Palaeoenvironmental significance of the green alga Botryococcus in the lacustrine rotliegend (upper carboniferous ‐ lower permian)

The green alga Botryococcus is an important component of the phytoplankton in lake sediments from the Rotliegend of Central Europe. The first microscopic fossils from the Saar‐Nahe Basin that can be assigned to this genus are described and illustrated here. Their distribution at various stratigraphic levels shows that the primary production of the lakes was at least partially controlled by these green algae. The frequency of fossils in the sediments is correlated with grain size, which varied with the depositional environment. Their abundance is greater in sediments deposited in shallow water, especially in small lakes and in the littoral environments of larger lakes. Sediments of deep‐water lake bottoms contain only minor amounts of algal remains. The abundance of kerogen originating from phytoplankton and occurrences of Botryococcus fossils are correlated in these lake deposits.     

Reconstruction of Pseudomariopteris busquetii, a vine-like Late Carboniferous-Early Permian pteridosperm

The growth habit of the Late Carboniferous-Early Permian pteridosperm Pseudomariopteris busquetii is reconstructed based on compression material from the upper Stephanian of the Blanzy-Montceau and Commentry Basins (Massif Central, France), and the upper Rotliegend of the Saar-Nahe Basin (Nahe Group, N 4, Rheinland Pfalz, Germany). Pseudomariopteris busquetii was a medium-sized, vine- to liana-like plant with slender stems to which small bipartite fronds were attached. What is most interesting is that the species used at least two different strategies to both anchor and support the plant body. Most specimens possess specialized climber hooks developed from apical extensions of the pinna axes, indicating that the fronds were used to attach the plant. A few specimens suggest that the stem may also have had some capacity for attachment. In the absence of suitable supports, however, P. busquetii was apparently able to grow in dense stands or thickets in which the individual plants supported each other.     

Late Carboniferous hydrocarbon-seep carbonates from the glaciomarine Dwyka Group,southern Namibia

Limestone deposits with columnar to lenticular geometry (max. 3.2 m in height and 1.5 m in diameter) occur within the uppermost part of the Ganigobis Shale Member, a marine mudstone unit capping the second deglaciation sequence of the glaciomarine Dwyka Group in southern Namibia. The limestones mainly consist of four authigenic carbonate phases (microspar, banded/botryoidal cement, yellow calcite, spheroidal calcite). Extremely negative δ¹³C values (as low as ? 51‰ VPDB) indicate a hydrocarbon-derived origin of the carbonates with biogenic methane being the most likely carbon source. The limestones contain a low-diversity but high-abundance faunal assemblage of tubular fossils. These fossils closely resemble the tubes of modern and fossil seep-dwelling vestimentiferan tube worms in terms of size, shape, arrangement, and taphonomical patterns.     

Die Verbreitung der limnischen MeduseMedusina limnica Müller 1978 im Rotliegenden Mitteleuropas

The fresh water medusoid fossilMedusina limnica Müller, 1978 has a large regional, but a rather restricted vertical distribution within the continental Rotliegend facies. Its main occurrence is in the higher, but not highest part of the Rotliegend supergroup in red coloured claystones, siltstones, and finegrained sandstones of Artinskian age. Any marine influence can be excluded in Rotliegend sediments of this age in the European hercynian intramontane basin. Kurzfassung: Die fossile limnische MeduseMedusina limnica Müller 1978 hat innerhalb der kontinentalen Rotliegend-Fazies (Oberkarbon-Unterperm) eine große regionale, aber eine ziemlich begrenzte vertikale Verbreitung. Ihr Hauptvorkommen liegt im höheren, aber nicht höchsten Teil des Rotliegenden in rot gefärbten Tonsteinen, Schiuffsteinen und feinkörnigen Sandsteinen, die in das Artinskian eingestuft werden können. In den varistischen Intramontanbecken Europas kann in Rotliegend-Sedimenten dieses Alters jeglicher marine Einfluß ausgeschlossen werden.     

