Hirnantian (Late Ordovician) brachiopod faunas

Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

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Hirnantian (Late Ordovician) brachiopod faunas across Baltoscandia: A global and regional context David A.T. Harper a,b,⁎, Linda Hints c a b c

Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK Department of Geology, Lund University, SE-223 62, Lund, Sweden Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia

a r t i c l e

i n f o

Article history: Received 18 September 2015 Received in revised form 21 November 2015 Accepted 27 November 2015 Available online 7 December 2015 Keywords: Ordovician Hirnantian Baltica Brachiopods

a b s t r a c t A diverse, typical Hirnantia brachiopod fauna from terminal Ordovician strata in Latvia extends the distribution of the Kosov Province across much of the Baltic Palaeoplate into the deeper-water facies of the East Baltic. The new data emphasise the co-occurrence of the core elements of the fauna, Eostropheodonta, Dalmanella, Cliftonia, Hindella, Plectothyrella and Hirnantia, in a siliclastic shelfal setting. The fauna has close similarities with faunas elsewhere on Baltica, including Jämtland, the Oslo Region and Västergötland and plot within the Kosov Province in analyses of the global distribution of Hirnantian assemblages. Carbonate facies, first, in Estonia (lower Hirnantian) and, second, in Oslo together with Östergötland (upper Hirnantian) support quite different faunas related to the margins of Laurentia and the Edgewood Province of the midcontinent, respectively. Stable isotope curves, when used with caution, have helped correlate the sections across the eastern Baltic into Sweden. © 2015 Elsevier B.V. All rights reserved.

1. Introduction The end-Ordovician marked a major event in the history of life on our planet (Harper et al., 2014). There were significant changes in the brachiopod faunas during the event; major extinctions in the deep sea and on the shallow shelves, particularly at lower latitudes, heralded the arrival of new groups of brachiopod communities, collectively assigned to the Hirnantia fauna (Temple, 1965; Bergström, 1968; Wright, 1968). These near-cosmopolitan associations, stretching from polar to subtropical latitudes, co-existed with Edgewood faunas that occupied carbonate environments in the tropics (Rong and Harper, 1988), against a background of initial global cooling. Ghienne et al. (2014) have recently suggested an alternative scenario, associating the initial extinction with a phase of warming and high sea levels. We examine here a regional development of the Hirnantian brachiopods and its implications for global biogeography. The Baltic Plate hosted a range of Hirnantian brachiopod associations extending from the Caledonian front in the northwest to the Baltic palaeobasin in the southeast. The conclusion of the taxonomic study of the Hirnantian brachiopod faunas of the Baltic states (Hints and Harper, 2015) now completes information on a remarkable range of Hirnantian faunas from shallow shelf to deepwater basinal settings and from both carbonate and siliciclastic environments on a single palaeoplate. ⁎ Corresponding author at: Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK. E-mail addresses: [email protected] (D.A.T. Harper), [email protected] (L. Hints).

http://dx.doi.org/10.1016/j.palaeo.2015.11.044 0031-0182/© 2015 Elsevier B.V. All rights reserved.

Major glaciation together with tectonic movements on the western margin of Baltica (Cocks and Forty, 1998) reduced the size of the Baltic palaeobasin and increased the range of depositional regimes across the basin, coincident with the major turnover in biotas (Harper et al., 2014). The basin, which extended as far as the Urals to the east, to Finland and Belorussia on the edge of the Baltic platform (Dronov and Mikuláš, 2010), during the beginning of the Late Ordovician (Sandbian), was restricted during the Hirnantian to just beyond the eastern parts of the Baltic states today (Fig. 1). In the East Baltic and Poland, Hirnantian strata form an almost continuous cover to the varied lithological units of the highest Katian Pirgu Regional Stage. The lower Hirnantian shallow-water stromatoporoid–coral reefs and associated deposits contain a distinctive association of brachiopods (Hints, 2012; Hints et al., 2012) cropping out in central Estonia across a relatively narrow belt (Estonian shelf of Harris et al., 2004; Hints, 2012). The offshore facies, which dips to the South, consist of carbonate and siliciclastic packages at a depth of about 1000 m in western Latvia (Ulst et al., 1982), and up to about 4400 m in Poland (Temple, 1965; Podhalańska, 2009). In contrast to the East Baltic, the uppermost Ordovician in Sweden and Norway occurs as sporadic outcrops (Fig. 1; Bergström et al., 2012) well known from numerous natural exposures and quarries, and complemented by several drill cores (Fig. 1A). The index graptolites of the Hirnantian Stage are missing from the carbonate sections on the continental part of the East Baltic. These graptolites or related species, however, have been recorded from some inshore drillcores (Ulst, 1992), in northern Poland (Podhalańska, 2009), and in the some localities in Sweden, for example, in western Scania (Nilsson, 1979; Pålsson, 2002), Östergötland (Rong et al.,

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83 Outer limit of the area with uppermost Ordovician rocks Outer limit of the area with continuous distribution of the Ordovician rocks Boundary between the shelves and basin Southwestern margin of Baltica

Osmundsberget

Boda

Oslo-Asker

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Fig. 1. Ordovician palaeobasin with (A) the locality occurrences (asterisk) of the Hirnantia brachiopod fauna in Scandinavia; S-8 drill core (Ulst, 1992) and (B) location of drill cores in the East Baltic. Black dots: drill cores; (1) Stirnas-18; (2) Pliekalne-14; (3) Dižrungi-17; (4) Vilcini-19; (5) Adze; (6) Dreimani-11; (7) Riekstini-15; (8) Mežmali-16; (9) Mežvagari-13, (10) Edole-60; (11) Anši-12. Empty dots mark localities of the Hirnantia brachiopod fauna reported by Paškevičus (1997).

2008), Västergötland (Bergström and Bergström, 1996; Bergström et al., 2011), and Jämtland (Dahlqvist et al., 2010). In the Oslo Region, the Solvik Formation contains, in its lowermost part, graptolites, indicating a Metabolograptus persculptus or Parakidograptus acuminatus Biozone age (Howe, 1982) and also an interesting relict Katian brachiopod fauna (Baarli and Harper, 1986). Baarli (1995) and Bergström et al. (2012) included this part of the formation within the Hirnantian Stage. Due to the lack of index graptolites, the lower boundary of the Porkuni Regional Stage is correlated across the different facies belts of the East Baltic by a level with the continuous occurrence of the zonal chitinozoan Spinachitina taugourdeaui (Nõlvak, 1999). Unfortunately, this zonal chitinozoan is unknown in Scandinavia (Grahn and Nõlvak, 2010). During the last few decades, the results of carbon isotope studies on the Hirnantian rocks have been successfully used in the correlation of sections located across the different facies belts of the East Baltic (Kaljo et al., 2001, 2008), Scandinavia (Schmitz and Bergström, 2007; Bergström et al., 2011, 2012), North America (Bergström et al., 2006), China (Chen et al., 2006; Bergström et al., 2008), and other regions of the world. Integrated carbon isotope and chitinozoan data have enabled reliable correlations of the shallow-water shelf sections with the basinal successions in the East Baltic, which differ substantially from each other in lithofacies and faunal development (Kaljo et al., 2001, 2004; Brenchley et al., 2003). The carbon isotopes together with micropaleontological data provide an operational stratigraphical background for the correlation of deeper-water lithologies with the Hirnantia brachiopod fauna, in more shallow-water settings. New data on brachiopod taxonomy and distributions together with those of other shelly fossils complement our previous (Brenchley et al., 2003; Kaljo et al., 2008) knowledge of the Hirnantian faunas in Baltoscandia. The Hirnantia brachiopod fauna is to date best known from Norway (Cocks, 1982; Brenchley and Cocks, 1982) and Sweden (Bergström, 1968), where brachiopods of two provinces, the Kosov and Edgewood, are represented. New Baltic data fill a major gap in the composition and diversity of the latest Ordovician brachiopods in the onshore–offshore successions in the Baltic Basin. The integrated analysis of the temporal and spatial distribution of the Hirnantian brachiopods in Baltica and Laurentia, together with the chemostratigraphy available, now permits the correlation of those successions characterised by different brachiopod faunas. Data on brachiopod occurrences were analysed using PAST software (Hammer et al., 2001) increasing the reliability of analytical data from drill cores. Analyses of the stratigraphical distribution and composition of the brachiopod assemblages greatly assist the interpretation of the successions in cases of incomplete

