Corresponding author: Gernot Arp ( garp@gwdg.de ) Academic editor: Alexander Nützel
© 2021 Gernot Arp, Sebastian Gropengießer, Christian Schulbert, Dietmar Jung, Andreas Reimer.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Arp G, Gropengießer S, Schulbert C, Jung D, Reimer A (2021) Biostratigraphy and sequence stratigraphy of the Toarcian Ludwigskanal section (Franconian Alb, Southern Germany). Zitteliana 95: 57-94. https://doi.org/10.3897/zitteliana.95.56222
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Extensive construction work at the canal cutting of the Ludwigskanal near Dörlbach, Franconian Alb, provided the opportunity to re-investigate a scientific-historical and biostratigraphically important reference section of the South-German Toarcian. The 16 m thick section, described bed by bed with respect to lithology and macrofossils, starts within the Upper Pliensbachian Amaltheenton Formation, covers the Toarcian Posidonienschiefer and Jurensismergel Formation, and ends in basal parts of the Opalinuston Formation. Carbonate contents are high in the Posidonienschiefer and successively decline within the Jurensismergel to basal parts of the Opalinuston. The high carbonate contents in the Posidonienschiefer are associated with comparatively low organic carbon contents. However, organic carbon contents normalized to the silicate fraction are similarily high if compared to other regions in Germany. Only the persistence of high organic carbon levels into middle parts of the Upper Toarcian differs from those of most regions in central Europe.
Ammonite biostratigraphy indicates a thickness of >9 m for the Upper Pliensbachian, 1.15–1.20 m for the Lower Toarcian, 5.04 m for the Upper Toarcian, and >0.5 m for the Lower Aalenian. Despite the low sediment thickness, all Toarcian ammonite zones and almost all subzones are present, except for major parts of the Tenuicostatum Zone and the Fallaciosum Subzone.
On the basis of discontinuities, condensed beds, and correlations with neighbouring sections in Southern Germany, a sequence stratigraphic interpretation is proposed for the Toarcian of this region: (i) The Posidonienschiefer Formation corresponds to one 3rd order T-R sequence, from the top of the Hawskerense Subzone to a fucoid bed at the top of the Variabilis Subzone, with a maximum flooding surface at the top of the Falciferum Zone. (ii) The Jurensismergel Formation exhibits two 3rd order T-R sequences: The first ranges from the basis of the Illustris Subzone (i.e., the Intra-Variabilis-Discontinuity) to the top of the Thouarsense Zone, with a maximum flooding surface within the Thouarsense Zone. The “belemnite battlefield” reflects a transgressive “ravinement surface” within the first Jurensismergel Sequence, not a maximum regression surface at its basis. The second sequence extents from the erosive basis of the Dispansum Zone to the top of the Aalensis Subzone, with a maximum flooding surface at the Pseudoradiosa-Aalensis Zone boundary. Finally, the Opalinuston starts with a new sequence at the basis of the Torulosum Subzone. Transgressive system tracts of these 3rd order T-R sequences are commonly phosphoritic, while some regressive system tracts show pyrite preservation of ammonites. The maximum regression surfaces at the basis of the Toarcian and within the Variabilis Zone reflect a significant submarine erosion and relief formation by seawater currents, while this effect is less pronounced at the basis of the Dispansum Zone and basis of the Torulosum Subzone (i.e., the boundary Jurensismergel-Opalinuston Formation).
Umfangreiche Bauarbeiten am Kanaleinschnitt des Ludwigskanals bei Dörlbach auf der Fränkischen Alb boten die Gelegenheit ein wissenschaftlich-historisch und biostratigraphisch wichtiges Referenzprofil des süddeutschen Toarciums neu zu untersuchen. Das 16 m mächtige Profil, dessen Lithologie und Makrofossilien Schicht für Schicht beschrieben werden, beginnt innerhalb der Amaltheenton-Formation des Oberpliensbachiums, umfasst die Posidonienschiefer- und Jurensismergel-Formationen des Toarciums und endet mit basalen Teilen der Opalinuston-Formation. Die Karbonatgehalte sind im Posidonienschiefer hoch und nehmen innerhalb des Jurensismergels sukzessive bis in basale Teile der Opalinuston-Formation ab. Die hohen Karbonatgehalte im Posidonienschiefer sind mit vergleichsweise niedrigen organischen Kohlenstoffgehalten verbunden. Die auf die Silikatfraktion normierten organischen Kohlenstoffgehalte sind jedoch im Vergleich zu anderen Regionen in Deutschland ähnlich hoch. Lediglich die anhaltend hohen organischen Kohlenstoffgehalte bis in den mittleren Teil des Obertoarciums unterscheiden sich von denen der meisten Regionen Mitteleuropas.
Biostratigraphisch verwertbare Ammoniten-Funde belegen eine Mächtigkeit von >9 m für das Obere Pliensbachium, 1.15–1.20 m für das Untere Toarcium, 5.04 m für das Obere Toarcium, und >0.5 m für das Untere Aalenium. Trotz der geringen Sedimentmächtigkeiten sind alle Ammoniten-Zonen und nahezu alle Subzonen nachweisbar, mit Ausnahme großer Teile der Tenuicostatum-Zone und der Fallaciosum-Subzone.
Auf Grundlage von Diskontinuitäten, kondensierten Horizonten und Korrelationen mit Nachbarprofilen in Süddeutschland wird eine sequenzstratigraphische Interpretation für das Toarcium dieser Region entwickelt: (i) Die Posidonienschiefer-Formation entspricht einer Sequenz dritter Ordnung, vom Top der Hawskerense-Subzone bis zu einem Fucoidenhorizont am Top der Variabilis-Subzone, mit einer maximalen Überflutung am Top der Falciferum-Zone. (ii) Die Jurensismergel-Formation weißt zwei Sequenzen dritter Ordnung auf: Die erste reicht von der Basis der Illustris-Subzone (d.h. der Intra-Variabilis-Diskontinuität) bis zum Top der Thouarsense-Zone. Das „Belemnitenschlachtfeld“ spiegelt einen transgressiven „Auswaschungshorizont“ innerhalb der ersten Jurensismergel-Sequenz wider, keinen Meeresspiegeltiefststand an ihrer Basis. Die zweite Sequenz reicht von der erosiven Basis der Dispansum-Zone bis zum Top der Aalensis-Subzone, mit einer maximalen Überflutung an der Grenze Pseudoradiosa-Aalensis Zone. Die Opalinuston-Formation beginnt schließlich mit einer neuen Sequenz an der Basis der Torulosum-Subzone. Transgressive Phasen dieser Sequenzen dritter Ordnung sind häufig phosphoritisch ausgebildet, während regressive Phasen eine Pyriterhaltung von Ammoniten aufzeigen. Die Meeresspiegeltiefststände nahe der Basis des Toarciums und innerhalb der Variabilis-Zone sind mit einer deutlichen submarinen Erosion und Reliefbildung durch grundberührende Meeresströmungen verbunden. Dieser Effekt ist an der Basis der Dispansum-Zone und Torulosum-Subzone (d.h. der Formationsgrenze Jurensismergel-Opalinuston) weniger stark ausgeprägt.
Ammonoidea, Jurensismergel, Lower Jurassic, Posidonienschiefer, sealevel changes, Southern Germany, stratigraphy
Ammonoidea, Jurensismergel, Unterer Jura, Posidonienschiefer, Meeresspiegel-Schwankungen, Süddeutschland, Stratigraphie
The Franconian Alb is a classical region of Jurassic geosciences in Europe, and specifically the area of Altdorf SE of Nürnberg has been of great importance in the early times of palaeontology (
However, the only contemporary description of the exposed strata was given by
Slope failure at the Ludwigskanal cutting near Dörlbach and following extensive construction activities re-exposed the section in 2010–2012, allowing a re-investigation of the complete succession from the middle part of the Amaltheenton, through the Posidonienschiefer and Jurensismergel, to the basis of the Opalinuston Formation (Fig.
The aim of the present study is to provide a detailed description of the lithologic succession and its macrofossils. The high-resolution biostratigraphy and sequence stratigraphy may form a basis for further investigations on seawater temperatures (δ18O of low-Mg calcite skeletons), seawater currents, sealevel changes, and causes for the persistence of the Toarcian Oceanic Anoxic Event (T-OAE;
Field images of the Ludwigskanal section and ammonites. A. Western section of the canal cutting, showing basal parts of the exposure, from the “Delta-Fossil Bed” to the basis of the Posidonienschiefer Formation. B. Eastern section of the canal cutting, showing the Amaltheenton, Posidonienschiefer, Jurensismergel, and basal parts of the Opalinuston Formation. C. Harpoceras falciferum (Sowerby), “Falciferum Shale”, bed 10, field image (specimen not recovered). D. Polished section of rock sample, from “Fucoid Bed” (bed 17), basal marl of Jurensismergel (bed 18) and “Belemnite Battlefield” (bed 19) to the “Main Phosphorite Bed” (bed 20).
