Review Article |
Corresponding author: Volker Dietze ( dietze.v@t-online.de ) Academic editor: Alexander Nützel
© 2022 Volker Dietze, Andreas Hofbauer, Hans Rieber, Norbert Wannenmacher, Günter Schweigert.
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:
Dietze V, Hofbauer A, Rieber H, Wannenmacher N, Schweigert G (2022) Ammonites and stratigraphy of the Achdorf Formation (Braunjura Group; Aalenian) at the Wochenberg hill near Schömberg-Schörzingen (W Swabian Alb, SW Germany). Zitteliana 96: 69-101. https://doi.org/10.3897/zitteliana.96.82835
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In sections of the Achdorf Formation at the Wochenberg hill (western Swabian Alb, SW Germany), a succession of five ammonite biohorizons is distinguished (from bottom to top): the crassicostatum and viallii biohorizons of the Lower Aalenian (Bifidatum Subzone, Opalinum Zone) and the latiumbilicus, discoidea α and discoidea β biohorizons of the Upper Aalenian (Murchisonae Subzone, Murchisonae Zone). The herein newly introduced viallii biohorizon is the youngest hitherto identified biohorizon of the Opalinum Zone (Bifidatum Subzone). A lectotype is designated for Staufenia latiumbilicus (Quenstedt, 1886), the index ammonite of the latiumbilicus biohorizon. The succession of biohorizons of the Murchisonae Subzone reflects the evolution of the graphoceratid late Aalenian ammonite genera Staufenia and Ludwigia.
Ammonite biohorizons, correlation, Germany, Graphoceratidae, Middle Jurassic, phylogeny
The Upper Aalenian Achdorf Formation is an up to 60 metres thick series of claystones, arenaceous claystones and occasional limestone beds that crops out in the Wutach area as well as in the adjacent western and middle Swabian Alb (
Since natural outcrops along the steep hillsides of the Wochenberg only expose short intervals of the lithological succession, the complete section could only be roughly estimated in former times and the succession of ammonite faunas was still incompletely known. Moreover, extensive ammonite material housed in institutional and private collections mostly lacked detailed information about the exact locality and bed from where it was collected. These deficiencies hampered the recognition of evolutionary trends in ammonite lineages, sexual dimorphism, and changes of faunal composition through time as well as faunal migrations. Thus, the only possibility to add these missing data are excavations, where the complete succession is sampled bed-by-bed. This precise sampling of sections allows deciphering the ammonite evolution and results in a high-resolution biostratigraphy, although intraspecific variation within large samples complicates determinations.
The aim of this study, which focusses on the ammonites, is to present the scientific results of our excavations, which were executed between 2014 and 2022.
Our scientific excavations (2014–2018) of the Staufensis-Bank took place at the southwestern edge of the Wochenberg hill, southeast of a model airfield. Several hundred ammonites of the genera Staufenia and Ludwigia/Brasilia and a sole Planammatoceras were collected precisely bed-by-bed. Subsequently (2021–2022), the rock interval between the Untere Wilflingen-Bank and the Staufensis-Knollenlage was excavated at another section c. 20 metres further to the west of the previous one, with special focus on the ammonite-bearing Obere Wilflingen-Bank. In addition, two smaller excavations (2017, 2021) at a distance of c. 50 m and c. 170 m further southeast (in the direction to road L 435 connecting the town Schömberg and the village of Deilingen) focussed on the Untere Wilflingen-Bank. Additional sections of the Untere Wilflingen-Bank were sampled at the headwaters of the Schörzinger Starzel River and 350 m in southeastern direction, as well as along the steep escarpment of the Wochenberg hill north of road L 435.
The herein studied ammonites have been prepared mechanically using pneumatic chisels and airbrasive iron powder. All illustrated specimens are stored in the collection of the Staatliches Museum- für Naturkunde in Stuttgart (acronym: SMNS). The specimens are illustrated in natural size, if not otherwise stated.
