Magnetostratigraphy of the Campanian/Maastrichtian bound ary suc ces sion from the Mid dle Vistula River sec tion, cen tral Po land
Tomasz PLASOTA1, Jerzy NAWROCKI2 and Ireneusz WALASZCZYK1, *
1 Uni ver sity of War saw, In sti tute of Ge ol ogy, ¯wirki i Wigury 93, 02-089 Warszawa, Po land
2 Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land
Plasota, T., Nawrocki, J., Walaszczyk, I. 2015. Magnetostratigraphy of the Campanian/Maastrichtian bound ary suc ces sion from the Mid dle Vistula River sec tion, cen tral Po land. Geo log i cal Quar terly, 59 (4): 831–842, doi: doi: 10.7306/gq.1262 The mag netic po lar i ties of the up per Up per Campanian–Lower Maastrichtian in ter val of the Mid dle Vistula River com pos ite sec tion (cen tral Po land), were stud ied. Sixty-six hand-ori ented sam ples for palaeomagnetic stud ies were taken from the sec - tions of Raj, Raj North, Podole, K³udzie and Dziurków. The inter-cor re la tion be tween them is based pri mar ily on bio-events.
The sam pled rocks gen er ally re vealed a very weak mag netic sig nal, how ever, quite re li able re sults were ob tained. The whole in ter val stud ied, well con strained biostratigraphically, is re ferred to magnetostratigraphic chron C32n. The Campan - ian/Maastrichtian bound ary, placed biostrati graphically in the up per part of the “Inoceramus” redbirdensis inoceramid Zone, is lo cated near the top of the C32n2n Subchron. Thin re versed po lar ity in ter vals in the rocks cor re lated with the C32n2n chron most prob a bly re sult from their par tial re mag net isa tion (maghemitisation).
Key words: magnetostratigraphy, Campanian/Maastrichtian bound ary, Po land.
INTRODUCTION
Due to endemism/pro vin cial ism (e.g., bel em nites, ammonites) and diachroneity (e.g., ammonites, planktic foraminifera) of a num ber of biostratigraphic mark ers across the Campanian/Maastrichtian bound ary (see e.g., Bur nett, 1998; Christensen et al., 2000; Howe et al., 2003; Mutterlose et al., 2005; Ward et al., 2012; Peryt and Dubicka, 2015), there are prob lems with sim ple long-dis tance bio-cor re la tion within this in ter val. The ap pli ca tion of the o ret i cally isochronous and po ten tially very ef fec tive meth ods, in de pend ent of avail able biostratigraphies, is thus of im por tance. Among the avail able tools cur rently used, magnetostratigraphy, be sides chemostratigraphic meth ods, is avail able herein.
The Campanian–Maastrichtian suc ces sion of the Mid dle Vistula River com pos ite sec tion is ex tremely fossiliferous, yield - ing all stratigraphically rel e vant palaeontological macro- and mi cro-groups, which en able straight for ward biostratigraphic cor re la tion to the basal Maastrichtian stratotype sec tion in Tercis, SW France. This gives a chance for a re li able biostratigraphic dat ing of the magnetostratigraphic sig nal, whose di rect cor re la tion is ham pered by the lack of po lar ity in - ver sions. The re corded mag netic sig nal in the Tercis sec tion does not range to the base of the Maastrichtian (see Odin and
Lamaurelle, 2001; also Voigt et al., 2012: fig 3). This makes the Mid dle Vistula an im por tant ref er ence point to other sec tions, with good/ex cel lent magnetostratigraphic scale, how ever, with lim ited biostratigraphic con trol (e.g., the Gubbio sec tions; Ar thur and Fischer, 1977; Lowrie and Alvarez, 1981; Coccioni and Premoli Silva, 2015) or to those quite re mote biogeographically (such as the Red Bird sec tion, US West ern In te rior; see Gill and Cobban, 1966; Hicks and Obradovich, 1995 and lit er a ture therein; or the east ern North Pa cific, see Ward et al., 2012).
