We here present a synopsis of the litho- and biostratigraphy of the Middle Jurassic Sengenthal Formation (Lower Bajocian, Discites Zone to Lower Oxfordian, Cordatum Zone) in the section Polsingen-Ursheim (Nördlinger Ries, Bavaria). The ammonite biostratigraphy, based on bed-by-bed collections from three excavation pits, is correlated with the microfauna (ostracods, foraminifera) from the nearby drillcore VB Polsingen-Ursheim. Our results are compared with literature data from other regions. The distribution of ostracods confirms the zonation for the Middle Jurassic of Southern Germany (Franz et al. 2014a; Ohmert 2004) when correlated with the ammonite biostratigraphy of the Nördlingen Ries area (Dietze & Dietl 2006; Dietze et al. 2002, 2007). This positive correlation could be underlined by the presence of seven biostratigraphically valuable species of foraminifera. The synoptical analysis of the three fossil groups leads to a more detailed subdivision of the Sengenthal Formation and to a more precise correlation.
The Sengenthal Formation (Zeiss 1977; Franz et al. 2014b) has been studied in detail several times during the last decade especially in respect to its ammonite fauna (Arp 2001; Callomon et al. 1987; Dietze & Dietl 2006; Dietze et al. 2002, 2007). Data concerning the microfauna have been published by Ziegler (1959), Munk (1978, 1993) and Franz et al. (2014a).
In the present paper the biostratigraphical subdivision of the Sengenthal Formation by ammonites, ostracods and foraminifera is described synoptically for the first time.
In 2012 we could study the Sengenthal Formation in Ursheim (northeastern part of the Ries impact crater) in a completely cored drill section. In the years 2010 to 2013 the first author investigated the greatest part of the formation exposed in three excavation pits.
Abbreviations : BAB = Bundesautobahn (Highway), GK = Geologische Karte (geological map), TK = Topographische Karte (topographical map), SEM = scanning electron microscope, VB = Versuchsbohrung (test boring).
2. Location and geological overview
Polsingen-Ursheim is a small village close to the northeastern margin of the Ries impact crater (TK and GK 25 of Bavaria, map sheet 7030 Wolferstadt; Fig. 1). The geology to the west of Ursheim is composed of sediments of the Tertiary Ries Crater Lake, to the north neighboured by a mosaic of allochthonous and parautochthonous megablocks from the Eisensandstein, Sengenthal, Dietfurt and Arzberg formations. In the eastern part of the village, outside of the crater, the bedrocks are built by Upper Jurassic limestones and marlstones (Dietfurt and Arzberg formations), partially overlain by allochthonous blocks of the Middle and Upper Jurassic up to several hundred square meters of size.
2. Stratigraphy of the Sengenthal Formation
The Sengenthal Formation consists of calcarenites and sandy mudstones in its lower part (Weiße-Laber Subformation), followed by a several meters thick alternation of iron oolitic marlstones and limestones (Berching Subformation). These are overlain by dark mudstones of the Winnberg Subformation, with a layer of sandy, glauconitic marlstone (Sachsendorf horizon) on top (Franz et al. 2014b).
In the following we use the traditional names for the members ‘Wedelsandstein’, ‘Humphriesi-Oolith’, ‘Bifurcaten-Oolith’, ‘Parkinsonien-Oolith’, ‘Varians-Oolith’, ‘Macrocephalen-Oolith’ and ‘Ornatenton’ (see Dietze et al. 2007: 107). These informal names are helpful for a pragmatic subdivision, but are also used for synchronous beds in other formations of the Braunjura Group (Middle Jurassic).
2.2. Core drilling
The test boring VB Ursheim has been brought down in 2012 in order to improve the public drinking water supply. It was located about 1 km southeast to the village (r 44 06 858, h 54 22 628). The 127 m deep boring sunk through the following set of strata:
2.3. Excavation pits in 2010/2011 and 2013
In the years 2010/2011 and 2013 three big fermenters for the production of biogas were constructed in the northern part of Ursheim (Fig. 2). The section in Fig. 3 could be composed from three parts that were exposed in these excavation pits. The basal part of the section could be reconstructed on the base of a number of photographs, kindly provided by the foundation expert. These pictures showed clearly, that the sequence of strata may vary substantially within a short distance. The different detail sections overlap one another so that the complete section could be reconstructed reliably.
The pits are situated in an isolated block in the transitional zone of the crater margin to the undisturbed Jurassic bedrocks of the southwestern Franconian Alb. In the third excavation pit (2013) the strata suddenly bent steeply downwards in a southward direction (towards the crater) and disappeared under the pit bottom.
In the following the section of the Sengenthal Formation is described top down; the strata have been numbered in the opposite direction:
Above the ‘Varians-Oolith’, the topmost part of the insitu sequence, there were yellow-beige oolitic rock fragments with big, dark brown ooids and rare fragments of Macrocephalites macrocephalus, which could be assigned to the ‚Macrocephalen-Oolith’ [bed 11].
‘Varians - Oolith’ (in-situ bedded: 0.4–0.45 m; only the lower part of this bed was preserved [bed 10]):
— 0.3 m Fe-oolitic marly limestone [bed 10b], varying in colours from carmine to brown and grey blue. Numerous Fe-ooids are arranged in clouds, brachiopods are frequent. The ammonites are often covered by a yellow-beige stromatolite-like crust. From the bed we got: Oraniceras wuerttembergicum, O. gyrumbilicum; from its bottom: Procerites laeviplex (Pl. 8, Figs. 3, 4), Oraniceras wuerttembergicum (Pl. 8, Figs. 1, 2) und O. gyrumbilicum (Pl. 8, Figs. 4, 5).
— 0.1–0.13 m Fe-oolitic clay marl [bed 10a]; no ammonites found.
‘Parkinsonien - Oolith’ (about 0.9 m [bed 9]):
Strongly weathered, predominantly red series of Fe-oolitic marly limestones, towards its base decreasing carbonaceous.
— 0.2 m Fe-oolitic marly limestone [bed 9d] with very rare brachiopods. From here we got one badly preserved fragment of Parkinsonia [„Gonolkites”] convergens (not figured).
— Fe-oolitic bedding joint.
— About 0.15 m red Fe-oolitic marly limestone [bed 9c]; Parkinsonia sp.
— 0.2–0.3 m carmine, Fe-oolitic limestone with densely packed ooids [bed 9b], splitting up to irregular small layers (0.03–0.1 m thick). These yielded: Parkinsonia pseudoparkinsoni (Pl. 6, Figs. 3, 6) and P. clapense (Pl. 7, Figs. 2, 3). A Strigoceras truellei (Pl. 7, Fig. 1), found by the late G. Schairer during the fieldwork for his diploma thesis in Ursheim, also comes from this part of the section, according to attached rock particles.
— About 0.3 m reddish-beige, strongly Fe-oolitic, crumbly marly limestone [bed 9a]. From the top of this bed we got: Parkinsonia rarecostata (Pl. 6, Figs. 1, 2) and Garantiana ipfensis (Pl. 6, Figs. 4, 5). From the lower part: Garantiana Wetzeli (Pl. 5, Figs. 11, 12); from the basis Prorsisphinctes pseudomartinsi (Pl. 5, Fig. 10).
‘Bifurcaten - Oolith’ (0.6–0.7 m [bed 8])
— 0.05–0.1 m thick layer of flat nodules of Fe-oolitic, light beige, marly limestone [bed 8b]: Garantiana suevica (Pl. 5, Figs. 3, 4).
— 0.4–0.5 m Fe-oolitic, yellow-beige marl with two to three layers of about 0.05 m thick flat layers of marly limestone [bed 8a]. According to the attached rock the Caumontisphinctes rota (Pl. 5, Figs. 1–2), which was found in the excavated material, comes from this part of the section.
‘Humphriesi - Oolith’ (2.5–2.6 m [bed 7])
Intercalation of Fe-oolitic, hard marly limestone beds (mostly 0.1–0.2 m thick) and as a rule a little thinner clay marl layers. The thicknesses of the layers in this sequence vary laterally within short distances. The three lowermost, fine Fe-oolitic marly limestone beds [beds 7a–c] are blue grey when unweathered; the upper marly limestone beds are predominantly brown/beige and also fine Fe-oolitic:
— A very fossiliferous, 0.25 m thick layer of weakly cemented, predominantly brown clay marl (with numerous bivalves, brachiopods and belemnites), with densely packed, small Fe-ooids, about 1–1.1 m above the top of this sequence [between beds 7e and 7f], yielded several specimens of Itinsaites (Pl. 3, Figs. 3, 4, 9, 10). We found only fragments and an inner whorl of the macroconch genus Stephanoceras, undeterminable to the species level (Pl. 3, Figs. 5, 6).
— The exact position of the bed with a monospecific accumulation of the brachiopod Loboidothyris perovalis (Pl. 4) could not be identified during the description of the section. In the excavated material — the layers partially were still linked together — this bed was found close to the above mentioned marls. This is why we assume that the brachiopod bed was situated close to the bed with Itinsaites [presumably beds 7d–f].
— The exact position of the chondroceratids (Pl. 3, Figs. 11–16) could not be located during the description of the section. These small ammonites were frequently found in an easily recognizable bed, but also firmly attached to the hardground on top of the bed. According to the rock composition, this layer should be two or three beds below the Itinsaites bed [bed 7c or 7d].
