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Echinoderm diversity of Cretaceous deposits at Le Mans (France) ... John W. M. Jagt3, Nicolas Morel4, Didier Néraudeau2, Mike Reich5, Michel Roux6 ... Université de Rennes 1, 236 avenue du Général-Leclerc, 35042 Rennes, France.
Echinoderm diversity of Cretaceous deposits at Le Mans (France) Loïc Villier1, Gérard Breton2, Delphine Desmares1, John W. M. Jagt3, Nicolas Morel4, Didier Néraudeau2, Mike Reich5, Michel Roux6 1 CR2P, Université Pierre & Marie Curie, 4 place Jussieu, 75005 Paris, France 3 Natuurhistorisch Museum Maastricht, de Bosquetplein 6-7, 6211 KJ Maastricht, the Netherlands 5 Geowissenschaftliches Zentrum der Universität Göttingen, Goldschmidt-Strasse 1-5, 37077 Göttingen, Germany

2 Géosciences Rennes, Université de Rennes 1, 236 avenue du Général-Leclerc, 35042 Rennes, France 4 Musée Vert, 204 avenue Jean Jaurès, 72100 Le Mans, France 6 BOREA, Muséum National d’Histoire naturelle, 43 rue Cuvier, 75005 Paris, France

The Cenomanian stage of the geological time scale was named for «Cenomanum», the Latin name of Le Mans (Sarthe, France). D’Orbigny (1847) chose the locality for its outstanding richness in marine fossils, especially molluscs, bryozoans, brachiopods and echinoderms. The geological formations

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cropped out in numerous clay, sand and limestone pits in the surroundings of Le Mans until the expansion of the city during the twentieth century. A revision of the historical Cenomanian stage was undertaken recently with the emergence of a National program for inventory of the French Geological Gazonfier

La Butte

Heritage. Historical sections of Le Mans, complimentary sections found in close villages and historical collections were investigated. Here they are

The study of the echinoderms revealed an especially rich and well preserved fauna. Two main results must be highlighted:

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1 - the rare and uncommon taxon assemblage collected in a level of exceptional preservation.

Geological map of Le Mans. The Cenomanian (in green) crop out the hill and valley slopes

2 - the major changes in echinoderm assemblages at the transition between the Cenomanian and Turonian stages (94 My ago).

Location of the historical quarries holding fossil echinoderms in Le Mans

1 - The so-called “lentilles à Echinodermes”, a level of exceptionnally preserved echinoderms

Wienberg Rasmussen (1961) referred Pentacrinus cenomanensis to the genus Isocrinus, albeit with a query, on the basis of only disarticulated material. As outlined by Hess (2011a), proper assignment of isocrinid taxa requires an in-depth analysis of articulation types of proximal brachials and of cup structure. It appears premature to assign this material to genus for now.

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Age 10 mm 5 mm

-93.9 Ma

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Ophiotitanos sp.

Undescribed ophiuroid taxon

As for other ophiuroids, articulated skeletons of Ophiotitanos are rare, but the skeletal elements are common in the Cretaceous sediments.

Guéranger planed to publish the 30 fossil ophiuroids he had at hand under the name Ophiura cretacea. There are at least three distinct species to be described.

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Archiacia gigantea d’Orbigny 1855 and Tetragramma roissyi (Pictet 1857)

LITHOLOGY

«Isocrinus» cenomanensis (d’Orbigny 1850)

FORMATIONS

The Guéranger Collection, at the Musée Vert (Le Mans), houses a unique echinoderm fauna, including many taxa unknown from elsewhere. Preservation is exceptional with the occurrence of echinoids with still-attached spines (Tetragramma roissyi), starfish body fossils with plates, spines, and granules, still looking as if ‘alive’ (Cenomanaster cenomanensis, Tethyaster guerangeri, an unpublished zoroasterid), two forms of ophiuroid (Ophiotitanos sp., an unpublished taxon) and two crinoids (“Isocrinus” cenomanensis, Glenotremites paradoxus) known from articulated bodies. All specimens were found in the so-called “lentilles à Echinodermes” of the “Sables du Mans” Formation. The sedimentary matrix usually combines clay and sand, in which Juignet (1974) recognized the effects of tidal currents under shallow-marine conditions. The individuals were buried rapidly and coated with clays brought by river floods, which favoured the preservation. The contrasted ecologies of the associated taxa suggest some mixing of individuals from, not necessarily distant, but distinct environments, probably transported by coastal and/or storm currents.

