emine lowe ring- H a tJ e B, 1977) which was bei ng filled with predominantly flysch sediments during the Turonian to Palaeocene. The Cretaceous - Palaeocene sediment complexes are strongly tectoni zed around Bjala, cropping out in blocks of different size or incorporated in nappe lamellae (Fig. 3). Previous studies on the KIT boundary interval in the region of the town of Bjala Stratigraphical data on the rock in the region of the town of Bj ala were first publi shed by 3 JI aT a p c K H (1905, 1907). He assigned the sa nd stones of Sveti Atanas Cape to the Cenomanian, and the carbonate rock in the vicinity of Bjala to the Upper 4 A N c t 4{\."-1. «X UJ ;;,.- '- Ill «l( ~ I ~( (.) BJALA 2b ~ <( (..) ...J 0 5 10k I 6 .--,J. 0 1 2km Emine Fig. / . L oc~! i o n o f l he investigated arC'a. A: tectonic subdivision of B ul .!.!aria (a fter Z . l v a 11 o v, !98::!. 1988): I - Mo esi~n platform: 2- Balk:Jn- F" re Halkan Zone: :l - - Luda l\amchia Zone; 4- Sredna gnr;J Zone : 5 - Rhodopcs: 13: coa ~ t · line o f BI;J c k Sc;J between thr town of Varna and Emine Cape; C : location o f the s t ndied srctinns in the v icini ty o f Bjala Senonian (Aturien) on the bas is of the prese nce of Ech{nocorys vulgaris. 6 o n lJ e B (1926. p. 17) described these rocks 5 Fig. 2 Relationships betw<'<'n the lithostratigraphical units within the K/T boundary interval nifers. J u r a n o v (1983), .LI. 1!< y p a H oR (!989) distinguished and characterized zones based on planktonic foraminifers for the Palaeocene - Lo\ver Eocene interval in a drill sections around the villages of Gorica and Bjala. The rocks of the boundary interval were included within the range of the limestone-marl suite (.ll. x< ::,• p ::1 II o B, 1983, 1989) or within the Bjala Formation (.LJ. * y p a 11 on, 1991). The authors have established an uninterrupted section across the K/T boundary in the vicinity of Bjala (S toy k ova & Ivanov, 1992). The neutron activation analysis of samples from the clay bed lws shov.. · n an 11bnormal content of lr of the or der of 7 pph (Preis i n g e r et al., 1993a, 1993b). Lithostratigraphy In the coastal part of the East B;llkan A\ountain the Upper Cretaceous and Pal:1eocene consist of the Emine, Vclikovo and Bjala Formations. The KiT boundary occurs in the Emine and Bjala Formation and probably in the Velikovo Form Emine Formation (Late Camp;mian - Late Palaeocene) Consists of an alternation of thin- to medium-bedded sandstones, siltstones, argillites and marls, which form the complete rhythms of a typict~l flysch . Velikovo Formation [Mat~strichtian (partly)- Palaeocene (partly)] Distinguished on the basis of a characteristic alternation of aleurolites, marls and marly limestones, forming the rhythms of a flysch of increased carbonate content. Bjala Formation (Maastrichtian- Palaeocene) Characterized by marls and marly limestones. The marls dominate in the lower part of the formation. They are dark to light-grey, indistinctly bedded, and include hori- ·6 zons of varying carbon<1te content. In the upper part of the form<1tion, the marls al ternate with li .l;hl-grey to \\hitisch marly limestones. A tendency toward increased carbonate content has been established in the sec tions of the fo1:mation north of the town of Bjala. The Bj<1la Formation is restricted to the area around Bjala and the Yillage of Gorica, Varna district. The clay bed, cha racteristic of the K:'T boundary and found in the Bjala Formation, is invaluable as a lithological marker. Its thickness is more commonly 1-3 em, but at certain places, it reaches 5-6 em. The bed consists of clark-grey, dark-brown, black, pure (almost non calcareous) clay, and is discernible in the field. Although it is difficult find, once lo cated, it is easily traced. Studied sections Studies have been carried out on four sections in the vicinity of Bjala, exposed on the coastline, situated at about 1-1,5 km from one another. Their exact location is shown on Fig. 1 B, C. The structural environment was taken into consideration when selecting sections studied. Some of the sections are next to the fault dislocations or are included ,_ BJALA 2b -N Sj NP1-2 50m S- BJALA 2c -N ~ NP 1-2 s- BJALA 3 -N Fig. 3. Tectonic situation of the studied sections (legend as in Fi". 