‘Wedelsandstein’ [beds 4–6]:
— [bed 6] In the wall of the fermenter built in 2013 the Fe-oolitic facies was underlain by 0.45 m grey blue clay [bed 6c], the uppermost 0.1 m passing over in a brownish grey. Here and there in the section these characteristic dark grey blue clays begin already higher in the section, replacing the brown-beige, Fe-oolitic marl layers between the marly limestone beds. Beneath it lies a fine Fe-oolitic marly limestone bed (0.1 m), breaking characteristically smooth [bed 6b]. The fresh bed is grey, brown when weathered. Several fragmentary preserved Dorsetensia (D. subtecta: Pl. 3, Figs. 7, 8) may come from bed 6b according to the attached rock fragments. In SW Germany Dorsetensia normally appears in somewhat older beds than Chondroceras.
Downwards follow grey blue clays again (about 0.4 m [bed 6a]). The photographs from the year 2010 show that bed 6 first wedges out in the upper part (bed 6c), some meters further also in the lower part (bed 6a). Finally it was replaced completely by brown marls.
— Bed 5 begins with a 0.3 m thick extremely hard, reddish Fe-oolitic limestone bed [bed 5c], present all over the exposed wall. Beneath the following, about 0.1 m thick marl layer [bed 5b] lies another hard, 0.1–0.2 m thick, brown to red Fe-oolitic limestone bed [bed 5a], which is also present throughout.
— Bed 4 consists of 0.4–0.6 m thick brownish marly limestones with intercalation of single, not constantly present hard beds. The specimens of Pseudoshirbuirnia stephani (Pl. 1, Figs. 1, 3), which were found in the excavated material, presumably come from one of these beds according to the rock composition. The specimen of Sonninia aff. strigoceroides (Pl. 3, Figs. 1, 2), when compared with its occurrences in other localities, must come from younger beds than Ps. stephani. Therefore, S. aff. strigoceroides, which was embedded in a beige, marly matrix, most presumably comes from the upper part of bed 4; however, bed 5b cannot be ruled out.
— Bed 3: The thickest hard limestone bed in the whole pit (0.45–0.7 m) varies from brown to red [bed 3b]. It is underlain by mostly reddish, here and there dark grey marls (ca. 0.1 m) [bed 3a].
— Bed 2: It is underlain by a bright red, Fe-oolitic sequence of beds (about 1.2 m), the uppermost part of which (0.3– 0.5 m [bed 2c]) as well as its base (ca. 0.3 m [bed 2a]) are developed as massive limestone beds. The middle part (0.4–0.6 m [bed 2b]) has a higher clay content and is less hard, with a 0.1 m thick hard bed intercalated in its upper part. The following ammonites were found in bed 2 from the excavated material: Pseudoshirbuirnia oechslei (Pl. 1, Figs. 2, 4), Sonninia adicra (Pl. 2, Figs. 1, 2) and a big Shirbuirnia gingensis (Pl. 2, Figs. 3, 4).
Bed 1: at the base up to 0.5 m of a grey-black, obviously clayey layer were exposed. No fossils could be assigned to this clay.
3.1. Material and methods
As far as possible the ammonites were collected bedby-bed. Specimens from the excavated material have been used for stratigraphical interpretation only when attached rock allowed it undoubtedly.
The originals illustrated on Pls. 1–13 are stored in the collection of the ‘Landesamt für Geologie, Rohstoffe und Bergbau in the Regierungspräsidium Freiburg, Albertstr. 5, 79104 Freiburg im Breisgau, Germany’, except for the Strigoceras truellei (Pl. 7, Fig. 1), which is stored in the ‘Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Str. 10, 80333 München, Germany’.
For the investigation of the microfauna we took 40 samples (two or three samples per meter) from the drill core VB Ursheim from 73.00 m (Middle Oxfordian) down to 90.50 m (Upper Aalenian). From each sample 0.5 kg was dried, disaggregated with hydrogen peroxide (H2O2) and subsequently washed through a 0.1 mm sieve. After drying the residues were divided into three fractions: >0.315 mm, 0.315–0.20 mm and 0.2–0.15 mm. The picking of the residues and the study of the microfauna was carried out using a binocular microscope. In the iron oolitic facies the number of microfossils in a given volume of rock is more or less ‘diluted’ by the ooid content. In order to obtain representative results, we looked through the whole residue, except for the finest fraction (0.15–0.20 mm), from which we investigated three selection trays. For the photographs of the ostracods and foraminifera we used the SEM.
The slides are stored in the collection of the Landesamt für Geologie, Rohstoffe und Bergbau in the Regierungspräsidium Freiburg, the figured specimens are stored under nos. Em 711–Em 791.
The 40 samples yielded a total of 1461 ostracods, with a maximum of 122 resp. 115 specimens per sample in the clays of the Weiße-Laber Subformation (‘Wedelsandstein’). For semi-quantitative analysis of the composition of the ostracod fauna single valves were counted as 0.5, resulting in a total of 1130 individuals. The number of foraminifera amounts to >3500; small (juvenile) specimens have not been picked quantitatively.
All over the studied section the ostracods are partly badly and/or fragmentary preserved or partly covered by remnants of rock. For this reason we were not able to figure all the index and the accompanying species, even though they could be reliably determined.
3.2. Short remarks on the ammonite faunas
Family Sonniniidae Buckman, 1892
Surprisingly the section yielded some sonniniids. Until now only few specimens of sonniniids had been found in the vicinity of Westhausen (BAB 7; Dietze et al. 2005), from the Ries area and the neighbouring Franconian Alb.
— Genus Pseudoshirbuirnia Dietze, Callomon, Schweigert & Chandler, 2005
The very rare species Pseudoshirbuirnia oechslei Dietze et al., 2005 (Pl. 1, Figs. 2, 4) was until now only recorded from the Middle Swabian Alb, the Wutach area and Alsace (Dietze et al. 2005, 2012). The fragmentary specimen figured in this paper is the first record of this species in the Ries area and the (southwestern) Franconian Alb. The same can be said for Pseudoshirbuirnia stephani (Buckman, 1883), which we figure in a typical specimen (Pl. 1, Figs. 1, 3). Ps. stephani is showing a rounded ventral side, a rounded umbilical edge and a highly oval cross section. In contrast the whorl section of the species Ps. oechslei is fastigate, its umbilical angle is sharp as well as its venter. Moreover, the latter species appears in little older strata.
— Genus Shirbuirnia Buckman, 1910
A big, badly preserved specimen (Pl. 2, Figs. 3–4) can be assigned to Shirbuirnia gingensis (Waagen, 1867). Dietze et al. (2005) published similar ammonites from the eastern Swabian Alb as Sh. gingensis α-form. S. gingensis sensu Dietze et al. (2005) with its very complex suture line bears close, but unexplained relationships to the genus Fissilobiceras Buckman, 1919.
— Genus Sonninia Bayle, 1879
A small ammonite bearing long spines on the inner whorls adjacent to the umbilical wall (Pl. 2, Figs. 1–2) belongs to the very variable group of Sonninia adicra (Waagen, 1867) [S. adicra var. berckhemeri ex Dorn sp., see Dietze et al. 2005: fig. 5]. A slightly corroded internal mold, found loose in the excavated material (Pl. 3, Figs. 1–2) can be assigned to S. aff. strigoceroides Dorn, 1935. In grazing light a faint row of papillae can be recognized in the outer third of the whorl flank. Dorn (1935) published a greater number of morphologically similar specimens from the northern Franconian Alb under different names.
— Genus Dorsetensia Buckman, 1892
In addition to the figured specimen (Pl. 3, Figs. 7, 8) two further whorl fragments of the easily recognizable species Dorsetensia subtecta Buckman, 1892 were found.
Family Sphaeroceratidae Buckman, 1920
— Genus Chondroceras Mascke, 1907
The species Chondroceras polypleurum Westermann, 1956 (Pl. 3, Figs. 11, 12), C. gerzense Westermann, 1956 (Pl. 3, Figs. 15–16) und C. multicostatum Westermann, 1956 (Pl. 3, Figs. 13, 14) could be proven. Numerous specimens collected bed-by-bed from the gervillii/cycloides horizon of the western Swabian Alb have been described by Dietze et al. (2015). For a detailed discussion of the genus Chondroceras see Westermann (1956).
Family Stephanoceratidae Neumayr, 1875
Subfamily Stephanoceratinae Neumayr, 1875
— Genera Stephanoceras Waagen, 1869 and Itinsaites McLearn, 1927
Only a few fragments and a nucleus of a macroconch of Stephanoceras (= Stephanoceras sp.; Pl. 3, Figs. 5–6), not identifiable to the species level, were found, together with several specimens of the genus Itinsaites, the microconch counterpart of the genus Stephanoceras (Ohmert et al. 1995). The two figured specimens are assigned to Itinsaites Quenstedti Roché, 1939 (Pl. 3, Figs. 3, 4, 9, 10). The identification of the numerous, partly very similar and even synonymous morphospecies ( Westermann 1954) is as difficult as for the genus Chondroceras.
Subfamily Garantianinae Wetzel, 1937
— Genus Garantiana Mascke, 1907
The morphospecies Garantiana suevica Wetzel, 1911 (Pl. 5, Figs. 3, 4), G. subgaranti Wetzel, 1911 (Pl. 5, Figs. 8–9) and G. aff. platyrryma (Buckman, 1921) (Pl. 5, Figs. 5–7) are closely related and represent only morphological variants of the genus Garantiana within a short time span (Dietze et al. 2000). Garantiana Wetzeli Trauth, 1923 (Pl. 5, Figs. 11, 12) is a morphological and stratigraphical transient form from the G. subgaranti Wetzel/G. garantiana (D'Orbigny) group to G. ipfensis Dietze et al., 2002 (Pl. 6, Figs. 4, 5). Following Dietze et al. (2007) we refuse the use of the genus Paragarantiana Gauthier, 2003 for Garantiana longidoides (Gauthier et al., 2000) and closely related forms. The morphological differences are insufficient for the erection of a separate genus Paragarantiana.
