Non-rigid cryptic sponges in oyster patch reefs (Lower Kimmeridgian, Langenberg/Oker, Germany)

Self Cite

The lower slope of the drowned Alpine Adnet Reef was recolonized in Hettangian time by sponge communities of hexactinellid (hexactinosid and lyssacinosid) taxa and a few demosponges. Special taphonomic processes caused an excellent preservation of these sponges. The preservation allows to define several growth forms and to study original spicule configurations of the mainly non-rigid skeletons. Sponge faunas of presumably similar associations are known from adjacent basins, but only by isolated spicules of completely collapsed specimens. In Adnet the sponges are embedded in biodetrital limestones of the Schnöll Formation. Orientation and distribution of the sponges reflect autochthonous faunas that have been mixed with dislocated individuals by local water currents. The predominance of erect sponge types indicates intermediate sedimentation rates and/or occasional high-energy events. Sponge types and community structures are comparable with those ones from Middle Paleozoic mud mounds. Several hiatuses, mostly characterized by ferromanganese crusts have been kept free of sponge settlement. Carbon stable isotopes of the sponge-rich sequence show a small negative δ 13 C carb excursion that covers the period from Lower Hettangian to Lower Sinemurian.

“…D Detail of Fig. 10c Delecat et al 2001). Although hexactinellids do not contain a lot of symbiotic sulfate-reducing bacteria, in Adnet this effect was not observed.…”

Section: Sponge Taphonomymentioning

confidence: 83%

Sponge communities from the Lower Liassic of Adnet (Northern Calcareous Alps, Austria)

Delecat¹,

Reitner²

2005

Self Cite

“…Cryptic non-rigid sponges communities similar to the described material are known to occur elsewhere in the Lower Saxony Basin (Reitner 1994;Delecat et al 2001: Lower Kimmeridgian oyster patch reefs characterized by prolific non-rigid sponge growth; Schülke 1998, 1999;Helm 2005: Oxfordian Thamnasteria dendroidea patch reefs exposed in the Süntel Mts).…”

Section: Microbialite Associated Reef Organisms and Bioerosional Ormentioning

confidence: 86%

“…All non-rigid sponges are restricted to the cavities left in the thickets after coating of coral branches with microbialites and encrusting organisms. They are preserved in situ and are imbedded within a mostly peloidal matrix that results from sponge automicrite formation (Delecat et al 2001).…”

Section: Microbialite Associated Reef Organisms and Bioerosional Ormentioning

confidence: 99%

Patch reef development in the florigemma-Bank Member (Oxfordian) from the Deister Mts (NW Germany): a type example for Late Jurassic coral thrombolite thickets

Helm

Schülke

2006

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.

“…9c, d). Thus, the formation of these leiolites may have resulted of a microbial inXuenced carbonate precipitation related to the decay of sponge tissues (Reitner 1993;Delecat et al 2001;Delecat and Reitner 2005;Reolid 2007;Dupraz et al 2009). The presence of leiolites suggests relatively long periods of high nutriWcation that may have led to anoxia in the benthos.…”

Section: Discussionmentioning

confidence: 98%

Microbial carbonates and corals on the marginal French Jura platform (Late Oxfordian, Molinges section)

Olivier

Colombié

Pittet

et al. 2010

International audienceMolinges was located on an Upper Jurassic ramp system of low-energy regime that developed at the southern margin of the French Jura platform. The sedimentary succession is characterized by the transition from a mixed siliciclastic-carbonate to a carbonate depositional setting that occurred during a long-term shallowing-upward trend. The disappearance of siliciclastics is explained by a climatic change, from humid and cold to drier and warmer conditions, previously identified in Late Oxfordian adjacent basins. The base of the section shows marl-limestone alternations of outer ramp. In its middle part, the section displays oncolitic marls, coral-microbialite beds and oncolitic limestones that deposited in a mid ramp position. Finally, the upper section part is made of oolitic limestones of inner ramp. In outer- to mid-ramp settings submitted to terrigenous inputs, the stacking pattern of deposits and facies evolution allow the identification of elementary, small-, medium-, and large-scale sequences. Small amplitudes of sea-level variations probably controlled rapid shifts of facies belts and reef window occurrences. In small-scale sequences, the coral beds developed during periods of sea-level rise. The decreasing rate of sea-level rise is marked by the downramp shift of the oncolitic limestone belt that led to the demise of coral-microbialite beds. These bioconstructions are mainly represented by thin biostromes in which corals never reach great sizes. The coral assemblages mainly include the genera Enallhelia, Dimorpharaea, Thamnasteria, and some solitary forms (Montlivaltia and Epistreptophyllum). They suggest relatively low-mesotrophic conditions in marine waters during the edification of the primary framework. Relatively cold water temperatures and periods of more elevated nutrient contents are probably responsible of the reduced coral development and the formation of a large amount of microbialites