STIG M . BERG STRO M N G U -B U L L 4 3 2,1 9 9 7 - PAGE 5 9
Conodonts of Laurentian faunal affinities from theMiddle Ordovician Svartscetra limestone in theTrondheim Region, Central Norwegian Caledonides
STIG M. BERGSTROM
Bergstr6m, S. M. 1997: Con od onts of Laurent ian affin it ies from th e Middle Ordovician Svartseetra limeston e in th eTrond heim region, Cent ral Norwegian Caledoni des.Norg es geo logiske un dersekelse Bulletin 432, S9-69.
Samples from a 122-me te r t hick lim esto ne succession at Svartszetra, about 13 km east of Meldal in the TrondheimRegi on, west- centra l Norway,yielded more than 100 conodo nt elements representi ng about a dozen multielementspecies. All are con specific wi th, or close ly similar to, taxa present in th e upper Middl e Ordovician of th e North
American Midco nti nent,a nd a biostrat ig raphic assessment indicates th at the Svartseet ra lim eston e is coeva l w ith t heShermanian Substage of the Chatfi eld ian Stage in th e uppermo st Middle Ordovician of North America. In term s ofNorth American and At lant ic conodo nt zones, th is interval is in th e Belod ina confluens and lowermost par t of th eAmorphog na thus superbus zones,respect ively. The faun a differs str ikingly from most ot her coeval Baltoscand ian eonodont faunas, th e only known exceptions being those of th e Mjesa Limestone in the Oslo Region and th eVasalemma Formati on in Estonia w hich exhibi t t he same Laurent ian faunal aff init ies. These un it s, as well as theKalstad Limestone of th e Meldal area, are interpr eted to represent the same brief period of shallow-wate r,subt ropical-t ropical. bahamitic limesto ne deposit ion wi th faunas of Laurentian aspect. Because many conodonts apparent lycould cross oceanic areas,conodonts alon e cannot be used to prove th e hypothesis t hat th e Svartseetra lim eston e,a swe ll as th e Kalstad Limeston e, were origi nally deposited offshor e from Laurentia rather than Baltic a.
Stig M.Berqstrom, Depa rtme nt ofGeological Sciences, The Ohio Sta te University, Columb us, Ohio 43210, USA.
IntroductionAlthough diverse and stratigraphically significant conodont
faun as have been described from Ordovician sequences in
Norway since th e early 1960's (see, for instance, Hamar
(1964, 1966),Kohut (1972),Bergst rtim (1979), Nickelsen et al.
(1985),Bruton et al. (1988),Rasmussen & Stouge (1988, 1989,
1995),Bruton et al. (1989),Rasmussen (1991) and Rasmussen
& Bruton (1994)), t hese fossils remain very poorly know n, or
unkno w n, in many Ordovician deposits both in the Oslo
Region and in other par ts of th e cou ntry. This is ill ustrated
by th e fact th at con odonts have previously been described
from only a single formation, th e Holond a Limestone, in th e
classical Trondheim Region (Bergst rti m 1979). Alt hough the
know n Ordovici an conodont faunas of th e Oslo Region are,
wi th one imp or tan t except ion (that of th e Mjosa Limestone),
closely simila r to, if not identical wi t h, t he coeva l ones in
Sweden (Lindstrti m 1955, Bergstrti m 1971, Ltifgren 1978),
the conodont fauna of th e Holonda Limeston e (Bergst rti m
1979) is quite different from equivalent Baltoscand ic faunas
but much more similar to corresponding faunas from th e
marginal areas of Laurent ia. The Laurent ian faunal aff inity of
t hese conodonts, as well as of many macrofossils in this and
ot her un it s in the Trond heim area, has led some invest iga
to rs (see, fo r instance, Bruto n & Bockelie (1980)) to suggest
th at th is region may represent a fragm ent of Laurentia that
became attached to Balt ica in post-O rdov ician time. In view
of th is, it is obviously of considerable interest to investi gate
th e conodon ts from other carb onate uni ts in th e Trondheim
area succession s. Equally important, such stud ies have the
potential to produce reliable biostratigraphic information
that may help clarify the very poorly know n age of several
important units in th is geologically complex region where
both strat igraphical and st ructu ral relat ion ships have long
been highly cont roversial.
The mo st promine nt, and proba bly most stu died, lim e
stone uni t in the Holon da-Me ldal succession s is the Kalstad
Limestone, wh ich is st ill well exposed at its classical locality
at Bergsbakk en along th e highway about 1 km no rth of
Meldal (Kicer 1932). Limestone s of substantial th ickness and
probably comparable age outcrop at several oth er localiti es
in th e Meldal area, particularly on th e slopes of th e valley of
t he Orkl a river 6-8 km sout h of Meldal. Several sets of sam
ples collected from the Kalstad Limestone at its type locality
were either barren,or contained only sparse conodont spec
imens of stratigraphically undiagnost ic forms of Panderodus.
In an attem pt to discover mo re signi ficant conodont occur
rences, 11 samples were collected in 1982 from a relati vely
th ick limestone succession at Svart seetra, about 13 km east
of Meldal. The purpose of the present cont ribution is to
describe the conodont fauna from these samples, which is
current ly un iqu e for the Central Scandinavian Caledonides
in term s of species association and age, and assess its blo
st ratig raphic and paleobiogeogr aphic significance.
