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Geological processes and products related to Miocene cold seeps.
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Reconstruction of Miocene fluid seepage activity in the northern Apennines (Italy) using authigenic carbonates
No full textMiocene fluid flow..
Miocene seep-carbonates as indicators of style and intensity of fluid migration.
No full textAncient hydrocarbon Miocene seep-carbonates of Miocene age have been reported from marine sedimentary successions of the northern Apennines. They are recognized by their peculiar palaeoecological, sedimentological, compositional and isotopic features as products of the microbial oxidation of methane-rich fluids and represent an excellent on-land example of carbonate bodies interpreted as the remains of ancient cold seeps. These seep-carbonates occur from internal tectonic zones (Piedmont Terziary basins, epi-Ligurian and minor basins) to external zones of the foredeep. In the Miocene foredeep, they occur crop out in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones). Dominant rock types are calcilutitic/marly limestones, calcareous marls and calcarenites. Enclosing sediments are hemipelagic/turbiditic mudstones, muddy sandstones and marlstones. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil methane-derived carbonates.On the basis of morphological and stratigraphic features two main types of seep-carbonates were distinguished in the field (type 1 and 2).The type 1 is composed of a horizontal repetition of decametric to heptometric carbonate bodies, lenses and pinnacles. They have a thickness of 5 - 30 m and an extension that ranges from 10 m to 100 m. The basal portions of these huge bodies are strongly brecciated, made up of intraformational polygenic breccias and rarely extraformational. The Sasso Streghe (Modena Apennines) and Monte Petra (Romagna Apennines) carbonate outcrops are excellent examples of this type of seep-carbonates. The type 2 is made of numerous marly-calcareous lenses, irregular column-like bodies with a dimension ranging from some decimetres to 3 – 4 m and a thickness of 20- 30 cm to 3 m. Carbonate bodies are aligned along bedding strikes, or horizontally and vertically scattered and not related to a precise stratigraphic level. The Vicchio outcrops (Tuscan Apennines) are representative of this second type of carbonates. Mineralogical analyses of type 1 carbonate samples indicate that dolomite and ankerite represent the most dominant phases while Low-Mg calcite represents type 2 dominant carbonate phase. The carbon and oxygen isotopic compositions of the carbonates display very large ranges, from -10‰ to -55‰ Vienna PeeDee Belemnite (V-PDB) and from -3‰ to 6‰ V-PDB, respectively. Seep-carbonates type 1 appear significantly depleted in δ13C (ranging from -30‰ to -55‰ V-PDB) while seep-carbonates type 2 are only moderately depleted (δ13C varying from -10‰ to -23‰ V-PDB). Petrographic observations show complex facies relationships, as indicative of different stages in seep-carbonates growth.Our presentation will report the result of a detailed field observation of the two types of seep-carbonates coupled with geochemical, petrographic and mineralogical studies. In particular we discuss distinctive characters, geometry, isotope geochemistry and mineralogy, in context relationship with precipitation and recrystallisation processes of the carbonates, the origin of carbon rich fluids, and with different mechanisms of seep-carbonate formation
Fluid flux and migration conditioning Miocene-seep carbonate precipitation in the northern Apennines.
No full textIn the Miocene satellite and foredeep basins of the northern Apennines, numerous outcrops of carbonate bodies share specific palaeoecological, sedimentological, compositional and isotopic features with present-day seep-carbonates.These carbonates occur in large turbiditic bodies (Mt. Cervarola and Marnoso-arenacea Formations) and in slope hemipelagites (Vicchio and Verghereto Marls, and Ghioli di letto mudstones). Apennine hydrocarbon seep-carbonates form isolated, irregularly-shaped masses of limestones with distinctive fabrics, specialized fossil fauna (chemosymbiotic clams and mussels) and exibit typical 13C-depleted signatures indicative of methane influence during precipitation. Several characteristics allow two type of seep-carbonates to be distinguished in the field (type 1 and 2). The type 1 is composed of a horizontal repetition of decametric to heptometric carbonate bodies, lenses and pinnacles. The basal portions of these huge bodies are strongly brecciated, made up of intraformational and rarely extraformational polygenic breccias. The type 2 is made of numerous and small marly-calcareous lenses, irregular column-like bodies aligned along bedding strikes, or horizontally and vertically scattered and not related to a precise stratigraphic level. Many of them consist of several lenticular units vertically stacked and separated by thin pelitic levels, thus suggesting periodic growth. Carbon isotope measurements show that carbonates from type 1 and 2 are typically depleted in 13C but the amount of depletion seem to differ between them. Therefore type 1 seep-carbonates appear significantly depleted in δ13C (δ13C ranging from -30‰ to -55‰ relative to the PDB standard) while type 2 seep-carbonates are only moderately depleted (δ13C varying from -10‰ to -23‰ relative to the PDB standard). Concerning oxygen isotopic measurements type 1 seep-carbonates seem to be enriched in δ18O (δ18O ranging from 1‰ to 6‰ relative to the PDB standard) whereas type 2 seep-carbonates show a more scattered range (δ18O varying from -3.00‰ to 2‰ relative to the PDB standard). Our presentation will report the result of detailed field observation of the two types of seep-carbonates coupled with petrographic, mineralogical and geochemical studies. In particular we discuss the isotope geochemistry, the mineralogy, the geometry in context with the precipitation and recrystallisation processes of the carbonates, the origin of carbon rich fluids and with different mechanisms of seep-carbonate formation
