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The Middle Cambrian of Bornholm,Denmark: A stratigraphical revision ofthe lower alum shale and associatedanthraconitesVivianne Berg-MadsenPublished online: 06 Jan 2010.

To cite this article: Vivianne Berg-Madsen (1984) The Middle Cambrian of Bornholm, Denmark: Astratigraphical revision of the lower alum shale and associated anthraconites, Geologiska Föreningen iStockholm Förhandlingar, 106:4, 357-376, DOI: 10.1080/11035898509454664

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The Middle Cambrian of Bornholm, Denmark: A stratigraphical revision of the lower alum shale and associated anthraconites

VlVlANNE BERGhl ADSEN

Berg-hfadsen, V., 19S5 1030: The hfiddle Cambrian of Bornholm, Denmark: A stratigra- phical revision of the lower alum shale and associated anthraconites. Geologiska Foreriiiigetis i Stockholtti Forhatidlitigar, Vol. 106 (for 1984). Pt. 4, pp. 357-376. Stockholm. ISSN 0016-

The hliddle Cambrian loiver alum shale and the associated anthraconites are reexamined and revised bio- and lithostratigraphically. New finds of predominantly agnostid trilobites show that the sequence is far more restricted stratigraphically than hitherto supposed. Lithologi- a l l y the anthraconite beds do not fulfil the definitions of the term anthraconite. Due to long tradition of use the name basal atitliracoiiire is maintained for the lower liniestonc. The anthraconite overlying the alum shale is referred to as Hjolirlies litiiesiotie. as it is a bio- and lithostratigraphical equivalent of the IIyolithes limestone in Sweden. The agnoslid zonation of \\'estergird, used in and outside Scandinavia, is reviewed. The absence of the Ptjcliag- tiosrru Irrridgretii - P. iinrliorsli Zone on Bornholm is proved. The validity of the zone of Prjchagtiosrirs Iitridgrerii - P. riarliorsri is questioned, not only in Scandinavia but wherever the agnostid zonation of Westergird is used. A correlation xith the interval-zones in North America is attempted. The Pijchagtiosrus atavrt~ Zone is tentatively divided into a lower subzone, Totringrios/iis fissris, and an upper with Ilypagtiosriu panifrotis. The zone of Pijclragriosrits rinrhorsri is merged with the zone of P. pitticriiosirs within the Paradoxides paradoxissitnits zonal group. 0 Lower aliirii shale, basal atihacotiire, Hjolirlres littiestotie, biostratigraphy, lithosrmtigrapliy, agtiosrid zotiarioti, radiography, FeS, organic C, Trilobira, Hjolirhidae, Protospongia, Ptychagnostus punctuosus puntcuosus, P. nathorsti, P. atavus, Tomagnostus fissus, Hypngnostus parvifrons, 1-cjopyge lundgreni, Solenopleura nuntia, S. brachymctopa, Paradoxides dnvidis, P. forchhamrneri, P. paradoxissimus. Pnmdo.rissimn zonal groiip. irirerval-zones, Scatiia (Skdtie). Swedeti, Noricxj , Polarid, Great Britain, Norih Greerilatid, Neivfoitridlatid, North Arrierica, Aiistralia, hfiddle Carribriarr, Lmsrf, @lei. Borti- holtti, easterr1 Derirtiark, NSJSY N5517 El442 E15OS. Viriatitie Berg-hladseti, Departtiierir of Paloeobiologj, Palneovrological Imtiriire, Box 5-58. S- 751 22 Uppsala, Swedeti. Presetit address: Geologiska iristiritrioneti, S-106 91 Srocklioltti, Swedeti. hlariitscripr received 31 htoy 1993.

GFF 786>(.

The Cambrian stratigraphy of Bornholm was chiefly established by Johnstrup (1874,1891) and Gronwall (1899, 1902). Minor corrections and supplements were added by C. Poulsen (1923, 1932, 1960), Hansen (1936, 1937, 1945). and V. Poulsen (1963, 1966).

The basal Middle Cambrian Exsulans Lime- stone was revised by Berg-Madsen (1981) who described the previously unknown anthraconite between the Kalby marl and the lower alum shale a t the rivulet LxsA near the farms at Kalby (Fig. 1B). This find demonstrated the sequential similarity with the section at the rivulet @lei a t Borregird (farm) (Fig. 1C). Further investiga- tions have provided a rich fauna, mainly of trilo- bites, from both the anthraconite and the lower alum shale. The material is regarded as sufficient for a stratigraphical revision of the Middle Cani- brian sequence: (1) basal anthraconite, (2) lower alum shale and (3) overlying anthraconite which

here is called IIyolithes limestone. The limestone represents the transition between the Paradox- ides paradoxissirillis and P. forclilinriiiiieri zonal groups (Fig. 2).

Previous investigations Several Cambro-Ordovician localities on Born- holm are former alum shale/limestone quarries, such as Limensgade, Kalby, Skelbro and Uorre- gird (Jespersen 1913). Associated with the quar- ries were wind mills where the first crushing of the limestone took place before transport to the cement factory at R o m e . Some limestones, for example the Andrarurn Limestone at Borregird, were also used for marling due t o their clay content (Gronwall 1899). At 01eb the crushing mill was situated at the highest point available, 200 m N N W of the rivulet W of Borregird

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358 Viviairtie Berg-Madsai GFF 106 (19SJ)

BORNHOLM SOUTHERN PART

7- FAULT - S E D I M E N T A R Y BOUN

4 @ORDOVICIAN-SILURIAN

LOWER ORDOVICIAN 3= MIDDLE-UPPER C A M B R I A N 1 ALUM SHALE

2 0 LOWER CAMBRLAN I D PRECAMBRIAN

fig. 1. hlaps showing: CIA. Somc of thc Scandinavian localilics mcntioncd. B. ‘I‘hc fuult block system around the rivulet Lasb. Nunibcrs rcfcr to lcgcnd below, scale as in C. OC. ’I‘hc fault block s)-stcm around the rivulet @lei3 and the localities mcntioncd on I3ornholm. 0 D. T h c southcrn part of Bornholm \vith thc distrihution of fault blocks (slightly simplified). Inscrtcd sketch maps I3 and C. hlodified after Gry (1960). Gry et 31. (1969). and hlnrtinsson (1974).

(Gr6nwall 1902, p. 8). The quarry at the rivulet Hjulmagerghd in connection with a well digging supplied this mill. (Fig. lB) , another is labelled ‘01ei’ and consists

Obviously, it was convenient to collect samples of Exsulans Limestone which was unknown t o at the crushing mill, and most samples collected Johnstrup. Furthermore, the manager of the by Johnstrup are in fact labelled ‘Cementmol- crushing mill systematically collected fossils for len’. A single sample was collected at the farm the Geological Museum in Copenhagen

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GFF 106 (19SJ)

LeJoDyg. *.vg.t.

c3

Solonopkura brachymetopa

c2

Plychagnotlus lundgronl

The htiddlr. Cnriibriaii of Uorrihobri 359

upper alum rhale upper alum Ihalo

Andrarum Llmerlone Andrarum Llmerlone

anlhraconllo and anthraconlle and

ZONAL GROUPS

Paradoxides

forchhammeri

Para doxide s para doxissimus

Eccaparadoxldes

o elandicus

LITHOSTRATIGRAPHICAL DIVISIONS TRILOBITE ZONES

POULSEN 1966 I BERG-MADSEN 1981

lower alum ahale lower alum rhale Hypagnostus parvllrons

Tomagnostus

Plychapnosfus

i lssus

a la rus 8 2

A 1 and A 2

NOT PRESENT

Fig. 2. The hliddle Cambrian stratigraphy from Poulscn (1966) and Dug-hladscn (19S1). The basal anthraconite is included in the lower part of the lowr alum shale (see also Fig. 10 herein).

(Griinwall 1902). These collecting procedures lead to confusion of the different anthraconites and serious mistakes in the stratigraphical inter- pretation.