Our lithostratigraphic description of the uppermost Opalinuston and Achdorf formations starts from the bottom of the section. It is a combination of our recent observations and measurements and those of
Above the ‘Wasserfallschichten’ [Waterfall Beds] (c. 8.8 m;
Section at the southern slope of the Wochenberg hill (modified after
Untere Wilflingen-Bank [Lower Wilflingen Bed] (= uWB; c. 1.6 m; = Comptum-Bank sensu
The Untere Wilflingen-Bank (formerly: Comptum-Bank, see
Bivalves: Isocardia cordata Buckman, Gresslya sp., Clavitrigonia brodiei (Lycett), Cl. sp. (small-sized), Pholadomya fidicula Sowerby, Entolium demissum (Phillips), Astarte elegans Sowerby, Inoperna sowerbyana (d’Orbigny), Parvamussium pumilus (Lamarck). Ammonites are concentrated slightly above the middle of the bed. Occasionally with a poorly lithified marly limestone layer (0.05 m) located slightly below the middle of the bed. In the latter case, the ammonites occur in the lower part of the bed.
Ammonites: Leioceras crassicostatum [M], L. goetzendorfense [M], L. paucicostatum [m], L. striatum [m]
Ammonites: L. goetzendorfense [M], L. paucicostatum [m], L. striatum [m]
Ammonites: L. goetzendorfense [M]
Tonmergel [Clay-Marl] (c. 3.2–4 m): this unit was not exposed and could not be studied. At the southern hillside of the Wochenberg we measured a vertical distance of c. 12–13 m between the top of the Untere Wilflingen-Bank (= Comptum-Bank sensu
Obere Wilflingen-Bank [Upper Wilflingen Bed] (1.6–1.7 m; Fig.
In one of his sections,
Ammonites (bed oWB-1b): Ancolioceras sp. [M], Leioceras sp. [M]
Ammonite: Ancolioceras subfalcatum [M]
Ammonites: Ancolioceras sp. [M], Leioceras sp. [M]
Ammonites: Leioceras sp. [?M]
Ammonites: Leioceras evertens [M], L. goetzendorfense [M], Ancolioceras subfalcatum [?m]
Ammonites: Ancolioceras noszkyi [M], A. viallii [M]
Ammonites: Leioceras goetzendorfense [M], Ancolioceras sp. [M]
Ammonites: Ancolioceras aff. subacutum [M], A. citaae [M], A. viallii [M], A. cf. viallii [M], A. krymholzi [M], A. subfalcatum [M], A. aff. substriatum [m], Leioceras goetzendorfense [M], L. capillare [M], L. striatum [m].
Marly limestone (1.9 m): brown, c. 0.2–0.3 m above its basis with a layer of small gray limestone nodules (c. 0.05–0.1 m in diameter) surrounded by layered rusty weathering rims; numerous burrows.
Ammonites: Ancolioceras sp.
Limestone / marly limestone (c. 0.8 m; = ? Sinon-Bank sensu
Clayey marl (c. 1.1–1.3 m): clayey to marly limestone, brown (not studied in detail).
Arenaceous limestone (0.9 m) [= Sehndensis-Knollenlage sensu
Ammonites: Staufenia “sehndensis” [after
Clayey marl (0.8–0.9 m): arenaceous, thin-bedded, brown-yellow, with rare reworked limestone pebbles, ichnofossils (Zoophycos) and occasional bivalves (Pholadomya sp.). The lowermost 0.1 m are lithified and amalgamated with the underlying calcareous marl.
