Early Miocene Continental Gastropods from New Localities of the Molasse Basin in Southern Germany

PalZ (2016) 90:469–491 DOI 10.1007/s12542-016-0291-y RESEARCH PAPER Early Miocene continental gastropods from new localities of the Molasse Basin in southern Germany 1,2 3 3 Rodrigo B. Salvador • Martina Pippe`rr • Bettina Reichenbacher • Michael W. Rasser1 Received: 23 February 2015 / Accepted: 17 January 2016 / Published online: 12 February 2016 Ó Palaöntologische Gesellschaft 2016 Abstract Here, we present the continental aquatic and latter can be considered a synonym of T. cyrtocelis). terrestrial gastropods found in samples of 11 new boreholes Finally, we present a paleoecological interpretation for the in the Molasse Basin, southern Germany. The samples USM, OBM and OSM based on the gastropod fauna. come from the Lower Freshwater Molasse (USM), the Upper Brackish Molasse (OBM; Grimmelfingen and Keywords Gastropoda Á Grimmelfingen Formation Á Kirchberg Formations) and the Upper Freshwater Molasse Kirchberg Formation Á Lower Freshwater Molasse Á Upper (OSM). The studied segments of these lithostratigraphical Brackish Molasse Á Upper Freshwater Molasse units represent the beginning of the lower Miocene (USM), and the uppermost lower Miocene (OBM, OSM). Twenty- Kurzfassung Basierend auf den Proben von 11 in den four species of terrestrial and freshwater gastropods are letzten Jahren durchgefu¨hrten Bohrungen im su¨ddeutschen reported here, belonging to the families Neritidae, Molassebecken wird die kontinentale aquatische und ter- Melanopsidae, Pachychilidae, Bithyniidae, Hydrobiidae, restrische Gastropodenfauna neu bearbeitet. Das Material Truncatellidae(?), Viviparidae, Valvatidae(?), Lymnaeidae, stammt aus Proben der Unteren Su¨ßwassermolasse (USM), Planorbidae, Carychiidae, Zonitidae, Helicidae, Hygromi- der Oberen Brackwassermolasse (OBM; Grimmelfingen idae and Discidae(?). We provide remarks on the taxonomy und Kirchberg Formationen) und der Oberen Su¨ßwasser- of some of the studied species, including a revision of molasse (OSM). Die hier bearbeiteten Abschnitte dieser Theodoxus cyrtocelis, T. obstusangula and T. sparsus (the lithostratigraphischen Einheiten sind in das unterste Unter- Mioza¨n (USM) bzw. in das oberste Unter-Mioza¨n (OBM, OSM) einzustufen. Insgesamt werden 24 Arten kontinen- taler Gastropoden aus den Familien Neritidae, Melanopsi- dae, Pachychilidae, Bithyniidae, Hydrobiidae, Truncatellidae(?), Viviparidae, Valvatidae(?), Lymnaeidae, Planorbidae, Carychiidae, Zonitidae, Helicidae, Hygromi- Electronic supplementary material The online version of this idae und Discidae(?) beschrieben. Die Taxonomie einiger article (doi:10.1007/s12542-016-0291-y) contains supplementary material, which is available to authorized users. dieser Arten wird kritisch beleuchtet und die Arten der Gattung Theodoxus (T. cyrtocelis, T. obstusangula, T. & Rodrigo B. Salvador sparsus) warden revidiert, T. sparsus wird als Synonym [email protected] von T. cyrtocelis interpretiert. Daru¨ber hinaus wird auf der Grundlage der Gastropodenfauna eine palaöo¨kologische 1 Staatliches Museum fu¨r Naturkunde Stuttgart, Stuttgart, Germany Interpretation fu¨r die USM, OBM und OSM gegeben. 2 Mathematisch-Naturwissenschaftliche Fakulta¨t, Eberhard Karls Universita¨tTu¨bingen, Tu¨bingen, Germany Schlu¨sselwo¨rter Gastropoda Á Grimmelfingen Formation Á Kirchberg Formation Á Untere 3 Department of Earth and Environmental Sciences, Palaeontology and Geobiology, Ludwig-Maximilians- Su¨ßwassermolasse Á Obere Brackwassermolasse Á Obere Universita¨tMu¨nchen, Munich, Germany Su¨ßwassermolasse 123 470 R. B. Salvador et al. Introduction R. Schlickum in the 1960s and 1970s, and some works dedicated to special aspects such as ontogenetic strategies Numerous samples from the cores of 11 boreholes located (Kowalke and Reichenbacher 2005), biogeographic distri- in the Molasse Basin of Bavaria, southern Germany bution (e.g., Reichenbacher 1993) or community studies (Fig. 1), have recently been investigated in the course of a (Schneider and Prieto 2011). The newly available material research program of the Bayerisches Landesamt fu¨r from the drilling research program mentioned above pro- Umwelt (project ‘‘Informationsoffensive Oberfla¨chennahe vides a unique opportunity to present a comprehensive Geothermie’’). The sampled lithostratigraphic units are taxonomical study of all the brackish, freshwater and ter- known as the Lower Freshwater Molasse (USM), the Upper restrial gastropods from the USM, OBM and OSM, and Brackish Molasse (OBM, Grimmelfingen and Kirchberg allows new paleoecological considerations. It was also Formations [Fms.]) and the Upper Freshwater Molasse possible to include type material for some species in order (OSM, Fig. 2). The studied samples from the USM are to achieve a better understanding of their taxonomy. dated