Responses of coral reefs to increased amplitude of sea-level changes at the Mid-Pleistocene Climate Transition

We show responses of coral reefs to increased amplitude of sea-level changes at the Mid-Pleistocene Climate Transition (MPT) based on lithostratigraphic, sedimentologic and calcareous nannofossil biostratigraphic investigations on Pleistocene reef-complex deposits (Ryukyu Group) on the Motobu Peninsula, Okinawa-jima, Central Ryukyus. Our data show that reef growth started in earliest Quaternary time (1.45-1.65 Ma) and that extensive reef formation dates back to ∼ 0.8 Ma. The mode of Quaternary sedimentation changed at ∼ 0.8 Ma in the study area. Before this time, thick siliciclastics and mixed carbonate-siliciclastics accumulated, which were followed by the deposition of bioclastic sediments (detrital limestone). No indications have been found of episodic subaerial exposures in these deposits and no calcareous nannofossil biozones are lacking. Since the detrital limestone includes biogenic components characterizing fore-reef to shelf environments, the coastal areas of the northern Motobu Peninsula mostly lay in fore-reef to shelf environments for > 0.6 million years (between ∼ 0.8 Ma and 1.45-1.65 Ma), when the sediments had not been subaerially exposed due to sea-level changes characterized by relatively small amplitudes. Coral limestone that formed in the latest Early to Middle Pleistocene between 0.4 Ma and 0.8 Ma extends over the study area, ranging in elevation from 0 to 70 m. This coral limestone grades upward into fore-reef to shelf carbonates (rhodolith, Cycloclypeus-Operculina, and detrital limestones) which is in turn overlain by coral limestone. This succession, combined with configuration of the lithofacies and paleobathymetry inferred from lithology and biogenic components, implies that the reef-complex deposits formed responding to sea-level changes with amplitude of > 60 m. Consequently, we suggest that the change in the mode of sedimentation results from increased amplitude of sea-level fluctuations at ∼ 0.8 Ma. This timing corresponds roughly to the timing of the Mid-Pleistocene Climate Transition (MPT).     

Pliocene facies and fossil contents of Qaret El-Muluk formation at Wadi El-Natrun depression, Western Desert, Egypt

Summary A sequence of late Pliocene sediments (Qaret El-Muluk Formation) covers large areas within Wadi El-Natrun depression; at the western periphery of the Nile Delta. The exposed sequence is composed of friable sands. mudstones, shales and minor limestones with combined total thickness of approximately 50 m. The fossil content consists of fresh and brackish water elements; charophytes, ostracods, gastropods, oysters and benthonic foraminifera. Planktonic forams which suggest marine influence have been also recorded. Terrestrial and aquatic continental vertebrate fauna includes mammals, reptiles, fish and aves. Several subtypes of ichthyoliths have been discovered in this study. Both lithological and paleontological data testify to a depositional environment which belongs to a marginal region where fluvial and marine deposition meet in shallow brackish lagoons. The sediments display changes from channelled fluvial sands to deltaic interbedded sands and mudstones to lagoonal shales and limestones to lacustrine chara limestones. Vertical stacking of facies is indicative of a series of transgressive-regressive events. The transgression brought shallow lagoonal conditions to the area. The transgressions were incomplete due to high rate of fluvial input. The lagoon dried up intermittently and calcretes and red brown soils were formed. Each regression is indicated by river generated clastic influx. During periods of active fluvial input, fluvial sediments prograded lagoonward. The clastic material was probably a mixture of reworked detritus from older sediments. An admixture of first cycle material from the basement rocks of the Red Sea hills cannot be ruled out. The diversity of provenance argues for several channels of a large river which existed during the late Pliocene.     