sections or too limited data. Critical is the distribution of the Hirnantian brachiopods in relation to the carbon isotope excursion, to tie bioevents with changes in the geochemistry of sediments. 2. Geological background In Baltoscandia, the Hirnantian (Porkuni) Stage consists of lithologically variable carbonate and siliciclastic deposits of the Kuldiga and Saldus formations (Fig. 2; Kaljo et al., 2001), which overlay a slight stratigraphic gap in the different formations of the Katian Pirgu Regional Stage. In the East Baltic, the Hirnantia brachiopod fauna consists of taxa characteristic of the Kosov Province, species of the genera Dalmanella, Hirnantia, Kinnella, Paromalomena, Eostropheodonta, Cliftonia, Plectothyrella and Hindella (Rong and Harper, 1988), which occur mainly in the Kuldiga Formation of the Porkuni Regional Stage. The thickness of that stage varies from about 25 m in western Latvia to a few metres in central Latvia (Ulst et al., 1982). In the eastern and south eastern areas of Latvia, the Kuldiga Formation is partly eroded or has a restricted thickness, or is replaced by the Saldus Formation. The latter formation began when the second Hirnantian transgressive episode was followed by a rapid retreat that generated pauses in sedimentation together with the redeposition and erosion of earlier deposits. In Baltoscandia, the thickest (up to 60 m) Hirnantian crops out in Norway, where deposition of sandstones and shales with limestone intervals (Owen et al., 1990) occurred within a major regressive phase on the Baltic craton (Brenchley and Newall, 1975). In the Oslo–Asker district, the Hirnantian is represented by the Langøyene Formation (sandstones), which thins laterally and is replaced by a unit of oolite breccia in some areas (Owen et al., 1990). The Langåra Formation (limestones and shales) has a thickness of up to 35 m and is a partial equivalent of the Langøyene Formation (Owen et al., 1990). These units comprise the richest Hirnantia brachiopod fauna in Baltoscandia, which are partitioned into several ecological associations (Brenchley and Cocks, 1982). In Sweden, the most diverse Hirnantian brachiopod fauna is known from the Loka Formation (Bergström and Bergström, 1996; Bergström et al., 2011) exposed in different localities in Västergötland (Bergström, 1968) and Östergötland (Rong et al., 2008). In the last area, the Hirnantian brachiopods occur within the well-known “Borenshult fauna” (Rong et al., 2008; Bergström et al., 2012). A characteristic Hirnantian shelly fauna with brachiopods and trilobites has been identified in the shallow-water environments in western and eastern Jämtland (Karis, 1982; Karis and Larsson, 1982; Dahlqvist, 2004; Dahlqvist et al., 2010). In the westernmost sections, the Hirnantian brachiopods occur in the uppermost part of the dark shaly siltstone of the Kogsta Siltstone

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

Porkuni

Katian

SIL.

Rhuddanian

U. ORD.

Juuru

Hirnantian

GLOBAL REGIONAL UNITS STAGE

Rhuddanian Hirnantian

CHITINOZOAN ZONE

P. acuminatus A. ascensus

Ancyrochitina laevaensis

N. persculptus

Conochitina scabra

D. anceps

Pirgu

D. complanatus

SCANIA (3)

ÖSTERGÖTLAND (5)

Central Baltic

Northern and Central Estonia

STURI

TAMSALU

STATCIUNAI

Ozarkodina hassi

Broceni Piltene

Noixodontus

Edole

ÕHNE

KULDIGA

Bernati

KUILI PAROVEJA

Amorphognathus ordovicicus

ÄRINA HALLIKU ADILA JELGAVA

JONSTORP

SILJAN (6)

VARBOLA

SALDUS

MOE

JÄMTLAND (7) N. POLAND (9) OSLO-ASKER (8) E. W. E. W.

KALLHOLN

MOTALA

SOLVIK

PASLEKA BARCIAN

EDE

Tommarp LOKA

LINDEGARD

EAST BALTIC (formations and members) (1,2) Western Latvia

Distomodus kentuckyensis

fauna

Spinachitina taugourdeaui Belonechitina gamachiana Tanuchitina anticostiensis Conochitina rugata Tanuchitina bergstroemi

VÄSTERGÖTLAND (4)

KALLHOLN

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Belonechitina postrubusta

N. extraordinarius

Katian

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SIL.

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LANGØYENE LANGÅRA

BODA KOGSTA

UPPER JONSTORP

ORNETY

KYRKÅS

HUSBERGØYA

PRABUT MORAGA

Fig. 2. The correlation chart of the Upper Ordovician–Lower Silurian stratigraphical units in Baltoscandia (regional formations). U.ORD.—Upper Ordovician, SIL.—Silurian; D. complanatus—Dicellograptus complanatus; D. anceps—Dicellograptus anceps; M. extraordinarius—Metabolograptus extraordinarius; M. persculptus –Metabolograptus perculptus; A. ascensus—Akidograptus ascensus; P. acuminatus—Paracidograptus acuminatus. Compiled for regions 1-9: Nõlvak et al. (2006) (note in Meidla et al., 2014 part of the Õhne Formation of the Juuru Stage is included in the Hirnantian), Männik (2014) (1, 2), Pålsson (2002), Grahn and Nõlvak (2007) (3), Bergström and Bergström (1996) (4, 5), Ebbestad and Högström (2007) (6), Dahlquist (2004) (7), Owen et al. (1990) (8) and Podhalańska (2009) (9).

(thickness 30–40 m), and in the easternmost sections in the quartzites, dark shales and mudstones of the Kyrkås Quartzite (thickness up to 35 m). The Hirnantia brachiopod fauna in the East Baltic (Hints and Harper, 2015) and Jämtland (Dahlqvist et al., 2010) is represented mainly by taxa characteristic of the Kosov Province. However, in the Östergötland and the Oslo–Asker district, associations with species of genera Brevilamnulella, Thebesia, Leptoskelidion and Stegerhynchus show similarity with the North American Midcontinent, shallow-water, Edgewood fauna (Brenchley and Cocks, 1982; Amsden, 1986; Rong and Harper, 1988; Bergström and Bergström, 1996; Bergström et al., 2006). The similarity of these Baltoscandian Hirnantian faunas, belonging to the Edgewood Province, with an exceptional reach in subtropical to tropical oolitic environments (Amsden, 1986), is of key significance in interpreting environmental changes at the end of the Ordovician. 3. Materials and methods This study is based on data from drill cores from Central East Baltic (southern Estonia, Latvia and northern Lithuania). The Baltic Hirnantian brachiopods (altogether 20 species and taxa under open nomenclature) have been described from 43 drill cores (Hints et al., 2010; Hints and Harper, 2015). The shelly fauna, brachiopods together with some associated fossils, was studied in 687 rock samples, from cores with a diameter of 70–90 mm. The associated trilobites noted on the figures were identified by Helje Pärnaste (Hints et al., 2010). The sample density is uneven in different sections, which makes the results of the statistical analysis, in some cases, less robust. The statistical analyses of the distribution of brachiopods and associated fauna have made use of the different options in the PAST software programme (Hammer et al., 2001; Hammer and Harper, 2006). The analysis of the Hirnantia brachiopod fauna is based on data from the East Baltic and Scandinavia (Norway and Sweden) presented in numerous publications referred to

below in the text. The carbon isotope curves used in this study (Ruhnu and Taagepera cores) are from earlier publications (see Brenchley et al., 2003). The brachiopod and carbon isotopes have been also studied in the Stirnas-18 core from western Latvia (Hints et al., 2010). The isotopes were determined by whole rock methods in the laboratory of the Geological Institute, Tallinn University of Technology. The core samples and shelly fossils from the East Baltic used in this study are housed in the Institute of Geology, Tallinn University of Technology and in the Natural History Museum in Riga. The corresponding collections are accessible from the online database of both institutions. The samples with the Hirnantian brachiopods mentioned by Paškevičus (1997) are housed at the University of Vilnus in Lithuania. The data on the lithology of core sections are based on some earlier publications (Oraspõld, 1975, 1986; Põlma, 1982; Ulst et al., 1982) and unpublished data by L. Põlma. Unpublished data on stratigraphy of Latvian core sections, housed at the Natural History Museum in Riga, compiled by Latvian specialists R. Ulst and L.-I. Gailite, are used for the identification of the stratigraphical positions of samples. These data based on the geophysically revised depths of core section are sometimes different than the palaeontological data based on the samples, where depths are identified by the initial interpretation of depth by drilling workers. Thus, the palaeontological data always show somewhat greater figures for depth (see Hints and Harper, 2015). In the East Baltic and Sweden, the uppermost Ordovician Porkuni Stage is accepted as a regional unit corresponding to the global Hirnantian Stage (Nõlvak et al., 2006; Ebbestad and Högström, 2007). The latter name is used in the stratigraphical classification of the Ordovician in Norway (Owen et al., 1990). In the present study, the term “Hirnantian Stage” is used for strata corresponding to the Porkuni Regional Stage. The facies differentiation of the Baltic Basin (Jaanusson, 1995; Kaljo et al., 2008) is described below using the terminology of Harris et al. (2004). According to this terminology, the Estonian and Lithuania shelves correspond to the Estonian and Lithuanian (con)facies belts, Livonian Basin to the Central–Baltoscandian (Con)Facies Belt with

74

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

the Livonian Tongue and the Scandinavian Basin corresponds to the Scanian (Con)Facies Belt (Fig. 1).