The Ludwigskanal cutting is located in Southern Germany, Bavaria, approximately 20 km ESE of Nürnberg (Fig.
Geologically, the deep subsurface of the region is formed by high-grade metamorphics and plutonites of the Variscan basement (Moldanubian gneiss and granite). These basement rocks are overlain by a Mesozoic cover sequence starting with Triassic fluvial coarse siliciclastics of the Buntsandstein (63 m), Muschelkalk (45 m) and Keuper Group (270 m) (drilling Eschertshofen:
Fieldwork and sampling was carried out on 16 days between September 2010 and August 2014. Lithological descriptions are based on field observation and binocular observations on hand specimens, supplemented by 21 thin sections between 5 × 7.5 cm and 7.5 × 10 cm in size, and about 80 µm thick.
Total carbon (Ctot), nitrogen (Ntot), and sulfur (Stot) of bulk rock samples were analysed with a Euro EA 3000 Elemental Analyser (HEKAtech, Wegberg, Germany) applying 2,5-bis(5-tertbenzoxazol-2-yl)thiophene (BBOT) and atropine sulfate monohydrate (IVA Analysetechnik, Meerbusch, Germany) as reference material. Organic and carbonate carbon (Corg, Ccarb) contents were determined by a LECO RC612 (Leco, St. Joseph, MI, USA) multi-phase carbon and water analyser. For calibration, Leco synthetic carbon (1 and 4.98 carbon %) and Leco calcium carbonate (12 carbon %) standards were used. All analyses were performed as duplicates. Analytical accuracy of all analyses was better than 3%. The carbonate-free fraction was calculated from the total weight minus the CaCO3 and Corg content.
Biostratigraphy is based on approximetaly 425 determinable ammonites that were recovered in situ. Few additional ammonites recovered by private fossil collectors were taken into account. Ammonite determinations follow the systematic descriptions in
Repository: The material is stored in the Museum and Collection of the Geoscience Centre, University of Göttingen, under the numbers GZG.INV.45641–GZG.INV.45644 and GZG.INV.70496–GZG.INV.70650.
Data Availability Statement: All data used in this publication are stored on the Göttingen Research Online Data repository (https://doi.org/10.25625/8PLFNS).
Figure captions: unless otherwise noted, all specimen are coated by ammonium chloride prior to photography. Abbreviations: diameter (d), diameter of penultimate half whorl (di), umbilical width (u), whorl height (wh), whorl breadth (wb), primary ribs per half whorl (rb/2).
Informal bed names are given in quotation marks. From bottom to top:
Bed 1: >100 cm bluish-grey, well bedded claystone;
Bed 2: 0–15 cm “Septaria Bed”: grey marlstone concretions with mm-thick, calcite-cemented shrinkage cracks;
Bed 3: 25 cm bluish-grey, well bedded claystone with scattered cm-sized septarian concretions; ammonoids: at the top one juvenile Pleuroceras solare (Phillips);
Bed 4: 10 cm “Delta-Fossil Bed”: bluish-grey, fissile, calcareous claystone to argillaceous marl with abundant ammonoids, belemnites, echinoderm remains and bivalves; lower part of the bed with reworked bluish-grey marlstone concretions with borings and serpulid tubes; ammonoids: Pleuroceras spinatum (Bruguière); Amaltheus sp. (juvenile), Pleuroceras solare (Phillips) (within reworked concretions; Fig.
Bed 5: 800 cm bluish-grey, slightly miceous, fissile claystone with scattered small bivalves; 15 and 75 cm below top layers of flat-lenticular, grey siderite nodules; ammonoids: Pleuroceras spinatum (Bruguière) (0.8 m, 1.5 m, 2.0 m, 3.0 m, 5.5 m, 7.25 m and 7.5 m below top: Fig.
Bed 6: 0–1 cm reworked flat concretions composed of bluish-grey pyrite-rich argillaceous limestone, with corroded surfaces;
Bed 7: 5–15 cm “Laibstein I”: dark grey, laminated calcareous marl with coarse shell debris and one 15-cm-sized limestone concretion composed of laminated bituminous pellet packstone, with intercalated layers of coarse shell debris and fish scales; basis with reworked flat concretions from the Amaltheenton; ammonoids: Tiltoniceras antiquum (Wright) (1–2 cm above basis; and one juvenile specimen in middle part; Fig.
Bed 8: 15 cm “Laibstein II”: dark grey, laminated bituminous limestone concretions (pellet packstone) up to 50 cm width, with abundant mm-sized holoplanktonic gastropods; ammonoids: Cleviceras elegans (Sowerby) (Fig.
Bed 9: 5–6 cm “Fish Scale Bed”: dark grey, bituminous argillaceous fissile limestone composed of mollusc shell fragments and fish scales, with abundant belemnites; ammonoids: Dactylioceras sp. (upper bedding plane), Cleviceras cf. elegans. (lower bedding plane); other fossils: Meleagrinella cf. substriata (von Münster), Pseudomytiloides dubius (Sowerby), belemnites, ichthyosaur vertebra;
Bed 10: 10 cm “Falciferum Shale”: dark grey, laminated, bituminous marl; lower part with one dark grey, 8 × 12-cm-sized, poorly laminated bituminous limestone concretion (pellet packstone) with mollusk shell debris, few phosphatic vertebrate microfragments and abundant small Dactylioceras shells (spar filled); ammonids: Harpoceras falciferum (Sowerby) (middle part; Fig.
Bed 11: 3–4 cm grey, bituminous argillaceous fissile limestone with abundant fish scale and shell debris; fossils: few large (2-cm-sized) Meleagrinella cf. substriata (von Münster);
Bed 12: 25 cm “Dactylioceras Bed”: grey, bituminous limestone consisting of densely packed Meleagrinella shells and shell fragments, faecal pellets, and scarce phosphatic vertebrate microfragments; abundant sparite and micrite filled casts of Dactylioceras; relictic cross-stratification in the lower part of the bed; ammonoids: Dactylioceras athleticum (Simpson) (abundant throughout the bed; Fig.
Bed 13: 1–2 cm grey, bituminous argillaceous limestone consisting of densely packed Meleagrinella shells and scattered phosphatic vertebrate microfragments; fossils: Meleagrinella substriata (von Münster);
Bed 14: 10–12 cm “Monotis Bed”: bituminous limestone (lumachelle) consisting of densely packed Meleagrinella shells, faecal pellets, and scarce phosphatic vertebrate microfragments; ammonoids: Dactylioceras cf. athleticum (Simpson); other fossils: Meleagrinella substriata (von Münster), Pseudomytiloides dubius (Sowerby);
Bed 15: 40 cm “Bifrons Shale”: dark-grey, bituminous marl, laminated; with scattered shell debris in layers, scattered phosphatic scale and bone microfragments, abundant belemnites 26 cm and 38 cm below top; ammonoids: Hildoceras semipolitum Buckman (2 cm, 17 cm, 18 cm, and 22 cm below top; Fig.
Bed 16: 70 cm “Variabilis Shale”: dark-grey, laminated to well bedded, bituminous marl (lower 60 cm) to calcareous marl (top 10 cm) with scattered shell debris, rare phosphatic fish scale and bone microfragments; ammonoids compressed or as pyrite casts preserved, scattered pyrite nodules up to 3 cm in size; light-grey Chondrites horizons 5–6 cm and 18–19 cm below top; ammonoids: Denckmannia cf. rude (Simpson) (1 cm below top), Haugia jugosa (Sowerby) (3 cm below top; Fig.
Bed 17: 2 cm “Fucoid Bed”: grey to white-grey, bioturbated marl, slightly phosphoritic, with Chondrites burrows; with compressed and deformed phosphoritic casts of ammonoids; ammonoids: abundant Catacoeloceras raquinianum (d’Orbigny), Haugia variabilis (d’Orbigny), Phylloceras heterophyllum (Sowerby), Lytoceras cf. cornucopia (Young & Bird); other fossils: Pseudomytiloides dubius (Sowerby), Camptonectes subulatus (Münster);
Bed 18: 5 cm grey, well bedded calcareous marl; ammonoids: Pseudogrammoceras subregale (Pinna) (Fig.