Family Parkinsoniidae Buckman, 1920
— Genus Parkinsonia Bayle, 1878
In addition to some fragments of older parkinsoniids a well preserved, only slightly compressed Parkinsonia rarecostata (Buckman, 1881) (Pl. 6, Figs. 1, 2) from the Acris Zone was recovered. In comparison to the P. arietis/acris/rarecostata group the finely ribbed and involute P. clapense Maubeuge, 1951 (Pl. 7, Figs. 2, 3) and the also finely ribbed P. pseudoparkinsoni Wetzel, 1911 (Pl. 6, Figs. 3, 6) are younger species in the family tree of the parkinsoniids that ranges up to the Bathonian.
— Genus Caumontisphinctes Buckman, 1920
The different species of this genus are difficult to distinguish and interconnected by numerous transitions (Dietl 1980). Our specimen can be assigned to the morphospecies Caumontisphinctes rota (Bentz, 1924) according to Bentz (1924, pl. 8, figs. 2a–b).
Family Perisphinctidae Steinmann, 1890
— Genus Prorsisphinctes Buckman, 1924
Despite its fragmentary preservation the big Prorsisphinctes pseudomartinsi (Siemiradzki, 1899) is distinctive (Dietze et al. 2002).
— Genus Procerites Buckman, 1898
The complete internal mold of a phragmocone of a Procerites laeviplex (Quenstedt, 1887) still exhibits the beginning of the body chamber.
Family Strigoceratidae Buckman, 1924
— Genus Strigoceras Buckman, 1924
The specimen of Strigoceras truellei (D'Orbigny, 1845) shows the distinctive inflated whorl section and the three deeply countersunk spiral furrows (Schweigert et al. 2007).
The obtained 1461 ostracods represent 177 species, belonging to 60 genera, not taking into account the indeterminable specimens. For the following coarse description of the faunal assemblages it should be kept in mind that the number of specimens is very low in the upper Bajocian, upper Bathonian and Lower Callovian.
In the Upper Aalenian (in the lower half of the ‘Disciteston’) only 10 specimens were found, representing the species Merocythere ovalis Plumhoff, 1963, Camptocythere cf. lincolnensis Bate, 1963, Procytheridea cf. teteimene Dilger, 1963, and Cytheropterina sp. The scarcity of ostracods does not allow any further interpretation. Moreover, the description of the Aalenian fauna is beyond the scope of this paper.
The Lower Bajocian assemblages as a whole (702 specimens) are dominated by the genus Praeschuleridea Bate, 1963, accompanied by the genera Kinkelinella Martin, 1960, Progonocythere Sylvester-Bradley, 1948, Eocytheridea Bate, 1963, Dolocythere Mertens, 1956, and the family Cytherellidae Sars, 1866.
In the following we list the taxa found in this part of the section in order of frequency [number of specimens in brackets]:
Discites Zone (4 samples):
Praeschuleridea ventriosa Plumhoff, 1963 , Praesch. sp. (smooth) , Praesch. sp. (punctate) , Kinkelinella sp. , K. (Ektyphocythere) cf. levata Ohmert, 2004 , K. sp. B Ohmert, 2004 , K. sp. A Ohmert, 2004 , Eocytheridea aff. carinata Bate, 1964 , Progonocythere sp. , Acrocythere sp. , Dolocythere maculosa Bate, 1963 , D. tuberculata Luppold, 2012 , D. sp. , Cytheropterina sp., , cf. Aphelocythere ? pygmaea Plumhoff, 1963 , Monoceratina cf. ungulina Triebel & Bartenstein, 1938 , Merocythere sp. , single findings of: Procytheridea cf. teteimene Dilger, 1963, Cytheropteron sp., ? Paracypris sp. D Oertli, 1963, Asciocythere sp., Procytheropteron sp., Schuleridea sp., Caytonidea sp., Fuhrbergiella sp.; additionally 37 Gen. et sp. indet.
Ovale—Laeviuscula zones (7 samples)
Praeschuleridea sp. (smooth) , Praesch. sp. (punctate) , Praesch. ventriosa Plumhoff, 1963 , Praesch. decorata Bate, 1968 , Dolocythere tuberculata Luppold, 2012 , Pleurocythere cf. laticosta Braun, 1958 , Pleurocythere laticosta Braun, 1958 , Fuhrbergiella (Praef.) horrida bicostata Brand & Malz, 1962, 1962 , Procytheridea cf. teteimene Dilger, 1963 , Eocytheridea cf. lacunosa Bate, 1963 , Eocyth. aff. carinata Bate, 1964 , Eocyth. ? acuta Bate, 1964 , Eocyth. cf. erugata Bate, 1964 , Praeschuleridea ornata Bate, 1963 , Praesch. sp. , Cytherella ascia incurvata Braun, 1958 , Progonocythere cf. triangulata Braun, 1958 , Prog. sp. , Prog. cf. ampla (Terquem, 1885) , Homocytheridea aff. cylindrica Bate, 1963 , Cytheropterina cribra (Fischer, 1962) , Cyth. cf. bicuneata (Braun) in Dilger, 1963 , Cytherella sp. , C. callosa ampla Braun, 1958 , Kinkelinella sp., , K. (Ekt.) triangula (Brand, 1961) , K. cf. malzi (Dépèche, 1973) , ? Procytheropteron trematon Dilger, 1963 , Paracypris bajociana Bate, 1963 (3), ? Systenocythere cf. exilofasciata Bate, 1963 (3), Syst. sp. , Cytherelloidea cadomensis Bizon, 1960 , single findings of: Clithrocytheridea vallata Braun, 1958, Eucytherura sp., Fuhrbergiella (Praef.) favosa Plumhoff, 1963, Isobythocypris sp., Oculocytheropteron sp., Polycope sp., Procytherura cf. reticulata Brand, 1990, Renicytherura sp., Schuleridea sp., Southcavea sp., additionally 26 Gen. et sp. indet.
Sauzei Zone (1 sample):
Palaeocytheridea blaszykina Franz et al., 2009 , Rutlandella sp. , R. transversiplicata Bate & Coleman, 1975 , Systenocythere perforata (Braun, 1958) , Fuhrbergiella (Praef.) sauzei Brand & Malz, 1962, 1962 , Procytherura cf. reticulata Brand, 1990 , Proc. cf. celtica Ainsworth, 1986 , Proc. cf. jordani Brand, 1990 , Praeschuleridea plana (Braun, 1958) , Praesch. sp. (smooth) , single findings of: Eocytheridea sp., Macrocypris sp., Paracypris bajociana Bate, 1963, Parac. sp., ? Plumhoffia sp., additionally 9 Gen et. sp. indet.
Humphriesianum Zone (4 samples):
Tethysia bathonica Sheppard in Brand, 1990 , ? Bythocypris sp. , Pleurocythere cf. regularis Triebel, 1951 , Bythocypris sp. , Fuhrbergiella (Fuhrb.) transversiplicata transversiplicata Brand & Malz, 1962, 1962 , Isobythocypris sp. , Procytheropteron trematon Dilger, 1963 , Palaeocytheridea blaszykina Franz et al., 2009 , Patellacythere paravulsa tenuis Brand, 1990 , Paracypris sp. , Fuhrbergiella (Praef.) horrida horrida Brand & Malz, 1962, 1962 , Glyptocythere regulariformis Brand & Malz, 1962, 1962 , ? Monoceratina sp. , Pontocyprella sp. , Procytherura sp.1 , single findings of Eucytherura sp., Procytherura sp. 2 and ? Pseudomacrocypris sp.; additionally 15 Gen et sp. indet.
In the Upper Bajocian (44 specimens) the genera Pleurocythere Triebel, 1951 and to a lesser extent Praeschuleridea Bate, 1963 are dominant.
Niortense—Parkinsoni zones (2 samples):
Pleurocythere regularis Triebel, 1951 , Praeschuleridea sp. , Tethysia bathonica Sheppard in Brand, 1990 , Wellandia sp. , Homocytheridea posteriohumilis (Blaszyk, 1967) , Homocytheridea triangulata Brand, 1990 , Cytheropteron ? infrasaxonicum Brand, 1990 , ? Ektyphocythere sp., single findings of Polycope sp., Patellacythere paravulsa tenuis Brand, 1990, ? Aphelocythere sp., Fuhrbergiella (Fuhrb.) projecta Brand & Malz, 1962, 1962, Fuhrbergiella (Fuhrb.) transversiplicata minuta Brand & Malz, 1962, 1962, Southcavea cf. concentrica Permyakova, 1973, Procytherura sp., Blaszykina pulcherrima Brand, 1990, Procytheropteron sp., ? Procytherura sp., additionally 4 Gen et sp. indet.
The Lower Bathonian ostracod assemblage (169) is characterized by the presence of the genera Glyptocythere Brand & Malz, 1962, 1962, Pleurocythere Triebel, 1951 and Cytheropteron Sars, 1866, whereas in the Upper Bathonian (22 specimens) the genus Praeschuleridea Bate, 1963 is dominant again.
