The distribution of chitinozoans in the Wenlock-Ludlow boundary
beds in five East Baltic drill cores (Ohesaare, Kolka, Ventspils,
Pavilosta, Gussev-1) has been described in Nestor (2007). Up to now only
a brief review of chitinozoan distribution in the Ludlow sections of
Estonia, based on the Ohesaare (V. Nestor 1990, 1997) and Ruhnu cores
(Nestor 2003), is available. The first, lowest stratigraphical level
identified by chitinozoans is at the base of the Torga Formation of the
Paadla Regional Stage, where Angochitina elongata appears. Chitinozoans
are absent below this level in the Soeginina Beds, recently attributed
to the Ludlow by Viira & Einasto (2003). Angochitina elongata is a
zonal species of the global biozone, widely distributed around the world
in the lower part of the Ludlow (Verniers et al. 1995). This biozone
forms a base for the discussion in the present paper.
Graptolite data are very scarce above the Lobograptus scanicus
Biozone in the East Baltic Ludlow. R Ulst (in Gailite et al. 1987) has
identified all the graptolites collected from the Pavilosta and
Ventspils drill cores, but these were only rare findings, which did not
allow exact identification of the biozonal boundaries. This is also true
for the graptolite records from the Dubovskoye core (Kaljo & Sarv
1976). Therefore, the boundary between the Gorstian and Ludfordian
stages in the studied drill cores has been drawn tentatively.
In the present paper the distribution of chitinozoans in the
Ohesaare, Ventspils, Pavilosta, and Dubovskoye (Northern-Gusevskaya 2)
core sections is considered. As Nestor (2007) discussed also the
distribution of chitinozoans in the lowermost Ludlow, this interval is
not dealt with in the present article. Chitinozoan data from the Kolka
core are also omitted due to their great similarity to those from the
Ohesaare core and the much greater number of samples in Kolka, empty of
chitinozoans. The data of the Gussev-1 core are replaced by the
chitinozoan succession of the Dubovskoye core, where the series of
samples is more representative, as chitinozoan samples are missing from
the uppermost 23 m of the Ludlow in the former core. Besides, all
chitinozoan data from the omitted drill cores confirm the information
The main aim of this paper is to present more biostratigraphical
information concerning the Ludlow of the East Baltic region and to
improve the chitinozoan distribution data in general. Most of the
studied samples have been collected together with colleagues in the
Skrunda, Riga, and Gussev depositories between 1980 and 1986. Several
papers have been published on these materials, concerning assemblages of
trilobites (Mdnnil 1982), ostracodes (Sarv 1982), conodonts (Viira
1982), and vertebrates (Mdrss 1986), which enabled us to compare
chitinozoan assemblages with some other faunas (see below).
The studied specimens are housed at the Institute of Geology at
Tallinn University of Technology (collection GIT 576).
The studied drill cores represent open shelf, transitional facies,
and shelf depression deposits (Fig. 1). The Torga Formation and the
upper part of the Kuressaare Formation of the Ohesaare core are
predominantly characterized by argillaceous nodular limestones; the
lower part of the Kuressaare Formation is represented by calcareous and
dolomitic argillaceous marlstones. Ludlow deposits in the Ventspils,
Pavilosta, and Dubovskoye cores are of deeper water origin. The Dubysa
Formation is characterized by argillaceous marlstones with rare thin
limestone interbeds, the Engure Formation by different marlstones with
limestone nodules, and the Mituva and Ventspils formations consist of
nodular limestones with a number of hardgrounds. The mainly dolomitic
mudstones in the upper Ludlow succession of the Dubovskoye core belong
to the Uljanov Formation (Koren & Suyarkova 2007) (Fig. 2).
[FIGURE 1 OMITTED]
Conodont-based correlations between Saaremaa (Estonia) and Gotland
(Sweden) have revealed a major gap in the middle part of the Ludlow
sequence of Estonia, between the Paadla and Kuressaare regional stages
(Jeppsson et al. 1994). The extent of this gap in the Ohesaare core is
supposed to be smaller than in the outcrop area (Viira & Aldridge
1998). A gap in the lowermost Ludlow of Estonia has been observed
earlier, based on the chitinozoan succession (missing biozones) (Nestor
1982). In the other East Baltic sections (Ventspils and Pavilosta), the
Ludlow deposits are represented more or less in full extent. In the
Dubovskoye core we have studied only the upper part of the Ludlow, i.e.
the Ludfordian Stage.