Discriminating fluid sources in Miocene cold seep systems using REEs in authigenic carbonates
No full textAuthigenic carbonates are a common feature in cold seep environments, where fluids enriched in methane and other hydrocarbon gases escape from the seafloor. Seep-carbonates have been reported worlwide both in modern and ancient sedimentary deposits. In the Northern Apennines (Italy), numerous outcrops of seep-carbonates are particularly well-preserved. Evidences from paleoecological, sedimentological, geochemical and isotopic (O and C stable isotopes) analyses cleary show that they were derived from the microbial oxidation of methane-rich fluids. REE patterns and abundances in fossil seep-carbonates may provide additional informations for better constraining the origin and the composition of the fluids from which they have precipitated.Here, we report REE data for a series of Miocene carbonate samples recovered from various geological settings in the Northern Apennines. Samples were leached with 5% HNO3, prior to analysis by SF-ICPMS using the Tm addition method [1]. Total REE concentrations (ΣREEN) in our studied carbonates are very similar to those reported for modern authigenic carbonates, suggesting negligible post-depositional diagenetic alteration. The shale-normalized REE patterns vary significantly amongst the different authigenic carbonate samples analysed in this study. These data indicate that they were formed from fluids having distinct REE signatures. These results, coupled with other geochemical, petrographic and mineralogical data, allow us to reconstruct the variation of fluid seepage activity in the Northern Appenines during the Miocene
Geological Processes and products related to Miocene cold seeps
No full textCold seeps are commonly associated with the presence of authigenic carbonates, due to interaction between hydrocarbons-rich fluids, geological processes (tectonics, sediment instability, chaotic bodies) and biological activity.In these environments hydrocarbon-rich fluid emissions support flourishing communities of mussel, clam bivalves, gastropods, tube worms and bacterial mats, which rely on chemosynthetic energy for their metabolism. The formation of authigenic carbonates at cold vents is closely related to the anaerobic oxidation of methane (AOM) which releases sulfide and bicarbonate into the pore water. Seep-carbonates have been reported worldwide both in modern and ancient sedimentary deposits. Fossil seep-carbonates provide unique archives of focused methane seepage in the geological record. by their geochemical, petrographic, mineralogical, isotopic and structural inventory. In the northern Apennines numerous outcrops of seep-carbonates are excellently exposed. In the Apenninic chain, the abundance and the extent of the outcrops provide a rare opportunity to study the geometry, facies distribution and internal structures of fossil hydrocarbon-derived carbonates. They were recognized as products of the microbial oxidation of methane-rich fluids on the basis of their megafaunal assemblages and geological, compositional and isotopic attributes Our investigations have been carried out by means of detailed field observations of the northern Apennine seep-carbonates coupled with geochemical, petrographic, mineralogical and isotopic studies.In particular, this multidisciplinary approach permits an assessment of the pathways and origin of the fluids from which carbonates have precipitated (marine seawater source, marine organic matter source, thermogenic and biogenic methane); the final aim is the creation of a model for fossil seep-carbonate formation and development. The case study of the Salsomaggiore Ridge has been reported. This Ridge, a thrust-related anticline forming inside the middle Miocene foredeep at the outermost front of the Apenninic orogenic wedge, revealed a patchy distribution of mound- to pod-shaped seep-carbonates which, in few cases, preserve the deeper fluids feeding system consisting in a randomly arranged web of cm- to dm-sized tube conduits. The seep-carbonate facies and morphotypes are highly variable; either or not associated to typical macrofauna, they both encrust and cement siliciclastic turbidites or they inter-finger with hemipelagic marls. Seep-carbonates appear also brecciated with mottled and vuggy fabrics; a chaotic body reworks the seep-carbonates and other intra-basinal clasts. Stack of mound-shaped and bivalves-rich seep-carbonates are mainly located on the northern limb of the anticline while cementing and inter-fingering carbonates predominate on the southern limb of the same anticline. Northern and southern limbs differ also in the isotopic signature of the seep-carbonates which, overall attributable to methane oxidation, present markedly negative δ13C and positive δ18O only on the northern anticline limb. The above variability and differences are attributed to two different seepage modes which correspond also to evolutionary steps of the Salsomaggiore Ridge: a slow seepage mode that allows deposition of carbonate crusts, pods, mounds and seep-related fauna; a fast seepage mode that produce brecciated fabrics and chaotic bodies. The latter mode is considered coeval to tectonic pulses that generated the Ridge. By this integrated methodology applied to other cropping out examples in the Northern Apennines, we aim to reconstruct the complex mechanism of methane-rich fluid venting through the geological record, in particular in the Miocen
Miocene seep-carbonates as indicators of fluid migration in northern Apennines (Italy).
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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