Lake Enspel Research Articles

New fossil ants of the subfamily Myrmicinae (Hymenoptera, Formicidae) from the Upper Oligocene of Enspel (Westerwald Mountains, Rhineland Palatinate, Germany)

New species of the subfamily Myrmicinae are described from the fossil volcanogenic Lake Enspel, Westerwald, Germany. This Fossil-Lagerstatte comprises lake sediments, which essentially consist of intercalated “oilshales” and volcaniclastics. The sediments were dated to be of late Oligocene age. Out of the 287 fossil ants from Enspel examined, 96.5% (n = 277) belong to the formicoid clade (Formicinae, Dolichoderinae, Myrmicinae), and only 3.5% (n = 10) to the poneroid clade (Ponerinae, Agroecomyrmecinae). The high proportion of Myrmicinae (36.6%) indicates that this subfamily was already strongly represented in Central Europe in the late Oligocene. However, it should be noted that the large number of specimens are alate reproductives. The number of workers is low: n = 19, or 6.1% of 312 specimens when 25 isolated wings are included. Ten new species, belonging to the genera Paraphaenogaster, Aphaenogaster, Goniomma and Myrmica are named. Taxonomic questions regarding the separation of the two genera Aphaenogaster and Paraphaenogaster as well as aspects of biogeography, palaeoenvironment and palaeobiology in Enspel are discussed.

Heterogeneity of free and occluded bitumen in a natural maturity sequence from Oligocene Lake Enspel

Sedimentation in Oligocene Lake Enspel was rapidly terminated by a basaltic lava flow. This introduced a preservational barrier while imparting a ‘natural flash pyrolysis’, during which the organic matter in underlying stratigraphic units was subjected to rapid thermal maturation resulting in hydrocarbon generation. Samples from these strata exhibit a steep maturity gradient (0.25–1.07% optical vitrinite reflectance, or RO) over uniform organofacies. This offers the opportunity to investigate bitumen generation during rapid thermal maturation mechanistically, in particular the nature of Bitumen 2—occluded bitumen, which is only recoverable after the digestion of the mineral matrix and was frequently dismissed as an artifact of incomplete extraction. Elaborate sequential extraction of the contact metamorphic sequence of oil shales at Enspel revealed systematic changes in bitumen composition. These trend progressively towards those of occluded bitumen, which exhibits a systematically elevated thermal maturity, a higher degree of catalytic biomarker-rearrangement and the conspicuous absence of molecular signatures from vascular plants that are present in the free bitumen. One plausible explanation involves a contribution of allochthonous clay-adsorbed organic matter to Bitumen 2. This could represent a mixture of older reworked bitumen and an early-diagenetic snapshot of clay adsorbed organic matter. Alternatively, a close association of early-generated bitumen with clay minerals may have led to enhanced isomerization and catalytically influenced ‘uniformization’ of alkane signatures. Deviations from the expected relationships between various thermal maturity parameters suggest variable dependence on the time-pressure-temperature pathway (i.e. metamorphic facies). The maturation of organic matter likely behaves differently under a contact metamorphic regime or during rapid subsidence and exhumation, as compared to slow maturation during regional subsidence. Our data also suggest that geologically brief shallow intrusive or extrusive magmatism might not be as destructive to the sedimentary hydrocarbon inventory as hitherto thought. This study draws attention to the small-scale compositional heterogeneity of bitumen that can be studied using sequential extraction methods. More importantly, it suggests that occluded bitumen could potentially harbor information on organic matter that pre-dates in situ primary productivity and may be derived from allochthonous biomass and detrital input.

First record of siliceous shell plates of Scutiglypha sp. (Amoebozoa: Thecamoeba: Euglyphidae) from Lake Enspel (upper Oligocene, Westerwald Mountains, Germany)

The laminated, bituminous sediments of the upper Oligocene (Chattian, MP 28) volcanic crater Lake Enspel preserve a large variety of fossils of the former flora and fauna of the lake and its surroundings. By means of FE-SEM techniques, we have identified the remains of globally rare Cenozoic testate amoebae (Amoebozoa: Thecamoeba) associated with gemmules of freshwater sponges. This is the first record of siliceous shell plates of Scutiglypha sp., an euglyphid testate amoebae from Lake Enspel. The existence of an intermittently swampy and/or near shore habitat of Lake Enspel is discussed.