A model of oceanic and climatic cyclicity, linked to the
sedimentological and biotic changes in the Ludlow, was proposed by
Jeppsson & Aldridge (2000). They determined two levels of intense
faunal extinctions, the Linde and Lau events in the mid-Ludlow.
According to Kaljo et al. (1998), carbon isotope cycling is one feature
of environmental cyclicity and the most positive excursions occur after
important faunal extinctions, usually tied to regression and cooling of
climate. Carbon isotopes have been studied and [[delta].sup.13]C curves
compiled for the Ohesaare and Ventspils cores (Kaljo et al. 1998; Kaljo
& Martma 2006). The [[delta].sup.13]C curve of the late Gorstian
Linde Event (Jeppsson & Aldridge 2000) is hardly recognizable in the
East Baltic cores (Kaljo & Martma 2006). The peak values of the
mid-Ludfordian [[delta].sup.13]C excursion occur within the limits of
the Lau Event, defmed by conodonts (Jeppsson & Aldridge 2000). Among
the studied sections the Lau Event is expressively reflected in the
Ventspils core, approximately within the depth interval 460-470 m, in
the upper part of the Mituva Formation (Kaljo et al. 1998; Kaljo &
Martma 2006). In the chitinozoan succession this event is characterized
by the extinction of 14 species. High values of the carbon isotope curve
have been reported from various localities around the world, giving
evidence of the global dimension of this event (Martma et al. 2005;
Calner & Eriksson 2006). In the Ohesaare core the peak level of the
carbon isotope excursion is represented by a gap (Kaljo et al. 1998).
[FIGURE 2 OMITTED]
ON THE BOUNDARY OF THE GORSTIAN AND LUDFORDIAN STAGES
According to Kaljo & Paskevicius (1993), the P. tumescens and
S. leintwardinensis graptolite biozones have not been established in the
East Baltic drill cores and the boundary between the Gorstian and
Ludfordian stages falls somewhere within the middle of the regional P.
tauragensis Zone. Graptolites are scarce, but chitinozoans occur
abundantly in the East Baltic upper Silurian sections, as well as in the
type Ludlow area, studied by Sutherland (1994). According to the last
paper, only minor changes occur in the chitinozoan succession at the
boundary of the Gorstian and Ludfordian stages. Most of the species
which appear in the Upper Elton or Bringewood formations range over this
boundary. However, there are some species (Sutherland 1994, text-fig. 6)
with overlapping ranges at the stages boundary, e.g. Belonechitina
mortimerensis disappearing below the boundary and E. lagenomorpha?
appearing a bit lower. After being absent in the Upper Elton Formation,
Angochitina elongata re-appears in the lowermost part of the Ludfordian
Stage. A similar situation occurs in the Ventspils core in the interval
512-516 m and in the Pavilosta core in 744.3-745.3 m, though A. elongata
is not found above this interval in the latter section. These
distribution data were not sufficient for recognizing this boundary in
the Ohesaare core (Fig. 3) but allowed us to establish the provisional
position of the stages boundary in the Ventspils and Pavilosta cores
(Figs 4, 5). In the Dubovskoye core only sediments of the Ludfordian
Stage are represented (Fig. 6).
The Ludlow chitinozoans from Baltic glacial erratics were first
described by Eisenack (1931), from Gotland by Eisenack (1964), and from
Estonia (Saaremaa = Osel) by Eisenack (1970). Laufeld (1974) identified
among other species, many Ludlow taxa from the Gotland sequence, but
without establishing biozonal units. V. Nestor (1990) distinguished six
preliminary biozones from the East Baltic Ludlow cores. The first short
account of chitinozoan biostratigraphy in the Ludlow of Shropshire was
published by Doming (1981). A complete review of chitinozoans from the
Ludlow type area was provided by Sutherland (1994), who established 12
numerical biozones in the interval from the Lower Elton Formation to the
Lower Whitcliffe Formation. A year later Vemiers et al. (1995) published
a global biozonation of Silurian chitinozoans with three biozones and
two undefined intervals in the zonal succession of the Ludlow Series.
