CARNIAN CONODONTS FROM UPPER TRIASSIC STRATA OF TAMARIN SECTION (SAN CASSIANO FM., DOLOMITES, ITALY)

A Late Triassic conodont fauna is described and illustrated for the first time from the San Cassiano Formation of the eastern Dolomites (Tamarin). The co-occurrence of Metapolygnathus auriformis, M. carnicus, M. baloghi, M. polygnathiformis, Gladigondolella  tethydis,  Gl. arcuata and Gl. malayensis malayensis indicates a Late Julian age. The fauna corresponds to the auriformis Zone (Austriacum Zone according to ammonoid  zones). This pelagic conodont  fauna, characteristic of relatively deep water, shows strong faunal affinities with coeval faunas from European Tethyan regions(mainly Greece, Turkey, NE Hungary, and Alps) and northern Kumaun region of Tethys Himalaya

CONODONT BIOSTRATIGRAPHY OF THE LATE TRIASSIC SEQUENCE OF MONTE COCUZZO (CATENA COSTIERA, CALABRIA, ITALY)

Preliminary results are reported from an investigation of the conodont associations found in the Late Triassic carbonate succession of the so-called "Catena Costiera Calabrese" that crops out in the tectonic window of Monte Cocuzzo. The succession of Colle del Crapio consists of alternating carbonate mud, breccia and calciturbidites deposited in a toe-of-slope to basin setting and contains rich and well-preserved conodont faunas pertaining to two biozones. The lower zone is characterised by the occurrence of Epigondolella slovakensis and may be referred to the Late Norian (Sevatian). The upper zone is characterised by Misikella hernsteini associated with M. posthernsteini. The chronostratigraphic setting of the latter zone is more controversial, as it may be regarded as latest Sevatian (Upper Norian) according to Krystyn (1990) and Golebiowski (1990), while according to the zonation of Kozur & Mock (1991) the first occurrence of M. posthernsteini marks the beginning of the Rhaetian stage.  &nbsp

Molecular fossils and other organic markers as palaeoenvironmental indicators of the Messinian Calcare di Base Formation: normal versus stressed marine deposition (Rossano Basin, northern Calabria, Italy)

A multidisciplinary study has been carried out on the Late Miocene (Messinian) Calcare di Base Formation in northern Calabria, Italy, with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone. The research has been developed through sedimentological (microfacies), organic petrography and geochemical analyses (palynofacies, Rock-Eval pyrolysis and gas chromatography/mass spectrometry). The carbonates studied preserve their original mineralogy (aragonite) and microstructure. The prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric. Larger and darker cylindrical–subcylindrical micritic grains, attributable to faecal pellets, are more or less randomly dispersed in the peloidal micrite. The faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies. Bright epifluorescence characterizes the faecal pellets and peloidal micrite, indicating their high content of organic matter. Detrital and stromatolitic microfacies occur rarely (around a few percent). The detrital microfacies is characterized by silt-sized grains organized in thin, sometimes bioturbated, graded laminae. The stromatolitic microfacies shows planar to gently curved/wrinkled laminae organized in dark and light couplets. The associated sedimentary organic matter shows low maturity, and preserves the original signatures of the source organisms. Rock-Eval pyrolysis revealed a transitional composition between Type II and Type III kerogen, suggesting a mixture of marine and terrigenous organic matter input. The molecular biogeochemical data indicate three main biological signatures: algae, bacteria and higher plants. Organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration. We conclude that the most probable bacterial process involved in carbonate precipitation of the Calcare di Base, considering the freshwater input and consequent probable enrichment in organic matter and Ca2+ ions, is ammonification of amino-acids in aerobic conditions

Reconstruction of tectonically disrupted carbonates through quantitative microfacies analyses: an example from the Middle Triassic of Southern Italy

AbstractThe 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

THE PRATI DI STUORES/STUORES WIESEN SECTION (DOLOMITES, ITALY): A CANDIDATE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASE OF THE CARNIAN STAGE

The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy) is proposed as a candidate Global Stratotype Section and Point for the base of the Carnian Stage. In addition to being a famous, richly fossiliferous locality, it includes the type-section of the Cordevolian substage. The section is located near Pralongià, along the southern slope of the crest separating the Badia/Abtei and Cordevole valleys. Below the levels with Trachyceras aon, the section contains a rich ammonoid fauna that chacterizes the lower part of the Regoledanus Subzone and subsequently records the first appearances of the mid-high latitude genus Daxatina (Daxatina sp., D. cf. canadensis) and of traditional Trachyceras with species different from T. aon. Moreover, the Daxatina cf. canadensis Subzone is recognised above the Regoledanus Subzone. Very rare conodonts of the Budurovignatus group and species of Gladigondolella from the diebeli Assemblage Zone occur. Gondolella polygnatyformis, already known from the Aon Subzone, is absent. Palynomorphs, foraminifers, gastropods, bivalves, brachiopods, microcrinoids and holothurian sclerites were studied. Variations in frequency and taxonomic diversity of these faunas suggest anaerobic-disaerobic bottom conditions for the lower-middle part of the section (0-105 m), followed by a more stable oxygen content in the upper portion. Magnetostratigraphy showed four intervals with normal polarity and three intervals with reversed polarity. The Daxatina cf. canadensis Subzone falls close to the normal polarity interval S2n. The present study proposes the FAD of the cosmopolitan genus Daxatina as a marker of the base of the Carnian Stage, placing it at a lower stratigraphic level than previously indicated in the Stuores area. The Prati di Stuores section is proposed as GSSP of the Ladinian-Carnian boundary.&nbsp

Autochthonous Micrite to Aphanodolomite: The Microbialites in the Dolomitization Processes

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

PRELIMINARY BIOGEOCHEMICAL DATA ON MICROBIAL CARBONATOGENESIS IN ANCIENT EXTREME ENVIRONMENTS (KESS-KESS MOUNDS, MOROCCO)

The Devonian Kess-Kess mounds, cropping out in the Hamar Laghdad Ridge (SE Morocco), provide a useful case-study for understanding the relationships between the microbial metabolic activities and micrite precipitation in an extreme environment. Very fine dark and white wrinkled laminae record microbial activity and the geochemistry of the organic matter allows the  characterization of the source organisms. The biogeochemical characterization of extracted organic matter was performed through the functional group analyses by FT-IR Spectroscopy. FT-IR parameters indicate a marine origin and low thermal evolution for the organic material. The organic matter is characterized by the presence of stretching ?C=C vibrations attributable to alkene and/or unsaturated carboxylic acids. Preliminary analysis with GC-MS provides evidence for an autochthonous (<C22) organic matter source for the free carboxylic acids. The origin of short-chain fatty acids that have a marked even over odd C number predominance is attributable to bacteria and/or algae and they are similar to those recorded in recent (Black Sea) and ancient (Late Jurassic to Early Cretaceous) methane-seep microbialites. These biogeochemical signatures of microbial carbonate precipitation in an ancient extreme environment may have implications in astrobiological research considering the recent discovery of carbonate deposits on Mars.