Johnstrup (1874) described the Middle Cam- brian of Bornholm as consisting of 100 cm lower alum shale overlain by 70 cm Andrarum Lime- stone. Determinable fossils were not found in the alum shale, but from presumed anthraconite lenses within the shale he listed: I’onmdoxidcs sp., Conocoryphe sp., PtjcIiogtiostiis piirictiiosiis,

Ilyprigiiostiis cxsciilptiis, Lejopygc loevignto, Di- plagtiostiis plmiicairdo and Hyolithes sp. (names revised after WestergArd 1916, 1953). It is worth noting that specific localities, LssA or (dleii, for these fossils were not reported.

Tullberg (ISSO) visited Bornholm in order to compare the Cambrian here with that of Scania

(Skdne). From the rivulet LxsA he recorded alum shale overlain by Andrarum Limestone, while a t - 0 l c b a n anthraconite bed - my I-Iyo- lithes limestone - was regarded as corresponding to the alum shale which was not observed at this locality. From the anthraconite he listed 17 spe- cies of trilobites, including in the material four specimens from the Geological Museum in Co- penhagen.

Johnstrup (1891) extended his description of the lithological division. At LxsA he distin- guished lower alum shale overlain by anthracon- ite followed by Andrarum Limestone. From a l e % he recorded less than 10 cm lower alum shale, 30 cm anthraconite (bed and lenses), 9 cm alum shale and finally SO cm Andrarum Lime- stone. To the fossils listed from the anthraconite, presumably from (dlei, Johnstrup added four

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360 Viviatitie Berg-Aladseti GFF 106 (1981)

species from the list of Tullberg (18SO). Two of the four were based on specimens from the Geo- logical Museum in Copenhagen and probably collected by Johnstrup himself.

Gronwall (1902) quoted this combined John- strup and Tullberg list referring it t o the lower alum shale belonging to the Pnrndoxides porn- doxissit)iiu - P. davidis zones. His own material from the lower alum shale was too poorly pre- served to be determinable, and only museum specimens collected by Johnstrup were listed, this time identified as: Paradoxides pnradoxissi- tiiics, Parasoleriopleiira litinnrssotii, Bailiella ae- qiialis, Dorypyge dntrica, Hypngttostiis pnrvifrotis and Ptyclingriostics piitictiiosils (names revised after Westergird 1946, 1953).

Studying the anthraconite (herein I Iyolithes limestone) overlying the lower alum shale at LzsB, Gronwall clearly noted that he was dealing with two faunas divisible in a lower and an upper part with a gradual transition in between. I le compiled four lists of trilobites and other fossils according to their distribution: 1) common in the lower part of the bed, 2) common or only present in the upper part, 3) common in both parts and finally 4) common in the transition layer, also called fragment limestone, making contact with the Andrarum Limestone.

At @le i Gronwall (1899, 1902) recorded the basal anthraconite overlying the Exsulans Lime- stone (Fig. 10) both of which he was the first to observe on Bornholm. The basal anthraconite only yielded a single specimen of Hypngtiostiis pnrvifroris collected in situ, and was regarded mostly as unfossiliferous since only a few addi- tional but indeterminable trilobites ( S o b i o - phrra?, P~irnsoletiopleiirn?) were found in spite of careful searching in connecting with blasting.

From @lei Gronwall (1902) recorded SO cm lower alum shale and listed the following species from the lower part: Ifypogtiostiis pnrvifrotis, Ptyhagnostits purictiiosiis?, 1’. ititeritiediirs, Per- oriopsis f a l l r ? . Only P. piitictiiosiis was not of his own finding (Gronwall 1902).

Undulation in the lower part of the lower alum shale made Gronwall accept Johnstrup’s as- sumed anthraconite lenses although he did not see any in place. In the museum he studied sam- ples, collected by Johnstrup and others, and from the fossil content referred these to two levels, i.c. Icnses in the lower and upper parts of the lower alum shale a t 0leA. In ‘note in proof Gronwall furthermore added a list of fossils found in an (assumed?) anthraconite lens by von SchmalensCe. This lens was regarded as repre- senting a third level, showing a transition from

the lenses presumed in the upper part of the alum shale to the overlying anthraconite bed ( I lyolithes limestone herein). The anthraconite overlying the lower alum shale was separated from the Andrarum Limestone by 10-30 mm alum shale. It yielded several new trilobite and other fossil species t o the list of Johnstrup and Tullberg.

Gronwall divided the Middle Cambrian into four zones including three subzones according to Torell (1870), Tullberg (lSSO), and Linnarsson (1883) based on the la) Exsulans Limestone, l b ) the basal anthraconite, l b + c) the lower alum shale including three levels with presumed anthraconite lenses, 2) the overlying anthracon- ite, 3).the Andrarum Limestone and 4) the up- per alum shale including its existing anthraconite lenses. His zonation was used with minor changes by Poulsen (1932, 1960) and Ilansen (1945). Compared with the type locality a t An- drarum in SkBne, Sweden (Fig. lA), the Middle Cambrian of Bornholm appeared to be very in- complete.

The Cambro-Silurian stratigraphy of Born- holm was revised by Poulsen (1966), and the Middle Cambrian divided into zones according to IVestergArd (1946, 1953). The lower alum shale including the basal anthraconite was believed to cover the topmost part of zone B2, the full range of B3 and almost all of B4 (Figs. 2 and 10). The lower boundary was based on the presence of Ptyclingnostirs ataviis which was found in the lower part of the alum shale at @lei (Poulsen 1966). The upper anthraconite - my Hyolithes limestone - was referred to the Pnrndoxides forclilinmmari zonal group, zone C1, since both Ptychngtiostiis hrndgreni and P. rintliorsti were found in the bed (Gronwall 1902). Due to the contained hyolithids Poulsen compared it with the Hyolithes limestone of Sweden but did not apply the name to the anthraconite. It might be noted, though, that Westergird (19.46) placed the IIyolithes limestone of Sweden in the zone C2, the Soletiopleiirn brnchyriietopa Zone.

Present investigations hiethotfs. - From the basal anthraconite a t @leg about 6 kg were collected from various places where the contact with the Exsulans Limestone was clearly visible and sharp. At L z s i the basal anthraconite is extremely thin and weathered (Berg-Madsen 1981) and did not yield any fos- sils. From the lower alum shale at LasA and 81e5 about 800 g have been collected from each 10 cm

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GFF 106 (1954) The hfitldlr Cariibriari of lloniholrrr 361

interval from bottom to top (LrcsS 1.4 m, 0 1 e i 0.S m) to cover the sequence as conipletely as possible. About 15 kg have been collected from the Hyolithes limestone at Lresi and 01ei.

Lirholog)1 Bnsnl nritlimcmiife. - The tcrm anihraconite has a long tradition in Denmark. Forchhammer (1S35) mentioned black, bituminous limestone lenses from the alum shale on Bornholm - called stirikstceri eller nrithracolitli. The size of the lenses clearly indicated the Upper Cambrian lenses at LresS. Ire also noted that the ordinary limestone beds were used for cement nianufae- ture.

Seebach (1865) mentioned anthraeonitc-likc lenses in the aluni shale at 0le5, and Johnstrup (1S74) named all Middle Cambrian limestones and lenses as anthraconite except for the An- drarum Limestone. According to a recent defini- tion (Walton et al. 1983) none of the Danish Middle Cambrian limestones are genuine anthra- conites or stinkstones.

The basal anthraconite at L Y S ~ overlies the phosphatic layer on top of the Kalby marl (Berg- Madsen 1981) and has a thickness of 20-50 mm. I t is extremely wcathercd, but the fibrous, plume-shaped calcite crystals (Hansen 1938; Hadding 19.58) can still be distinguished. The lateral extent is unknown as the stratum is only exposed over a distance of maximum 1.5 m due to the dip of the strata.

