Nomenclature, stratigraphy, chemical fingerprinting, and areal distribution of some Middle...

GFF volume 117 (1995), pp. 1-13. Article

Nomenclature, stratigraphy, chemical fingerprinting, and areal distribution of some Middle Ordovician K-bentonites in Baltoscandia

STIG M. BERGSTROM, WARREN D. HUFF, DENNIS R. KOLATA, and HEIKKI BAUERT

Bergstrom, S.M., Huff, W.D., Kalata, D.R. & Bauert, H., 1995: Nomenclature, stratigraphy, chemical fingerprinting, and areal distribution of some Middle Ordovician K-bentonites in Baltoscandia. GFF, Vol. 117 (Pt. 1, March), pp. 1-13. Stockholm. ISSN 1103-5897.

Abstract: Based on biostratigraphic position, chemical fmgerprinting, and lithic characteristics such as relative thickness, several of the numerous K-bentonite beds, or complexes of beds, in the Middle Ordovician of Baltoscandia are shown to be traceable over large areas. Because the type of volcanic eruptions that produced such widespread ash beds lasts only a short time (a couple of weeks, or less), the individual ash layers represent as close equivalents of time planes as one is likely to find in the Lower Paleozoic stratigraphic record. Although these clay beds were recorded in section descriptions as far back as in the 1880's, their volcanic nature was recognized in Baltoscandia only in the mid-1940's. Subsequent research has added important data on the occurrence and chemical composition of the Middle Ordovician K-bentonites, but the present study is the first detailed regional investigation of these beds across their entire distribution area in Baltoscandia. Four beds, or complexes of beds (the Grefsen, Sinsen, Kinnekulle, and Grimstorp Kbentonites), are formally named and traced from Norway to Ingria in westernmost Russia. Type sections are proposed, and the biostratigraphic position of each unit is established in terms of standard conodont, graptolite, and chitinozoan zonal units. Trace element study of many samples indicates that the named beds and bed complexes have individual geochemical signatures and can be separated by chemical fmgerprinting. Thus far, only one of the many Baltoscandic ash beds, the Kinnekulle Kbentonite, has been correlated to North America but investigation of melt inclusion chemistry in quartz phenocrysts may lead to trans-Atlantic recognition of additional beds. Keywords: K-bentonites, Middle Ordovician, chemical fingerprinting, stratigraphy, Baltoscandia, Norway, Sweden, Denmark, Estonia, Russia, Poland.

Stig M. Bergstrom, Department of Geological Sciences, The Ohio State University, 155 S. Oval Mall, Columbus, OH 43210, USA. Fax: 614-292-1496. Warren D. Huff, Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA. Dennis R. Kalata, ll/inois State Geological Survey, 615 E. Peabody Drive, Champaign, 1L 61820, USA. Heikki Bauert, Estonian Academy of Sciences, Institute of Geology, 7 Estonia Avenue, EE-01 00 Tallinn, Estonia. Manuscript received 26 July 1994. Revised manuscript received 7 November and accepted 25 November 1994.

During the late 19th and early 20th centuries, several authors (for instance, Tullberg 1882; Olin 1906; Hadding 1913; Funkquist 1919) recorded light-colored clay beds in their descriptions of sections in the Middle Ordovician of southernmost Sweden, but no detailed investigations were carried out on these beds that were unfossiliferous and seemingly uninteresting lithologically. In the early 1920's, investigations of lithologically similar clay beds in

the Middle Ordovician of Tennessee and adjacent states disclosed that these beds were altered volcanic ashes that in many respects were comparable with the Cretaceous and Tertiary bentonites in western North America (Nelson 1921, 1922). In the ensuing years, the Middle Ordovician ash beds in eastern North America received rather extensive study (e.g., Sardeson 1924, 1928; Nelson 1925, 1926; Stose & Jonas 1927; Ross 1928; Kay 1931, 1935, 1937; Whitcomb 1932a, 1932b, 1935; Rosenkrans 1933, 1934, 1936; Fox & Grant 1944). Most of these investigations focused on the areal distribution and stratigraphic usefulness of individual beds and on their chemical composition and probable source area(s). In view of the fact that much of this research was published in well-known journals, it is perhaps somewhat surprising that the nature and significance of the Baltoscandian clay beds remained unrecognized until the 1940's (Thorslund 1945, 1947a, 1947b, 1948; B~gvad 1947a, 1947b; Gry 1948; Jaanusson 1948; Jaanusson & Martna 1948). In a study of the Middle Ordovician of the Tallinn area, Estonia, Jaanusson & Mlinnil (1941) pioneered the use of K-bentonite beds as stratigraphic index horizons in the Ordovician of Baltoscandia. These early investigations ofBaltoscandic K-bentonites were followed by studies by, among others, Hagemann & Spjeldmes (1955), Bystrom (1956, 1957), Manni! (1958, 1966), JUrgenson (1958), Skoglund (1963), Jaanusson (1964), R66musoks (1970), Vingisaar (1972), Bergstrom & Nilsson (1974), Snail (1978), Velde & Brusewitz (1982), Brusewitz (1986, 1988), and Huff et al. (1992).

For several years, we have been engaged in a broad study of the stratigraphic and geographic distribution, geochemistry, and tectonomagmatic and biologic significance of Ordovician and Silurian K-bentonites in northwestern Europe and eastern North America (Huff et al. 1992; Bergstrom et al. 1992). During our regional investigations in northwestern Europe, it became apparent that there is a need to have formal lithostratigraphic designations applied to some of the important K-bentonite beds, particularly those that can be traced with confidence over long distances. During the pioneer study phase of Middle Ordovician K-bentonites in North America, a letter and number identification system was applied to many individual beds (e.g., Fox & Grant 1944). Regrettably, in several cases different systems were used in different states resulting in a very cumbersome nomenclature that also tended to obscure the lateral continuity of individual beds. Subsequently, this nomenclature has been greatly improved by applying geographic names to prominent beds and following standard practice in lithostratigraphic classification (e.g., Kay 1931; Willman & Kolata 1978; Conkin & Dasari 1986; Cnnkin & Conkin 1992). In Baltoscandia a number system for 24 individual beds in the Sinsen section, Oslo, Norway was introduced by Hagemann & Spjeldnres (1955), and letter designations have been applied to some beds in Estonia (e.g., JUrgenson 1958; Mlinnil 1966; Roomusoks 1970; Vingisaar 1972). The most prominent K-bentonite in the Middle Ordovician in Baltoscandia

2 Bergstrom et al.: Middle Ordovician K-bentonites in Baltoscandia GFF 117 (1995)

KINNEKULLE SMEDSBY GARD FYLLA MOSSE

SINS EN GROTLINGBO

15

1

2

3

-GOTSKA SANDON

125 __......_..............,

OANOUAN

0 150km ......_____.