Zigzag Zone (6 samples):
Procytheropteron aff. gramanni Brand, 1990 , Glyptocythere tuberosa Brand & Malz, 1962, 1962 , Gl. obtusa Lutze, 1966 , Gl. comes Brand & Malz, 1962, 1966 , Gl. similis Brand & Malz, 1962, 1966 , Gl. cf. tuberosa Brand & Malz, 1962, 1962 , Gl. polita Bate, 1965 , Gl. reticulata Brand & Malz, 1962, 1966 , Gl. sp. , Pleurocythere connexa Triebel, 1951 , Pl. favosa Triebel, 1951 , Pl. impar Triebel, 1951 , Pl. richteri Triebel, 1951 , Pl. sp. , Fuhrbergiella (Fuhrb.) transversiplicata minuta Brand & Malz, 1962, 1962 , F. (F.) gigantea gigantea Brand & Malz, 1962, 1962 , F. sp. , Palaeocytheridea carinilia (Sylvester-Bradley, 1948) , Palaeocyth. aff. blaszykina Franz et al. 2009 , Morkhovenicythereis polita Brand, 1990 , Eucytherura rectodorsalis Blaszyk, 1967 , Tethysia bathonica Sheppard in Brand, 1990 , Cytheropteron tenuis Blaszyk, 1967 , C. spinosum Lyubimova, 1955 , Wellandia trituberosa Brand, 1990 , Polycope sp. , Isobythocypris sp. , Oligocythereis capreolata Sheppard in Brand, 1990 , Blaszykina convexa (Blaszyk, 1967) , Bl. pulcherrima Brand, 1990 , Renicytherura cf. parairregularis Brand, 1990 , R. angulocostata (Knitter, 1983) , R. sp. , Procytherura sp. , Pr. ovaliformis Brand, 1990 , Tropacythere verrucosa (Blaszyk, 1967) , Paracypris bajociana Bate, 1963 , P. sp. , single findings of Praeschuleridea sp., ? Infracytheropteron sp., Fissocythere sp. Bythoceratina scrobiculata (Triebel & Bartenstein, 1938), B. separata Brand, 1990, Pontocyprella subaureola Sheppard in Brand, 1990, Cytherella limpida Blaszyk, 1967, Patellacythere paravulsa paravulsa Brand, 1990; additionally 10 Gen et sp. indet.
Orbis Zone (1 sample):
Praeschuleridea subtrigona Jones & Sherborn, 1888 , Procytheropteron aff. gramanni Brand, 1990 , Palaeocytheridea carinilia (Sylvester-Bradley, 1948) , Neurocythere plena (Triebel, 1951) , single findings of Procytherura sp. 5, Renicytherura cf. parairregularis Brand, 1990, V. acostata Tesakova, 2002, Blaszykina convexa (Blaszyk, 1967), Bythocypris sp., Aphelocythere aff. hamata Plumhoff, 1963, Pleurocythere kurskensis Tesakova, 2009, and Wellandia mesojurassica Brand, 1990; additionally 2 Gen et sp. indet.
The Lower Callovian ostracod fauna (27 specimens) is dominated by the genera Neurocythere Whatley, 1970 and Tethysia Donze, 1975, followed in the Middle and Upper Callovian (96 specimens) by an assemblage with the dominant genera Neurocythere Whatley, 1970, Patellacythere Gründel & Kozur, 1971 and Bythoceratina Hornibrook, 1952, Vesticytherura Gründel, 1964, and Polycope Sars, 1866.
Herveyi Zone (1 sample):
Tethysia bathonica Sheppard in Brand, 1990 , Neurocythere cruciata cruciata (Triebel, 1951) , N. cruciata alata (Whatley, 1970) , Micropneumatocythere brendae Sheppard, 1978 , Bythocypris sp. , ? single findings of ? Monoceratina sp., Renicytherura angulocostata (Knitter, 1983), R. sp., Cytheropteron spinosum Lyubimova, 1955, Procytheropteron aff. gramanni Brand, 1990; additionally 1 Gen. et sp. indet.
Koenigi—Calloviense zones (3 samples):
Neurocythere cruciata intermedia (Lutze, 1960) , Patellacythere paravulsa paravulsa Brand, 1990 , Polycope sp. , Bythoceratina cf. stimulea (Schwager, 1866) , B. scrobiculata (Triebel & Bartenstein, 1938) , B. separata Brand, 1990 , Bairdia sp. , Vesticytherura sp. , V. sp. 1 , Bythocypris sp. , Macrocypris sp. , Eucytherura bicostata Ballent , single findings of Cytheropteron spinosum Lyubimova, 1955, Procytherura sp. and Cytherella fullonica Jones & Sherborn, 1888; additionally 5 Gen. et sp. indet.
In the very poor microfaunas of the Lower to Middle Oxfordian (56 specimens) the dominant genera are Vesticytherura Gründel, 1964, Polycope Sars, 1866, Platylophocythere Oertli, 1960, and Bythoceratina Hornibrook, 1952.
Cordatum — ? Plicatilis zones (7 samples):
Polycope sp. , Vesticytherura sp. , V. sp.1 , V. acostata Tesakova, 2002 , Platylophocythere hessi Oertli, 1960 , Bythoceratina stimulea (Schwager, 1866) , B. scrobiculata (Triebel & Bartenstein, 1938) , Neurocythere cruciata intermedia (Lutze, 1960) , N. dulcis (Lyubimova, 1955) , single findings of Patellacythere paravulsa paravulsa Brand, 1990, Pontocyprella sp., Praeschuleridea decorata Bate, 1968; additionally 7 Gen. et sp. indet.
Most of the 40 samples contained a rich benthonic foraminiferal fauna (Table 1) except for the three lowermost samples, which yielded some crinoid remains only. The spectrum of the foraminifera is dominated by calcareous forms, mainly Nodosariids. Agglutinated and miliolid taxa appear only in the upper half of the section studied.
The major part of the nodosariid taxa belong to the subfamily Lenticulininae Chapman, Parr & Collins, 1934, comprising the genera Marginulina D'Orbigny, 1826, Lenticulina Lamarck, 1804, Astacolus DE Montfort, 1808, Planularia Defrance, 1826, Palmula Lea, 1833, Vaginulina D'Orbigny, 1826, Saracenaria Defrance in De Blainville, 1824, and Citharina D'Orbigny in La Sagra. 1839. The remaining are mostly representatives of the genera Nodosaria Lamarck, 1812 and Dentalina Risso, 1826.
Taxonomical remarks on some fora-minifera:
— Planularia eugenii (Terquem, 1863). It is questionable whether this Early Jurassic species is identical with the closely related Planularia semiinvoluta ( Terquem, 1869) and Planularia subinvoluta (Terquem, 1869), described from Upper Bajocian sediments of Fontoy. For reasons of conventional taxonomy and comparability with the literature this name was maintained. Astacolus pseudoradiata Frentzen, 1941 might be identical as well.
— Astacolus volubilis Dain, 1958. There is a close morphological relationship between this species and Subhercynella parkinsoniana Bartenstein & Luppold, 2005 from the uppermost Bajocian of NW Germany. Differences concern the umbilical region and the sutures, but further comparative investigations are indicated. Stratigraphical distribution: Bajocian and Bathonian of Germany and Poland (Bielecka & Styk 1969; Munk 1978; Blank 1990).
— Subhercynella arachne (Kopik, 1969). Middle Jurassic foraminifera formerly referred to Cristellaria tricarinella Reuss, 1863 from the Cretaceous or Cristellaria polymorpha Terquem, 1870 from the Bajocian were revised by Kopik (1969) as Lenticulina (Astacolus) polymorpha arachne n. ssp. Bartenstein & Luppold (2005) pointed out, that this morphotype differs essentially from other Middle Jurassic lenticulinids, and therefore should be treated as a distinct species rather than a subspecies of Lenticulina polymorpha. They referred it to the genus Subhercynella Bartenstein, 2000.
— Lenticulina helios (Terquem, 1870). Starting in the Toarcian, the genus Lenticulina Lamarck, 1804 tends to produce morphotypes with a prominent umbilicus and radial ribs. Such specimens have been commonly referred to Lenticulina subalata (Reuss, 1854) from the Cretaceous, whereas Terquem (1870) described a very similar species from the Middle Jurassic. Lenticulina helios is most common between 86.45 m and 88.00 m in the section studied.
3.5. Further microfossil groups
Other components of the microfauna besides ostracods and foraminifera are echinoderm remains (crinoids, ophiurids, echinids, asterozoans and holothurians), bryozoa, gastropods, belemnite tentacle hooks and fish teeth.
The two samples between 88.95 m and 89.50 m contained exclusively skeletal remains of the crinoid species Chariocrinus wuerttembergicus (Oppel, 1856). Except for this two samples the section below 79.70 m was void of echinoderm remains. Gastropods are more abundant in the lower half of the sampled section. Fish teeth are present in most samples but more common above 77.00 m. Bryozoa were found between 77.33 m and 79.70 m only.
3.6. Remarks on the associated fauna
In the drill core the number of macrofaunal elements is to low for any kind of interpretation. In the excavation pits our primary focus was on ammonites, notes on the associated fauna are restricted to peculiar occurrences. Besides nectonic species (ammonites, belemnites) the iron oolites are often characterized by endo- and epibiontic faunas, rich in species and specimens (Franz 1986; Kästle 1990).
