Joachim Reitner

Modern cryptic microbialite/metazoan facies from Lizard Island (Great Barrier Reef, Australia) formation and concepts

SummaryFrom shallow water caves of fringing reefs related to continental islands of the Lizard Island Section thrombolitic micritic microbialites were observed. The microbialites exhibit always a light decreasing facies succession. The succession starts with a coralgal community and ends with light independent microbial biofilms and benthos (coralline sponges). The sessile mineralized benthos community is constructed of crustose foraminifera, serpulids, thecidean brachiopods, bryozoans, and coralline sponges. The observed benthic community is very similar to those one observed in cryptic habitates of Aptian and Albian reefs of northern Spain.For longtime studies of the microbialite formation and growth rates of coralline sponges the specimens were stained in vivo, within their natural habitat with histochemical fluorochromes and nonfluorescent agents. Main results are a very slow growth of the microbialite and associated sponges (50–100 μm/y). Only few calcifying microbes are participators during microbialite formation. Calcifying acidic organic macromolecules are mainly responsible for microbialite formation by cementing detritical material. Fe/Mn-bacterial biofilms are responsible for strong corrosion of the microbialite. Beside the corrosive activity of the Fe/Mn-bacterial biofilms boring sponges (Aka, Cliona) are the main destructors.Geochemically the observed microbialites are composed of mainly high-Mg calcites and exhibit high positive δ13C (+3 to +4) values.

Microbial carbonate crusts-a key to the environmental analysis of fossil spongiolites?

SummaryMorphological and geochemical comparisons between modern cryptic microbialites from Lizard Island/Great Barrier Reef and fossil counterparts in the Upper Jurassic (Southern Germany, Dobrogea/Romania) and late Lower Cretaceous (Aptian/Albian from Cantabria/Spain) spongiolitic environments show that there are common factors controlling the crust formations mostly independent of light despite of diverging (paleo-) oceanographic positions as well as relationships of competitors. Factors such as increased alkalinity, oligotrophy, and reduced allochthonous deposition are of major importance. Thrombolitic microbialites are interpreted as biologically induced and therefore calcified in isotopic equilibrium with the surrounding sea water. Corresponding with shallowing upward cycles, microbial mats which produce stromatolitic peloidal crusts become more important. Different biomarkers are introduced for the first time extracted and analyzed from spongiolitic limestones of Lower Kimmeridgian age from Southern Germany.

Facies belts and communities of the arctic Vesterisbanken Seamount (Central Greenland Sea)

SummaryThe Arctic Vesterisbanken Seamount, situated far offshore in the central Greenland Sea, provides a unique facility for studing modern cold water siliceous carbonate deposits. A nearly year round sea ice cover, which retreats on average only during two months, and a rather constant temperature and salinity structure of the water column characterize the Arctic conditions of the area.Despite predominantly oligotrophic conditions with a pronounced food supply from the pelagic realm only during the ice-free season, the seamount is covered extensively by extended sponge-bryozoan constructions. Three distinct facies belts reveal a pronounced depth zonation which depends on variations in downslope food transfer and which is specifically effective due to the development of aTaylor current regime over the seamount: i) the crest facies from the summit at −133m to −260 m, ii) the shallow slope facies from −260 m to −400 m, iii) the deep slope facies from −400 m down to the abyssal plain at about— 3.000 m. Different biogenic structures and communities are found within these facies belts, including widely extended biogenic mats, sponge bryozoan-serpulid buildups with mounds, hedges, spurs and flatcake-like structures, bryozoan thickets and sponge-crinoid mounds. Depth zonation, internal structure and controlling parameters in the formation of these biogenic structures are discussed in the context of their significance as a modern end member of the Foramol facies and their implication for the fossil record. In addition, the younger volcanic and hydrothermal history of the seamount is presented with special reference to its bearing on Holocene biogenic colonization patterns.

A Comparative Study of the Diagenesis in Diapir-Influenced Reef Atolls and a Fault Block Reef Platform in the Late Albian of the Vasco-Cantabrian Basin (Northern Spain)

The Mesozoic Vasco-Cantabrian Basin is situated in the Spanish Basque-Lands of northern Spain, close to the French border (Fig. 1). To the west the basin is delineated by the Paleozoic massifs of the Cantabrian Mountains, to the east by the Pyrenees, and to the south by the Late Tertiary Ebro Basin. The tectonic history of the Vasco-Cantabrian ranges from the Triassic to the Tertiary but the major part of its fill (8000 m) is attributed to Late Mesozoic deposition. During the Late Albian due to rapid subsidence, salt diapirs (Keuper age) developed between basement fault blocks. Shallow marine carbonate reefs (Urgonian Facies) developed on these highs. Two types of reef can be distinguished: (1) larger fault block reef platforms on tilted basement segments and (2) smaller reef atolls on top of rising diapirs. The diapir reefs can be differentiated from the fault block reefs through sedimentological, paleobiological, diagenetic, and geochemical criteria.

Contributions to the systematics and the paleoecologyof the family Acanthochaetetidae (Order Tabulospongida, class Sclerospongiae)

Abstract The Tabulospongida species Acanthochaetetes seunesi and A. ramulosus from Midcretaceous reefs in Northern Spain show siliceous spicules incorpored in its rigid, High-Mg-calcite skeleton. The modern genus Tabulospongia Mori , 1976 is synonymous with the fossil genus Acanthochaetetes Fischer , 1970 . The habitat of Acanthochaetetes in Midcretaceous reefs is almost identical with that of living representative of the same genus in Caribbean and Pacific reefs.

Skeletal structure, growth, and paleoecology of the patch reef-buildingpolychaete worm Diplochaetetes mexicanus wilson, 1986 from the oligocene of baja california (Mexico)

Abstract Worm reeflets discribed here are composed of parallel and straight, curved, or bifurcated tubes, which are up to 10 cm long and have an average diameter of 1.4 mm. Their walls are composed of microgranular calcite and are multilamellar. The reef-builders settled on soft bottoms within the tidal or uppermost zone. They tolerated high water turbulence and a certain rate of sedimentation. Dead parts of the reef were recolonized by a new population. The reefs stabilized the sediment, produced biogenic debris, and offered new ecological niches for endo- and epilithic organisms. They mark a regional ecological event at the Oligocene/Miocene boundary. Diplocbaeteles mexicanus as well D. longitubus demonstrate close relationships to a modern skeletal-forming polychaete worm, Dodecaria. Diplochaetetes is definitly not a sclerosponge and demonstrates a convergence with the chaetetid basal skeletons of sponges and favositid corals.