5). 7 in nappe structures. For that reason, separate tectonic situations for each section are shown (Fig. 3). The B jala 1 section The sequence crops out in a cliff-section to the south of Bjala, 210 m south of the wa ter-slide. The KT boundary in this section is discontinuous and bears the characteris tic of <1 "hardground". The uppermost .M Bjala limestone-marl Formation (No. 6-l. Upper Maastrichtian-Palaeocene) 6. (10 m) Alternation of the marls ~nd marly limestones. The marl s are light grey to dark grey, and the limestones are grcy-heige with grey spots. The limestone beds are 0,3 m thick. ln !he upper mo 8 can be see n in i I. No nannofossi Is have been found. Several speci mens of irrcgul ar Echi noi den have been est abli shed. I. (4,70 m) Grey, indi sii ndly bedded mnrl s of varying cm hon ntc co nt ent. There nre lenscs or lnyers of /no· ceramus-shell dclritc and rcm;tins of Echinoidea in some of the beds. In the upper pnrt of the p Underground - tectonic conbc~ with m;1r Is st rong! y cl enved. The Bjala 2/J srrfinn The section is located at the coast-line, about 800 m north of the central entrance to the beac h (Fig. !C) . This is the most comp lex and mos t represe nt3tive of the section studied . The Maastrichtian to Palaeocene succession crops out to the north of the town, where an southwes tward dipping sequence (210 °- 235 c) complic;.ded by faulting, rep resen ted the best exposures of the Cretaceous/Tertiary boundar~r. Th e sequence can be follo\ved in sev eral adjacent. tectonicall y dislocated bl oc ks (Fig. 3). There are some recent investigations of bio-, m<1gneto- Bjnln limestone·mnrl Formati on (No 5-l, Upper i'.-\n nst richtinn·Pni:Jeo ce ne ) 5. (over 25 m) Alternati on of limestones and marls. rep rese nted by beds of npproximntel~ ' equal thickness (0,3-0,4 m), The limestones me li ght beige to whiti sh, i 11 certain cnses form ing bed s up to 2·2.5 m thick. Fossil remai ns of Echinoidr 9 0 ., 0"' ~ · - y y 0 c R E T A c E 0 u s T E R T I A R s s T 6 M (]Q ;::;· :"" z u PPER M A A s T R I c H Tl AN D A N I A N s T A G E "'tll "'::s ::s "';::;- 0 0 CC25C M. mu rus ICC26 M.prinsii NP11 NP 2 NP 3 Nannofossil' zond "'::s I "'~. + + + + n ' w' 1'.)' ' 1'.) w 0• 0 -0 (~ 0 0 0 ~ Distance ( m) "-!)"' 0.. 9 ol>o u;· i 0 .flrkbaogcl~kid/11 t,,'f'Jn'lliforlll.b ~ ------· --- -- "' cr ------. -- - 2. O:ibrosphat>ra cbxt:n.b~>J'Kil s.. - - -.. ;1. C dliJ!tica < 0 ------::s - 4. 8raaruiosphacl'li .blgeiowb "' ------·~ ------::s ::s - - - -· - - - ;;. llffellithu.<: lurdsciifcD 0 ------...... - e. £: parallelus· :: ::r ------"' "' - -~ 7'. C.J"clalfelo.-;pJJaeru. l'tmhllttl.i{i ?' tll - - - - - ';;;' s. Utbraphiriitc:;. quair,lt/.1$ (ll ------"' - -- ..'J'[;Jr/;. ;~ liu . 10 The Bfalo 2c section The section is situated about 2 km north of the centr Bjala rormation (:\o. 4-1, Uprer Maa~trichtian- Lower Danian) ------t hru~t pi ;Ji n ------4. (R m) Alternation of marls and clayey limrstonrs. The marls arc lii!hl [.!rcy to whitish; form beds from O,R to lm in thickness. The clayey limestones are light grey to \\·hitish, of varyin,r.; thickness (from 1,5 to 0,3 m) . A rich n;mnoflora h;Js been found in 1 he p;Jckcl, which has been invesli!!ated in metres and centimetres. The species distinguished within the inler\';il of 8--6 m ;1re : Cruciplncoli!hus tenuis, C. intermedius, C. USIJmme!ricus, Planm;gus sigmoidrs, Mor!mlius invl'fsus, ,VI. apcr/us, Binntholithus sparsus, Micro nlholi tlws crenulatus, M. en tusti'T, Bruurudosplwcra bir;l'iou:.