Biostratigraphy and Paleoecology of Continental Tertiary Vertebrate Faunas in the Lower Rhine Embayment (NW-Germany)
Total Page：16
File Type：pdf, Size：1020Kb
Netherlands Journal of Geosciences / Geologie en Mijnbouw 81 (2): 177-183 (2002) Biostratigraphy and paleoecology of continental Tertiary vertebrate faunas in the Lower Rhine Embayment (NW-Germany) Th. Mors Naturhistoriska Riksmuseet/Swedish Museum of Natural History, Department of Palaeozoology, P.O. Box 50007, SE-104 05 Stockholm, Sweden; e-mail: [email protected] Manuscript received: October 2000; accepted: January 2002 ^ Abstract This paper discusses the faunal content, the mammal biostratigraphy, and the environmental ecology of three important con tinental Tertiary vertebrate faunas from the Lower Rhine Embayment. The sites investigated are Rott (MP 30, Late Oligocene), Hambach 6C (MN 5, Middle Miocene), Frechen and Hambach 11 (both MN 16, Late Pliocene). Comparative analysis of the entire faunas shows the assemblages to exhibit many conformities in their general composition, presumably re sulting from their preference for wet lowlands. It appears that very similar environmental conditions for vertebrates reoc- curred during at least 20 Ma although the sites are located in a tectonically active region with high subsidence rates. Differ ences in the faunal composition are partly due to local differences in the depositional environment of the sites: lake deposits at the margin of the embayment (Rott), coal swamp and estuarine conditions in the centre of the embayment (Hambach 6C), and flood plain environments with small rivulets (Frechen and Hambach 1 l).The composition of the faunal assemblages (di versity and taxonomy) also documents faunal turnovers with extinctions and immigrations (Oligocene/Miocene and post- Middle Miocene), as a result of changing climate conditions. Additional vertebrate faunal data were retrieved from two new assemblages collected from younger strata at the Hambach mine (Hambach 11C and 14). They are important for the understanding of the Plio-Pleistocene transition in the southern part of the Lower Rhine Embayment and for correlating depositional sequences in the Dutch/German borderland. Keywords: mammal biostratigraphy, Middle Miocene, Late Oligocene, Late Pliocene, vertebrate environments Introduction mic acids in the deposits. The acids decalcified the sediments and often resolved both mollusc shells as The southern part of the Tertiary graben structure of well as vertebrate bones and teeth. In contrast to the the Lower Rhine Embayment in NW-Germany is oil shale deposits of Rott, from which vertebrate re characterised by the intercalation of marine and con mains were studied for 170 years (Bronn, 1828; for tinental sediments. They contain the thick, economi further references see von Koenigswald et al., 1992; cally important deposits of Miocene lignitic brown Mors, 1997), the first vertebrate fossils from the large coal which is exploited in vast open cast mines by the open cast lignite mines were published by Strauch Rheinbraun AG mining company. Although well ex (1990) ten years ago. posed due to intensive mining, and studied by geolo New discoveries of vertebrate, especially mam gists and palaeontologists for two centuries, these de malian remains from boreholes near Rott as well as posits yielded only few biostratigraphical and from different stratigraphic levels in the Frechen and palaeoecological data. The reason for the rare occur Hambach coal mines (Fig. 1) were described in the rence of faunistic remains is the high content of hu- last years (e.g. Mors, 1995; van Kolfschoten et al., Netherlands Journal of Geosciences / Geologie en Mijnbouw 81 (2) 2002 177 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.234, on 28 Sep 2021 at 14:12:28, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022411 upper part of this zone. This indicates a depositional age of latest Oligocene (Chattian) for the sediments at the southern margin of the basin. The Middle Miocene fauna of Hambach 6C (Table 2) In the Lower Rhine Embayment west of Koln, large open cast mines expose thick series of Miocene and Pliocene strata. The Miocene Ville Series with the Main Coal Seam never produced any vertebrate re mains due to slightly acidic ground waters. The dis covery of a well preserved and rich vertebrate fauna in a channel fill within the Frimmersdorf seam at the Hambach mine (Fig. 1) is therefore of immense inter Fig. 1. Geological sketch map of the southern part of the Lower est. Among various marine and freshwater fish, am Rhine Embayment with the location of the palaeontological sites phibians and reptiles, more than 70 mammal species Rott, Hambach, and Frechen. were identified to date (Mors et al., 2000).They