Staufensis-Bank (sensu
Ammonites: Staufenia latiumbilicus [M]
Ammonites: St. latiumbilicus [M]
Ammonites: St. latiumbilicus [M and m], Ludwigia aff. crassa [M], L. armipotens [M], L. cf. subtuberculata [m]
Ammonites: St. discoidea α [M and m], Ludwigia tuberata [M], Brasilia howarthi [M]
Ammonites: St. discoidea α [M], Ludwigia murchisonae [M], L. subtuberculata [m]
Ammonites: St. discoidea α [M and m], Ludwigia depilata [M], L. cf. depilata [M], L. tuberata [M], L. armipotens [M], L. reflua [M], L. murchisonae [M], L. subtuberculata [m], Brasilia theobaldi [M], B. elmii [M], B. falcatiformis [M]
Ammonites: St. discoidea α [M and m], Ludwigia depilata [M], L. tuberata [M], L. murchisonae [M], L. armipotens [M], L. reflua [M], L. subtuberculata [m], Brasilia baldii [M], B. theobaldi [M], B. falcatiformis [M], B. howarthi [M]
Ammonites: St. discoidea β [M and m], Ludwigia aff. murchisonae [M], L. fueloepi [M], L depilata [M], L. reflua [M], L. gradata [M], Brasilia bradfordensis [M], B. elmii [M], Planammatoceras aff. planinsigne [M]
Clayey marl (0.05–0.1 m).
Clayey marl (0.1 m): with scattered siderite concretions, often rusty weathered.
Quaternary cover (0.3–0.8 m): up to the surface c. 0.3–0.8 m talus, loam and soil.
The beds of the Concava-Bank and the Sowerbyi-Oolith (
Within Graphoceratidae, the Staufenia lineage is easily divisable into a succession of only moderately variable chronospecies. In contrast, the taxonomy of Leioceras/Ancolioceras and Ludwigia/Brasilia is much more complex. There are no focussed evolutionary trends observable, and some morphologies can reappear independently multiple times. Moreover, ammonites of these groups vary considerably within a single biohorizon. Plenty of the recorded morphologies are not restricted to a single biohorizon, but range within several succeeding ones. Finally, from some well-sampled Aalenian beds such as the Scissum Bed of southern England (
Despite the partly large samples recovered by bed-by-bed sampling it was often impossible to identify corresponding macroconchs (M) and microconchs (m) – females and males – with accuracy. Specimens of the Tethyan genera Planammatoceras and Tmetoceras are very rare.
The ammonite fauna of the Untere Wilflingen-Bank (formerly: “Comptum-Bank”) in the western Swabian Alb was described by
(1a, b) Leioceras crassicostatum (Rieber) [M], SMNS 70640/1. (2a–4b, 8a, b, 10a, b) L. goetzendorfense (Dorn) [M]; (2) uWB-4, SMNS 70640/2; (3) uWB-7, SMNS 70640/3. (4) uWB-4, SMNS 70640/4; (8) uWB-8, SMNS 70640/5; (10) SMNS 70640/6. (5) L. striatum (Buckman) [m], SMNS 70640/7. (6a–7b) Tmetoceras scissum (Benecke); (6) SMNS 70640/8; (7) uWB-4, SMNS 70640/9. (9) L. paucicostatum Rieber [m], SMNS 70640/10. 2–4, 6, 8: southern slope of the Wochenberg hill. 1, 5, 7, 9, 10: headwaters of the Schörzinger Starzel river. 1–10: Achdorf Formation, Untere Wilflingen-Bank, Lower Aalenian, Opalinum Zone (Bifidatum Subzone), crassicostatum biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
Tmetoceras scissum
(Figs
The taxonomy and determination of the ammonites from the Obere Wilflingen-Bank is extremely complicated, since the stratigraphical position of this fauna is transitional between formally named taxa from older horizons of the Bifidatum Subzone (Opalinum Zone) and younger ones of the Haugi Subzone (Murchisonae Zone), similarly to the recently described case of the slightly younger subfalcatum biohorizon (
A relatively small ammonite with a ventrally rounded bodychamber bearing a prominent ribbing (Fig.