The exposed parts of the basal anthraconite a t @lea follow that of the Exsulans Limestone (Berg-Madsen 1981). Gronwall (1S99, 1902) de- scribed it as half lenses lying close together and therefore seemingly a continuous layer. Hansen (1915) described the bed as a continuous layer. The thickness of the anthraconite is difficult to estimate since it is only found in the stream bed but 15-20 cm seems likely. At most places the contact bet\veen the Exsulans Limestone and the anthraconite is uneven but sharp with plume- shaped calcite crystals growing from the bounda- ry into the anthraconite. A t other places the transition is more gradual with rounded quartz grains, phosphorite and-glauconite accumulated in hollows on the eroded surface of the Exsulans Limestone. The material comes from the Exsu- lans Limestone itself and the Lower Cambrian Rispebjerg Sandstone. According to Bjorn BII- chardt, Institute of Historical Geology PC: Pa- laeontology, University of Copenhagen, (person- al communication 1983) the basal. anthraconite contains about 2% FeS and 3 4 % organic C,

which is not enough to make i t smell. In conse- quence, the basal anthraconite is not an nnthra- conite serisii stricto, but the name is retained here due to its long tradition of use.

Lower nlirrii shnle. - According to liansen (1945) the lower alum shale on Bornholm has a content of 7.07 570 FeS and 2.6 5% organic C, whereas the upper alum shale contains 14.3 56 FeS and 8.2 r/o organic C. Recent investigations confirm the val- ues from the upper alum shale. The predominant clay mineral is illite. Low grade metamorphism is indicated from the graphite (XRD) structure (Thomsen et al. 19S3).

At Lxs5 the lower alum shale lies uncomfor- mably on the thin bed of basal antliraconite and has a maximum thickness of 1.4 m. The lotver- most 30 cm are slightly folded, but the fossils are still determinable in spite of contortion. It has good fissility along the bedding planes, especially where the weathering is notable (Berg-Madsen 19S1). A soft and more micaceous level occurs 50-60 cm from the bottom. I t contains abundant but undeterminable fossils. The top of the alum shale is partly phosphatized.

At 0 l e 3 the lower alum shale overlies the Lower Cambrian Rispebjerg Sandstone at the left bank of the rivulet and the Exsulans Lime- stone at the quarry. Presumably it also overlies the basal anthraconite at places but this has not been observed. The folding is less prominent here and restricted to only about 20 cm. Also the total thickness is less, maxinium 80 cm according to Gronwall (1899). The micaceous layer is found higher, about 65-75 cm from the bottom.

Hyolithes littressforte. - The lithology of the Hyo- lithes limestone on Bornholni was first described in detail by Hansen (1945). l l e noted the division in slightly different lithological units correspond- ing to the.faunal division. The phosphoritic con- glomerate found in the upper part of the lowcr unit contained more nodules at Lresi than at 0le5. Occasionally the lower unit was entirely missing, and W of the quarry at 0 l e i the con- glomerate formed the base of the bed. The boundary between the conglomerate and the middle unit of black crystalline limestone was very uneven. The topmost unit was developed as a coarse crystalline 'lime-sand' limestone, and often with plume-shaped calcite devcloped as in the basal anthraconite.

Hadding (1958) called the whole bed a lime- stone containing a conglomerate in the lower and middle part, and with the upper part developed as anthraconite. T h e topmost part at L z s i was

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362 Yivianiie Berg-Aiaciseii GFF 106 (19S-f)

the called fragment limestone containing a transi- tional fauna, small lumps of phosphorite, pyrite and glauconite. The quartz and barytes niention- cd by Hansen (1915) were not found.

Larsen Sr Thiede (1971) examined the litho- logy at LxsH radiographically. Whereas Hansen included the conglonierate in the lower unit, Lar- sen and Thiede placed the conglomerate in the middle unit. Considerable erosion was suggested to have taken place prior to the deposition of the phosphatic nodules. Before deposition of the up- per unit, erosion cut through the conglomerate as well as the lower unit. This was demonstrated by erosional channels (Fig. 3A). Small faults in the lower unit (Larsen & Thiede 1971; Thiede f;: Larsen 1971) were referred to as a result of slumping. Unfortunately, the illustrated sample has a thickness of less than half the average of the bed.

At 0 1 e i , the development is slightly different, and. as mentioned by Hansen (1945), the local variation within short horizontal distance is con- siderable. The bed lies uncomformably on the lower alum shale and has a thickness of 15-20 cm. Lumps of pyrite are found at the lower boundary and in the lowermost centimetre of the limestone. The top of the alum shale is not phos- phatized, and there is no evidence of erosion. The lowermost centimetre of the limestone is developed as fibrous calcite crystals growing downwards towards the alum shale. The lower two thirds of the bed consists of black, laminated limestone with minute pyrite crystals, indicating the bedding planes. In the upper part are veins of light calcite. The thickest veins, 1-2 mm, lie mostly parallel to the bedding plane while thin- ner veins cross then1 vertically. The upper third consists of the conglomerate containing less phosphorite than at LxsH (Fig. 3B). Pyrite occurs as lumps, and fossils are abundant. Bioturbation occurs. The upper unit of Larsen & Thiede (1971) has not been found. T h e erosion and the conglomerate appear t o be results of slumping, and the conglomerate is therefore regarded as a gravity-transported deposit. There is, however, no evidence of considerable erosion before or contemporary with the conglomerate as suggest- ed by Larsen & Thiede (1971) and Thiede & Larsen (1971). Thus a longer lasting hiatus with- in the Hyolithes limestone, for example compris- ing the entire zone C1, is highly improbable.

The sedimentological evidence indicates early diagenetic origin, e.g. cementation before com- paction, of both the basal anthraconite and the Ilyolithes limestone. Buchardt & Thorshoj Niel- sen (1985) have studied the Lower Palaeozoic

limestones from Bornholm with regard t o differ- ences in 13C/'2C and lsO/"O compositions.

Fossils Basal arrtliracorriic. - The basal anthraconite a t 01eii yielded: Sofciropferirn rrririlin, ffypngriostiis panijroris ninnirriillntiis, H . pclrvifroris subsp. in- det., I'tyclrngriostiis piiriciiiosiis piirrciiiosiis, P. piiriciriosris subsp. indet., P. riniliorsti?, Piyclrng- riostiis n. sp.?, Lcjopyge clcgnrrs, Pcrorropsis pii- silla, Diplngriosiiis plariicnitrin as well as larvae and thoracic segments from Piyclingtiostris sp. (Figs. 4A-F, J-K, M , 0; 5A-B; 6 ) . Other fossils, e.g. inarticulate brachiopods were lacking. The trilobites often occur in minor concentrations in the most coarsely crystalline parts.

Loitrr alrir~i slrnfc. - The lower alum shale is highly fossiliferous, especially at L ~ I , and main- ly in the lowermost 20-30 cm and from SO cm upwards. In all, more than 400 specimens have been found: agnostid and other trilobite frag- ments as well as inarticulate brachiopods, Proto- sporigia, hyolithids?, conodonts? and other prob- lematica. Most of these are not determinable, but sufficient material has been determined t o species level to give a general picture of the ranges included.

From the lowermost 20 cm lower alum shale from h s i and 0leH were determined: Pnrntio.ox- ides dnvitiis?, Corynexochiis sp., Hypagrrosiris pnrvifrorts mnmvtillnfirs, H . parvifrons subsp. in- det., Prychngriosiiis piirictiiosiis prirrciiiosris, P. piitrctriosris subsp. indet., Perorropsis prisilln, Di- plngriostiis plnriicaiida, Tomngnostris perriigatiis. Furthermore from 20 cm upwards occur: f'nro- doxiries parodoxissimris?, Hypngriosiiis pnrr i - from cicntricosw, Perorropsis sp. and Sbirrngnos-

Fig. 3. CIA. Cross section of the IIyolithes limestone, LTS~, shoiving the base of conslomerate located in the pyritic part of the lower unit. Fine grained limestone (upper unit) fills the erosional channel cuttins through both the middle and lower unit. Detail of radiography, scale as in B, Larscn L! Thiedc (1971. Fig. 1). Puh- lished by permission of G . Larsen, Geological Insti- tute, Anrhus Univcrsity, Denmark. 0 B. Radiography of Hgolithes limestone, @leg, made in sections to eliminate differences in thickncss of thc plate. The pyrite indicates the different bedding planes where it occurs as small crystals. Larger lumps occur in the conglomeratic part and on top of the bed. Note the conglomeratic part almost totally without phosphorite. Thick arrow indicates the presence of a hgolithid, thin arrow the plume-shaped calcite crystals growing d o a n - wards to\vards the alum shale.

