Unique fossil preservation in ferruginous Silurian deposits from the Carnic Alps, Italy

A carapace of a new horseshoe crab (Arthropoda: Chelicerata: Xiphosura) is described from the Upper Carboniferous (Kasimovian) Meledis Formation of the Carnic Alps, Friuli, Italy. It is named as Stilpnocephalus pontebbanus n. gen. & n. sp., and belongs to the family Belinuridae Zittel in Zittel & Eastman, 1913. The large (>8 cm width) carapace is strongly effaced and appears to lack eyes. The new specimen is the first fossil horseshoe crab to be described from Italy and the largest known belinurid.

The tetrapod footprints from the Carboniferous (Pennsylvanian) of Italy come from the late Moscovian San Giorgio Formation of Sardinia and the early Ghzelian Corona Formation of the Carnian Alps. They include exclusively anamniote tracks: the ichnogenera Batrachichnus and Limnopus and tetrapod tracks indet. similar to Matthewichnus . The occurrence of anamniote tracks may have a marked palaeoecological meaning, since these tetrapods were tied to water for reproduction. These tracks represent the oldest record of tetrapods from Italy (either from trace fossils and skeletons) and the oldest Italian record of these ichnogenera. Despite the fragmentary material and the few known localities, the Pennsylvanian of Italy has a noteworthy potential for further prospecting, because of the relatively good preservation and the stratigraphy of the track-bearing formations. The Italian ichnoassociation could be the key for the understanding of the Notalacerta and Dromopus footprint biochrons in the Carboniferous of W Europe, which is less extensively known than the North American record.

Ironstones and iron-rich limestones regularly occur as components of time-specific intervals of the Palaeozoic as well as in younger times (Brett et al., 2012--this issue). Silurian sediments deposited at high latitudes along the peri-Gondwana border are characterized by black and white limestone and graptolitic shale sequences. Those in the Carnic Alps (southern Austria) additionally contain colourful pink to red limestones and ironstones. Laminated structures such as the (ferruginous)-coatings around skeletal fragments (mostly trilobites and some cephalopods and echinoderms) and stromatolitic features along discontinuity surfaces display dark red, green, white and brownish colours due to the presence of goethite, magnetite, hematite, chamosite, calcite and subordinate apatite. Confocal laser Raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites, filaments and coccoids, suggesting a microbial role in the colouring of the Silurian world of the Carnic Alps. Iron concentrations up to 30× that of matrix and surrounding non-ferruginous rocks suggest blooms of iron microbe activity in response to the time-specific occurrence of chemically charged sea water during global biotic events.

Trace fossils are important evidence of benthic activity, but they have received less study than body fossils for investigating the aftermath of the end-Permian extinction. There is therefore a need to document Lower Triassic ichnofaunas to understand their significance with respect to the end-Permian crisis. In light of this need, this paper describes a novel Lower Triassic ichnosite at Mount Pallone (Carnic Alps, Italy), where the Campil Member (Smithian) of the Werfen Formation (Griesbachian–Spathian) presents an abundant ichnofauna characterized by excellent preservation and low diversity. Documented ichnogenera include Asteriacites lumbricalis, Gyrochorte comosa, Diplocraterion habichi and Planolites beverleyensis. The ichnofaunal composition and the bioturbation style suggest a marginal marine paleoenvironment ranging from intertidal to shallow subtidal settings. Storm influence, hydrodynamic energy, sedimentation rate, freshwater input and/or water temperature played an important role in structuring the benthic ecosystem. Dense (300 specimens/m2) aggregations of the trace fossil Asteriacites lumbricalis reveals social behavior of their inferred brittlestar producers (Echinodermata, Ophiuroidea). In line with modern brittlestar beds, social behavior provided significant advantage because raised arms of brittlestars dampened hydrodynamic energy. This study suggests that Asteriacites beds may be considered ichnological proxies for marine settings, low bioturbation intensity, shallow tiering, high sedimentation rate and/or event-bed deposition, significant levels of hydrodynamic energy, and low predation pressure. The studied ichnofauna reflects stressed environmental conditions, but it is unclear whether this reflects local brackish conditions (‘Gazpacho model’) or global hot temperatures (‘Hot Soup model’).