Mežmali-16 Saldus Fm.

900.0

4. Hirnantia brachiopod fauna in Latvia

?

Rugose corals

995

(Kuili Fm.)

914

Trematis sp.

Edole Member

912

OTHERS

BRACHIOPODA Fig. 4. Distribution of fossils through the Kuldiga Formation of the Porkuni Stage in the Mežmali-16 core. For lithological legend, see Fig. 3.

Bryozoa Tentaculites Gastropoda Bivalvia Cephalopoda

1002.6

PIRGU STAGE

911.5

916

?

1000

910

916.4

Kinnella sp. Cliftonia sp. Cliftonia sp. A Leptaena sp. Cliftonia? sp. Cliftonia psittacina Onniella sp. E. cf. parvicostellata Kinnella cf. kielanae Hindella crassa incipiens L. (L.) rugosa Dalmanella spp. D. testudinaria Paromalomena sp. Atrypidae Paramalomena polonica Plectothyrella? sp. Leptostrophiidae Eostropheodonta sp. E. hirnantensis Proboscisambon sp. Plectothyrella crassicostis Hirnantia sp. Hindella sp.

Kuldiga Formation

990

908

PIRGU STAGE

Microgastropoda Mucronaspis sp.

Saldus Fm.

985

986.4

P O R K U N I S T A G E (H I R N A N T I A N)

?

906

Onniella sp. Cliftonia sp. A Cliftonia sp. Plectothyrella sp. Plectothyrella? sp. Leptostrophiidae Eostropheodonta hirnantensis Eostropheodonta sp. Eostropheodonta schmalenseei Dalmanellidae Dalmanella testudinaria Hirnantia sp. Drabovia sp. Hirnantia sagittifera Hindella sp. Draborthis cf. caelebs P. crassicosta Leptaena sp. Coolinia? sp. Proboscisambon? sp. Paramalomena polonica Cliftonia psittacina Bivalvia Bryozoa Gastropoda Tentaculites sp.

Aispute-41 Silurian 983.45

904

Bernati Member

In the East Baltic, the most diverse Hirnantia brachiopod fauna occurs in western Latvia, where about 20 taxa have identified (Hints and Harper, 2015). The composition and stratigraphical distribution of Hirnantian brachiopods is mapped here in drill cores Aispute-41 and Mežmali-16 (Figs. 3 and 4), which were studied in closely spaced samples. The study of the brachiopods from 21 sections in western Latvia (in 674 samples) shows the increase in brachiopod diversity upwards through the Kuldiga Formation, during the early Hirnantian (Hints et al., 2010). The acme of brachiopod diversity occurs, according to the correlation accepted here, in the graptolite Metabolograptus extraordinarius Biozone and lowermost M. persculptus Biozone (Fig. 2). The siliciclastic and oolitic lithologies in varying thickness (up to about

PORKUNI STAGE (Kuldiga Formation)

902

OTHERS

BRACHIOPODA

1

2

3

4

5

8

9

10

11

12

6

7

Fig. 3. Distribution of fossils through the Kuldiga Formation of the Porkuni Stage in the Aispute-41 core. Black boxes on right side of log mark the sampling intervals. Lithological legend: 1—limestone, 2—organodetrital limestone, 3—argillaceous limestone, 4—sandy limestone, 5 and 6—oolitic limestone with microlaminated beds, 7—nodular limestone, 8—marl with limestone nodules, 9—marl, 10—burrows (the upper part), hardground (in the middle), sand component (below), 11—oolites (above), glauconite (below), 12—red colouration of the rock.

12 m) of the uppermost Hirnantian Saldus Formation are barren or include very few shelly fossils in the core sections (Hints and Harper, 2015). The lowermost few metres of the Porkuni Stage, belonging at least partly to the chitinozoan S. taugourdeaui Biozone, has few brachiopods, such as of genera Kinnella, Eoplectodonta, Cliftonia, Dalmanella, Eostropheodonta, Cliftonia and Onniella. The fragments of nautiloids often occur in these strata. A similar concentration of orthoconic nautiloids is described in the Siljan district, Sweden, above the Boda mud mound in the Glisstjärn Formation (Ebbestad et al., 2007; Rasmussen et al., 2010), which belongs to the upper part of the Hirnantian (Ebbestad and Högström, 2007). Despite the differences in the age of the Baltic and Swedish occurrences, the distribution of nautiloids is apparently related to transgressive episodes. In the lower half of the Kuldiga Formation, the frequency of successive occurrences of Cliftonia psittacina (Wahlenberg) and Hindella sp. has enabled comparison of the whole brachiopod assemblage with the Hindella–Cliftonia Association in Norway (Hints et al., 2010). In the studied drill cores, brachiopods of the genera Cliftonia and Hindella are represented in about 20% of all 674 samples. At some levels, they form shell coquinas. Data from several other sections (Aispute-41, Riekstini15, Vilcini-14, Mezmali-16, Remte-3, Kandava-52, Dižrungi-17, Kuili-9, Mežvagari-13; Fig. 1) show a similar dominance of those brachiopods in the lower half of the Kuldiga Formation. The Hindella–Cliftonia Association comprises mainly species characteristic of the Hirnantia brachiopod fauna, such as Hirnantia sagittifera (M´Coy), Dalmanella testudinaria (Dalman), Paramalomena polonica (Temple), Leptaena (L.) rugosa Dalman, Eostropheodonta hirnantensis (M´Coy) and Plectothyrella crassicostis (Dalman). In Latvia, the richest brachiopod fauna belongs to the Hindella–Cliftonia Association, and Norway has the highest diversity (20 genera) among the Hirnantian brachiopod associations