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364 Viviatitie Berg-hfarfseti GFF I06 (19S4)

fig. 4. Agnostids from the basal anthraconite (ba) and the lower alum shale (las.) OA. Pfjchagriosrio meraspis pygidium X 20 (ba). OB. Pfjchugriosfio rrafhorsfi? plasteline cast of cephalon x 12 (ba). OC. Lejopjge elegatis cephalon x 12 (ba). 0 D. Pfjcltngriosriu piriicfirostts pirricrrrosrts cephalon, partly exfoliated x 8 (ba). OE. Ply- c/iagtiosf~o pirncrirosiu pam~riosin external mould of cephalon x 7 (ba). 0 F. Pfjrhagriosrics putcc/msits p~uic~iro- sics external mould of pygidium X 10 (ba). OG. FfycIiagriosfiu pirricrrrostrs pwcriiosiu pygidium x 8 (13s). 0 H. Pfjckugnosfio picnc~irosiu subsp. indet. pygidium x 8 (las). 0 1. Toniognorfcts perncgafio cephalon slightly contorted X 12 (las). 0 J-K. Thorax segments from Pijclingriosfirs? sp. X 16 (bn). 0 I, tljpngriosfiis pnrvijroris cirnfrirosics cephalon x 10 (las). 0 hl. Ifjpngiiosfits parvifroris subsp. indet. cephnlon x 10 (ba). 0 N. ffjpagrios- hu pnrvifrons subsp. indet. cephalon X 10 (las). 0 0. Hjpagriosfirs pnrr9ifroris riianirriilluftrs pygidium X 10 (ba).

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G FF 106 ( I 984) The htidiilc Carnbriari of Bonilrolr,i 365

Fig. 5. 0 A-B. Piyhagrtosrilr n. sp.? cephalon x 10 (ba). 0 C. Coryriexocliilr sp. cephalon X 15 (Ins). Con- trary to C. borrihohriemis Gronwall this spccimen has a narrow but distinct anterior border, shorter eyes and wider occipital ring. A spine may have been present. but othenvise the similarities with almost contempo- rary C. spiirttlosits Angelin known from the Andrarum Limestone on Hornholm and S k h e are few. C. curri- brerrris (Nicholas 1916; Lake 1934) has a narrow antcr- ior border but much more outward curved axial fur- rows and cheeks curving more steeply towards the lateral margins.

tiis sp. Inaticulate brachiopods referable to Acro- treta, Dictyotiitici, Litigiilelln and Acrotlde occur evenly distributed throughout the sequence (Bas- sett 6r Berg-Madsen, unpublished results). Pro- tospotzgia fenestmfn occurs frequently in the lowermost 30 cm and from 100 cm upwards at Lresi. It should be noted that these fossils occur in the shale propcr, tiot in anthraconite lenses in the shale (Figs. 4G-I, L, N; 5C; 6; 7).

All fossils are small compared with those at similar levels elsewhere in Scandinavia. Most ag- nostids in the basal anthraconite are less than 2 mm in length and width, and less than 5 mm in the lower alum shale. This has been observed before (Berg-Madsen 1981) and apparently is typical of the Middle Cambrian of Bornholm.

Ifyolitlies limestone. - It has not been particular- ly investigated for trilobites by the present au- thor. The few specimens found are all known species from this limestone and the zones B3 and C2. Most samples a t the Geological Museum in Copenhagen are assumed to derive from this part of the sequence (Figs. 8 and 9). T h e revised determinations of Westergird (19.46, 1953) are regarded as fully reliable.

The inarticulate brachiopods found belong to the same species as those found in the lower alum shale and the Andrarum Limestone. Hyo- lithids occur as well as the conodont Gapporodiis bisiilcntiis and problematic specimens. Minute molluscs, probably pelagiellaceans, are distinctly different from the forms found in the Andrarum Limestone (Berg-Madsen, unpublished). There is no difference between moulds and matrix and preparation is generally difficult, especially in the coarse crystalline parts.

Discussion Agiiostid zotiatiotr it1 Scnrtdiiravia Westergad (1936) introduced his zonation of the lower Middle Cambrian in S w d e n basing it on the initial zonation by Torcll (1870), Tullberg (1880). and Linnarsson (-1883). In 1934 he ex- tended the zonation to comprise the additional Middle Cambrian shale and limestones, partly based on drill cores from Andrarum, Sijdra Sandby, Akarpsmolla and Gislovshamniar, part- ly the exposed localities in SkAne. The ranges of the trilobites used as index fossils were discussed, especially with regard t o their occurrence at simi- lar levels outside S h e .

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GFF 106 (19SI)

Po cm

4. ANDRARUM LIMESTONE

3. HYOLITHES LIMESTONE 2. LOWER ALUM SHALE 1. BASAL ANTHRACONITE

+

. . I

Fig. 6 . Observed stratigraphic distribution of polynicrid trilohitcs. agnostids and Proiospor@o found at 81cb hy the author. 1Iyofithids are taken from Griinnatl(1902). Arrow marks the thin laycr of alum shale hcttvccn thc Hyolithes limestone and the Andraruni Limcstonc.

Pnradoxirles dnvidis is known from several places in Skane and from Bornholm but it is unknown in most of Scandinavia. On I3ornholm the Andrarum Limestone immediately overlies a stinkstone bed containing 1’. tlrrr*idis. In Norway it seems to be replaced by Eccni~nrndoxidcs riigrr- losirs (Brogger 1878). Pfyclingrrosfrrs Irrridgrerri has a wide range and is found immediately below and above the Andrarum Limestone. It occurs in SkSne, on Bornholm, in Vistergotland, JBmt- land and the Mjosa region in Norway. Both Griinwall (1902) and Moberg (1910) questioned Tullberg’s reasons for regarding P. Irrrrrlgrerii as ‘index fossil’ for an individual zone. Apparently i t represented an independent layer only in Skane. However, WestcrgArd decided to retain the zone provisionally, at least for Skine. Pam- doxides forchlrnrririieri, characteristic of the An- drarum Limestone, occurs already in the IIyo- litlies limestone at Andrarum. WestergSrd (1914) noted that the ‘so called I Iyolithes limestone’ y a s absent at Kiviks-Esperod, Baskeniijlla and Gislijvshammar.

A more detailed Middle Cambrian strati-

graphy was finally established by Westerghi (1916, 1918, 1950, 1953). H e ninde a threefold division into ‘stages’ (zonal groups) each divided into several zones. I I e also introduced the wetl- known letter symbol nomenclature. T h e lower hliddle Cambrian Eccnpnrndoxitles oelarrtlicrrs beds (A) were divided into two zones with E. irisrrlnris and E. piriirs as indes fossils. (B) - the I’nmdoxides pnrdosissirrirrs zonal group was di- vided into four zones, and (C) - the P. forclrtrnrir- rrreri zonal group into three zones (Figs. 2 and 10). \VestergSrd omitted references to I’. dnnrsidis and Ifyrlroccpyhnhis hicksi which are important for correlation with the Acadian and British stan- dards. A stratigraphy based upon species of Pnr- ndoxides was regarded as unsatisfactory because of tlie difficulty i n identifying the mostly frag- mentary material with certainty to a species. Ag- nostids were regarded as stratigraphically more valuable, and most zones were therefore charac- terized by agnostids. The hliddle Cambrian zones, however, were less sharply delimited than the Upper Cambrian olenid zones as the agnos- tids have longer ranges.

Westergird (1916) then introduced two index fossils for the lowermost zone in the P. forch- hnnrrtieri zonal group (CI) - P/yc/rngrrosriis hrrid- grerii and P. rmtlrorsti. P. liirrdgrerri supposedly ranged from the upper part of the Plychngrrostrrs prrrrcfriosiis Zone (B4) to the lower part of the Solei r nplerrrn brnclry n r e t o p Zone (C2). P. I i ntlr- orsfi was considered rare in both these zones and had its main occurrence in C1. Only one agnostid species, Ptyclrngrrostrrs scnrierrsis, was restricted in range to zone C1, and it was found in a boulder associated with I’. rrnthorsfi.

