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Nov 25, 2017 - más estudiadas corresponde al Sinclinal Torgau-Doberlug (TDS), donde afloran estratos fosilíferos del Cámbrico medio a temprano ..... Cambrian sediments (final depth of the core is 475 m below surface). ...... Grand-Halleux.
Journal of Iberian Geology (2017) 43:601–614 https://doi.org/10.1007/s41513-017-0041-3

RESEARCH PAPER

First evidence of middle to late Cambrian deposition by first palynological data from the Torgau–Doberlug Syncline (subsurface Central Germany, Mediterranean shelf of Gondwana) Abubaker Atnisha1 · Oldřich Fatka2 · Olaf Elicki1 Received: 6 June 2017 / Accepted: 6 November 2017 / Published online: 25 November 2017 © Springer International Publishing AG, part of Springer Nature 2017

Abstract Purpose  Cambrian to Ordovician sequences in Germany are known from only a few regions of limited geographic extent. One of the largest of these regions is represented by the Torgau–Doberlug Syncline (TDS) where fossiliferous early to midCambrian strata occur in the subsurface. Cambrian skeletal fauna and archaeocyathan-calcimicrobial reef mounds from this area indicate a West-Gondwanan Mediterranean palaeogeographic affiliation. However, organic-walled microfossils were not studied so far. Methods  New palynological research on the old and recently sampled, but hitherto non-investigated drilling core Wis BWA 1686-81 provided a moderately diverse acritarch microflora. Results  The moderately diverse acritarch assemblage is dominated by diverse leiosphaerids and the stratigraphically important genera Cristallinium, Eliasum, and Timofeevia associated with specimens representing most probably the “galeate” acritarch plexus (particularly Cymatiogalea, Priscogalea, and Stelliferidium) and a few further acritarch genera. This microflora points to a biostratigraphic position within the Cambrian Series 3 to possibly early-Furongian age including indicating for the first time that there was deposition in this palaeogeographic region continuing to the latest mid-Cambrian. The hitherto assumed sedimentary gap from early mid-Cambrian until Ordovician which seems to be common in whole Saxo-Thuringia is now slightly shorter. Conclusion  The results support the model of a connected Cambro-Ordovician “Mediterranean shelf” with closely related internal areas and with well comparable early Palaeozoic sequences from Spain in the Southwest of Europe until East-Central Europe at least with the TDS as their today northernmost occurrence. Keywords  Acritarchs · Palynomorph · Cambrian · Saxo-Thuringia · Torgau-Doberlug Syncline Resumen Objetivo  Las secuencias del Cámbrico a Ordovícico son reconocidas sólo en pocas áreas de Alemania. Una de las regiones más estudiadas corresponde al Sinclinal Torgau-Doberlug (TDS), donde afloran estratos fosilíferos del Cámbrico medio a temprano. Paleofauna esquelética del Cámbrico y montículos microbianos compuestos por arqueociatios y colonias de microfósiles calcáreos indican que está zona posee una relación paleográfica con el Mediterráneo del Gondwana Occidental. Sin embargo, los microfósiles de paredes orgánicas aún no han sido estudiadios. Metodología  Nueva investigación palinológica en muestras antiguas y recientemente muestreadas, pero hasta ahora no investigado, Wis BWA 1686-81 proporcionaron una microflora de acritarco moderadamente diversa. Resultados  Se logró determinar un conjunto moderadamente diverso de acritarcos, dominado principalmente por leiosphaeridia y los géneros estratigráficamente importantes como Cristallinium, Eliasum y Timofeevia, los que se encuentran asociados con otros especímenes que problablemente representan al plexo de acritarcos “galeate” (como Cymatiogalea, Priscogalea y Stelliferidium) entre otros del género de acritarcos. Conclusiones  Esta microflora apunta a una posición bioestratigráfica del Cámbrico, específicamente dentro la Serie/Época 3 a probalemente al Furongiense temprano, indicando por primera vez una depositación en esta región paleogeográfica que Extended author information available on the last page of the article

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continúa hasta la última mitad del Cámbrico. La brecha sedimentaria, hasta ahora asumida desde principios del Cámbrico hasta el Ordovícico que parece ser común en toda Saxo-Thuringia, ahora es un poco más corta. Los resultados apoyan el modelo de una "plataforma mediterránea" Cambro-Ordovícica conectada con áreas internas estrechamente relacionadas y con secuencias paleozoicas tempranas comparables con las del sudoeste de Europa (España) hasta Europa Centro-Oriental, al menos con el TDS como su ocurrencia más septentrional. Palabras clave  Acritarcos · Palinomorfo · Cámbrico · Saxo-Thuringia · Sinclinal Torgau-Doberlug

