Markus Reuter

Shallow-marine carbonates of the tropical-temperature transition zone: effects of hinterland climate and basin physiography (late Miocene, Crete, Greece)

Abstract In modern oceans, the transition zone between the tropical and temperature carbonate province is gradual and covers a wide latitudinal belt. Little knowledge exists regarding the geological signatures of this zone. This paper describes a late Miocene (early Tortonian-early Messinian) transitional carbonate system that combines elements of the tropical and cool-water carbonate systems (Iraklion Basin, island of Crete, Greece). As documented in stratal geometries, the submarine topography of the basin was controlled by tilting blocks. Coral reefs formed by Porites and occurred in a narrow clastic coastal belt along a central Cretan landmass and steep escarpments formed by faulting. On the gentle dip-slope ramps of those blocks having the widest geographical distribution within the basin, extensive covers of level-bottom communities existed in a low-energy environment. Isolated colonial corals were present in the shallow segments of the ramps. Consistent patterns of landward and basinward shift of coastal onlap in all outcrop studies reveal an overriding control of third- and fourth-order sea-level changes on sediment dynamics and facies distributions over block movements. An increasingly dry climate and the complex submarine topography of the fault-block mosaic kept sediment and nutrient discharge from a central Cretan landmass at a minimum. The skeletal limestone facies therefore reflects oligotrophic conditions and sea surface temperatures near the lower threshold temperature of coral reefs in a climatic position transitional between the tropical coral reef belt and the temperate zone. It is suggested that the recognition of an overall late Miocene aridification trend helps to explain the Mediterranean-wide distribution of shallow-marine carbonates, both cool-water and warm-water, in settings adjacent to uplifting mountain ranges (intramontane basins).

A FOSSIL EVERGLADES-TYPE MARL PRAIRIE AND ITS PALEOENVIRONMENTAL SIGNIFICANCE

Abstract Located at the interface between land and sea, marl prairies are sensitive to changes in water balance and useful recorders of climate and sea-level changes. Palustrine carbonate in marl prairies precipitates in temporary, barely flooded grasslands within microbial mats. Despite the special mode of carbonate production, descriptions of the sedimentary facies are exceptional and cursory because marl prairies are so far reported only from the recent of the Everglades (Florida, USA), where they produce an unspectacular calcite mud. We present a Pleistocene Everglades-type marl prairie from coastal Tanzania as the first fossil example. The unique preservation and high productivity (two times higher than in the Everglades) of the periphyton community in this marl prairie is due to increased calcification of coccoid and filamentous cyanobacteria. The excellent preservation allows us to characterize a marl prairie facies in great detail for the first time. Facies analyses of the sediments reveal a transition from tidal to terrestrial settings that started at ca. 44 14C ka in response to eustatic sea-level fall and coastal tectonic uplift. The resultant drop of the groundwater table triggered the development of the marl prairie. The decline of the marl prairie was initiated at ca. 33 14C ka due to the onset of the Last Glacial Aridity Maximum in equatorial East Africa.

Die Korallenfauna des Korallenooliths (Oxfordium, Oberjura, NW-Deutschland): Zusammensetzung, Stratigraphie und regionale Verbreitung

KurzfassungDie stratigraphische und regionale Verbreitung der Korallen im Korallenoolith des Süntels, Deisters, Kleinen Deisters und Osterwaldes (NW-Deutschland) wird beschrieben. Im bearbeiteten Gebiet sind vier Korallen führende Niveaus innerhalb des Korallenooliths ausgebildet, von denen zwei eine überregionale Verbreitung haben (Untere Korallenbank,florigemma-Bank / Obere Korallenbank) und zwei weitere (Fossilschicht, Nerineenbank) sich nur lokal nachweisen lassen.Die Korallenvorkommen sind in den genannten Horizonten unterschiedlich ausgebildet. Innerhalb der Unteren Korallenbank bilden die Korallen artenarme, weitflächig verbreitete, Mikrobolith-freie biostromale Konstruktionen. In derflorigemma-Bank sind hingegen z.T. sehr artenreiche und regional hochdiverse „Korallengestrüppe“, Fleckenriffe und Biostrome entwickelt, die weitgehend unter Beteiligung von Mikrobolith aufgebaut sind. Die größten und artenreichsten Riffe mit nahezu 40 Korallentaxa sind aus der Oberen Korallenbank des Osterwaldes bekannt.Korallen sind im Korallenoolith regional weiter verbreitet und wesentlich artenreicher als bisher angenommen. Es konnte der Nachweis von ca. 20 bisher aus dem Korallenoolith unbekannten Arten erbracht werden.AbstractThe stratigraphie and regional distribution of Oxfordian scleractinian reef corals in the Korallenoolith Formation (NW German Malm Group) is described from the Süntel, Deister, Kleiner Deisler and Osterwald Mountains. In the study area four horizons with (par-) autochthonous corals are developed two of which can be traced region-wide (Untere Korallenbank Member andflorigemma-Bank Member / Obere Korallenbank Member).The coral fauna of the biostromes, forming the Untere Korallenbank Member, is impoverished and dominated by ubiquitous r-strategists. In contrast, the reefal bioconstruetions of theflorigemma-Bank Member show a high variability in their regional appearances, partly forming highly diverse coral associations. The highest diversity is developed in the patch reefs from the Obere Korallenbank Member of the Osterwald Mountains (about 40 species).Corals are an important part of the Korallenoolith fauna. Altogether, 20 species belonging to 15 genera have been identified which were formerly unknown from NW German Oxfordian successions.

