The main goal of the paper is the reconstruction of a Middle Triassic buildup cropping out in the central part of the Southern Apennines. Middle Triassic reefs of the western Tethys realm are well known in the Northern and Southern Alps. In contrast, few studies of the Anisian–Ladinian carbonate platforms of the southern Apennines are available, due to the diagenetic alteration and tectonic disruption that hinder their paleoenvironmental and stratigraphic reconstruction. In an attempt to fill this gap, and to improve the knowledge on the Anisian–Ladinian carbonates of central Mediterranean area, this research is focused on a carbonate buildup cropping out in the “La Cerchiara” area, Sasso di Castalda (Basilicata, Southern Italy). The buildup, affected by intense tectonic deformation associated with the development of the Apennine thrust and fold belt, was studied using a statistical evaluation of the quantitative microfacies data. The research enabled a reconstruction of the original stratigraphic relationships of the various buildup fragments. A positive linear regression between the sample positions vs the percentage of autochthonous carbonates indicates an increase of the autochthons carbonate toward the top of the succession. The allochthonous fabrics (packstone/wackestone) at the base of the section (Unit IIIa) pass gradually upward into autochthonous (boundstones) facies (Units IIIb, I), consisting of microbialites (clotted peloidal micrite, microbial-derived laminae, and aphanitic micrite), microproblematica and cyanobacterial crusts, with few encrusting skeletal organisms. Statistical data suggest that units IIIa, IIIb, and I are in stratigraphic order while unit II appears to have been moved by tectonic dislocation from its original position at the base of the succession. The absence of metazoan reef framework, and the richness of micro-encrusters, autochthonous micrite and synsedimentary cements, suggest a mud-mound style of growth for the carbonate bodies of the Southern Apennine during the Anisian.

ABSTRACTMicrobialites are common carbonate structures in cryptic niches of marine environments throughout geological time. In this research we compare the microbialites of small bioconstructions (biostalactites) of modern submarine caves of Sicily with those developed in small crypts of Carnian patch reefs of the Dolomite Mountains (Heiligkreuz Formation, Alpe di Specie) using Raman spectroscopy, a method that allows in situ determination of the organic content of microbial components. This methodology partly solves the uncertainty of geomicrobiological studies that use bulk measurements (i.e., biomarker analyses), which make it difficult to associate mineral precipitates with a specific microbial process. In the modern marine caves, the complex biotic relationships among skeletal organisms (mainly serpulids) and microbial communities produced biostalactites in which microbially induced biomineralization is the consequence of autotrophic and chemoheterotrophic bacterial activities. Sulfate-reducing bacteria, fed by metazoan organic matter, flourish in millimetric oxygen-depleted cavities of the skeletal framework, and induce autochthonous micrite deposition and early stabilization of the biostalactites. Similar processes have been interpreted to induce the deposition of the microbialites in the Upper Triassic patch reefs of the Dolomites. These small shallow water reefs, made up mainly of scleractinian corals, sponges and red algae, hold a skeletal framework rich in millimeter- to centimeter-size cavities, ideal cryptic niches for growth of microbial communities. Specific sulfate-reducing bacteria biomarkers are first identified using bulk measurements obtained by solvent extraction. The subsequent in situ characterization of organic compounds through micro-Raman spectroscopy indicates the same biogeochemical signatures of the microbialites within the cryptic cavities of the biostalactites of modern marine caves as those inside the skeletal framework of Carnian patch reefs. These data, showing the same processes in Triassic and modern cryptic microenvironments, is evidence that the microbially mediated precipitation in confined environments is a process independent of geological time that further investigation may be able to test.

This dataset aims at illustrating the relationships between Metazoa and Bacteria in confined environments. For this purpose, the biotic crusts inside two submarine caves of the Aegean Sea were examined in order to characterize organisms involved in their formation. The present manuscript provides additional data and information to our research article "Composition and biostratinomy of sponge-rich biogenic crusts in submarine caves (Aegean Sea, Eastern Mediterranean)" [1] (Guido et al.). The data were collected with an integrated approach utilizing microfacies observations in optical microscopy and micromorphological and geochemical characterization in electron microscopy (SEM and EPMA). We present here microfacies showing the boundstone framework, which is rich in microcavities partly filled by sponge spicules and scant autochthonous micrite. SEM and EPMA data put in evidence the abundance of sponge spicules inside the crusts and allow discriminating between two types of micrite: detrital micrite and autochthonous micrite. The data presented in this article and those described in Guido et al. [1] allow the evaluation of the relationship between sponges and carbonatogenetic bacteria in the cryptic conditions of submarine caves, and provide new knowledge to interpret the fossil record.

