O. K. Lenz

A 600 k.y. record of El Niño–Southern Oscillation (ENSO): Evidence for persisting teleconnections during the Middle Eocene greenhouse climate of Central Europe

The El Nino–Southern Oscillation (ENSO) is a globally important factor in today’s climate dynamics. Annually laminated oil shales from the maar lake of Messel (Germany) provide high-resolution sedimentological and paleoenvironmental data of a time interval of ~600 k.y. during the Eocene greenhouse phase. Individual laminae consist of a light spring and summer algal layer (Tetraedron minimum layer) and a dark winter layer composed of terrigenous background sediment. Four sections were selected from the core of the Messel 2001 well in order to count varves and to measure total varve thickness and the thickness of light and dark laminae. Spectral analyses were done in order to detect possible cyclic fl uctuations in varve thickness. Fluctuations are signifi cant in the quasi-biennial (2.1–2.5 yr) and low-frequency band (2.8–3.5 yr, 4.9–5.6 yr), thus showing that algal growth as well as the background sedimentation were controlled by ENSO effects at least over a time interval of 600 k.y. This confirms the existence of a previously postulated robust Eocene ENSO. Significant peaks within a quasi-decadal (10–11 yr), interdecadal (17–26 yr), and multidecadal band (~52 yr, ~82 yr) show either the enduring influence of more or less cyclic instabilities or the influence of solar cycles.

Isopollen maps as a tool for the reconstruction of a coastal swamp from the Middle Eocene at Helmstedt (Northern Germany)

SummaryIn the Middle Eocene lignite bearing succession at Helmstedt, isopollen maps have been constructed from a thin, highly carbonaceous horizon in the interbed between two seams of the Wulfersdorf member. During mining progress this carbonaceous band could be traced in the mine high wall over an area of 2 km by 0.5 km and is considered to represent an isochronous horizon. 28 samples were collected and analyzed.On the basis of the isopollen maps it is possible, to distinguish between allochthonous and autochthonous elements. Ultimately, by comparison of the maps individual plant associations and environmental conditions may be recognized. In case of the carbonaceous horizon of the Wulfersdorf seam group a coastal swamp succession can be traced from a mangrove fringe through a brackish marsh and a freshwater marsh to a mire forest. The distribution of mangrove elements likeRhizophora, Avicennia andNypa in this horizon clearly shows that the shoreline was to the northwest and advanced from there inland to the southeast. A fourth element,Psilodiporites iszkaszentgyoergyi, is restricted in distribution and closely associated with the other known mangrove types and therefore considered here to be a part of the mangrove fringe. Behind the mangrove zone, pollen of Restionaceae and Sparganiaceae as well as fern spores are more abundant than elsewhere in the Wulfersdorf seam section suggesting that a reed-like vegetation with fern and aquatic herbs developed here under rather wet conditions. A hammocky distribution of corresponding plants is indicated by the isopollen map of palms likeArecipites spp. and other elements. The main peat forming vegetation, however, was a mire forest dominated by Fagaceae alternating with a Betulaceae dominated forest including Myricaceae and Juglandaceae.

Chemical and ecological evolution of the Miocene Ries impact crater lake, Germany: A reinterpretation based on the Enkingen (SUBO 18) drill core

