342 research outputs found
Litostratigrafia e petrografia delle areniti di Monte Tiriolo (Trias superiore), Calabria Centrale
No full textLitostratigrafia e petrografia delle areniti di Monte Tiriolo (Trias superiore), Calabria Centrale
No full textTriassic redbeds in the Malaguide Complex (Betic Cordillera — Spain): petrography, geochemistry and geodynamic implications
No full textSandstone petrography and mudstone mineralogy and geochemistry of Triassic mudstones and sandstones from continental redbeds of the Malaguide Complex (Betic Cordillera, southern Spain) provide useful information on provenance, palaeoclimate and geodynamics during the early stages of the Pangea break-up, and on their diagenetic evolution. The sandstones are quartzarenites to sub-litharenites, with minor lithic fragments and rare feldspars. The mudstone samples show a PAAS like elemental distribution. The samples likely record recycling processes from their metasedimentary basement rocks that significantly affected the weathering indices, and monitors cumulative effects, including a first cycle of weathering at the source rocks. Sandstone composition and chemical–mineralogical features of mudstones record a provenance derived from continental block and recycled orogen that were weathered under warm and episodically wet climate. Source areas were located towards the east of the present-day Malaguide outcrops, and were formed by fairly silicic rock types, made up mainly of Palaezoic metasedimentary rocks, similar to those of the Paleozoic underlying series, with subordinate contributions from magmatic–metamorphic sources, and a rare supply from mafic metavolcanic rocks. Clay-mineral distribution of mudstones is dominated by illite and illite/smectite mixed-layer that result from differences in provenance, weathering, and burial/temperature history. Illite crystallinity values, illitization of kaolinite, occurrence of typical authigenic minerals and apatite fission-track studies, coupled with a subsidence analysis of the whole Malaguide succession suggest burial depths of at least 4–6 km with temperatures of 140–160 °C, typical of the burial diagenetic stage, and confirm the Middle Miocene exhumation of the Betic Internal Domain tectonic stack topped by the Malaguide Complex.This research has been carried out within the MIUR-COFIN Project 2001.04.5835 “Age and characteristics of the Verrucano-type deposits from the Northern Apennines to the Betic Cordilleras: consequences for the palaeogeographic and structural evolution of the central-western Mediterranean Alpine Chains” (support to V. Perrone), MIUR-ex60% Projects (Palaeogeographic and Palaeotectonic Evolution of the Circum-Mediterranean Orogenic Belts, 2001–2005; and Relationships between Tectonic Accretion, Volcanism and Clastic Sedimentation within the Circum-Mediterranean Orogenic Belts, 2006; support to S. Critelli), and the 2006–2008 MIUR-PRIN Project 2006.04.8397 “The Cenozoic clastic sedimentation within the circum-Mediterranean orogenic belts: implications for palaeogeographic and palaeotectonic evolution” (support to S. Critelli). Financial support from the Projects CGL2009-09249 and CGL2011-30153-CO2-02 (MCI, Spain) and from the RNM-208 and P08-RNM-03715 Research Groups of the Junta de Andalucia is also acknowledged
Compositional and Geochemical Signatures for the Sedimentary Evolution of the Middle Triassic–Lower Jurassic Continental Redbeds from Western-Central Mediterranean Alpine Chains
No full textCompositional and chemical analyses suggest that Middle Triassic–Lower Liassic continental redbeds (in the internal domains of the Betic, Maghrebian, and Apenninic chains) can be considered a regional lithosome marking the Triassic-Jurassic rift-valley stage of Tethyan rifting, which led to the Pangaea breakup and subsequent development of a mosaic of plates and microplates. Sandstones are quartzose to quartzolithic and represent a provenance of continental block and recycled orogen, made up mainly of Paleozoic metasedimentary rocks similar to those underlying the redbeds. Mudrocks display K enrichments; intense paleoweathering under a hot, episodically humid climate with a