Schwermineral-Untersuchungen in quartär-zeitlichen Sanden nordwestlich von Hannover

A total of 117 samples of quarternary sediments, mostly sands, from a region NW of Hannover (Lower Saxony) has been investigated with regard to their content of heavy minerals. The absolute percentage of transparent heavy minerals approximates 0.2 Vol.%. If several samples of glaciofluvial sands (Drenthe-stage) or dune sands (Late Weichsel-stage to Holocene) are taken from one outcrop they show great similarities in their heavy minerals contents. Glaciofluvial sands of the Elster-stage evidently have less Garnet, Hornblende and minerals of volcanic origin (Augite, partly also Orthopyroxenes, Oxyhornblende and Olivine) than those of the Drenthe-stage, Weichsel-stage, and the Holocene. All these groups hold nearly the same average assemblages of heavy mineral, thus indicating that within the Drenthe-stage or later material from north and from south has been mixed and/or reworked. In the area investigated the proportions of heavy minerals do not help to identify either the stratigraphic position or the way of deposition of different sandy sediments younger than the Elster-stage. The distributional pattern of several heavy minerals point out that Kyanite, Hornblende and Epidote have been transported predominantly from the north, whereas Garnet and Staurolite have sources both in the north and the south. Tourmaline, Apatite and the minerals of volcanic origin mainly must be derived from the south. All results obtained in the region examined should not be transferred to other zones of the lowlands of Northern Germany automatically.

Fluviatile und äolische Prozesse im Gebiet der unteren Elbe bei Neuhaus (Niedersachsen) seit dem Weichselspätglazial

The Late Glacial and Holocene landscape development in the vicinity of the River Elbe near Neuhaus, Lower Saxony, was studied during geological mapping of the area. The geological and geobotanical methods used in these investigations were chosen to cope with the difficulties which arise during research on Quaternary flood plains in low country. Paleochannel fill and areas of flood-plain sediments were drilled, the lithology examined, and the sediments dated on the basis of their pollen content. No evidence was found for the existence before the Middle Ages of paleo- channels the size of the present River Elbe. Before the first measures were made to regulate the Elbe River, it was an anastomosing river system with numerous small branches. The lower parts of the flood-plain profiles are predominantly sand and the upper parts silty-clayey loam. With the construction of effective levees over the last several centuries, the flow velocity of the Elbe has increased considerably during high water periods and instead of the deposition of meadow loam, sand was deposited as natural levees. The main belt of sand dunes on the east bank of the Elbe overlies Preboreal to Boreal lake mud and is, therefore, of Holocene age.

Lithostratigraphische, technologische und geochemische Untersuchungen Im Muschelkalk des Osnabrücker Berglandes

Im niedersächsischen Teil des Osnabrücker Berglands wurde der Muschelkalk lithostratigraphisch untersucht und sein Gesteinsinventar im Hinblick auf dessen Eignung für die Herstellung von Straßenbaumaterial sowie andere Nutzungsmöglichkeiten überprüft. Die methodischen Schwerpunkte lagen bei der Aufschluß-Bearbeitung, der Ermittlung technologischer Kennwerte nach den einschlägigen Prüf-Vorschriften für Straßenbaustoffe und der Bestimmung der durchschnittlichen geochemischen Zusammensetzung von Teilschichtfolgen mittels RFA-Analysen. Durch geologische Aufnahme und Korrelation von zahlreichen Tagesaufschlüssen und zwei Kernbohrungen gelang es, eine detaillierte lithostratigraphische Regionalgliederung des ca. 80 m mächtigen Unteren Muschelkalks für den Raum Osnabrück zu erarbeiten. Eine von DUCHROW & GROETZNER (1984) publizierte lithostratigraphische Gliederung des Oberen Muschelkalks (ca. 60 m mächtig) im Arbeitsgebiet erwies sich als nachvollziehbar und wird auch in Gamma- Ray-Logs aus Bohrungen deutlich. Die Interpretation der geologischen Befunde ergab, daß die 1ithofaziellen Voraussetzungen für den Hartsteinabbau im Oberen Muschelkalk am günstigsten im Raum SW Osnabrücks sind. Nach den Ergebnissen der technologischen Untersuchungen sind nicht nur die zur Zeit bereits im Abbau stehenden, dickbankigen, sehr karbonatreichen Einschaltungen in den Oberen Muschelkalk (Haupt-Trochitenkalk, Terebratelkalk) für die Herstellung von Straßenbaumaterial geeignet, sondern mit einigen Einschränkungen auch der hierfür bisher nicht genutzte Untere Muschelkalk und die Gelben Basisschichten (Oberer Muschelkalk). Der Abbau und Einsatz dieses Gesteinsmaterials im Straßen- und Wegebau kann einen wichtigen Beitrag zur Streckung der nur noch geringen Vorräte an hochwertigem Kalkstein liefern. Die Gesteine des Unteren Muschelkalks und der Gelben Basisschichten (Oberer Muschelkalk) sind darüber hinaus aufgrund ihrer geochemischen Zusammensetzung ein gutes Rohmaterial für die Herstellung von "Kohlensaurem Kalk" und "Kohlensaurem Magnesiumkalk". Diese Produkte werden in zunehmendem Maße in der Forst- und Landwirtschaft eingesetzt, um durch saure Niederschläge hervorgerufene Vegetationsschäden zu begrenzen.