This pa per pro vides the magnetostratigraphy of the up per Up per Campanian through to basal Maastrichtian of the Mid dle Vistula sec tion (cen tral Po land; Fig 1), con strained by biostratigraphic meth ods (see Walaszczyk, 2012; Remin, 2012;
Keutgen et al., 2012; Machalski, 2012; and also Peryt and Dubicka, 2015). The goal was the chronostratigraphic cor re la - tion of the stud ied Campanian-Maastrichtian in ter val. With the ex cep tion of a nar row in ter val across the Cre ta ceous–Danian bound ary (Hansen et al., 1989), the mag netic prop er ties of the Mid dle Vistula River suc ces sion, have never been pub lished pre vi ously (al though at least one at tempt was an nounced by Hambach et al., 1995).
GEOLOGICAL SETTING AND PREVIOUS STUDIES
The Mid dle Vistula River val ley com pos ite sec tion is lo cated in south-cen tral Po land, about 150 km SSE of War saw (Fig. 1).
This com pos ite sec tion, con sist ing of a set of nat u ral and ar ti fi - cial ex po sures along the Vistula River val ley, ex poses the Mid - dle Albian–Danian suc ces sion, al beit with nu mer ous ob ser va -
* Corresponding author, e-mail: i.walaszczyk@uw.edu.pl Received: May 16, 2015; accepted: November 30, 2015; first published online: November 30, 2015
Fig. 1. Geological sketch-map of the investigated area (after Walaszczyk, 2004, 2012)
tional gaps. The Campanian/Maastrichtian bound ary in ter val is best ex posed in the vi cin ity of the town of Solec, on the west ern bank of the river, be tween the vil lages of Paw³owice and K³udzie North. The only good ex po sure on the east ern bank is a huge aban doned quarry south of the vil lage of Piotrawin (Fig. 1). Struc tur ally, the area of the Mid dle Vistula val ley be - longs to the south ern wing of the Bor der Synclinorium, one of the main geo log i cal struc ture of ex tra-Carpathian Po land, trending NW–SE through the whole coun try (Po¿aryski, 1974;
Kutek, 2001; ¯elaŸniewicz et al., 2011). Con se quently, the ob - served strata gently dip (5 to 10°) homoclinally to the NE (Po¿aryski, 1948). With the ex cep tion of the basal Mid dle–Up - per Albian part of the suc ces sion, the rest of the Cre ta ceous is rep re sented by mo not o nous car bon ate fa cies, dom i nated by si - li ceous marls (named opokas), rarely chalk (Po¿aryski, 1948).
The first re li able re port on its Up per Cre ta ceous suc ces sion and biostratigraphy was pub lished by Po¿aryski (1938, 1948).
He sub di vided the Campanian/Maastrichtian bound ary in ter val stud ied herein into three suc ces sive units: t, u, and v, dated by him en tirely as Maastrichtian (Fig. 2). These units show a mixed lithological-biostratigraphic char ac ter and, al though use ful in the early stages of the rec og ni tion, are no lon ger used. Sub se - quent stud ies of the bound ary in ter val com prised macro- and microfossil groups, pri mar ily those biostratigraphically mean - ing ful (Fig. 2): ammonites (B³aszkiewicz, 1980; Machalski, 1996, 2012; Remin et al., 2015), bel em nites (Kongiel, 1962;
Remin, 2012, 2015; Keutgen et al., 2012), inoceramids (Walaszczyk, 2004), foraminifers (Po¿aryska, 1954, Po¿aryska and Peryt, 1979; Peryt, 1980, 2000; Peryt and Dubicka, 2015),
and nannofossils (GaŸdzicka, 1978; Bur nett et al., 1992). Also groups with lit tle or poorly known biostratigraphic po ten tial, but rep re sent ing dom i nant el e ments of the re cord, were in ten sively stud ied; gas tro pod and bi valve molluscs (Abdel-Gawad, 1986) or sponges (Œwierczewska-G³adysz, 2006, 2012). Kongiel (1962) raised the base of the Maastrichtian into the mid dle part of Po¿aryski’s unit t, cor re spond ing to the low est oc cur rence (FO) of the bel em nite Belemnella (Belemnitella ac cord ing to that au thor) lanceolata (Schlotheim), in agree ment with the place ment of the bound ary at that time, as widely used in Bo real and West ern Eu rope (Arkhangelsky, 1912; Jeletzky, 1951; see also Birkelund et al., 1984). This bound ary place ment was used since then, un til the FO of the ammonite Pachydiscus neubergicus (Hauer) was ac cepted pro vi sion ally as the best basal Maastrichtian marker (Odin, 1996). Fi nally, the base of the Maastrichtian was raised up to around this level when the base of the stage was de fined at a level cal cu lated as an arith - me tic mean of 12 bioevents as rec og nized in the Tercis quarry, the ac cepted stratotype sec tion of the basal Maastrichtian bound ary, which ap peared to be slightly lower than the FO of P.