Shales bearing abundant amount of organic materials can generate oil and gas by the thermogenic variations of the contained kerogen under the conditions of increasing burial pressure and heat. Some of the generated fossil fuels are expelled from these source rocks but majority of them are still confined. Those unexpelled hydrocarbons are considered as a new energy source and being produced by the application of unconventional techniques recently developed in North America. The shales being source rock may be a new energy resource for natural gas if overheated (Ro>1.2) or for oil in existence of under-normal heat influence (Ro=1.2). Shales have been considered as seal or source rocks up to date. However, they recently need to be analysed and investigated with different techniques and new point of view, because they are accepted another type of reservoirs as well, and they need to be studied for lithology, faciess distribution, petrographic, minerological and geochemical composition, porosity & permeability parameters, clay silica and carbonate contens and compositions and fraccability of them. In addition, new rock mechanics analyses and extra lab-works are also demanded because plastic, elastic and fraccability characteristics of shales directly involve to the operational success. Moreover, distinguishing organic and litho-faciesses of the production intervals are also crucial for the unconventional operations and horizontal drilling that becomes a standart for the unconventional industry. Silurian Dadas Formation which has very vast extension (12.000 km2) in the SE Anatolia, has been accepted as the main source rock for the “palaeozoic oil system” and the oil fields around Diyarbakir, similar to the Middle East and North Africa. This study aims to investigate the convenience for being an unconventional resource and evaluation of the Silurian deposits (Dadas Formation) having thicknesses up to 400 m in the SE Anatolia. While investigating whole Dadas section, potential intervals and their characteristics, their extension and propagation with potential faciesses, palaeogeographic properties in the study area have also been described by the help of lab results. In addition, prospective zones for shale gas and shale oil are aimed to determine together with the descriptions given above.

