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Anatomy and emplacement mechanism of a large submarine slide within a Miocene foredeep in the northern Apennines, Italy: A field perspective
No full textThe Casaglia Monte della Colonna (CMC) body, from the middle Miocene Marnoso-arenacea Formation of the Northern Apennines, covering more than 350 square kilometers, provides a rare opportunity to study the geometry and the internal deformation of a large, basin-wide submarine landslide. Although the head zone of the landslide has not been preserved, the body has a transitional zone, a contractional ramp cutting off more than 200 meters of the footwall stratigraphic succession, and a very wide lobe spilling over onto. the adjoining basin plain deposits. The extent of the body, the depth of the ramp cut-off and the widening of the lobe are comparable with the largest present-day submarine landslides, not often observed in fossil examples.
Internal deformation structures are distributed differently in the ramp and lobe zones. The ramp zone has antiformal stacking of duplexes and steeply inclined folds. The lobe has a well-defined strain partition: the upper part of the body is affected by extensional structures such as listric normal faults and extensional duplexes; the lower part is de formed by recumbent folds, boudinage and stacking of blocks, which are compatible with flow-induced, heterogeneous simple shear. This distribution is consistent with a kinematic model of extrusion-spreading, implying rear compression in the ramp zone with thickening and shortening of the body, and spreading in the lobe with thinning and stretching. The localized buckling present in the distal part of the lobe may be related to the onset of lateral confinement,, due to local topographic features of the basin plain (synsedimentary intrabasinal high).
The various degrees and styles of stratal disruption in the mass wasting body depend on the different combination of progressive simple shear, layer-parallel extension and shortening. Different structural associations occur in well-defined parts of the body due to kinematics of emplacement (spreading, flow and buckling). These associations may be diagnostic of. gravitational mass wasting processes rather than shallow-level tectonic deformation
Stratigraphic correlation and some submarine slide bodies in the lower Serravallian Marnoso-arenacea Formation, northern Apennines, preliminary analysis
No full textNel Serravaliano inferiore “post-Contessa”, all’interno dei sedimenti torbiditici di piana bacinale della F.ne Marnoso-arenacea, si registra un’alta concentrazione di estesi orizzonti di frana sottomarina (slide e olistostromi), soprattutto nel settore romagnolo dei I’Appennino.
In questa nota viene presentato un tentativo di correlazione di questi eventi gravitativi attraverso la misura di sezioni litostratigrafiche di dettaglio nel Settore appenninico compreso fra le valli del F. Santerno e del Savio. L’analisi stratigrafica ha permesso di riconoscere e correlare nuovi livelli guida litostratigrafici ignorati prima di questa nota. In particolare strati di tre strati torbiditici a composizione carbonatica note genericamente come “colombine” e di una megatorbidite a composizione silicoclastica. Altri livelli guida sono stati riconosciuti ma presentano un carattere più locale. Dallo schema stratigrafico proposto in questa nota si possono avere indicazioni sulla paleotopografia dei bacino della Marnoso-arenacea nel Serravalliano inferiore. L’alta correlabilità di alcuni livelli guida suggerisce l’esistenza di un fondo complessivamente piatto, anche se localmente si registrano degli alti e bassi relativi desumibili dalla variazione di spessore, da una sezione all’altra, degli intervalli stratigrafici fra un marker e quello successivo. Gli orizzonti di frana sottomarina rappresentano l’altro elemento di rilevanza stratigrafica, anche se al momento la loro correlazione non è ancora definita con precisione. Molto probabile è la correlazione fra i corpi di frana di Casaglia-Monte della Colonna e Nasseto, nonostante l’assenza di un livello guida al tetto di entrambi i corpi e la presenza di complicazioni derivanti da una rampa basale nel caso di Casaglia-Monte della Colonna, che rendono incerta la correlazione. Un fatto rilevante è la frequente associazione di sedimenti intrabacinali e extrabacinali all’interno delle frane sottomarine, con quelli extrabacinali che ne occupano la parte sommitale. Questa particolare associazione ha delle implicazioni stilla dinamica di deposizione delle frane; in particolare, la presenza dei materiali extrabacinali chiama in causa la messa in posto della Coltre Ligure e i relativi rapporti con l’avanfossa della Marnoso-arenacea
The Montandone Melange in the Northern Apennines: evidente of mud diapirism.