Paleovegetation and paleoclimate in middle-late Pliocene, Shanxi, central China

Sequences of lacustrine sediments developed in intermontane basins in the middle-eastern Shanxi Plateau of China have been investigated in order to reconstruct the paleovegetation and paleoclimate for the middle-late Pliocene. According to the magnetostratigraphy and the fossil assemblages, the lacustrine sediments of Yushe and Taigu Basins were deposited between 5.5 and 2.5 Ma BP. The Zhangcun and Xiaobai Formations are considered to cover a similar period, ranging from 3.5 to 2.5 Ma BP. An increase of Picea and Abies shows that the climate began to become cold after about 4.4 Ma BP. A cold-wet episode, with relatively warm-dry and warm-humid intervals, occurred between 3.6 and 2.5 Ma BP in the Yushe and Taigu Basins. An increase Artemisia, Chenopodiaceae and Ephedra shows that the climate became drier after 2.5 Ma BP. The climate changes of this period probably reflect variations of the East Asian winter and summer monsoons, with an increase winter monsoon activity during the early Pleistocene.     

Lower Devonian spore assemblages from the Arbuthnott Group at Canterland Den in the Midland Valley of Scotland

The Canterland Den locality in the Midland Valley of Scotland exposes sediments belonging to the Arbuthnott Group. They consist of typical Lower Old Red Sandstone terrestrial fluviatile deposits, which probably accumulated in an inland intermontane basin. Palynological investigation of these sediments has yielded diverse and well preserved palynomorph assemblages dominated by land-derived forms: spores, phytodebris (dispersed cuticles and tubular structures) and rare fragments of arthropod cuticle. Interestingly, rare acritarchs interpreted as deriving from non-marine algae are also present. The spore assemblages all belong to the lower subzone of the micrornatus–newportensis Spore Assemblage Biozone, indicating an early Lochkovian (Early Devonian) age. They are similar in general characteristics to previously described spore assemblages from the Arbuthnott Group, but exhibit minor differences in terms of taxon composition. They differ more significantly from coeval spore assemblages from the lowland floodplain deposits of the Anglo-Welsh basin, in terms of both relative abundance of morphotypes and taxon composition. An intriguing feature of the assemblage is the high abundance of undissociated spore tetrads. It is suggested that such tetrads are a genuine feature of Lochkovian spore assemblages, perhaps reflecting more flexible and unconventional reproductive strategies exhibited by early land plants.     

Lacustrine sedimentation in the diapir-controlled Miocene Bicorb Basin, eastern Spain

The Miocene Bicorb Basin is a small elongated basin developed by normal faulting of a thick Jurassic–Cretaceous carbonate succession and subsequent diapirism of Upper Triassic mudstones and evaporites. The basin fill comprises a sequence over 650 m thick formed by two units. The lower, alluvial unit consists of a complex alternation of conglomerates, sandstones, mudstones, and minor lacustrine limestones. The upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished. The inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits. At the northeast and southwest basin edges, alluvial inputs led to the development of delta and fan-delta environments where sandstone and conglomerate deposits dominate. The latter stages of the lake evolution are represented by an expansive thick limestone sequence which close to the NW fault-bounded margin pass laterally to breccias. The hierarchical arrangement of the upper unit shows five different orders of sequences. The first-order sequence defines a major vertical trend of lake expansion whereas three second-order sequences are linked to major flooding-expansion episodes. All these sequences are related to the tectonic evolution of the diapir. Metre-scale, third- and fourth-order sequences and fifth-order sequences, which consist of finely laminated rhythmite deposits probably record climatically forced processes. The diapir–graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evolution of the lacustrine system. Both factors have also strongly influenced the changes in the gastropod assemblages.     