The Elba Island is located in the Northern Tyrrhenian Sea at midway between Tuscany (Northern Apennines Chain) and Corsica (Alpine Corsica structural pile). The complex Elba I. stack of nappes, which is considered the innermost outcrop of the Northern Apennines Chain, is also well known for its Fe-ore bodies and the relationships between the emplacement of the Mio-Pliocene magmatic bodies and tectonics. The geological survey of Elba I. performed at a scale of 1:10,000 and 1:5,000 (geological map at 1:15,000) allowed a revision of the stratigraphic and structural setting of the central and eastern Elba I. This new scheme results more complex compared to Trevisan’s classical one, which was based only on five tectonic “Complexes” (Trevisan, 1950; Barberi et al., 1969). Nine tectonic units were defined, and they all pertain to the Tuscan and Ligurian (including the Ligurian-Piedmontese Units) paleogeographic domains. Before their final emplacement in the Elba’s tectonic pile during the 8.5 to 5.4 Ma time interval, some of these units were intruded by two acidic plutons (Mt. Capanne and La Serra-Porto Azzurro monzogranites), and by dikes of variable composition. A total of nine units were recognised, from bottom to top: 1- Porto Azzurro Unit (PU). It is made up of phyllites, quartzites and micaschists (Mt. Calamita Fm.), probably of Paleozoic age. It shows a strong static recrystallisation due to the La Serra-Porto Azzurro intrusion and the related aplitic dike network (6.0-5.4 Ma). On top of the Mt. Calamita Fm., crystalline dolostones and dolomitic marbles were recognised and were attributed to its Mesozoic cover. The aplitic dikes are cut along the tectonic contact (Zuccale Detachment Fault) with the overlying units described below. 2- Ortano Unit (UO). It includes metavolcanites (Porphyroids) and quartzitic-phyllitic metasediments (Capo d’Arco Schists) which can be correlated to the Ordovician formations of Central Sardinia and Tuscany (Apuan Alps). A few aplitic dikes were also recognised, and they occur along the coast between Capo d’Arco and Ortano Valley. 3- Acquadolce Unit (AU). It is composed of marbles, grading upwards into calcschists and, finally, into phyllites, metasiltstones and metasandstones with intercalations of calcschists which contain fossils of Early Cretaceous age. At its top a serpentinite slice crops out. This Unit has been attributed to the Ligurian Domain (Ligurian-Piedmontese Units) and can be correlated with the “Calcschists with ophiolites” of the Gorgona Island. Near Capo d’Arco Residence, some lamprophyric dikes (Casa Carpini Lamprophyries) also occur. Locally, the carbonate lithotypes are transformed into Fe-skarn bodies (e.g., Torre di Rio skarn). 4- Monticiano-Roccastrada Unit (MU). This Tuscan Unit largely consists of Upper Carboniferous-Triassic metasiliciclastic rocks (the Permian-Carboniferous Rio Marina Fm. and the Triassic “Verrucano” Group). It also includes a Jurassic to Oligocene epimetamorphic succession (from the Capo Castello Calcschists to the Pseudomacigno) which crops out along the coast between Capo Pero and Capo Castello, and in the Valle Giove mining area. 5- Tuscan Nappe (TN). South of the locality La Parata, this unit is composed only of calcareous-dolomitic, at times vacuolar, breccias (“Calcare Cavernoso”), while northwards these rocks are overlain by Upper Triassic to Hettangian shallow marine carbonates, and Sinemurian to Dogger carbonatic, siliceous and marly pelagic sediments. 6- Grassera Unit (GU). It mostly consists of varicoloured slates with rare carbonate-siliceous and radiolarian cherts intercalations (Cavo Fm.). Between Cavo and La Parata, a basal decametric Calcschist Member also occurs. This anchimetamorphic unit, possibly of Cretaceous age, could have been originated in the Ligurian Domain: because of its peculiar lithologic association and metamorphic overprint it is considered a Ligurian-Piedmontese Unit.. 7- Ophiolitic Unit (OU). This Ligurian Unit is composed of seven tectonic subunits (Acquaviva “ASU”, Mt. Serra “SSU”, Capo Vita “CSU”, Sassi Turchini “TSU”, Volterraio “VSU”, Magazzini “MSU” and Bagnaia “BSU”), which are characterised by serpentinites, ophicalcites, Mg-gabbros, and by their Jurassic to Lower Cretaceous volcanic-sedimentary cover (Basalts, Mt. Alpe Cherts, Nisportino Fm., Calpionella Limestones and Palombini Shales). A shoshonitic dike (Mt. Castello Dike: 5.8 Ma) fills two ENE-WSW-trending normal faults cutting VSU in the Porto Azzurro area. Some calc-alkaline dikes (Mt. Capo Stella Dikes) were also identified in the Ligurian basalts along the western coast of Golfo Stella 8- Paleogene Flysch Unit (EU). It is constituted by shales with calcareous-marly, calcarenitic and arenaceous intercalations and, locally, by ophioliticcarbonate breccias (Colle Reciso Fm.). The fossiliferous content of the carbonate lithotypes points to a Middle Eocene age. This unit can be interpreted as a 98 syn-tectonic oceanic unit (Epiligurian Unit), which has the same paleogeographic origin of the Lanciaia Fm. in Southern Tuscany. Aplites (Capo Bianco Aplites: 7.9 Ma), locally sericitised (the so-called “Eurite”), and porphyries (Portoferraio Porphyries: 8.2 Ma and San Martino Porphyries: 7.4-7.2 Ma) intrude the sedimentary succession, but do not crosscut the basal contact with the underlying Ophiolitic Unit. 9- Cretaceous Flysch Unit (CU). It is a Ligurian, Helminthoid-type, oceanic succession. It consists of a basal tectonised complex, similar to OU (ophiolites, basalts and Jurassic-Cretaceous sedimentary cover slices), and of a sedimentary succession formed by Cretaceous Palombini Shales and Varicoloured Shales, which grade upwards into an arenaceous-conglomeratic (Ghiaieto Sandstones) and then to a calcareous-marly-arenaceous (Marina di Campo Fm.) flysch of Late Cretaceous Age. Similar to the EU, this unit is frequently intruded by locally thick acidic dikes and laccoliths. The structural setting of central and eastern Elba is characterised by a pile of eight structural units (Units 2-9), separated by low angle tectonic surfaces (thrusts and detachments), which lays onto the lowermost Porto Azzurro Unit 1, by a low-angle detachment fault marked by a decametric cataclastic horizon (Zuccale Fault and related cataclasite). The thrust surfaces (Late Eocene-Early Miocene) have been tentatively distinguished from the low-angle detachments, due to the extensional tectonics, which probably began during Burdigalian-Langhian, and continued during Messinian-Pliocene times, accompanied by magmatic intrusions. Other low angle tectonic surfaces are of complex interpretation because they derived from the superposition of tectonic events which occurred in different times and/or in different tectonic regimes. Among the high-angle faults, we recognised a NW-SE trending transfer fault system, which was preceded and followed by generations of normal faults, with WSW-NNE and N-S trends, respectively. The N-S-trending faults cut the whole tectonic pile, comprising all the detachment faults. The study of the tectonic relationships between the previous nine tectonic units and between these tectonic units and the Messinian-Pliocene magmatic events, suggests the following geological scenario for the evolution of the Elba Island: 1) Pre-magmatic stages (>8.5 Ma). They are recorded by: a- relics of the pre-Alpine schistosity within PU and UO, which can be attributed to the Sudetic phase of the Variscan orogeny; b- folding and thrusting of OU, EU and CU, with production of ophiolitic-carbonate breccias within PU, and the D1 tectono-metamorphic event (S1 relics) in AU, related to Eocene intra-oceanic deformation events; c- main deformation and metamorphic events of Tuscan (PU, UO, MU) and Ligurian-Piedmontese Units (and 19 Ma S2 in AU), overthrusting of the oceanic units (AU, OU, GU, EU+CU) onto the Tuscan ones, and a later refolding of the tectonic units, probably related to the Oligocene-Early Miocene collisional events; d- emplacement of AU between OU and MU, and of TN onto MU. The superposition of TN onto MU can be considered the older extensional event by low-angle detachments (Middle Miocene). 2) Syn-magmatic stages (8.5-5.4 Ma). This stage begins with the genesis and rise of anatectic melts due to the uplift of the asthenospheric mantle, within the stretched inner part of the Apenninic orogenic belt. During the uprise of the Mt. Capanne granitoid (6.8 Ma), the most of its cover, that was constituted by EU and CU (already injected by acidic dikes), was detached and shifted eastwards along a low-angle fault (Central Elba Fault, “CEF”). During this event the acidic dykes of the basal part of the flysch were sericitised (“eurite”: 6.7 Ma). Farther east, a shoshonitic dike intruded OU at 5.8 Ma and, possibly, lamprophyric dikes were emplaced within AU. A new uplift of the Mt. Capanne caused a further glide eastwards of EU+CU onto OU in the central Elba, and the development of transfer faults (as lateral ramps of detachments) within the Ligurian Units and, probably, the onset of the Zuccale Fault. At 6.0-5.4 Ma the emplacement of the La Serra-Porto Azzurro granitoid produced a wide thermometamorphic aureola and local skarn bodies within the host PU, UO, AU and MU. The uplift of this granitoid caused, or completed, the separation of the eastern and central Elba tectonic pile through the Zuccale detachment Fault. During this stage, the back-gliding of OU onto EU+CU in the Colle Reciso area, and the north- or north-eastwards gliding of CSU, completed the present tectonic pile of central and eastern Elba. 3) Post-magmatic events (