doc ument the occurrence of the didelphid Amphipe- 1998; Mors et al., 2000). The unusually rich and to ratherium, of insectivores like erinaceids, the meta- some degree spectacular material especially provides codontid Plesiosorex, talpids, soricids, and dimylids, of new and reliable biostratigraphic data for the sedi chiropterans, of rodents like sciurids, petauristids, mentary fill of the Lower Rhine Embayment. The ver glirids, eomyids, cricetids, and castorids, and of lago- tebrate fossils from the Hambach and Frechen mines morphs (Ziegler & Mors, 2000; von Koenigswald & also provide insight into palaeoecological conditions Mors, 2001). Large mammals are represented by the of terrestrial environments in NW Europe during the primate Pliopithecus, by carnivores like the hyaenid Neogene, and supply new data for palaeobiogeo- }Protictitherium, mustelids, amphicyonids, and the ur- graphical analysis. sid Ursavus, by artiodactyls like the suid Hyotherium, the palaeochoerid Taucanamo, tragulids, cervids, and Vertebrate faunas and biostratigraphic setting bovids, by cetaceans, by perissodactyls like the equid Anchitherium, rhinos, and by proboscideans (Rossner The Late Oligocene fauna of Rott (Table 1) & Mors, 2001). Small mammals are predominant within this fauna with at least 50 species. Of particu lar interest is that usually rare taxa like Lanthanotheri- The fossil site Rott near Bonn at the southern margin um, Plesiosorex, Miopetaurista, Myoglis, Fahlbuschia, of the Lower Rhine Embayment (Fig. 1) is famous for and Karydomys are very abundant. Larger mammals its rich flora, as well as its insect and vertebrate fauna are dominated by beavers and tragulids of the genus (von Koenigswald, 1996). The lacustrine oil shales Dorcatherium. In addition, at Hambach 6C there is produced exceptionally well preserved, articulated evidence for extremely rare mammals like Orygotheri- skeletons with imprints of scales, skin, feathers, and um, Anchitheriomys and Pliopithecus. fur ('Messel-like' preservation). The vertebrate fauna consists of freshwater fish, many amphibian species, Based on the rich association of mammalian taxa reptiles, and mammals. The biostratigraphic setting that includes about 30 rodent species, this late Or- into the Mammalian Paleogene biozones MP 28-30 leanian fauna can be correlated with the upper part of was based on the occurrence of the small anthra- the Mammalian Neogene biozone MN 5 (Mors et al., cotheriid Microbunodon (von Koenigswald et al., 2000). The depositional age of the middle part of the 1992). Main Coal Seam (horizon 6C of the local lithostratig- A recently discovered fauna from overlaying lake raphy) can therefore be assigned to the early middle shore and flood plain deposits consists of 20 small Miocene. This means Langhian or Reinbekian ac mammal species including the didelphid Am- cording to the stratigraphy of the NW German Ter phiperatherium, talpids, dimylids, soricids, chiropter- tiary, and a numerical age range between 15.2-16.0 ans, the flying squirrel Blackia aff. miocaenica, the cas- Ma. The vertebrates of Hambach 6C are also of great torid Steneofiber, glirids, eomyids, and cricetids palaeobiogeographic importance as they represent the (Mors, 1995, 1996). This newly recorded mammal northwesternmost extension of terrestrial Miocene assemblage enhances biostratigraphic precision and faunas in Europe. places the deposits in MP 30, most probably in the 178 Netherlands Journal of Geosciences / Geologie en Mijnbouw 81 (2) 2002 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.234, on 28 Sep 2021 at 14:12:28, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0016774600022411 The Late Pliocene composite fauna of Frechen and Ham- discoglossid anurans as well as of toads are rare at all bach 11 (Table 3) three localities. Only at Rott the aquatic tadpoles are common. Due to the different stratigraphic setting of The Pliocene Reuver Clay, exposed at the Frechen the localities, the discoglossids are represented by dif and Hambach mines (Fig. 1), produced two excel ferent taxa. Aquatic palaeobatrachid anurans are very lently preserved small vertebrate faunas with freshwa common in Rott (Wuttke, 1996), indicating optimal ter fish, amphibians, reptiles, and mammals. The living conditions in a currentless freshwater lake. composite mammalian fauna of the Reuver Clay in They are absent at Hambach 6C and rare at Ham cludes talpids, soricids, a mustelid, petauristids, sci- bach 11. Their absence at Hambach 6C may be due urids, castorids, glirids, arvicolines, murids, a lago- to pronounced estuarine conditions. morph, a cervid, and a rhino (Strauch, 1994; Turtles are common at all three localities, but differ Reumer, 1995; van Kolfschoten et al., 1998; Mors et in