Four-dimensional virtopsy and the taphonomy of a mole from the Oligocene of Lake Enspel (Germany)

A series of actualistic experiments were conducted to reconstruct probable taphonomic scenarios for a fossil mole specimen from the Enspel locality. Extant Talpa europaea carcasses immersed in water initially floated at the water surface then sank after a few hours or remained floating. Soft tissues started to decompose immediately and concomitantly putrefaction gas was produced and accumulated inside the body. Consequently, the carcasses became bloated, and the submerged ones re-surfaced. Gas formation and decomposition of soft tissues accelerated with increasing temperature, as expected. The skeletons of primarily floating specimens successively disarticulated with ongoing decomposition. In moderately warm water (19 °C) disarticulation began with the phalanges of the feet, while in warmer water (27 °C), disarticulation started with the phalanges of the hands and the lower jaws. Skeletal components of the re-surfaced specimens successively sank until the entire skeleton was disarticulated. Applying these experimental results to a partial skeleton of the Oligocene mole Geotrypus antiquus from Enspel (Germany) suggests that carcass sank whole to the bottom of the lake and did not undergo an extended period of floatation. This interpretation is supported by the following characteristics: (1) upper and lower jaws in occlusion, (2) presence of distal hand elements and the left femur and (3) the positions of the elements of the anterior extremities. After decomposition of most or all soft tissues at the bottom of the lake an underwater current from the right side shifted some bones to the left side of the body axis, while the humeri and the still-articulated skull stayed in their original anatomical position.

A revised sedimentological model for the late Oligocene crater lake Enspel (Enspel Formation, Westerwald Mountains, Germany)

New longitudinal profiles through the upper Oligocene Enspel Formation have been constructed based on previously published data and unpublished drilling records. The lithofacies is reinterpreted. The Enspel Formation represents deposits of a deep crater lake, Lake Enspel. The crater rim had steep inner slopes that remained intact until the end of deposition. There was no fluvial input. Alluvial inputs (mud flows) were derived from gullies on the crater’s inner rim, with some of these sediments deposited temporarily in alluvial fans. Thin subaerial pyroclastics from nearby volcanic eruptions also accumulated. Crater floor subsidence, episodic heavy rains, and earthquakes triggered flank collapses and slides on the alluvial fan slopes and led to the creation of thick debrites on the lake bottom. These debris flows are partly correlatable over the entire profundal zone. A new sedimentological–limnological cross-section through the Stoffel crater is presented here, and the levels of the lake water and groundwater and the altitudes of the surrounding landscape are given.

Lost in action–the isolated crocodilian teeth from Enspel and their interpretive value

Between 1991 and 2009 a total of 50 isolated crocodilian tooth crowns were collected from the Oligocene crater lake Enspel. These tooth crowns are basically conical, with some being channeled and others showing smooth carinae. Due to their insignificant morphology the crown can only be referred to as an Eusuchia indet. All teeth are lacking their roots and therefore are very likely to represent shed teeth. The height range of the Enspel tooth crowns falls within the height variation found for those from extant Eusuchia, such as Osteolaemus and Caiman, and likely come from eusuchans with a body length of about 2 m. The presence of shed teeth proves that eusuchian Crocodilia lived in the Oligocene Lake Enspel. The taphonomy of the Enspel crocodilian tooth crowns contrasts with that of the early Freshwater Molasse locality Langenau near the City of Ulm, where most of the teeth still have their root and thus fell out post mortem, and with that for the Eocene Lake Messel, where isolated crocodilian teeth occur rarer than fully articulated ones of fragmentary skeletons.

The Fossil-Lagerstätte Enspel—exceptional preservation in an Upper Oligocene maar