prolonged dry season; and sediment recycling. Redbeds experienced temperatures in the range of 100°–160°C and lithostatic/tectonic loading of more than 4 km. These redbeds represent an important stratigraphic signature to reconstruct a continental block (Mesomediterranean Microplate) that separated different realms of the western Tethys from Middle-Late Jurassic to Miocene, when it was completely involved in Alpine orogenesis.This work was funded by the Ministero dell’Universtità e della Ricerca Scientifica–Progetto di Ricerca Nazionale (MIUR-PRIN) 2001–2003 Project (“Age and Sedimentary Characters of the Mesozoic Continental Redbeds [Verrucano] from Northern Apennines to the Betic Cordillera: Implications for Paleogeographic and Tectonic Evolution of the Central-Western Mediterranean Alpine Belts,” S. Critelli, G. Mongelli, V. Perrone), MIUR-ex60% Projects (“Paleogeographic and Paleotectonic Evolution of the Circum-Mediterranean Orogenic Belts, 2001–2005” and “Relationships between Tectonic Accretion, Volcanism, and Clastic Sedimentation within the Circum-Mediterranean Orogenic Belts, 2006,” S. Critelli), the 2006–2008 MIUR-PRIN Project 2006.04.8397 (“The Cenozoic Clastic Sedimentation within the Circum-Mediterranean Orogenic Belts: Implications for Paleogeographic and Paleotectonic Evolution,” S. Critelli, G. Mongelli, V. Perrone), and Research Project CGL2005-03887 MEC (A. Martin-Algarra)
Sedimentary recycling, provenance and paleoweathering from chemistry and mineralogy of Mesozoic continental redbeds mudrocks, Peloritani Mountains, Southern Italy.
No full textThe Triassic to Lowermost Jurassic mudrocks from continental redbeds of the Longi-Taormina Unit (Calabria-Peloritani
Arc; southern Italy) have been mineralogically, chemically and petrographically analyzed, in order to reveal their complex
history, which record an important phase of the geological evolution of the Mediterranean area.
The Late Triassic corresponds with a low first-order sea level stand and a time of high continental emergence whereas
the Early Jurassic was the time of the initiation of the first-order sea level rise in the mid-Mesozoic, generally marked by
a transgressive trend.
The mineralogical assemblage, dominated by the occurrence of illite and illite/smectite mixed layers, coupled to the
CIA index and to the A-CN-K plot, indicates post-depositional K-enrichments.
Palaeoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that they
likely record a recycling effect from their metasedimentary basement rocks. A recycling effect is also suggested by the
distribution of Al2O3, TiO2, and Zr. In the Zr/Sc vs. the Th/Sc plot the redbeds are not clustered along the primary
compositional trend but fall along a trend involving zircon addition and thus sediment recycling. Recycling could significantly
affect the weathering indices which likely monitor a cumulative effect including a first cycle of weathering at the
source rocks. Weathering occurred under hot, episodically humid climate with a prolonged dry season. Wet-humid conditions
favored the formation of stream channels that eroded the soil profiles, whereas the dry season promoted the sedimentation.
The climate alternation in the Early Jurassic favored recycling.
An additional provenance terrane occurring in the basement, including metavolcanic rocks having mafic composition
cannot be excluded, since the Eu anomaly is slightly higher than the PAAS value. Although the effects of recycling on
REE distribution are uncertain, the Eu/Eu* should increase, as more feldspar is destroyed during weathering and diagenesis.
This involves that the Eu/Eu* ratio could monitor a supply of low Eu/Eu* mafic detritus which compensate for the recycling
effect by reducing Eu/Eu*. Eu released during the dissolution of feldspar could be retained by clay minerals contributing
to minimize the recycling induced increase of the Eu-anomaly. This may involve that the recycling effect on the Euanomaly
was minor and that the low Eu/Eu* mafic detritus supply was also minor. The subordinate importance of a mafic
supply is confirmed also by other provenance proxies including the La-Th-Sc plot and the Cr/V and Y/Ni ratios.