•i i, B. I urbincn, Ct;clagelos phaera rrinhard!ii, Arf!lzangelskiello u;mbi/ormis. FiffeliL/ws turriscilfeli, U7otznoucria borncsae, Pre discosphal'ra cre!acra. The s;1me ;;ssoci;Jtion, supplemented by species Crucip!acoli/hus primus, Cyc lawlosphacra oltu, Braarudosphucru disculu, M iCttla murus, .'\1. dccussa tu , Cribrosplwcru chrenbergii, Thora uJ~phacro opcrculata, T. saxeo is situaterl bet\\'een the 6th and 4th m. The 'Jlccies found at +3.50 m from the p:1ckd base are: Crttciplacolithus /enuis, C. primus. C. in/rrmcdius, Plocozl!gus si[Jmoides, Thoracosphal'ra oprrcula fa, Nephrolithus f requens, A rkhangclsf!iclla cymhiformis, i\11 icula prinsii, Cri brosphaera chrl'nberrzii, Braarudosphaera bi[fl'lorm'i, B. disculo, Marlmlius invNsus, \'Vatznoueria bar nesae. Reworked Creiaceou' 'Jlccies are abund;:nt at -c -l m in nannofossil association: Stradneria crenulala, Ahrrwcll'rcllu oc/oradia/a, MiCitla dccussata, \Fatznaurria barncsac, Lilhrophidites praequad ratus, Arfilwngelskiella CtlmiJiformis, Mictlla prinsii. At -- 1-2 ,60 m the following species were found : Cru ciplacolit!ws intermrdius, .\'!'OhisClltum romeinii, Staurolithites crux, Placozt/gus sigmoidcs. Braamdos phaera turbinca, Marfwlius invrrsus, Miaun/holithus cretwlatus. The first. occurrence of the species Cruciplacolithus primus is at -'--1,60 m from the b;Jsc of that packet; in addition numerous cocco sphaeres of Tlwracosphacra opercula/a, as we! I ;~sa lot of "Cretaceous" species h:1ve been observed. The following srecics have been eli .sti ngui shed from _: _1 to -:-o, 1 m: Biuntholitlzus s;Jarsus, Cyclagelosphae ra alta, C. reinlwrdfii, C. marwrc!ii, l\'eochiaslozclgus primitivus, Prcdiscosplwcra cretocea, Braarudos pharra tur!Jinl'u, B. hi[!dou:.•ii, Placozc;gus sigmoides, Marlmlius inuersus. Mintlo dccussata, Thoracos p!wera opercula Ia, I\" a twa ucria barnl'soc, A hmuclerclla onomdia Ia . 3. (0.01-0,06 m) Boundary clay bed- dark brown to black cl:1y v:Jrving in thicknrss. usually from 1 to 3 em, at certain places up to 6 em. The clny is filling in the craciZs of thr undcri:J\'ing limestone hed . Nanno fossils are rare in that cl<~y; thcrc ;ire only established Mie1tla d{'{usso/a ':nHI Thorocosphacra operw lata . ------Crc!accousjTerti:Jry hounrL1ry ------2 . (0,5-0,6 m) Clayey limestone- liQht beige to whitish. uncqu:!l upper surface. The species established in that packet arc: Miwla murus, Nephrolithus frcquens, Marfwlius invcrsus, Ct;rlagelasphaera margere lii, Cribrosphaera chrl'lr.bNgii, Arlilwnwlskiclla cumbiformis. Ahmurlcrl'!la nctriradia/o, Predisrasphaera spinoso, P. cre/acC'o, Braurudosp!zacra lurhinra, Thorecosplwcra opNmlota. I. (7 m) . Marls- grey to light grey. of varying c;Jrbonate content. i\t certain levels they arc banded, sli[.!h!ly aleuritic, thin-bedded. The species distinguished 6 m from the b;Jsc nrr: Mie1tla murus. M. prins_ii. M. decuss~l/a, Arkhan{!,l'lsflicllu u;mhiformi, Lithmphiditcs !Jllllrimtus, Cribrosphaera ehrenbergii, Predrscosphaera cretucea, Thoracosphaera opercula Ia, W' a /znuueria barncsoe. 11 -t-.J 1.