Middle Triassic basin evolution and stratigraphy in the Carnic Alps (Austria)

Summary A local intraplatform basin developed in the Gartnerkofel-Zielkofel area of the Carnic Alps (southern Carinthia, Austria) during the Middle Triassic (Ladinian). This basin was filled with a transgressive basinal sequence composed of the Uggowitz Formation and overlying Buchenstein Formation. At the northwestern slope of the Gartnerkofel, the platform carbonates of the Schlern Dolomite interfinger with the Buchenstein Formation, causing the formation of two depositional sequences. The Uggowitz Formation consists of the Uggowitz Breccia and the Kühweg Member. Sediments of the Uggowitz Breccia were formed by different types of gravity induced processes. The Kühweg Member is a thin sequence of silt-and fine-grained sandstones which were deposited in a slope to basin margin environment by turbidity currents. The overlying Buchenstein Formation consists of hemipelagic to pelagic limestones of Fassanian age with intercalated pyroclastic rocks (Pietra verde). Nodular limestones were deposited under slow rates of accumulation during a relative sea-level highstand. The uppermost Buchenstein Formation is composed of hemipelagic limestone beds with intercalated graded calcarenites and breccias of platform-derived debris, showing characteristics features of a fore-reef slope of the prograding Schlern Dolomite. Uggowitz Formation and basal Buchenstein Formation are interpreted as a transgressive systems tract, nodular limestones from the middle part of the Buchenstein Formation mark an early highstand systems tract, forereef slope sediments of the upper Buchenstein Formation formed during the beginning regression of a late highstand systems tract, the basal part of the overlying Schlern Dolomite probably reflects a lowstand systems tract. The intercalated bedded limestone facies within the Schlern Dolomite is characterized by large, platform derived blocks, slump structures, breccia beds, graded calcarenites and hemipelagic limestones indicating a forereef slope environent. This intercalated facies belongs to the Buchenstein Formation and interfingers with the Schlern Dolomite. Conodonts from this intercalated slope facies point to Late Fassanian age. Therefore, the two Middle Triassic depositional sequences of the Gartnerkofel area can be correlated with the depositional sequences ‘Ladinian 1’ and ‘Ladinian 2’ of the Dolomites, proposed byDe Zanche et al. (1993). A brief comparison with the basinal sequences of similar age of the karawanken Mountains and the Carnia is presented.     

Un exemple de sequence d'estrandans le Portlandien du Jura meridional

The study of the portlandian limestones of the Vouglans dam outcrop in the southern Jura mountains hasprovided the elements to establish the theoretical succession of the sediments (virtual sequence) and to show the similarities with the recent western Andros tidal flats. Their respective bathymetry is here compared, allowing to think that a part of the jurassian portlandian limestones are located from the shallow subtidal to the supratidal, creating short rhytmic sequences, sometimes only a few centimeters high.     

Evidence of Active Methanogen Communities in Shallow Sediments of the Sonora Margin Cold Seeps

In the Sonora Margin cold seep ecosystems (Gulf of California), sediments underlying microbial mats harbor high biogenic methane concentrations, fueling various microbial communities, such as abundant lineages of anaerobic methanotrophs (ANME). However, the biodiversity, distribution, and metabolism of the microorganisms producing this methane remain poorly understood. In this study, measurements of methanogenesis using radiolabeled dimethylamine, bicarbonate, and acetate showed that biogenic methane production in these sediments was mainly dominated by methylotrophic methanogenesis, while the proportion of autotrophic methanogenesis increased with depth. Congruently, methane production and methanogenic Archaea were detected in culture enrichments amended with trimethylamine and bicarbonate. Analyses of denaturing gradient gel electrophoresis (DGGE) fingerprinting and reverse-transcribed PCR-amplified 16S rRNA sequences retrieved from these enrichments revealed the presence of active methylotrophic Methanococcoides burtonii relatives and several new autotrophic Methanogenium lineages, confirming the cooccurrence of Methanosarcinales and Methanomicrobiales methanogens with abundant ANME populations in the sediments of the Sonora Margin cold seeps.     