In the present paper, we examine the influence of micrite types, autochthonous or allochthonous, on the dolomitization processes. The recrystallized and dolomitized Carnian samples from Rifugio Vallandro and Alpe di Specie erratic boulders (South Tyrol, Italy) offer a unique example for studying the relationship between microbialites and dolomitization processes. The comparison between the carbonates of the well-preserved erratic boulders of Alpe di Specie and the isochronous, recrystallized, and dolomitized, samples of Rifugio Vallandro, allows for hypothesizing the role of microbialites on dolomitization processes. The Rifugio Vallandro samples represent variously dolomitized boundstone (made of corals, sponges, and peloidal crusts) with a fine texture (aphanodolomite) which contain organic matter relics, suggesting microbial-mediated mineralization. Geomicrobiological characterization of the microbialites from Alpe di Specie indicates that they formed through microbial metabolic activity of sulfate-reducing bacteria, which thrive on organic matter accumulated in the suboxic to anoxic interspaces of the skeletal framework. Similar processes can be hypothesized for the microbialite precursor of Rifugio Vallandro. Extracellular polymeric substance (EPS) and other organic compounds trapped inside the fine crystal matrix can have a role in the dolomitization processes of the microbialites. High pH and high alkalinity, derived from the degradation of organic matter, may be critical in promoting the dolomitization of microbialites because the high pH increases the concentration and activity of the dissolved CO32−, thereby increasing the dolomite supersaturation and reaction rates. This process produces very fine dolomite (aphanodolomite) that replaces the original organic-rich micrite, while the fine crystalline dolomite forming larger euhedral crystals seems to derive from the allochthonous micrite due to the presence of a large amount of siliciclastics and the absence of organic remains.

The biostalactites from the Kakoskali cave in Cyprus represent a new example of the complex biotic relationships between skeletal organisms and microbial communities in building bioconstructions of cryptic marine environments. Biostalactites are mainly constituted of polychaetes of the family Serpulidae and, to a lesser degree, foraminifers and bryozoans. Within the skeletal framework of these organisms, two types of microcrystalline calcite (micrite) have been recognized: autochthonous and detrital micrite. The autochthonous fraction is syndepositionally lithified and occurs as clotted peloidal and, subordinately, aphanitic (structureless) textures, suggesting the presence of heterotrophic microbial activities thriving on decaying metazoan organic matter. This fraction is limited to the protected portions of the bioconstructions, especially in the inner and lower parts. The presence of iron and manganesiferous oxidizing bacteria is suggested by the deposition of ferromanganesiferous crusts and Frutexites-like structures. These microbial-induced biomineralizations are the main evidence of carbonatogenetic and Fe–Mn, autotrophic and chemoheterotrophic, bacterial activities. The Kakoskali cave is frequently visited by divers who, during their immersions, resuspend the fine bottom sediment, which later covers the surface of the bioconstructions, disturbing the delicate equilibrium of the biotic association. This perturbation, which is also caused by strong waves and currents, during winter months, reflects on the bioconstruction morphologies, community composition, and colonization pattern. Bioconstructions exhibit an upper smooth surface, produced by few taxa (e.g., polychaetes, foraminifers), hosting a low number of living individuals, and a lower comparably rough surface, colonized by a more abundant community showing a higher species richness. The ratio surface roughness/smoothness is related to micrite sediment type: the upper part is mainly characterized by loose detrital micrite while the internal and lower parts by syndepositional cemented autochthonous micrite.

Biotic crusts occurring in the Early Pleistocene Rumena Cave, in NW Sicily, have been analyzed from a geomicrobiological point of view. The crusts consist largely of scleractinians and of subordinate bryozoans and serpuloideans, all typical of submarine cave biota. Encrustations document a blind cave in a shadowed setting, or possibly below the fair weather swell zone. Autochthonous and, subordinately, detrital fractions were observed within the skeletal framework of biotic crusts. The syndepositional lithified fraction occurs mainly as very fine-grained laminations. Clotted peloidal and aphanitic (structureless) textures occur in the micrites as well. Autochthonous micrite is always associated with a significant amount of organic matter remains. In caves from the Plemmirio area in SE Sicily, the autochthonous microbial micrite, occurring in the bioconstructions, contains bacterial lipid biomarkers, including abundant compounds derived from sulfate-reducing bacteria. It is likely that a similar microbial mediation was involved in the formation of the autochthonous micrite present in the biotic crusts of the Rumena Cave.