No full textThe Montardone melange (MM) is a chaotic unit consisting of polygenic breccias in a shale matrix (olistostrome texture) outcropping in the core of the E-W trending Montebaranzone syncline in the northern Apennines. The MM occurs mainly at the top of the Termina Formation, a Serravallian-Tortonian unit belonging to the Epiligurian succession; minor, lens-shaped bodies of MM occur at lower stratigraphic positions. The Termina Formation consists mainly of marlstones and includes lens-shaped sandstones and bodies of authigenic seep-carbonates (13C-depleted). Reworked blocks and slabs of the Termina marls are found within the MM.The succession is interpreted here as the filling of a tectonically active slope basin characterized by topographic constrains (lateral confinement) as testified by pinch-out, onlapping, and lateral facies changes to sandstone lobes.The main body of the MM covers the entire syncline with strong lateral thickness changes, making it possible to distinguish two different sectors of the syncline. In the eastern sector the MM achieves the maximum thickness of more than 200 meters. In the western sector it reduces to 40 meters, becoming progressively thinner westwards. In the eastern sector the MM shows a vertical contact with the hosting Termina marls. Bodies of authigenic carbonates occurs close to the contact within the hosting marls, and at the base of the melange. These carbonates, located in the southern flank of the Montebaranzone syncline, have systematic polygenic breccias at the base, with the same composition as the MM. Seep-carbonates occurring in the northern flank do not have these basal polygenic breccias. Previous interpretations suggested a gravity-driven emplacement for the MM, recognized as a large olistostrome. We propose here an alternative hypothesis interpreting the main body of the MM as a mud diapir on the basis of the following evidence: 1) distribution and geometry of the melange; 2) the vertical, abrupt contact with the hosting marls; and 3) the occurrence of basal polygenic breccias characterizing the seepage-carbonates close to the main diapiric body, along the southern flank of the syncline.Most likely, the surface expression was a mud volcano or a mud ridge affected by diffuse slope-instability with the emplacement of coalescent debris flows (olistostromes) also involving blocks of authigenic carbonates. Alternatively, the minor lens-like bodies of MM at different stratigraphic levels could be explained as sill-like intrusions of diapiric material. Mud diapirism and the formation of a mud volcano/mud ridge are attributed here to tectonic loading by overthrusting and the generation of a large amount of methane-rich fluid in the source rocks, i.e. a large older olistostromal body. The occurrence of methane-rich fluids, testified by authigenic carbonates, contributed to generate overpressured shales ascending along sin-sedimentary faults
Sedimentary filling of a wedge-top basin and relationship with the foredeep (Middle Miocene Marnoso-arenacea Formation, northern Apennines)
No full textThe Middle Miocene Marnoso-arenacea Formation at Deruta in the northern Apennines of Italy rests unconformably on an orogenic wedge adjacent to the Adriatic foredeep. Based on a detailed facies analysis, the succession reveals two genetically related depositional systems: a distal delta-fed sand-rich system and a more proximal fan-delta slope system. Petrographic data confirm the genetic relationship between the two depositional systems, with the fan-delta slope feeding the basinward sand-rich system. The Deruta depositional setting shows a multi-step sedimentary evolution controlled by tectonically induced relative sea-level changes. The first stage, corresponding to a sea-level rise, promoted deposition in a wedge-top basin of pebbly sand and sand lobes (delta-fed). The second stage, characterized by intense tectonic activity (uplift) and sea-level fall, promoted accumulation of a prograding fan-delta slope replacing the sand-rich lobes. This phase was dominated by mass failures and methanogenic cold seepages. During these two stages, the wedge-top basin was isolated from the adjacent foredeep. Only during the third stage was a connection established, with the development of a deep-sea fan in the foredeep, fed by a deltaic depositional system. © Springer-Verlag 2008
Basin-wide mass-wasting complexes as markers of the Oligo-Miocene foredeep-accretionary wedge evolution in the Northern Apennines, Italy.