neubergicus (Odin and Lamaurelle, 2001). In the Mid dle Vistula River sec tion the new place ment of the bound ary was rec og - nized based on inoceramid bi valves (Walaszczyk, 2004; see also Walaszczyk et al., 2002a, b) and ammonites (Machalski, 2012); the en tire Po¿aryski’s units t and u, and lower part of his unit v were re ferred to the Maastrichtian. The bel em nite and foraminiferal prox ies of the bound ary (af ter Remin, 2012;
Keutgen et al., 2012; Peryt and Dubicka, 2015) are shown in Fig ure 2.
Fig. 2. Chronostratigraphy and biozonations, and vertical ranges of critical ammonite species (after various authors) of the uppermost Campanian and basal Maastrichtian of the Middle Vistula section
P. – Pachydiscus
SAMPLING LOCATIONS
Sixty-six hand-ori ented sam ples for palaeomagnetic stud - ies were taken from the sec tions of Raj, Raj North, Podole, K³udzie and Dziurków (Fig. 1 and Ta ble 1). The inter-cor re la tion be tween them is based pri mar ily on bio-events. Brief char ac ter - is tics of the sam pled lo cal i ties in strati graphic or der are given be low (see Fig. 1 for the geo graphic lo ca tion); inoceramid biostratigraphy is af ter Walaszczyk (2004).
Raj. Small ru ral quarry lo cated south of the vil lage of Raj, in the north ern wall of a lit tle river val ley flow ing from the west into the main Vistula val ley. 7 m of the suc ces sion, as signed to the
“Inoceramus” inkermanensis Zone, are ex posed.
Raj North. Small ru ral quarry, lo cated about 500 m south-west of the main cross-road in the town of Solec. 12 m of the suc ces sion are ex posed in the south ern wall of the quarry, as signed to the Trochoceramus costaecus Zone and basal part of the “Inoceramus” redbirdensis Zone. The low est oc cur rence of Belemnella lanceolata (Schlotheim), a bel em nite marker of the base of the Maastrichtian in the tra di tional Eu ro pean def i ni - tion of this bound ary (see B³aszkiewicz, 1980; also Keutgen et al., 2012; Remin, 2012) is rec og nized in this quarry.
Podole. 15 m high wall in the west ern Vistula bank, close to the north ern edge of the vil lage of Podole, about 300 m north of the cas tle ru ins in the town of Solec. The suc ces sion is as - signed to the zones of Trochoceramus costaecus and
“Inoceramus” redbirdensis.
K³udzie South. The ex po sure is in the west ern bank of the Vistula River, south of the ferry river port in the vil lage of K³udzie. 18 m of the suc ces sion are ex posed. There is a dis tinct marly ho ri zon (“bound ary marl”, close to the Campanian/Ma - astrich tian bound ary as de fined by Walaszczyk, 2004), lo cated in the mid dle part of the ex posed suc ces sion. The suc ces sion be longs to the “Inoceramus” redbirdensis Zone and to the lower part of the Endocostea typica Zone.
Dziurków. Work ing ru ral quarry lo cated at the east ern edge of the vil lage of Dziurków, south of the road Solec–Lipsko. The quarry ex poses 15 m of the suc ces sion of the Endocostea typica Zone.