Due to its long range and the fact that i t does not always occur together with P. rrnrhorsfi, P . Irrridgrerii has been excluded as index fossil by several authors, aniong others Henningsmoen (1956). Most authors, however, are not consist- ent and later reinstate i t (Lendzion 1970, 1976, 1982; Bergstriim 6: Levi-Setti 1978; Bergstrom 1980; Bergstrom e t al. 1982).

In SkSne the sections at Andrarum and the cores from Andrarum and Gislijvshammar (Wes- tergird 1914) were regarded as showing the com- plete sequence of the Pnrarlo.vitles i>nrado.rissi- tiiris and P. forchlronirrreri alum shales and linie- stones. In all it has a thickness of about 20 m compared with 26 in Norway (Brbgger 1878) and 4 m on Bornholm (Gronwall 1902).

Westergird (1916) described the ‘so called IIyolithes limestone’ as a discontinuous bed of stinkstone but emphasized its belonging to the same zone - C2 - as the Andrarum Limestone.

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GFF 106 (1984)

L R S A

0 1

t I

f i g . 7. Stratigraphic distribution of spccics found at Lrcsb, as in Fig. 6 . Arrow marks thc transition l a p , the fragment limcstonc. I t should bc noted that D i / ~ h g - m s i i ~ s plnriiraurln is rccorded from the same level as P/yr/rngizosrrrr nnrliorsti hy Gronwnll ( I903

From Kiviks-Esperod, where only niinor parts of the Middle Cambrian are accessible, the An- drarum Limestone was described as underlain and grown together with a thin stratum of stink- stone. The fossils found indicated a transition be- tween the zones B-l and C1 although the trilo- bites ranged into zone C2.

From Baskeniolh 4 m alum shale including a stinkstone lens in situ 70 cm below the Andraruni Limestone was referred to zone B4. Five stink- stone lenses partly grown into the Andrarum Limestone were referred to zone CI. All six trilobite species recorded from the five lenses had ranges including both B3 and C2, and three were found in the alum shale as well.

Along the shore between Brantevik and Gislovshaniniar, where the upper part of the Middle Cambrian is not exposed, two boulders consisting of stinkstone partly grown into the Andrarum Limestone were found. The stink-

stone was rich in Pryclingtiustiis yiiric/iiosiis intli- cating its belonging to zone BJ. As thesc boul- ders were found close to the location of the core at Gislovshammar, Westerghd concluded that the zone C1 was absent here although the core showed no such break. hlore than 1000 boulders found along the shore were examined, and, apart from the one yielding Pryclingnos/irs scnrreiisis, most were referred to zone B-1.

In the core from Gislovshaniniar zone C1 was estimated to be about 50 cm in thickness, and only a few specimens of Ptychngiiusriu Iiriidgrerii were found (Westerg5rd 19-11). The equivalent level in the cores from Andraruni and Sodra Sandby yielded trilobites with a range including B4 and C2 as well as hyolithids and inarticulate braehiopods known from the IIyolithes lime- stone and the Andrarum Limestone. Considering the description of the Hyolithes limestone as a stinkstone bed and the occurrence of stinkstone grown into the Andrarum Limestone it is diffi- cult t o see \Vestergird’s reasons for separation, especially as all stinkstones contain mostly the same trilobite species.

The Middle Cambrian is poorly developed and exposed in other parts of Sweden (Lundeghdh et al. 1967; Martinsson 1974). In Viistergotland a continuous, 50-100 cm thick stinkstone bed of considerable regional distribution fornis the top of zone B3. Zone B4 is absent, and the ininiedi- ately overlying P. furchhniiirrieri zonal group is developed as the so called Exporrecta conglom- erate. North of S k h e the Andraruni Limestone is in most places replaced by this conglomerate (for example in Kinnekulle, Falbygden, Billin- gen, Niirke, and on oland) .

In Jam t Ian d the I’nrnduxidcs pnrntlusissiir i i is

and P . forclihnrririieri zonal groups are represent- ed along the Caledonide margin. The presence of the Hypngriustirs pnrv(froris Zone (B3) was es- tablished by Thorslund (1910), whereas zone B4 is missing (cf. Vistergijtland). The basal 1’. furclilinriiriieri zonal group i n developed as Ex- porrecta conglomerate. The zone C1 has only been encountered in northern Jiimtland (Bergstrom 1980).

From Nonvay BrOgger (1878) recorded Pcirn- doxides pnradoxissiitizrs from f he zone of P. c h i - dis, now zone B4 o r lcbl local standard (I-len- ningsmoen 1956). T h e species P. (Inridis itself was missing and probably replaced by Eccnpnr(i- cfoxides riigirlusiis; Ptychngiiusfrrs piiiictiiusiis and P. iinrliursti were found together below the first occurrence of Poradoxides forcliharziriicri. The fauna described from Krekling mostly coincides with that of similar levels elsewhere, i.e. the

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368 Viviarrnc Berg-hfadserl GFF 106 (1983)

lower alum shale and the Iiyolithes limestone, in S k i m and on Bornholm. From the Mjosa district Strand (1929) noted the two faunas in the P. davidis zone where also Ptjclingriostiis piinctiio- sirs, P. rintliorsti and P. ataviis were found to- gether. The latter has been revised as Lejopyge Iiiridgrerii (Robison 1984). The zone was divided into B4 ( 1 ~ 6 ~ ) and C l (lcBz) by Spjeldnrrs (1955); Henningsmoen (1956) moved the zone of Ptychagriostiis riatlzorsti down from the Pnradox- ides forchhnrrirrieri zonal group to the P. pnrn- cloxissirriin zonal group. The P. forchhnrizrrieri zonal group is developed chiefly as alum shale in the Oslo region (Fig. 1A) where local breaks are not known but may be present. The Exporrecta conglomerate occurs outside the Oslo region in Noway (Strand & IIenningsmoen 1960).

Middle Canibriati stratigraphy outside Scanditiavia Outside Scandinavia correlation becomes diffi- cult because of the differences in fauna and stan-1 dards used. A direct zone-to-zone correlation is generally either impossible or extremely difficult. Even when the same genera and species are found, their first occurrences and ranges may be different. A few regions of importance for corre- lation with Scandinavia will be discussed here.

The Polish Middle Cambrian is closely con- nected with that of Bornholm and Skine al- though it differs in thickness and lithology. The zonation of Westergird is also used in Poland. Drilling cores from the Gdarisk Bay area (Fig. 1A) in northern Poland (Bednarczyk gL Przy- bylowicz 1980) proved the presence of the zone B3 while B4 and the lowermost Paradoxides forchhnrrirrieri zonal group are missing.

In Great Britain the Middle Cambrian Solva and Menevian groups are united under the name St. David’s Series for local use (Cowie et al. 1972; Cowie & Rushton 1974; Rushton 1974). A direct zone correlation with Scandinavia has been attempted by Rushton (1979). The overlap between Pfychagrzostzn prrrictiiosin and P. cf. rinthorsti (Illing 1916) is unimportant as the de- termination of the latter species is dubious. Zone C1 is not present in Wales but the agnostids found in Shropshire af this level are suggestive of the zone (Thomas et al. 19S4). Breaks and changes in lithology are found at levels roughly corresponding to those of Scandinavia.

