1,721,109 research outputs found
Sea-level fall, carbonate production, rainy days : how do they relate? Insight from Triassic carbonate platforms (Western Tethys, Southern Alps, Italy)
No full textThe interplay of sea-level fall, climate, and sedimentological changes is recorded across two sequence boundaries at the top of two Triassic carbonate platform systems in the Western Tethys (earliest Carnian and Norian-Rhaetian boundary in age, paleolatitude 18 degrees-25 degrees N). The sea-level falls caused subaerial exposure of the platform top and decreased carbonate production, leading to starvation in the intraplatform basins, followed by deposition of shale. Evidence of freshwater input indicates that the change in sedimentation was driven by increased rainfall on the previously arid European hinterland and Tethys coast. A uniformitarian approach (Holocene sea-level changes and global warming are coupled with changes in the distribution of precipitation) implicates global cooling as the probable cause of the observed sea-level, climate, arid sedimentological changes. Global cooling likely triggered the sea-level fall by increased storage of fresh water in continental settings and change in seawater density, probably coupled with ephemeral ice sheet development, possible even during greenhouse intervals such as the Triassic. Furthermore, global cooling caused a shift toward the equator of the poleward boundary of the arid belt. This model is supported by the traceability of the sequence boundaries and climate-sensitive facies from the Tethys shelf up to the European continent. The observed association of global climate changes, sea-level fall, sedimentological changes, and shift toward humid climate documents how climate-sensitive facies record the control exerted by global changes on local sedimentation
Sedimentation in shallow to deep water carbonate environments across a sequence boundary: effects of a fall in sea-level on the evolution of a carbonate system (Ladinian-Carnian, eastern Lombardy, Italy)
No full textIn the Concarena-Pizzo Camino Massif (Lombardy Basin, Southern Alps, Italy)
the lateral transition from Ladinian-Carnian carbonate platforms to coeval
intraplatform basins is preserved. The succession records the sedimentological
evidence of a sea-level fall on a flat-topped platform with a narrow marginal
reef rim and its effects in the adjacent deeper-water basin. Repeated highfrequency
exposures of the platform top are recorded by a peritidal–supratidal
succession that overlies subtidal inner platform facies of the former highstand
system tract (HST). On the slope and in the basin, the sea-level fall is recorded
by a few metre thick succession of bioclastic packstones. These facies directly
lie on coarse clinostratified breccia bodies (slope facies of the former HST) or
on resedimented, well-bedded, dark laminated limestones (basinal facies of
the HST). This facies distribution indicates that during the sea-level fall
carbonate production on the platform top decreased rapidly and that
sedimentation in the basin was mainly represented by condensed facies.
Microfacies record an enrichment, during low stand, in pelagic biota
(packstones with radiolarians and spiculae), whereas the occurrence of
platform-derived, shallow-water materials is limited to thin lenses of
reworked and micritized Fe-rich oolites and bioclasts (mainly pelecypods
and echinoderms). The facies association in the Concarena-Pizzo Camino
Massif demonstrates that a highly-productive carbonate factory was almost
completely turned off during the emergence of the platform top at a sequence
boundary, leading to low-stand starvation in the basin. The reconstruction of
the stratigraphic evolution of the Concarena-Pizzo Camino carbonate platform
therefore represents a significant case history for the study of the behaviour of
ancient carbonate systems during a fall in sea-level, independent of its origin
(eustatic or tectonic)
Syndepositional tectonics recorded by soft-sediment deformation and liquefaction structures (continental Lower Permian sediments, Southern Alps, Northern Italy): Stratigraphic significance
Full text linkThe Lower Permian succession of the Central Southern Alps (Lombardy, Northern Italy) was deposited in fault-controlled continental basins, probably related to transtensional tectonics. We focussed our study on the stratigraphic record of the Lower Permian Orobic Basin, which consists of a 1000. m thick succession of prevailing continental clastics with intercalations of ignimbritic flows and tuffs (Pizzo del Diavolo Formation, PDV) resting on the underlying prevailing pyroclastic flows of the Cabianca Volcanite. The PDV consists of a lower part (composed of conglomerates passing laterally to sandstones and distally to silt and shales), a middle part (pelitic, with carbonates) and an upper part (alternating sandstone, silt and volcanic flows). Syndepositional tectonics during the deposition of the PDV is recorded by facies distribution, thickness changes and by the presence of deformation and liquefaction structures interpreted as seismites. Deformation is recorded by both ductile structures (ball-and-pillow, plastic intrusion, disturbed lamination, convolute stratification and slumps) and brittle structures (sand dykes and autoclastic breccias). Both the sedimentological features and the geodynamic setting of the depositional basin confidently support the interpretation of the described deformation features as related to seismic shocks. The most significant seismically-induced deformation is represented by a slumped horizon (about 4. m thick on average) which can be followed laterally for more than 5. km. The slumped bed consists of playa-lake deposits (alternating pelites and microbial carbonates, associated with mud cracks and vertebrate tracks). The lateral continuity and the evidence of deposition on a very low-angle surface along with the deformation/liquefaction of the sediments suggest that the slump was triggered by a high-magnitude earthquake.The stratigraphic distribution of the seismites allows us to identify time intervals of intense seismic activity, which correspond to rapid and basin-wide changes in the stratigraphical architecture of the depositional basin and/or to the reprise of the volcanic activity.The nature of the structures and their distribution suggest that the magnitude of the earthquakes responsible for the observed structures was likely higher than 5 (in order to produce sediment liquefaction) and probably reached intensity as high as 7 or more. The basin architecture suggests that the foci of these earthquakes were located close to the fault-controlled borders of the basin or within the basin itself
Sedimentological and paleontological evidences of a “Mid Carnian” transgression in the Western Southern Alps (S. Giovanni B. Fm. Lombardy, Italy: stratigraphic and paleogeographic implications).