Scientific drilling conducted at the inner slope of the Miocene central Ries impact crater recovered a partial section of crater lake sediments. Four sequences were recovered, composed of suevite-derived sandstones, thin lignite seams, bituminous shales, and marlstones to claystones. These flooding-evaporation sequences reflect the impact of short-term climatic fluctuations on a hydrologically closed basin. The superimposed trend from sequences rich in bituminous shales in the lower parts of the section to sequences dominated by organic-poor claystones and intercalated lignites in the upper parts of the section resembles that of the 300-m-thick central crater basin succession, which has previously been considered to reflect a climate-controlled development from an alkaline saline lake to a freshwater lake with temporary coal swamps. In the sediment core of Enkingen, however, the change from bituminous shales to organic-poor claystones with intercalated lignites is associated with a general increase in salinity, as indicated by (1) palynomorphs, (2) increase in δ13C of the lipid biomarker archaeol (bis-O-phytanylglycerol), and (3) the occurrence of 13C-enriched C20/C25-archaeol (O-phytanyl-O-sesterterpanylglycerol) specific to halophilic Archaea. In addition, the unidirectional trend in 87Sr/86Sr of carbonates, declining from ratios of Variscan basement rocks toward marine ratios, indicates a change from (1) weathering of crystalline rocks and suevite to (2) ejected Jurassic sediments (Bunte Breccia) in the catchment area as the major source of ion influx to the lake. From that trend, a change in lake water composition and a general increase in ion concentrations are inferred. These new results can be applied to a reassessment of major parts of the lacustrine succession of the Ries crater. We use these data to propose a new hypothetical model for the chemical and ecological evolution of the Ries crater lake: (1) After the establishment of a stratified brackish eutrophic soda lake due to silicate weathering and evaporation, the increasing influx of waters from the Bunte Breccia carbonate and authigenic silicate precipitation led to a mesotrophic halite lake with marine-like ion ratios and concentrations. (2) Further increase in ions, among them Mg2+ and Sr2+, resulted in hypersaline conditions with gypsum precipitation, low primary production, and phreatic Sr-rich dolomitization in marginal carbonates. (3) The final, sudden change to oligotrophic freshwater conditions is explained by the formation of an outlet late in the lake history. We conclude that the chemical and ecological evolution of the Ries lake therefore appears to have been mainly controlled by the weathering history of the catchment area, with climate fluctuations causing superimposed cycles. Similarly, changes in terrestrial palynomorph associations may at least partly reflect a change in soil types in the catchment area, from fertile, moist soils on suevite to dry karst soils and soils on Bunte Breccia. These interpretations imply that the initial suevite blanket of the Ries crater was much more continuous and widespread than previously assumed.

DISTRIBUTION AND PALEOECOLOGIC SIGNIFICANCE OF THE FRESHWATER DINOFLAGELLATE CYST MESSELODINIUM THIELEPFEIFFERAE GEN. ET SP. NOV FROM THE MIDDLE EOCENE OF LAKE MESSEL, GERMANY

Abstract An exploration well drilled at the Middle Eocene fossil site of Messel, near Darmstadt, Germany proved that the famous Messel oil shale was deposited in a maar lake. During a quantitative palynological investigation of the entire succession of lake sediments, a monospecific population of dinoflagellate cysts was encountered. Based on transmitted light and scanning electron microscope (SEM) studies, they are assigned to the new peridinioid taxon Messelodinium thielepfeifferae gen. et sp. nov. because they are acavate and lack distinct apical or antapical horns. The dinoflagellate cysts exhibit considerable intraspecific variation in surface ornamentation. Messelodinium thielepfeifferae gen. et sp. nov. is abundant in sediments of the early holomictic stage of Lake Messel, but generally is reduced in frequency in the oil shale which represents the meromictic stage. These dinoflagellate cysts appear in peak abundances in mass flow and debris flow deposits in which material from the lake shore was transported downslope to the basin center. Thus, major concentrations of Messelodinium thielepfeifferae gen. et sp. nov. occurred in nearshore environments either due to primary population density of the parent motile stage, or due to secondary cyst accumulation by wind and wave action. The dinoflagellate cysts are notably absent in the uppermost 25 m of the core, where Botryococcus dominates. This shift in algal populations is interpreted as a response to changes in the chemistry of the water body.