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

(Brenchley and Cocks, 1982). However, several genera (Epitomyonia, Platystrophia, Skenidiodes, Katastrophomena and Parastrophina), identified in Norway, are not present in the East Baltic. In the Latvian collection, the most common brachiopods belong to the genus Dalmanella appearing in the lower part of the Porkuni Stage. They are represented in about a half of the samples, occurring as single or numerous shells, or as coquinas in many samples, where other macrofossils are absent. The monospecific occurrences in life position or unsorted by shell size population (fig. 10A in Hints and Harper, 2015) indicate the autochthonous nature of these brachiopods at some levels. The Dalmanella Association (Hints et al., 2010), which is less diverse than the Hindella–Cliftonia Association, differs by the presence of Eostropheodonta and Plectothyrella compared to that association in Norway (Brenchley and Cocks, 1982). Eostropheodonta and leptostrophiid brachiopods supposedly representing this genus occur throughout most of the Kuldiga Formation, being frequent in some parts of the lower, elsewhere in the upper half of the formation. In the Latvian cores, these brachiopods occur in about 30% of the samples, in some interbeds as coquinas, which in contrast to Dalmanella, are apparently allochthonous. The delicate shells are exquisitely preserved suggesting minimal transport. Plectothyrella is common in the studied sections, but is less frequent (occurring in about 16% of samples) than the taxa mentioned above. Plectothyrella is distinctive, presenting as in situ occurrences (fig. 14E in Hints and Harper, 2015). In the Mežmali-16 and Anši-12 cores, this coquina occurs in the interval with the frequent occurrence of Hindella and Cliftonia, extending in some other sections (Mežvagari-17, Dreimani) into the higher parts of the formation. The shelly fauna in the topmost part of the Kuldiga Formation and the Saldus Formation is insufficiently known, at least partly due to a lack of productive rock samples, which appeared barren during the sampling process. Similar silty and oolitic rocks in Sweden (Bergström et al., 2011, 2012) and Norway (Brenchley and Cocks, 1982) comprise, besides several typical Hirnantian brachiopods, some taxa (Thebesia and Brevilamnulella) not known anywhere outside the Midcontinent fauna in North America (Edgewood Province of Rong and Harper, 1988). The very specific environments, similar to the oolite province (Amsden, 1986) in the Midcontinent and tidal channels and shoals in Scandinavia (Brenchley and Cocks, 1982), thus might be found eventually in the East Baltic particularly on the Estonian Shelf and in the transitional area towards the Livonian Basin (Fig. 5). 5. Offshore–onshore succession of the Hirnantian fauna in Estonia The onshore succession of the Hirnantia brachiopod fauna is illustrated by data from the Ruhnu (Fig. 6), Ikla (Fig. 7) and Taagepera (Fig. 8) wells located in southern Estonia on the northern periphery of the Kuldiga and Saldus formations (Fig. 5). The latter unit is marked by an initial transgressive episode, and corresponding deposits extend more inshore in comparison with those of the underlying Kuldiga Formation. The drill cores are located in areas where the Kuldiga Formation overlies the red-coloured Jonstorp Formation of the Pirgu Stage (Hints et al., 2005). The thickness of the Porkuni Stage varies from 14.2 m (in Ikla) to 18.1 m (in Taagepera). The occurrence of the zonal chitinozoan S. taugourdeaui (Eisenack) demonstrates that in this transitional area, the Livonian Basin and Estonian Shelf, the lowermost Porkuni is represented by more or less contemporaneous strata belonging to the same biozone. The lowermost 1.5 m of the Kuldiga Formation includes few fossils; however, the occurrence of cephalopod fragments in Taagepera (Fig. 8) is similar to several other sections in the lowermost Kuldiga in Latvia. In the Ruhnu core (Fig. 5), which is the closest, geographically, to the most fossiliferous section in the central part of the Livonian Basin, the Hirnantian brachiopods are represented by about 10 genera of the 16 reported in the latter area. Strophomenide brachiopods are most

75

N

50 km

TALLINN

7/5.4

Porkuni

16/3.8+ 19/3.6

8/4.1 5/1.0

? 9/4.6D

4/1.3

12/0.9

10/2.15

A

13/17.5

B

C

20/1.0

17/4.9 21/23.1

6/3.4 3/0?

14/3.0

11/0

1/2.7

18/6.4 (1. GV)

15/3.2

22/4.0 2/0

Ruhnu 18.1

Ikla 14.2

Taagepera 15.5

2 1 3 4 5 6 1 7

8 9 10 11

Fig. 5. Distribution of lithofacies of the Porkuni Stage in Estonia (modified by Oraspõld, 1975, 1986). 1—Porkuni quarry, the stratotype of the Porkuni Regional Stage; 2—drill cores (number, and thickness of the Porkuni Stage); 3—channel sections: (A) Tootsi (Oraspõld, 1986), (B) Jõgeva, (C) Ruskavere (Perens, 1995); 4—outer limit of the distribution area of the Porkuni Stage; 5—offshore limit of the Ärina Formation; 6—onshore limit of the Saldus Formation; 7—onshore limit of the Kuldiga Formation; 8—outcrop area; 9—sandy facies; 10—Porkuni Stage is probably missing; 11—reefs. Drill cores: number/ thickness of the Porkuni Stage: 1—Kaugatuma (Kaljo et al., 2001, 2008; Ainsaar et al., 2010); 2—Ohesaare (Nõlvak, personal. comm.); 3—Kuressaare K-3 (www.geokogud. info); 4—Eikla (Nõlvak, 1984); 5—Undva; 6—Viki (Röa Member underlies the Saldus Formation; Põldvere and Nestor, 2010; compare Hints et al., 2014); 7—Orjaku (Meidla, 1996); 8—Virtsu (Hints and Meidla, 1997; 9—Kirikuküla (Nõlvak, 1984; Oraspõld, 1975); 10—Paatsalu (Põlma, unpublished data); 11—Seliste; 12—Are; 13—Pärnu (Hints and Meidla, 1997); 14—Ristiküla (Oraspõld, 1975); 15—Häädemeeste (Oraspõld, 1986); 16—Äiamaa (Oraspõld, unpublished data); 17—Viljandi (Oraspõld, 1975; Meidla, 1996); 18—Abja; 19—Aidu; 20—Laeva; 21—Kardla (Kaljo et al., 2008); 22—Otepää (Männil, 1966).

common in the burrowed marls and limestones. Brachiopods of the genus Dalmanella are relatively rare in the Ruhnu section in comparison with that in the deeper part of the basin in Latvia. The offshore increase in abundance of Dalmanella is known also from China (Rong and Harper, 1988). The occurrence of large-stem ossicles, with a uniform morphology in many sections, is also typical of the lowermost part of the stage. The upper half of the Kuldiga is characterised by the occurrence of dasycladacean alga (Rhabdoporella) and rugose corals, indicating changes in environment. In the Ikla core (Fig. 7), only seven brachiopod genera are represented; they range through the whole Kuldiga Formation up to the level of 530.5 m where the carbonate oolites first appear (Oraspõld, 1975), marking the onset of warmer, near-shore, more turbulent conditions. Similar oolitic facies appear in the pre-reef or inter-reef facies (Vohilaid Member) in Central Estonia. These oolites are older than those in the topmost part of the Saldus Formation, responding to specific shallowwater environments, possibly due to very shallow, warm-water conditions. In the lowermost part of the stage, above the occurrences of the zonal S. taugourdeaui, the cystoids (identified as Heliocrinites and Eucystis, in Männil et al., 1968) occur. In the Ruhnu core (Fig. 6), a single cystoid record has the same stratigraphical position as in the Ikla core—above the S. taugourdeaui zone and below the most abundant brachiopods. In the Norwegian section on Rambergøya, the cystoids (the Tetreucystis tetrabrachiolata association by Bockelie, 1984) occur in the topmost Husbergøya Shale (stage 5a) below the first occurrences of Hirnantia sp., Cliftonia sp. and Dalmanella sp. (Brenchley and Cocks, 1982). The analogous stratigraphical position of cystoids in the Pirgu (Rawtheyan)–Porkuni (Hirnantian) transition possibly allows a correlation with the Hirnantian Stage in both regions. The carbon isotope data (Bergström et al., 2006) and the occurrence of the trilobite Mucronaspis mucronata (Brongniart) in the Oslo Region, further support a Hirnantian age. According to Owen (1986), this trilobite “represents an early stage in the spread of Gondwana elements onto lower latitude shelves”. The distribution of the cystoids is constrained to specific environments in the onshore–offshore transitional area; however, the correlation of

76

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

δ 13 Ccarb, 000

Ruhnu Silurian

2.0

4.0

6.0

..

602

Saldus F ormation Piltene Member

603.0 604

606

608

612

614

616

Bernati Mb.

617.1 618

619.1 Pirgu Stage (Jonstorp Fm.)

BRACHIOPODA

Bryozoa Heliocrinites? sp. Tentaculites sp. Dasyclad algae (Rhabdoporella) Rugose corals Gastropods

610

Sampo? sp. Coolinia sp. Eostropheodonta hirnantensis Atrypida? Eostropheodonta sp. Leptaena (L.) rugosa Leptostrophiidae E. cf. schmalenseei Dalmanella testudinaria Leptaena sp. Plectothyrella crassicostis Paromalomena polonica Cliftonia sp. Cliftonia psittacina Hindella sp. Hirnantia sagittifera Hirnantia sp. Dalmanella sp. Plectothyrella sp. Reuschella? sp. Proboscisambon? sp. Draborthis cf. caelebs

609.5

K uldiga F ormation Edole Member

P O R K U N I (H I R N A N T I A N) S TA G E

Broceni Mb.