Correlating carbon and oxygen isotope events in early to middle Miocene shallow marine carbonates in the Mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy.

Abstract During the Miocene prominent oxygen isotope events (Mi‐events) reflect major changes in glaciation, while carbonate isotope maxima (CM‐events) reflect changes in organic carbon burial, particularly during the Monterey carbon isotope excursion. However, despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions. The Decontra section on the Maiella Platform (central Apennines, Italy), however, allows to resolve them for the first time in such a setting during the early to middle Miocene. The present study improves the stratigraphic resolution of parts of the Decontra section via orbital tuning of high‐resolution gamma ray (GR) and magnetic susceptibility data to the 405 kyr eccentricity metronome. The tuning allows, within the established biostratigraphic, sequence stratigraphic, and isotope stratigraphic frameworks, a precise correlation of the Decontra section with pelagic records of the Mediterranean region, as well as the global paleoclimatic record and the global sea level curve. Spectral series analyses of GR data further indicate that the 405 kyr orbital cycle is particularly well preserved during the Monterey Event. Since GR is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the Decontra section, it follows the same long‐term orbital pacing as observed in the carbon isotope records. The 405 kyr GR beat is thus correlated with the carbon isotope maxima observed during the Monterey Event. Finally, the Mi‐events can now be recognized in the δ18O record and coincide with plankton‐rich, siliceous, or phosphatic horizons in the lithology of the section.

Orbitally paced phosphogenesis in Mediterranean shallow marine carbonates during the middle Miocene Monterey event

Abstract During the Oligo‐Miocene, major phases of phosphogenesis occurred in the Earths oceans. However, most phosphate deposits represent condensed or allochthonous hemipelagic deposits, formed by complex physical and chemical enrichment processes, limiting their applicability for the study regarding the temporal pacing of Miocene phosphogenesis. The Oligo‐Miocene Decontra section located on the Maiella Platform (central Apennines, Italy) is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting. Of particular interest are the well‐winnowed grain to packstones of the middle Miocene Bryozoan Limestone, where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the Monterey event. This unique setting allows the analysis of orbital forcing on phosphogenesis, within a bio, chemo, and cyclostratigraphically constrained age‐model. LA‐ICP‐MS analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates, allowing natural gamma‐radiation (GR) to be used as a qualitative proxy for autochthonous phosphate content. Time series analyses indicate a strong 405 kyr eccentricity forcing of GR in the Bryozoan Limestone. These results link maxima in the GR record and thus phosphate content to orbitally paced increases in the burial of organic carbon, particularly during the carbon isotope maxima of the Monterey event. Thus, phosphogenesis during the middle Miocene in the Mediterranean was controlled by the 405 kyr eccentricity and its influence on large‐scale paleoproductivity patterns. Rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates, indicating generally oxic formation conditions, which are consistent with microbially mediated phosphogenesis.