The proportions of illitic layers in I/S mixed layers coupled with the illite crystallinity values, expressed as Kübler
Index (KI), suggesting an estimated temperature experienced by the Longi Units in the range of 100–150°C. Starting fro
Reconstructing parental affinity and climatic and physiographic conditions from the compositional signatures of Triassic-Early Jurassic continental redbeds, Peloritani Mountains, Sicily, Italy.
No full textSedimentary evolution of the Mesozoic continental redbeds using geochemical and mineralogical tools: the case of Upper Triassic to Lowermost Jurassic Monte di Gioiosa mudstones (Sicily, southern Italy)
No full textThe continental redbeds from the Internal
Domains of the central-western Mediterranean Chains have
an important role in the palaeogeographic and palaeotectonic
reconstructions of the Alpine circum-Mediterranean
orogen evolution since these redbeds mark the Triassic-
Jurassic rift-valley stage of Tethyan rifting. The composition
and the sedimentary evolution of the Middle Triassic
to Lowermost Jurassic continental redbeds of the San
Marco d’Alunzio Unit (Peloritani Mountains, Southern
Italy), based on mineralogical and chemical analyses,
suggests that the studied mudrock sediments share common
features with continental redbeds that constitute the Internal
Domains of the Alpine Mediterranean Chains. Phyllosilicates
are the main components in the mudrocks. The
10 A ° -minerals (illite and micas), the I–S mixed layers,
and kaolinite are the most abundant phyllosilicates. The
amount of illitic layers in I–S mixed layers coupled with
the illite crystallinity values (IC) are typical of high degree
of diagenesis, corresponding to a lithostatic/tectonic loading
of about 4–5 km. The mineralogical assemblage coupled
with the A-CN-K plot suggest post-depositional
K-enrichments. Palaeoweathering proxies (PIA and CIW)
record intense weathering at the source area. Further, the studied sediments are affected by reworking and recycling
processes and, as consequence, it is likely these proxies
monitor cumulative effect of weathering. The climate in
the early Jurassic favoured recycling and weathering
occurred under hot, episodically humid climate with a
prolonged dry season. The source-area is the low-grade
Paleozoic metasedimentary basement. Mafic supply is
minor but not negligible as suggested by provenance
proxies
Mn- and Fe-carbonate rich layers in Meso.Cenozoic shales as proxies of environmental conditions: a case study from the southern Apennine, Italy
No full textMn-rich layers and interbedded shales from a well exposed natural section of the Northern-Calabrian Unit (Late Jurassic–
Early Oligocene) in the surroundings of the Terranova del Pollino village, southern Italy, have been mineralogically and
chemically analyzed, in order to reveal the factors controlling their formation. Mn-rich layers are composed of micas/clay
minerals, rhodochrosite, siderite, chlorite and quartz whereas shales are formed by micas, clay minerals, chlorite, quartz,
and feldspars. The MnO abundances in the Mn-rich layers, which are depleted relatively to the UCC in SiO2, TiO2, Al2O3,
Na2O, K2O, and P2O5, are in the range of 11.01 18.41 (wt. %). R-mode Factor analysis indicate that SiO2, Al2O3, TiO2,
Na2O and K2O have high positive weights in the first factor (59.8% of the total variance) whereas high negative weights
are observed for Fe2O3, MnO, and CaO. This factor accounts for the competition between the terrigeneous component, the
authigenic carbonate phases accumulating Mn and Fe which likely formed during paucity of detrital supply. The negative
weight of CaO and MnO in this factor, the higher Ca contents in the Mn-rich layers compared to shales, and the lack of
calcite, suggest the presence of a mixed Mn–Ca carbonate rather than pure rhodochrosite. It is generally retained that Ca–
rhodochrosite precipitates within the pore waters of reducing sediments since neither rhodochrosite nor siderite can form
in equilibrium with bottom seawater. Thus the resulting sediment should be a mixing between the detrital component and
the authigenic one. Assuming Al2O3 as an index of the detrital component, it is clearly envisaged that in the Al2O3/MnO
vs. Al2O3 diagram the carbonate-rich samples fall on the mixing curve having as end members the average shale and the
richest MnO sediment. This supports the idea that carbonate-rich samples formed through precipitation of carbonate