1 Introduction Palaeontologically dated Cambro-Ordovician rocks are very scarce in Germany (Geyer et al. 2008; Servais et al. 2008; Heuse et al. 2010). One of such regions is represented by

the subsurface Torgau–Doberlug Syncline (TDS) (about 50–100 km NE of Leipzig, Fig. 1), where fossiliferous early to mid-Cambrian sequences containing skeletal fauna (e.g. trilobites and so-called small shelly fossils) and reef mounds (archaeocyathan-calcimicrobial buildups) have been known

Fig. 1  Geological map of the Torgau–Doberlug Syncline (TDS) with core localities shown by red circle notations. Modified from Linnemann et al. (2010)

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from drilling cores for quite a long time (history of research see Geyer et al. 2014). Within the TDS search for acritarchs or other organic-walled microfossils have never been subject of investigation so far. Until today, the palaeontological and biostratigraphic research was focused on trilobites, archaeocyaths, small shelly fossils and algae. The first study of Cambrian fossils in the TDS was published by Schmidt (1942), followed in more detail by the work of Sdzuy (1957a, 1957b, 1958, 1970, 1972), Freyer and Suhr (1987, 1992), Elicki (1992, 1994, 1997, 1999a, 2003, 2005, 2007, 2012), Elicki and Debrenne (1993), Buschmann et al. (1995), Elicki and Wotte (2003), Wotte (2004), Elicki and Geyer (2010), and Geyer et al. (2014). Whereas the dominating carbonatic early Cambrian strata of the area are palaeontologically characterized by archaeocyaths and by small shelly fossils, the nearly exclusively siliciclastic mid-Cambrian succession, however, is defined by trilobites (for details see below). Nevertheless, many drilling cores of various lithologies of these Cambrian subsurface deposits do not have delivered any suitable fauna so far, making stratigraphic correlation within this highly tectonised area difficult or even impossible. The target of this paper is the first announcement of acritarchs from the early Palaeozoic strata of the TDS: for the first time, some up to now seemingly non-fossiliferous siliciclastic subsurface deposits are biostratigraphically datable. Acritarchs are organic-walled marine microfossils (OWM) of uncertain biological affinity. They first appear in the late Palaeoproterozoic and underwent at least two Proterozoic radiations and the first documented mass extinction in Earth history, too (Xiao and Kaufman 2006; Nowak et al. 2015). However, acritarchs dominate in the early Palaeozoic (Servais et al. 2016). Conventionally, these microfossils have been interpreted as cyst stages of eukaryotic algae, but the group probably also includes prokaryotic envelopes, heterotroph protists, vegetative parts of cells or of multicellular organisms, and even animal egg cases or possible chlorophyte, eustimatophyte and dasycladacean algae (Servais et al. 1997; Marshall et al. 2005; Agić et al. 2016). Despite their problematic biological affiliation, acritarchs represent a significant part of the Palaeozoic marine phytoplankton and they have proven to be a useful complement to trilobite-based biostratigraphic correlation of Cambrian sedimentary rocks across Avalonia, Armorica, Baltica and northern Gondwana (e.g. Moczydłowska 2011; Palacios et al. 2009, Palacios 2015). They are very useful for long-range correlation and biostratigraphic zonation and for dating of problematic Palaeozoic sequences that lack other diagnostic fossils as, e.g., trilobites, conodonts, or graptolites. Already in the Cambrian the acritarchs are morphologically diverse and range in size from 25 to 200  µm (Moczydłowska 1998). Generally, their diversity increased from the Cambrian to Ordovician and Silurian up to their major extinction in the Late Devonian and subsequently to their near disappearance in the Carboniferous (Mullins et al. 2005; Huntley et al. 2006). Post-Palaeozoic acritarchs only

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represent a negligible component of the marine phytoplankton assemblages.