(1, 11, 13) Ancolioceras subfalcatum (Buckman) [M and ?m]; (1) oWB-2, SMNS 70640/74; (11) oWB-9, SMNS 70640/90; (13) oWB-6, SMNS 70640/75. (2) Leioceras sp. [?M], oWB-5, SMNS 70640/76. (3) A. viallii (Géczy) [M], oWB-7, SMNS 70640/81. (4) L. evertens (Buckman) [M], oWB-6, SMNS 70640/77. (5) A. noszkyi (Géczy) [M], oWB-7, SMNS 70640/80. (6) A. krymholzi (Géczy) [M], oWB-9, SMNS 70640/84. (7) A. sp. [M], oWB-9, SMNS 70640/85. (8) L. goetzendorfense (Dorn) [M], oWB-6, SMNS 70640/78. (9, 16) L. striatum (Buckman) [M]; (9) oWB-7, SMNS 70640/82; (16) oWB-9, SMNS 70640/83. (10, 15) L. capillare (Buckman) [M]; (10) oWB-9, SMNS 70640/86; (15) oWB-9, SMNS 70640/93. (12, 14) A. aff. substriatum (Buckman) [m]; (12) oWB-9, SMNS 70640/98; (14) oWB-9, SMNS 70640/91. 1–16: Obere Wilflingen-Bank, southern slope of the Wochenberg hill; Opalinum Zone (Bifidatum Subzone), viallii biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
Due to the gradation from the genus Leioceras into the genus Ancolioceras, some specimens cannot be assigned with confidence to the one or the other genus. Specimens closely resembling L. goetzendorfense (compare
(1) Ancolioceras citaae (Géczy) [M], oWB-9, SMNS 70640/87. (2) A. cf. viallii (Géczy) [M], oWB-9, SMNS 70640/97. (3) A. aff. subacutum (Buckman) [M], oWB-9, SMNS 70640/92. (4, 5) A. viallii [M]; (4) oWB-9, SMNS 70640/88; (5) oWB-9, SMNS 70640/89. (6): Leioceras goetzendorfense (Dorn) [M], oWB-8, SMNS 70640/79. 1–6: Obere Wilflingen-Bank, southern slope of the Wochenberg hill; Opalinum Zone (Bifidatum Subzone), viallii biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
Graphoceratids of the genus Staufenia from beds St-B 3–5 (latiumbilicus biohorizon) are generally assigned to Staufenia latiumbilicus (Quenstedt, 1886). Quenstedt (1886, pl. 57, Figs
For an exhaustive description of St. latiumbilicus we refer to Rieberʼs (1963) description of St. sehndensis, since he described St. latiumbilicus under that name. The previous identification of specimens from the latiumbilicus biohorizon as St. sehndensis (Hoffmann) should be abandoned after the formal validation of Quenstedtʼs third names. The taxon St. sehndensis, originally described from North Germany, is either a younger subjective synonym of St. latiumbilicus or a morphologically very close predecessor of St. latiumbilicus. Since the latiumbilicus biohorizon at the Wochenberg hill is the type horizon and locality of St. latiumbilicus, the herein documented specimens are topotypes.
The maximum size of Staufenia latiumbilicus is represented by a specimen of nearly 30 cm diameter (Fig.
Microconchiate St. latiumbilicus vary in a wide range from almost smooth (Fig.
(1a–5) Staufenia latiumbilicus (Quenstedt) [M and m]. Southern slope of the Wochenberg hill; Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), latiumbilicus biohorizon. 1: SMNS 70640/11 ([M], bed 3; 2: SMNS 70640/12 [m], bed 3; 3: SMNS 70640/13 [m], bed 4; 4: SMNS 70640/14 [M], bed 4; 5: SMNS 70640/15 [M], bed 5. Asterisk marks beginning of bodychamber. Scale bars: Figs