In the lowest part of the ‘Humphriesi-Oolith’ a hardground is developed, which is often the case in midjurassic iron oolites (Franz 1986). The rich fauna in the bed with Chondroceras in Ursheim is a colluviation of bivalves (Actinostreon marshi [Sowerby, 1814], ‘Ostrea’ eduliformis Schlotheim, 1820, Pseudolimea sp., Gresslya abducta [Phillips, 1829], Pholadomya), brachiopods (Loboidothyris), and belemnites (Megateuthis, Hibolithes). The chaoticly embedded and partly fragmented shells are densely overgrown by serpulids. In the ‘Varians-Oolith’ ammonite shells and other hard substrates are encrusted by stromatolites. All these observations indicate a shallow, high energy environment with repeated events of reworking. A few bigger bone fragments — presumably from marine reptiles — have been found in the ‘Parkinsonien-Oolith’.
Distribution of the foraminifera in the drillcore VB Ursheim. For abbreviations see Fig. 4; s = selten (rare, 1–3 specimens), ns = nicht selten (not rare, 4–10 specimens), h = häufig (frequent, 11–20 specimens), sh = sehr häufig (very frequent, >20 specimens). N.-G. = Niortense — Garantiana, Pa = Parkinsoni, Zigz.-Morr. = Zigzag — Morrisi, O = Orbis, H.-L. = Herveyi — Lamberti.
In some beds brachiopods are notably frequent, e.g. in Ursheim in the ‘Varians-Oolith’, in the ‘Bifurcaten-Oolith’ and in the ‘Humphriesi-Oolith’. The first author of this paper found a greater piece of such a brachiopod bed in the excavated material in Ursheim, which, according to its lithology, comes from the level with frequent Itinsaites. The sample (Pl. 4) exhibits 45 specimens of 40–45 mm long Loboidothyris perovalis (Sowerby, 1825) in an area of 30 × 20 cm; the bed thickness is only 6 cm.
Repeatedly in the geological record the fauna of single beds is monospecific or at least by far dominated by one species. Franz (1982, 1986) described examples from Middle Jurassic iron oolites with terebratulid and rhynchonellid brachiopods, bivalves (Catinula sp., Gryphaea calceolaeformis Schäfle, 1929), and serpulids. In most cases these layers reflect local or regional short-time specific living conditions. Some may also indicate the domination of pioneer species after the breakdown of the previously existing benthic fauna, presumably caused by storm or other catastrophic events.
3.7. Ecology of foraminifera and other microfauna
The mixed benthic foraminiferal fauna and the accompanying microfaunal elements in most samples are typical for shallow marine environments of normal salinity.
An important feature is the low species diversity and the absence of agglutinated and miliolid foraminifera as well as of the genus Spirillina in the samples below 81.50 m. The foraminiferal fauna in the lower part of the section is dominated by genera of the subfamily Lenticulininae. In these samples gastropods are more abundant. This might indicate rather shallow marine or regressive conditions, which corresponds to the lithofacies of oolitic marls and limestone beds between 79 m and 86 m in the section.
The samples between 76.93 m and 79.70 m contain a diverse foraminiferal fauna with a higher amount of agglutinated and miliolid taxa, in addition Spirillina and Epistomina, more echinoderms and bryozoans. This might suggest somewhat deeper and warmer conditions. Rotaliids (Epistomina) correlate with a lower Calcium carbonate content of the sediment (Seibold & Seibold 1960) and are more abundant in the Oxfordian of France, Switzerland and South Germany than in Boreal European regions (Groiss 1970).
The Middle Jurassic strata exposed during the construction of the biogas plant range from the Lower Bajocian to Lower Callovian. An overview of the Bajocian in SW Germany is given in Dietze et al. (2011).
— Discites Zone: The oldest Bajocian ammonite zone could not be proven reliably. Sonniniids with a wide umbilicus and spines on the inner whorls as the figured Sonninia adicra (Waagen, 1867) (Pl. 6, Figs. 1, 2) appear in South Germany from the Discites Zone up to the Laeviuscula Zone (Dietze et al. 2005). Sonniniids from the Discites Zone usually show a more subquadrate whorl section.
— Ovale Zone: This zone was only recorded by Pseudoshirbuirnia oechslei Dietze et al., 2005. At least a part of bed 2 belongs to the oechslei horizon, characterizing the younger part of the Ovale Zone, which was previously described from the Eastern Swabian Alb and the Wutach area (Dietze et al. 2005, 2012).
— Laeviuscula Zone: The Trigonalis Subzone is proven by specimens of Shirbuirnia gingensis (Waagen, 1867) and Pseudoshirbuirnia stephani (Buckman, 1883). The big Sh. gingensis comes from bed 2. Hence bed 2 belongs at least partly to the Trigonalis Subzone, which is represented in the eastern Swabian Alb by the adicra α and adicra β horizons (with Sh. gingensis and S. adicra; Dietze et al. 2005). Ps. stephani is eponymous and characteristic for the stephani horizon. The brownish calcareous marl layer, which yielded this species and which presumably comes from bed 4, belongs to this youngest faunal horizon of the Trigonalis Subzone.
The single specimen of a Sonninia aff. strigoceroides Dorn, 1935 does not allow us to assign it to the Laeviuscula Subzone or to the Sauzei Zone. Very similar sonniniids with an extremely narrow whorl section, a high keel and more or less distinctly visible lateral papillae appear in the transient region of both these zones (Dorn 1935: specimens from Oberleinleiter; Chandler et al. 2006, pl. 9, figs. 1a–b, pl. 10, figs. 1a, 2b); Dietze et al. 2009, Pl. 1, Figs. 1, 2).
— Sauzei Zone: As mentioned above, this zone might be present in Polsingen-Ursheim but could not be proven positively.
— Humphriesianum Zone: Dorsetensia subtecta Buckman, 1892 appears in the Pinguis Subzone as well as in the Romani Subzone (Dietze et al. 2011, 2013). Bed 6b, where our specimen supposedly came from, can be assigned to one of these subzones. The bed with Chondroceras polypleurum Westermann, 1956, C. gerzense Westermann, 1956 and C. multicostatum Westermann, 1956 (bed 7c or 7d) can be dated clearly to the base of the Humphriesianum Subzone (Dietze et al. 2013, 2015). The gervillii/cycloides horizon, characterized amongst others by the frequency of mostly small Chondroceras is now traceable in South Germany from the Upper Rhine Graben to the northwestern Ries area. The marl layer with stephanoceratids and frequent Itinsaites between beds 7e and 7f belongs also to the Humphriesianum Subzone, but is slightly younger than the gervillii/cycloides horizon.
— Niortense Zone: The Polygyralis Subzone could be proven by a loose specimen of Caumontisphinctes rota (Bentz, 1924) according to Dietl (1980). According to the adherent rock fragments this specimen comes from the middle or lower part of the ‘Bifurcaten-Oolith’.
— Garantiana Zone: Dietze et al. (2002) stated by means of several Garantiana spp. collected bed-by-bed, that the genus Garantiana is highly variable within a faunal horizon and that the several morphospecies of the genus can appear in several successive faunal horizons. Therefore, the specimens of Garantiana suevica Wetzel, 1911 and G. subgaranti Wetzel, 1911 only prove, that the upper part of the ‘Bifurcaten-Oolith’ can be dated in the Garantiana Subzone. The specimens of Prorsisphinctes pseudomartinsi (Siemiradzki, 1899) and G. Wetzeli Trauth, 1923 indicate that the basal part of the ‘Parkinsonien-Oolith’ belongs to the Tetragona Subzone.
— Parkinsoni Zone: Garantiana ipfensis Dietze et al., 2002 and Parkinsonia rarecostata Buckman, 1881 are diagnostic ammonites of the Acris Subzone (Dietze 2000, Dietze et al. 2002). The Truellei Subzone is proven by its index species Strigoceras truellei (D'Orbigny, 1845) (Pl. 7, Fig. 1), Parkinsonia pseudoparkinsoni Wetzel, 1911 (Pl. 6, Figs. 3, 6) and P. clapense Maubeuge, 1951 (Pl. 7, Figs. 2–3) (Dietze & Dietl 2006). We were not successful to verify the Bomfordi Subzone, probably present below the Convergens Subzone in the upper third of the ‘Parkinsonien-Oolith’ (Dietze & Dietl 2006).
— Zigzag Zone: The unfigured fragment of a Parkinsonia [“Gonolkites”] convergens (Buckman, 1925) indicates — as in the nearby Ipf area (Dietze & Dietl 2006) – that the uppermost bed of the ‘Parkinsonien-Oolith’ belongs to the Convergens Subzone of the Lower Bathonian. Hence, the lithostratigraphical and biostratigraphical boundaries do not coincide. The Macrescens Subzone is proven by specimens of Oraniceras wuerttembergicum (Oppel, 1857), O. gyrumbilicum (Quenstedt, 1886) and Procerites laeviplex (Quenstedt, 1887) in the composite beds of the ‘Varians-Oolith’ (Dietze & Dietl 2006).
Fragments of Macrocephalites macrocephalus (Schlotheim, 1813) in the weathered residuals of the ‘Macrocephalen-Oolith’ in the overburden indicate the early Koenigi Zone (Callomon et al. 1992).
About one third of the 177 ostracod species recorded in the Ursheim section (se Pls. 9–12) are stratigraphically useful. Their vertical distribution is shown in Table 2. Most of the index species according to Ohmert (2004) and Franz et al. (2014a) could be proven, except for those of the “Plana” and Primitiva ostracod zones.