Bed 19: 6 cm “Belemnite Battlefield”: grey, bituminous calcareous marl with abundant bivalve shell debris (Propeamussium), belemnite accumulation, and reworked phosphorite nodules; at the basis reworked plate-like, bored white-grey phosphorites nodules up to 2.5 × 5 × 10 cm in size; thin burrows; ammonoids: Lytoceras cf. cornucopia (Young & Bird), Pseudogrammoceras sp., lower bedding plane with Catacoeloceras raquinianum (d’Orbigny) (Fig.
Bed 20: 6–7 cm “Main Phosphorite Bed”: grey, marl to calcareous marl, poorly bedded, with abundant bivalve shell debris (Propeamussium) with white-grey phosphorite nodules up to 1 × 3 × 6 cm and abundant belemnites; Chondrites burrows; ammonoids: Lytoceras cornucopia (Young & Bird) (Fig.
Bed 21: 14–15 cm “Toarcensis Shale”: dark grey, well bedded, bituminous marl transected by numerous small branching burrows (Chondrites); abundant compressed ammonoids (solely Grammoceras) and bivalves (solely Pseudomytiloides); ammonoids: Grammoceras thouarsense (d’Orbigny) (Fig.
Bed 22: 5 cm “Belemnite accumulation”: grey, poorly stratified argillaceous marl full of belemnites (Dactyloteuthis); nubeculariid foraminifera on shell fragments and belemnites; one compressed Lytoceras shell fragment with stromatolithic crust at the top inside of the body chamber; one phosphorite nodule with microbialite-like corroded upper surface; locally small lenticular phosphorite nodules; basis with flat corroded phosphorites (11 × 7 × 1 cm in size) and double-sided-corroded belemnite rostra; ammonoids: Alocolytoceras cf. rugiferum (Pompeckj); other fossils: Liostrea erina (d’Orbigny) attached to belemnite rostra, Chladocrinus sp.;
Bed 23: 30 cm “Levesquei-Dispansum-Marl”: grey, poorly bedded marl rich in nubeculariid foraminifera, shell debris, and with small phosphorite nodules; abundant mid-sized and large compressed ammonites (top 12 cm and at 20–25 cm below top); deformed phosphorite casts of smaller ammonoids, rare pyrite casts;
ammonoids: Phlyseogrammoceras dispansum (Lycett) (12–20 cm and 20–25 cm below top; Fig.
Bed 24: 95 cm grey, well bedded argillaceous marl to marl with abundant shell microdebris; lower 60 cm rich in nubeculariid foraminifera; lower 45 cm with small marcasite nodules; 40–45 cm below top accumulation of phosphorite nodules and ammonites, 70 cm below top accumulation of compressed ammonites; ammonoids: Paradumortieria cf. tectiforme Elmi & Caloo-Fortier (20 cm, 25 cm, 40–45 cm, and 50 cm below top; Fig.
Bed 25: 2 cm grey, poorly bedded, argillaceous marl with shell microdebris and abundant ammonites (pyrite casts and marcasite-veneered imprints), abundant belemnites, and small phosphorite nodules; ammonoids: Cotteswoldia mactra (Dumortier) (Fig.
Bed 26: 50 cm grey, well bedded, argillaceous marl rich in shell microdebris of Bositra suessi, with scattered small branching burrows (Chondrites), scarce nubeculariid foraminifera, small pyrite nodules and pyrite ammonite casts; Bositra suessi pavement 32 cm below top; Pleydellia subcompta (Branco) (35 cm below top; Fig.
Bed 27: 5–10 cm grey (unweathered) to yellowish-brown (weathered), well bedded, calcareous claystone with scattered small branching burrows (Chondrites), minor shell microdebris, very few nubeculariid foraminifera, and very few echinoderm bioclasts; abundant small pyrite casts of ammonites, especially near the basis of the bed; ammonoids: Pleydellia subcompta (Branco), Pleydellia distans (Buckman) (Fig.
Bed 28: 80–85 cm grey, well bedded, calcareous claystone rich in shell microdebris of Bositra suessi and nubeculariid foraminifera; with scattered small pyrite nodules and pyrite ammonite casts; at the top accumulation of small pyritic ammonites (embedded in various orientation); Bositra suessi pavement 50 cm below top; ammonoids: Pleydellia subcompta (Branco) (1 cm below top), Pleydellia costulata (Zieten) (1 cm below top; Fig.
Bed 29: 10–12 cm grey, poorly bedded, calcareous marlstone with abundant nubeculariid foraminifera;
Bed 30: 30 cm grey, well bedded, marl to calcareous claystone rich in shell microdebris of Bositra suessi (Oppel) and nubeculariid foraminifera;
Bed 31: 2 cm grey (unweathered) to brownish-grey (weathered), poorly bedded calcareous claystone with abundant, partially aligned belemnites of the Hastites group;
Bed 32: 80 cm grey, well bedded, calcareous claystone rich in shell microdebris of Bositra suessi (Oppel); at 50 cm below top rich in nubeculariid foraminifera;
Bed 33: 2–3 cm grey (unweathered) to brownish-grey (weathered), poorly bedded calcareous claystone with few small phosphorite nodules, abundant belemnites and compressed ammonoids; one shell fragment of Lytoceras with a stromatolitic crust at the top inside of the body chamber; ammonoids: Cotteswoldia lotharingica (Branco) (Fig.
Bed 34: >50 cm grey (unweathered) to brownish-grey (weathered), well bedded clay;
The Amaltheenton Formation is characterized by low CaCO3 contents (2.5–3.3 wt%) as well as low Corg contents (0.8–1.0 wt%) (Table
The Posidonienschiefer Formation, however, shows a sudden and strong increase in CaCO3 to 94 wt% at its basis, followed by consistently high values (73–98 wt%) in the lower part of the formation (i.e. limestone and argillaceous limestone), with only the Falciferum Shale showing a lower value (45 wt%). Higher parts of Posidonienschiefer exhibit marl equivalent values around 50–65 wt% CaCO3, with only two intercalations of reduced CaCO3 content (35 wt%) in the upper third (Table
CaCO3 contents at the basis of the Jurensismergel Formation correspond to calcareous marl (65–71 wt%) and marl (44–53 wt%), then decrease to marls (37–62 wt%) and argillaceous marls (17–34 wt %). Near the top of the formation, one last bed of calcareous marl (66 wt%) is found. Increased Corg values (3.0 and 4.3 wt%) were found near basis (bed 18, “Belemnite Battlefield”, “Toarcensis Shale”), followed by low values of 1–2 wt% in middle and upper parts of the formation. Only two horizons, basis of bed 24 and bed 25, show slightly increased Corg contents (2.5 and 2.8 wt%). Finally, the Opalinuston Formation revealed CaCO3 contents only slightly lower than top parts of the Jurensismergel, and Corg as low as in the Amaltheenton (Table
The assignment of beds to specific formations of the Schwarzjura Group follows the definitions given in
The lower boundary of the Jurensismergel has previously been drawn at the top of the “Belemnite Battlefield”:
The biostratigraphic subdivision of the investigated section follows the standard scheme by
The first Pleuroceras solare of the investigated section has been found 5 cm below the “Delta-Fossil Bed” (bed 4), indicating the Apyrenum Subzone of the Spinatum Zone. Abundant specimens of this species were found enclosed within reworked concretions of the “Delta-Fossil Bed” (bed 4), together with rare Amauroceras ferrugineum (Fig.
The marl matrix of the “Delta-Fossil Bed” (bed 4) enclosing the reworked concretions already yielded compressed Pleuroceras spinatum with clear tubercles, while P. solare is absent. This suggests that the conglomeratic bed represents the base of the Hawskerense Subzone (sensu
The following top 8 m claystones of the Amaltheenton (bed 5) contain siderite concretions with typical morphotypes of Pleuroceras spinatum (strong ribs with clear tubercles, whorl section square; Fig.
Posidonienschiefer Formation starts with a clear discontinuity and Amaltheenton-derived intraclasts within the shell-debris-rich “Laibstein I” (bed 7). These laminated limestone concretions revealed a layer with several Tiltoniceras antiquum 2–3 cm above their basis (Fig.
The following “Laibstein II” (bed 8), with the abundant holoplanktic gastropod Coelodiscus minutus, comprises an ammonoid assemblage typical of the Elegans Subzone: Cleviceras exaratum (Fig.
Higher parts of the Falciferum Zone are less well documented at the Ludwigskanal section as well as in the whole region. One compressed specimen of Harpoceras falciferum (Fig.