Fig. 1. Comparison of Middle Ordovician K-bentonite successions in a 1300 km long transect from S.E. Norway across southern Sweden to northeastern Estonia. Conodont biostratigraphy in the Kinnekulle (composite of the Kullatorp drill-core and Mossen quarry sections), Fylla Mosse, Smedsby Gard, Gotska Sandon, Kiirdla, and Piilsi successions is after Bergstrom (unpubl.). Numerical designations of K-bentonite beds in the Sinsen section follow Hagemann & Spjeldnres ( 1955). Chitinozoan biostratigraphy is interpreted after Laufeld ( 1967), Grahn (1981, 1982a, 1982b ),

has provisionally been referred to as the "Main Metabentonite Bed" (Vingisaar 1972), "Big Bentonite Bed" (Bergstrom & Nilsson 1974) or the "Big Bentonite" (Huff et al. 1992). Clearly, this nomenclature does not meet modern requirements of precision and regional applicability.

In recent years, much new information has been gathered about the local and regional distribution of Middle Ordovician Kbentonite beds in Baltoscandia, their geochemistry and isotope ages, and the stratigraphic position of individual beds in terms of conodont, graptolite, and chitinozoan biostratigraphy. Thus, we have now reached a stage when a regionally useful lithostratigraphic nomenclature can be applied to individual beds in some cases and to bed complexes in others, hence following the practice that has developed in the Ordovician and Devonian in North America.

The purpose of the present report is to formally name some of the Baltoscandic Middle Ordovician K-bentonite beds, or complexes of beds, that can be traced with confidence over substantial areas, to comment on their stratigraphic position and geographic distribution, and to briefly outline those aspects of their chemical

composition that can be used to set them apart from one another.

Data base During the course of the present study we have visited most of the significant outcrops of Middle Ordovician K-bentonites in Baltoscandia and we have also investigated such beds in a representative number of drill-cores, particularly in areas having few, if any, outcrops. We have studied 16 outcrop sections, namely Hullegard and Vasegard, Isle of Bornholm, Denmark; Rostanga Kyrkback and Fagelsang, Scania; Mossen (Kinnekulle), Jonstorp (Mosseberg), Skultorp and Gullhogen (Billingen), Vastergotland; Fjacka and Kargarde, Dalarna; Lugnvik and brAn, Jamtland, Sweden; Sinsen and Vollen, Oslo region, Norway; and Aluvere and Peetri, northern Estonia. The 28 drill-cores investigated include 11 from Sweden, namely those from Kolingen and Lovisefred, Scania; Kullatorp (Kinnekulle), Fardala (Varvsberget), Bestorp (Mosseberg), and Stora Asbotorp (Billingen), Vastergotland; Smedsby Gard and Fylla Mosse, Ostergotland; Gotska Sandon, Nar, and Grotlingbo, Gotland; and 17 from Estonia. Geographic

------------------------

GFF 117 (1995) Bergstrom et al.: Middle Ordovician K-bentonites in Baltoscandia 3

KALESTE F-356

SOOVALJA K-1

m ... 170 •······· .... 011

m 100 ... 105

TURBA D-76

OOSTRIKU 37

PilLS I 729

VASKNARVA 639

··t>;l·· ...... ,- I

~ I~KINNEKULLE.J.-' ---fe.."""'""""""""""-t----111;;;;;;;;;;;;;;;;;;;;.....,-.;;j----11=--I""SINSEN•IiO"~---fl lOS t •··•········ 5

I 8 o, /8 .,.ft--no "a

:::::? 01 1 ~N B. alobatu:o 01

'l .,~;;1 E;;:.-5~~~¥-~~~{::=~~_:-__ Sujbzo-oo" 1----la--

.. ·· . ..

7

,. __

~ ········· ....

110

115

CUI 190

·· .. 195

·· .. .. .. 200

~ ..

'~ 8

~~ -a a /I ~~ ern :::a

8 115 a -I 9

IDAVEREAN ~=~I c .Jo a en, 10 111

\ F"""'""""'fa? 115 8. gerdae \ a

1iubzone10

120 ~====~:T:~~= 11

?

I B. gerdae Subzone

I

Nolvak & Grahn (1993), and Grahn et al. (1994). The unusual thickness of the Fylla Mosse and Kiirdla successions is due to the fact that they represent infillings in impact structures. Note that the Grirnstorp and Kinnekulle ash beds are recognizable along the entire transect whereas the thin Sinsen K-bentonites have a more irregular occurrence. The upper part of the Grefsen K-bentonite Complex is present in most sections but it is not yet established whether or not the top bed is of precisely the same age everywhere.

locality data and pertinent references of the sites are given in the Appendix. We have secured K-bentonite samples from 40 out of these 44 successions. About a dozen, mostly small, outcrops of K-bentonites in Baltoscandia have for various reasons not been included in our study but we believe it unlikely that data from those exposures will affect the conclusions presented below. By and large, we feel that our data base is representative of the Middle Ordovician K-bentonites in Baltoscandia; however, it would be of considerable interest to have access to samples of the Kbentonites reported from Poland, Latvia, and Lithuania.

The Oslo-Estonia and Fjacka-Ingria (W. Russia) transects To illustrate how several K-bentonite beds, or complexes of beds, can be traced across large parts of Baltoscandia, we have constructed one W-E transect of selected K-bentonite sections from the Oslo region, Norway to Estonia and one N-S-NE transect from Fjacka, Dalarna, to northern Poland, and to westernmost Ingria

in western Russia (Figs. 1-2). In the various columnar sections, we also illustrate the known ranges of conodont zones and subzones, East Baltic stages, and some biostratigraphic data from chitinozoans and graptolites. The proposed regional correlations are mainly based on biostratigraphy but they are fully supported by chemical fingerprinting data where such information is available.

In this report, we show that correlation of several individual beds, or complexes of beds, is now established well enough that it is appropriate to introduce formal lithostratigraphic designations that can be used regionally in Baltoscandia. We propose four new names, designate a type locality of each unit where it is well exposed, and discuss the stratigraphic position and known geo-graphic range of each of these beds. For convenience, we sum-marize data on the stratigraphic position, relative thickness, and mutual relations of the several named K-bentonite units in a standard stratigraphic column (Fig. 3). In the text below, we will first deal with the most prominent K-bentonite in the Middle Ordovician of Baltoscandia, and then discuss the beds just above and below this important stratigraphic marker horizon.