Upper Aalenian — Lower Bajocian
— Pusilla ostracod Zone. The ostracod fauna of the uppermost Aalenian is very poor (total of 10 individuals in 3 samples). Camptocythere pusilla Triebel, 1950, index species of the Pusilla ostracod zone (Ohmert 2004) could not be found here nor in the lowermost Bajocian, the basal boundary of which is indicated by the first appearance of Kinkelinella (Ekt.) cf. levata Ohmert, 2004, ranging from 88.00 m to 86.45 m. The index species of the Levata ostracod Subzone is accompanied by Praeschuleridea ventriosa ventriosa Plumhoff, 1963 (unfigured), which persists a little higher up (86.0 m), and Dolocythere maculosa Bate, 1963 (unfigured), occurring in sample 87.50 m only.
— Triangula ostracod Zone. The ostracod fauna of the Weiße-Laber Subformation is characterized by Dolocythere tuberculata Luppold, 2012, the zonal index species Kinkelinella (Ekt.) triangula (Brand, 1961) and the subzonal index species Progonocythere triangulata Braun, 1958 and Fuhrbergiella (Praef.) horrida bicostata Brand & Malz, 1962, 1962. Pr. triangulata ranges from 86.25 to 85.05 m and F. (Praef.) horrida bicostata ranges from 84.60 to 83.70 m. The index species are accompanied by Pleurocythere laticosta Braun, 1958 (unfigured), Praeschuleridea ornata Bate, 1963, Cytherella callosa ampla Braun, 1958 (unfigured), and Cytherelloidea cadomensis Bizon, 1960. In the upper part of the Weiße-Laber Subformation, persisting up to the ‘Humphriesianum-Oolith’, we found several specimens of a transitional form of Pleurocythere laticosta Braun, 1958 to Pl. regularis Triebel, 1951. In our opinion this transitional form is closer to the latter species which lead us to the determination as Pleurocythere cf. regularis (Pl. 10, Fig. a).
— Sauzei ostracod Zone. Fuhrbergiella (Praef.) sauzei Brand & Malz, 1962, 1962 occurred only in sample 82.95–83.00 m, together with moderately preserved ? Clithrocytheridea aff. plana (Braun, 1958) (unfigured). We assigned this sample to the Sauzei Zone, because the identification of C. plana is somewhat doubtful. These two species are accompanied by Pleurocythere cf. regularis, Palaeocytheridea blaszykina Franz et al., 2009 and single representatives of several species of the small genera Procytherura, Plumhoffia and Rutlandella.
— ? Plana/Primitiva Ostracod zones. Neither index species could be proven. The overlying part of the section is characterized by the co-occurrence of Tethysia bathonica Sheppard in Brand, 1990, Pleurocythere cf. regularis Triebel, 1951, Palaeocytheridea blaszykina Franz et al., 2009, Fuhrbergiella (Fuhrb.) cf. transversiplicata Brand & Malz, 1962, 1962, Fuhrbergiella (Praef.) horrida horrida Brand & Malz, 1962, 1962, Patellacythere paravulsa tenuis Brand, 1990 (unfigured) and Rutlandella transversiplicata Bate & Coleman, 1975.
Vertical distribution of biostratigraphically valuable ostracods in the drillcore VB Ursheim.
s. = sauzei, p. = plena, c. = cruciata; for further abbreviations see Fig. 4.
Lower – Upper Bajocian
Lower — Upper Bajocian — Regularis Ostracod Zone. Besides the index species Pleurocythere regularis Triebel, 1951, which first appears in sample 80.90–80.95 m, the most significant species are Fuhrbergiella (Fuhrb.) transversiplicata minuta Brand & Malz, 1962, 1962, Blaszykina pulcherrima Brand, 1990 and Tethysia bathonica Sheppard in Brand, 1990.
— Connexa Ostracod Zone. The lower Bathonian ostracod assemblage is characterized by the index species Pleurocythere connexa Triebel, 1951 and other species of this genus, Pl. favosa Triebel, 1951 (unfigured), Pl. impar Triebel, 1951 (unfigured), Pl. richteri Triebel, 1951. Accompanying elements are several species of Glyptocythere as Gl. tuberosa Brand & Malz, 1962, 1962 (un figured) and Gl. obtusa Lutze, 1966 and Procytheropteron aff. gramanni Brand, 1990. The first appearance of Oligocythereis capreolata Sheppard in Brand, 1990 in sample 79.06–79.14 m defines the base of the Capreolata Subzone.
— Plena Ostracod Zone. Only sample 77.65–77.70 m can be assigned to this zone, indicated by the appearance of Neurocythere plena (Triebel, 1951) (unfigured). Pleurocythere connexa Triebel, 1951, Palaeocytheridea carinilia Franz et al., 2009 and Blaszykina convexa (Blaszyk, 1967) (unfigured) have their last occurrences here.
Lower — Middle Callovian
— Cruciata Ostracod Zone. At the base of the Callovian Neurocythere cruciata cruciata (Triebel, 1951) and N. cruciata alata (Whatley, 1970) (unfigured) appear, together with Micropneumatocythere brendae Sheppard, 1978. Tethysia bathonica Sheppard in Brand, 1990 is still frequent and has its last occurrence here.
— Intermedia Ostracod Zone. Besides the index species Neurocythere cruciata intermedia (Lutze, 1960) the most significant ostracods in this assemblage are Patellacythere paravulsa paravulsa Brand, 1990, Bythoceratina stimulea (Schwager, 1866) (unfigured), vesticytherurids and polycopids.
Upper Callovian — Middle Oxfordian
— Unnamed “Zone”. In this part of the section, comprising the upper part of the Sachsendorf horizon (the former ‘Glaukonitsandmergel’) and the upward following claystones, Platylophocythere hessi Oertli, 1960 appears new, Bythoceratina stimulea (Schwager, 1866) still persists, again accompanied by vesticytherurids and polycopids.
Most foraminiferal taxa encountered in the Ursheim section (see Pl. 13) have long ranges within the Jurassic. Only few species have a certain stratigraphical value. Astacolus volubilis Dain, 1958 ranges from the Bajocian to the Lower Bathonian of Germany and Poland (Bielecka & Styk 1969, 1981; Munk 1978), Palmula semiinvoluta (Terquem, 1870) occurs in the Upper Bajocian and Bathonian of Southwest Germany (Blank 1990). Subhercynella arachne (Kopik, 1969) ranges from the Bathonian to the Oxfordian. Lingulina franconica (Gümbel, 1862) and Epistomina mosquensis Uhlig, 1883 are mostly restricted to the Callovian and Oxfordian (Brand & Fahrion 1962; Klingler et al. 1962). Ophthalmidium strumosum (Gümbel, 1862) is a characteristic species of the Callovian to Kimmeridgian of Europe (Munk 1978; Shipp 1989).
In the Ursheim section Astacolus volubilis Dain, 1958 was present from 86.20 m to 80.90 m, Palmula semiinvoluta (Terquem, 1870) extended between 81.50 m and 84.60 m. Subhercynella arachne (Kopik, 1969) was found in most samples between 76.33 m and 79.70 m. Ophthalmidium strumosum (Gümbel, 1862) has a first occurrence at 77.40 m and extends to the top of the section. Epistomina mosquensis Uhlig, 1883 was frequent in all samples between 73.95 m and 75.50 m, whereas Lingulina franconica (Gümbel, 1862) was observed in two samples only (at 74.50–74.55 m and at 75.50–75.55 m).
The following species are also characteristic for the Bajocian to Oxfordian in Western Europe: Ammobaculites suprajurassicus (Schwager, 1865), Tristix acutangula (Reuss, 1863), Lingulina longiscata (Terquem, 1870), Planularia beierana (Gümbel, 1862), Planularia lanceolata (Schwager, 1865), Planularia pseudoparallela Seibold & Seibold, 1956, Citharina proxima (Terquem, 1867), Marginulina hirta Paalzow, 1922, Lenticulina Quenstedti (Gümbel, 1862), Saracenaria cornucopiae (Schwager, 1865), Saracenaria triquetra (Gümbel, 1862), Spirillina polygyrata Gümbel, 1862, and Spirillina tenuissima Gümbel, 1862.
4.4. Biostratigraphical correlation
The combination of biostratigraphy by macro- and microfauna allows us to define previously unknown zonal boundaries or to state some boundaries more precisely in the section studied (see Fig. 4):
The base of the Discites Zone could be defined in the middle of the ‘Disciteston’ only by the first appearance of Kinkelinella (Ekt.) cf. levata.
The Ovale Zone and the lower Laeviuscula Zone are proven by Pseudoshirbuirnia oechslei, Shirbuirnia gingensis and Pseudoshirbuirnia stephani on the one hand and the first occurrences of Kinkelinella (Ekt.) triangula and Progonocythere triangulata, which all appear in the peculiar red bed 2. In sample 86.12–86.14 m (~ bed 2a) Astacolus volubilis also appears first.
Fuhrbergiella (Praef.) horrida bicostata is characteristic for the upper Laeviuscula Zone (samples 84.55–84.60 to 83.70–83.75 m), presumably corresponding to beds 3–5. Palmula semiinvoluta, which ranges from sample 81.50– 81.55 m to 84.55–84.60 m (= bed 5 to the middle of bed 7), has its first occurrence here.