2 Geological setting The studied material was collected from two biostratigraphically hitherto not defined drilling cores of the TDS. The wells have been drilled in 1980–1981 within the scope of a regional mineral exploration programme. Tectonostratigraphically, the area is part of the Saxo-Thuringian Zone of eastern Germany (Fig. 1), which represents one of the Variscan zones defined by Kossmat (1927) and which is situated in the northeastern region of the Bohemian Massif (Linnemann 2007). In the TDS, Proterozoic and Palaeozoic strata represent subsurface units known only from boreholes (Proterozoic rocks crop out at surface very locally, too). They are covered by up to 200 m of Cenozoic sediments (Geyer et al. 2014). Proterozoic to earliest Cambrian rocks represent the Cadomian Basement (Rothstein Formation), unconformably overlain by early Cambrian (Zwethau Formation) and midCambrian strata (Tröbitz and Delitzsch formations, known as Arenzhain Group; see Freyer and Suhr 1987; Brause and Elicki 1997; Elicki 1999b; Geyer et al. 2014; Fig. 2). During early to mid-Cambrian time, the TDS region was part of the Mediterranean facies realm of the European shelf of western Gondwana (see Sdzuy et al. 1999) (Fig. 3). According to Elicki and Wotte (2003), the area represents the northernmost occurrence of this palaeogeographic facies belt. The Cadomian basement (Rothstein Formation) represents the oldest unit and consists of very low-grade metasedimentary rocks, predominantly of dark-gray to black distal turbidites composed of an intercalation of greywacke and mudstone beds and thick layers of massive black chert (Buschmann 1995). The Rothstein Formation is interpreted as a fragment of a Cadomian back-arc basin developed on thinned continental crust, which has been slightly deformed during the Cadomian Orogeny (Buschmann 1995; Linnemann et al. 2000, 2007). Fossil content is lacking except for some non-significant pyritized spherical and filamentous microforms (Buschmann et al. 2006). Chronological dating of an ash layer from the middle part of the formation yielded ages between 570 and 565 Ma, which assigns the formation to the Late Ediacaran (Buschmann 1995; Linnemann et al. 2000, 2007). The early Cambrian of the TDS (Zwethau Formation) is unconformable overlying the Rothstein Formation and has an estimated thickness of about 700–1000 m (Brause 1969) (Fig. 2). The succession is represented by shallow marine carbonates (with common calcimicrobial structures and archaeocyaths), minor siliciclastics and locally developed debris flows (Freyer and Suhr 1987, 1992; Elicki and Debrenne 1993; Buschmann et al. 1995; Elicki 1999b; Geyer

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Fig. 2  Stratigraphic scheme, lithological column and detailed profiles of the early Palaeozoic sedimentary succession of the Torgau–Doberlug Syncline (TDS). Modified from Elicki (2015)

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Fig. 3  Reconstruction of Cambrian palaeogeography modified after Cocks and Torsvik (2002) and Torsvik and Cocks (2013). Location of Torgau–Doberlug Syncline indicated by a black triangle; ATA Armorican Terrane Assemblage

et al. 2014). The Zwethau Formation comprises two members, the Torgau Member below consists of up to 500 m or more of fossiliferous limestones and dolostones. Calcimicrobial, oolitic, and intraclastic limestones are common. Cyanobacteria, archaeocyaths, and skeletal fossils occur widely (Fig. 2) (Sdzuy 1962; Freyer and Suhr 1987, 1992; Elicki 1992, 1994, 1999b; Elicki and Debrenne 1993; Elicki 2007). The sedimentary environment of this member is interpreted as a carbonate-dominated subtidal ramp with calcimicrobialarchaeocyathan buildups succeeded in the uppermost part by a shallow subtidal to intertidal mixed ramp regime with oolitic shoal complexes and restricted areas (Elicki 1994, 1999b). The biostratigraphic age of the Torgau Member is mid-early Cambrian indicated by archaeocyaths (corresponding to lower Ovetian archaeocyathan zones of the Ossa–Morena Zone, SW Iberia, which is correlated to the Issendalenian of Morocco; see Elicki 1997; Geyer and Landing 2004; Liñán et al. 2015). In contrast, the overlying Rosenfeld Member (up to 280 m thick) is dominated by siliciclastics and only very few carbonate–siliciclastic alternations. The fossil content consists of re-deposited and non-determinable archaeocyaths, algae and shelly remains. According to Elicki (2015) the Rosenfeld Member represents a subtidal mixed ramp environment similar to the uppermost part of the Torgau Member,