B. alobatus Subzone

!i ~ <'!:

B. getdae Subzone

B. variabilfs SubzOne

P. anserinus

KULLATORP

FJACKA

1

2

FARDALA 1

B. gsrdae Subz~ __ - -

B B

4

KOANGEN

30

Dicranograptus c/ingani Zone

Diplograptus multidens Zone

Nsmagraptus gracilis Zone

Fig. 2. Comparison of Middle Ordovician K-bentonite successions in a 2000 Ian long transect from central Sweden across Bornholm (Denmark) and northern Poland to eastern Estonia and Ingria in western Russia. Conodont biostratigraphy in the Fjacka, Kullatorp, Fylla Mosse, Kiirdla, and Valgu successions is after Bergstrom (unpubl.). Graptolite biostratigraphy of the Koiingen section is after Nilsson (1977), and that of the Vasagard section after Bergstrom & Nilsson (1974). The K-bentonite bed correlation of the Bialogora succession, although in general agreement with the

The Kinnekulle K-bentonite (new name)

Derivation of name.- The Kinnekulle K-bentonite bed is named for the Mountain of Kinnekulle where it was flrst described in some detail (Thorslund 1948). It has previously been referred to as "bed X:Xll" in the Oslo region, Norway (Hagemann & Spjeldnres 1955), ''The Big Bentonite" in Sweden (Huff et al. 1992), and "bed d" in the East Baltic (JUrgenson 1958; Mannil1966).

Type locality.- The type locality of this bed is the Mossen section on the eastern slope of Kinnekulle. This abandoned quarry is situated 2.0 km N of Osterplana church and 0.2 Ian W of Mossen farm (Thorslund 1948; Jaanusson 1964). AtMossen, it has a total thickness of 180 em (Fig. 4) but at the present time, only the

uppennost part of the bed is exposed due to slumping of overlying rocks of the Skagen Fonnation. However, the total thickness of the bed can be exposed by digging, as was done in 1985 and 1990. The Kullatorp drill-core, the site of which is only 1.25 km NW of the Mossen section, may serve as a secondary reference section of the Kinnekulle K-bentonite; unfortunately, only part of this bed was recovered in this core and subsequent collecting of samples has greatly reduced the amount of K-bentonite available for study.

Stratigraphic position. -In the Moss en section, as at other sections in Vastergotland, Ostergotland, and the Siljan district in Dalarna, the Kinnekulle K-bentonite is overlain by the Skagen Fonnation and underlain by the Dalby Fonnation (Jaanusson 1963, 1964).


VASAGARD

BIAlOGORA 1 .. 2US

2650

2655

2670

8

D. clinganl

Zone

-340

K\JKRUSEAN c II

VIKI

9

IDAVEREAN

(Ill

SOOVALJA K-1

.. 170 ... lo

VALGU V-99

SLANTSY

• po•l----11 N

"" 1". ... lo

·······,9o• a•.o."-uas10~n ~~=:::~·: ~~~:;KINNEKULLfii;·'l----~·

17S

180

185

190

195

00

I

/I ~.~ 4 ""11 .... ~ • 1'1

•

•

•

JOHVIAN D1

B.

10

11 12

graptolite biostratigraphy (Podhalanska 1980), is yet somewhat uncertain and requires confirmation by chemical fingerprinting. Note that the Grinistorp and Kinnekulle ash beds have a persistent occurrence along the transect whereas the Sinsen K-bentonites are missing in some sections. As indicated in Fig. 1, the top of the Grefsen K-bentonite Complex, although certainly broadly coeval, may not be of exactly the same age in all sections.

Conodonts of the Baltoniodus alobatus Subzone of the Amorphognathus tvaerensis Zone are present just below this horizon in the Kullatorp drill-core, the Smedsby Gard drill-core, and in the Fjacka section. The Skagen Formation at Mossen has not produced a diagnostic conodont fauna but evidence from the Fjacka and Smedsby Gard successions indicates that the rocks just above the Kinnekulle K-bentonite belong in the upper Amorphognathus tvaerensis Zone. As shown by the Koangen (Fagelsang) sequence in Scania (Bergstrom & Nilsson 1974), this bed is in the upper, but not uppermost, part of the Diplograptus multidens Zone in the graptolite succession. In terms of the Baltoscandic chitinozoan zonation introduced by Nolvak & Grahn (1993), the Kinnekulle bed is in the Spinachitina cervicornis Zone within which it is directly overlain by the Angochitina multiplex Subzone. The base

of this bed defmes the boundary between the Johvian (DI) and Keilan (DII) stages (Jaanusson & Martna 1948; Jaanusson 1948; Mannil 1958; Mannil 1990) in the East Baltic region. In the succession in the Oslo region, Norway, the Kinnekulle bed occurs somewhat above the middle of the Arnestad Formation (4ba) (Hagemann & Spjeldnres 1955; Owen et al. 1990). This level is in the lower half of the Spinachitina cervicornis Chitinozoan Zone (Grahn et al. 1994).

Regional distribution.- The Kinnekulle K-bentonite is the thickest and most widespread among the many K-bentonites in the Middle Ordovician of Baltoscandia and it is generally present in sections having an apparently uninterupted J6hvian-Keilan succession from southeastern Norway to Scania and Bornholm and the East


:z. Ill

""' <

~ c ""' :Z.I:Il N :s ~!:! u.., !:!Ill

C:z. c c .. Ill ~ ~c :z.

t:l:ll !- .. !-C Cl:ll ON .. r.l !:iii! ..JDC ..J< :z.:z. :Z.GQ !::z. ~~ Der.:~ <r.l <!-o co c., ::c Ill.., Ill.., lllfll tJN tJI'Il tJN CN

z B }- GRIMSTORP A K-BENTONITES

< ..:I ... [;a;l

:Ill r KINNEKULLE .. K-BENTONITE r-- - -- .. .. - ..

c: c: I:

" ..

" .. 0 ~ z .. ... - B }- SINSEN .. -< "' ::s .. ... A K-BENTONITES ... .. - .. -z > ... ::s

< "' .. = .., .c ... E ... z Cl ~0 ::s {.) < - "' ..

0 .... .It

"' :;J ... I: ::s Q "' - ...

cc .. ... Q. < c: ::s -... "' cc > - ""' ~ ,z:: ..

Cl Cl ... < ""' ,z:: - "' C) c.. 0 c: c: -.. Cl - Q.

Cl - Q. -z E - "'l ~ "' < ~ CQ

[;a;l GREFSEN cc ~ K-BENTONITE [;a;l COMPLEX > < Q ... ... ..

{I .... .. s .. ::s ""' .s .::: ,z::

"' CQ eli

Fig. 3. Composite standard section of the Middle Ordovician IdavereanKeilan interval in Baltoscandia showing relations between named Kbentonite beds and biostratigraphic, stadial, and series units. Note that the correlation of the lower portion of the Grefsen K-bentonite Complex is not yet flrmly established in terms of conodont and chitinozoan biostratigraphy and requires further study.