The lower bedding plane of “Dactylioceras Bed” (bed 12) and the fish-scale-rich argillaceous limestone layer at its base (bed 11) exhibit poorly preserved specimen of Dactylioceras commune (Fig.
Between 18 and 38 cm above the basis of the “Bifrons Shale” (bed 15), the occurrence of compressed Hildoceras semipolitum (Fig.
The first appearance of Haugia sp. at the basis of bed 16 (“Variabilis Shale”), i.e. one compressed fragment at 40 cm above the “Monotis Bed”, indicated the lower boundary of the Variabilis Subzone, Upper Toarcian. Only a minor overlap of this genus with Hildoceras was observed at the Ludwigskanal/Dörlbach. Pyritized and compressed Catacoeloceras raquinianum (Fig.
One compressed Haugia jugosa 3 cm below top (Fig.
A change in the ammonoid assemblage, however, is evident for bed 18, i.e., the 5 cm calcareous marl below the “Belemnite Battlefield”: Pseudogrammoceras subregale (Pinna) (Fig.
The “Belemnite Battlefield” (bed 19) is rather poor in ammonoids. Catacoeloceras raquinianum (d’Orbigny) has been recovered at the lower bedding plane (Fig.
The following “Main Phosphorite Bed” (bed 20) has been assigned by Krumbeck (1943: p. 305) to the Thouarsense Zone because of findings of Grammoceras thouarsense in the neighbouring section Hausheim. At the Ludwigskanal/Dörlbach, this bed yielded a number of Lytoceras cornucopia (Fig.
Numerous, compressed Grammoceras cf. thouarsense (Fig.
The “belemnite accumulation” of bed 22 yielded, except for Alocolytoceras cf. rugiferum, no determinable ammonoids. The range of A. rugiferum is not well constrained, but shows a maximum abundance in the Dispansum Zone in northern and southwestern Germany (
First Phlyseogrammoceras dispansum (Fig.
At 11 cm below top of bed 23, first Dumortieria occur, specifically Dumortieria insignisimilis (Fig.
The top 4 cm of bed 23 finally show an ammonite accumulation with Dumortieria pseudoradiosa (Fig.
Bed 25 clearly forms a minor condensation with the enrichment of phosphorite nodules, ammonites and belemnites. Cotteswoldia mactra (Fig.
With a minor overlap with Cotteswoldia mactra, Cotteswoldia aalensis (Fig.
No Leioceras opalinum has been found in the Ludwigskanal/Dörlbach section. However, compressed Leioceras opalinum found in a drill core (highway viaduct Pilsach, unpublished observations) immediately above the equivalent of bed 33 suggests that the Toarcian-Aalenian boundary is located at the basis of bed 34.
Sequence stratigraphic interpretations require correlation and comparison of sections across the shelf with respect to discontinuities, facies trends, geometry and stacking patterns (e.g.,
This also applies to the South German Toarcian succession, because of low sedimentation rates and high distance to deltaic siliciclastic influx, no evident subaerial exposure surfaces, and (with respect to the Upper Toarcian) a limited number of sections with both, detailed sedimentological plus biostratigraphic observations. The following sequence stratigraphic interpretations, therefore, remain preliminary (Figs
A sequence stratigraphic framework, however, has been developed for the Toarcian of Northern Germany, based on a comprehensive analysis of drillings (sedimentology and gamma ray logs) covering the transition from marine to fluviodeltaic deposits of the NE-German Basin to fully marine deposits of the NW-German Basin (
For the Upper Toarcian of Southern Germany, no such detailed analysis exists, but important information can be derived from proximal sections near Regensburg, where minor coarse siliciclastic influx during regressive phases intercalate between fine-grained open-marine sediments with ammonoids (Fig.
The total duration of the Toarcian is about 8.5 Ma (
Only two stratigraphic gaps in the otherwise monotonous claystones of the Amaltheenton are evident: The first gap is located within higher parts of the formation. Here, the “Delta-Fossil Bed” (Fig.
The second gap is developed at the top of the Amaltheenton, where reworked nodules indicate an erosion at the Ludwigskanal (Fig.
Based on these observations, sediments of the Spinatum Zone in the Franconian Alb are considered to reflect a regression with prograding siliciclastics from NE, and a corresponding maximum regression surface in top parts of the Hawskerense Subzone (Fig.
Carbon (Ctot, Corg, Ccarb), total sulphur (Stot), and total nitrogen (Ntot) contents of sedimentary rocks of the Ludwigskanal section.
Sample number | Formation | Bed number | Section from–to [cm] | Lithology | Remarks | Ctot mean [wt %] | Corg mean [wt %] | Ccarb mean [wt %] | CaCO3 calculated [wt %] | Corg carbonate-free [wt %] | Ntot mean [wt %] | Stot mean [wt %] | Stot carbonate-free [wt %] |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Lud 72 | Opalinuston | 34 | 639 | calcareous claystone | 3.23 | 0.33 | 2.90 | 24.2 | 0.44 | 0.035 | 0.013 | 0.02 | |
Lud 1 | Opalinuston | 34 | 629 | clay | 0.37 | 0.35 | 0.02 | 0.2 | 0.35 | 0.057 | 0.016 | 0.02 | |
Lud 2 | Opalinuston | 33 | 618 | argillaceous limestone | stromatolitic crust | 9.66 | 0.30 | 9.36 | 78.0 | 1.36 | 0.019 | 0.040 | 0.18 |
Lud 3 | Opalinuston | 33 | 617–619 | calcareous claystone | matrix of belemnite accumulation | 2.60 | 0.60 | 2.00 | 16.7 | 0.72 | 0.047 | 0.009 | 0.01 |
Lud 4 | Opalinuston | 32 | 607 | calcareous claystone | 2.70 | 0.42 | 2.28 | 19.0 | 0.52 | 0.039 | 0.011 | 0.01 | |
Lud 73 | Opalinuston | 32 | 602 | calcareous claystone | 3.25 | 0.78 | 2.47 | 20.6 | 0.98 | 0.047 | 0.011 | 0.01 | |
Lud 74 | Opalinuston | 32 | 567 | calcareous claystone | 3.33 | 0.55 | 2.78 | 23.2 | 0.72 | 0.041 | 0.014 | 0.02 | |
Lud 75 | Opalinuston | 32 | 557 | calcareous claystone | rich in nubeculariid foraminifera | 2.93 | 0.66 | 2.27 | 18.9 | 0.81 | 0.046 | 0.010 | 0.01 |
Lud 76 | Jurensismergel | 30 | 533 | calcareous claystone | rich in nubeculariid foraminifera | 3.61 | 0.74 | 2.87 | 23.9 | 0.97 | 0.048 | 0.020 | 0.03 |
Lud 5 | Jurensismergel | 30 | 515 | calcareous claystone | rich in nubeculariid foraminifera | 3.16 | 0.68 | 2.48 | 20.7 | 0.86 | 0.046 | 0.014 | 0.02 |
Lud 6 | Jurensismergel | 29 | 495 to 505 | calcareous marl | 8.24 | 0.28 | 7.96 | 66.3 | 0.83 | 0.024 | 0.012 | 0.04 | |