Nestor (2007) defined and described two new regional biozones
(Conochitina postarmillata and Ancyrochitina desmea), which filled the
previous lower Ludlow gap in the chitinozoan zonal succession (Fig. 7).
The younger biozones from the Ludlow of East Baltic drill cores are
described in ascending order.
The Angochitina elongata Biozone
Eisenack (1931) described the holotype of Angochitina elongata from
an erratic boulder and defined a neotype from the Hemse Marl of Gotland
(Eisenack 1964). In the type Ludlow area this species appears 24 m below
the top of the Middle Elton Formation, Gorstian Stage, correlated with
the uppermost part of the Lobograptus scanicus graptolite Biozone
(Sutherland 1994). In the Pavilosta core R Ulst identified the highest
L. cf. scanicus at 806.50 m and Saetograptus chimaera at 811.30 m, but
the lowest Pristiograptus tumescens at 784.10 m. In the Ventspils core
L. ex. gr. scanicus was established at 609.40 m, S. chimaera at 600 m,
and P. tumescens (single fording) at 574.30 m (Gailite et al. 1987).
Thus, the East Baltic chitinozoan data confirm the opinion of Sutherland
(1994) that the lower boundary of the A. elongata Biozone corresponds to
the uppermost part of the scanicus graptolite Zone.
In the East Baltic sequences the A. elongata Biozone coincides with
the lower and middle parts of the Torga Formation, the upper part of the
Dubysa Formation, and the lower part of the Engure Formation, which all
are characterized by a diverse and abundant assemblage of chitinozoans.
Many species from the uppermost Wenlock range into the Ludlow of the
Ventspils and Pavilosta cores: Conochitina pachycephala Eisenack (Fig.
8M), C. claviformis Eisenack (Fig. 8N), C. tuba Eisenack (Fig. 80), C.
rudda Sutherland (Fig. 8L), Cingulochitina convexa (Laufeld) (Fig. 8T),
Linochitina erratica Eisenack (Fig. 8V), and Cingulochitina gorstyensis
Sutherland (Fig. 8U). According to Sutherland (1994, p. 39), the lowest
occurrence of the last species is in the midGorstian in the type Ludlow
area (see also Nestor 2007, p. 123). Belonechitina latifrons (Eisenack)
(Fig. 8P), B. lauensis (Laufeld) (Fig. 8R), Ancyrochitina diabolus
Eisenack (Fig. 8I), A. desmea Eisenack (Fig. 8H), and A. gogginensis
Sutherland (Fig. 8J) range from the basal Ludlow upwards. According to
Sutherland (1994, p. 39), the last species appears already in the upper
part of the Much Wenlock Limestone.
The zonal species, Angochitina elongata Eisenack (Fig. 8A), appears
together with Angochitina echinata Eisenack (Fig. 8F) in the Ohesaare
and Ventspils cores (Figs 3, 4), Palencia (North Spain) (Schweineberg
1987), Skane (Sweden) (Grahn 1996), Amazonas Basin (North Brazil) (Grahn
2005), and probably also in the type Ludlow area (Angochitina sp. aff.
echinata in Sutherland 1994). Angochitina ambrosi Schweineberg (Fig. 8B,
C) is previously only known from Gondwana, Palencia, and is for the
first time identified in Baltic sections. Sphaerochitina impia Laufeld
(Fig. 8E) and Ancyrochitina brevispinosa Eisenack (Fig. 8D) were
identified only in the Ohesaare core. Ramochitina spinipes (Eisenack
1964) (Fig. 8G), a characteristic species of the lower part of the Hemse
Beds, was recognized only in the Pavilosta core. Eisenackitina
intermedia (Eisenack) (Fig. 8Y) is widely distributed, but the
appearance level of this taxon is variable. In the outcrop area of the
Brabant Massif, in the Ronquieres Formation (Verniers et al. 2002) and
in the Prague Basin of the Barrandian area (Moravek 2007) it appears in
the lowermost Ludlow, in the type Ludlow area (Sutherland 1994) and in
the Ventspils and Pavilosta cores it appears in the middle of the
Gorstian Stage, in the lower part of the Angochitina elongata Biozone.