601.0

0

S. taugourdeaui Biozone

N. girardeauensis A. ordovicicus

OTHERS

Fig. 6. Distribution of fossils and carbon isotope data of the Porkuni Stage (after Kaljo et al., 2001; Ainsaar et al., 2010) through the Ruhnu core. Description of the section see Põldvere, 2003). First or last occurrences of conodonts N. girardeauensis—Noixidontus girardeauensis and A. ordovicicus—Amorphognathus ordovicicus (Männik, 2003), and the range of the biozone S. taugourdeaui—Spinachitina taugourdeaui by Nõlvak, 2003 are marked. For lithological legend, see Fig. 3.

corresponding strata with the lowermost part of the Porkuni Stage in the Latvian sections is imprecise. The strata containing cystoids may correspond to the oldest part of the Hirnantian with a few brachiopods associated with cephalopods and large-stem ossicles, recorded in several drill core sections in Latvia. Only four genera of brachiopod occur in the Taagepera section (Fig. 8). Additionally, several samples with brachiopods occur in the uppermost Kuldiga. The association with algae and rugose corals in the Ikla core above the most frequent brachiopod occurrences are present in Taagpera in the lower half of Kuldiga Formation. At one level (422.2 m), microbial limestone interbeds occur. Possibly in the Taagepera area, the shallow-water conditions characterised the early Porkuni and some Hirnantian brachiopods reached this area somewhat later than in the Ruhnu area. The lack of brachiopod coquinas, which occur in several sections in western Latvia indicates the relative rarity of brachiopods in these transitional sections. The occurrence of algae and rugose corals suggests some relationship with the shallow-water faunas. This is replicated by the ostracode fauna in the Taagepera section, where the lower part of the Kuldiga Formation comprises the Rectella composite association, which is comparable to the association in the fossiliferous part of the Ärina Formation in Central Estonia (Meidla, 1996). The Ärina Formation of the shallow Estonian Shelf is represented by the reefs and related inter-reef lithologies with the specific Streptis

fauna (Harper and Hints 2001, Hints and Harper 2003), with dolomitic deposits (Röa Member) on the bottom and overlied partly by sandy and oolitic deposits (Kamariku Member). The replacement of the onshore (Ärina Formation) lithologies with more offshore analogues (Kuldiga and Saldus formations) unfortunately occurs in the area where the Porkuni Stage is restricted in thickness or the stage is missing (in the following cores Ohesaare, Kuressaare, Seliste and File Haidar on Gotland) (Fig. 5). The dolomites and dolomitic limestones (in thickness 1–2 m) of the Röa Member of the Ärina Formation (Viki; Põldvere, 2010; Kirikuküla, Undva; Nõlvak, 1984; Kaugatuma; Kaljo et al., 2008) together with most of the reef complex correspond to the chitinozoan S. taugourdeaui Biozone of the lower Hirnantian. The sandy carbonates (Kamariku Member; in thickness 3–4 m; Oraspõld, 1975) that are sometimes cross-laminated (Viki, Ruhnu-500) or are oolitic grainstones (2.15 m in Paatsalu) have been correlated with the Kuldiga Formation (Kaljo et al., 2001) or are considered as a unit corresponding to the Kuldiga/ Saldus transitional interval (Ainsaar et al., 2015). These lithologies, commonly barren of fossils, are not of direct relevance to a study of the brachiopod successions; however, they complement understanding of the restriction of the habitable areas and disappearance of benthic faunas on some parts of the shallow shelf. In Estonia, these rocks were deposited in lagoonal to high energy to lagoonal shoal environments in the easternmost areas with an influx of clastic material and fresh

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

Ikla

Taagepera

? Saldus Fm.

528.0

water from the east or northeast (Viiding and Oraspõld, 1972). Oolitic limestones and grainstones in the westernmost Estonia formed in high-energy inter- and subtidal shoals (Oraspõld, 1975). Similar rocks of the Saldus Formation in central East Baltic represent variable (Ulst et al., 1982) high-energy, partly redeposited shallow shelf sediments (Harris et al., 2004). The range of lithologies in the Hirnantian Stage in Estonia is not essentially different from those which enabled reconstruction of palaeogeography in the Oslo Region during the Hirnantian (Brenchley and Cocks, 1982, text; Fig. 6). The lagoonal stromatoporoid–coral reefs in central Estonia are limited by an offshore belt of biodetrital grainstones. Farther offshore, sandy and oolitic packages and dolomites occur. The facies and faunal differentiation in the shallow shelf and in the transitional onshore/offshore areas was extremely complicated. The distribution of facies and faunas was controlled by an uneven seabed topography and oscillation of sea level with similar deposits formed diachronously across the shelf, complicating precise correlation and reconstruction of palaeogeography across the shallow shelf of the Baltic Basin. 6. Multivariate analyses of brachiopod fauna in the East Baltic Data on brachiopod occurrences were analysed using PAST software (Hammer et al., 2001; Hammer and Harper, 2006), and matrices of cooccurrences, using the Raup–Crick coefficient, form the basis for the multivariate analyses. The brachiopod frequency analysis includes 687 samples from 21 core sections in western Latvia and demonstrates that on average 2.7 brachiopods occur in each sample from the drill core sections, and the co-occurrence of brachiopods identified at the

Gastropoda

Saldus Fm.

BRACHIOPODS

Bivalvia S. taugourdeaui Biozone

Lingulata

428.0

Algae (Rhabdoporella?) Indet. organic matter Rugose corals Bryozoa

Edole Member

425.7

Stem ossicles

Fig. 7. Distribution of the fossils through the Porkuni Stage through the Ikla core. Occurrence of zonal chitinozoan Spinachitina taugourdeaui in the Ikla core based on unpublished data by Nõlvak; chitinozoan data in the Taagepera core after Brenchley et al. (2003). For lithological legend, see Fig. 3.

424.1

Dalmanellids Dalmanella sp. Plectothyrella? sp. Eostropheodonta hirnantensis Cliftonia sp. Cephalopoda Eostropheodonta sp. Atrypids? Cystoidea? Leptostrophiidae

OTHERS

422.0

OTHERS

Fig. 8. Distribution of fossils and carbon isotope data (Brenchley et al., 2003) through the Porkuni Stage in the Taagepera core. For lithological legend, see Fig. 3.

Atrypidae Plectothyrellacrassicostis Hirnantia sagittifera Leptaena (L.) rugosa + sp. Proboscisambon? sp. Onniella sp. Draborthis cf. caelebs Kinnella sp. Eostropheodonta cf. schmalenseei Cliftonia sp. A Foliomena sp. Drabovia sp. Kinnella cf. kielanae Paromalomena sp. Paromalomena polonica Leangella sp. Eostropheodonta cf. parvicostellata Coolinia sp. Eoplectodonta sp.

BRACHIOPODA

420.0

Bernati Mb.

542

416.0

Jonstorp Fm.

541.5 Jonstorp Fm.

PIRGU STAGE

540

414.0

PORKUNI (HIRNANTIAN) STAGE

538

413.0

PIRGU STAGE

536

4.0

Cliftoniapsittacina Hindella sp. Dalmanella sp. Leptostrophiidae Eostropheodonta hirnantensis Dalmanella testudinaria Plectothyrella sp.

534

2.0

?

Eospirigerina sp. Plectothyrella? sp. Leptaena sp. Eoplectodonta sp. indet. Atrypidae ? Dalmanella sp. D. aff. testudinaria Cliftonia sp. Leptostrophiidae Eostropheodonta sp. Paromalomena polonica Trematis sp. Hindella? sp. indet. S. taugourdeaui Rhabdoporella ? Brongniartella platynota Bryozoa Heliocrinites ? Stem ossicles Eucystis sp. Bivalvia Lingulata Gastropoda Mucronaspis spp. Cephalopoda Rugose corals Tentaculites sp.

S TAGE Kuldiga Formation

P O R K U N I (H I R N A N T I A N)

532

δ 13 Ccarb, 000

411.1

530

530.5

0

Silurian JUURU STAGE 410.2

Kuldiga Formation

Silurian JUURU STAGE 527.3

77

Fig. 9. Nearest neighbour R-mode cluster analysis based on the Raup–Crick similarity coefficient. The core, shallower-water elements of the fauna are clustered at the top of the figure.