The Sauzei Zone could not be proven by ammonites. Fuhrbergiella (Praef.) sauzei, index ostracod of the Sauzei Ostracod Zone, according to Ohmert (2004) corresponding to the upper part of the Sauzei Ammonite Zone and the lowermost Humphriesianum Zone, could be found only in one sample (82.95–83.00 m). The Pinguis Subzone is proven by Dorsetensia subtecta in bed 6b, which seemingly is situated a little deeper in the section. As a consequence, the base of the Sauzei Ostracod Zone might be situated a little deeper or we must assume a hiatus.
Beds 7a–7i represent the Humphriesianum Zone, proven by the genera Chondroceras, Itinsaites and Stephanoceras, though not collected bed-by-bed. The index ostracods Schuleridea “plana” and Fuhrbergiella (Fuhrb.) primitiva could not be found in the corresponding part of the drillcore. The assemblage instead is characterized by Fuhrbergiella (Praef.) horrida horrida, Procytheropteron trematon — according to Brand & Malz, 1962 (1962) and Braun (1958) typical ostracods of the Humphriesianum Zone — and Pleurocythere cf. regularis. In sample 82.20–82.25 m Planularia eugenii, which is closely related to Planularia pseudoradiata, appears.
The Niortense to Parkinsoni zones (beds 8 and 9) are well documented by ammonites of the genera Caumontisphinctes, Garantiana, Parkinsonia, Strigoceras, which correlate well with the occurrence of Pleurocythere regularis together with Fuhrbergiella (Fuhrb.) projecta and Fuhrbergiella (Fuhrb.) transversiplicata transversiplicata in samples 80.55–80.60 to 80.90–80.95 m.
In sample 79.62–79.70 m (= bed 9d) Pleurocythere connexa, the index species of the Connexa Ostracod Zone, appears together with Subhercynella arachne. According to Franz et al. (2014a) Pl. connexa ranges from the base to the top of the Bathonian. The highly diverse ostracod fauna comprises, among others, the typical Bathonian species Blaszykina convexa, Fissocythere sp., Fuhrbergiella (F.) gigantea gigantea, F. (F.) transversiplicata minuta, Glyptocythere tuberosa, Gl. similis, Gl. comes, Pleurocythere favosa, Pl. impar, Pl. richteri, and Morkhovenicythereis polita.
The first appearance of Oligocythereis capreolata defines the base of the Capreolata Subzone, which corresponds to the Macrescens through the Tenuiplicatus subzones, thus confirming the results of Dietze & Dietl (2006) and Dietze et al. (2007).
The upward following part of the section was eroded in the excavation pits, so we can correlate it only on the base of ostracods and foraminifers from the drillcore.
Together with Neurocythere plena, the index ostracod of the Plena Ostracod Zone, Pleurocythere kurskensis and Praeschuleridea subtrigona appear in sample 77.65– 77.70 m. Subhercynella arachne is still present.
While Subhercynella arachne still persists in sample 77.33–77.40 m, Neurocythere cruciata cruciata and N. cruciata alata appear, accompanied by Micropneumatocythere brendae.
The assemblage with Neurocythere cruciata intermedia, Bythoceratina stimulea and Eucytherura bicostata ranges from 76.33 m to 77.0 m. At this level Subhercynella arachne has its last occurrence.
The yet unnamed ostracod zone above the Sachsendorf horizon (73.00–75.95 m), presumably belonging to the Transversarium Zone, is characterized by the co-occurrence of Platylophocythere hessi, Neurocythere dulcis and Bythoceratina stimulea, partly accompanied by Lingulina franconica (74.5–75.55 m) and Epistomina mosquensis (73.95–75.55 m).
5. Correlation with neighbouring areas
5.1. Lithostratigraphy and ammonites in the Sengenthal Formation
Zöllner (1946) described a section Hechlingen-Kapellenberg (ca. 1 km north of the Ursheim section) from the ‘Braunjura β’ [= Eisensandstein Formation] to the uppermost ‘Braunjura γ’ [= Wedelsandstein Formation]. Concerning lithology and thickness of the strata this section differs remarkably from the Ursheim section, so that a correlation is virtually impossible. Some 5–6 m thick yellow to yellowish-grey sandstones with single thin clay-layers of the upper ‘Braunjura β’ are overlain by 0.1 m calcareous sandstone, named ‘Grenzbank β/γ’ [boundary bed] by Zöllner (1946). Above follow 0.4 m clayey sands, overlain by a 0.15 m thick red calcareous marlbed with red clay marl lenses. Section-up follow ca. 2 m thick green, weathered yellow “clays” with concretions and “rattle stones”, in their lower fourth with a horizontally consistent “red layer”. The red beds may partly correlate to our characteristic red bed 2. The following 0.8 m thick alternation of dark clays, marls, calcareous sandstones and sands may eventually correspond in part with our beds 3 and 4. The top of the ‘Braunjura γ’ is built by 0.6 m thick yellowish-brown, calcareous sandstones with small ooids. These beds may partly correlate to our beds 4 and 5.
Some 600 m east of Hechlingen Schairer (1973) described a section from the ‘Braunjura β’ to the ‘Weißjura α’ — figured in Gall et al. (1977) and Schmidt-Kaler (1991). Hence, his observations are questionable concerning the partly abnormally small thicknesses as well as the bed sequence and its fossil content. Eventually the strata were strongly weathered and/or slidden; otherwise his descriptions of the Sengenthal Formation are difficult to interprete, especially because the succession of ammonites is confusing, namely the occurrence of Garantiana and Caumontisphinctes (Garantiana and Niortense zones) above fragments of parkinsoniids (Parkinsoni Zone) and directly below stephanoceratids (Humphriesianum Zone).
In the explanations of the geological map of Bavaria, sheet no. 6930 Heidenheim (Schmidt-Kaler, 1970) a section at the eastern outskirts of Heidenheim am Hahnenkamm, nearly 10 km north of Ursheim, first published by Wagner (1963), is reproduced. Therein, the calcareous marl (0.3 m) between the ‘Varians-Oolith’ and the ‘Parkinsonien-Oolith’ as well as the ‘Parkinsonien-Oolith’ (1.1 m) are slightly thicker, the ‘Bifurcaten-Oolith’ (1.25 m) notably thicker as the corresponding beds 10a–8 in Ursheim. Near Heidenheim, below the ‘Bifurcaten-Oolith’ follow several meters thick “Oolithkalke” [calcareous iron oolites], which at least partly can be correlated with bed 7 in Ursheim. The correlation of deeper parts of the section is difficult due to the short descriptions by Schmidt-Kaler (1970).
From a location near Erlbach (sheet Öttingen), at the northern Ries margin, Gerstlauer (1940) described the lower “Sowerbyi-Schichten” [= Wedelsandstein Formation] as similar to the Eisensandstein Formation. This corresponds well to the lithology of bed 2 in Ursheim. Above follow blueish-grey limestones with Sonninia crassispinata Buckman, 1892 and Dorsetensia liostraca Buckman, 1892 (Ursheim: beds 3–5), overlain by blue clays void of fossils (Ursheim: bed 6). The “Wedelsandstein- und Coronaten-Kalke” [‘Humphriesi-Oolith’] near Erlbach, Niederhofen and Hausen are very rich in fossils like the approximately correlatable bed 7 in Ursheim. In addition to several Stephanoceras spp. Gerstlauer (1940) mentioned a Witchellia sp. [= ?Dorsetensia sp.] and numerous belemnites, bivalves, gastropods, etc. The ‘Bifurcaten-Oolith’ was not exposed in the area of map sheet Öttingen. The ‘Parkinsonien-Oolith’, ‘Varians-Oolith’ and ‘Macrocephalen-Oolith’ near Erlbach and in its vicinity are similarly developed as in Ursheim (beds 9–11). The Sengenthal Formation as a whole in the region northwest of Öttingen corresponds largely with the one in Polsingen-Ursheim.
In the area of map sheet Wemding, situated southwest of Ursheim at the Ries margin, Weber (1941) could not describe a complete section. Due to the Ries impact there are only small blocks with Middle Jurasssic sediments exposed. But he found out that on the southwestern slope of the Wart as well as east and north of Wemding — in contrast to the Ries foreland (Bentz 1924) —, the red “Pectinidenbank” (Ursheim: bed 2) and the overlaying, irregularly composed, 0.4–0.65 m thick “Sowerbyibank” (Ursheim: beds 3–4) are amalgamated to a calcareous sandstone. Weber recovered in his so-called “Sowerbyibank” a fragment of a S. gingensis (Waagen, 1867) and a cast similar to “S. sowerbyi”, and slightly higher up in the section a Witchellia cf. laeviuscula (Sowerby, 1824) [ = ? Dorsetensia sp.], determined after Dorn (1935). Unfortunately he could not describe the section. From the Wart Weber (1964) described directly above the “Sowerbyi-Sandkalksteinbank” fossil-rich, hard, strongly oolitic limestones, corresponding with the lower ‘Braunjura δ’ of the Bopfingen area, with a fragment of a Stephanoceras (Ursheim: lower part of bed 6). Along the old road Wemding—Wolferstadt he observed “higher strata of the Braunjura δ of the Bopfingen area” (Ursheim: upper part of bed 6), 0.6 m thick “Coronaten-Schichten” with Teloceras blagdeni (Sowerby, 1818). He could neither prove the ‘Bifurcaten-Oolith’, ‘Parkinsonien-Oolith’, ‘Varians-Oolith’, and ‘Macrocephalen-Oolith’ (Ursheim: beds 9—11), which were recorded only as rubblestones.
For the correlation of the strata at the Hesselberg (northwest of the Ries) and at the Ipf (western Ries margin) we can refer to Gall et al. (1977) and Schmidt-Kaler (1991), where the Hechlingen section by Schairer (1963) is correlated with the Ipf and Hesselberg sections.
5.2. Ostracoda (Sengenthal Formation)
The microfauna (mainly foraminifera) of 31 cores from Middle Jurassic strata in Northern Bavaria were studied by Ziegler (1959). Concerning the Sengenthal Formation (‘Braunjura γ’– ‘Braunjura ζ’) he found no index ostracods in the Lower Bajocian. According to Ziegler (1959) Pleurocythere regularis Triebel, 1951 is indicative for the Niortense to Parkinsoni zones, Pl. connexa Triebel, 1951 is the index species of the Bathonian, Lophocythere (= Neurocythere) plena (Triebel, 1951) of the Aspidoides-Schichten (= Orbis Zone). The Lower and Middle Callovian is characterized by Neurocythere cruciata cruciata (Triebel, 1951) and N. cruc. franconica (Triebel, 1951).
Franz et al. (2014a) published the Bathonian and Lower Callovian ostracod fauna of the Röttingen section. There, the Bathonian ostracod fauna was very poor; this is why the index species for the Bathonian could not be proven. The Callovian could be documented by several specimens of subspecies of Neurocythere cruciata (Triebel, 1951) besides Micropneumatocythere brendae Sheppard, 1978, Vesticytherura acostata Tesakova, 2002, and others.
5.3. Foraminifera (Western Europe)
In NW Germany Bartenstein & Brand (1937) for the first time investigated extensively the foraminiferal fauna of the Middle and Upper Jurassic. Lutze (1960) described Callovian and Oxfordian microfaunas (foraminifera and ostracoda), Brand (1990) the foraminifera and ostracoda from an Upper Bathonian section near Hildesheim, NW Germany.
Stratigraphical investigations from South Germany were contributed by Frentzen (1941: Lower, Middle and Upper Jurassic of the Blumberg area, SW Germany), Seibold & Seibold (1953, 1960: Upper Jurassic of S Germany), Ziegler (1959: Middle Jurassic of Northern Bavaria), Groiss (1970: Oxfordian of the Franconian Alb), Munk (1978, 1993: Bajocian to Oxfordian of the Franconian Alb), Riegraf (1988; Callovian foraminifera from SW Germany), and Blank (1990: Bajocian to Callovian of the Swabian Alb).
In 1962, as a result of a consensus of German micropalaeontologists, commented range charts of stratigraphically important microfossils were published (Brand & Fahrion 1962; Klingler et al. 1962). Important index foraminifera of the Middle Jurassic of Northwest Germany are Frondicularia nodosaria [= longiscata] Terquem, 1870 for the Upper Bajocian, Lenticulina tricarinella (Reuss, 1863) for the Bathonian to Oxfordian, Frondicularia franconica Gümbel, 1862 and Epistomina mosquensis Uhlig, 1883 for the Callovian to Oxfordian.
From Great Britain essential stratigraphical investigations based on foraminifera include Cifelli (1959: Bathonian of England), Coleman (1982: Middle Jurassic of England), Gordon (1967, 1970: Middle Jurassic of England and Scotland), Barnard et al. (1981; Callovian to Oxfordian of England).
Morris & Coleman (1989) compiled range charts of stratigraphically important British Middle Jurassic foraminiferal species from the literature. Relevant species in common with those of the Ursheim section are Lingulina longiscata (Terquem, 1870), Lenticulina Quenstedti (Gümbel, 1862) and Lenticulina exgaleata Dieni, 1985 in the Bajocian and Bathonian. More restricted Bathonian markers are Lenticulina tricarinella (Reuss, 1863) [syn. Subhercynella arachne (Kopik, 1969)], Planularia eugenii (Terquem, 1863), Nodosaria ingens (Terquem, 1870) and some others. In the Callovian appear Frondicularia franconica Gümbel, 1862 and Saracenaria oxfordiana Tappan, 1958 [syn. Saracenaria triquetra Gümbel, 1862]. According to Shipp (1989) the Oxfordian and Kimmeridgian is characterized by Citharina serratocostata (Gümbel, 1862), Epistomina mosquensis Uhlig, 1883, Epistomina parastelligera (Hofker, 1954), Epistomina ornata (Roemer, 1841), Frondicularia nikitini Uhlig, 1883, Lenticulina subalata (Reuss, 1854) [syn. Lenticulina helios (Terquem, 1870)], Tristix triangularis Barnard, 1953 [syn. Tristix acutangula (Reuss, 1863)], Planularia beierana (Gümbel, 1862), and Ophthalmidium strumosum (Gümbel, 1862).
There are only few biostratigraphical data on Middle Jurassic foraminifera from France (Bizon 1958; Garrot et al. 1958; Wernli 1971). Wernli (1971) listed Ammobaculites coprolithiformis (Schwager, 1867), Lingulina nodosaria (Terquem, 1870) [related to Lingulina longiscata (Terquem, 1870)], Planularia eugenii (Terquem, 1863), Lenticulina Quenstedti (Gümbel, 1862), Lenticulina subalata (Reuss, 1854) [syn. Lenticulina helios ( Terquem, 1870)] and Vaginulina clathrata (Terquem, 1863) [related to Citharina proxima (Terquem, 1867)] from the Bajocian to Oxfordian, Lenticulina tricarinella (Reuss, 1863), Marginulina glabra D'Orbigny, 1826 [syn. Marginulina hirta Paalzow, 1922], Saracenaria cornucopiae ( Schwager, 1865), Vaginulina macilenta (Terquem, 1867) in the Bathonian to Oxfordian, and Epistomina mosquensis Uhlig, 1883 in the Oxfordian.
The Bathonian foraminifera from the Mecsek Mountains (South Hungary) studied by Görög (1995) possess several characteristic species in common with the Ursheim section and other West European localities, but there are more Tethyan elements and similarities to the Bathonian fauna of Portugal or Sicily.
When compared to foraminiferal faunas from the Bathonian and Callovian of Poland there are many similarities, suggesting a communication of the German and Polish basins, with a higher faunal exchange during the Callovian (Bielecka & Styk 1969, 1981).
The major part of the Sengenthal Formation was exposed in three excavation pits in the years 2011–2013 in Ursheim-Polsingen. The upper part of the formation, i.e., a part of the Bathonian and the Callovian, was missing by local erosion. At the same time, the drillcore VB Ursheim-Polsingen, below 73 m of Upper Jurassic sediments sunk through the complete Sengenthal Formation in a thickness of 13 m.
The ammonite collections from the excavation pits documented the Lower Bajocian Ovale, Laeviuscula and Humphriesianum Zones, the Upper Bajocian Niortense, Garantiana and Parkinsoni zones and the Lower Bathonian Zigzag Zone. The ostracod fauna from the drillcore, the relative richness of which may be due to its deep position below the reach of weathering, has proven the Kinkelinella levata Subzone of the Pusilla Zone, the Kinkelinella triangula Zone (with the Progonocythere triangulata and the Fuhrbergiella (Praef.) horrida bicostata subzones), the Fuhrbergiella (Praef.) sauzei Zone and the Pleurocythere regularis Zone in the Bajocian. In the Bathonian the Pleurocythere connexa and the Neurocythere plena zones could be documented. In the Callovian the Neurocythere cruciata cruciata and the N. cruciata intermedia zones could be proven.
From the surprisingly great number of species of foraminifera only seven seem to have a biostratigraphical value: Astacolus volubilis, Palmula semiinvoluta, Planularia eugenii, Subhercynella arachne, Lingulina franconica, Epistomina mosquensis, and Ophthalmidium strumosum.
Our results confirm the correlation of the well-established ammonite biostratigraphy of the Sengenthal Formation (Dietze & Dietl 2006, Dietze et al. 2007) with the ostracod zonations published by Ziegler (1959), Ohmert (2004) and Franz et al. (2014).
We thank D. Jung (LfU Bayern) for his cooperation in the description of the drillcore VB Ursheim and the permission to take samples from it. We gratefully acknowledge the permission for the publication of data from VB Ursheim, granted by H. Meyer, mayor of Ursheim. Our sincere thanks go to M. Ott (Polsingen-Ursheim), who allowed us to describe the sections of the excavation pits and to collect fossils. We also thank the engineering office igi Consult GmbH in Westheim (C. Früh, S. Niedermeyer) for providing the ground expertise and numerous photos, which helped us by the reconstruction of the lowermost part of the section. F. Rietze (Bopfingen) provided important ammonites; D. Pollerhoff (Schwieberdingen) helped with the description of the section. U. Menkveld-Gfeller (Bern) and M. Reich (Munich) transmitted the pdfs of the doctoral thesis Zöllner and the diploma thesis Schairer. For fruitful discussions and useful hints we thank F. Luppold (Hannover) and W. Ohmert (Britzingen). U. Thewalt (Gerstetten) and C. Schulbert (Erlangen) are thanked for taking the SEM photographs. Our warmest thanks go to A. Schill and S. Wendt for the thorough washing of the samples, J. Crocoll, G. Fischer, B. Schmücking and A. Ziller (all RP Freiburg, LGRB) for preparing the figures to a high quality. The referees A. Lord (London), B. L. Nikitenko (Moscow) and G. Schweigert (Stuttgart) are thanked for their thorough reviews and their suggestions for improvements of the manuscript.