In Gotland (Laufeld 1974), Skane (Gratin 1996), and in the Ohesaare core
its first occurrence is higher, within the Ludfordian Stage. It is not
excluded that these differences in the species appearances might have
been caused by local facies differences. Ramochitina swifti Sutherland
(Fig. 8W), Eisenackitina toddingensis Sutherland (Fig. 8Z), E. kerria
Miller, Sutherland & Doming (Fig. 8X), and E. clunensis Miller,
Sutherland & Doming (Fig. 9A) are previously known from the Welsh
Basin, and were for the first time identified in the East Baltic Ludlow.
The first two species occur in the upper Gorstian of the type Ludlow
area (Sutherland 1994) and two others in the uppermost Ludfordian of the
Clun area (Miller et al. 1997). Belonechitina mortimerensis Sutherland
(Fig. 8S) has been identified in the upper Gorstian of the type Ludlow
area (Sutherland 1994) and at the same stratigraphic level in the
Pavilosta and Ventspils cores. The fording of Ancyrochitina brevis
Taugourdeau & Jekhowsky (Fig. 8K) in the upper part of the Gorstian
Stage in the Pavilosta core is also notable, as this species is known
from the Pridolian strata (Jaglin & Paris 2002).
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
A number of chitinozoan species of the studied cores are left in
open nomenclature, as the material is insufficiently or badly preserved
and the ornamentation is hardly visible. Some of these forms are
represented in Figs 9 and 10. The Angochitina elongata Biozone includes
Eisenackitina sp. 1 (Fig. 9C), Eisenackitina sp. 2 (Fig. 9D), and
Sphaerochitina sp. (Fig. 9L) in the Pavilosta core and Ramochitina? sp.
1 (Fig. 9N) and Ramochitina sp. 2 (Fig. 9T) in the Ventspils core.
[FIGURE 7 OMITTED]
The chitinozoan succession in the Ohesaare core (Fig. 3) is
interrupted by many barren intervals, where chitinozoans are missing,
referring to unfavourable conditions for these microfossils
(regression?) or their preservation. In the Ventspils core (Fig. 4) two
intervals of chitinozoan extinctions can be recognized in the
Angochitina elongata Biozone, one in the upper part of the Dubysa
Formation (564-568 m) and the other step by step disappearance of
species in the lower-middle part of the Engure Formation (527-546 m).
Six species disappear in the uppermost Dubysa Formation in the Pavilosta
core (742-752 m) (Fig. 5).
The Eisenackitina lagenomorpha Biozone
Vemiers et al. (1995) distinguished the global E. philipi Biozone
in the middle-upper Ludlow. In the present paper, as E. philipi is rare
in the East Baltic sections, we used the regional E. lagenomorpha
Biozone instead of the E. lagenomorpha E. philipi Biozone, which has
been published earlier by V. Nestor (1990, 1997).
In the Pavilosta core Eisenackitina philipi Laufeld (Fig. 9H)
ranges for only about 10 m in the lowermost Ludfordian, i.e., in the
upper part of the Dubysa Formation. It is rare in about 50 m at the
boundary interval of the Engure and Mituva formations in the Ventspils
core and is missing from the Dubovskoye core. Eisenackitina lagenomorpha
(Eisenack) (Fig. 9G) is well represented in all studied sections, except
for the upper part of this zone in the Dubovskoye core. According to
Doming (1981), E. lagenomorpha and E. philipi appear together in the
Lower Leintwardine Formation in the Welsh Basin. In the sections of the
Ludlow area E. lagenomorpha? was identified in the uppermost part of the
Bringewood Formation (Sutherland 1994). Actually this taxon is rather
similar to E. lagenomorpha in the East Baltic cores. In the Pavilosta
and Dubovskoye cores different Cingulochitina species occur abundantly
throughout the biozone: Cingulochitina wronai Paris & Kriz (Fig.