The Svartseetra limestone outcropAs noted by Bruton & Bockelie (1982,p.88), th e relation ships
between th e limestone succession at Svart seetra and the
Kalstad and Holonda limestones in the north and west, res-
NG U -B UL L 432 ,199 7 - PA GE 60 STlG M . BERGSTROM
o Volcanic sands tone and shal e
~ Rhyo li te tuff @ Kalsta d Limestone
SVARTSAETRA
SVORKARIVER
100I
m
o!
~ HORG FAULT
0.5
km
SVARTSAETRA
oI
A 8
1I
.~
I .:."
o I,km
8
Fig. 1. Sketch maps showing the location of the Svart seetra limestone locality 13 km east of Meldal in the Trondheim Region . A, map showing the general geology south of the Horg Fault; B, map showing the geographic locat ion of the Svart seetra section; C, map of the Svartseetra limestone outcropand collect ing levels of conodont samples. The beds in the outcrop are essentially vertical. Collect ing levels were measured from the top of the basaltuff bed at the nort hwestern end of the section. D,map of south ern and central Norway showing location of study area (star).
pectively, remain unknown, and there are rather conspi
cuou s lithological differences between th ese units. Unti l the
regional relation ships of th e former unit have been clarified,
the informal term Svattseetra limestone is used herein for the
unit under discussion. A total thicknessof about 122 m of li
mestone was measured along the forest track just southeast
of Svart seetra in 1982 when there was an almost cont inuous
exposure becauseof recent logg ing and bulldozing of a several meters wide area along both sides of the t rack (Fig. 1).
The lithologically rathe r monotonous carbonate succession
consists of grey to dark-grey, fine -grained, somewhat nod u
lar, irregul arly bedded, in places shaly, limestone form ing es
sent ially verti cal, in some cases rather massive, beds wi th nu
merous calcite veins. Near the bottom of the Svartszetra
limestone, just above the under lying poo rly exposed darkshale is a pale-weathering reddi sh tuff bed. Oth er tuff beds
occur near the middle of the limestone succession and ju stabove the highest exposed limeston e beds at the road intersecti on (Fig. 1). Because there is a few meters thick unexpo
sed interva l between the latt er tuff bed and the overlyingdark-grey silty shales, the nature of the limestone/shale con-
tact is unknown. No indication of any significant fault or of a
possible strat ig raphic gap has been seen in the limestone
outcrop.
Material and methodsMost of the 11 sampl es from the Svartseetra out crop were
collected from the northeastern side of the track where the
soil cover had been largely removed exposing many lime
stone ledges. The posit ion of each sample in relation to the
basal tuff bed is given in Fig. 1. About 2 kg of each samp le
were dissolved in 15% acetic acid fol low ing standard cono
dont ext racti on procedures. The frequ ency of conodont ele
ments proved to be low in all samples and one was barren(see Appendix). As is the case at most other localities in the
Holonda-Meldal region (Berqstrorn 1980), the conodont eo
lor alterat ion index (CAI) is 5, indicati ng a heating of at least
300°C. The state of preservation of most specim ens is med i
ocre, many elements being both broken and tecton ically de
formed. This,along wi th the fact that the ent ire collect ion at
hand, also including indeterminable fragments, conta ins
on ly sligh tly more than 100 specimens. makes safe ident ifi -
STlG M. BERGSTROM
cation of the species difficult. Access to large collections of
much better preserved specimens of similar, and apparently
coeval, faunas fro m the Oslo Region and eastern North
America hasgreatly facili tated the taxonomic work . Because
of th e limited number of specimens available, and th eir rat
her poor preservat ion, no formal taxon om ic description s are
included in this paper but brief comments on most of th e
species ident if ied are given below. Specimens illus tra ted in
Fig. 2 are hou sed in the type col lection of t he Orto n
Geological Museum (OSU) at the Ohio State University, and
other specimens are deposited in th e Microfossil Collect ions
at t he Department of Geological Sciences at the same uni
versity.
The Svartseetra conodont faunaThe general aspect of the conodont fauna of the Svartseetra
lim estone is quite different from th at of most broadly coeval
Balto scandic Middle Ordovician faunas in that it lacks repre
sentatives of Amorphognathus, Baltoniodus, Dapsilodus,
Hamarodus, Periodon, Protopanderodus, and Scabbardella,
which are the common genera in those faunas (Sweet &
Berqstrorn 1984). Howeve r, someone famil iar w ith the
Middle and Upper Ordovician conodont faunas of eastern
North America will immediately recognize the Svartseet ra
conodo nt species association as being of a type present in
th e Ohio Valley Province (Sweet & Berqstrorn 1984) of th e
Midcont inent Faunal Realm (Berqst rorn 1990b) as indica ted
by the presence of, among others, Aphelogna thus, Belodina,
Phragmodus, and Pleetodina. Asshown by large und escribed
collections, t he fauna of th e Middle Ordovician Mjosa
Limestone in the Mjosa district in th e nor thern Oslo Region,
altho ugh more div erse th an that from Svartseetra, is of the
same type and in all like lihood of th e same age. Likew ise, as
noted by Jaanusson & Berqst rorn (1980) and Sweet &
Berqstrorn (1 984),upper Middle Ordovician low-divers ity eo
nodont faunas of North American aspect also occu r in theSaku Member of th e Vasalemma Format ion (Oandu Stage) inEstonia (see also Viira 1974, Mannik 1992). Rare specim ens
of Belodina (Berqst rorn & Berqstrorn 1996) and Phragmodus
are known to be present in the Upp er Ordovician of Sweden
but represent at ives of th ese genera are un known in older
strata of that coun try. As is well kno wn, th e Mjosa
Limestone, the Kalstad Limeston e, and the Saku Member of
the Vasalemm a Format ion contain shelly fossils with Nor th
Am erican affi nities (see, for instan ce, Kizer 1932, Spjeldnces
1978, 1985,Jaanusson 1979). Several auth ors have interpre
ted th ese as represent ing a shor t-lived immigrat ion of North
American forms du ring a brief period of depo sition of shal
low-water, tro pical-subtrop ical, bahamitic limeston es in the
Oslo Region and Estonia . The Svartscet ra limestone may be
of th e same type although it appears to lack the carbonate
mound s ('reefs') present in the Mjosa (Opalinski & Harland
1981; Spjeldnces 1982) and Kalstad Limestones (Kizer 1932,
Opalinski 1980) and in the Vasalemma Format ion (Hints
1990).