Lud 7 | Jurensismergel | 28 | 475 to 480 | calcareous claystone | rich in nubeculariid foraminifera | 3.39 | 1.07 | 2.32 | 19.3 | 1.33 | 0.061 | 0.015 | 0.02 |
Lud 8 | Jurensismergel | 28 | 465 to 470 | calcareous claystone | 3.20 | 0.43 | 2.77 | 23.1 | 0.6 | 0.05 | 0.03 | 0.04 | |
Lud 9 | Jurensismergel | 28 | 455 to 460 | calcareous claystone | 3.49 | 0.52 | 2.97 | 24.7 | 0.7 | 0.04 | 0.02 | 0.02 | |
Lud 10 | Jurensismergel | 28 | 445 to 450 | calcareous claystone | rich in nubeculariid foraminifera | 3.60 | 1.18 | 2.42 | 20.2 | 1.5 | 0.07 | 0.04 | 0.06 |
Lud 11 | Jurensismergel | 28 | 435 to 440 | calcareous claystone | rich in nubeculariid foraminifera | 4.01 | 1.35 | 2.66 | 22.2 | 1.7 | 0.07 | 0.06 | 0.07 |
Lud 12 | Jurensismergel | 28 | 425 to 430 | calcareous claystone | rich in nubeculariid foraminifera | 3.11 | 1.12 | 1.99 | 16.6 | 1.3 | 0.06 | 0.04 | 0.05 |
Lud 13 | Jurensismergel | 28 | 415 to 420 | calcareous claystone | 2.88 | 1.18 | 1.70 | 14.2 | 1.4 | 0.07 | 0.03 | 0.04 | |
Lud 14 | Jurensismergel | 27 | 405 to 410 | calcareous claystone | “Yellow Bed” | 3.62 | 1.07 | 2.55 | 21.2 | 1.4 | 0.07 | 0.05 | 0.07 |
Lud 15 | Jurensismergel | 26 | 395 to 400 | calcareous claystone | 3.31 | 0.85 | 2.46 | 20.5 | 1.1 | 0.05 | 0.05 | 0.06 | |
Lud 16 | Jurensismergel | 26 | 385 to 390 | calcareous claystone | 4.14 | 1.17 | 2.97 | 24.7 | 1.6 | 0.06 | 0.05 | 0.06 | |
Lud 17 | Jurensismergel | 26 | 375 to 380 | argillaceous marl | 4.57 | 1.29 | 3.28 | 27.3 | 1.8 | 0.07 | 0.12 | 0.17 | |
Lud 18 | Jurensismergel | 26 | 365 to 370 | argillaceous marl | 4.34 | 0.92 | 3.42 | 28.5 | 1.3 | 0.05 | 0.05 | 0.07 | |
Lud 19 | Jurensismergel | 25 | 355 to 360 | bituminous marl | matrix of “Mactra Bed” | 10.26 | 2.83 | 7.43 | 61.9 | 7.4 | 0.09 | 0.61 | 1.60 |
Lud 20 | Jurensismergel | 24 | 345 to 350 | argillaceous marl | 4.82 | 1.01 | 3.81 | 31.7 | 1.5 | 0.06 | 0.16 | 0.23 | |
Lud 21 | Jurensismergel | 24 | 335 to 340 | argillaceous marl | 5.02 | 1.36 | 3.66 | 30.5 | 2.0 | 0.07 | 0.80 | 1.15 | |
Lud 22 | Jurensismergel | 24 | 325 to 330 | argillaceous marl | 5.09 | 1.09 | 4.00 | 33.3 | 1.6 | 0.07 | 0.94 | 1.41 | |
Lud 23 | Jurensismergel | 24 | 315 to 320 | calcareous claystone | rich in nubeculariid foraminifera | 3.60 | 1.03 | 2.57 | 21.4 | 1.3 | 0.07 | 0.52 | 0.67 |
Lud 24 | Jurensismergel | 24 | 305 to 310 | calcareous claystone | rich in nubeculariid foraminifera | 3.53 | 1.04 | 2.49 | 20.7 | 1.3 | 0.07 | 0.60 | 0.75 |
Lud 25 | Jurensismergel | 24 | 295 to 300 | argillaceous marl | rich in nubeculariid foraminifera | 4.75 | 0.94 | 3.81 | 31.7 | 1.4 | 0.06 | 0.51 | 0.75 |
Lud 26 | Jurensismergel | 24 | 285 to 290 | marl | rich in nubeculariid foraminifera | 6.22 | 0.90 | 5.32 | 44.3 | 1.6 | 0.05 | 0.66 | 1.18 |
Lud 27 | Jurensismergel | 24 | 275 to 280 | argillaceous marl | rich in nubeculariid foraminifera | 5.89 | 1.78 | 4.11 | 34.2 | 2.7 | 0.08 | 1.45 | 2.20 |
Lud 28 | Jurensismergel | 24 | 265 to 270 | poorly bituminous, argillaceous marl | rich in nubeculariid foraminifera | 5.83 | 2.54 | 3.29 | 27.4 | 3.5 | 0.08 | 1.53 | 2.11 |
Lud 29 | Jurensismergel | 23 | 255 to 260 | marl | rich in nubeculariid foraminifera | 5.41 | 1.09 | 4.32 | 36.0 | 1.7 | 0.05 | 0.18 | 0.28 |
Lud 30 | Jurensismergel | 23 | 245 to 250 | marl | 5.65 | 1.06 | 4.59 | 38.2 | 1.7 | 0.04 | 0.25 | 0.40 | |
Lud 31 | Jurensismergel | 23 | 235 to 240 | marl | rich in nubeculariid foraminifera | 5.30 | 0.88 | 4.42 | 36.8 | 1.4 | 0.04 | 0.25 | 0.39 |
Lud 32 | Jurensismergel | 23 | 225 to 230 | argillaceous marl | rich in nubeculariid foraminifera | 4.59 | 1.04 | 3.55 | 29.6 | 1.5 | 0.07 | 0.10 | 0.15 |
Lud 33 | Jurensismergel | 22 | 220 to 225 | argillaceous marl | matrix of belemnite accumulation | 4.24 | 1.03 | 3.18 | 26.5 | 1.4 | 0.06 | 0.16 | 0.21 |
Lud 34 | Jurensismergel | 21 | 205 to 220 | bituminous marl | “Toarcensis Shale” | 8.49 | 3.00 | 5.49 | 45.7 | 5.5 | 0.10 | 1.23 | 2.26 |
Lud 35 | Jurensismergel | 20 | 198 to 205 | marl | matrix of “Main Phosphorite Bed” | 5.96 | 0.73 | 5.23 | 43.6 | 1.3 | 0.04 | 0.69 | 1.21 |
Lud 36 | Jurensismergel | 19 | 195 to 198 | poorly bituminous, calcareous marl | “Belemnite Battlefield” | 9.87 | 1.30 | 8.57 | 71.4 | 4.5 | 0.04 | 0.69 | 2.41 |
Lud 37 | Jurensismergel | 19 | 192 to 195 | bituminous marl | “Belemnite Battlefield” | 10.62 | 4.30 | 6.32 | 52.7 | 9.1 | 0.12 | 0.99 | 2.10 |
Lud 38 | Jurensismergel | 18 | 187 to 192 | poorly bituminous, calcareous marl | 9.58 | 1.75 | 7.83 | 65.2 | 5.0 | 0.06 | 0.99 | 2.84 | |
Lud 39 | Posidonienschiefer | 17 | 185 to 187 | poorly bituminous marl | “Fucoid Bed” | 8.69 | 1.88 | 6.81 | 56.7 | 4.3 | 0.06 | 1.09 | 2.52 |
Lud 40 | Posidonienschiefer | 16 | 180 | bituminous, calcareous marl | “Variabilis Shale” | 11.69 | 3.57 | 8.12 | 67.7 | 11.0 | 0.11 | 0.66 | 2.05 |
Lud 41 | Posidonienschiefer | 16 | 179 | bituminous, calcareous marl | “Variabilis Shale” | 11.44 | 3.40 | 8.04 | 67.0 | 10.3 | 0.10 | 0.83 | 2.50 |
Lud 42 | Posidonienschiefer | 16 | 175 | bituminous, calcareous marl | “Variabilis Shale” | 12.68 | 4.79 | 7.89 | 65.7 | 14.0 | 0.15 | 0.75 | 2.18 |
Lud 43 | Posidonienschiefer | 16 | 165 | poorly bituminous, argillaceous marl | “Variabilis Shale” | 4.93 | 1.04 | 3.89 | 32.4 | 1.5 | 0.05 | 0.10 | 0.15 |
Lud 44 | Posidonienschiefer | 16 | 155 | bituminous marl | “Variabilis Shale” | 11.63 | 4.70 | 6.93 | 57.7 | 11.1 | 0.14 | 0.72 | 1.69 |
Lud 45 | Posidonienschiefer | 16 | 145 | poorly bituminous marl | “Variabilis Shale” | 5.70 | 1.08 | 4.62 | 38.5 | 1.8 | 0.05 | 1.03 | 1.68 |
Lud 46 | Posidonienschiefer | 16 | 135 | bituminous marl | “Variabilis Shale” | 11.63 | 5.34 | 6.29 | 52.4 | 11.2 | 0.16 | 1.27 | 2.66 |
Lud 47 | Posidonienschiefer | 16 | 125 | bituminous marl | “Variabilis Shale” | 10.23 | 3.81 | 6.42 | 53.5 | 8.2 | 0.11 | 0.64 | 1.38 |
Lud 48 | Posidonienschiefer | 15 | 115 | bituminous marl | “Bifrons Shale” | 11.29 | 5.01 | 6.28 | 52.3 | 10.5 | 0.14 | 1.41 | 2.95 |
Lud 49 | Posidonienschiefer | 15 | 105 | bituminous marl | “Bifrons Shale” | 10.26 | 3.80 | 6.46 | 53.8 | 8.2 | 0.11 | 1.05 | 2.28 |
Lud 50 | Posidonienschiefer | 15 | 95 | bituminous marl | “Bifrons Shale” | 10.82 | 4.02 | 6.80 | 56.7 | 9.3 | 0.13 | 1.39 | 3.20 |