() ----- . Bja l a 2b------.. l{) a.. I a.. z I z I ~s (!) .2 I . I ' ' >- lwn~ I Bj <~ la 1 I ' § I 5 :;::r ' cr I !t~--=y--·; ' Fig. 5. (orrci The section i~ loca ted 01 1 tlte Black Sea co;1 s t, nbout 2.5 km north of Bja la. 250 11 1 south of the mout h of t he Bj ala Reka RiYer (Fi g. !C). The section lies immediately nex t to a f I3j ul a limcstune· Jn Biostratigraphy In most of the KtT boundan · sections in the \\' Orld till' zona l su bdiv isio11 of the t\ \aas trichtian and Palaeocene has bee n based on nan nofossil an d .. or plankt on ic foram ini feral bi os trati graph y. On ly in a fe,,· sections has t he Upper J\\aastri chtian bee n su bd i vid ed using macro-im·ertebri:l tes as ,,·ell. These sections arl' di scussed in detai l in the parers of W i e d m a n n (1 988), W a rd (1 990) . \V a r d & K e 11 n e d y (1 993). K e n n e d y ( 1993) . The sections around the t0\\'11 of Bjal Calcareous nannoplanllton The standard zonal scheme of 1\\ a rt i n i (1971 ) \\' as app li ed to t he Palaeocene sed i me nts. The stand ard zonation of S i s s i n g h (1977) and P e r c h- l i e I s e n (1 979, 1985a) was applied to the Upper Cretaceous sedi me11t s. Th e rare occurrenc e of the ge nus Ellipsolithus in the upper pa rts of the Dan ian and the abun dance of Neochiastozygus spp . within the same strat igraphic in terval have all owed also the ap pl ica ti on of va u H eck & P r i n s 's (1987) zonati on. Other \\·orks on nannop lankton at the KIT 13 fCRET~ ;-.:~C)_1 _1~7' ------l--;:~~- ~-:- ~ ~ -;.,: :_;------r-- - .. Y -~ --=--f.-r;--- ·l ~~: --~~':~ _____ :__' _. _. ~'------r -- -' -~ -·~ _! __ _-_ ·_·----1 U. r.~A ;>.STP.ICHT ! AO~ [) '~ N I A N I s T A G E__j ~~-1 7:;-2~1 NP,I :o:J Nan:-tofos " il Zone ·j-'M--.:r :n.· "U ' ..... I M. mtJ rus 'jij \8.!':p:1r:.u .:; C nu;::; j c . c.:anic l..f ~/T .:.: :ei !L r, Oll Species J\rkJwngds!;ictla cymhijom1is .ft1icula decussata JHiculu munts JUicula prinsii - Cribrosphaera ehre11bergii Prediscosphaera cretacea Lilhrophidites quadroJus Ej[{elithus turriseiffcii .'tlicrnrhaUulus •~curntus -1-- Nephrolithus jrequens Th orocosphaero opercula/a Thoracosphaera saxea Broarudosphaera bigelowii Braarudosplwero turbinea '-- Cyc/o.gello sphacra reinlwrdtii -- Cyclagellosphaera alta Markalius in versus P/o.cozygus sigmoidcs Biantlwlithus sparsus Cn.~eip lacolitlws prim us --- Cru ciplacolithus intermedius Cnlciplacolilhwi ten11i., L'ntcip/acolith us asymmf• l ti<"tt~ Cocco/ithus cavu .\· .Veobisculum mmL'i11ii - L'lziusmolitlw.'i danifU\ Chiasmvlitfl us in<·onJpic'''' ·'· Chiasmolillws edmrcbii 1- Chiasmolithtu biliCia C!Jiasmolitlws con.metw; - Prinsius maninii Pn'n:."ius hisu/cus .Veochiastnygu.\· modcrius 1---- /'1/eochfastoz.ygh.\' eosaepcs t-- .'Veochiasto:ygus Slli'pcs Neoclriastoz.y~ u s p c ,f~_·c t!l S Ellipsolilhus ho!lii FaJciculithus janii Fasciculilhus u!ii Fa scicu /it.':u .\ tympuniformi.,· l'hyllocero.'\ (Neophy/Joceras) rumu.wm 1-. ··------Anagamlryceros politin imwn - -- --1- Vettebrites kayci --- t---- P.c;eudophyllitcs indra Sa ~: lzalinil e 'O wlighti 1-- 1/op/os.:aphilc.\· constri<:tt'·' l'hyl/oplydwcem 'l .\p . indf'l ~--- IJip/omocems cylindmcaun Haculites ancep,,· ---·- Gl\•otoxocerol· c( suhwmpl\"ssum 1-- olllllpHrflytfi.... rlls f~t.'f.,· ~ · ff/nu> i.' r Pu chydi.H:us tleuhcrr, [c t:s r-- l}achydiscwt ;:o flnill<'ll sis a m:t' I!ICU.\ 1-- l'acltydiscu s go{/t-rilf!:ll.\1 ., x·d :~ · \ ' i!kn,i, - Pacltrdi., r;t,. iac<; t Fig. 6. R an~ e- chart o f the important nannofo s~ il s and macroinvcrle hrai('s across the KiT boundary i11 the sections studied- zonal s ubdivision I - A napachttdiscus f reiwillensis Zone; 2 - Parhydiscus go/levillensis gollcuillcnsis Zone; :3 - A napachtJdiscus terminus Zone boundary (P e r c h- 1\ i e I s e n, 1979. 198 1. 1985b; Perc h- N i e I s e n et al., 1982; Rom e in, 1979; S l' y v e, 1984. 