LABORATORY METHODS
Palaeomagnetic sam ples were hand-sam pled and ori ented with trend and plunge and taken man u ally off the solid rock.
They were cut in the lab o ra tory to one inch di am e ter cy lin dri cal spec i mens (no less than two spec i mens from each sam ple) and sub se quently ther mally de mag net ised. The in ten sity of nat - u ral remanent mag net is ation (NRM) was mea sured on JR6A spin ner mag ne tom e ter, and mag netic susceptilibity with a kappa bridge KLY-2. Spec i mens were heated to 450°C with the fol low ing steps: 100, 150, 200, 250, 300, 325, 350, 380, 400, 425 and 450°C. Fur ther de mag neti sa tion was not ef fec tive be - cause the in ten si ties of remanent mag net is ation were be low the sen si tiv ity of the mag ne tom e ter. Mag netic susceptilibity changes were mon i tored af ter each step of de mag neti sa tion.
The ob tained data were com puted sta tis ti cally on Remasoft com puter soft ware (Chadima and Hrouda, 2006), which pro - duced dec li na tion and in cli na tion val ues for ev ery de mag neti sa - tion step and mean mag netic di rec tions. The re sults of de mag - neti sa tion were eval u ated ac cord ing to the least square line-fit method as de scribed by Kirschvink (1980). Lowrie’s test (Lowrie, 1990) was ap plied in or der to de ter mine the na ture of mag netic car ri ers. For this pur pose ten sam ples from the Dziurków and Podole sec tions were se lected. All stud ies were per formed in the Paleomagnetic Lab o ra tory of the Pol ish Geo - log i cal In sti tute – NRI.
RESULTS
MAGNETIC CARRIERS
The iso ther mal remanent mag net is ation (IRM) ex per i ment and sub se quent de mag neti sa tion of sam ples mag net ised in three per pen dic u lar di rec tions ac cord ing to the Lowrie test (Lowrie, 1990) in di cate the pre dom i nance of two phases of low to me dium coercivity mag netic car ri ers. One of them gives a sig nif i cant drop of IRM at tem per a tures up to ca. 450°C, and an - other has un block ing tem per a tures be tween 550 and 600°C (Fig. 3). Such prop er ties point to the pres ence of maghemite and mag ne tite in the stud ied rocks (e.g., Dunlop and Özdemir, 1997). It should be noted, how ever, that the low coercivity car - rier of IRM does not de mag net ise com pletely even at a tem per - a ture of 600°C. Most prob a bly it is be cause the ox i da tion of maghemite dur ing the heat ing in air con di tions that leads to the pro duc tion of he ma tite with un block ing tem per a tures >600°C that is not pri mary, be ing not de tected dur ing ac qui si tion of IRM.
It can not be ex cluded that a sig nif i cant drop of IRM at tem per a - tures <500°C can be partly linked also with the pres ence of ti ta - nium-rich mag ne tite.
DEMAGNETISATION RESULTS –
PALAEOMAGNETIC COMPONENTS AND PALAEOPOLE
Al most all sam ples show weak nat u ral rem nant mag net is - ation (NRM). The in ten si ties of NRM lie be tween 0.17 and 1.65 ´1 0–4 A/m, with mean a value of about 0.8 ´ 10–4 A/m. This fact and min er al og i cal changes dur ing sub se quent heat ing re - Lo cal ity Num ber of hand sam ples and
spec i mens (in the brack ets) for palaeomagnetic stud ies
GPS co or di nates of stud ied lo cal ity
Raj 13 (27) N51°6’51.8508"
E21°45’18.7056"
Raj North 13 (32) N51°7’33.8268"
E21°44’ 50.7048"
Podole 22 (59) N51°8’17.8656"
E21°46’23.2284"
K³udzie
South 15 (41) N51°9’9.3564"
E21°46’43.6764"
Dziurków 13 (36) N51°8’17.97"
E21°42’54.1296"
T a b l e 1 Sam pling sta tis tics and GPS co or di nates for par tic u lar lo cal i ties