In North Greenland a Middle Cambrian fauna from Nyeboe Land was described by Poulsen (1969). The trilobites, predominantly agnostids, were similar to those described from southeast-

ern Newfoundland by Hutchinson (1962). The presence of Eodisciis pirrrcmtis, Ptjclragnostris piirictirosirs, Otijniogriostis ciceroides, Pcroriop- sir sciitalis and Diplngriostiis plnriicniidn bilobntiis suggested zone B4 according to Westergird (1946). I t was overlain by zone C2 represented by Grnridngnostin glnridiforriiis together with an indeterminable ptychopariid. Absence of species from zone C1 was explained as due to either a hiatus, disturbances due to folding, or a restrict- ed presence in an extremely thin layer not found. The possibility that the Scandinavian zonation was not entirely applicable in North Greenland was also suggested. Whereas the fauna in Nye- boe Land is ‘Atlantic’ and therefore correlatable with .Scandinavia, a ‘Pacific’ fauna is found in Inglefield Land further to the southwest. A simi- lar short distance between the faunas is seen on Newfoundland. In Canada the Acadian standard covers New

Brunswick, Cape Breton Island and southeastern Newfoundland. Hutchinson (1962) described about forty species of agnostids from Newfound- land and discussed the trilobite zonation. The upper part of Iiutchinson’s Pardoxides doridis zone was correlated with the zone C1 (Poulsen & Anderson 1975). As the status of the zone was still unsolved Poulsen observed that a transition- al fauna between the zones B4 and C1 was a possibility. The ‘Pnrndoxides forchhnrrzrrieri Zone’ fauna of Hutchinson was referred to the lower part of the Soleriopleiirn braclzyrrietop Zone. This has been discussed by Rushton (1978) who regarded the paIaeontological evi- dence insufficient to support this correlation. Therefore the zone C? has not yet been proved present in Newfoundland.

The Middle Cambrian of North America and Greenland has been divided into five successive interval-zones based on agnostids. Although the species represent open-shelf facies, most have intercontinental distributions and are important for global biostratigraphy (Robison 1984). The base of each zone is defined by a biohorizon corresponding to the first appearance of a single species selected for its abundance and wide geo- graphic distribution. The upper boundary is the lower boundary of the overlying zone. The lowermost interval-zone, represented by Pty- chagriostus prneciirreru, is not present in Green- land or correlatable with Scandinavia. The Pty- ckagrioslin gibbin Interval-zone is correlative with the P. gibbiis Zone of WestergArd (1944, 1946) who characterized this species as the most abundant in the drilling core from Gislovsham- mar. The first occurrence of Ptychagnostics atn-

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GFF 106 (19S4) The hfiddle Cambrian of Bortiliolrti 369

virs in Sweden is correlatable with that of western North America. It is rare in the eastern North America and not known from Greenland. Robi- son (1984) includes the zone of Hypagriostits pnr- vifroris in the P. atniws Interval-zone. The Ply- cliagriosfiis pirrictirosiis Interval-zone of the chief- ly western North America and central North Greenland (NE of Nyeboe Land) includes the zones B4 and C1 of Westergird. A subdivision of this interval-zone probably will be warranted (Robison 1984) as in the Lejopyge Inevigatn In- terval-zone. This has been divided in a lower subzone, corresponding to C 2 of Westergird. and an upper subzone including C3 and the lowermost Upper Cambrian zone of Agriostirs pisifortrris which is regarded a s Middle Cambrian in North America. The upper subzone is the only present in central North Greenland. Pfychngrios- fils pirricrirosirs and P. rinthorsfi occur together in the P. piincfirosirs Interval-zone where P. rinflior- sti is recorded from the upper part. It is also found in the overlying lower subzone of the Lejo- pyge luevignm Interval-zone.

In Australia (Opik 1979) Pfyclingtiosfiis piiric-

tirosirs and P. rinfhorsti occur together in the middlemost zone (Dorynpiosfiu riotnlibroe) of the Undillan stage, separating the 'pure' pirric- fiiosilr and the 'pure' riotliorsti zones. P. rintliorsti ranges into the lowermost of three subzones (Le- jopyge 1-111) of the overlying Boomerangian stage. The subzone corresponds to the zone C2 of Westergird.

Validity of the zone CI. - As lias been shown, \VcstergArd (1914, 1916) had an extremely re- stricted number of localities within a small area in S k h e with the zone C1 present. Furthermore, his premises for retaining the original zone of Tullberg (1880) and adding another index fossil are somewhat doubtful. Most of his zones are defined as biohorizons corresponding to the first appearance of a characteristic species and there- fore correlatable globally. Other zones (B3 and C1) are based on local abundance of a species not exclusive to its biohorizon. Lejopyge hirid- grerii was first chosen as index fossil for C1 (Wes- tergird 1914) because it was present in all four drilling cores from Skine. Pfychnggriostiis rinflior- sfi was absent in one, rare in another and infre- quent in the remaining two, but its global occur- rence made it the superior index fossil when the final zonation was presented. Similarly to Hypng- riostirs parvifrorls, P. riafhorsti occrrs in the im- mediately under- and overlying zones but where- as zone B3 can be recognized a's a subzone (see p. 372) the presence of C1 is neither evident in

Scandinavia nor anywhere else where the Scandi- navian agnostid zonation is applicable.

Previoiis Middle Cnriibrinri stmtigrpliy of Borttlro hit

The existing Middle Cambrian stratigraphy suf- fers from mistakes made during the initial stages of investigations and collecting. Collecting at the crushing mill, it was possible for Johnstrup (1874, 1891) to mix three different lithologies resembling anthraconite: 1) the basal anthracon- ite overlying the Exsulans Limestone; 2) the IIyolithes limestone, and 3) the lenses in the up- per alum shale. Therefore his lists of fossils are of liniited stratigraphical value.

When Grijnwall (1902) revised the strati- graphy, he included samples collected by John- strup. A comparison with the fossils listed in Gronwall (1899) shows that roughly 75 % of specimens listed in 1902 must have been collect- ed by Johnstrup and others.

I-Iansen (1915) did not describe any fossils but concentrated on the lithology. From 0leA he mentioned two places with anthraconite lenses presumably in the lower alum shale. At the for- mer quarry where the presumed lenses of John- strup and Grijnwall were supposed to be, no lenses were seen.

Westerghd (1916, 1918, 1950. 1953) examined the collections at the Geological Museum in Co- penhagen and revised some of Gronwall's deter- minations. Concerning the agnostids (1916) many of Gronwall's determinations (1902) are included in Westergird's synonymy lists and his determination are regarded as valid when noth- ing else has been shown.

Although most samples collected by Johnstrup probably came from the IIyolithes limestone o r the lenses overlying the Andraruni Limestone, the later division by Gronwall resulted in not easily discovered confusion. The present Middle Cambrian stratigraphy of Bornholm is mainly based on Griinwall (1902) with only minor ad- justments by Poul.sen (1963, 1966) and therefore in need of revision.

Fig. 8 shows the polymerid trilobites of the basal anthraconite, the lower alum shale, the Hyolithes limestone and the presumed lenses of Gronwall (1902). A few species endemic to Bornholm are unrevised.

A few species clearly lie outside the predomi- nant ranges and should be ignored. They are mostly doubtful genera and species, but provided the determinations .are correct, redeposition is a

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370 Vivioririe Berg-,\todscii

Agraulos c e ticephalus A. depressus An o mo care ext orna tum A. laeve Bailiella aequalis Con0 c oryphe sulz eri? Con ok ep halina orna t a Corynexochus bornholmiensis Corynexochus sp. Ctenocephalus tumidus Dorypyge danica Ec c ap ara doxide s ruguio sus Holocephaiina teres Hydrocephalus brachyrrhachis H. h icks i H. palpebrosus Ma c r o t o xus an g e lini Mene vielia venulose Basso via giobiceps Para s ole n o p le ura linn a rs s o ni Paradoxides affinis P. davidis P. paradoxissimus “Ptychoparia “ johnstrupi Solenopleura brachymetopa S. bucculenta S. canaiiculata S. holometopa S. nuntia IF4

- A 2

I. 0

- 52

GFF I06 (19SJ)

83 84 C 1 C 2 C3

0 0 0 0

0 0 .O

0

0 0 0

00

0

00

a 7

0 0 0

0 0 am 0 0

0

00

Fig. 8. Polymerid trilobitcs rccordcd from the basal anthraconitc, the lo\vcr alum shalc and the Hyolithcs limestone. Compiled from lists by Johnstrup (IS7-1, IS9l). Tullbcrg (ISSO), GrGnivall (lS99, IStOZ), and new findings by the author. Species rccordcd from Obasal anthraconitc and l o w r alum shale, Oprcsumcd lcnscs of Gron\vall (1907), 0 llyolithes limestone. I n many cases the presumed Icnscs can bc rcfcrrcd t o thc llyolithcs limestone m. 1-css well known or dubious ranges (endemic or unrcviscd species) arc shotvn slightly thinner. Names and ranges revised when possible after Lorcnz (1906). Ho\vcll (1937), Westergird (1948, 1950, 1953). and Snajdr (1958).

probable explanation. Extended ranges are an- other possibility.

tiydroreplinlus lticksi is a nice example of a problematic species in niore than one way. Gronwall (1902) listed ‘Pnrndoxides lricksi var. pnlpebrosirs’ from the Essulans Limestone and ‘P . hicksi’ from the lowermost level of presumed lenses (museum sample) in the test. Later in his description of the species (p. 117) and his list (p. 165) he mixed the two specimens. In the collec-

tion at the Geological Museum in Copcnhagen Ifydrocephnlrrs hicksi is found in anthraconite together with H y p n g t i ~ s ~ i i ~ ynriifrom, I’crotfop- sir fn1ln.r and P/ychngriosrru yctncfrrosirs, most likely i t is the basal anthraconite and thus a case of redeposition.

Another example is Airoriroccrre 1nei.e listed from the transition layer at 1 . ~ ~ 5 by Griinwall (1902 p. 15), but later (p. 117) mentioned from the Andrarum Limestone. I t is evidently two

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GFF 106 (195-1)

"A gnostus insularis" Eodiscus punctatus Co tala gnbs tus lens C. rotundus Diplagnostus planicauda D. p. bilobatus Dorygagnostus incertus Gran da gn o s tus c ic er Hypagnostus brevifrons H. nepos H. parvifrons H. p. cicatricosus H. p. mammillatus H. truncatus Lejopyge elegans L. laevigata L. lundgreni Linguagnostus groenwalli Onymagnostus ciceroides 0. hybridus Peronopsis fallax P. f. ferox P. pusilia P. scutalis exaratus Phalagnostus resec tom P. scanicus Ptychagnos tus in t ermedius P. nathorst i P. punctuosus P. p. punctuosus Ptychagnostus n. sp.? Tomagnostus perrugatus Valenagnostus marginatus

Fig. 9. Agnostid trilobites from the same lithological divisions as in Fig. 8. Note the overlap in ranges bct\veen the basal anthraconiteAowr alum shale and the Hyolithcs limestone in [he presumed lenses of Griin\vall. The limestones arc practically identical lithologically. and loose blocks, both in ficld and in museum collcctions, cannot be distinguished from each other. Names and ranges revised after Ilo\vell (l93j), \\'estcrgird (19x9, I Iutchinson (1962), Jago (1976), Robison (1982, 19S-I). and Rushton (1978, 1979).

different species, A. Inere arid A. estorrrnlirrii (Westergird 1950). Which of the two species is actually found in the transition layer is not evi- dent.

Solcrioplcirm p n n w listed from the presumed lenses has been reassigned to S. ritrtifin (Valde-

niar I'oulseri, Copenhagen. personal coniniunica- tion 1983).

Fig. 9 shows the agnostids from the same litho- logical divisions as in Fig. 8. Doubtful genera and species, extended ranges and redeposition niag explain the inconsistences.

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372 Vitianrie Berg-Aladseri GFF 106 (19SJ)

Westergird’s distinction between Eodiscin scariicis and E. pirrictnfirs is not quite evident, and only the latter is listed here. Hypngnosiiis friiricatis was regarded as a problematic species by WestergArd, and his Forma I was correlated with the specimen from Bornholm recorded from the lowermost presumed lenses. This coincides fairly well with the presumed range and the basal anthraconite. I’eroriopsis sciitalis listed by Gronwall was regarded as atypical for the species by Westergird, and therefore not included in the synonymy list. It is now referred to P. sciiialis exaraia (Rushton 1979).

Griinwall (1902) recorded Piychagriosriis iriier- rtiediiis from the lowermost lower alum shale at 01~5, where it occurs together with lfypugriosfw parvifrotrr, Pfychagriosiiis pirriciiiosin, I’erotiop- sis fallax? and fragments of Paradoxides pnra- doxissirtiiis. Poulsen (1963) recorded a very worn and very small specimen of Ptycliagriostirs AIALWS

from the pyritic part of the Kalby marl at LxsS (equivalent to the Exsulans Limestone), and re- ferred Gronwall’s specimen to f’. afavris as well. Thus the upper boundary of the Exsulans Lime- stone as well as the lower boundary of the lower alum shale were both placed in the zone B2 (Fig. 2). Because of unsolved problems concerning the species P. afaviis and P. inierniediiis Berg-Mad- sen (1981) retained the upper boundary for the Exsulans LimestonelKalby marl. Lately Robison (1982, 1984) seems to have solved these prob- lems and even includes the Gronwall specimen in the synonymy list for Ptychngnosiiis iriierriiediiis but he does not list Denmark among the places of occurrence. Whereas P. U ~ A W L S occurs togeth- er with both ffypagnosiis parvifroris and Pry- chagriosiis piiriciiiosin i n the lower part of the P. piiricfiiosiis Interval-zone in North America (Robison 1984), P. irrierrriediiis is restricted to the Plychagriosiis gibbiis Zone and Interval- zone. Although extended range may be possible it is hardiy believable that P. itifcniieriitis could range into the zone of P. piirictiiosiis. Redeposi- tion is more probable alternative but other alter- natives might be possible. The specimen has nev- er been figured.

Although Grijnwall corrected Johnstrup with regard to Lejopyge lae&$pia he himself (1902) listed it from the upper part of the IIyolithes limestone. In the discussion (pp. 60-62), though, he suggested confusion with Cotalagriostiis Ieris as the specimens found were atypical of the spe- cies. According to Westergird the range possibly includes the zone C1, but considering that the Hyolithes limestone in Sweden and the upper part of the I iyolithes limestone on Bornholm

(Fig. 10) are placed in zone C2 its presence here is quite natural. The Solerioplciira brachyrtieiopa Zone (C2) corresponds to the lower subzone of the Lejopyge Inevignia Interval-zone in North America (Robison 198-1).

The lowermost approximately 2 m of the up- per alum shale (including the anthraconite lenses immediately overlying the Andrarum Lime- stone) belong to the zone C3. The lenses have yielded a few specimens of Lejopygc laevignto (Poulsen 1966), and the possibility exists that some of the species listed here actually belong to these lenses. As a whole most species are found in zone B4, overlapping either down to U3 or up to C2. There is no distinct difference between the species from the different lithologies.

Revised biostrntigrizpliy B L I S A ~ ariilirmcoriiie arid lower aliirri shale. - As can be seen (Figs. G9), all species, with excep- tion of above mentioned problematic species, range through the zones B3 or B4 or both. A few have their ranges within U3, none within B2. All species recorded from the presumed lenses by Gronwall also belong to B3-B4.

Therefore it seems appropriate to move the lower stratigraphical limit of the sequence from its present position at the top of zone B2 (Fig. 2). the Tornagriosfiis fissiis - Pfychngtiosiiis alnvris Zone, to the top o f the zone B3, the Hypagrios- iiis parvifrotis Zone (Fig. 10). The top of the lower alum shale is retained within zone B4, the Piychagrzostzrs piiriciiiosiis Zone. In order to be better correlatable with the Middle Cambrian of North America the zone of Ptjcliagtiosfiis aiavirs should comprise the Tortiagrzosiiis fissirs as well as the Hypagtiosirrs pnrvifroris zones here regard- ed as subzones.