minerals in the pore waters of the terrigenous detritus accumulating at the sea bottom. Further the REE distribution of
unaltered marine carbonates is expected to be representative of ambient seawater where carbonates precipitated. Carbonates
normalized to fine-grained siliciclastic sediments, have typical HREE enrichment, negative Ce-anomaly, and lower
total REE. In our case, the carbonate-rich samples normalized to the average composition of the interbedded freecarbonate
shale, show HREE enrichment, lower total REE contents, and the lack of negative Ce-anomaly, due to the
anoxic environment of formation for Mn– and Fe–carbonate. Finally was observed that the mineralization is enhanced if
the site of accumulation is protected from dilution by clastic sediment input. The alternation between Mn– and Fe–carbonate
silts and carbonate-free shales along the studied sedimentary succession, were likely controlled by eustatic sea-level
oscillations which are well documented in the western Tethys during Middle and Late Triassic
Submarine Mass-Movements Along the Slopes of the Active Ionian Continental Margins and Their Consequences for Marine Geohazards (Mediterranean Sea)
No full textThe Ionian margins of Calabria and Apulia (IMCA) have been affected by mass movements of varying style, scale and age. Here we present examples of seabed and subsurface features identified along more than 400 km of the IMCA from multibeam seabed imagery and subbottom profiles acquired by OGS since
2005. Four different types of mass movement phenomena are recognized with expression at seabed and in the shallow subsurface: (1) mass transport complexes (MTCs) within intra-slope basins, (2) isolated slide scars (ISS) along open slopes, (3) slope-parallel sediment undulations (SPSU) recording block-rotations linked to fluid migration, and (4) headwall and sidewall scarps (HSC) in submarine canyons.
Preliminary analyses of sedimentary processes suggest that both open-slope failures capable of triggering tsunamis and retrogression of canyon headwallswithin 1–3 km
of the Calabrian coast represent potential geohazards for coastal populations and offshore infrastructures
Late Permian-Triassic sedimentary evolution of the Southern Adriatic area based on wells and cores analysis
No full textRock samples from two cores within the Triassic interval of the Puglia 1 well, were studied to reveal the sedi-mentary facies and diagenesis. The Core 1 (5.048-5.056 m deep) is characterized by laminated dolomudstones with thinly microbial laminae alternated to lenticular/tabular shaped anhydrite crystal levels, suggesting an intertidal/sabkha-type environment. The Core 2 (6.067-6.075 m deep), shows coarse-grained crystalline massive dolomite with remnants of oolites and shell fragments, suggesting a marginal shallow-water setting. Dolomiti-zation is ubiquitous and occurred early after the deposition through the circulation of high saline dolomitizing fluids under general reducing conditions. The early-dolomitization preserved the dolomites from major burial diagenetic transformations, permitting only the ordering and the development of xenotopic textures in the dolomite crystals (aging). Primary anhydrite crystals were lately affected at least by one burial hydration -dehydration cycle, whereas fracture-filling anhydrite is a later-stage diagenetic product of circulating sulphate-rich fluids. Moreover, the integration of Puglia 1 well data with other six exploration wells and a seismic line allowed a possible reconstruction of the Permian-Triassic sedimentary evolution of the Southern Adriatic area. During Permian continental/coastal lagoon settings developed, while in the Ladinian, after a generalized subaerial exposure and an erosional phase, the extensional tectonic inputs linked to Tethys rifting brought to a relative sea-level rise and to the formation of carbonate shelves in NW-SE oriented tectonic depressions. During Carnian-early Norian a further extensional tectonic pulse coupled with a relative sea-level drop, led to the for-mation of NW-SE elongated intrashelf basin with a consequent enhancement of salinity and settlement of evaporative conditions. This triggered a massive evaporite deposition during the Norian, that filled the basinal areas. Lastly, in the late Norian-Rhaetian a marked relative sea-level rise, restored the connections with open-sea and shifted the evaporite deposition up to the shallowest parts of the basins that previously remained under subaerial conditions
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