Baltic. As shown in Figs. 1 and 2 it can be traced for some 1000 km across Baltoscandia. Its thickness ranges from more than 2m in the Fylla Mosse drill-core in Ostergotland, Sweden to less than 5 em in south-eastern Estonia, central Latvia, and western Russia (Ingria). Its regional thickness variation is illustrated by an isopach map in Fig. 5. In central Wales, we have recognized a prominent K-bentonite with the geochemical signature of the Kinnekulle bed in the upper Diplograptus multidens Zone in a road cut along highway A44 about 1 km WSW of Nantmel church, and in a small quarry 0.3 km NW of the nearby Maesygilli farm (British Grid Reference SO 0374 6614). Based on biostratigraphic and geochemical information we tentatively correlate this bed with the Kinnekulle K-bentonite. Using biostratigraphic, geochemical, and isotopic age evidence, Huff et al. (1992) correlated the Kinnekulle K-bentonite with the equally prominent and widespread Millbrig K-bentonite in eastern North America. Based on this correlation, it could be argued that the designation Millbrig, which was proposed by Willman & Kolata (1978), has priority

MOSSEN, SWEDEN

:S m

B 1

'"" 0

z [;a;l ~;!) SWE50 < 2 84 ~ :Ill 15 /SWE 49 GRIMSTORP I'll

14 -SWE 48 · ~ K-BENTONITES --3 SWE5l r KINNEKULLE

4 SWE 52 & 53 K-BENTONITE SWE 54

:S 5 SWE 55 ~ SINSEN

'"" ~SWE 56 K-BENTONITES :;.. 6

= 4 SWE 57

..:I 7 SWE 58 < Q

8 GREFSEN

9 K-BENTONITE COMPLEX

10

Fig. 4. Schematic diagram of the Middle Ordovician K-bentonite succession in the Mossen quarry, Kinnekulle, Viistergotland (slightly modified after Thorslund 1948). SWE designations refer to our K-bentonite samples, B 1, etc. designations indicate K-bentonite beds and their thickness. The lower part of this section (including most of the Kinnekulle Kbentonite and underlying strata) is now covered and ac-cess to that interval requires some excavation. In the present study, this section is designated the type locality of the Grimstorp and Kinnekulle K-bentonites.

and should be applied also to the bed here named the Kinnekulle K-bentonite. However, pending further studies on these beds we feel it advisable to use a separate term for this bed in northwestern Europe.

Remarks.- When well developed, as is the case in most sections in Norway, south-central Sweden, and Denmark (Bornholm), the Kinnekulle bed is easily recognized because of its large thickness and stratigraphic position. Our geochemical data suggest that the Middle Ordovician K -bentonites in the Storsjo region of Jamtland, north-central Sweden, which are the northernmost known Kbentonites of that age in Baltoscandia, do not include the Kinnekulle K-bentonite but represent the Grefsen K-bentonite complex described below. At many localities, the Kinnekulle bed consists of several distinct layers as already observed by Thorslund (1948) and confirmed by our studies. These layers differ in color, texture, and grading and appear to be laterally continuous on a regional scale. This suggests that the Kinnekulle bed represents either a single event characterized by several dynamically distinct phases or several chronologically closely spaced eruptions. Grain-size studies tend to suggest the latter but the former remains a distinct possibility. Detailed studies of the Millbrig K -bentonite in eastern North America reveal a similar internal structure which has been interpreted (Zhang & Huff 1994) as representing both plinian and co-ignimbrite phases of the same eruption. Interestingly, in two sections, namely the Koangen drill-core, Scania (Bergstrom & Nilsson 1974) and in a now caved-inK-bentonite mine adjacent to the Mossen quarry, Kinnekulle (Jaanusson, pers. comm. 1992), the Kinnekulle K-bentonite is divided into two parts by a thin, probably discontinuous, bed of limestone or mudstone indicating a, presumably short, interruption of the volcanic activity.


140cm 0 •60+

~

• 18

?

?

?

~ ? N

0 j

300

km

Fig. 5. Isopach map of the Kinnekulle K-bentonite in southern Baltoscandia. Note that some local thickness variations, which apparently are caused by conditions in the depositional environment, along with the lack of reliable control in much of northern Poland and the East Baltic region northeast of Poland, complicate the establishment of the position of some isopachs. Hence, the map is provisional in some details but it does show the general thinning of this ash bed eastward across Baltoscandia. The thickness data are based on our own measurements, some of the Estonian data published by Vingisaar (1972), and a few other data from the literature.

The Grimstorp K-bentonites (new name)

Derivation of name.- These beds are named for the Grimstorp farm, about 0.2 km SE of the Mossen quarry on the eastern slope of Kinnekulle, Vastergotland. In some sections, especially in the East Baltic (Figs. 1 and 2), the Grimstorp is a single bed but at other localities such as the type section (Fig. 4), there are two or more closely spaced beds. In the Sinsen section, Oslo, Norway (Fig. 6) the Grimstorp includes two beds, beds XXIll and XXN of Hagemann & Spjeldnres (1955). In Estonia, JUrgenson (1958) and Mannil (1958, 1966) used the designation "bed e" for the bed present just above the Kinnekulle bed (Fig. 1) that we correlate with the Grimstorp beds.

Type locality. - The type locality is the Mossen quarry on the eastern slope of Kinnekulle. For location, see above (p. 4). Both the Grimstorp beds are readily accessible in this section (Thorslund 1948; Jaanusson 1964).

Stratigraphic position. - In the type section, the Grimstorp Kbentonites occur 0.28 m above the top of the Kinnekulle bed in the lowermost part of the Skagen Formation (Fig. 4 ). The two beds, here referred to as Grimstorp A and B, are 14 and 15 em thick, respectively, and separated by a 4 em thick bed of argillaceous limestone. In the Sinsen section (Fig. 6), the Grimstorp

K-bentonites occur in the upper part of the Amestad Formation (4ba) about 2.2 m above the Kinnekulle K-bentonite, and about 10 rn below the base of the Frognerkilen Formation ( 4ap) (Hagemann & Spjeldnres 1955). At the Vollen section in the Oslo region (Fig. 7), there are two 3 em thick K-bentonites (Grimstorp A and B) at 5.80 m and 6.85 m, respectively, above the top of the Kinnekulle bed. Both ostracodes (Qvale 1980) and numerous megafossils from the upper Amestad Formation (Owen et al. 1990) suggest a correlation with the Skagen Formation of Sweden. In terms of the graptolite succession, the Grimstorp K-bentonites occur in the upper part of the Diplograptus multidens Zone as indicated by the Koangen (Fagelsang) succession (Bergstrom & Nilsson 1974). Although the evidence at hand is somewhat inconclusive, these beds are likely to occur in the upper Amorphognathus tvaerensis Conodont Zone. Also, the Grimstorp beds occur within the Spinachitina cervicornis Chitinozoan Zone of Nolvak & Grahn (1993).