but up-section with some sedimentological indication for increasing depth. The mid-Cambrian strata of the TDS consist of two formations (the Tröbitz Formation and the Delitzsch Formation) summarized within the Arenzhain Group with a total thickness of up to 1000 m (Fig. 2). This group is represented by siliciclastic sediments with extremely rare and thin intercalations of limestone (Brause 1969, 1970; Elicki 1997; Geyer et al. 2014). The Tröbitz Formation is dominated by alternating quartzitic sandstones and minor dark-gray micaceous claystone, including thin calcareous layers near the transition to the overlying Delitzsch Formation (Heuse et al. 2010). The dominant fauna is of trilobites, inarticulate brachiopods, and some hyoliths. The trilobites indicate a stratigraphic level which is equivalent to the Iberian Eccaparadoxides sdzuy Biozone, corresponding to the middle Leonian sensu Liñán et al. (2002) or the middle to upper Agdzian (Celtiberian) (Paradoxides insularis Biozone) of West Gondwana sensu Geyer and Landing (2004) and Buschmann et al. (2006). The overlying Delitzsch Formation is dominated by quartzitic sandstone alternating with micaceous claystone and by a decrease of the sandstone towards the top. The predominant fauna is again of trilobites, inarticulate brachiopods, and hyoliths (Heuse et al. 2010) and is assigned to the mid-Cambrian (Paradoxides insularis to lowest Paradoxides paradoxissimus biozones),

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preserved acritarchs. However, two samples from the drilling core Wis BAW 1686-81 revealed a comparatively well preserved and diverse acritarch assemblage. Wis BAW 1686-81 (UTM r5732621, h5421637) delivered a succession of approximately 270 m of supposedly Cambrian sediments (final depth of the core is 475 m below surface). The samples collected from the core are dark-gray silty mudstone from depth at 219, 374, 433.3, and 448 m, respectively (Fig. 4). Acritarchs have been recovered from two samples and are reported in this contribution: sample MICH-Fa-1 comes from the depth of 217.7–220.7 m, and sample MICH-Fa-2 from depth 443.1–449.1 m respectively (Fig. 4). OWM were extracted following a standard palynological method using hydrochloric and hydrofluoric acids. The residue was sieved to get > 63 and 63–10 μm fractions and strew-mounted onto microscope slides; slides were studied by light-transmitted microscopy. Photographic documentation was made with the Olympus BX51 microscope, Olympus DP73 camera and Quick PHOTO MICRO 3.0 image analysis software at the Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague. Program Picolay Version 2017-0506© Heribert Cypionka was used to stack the images for sufficient depth of focus. All the figured specimens and residues of samples used in this study are stored in the palynological collections of the palaeontological department at Charles University, Czech Republic under the numbers: MICH-Fa-1 for Wis BAW 1686-81, 217.7–220.7 m and MICH-Fa-2 for Wis BAW 1686-81, 443.1–449.1 m. Fig. 4  Lithological log of drilling core Wis BAW 1686-81. The black arrows indicate the sampled levels

corresponding to the late Agdzian to early Caesaraugustan (Celtiberian) of western Gondwana (Buschmann et al. 2006; Geyer et al. 2014).

3 Materials and methods Seven samples collected from four hitherto stratigraphically not defined drilling cores of the TDS were investigated for organic-walled microfossils (OWM). The following cores were sampled: Wis BAW 1640-80 (depth 448.4–454.5 m); Wis BAW 1209-78 (depth 300.1–301.5  m); Wis BAW 1686-81 (depth 217.7–220.7 m; 368.2–374.7 m; 429.0–434.1 m; 443.1–449.1  m), and Wis BAW 1673A-81 (depth 290.5–292.1 m). All samples contained remains of OWM, particularly prasinophytes associated with usually poorly

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4 Microfossil assemblages The moderately diverse acritarch assemblage is dominated by leiosphaerids associated with several Cambrian genera. Stratigraphically important is the occurrence of specimens showing slightly polygonal to rounded central body provided with numerous stout to flexible, distally branched processes of variable length. More than 100 specimens showing such morphology can be assigned either to the genus Timofeevia Vanguestaine 1978 and/or could belong to specimens showing morphology intermediate between Timofeevia and some of genera grouped under the name “galeate” acritarch plexus (particularly Cymatiogalea Deunff 1961, Priscogalea Deunff 1961 emend. Rasul 1974 or Stelliferidium Deunff et al. 1974). Stratigraphical restriction of the analysed samples is provided also by the Cristallinium Vanguestaine 1978, Eliasum Fombella 1977 and the possible occurrence of Pirea Vavrdová 1972. The other long-ranging genera are not treated in detail. Genus Timofeevia Vanguestaine 1978