9M), C. hedei Laufeld (Fig. 9V), Cingulochitina sp. 1 (Fig. 9S) as well
as C. gorstyensis and C. convexa. The facies control on Cingulochitina
species is obvious, as they are completely missing in the Ohesaare core
and occur only sparsely in the Ventspils core. The chitinozoan
assemblage of this biozone is better represented in the Pavilosta and
Dubovskoye cores. Ancyrochitina pedavis Laufeld (Fig. 9U), Ramochitina
villosa Laufeld (Fig. 9P), and Pterochitina perivelata Eisenack (Fig. I
OE) appear in the lowermost part of the Pagegiai Formation in the
Pavilosta core. The same species are present in the Hamra Formation on
Gotland, also including Eisenackitina oviformis Eisenack (Fig. IOD),
which appears in a somewhat higher level in Pavilosta. Angochitina
paucispinosa Miller, Sutherland & Doming (Fig. IOB, C) is known from
the Ludfordian of the Clun area, Shropshire (Miller et al. 1997). It
occurs in the Ohesaare, Dubovskoye, and Pavilosta cores within the
overlying Eisenackitina barrandei Biozone. Angochitina crassispina
Eisenack (Fig. l0A) is found only sporadically. Atypical specimens of
Eisenackitina elongata Eisenack (Fig. 9R) are represented in the
Pavilosta and Dubovskoye cores, Calpichitina squamosa (Laufeld) (Fig.
9E) and Angochitina aff. echinata Eisenack (which has spines with wide
bases) (Fig. 91) have been identified in the Dubovskoye core, and
Sphaerochitina acanthifera Eisenack (Fig. 9F) is found only in the
Pavilosta core. The last two species are characteristic of the Eke
Formation of Gotland.
[FIGURE 8 OMITTED]
In addition, some species kept in open nomenclature are also
identified from the E. lagenomorpha Biozone: Belonechifna sp. 1 (Fig.
9J), Sphaerochitina sp. (Fig. 9K), Belonechitina sp. 2 (Fig. 90),
Ramochitina sp. (Fig. 9W), and Plectochitina sp. (Fig. 10F).
The Eisenackitina barrandei Biozone
The index species, Eisenackitina barrandei Paris & Kriz (Fig.
10G) has been described from the uppermost Ludlow of the Prague Basin
(Paris & Kriz 1984). In the East Baltic this species is best
represented in deep-water silt- and mudstones of the Pavilosta and
Dubovskoye cores, in the upper parts of the Pagegiai and Uljanov
The assemblage of chitinozoans in the E. barrandei Biozone in its
type area (Khz et al. 1986) is similar to the corresponding assemblage
in the East Baltic upper Ludlow sections. Angochitina echinata occurs in
all studied drill cores, Ancyrochitina pedavis in Pavilosta.
Sphaerochitina sphaerocephala (Eisenack) (Fig. 10M) is best represented
in the upper part of the biozone in the Pavilosta and Ohesaare cores.
Eisenackitina intermedia, E. oviformis (Eisenack) (Fig. 10D), and E.
lagenomorpha occur in all studied sections, but more abundantly in the
Pavilosta core. These species are also found in the Hamra and Sundre
formations of Gotland (Laufeld 1974). Calpichitina gregaria Paris &
Kriz (Fig. 10P) has been identified in the Dubovskoye core. Atypical
specimens of Ancyrochitina ansarviensis Laufeld (Fig. 10J) are recorded
in the Pavilosta core and Belonechitina? cf. granosa (Laufeld) (Fig.
10L) is present in all studied cores, except the Dubovskoye core. Some
taxa with open nomenclature are also identified in the E. barrandei
Biozone, mainly in the Pavilosta core: Plectochitina sp. (Fig. 10H),
Ramochitina sp. 2 (Fig. 10I), Eisenackitina sp. 3 (Fig. 10R),
Eisenackitina sp. 4 (Fig. 100), and Belonechitina sp. 3 (Fig. 10N) in
the Ventspils core.
The lower boundary of the E. barrandei Biozone is fixed by the
appearance of the index species. V. Nestor (1990) and Grahn (1996)
distinguished the Sphaerochitina sphaerocephala Biozone in the topmost
Ludlow. This zone can be traced in the Ohesaare and Pavilosta cores, but
not in the other studied sections.
In the Ventspils core the Lau Event, related to intense extinction
of chitinozoans, has been established in the topmost Mituva Formation
(Kaljo et al. 1998), roughly in the depth interval 460-470 m (Fig. 4).