Density banding in corals: barcodes of past and current climate change

The predicted sea surface temperature (SST) rise over the next decades is likely hazardous to coral health because precipitation of the calcareous skeleton depends primarily on SST. Temperature modulates vertical growth and density of the skeleton with seasonal SST changes resulting in an alternation of high-density and low-density bands (HDB and LDB). Notably, growth rates and the timing of the HDBs and LDBs relative to the seasons differ on a global scale within geographic regions. In this contribution, we use combined information of skeletal density and seasonally resolved oxygen isotope SST estimates from massive Porites from a Late Miocene (9 Ma) reef in the eastern Mediterranean Sea (Crete, Greece) to understand reef vulnerability over short and geological periods of time. Three types of HDB–SST relationships have been found: (1) coincidence of HDB with summer, (2) winter or (3) autumn and spring. The latter doubles HDBs in a year and implies maximum calcification is coupled to the taxon-specific optimum SST during the transitional seasons and reduced at its respective critical winter and summer SSTs. Modeling with a nonlinear temperature–calcification relationship reproduces the climate barcode of density bands. The model should be relevant for other poikilothermic carbonate producers in reefs and platforms and has implications for judging geographic distributions and causes of extinctions of corals, benthic carbonate communities and entire carbonate systems. With regard to the causes underlying expansion and demise of carbonate platforms and reefs in geological history, we expect the model predictions to help for a deeper understanding of biotic responses during hyperthermals or coolings and possibly also for identifying regions in the modern ocean where corals are endangered or taking advantage of global warming.

An unusual Pocillopora reef from the Late Miocene of Hispaniola

Pocillopora, a common reef coral in the present-day Indian Ocean, Red Sea, and Pacific Ocean, exhibits a wide range of environmentally controlled morphologic variation from submassive to bush-like uprightbranching colony forms (Veron 2000). Herein, we report on extinct reef-building P. crassoramosa from the Messinian Cercado Formation of the Cibao Basin in the Dominican Republic (N 19 29¢07.55†, W 071 14¢47.78†; Maier et al. 2007) that has an unusual robust-branching growth morphology and horizontally disposed lifestyle—both not reported for recent Pocillopora. Large branches of P. crassoramosa, many of which appear to be lying horizontally, are embedded in bioclastic silty marl (Fig. 1a) and form a 5-m-thick and 100-m-long buildup, which interfingers with an in situ coral thicket composed of upright standing, thin-branched Porites and Stylophora as well as plate-like agariciids (Fig. 1b). Single Pocillopora colonies reach nearly 2-m-length and consist of up to 10-cm-thick branches (Fig. 1a). The undersurface of these branches is smooth while the upper surface exhibits bulbous outgrowths and is covered by wide-spaced verrucae (Fig. 1c). In cross-sections, the growth increments reveal asymmetric circumferential growth that is directed toward the textured side (Fig. 1d). Regrowth patterns such as changes in growth direction and/or shape are not observed. This indicates the horizontally lying branches are in place and implies a creeping mode of life. Accordingly, bioerosion was found preferentially on the upper sides of the corals (Fig. 1d). It is assumed that the flat, spacious colony form is adapted for shallow, muddy bottoms because it is resistant to wave action and prevents the coral from sinking in the unstable substrate. The pronounced surface relief (Fig. 1c) may have favoured passive sediment removal due to steep gradients.

Early Miocene reef- and mudflat-associated gastropods from Makran (SE-Iran)

A new gastropod fauna of Burdigalian (early Miocene) age is described from the Iranian part of Makran. The fauna comprises 19 species and represents three distinct assemblages from turbid water coral reef, shallow subtidal soft-bottom and mangrove-fringed mudflat environments in the northern Indian Ocean. Especially the reef-associated assemblage comprises largely new species. This is explained by the rare occurrence of reefs along the northern margin of the Miocene Indian Ocean and the low number of scientific studies dealing with the region. In terms of paleobiogeography, the fauna corresponds well to coeval faunas from the Pakistani Balochistan and Sindh provinces and the Indian Kathiawar, Kutch and Kerala provinces. During the early Miocene, these constituted a discrete biogeographic unit, the Western Indian Province, which documents the near complete biogeographic isolation from the Proto-Mediterranean Sea. Some mudflat taxa might represent examples of vicariance following the Tethys closure. The fauna also displays little connection with coeval faunas from Indonesia, documenting a strong provincialism within the Indo-West Pacific Region during early Miocene times. Neritopsis gedrosiana sp. nov., Calliostoma irerense sp. nov., Calliostoma mohtatae sp. nov. and Trivellona makranica sp. nov. are described as new species.KurzfassungEine neue Gastropoden-Fauna aus dem Burdigalium (frühes Miozän) des Makrans (SE-Iran) wird beschrieben. Die Fauna umfasst 19 Arten und repräsentiert drei distinkte Vergesellschaftungen: ein Trübwasser-Korallenriff, subtidale Weichböden und Mangroven gesäumte Wattflächen des nördlichen Indischen Ozeans. Die Riff-assoziierte Vergesellschaftung besteht mehrheitlich aus bisher unbeschriebenen Arten. Das erklärt sich aus der geringen Zahl an Korallenriffen im nördlichen Indischen Ozean während des Miozäns und deren unzureichendem Bearbeitungsstand. Paläobiogeographisch zeigt die Fauna deutliche Bezüge zu gleichalten Faunen aus den pakistanischen Provinzen Belutschistan und Sindh sowie zu den westindischen Provinzen Kathiawar, Kutch und Kerala. Während des frühen Miozäns bildeten diese Faunen eine diskrete biogeographische Einheit, die Western Indian Province, die eine nahezu vollständige biogeographische Isolation vom Proto-Mittelmeer zeigt. Die morphologische Ähnlichkeit von einigen Arten aus der Wattflächenvergesellschaftung mit Arten aus der WIP/MIP ist vermutlich ein Beispiel für Vikarianz infolge der Tethys-Schließung. Zu gleichalten indonesischen Faunen sind die biogeographischen Bezüge ebenfalls sehr gering, was auf einen starken Provinzialismus innerhalb der Indo-West Pacific Region während des frühen Miozäns hinweist. Neritopsis gedrosiana sp. nov., Calliostoma irerense sp. nov., Calliostoma mohtatae sp. nov. and Trivellona makranica sp. nov. werden als neue Arten beschrieben.