Correlation of the Middle and Upper Permian marine and terrestrial sedimentary sequences in Polish, German, and USA Western Interior Basins with reference to global time markers

Here we discuss the duration and position of Upper Rotliegend and Zechstein stratigraphic units in relation to the absolute time scale, and reinterpret a carbon isotope (δ¹³C) global event recorded from Late Permian (Lopingian/Guadalupian) marine deposits. Based on δ¹³C isotope correlation (chemostratigraphy) and of climatic evidence related to the end-Guadalupian global marine and terrestrial crisis, the Guadalupian/Lopingian boundary is proposed as the boundary between both the European Upper Rotliegend (URII)/Zechstein sediments and the parallel south-west USA Ochoan/Bell Canyon Formation units. The Zechstein deposition was strongly influenced by climatic oscillations, and the marine ingressions recorded in the North German Basin and North American Delaware Basin are presumed to have resulted from the same eustatic sea-level changes in western and northern coasts of the Northern Pangaea Supercontinent. Existing constraints on the age of the Upper Rotliegend II (UR II) deposits are imposed by the uncertainty of the chronostratigraphic boundary of the Kupferschiefer and by a time marker that is Illawarra, the boundary of the reversed polarity megachron (Kiaman) and mixed polarity megachron. Three options (A, B, C) have been discussed, which are connected with a time span comprising deposition of the UR II rocks, assuming that the time span needed for the Dethlingen/Lower Noteć formations and Hannover/Upper Noteć formations is about 6 myr. The time left for the deposition of the Parchim/Lower Drawa, Mirow/Upper Drawa deposits and the time hidden in the erosional gaps and hiatuses range from 1.6 myr to 4 myr or even 8 myr. These were based on the time interval related to the Kiaman Reversed Polarity megachron, which can contain more transient normal polarity zones than currently accepted. The presence and absolute dating of all such magnetozones is difficult to determine because they are represented in continental strata characterized by numerous, poorly time-constrained erosional gaps. The proposed option C is provisionally integrated with magnetostratigraphic results and shows an alternative stratigraphical scheme for the Upper Rotliegend. This alternate Upper Rotliegend stratigraphy helps correlate rocks (deposited in dry arid climatic conditions) in the lower part of the Upper Rotliegend II of the Southern Permian Basin (Havel and Drawa subgroups) with similar rocks in the Delaware Basin (attributed to formations within the Leonardian Regional Series).     

Growth inacanthodes (acanthodii: pisces) data and implications

Body proportions did not change during ontogeny and were very similar in most, if not all,Acanthodes species. The length/width ratio of circumorbital bones decreased during growth. The mandibular-splint-length/prepectoral-length and mandibular-splint-length/total-specimen-length ratios remained stable throughout life. The pectoral girdle grew isometrically with the pectoral spine. Large scapulocoracoids could not have borne suprascapulae relatively as large as the small scapulocoracoids, and, therefore, negative allometry is indicated for the suprascapula. The scale size relative to the total specimen size is remarkably similar in all the species studied. The rates of squamation development, on the other hand, differ considerably in species from different stratigraphic levels. In the tail, the scale zones 1,3, and 4 are present in even the smallest known specimens. The epichordally situated scales of zones 2 and 2” appeared only later in ontogeny. With the exception of the scale cover and possibly the tesserae on the head, the components of the exoskeleton are fully developed in even the smallest available specimens (ca. 50 mm long), in which no trace of ossification of the endoskeleton can be detected. The first component of the endoskeleton to ossify was the scapulocoracoid. The ossification of the labyrinth, co-ossification of divisions of the jaws, and development of the squamation all commenced, and were completed, earliest in ontogeny of the oldest (Namurian) species and latest in ontogeny of the youngest (Autunian) species considered in this study. This implies a regressive trend which is further evidenced by a tendency in ontogeny toward the loss of posterior rows of gillrakers. At least four species ofAcanthodes co-existed at Lebach. The entire material ofAcanthodes from Lebach needs to be re-examined in a manner suited for resolving the taxonomic situation, i. e. more quantitatively, which will also describe the ontogenetic development of the species present. The branchiostegal rays and gill-rakers ofAcanthodes are exoskeletal. The mandibular splint is a serial homologue of the ceratohyal branchiostegals, i. e. the dermal component of the ceratomandibular.     