Geyserite is a type of terrestrial siliceous hot spring deposit (sinter) formed subaerially in proximal vent areas, with near-neutral pH, alkali chloride discharge fluids characterized by initial high temperatures (~73°C to up to 100°C) that fluctuate rapidly in relation to dynamic hydrology, seasonality, wind, and other environmental parameters. We analyzed sinters at the Claudia paleogeothermal field from the Late Jurassic (~150 Ma) Deseado Massif geological province, Argentinean Patagonia. The geyserite samples-with spicular to columnar to nodular morphologies-contain abundant microfossils in monotypic assemblages that occur in three diagenetic states of preservation. The best-preserved microfossils consist of vesicle-like structures with radial heteropolar symmetry (~35 μm average diameter), circular apertures, smooth walls lacking ornamentation, and disk- or beret-like shapes. Comparisons with extant, morphologically similar organisms suggest an affinity with the testate amoebae of the Arcella hemisphaerica-Arcella rotundata complex and Centropyxis aculeata strain discoides. These species occur in active geothermal pools between 22°C and 45°C, inconsistent with the temperature of formation of modern geyserites. We propose that the testate amoebae may have colonized the geyserite during cooler phases in between spring-vent eruptive cycles to prey on biofilms. Silica precipitation through intermittent bathing and splashing of fluctuating thermal fluid discharge could have led to their entrapment and fossilization. Petrographic analysis supports cyclicity in paleovent water eruptions and later diagenesis that transformed the opal into quartz. Spatially patchy degradation and modification of the silicified microorganisms resulted in variable preservation quality of the microfossils. This contribution illustrates the importance of microscale analysis to locate early silicification and identify high-quality preservation of fossil remains in siliceous hot spring deposits, which are important in early life studies on Earth and potentially Mars.