1990; V a r o I, 1989; L c: m o I da et al., 1983; B u r n e t et a!. , 1992 etc .) were consulted for purposes of co rnpari son. 14 Micula murus Zone The ba se of that zone could not be di stinguished in the sections studied (see above). The nannofl oral association is rich and species diversity is hi gh. The zone has been recog ni sed in the sections of Bjala 1 ami Bjala 2b with a thickness of 30 111. ~\icula prin s ii Zone The base of the zone \vas recogni sed by the first occurence of Micula prinsii; it is drawn in the upper part of packet No 1 of Bj ala 2b section. We detected M . prinsii in the top 17m. and Nephrolithus frequens - in the top 14 m of the Maastrichtian of Bjala 2b. Th e prese nce of M . prinsii Zone proves the copmleteness of the Maastrichtian stage. Thickness- 15-17 min Bjala 2b section; 5-7 min sections Bj ala 2c and 3. Bi ant holithu s s par s u s Zone The base of the zone coincides with the KiT boundary. The first occurence of the index speci es Biantholithus sparsus is immediately above the boundary clay bed. Only within that zone the species Cyclagelosphaera alta has been found. The zone is characterized by !he dominance of Thorasphaera operculata - a species. which amount of 2-3% in the la st centimetres of the Upper Maastrichtian reaches over 80%, immediately above the K:T boundary (S t o y k ova in Prei s i n g e r et al.. 1993a, Fi g. 4). In the base of that zone together with Biantholithus sparsus and Cyclagellosphaera alta, almost all "Upper Cretaceous" nannofoss il taxa from the underlying zones (M. prinsii Z., M . murus Z.) were found . In the middle and upper part of that zone the first occurrence of the genus Cruciplacolithus - C. primus, C. intermedius, as well as the species Neobis cutum romeinii, Futyania petalosa, has been recorded . Thickness- 3,50 m in the Bja la 2c sect ion; 4m in the Bjala 2b sect ion ; over 3m in the Bjala 3 section. Cruciplacolithus tcnui s Zone Within !hal zone a gradual quantitative decrease of Thoracosphaera operculata down to 10-20 % has been mentioned (S toy k ova in Prei s i 11 g e r et al., 1993. Fig. 4). On can reg istcres here the first occurrence of the speci es Cocco lithus cavus (appea ring sli ghtly after the first occurrence of C. tenuis), Prinsius dimorplwsus and Crucip lacolithus asymmetricus. Thickness- 18 m in the Bjala 2b section. C hia smo lithus danicus Zone The base of the zone is drawn by the first occurrence of the genus Chiasmolitlws (Ch. danicus a11d Ch. edwardsii). The first occurrence of Chiasmolithus inconspicuus, Prinsius martini, P . bisulcus, N eochiastozygus modest us has bee11 recorded in that zone <.:s well. The speci es . considered to be Cretaceous occur here much more rarely comp aring with two perceding zo nes. Thickness: about 35m in the sect ion Bj ala 2b; reduced thickness - 7,70 m in Bj ala I sect ion . Ellipsolithus rnacellu s Zone There are some problems assoc iated with the recognition of the base of E . macellus zone. \\·hi ch we ha\'e been unable to recogni ze because of the poor presence or abse nce of the gen us Ellipsolitlzus used in the standart zonal scheme of 1\\ art i 11 i (1971). The first occurrence of genu s Ellipsolithus approxi ma!ely coincides with that of Neo chiastozygus eosaepes. That fact allowed to use N . eosaepes for drawing the base of the 15 EXPLANATIONS TO THE PLATES PL.\ T E I Cret;Jceou~ : Tcrti PLATE II Upper ,\l aa ~ triclilian- Loll'cr Dania11 nann u fo ~s il s frnm tlw . P L ,\ T E III Upper }'1'\aastrichtian ammonites from lhe section Bj ;~ l a 2b, Bj:ila Formation , packet !\o I A-B - Hoplosca phites constrict tis (J . S o w e r b y); A - s m~ll macroconch, MP- US 1( 1 I 0208, B - microcoiich , MP-US K1 10209, from -:15 to -42 m, A. frcist•illensis Zone C- Pachydiscus gullcvillcnsis gollevillcnsis (d'O r bi g n y), -31 m, MP-US 1( 1 10210, P . gullevi llensis gollevillensis Zone D - Pachydisws gollevillensis armenims i\ l a b c k i a n & A c o p i a n , -42 m , }'1·\P- US 1\.1 10211, A napuchydisws lreisvi 1/ensis Zot1c E- - Pachydisws ncuhergicus neu !Jcr.Qiws (Hauer), from -39 lo -45 rn; E- MP-US 1\ 1 10212 ; F -MPUS K1 10213; .4. freisvillcnsis Zone All figures are in natural size. Photo B . .labljans ki. PLATE IV Uppermost Ma<.