Middle-late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstatte from the Central Kenya Rift (East Africa)

The Miocene epoch was a time of major change in the East African Rift System (EARS) as forest habitats were transformed into grasslands and hominids appeared in the landscape. Here we provide new sedimentological and palynological data on the middle-upper Miocene Ngorora Formation (Tugen Hills, Central Kenya Rift, EARS), together with clay mineral characterizations, mammal finds and a description of the Ngorora fish Lagerstatte. Furthermore, we introduce a revised age of c. 13.3 Ma for the onset of the Ngorora Formation. The older part of the Ngorora Formation (c. 13.3-12 Ma) records low-energy settings of lakes, floodplains and palaeosols, and evidence of analcime indicates that lakes were alkaline. The palynomorph spectrum consists of tree pollen (Juniperus, Podocarpus), Euphorbiaceae pollen (Acalypha, Croton) and herbaceous pollen of Poaceae and Asteraceae, suggestive of wooded grasslands or grassy woodlands. Alkaline lakes, floodplains and palaeosols continue upsection (c. 12-9 Ma), but environmental fluctuations become more dynamic. Paucity of palynomorphs and the presence of an equid may point to progressively drier conditions. A total of about 500 articulated fish fossils were recovered from distinctive layers of almost all sections studied and represent different lineages of the Haplotilapiines (Pseudocrenilabrinae, Cichlidae). Some of the fish kills may be attributable to rapid water acidification and/or asphyxiation by episodic ash falls. Repeated instances of abrupt change in water depth in many sections are more likely to be due to synsedimentary tectonic activity of the Central Kenya Rift than to climatic variation. Overall, the preservation of the Ngorora fish Lagerstatte resulted from the interplay of tectonics, formation of alkaline lakes and explosive volcanism. As records of grasslands that pre-date late Miocene time are rare, our finding of middle Miocene (12-13 Ma) grassy savannah in the Central Kenya Rift is also relevant to models of human evolution in East Africa.

ENSO- and solar-driven sub-Milankovitch cyclicity in the Palaeogene greenhouse world; high-resolution pollen records from Eocene Lake Messel, Germany

The annually laminated oil shale from the Eocene maar lake at Messel (Germany) provides unique palaeoenvironmental and palaeoclimatological information for the Palaeogene greenhouse phase. Two palynological analyses of 6.3 and 70 kyr long records with a temporal resolution of 70 and 700 years respectively confirm vegetation and climate variability in the sub-Milankovitch range. This variability clearly corresponds to cyclic climate fluctuations indicating the influence of solar activity and a millennial-scale variability of the El Niño–Southern Oscillation also seen during the Quaternary icehouse system. This provides strong evidence of cyclic fluctuations in the sub-Milankovitch frequency band that represent a pervasive and persistent system not only of the Quaternary icehouse, but also throughout the entire Neogene and the Palaeogene greenhouse. This is proof for the long-term stability of the driving forces of natural climate change on Earth. Fluctuations in the frequency of palynomorphs indicate cyclic short-term quantitative changes in the composition of the vegetation. These changes were related to precipitation and corresponding fluctuations of the lake level as well as to changes in pollen production, transport and deposition. Supplementary material: A complete list of variables and palynomorphs used for pollen diagrams and statistical analyses, as well as additional time series analyses, are available at https://doi.org/10.6084/m9.figshare.c.3458778

FROM OPEN ESTUARY TO MEANDERING RIVER IN A GREENHOUSE WORLD: AN ECOLOGICAL CASE STUDY FROM THE MIDDLE EOCENE OF HELMSTEDT, NORTHERN GERMANY