Lud 51 | Posidonienschiefer | 15 | 85 | bituminous marl | “Bifrons Shale” | 9.67 | 2.88 | 6.79 | 56.6 | 6.6 | 0.10 | 1.25 | 2.89 |
Lud 52 | Posidonienschiefer | 15 | 76 | bituminous marl | “Bifrons Shale” | 11.58 | 4.58 | 7.00 | 58.3 | 11.0 | 0.14 | 1.14 | 2.74 |
Lud 53 | Posidonienschiefer | 14 | 66 to 75 | poorly bituminous limestone | “Monotis Bed” | 12.02 | 0.31 | 11.71 | 97.6 | 12.8 | 0.02 | 0.05 | 2.11 |
Lud 54 | Posidonienschiefer | 13 | 65 to 66 | poorly bituminous, argillaceous limestone | 12.04 | 2.44 | 9.60 | 80.0 | 12.2 | 0.09 | 0.60 | 3.00 | |
Lud 55 | Posidonienschiefer | 12 | 40 to 65 | poorly bituminous limestone | “Dactylioceras Bed” | 12.12 | 0.80 | 11.32 | 94.3 | 14.1 | 0.03 | 0.24 | 4.22 |
Lud 56 | Posidonienschiefer | 11 | 37 to 40 | poorly bituminous, argillaceous limestone | 12.31 | 2.17 | 10.14 | 84.5 | 14.0 | 0.07 | 0.18 | 1.13 | |
Lud 57 | Posidonienschiefer | 10 | 27 to 37 | bituminous marl | “Falciferum Shale” | 12.84 | 7.47 | 5.37 | 44.7 | 13.5 | 0.21 | 2.18 | 3.94 |
Lud 58 | Posidonienschiefer | 9 | 22 to 27 | poorly bituminous, argillaceous limestone | “Fish Scale Bed” | 11.89 | 1.29 | 10.60 | 88.3 | 11.1 | 0.05 | 0.28 | 2.38 |
Lud 59 | Posidonienschiefer | 8 | 17 to 22 | poorly bituminous, argillaceous limestone | “Laibstein II” (top) | 11.63 | 1.97 | 9.66 | 80.5 | 10.1 | 0.06 | 0.77 | 3.92 |
Lud 60 | Posidonienschiefer | 8 | 12 to 17 | poorly bituminous limestone | “Laibstein II” (centre) | 12.01 | 0.56 | 11.45 | 95.4 | 12.2 | 0.02 | 0.09 | 1.92 |
Lud 61 | Posidonienschiefer | 8 | 7 to 12 | poorly bituminous, argillaceous limestone | “Laibstein II” (bottom) | 11.64 | 1.75 | 9.89 | 82.4 | 10.0 | 0.06 | 0.59 | 3.35 |
Lud 62 | Posidonienschiefer | 7 | 0 to 7 | poorly bituminous, calcareous marl | lateral to “Laibstein I” | 10.75 | 1.99 | 8.76 | 73.0 | 7.4 | 0.07 | 1.32 | 4.88 |
Lud 63 | Posidonienschiefer | 7 | 5 to 7 | poorly bituminous, argillaceous limestone | “Laibstein I” (top) | 11.57 | 1.02 | 10.55 | 87.9 | 8.4 | 0.04 | 0.68 | 5.59 |
Lud 64 | Posidonienschiefer | 7 | 2 to 5 | poorly bituminous limestone | “Laibstein I” (centre) | 12.33 | 1.03 | 11.30 | 94.2 | 17.7 | 0.03 | 0.33 | 5.67 |
Lud 65 | Posidonienschiefer | 7 | 0 to 2 | poorly bituminous, argillaceous limestone | “Laibstein I” (bottom) | 12.02 | 1.07 | 10.95 | 91.2 | 12.2 | 0.05 | 0.38 | 4.35 |
Lud 66 | Amaltheenton | 5 | -15 | claystone | 1.23 | 0.88 | 0.35 | 2.9 | 0.9 | 0.06 | 2.00 | 2.06 | |
Lud 67 | Amaltheenton | 5 | -40 | claystone | 1.11 | 0.82 | 0.29 | 2.4 | 0.8 | 0.05 | 2.05 | 2.10 | |
Lud 68 | Amaltheenton | 5 | -230 | claystone | 1.33 | 0.94 | 0.39 | 3.2 | 1.0 | 0.06 | 0.73 | 0.76 | |
Lud 69 | Amaltheenton | 5 | -300 | claystone | 1.31 | 0.98 | 0.33 | 2.7 | 1.0 | 0.06 | 0.64 | 0.66 | |
Lud 70 | Amaltheenton | 4 | -800 to -810 | calcareous claystone | matrix of “Delta-Fossil Bed” | 2.16 | 0.78 | 1.38 | 11.5 | 0.9 | 0.05 | 0.56 | 0.63 |
Lud 71 | Amaltheenton | 1 | -930 | claystone | 1.24 | 0.84 | 0.40 | 3.3 | 0.9 | 0.06 | 2.48 | 2.57 |
Correlation of the investigated section Ludwigskanal/Dörlbach with sections from the northern Franconian Alb (Mistelgau:
Ammonite zones, subzones, and horizons for the NW-European Toarcian according to different authors. 1)
Sequence stratigraphic interpretation of the Toarcian succession in the Franconian Alb (including Ludwigskanal/Dörlbach section) and adjacent areas. Sedimentary succession and ammonite biostratigraphic evidence according to
The Posidonienschiefer shows a very low thickness, combined with high carbonate contents. Corg contents normalized to the silicate sediment fraction show that the T-OAE clearly peaks in the Exaratum Subzone (Fig.
All other ammonite subzones from top of the Semicelatum to the Crassum Subzone are present in the bituminous and laminated sediments of the Ludwigskanal/Dörlbach area (Fig.
Towards the basin margin (Regensburg area), bituminous shales of the Falciferum Zone are overlain by prograding sandstones containing Dactylioceras commune and D. athlecticum (
Consequently, the sequence stratigraphic interpretation is as follows (Fig.
This interpretation is similar to the 3rd order T-R cycle previously proposed for the Swabian and Franconian Posidonienschiefer by
Considerable differences exist with respect to the proposed 3rd order sequences in France.
Similar to the previous formation, the thickness of the Jurensismergel Formation is low (5 m). Ammonite zones and subzones are densely spaced and condensed at the phosphoritic and (slightly) bituminous basis of the formation (Fig.
The erosive basis of the Jurensismergel Formation, forming a sequence boundary, has early been recognized in the Swabian Alb, with an apparent transgression beginning with the Variabilis Zone (
At the Ludwigskanal/Dörlbach, the Semipolitum Subzone is overlain by a Variabilis Subzone, characterized by abundant Catacoeloceras raquinianum, Pseudolioceras compactile, and Mucrodactylites mucronatus (Fig.
Therefore, we suggest that the erosive basis of the Jurensismergel Formation and sequence boundary lies within the Variabilis Zone, specifically at the basis of the Illustris Subzone (Figs
Consequently, the “Belemnite Battlefield” with its fossil accumulation and phosphorite nodules rather represents a transgressive sediment, and indeed grades in basin margin sections into a cephalopod-rich sandstone bed (“Crassum Bed” with Dactylotheutis irregularis, Catacoeloceras raquinianum, Haugia sp., Mucrodactylites mucronatus and Pseudolioceras compactile:
In the Swabian Alb, submarine “swells” (i.e., remaining topographic highs after erosion within Variabilis Zone;
A clear and significant discontinuity is developed at the basis of the Dispansum Zone in the Franconian Alb. This erosive sequence boundary, commonly associated with a belemnite accumulation and aphotic microbialites (Dörlbach, Mistelgau: Fig.
Subsequently, condensation and phosphorites characterize the transgressive sediments of the Dispansum Zone at the Ludwigskanal/Dörlbach and elsewhere in the Franconian Alb, while in the following Pseudoradiosa Subzone with several beds of compressed Dumortieria accumulations may reflect further deepening. A flooding at the basin margin area might be indicated by findings of
The condensed bed 25 (i.e., basis of Mactra Subzone; Fig.