NG U -BULL 43 2,1 9 9 7 - PA G E 61
Stratigraphic ageAlthough a total of less than a dozen conodont species have
been identi fied in the Svartseet ra samples (see Appendix),
several of th ese are biostrat igraphically high ly significant,
and, in combi nat ion, t hese species permit a rather precise
dati ng of the unit in term s of standard chronost rat igraphic
un it s in th e Midd le Ordo vician of th e North American
Midcontinent. The up per and lower 20-30 mete rs of th e ap
proximately 120 m thick Svart seetra limestone are less we ll
biost rat igraphically contro lled than its main part, but t here
is no evidence of any important faunal change at any level in
th e succession, and no sign ifi cant new taxa appear in the
upper portion of the unit. Hence, in the absence of eviden ce
to the contrary, it is suggested that the Svartscetra limestone
represents a period of carbonate deposit ion wi t ho ut major
breaks.
Four conodont species are part icu larly important for the
biostrati graphically dating of th e Svart szetra limestone (Fig.
3). The hig hly characteristic species Phragmodus undatus
Branson & Mehl appears in the North American succession
in the upper Turin ian (upper Midd le Ordovician; upper
Mohawkian; Leslie & Berqstrorn 1995) and ranges through
most, if not all, of the Upper Ordovician (Barnes & Berqst rorn
1988, Fig. 4). This species is exceedingly com mon in many
faunas of the Ohio Valley Province (Berqstrorn & Sweet
1966), and its presence in the Svart seetra col lections indica
tes th at t his un it is no old er th an the upper Turinian.
Anoth er significant Svartscetra species is Belodina confluens
Sweet, w hich ranges from th e bottom to th e top of th e unit.
Because this species evolved from B. compressa (Branson &
Mehl) in the upper portion of the Amorphognathus tvaeren
sis Zone (Sweet 1984), which corresponds to an interval in
the middle Shermanian Substage of the Chatfie ldian Stage,
the base of the Svartseetra limestone is no older than that in
terval. The appearance of Belodina confluens has been used
as the base of the Belodina confluens Zone in Sweet's (1984)Midcontinent zone scheme. Of stratigraphic impor tance isalso Pleetodina cf. aculeata (Stauffer). The nominal species
appears in th e Chazyan Substage and ranges into th e mid
dle Chatfield ian Stage (Kirkfie ldian-Shermanian substages)
(Sweet 1981). Finally,Aphelognathus cf.gigas Sweet is known
from the upper Kirkfieldian and Shermanian substages of
th e Chatfieldian Stage. Specimens that are indistinguish
able from the Norwegian form occur in th e up per
Kirkfie ldian-Shermanian part of the Trenton Group of New
York and Ontario (for excellent illustrations of elements of
t his fo rm (identified as Pleetodina aculeata) from th e
Kirkfi eldi an Hull Format ion of Ontario, see Uyeno (1974, PI.
2)). Based on the presence of t hese for ms, it is concluded
that the Svartseetra lim estone in all likelih ood is coeval wi t h
th e Chatfie ldian Stag e, and th at it appears to represent t he
Shermanian Substage and the Belodina confluens Zon e in
th e Nor th American Midcontinent succession. The latter
zone is equi valent to th e lower portion of the
Amorphognathus superbus Zone in th e Atlantic conodont
NGU - BULL 4 32 , 199 7 - PAG E 62 S TlG M. BE RGSTROM
STI G M . BE RGSTROM NGU -BULL 432 , 1997 - PAGE 6 3 I
zone succession (Sweet 1984). There is no evidence in th e
collect ions at hand that the Svartseetra limestone rangesinto th e Cincinnatian (Upper Ordovician). That the Mj0saLimestone is of closely similar age is also supported by theoccurrence in that unit of Yaoxianognathus abruptus
(Branson & Mehl). This species has its principa l occurrencesin Chatfieldian strata although a few specimens have beenfou nd in the lowermost Cincinna tian in eastern NorthAmerica (Sweet & Bergstrbm 1971).
