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Germany) and Its Bearing on the Tectonostratigraphic History of the Saxothuringian Domain

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Germany) and Its Bearing on the Tectonostratigraphic History of the Saxothuringian Domain Pala¨ontol Z (2014) 88:239–262 DOI 10.1007/s12542-013-0195-z RESEARCH PAPER A new lowermost middle Cambrian (Series 3, Stage 5) faunule from Saxony (Germany) and its bearing on the tectonostratigraphic history of the Saxothuringian domain Gerd Geyer • Bernd Buschmann • Olaf Elicki Received: 11 February 2013 / Accepted: 18 July 2013 / Published online: 10 August 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The core of borehole 1209/78 west of Dober- Middle Cambrian fauna known from the Saxothuringian lug–Kirchhain and south of Herzberg in the Torgau– domain and reconfirm the palaeogeographic position in the Doberlug Syncline records an atypical lower part of the Perigondwanan segment. The lithological differences of the Tro¨bitz Formation with thin limestone horizons. These fossiliferous cores from those of the typical Tro¨bitz For- limestone layers include the remains of a low to moderately mation and the recorded high-energy conditions indicate diverse fauna with the trilobites Protolenus (Hupeolenus) high-frequency sea-level changes suggesting that this part bergstroemi n. sp., Cambrunicornia saxonica n. sp., of the succession may be a late stage of the subglobally Ornamentaspis? aff. todraensis Geyer 1990a, Calodiscus? recognizable eustatic sea-level fluctuations at the traditional n. sp., the remains of two undetermined olenelloid? and Lower–Middle Cambrian boundary interval. paradoxidid? species, at least two brachiopods (Tremato- bolus, undetermined acrotretoid), and one hyolith. The Keywords Cambrian Á Trilobita Á Brachiopoda Á fauna clearly suggests a position in the lower Agdzian stage Biostratigraphy Á Sea-level fluctuations Á of the West Gondwana chronostratigraphic scheme and Saxo-Thuringian Zone Á Germany correlation with the lowermost to lower Middle Cambrian strata in regions such as the Moroccan Atlas ranges and Kurzfassung Bohrkerne der westlich von Doberlug–Kir- northern Spain, so the assemblages represent the oldest chhain und su¨dlich von Herzberg in der Torgau–Doberlug– Synkline niedergebrachten Bohrung 1209/78 zeigen einen atypisch ausgebildeten unteren Teil der Tro¨bitz-Formation & G. Geyer ( ) mit du¨nnen Kalkstein-Horizonten. Diese Kalkstein-Lagen Institut fu¨r Geographie und Geologie, Lehrstuhl fu¨r Geodynamik und Geomaterialforschung, Bayerische Julius-Maximilians- beinhalten eine gering bis mittelstark diverse Fauna mit den Universita¨tWu¨rzburg, Am Hubland, 97074 Wu¨rzburg, Germany Trilobiten Protolenus (Hupeolenus) bergstroemi n. sp., e-mail: [email protected] Cambrunicornia saxonica n. sp., Ornamentaspis? aff. to- draensis Geyer 1990, Calodiscus? n. sp., Resten von zwei G. Geyer Department of Earth Sciences (Palaeobiology), unbestimmbaren Arten vermutlich olenelloider und para- Uppsala University, Villava¨gen 16, doxidider Trilobiten, mindestens zwei Brachiopoden (Tre- 752 36 Uppsala, Sweden matobolus, ein nicht pra¨zise bestimmbarer Acrotretide) sowie einem Hyolithen-Operculum. Die Fauna belegt eine B. Buschmann Á O. Elicki Institut fu¨r Geologie, TU Bergakademie Freiberg, stratigraphische Position im unteren Agdzium der fu¨r West- Bernhard-von-Cotta-Straße 2, 09599 Freiberg, Germany Gondwana gu¨ltigen chronostratigraphischen Gliederung e-mail: [email protected] und korreliert mit Schichten des untersten bis unteren Mit- O. Elicki telkambrium in Regionen wie den marokkanischen Atlas- e-mail: [email protected] Ketten und Nord-Spanien. Damit repra¨sentieren die Verge- sellschaftungen die a¨ltesten mittelkambrischen Faunen, die B. Buschmann Erz & Stein GbR, Hof am Alten Fernweg, Talstraße 29, aus dem Saxothuringikum bekannt geworden sind. 09627 Bobritzsch, Germany Sie besta¨tigen ebenso die pala¨ogeographische Position 123 240 G. Geyer et al. im Perigondwana-Segment. Die lithologischen Unterschiede relatively narrow stratigraphic interval of mid Middle der fossilfu¨hrenden Schichten zur typischen Ausbildung der Cambrian age (early Caesaraugustan) (Geyer et al. 2008; Tro¨bitz-Formation und die dokumentierten hochenergetis- Elicki and Geyer 2010). chen Ablagerungsbedingungen lassen hochfrequente Meer- Unfortunately, the transition from Lower to Middle esspiegelschwankungen in diesem Teil des Profils vermuten Cambrian strata is unknown. This led to the assumption und scheinen eine spa¨te Phase der subglobal nachweisbaren that a significant stratigraphic gap between the strata of the eustatischen Meeresspiegelschwankungen im traditionellen two series is present in this area, which leaves space for the U¨ bergangsbereich Unter-/Mittelkambrium abzubilden. assumption of a major hiatus synchronized with subglo- bally recognizable eustatic sea-level fall commonly