~slrichtian ammonnitc.-; fr om the section Bjala 2!J, Bjai 16 PLATE I T K T K Geologica Balcanica 24.6 - I v a n o v, K. S t o y k o v a - Gretaceous{fertrary bonnolary in the area of Bjala .. . PLAT E II a b c e f g h k m n 0 p 10fo q r PLATE III PLATE IV B zone. In the lower part of that zone the first occurrence of Neochiastozygus perfcctus and Chiusmolithus bidcns has been recorded. Thickness: about 15 m in the Bjala I sec tion; O\'er 20 m in the Bjala 2b sedio1 1. F a .~ c i c u I i t h u s t y 111 p a 11 i f o r 11 1 i s Z o : 1 l' The base of the zone is clearly markcil uy the inc! ·ming of the gciiUS fasciculitlws. The first occurrence of the index species i:> s li g htly later ;1fter the :1ppearancc of the diver se Fasciculithus janii, F. bitectus, F. /Jillii, F. pileatus, F. ulii. Within the zone the first occurrence of Chiasmolithus consuetus h2s been registered . The upper boundary of that zone has been established in none of the sections studied near the town of Bjala. Thickness: over 6 m in the Bjala I section. Ammonite successions Only in fe\v sections, containing ammonite fauna, the KiT boundary has been docu mented (B i r k e I u n d, 1979, 1993; Ward e t a!., 1986; Wiedmann, 1986; 1988; S tin n e s beck, 1986; i\\ ace I I a r i, 1986; Kennedy, 1989, 1993; Ward, 1990; Ward, Ken 11 e d y, 1993). An attempt for the ammonite subdivision of the Upper /1\aastrichtian has been made in a few sections only (J\1 ace I I a r i, 1986; W i e d mann, 1988; Ward, Kennedy, 1993). There are no standard ammonite zonation scheme for the Upper ;\\aastrichtian so far . Ammonites, inoceramids and echinoids have been found in the sections near the town of Bjala. A special attention has been paid to the ammonite successions. They have been studied in the most complete section- Bjala 2b, where below the K.'T boun dary about 45 m of Maastrichtian are exposed. Additional data were obtained from the Bjala 3 section. An amount of 22 ammonite species has been identified belon ging to 13 genera. The following genera are represented: Plzylloceratina- Phylloceras (Neophylloceras) (2 species); Gaudryceratidae- Anagaudryceras (2 species), Vertebrites (I species); Tetragonitidae- Pseudophyllites (2 species). Saghalinites (I species); he teromorphs- Hoploscaphites (I species), Diplomoceras (I species), Baculites (I species), Glyptvxoceras (I species), Phylloptychoceras. The representatives of Desmocerataceac Pachydiscus (6), Anapachydiscus (2) and Desmophyllites (2) are of greatest diversity. The attempts for dividing the Upper J\·\aastrichtian have been based so far on Pachy discidae (A\ ace II a r i, 1986; Wiedmann, 1986, 1988; Ward, K. en ned y, 1993) . Our observations have corroborated the concept that Pachydiscus and Anapachy discus have a rapid evolution during the Late .Maastrichtian and their filiations could be used for an ammonite zonation. The following species forming a vertical succession and partly overlapping, have been found in the Bjala 2b section: Anapachydiscus freisvillensis, Pachydiscus neuber gicus, P. gollevillensis armenicus, P. gollevi llensis gollevillensis, P. jacquoti, A napachy discus terminus. In the lowermost part of that section Anapachydiscus freisvillensis, Pachydiscus neubergicus and Pachydiscus gollevillensis armenicus occur together. The species P. neubergicus has been considered to be characteristic for the upper part of Lower Maastrichtian (B I a s z kiev i c z, 1980; Kennedy, 