Genesis of stromatactis in an upper jurassic carbonate buildup (Mlynka,Cracow region,Southern Poland): Internal reworking and erosion of organic growth cavities

Summary The Middle Oxfordian strata in the southern part of the Cracow-Wielun Upland consist of platy and bedded limestones (‘normal facies’), of massive limestones as well as locally of mass flow sediments. Massive limestones, prevailing in the Upper Oxfordian, form commonly carbonate buildups, which are made up predominantly of cyanobacterial allochems and to a minor amount of siliceous sponges. Stromatactis can be best observed in the Mlynka quarry. They occurs in the uppermost part of slope sediments close to a cyanobacterial-sponge buildup. The bedding-plane of the slope sediments is directly overlain by debris-flow and grain-flow sediments. Fragments of a primary laminar framework rich in growth-cavities occur in the uppermost part of the slope sediments as precondition for the formation of stromatactis. The stromatactis cavities were formed by internal reworking and erosion within these organic growth cavities, caused by strong bottom currents due to mass transport from higher parts of the buildup.     

Mise en évidence par charophytes et ostracodes de l’âge Paléocène des dépôts discordants sur les rides anticlinales de la région d’Imilchil (Haut Atlas,Maroc) : conséquences paléogéographiques et structurales

New sedimentological and biostratigraphical data have been obtained from unconformable series (Tasraft Formation) on some intruded anticlines located in the Central High Atlas of Morocco. Our results lead us to contest the previous Middle Jurassic to Middle Cretaceous ages only based on lithostratigraphic similarities. The Tasraft Formation proves to be a syntectonic series characterized by detritic fluvial sediments followed by lacustrine and lagoonal-marine limestones. Ostracods and charophytes found in different levels of the unconformable series indicate Thanetian ages. According to these new stratigraphical data, we can conclude that the main structures of the axial part of the High Atlas (folds, cleavage and exhumation of gabbroic bodies) were settled before the Late Paleocene. Moreover, the occurrence of Paleocene nonmarine beds in the axis of the High Atlas Belt implicates to modify the paleogeographic boundaries of the Atlantic transgressions in the beginning of the Tertiary.     

The Radiolarian biotic response during OAE2. A high-resolution study across the Bonarelli level at Bottaccione (Gubbio, Italy)

In order to improve our understanding of the radiolarian biotic response and the palaeoceanographic changes associated with the Late Cenomanian oceanic anoxic event (OAE2), a high-resolution radiolarian study was carried out across the Bonarelli level at its typical locality (Bottaccione section, central Italy). Our results confirm that a drastic radiolarian faunal change took place during the OAE2. The radiolarian turnover took place within the median part of the Bonarelli level, associated with an interval of high organic matter preservation, but relatively low values of silica. Therefore, this part constitutes a critical period in the evolutionary history of Radiolaria. A synthesis of all data available in the Umbria-Marche basin suggests that the lower part of the Bonarelli level (and underlying limestones) records mainly radiolarian extinctions (ca. 41%), while its upper part (and overlying limestones) records mainly first occurrences (ca. 35%). Our results improve understanding of the paleoecology of the family Saturnalidae, which would seem to prefer oligotrophic environments.     

Pleistocene coral reefs associated with claystones, Southwestern Taiwan

 Scleractinian coral reefs, when coexistent with siliciclastic sediments, usually occur in association with deltaic or coastal sands. Nevertheless, Pleistocene reef limestones in southwestern Taiwan are developed in association with thick claystones that were deposited in a deeper-water environment. These reef limestones are characterized by: (1) rapid transition from underlying claystones upward to reefal limestones, (2) lateral interfingering with open-shelf claystones, (3) being overlain by terrestrial deposits or exposed with no covering strata, and (4) being located in close association with anticlines. The authors propose that these reef limestones developed on anticlinal ridges raised above the adjacent sea floor by thrust-front migration in a foreland setting. Accepted: 21 April 1998