It coincides with the lowermost part of the E. barrandei Biozone and is
characterized by the disappearance of 14 chitinozoan species. Above the
layers barren of chitinozoans at the boundary of the Mituva and
Ventspils formations, only three species reappeared. In general,
chitinozoans are scarce in the whole of the Ventspils Formation. In the
Ohesaare core a stratigraphic gap corresponds to the Lau Event (Kaljo et
RELATIONS BETWEEN CHITINOZOAN, NHCROVERTEBRATE, AND CONODONT
OCCURRENCES IN THE OHESAARE CORE
Vertebrate microfossils (scales), conodonts, and chitinozoans have
been studied in the same East Baltic cores, permitting comparison of
their ranges. The distribution of all three microfossil groups is facies
controlled, as was proved by the integrated study of the Ohesaare,
Ventspils, and Pavilosta cores (Kaljo et al. 1986). Although many
samples lack chitinozoans in the Ludlow strata of the Ohesaare core,
this section still offers the best opportunity for comparison of the
zonal successions of vertebrates (Marss 1986; Marss & Miller 2004),
conodonts (Viira 1982; Viira & Aldridge 1998), and chitinozoans
[FIGURE 9 OMITTED]
According to Marss (1986, fig. 41), the lowermost Ludlow strata
(113.40-124.4 m) are barren or contain only scarce fragments of
vertebrates. Upwards the zonal species appear successively: Phlebolepis
ornata, P. elegans, Andreolepis hedei, Thelodus sculptilis, and T.
admirabilis. In the Ohesaare core two zonal boundaries of vertebrates
coincide with those of chitinozoans: (1) Andreolepis hedei, appearing at
99.50 m, correlates with the Eisenackitina lagenomorpha Biozone boundary
and (2) T. admirabilis, appearing at 83.10 m, correlates with the
Eisenackitina barrandei Biozone boundary. The richest assemblage of
vertebrates occurs in the lower part of the Kuressaare Formation,
whereas the chitinozoan assemblages are the most diverse and abundant in
the lower part of the Torga Formation.
The succession of conodonts in the Ohesaare core was published by
Viira (1982). Later, Viira & Aldridge (1998, figs 5, 6) provided
more precise distribution of conodont species in the Ludlow of the
Ohesaare core. In the Paadla Stage they established the Ozarkodina
snajdri snajdri and O. crispa biozones, and the O. snajdri parasnajdri
Biozone in the Kuressaare Stage. No direct criteria for correlation of
chitinozoan and conodont biostratigraphical units have been observed.
The zonal species of conodonts and vertebrates appear more closely tied
in the Ohesaare core: O. s. parasnajdri (at 93.40 m) and Thelodus
sculptilis (95.15 m), as well as Phlebolepis ornata (112.25 m) and O. s.
snajdri (113.35 m).
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
1. Chitinozoans are well represented in the studied core sections
with the highest diversity in the deepest-water Pavilosta core (57
2. In most sections the Wenlock species range into the Angochitina
elongata Biozone, except in the Ohesaare core, where a sedimentation gap
exists in the early Ludlow.
3. Many chitinozoan species, previously known only from Avalonia
(Welsh Basin) and Gondwana (Prague Basin, Palencia), were for the first
time identified in Baltic sections.
4. Pterochitina perivelata has its first appearance in the E.
lagenomorpha Biozone earlier than previously supposed (Verniers et al.
5. The Lau Event, recognized in the uppermost part of the Mituva
Formation in the Ventspils core (Kaljo et al. 1998), coincides with the
lowermost part of the E. barrandei Biozone, characterized by the
disappearance of 14 chitinozoan species.
6. Several chitinozoan and vertebrate zonal boundaries coincide in
the Ludlow of the Ohesaare core.
Acknowledgements. This study was supported by the target funding
project SF 014002008. I am grateful to H. Nestor and R. Einasto for the
opportunity to use their unpublished lithological colums and to D. Kaljo
and H. Nestor for valuable suggestions on the manuscript. Special thanks
to F. Paris and an anonymous reviewer for thorough reviews. I thank also
O. Hints and G. Baranov for technical help with the SEM study and
Received 17 December 2008, accepted 3 March 2009
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