Riffe und fazielle Entwicklung der florigemma-Bank (Korallenoolith, Oxfordium) im Süntel und östlichen Wesergebirge (NW-Deutschland

During the Sedimentation of the platform carbonate deposits of the Korallenoolith Formation (middle Oxfordian to early Kimmeridgian) small buildups ofcorals formed in the Lower Saxony Basin. These bioconstructions are restricted to particular horizons (Untere Korallenbank,ßorigenuna-Bank Member etc.) and represent patch reefs and biostromes. In this study, the development of facies, fossil assemblages, spatial distribution of fossils, and reefs of the ßorigenuna-Bank Member (upper Middle Oxfordian) in the Süntel Mts and the eastern Wesergebirge Mts is described; the formation of reefs is discussed in detail. Twelve facies types are described and interpreted. They vary between high-energy deposits as well winnowed oolites and quiet-water lagoonal mudstones. Owing to the significance of biota, micro- and macrofossils are systematically described. The reefs are preserved in growth position, are characterized by numerous corresponding features and belong to a certain reef type. According to their size, shape and framework, they represent patch reefs, coral knobs (sensu James, 1983), coral thrombolite reefs (sensu Leinfelder et al., 1994) or “Klein- and Mitteldickichte” (sensu Laternser, 2001). Their growth fabric corresponds to the superstratal (dense) pillarstone (sensu Insalaco, 1998). As the top of the ßorigenuna-Bank displays an erosional unconformity (so-called Hauptdiskontinuität), the top of the reefs are erosionally capped. Their maximum height amounts to at least the maximum thickness of the ßorigenuna-Bank which does not exceed 4 metres. The diversity of coral fauna of the reefs is relatively low; a total of 13 species is recorded. The coral community is over- whelmingly dominated by the thin-branched ramose Thamnasteria dendroidea (Lamouroux) that forms aggregations of colonies (77?. dendroidea thickets). Leafy to platy Fungiastrea arachnoides (Parkinson) and Thamnasteria concinna (Goldfuss) occur subordinately, other species are only of minor importance. In a few cases, the reef-core consisting of Th. dendroidea thickets is laterally encrusted by platy F. arachnoides and Th. concinna colonies, and microbial carbonates. This zonation reflects probably a succession of different reef builders as a result of changing environmental conditions (allogenic succession). Moreover, some reefs are overlain by a biostrome made of large Solenopora jurassica nodules passing laterally in a nerinean bed. Mikrobial carbonates promoted reef growth and favoured the preservation of reef organismn in their growth position or in situ. They exhibit a platy, dendroid, or reticulate growth form or occur as downward-facing hemispheroids. According to their microstructure, they consist of a peloidal, clotted, or unstructured fabric (predominately layered and poorly structured thrombolite as well as clotted leiolite) (sensu Schmid, 1996). Abundant endo- and epibiontic organisms (bivalves, gastropods, echinoids, asteroids, ophiuroids, crabs etc) are linked to the reefs. With regard to their guild structure, the reefs represent occurrences at which only a few coral species serve as builder. Moreover, microbial carbonates contribute to both building and binding of the reefs. Additional binder as well as baffler are present, but not abundant. According to the species diversity, the dweller guild comprises by far the highest number of invertebrate taxa. The destroyer guild chiefly encompasses bivalves. The composition of the reef community was influenced by the habitat structure of the Th. dendroidea thickets. Owing to the increase in encrusting organisms and other inhabitants of the thickets, the locational factors changed, since light intensity and hydrodynamic energy level and combined parameters as oxygen supply declined in the crowded habitat. Therefore a characteristic succession of organisms is developed that depends on and responds to changing environmental conditions („community replacement sequence“). The succession allows the differentiation of different stages. It started after the cessation of the polyps with boring organisms and photoautotrophic micro-encrusters (calcareous algae, Lithocodium aggregatum). Following the death of these pioneer organisms, encrusting and adherent organisms (serpulids, „Terebella“ species, bryozoans, foraminifers, thecideidinids, sklerospongid and pharetronid sponges, terebratulids), small mobile organisms (limpets), and microbial induced carbonates developed. The final stage in the community replacement sequence gave rise to small cryptic habitats and organisms that belong to these caves (cryptobionts, coelobites). The habitat conditions especially favoured small non-rigid demosponges (“soft sponges”) that tolerate reduced water circulation. Reef rubble is negligible, so that the reefs are bordered by fossiliferous micritic limestone passing laterally in micritic limestone. Approximately 10% of the study area (outcropping florigemma-Bank) corresponds to reefal deposits whereas the remaining 90% encompass lagoonal inter-reefal deposits. The reef development is a good example for the interaction between reef growth, facies development and sea-level changes. It was initiated by a sea-level rise (transgression) and corresponding decrease in the hydrodynamic energy level. Colonization and reef growth took place on a coarse-grained Substrate composed of oncoids, larger foraminifers and bioclasts. Reef growth took place in a calm marine lagoonal setting. Increasing abundance of spherical coral morphs towards the Northeast (section Kessiehausen, northwestem Süntel Mts) reflects higher turbidity and a facies transition to coral occurrences of the ßorigenuna-Bank Member in the adjacent Deister Mts. The reef growth was neither influenced by stonns nor by input of siliciclastic deposits, and took place in short time - probably in only a thousand years under most probably mesotrophic conditions. The mass appearance of solenoporids and nerineids in the upper part of the ßorigenuna-Bank Member point to enhanced nutrient level as a result of regression. In addition, this scenario of fluctuations in nutrient availability seems to be responsible for the cessation of reef corals. The sea level fall reached its climax in the subaerial exposure and palaeokarst development of the florigemma-Bank. The reef building corals are typical pioneer species. The blade-like, flattened F. amchnoides colonies are characterized by their light porous calcium carbonate skeleton, which is a distinct advantage in soft bottom environment. Thus, they settled on soft bottom exposing the large parts of its surface to the incoming light. On the other hand, in response to their light requirements they were also able to settle shaded canopy structures or reef caves. Th. dendroidea is an opportunistic coral species in very shallow, well illuminated marine environment. Their thin and densely spaced branches led to a very high surface/volume ratio of the colonies that were capable to exploit incoming light due to their small thamasterioid calices characterized by “highly integrated polyps”. In addition, sideward coalescence of branches during colony growth led to a wave-resistant framework and favoured the authochthonous preservation of the reefs. Asexual reproduction by fragmented colonies promoted reef development as Th. dendroidea thickets laterally extend over the sea floor or new reefs have developed from broken fragments of parent colonies. Similar build ups with Th. dendroidea as a dominant or frequent reef building coral species are known from the Paris Basin and elsewhere from the Lower Saxony Basin (Kleiner Deister Mts). These buildups developed in well-illuminated shallow water and encompass coral reefs or coral thrombolite reefs. Intra- and inter-reef deposits vary between well-winnowed reef debris limestone and mudstones representing considerably calmer conditions. Solenoporid, nerineids and diceratides belong to the characteristic fossils of these occurrences. However, diceratides are missing in theflorigemma-Bank Member. Th. dendroidea differs in its colonization of low- to high-energy environment from recent ramose scleractinian corals (e.g., Acropora and Porites sp.). The latter are restricted to agitated water habitats creating coral thickets and carpets. According to the morphologic plasticity of Th. dendroidea, thick-branched colonies developed in a milieu of high water energy, whereas fragile, wide- and thin-branched colonies prevail in low-energy settings. Due to its relatively rapid growth, Th. dendroidea was able to keep pace with increased Sedimentation rates. 68 benthonic foraminiferan species/taxa have been recognized in thin sections. Agglutinated foraminifers (textulariids) predominate when compared with rotaliids and milioliids. Numerous species are restricted to a certain facies type or occur in higher population densities, in particular Everticyclammina sp., a larger agglutinated foraminifer that occurs in rock building amounts. Among the 25 reef dwelling foraminiferal species, a few were so far only known from Late Jurassic sponge reefs. Another striking feature is the frequency of adherent foraminiferal species. Fauna and flora, in particular dasycladaleans and agglutinated foraminifers, document palaeobiogeographic relationships to the Tethys and point to (sub)tropical conditions. Moreover, in Germany this foraminiferan assemblage is yet uncompared. In Southern Germany similar tethyan type assemblages are not present in strata as young as Middle Tithonian.