The proposed changes agree well with the con- ditions at Andrarum in Skane which is the type locality for the Middle Cambrian in Scandinavia. Linnarsson (1883) mentioned the abundance of Profosporigiu feriestrafa in the alum shale sur- rounding the Hyolithes limestone. It was also found at several other levels in the zones B3 and B4 at Andrarum (Nathorst 1877; Tullberg 1880, 1882; Moberg lYlO), and at Gislovsharnmar (WestergArd 1914). At one of these levels, con- taining Profospotigia ferzesfrain, Graridngriosfiis cicer, Peroliopsis f . l /ax, i’halagnostis scariiiirti and Parasoleriopleiira litirinrssoni, the fossils are described as ‘somewhat distorted’. a state which is othenvise unknown in the Andrarum se- quence. The same species occur on Bornholm in

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P fychsgnortus punctuosus

The hiiddle Caiiihriotr of Born/iolt,i 373

'* Hyolithes l imestone -.

lower alum shale

ZONAL GROUPS

Paradoxides

forchhammeri

Para d oxid es

paradoxissimus

E c caparadoxides

o eland ic us

REVISED

DIVISIONS TRILOBITE ZONES

Lelopyge h e v i g a t ~ upper alum shale

I Andrarum Limcsfone Solenopleura brachyrnetopa I

Hypagnostus parvlfrons su b z o n e

Plychagnosfus afavus --- ---

Tomagnosfus fissus su b z o n e

Exsulans l imestone Pfyc hagnostus gib bus

NOT PRESENT

f7g. 10. Revised hiiddlc Cambrian stratigraphy of Bornholm. The position of the basal anthraconitc within thc lower alum shale i s indicated.

the lowermost 30 cni of the lower alum shale which is slightly folded.

Bragger (1 878) recorded Protospotigin ferres- trrrtn (Kigby 1966, 1976) from Krekling in Nor- way from both the Pnrndoxidcs pnrndo.rissirriris and the P. forclrhnrrirrreri zonal groups, together with Ptychngrrostrrs rinthorsti and Hyolilhes ten- iiistrintrrs.

Hyolitlies lirmwone. - Neither Nathorst (1877), nor Tullberg (1880, 1882) made any distinction between the limestone containing hyolithids and the Andrarum Limestone. Linnarsson (1883) named it IIyolithes limestone, partly because of the hyolithids, partly because of the slightly dif-

ferent lithology. T h e Hyolithes limestone was regarded as a stinkstone by \Vesterghi (1946) but was still retained in the zone C2. Hadding described it as a limestone.

When Poulsen (1966) compared the Hyolithes limestone in Ski& with that on Bornholm, he noted the similarities in 'the fauna but did not discuss the lithology in detail. Tentatively the Hyolithes limestone on Bornholm was placed in zone C1.

From the Hyolithes limestone on Bornholm Gronwall (1902) recorded several hyolithids - Hyolithes socinlis, Lirievitiis obscrirrrs, Orthoth- ern offinis and 0. litientrrln - while 11. tetruisfrirr- f i l s was found only in the Andrarum Limestone.

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These species were all known from the type lo- cality at Andrarunl in Skdne (Holm 1893). Al- though the hyolithids are of limited stratigra- phical value, Some ranges can be suggested from I[olm (1893) ;ind hiartinsson (1971): H d i ~ l l c s soc;ol;s (’I?) 133-B4, Liriei*itirs oh5cirrlls BAc2,

fcillii.xrrinrrrs C?. Brclggcr (1878) recorded H . tc‘l-

Irjstricitirs also from B4, H . plicfltlrJ from c 2 and H . soc;n~i~? from equivalent levels at Krekling. Nonvay.

Of 21 agnostiti species recorded from the Hyo- litties limestone on Bornholm, 75 lo have a range including B4 (Fig. 9) , and more than 20% are restricted to this particular zone. This nieaiis that a species overlap with the basal anthraconite/ Iower alum shale is present. This overlap was already known by Gronwall(1902) and described from Norway (Strand 1929). It seetiis reasonable to move the lo\vcr limit of the Hyolithes lime- stone down from the zone of Ptyclingriostiu riotli- orsti to the zone of P. pirrictiiosirs. The hiatus between the lower alum shale and the Hyolithes limestone (Figs. 2 and 10) is to be excluded since no sufficient bio- or lithostratigraphical evidence for its presence has been found.

k h n y polymerid trilobites and agnostids are restricted in range to C2. These are mostly found in the transition layer t o the Andrarum Lime- stone at Lxsi or in the upper part of the Iiyo- lithes limestone. Thus this limestone differs from the Hyolithes limestone in Skine by containing a mixed fauna covering the ranges B4-C2. If, how- ever, all stinkstones grown into the Andrarum Limestone In S k i m are regarded as IIyolithes liniestone the same ranges a re found. This is quite possible as \Vesterghi (1914, 1946) regard- ed the I lyolitlies limestone as a stinkstone (anth- raconite). Anthraconite developed in the upper part of the Hyolithes limestone on Bornholm was noted by Hansen (1915). and I Iadding (1958). According to the present zonation (Fig,. 2) the upper limit of the Hyolithes limestone is moved upwards into the Solerropleirrn braclijrtictopo Zone, C2.

As the indications of zone C1 are doubtful, not only on Bornholm but also in Sweden. and no significant hiatus comprising the zone on Born- holm has been proved, a new zonation is needed. I t is suggested that the zone of Prychogriosriis rinthorsri is included in the zone of P. pirrictiro- sirs, this zone still to be retained in the Pomdox- ides pomdo.rissitiiics zonal group. The presence of Ptyclingnostiis ~ I ~ I I ~ ~ I I ~ ~ I I ~ and 1’. irntliorsri to- gether known from all Scandinavia and several places outside Scandinavia. A combination of the

OrrIiotlicca nffitii~ B 1-U. 0. Iiriiwmln c- 7 and li.

zones makes the correlation easier with both :he local Norwegian standard and the P. pi~~ictr~osi is Interval-zone in North America. A possible divi- sion of this interval-zone in North America (Robison 1984) should be the norm for Scandina- vian zonation. As for now the zone C1 cannot be recommended cven as a subzone.

The new zonation may cause problems with regard to the practical use of \kstergard and the Norwegian system. If used, zone Cf should be merged with B4 (B4?C1), not with C2. CI may also simply be ignorcd.

Summary and conclusions New finds of polymerid trilobites and agnostids in the basal anthraconite and the lower alum shale initiated a revision of the hliddle Cambrian on Bornholm. A close exaniination of tlie back- ground for the present stratigraphy showed im- portant inconsistencies in the form of doubtful collecting procedures and mixing of faunas from different lithological units. This was in itself enough to justify a revision. The results show that tlie Middle Cambrian on Bornholm corresponds to a far shorter time span than hitherto supposed compared with the type locality a t Andrarum in Skane. llowever, thc revised bio- and lithostratigraphy iniproves the correlation not only with Skine but also with North America.

The status of the I’tjcliognostirs Iiiridgrerii - P. rintliorsti Zone (Cl) has been unsolved for many years. It is now not only regarded as absent in the Bornholm sequence, but its validity is ques- tioned. A change in the zonation is so far sug- gested only for the Bornholm sequence, but the indications for a similar change in Sweden and Norway are strong, and should be tested.

rlrX.iioi~fedgeiireiirs. - I am grateful to many fricnds and colleagues for critical reading and comments on the manuscript. In particular. I thank Gunnar Larscn (Geological Institutc, University of Aarhus, Denmark) for permission to puhlish his figure from Lcilrnirr 1971 and for help tvith the radiography. Jan Bergstriim (Geological Survey of Sweden, Lund), and Valdcmar Poulsen (Institutc of 1 iistorical Geology and Falaeon- ~ology, University of Copenhagen, Denmark) idcnti- lied and confirmed the trilobite material. Bjorn Uu- chardt (Institute of IIistorical Geology and Palaconto- logy, University of Copenhagen, Denmark) kindly pro- vidcd the analyses of the anthraconirc. J. Keith Rigby (Dcpartment of Gelogy, Brigham Young University. Provo, Utah, USA) identified and confirmed all my hliddle Cambrian sponge spicules. Spccial thanks to the technical staff at the I’alncontological Institute, Uppsala University: Tommy \Vestberg for his excellent photographic work and Dagmar Engstrh for help

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GFF 106 (19S-I) The hlidrlle Catribriati of Bortilioltri 375

with the drawings. I also thank Torhjorn Alcsantlcrs- son. (Dcpartnicnt of Quaternary Gcology. Institute of Gcology, Uppsala. S\vcdcn), my thesis ad\isor \\ho also improved thc Enplish. This is a contrihution to Project Tornquist (IGCP Accession No. 86). Financial support \vas rcccived from the Stvcdish Natural Scicncc Research Council (NFR) grants Nos. 235.3-105, 304.5- I 1 1 and 3046-104.

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