Abstract Tropical climates reached their northernmost expansion during the early Paleogene greenhouse phase, supporting a paratropical biota as far north as the southern shore of the ancient North Sea. There, relative sea-level fluctuations led to the formation of transgressive-regressive sequences, exposed in open-cast lignite mines in the area of Helmstedt (Lower Saxony, Germany), which record environmental changes at the marine-terrestrial interface. We studied an example from the middle Eocene of the Helmstedt Mine from which we reconstruct ecological successions from open estuary to meandering river environments, which represent vegetation at the Paleogene climatic optimum. In the absence of vertebrate and shelly fossils, environmental interpretations are made exclusively on plant matter in the sediment. Vegetational reconstructions are based mainly on quantitative palynological analyses, supported by paleobotanical and organic-petrographical evidence and confirmed by Principal Component Analysis. Diverse dinocyst assemblages in conjunction with Ophiomorpha-type bioturbation indicate open estuarine conditions. These are succeeded by mangrove, represented by pollen of Rhizophora, Avicennia, Nypa and the form species Psilodiporites iszkaszentgoergyi, and marsh environments, indicated by pollen of Restionaceae, Sparganiaceae/Typhaceae and fern spores. Subsequent lowland mire forests are characterized by a dominance of either the Tricolporopollenites cingulum group (Fagaceae) or triporate pollen of the Triporopollenites robustus/rhenanus complex (Myricaceae/Betulaceae). Within this landscape coexists a meandering river system, represented by channel lag and point-bar deposits of the active channel and by the clastic to lignitic sedimentary fill of an abandoned channel.

Palynology as a High-Resolution Tool for Cyclostratigraphy in Middle Eocene Lacustrine Sediments: The Outstanding Record of Messel (Germany)

The annually laminated oil shale from the early middle Eocene maar lake at Messel provides unique palaeoenvironmental and climatological data for a time interval of ~640 kyr during the Palaeogene. Therefore, the research core Messel 2001 opened a unique window into ecological changes in the Palaeogene greenhouse environment, which are documented at the site by an undisturbed succession of 230 m of lacustrine sediments including >90 m of varved oil shale. For studying these sediments with respect to short-term climate variations, we applied different approaches such as high-resolution palynology and varve analysis. As a result, we have found changes in the vegetation following Milankovitch cycles in the range of precession, obliquity, and eccentricity as well as sub-Milankovitch cycles. Furthermore, ENSO signals have been detected in the varves.

Potential of palynostratigraphic resolution in a homogeneous lacustrine succession: the Middle Eocene Messel Formation

Palynologieal results from two cores of the Middle Eocene Messel oil shale (Germany)are compared and tested for their reliability in stratigraphic correlation and suitability for time series analysis. The studied section of 139 m respectively 126.5 m mainly of annually laminated oil shale represents a time interval of less than I my during the Eocene greenhouse phase. Frequency curves and running means are shown for examples of restricted distribution (Restionaceae, Pinaceae pollen), rare (Labrapollis labraferus, Pentapollenites spp.), common (various pollen of Juglandaceae) and dominat occurrence (Plicatopollis spp., Tricolpopollenites liblarensis /Tricolporopollenites cingulum group). They show good correspondence between the two cores even in minor quantitative changes and thus confirm the fidelity by which vegetation changes in the vicinity are reflected in the homogeneous sediments of a lacustrine basin.

Changes in Eocene plant diversity and composition of vegetation: the lacustrine archive of Messel (Germany)

Abstract Based on high-resolution palynological analysis of 680 samples froma core, short-termchanges in plant diversity and floristic compositionwithin the Paleogene greenhousewere detected in the lacustrine succession of a lower to middle Eocene maar lake at Messel (Federal State of Hesse, Germany). The microfloristic data show that taxonomic diversity increased rapidly within some decades during recolonization of a volcanically devastated area around the lake. With the establishment of a climax vegetation at the end of recolonization, the maximum in palynological diversity was reached within the crater area. During the following 640 Kyr the composition of the palynospectrum changed only gradually. However, different richness and evenness estimations show that alpha and gamma diversity decreased up to 35%, which can be related to the establishment of an equilibrium stage within the climax vegetation that led to the dominance of an assemblage of self-replacing species. Nevertheless, time-series analysis of alphadiversity changes within the climax vegetation reveals that orbitally controlled climate change of Milankovitch and sub-Milankovitch order influenced the diversity of the vegetation, resulting in a rise of beta diversity. Based on the composition of the vegetation and comparison to modern analogues, our analysis proves that Eocene paratropical plant diversity increased during periods of slightly higher temperature and precipitation. Therefore, both composition and diversity of the vegetation was highly susceptible to minor-scale, short-term changes in climate, even during equable greenhouse conditions.