Finally, the increasingly thick marls with pyritic ammonites of the Aalensis Subzone could reflect the regressive system tract of this 3rd order cycle, with increasing clay supply from N. Indeed, at the basin margin (Regensburg area) quartz-pebble and feldspar-containing calcareous sandstones document this regressive interval (
While basal parts of this formation, i.e., the Torulosum Subzone, still show a low thickness, discontinuities, phosphorite, and some carbonate, major parts are composed of a thick monotonous series of claystones. Discontinuities within the formation and lateral facies trends are poorly documented. However, the sections Grossenbuch (middle Franconian Alb) and Wittelshofen (southern Franconian Alb) described by Krumbeck (1943) demonstrate that the Aalensis-Torulosum Subzone boundary is associated with erosion, locally removing the complete Aalensis Subzone.
Therefore, the belemnite accumulation (bed 31) at the Aalensis-Torulosum Subzone boundary of the Ludwigskanal/Dörlbach section (Fig.
In the Ludwigskanal/Dörlbach section (Figs
The monotonous and about 50 m thick claystone succession of the Opalinum Subzone, with only the lowermost 0.5 m exposed in the Ludwigskanal/Dörlbach section, reflects a progradation of siliciclastic influx from North, finally leading to shallow water conditions during deposition of the Upper Aalenian Eisensandstein Formation.
1. Pleuroceras solare (Phillips), reworked concretion in bed 4, basis of Hawskerense Subzone, Amaltheenton Formation. GZG.INV.70496: d = 53 mm, di = 39 mm, u = 22 mm, wh = 17 mm, wb = 15 mm, rb/2 = 15. 2. Two specimens of Pleuroceras solare var. solitarium (Simpson), together with a juvenile Amauroceras ferrugineum (Simpson), reworked concretion in bed 4, basis of Hawskerense Subzone, Amaltheenton Formation. GZG.INV.70497a: d = 54 mm, di = 39 mm, u = 21 mm, wh = 17 mm, wb = 15 mm, rb/2 = 15; GZG.INV.70497b: d = 56 mm, di = 40 mm, u = 24 mm, wh = 18 mm, wb = 14 mm, rb/2 = 15; GZG.INV.70497c: d = 11 mm, di = 7 mm, u = 3 mm, wh = 5 mm, wb = 3 mm, rb/2 = 28. 3. Pleuroceras spinatum (Bruguière), 2 m below top of bed 5, Hawskerense Subzone, Amaltheenton Formation. GZG.INV.70498: d = 54 mm, di = 37 mm, u = 23 mm, wh = 19 mm, wb = 18 mm, rb/2 = 11. 4. Pleuroceras spinatum (Bruguière), 50 cm above basis of bed 5, Hawskerense Subzone, Amaltheenton Formation. GZG.INV.70499: d = 76 mm, di = 58 mm, u = 36 mm, wh = 24 mm, wb = 24 mm, rb/2 = 14. 5. Tiltoniceras antiquum (Wright), 1–2 cm above basis of bed 7, Semicelatum Subzone, Posidonienschiefer Formation. Minor part (bright area) of the body chamber restored. GZG.INV.45641a: d = 48 mm, di = 33 mm, u = 12 mm, wh = 20 mm, wb = 12 mm, rb/2 = 22. 6. Tiltoniceras antiquum (Wright), 1–2 cm above basis of bed 7, Semicelatum Subzone, Posidonienschiefer Formation. GZG.INV.45641b: d = 38 mm, di = 26 mm, u = 9 mm, wh = 17 mm, wb = 9 mm, rb/2 = (33); GZG.INV.45641c: d = 27 mm, di = 18 mm, u = 6.5 mm, wh = 11 mm, wb = 7 mm, rb/2 = (30). 7. Lytoceras ceratophagum (Quenstedt), middle part of bed 7, Exaratum Subzone, Posidonienschiefer Formation. GZG.INV.70500: d = 29 mm, di = 18 mm, u = 9 mm, wh = 12 mm, wb = 11 mm, rb/2 = 46. 8. Hildaites murleyi (Moxon), bed 7, Exaratum Subzone, Posidonienschiefer Formation. GZG.INV.70501: d = 41 mm, di = 27 mm, u = 14 mm, wh = 16 mm, wb = 12 mm, rb/2 = 21; (leg. Arno Garbe). 9. Hildaites murleyi (Moxon), together with juvenile Cleviceras exaratum (Young and Bird), bed 7, Exaratum Subzone, Posidonienschiefer Formation. GZG.INV.70502: d = 44 mm, di = 32 mm, u = 17 mm, wh = 15.5 mm, wb = 10 mm, rb/2 = 24; (leg. Arno Garbe). 10. Cleviceras exaratum (Young and Bird), middle part of bed 7, Exaratum Subzone, Posidonienschiefer Formation.GZG.INV.70503: d = 39 mm, di = 27 mm, u = 10 mm, wh = 17 mm, wb = 8 mm, rb/2 = 24.
1. Harpoceras serpentinum (Schlotheim), bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70504: d = 197 mm, di = 144 mm, u = 80 mm, wh = 70 mm, wb = 40 mm, rb/2 = n.a.; (leg. Matthias Weißmüller). 2. Dactylioceras sp. forma aegra circumdata (Martin 1858) Hölder 1956, bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70505a: d = 53 mm, di = 40.5 mm, u = 22 mm, wh = 13.5 mm, wb = 15 mm, rb/2 = 30. 3. Dactylioceras anguinum (Reinecke), bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70505b: d = 40 mm, di = 30 mm, u = 14.5 mm, wh = 11 mm, wb = (11 mm), rb/2 = 31. 4. “Peronoceras” desplacei (d’Orbigny), bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70506: d = 68 mm, di = 53 mm, u = 38 mm (56%), wh = 16 mm (24%), wb = 16 mm, rb/2 = 41. 5. Phylloceras heterophyllum (Sowerby), bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70507: d = 44 mm, di = 29 mm, u = 4.5 mm, wh = 24 mm, wb = 12 mm, rb/2 = n.a. 6. Cleviceras elegans (Sowerby), bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70508: d = 86 mm, di = 53 mm, u = 15 mm, wh = 43 mm, wb = 19 mm, rb/2 = 49. 7. Dactylioceras semiannulatum Howarth, bed 8, Elegans Subzone, Posidonienschiefer Formation. GZG.INV.70509: d = 49 mm, di = 39 mm, u = 26 mm, wh = 12 mm, wb = 13 mm, rb/2 = 30.
1. Dactylioceras cf. commune (Sowerby), lower bedding plane of bed 12, Commune Subzone, Posidonienschiefer Formation. GZG.INV.70510a: d = 61 mm, di = 49 mm, u = 34 mm, wh = 14 mm, wb = n.a., rb/2 = (24); GZG.INV.70510b: d = 45 mm, di = 35 mm, u = 27 mm, wh = 10 mm, wb = n.a., rb/2 = (25). 2. Hildoceras cf. lusitanicum Meister, lower bedding plane of bed 12, Commune Subzone, Posidonienschiefer Formation. GZG.INV.70511: d = 92, di = (68 mm), u = 43 mm, wh = 26 mm, wb = (12 mm), rb/2 = (27). 3. Dactylioceras athleticum (Simpson), middle part of bed 12, Commune Subzone, Posidonienschiefer Formation. GZG.INV.70512: d = 64 mm, di = 51 mm, u = 38 mm, wh = 13.5 mm, wb = 13.5 mm, rb/2 = 37. 4. Hildoceras semipolitum Buckman, 18 cm below top of bed 15, Crassum Subzone, Posidonienschiefer Formation. GZG.INV.70513: d = 40 mm, di = 28 mm, u = 12 mm, wh = 16.5 mm, wb = n.a., rb/2 = (23). 5. Hildoceras semipolitum Buckman, 18 cm below top of bed 15, Crassum Subzone, Posidonienschiefer Formation. Field image: d = (30 mm), di = (23 mm), u = 11 mm, wh = 10 mm, wb = n.a., rb/2 = (24). 6. Mucrodactylites mucronatus (d’Orbigny), 43 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.70514: d = 20 mm, di = (15 mm), u = 9 mm, wh = 6.5 mm, wb = 8 mm, rb/2 = 17. 7. Mucrodactylites mucronatus (d’Orbigny), bed 16 ex situ, Variabilis Subzone, Posidonienschiefer Formation. leg. Volker Münzner: d = 22 mm, di = 16.5, u = 10 mm, wh = 6 mm, wb = 6 mm, rb/2 = 18. 8. Haugia variabilis (d’Orbigny), 13 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.45642: d = 67 mm, di = 44 mm, u = 20 mm, wh = 27 mm, wb = n.a., rb/2 = 27. 9. Haugia jugosa (Sowerby), 3 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.70515: d = 71 mm, di = 46 mm, u = 19 mm, wh = 30 mm, wb = n.a., rb/2 = 34. 10. Pseudolioceras compactile (Simpson), 37 cm below top of bed 16, Crassum Subzone, Posidonienschiefer Formation. GZG.INV.70516: d = 32 mm, di = 19 mm, u = 4.5 mm, wh = 17 mm, wb = 7 mm, rb/2 = 21. 11. Pseudolioceras compactile (Simpson), 32 cm below top of bed 16, Crassum Subzone, Posidonienschiefer Formation. GZG.INV.70517: d = 30 mm, di = 20 mm, u = 5 mm, wh = 15 mm, wb = n.a., rb/2 = 15.