Regional distribution.- The Grimstorp K-bentonites are relatively persistent in their occurrence and can be traced readily from the Oslo region across south-central Sweden to Estonia (Figs. 1 and 2). In most Swedish sections, both Grimstorp A and B are present but at some localities (Fylla Mosse, some Estonian sections) there is only a single bed, perhaps due to incomplete preservation brought about by bioturbation or deposition in a relatively high-


::; ""' ~

< E-< Cl.l

r"l :z; ~

<

SINSEN, NORWAY m 20

15

10

5

0

t-------t B ""f---------1 B NOR 4

~GRIMSTORP K-BENTONITES

l NOR 5 B 65 NOR 6 t KINNEKULLE 130 NOR 7 K-BENTONITE

B NOR 24 ~ SINSEN B NOR 23 K-BENTONITES

B NOR 22

B NOR 21

B NOR 20

B NOR 19

B NOR 18

B NOR 17

B NOR 16

B NOR 15

B NOR 14 GREFSEN K-BENTONITE COMPLEX

B NOR 12

B NOR 11

B NOR 10

B NOR 9

Fig. 6. Schematic diagram of the Middle Ordovician K-bentonite succession in the Sinsen railway cut, Oslo, Norway (cf. Hagemann & Spjeldnres 1955). As in Fig. 7, NOR numbers refer to our K-bentonite samples and B65, etc. indicates a K-bentonite bed and its thickness. This is the type section of the Sinsen K-bentonites and the Grefsen K-bentonite Complex.

energy environment. There are several beds in the stratigraphic interval of the Grimstorp in the Koiingen drill-core (Bergstrom & Nilsson 1974; Fig. 2) and in the section along Rosta.nga Kyrkback in Scania. Further studies are needed to establish which beds, if any, in southeastern Scania, Bornholm, and northern Poland (Fig. 2), are identical with the Grimstorp beds. Based on stratigraphic position, the K-bentonite at 3.2 m above the Komstad Limestone at Vasagard on Bornholm (Bergstrom & Nilsson 1974) may well be interpreted to represent one of the Grimstorp K-bentonites.

Remarks.- Outside the Oslo region, exposures of the Grimstorp K-bentonites are rare in Baltoscandia. In 1959, they were observed in temporary excavations on the slope ofBillingen above Skultorp railway station, Viistergotland (Bergstrom, unpubl.) and as just noted, there is a good section through this interval along Rostanga Kyrkblick, Scania. The correlation from Scandinavia across the Baltic Sea to the beds of early Keilan (Dll) age in Estonia (Figs.

1, 2), although supported by geochemical evidence, is still somewhat tentative.

The Sinsen K-bentonites (new name)

Derivation of name.- The Sinsen K-bentonites are named for the Sinsenrailway section 0.7 km S ofGrefsen station, Oslo, Norway. This appears to be the same K-bentonite as "bed c" in Estonia (JUrgenson 1958; Miinnil1966). Hagemann & Spjeldnres (1955) referred to the two Sinsen beds as "bed XX'' and "bed xxr• in their description of the Sinsen K-bentonite sequence.

Type locality.- The type locality is the Sinsen railway cut, where two beds, Sinsen A and Sinsen B, are well exposed (Fig. 6). For a description of this section, see Hagemann & Spjeldnres (1955).

Stratigraphic position. - In the type section, the Sinsen B bed, which has a thickness of 6 em, is located 2.62 m below the base of the Kinnekulle K-bentonite in the Amestad Formation. The Sinsen A bed, 5 em thick, is 0.53 m below the Sinsen B bed. There is no published information about the biostratigraphy of this interval in the Sinsen section. In south-central Sweden, the Sinsen K-bentonites occur in a similar stratigraphic position below the Kinnekulle K-bentonite (Figs. 1 and 2) in strata classified as the Dalby Formation (Vastergotland, Ostergotland) or the Sularp Shale (south-central Scania). In the East Baltic, the Sinsen bed(s) are in the middle to upper part of the Johvian Stage (DI). In Sweden, as well as in Estonia, the Sinsen K-bentonites occur in the Baltoniodus alobatus Subzone of the Amorphognathus tvaerensis Conodont Zone, in the upper Diplograptus multidens Graptolite Zone, and in the lower part of the Spinachitina cervicornis Chitinozoan Zone.

Regional distribution. - The Sinsen K-bentonites have been identified in many sections in southern Scandinavia and in western and central Estonia. We have not yet recognized these beds in the very condensed sections at Fjiicka and Kargiirde in Dalarna, nor in southeastern Scania or on Bornholm (Figs. 1 and 2). Likewise, it is currently not recognized in the drill-cores from Gotland or easternmost Estonia.

Remarks.- The Sinsen K-bentonites are relatively thin and far less prominent than the Kinnekulle and Grimstorp ones. However, they occupy a rather isolated stratigraphic position between the base of the Kinnekulle bed and the top of the Grefsen K -bentonite complex somewhat above the middle of the Johvian Stage in an interval with few K-bentonite beds.

The Grefsen K-bentonite complex (new name)

Derivation of name.-The Grefsen K-bentonite complex is named for the Grefsen railway station, which is situated near the type section in Oslo, Norway. The complex includes beds I-XIX of Hagemann & Spjeldnres (1955) in the Sinsen section (Fig. 1) and beds a and b of JUrgenson (1958) and Mlinnil (1966) in the uppermost Idaverean Stage (Cll) of Estonia.

Type locality.- The Sinsen railway section 0.7 km S ofGrefsen station, Oslo, Norway, where most, if not all, of the beds are well exposed. As far as we are aware, this is the only outcrop in Baltoscandia providing a continuous exposure of the many Kbentonite beds in this complex.


Stratigraphic position. - In its type section, the Grefsen Kbentonite complex occurs in the lower to middle part of the Ames tad Formation ( 4ba). Biostratigraphic control is poor in the type section but conodonts from the topmost part of the underlying Vollen Formation at another locality in the Oslo region (Hamar 1966) are interpreted to represent the uppermost Baltoniodus variabilis Subzone of the Amorphognathus tvaerensis Conodont Zone (Bergstrom unpubl.). In south-central Sweden (Kinnekulle, etc.), as well as in Estonia, most of the Grefsen K-bentonite complex is in the Baltoniodus alobatus Subzone oftheAmorphognathus tvaerensis Zone but it is possible that it may extend downward into the Baltoniodus gerdae Subzone of the Amorphognathus tvaerensis Zone. It is within the Diplograptus multidens Graptolite Zone as shown by the Kolingen (Fagelsang), Scania succession (Bergstrom & Nilsson 197 4 ). The range of the complex in terms of chitinozoan zones (Nolvak & Grahn 1993) is not yet firmly established. Its upper part is certainly in the lower Spinachitina cervicornis Zone and lower parts of the complex may be coeval with the Belonechitina hirsuta Zone, and possibly, the Lagenochitina? dalbyensis Zone. It is within the Idaverean (Cill) Stage in the East Baltic, its uppermost bed being taken as the top of the Idaverean Stage.

Regional distribution.- The Grefsen K-bentonite complex in the Oslo region has been correlated in some detail with the extensive K-bentonite successions at Kinnekulle (Hagemann & Spjeldnres 1955; Bergstrom & Nilsson 197 4) and in the Kolingen core, Scania (Bergstrom & Nilsson 1974). Because most other sections in Baltoscandia lack some, or many, of the beds, precise bed-bybed correlations will not be possible in such sections until more detailed geochemical studies have been carried out on individual beds. As shown in Figs. 1 and 2, the upper beds of the complex can be traced widely across Baltoscandia from southeastern Norway to eastern Estonia. Yet, without chemical fmgerprinting there is some question whether or not the topmost bed, taken as the top of the Idaverean Stage, is of precisely the same age everywhere. As noted by, among others, Mlinnil (1966) and Jaanusson (1976), the absence in Scandinavia of the ostracode and megafossil fauna typical of the Estonian Johvian Stage makes it difficult to recognize this stage in Sweden and Norway. However, based on our K-bentonite bed tracing, and in the absence of evidence of a significant stratigraphic gap in the central Baltoscandian Confacies Belt and the Oslo-Scanian Confacies Belt, there appears to be little doubt that the stratigraphic interval in Scandinavia between the top of the Grefsen K-bentonite Complex and the base of the Kinnekulle K -bentonite corresponds to the Johvian Stage in the East Baltic. Most of the beds in the lower part of the Grefsen K-bentonite Complex are relatively thin and they are irregular in their geographic occurrence, especially in carbonate facies, and at the present time, they are of limited stratigraphic use.

Outcrops of this K -bentonite complex are uncommon in B altoscandia. There are good exposures along Rostanga Kyrkblick, Scania and at Fjacka (Jaanusson & Martna (1948) and Kargiirde (Jaanusson 1982) in the Siljan district, Dalarna. Sections in Estonia include Peetri near Tallinn (Polma et al. 1988; Hints & Nolvak 1990) and the Aluvere quarry 30 km E of Tallinn (Roomusoks 1970; Polma & Hints 1984). Based on their geochemical signature, the K-bentonites in the Kargiirde, Dalarna (Jaanusson 1982; Holmer 1989) and Lugnvik, Jiimtland (Karis & Larsson 1982) sections belong to the Grefsen K-bentonite Complex. Also, the lower of the beds below the Kinnekulle K-bentonite in south-

VOLLEN, NORWAY

m

I GRIMSTORP f K-BENTONITES

0 {

1t l KINNEKULLE 8 95 NOR 1m f K·BENTONITE

1 6

Fig. 7. Schematic diagram of the section along Highway 165 (Slemmestadveien) about 0.3 km south of Vollen and opposite Amestad Sport Center, Oslo, Norway. This new road-cut is the most extensive exposure of the Kinnekulle and Grimstorp K-bentonites known anywhere in Baltoscandia. For explanations of letter and number designations, see Fig. 6.

eastern Scania and on Bornholm are likely to represent this complex but chemical fingerprinting is needed to confirm this suggestion.

Geochemistry Trace elements have been widely used to identify, classify, and discriminate between plutonic and volcanic rocks formed in different tectonic settings and derived from different parental sources. They have also proved useful in refining and improving stratigraphic correlation of pyroclastic beds, particularly those beds representing explosively erupted and rapidly deposited airfall ashes. For the study of K-bentonites as well as other altered volcanics the practical use of trace elements is restricted to the so-called immobile elements, that is, those elements which tend to be partitioned into the liquid phase during partial melting and into the residual liquid of a crystallizing magma. Of these, Ta, P, Hf, Th, Zr, Ti, Y, and REE have been widely used to construct discrimination diagrams, and they are also among the most powerful discriminators in chemostratigraphic fingerprinting where within-bed variations are consistently less than betweenbed variations. Such relations enable the stratigraphic recognition and correlation of individual K-bentonites over wide areas, even where associated K-bentonites have similar chemistries (Kalata et al. 1987). Also in Baltoscandia, distribution and characteristics of some trace elements in Middle Ordovician K-bentonites can serve to complement and amplify the regional relations of Kbentonite beds as recognized primarily on the basis of biostratigraphy and lithostratigraphy. In particular, the Kinnekulle Kbentonite has a unique composition that allows it to be distinguished from adjacent widespread beds, and based on its trace element characteristics it can be traced more than 1000 km across


Baltoscandia and in complete agreement with its position inferred from biostratigraphic data.

Chemostratigraphy

Explosively erupted volcanic ash has long been known to have event-stratigraphic importance in regional stratigraphic analysis. This use has been enhanced by the identification of characteristic chemical fingerprints unique to each bed and reflective of the relative proportions of immobile elements in parental felsic magmas. The most widely used method employs multivariate statistical analysis of whole-rock chemical data (Huff & Kolata 1989), although recent studies have shown that microprobe data from quartz melt inclusions inK-bentonites can also provide a powerful basis for chemostratigraphic correlation (Delano et al. 1994).

Methodology

For this study the whole-rock method was employed, and the selection of particular elements for chemical fmgerprinting was based on discriminant function analysis of data from stratigraphically well constrained samples. The computed discriminant functions were used to construct a discrimination diagram (Fig. 8) which is a graphic portrayal of the extent of separation between the groups of samples achieved by the analysis. The discrimination diagram is also useful for identifying and correlating samples of unknown or uncertain stratigraphic position, once their discriminant scores are computed based on analyzed values of the same elements used to construct the original diagram. We used as our reference group Middle Ordovician K-bentonite samples from Estonia. These were selected on the basis of the extraordinarily abundant Ordovician cores, and drillhole information, accumulated during regional mapping and the search for raw materials in that country during the past several decades. No comparable regional record of Ordovician subsurface information exists in Scandinavia but numerous drillings have been carried out also in Lithuania, Latvia, and northern Poland. In Estonia, the Kinnekulle K-bentonite occurs just at the base of the Keila Formation and can be easily traced throughout the northern part of the country and into Ingria in western Russia on the basis of stratigraphic position, lithology, and thickness (Figs. 1, 2). A previous report on the stratigraphy of this bed in Estonia (Vingisaar 1972) demonstrated that it extends into Russia nearly as far as St. Petersburg, and that, based on its biostratigraphic position, it is most likely equivalent to bed XXII in the Oslo region and to the "Big Bentonite" at Kinnekulle, Sweden (also see Miinnil1966). However, definitive evidence for these correlations has not been provided until now.