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

Cliftonia spp. Hindella spp.

species level and under open nomenclature is noted in 1866 cases. Among the 20 Hirnantian taxa (Hints and Harper, 2015), a few key genera (Eostropheodonta, Dalmanella, Cliftonia, Hindella, Plectothyrella and Hirnantia) co-occur with each other and/or with other species in more than in 10 cases (Fig. 9). These form most of the core taxa of the typical Hirnantia brachiopod fauna (Rong and Harper, 1988; Harper and Rong, 2008) and signal the presence of the Kosov Province. Brachiopods of these genera represent about 80% of all occurrences, whereas the monotaxic occurrences of Eostropheodonta, Cliftonia and Dalmanella form 5%. The close relationship between Cliftonia and Hindella is illustrated by multivariate cluster analysis and by the PCA scatter diagram (Figs. 10 and 11). The frequency and stratigraphical range of the genus Dalmanella separate this genus from the distribution of Hindella and Cliftonia. The diversity increase of the Hirnantia brachiopod fauna in western Latvia is revealed by the Ranked Level analysis (Fig. 12).

Component 2

2.4 1.8 Principal components

1.2 Leptostrophiidae

0.6 H. sagittifera Leptaena rugosa

E. hirnantensis

P. crassicostis 0.5 1.0 1.5 Plectothyrella sp. -0.6

-1.0

-1.8

7. Distribution of brachiopod fauna in relation to carbon isotope stratigraphy

3.0

3.5

D. testudinaria Dalmanella spp. Component 1

-3.0

Fig. 11. R-mode principal components analysis associating the core elements of the Hirnantia fauna across the Latvian sections, highlighting the co-occurrence of many of the taxa.

Hindella sp.

Cliftonia psittacina Hirnantia sagittifera + sp.

Leptaena (L.) rugosa + sp.

Proboscisambon? sp.

Leptostrophiidae

Paromalomena polonica

Paromalomena sp.

Eostropheodonta hirnantensis Eostropheodonta cf. parvicostellata

Foliomena sp.

Drabovia sp.

Dalmanella sp.

The early Hirnantian, low-diversity brachiopod fauna with Eoplectodonta sp. and Cliftonia sp. A occurs in strata with increasing values of δ13C on the carbon isotope curve (Figs. 6 and 8; Stirna-18 in Hints et al., 2010). In all sections, the climbing positive trend of the carbon isotope excursion with high values up to about 6‰ corresponds to the interval with diverse brachiopod faunas (Hindella–Cliftonia

Eoplectodonta sp.

Kinnella cf. kielamae

Cliftonia sp. A

Draborthis cf. caelebd

Kinnella sp.

Leangella sp.

Onniella sp .

Plectothyrella crassicostis

Atrypidae

Plectothyrella sp.

Dalmanella testudinaria Coolinia sp.

2.5

-2.4

The distribution of chitinozoans and carbon isotope analyses has enabled the correlation of the Ärina Formation of the Estonia Shelf with the lower half of the Kuldiga Formation in the East Baltic (Kaljo et al., 2001), confirming its Hirnantian age. Accordingly, the stromatoporoid–coral reefs of the Ärina Formation developed on the Estonian Shelf contemporaneously with the more diverse Hirnantia brachiopod fauna in the Livonian Basin. The earlier isotope studies of the Porkuni Stage in Stirnas-18 (Hints et al., 2010) and Ruhnu and Taagepera (Brenchley et al., 2003) drillings allows analysis of the distribution of brachiopods in relation to geochemical composition (whole rock carbon isotopes) of rocks.

1.0

2.0

-1.2

Eostropheodonta cf. schmalenseei

78

0.9 0.8

Similarity

0.7 0.6 0.5 0.4 0.3 0.2

Raup-Crick cluster 0.1

Fig. 10. R-mode cluster analysis based on the Raup–Crick similarity coefficient, separating out the distribution of Dalmanella testudinaria from the rest of the fauna.

D.A.T. Harper, L. Hints / Palaeogeography, Palaeoclimatology, Palaeoecology 444 (2016) 71–83

45 40

30 25 20 15 10 5

Foliomena sp. Kinnella sp. Cliftonia sp.A Paromalomena poonica + sp. Coolinia sp. Leangella sp. Onniella sp. Dalmanella testudinaria Atrypidae Eoplectodonta sp. Cliftonia psittacina + sp. Dalmanella sp. Draborthiscaelebs Hirnantia sagittifera Eostropheodonta sp. Leptostrophiidae Hindella cassidea Eostropheodonta hirnantensis Proboscisambon sp. Hirnantia sp. Leptaena (L.) rugosa + sp. Plectothyrella sp. Eostropheodonta schmalenseei Plectothyrella crassicostis Eostropheodonta parvicostella

Ranked level

35

Fig. 12. Species distribution. Ranked scaling indicates diversity increase of taxa.

Association) in the lower half of the Kuldiga Formation of the Hirnantian Stage. The plateau and falling trend on the isotope curve correspond to strata with the Dalmanella Association and upper half of the stage with the sparse shelly fauna. The Hirnantian brachiopod faunas in the East Baltic apparently have no precise relationship to the carbon isotopic zones, identified by Ainsaar et al. (2010), although some crude relationships are apparent. Those authors noted that the Hirnantian carbon isotope curve is divided into two—the lower part with the rising limb up to the peak values of δ13C (isotopic zone BC 16) and the upper part (BC 17) with the falling segment continuing to the top of the Porkuni Regional Stage and reaching the basinal values in strata traditionally included to the lowermost Silurian (Hints et al., 2014; Ainsaar et al., 2015). The BC 17 zone is missing in some shelf sections (Tamme, Brenchley et al., 2003; Orjaku, Rapla, Kaljo et al., 2004; Kaugatuma, Kaljo et al., 2008; Männamaa, Ainsaar and Meidla, 2008) due to the stratigraphical gap at the top of the stage. In the Stirnas-18 (Hints et al., 2010) core, most of the Kuldiga Formation is characterised by the arrival and diversification of Hindella– Cliftonia and Dalmanella associations in BS 16. Only a few metres of the topmost Kuldiga Formation together with the overlying Saldus Formation with a sparse fauna or a barren interval belong to zone BC 17, characterised by a decline in diversity. By contrast, in the Ruhnu and Taagepera cores, only the lowermost three metres correspond to BS 16, the fossiliferous part of the Kuldiga Formation together with overlying strata (about 10 m) belongs to BS 17. These isotopic zones probably are not entirely time-related and could indicate some environmental differences that are also tracked by the faunas. The first two sections (Stirnas-18, Aizpute-41) are located, as predicted, in somewhat deeper parts of the basin than in the Estonian sections (Ruhnu, Taagepera). 8. The global and regional context The occurrence of two fundamentally different Hirnantian brachiopod faunas in Baltoscandia has enabled association of parts of the region with the Kosov, and partly with the Edgewood Province (Harper, 1986; Rong and Harper, 1988; Dahlqvist et al., 2010). As discussed above, the Kosov-type brachiopod fauna is distributed widely in Baltica, but in the