1986; Kennedy, S u m me s b erg e r, 1986). Recently, the species has been found in the lower part of the Upper 11\aastrichtian (W a r d , 1990; War d, Ken 11 e d y, 1993; Ken n e d y, 1993) . Within that interval A. freisvi!lensis and P. gollefvllensis armenicus often occur. The latter realizes the transition in the phylogenetic lineage- P. neubergicus P. gollevillensis armenicus- p. gollevillensis gollevillensis. The divided here Anapachydiscus freisvillensis Zone is defined as an interval of concurent occurrence of A . freisvillensis, P. neubergicus and P. gollevillensis armenicus. The base of the zone could not be drawn. Its top is marked by the last occurrence Of 17 2 Geologica Bulcanica, 24, 6 A . freisvillensis anti the first occurence of Pachydiscus gnllevillcnsis gollcvil!cnsis. The ammonite association comprises: Phyl!oceras (N.) ramosum, Anagaudryccras Jio[ifissi mum, Vertebrites kayei, Pseudophyllites indra. Phylloptychoceras sp. i ndet., Hoploscaph ites constrictus, Diplomoceras cylindraceum, Baculites al1(·eps, Glyptoxoceras cf. subcomp ressum. Desmophyllites larteti. Anapachydiscus freisvillensis, Pachydiscus neubcrgicus, P . gollevillensis armenicus. Thickness- 12 m. Pachydiscus gollevillensis gollevillensis Zone is d ist i ngu ished as an i nterv 18 trichtian by War d. Ken ned y (1993) and probably with P . epiplectus Zone of W i e d mann (1896). 1988). The correlation with the Sey mour Island sect ion (Antarctica) (A\ ace I I a r i, 1986) is impossible due to the endemic character of the ammonite fauna. Comparison of the biostratigraphic data This parallel study of nannofossil and ammonite successions across the KIT boundary allow us to draw the following conclusions: I) The presence of Micula murus within the whole interval studied below the KIT boundary proves a Late /v\aastrichtian age according to nannofossils. The same age is determined by the occurrence of the ammonites Pachydiscus go/levillensis gollevillen sis, p. jacquoti, A napachydiscus terminus, Hoploscaphites constrictus, Saghalinites wrighti, Vertebrites kayei. 2) In the IO\ver part of Bjala 2b section, A. freisvillensis, P. neubergicus and P. gollevillensis armenicus were found together with M icula murus. 3) The ammonite species P. jacquoti occurs together with the CC26 marker species Nephrolithus frequens in the higher levels of the Bjala 2b section. 4) Anapachydiscus terminus has been found together with Nephrolithus frequens and rare specimens of Micula prinsii. 5) The "youngest" ammonites - Pseudophyllites indra and Anagaudryceras poli tissimum were found 40 em below the KIT boundary. They are associated with M. prinsii. Thus, ammonites still existed during the Latest Maastrichtian. 6) The ammonite zones A . freisvillensis (represented by its upper part in Bjala 2b section) and P. gollevillensis gollevillensis correspond to the nannofossil zone Mi cula murus. The topmost Cretaceous ammonite zone A. terminus almost coincides with the range of the nannofossil zone Micula prinsii. With respect to palaeobiogeography the Late Maastrichtian nannofossils and ammo nites found in the region of Bjala are characteristic of the low latitudes ("Tethyan"). This conclusion is indirectly corroborated by the almost complete lack of belemnites. An exception here is the occurrence of the genus Hoploscaphites, which is considered to be Boreal (Wiedmann, 1988). Conclusion The KIT boundary is considered to be a surface. marked by a boundary clay bed and by considerable change in the calcareous nannoplankton assemblages. In the vicinity of Bjala. on the Black Sea coast, the KIT boundary has been located in an uninterrup ted sedimentary sequence. The biostratigraphic boundary is defined on the basis of reduction