Parascolymia (Scleractinia: Lobophylliidae) in the Central Paratethys Sea (Vienna Basin, Austria) and its possible biogeographic implications

Palaeobiogeographical and palaeodiversity patterns of scleractinian reef corals are generally biased due to uncertain taxonomy and a loss of taxonomic characters through dissolution and recrystallization of the skeletal aragonite in shallow marine limestones. Herein, we describe a fossil lobophylliid coral in mouldic preservation from the early middle Miocene Leitha Limestone of the Central Paratethys Sea (Vienna Basin, Austria). By using grey-scale image inversion and silicone rubber casts for the visualization of the original skeletal anatomy and the detection of distinct micromorphological characters (i.e. shape of septal teeth, granulation of septocostae) Parascolymia bracherti has been identified as a new species in spite of the dissolved skeleton. In the recent era, Parascolymia like all Lobophylliidae is restricted to the Indo-Pacific region, where it is represented by a single species. The new species proves the genus also in the Miocene Mediterranean reef coral province. A review of the spatio-temporal relationships of fossil corals related to Parascolymia indicates that the genus was probably rooted in the Eastern Atlantic‒Western Tethys region during the Paleocene to Eocene and reached the Indo-Pacific region not before the Oligocene. The revealed palaeobiogeographical pattern shows an obvious congruence with that of Acropora and tridacnine bivalves reflecting a gradual equatorwards retreat of the marine biodiversity center parallel to the Cenozoic climate deterioration.

FOSSIL PSAMMOBIONTIC SPONGES AND THEIR FORAMINIFERAL RESIDENTS, CENTRAL APENNINES, ITALY

ABSTRACT Sponges generally live firmly attached on firm- and hardgrounds but a few species are known to colonize mobile sediments in shallow water. These psammobiontic sponges are anchored to the bottom by incorporating sediment particles at their base. Herein we relate so-far enigmatic bowl-shaped structures from seagrass deposits of the lower Miocene (Burdigalian) Calcari a Briozoi e Litotamni Formation on the Latium-Abbruzzi carbonate platform (Central Apennines, Italy) to the in-ground parts of psammobiontic sponges. The sponge fossils yield a peculiar foraminiferal assemblage with an increased abundance of Bulimina and Bolivina compared to the surrounding sediments as well as with planktic foraminifers and spirillinids (Spirillina, Patellina), which are not recorded outside the sponges. Drifting planktic foraminifers became trapped on the sponge surface exposed to the water column before agglutination. In contrast, high quantities of Bulimina, Bolivina, and spirillinids indicate commensalistic relationships with the sponges. Generally, ecological interactions between foraminifers and living sponges are poorly documented. In the present case the infaunal Bulimina and Bolivina have been attracted by a low-oxygen and nutrient-rich environment, which developed in the progressively decaying buried part of the sponges along with early lithification, while the epifaunal spirillinids populated the internal network of water channels, which provided protection and food supply. The high abundance of generally rare Spirillina in Late Jurassic sponge reefs indicates a persistent ecological preference of spirillinids to sponge microhabitats.