The occurrence of several components of this fauna in
the Saku Member of the Vasalemma Formation in Estoniafits well with th is age assignment. That is, in eastern Nort hAmerica these species occur in a relatively narrow inter valsomewhat above the Mil lbrig K-bentonite that marks thebase of the Chatfieldia n (Leslie & Bergstrbm 1995). This Kbentonite was correlated with the equal ly prominent
Kinnekul le K-bentonite in Baltoscandia (Huff et al. 1992,
Bergstrbm et al. 1995) which marks the base of the KeilaStage (DII) in Estonia. The Saku Memb er of the VasalemmaFormation is placed in the lower part of the overlying OanduStage (Dill), hence in a similar stratigraphic position in relat ion to the Kinnekulle K-benton ite asthat of th e ShermanianSubstage to the Millbrig K-ben tonite in North America (Fig.4). A link support ing this correlation is also the relativelyshort-ranging and dist inctive graptol ite zone indexClimacograptus spiniferus Ruedemann. This species, recorded in older literature as Climacograptus dip/acanthus
Bulman, wh ich is a junior synonym of C. spiniferus (cf. Riva1976), has long been known from the Oandu (Dill), Rakvere(E), and lowermost Nabala (Ea) stages in Estonia (Kaljo &
Manni l 1990; Manni l 1990) whereas in the Cincinnati regionin east-centra l North America this species occurs in the upper Chatfieldian (Shermanian Substage) and lowermostCincinnatian (lower Edenian Stage) (Mitchell & Bergstrbm1991). This Estonian-North American correlatio n is also inagreement with the fact that the Saku Member of the
Vasalemma Formation has been placed in the lowermost
Fig. 2. sDiztacodus» cf. trigo nius Scho pf, Phragm odu s unda tus Branson &Meh l, Drepanoistodu s sp., Panderodu s cf. feu/neri (Gleniste r),Staufferella sp., Belodina confluens Sweet, Aphelogna thus cf. gigas
Sweet, Plectodina cf. tenuis Branson & Mehl,and Pleetodin a cf.acu/e
ata (Stauffer).
A, «Distacodus» cf. trigonius Schop f (OSU 48630 ), symmetrical ele
ment , lateral view,x l 00.Sample 82B15-l.
Phragmodus undatus Branson & MehlB, geniculate eleme nt (OSU 48631), lateral view,x150.Samp le 82B15
3.G, Seleme nt (OSU 48632), lateral view,x 120.Sample 82B15-9.
C, Drepanoistodu s sp, broken specimen (OSU 48633), lateral view,x120.Sam ple 82B15-7.
D, Panderod us feulneri (Glenister) (OSU 48634), late ral view, x100.Sample 82Bl s-1.
E, Staufferella sp. (OSU 48635), po sterior view,x l 00.Sample 82B15-1.
F, Belodina confluens Sweet (OSU 48636), rost rate element, lateral
view,x140, Sample 82815-9.Aphelognathus cf.gig as Sweet
NORTH AMERICA CONODONTS
en s Ranges of species 5i<I>
.~ ~ .~ ~.Q! 0> ~Jj '"{jj .0 ~N:>(f)
~
~0
z w'"Z c: '"Zz -c u:: <I> "~ « Z w " £
w 0 "" .. '"()- s ~ ~~z 0 f-w .. o(3 a !!? .. ~§.z " ~
<:>(; '"z ..~-c ..
'"z~
!Xl< -~a:
~I----
.!!1Z w '" ":I: ~ ~-c~ ~z Ci Z en 8 it-c ...J < ~ c -- w 15 ill .. ? .!!1u:: ...J
~Z w c '"u: " Ul~- f- Ul .2 ..
< >.:
~ '" .g: '" ..-c :I:
a: !Xl ~~
-' o ~
~ 13 ill---z-- '"§ !!Ja. -c l.'1 " Ul £
:::;; 15 it , s -5 ..z .. §.:'S §. 0
-c E 0
:I: I<: Q 0) "§.8 '" s.c if 0o ~ Ea: «:0
~wz
:::!: u:: --wif 0~ f-az
Fig.3. Chart show ing the know n vertical range s of some conodont spe
cies in terms of standard upper Middle and lower Upper Ord ovicianchro nost rati g raphic and biostratigraphic units in North America.
part of the Amorphognathu s superbus Conodont Zone(Mannik 1992) , the base of which is near the midd le of theShermanian Substage in North America (Goldman et al.1995, Fig. 14). Hence,several lines of independent evidenceare in agreement with the t rans-Atlantic correlations proposed herein (Fig.4).
Alt hough it cannot yet be proved by biostratigraphic orothe r evidence, it seems quite probable that the Kalstad
H, Paelement (OSU 48637), lateral view,x l 00.Sample 82B15-9.
I, Sc element (OSU 48638), lateral view, x90.Sample 82B15-2.J, Pb element (OSU 48639), latera l view,x90. Sample 82B15-7.M, Pb element (OSU 48640),anterior view,x l 00.Sample 82B15-3.
0, Saelement (OSU 4864l), po sterior view,x l 00. Sample 82B15-8.
P/ectodin a cf. tenuis Branson & MehlK, M eleme nt (OSU 48642), lateral view,x75.Sample 82B15-2.
L, Sc element (OSU 48643), late ral view, x l 00.Sample 82B15-2.
Q, Sb element (OSU 48644), posterior view,x l 00.Sample 82B15-7.
R, Pb eleme nt (OSU 48645), inner posterior view,x85.Samp le 82B157.
5, Pa eleme nt (OSU 48646), lateral view of fragment th at probablybelongs to thi s species,x60.Sample 82B15-2.
T, Sa element (OSU 48647), po sterior view of incomplete specimenth at tentatively is referred to thi s species.x8s.Sample 82815-1.
Plectodina cf.aculeata (Stauffer)
N, Sb element (OSU 48648), posterior view,x l 00.Sample 82B15-2.P, Pb eleme nt (OSU 48649), lateral view,x1 40.Sample 82B15-1.