sulted in 12 sam ples a very un sta ble de mag neti sa tion path in 12 sam ples. For tu nately other sam ples en abled the char ac ter - is tic rem nant mag net is ation (ChRM) to be de fined in at least two spec i mens. The Late Cre ta ceous geo mag netic field in the study area, be ing a part of sta ble Eu rope, should pro vide a char ac ter is tic di rec tion with dec li na tion ori ented ap prox i mately N–S and in cli na tion close to ca. 60° (see e.g., Besse and Curtillot, 2003). Well-de fined char ac ter is tic com po nents of re - versed or nor mal po lar ity cor re spond to a wide spec trum of un - block ing tem per a tures. The big gest drops of the NRM in ten si - ties can be ob served at 100–200°C and 350–450°C (Fig. 4). It should be stressed, how ever, that these two tem per a ture in ter - vals do not al low two sep a rate com po nents of the NRM to be dis tin guished. The low and me dium tem per a ture di rec tions have the same po lar i ties and their spa tial sep a ra tion is im pos si - ble. It is likely that these magnetisations were ac quired dur ing the same geo mag netic po lar ity in ter val, close to each other in time. Be cause of the low ini tial val ues of the NRM most of the sam ples were not com pletely de mag net ised and it is very likely that mag ne tite doc u mented by the IRM de mag neti sa tion curves (Fig. 3), car ries also the ChRMs. In some sam ples the char ac ter is tic com po nents were not suf fi ciently sta ble for their de ter mi na tion by the line-fit method (Fig. 5, sam ples: SN 7A and SN 10A). In this case, the di rec tion de fin ing the po lar ity was cal cu lated as the mean from at least three steps of de mag neti - sa tion. Eleven sam ples re vealed the pres ence of anom a lous char ac ter is tic di rec tions with de vi ated val ues of in cli na tion or dec li na tion (Fig. 5, sam ples: SN 9A and SN 6A; Fig. 6). In spite
of par tial de mag neti sa tion, these di rec tions can be still re sul tant in or i gin i.e. con tain ing an ad mix ture of com po nent with op po - site po lar ity. This fact in di cates that the rocks stud ied can also con tain sec ond ary com po nents of mag net is ation. These could be linked with maghemite formed due to the ox i da tion of mag - ne tite grains af ter their sed i men ta tion.
Only a few good qual ity ChRM di rec tions de fined by the line-fit method were ob tained. Most of them were ob tained from the Dziurków and Podole lo cal i ties. Be cause of this, the mean palaeomagnetic di rec tion and the palaeopole were cal cu lated only for these lo cal i ties (Fig. 7). The re versed po lar ity di rec tions with neg a tive in cli na tions are lo cated in the op po site part of the hemi sphere from the nor mal po lar ity ones. With a cal cu lated crit i cal an gle gc = 10.12 and an ob served an gle g = 2.07 they ev i - dently pass the re ver sal test (McFadden and McElhinny, 1990).
Di rec tions de fined on sam ple sta tis ti cal level group rel a tively well, with the re sult that the palaeomagnetic pole lies at a lat i - tude of 78°N and a lon gi tude of 173°E. This palaeopolar po si - tion was com pared with the ap par ent po lar wan der path char ac - ter is tic for sta ble Eu rope (Besse and Courtillot, 2003). It fits well to the Late Cre ta ceous seg ment of this path.
MAGNETIC POLARITIES
The nor mal and re versed po lar ity di rec tions are grouped se - quen tially in nor mal and re versed po lar ity zones. Mixed po lar ity zones are doc u mented in the sec tions of K³udzie and Raj North.