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Type species. Multiplicisphaeridium lancarae Cramer and Diez 1972; mid-Cambrian, Cantabrian Mountains at Láncara de Luna, Spain. Discussion. This genus includes at least 12 species (Mullins et al. 2007, p. 1020) ranging from the mid-Cambrian to the late Tremadocian (Molyneux et al. 1996). Most probably the earliest occurrence of Timofeevia (T. lancarae) has been reported by Vanguestaine and Van Looy (1983) from levels with the trilobite Parasolenopleura cf. cristata of Morocco (this levels is supposed to be equal to the Cambrian Stage 5; see Fletcher 2005). Rasul (1979, p. 68–69; pl. 3, Fig. 9; text—Fig. 3) published the supposedly youngest of occurrence Timofeevia (T. acremonia Rasul 1979) from the late Tremadocian Shineton Shale of Shropshire of England. Timofeevia sp. Figure 5a, b, d, e, n (?) Material. Thirty-four specimens in samples MICH-Fa-1 Wis BAW1686-81 borehole. Remarks. Only specimens showing the typical polygonal outline of the central body (Fig. 5a) as well as specimens with tubular processes or with processes with widened bases are assigned to this taxon (Fig. 5b, d, e). The preservation in slightly metamorphosed rocks excludes to determine the completeness of the distally branched processes. Some of studied specimens show a second order of distal branching (e.g. Fig. 5e), in other specimens, the distal part is unbranched or could be completely broken off (e.g. Fig. 5n). Consequently, the morphologic variability of processes varies from specimens with comparatively short, poorly branched to unbranched processes, to specimens with quite long processes, which are distally well branched (compare Fig. 5a, d). Such preservation excludes reliable separation of the species T. lancarae (Cramer and Diez 1972) Vanguestaine 1978, T. phosphoritica Vanguestaine 1978, T. pentagonalis (Vanguestaine 1974) Vanguestaine 1978 and T. heteromorpha Palacios 2015. Discussion. Palacios (2015, p. 94) observed specimens of morphology intermediate between Timofeevia (T. phosphoritica and T. pentagonalis) and Stelliferidium (S. magnum and S. albani) showing a presence of polygonal pylome, clear plate rupture and tubular processes. In about sixty studied specimens, it is hard to impossible to decide, if they could be classified as Timofeevia, or if they represent Cymatiogalea or Stelliferidium, e.g. if they belong to the “galeate” acritarch plexus. The stratigraphic distribution of specimens representing such intermediate morphology is mainly upper Drumian–Furongian (IMC6 and Furongian) and corresponds to Furongian (= A2 Zone of Martin and Dean 1981, 1988). Timofeevia or “galeate” acritarch plexus Figure 5c, f, h, i Material. More than 60 specimens in samples MICHFa-1 and MICH-Fa-2 from Wis BAW 1686-81 borehole.

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Remarks to systematics. The “galeate” acritarch plexus has been defined by Servais and Eiserhardt (1995) and includes four genera, particularly Caldariola Molyneux in Molyneux and Rushton 1988, Cymatiogalea Deunff 1961, Priscogalea Deunff 1961 emend. Rasul 1974, and Stelliferidium Deunff et al. 1974. The “galeate” acritarch plexus comprises more than eighty Cambro-Ordovician species of which a major part is very difficult to impossible to be objectively recognized. Stratigraphic ranges of numerous species of this acritarch plexus are largely concurrent in the late Cambrian—lower Ordovician. Rounded outline of the central body and presence of a large polygonal to rounded pylome are the most typical morphology of this plexus; processes could be short to long, distally branched to nonbranched; base of process could be widened (in Priscogalea and Cymatiogalea) but also constricted and associated with the star-like striae on the surface of central body around base of process (in Stelliferidium). The main diagnostic feature differentiating particular “galeate” species is the process length, the shape of the distal process termination and the type of process base, width and density of process distribution, presence or lack of striae extending into the vesicle wall. Stricanne and Servais (2002) evaluated morphologic variability of the “galeate” plexus and explained the large number of species as a taxonomic over splitting. We agree with Agić et al. (2016, p. 9), that such over splitting most probably arises from morphological variability induced by environmental differences (as temperature and salinity, see Servais et al. 2004) in combination with poorly known life cycle. Based on studies of laboratory cultures of extant dinoflagellates showing morphological variability in response to environmental fluctuations (Kokinos and Anderson 1995; Mertens et al. 2009), the high variability of processes length has been interpreted as an environmental signal (Servais et al. 2004). Consequently, some of the conspecific nominal taxa supposedly represent developmental ontogenetic stages and ecological variants (see Servais and Eiserhardt 1995; Servais et al. 2004). Agić et al. (2016) also suppose that the “galeate” acritarch plexus represents the developmental stages or ecophenotypes and that the identification of developmental stages belonging to a single genotype would reduce the number of fossil genera and potentially to synonymyfication of Caldariola, Priscogalea and Stelliferidium. All these genera have been established in the Late Cambrian (Rasul 1974; Raevskaya 2005), with more complex “galeate” acritarchs diversifying later through the GOBE (Servais et al. 2008). The first forms of the “galeate” plexus, particularly specimens classified as Stelliferidium appear in the lower-most Furongian (Palacios 2008, Fig. 2). However, the characteristic striation around the base of long and branching processes could be absent (see Palacios 2008, fig. 3I; Palacios 2015,