NGU - BU LL 4 32 ,1 9 9 7 - PAG E 6 4 S TlG M. BERGSTROM
NORTH AMERICA NORWAY C. SWEDEN ESTO NIA S. SCOTLAND BALTOSCANDIA
(/)
N. Oslo(/) ID ci (/) Tron dheim (/) (/) ci (/)(/) Cl Fms. &IDID
'" 'O C) region Format ions Un its CD . Q) 'OC)Cl en o c region (Melda l· .~ Cl
.~ '" c 0 (Mj0sa) Mbrs. '"o c
Ci5 .0 C 0(f) :J 8 N H010nda) Fms. (f) Ci5 8 N
(f) Fms.
Z SLAN DROM HAR-
« z 0 (/) .AJMI
'i= <l: f- UJ c:~Z Q) RAK-
~« O~ ::> RAGAVEREoz UJ zLL. ;;::: ? VERE -e
0 UJ c: Cl>Z UJ 0 0 ARDWELL I- --- g-O
0MOLDAC\l GRP .
(/)
z s SVART- pANDUE
-c .2 SAETAA & MJ0SA SAKU CRAIGHEADoq:
Z Q)
<l: en ?KALSTAD MBR.::2: ? .... - - -a: .!(! ZUJ ::>
z I c: «Z (f) s« <l: Z -: VASALEMMA
- <l: 0... :::)
- 0 CS er:...JZ ...J(/) -UJ UJ .!(!- - u::: ::> (/)
« LL. ~ {g > c:
....J f- a: c: FURU BERGET SKAGEN KE ILA ~
-c 52 ::> Cl>
? ~o, I(/) BALLANTAAE::>
~ o 'b VOLC ANIC(/)
z 0 ::>
« ~ -c EO: COM PLEX -So CS Ol C\le: c:
I 0 z Ola: :5 et 0
0 -cKAHALAGRP. e-
o
MILLBRIG K·BENT. K!NNEKULLE K-B EO:oq:
z 0 ---- Z-cZ
f-UJDALB Y
<l:JOHVIoz =:l
er Z[[ HOVINS- a:=:l UJ 5f- 0 HO LM
Fig. 4. Correlation diagram showi ng prop osed strat igraph ic positions of the Svartseetra, Kalstad, Mj0sa, and Craighead limestones and the SakuMember of the Vasalemma Formation, as well as some other important st rat igraphical units, in terms of the standard chronostratigraphic schemesused for the upper Middle and lower Upper Ordovician in North America and Baltoscandia, respectively. Note the posit ion of the unit swith Laurentianfaunal aff init ies in relat ion to the North American Millbr ig and the Baltoscandic Kinnekulle K-bentonites,which have been interpre ted to represent thesame gigantic ash fall (Huff et al. 1992).
Limestone represents the same period of unusual carbon ate
deposition as the Sva rtseetra and Mjosa limestones. Severalaut hors (see, for in st an ce, Kicer 1932 ) hav e co m pa red th e fo s
sils of the Kalstad Limestone with those of th e Craigh ead
Limeston e in South Scotland . A recent study of the
Craighead conodont fauna (Bergst rbm 1990a) showed it to
be of mixed provincial character but it seems to be of the
same age (Iowermost Amorphognathus superbus Zone; cf.Bergstrdm 1990a) as th e Baltoscandian units under discus
sion. The Craighead is also a unique local carbonate deposit
surrounded by clast ics and it rests on the Ballantrae Volcaniccomple x, an ophio lite. Hence, it depositional setting is remi
niscent of th at of the Kalstad Limestone, which Spjeldn ees
(1985) interpreted to have been on the flanks of a volcanic
island. It is uncertain if the Svartseetra limestone was laid
dow n und er similar environmental conditions but the volca
nic island sett ing certainly does not apply to the Mjo saLimestone and Saku Member of the Vasalemma Formation
that represent shallow-water continental platform, or in the
case of th e Mjosa Limestone possibly shelf, carbonates
which are underlain by a stratigraphically rath er comp lete
succession of Lower and Middle Ordovician marine sedim ents.
Paleoecologic and paleogeographic significanceAs not ed above, the Svartseetra conodont species, like those
of the Mjosa Limestone and the Saku Member of the
Vasalemma Formation, are forms that in North America are
typ ically found in shallow-water deposits in the Ohio ValleyProvince. In the biofac ies mod el of Sweet (1988, Fig. 7.3),
species assemblages having common representat ives of
Pleetodina and Aphelognath us and somewhat less com monPhragmodus, as that of th e Svartseetra limesto ne,are placed
in an intermediate shallow-water depth zone between that
of the very shallow -water Rhipidogna th us biofacies and that
of the deeper-water Amo rph ogna thu s-Phragmodus biofa ci
es (Fig. 5). For the biofacies present in the Mjosa Limesto ne
and the Saku Member of the Vasalemma Formation,Sweet &
Bergstrdm (1984) int roduced the designation the
'Phragmodus-Icriodella-Plectodina biofacies' and this term
S TlG M. BERGSTROM
f---- - --- - - --- INCREASEDWATER DEPTH
Fig.5. Project ed position of the Svartseetra limestone conodont fauna intermsof Sweet's (1988,Fig.7.3) Midd le-Upper Ordovician conodont blofad es mode l for th e North American Midcontinent. As described in th etext, the non-coniform port ion of the Svartseetra conodont fauna is dominated by Plectodino and Apheloqnathu: with more sparse occurrencesof Phraqmodus.
may be applicable also to the Svartseet ra species associati ondespite th e fact that no specimen of Icriodella has yet been
found in th at unit. This biofacies is unknown in coeval strata
in Sweden although rare specimens of Icriodella have been
collected from the Mold a Formation (Bergst r6m, unpublis
hed),which is a likely equiva lent of the Svartseetra limestone(Fig.4). It is prob able th at the water depth in the depositi on
al environment of the Mold a Formation and coeval strata in
Sweden was too great for the development of thePhragmo dus-Icriodella-Plectodino biofacies whi ch is here re
placed by the Hamarodus europoeu s-Oopsilodus tnu tatus
Scobbordello oltipes biofacies of Sweet & Bergstr6m (1984).
The recognition of water depth asa significant control of
the distribution of som e conodont species is important inpaleogeographic int erpretations using these fossils. For
example, the occurrence of conodont faunas of North
American aspect in the Mjesa Limestone and the Saku
Member of the Vasa lemm a Formation proves the existenceof faunal interchange but it does not prove geographic pro
ximity between Baltica and Laurent ia because many
Ordovician cono donts clearly were able to migrat e across
the lapetu s and other Early Paleozoic oceans (Bergstr6m
1990b). The conodont faunasof the Svartseetra and H010nda
limestones in the Trondheim region show profound
Laurentian faunal affinities but it is uncertain whether this isdue to part icular environmenta l condit ions that led to the
development of a special biofa cies in two rather widely se
parated regions,or to geographic proximity of the H010nda
Meldal area to Laurentia that led to faunal exchange.
Accordingly, it is pertinent to be very cautious when usingconodonts like tho se discussed herein as tools for recon
structions of the paleogeog raphic relations of the
Trondheim distr ict and oth er areas in th e lapetus region.
Concluding remarks
The present study is th e fi rst repor t of conodonts of
Laurent ian faunal affi nities in th e upp er Middl e Ordovician
of the Trondh eim region. These conodonts, alth ough scarce
NGU -BULL 432,199 7 - PAGE 65
and not wel l preserved, provide a rather precise age of thepreviously undated Svartseetra limestone. Furthermore, ba
sed on th e reasonable assumption that th e well-known
Kalstad Limestone at its classical occurrence 13 km west ofSvartseetra represents the same phase of unique carbona tedeposition in theTrondheim region as that of the Svartszet ra
limestone, th e age of the former unit,which has been highl y
controversial, may also be final ly sett led.Attempts to obtai n conodonts from other, more or less
metamorphosed, limestone units elsewhere in the
Trondh eim Region, such as those at Grut south of Meldal
and Asen 40 km northeast of Trondheim (Spjeldnees 1985)
have been unsuccessful. However,some conodont elemen tsthat appear to have North American Whiterockia n faunal affinity have been isolated from the Snasa Limestone in out
crops along the E6 Highway southwest of F011ing (GR 235
202) near the western end of Lake Snasaabout 95 km north
east of Trondh eim. A few conodonts that appear to be ofMiddle Ordovician age have also been foun d in the Skelberq
Form ation of Bruton & Bockelie (1979) on the Island of
Sm01a off the west coast of Central Norway about 120 kmwest-southwest ofTrondheim, but fur ther sampling is nee
ded to clarify the age and aff ini ty of th at fauna. Clearly, eonod ont research in the Ordovi cian of the Trondhe im Region
is both challengin g and ti me-consuming, but as shown bythe present study, low- metamorphic Caledonian rocks that
look unprom ising for this kind of investigations may produ
ce faunas of considerable strat igraphic and paleonto logic
interest.
Remarks on selected speciesAphelognothus cf.gigos Sweet, 1983Figu res 2; H, I,J, M,0 , S
This disti nct species is characterized by well-developed, in
most casespeg-like, process denticles; a slightly angulate Paelement with flaring basal cavity and, in some but not all
specimens,a gap in the dent icle row just in front of the cusp;
angulate (not pastinate) Pb element; bipennate M element;
and a bipennate Sc element w ith several distinct denti cles
laterally on the anter ior process.
The present species appears to be unn amed but it
should be noted that some aspects of the taxonomy of
Aphelognothus are still not well understood. It differs from
Aphelognothus gigas Sweet from the lower Chatfieldian Fite
Formation of Oklahom a (Sweet 1983) in the appearance of
the Pa eleme nt (=Pb element in Sweet 1983) and in having a
Pb element (Pa element in Sweet 1983) that is not clearlypastinate (dichognathiform). However, th ese differences are
relat ively small and the present species may wel l be a direct
descendant of A. qiqas. A form described by Leslie (1995) as
Apheloqn athus cf.A. gigos from the upper Turinian and lowes t Chat fie ld ia n o f th e North American Midcontin ent is
closely similar to the Norwegian species and differs only inthat the Pb element tend sto be pastinate rather than bip en
nate. The present species differs from Aph elognothuspolitus
NGU-BU LL 432 ,1997 - PA GE 66
Hinde in, among oth ers, t he denticulated margin of t he Sc
eleme nt. The species is well repres ented in coll ections from
midd le-u pper Chatf ield ian strata in th e Trenton Group of
New York and Ontario assem bled by Scho pf (1966) and from
the Lexington Limestone of Ken tucky and Ohio (Berqst ro rn
& Sweet 1966). It is qu ite abundant in undescribed co llec
tions from t he Mjosa Limesto ne and also occu rs in the Saku
Me mber of th e Vasalem ma Format ion in Estonia. It appears
to have a short range and be an excellent index of the up
permost M iddle Ord ovici an in Nort h America.