Early Turonian

Craie à I. labiatus

Late Cenomanian

Craie à T. carentonensis Sables à C. obtusus Marnes à P. biauriculata

Tetragramma roissyi (Pictet 1857)

Individual specimen with still attached spines and Archiacia is usually considered a Tethyan form, with a northern occu- elements of the Aristotle's Lantern. rence in the Aquitaine basin during the Cenomanian. Its discovery at Le Mans would suggest migration from the south during a warming event or temporary changes in the regional current directions.

Sables du Perche

Middle Cenomanian Craie de Théligny Grès de Lamnay Sables de La Trugalle

Early Cenomanian Marnes de Ballon

-100.5 Ma

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Cenomanaster cenomanensis (Mercier 1935)

Holotype and unique specimen of the species. Goniasteridae.

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Late Albian

Tethyaster guerangeri Breton 1995

Probable new Zorasterid taxon

A precise taxonomic assignent would require preparation of the oral side.

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Holotype and paratype, Astropectinidae.

2 - changes in echinoderm assemblages at the Cenomanian - Turonian stage transition

Craie à I. labiatus

Late Cenomanian

Craie à T. carentonensis Sables à C. obtusus Marnes à P. biauriculata

Roveacrinus? sp.

Ophiotitanos sp.

Pycinaster sp.

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1 mm Cup, close to R. communis and R. alatus

Crateraster ? sp.

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Disc scale. Isolated ossicles of several other ophiuroid taxa occur in the samples.

Marginal ossicle

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1 mm Abactinal ossicles

Marginal ossicle

Marginal ossicle

1 mm isolated brachials

Parataxon: ‘Parvispina’ sp.

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Myriotrochidae

Lithology 12 m 11

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50 µm Parataxon: ?Palaeotrochodota sp.

interradial calcareous ring element

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100 µm

50 µm ?Chiridota sp. 1 [parataxon: Jumaraina]

?Myriotrochus sp., fragment of a wheel [paragenus: Hemisphaeranthos]

?Myriotrochus sp., interradial calcareous ring element, outer view

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Craie à T. carentonensis Sables à C. obtusus

Sables du Perche

Roveacrinus aff. rugosus

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Comptonia sp.

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Grès de Lamnay

Cushmani Zone

CENOMANIAN

Craie de Théligny

Naviculare Zone

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Middle Cenomanian

Marnes à P. biauriculata

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Sable du Perche

Early Cenomanian

Sampling in glauconite rich chalk of the «Craie à T. carentonensis»

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Sables de La Trugalle

partial cup, showing the surface for insertion of a primibrachial

partial cup

Fredaster guyaderi

1 mm Marginal ossicle

proximal brachial

Tethyaster guerangeri

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Marnes de Ballon

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Late Albian

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Parataxon: Pravuscucumis sp.

Parataxon: ‘Priscopedatus’ sp.

Chiridotidae

Craie à I. labiatus

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Holothuriidae

Isocrinida indet.

1 mm Articulation face of an isolated columnals

Metopaster parkinsoni

Stauranderasteridae indet.

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100 µm

Formations

Planktonic foraminifera biostratigraphy

TURONIAN

geslinia Nodosoides Zone -num Zone Archaeocretacea Zone Helvetica Zone

Early Turonian

LITHOLOGY

FORMATIONS

Stratigraphy

Ammonite biostratigraphy

We have investigated the effects of the major environmental changes of the Cenomanian–Turonian transition on echinoderm fauna, with fine stratigraphic sampling, at Mezières-sur-Ponthouin, about 15 km north of Le Mans. Every sedimentary facies is characterized by an association of echinoderm taxa comparable to those found in other places of the Paris Basin, southern England or the Aquitaine Basin. From base to top: - The echinoderms of the upper Cenomanian “Sables à Catopygus obtusus” are obviously dominated by the cassiduloid echinoid Catopygus obtusus and astropectinid starfishes (Thetyaster guerangeri). Associating serpulid worms, bryozoans and terebratulid brachiopods, the ecological communities are typical of shallow, well-oxygenated sandy bottoms. - The “Craie à Terebratella carentonensis” records an outstanding abundance of planktonic roveacrinids, which is also reported in England, Germany, Brazil, and is consistent with the hypothesis of increasing plankton productivity on the continental shelf during the Cenomanian–Turonian transition. The benthic association of taxa mark the transition to chalk ooze. - The lower Turonian “Craie à Inoceramus labiatus” records an increasing echinoderm taxonomic diversity, with several echinoids, a high diversity of valvatacean starfishes and holothuroids representing the Chiridotidae, Myriotrochidae, and Holothuriidae. Most groups are sediment dwellers and/or deposit feeders.

Inferomarginal ossicle

Inferomarginal ossicle

Superomarginal ossicle