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Oslo–Asker district in Norway and in Östergötland in Sweden, the Hirnantian brachiopod fauna apparently occurs together with elements of the Edgewood fauna of the North American Midcontinent (Amsden, 1974, 1986). This fauna inhabited the shallow-water environments of subtropical to tropical belts promoting the deposition of the Bahamitic type oolitic carbonates. The typical Hirnantia fauna originated in the colder-water environments of the Kosov Province. The oolitic lithologies, which formed an essential part of the Hirnantian on the Midcontinent (Amsden, 1986), have restricted distributions in Baltoscandia. Only in Norway, the Langøyene oolitic limestone at the very top of the Hirnantian Stage has thicknesses up to 8 m. These limestones, containing the Brevilamnulella Association and the channel filling Thebesia Association (Brenchley and Cocks, 1982), mark the final shoaling of sediment over a large area, which terminated with the formation of breccias during channelling (Brenchley and Newall, 1975). The earlier, deeper-water brachiopod faunas in Norway (Hindella–Cliftonia and Dalmanella associations; Brenchley and Cocks, 1982) belong to the Kosov Province similar to the Hirnantia brachiopod faunas in the East Baltic, Central Sweden (Västergötland; Bergström, 1968) and Jämtland (Bergström, 1968; Dahlqvist et al., 2010). The Hirnantian brachiopods from Östergötland are best known from a large collection, the Borenshult fauna (Bergström and Bergström, 1996; Rong et al., 2008; Bergström et al., 2011, 2012) in the Swedish Museum of Natural History, Stockholm. Bergström et al. (2012) indicated that the entombing rocks, fine grained, sparry skeletal grainstone (Brood, 1978; Rong et al., 2008), in the Borenshult collection are coeval with the oolitic limestone of the Skulptorp Member in the middle part (Stridsberg, 1980) of the Loka Formation. The lithologies, where the Midcontinent brachiopods might occur in the East Baltic, belong to the Saldus Formation. Unfortunately, the corresponding rocks of the Saldus Formation, the oolitic limestones, locally silty or sandy (the Piltene Member), and siltstones and marls with mud cracks and ripple marks (Broceni Member) (Kaljo et al., 2001) are practically barren of shelly faunas in drill core sections. Bergström et al. (2006) concluded that the Leemon Formation in Midcontinent is coeval with the limestone (Skultorp) and upper members of the Loka Formation in Sweden and Saldus Formation in the East Baltic and their lower boundary is marked by the HA lowstand (HA stratigraphical gap; Schmitz and Bergström, 2007). This correlation scheme supports the more or less contemporaneous occurrence of the Edgewood brachiopod fauna in Laurentia and Baltica in similar shallow-water environments at the end of the Ordovician. The results from study of the Borenshult drill core in Östergötland (Bergström et al., 2011, 2012) are somewhat confusing for the correlation of the Loka Formation, which is represented in this core by the middle (Skulptorp or Limestone Member) and upper members. In the Borenshult core, the stratigraphical gap (HA) is marked at the upper boundary of the Skultorp (limestone) Member, differently from earlier interpretations (Bergström et al., 2006). It seems that this ambiguous correlation of the Loka Formation is based on the comparison of the carbon isotope curves of the two sections. In the Borenshult core, the HICE corresponds to the Skultorp and the upper member of the Loka Formation having a thickness of 3.86 m. The lower member is missing in the Borenshult core. The HICE in the Borenshult core is correlated with the HICE in the Ruhnu core comprising there, the 16.1 m thick part of the Hirnantian Stage (Bergström et al., 2011). Only the lowermost 2 m with the highest occurrences of the zonal conodonts Amorphognathus ordovicicus in the Kuldiga Formation are considered to be the equivalent of the lower missing part of the Loka Formation in Borenshult core. In this case, the Hindella–Cliftonia and Dalmanella associations should be more or less contemporaneous with the Borenshult fauna in Östergötland related to the North American Edgewood fauna and which is described in the Oslo–Asker area as the Brevilamnulella Association (Brenchley and Cocks, 1982). This correlation, however, is contrary to the distribution of facies (oolitic and sandy carbonates) and brachiopod faunas in the East Baltic and

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Basin). The restricted thickness of the Loka Formation is similar in terms of its geological architecture to sections in the transitional area between the Livonian Basin and Estonian Shelf in SW Estonia. In the Viki core (Fig. 5; Põldvere, 2010), the Hirnantian Stage is 3.4 m thick (in the Borenshult core 3.86 m) and consists of dolomitic limestone (1 m) with a discontinuity at the top (HA), oolitic limestone (1.1 m, Piltene Member; Skultorp Member 1.95; Bergström et al., 2012) and silty carbonates (1.3 m, Broceni Member; Upper Member of Loka Formation, 1.95 m) of the Saldus Formation. The lowermost strata supposedly correspond to the offshore periphery of the Ärina Formation. The occurrence of the conodont Noixodonthus girardeauensis (Satterfield) in the Saldus Formation of the Viki core (Männik, 2010) indicates a faunal relationship with the basinal section, where this conodont occurs in several sections (Männik, 2001, 2003, 2010; Hints et al., 2010). Notable is the occurrence of another conodont, Ozarkodina ex gr. hassi (Pollock, Rexroas and Nicoll) above the last occurrence of N. girardeauensis, and the similarities in the carbon isotope curves in the Viki (Hints et al., 2014) and Borenshult cores. In Sweden, the uppermost part of the Loka Formation belongs to the conodont Ozarkodina hassi Biozone (Bergström et al., 2012). The same biozone is identified in the topmost Ordovician in the East Baltic (Männik and Viira, 2012). The correlation of the Loka and Saldus formations shows in broad terms, that the strata which could contain the Edgewood fauna in the East Baltic are very restricted and accessible only in drill core sections. The appearance of the Edgewood brachiopod fauna in Baltica is related to climatic warming (Bergström et al., 2006) and narrowing of the Iapetus Ocean invoking the decreasing separation of Baltica and Laurentia (Cocks and Torsvik, 2002, 2005). The occurrence of the Hirnantian Edgewood fauna in Baltica could therefore be a random remnant of a much wider distribution excised by latest Ordovician–earliest Silurian emergence and erosional processes.

Edgewood and related faunas

Baltic-SwedenV South-China Baltic-Latvia

Precor-Argentina-SanJUan Perunian-Szech

Sibumasu-Thailand

Sibumasu-Burma

Chu-Ili

Ganderia-EnglandN Tibet

Sardinia

Baltic-Poland

AfricaS

Iberia-Portugal

Iberia-SpainEC Armor-France-Brittany

AfricaN Av-Maine

Carnic Alps Laur-Canada-Quebec

Ganderia-IrelandE

Av-WalesC

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Av-WalesC Av-WalesN Baltic-Norway-Oslo

Laur-Canada-Anticosti

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MidValley-Scotland-Girvan Altai-Gorny Altai

Kolyma

Laurentia-Mid

Tien-Shan-Uzbekistan

Norway, and to the earlier interpretation of the level of the main (HA) stratigraphical gap by Bergström et al. (2006). Kaljo et al. (2012) studied the chemo- and biostratigraphy of the Ordovician–Silurian boundary beds at Mirny Creek section, NE Russia, urging caution with the interpretation of specific isotope curves. In the Mirny Creek and some East Baltic sections (see Figs. 6 and 8), the high or the highest carbon isotope values occur also in the upper part of the isotope excursion. In the Mirny Creek section, the high δ13C values occur within the M. persculptus graptolite biozone. Notable is the occurrence of that graptolite in the Borenshult fauna (Bergström and Bergström, 1996), indicating a late Hirnantian age. The stratigraphical gap (HA), lithological similarity and also restricted thickness of the Loka Formation allow the correlation of the HICE in the Borenshult core with the uppermost part of the carbon isotope curve with relatively high δ13C values in the East Baltic cores (Stirnas-18; Hints et al., 2010; Taagepera, Brenchley et al., 2003), corresponding to the Saldus Formation (Fig. 8). The latter formation and the Skultorp Member of the Loka Formation mark the beginning of a transgressive episode with sharp discontinuity and/or gaps (HA) at the lower boundary. Most of the lower and middle Hirnantian in Östergötland, due to a complicated depositional regime and tectonic movements in the region, is probably absent and explains the lack of a Kosov-type brachiopod fauna. As mentioned previously, the Kosov-type brachiopod fauna, displaying a range of different associations, occurs in Norway, where it is replaced in the topmost part of the Hirnantian by the Edgewood fauna. The Langøyene Formation with the Edgewood-type brachiopod fauna (Brevilamnulella Association) is also characterised by high δ13C values (Bergström et al., 2006), similar to those in the Borenshult core. Within the context of facies differentiation across the Baltic Basin, the Östergötland section with its specific lithologies and faunas is located on the outer periphery of the Baltoscandian Facies Belt (Livonian

Bani and Kosov provinces

Fig. 13. Nearest neighbour cluster analysis based on the Raup–Crick similarity coefficient, associating the Latvian faunas with those of the Bani and Kosov provinces (locality data for the sites are available in Harper et al., 2013 and its supplementary information).