(1a, b) Ludwigia aff. crassa Horn [M], St-B 5, SMNS 70640/16. (2a, b) L. armipotens (Buckman) [M], St-B 5, SMNS 70640/17. (3a–4b) Staufenia latiumbilicus (Quenstedt) [m], St-B 5; 3: coarsely ribbed, evolute variety, SMNS 70640/18; 4: SMNS 70640/19. (5a, b): S. latiumbilicus (Quenstedt) [M], giant-sized specimen, ?pathological, SMNS 70640/20. 1a–5b: southern slope of the Wochenberg hill; Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), latiumbilicus biohorizon. Asterisk marks beginning of bodychamber. Scale bars: Figs
(1–3, 5–7) Staufenia latiumbilicus (Quenstedt) [M], (1) SMNS 70640/21; (2) SMNS 70640/22; (3) SMNS 70640/23; (5) SMNS 70640/24; (7) SMNS 70640/25. (6) Paralectotype, original of Ammonites discus latiumbilicus Quenstedt, 1886, pl. 57, fig. 14, Paläontologische Sammlung der Universität Tübingen (formerly: Geologisch-Paläontologisches Institut der Universität Tübingen), GPIT-PV-61327, Schörzingen [= Wochenberg]. (4) St. sehndensis (Hoffmann) [M], holotype, original of Ludwigia sehndensis (Hoffmann, 1913, pl. 6, fig. 4) from Sehnde, Sehndensis Subzone, Geowissenschaftliches Museum der Universität Göttingen no. 73226 (459-78). 1–3, 5, 7: southern slope of the Wochenberg hill. 1–3. 5–7 Achdorf Formation, St-B 5; Murchisonae Zone (Murchisonae Subzone), latiumbilicus biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1a–2b) Staufenia latiumbilicus (Quenstedt) [M]. (1a, b) Lectotype, original of Ammonites discus latiumbilicus Quenstedt (1886, pl. 57, fig. 8), St-B 3–5, Wochenberg, Paläontologische Sammlung der Universität Tübingen (formerly: Geologisch-Paläontologisches Institut Tübingen), GPIT-PV-6132. (2a, b) St-B 5, SMNS 70640/26. 1–2: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), latiumbilicus biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
In the latiumbilicus biohorizon of the Wochenberg hill, ammonites of the genus Ludwigia are extremely rare. Besides c. 65 specimens of Staufenia only three fragmentary Ludwigia were recorded from bed St-B 5. These are morphologically intermediate between Ludwigia specimens from the opalinoides biohorizon below and those from the discoidea α biohorizon above; the ribbing is not falcate but only falcoid, like in most early representatives of the opalinoides biohorizon of the western Swabian Alb. In contrast to these early representatives, the younger forms of the latiumbilicus biohorizon lack the ventral bending of the ribs towards the aperture (
The ammonites of the genus Staufenia from the interval St-B 6 to St-B 8b represent Staufenia discoidea (Quenstedt, 1886).
St. latiumbilicus
is more evolute than St. discoidea α and exhibits a more gradational egregation of the outer whorl as indicated by the preserved spur line (Fig.
Concerning macroconchs, in the discoidea α biohorizon Ludwigia section predominate; however, in several specimens, the ventral shoulder is rounded. In contrast, ammonites of the morphogenus Brasilia are comparatively rare. Most specimens of Ludwigia spp. correspond to the “Artengruppe der L. murchisonae (Sowerby)” (“species-group of L. murchisonae (Sowerby)”) of
Ludwigia tuberata
Buckman, 1904 [in
Specimens showing a high and slender whorl section are assigned to Brasilia. They vary in the shape of the venter (rounded to quadratic/subquadratic), the strength of the ribbing and in their involution. A relatively coarsely ribbed Brasilia (Fig.