No full textA "mid-Carnian" transgressive succession, developed between the Breno carbonate platform and the semiarid coastal carbonates-sabkhas facies of the S. Giovanni Bianco Fm., is recorded in the northern Bergamasc Alps. This episode is characterized by the presence of two stratigraphic markers: a) Dark grey shales and siltstones ("Black Pelites"), considered previously as the northern closure of the Gorno-Lower S. Giovanni Bianco Fms., but re-interpreted as the western pinch-out of the Lozio Shale depositional system. The Early Carnian Lozio Shale was deposited first in the Valle di Scalve-Lozio trough and later covered the carbonate platform (Breno Fm.). b) Fossiliferous, open subtidal limestones, marls and burrowed marly limestones ("Bioclastic Horizon") of the northern Bergamasc Alps. The spreading of shales and siltstones represents the first transgressive stage of the last Carnian sequence in Lombardy, after the "mid-Carnian" (Julian substage) regional carbonate platform crisis (top of the Valcamonica Breno Fm.). The "Bioclastic Horizon" records the mfs represented by normal, open marine facies, identified and correlated throughout the Bergamasc Alps. Different petrographic and chemical characters between the Lozio Shale - "Black Pelites" and the Gorno-San Giovanni Bianco Fms. suggest different source areas: the former units are characterized by clasts derived from a metamorphic-intrusive area (placed northward and westward), whereas the latter units are characterized by prevailing volcaniclastic material. A climatic change (from arid to relatively humid conditions) may be invoked to explain the crisis of the "mid-Carnian" carbonate platforms in the western Southern Alps and the regional spreading of fine-grained terrigenous material
Controllo litologico e stratigrafico sull'assetto strutturale delle Alpi Meridionali lombarde: il ruolo degli orizzonti di scollamento
No full textSedimentological structures as evidence of syndepositional tectonics : liquefaction and convolution structures from continental Early Permian sediments (Southern Alps, Northern Italy)
No full textThe evolution of the Tethys region throughout the Phanerozoic: A brief tectonic reconstruction
No full textPaleogeographic evolution of the ladinian platforms in the Western Southern Alps (Lombardy, Northern Italy)
No full textDifferential compaction and early rock fracturing in high-relief carbonate platforms: numerical modelling of a Triassic case study (Esino Limestone, Central Southern Alps, Italy)
No full textNumerical models were used to investigate the effects of differential compaction on strain development and early fracturing in an early cemented high-relief Triassic carbonate platform prograding onto basinal sediments, whose thickness increases basinward. Results show that basinal sediment compaction induces stretching of internal platform and slope strata in prograding platforms. When sediments are early cemented, such extensional strain is accommodated by the generation of syndepositional fractures. The amount of stretching is predicted to increase from the oldest to the youngest layers, due to the thickening of the compactable basinal sequences towards the external parts of the platform. Stretching is also controlled by the characteristics of the basin: the thicker and the more compactable the basinal sediments, the larger will be the stretching. Numerical modelling has been applied to the LadinianEarly Carnian carbonate platform of the Esino Limestone (Central Southern Alps of Italy). This case study is favourable for numerical modelling, as it is well exposed and both its internal geometry (inner platform, reef and prograding clinostratified slope deposits) and the relationship with the adjacent basin can be fully reconstructed, as the Alpine tectonic overprint is weak in the study area. Evidence for early fracturing (fractures filled by fibrous cements coeval with the platform development) is described and the location, orientation and width of the fractures measured. The fractures are mainly steeply dipping and oriented perpendicularly to the direction of progradation of the platform, mimicking local platform-margin trends. The integration of numerical models with field data gives the opportunity to quantify the extension triggered by differential compaction and predict the possible distribution of early fractures in carbonate platforms of known geometry and thickness, whereas the interpretation of early fractures as the effects of differential compaction can be supported or rejected by the comparison with the results of ad hoc numerical modelling
Geometry, facies association and stratigraphic evolution from birth to demise of a prograding ladinian carbonate platform (Pegherolo Massif, Lombardy Southern Alps, Italy)
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