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fig. IV/4), such specimens resemble Timofeevia taheddirtensis Vanguestaine and van Looy 1983. Some of herein studied specimens show polygonal pylome (e.g. Fig. 5f, h), but specimens with a very large circular pylome are also present (e.g. Fig.  5i); in such

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specimens, the pylome reaches up to 50% of the central body diameter. Thicker wall of the central body in comparison with thinner wall of the distally branched processes is the other very characteristic feature of the “galeate” acritarch plexus. Such difference in wall thickness is possible

Journal of Iberian Geology (2017) 43:601–614 ◂Fig. 5  All scale bars represent 10  μm. The specimens (a, b, d, f, g,

h, j, k, m, n, o) observed from sample MICH-Fa-1. The specimens (c, e, i, l) observed from sample MICH-Fa-2. The England Finder coordinates (E.F) is indicated for all specimens. a Timofeevia sp. cf. Timofeevia lancarae, E.F. H26-4. b Timofeevia sp. cf. Timofeevia lancarae, E.F. F24. c Timofeevia or “galeate” acritarch plexus, cf. Cymatiogalea sp., E.F. E31-3. d Timofeevia sp., E.F. H41. e Timofeevia sp., E.F. H33. f Timofeevia or “galeate” acritarch plexus, cf. Stelliferidium sp., E.F. L42-2. g Cristallinium sp. aff. Cristallinium dubium Volkova 1990, E.F. V42. h Timofeevia or “galeate” acritarch plexus, cf. Cymatiogalea sp., E.F. E35. i Timofeevia or “galeate” acritarch plexus, cf. Cymatiogalea sp., showing the rounded pylome, E.F. M40. j Eliasum sp. aff. Eliasum llaniscum Fombella 1977, E.F. P33-1. k ?Pirea sp. left, leiosphaerids right and left lower corner, E.F. M34-2. l Leiosphaeridia sp., E.F. P28. (M). Comasphaeridium sp. cf. Comasphaeridium silesiense Moczydłowska 1998, E.F. L35-1. n ?Timofeevia sp., specimen with distally broken processes, E.F. H331. o Leiosphaeridia sp., E.F. H39-3. Arrows mark apparently thinner processes wall in comparison with the central body wall

to observe in some studied specimens (e.g. Fig. 5c, marked by arrows). As discussed above, the morphology of studied specimens does not provide the possibility to distinguish specimens of Timofeevia from specimens of the “galeate” acritarch plexus. Genus Cristallinium Vanguestaine 1978 Type species. Dictyotidium cambriense Slavíková 1968; mid-Cambrian, Drumian, Jince Formation, Příbram-Jince Basin, Czech Republic. Discussion. Cristallinium includes at least 12 species (Mullins et al. 2007, p. 246) ranging most probably from the latest Stage 4 of Cambrian Series 2 (the base of the Eliasum-Cristallinium Assemblage Zone has been suggested to define the base of the mid-Cambrian, see Moczydłowska 1999; it corresponds roughly to the upper levels of the Stage 4). The youngest occurrence of Cristallinium (Cristallinium sp.) has been reported by Wang et al. (2013, p. 4) from the upper Tremadocian of South China and Kui et al. (2013, p. 113) who described Cristallinium dentatum (Vavrdová 1976) Martin 1982 from the early Floian graptolitic shales (lower levels of the Tetragraptus approximatus Zone of the Dacao Formation) of the Sichuan Province, South China. Cristallinium sp. aff. Cristallinium dubium Volkova 1990 Figure 5g Material. Twenty-two specimens in samples MICH-Fa-1 and MICH-Fa-2 from the Wis BAW 1686-81 borehole. Remarks. Specimens are dark-brown in colour and usually well preserved. The variability, however, excludes final species determination; large part of specimens is very similar to Cristallinium dubium Volkova 1990, while some other are specimens recall the type species Cristallinium cambriense (Slavíková 1968) Vanguestaine 1978. Genus Eliasum Fombella 1977