(1a–6b) Staufenia discoidea (Quenstedt) α. (1) [M], SMNS 70640/27, (2) [m], SMNS 70640/28, (3) [m], SMNS 70640/29, (4) [m], SMNS 70640/30, (5) [M], SMNS 70640/31. (6) Lectotype of Ammonites discoideus Quenstedt, 1886, pl. 58, fig. 3, SMNS 70640/32 [plaster cast; original in the Paläontologische Sammlung der Universität Tübingen (formerly: Geologisch-Paläontologisches Institut der Universität Tübingen), GPIT-PV-61330], Schörzingen [= Wochenberg]. 1a–5: St-B 6, southern slope of the Wochenberg hill. 6: St-B 6–8b. 1a–6b: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1–3b) Staufenia discoidea (Quenstedt) α [M], St-B 6. (1) SMNS 70640/32, (2) SMNS 70640/33, (3) SMNS 70640/34. (4a, b) Brasilia howarthi (Géczy) [M], St-B 6, SMNS 70640/35. (5) Ludwigia subtuberculata Rieber [m], St-B 7, SMNS 70640/36. (6a, b) L. murchisonae (Sowerby) [M], St-B 7, SMNS 70640/36. (7a, b): L. tuberata (Buckman) [M], St-B 6, SMNS 70640/37. 1–7b: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1–6) Staufenia discoidea α (Quenstedt). (1) [M]¸ almost complete adult specimen, St-B 8b, SMNS 70640/38. (2) [m], almost complete specimen, with proximal part of apophysis, St-B 8a, SMNS 70640/39. (3) [M], smooth nucleus, St-B 8a, SMNS 70640/40. (4) [M], ribbed nucleus, St-B 8b, SMNS 70640/41. (5) [m], complete with apophysis, St-B 8a, SMNS 70640/42. (6) [m], coarsely ribbed variety, St-B 8b, SMNS 70640/43. 1a–6: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1a, b) Ludwigia armipotens (Buckman) [M], St-B 8a, SMNS 70640/44. (2a, b) L. tuberata Buckman [M], St-B 8a or 8b, SMNS 70640/45. (3a, b) Staufenia discoidea α (Quenstedt) [M], St-B 8a, SMNS 70640/99. 1a–3b: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1a, b) Ludwigia depilata (Buckman) [M], St-B 8a, SMNS 70640/46. (2a–4b) L. subtuberculata Rieber [m], St-B 8a. (2) SMNS 70640/47, (3) SMNS 70640/48. (4) SMNS 70640/49. (5a, b) Brasilia elmii (Géczy) [M], St-B 8a, SMNS 70640/50. 1a–5b: Southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bars: Fig.
All Staufenia specimens from this biohorizon represent St. discoidea β. In contrast,
From the discoidea β biohorizon, we recovered only a single, weakly sculptured microconchiate specimen of St. discoidea β (Fig.
Specimens of Ludwigia spp. from the discoidea β biohorizon generally exhibit a more slender whorl section than those from the discoidea α biohorizon. Specimens assignable to the genus Brasilia are still rare.
L. reflua
(Buckman, 1899 [in
Ammonites
of the genus Brasilia from the discoidea β biohorizon are represented by B. bradfordensis (Buckman, 1887) [in
A single, strongly weathered specimen (Fig.
Quenstedt (1886) not only mentioned the Wochenberg hill itself but also the nearby village Schörzingen as finding localities of some ammonites listed below. Since the Achdorf Formation is not present within the village of Schörzingen, the specimens labeled with “Schörzingen” must either originate from the western or from the southern hillside of the Wochenberg. All specimens originate from the Murchisonae Subzone of the Murchisonae Zone (Upper Aalenian).
(1a, b) Ludwigia armipotens (Buckman) [M], St-B 8a, SMNS 70640/51. (2) L. reflua (Buckman) [M], St-B 8b, SMNS 70640/52. (3a, b) Brasilia howarthi (Géczy) [M], St-B 8b, SMNS 70640/53. (4a, b) B. falcatiformis (Géczy) [M], St-B 8a, SMNS 70640/54. ((5a, b): L. murchisonae (Sowerby) [M], St-B 8b, SMNS 70640/55. 1a–5b: Southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1) Ludwigia reflua (Buckman) [M], SMNS 70640/71. (2) L. murchisonae (Sowerby), SMNS 70640/72. (3) Brasilia baldii (Géczy) [M], SMNS 70640/94. (1–3) Southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, St-B 8b, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea α biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1a–8) Staufenia discoidea (Quenstedt) β [M], St-B 8c, Southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea β biohorizon. (1) SMNS 70640/56, (2) SMNS 70640/57, (3) SMNS 70640/58, (4) SMNS 70640/100, (5) SMNS 70640/59. (6) SMNS 70640/60. (7) SMNS 70640/61, coarsely ribbed variety. (8) SMNS 70640/62, weakly ribbed variety. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1a, b, 4a, b) Ludwigia aff. murchisonae (Sowerby) [M], (1) SMNS 70640/63, (4) SMNS 70640/64. (2a, b) L. fueloepi (Géczy) [M], SMNS 70640/65. (3a, b). L. gradata Buckman [M], SMNS 70640/66. 1a–4b: southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, St-B 8c, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea β biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
(1) Planammatoceras aff. planinsigne (Vacek) [M], SMNS 70640/67. (2a, b) Brasilia bradfordensis (Buckman) [M], SMNS 70640/68. (3a, b) Ludwigia gradata Buckman [M], SMNS 70640/ 69. (4a, b): L. reflua (Buckman) [M], SMNS 70640/70. 1a–4b: Southern slope of the Wochenberg hill, Achdorf Formation, Staufensis-Bank, St-B 8c, Upper Aalenian, Murchisonae Zone (Murchisonae Subzone), discoidea β biohorizon. Asterisk marks beginning of bodychamber. Scale bar: 3 cm.
Revision of Quenstedtʼs (1886) ammonites from the Achdorf Formation of the Wochenberg hill or from Schörzingen.
Original name in Quenstedt (1886) | Locality | Revised name and nomenclatorial status | Biohorizon |
---|---|---|---|
A. discus latiumbilicus , p. 462, pl. 57, fig. 8 | Wochenberg | St. latiumbilicus (Quenstedt), lectotype (designated herein) | latiumbilicus |
A. discus latiumbilicus , p. 464, pl. 57, fig. 14 | Schörzingen | St. latiumbilicus (Quenstedt), paralectotype | latiumbilicus |
A. discoideus , p. 466, pl. 58, fig. 5 | Schörzingen | St. latiumbilicus (Quenstedt) | latiumbilicus |
A. discoideus , p. 465, pl. 58, fig. 3 | Schörzingen |
St. discoidea
(Quenstedt), lectotype, selected by |
discoidea α |
A. discus Zieten, p. 462, pl. 57, fig. 7 | Wochenberg | Staufenia discoidea (Quenstedt) | discoidea α |
Ammonites discus Zieten, p. 461, pl. 57, fig. 6 | Wochenberg | Staufenia discoidea (Quenstedt) | discoidea α |
Biohorizons in the Aalenian of SW Germany. Those which are recorded at the Wochenberg hill are shaded in dark gray.
Concavum | Formosum | yet to be worked out | ?Geisingen, Ringsheim, Wutach |
Concavum | cavatum | Zollernalb ( |
|
Bradfordensis | Gigantea | decipiformis | Geisingen ( |
geisingensis | Geisingen, Öfingen ( |
||
gigantea sensu Contini | Geisingen ( |
||
Bradfordensis | yet to be worked out | Aalen [Quenstedt 1886, |
|
staufensis | Swabian Alb, Wutach [Quenstedt 1886, |
||
Murchisonae | Murchisonae | discoidea β | Wochenberg, Plettenberg [Quenstedt 1886, |
discoidea α | Wochenberg, Gosheim | ||
latiumbilicus | Wochenberg [Quenstedt 1886, |
||
yet to be worked out | Gosheim | ||
Haugi | yet to be worked out | Gosheim, Geisingen, Aalen | |
opalinoides | Geisingen, Wutach [ |
||
subfalcatum | Aichelberg [ |
||
Opalinum | Bifidatum [ex Comptum] | viallii | Wochenberg [here], ?Gosheim |
evolutum | Aichelberg area [ |
||
crassicostatum | Swabian Alb, Wutach [ |
||
uncinatum | Aichelberg area [ |
||
bifidatum/rieberi | Aichelberg area [ |
||
Opalinum | hansrieberi | Swabian Alb [ |
|
opaliniforme | Swabian Alb [ |
||
dilucidum 1 | Swabian Alb [ |
||
opalinum 1 | Swabian Alb [ |
In our stratigraphical analyses, we focus on the beds of the Achdorf Formation and the directly overlying Sowerbyi-Oolith of the Wedelsandstein Formation.
The Untere Wilflingen-Bank contains the crassicostatum biohorizon. Typical ammonites of this horizon are the coarse-ribbed L. crassicostatum along with L. goetzendorfense [formerly misidentified as L. “comptum”] and numerous morphological varieties. For a distinction from the older uncinatum biohorizon we refer to
The herein newly introduced viallii biohorizon of the Wochenberg hill was detected in the c. 1.7 m thick Obere Wilflingen-Bank. Its ammonite fauna is transitional between the ammonite fauna of the crassicostatum biohorizon (
The ammonite fauna of the crassicostatum biohorizon is more uniform than that of the viallii biohorizon. It is dominated by L. goetzendorfense (= L. comptum sensu
The Haugi Subzone was not recorded at the Wochenberg hill. However, it is quite possible that sediments of this age locally occur, such as the calcareous marls below the „Sehndensis-Knollenlage“ („Sehndensis nodular layer“) which were not studied in detail by us or a 0.8 m thick alternation of limestones and marly limestones which correspond to the questionable Sinon-Bank sensu Rieber.
This biohorizon (beds St-B 4–5) is exclusively characterized by its index ammonite Staufenia latiumbilicus. Ammonites of the genus Ludwigia are extremely rare and do not contribute to the recognition of this biohorizon. A differentiation towards the next older described opalinoides biohorizon is rather simple, since in the latter the genus Ancolioceras predominates (see
The discoidea α biohorizon (beds St-B 6–8b) is characterized by its name giving species Staufenia discoidea α together with ammonites of the genus Ludwigia, which
The discoidea β biohorizon (Schicht St-8b) is characterized by the index species Staufenia discoidea β and an accompanying fauna containing Ludwigia spp., which
Beds of the staufensis biohorizon (
From a bed following immediately below the “Sowerbyi-Oolith-Knollenlage” [“Sowerbyi-oolith nodular layer”],
North Germany:
SW Germany: The crassicostatum biohorizon is widespread in the western Swabian Alb (
France (Franche-Comté):
This is why we prefer the more consistent and reproducable subdivision of
South England (Dorset): Despite of numerous previous studies (
Scotland (Isle of Skye):
Switzerland (Central Swiss Jura):
In the Aalenian of Luxembourg,
Evolution of the genus Staufenia in the Upper Aalenian of the Swabian Alb. Staufenia staufensis originates from the Plettenberg hill (
The evolution of the genus Staufenia is well-recorded in sections of the Wochenberg and nearby Plettenberg hills (
But why are evolutionary trends in Staufenia appear to be continuous and targeted, whereas they are discontinuous and random in Leioceras/Ancolioceras? A possible reason could lie in the different distribution ranges of these genera. Staufenia is an endemic genus restricted to present-day Germany, E France and S England [only recorded there up to the Obtusiformis Subzone], whereas Leioceras/Ancolioceras had a much wider geographic distribution including the entire Tethyan realm. In the latter taxa, different environmental conditions (e.g. water temperature, food supply) in various parts of the distribution area might have led to different adaptations in the various populations. When such temporarily spatially isolated populations of Leioceras/Ancolioceras showing an onset of speciation later became reunified, e.g. in the course of a sealevel rise reconnecting neighbouring basins and thus allowing an interbreeding of their populations, this may have resulted in seemingly random developments.
We thank our friends who assisted in the very hard fieldwork, some of them even for a couple of days: Rolf Chiarini (Esslingen, Switzerland), Toni Chiarini†, Uwe Fidder (Reutlingen, Germany), Matthias Grupp (Göppingen-Holzheim, Germany), Klaus Jenne (Bötzingen, Germany), Martin Kapitzke (Remshalden-Geradstetten, Germany), and Jochen Rath (Bietigheim-Bissingen, Germany). Numerous fruitful discussions with Robert B. Chandler (London, England) added to this contribution. The authorities of the town of Schömberg, the Landratsamt Zollernalbkreis and the Landesamt für Denkmalpflege Baden-Württemberg at the Regierungspräsidium Stuttgart provided the necessary permissions for our scientific excavations. The manuscript greatly benefitted from the constructive criticism by the journalʼs referees Matthias Franz (Freiburg im Breisgau, Germany) and Bernhard Hostettler (Glovelier, Switzerland).