Fig. 3. Thermal demagnetisation of selected samples in artificial magnetic field (so called three axies experiment; Lowrie, 1990) Samples DZ 1, DZ 5 and DZ 9 were taken from the Dziurków locality, samples SN 7, SN 14 and SN 16 represent rocks from the Podole outcrop
Fig. 4. Ex am ples of ther mal de mag ne ti sa tion of palaeomagnetic sam ples from the Dziurków (sam ples DZ 4B, DZ 4C, DZ 6AB, DZ 9A) and Podole (sam ples SN 12C, SN 19B) sec tions that pro vided a good qual ity data i.e. char ac ter is tic di rec tions de fined by the line-fit method (ste reo graphic plot of palaeomagnetic di rec tions dur ing de mag neti sa tion (left-up per fig ure), or thogo nal plot (right fig ure) and in ten sity de cay curve (left down fig ure)
Cir cles in the or thogo nal plots rep re sent ver ti cal pro jec tions, squares rep re sent hor i zon tal pro jec tions; Irm – in ten sity of remanent mag net is - ation, Inrm – ini tial in ten sity of nat u ral remanent mag net is ation; the di a grams were pre pared by the means of com puter pack age writ ten by Lewandowski et al. (1997); in the ta ble pre sented be low the di a grams the line-fit di rec tions are listed (D – dec li na tion, I – in cli na tion, INT – drop of NRM in ten sity re lated to par tic u lar line-fit di rec tion, A.S.D – an gu lar stan dard de vi a tion, RANGE – tem per a ture in ter val for which par - tic u lar line-fit di rec tion was cal cu lated)
Fig. 5. Examples of thermal demagnetisation of samples from the Podole section with oscillating palaeomagnetic direction (samples SN 7A, SN 10A) and providing characteristic directions deviated from
the expected locations (samples SN 9A, SN 6A) Explanations as in Figure 4
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Sam ples from the Dziurków, K³udzie and Raj sec tions were mag net ised ho mo ge neously in the re versed or nor mal po lar ity di rec tion (Fig. 8). Un cer tain po lar i ties were con nected with the un sta ble and re sul tant di rec tions. The re versed po lar ity zones pos tu lated in the mid dle part of the Podole sec tion and the low - er most part of the Raj North sec tion were drawn with a ques tion mark be cause they are based on sin gle sam ples with still shal - lower (be tween –20 and –30°) than ex pected val ues of in cli na - tions. The thick nor mal po lar ity zone de fined in the syn thetic magnetostratigraphic col umn ac cord ing to data from the Podole and Raj North sec tions is not con tin u ous. In fact, it was bro ken three times by re versed po lar i ties. It should be stressed, how ever, that only the re versed zone from the top most part of the Podole sec tion is based on fully re versed di rec tions iso lated in more than one sam ple. Be cause of this, it is not drawn with ques tion mark.
DISCUSSION
Magnetostratigraphic study was un der taken for the in ter val rep re sented by the Raj, Raj North, Podole, K³udzie and Dziurków sec tions, which span the top most Campanian (inoceramid bi valve zones of “Inoceramus” inkermanensis; “I.”
costaecus and “I.” redbirdensis (lower two-third of the zone), and the basal Lower Maastrichtian (the top third of the “I.”
redbirdensis Zone, and the zone of Endocostea typica; see
Figs. 2 and 8). Ref er ence is made be low to the re cently pub - lished scale by Ogg and Hinnov (2012). A nor mal po lar ity re - cord from the K³udzie sec tion falls into the “Inoceramus”
redbirdensis Zone and the basal part of the Endocostea typica Zone and, based on the global magnetostratigraphic scale, it is at trib uted to subchron C32n2n. Such con straints lead to the con clu sion that all out crops apart from Dziurków are co eval with subchron C32n2. Thin re versed po lar ity in ter vals noted in the Podole and Raj North sec tions could rep re sent cryptochrons that have not been rec og nized be fore this study. How ever, it is dif fi cult to ac cept this in ter pre ta tion be cause this part of the GPTS is based on good qual ity, densely-spaced data (see Ogg and Hinnov, 2012). More likely these thin re versed po lar ity in - ter vals could re sult from par tial re mag net isa tion of the stud ied rocks caused by late maghemitisation of mag ne tite grains. It should be stressed, how ever, that Lerbekmo and Braman (2002) pub lished magnetostratigraphic data from Can ada (Al - berta) with three short re versed po lar ity zones in side subchron C32n2n. Fur ther palaeo- and petromagnetic stud ies are nec es - sary to re solve this prob lem.
The re versed po lar ity re cord from the Dziurków sec tion falls into the Endocostea typica Zone, so it was as sumed to be a part of chron C32n1r (Fig. 8). Its cor re la tion with the subchron C31r is not prob a ble. Inoceramids char ac ter iz ing the Dziurków suc - ces sion are typ i cal of the lower half of the E. typica Zone; its up - per part, char ac ter ized by “Inoceramus” incurvus (or re ferred to this zone; see Walaszczyk et al., 2001; see also Ogg and Fig. 7A – ste reo graphic pro jec tion of palaeomagnetic di rec tions cal cu lated for the best qual ity sam ples from the Dziurków and Podole sec tions with their sum mary sta tis tics; B – palaeopole cal cu lated for the same sam ple set plot ted as the black cir cle (named VRS) on the back ground of the ap par ent po lar wan der path (APWP) char ac ter is tic for sta ble Eu rope (Besse and Courtillot, 2003); C – sum mary sta tis tics for the best qual ity sam ples from Dziurków and Podole
a95 – semi-an gle of 95% con fi dence, K – pre ci sion pa ram e ter, N – num ber of sam ples, D – mean dec li na tion, I – mean in cli na tion, L – lat i tude of palaeopole, F – lon gi tude of palaeopole, D1 – er ror of the dis tance be tween site and palaeopole, D2 – palaeodeclination er ror
Hinnov, 2012: fig. 27.6), is not rep re sented. Sim ple cor re la tion with the GPTS of magnetozones from Raj and Raj North sec - tions could lead to the con clu sion that these rocks were de pos - ited dur ing chron C33. This is not pos si ble as all the biostratigraphic ev i dence show this part of the suc ces sion to be of lat est Campanian (see Figs. 2 and 8). The nor mal po lar ity re - cord from the Raj sec tion cor re sponds to nor mal subchron C32n2n. The re main ing nor mal po lar ity in ter vals from the
Podole and Raj North sec tions be long to the “Inoceramus”
redbirdensis and “Inoceramus” costaecus zones re spec tively.
Both mag netic po lar ity re cords were also at trib uted to nor mal chron C32n2n. Ac cord ingly to our magnetostratigraphic cor re - la tion, the Maastrichtian/Campanian bound ary is prob a bly lo - cated in the mid dle part of the K³udzie sec tion, in the up per part of nor mal po lar ity subchron C32n2n.
Fig. 8. Magnetostratigraphy of the Dziurków, K³udzie, Podole, Raj and Raj North sections and their correlation with the global magnetostratigraphic (scale after Ogg and Hinnov, 2012); biostratigraphy after Walaszczyk (2004; inoceramids); Machalski
(2012; ammonites); Remin (2012; belemnites); Peryt (1980; foraminifers)
CONCLUSIONS
1. Cre ta ceous rocks from the Mid dle Vistula River val ley are use ful for magnetostratigraphic stud ies de spite their weak in - ten sity mag net is ation and a par tial late re mag net isa tion that most prob a bly re sults from maghemitisation of mag ne tite grains; fur ther palaeo- and petromagnetic stud ies are nec es - sary.
2. The biostratigraphically con strained Campanian/Ma - astrichtian bound ary, placed in the stud ied suc ces sion close to the FO of the inoceramid bi valve Endocostea typica (Whitfield), and the ammonite, Pachydiscus neubergicus (Hauer) FAD, is lo cated in the up per part of the nor mal po lar ity subchron C32n2n. The stratigraphically youn gest Dziurków sec tion, as -
signed to the Endocostea typica inoceramid Zone should be placed in the re versed po lar ity subchron C32n1r.
3. Fine re versed po lar ity in ter vals are noted in the Podole and Raj North sec tions. They could re sult from par tial and se - lec tive remagnetisation of the stud ied rocks due to late maghemitisation.
Ac knowl edge ments. I. Walaszczyk ac knowl edges the fi - nan cial sup port of the Fac ulty of Ge ol ogy of the Uni ver sity of War saw (BST grant No. 173502). We are grate ful for help ful re - views from J. Grabowski, S. Satolli and an anon y mous re - viewer, as well as for lin guis tic im prove ment of the fi nal ver sion by Ch.J. Wood.
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