The Late Oligocene was characterized by pronouncedclimatic changes, which were accompanied by changes incontinental ecosystems. Due to excellent age control bybiostratigraphical dating (MP 28; Storch et al. 1996) as wellas the absolute dating of basalts on the base and top of thesedimentary sequence (24.79–24.56 Ma; Mertz et al. 2007),Enspel (Westerwald, W-Germany) is an important point ofreference for studies on the development of continentalclimates and ecosystems in the Late Oligocene of CentralEurope.Excavations at this important locality have been con-ducted during the last 20 years under the authority of theGeneraldirektion Kulturelles Erbe Rheinland-Pfalz (formerlythe Landesdenkmalamt Rheinland-Pfalz). During thisperiod, nearly 20,000 macrofossils, representing a richflora and fauna, have been collected. Many fossils fromthis Lagerstatte show an outstanding and even extraordi-nary preservation in terms of detailed morphological andanatomical structures (e.g., Storch et al.1996;Wedmann2000), partly due to the preservation of fine structures bybiofilms (e.g. Toporski et al. 2002), and complex bio-molecules, such as chitin (e.g. Gupta et al.2007).This special issue presents an overview of currentgeological and palaeontological knowledge on Enspel,together with new data covering several aspects of recentstudies dealing with this important Fossil-Lagerstatte.Poschmann et al. summarize the body of knowledgeavailable on the Fossillagerstatte Enspel, reaching back intime for almost two decades, when the GeneraldirektionKulturelles Erbe Rheinland-Pfalz initiated annual fieldcampaigns with the aim of investigating the geologicaland palaeobiological aspects of this upper Oligocene craterlake. This contribution briefly summarizes the current stateof our knowledge on this site, provides a taxonomic listingof the fossil association, and includes a bibliography.Schindler and Wuttke summarize the geological andlimnological investigations carried out to date. They focuson the genesis of Lake Enspel within a volcanic diatrem orcaldera. The findings from five scientific drillings, twodozen drillings carried out by the basalt industry, andadditional drillings exploring the use of geothermic energyhave enabled a refining of both the geological mapping ofthe Enspel formation and the overlying basalt as well as amore detailed cross section through the lake hollow form.These authors describe the development of the sedimentsand the limnological conditions through time.Herrmann presents the results of an analysis oflacustrine organic-walled algae from the research coreEnspel 1996/1. Two organic-walled primary producers havebeen recognized (Botryococcus and the freshwater dinofla-

Palaeoclimate estimates for the Late Oligocene taphoflora of Enspel (Westerwald, West Germany) based on palaeobotanical proxies

The Late Oligocene was characterized by pronounced climatic changes that were accompanied by vast vegetational changes. Due to excellent age control by biostratigraphical dating (MP28), as well as absolute dating of basalts on the base and top of the Enspel sedimentary sequence (24.79−24.56 Mya), the Enspel taphoflora (belonging to the floral complex Rott-Thierbach) is an important point of reference for the development of terrestrial climates and vegetation in the Late Oligocene of Central Europe. To infer as accurately as possible the climatic conditions during deposition of the Lake Enspel sedimentary sequence, we compare the results of the application of three different methods based on palaeobotanical micro- and macro-remains [i.e. the coexistence approach (CA) (based on nearest living relatives), leaf margin analysis, and CLAMP, a multivariate leaf physiognomic technique]. For our comparison, we used not only previously published data based on leaves and carpo-remains but also new data derived from leaf physiognomic methods and the palynoflora. The results of different methods were inconsistent, but we favor those from the CA, which fit with the occurrence of fossil crocodiles in the same sediments as an independent climatic marker. Considering only the results derived from the CA, we can conclude that mean annual temperature was about 15–17°C, the warmest month mean was about 25°C, the coldest month mean was about 5–7°C and mean annual precipitation was at least 900 mm/year (up to 1,355 mm/year). The temperature values are slightly colder than CA estimates for the somewhat younger nearby locality Rott (MP30), possibly pointing to a warming tendency within the Late Oligocene Rott-Thierbach floral complex, followed by another cooling as indicated by CA estimates for the Latest Oligocene locality Oberleichtersbach in the Rhon and other localities.

First finding of fish in the diet of a water-dwelling extinct frog Palaeobatrachus from the Upper Oligocene Fossil-Lagerstätte Enspel (Westerwald Mountains, Western Germany)

Lake Enspel was a deep lake which developed in a small trachytic caldera or a bims volcano. One of two finds of aquatic palaeobatrachid specimens from Enspel contains a fish prey as stomach content, which is described for the first time. At the critical time, the lake was meromictic, eutrophic, and without an outlet. The rarity of such finds of water-dwelling frogs is possibly due to the lake margin vegetation acting as some kind of taphonomic filter.

Palaeoecological reconstruction of the late Oligocene Maar Lake of Enspel, Germany using lacustrine organic walled algae

The fine laminated black pelites of fossil Lake Enspel (Upper Oligocene, Westerwald, W-Germany) have been analysed using palynological methods. With the help of lacustrine organic walled algae it was possible to reconstruct some aspects of the ecology of the palaeolake. Two organic walled primary producers have been recognized (Botryococcus and the freshwater dinoflagellate Cleistosphaeridium lacustre). During holomictic periods of the lake, freshwater dinoflagellates and Botryococcus coexisted. In more meromictic phases, however, Botryococcus and Cleistosphaeridium lacustre act as competitors. During times of oligotrophic and acidic water conditions with less or nearly no nutrient input into the lake, Botryococcus was prevailing. In times with more eutrophic and alkaline water chemistry caused by increasing nutrient input into the palaeolake, Cleistosphaeridium lacustre was predominant. Subordinate algal cysts of Zygnemataceae together with pollen of shore plants (Typha, Sparganium) indicate areas of shallow water or even a swampy shoreland of unknown size around Lake Enspel during some time periods.

Geology and limnology of the Enspel Formation (Chattian, Oligocene; Westerwald, Germany)

Lake Enspel was a deep lake which developed in a small trachytic caldera or Bims volcano. In normal times, the lake was meromictic and eutrophic and had no outlet. Background sedimentation together with periodical phytoplankton blooms led to laminated, undisturbed sediments that alternated with coarse mass flows and/or turbidites. During turnovers caused by these episodical sediment inputs, the lake became oligotroph. Mesophytic forest extended right down to the lake edge. Approximately, 230,000 years after the onset of lake sedimentation, a basaltic lava flow, caused by a nearby eruption, filled the lake up in a single event.

Characterisation of sedimentary organic matter by bulk and molecular geochemical proxies: an example from Oligocene maar-type Lake Enspel, Germany

Abstract Characterisation of organic matter composition of fossil lake sediments is important in reconstruction of fossil ecosystems and paleoclimates. High time-resolved organic matter analysis is needed to characterize sediments from small lake environments, due to their rapidly changing environmental conditions. A suitable technique for rapid analysis of organic matter in such sediments is Rock Eval pyrolysis. In small lakes, however, routine interpretation of Rock Eval data can be misleading. Lack of tributaries capable of transporting larger woody fragments into small lakes causes a bias towards the input of lipid-rich leaf waxes and cuticles. This hydrogen-rich and oxygen-depleted terrigenous organic matter (HI=250–600 [mg HC/g TOC] and OI=20–40 [mg CO 2 /g TOC]) can easily be misinterpreted as being of algal origin. Differentiation of terrigenous plant-derived hydrogen-rich organic matter from algal organic matter is readily achieved by including C/N-elemental ratios and lipid biomarker data.

Taxonomy and palaeoecology of dinoflagellate cysts from Upper Oligocene freshwater sediments of Lake Enspel, Westerwald area, Germany

Freshwater dinoflagellates play an important role as primary producers in the lacustrine environment. A new species of dinoflagellates, Cleistosphaeridium lacustre, is described from Upper Oligocene sediments of palaeo-lake Enspel. They are associated with other phytoplankton, such as diatoms, chrysophytes, green algae and benthic cyanobacteria. Mass occurrences of this species are interpreted as algal blooms and may partly reflect seasonal successions. This phenomenon was controlled by volcanic activities in the depositional area, which led to an increase in nutrient supply.

Die Cypriniden (Teleostei: Cypriniformes) des oberoligozänen Maares von Enspel nebst Bemerkungen zur Phylogenie und Biogeographie der Phoxininae

Palaeorutilus enspelensis (Bohme 1996), the only fish species from the Upper Oligocene maar lake Enspel (Westerwald), is described and its phylogenetical position within the subfamily Phoxininae is discussed. The cladistic analysis of osteological and lepidological features indicates that the genusPalaeorutilusGaudant 1988 is a member of the Chub Clade. Furthermore, including of the recent Eurasian taxaLagowskiella andEupallasella in the analysis, the Chub Clade can be divided into two monophyletic Clades: the EurasianPhoxinus Clade (including the holarcticPhoxinus) and the eastern North American Creek Chub Clade which includes the fossil genusPalaeorutilus as its basal sister taxon. These phylogenetical investigation as well as the recent and fossil distribution pattern of the Phoxininae support the following biogeographical hypothesis: The settlement of cyprinids in North America took place in several waves and different directions. The separation of Western Clade and Chub Clade did not occur in North America but in Eocene times in Asia. Members of the Creek Chub Clade migrated from Europe to eastern North America via a transatlantic route prior to the Middle Miocene.