W. Riegel

Spore stratigraphy and correlation with faunas and floras in the type marine devonian of the Ardenne-Rhenish regions

A spore zonation scheme comprising fifty-one zones is proposed for the marine Devonian strata of the Ardenne-Rhenish regions of Western Europe. The zonation comprises a series of Oppel and interval-type zones and these are closely intercalibrated with the associated marine faunal zonations to give a seventy-five level scale of correlation for the Devonian succession. The spore zonation provides stratigraphical dating of the Devonian megafloras of the region, particularly those from the Lower and Middle Devonian. The proposed spore zonation is closely compared with that erected for the Devonian of the Old Red Sandstone Continent.

Signatures of hydrocarbon venting in a Middle Devonian Carbonate Mound (Hollard Mound) at the Hamar Laghdad (Antiatlas, Morocco)

SummaryThe Middle Devonian Hollard Mud Mound is situated in the eastern Hamar Laghdad, which is a small mountain range in the Tafilalt in SE Morocco. In contrast to the well known Lower Devonian Kess-Kess mounds, the Hollard Mound is of Middle Devonian age. The facies in the core of this mud mound differs from that of the other parts of the mound, and exhibits signatures of ancient hydrocarbon venting. The carbonate phases of the core facies are derived from the oxidation of vent fluids and consist of clotted micrite, a cryptocrystalline carbonate associated with spheres of uncertain origin, and a calcitic rim cement (rim cement B). These vent carbonates show δ13C values in the range of −11 to −20% PDB indicating that some of their carbon is derived from isotopically light hydrocarbons. Fossiliferous micrite has been affected by hydrocarbon venting in the proximity of the vent site, which is indicated by intermediate δ13C values between vent carbonates and not affected sediments. Bivalves occur in dense populations within the core facies. They form autochthonous shell accumulations and are almost exclusively articulated. it is likely that these bivalves were dependent on chemosynthesis similar to their counterparts at modern vents. The vent deposits also exhibit an unusual prasinophyte assemblage, which might have been linked to the specific nutrient availability at the vent site.The ancient vent site is characterized by an enhanced carbonate precipitation and rapid lithification. The latter is corroborated by the three-dimensional preservation of phytoplankton (prasinophytes and acritarchs) and the occurrence of stromatactoid pores. An early phase of carbonate corrosion predating the formation of vent carbonates affected the fossiliferous micrite of the core facies and is thought to be related to a phase of H2S-rich venting.

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.

Phytoplankton from the upper Emsian and Eifelian of the Rhineland, Germany — A preliminary report

Abstract The predominantly marine Lower and Middle Devonian of the Rhineland is relatively poor in phytoplankton. Moreover, the composition of the assemblages found is rather undiversified. However, the assemblages gain some interest because of their relation to the Emsian-Eifelian type-region and their close association with diversified spore floras. The composition and stratigraphic distribution of the assemblages are briefly described. Comparisons are made with more prolific phytoplankton assemblages from the Daleje shales of Bohemia (Upper Emsian) and the Nehden shales of the Eifel region (Upper Devonian). Paleoecological considerations seem to indicate that in the Devonian of Central Europe the neritic facies is connected with poor phytoplankton assemblages, the pelagic facies more often with rich and diversified assemblages.

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.

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.

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.

The laminated lake sediments of the Eckfeld maar (Middle Eocene, Germany): Types of stratification and role of organic matter

SummaryThe Middle Eocene lake sediments of the Eckfeld maar are situated on the southwestern margin of the Tertiary High-Eifel volcanic field (Germany) and are well known for excellently preserved fossil remains. During a driling campaign in 1996 six well sections were cored at three different locations. Three cores (E1/96, E2/96 and E3/96) penetrated deposition of the central lake facies, which is dominated by laminated organic-rich pelites within the uppermost 40 m.It is the aim of this paper to present a brief survey over the main types of stratification observed within the organic-rich portions of the Eckfeld lake sediments. Based on the varying distribution of mineral and organic matter three sediment sequences are distinguished representing different phases of lake development. The “minerogenic laminites” represent the purely clastic mineral sedimentation in a lake, which was surrounded during this early phase by a tephra rim barren of vegetation. The gradual overgrowth of the tephra rim by vegetation is reflected by the predominance of land plant detritus in the sediments of the “transtion beds”, though the siliciclastic input is still significant. In contrast, the succeeding sequence of the “biogenic laminites” is characterised by the frequent occurrence of centric diatoms (mainly of the planktonic speciesAulacoseira cf.granulata) and Chlorophyceae (mainlyBotryococcus andTetraedron) documenting the increase in autochthonous organic sedimentation in a meromictic lake.

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.