Belodina confluens Sw eet, 1979
Figures 2; F
Representatives of thi s chara cter ist ic species occur th rough
v irt ua lly th e entire Svartseetra limestone sequ ence and both
rastr ate and gen iculate elements are pre sent. These are clo
sely sim ilar to specimens fro m th e upper Lexing ton
Limestone in Kentucky (Berqstr o rn & Swe et 1966, PI.31, fig s.
14-17, 19) and other upper Middle and Upper Ord ovic ian
units in th e North American Midcontinent (fo r d ist rib ution
data, see Sweet 1981). The species is rare in north western
Europ e but is kno wn from t he Craig head Limestone in the
Girvan area, South Scot land (Bergst rbm 1990a, PI. 3, fi gs. 8
12), the Jon storp Form at ion and coeval st rata in Sweden
(Berqst ro rn & Berq st rorn 1996, Fig. 9.P), t he Saku Member of
t he Vasalem ma Fo rmat ion in Eston ia (Viira 1974, PI. 13, f ig .
11), and errat ic boulders in Po land (Dzik 1976, Fig. 14.g -h).
The species is also present in undescr ib ed co llection s from
the Mjosa Lim estone.
«Oistacodus»cf. trig onius Schopf, 1966
Figure 2; A
A sing le specime n appears so sim ilar to t he symmet rical ele
ment of t he ap par at us of Schopf's (1966) Chatfield ian speci
es from the Trenton Gro up of New York t hat it is likely to be
th e same fo rm bu t addi tiona l specime ns are needed to con
fi rm th is. It is certainl y not congeneric w it h DistacodusPa n der, 18 5 6 a n d probabl y repre sents a n e w gen us. T h is is
an unusual fo rm in th e North Am erican Middle Ordov ician
Mi dcont ine nt faunas. Specim en s from th e Upp er
Ordovician, such as those of the Dubuque Format ion of
Iowa, are simi lar morpho logically and may repr esent th e
same species.
Drepanoistodu s spp.
Fig ure 2;C
Specimen s of the w idesp read ge nus Drepa no istodu s
l.indstrom, 1971 are pre sent in moderate numbers in the
Svart seetra samples. Some are conspecif ic wi th D. superbus
(Branson & Me hl, 1933) w hereas t he affini ti es of ot hers, such
as th e il lustrated eleme nt, rem ain in doubt. The taxonomy of
t he genus is cur rent ly un satisfacto ry,and large collecti ons of
spec ime ns are need ed fo r safe ide nt ifi cati on of severa l spe
cies. At the present t im e, Middle Ordovician spec imens of
Drepanoistodus have litt le, if any, biostratig raph ic signifi cance.
STlG M. BERGSTROM
Panderodus cf.feulneri (Glenister, 1957)
Figu re 2; D
Some of the Svartseetra samples contain robust elements of
a spec ies of Panderodus chara cterized by a very large base
and a relat ively short cusp . Although rem in iscent of P. feul
neri (Glenister) in genera l shape, they lack the well- defin ed
lateral costae present in representat ives of that spec ies. The
p resent species also resembles Panderodus breviusculus
Barn es, 1977, but di ffers in the outline of the base. The
Svartseetra species is also present in undescribed co llections
from t he Mjosa Limestone. Panderodu s feulner i was or ig ina l
ly describ ed from the Upper Ordovician Maquoket a Shale of
Iowa (Gleniser 1957) and similar form s are w idely distributed
in t he Mi ddle and Upper Ordovician of the North American
Mi dcontinent. These faunas, as w ell as th at of Svartseet ra,
also cont ain a much more slender form, w hich is commonly
ide nt if ied as Panderodus gracilis (Branson & Mehl). These
species have lit t le, if any, biostra tigraph ic significance.
Phragmodus undatus Branson & Mehl, 1933
Figure 2;G
Th is highly characteristic species, w hich has recently bee n
d iscussed in some de tail by Leslie & Berqstrom (1995), rang
es through the entire Svartszetra succession but is represen
ted by only a small number of spec imens that in all respects
are ide nt ic w ith North American specimens. It is one of the
most common conodonts in the upper Midd le and Upper
Ord ov ician of North America (fo r occurrence data, see Sweet
1981) bu t it is rare in Europe, be ing recorded, in most cases
just as sing le spec imens, from t he upper Middle Ordovician
of Wales (Savage & Basset t 1985), the Upper Ordovic ian of
t he Girvan area, South Scotland (Bergst rbm 1990a, PI. 4, fig .
10), th e Saku Member of the Vasalemma Form at ion (Viira
1974, PI. 12, fig. 19), and the Upper Ordovician of Sweden
(Berqst ro rn unpublished). The species is quite abundant in
t he Mjosa Limestone.
Plectodinu cf . a culeata (St a u f fe r, 19 3 0 )
Figures 2; N, P
A few, rather poorly pr eserved, spec ime ns in th e Svartszetra
colle ction are ten tatively referred to th is spec ies but add it ion
al specimens are clearly needed fo r safe identification . The
ten tati ve iden ti fication of the Svartseetra specime ns is ma in ly
based on the pasti nate Pb elem ent. In Nor th America,
Plectodina aculea ta is wi dely d istr ibuted in,and highly charac
terist ic of, strata of Chazyan to early Chatfield ian age (Sweet
1981). The lowest par t of its stratigraphical range wa s d istin
guished as the Pleetodina aculeata Zone by Sweet (1984).