1. Lytoceras sublineatum (Oppel), 38 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. The telescope-like, shallow constrictions in this juvenile specimen are reminiscent of Pleurolytoceras propehircinum Krumbeck of the Aalensis Subzone, but the high wb/wh ratio points to Lytoceras sublineatum (Oppel). GZG.INV.70518: d = 17 mm, di = 10.5 mm, u = 5 mm, wh = 7.5 mm, wb = 10 mm, rb/2 = 10. 2. Catacoeloceras raquinianum (d’Orbigny), 19 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.70519: d = 45 mm, di = 35 mm, u = 21 mm, wh = 12.5 mm, wb = 16 mm, rb/2 = 18. 3. Catacoeloceras raquinianum (d’Orbigny), 13 cm below top of bed 16, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.70520: d = 35 mm, di = 26 mm, u = 14 mm, wh = 11.5 mm, wb = 15 mm, rb/2 = 13. 4. Pseudogrammoceras subregale (Pinna), 4 cm below top of bed 18, Illustris Subzone, Jurensismergel Formation. GZG.INV.70521; d = 107 mm, di = 77 mm, u = 46 mm, wh = 34 mm, wb = n.a., rb/2 = (48). 5. Haugia cf. phillipsi (Simpson), 3 cm below top of bed 18, Illustris Subzone, Jurensismergel Formation. GZG.INV.70522; d = (125 mm), di = n.a., u = n.a., wh = 46 mm, wb = n.a., rb/2 = (22). 6. Catacoeloceras raquinianum (d’Orbigny), basis of bed 19, Variabilis Subzone, Posidonienschiefer Formation. GZG.INV.70523: d = 62 mm, di = 49 mm, u = 31 mm, wh = 15 mm, wb = (16 mm), rb/2 = 13. 7. Osperleioceras bicarinatum (Zieten), phosphorite nodule in bed 20, condensed transition Variabilis-Thouarsense Zone, Jurensismergel Formation. GZG.INV.70524: d = 25 mm, di = 15 mm, u = 3.5 mm, wh = 14 mm, wb = 6 mm, rb/2 = (18). 8. Lytoceras cornucopia (Young & Bird), marl matrix of bed 20, condensed transition Variabilis-Thouarsense Zone, Jurensismergel Formation. GZG.INV.70525: d = 66 mm, di = 46 mm, u = 23 mm, wh = 27 mm, wb = (28 mm), rb/2 = n.a. 9. Denckmannia rude (Simpson), phosphorite nodule in bed 20, condensed transition Variabilis-Thouarsense Zone, Jurensismergel Formation. GZG.INV.70526: d = 86 mm, di = 58 mm, u = 32 mm, wh = 32 mm, wb = (26 mm), rb/2 = n.a.
1. Grammoceras thouarsense (d’Orbigny), 10 cm below top of bed 21, Thouarsense Subzone, Jurensismergel Formation. GZG.INV.70527: d = 72 mm, di = 50 mm, u = 25 mm, wh = 27 mm, wb = n.a., rb/2 = (25). 2. Alocolytoceras rugiferum (Pompeckj), 20–25 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70528: d = (39 mm), di = (27 mm), u = 12 mm, wh = 16 mm, wb = n.a., rb/2 = (42). 3. Pseudolioceras cf. boulbiense (Young and Bird), 12–20 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70529: d = 26 mm, di = 17 mm, u = 5.5 mm, wh = 13 mm, wb = n.a., rb/2 = 13. 4. Alocolytoceras rugiferum (Pompeckj), 20–25 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70530: d = 76 mm, di = 56 mm, u = 21 mm, wh = 31 mm, wb = n.a., rb/2 = n.a. 5. Phlyseogrammoceras dispansum (Lycett), 12–20 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70531: d = (30 mm), di = n.a., u = (9 mm), wh = 12 mm, wb = 9 mm, rb/2 = n.a. 6. Dumortieria insignisimilis (Brauns), 11 cm below top of bed 23, basis of Levesquei Subzone, Jurensismergel Formation. GZG.INV.70532: d = 22 mm, di = 17 mm, u = 12 mm, wh = 6 mm, wb = n.a., rb/2 = 20. 7. Dumortieria insignisimilis (Brauns), 11 cm below top of bed 23, basis of Levesquei Subzone, Jurensismergel Formation. GZG.INV.70533: d = 25 mm, di = 17 mm, u = 10.5 mm, wh = 8.5 mm, wb = n.a., rb/2 = 18. 8. Phlyseogrammoceras dispansum (Lycett), 20–25 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70534: d = 83 mm, di = 61 mm, u = 27 mm, wh = 31 mm, wb = n.a., rb/2 = (45). 9. Dumortieria radiosa (Seebach), 75 cm below top of bed 24, Pseudoradiosa Subzone, Jurensismergel Formation. GZG.INV.70535: d = 73 mm, di = (54 mm), u = 30 mm, wh = 23 mm, wb = n.a., rb/2 = n.a. 10. Hammatoceras insigne (Schübler in Zieten), 15 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70536: d = (56 mm), di = (42 mm), u = 26 mm, wh = (16 mm), wb = n.a., rb/2 = (28). 11. Dumortieria levesquei (d’Orbigny), 6 cm below top of bed 23, Levesquei Subzone, Jurensismergel Formation. GZG.INV.70537a: d = 34 mm, di = 24 mm, u = 13 mm, wh = 12 mm, wb = n.a., rb/2 = 18. 12. Hammatoceras insigne (Schübler in Zieten), 15 cm below top of bed 23, Dispansum Subzone, Jurensismergel Formation. GZG.INV.70538: d = 29 mm, di = (22 mm), u = (10 mm), wh = 10 mm, wb = 17 mm, rb/2 = (16). 13. Dumortieria levesquei (d’Orbigny), 9 cm below top of bed 23, Levesquei Subzone, Jurensismergel Formation. GZG.INV.70539: d = 32 mm, di = (23 mm), u = (13 mm), wh = 11 mm, wb = 10 mm, rb/2 = 21. 14. Dumortieria pseudoradiosa (Branco), 4 cm below top of bed 23, Levesquei Subzone, Jurensismergel Formation. GZG.INV.70537c: d = 92 mm, di = 70 mm, u = 41 mm, wh = 28 mm, wb = n.a., rb/2 = 32.
1. Pleurolytoceras wrighti (Buckman), bed 27, Aalensis Subzone, Jurensismergel Formation. This species has previously been assigned to Pachylytoceras Buckman 1905, which is a junior subjective synonym of Pleurolytoceras Hyatt 1900 (
We are grateful for the permission by the water management office Nürnberg, Rainer Ketterle, to investigate and sample at the construction site of the Ludwigskanal cutting. Thin sections were prepared by Axel Hackmann, geochemical analyses were performed with the help of Birgit Röhring and Wolfgang Dröse, and fieldwork was supported by Christian Strobl, Barbara Seuß, and Georg Maier. We thank Matthias Weissmüller, Arno Garbe, Martin Görlich, Sebastian Demmel, Volker Münzner, and Gernot Smolle for their generous donation of ammonites. Difficult ammonite preparations were preformed by Klaus Weiß and Stephan Seppelt. Photographs of the ammonites were taken by Max Hundertmark. Günter Schweigert and Ingmar Werneburg are gratefully acknowledged for access to original ammonite specimens hosted at the Stuttgart State Museum of Natural History and the Paleontological Collection of the University of Tübingen IGPT, respectively. We thank the engineering office Dr. Ing. Johann Spotka for the report on the landfill exploratory drilling Dörlbach D2. The manuscript significantly benefited from discussions with René Hoffmann. Charlotte Kniest helped with the acquisition of rare papers. We thank Eckhard Mönnig and Matthias Franz (Göttingen) for their constructive and helpful reviews of the manuscript.