in abundance of the Cretaceous nannoplankton species and the regular appearance of Biantholithus sparsus. Seven nannofossil zones (CC25- NP 5) covering the Upper Maastrichtian to Upper Palaeocene, were assigned to the succession. The Bjala 2b section is one of only a few complete Upper /1'\aastrichtian sections in the world, where macro-invertebrates (ammonites, echinoids and inoceramids) occur commonly. Three ammonite zones have been erected here, based on members of the Pachydiscidae. The integrated zonation using nannoplankton and ammonites allows us to com pare and correlate biostratigraphically important events. Thus. in the uppermost Maastrichtian Nephrolithus frequens and Pachydiscus jacquoti have been reported to gether, while the first specimens of Micula prinsii occur together with Anapachydis cus terminus. 19 The :1mmonitcs commonly occur in the Upper ;\\a(lstrichtian. The "youngest'' onrs arc regi :-, lcred immedi Acknowledgments The authors exprc~~ t hci r J.(r References A Iva r c z, L. \V., A I v <1 r c z. \V., ,\ s a r o, f., ,\\ i c II l' I, H. V. 1980. Extratcrrc>trial cause fur the C:rctaceousjTerliary c:di11clio11.- Scirnce , 208; 1005-tl08. A r chi b a I d, J . D. 1987. Stepwise and nul!-cata ~drop!Jil: I. ate CreL1ceous tl'rrc ~ tri 20 K e 1 1 e r, G . 1988 . Extinction , survivorship a11.d evo_lutio.n of plan kt o11ic _forami11ifera ac r?ss the CretaceousfTcrti ar y boundary at F.l h.cf, 1unl. 21 S toy k ova, K. & Ivanov,. M . 1992. An uninterrupted se~tion hetween Cretaceous ~nd Tertia r y nea r the lllWll of Bjala (East Bulgarra)- C. R . d A cad. Bulg. Sci., 45, 7; 61-64 . V a r o I , 0 . 1989. Pal eocene ca lcareous nannofoss il biostratigraphy. ~ In : Nannofossil and their ap plication (Eds. C r 1.1 z, J . A ., van Heck, S. E .); pp. 267-110. Britisch Micropalaeontol. Soc. Ser .. Ellis Horwood Ltd, Chichester. Ward, P . D. 1990. A review of Maas trichtian ammonite ranges. -In: Global catastrophes in Earth history. An interdisciplinary conference on impacts, volcanism and mass mortality (Eds. S h a r p ton, V . L., Ward, P. D.). Geo l. Soc. America Spec. Pap., 247; 519-530 . Ward, P . D., Kennedy, W . J. 1993. Maastrichtian Ammonites tram the Biscay region (France , Spain)- Pal. Soc. Mem ., 34 (J. Palaeon/ol., 67, 5); 58 .P· Ward, P. D ., W i c d m a nn, J., Mount, J. F . 1986. Maastnchtian molluscan biostrntigraphy and extinction patterns in a Crctaceo usjTertiary boundary section exposed at Zumaya. Spain. - Geology, 14; 899-903. Wiedmann, J. 1986. Macro-invertebrates and the Cretaceous/Tertiary boundary.- Lecture notes in Earth Science, 8; 397-409 . Wiedmann, J. 1988. The B asque coastal sections of the K/T b()undary- a key to understan ding "mass extinction" in fossil records. -Rev. Espan. Palaeontnl., N . Extraord.; 127- 140. AT a 6 e K H H. A . A., A K 0 11 H H, B. T . 1969. no3nHeMe.~OBhiC a~IMClJii!Tbl ApMHHCKOi'l CCP (Pachy discidae). - l1 a8 . All ApAt. CCP, HayKu a JeAtAI'. 22, 6; 3-~0 . B o u ''en, r . 1926. CKaJJHTC n cenepHHTe oTneJJH Hn BaJJKaHa ~re}Kny 4epHo ~1 o pe, KoTcJJ-llcpneHT· CKHH npoxo,'l, rpe6eHa na BnJJKn!la H JlCKHTe Bpaua H fomnra Ka~r·IH!! . - Cn. 5AH, :14; 1-100. BoTe a, B. 1953. BeJJe}KKH Bbp xy reoJJornHTa 11a Haii-HJTo•rnaTa •racT 11a 113T04Hn CTapn nJJaHHHa. /138 . r eoA. Ul~cm . 5AH, 2; 1-26. f 0 'I C B, n. 1932 . feOJIOrH4HH 1136JIIoneHHH no 4epHOMOpCKOTO Kp3ii6pe>KHe MC}Kny YCTHCTO 113 p. KaM•IHH H noc E~nrne. - Cn. 57>Ae . eeoA. o-80, 4, 3; 200-212. Ll >K y p a H 0 B, C. 1983. JIHTOCTp3THrpaljJHH H3 cenHMCHTHTC OT CCIIQH - cpenHoeOUCHCKH!! HIITep B3JI B OKOJIHOCTHTe Ha ceJJaTa BHJ!a H fopnua, B apHeHCKO . - roa. BMr/1, 30, 2; 13-23. 2l )f{ y p a H on, C. 1989 . llaHHH Ja reoJJO}KKH!! cTpoe>K Ha BeJJeHCK 22