sum- Schlu¨sselwo¨rter Kambrium Á Trilobita Á marized as the ‘‘Hawke Bay regression’’ (Palmer and Brachiopoda Á Biostratigraphie Á James 1980). The supposition of a major break in deposi- Meeresspiegelschwankungen Á Saxothuringikum Á tion starting well within the Early Cambrian would have Deutschland suggested a late transgression so that part of the lower Middle Cambrian would not be recorded by strata. How- ever, a newly identified faunal assemblage from the Tro¨bitz Introduction Formation in a drill core from west of Doberlug–Kirchhain and south of Herzberg (drill core 1209/78; Fig. 1), briefly Fossiliferous Cambrian rocks are rare in Central Europe reported in 2006 (Geyer and Buschmann 2006) and but fairly well preserved in Lusatia and northern Saxony, described in detail below, reduces this supposed hiatus Germany. Although the mode of preservation is quite dif- considerably. This fauna represents the lowermost Middle ferent between the two regions, the lithologies suggest a Cambrian lower Agdzian as recorded in areas with a nearly common depositional domain that also indicates a common complete record of the Lower–Middle Cambrian boundary faunal province with distinct signatures of the West Gon- interval (for example northern Spain and southern Mor- dwanan faunal realm. The Cambrian subsurface rocks of occo). Consequently, the presently recognized gap may the Delitzsch–Torgau–Doberlug Synclinorium in northern indeed be created by incomplete biostratigraphic data Saxony and adjacent areas do not represent a continuous rather than physical absence of strata. succession, because of subsequent tectonic displacement. Deposition during the Cambrian sedimentation starts after a stratigraphic and structural gap (Cadomian unconformity) with local conglomeratic debris flow deposits, followed by the Lower Cambrian composed mainly of shallow marine carbonates and minor siliciclastics with common calcimi- crobial biogenic carbonates. The Middle Cambrian gener- ally comprises siliciclastics with scarce carbonate intercalations. The Tro¨bitz Formation, dominated by quartzitic sandstones and alternating with micaceous claystones is early but not earliest Middle Cambrian (Cambrian Series 3 and Stage 5) in age as indicated by comparatively rich fossil assemblages with trilobites, inarticulate brachiopods, and hyoliths (Schmidt 1944; Sdzuy 1957a, b, 1970). The trilobites indicate a strati- graphic level corresponding to the middle to upper Agdzian sensu Geyer and Landing (2004) (=Leonian in the Iberian regional scheme; Sdzuy et al. 1999). The overlying Deli- tzsch Formation consists of quartzarenitic sandstones alternating with claystones. As in the Tro¨bitz Formation, Fig. 1 Distribution of Hercynian Massifs and selected structural units the faunas are dominated by trilobites, inarticulate bra- in present-day central and western Europe (modified from Franke chiopods, and hyoliths. Two different stratigraphic levels 1989 and Buschmann et al. 2006). Abbreviations of structural units: can be distinguished. The older level has an early Middle AF Alpine front, AM Armorican Massif, BM Bohemian Massif, Cambrian age equivalent to the younger fauna of the MGCH mid-German Crystalline High, RH Rheno-Hercynian Zone, ST Saxo-Thuringian Zone, TB Tepla´–Barrandian Zone, TDS Torgau– Tro¨bitz Formation. A younger fauna with trilobites, bra- Doberlug Syncline, TESZ Teiseyre-Tornquist Line forming the chiopods, and helcionelloid molluscs characterizes a northern border of the Trans-European Suture Zone 123 A new lowermost middle Cambrian 241 Geology and Cambrian stratigraphy Cambrian formations known thus far can be interpreted of the Delitzsch–Torgau–Doberlug Synclinorium either as because of a gap in the drilled rocks or as a true hiatus because the studied core profiles provided either The Delitzsch–Torgau–Doberlug Synclinorium consists of exclusively Lower Cambrian or Middle Cambrian strata. two synclines, known as the Torgau–Doberlug Syncline Some authors suggested ‘‘Sardic’’ tectonic deformation (TDS) and the Delitzsch Syncline (Figs. 1, 2). The TDS is (Brause 1969); this can be rejected on the basis of current a subsurface structural unit of Ediacaran and Palaeozoic information. Apparent gaps between the Middle Cambrian rocks in the Saxo-Thuringian Zone covered by up to 200 m units are most likely to be because of the contemporary of Cenozoic strata. The pre-Cenozoic rocks have been exposure situation. The total thickness of Cambrian strata explored by use of drill holes reaching depths of up to in the TDS is estimated at up to 1,500? m. 1,200 m. This pre-Cenozoic succession comprises Ediac- Deposition during the Cambrian started after a strati- aran, Lower and Middle Cambrian strata. In central parts of graphic and structural gap termed the Cadomian uncon- the TDS Vise´an rocks are present (Buschmann et al. 1995, formity (Buschmann et al. 2006;
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