Above and below the Kinnekulle K-bentonite are similarappearing, but thinner, beds that are equally widespread in northern Estonia and whose biostratigraphic position plus their position with respect to the Kinnekulle K-bentonite allows them to be equated with the Grimstorp and Grefsen beds in Sweden (Figs. 1, 2). K-bentonites occupying the approximate stratigraphic position of the Sinsen beds are known in Estonia, but have not been collected or geochemically studied by us on a regional basis, and will not be discussed further here.

Previous investigations of K-bentonite correlation in North America by discriminant function analysis (Huff & Kolata 1989) demonstrated the importance of having a minimum number of samples, generally 7-10, whose stratigraphic position is precisely

known a priori. This permits a detailed quantitative assessment of their within-bed vertical and lateral chemical variability, and thus the establishment of a quantitative chemical profile of each bed. Fewer samples will greatly increase the confidence interval of the calculated means of the groups and thereby render their stratigraphic identify less certain. Of the three beds or complexes described herein, all were sampled with enough density as to make them suitable for statistical study. The Grimstorp, Kinnekulle, and Grefsen beds are of sufficiently distinct and characteristic trace element composition that one may reasonably predict the Sinsen beds likewise to contain diagnostic trace element features. To study the Grimstorp, Kinnekulle, and Grefsen beds, 57 Kbentonite samples from these 3 groups were analyzed for major and trace elements. The representation of each group was as follows: Grimstorp 7 samples representing both Grimstorp A and B, Kinnekulle 20 samples, and Grefsen 30 samples representing the two most prominent beds near the top of the Idaverean Stage. These samples constituted the highest confidence level attainable using all available stratigraphic means with respect to actual group membership. The discriminant model created by this experiment was then used to test the hypothesis that 14 K-bentonite samples from Sweden, Denmark, and Norway representing beds thought to be equivalent to the Kinnekulle K-bentonite on the basis of biostratigraphic and lithostratigraphic evidence were chemically more like the Kinnekulle K-bentonite than the other 2 K-bentonite groups. These samples included two representatives from the type Kinnekulle K-bentonite at Mossen, Sweden. Similarly one suspected Grimstorp each from Sweden and Denmark were tested for chemical similarity against the Estonian reference group.

Results Analysis of variance (ANOVA) of the 57 Estonian samples using the SPSS statistical package revealed that some immobile trace elements had subtle but distinctly different abundances between the 3 groups. These differences were expressed by the group means whereas the full range of values showed some overlap between beds. In other words, based on single element abundances alone the 3 groups could be distinguished from one another. Back classification is one measure of the quality of the separation described by the discriminant analysis. Both the Grimstorp and Kinnekulle samples are classified 100% correctly, and the Grefsen samples are classified 63% correctly, with 11 of the 30 samples identified more closely with the other two groups.

Discriminant function analysis identified a combination of 5 elements which markedly improved group separation. Table 1 lists the 5 elements and their corresponding Wilks' lambda values. Wilks' lambda is the inverse of the between-group variance accounted for by each element. Thus, Ti alone accounted for 55% of the between-group variance leaving a Wilks' lambda of 0.45. Ti combined with Hfimproved the discrimination with a Wilks' lambda of 0.23, and so on until 6 elements grouped together accounted for 90% of the between-group variance. The remaining 10% is explained by several additional elements. Only the five will be discussed here since they more than adequately separate and identify beds belonging to one of the 3 groups.

Fig. 8 shows the territorial discrimination plot of the Estonian reference samples. Group boundaries are drawn at the midpoint between group means. It can be clearly seen that the Grimstorp and Kinnekulle samples are well separated from one another. The Grefsen beds have a higher covariance than the other two and show some overlap with both the Grimstorp and Kinnekulle beds.


Fig. 8. Discrimination Discriminant Function 1 diagram for three groups of Middle Ordo- ~

'<)

vician K-bentonite beds from Estonia, the

6 6

Grimstorp, Kinnekulle, and Grefsen beds. The axes represent the first 4

Grefsen 4 0 Grimstorp/Estonia and second discrirni-nant functions com- • Kinnekulle/Estonia puted by discriminant Kinnekulle 0 function analysis of 57 N

0 8: Grefsen/Estonia c: 2 2 0 samples from these 0 ·a 0 three groups. Group

~ 0 8 6. Kinnekulle/Sweden means are shown and

~~"' ~0 used to construct ~ 0 ··~~ 0 m Grimstorp/Sweden

territorial boundaries :! 6. A o• •til 0 representing maximum 6. • 0 • Grimstorp/Denmarlc separation of the three 0 groups. Additional "' • Kinnelc:ulleiDenmarlc samples thought to i5 -2 IB -2 • represent the Kinne- <> Kinnekulle/Norway kulle and Grimstorp beds from Sweden,

-4 Grimstorp -4 * Group Means Norway, and Denmark are plotted and are shown to have a high degree of correlation

-6 with the reference beds. ~ ~ 0

This probably reflects the greater diversity of single beds that compose the Grefsen K-bentonite complex and thus introduces more chemical variability into the system than is found in, say, a single episode event like that of the Kinnekulle K-bentonite. A larger population of samples from all three groups might produce improved resolution for the Grefsen group, particularly since groups means are well separated (Fig. 8). However, the present data set provides strong evidence that real and persistent chemical differences exist between the three groups throughout the study area.

The significance of these 5 discriminating elements most likely can be related to the primary phenocryst mineralogy of the beds. The Kinnekulle K-bentonite is rich in biotite which has been shown to be a significant carrier ofTi (Yost & Huff 1994). Apatite, zircon, and feldspar are also present in these beds and are the most likely hosts for the other 5 elements.

The results of the test of the 14 suspected Kinnekulle equivalents are illustrated by their position on the discrimination plot in Fig. 8. Of the 14 samples, all are chemically more similar to the reference Kinnekulle K-bentonite than to samples from the Grimstorp or Grefsen beds. Of the compositional variance among the 3 beds, 100% can be explained by 5 elements out of a total of 69 analyzed: Ti, Th, Hf, Zr, and Cr. Fourteen samples of the Kinnekulle K-bentonite from Sweden, Denmark, and Norway all

Table 1. Summary of the discriminant analysis of the Estonian reference group.

Element Step Wilks' lambda

Ti 1 0.52 Th 2 0.55 Hf 3 0.59 Zr 4 0.61 Cr 5 0.91

-6 '<)

have discriminant scores that fall within the Kinnekulle Kbentonite region of the discriminant diagram and thus are taken to represent the same bed.

Adjacent K-bentonites of the Grimstorp and Grefsen complexes show a subtle but consistent difference from the Kinnekulle Kbentonite. Because they belong to complexes rather than individual beds the samples used represent composite values of two or more closely spaced beds. This results in some slight overlap in discriminant scores of the Grimstorp and Grefsen groups. However, their mean discriminant scores are distinctly different and thus may serve as useful indicators of their respective stratigraphic positions. The unanimity of this agreement provides powerful confirming evidence that the Kinneulle K-bentonite is indeed widespread throughout Baltoscandia and that it is sufficiently unique in its trace element composition that it can be separated geochemically from K-bentonites occurring stratigraphically above and below it.

Concluding remarks The present study shows that not only the Kinnekulle K-bentonite but also some other Middle Ordovician ash beds can be traced with confidence over long distances in Baltoscandia and represent exceptional stratigraphic markers. In view of the fact that the individual volcanic eruptions that produced these ash beds are unlikely to have lasted more than a couple of weeks (Huff et al. 1992), it is evident that each regionally traceable ash layer represents an isochronous surface with a time resolution not attainable by other means in the Lower Paleozoic. As shown by Bergstrom & Nilsson (1974), there are more than 150 K-bentonite beds in the Middle Ordovician shale succession of the Koiingen drill-core in south-central Scania, but the vast majority of these are thin and apparently not represented in the shallower-water carbonate-dominated successions in much of south-central Balto-

12 Bergstrom et al.: Middle Ordovician K-bentonites in Baltoscandia GFF 117(1995)

scandia. Correlation of many individual K-bentonite beds from shale to carbonate facies in this region is still a problem, especially in the case of the Grefsen K-bentonite complex. However, recently developed methods involving chemical fingerprinting based on glass inclusions in volcanic quartz phenocrysts (Delano et al. 1994; Mitchell et al. 1994) show great potential to make it possible to match coeval ash layers with substantially greater precision than by using whole-rock trace element fmgerprinting methods (Huff et al. 1992). Application of this method to Baltoscandian Middle Ordovician K-bentonites will undoubtedly not only result in the establishment of many more time-lines in the succession of that region but also, and probably more important, it will open up the possibility of establishing trans-Atlantic ties other than that of the Millbrig-Kinnekulle K-bentonite. In view of the well-known Middle Ordovician faunal provincialism and the limitations in biostratigraphic resolution in both North America and northwestern Europe, we do not expect that it will be possible to greatly increase the current precision in trans-Atlantic biostratigraphic correlations in the near future. However, trans-Atlantic correlations of individual K-bentonite beds using geochemical methods may well revolutionize the regional Ordovician chronostratigraphy in the Iapetus region.

Achlowledgements.-We are particularly indebted to Valdar Jaanusson for reading the manuscript and offering very valuable comments. We thank Nils Spjeldnres, David Bruton, Dimitri Kaljo, Lars Karis, Stephen Leslie, Karen Tyler, Helen Hayes, Sven Laufeld, Goran Kjellstrom, Teresa Podhalanska, Kent Larsson, and Nils Malmsten for valuable assistance. The present research has been supported by National Science Foundation grants EAR-9004559, EAR-9005333, EAR-9205981, and EAR-92054893.

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Appendix Geographic location of K-bentonite successions illustrated in Figs. 1 and 2.

Denmark VASAGARD: outcrop along Laesa rivulet near Vasagard, Isle of Bomholm

(Bergstrom & Nilsson 1974).

Estonia KALESTE F-356: core drilled c. 4 km E of Kopu on W coast of Hiiumaa Island. OOSTRIKU 37: core drilled 30 km E of Paide, c. 70 km NNW of Tartu. PilLS I 729: core drilled 4 km ENE of Ulvi, 8.5 km NNW of Mustvee, near the

NW comer of Lake Peipsi. SOOV AIJA K-1: core drilled in the Kiirdla impact structure, 4 km E of Kiirdla in

the NE part of Hiiumaa Island. TURBA D-76: core drilled 2 km SW of Turba, c. 50 km SW of Tallinn. VASKNARVA 639: core drilled at Vasknarva, at the NE comer of Lake Peipsi. VALGU V-99: core drilled 1 km SW ofValgu, c. 65 km S of Tallinn. VIKI: core drilled at Viki near the W coast of Saaremaa Island, c. 26 km NW of

Kuressaare.

Norway SINSEN: outcrop along railway 0.7 km S of Grefsen station, Oslo (Hagemann &

Spjeldnres 1955).

Poland BIALOGORA 1: core drilled near the coast of Baltic Sea ca. 50 km NW of Gdynia

(Podhalanska 1980).

Russia SLANTSY: core drilled at Slantsy, ca. 150 km SW of St. Petersburg.

Sweden F ARDALA 1: core drilled near Fardala farm on S slope of V arvsberget, c. 13 km

ENE ofFalkoping, Province ofViistergotland (Skoglund 1963). FJACKA: outcrop along Fjlickan rivulet near MoldA farm, 1 km W of Dalbyn,

Siljan area, Province of Dalarna (Jaanusson & Martna 1948). FYLLA MOSSE: core drilled in the Granby impact structure c. 2 _km SE of

Vadstena, Province of Ostergotland. GOTSKA SANDON: core drilled c. 0.1 km SE of the lighthouse at Harnnudden,

SW comer of Gotska Sandon, c. 40 km N of Gotland, Province of Gotland (Grahn 1982a).

GROTLINGBO: core drilled c. 6.3 km ESE of Grotlingbo church, Province of Gotland (Grahn 1982a).

KINNEKULLE: composite section of core drilled 25 m NE of Kullatorp spring, 4.1 km NE of Medelplana church, and the Mossen quarry, 1.25 km SE of Kullatorp, Kinnekulle, Province of Viistergotland (Thorslund 1948).

KOANGEN: core drilled 0.2 km SE of Kolingen farm, c. 4.7 km E of Lund, Province of Skane (Nilsson 1972).

KULLATORP: see Kinnekulle. SMEDSBY GARD: core drilled at Smedsby Gard, c. 4 km NW of Motala railway

station, Province of Ostergotland. TOMMARP: excavated well 0.65 km WSW ofTommarp church, c. 7.5 km WSW

of Sirnrisharnn, Province of S!clne (Bergstrom & Nilsson 1974).

Nomenclature, stratigraphy, chemical fingerprinting, and areal distribution of some Middle...

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