Plectodina cf. tenuis (Branson & Meh l, 1933)
Figures 2; K, L, Q, R, T
A few specimens in the Svartszetra collections are closely si
milar to Pleetodina tenuis (Branson and Mehl) and four suc h
ele ments are ill ust rated in Fig. 2. Because of th e small num
be r of specim ens at hand, t he identification is tentative but
STlG M . BERGSTRO M
no signi ficant morphological differences were noted at a direct comparison with the North American form (cf. Sweet1981 , PI. 12, figs. 11-12, 14,18). In North America, representatives of P. tenuis are known from many localities in strata
ranging in age from the Chatfield ian Stage to the Upper
Ordovician Richmondian Stage.
Staufferella sp .
Figure 2; EA sing le specimen in the Svartscetra samples is simi lar torepresentatives of Staufferella, especially S. falcata (Stauffer,1935), but add it ional specimens are needed for specificidentification. This specimen has the conspicuous lateralcostae with weakly developed nod-like basal structures cha
racteristic of the genus but the posterior face of the cuspdoes not exhibit the carinae seen in most specimens fromthe Middle and Upper Ordovician of North America. Moretyp ical Staufferella specimens occur in unpublished collecti ons from the Mj0sa Limestone.
AcknowledgementsI am indebted to D. Bruton, R.B. Neuman and the reviewers J.A.
Rasmussen, and N. Spjeldnees for reading the manuscr ipt and offeringusefu l comments. Thanks are also due to D. Goldman, H. Hayes, l CMitchell, and K. Tyler for valuable technical assistance, and to my w ife.Birg itta Bergst rbm , for help in collecting the conodont samples.
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east of Meldal , Sor-Trc ndelaq, Nor way. Norges geo logiske undetsoke lse Bulle tin 406, 57-66 .
Manuscript received February 7997; revisedmanuscript acceptedJune 7997.
AppendixList of con od onts in each of th e Svartseetra samp les.Sam ple m-levels given wi thin brackets repr esent measurem ent s fromth e top of th e tuff bed near the northwestern end of the sect ion.Num ber of specimens is gi ven in bracket s after each ent ry.Sample 82Bl 5-1 (25 m). Be/odina confluens Swee t (l ); Belod ina ? sp. (l );
Panderodus cf. feulneri (Glenister) (2); " Distacodus» cf. trigonius Schopf
(1); Panderodus gracilis (Branson & Me hl) (3); Phragmodus undatus
Branson & Mehl (2); Plectodin a cf. tenu is Branson & Meh l (3); Stau ffere lla
sp. (1); Walliserodus? sp. (1); coni fo rm elements indet. (2); bl ade frag men t
of Plectodina or Aphelognath us (1).
Sam ple 82Bl 5-2 (34 m ).Aphelognathus cf.gigas Sweet (2); Belodina con
fluens Sweet (2); Drepanoistodus suberectus (Branson & Mehl) (2);Panderodus gracilis (Branson & Mehl) (4); Plectodina cf. tenuis Branson &Meh l (5); Pb eleme nt indet. (2); blade frag ment (1).
Sam ple 82Bl 5-3 (43 m).Aphelognathus cf.g igas Sweet (1);Panderodus cf.feulneri (Glenister) (3); Phragmodus undatus Branson & Meh l (1);
Plectodina cf. acu leata (Stauffer) (1); Plectodina cf.tenuis Branson & Meh l
(2); coni fo rm elem ent indet. (1); blade fragment ind et. (2).
Sample 82B15-4 (45 m).Belod ina confluens Sweet (2);Panderodus gracilis
STI G M . BERG ST RO M
(Branson & Mehl) (1);Phragmodus? sp. (1);Pleetodi na cf. tenuis Branso n &
Mehl (1);conifo rm element indet. (1); fragment indet . (1).
Samp le 82B15-5 (54 m). Barren.
Sample 82B 15-6 (62 m). Belodina confluens Sw eet (2); Plectodina? sp. (2);
co niform eleme nts indet. (2); blade fragments in det. (5).
Samp le 82B 15-7 (70 m). Aph elognathus cf.gigas Sweet (1); Belod ina con
f1uens Sw eet (1); Drepanoistodus suberectus (Branson & Mehl) (1);
Phragmodus undotus Branson & Mehl (l); Pand eradu s cf. feu/neri
(Glenister) (1);Panderodus gracilis (Branso n &Mehl) (6); P/ectodina cf. te
nuis Branson & Mehl (1);P/eetodina sp. (4); con iform elements indet . (4).
Sample 82B15-8 (76 m). Aphe/ognathus cf. gigas Sweet (1); Panderodus
graci lis (Branson & Me hl) (3); bla de frag ment (3).
Samp le 82B15-9 (81 m).Aph e/ognathu s cf.gigas Sweet (1);Be/odina con
f1uens Sweet (1); Phragmodus undatus Branson & Mehl (3); P/ectodina cf.tenuis (Branson & Mehl) (1); Panderadusgracilis (Branson & Meh l) (4);b la
de fragm ents indet . (2); conifo rm element indet . (1).
Sample 82 B15-10 (85 m). Fragm ent of b lade (1).
Sam ple 82B15-11 (97 m). Be/odina conflu ens Sweet (1); Pan derodus cf.feu/neri (Gleniste r) (3); Phragm odus undatus Branson & Mehl (2);
P/ectodina?sp. (1); coni for m elements indet. (4).
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