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typical Hirnantia fauna of western Latvia, however, are the data from the lower Hirnantian succession of North Estonia (e.g., Hints, 2012) and from the upper Hirnantian of Östergötland (Bergström and Bergström, 1996; Rong et al., 2008; Jin and Bergström, 2010). The global database constructed for previous studies (e.g., Harper et al., 2013) has been updated, analysed and interrogated using the Raup–Crick similarity coefficient; the results have been displayed graphically using both cluster (Fig. 13) and non-metric multidimensional scaling (Fig. 14) analyses. In the former, the global patterns illustrated by Harper et al. (2013) are largely confirmed. The Latvian faunas fit comfortably into the body of the Kosov Province. On the other hand, the faunas associated with carbonate environments, Central Estonia and Östergötland, are associated with those located on or around the margins of Laurentia. In the latter, NMDS analysis, the Bani and Kosov provinces (atypical and typical Hirnantia faunas), occupy the left side of the figure, connected by the left branches of the minimum spanning tree; those sites on the right connected by the second major branch of the MST include those on the upper part that are essentially the Edgewood Province while those on the lower part are related to that province. Both are linked to the other Hirnantian faunas through the very diverse assemblage from Meifod, central Wales (Williams and Wright, 1981). In terms of Baltoscandia, the highest Ordovician strata in the central Oslo Region contain elements of the Edgewood Province. The lower Hirnantian strata of central Estonia are linked with Laurentian marginal faunas (Anticosti Island and Girvan, SW Scotland), whereas the younger Hirnantian Östergötland fauna has links with both these and the Edgewood Province. This suggests that first the specialised Estonian habitats of the Ärina Formation and its counterparts on

In the present study, we have concentrated only on the Ordovician Hirnantian brachiopod fauna. The complicated palaeogeographical and biofacies patterns at the very end of the Ordovician, the gaps at the Ordovician/Silurian boundary interval and missing brachiopod data do not allow a precise description of the extinction—survival history of the brachiopod fauna in the East Baltic although some broad trends are clear. At the genus level, there are several taxa in common between the latest Ordovician and Silurian (Rubel, 2011) in the deepest part of the Baltic Basin, suggesting the presence of a refugium similar to that in the deeper parts of the Oslo Basin (Baarli and Harper, 1986). The new data from the East Baltic open up the opportunity to examine the distribution of the Hirnantian brachiopod faunas across much of the palaeocontinent of Baltic from the edge of the Caledonian mountain in the west to the Baltic palaeobasin in the East but also places the faunas in a more global context. The global distribution of the Late Ordovician (Hirnantian) brachiopods was recently reviewed (Harper et al., 2013) and provincial clusters, generated by cluster analysis, mapped onto a palaeogeographic reconstruction for the stage. Three clear groups were identified, conforming to the Edgewood, Kosov and Bani provinces of previous studies (e.g., Rong and Harper, 1988; Harper and Rong, 2008; Rong et al., 2008), occupying low, mid and high latitudes, respectively. The recently described Hirnantian fauna from western Latvia (Hints and Harper, 2015) adds critical new data on the distribution of the Brachiopoda across the varied environments across the ancient continent of Baltica. There is thus the consistent development of the typical Hirnantia fauna of the Kosov Province, dominating siliciclastic environments from Jämtland (Dahlqvist et al., 2010) to western Latvia (Hints and Harper, 2015). Key additions, besides the

0.25 Tien-Shan-Uzbekistan

0.20 Sibumasu-Thailand

0.15 Chu-Ili

Laurentia-Mid

0.10

Coordinate 2

South-China Perunica-Czech

0.05

Kolyma

Precor-Argentina-SanJuan Sibumasu-Burma Ganderia-EnglandN

Baltic-Norway-OsloU

Carnic Alps Baltic-Norway-Oslo

Tibet

Av- Wales N

Baltic-Latvia Baltic-Poland Laur-Canada-Quebec

0.00 Iberia-Portugal

Ganderia-IrelandE Aw-Wales

Sardinia Baltic-SwedenV

-0.05 Armor-France-Brittany

Av-Wales C

Altai-GornyAltai

Iberia-SpainEC AfricaN

Baltic-Sweden Ö

-0.10 Laur-Canada-Anticosti

Av-Maine

-0.15 AfricaS MidlValley-Scotland-Girvan Baltic-Estonia

-0.20 -0.24

-0.16

-0.08

0.00

0.08

0.16

0.24

0.32

0.40

Coordinate 1 Fig. 14. Non-metric multidimensional scaling, indicating the positions of the Hirnantia faunas of the Bani and Kosov provinces on the left and those related to Laurentia and its margins on the right (locality data for the sites are available in Harper et al., 2013 and its supplementary information).

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Anticosti Island and Girvan, SW Scotland potentially captured a selection of Katian taxa, following the first wave of the Late Ordovician extinction, some of which survived and populated early Silurian communities. Second, as noted above, carbonate facies developed across parts of Baltica during the later Hirnantian, encouraging the expansion of the Edgewood Province southwards to occupy most of the tropical belt. Environments were more euxinic in the deeper-water habitats south of the tropics (Rong and Harper, 1988). 9. Conclusions 1. The analysis of the distribution of brachiopods and different facies can be summarised as follows: The Baltic Basin was colonised by three main Hirnantian brachiopod assemblages: the Hindella– Cliftonia, Dalmanella and Brevilamnulella associations with some additional more specialised faunas. The last occurs only in restricted areas. The development of the Hirnantia brachiopod fauna in Baltica was related to, first, the shallowing of the basin (early Hirnantian) and, second, by later climatic warming (late Hirnantian). 2. Many of the Hirnantian brachiopods from the colder-water Kosov Province did not reach the Midcontinent of Laurentia that then was located in low latitudes. 3. The Loka Formation in Sweden corresponds mainly to the Saldus Formation in the East Baltic, and at least partly to the Langøyene oolitic limestones with the Brevilamnulella Association at the very top of the Hirnantian in Norway. It contains some elements of the Edgewood Province. 4. Both Hirnantian faunas of the Kosov and Edgewood provinces occur in strata with relatively high δ13C values. In the Borenshult drill core, the HICE corresponds to the upper part of Hirnantian carbon isotope excursion. 5. The second regressive–transgressive episode (HA) following that at the Katian–Hirnantian boundary is followed by the development of the more or less contemporaneous Saldus and Loka formations. 6. The carbon isotope data (HICE) serve as a useful tool in the correlation of sections, which preferably should be confirmed by other palaeontological and sedimentological data. 7. There are two key developments of the Hirnantian in carbonate facies: the older, corresponding to the specialised fauna in the Ärina Formation, and the younger in the Langøyene (Oslo) and Loka (Östergötland) formations; both are characterised by survivors and some progenitors of the Silurian fauna, for example, the pentamerides (Brevilamnulella) and rhynchonellides (Rostricellula and Thebesia). Acknowledgements We thank D. Kaljo for the critical reading of the manuscript and valuable suggestions. Per Ahlberg and Mikael Calner (Lund) helped with some literature. We are grateful to A. Saulene and L. Lukševiča from the Latvian Museum of Natural History for their help in the study of the Latvian brachiopod collections. We are very grateful for insightful and positive reviews from Peter Sheehan and Jia-yu Rong that greatly improved the MS. The study was supported by the Estonian Research Council and the Danish Council for Independent Research. References Ainsaar, L., Meidla, T., 2008. Ordovician carbon isotopes. In: Põldvere, A. (Ed.), Estonian geological sections. Bull, 9. Männamaa (F-367) drill core. Estonian Geological Survey, Tallinn, pp. 27–29. Ainsaar, L., Kaljo, D., Martma, T., Meidla, T., Männik, P., Nõlvak, J., Tinn, O., 2010. Middle and Upper Ordovician carbon isotope chemostratigraphy in Baltoscandia: a correlation standard and clues to environmental history. Palaeogeogr. Palaeoclimatol. Palaeoecol. 294, 189–201. http://dx.doi.org/10.1016/j.palaeo.2010.01.003. Ainsaar, L., Truumees, J., Meidla, T., 2015. The position of the Ordovician–Silurian boundary in Estonia tested by high-resolution δ13C chemostratigraphic correlation. In:

Ramkumar, Mu (Ed.), Chemostratigraphy Concepts, Techniques, and Applications. Elsevier, pp. 395–412. Amsden, T.W., 1974. Late Ordovician and Early Silurian articulate brachiopods from Oklahoma southwestern Illinois, and eastern Missouri. Oklahoma Geol. Surv. Bull. 119, 1–154. Amsden, T.W., 1986. Part I. Paleoenvironment of the Keel–Edgewood oolitic province and the Hirnantian strata of Europe, USSR, and China. Oklahoma Geol. Surv. Bull. 139, 1–55. Baarli, B.G., 1995. Orthacean and strophomenid brachiopods from the Lower Silurian of the central Oslo Region. Fossils Strata 39. Baarli, B.G., Harper, D.A.T., 1986. Relict Ordovician brachiopod fauna in the Lower Silurian of Asker, Oslo Region, Norway. Nor. Geol. Tidsskr. 66, 87–98. Bergström, J., 1968. Upper Ordovician Brachiopods from Västergötland, Sweden. Geol. Palaeontol. 2, 1–35. Bergström, S.M., Bergström, J., 1996. The Ordovician–Silurian boundary successions in Östergötland and Västergötland, S. Sweden. GFF 118, 25–42. 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