from the lowermost Miocene (Aquitanian), while those from the OBM and the OSM correspond to the uppermost lower Miocene (upper Burdigalian). Geological setting Whereas the molluscan fauna from the USM has not yet been studied, several works are available for the OBM and The boreholes are situated in the western to central part of USM including the pioneering works of nineteenth century the Molasse Basin (Fig. 1), which is part of the North paleontologists (e.g., Krauss 1852), the later works of W. Alpine Foreland Basin and belongs to the Paratethys realm. Fig. 1 Map showing the localities studied in the present work. a Schematic map of the Molasse Basin (modified after Jin et al. 1995). b Geographic locations of the boreholes 123 Early Miocene continental gastropods from new localities of the Molasse Basin in southern… 471 Fig. 2 Miocene lithostratigraphic units in the south German Molasse Basin (after Doppler et al. 2005; Reichenbacher et al. 2013) and stratigraphic range of drill cores. Dotted lines indicate stratigraphic units not present in the drill cores In the German segment of the North Alpine Foreland et al. 1998). The thick marls of the Kirchberg Fm. (up to Basin, the Molasse succession as a whole is divided into 22 m) overlie the Grimmelfingen Fm. without a disconti- two transgressive–regressive megacycles, which are sepa- nuity. Typically, these marls contain rich and diverse fossil rated by an unconformity (e.g., Lemcke 1988; Bachmann assemblages with bivalves, gastropods, ostracods, fish oto- and Mu¨ller 1992; Schwerd et al. 1996; Doppler et al. 2005). liths and charophytes that allow for a subdivision into the The first megacycle, spanning the lower Oligocene (Ru- brackish–marine lower Kirchberg Fm. and the brackish– pelian) to lowermost Miocene (Aquitanian), comprises the lacustrine upper Kirchberg Fm. (Reichenbacher 1989; Lower Marine Molasse, the Lower Brackish Molasse, and Doppler 2011; Reichenbacher et al. 2013). the USM. The second megacycle includes the Upper Reichenbacher et al. (2013) have suggested an upper Marine Molasse (OMM), the OBM and OSM deposits and lower Miocene (upper Burdigalian) age for the OBM sed- is late Early Miocene (latest Aquitanian and Burdigalian) iments, based on a combination of bio-, litho- and magne- to early Late Miocene (Tortonian) in age. tostratigraphy, with the Kirchberg Fm. representing the This study focuses on the USM, OBM (Grimmelfingen uppermost Burdigalian (lower Karpatian). The OBM/OSM and Kirchberg Formations) and OSM gastropods (note that, transition is gradual in all drill cores. In most of the cores, here, we opt for the more widely used German abbrevia- only the lowermost OSM sediments, which are middle tions; USM: ‘‘Untere Su¨ßwassermolasse’’; OBM: ‘‘Obere Karpatian in age (Reichenbacher et al. 2013), contain few Brackwassermolasse’’; OSM: ‘‘Obere Su¨ßwassermolasse’’; freshwater fossils and rare brackish microfossils. Fig. 2). The USM sediments of the drill cores have yielded partially rich fossil assemblages with charophytes, gastropods, ostracods, fish otoliths and small mammal teeth, Materials and methods which are most probably late Egerian (earliest Miocene, Aquitanian) in age (unpublished data). Our new material has been assembled from the cores of The Grimmelfingen and Kirchberg Formations are gen- several boreholes drilled under the auspices of the Bavarian erally summarized as OBM. The Grimmelfingen Fm. over- Environment Agency (Landesamt fu¨r Umwelt) between lies discordantly the USM (Fig. 2) and is between 7 and 2010 and 2013 (Offingen 1, Glo¨tt 1, Gundremmingen 1, 41 m thick. This discordancy is due to the incision of a river Holzheim 1, Dillingen 1, Buttenwiesen 1, Druisheim 1, (Graupensand River) that extended along the northern Hamlar 1) as well as from the boreholes ‘‘Gu¨nzburg margin of the Southwest German Molasse Basin and eroded Brunnen 3 neu’’, ‘‘Vogelho¨lzl N Lauingen’’ and ‘‘WWA the entire OMM and partly also the upper USM in this area Donauwo¨rth, Kernbohrung Gempfing W4’’. (Kiderlen 1931; Reichenbacher et al. 1998). The Grim- Core samples were processed by soaking in hydrogen melfingen Fm. represents deposition of the Graupensand peroxide solution for several hours, washing through sieves River and consists of fine- to coarse-grained sands that are of 63-, 200- and 400-lm mesh size, and drying at a tem- predominantly carbonate- and fossil-free; only a few beds perature of 40 8C. Identification of USM, OBM and OSM contain mollusks, fish teeth and charophytes (Reichenbacher in borehole segments and samples has been conducted 123 472 R. B. Salvador et al. based on litho and biofacies as well as taxonomic and Family Neritidae Rafinesque, 1815 biostratigraphic analyses involving presence/absence of Genus Theodoxus Montfort, 1810 index taxa and characteristic

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