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Type species. Eliasum llaniscum Fombella 1977; lower part of mid-Cambrian, Oville Formation, Cantabrian Mountains, Spain. Discussion. Eliasum includes about ten species (Mullins et al. 2007, p. 345) which stratigraphically range from the latest early Cambrian until the Tremadocian, with a diversity peak in mid-Cambrian (Molyneux et al. 1996; Moczydłowska and Stockfors 2004; Palacios et al. 2017). The oldest specimens of this genus have been reported near the top of the Cambrian Series 2 (see Jankauskas and Lendzion, 1992, p. 522, Fig. 2), particularly from the Volkovia dentifera–Liepaina plana Acritarch biozone of Moczydłowska (1991, 1999), a level correlated with the Protolenus trilobite Zone (see Geyer and Shergold 2000). Eliasum sp. aff. Eliasum llaniscum Fombella 1977 Figure 5j Material. Six specimens in the sample MICH-Fa-1 from Wis BAW 1686-81 borehole. Remarks. Any of observed specimens does not show excystment along lines of suture (see Palacios 2015, p. 90), however the occurrence of this form is well evidenced in the studied sample. Genus Pirea Vavrdová 1972 Type species. Pirea dubia Vavrdová 1972; Middle Ordovician, Dapingian, Klabava Formation, Prague Basin, Czech Republic. Discussion. At least 16 species have been assigned to Pirea (Mullins et al. 2007, p. 778), they range from the latest mid-Cambrian of the East-European Platform (P. orbicularis Volkova 1990) to the middle Ordovician of West and East Gondwana (see Vavrdová 1972; Molyneux et al. 2013). ? Pirea sp. Figure 5k Material. Two specimens in the sample MICH-Fa-1 from Wis BAW 1686-81 borehole. Remarks. The morphology of both specimens agrees well with the diagnosis of Pirea. However, the central body and process are not always well differentiated. Limited number of observed specimens does not exclude, that they could represent flattened Leiosphaeridia. A number of long-ranging acritarch genera occur in organic residuum of both discussed samples. In this report, only two taxa are figured, particularly Comasphaeridium sp. cf. Comasphaeridium silesiense Moczydłowska 1998 (Fig. 5m), and Leiosphaeridia sp. (Fig. 5l, o).

5 Discussion Three acritarch genera, particularly Cristallinium, Eliasum, Timofeevia, as well as probably occurring “galeate” acritarch plexus show stratigraphic range from the latest Stage 4 of the Cambrian Series 2 to the lower Ordovician (Fig. 6). The

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Fig. 6  Stratigraphic range of palynological taxa from Cambrian succession in TDS, eastern Germany

most important is stratigraphic range of this taxa: (1) The FAD of the genera Cristallinium and Eliasum is in the upper third of the Cambrian Series 2 (Fig. 6). (2) The FAD of the genus Timofeevia is in early Drumian (see Palacios 2015), e.g. in levels corresponding to the youngest part of the Tröbitz and Delitzsch formations (Fig. 6). (3) The FAD of the oldest known specimens belonging to the “galeate” acritarch plexus (classified as Stelliferidium) is in levels correlated with the latest pre-Furongian (Fig. 6). Consequently, based on stratigraphic ranges of the above-named taxa, the age of sample MICH-Fa-1 from Wis BAW 1686-81 points distinctly to the late pre-Furongian age. The slightly younger,

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later Cambrian (late Series 3 to Furongian) age could not be at this stage of research definitely excluded (Fig. 6). However, the apparent absence of typical late Cambrian and lower Ordovician taxa (like Acanthodiacrodium, Lusatia, Vulcanisphaera), makes the post-Drumian age unlikely (compare Albani et al. 2006). From a regional perspective, the observed acritarch assemblage opens a fresh view on the stratigraphic inventory and the subdivision of the early Palaeozoic succession of the TDS and its comparison with neighbouring areas. The early Cambrian unit (Zwethau Formation) as well as the early mid-Cambrian strata (Tröbitz and Delitzsch formations) are