New Zealand and Argentine (Late Jurassic-Recent) siliceous hot-spring deposits (sinter) reveal preservation pathways of environmentally controlled, microbe-dominated sedimentary facies over geological time scales. Texturally distinctive, laminated to thinly layered, dense and vertically oriented, microtubular "palisade" fabric is common in low-temperature (<40°C) sinter-apron terraces. In modern hot springs, the dark green to brown, sheathed, photosynthetic cyanobacterium Calothrix spp. (family Rivulariaceae) constructs felted palisade mats in shallow terrace(tte) pools actively accreting opaline silica. The resulting stacked layers of silicified coarse filaments-a stromatolite-are highly porous and readily modified by postdepositional environmental perturbations, secondary silica infill, and diagenetic silica phase mineral transformations (opal-A to quartz). Fossil preservation quality is affected by relative timing of silicification, and later environmental and geological events. A systematic approach was used to characterize palisade fabric in sinters of different ages to refine tools for recognizing biosignatures in extreme environments and to track their long-term preservation pathways into the geological record. Molecular techniques, scanning electron microscopy, Raman spectrometry, X-ray powder diffraction, petrography, and lipid biomarker analyses were applied. Results indicate that microbial communities vary at the micron scale and that early and rapid silicification is paramount to long-term preservation, especially where minimal postdepositional disturbance follows fossilization. Overall, it appears that the most robust biomarkers of fossil microbial activity in hot-spring deposits are their characteristic macro- and microtextures and laser micro-Raman identified carbon. Studies of Phanerozoic geothermal deposits with mineralized microbial components are relevant analogs for Precambrian geobiology because early life is commonly preserved as microbial microfossils and biofilms in silica, some of it hydrothermal in origin. Yet the diagenetic "movie" has already been run. Hence, studying younger sinters of a range of ages provides an opportunity to "play it again" and follow the varied influences on biosignatures into the deep-time geological record.

Seasonal changes in silica deposition in hot spring systems