No full textSedimentary bodies emplaced by mass-wasting processes and exceeding tens of metres of thickness and a hundred of square kilometres in area are widespread in the Cretaceous-Pleistocene marine successions of the Northern Apennines of Italy. At least 10 such bodies are present in the stratigraphic record of the Oligo-Miocene foredeep during the northeastern, time-transgressive migration of the accretionary wedge-foredeep system. The term mass-wasting complex (MWC) is here adopted for these bodies to emphasize their multistory emplacement mechanism and polymictic composition with variously deformed slabs of different lithology, age and provenance. As one of the more intriguing features, their occurrence was associated with changes in turbidite deposition from basin plain to slope. Wide sectors of the internal margin of the basin (lobe-fan) and even of the basin plain become a slope at the front of the accretionary wedge for a limited period of time (temporary slope). The temporary slope supplied the intrabasinal components of the MWCs, whereas the diffused extrabasinal components came from the front of the accretionary wedge. Therefore, an enhanced instability of the entire foredeep-wedge system occurred systematically and cyclically. As a consequence, many variously consolidated sediments were transferred into the foredeep basin invading the depocentre and forcing the turbidite deposition towards the foreland, in a more northeasterly position. The presence of such MWCs therefore conditioned basin size and geometry in an analogous way as that reported for some modern convergent margins, as in the case of Costa Rica. Normal sedimentation was restored on top of the MWC only after the levelling of topographic irregularities
Relationships between seep-carbonates, mud volcanism and basin geometry in the Late Miocene of the northern Apennines of Italy: the Montardone mélange
No full textThe Montardone mélange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle-Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, characterized by negative values of δ13C (from -18.22 to -39.05 ‰ PDB) and chemosynthetic benthic fauna (lucinid and vesicomyid bivalves). In this paper, we propose that the Mm is a mud volcano originated by the post-depositional reactivation and rising of a stratigraphically lower mud-rich mass transport body (Canossa-Val Tiepido sedimentary mélange or olistostrome) triggered by fluid overpressure. We base our conclusion on (1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa-Val Tiepido mélange; (2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; (3) the systematic presence of large-scale (lateral extension 300-400 m) seep-carbonates associated with the mélange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; (4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids. The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary mélange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed
La Geologia della Rupe di San Leo
No full textL’obiettivo principale di questo articolo è di presentare la nuova carta geologica in scala 1/2000 della Rupe di San Leo (versione ridotta in Figura 1). La carta è il primo passo dell’elaborazione di un modello tridimensionale che possa esprimere in modo immediato le relazioni tra stratigrafia, tettonica e geomorfologia che hanno determinato lo sviluppo di questa spettacolare e delicata forma del rilievo in Val Marecchia
Did the Ligurian Sheet cover the whole thrust belt in Tuscany and Romagna Appennines? Some evidence from gravity emplaced deposits.
No full textMechanism of emplacement and significance of chaotic bodies embedded in turbidite successions of the Northern Apennines
No full textDue to the good exposures and the already available, detailed stratigraphic and geological data, the Marnoso-arenacea Formation (MA) represents a unique opportunity for the study of the overall geometry and internal organization of slide bodies and related sedimentary structures. Submarine slides are common within the MA and involve sediments of various origin and degrees of consolidation. Slides are sandwiched between both deep-sea plain sediments and slope deposits. Attention is focused here on the large-scale bodies cropping out in the Romagna sector of the Marnoso-arenacea basin, between the Sillaro and the Marecchia valleys. They crop out extensively and represent unique opportunity to see how the internal structures of flow developed during the traslation and emplacement of the mass-transport bodies, in response to slope/basin morphology and the interaction with the substratum
Basin-wide mass wasting deposits as marker of accretionary wedge kinematics in the Cenozoic structural evolution of the Northern Apennines of Italy
No full textDue to the good exposures and the already available, detailed stratigraphic and geological data, the Marnoso-arenacea Formation represents a unique opportunity for the study of the overall geometry and internal organization of slide bodies and related
sedimentary structures. Submarine slides are common within the MA and involve sediments of various origin and degrees of consolidation. Slides are sandwiched between both deep-sea plain sediments and slope deposits. Attention is focused here on the large-scale bodies cropping out in the Romagna sector of the Marnoso-arenacea basin, between the Sillaro and the Marecchia valleys. This contribute reports the outline of the internal geometry and structures, and focus on the issue of mass-transport bodies distribution in time and space inside the paleobasin
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