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internally subdivided based on lithological features (Fig. 2). Nevertheless, for the mid-Cambrian three different biostratigraphic levels are indicated by distinct trilobite assemblages: (1) earliest mid-Cambrian (early Leonian) and (2) early midCambrian (middle Leonian) both within the Tröbitz Formation (level 2 is also indicated for the older portion of the Delitzsch Formation), and (3) middle mid-Cambrian (early Caesaraugustan) for the younger Delitzsch Formation (Geyer et al. 2014). So, it is obvious that the differentiation of the Tröbitz Formation and the Delitzsch Formation is, at least to some extent, facies controlled (same age of late Tröbitz and early Delitzsch formations). Additionally, the classic differentiation of these two formations within the TDS is often not applicable and also not comprehensible in the drilling cores of the TDS due to many facies variations and the lack of distinct marker horizons. The biostratigraphic results from the here described acritarch microflora further illustrates the limitations of the lithostratigraphic approach and support the emerging question on the practicability of the classic regional stratigraphic subdivision. Interestingly, no rock record was hitherto known in the TDS from the post mid-Cambrian until the early Carboniferous. Post mid-Cambrian to early Ordovician rocks—as indicated by the here presented study—from other Saxo-Thuringian areas close to the TDS are generally very rare and concluded from only one problematic report: sandstones from a no more existing outcrop about 60 km to the Southwest (outside TDS, near Borna close to Leipzig), delivered few trace fossils (Cruziana semiplicata, Rusophycus isp., Skolithos isp.). Originally, C. semiplicata was interpreted as to indicate late Cambrian age by Freyer (1981), but, today it is generally accepted that the biostratigraphic occurrence of this ichnospecies is late Cambrian to Early Ordovician (Jensen et al. 2011), but rather early Ordovician in this special palaeogeographic part of Gondwana (pers. comm. to the third author by J.-A. GamezVintaned). Next Gondwanan mid-Cambrian and/or early Ordovician deposits in the Saxo-Thuringian zone are located distinctly more distant in the Thuringian Slate Mountain and the Frankenwald Forest (more than 180 km southwest), as well as in upper Lusatia (about 150 km southeast). For major parts of Saxo-Thuringia a depositional gap is postulated for the late Cambrian, e.g., by Linnemann et al. (2007). The here newly described Furongian to earliest Ordovician palynomorphs provide new insights into the duration of this gap in the TDS: either, the post mid-Cambrian deposition started again quite earlier as hitherto assumed (already in the earliest Ordovician) or the suggested gap is much shorter or/and was not as permanent as hitherto thought. This gap is similar to the gap between mid-upper Cambrian and lower Ordovician material in the Ossa–Morena Zone (Southern Spain; Liñán et al. 2002; Gutiérrez-Marco et al. 2002; Perejón et al. 2004) Due to the lithological character of the investigated sequences, of missing of any facies indication for significant

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depositional interruption, and further of taking into consideration the depositional character in regional scale, then the latter interpretation of a rather discontinuous sedimentation in the Late Cambrian to early Ordovician seems to be most plausible. Comparing the here presented results with data from palaeogeographically close regions of the peri-Gondwanan Mediterranean realm, as Spain, southern France and Italy (Sardinia), it can now be stated that deposition has not abandoned by the end of the mid-Cambrian, but has taken place—at least occasionally—over large areas also in the Upper Cambrian to early Ordovician interval with a pattern record similar to Ossa–Morena Zone in Spain. This is indicated by several, but, patchy preserved Cambrian sedimentary deposits in southwestern Europe and now also in the closely related, stratigraphically correlatable, and today northernmost situated area of the Mediterranean realm, the Torgau–Doberlug Syncline. Acknowledgements  Many thanks goes to the Geological Survey of Brandenburg (LBGR) and especially to M. Göthel for the allowance to and the help in investigation of drilling cores. This research was supported by the project PROGRES Q45 of the Ministry of Education, Youth and Sports of Czech Republic (support of O.F.).

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Affiliations Abubaker Atnisha1 · Oldřich Fatka2 · Olaf Elicki1 * Abubaker Atnisha [email protected]; Abu‑[email protected]‑freiberg.de

1

Oldřich Fatka [email protected]

2

Olaf Elicki [email protected]‑freiberg.de

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Department of Palaeontology, Geological Institute, TU Bergakademie Freiberg, Bernhard‑von‑Cotta Street 2, 09599 Freiberg, Germany



Institute of Geology and Palaeontology, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic