Small reefal bioconstructions that developed in lagoonal settings are widespread in a few horizons of the Late Jurassic (Oxfordian) succession of the Korallenoolith Formation, exposed southwest of Hannover, Northwest Germany. Especially the florigemma-Bank Member, "sandwiched" between oolite shoal deposits, exposes a high variety of build-ups, ranging from coral thrombolite patch reefs, to biostromes and to coral meadows. The reefs show a distribution with gradual facies variations along an outcrop belt that extends about 30 km from the Wesergebirge in the NW to the Osterwald Mts in the SE.The patch reefs from the Deister Mts locality at the "Speckhals" are developed as coral-chaetetid-solenoporidmicrobialite reefs and represent a reef type that was hitherto unknown so far north of its Tethyan counterparts. They are mainly built up by coral thickets that are preserved in situ up to 1.5 m in height and a few metres in diameter. They contain up to 20 coral species of different morphotypes but are chiefly composed of phaceloid Stylosmilia corallina and Goniocora socialis subordinately. The tightly branched Stylosmilia colonies are stabilized by their anastomosing growth. The coral branches are coated with microbial crusts and micro-encrusters reinforcing the coral framework. Encrusters and other biota within the thicket show a typical community replacement sequence: Lithocodium aggregatum, Koskinobullina socialis and Iberopora bodeuri are pioneer organisms, whereas the occurrence of non-rigid sponges represents the terminal growth stage. The latter are preserved in situ and seem to be characteristic so far poorly known constituents of the Late Jurassic cryptobiont reef dweller community. The distance and overall arrangement of branches seems to be the crucial factor for the manifestation of a (cryptic) habitat promoting such community replacement sequences. Widely spaced branches often lack any encrusting and/or other reef dwelling organisms, whereas tightly branched corals, as is St. corallina, C. Helm ( ) · I. Schülke stimulate such biota. Hence, such reefs are well suited for research on coelobites and community sequences of encrusting and cavity dwelling organisms.
Mass extinction events encompass three different intervals: extinction, survival, and recovery. While studies concerning extinction patterns of taxa have frequently been carried out, only a few studies focus on the recovery of faunas, especially at the FrasniardFammenian boundary (Kellwasser Event). This paper examines extinction and recovery fabric of conodonts, a nektonic group highly abundant within pelagic calcareous sediments of this stratigraphic interval throughout the world. On the basis of high-resolution stratigraphy and statistic analysis of species diversity, the above three intervals can be distinguished within extinction and recovery phases of conodonts at the Kellwasser Event. Additionally, conodont samples and lithology of the Sessacker Trench VI section allow to subdivide at least the conodont extinction within the FrasniardFamennian boundary interval which was interpreted as merely single stepped into four different steps. Dependent on their niche's position within the Late Frasnian ecosystem, the taxa of this fossil group reveal different evolutionary "strategies" or mechanisms to survive mass extinction.
High resolutional microfacies data from the Beringhauser Tunnel section in the northern part of the Rheinisches Schiefergebirge allow the reconstruction of a relative sea-level curve. Distinctive sedimentological signals in this cephalopod limestone section indicate the positions of sea-level lowstands that correlate well with preexisting sea-level curves. Only slight differences in some lowstand positions have been observed by means of conodont biostratigraphy. The basal Famennian portion of the succession at the Beringhauser Tunnel section exposes microbial sedimentary structures reported from the Rheinisches Schiefergebirge for the first time that are indicative of initial mud-mound formation or mud-mound flanks. Further mud-mound growth with the development of a synsedimentary relief was stopped, probably due to drowning.
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