Numerous studies have been carried out on microbialite/metazoan associations and their relative role in forming bioconstructions. It has often been suggested that microbial carbonate acts as stabilizing element of the primary skeletal framework. Here we describe unusual bioconstruction occurring in submerged marine caves. They are randomly distributed within the caves, and show different sizes and morphologies, as well as surface roughness/smoothness. These bioconstructions, named biostalactites, are constituted by a few cm-thick crust of serpulids and other metazoans associated with carbonate micrites. All the identified sessile faunas largely consist of cryptic and sciaphilic organisms indicating cave conditions. Biostalactites are the result of the interaction between metazoans and microbial activity. Their distinctive vertical or oblique downward growth from the ceiling and walls of the caves reflects the skeletal/microbial relationship. The skeletal framework produced mainly by serpulids is syndepositionally stabilized by autochthonous microbial induced micrite.

Biostalactites formed by metazoan-microbialite associations from three submerged marine caves in the Plemmirio Peninsula (south of Syracuse, Ionian Sea) are randomly distributed and show different sizes and morphologies, as well as variations in surface roughness/smoothness. The biostalactites consist of crusts a few centimeters thick of small serpulids and other metazoans, associated with fine-grained carbonate; the larger ones often include a nucleus of serpulid tubes (Protula). The metazoans include mainly serpuloideans, sponges, bryozoans and foraminifers but microbial carbonates are also significant components. The composition of both the living communities and thanatocoenoses on the outer surfaces, as well as the composition and fabric of the internal framework, were analysed and used to reconstruct the history of the caves. All of the identified sessile faunas mainly consist of cryptic and sciaphilic dwellers that reflect cave conditions and their variations through time. The distribution pattern, composition and abundance of the present-day dwellers largely depend on the degree of roughness of the biostalactite surfaces and their positions within the caves. It has been suggested that the Protula specimens in the nuclei represent pioneer populations that formed aggregates during the early cave colonization phase, in response to relatively high food supply from seawater inflow and intruding continental waters. By contrast, the outer metazoan-microbialite carbonates reflect more confined conditions in the caves caused by Holocene sea-level rises. Hypotheses are proposed for biostalactite growth, taking into account information about the growth rates of some constituents, and evidence of dissolution effects. Similarities and differences between these bio-stalactites and other Holocene deposits previously described from submarine caves in the Mediterranean Sea and in tropical reefs are discussed.

The role of microfossils for the ceramic paste characterization has been revealed through firing experiment. Ceramic samples were prepared with the clay of Monte San Giorgio (Sicily, Italy), that contains many microfossils that suffered relevant changes in the microstructure and chemical composition during firing temperature. The samples were fired at different conditions according to the presumed ancient techniques. The alteration and/or decomposition of mineral phases with temperature was observed with optical and electron microscopy by monitoring the mineral modifications at different firing conditions. In order to validate our approach on archaeological material, the analyses were performed also on ceramic fragments, furnished by the Ceramics Regional Museum “Antonino Ragona” of Caltagirone. The micropaleontological study, as component of the archaeometric analyses, seems to be a useful archaeothermometry for the evaluation of firing processes and sometimes decisive to distinguish the characteristics of the clay used in a given production.

Geochemical signatures and carbonate microfacies highlight contrasts between two distinctive mid–late Triassic reef communities in the Dolomite Alps, Italy. In the first community, sponges, bryozoans, calcified cyanobacteria and problematic organisms (Archaeolithoporella, Shamovella), together with a variety of micritic fabrics, formed compact reefs in high energy shallow-water at the margins of high-rise Ladinian–Carnian carbonate platforms. Debris from these margins created steep foreslopes, and some large blocks of the allochthonous material (Wengen–Cassian formations, Cipit Boulders) were buried in basinal shales that protected them from subsequent alteration and regional dolomitization. In the second and slightly younger community, small Carnian patch reefs (Heiligkreuz Formation, Alpe di Specie) developed in quieter shallow water, where they too were protected against alteration by enclosing shales. They were constructed mainly by scleractinian corals, sponges and red algae, and contain relatively large framework cavities with clotted-peloidal micrite. These early examples of coralgal reefs have broad similarities to present-day examples, whereas the community represented by the Cipit Boulders has more in common with Late Permian reefs.

In upcoming years several space missions will investigate the habitability of Mars and the possibility of extinct or extant life on the planet. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate biogenic carbonate samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced microcrystalline carbonate deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. In this work we show that, by applying our method to different parts of the same carbonate rock, we are able to discriminate the presence, nature and biogenicity of various micrite types (i.e. detrital vs autochthonous) and to distinguish them from the skeletal grains. To test our methodology we preliminarily used the epifluorescence technique to select on polished samples, skeletal grains, autochthonous and allochthonous micrites, each one characterized by different organic matter content. The results on the various components show that, applying the infrared spectral modifications induced by thermal processing, it is possible to determine the degree of biogenicity of the different carbonate samples. The results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms.