Anatomy and emplacement mechanism of a large submarine slide within a Miocene foredeep in the northern Apennines, Italy: A field perspective

Abstract

The 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

Distribution and characterization of failed (mega)blocks along salt ridges, southeast Brazil: Implications for vertical fluid flow on continental margins

“…[50] Analogue complex failures identified in fossil MTDs show similar features to the one analyzed in this work, where block and matrix deformation provide indicators to assess flow movement and delimit different components [Alves and Lourenço, 2010;Butler and McCaffrey, 2010;Callot et al, 2008;Lucente and Pini, 2003;Lucente and Pini, 2008;Odonne et al, 2011]. When derived from distinct sources, often due to tectonically influenced topographic oversteepening and failure, the components are likely to exhibit both distinct lithogical compositions and bulk deformation styles [e.g., Callot et al, 2008].…”

“…The development of microfractures is common in these deposits [Tripsanas et al, 2008], especially in higher cohesion sediments. Fractures within rafted blocks commonly develop upon the initial failure [Alves and Lourenço, 2010] but the effects of shear stress during transport must also be considered, regardless of the travel distances, which can either enhance previous fracturing or develop new ones [Alves and Lourenço, 2010;Lucente and Pini, 2003]. This, associated with overpressure along the basal shear zone, favors the formation of clastic injectites propagating upwards either through the heterogeneous MTD matrix or tensile fractures in the block base [Alves and Lourenço, 2010;Butler and McCaffrey, 2010;Callot et al, 2008].…”

Late Oligocene–early Miocene olistostromes (sedimentary mélanges) as tectono-stratigraphic constraints to the geodynamic evolution of the exhumed Ligurian accretionary complex (Northern Apennines, NW Italy)

“…In particular, the internal structure of the deposits from mass transport (hereafter defined as mass-transport deposits, or MTDs, and mass-transport complexes, or MTCs when they consist of different superposed MTDs, see, e.g., Ogata et al 2012b) is commonly difficult to be deciphered in detail mainly because of the acoustic transparency and the small-scale of the related features (meters to tens of meters) that is below the standard seismic resolution. Detailed studies on exhumed analogues can than provide useful information on the small-scale internal geometry and on deformation mechanisms, which are complementary to those obtained through off-shore geophysical investigations and drilling (e.g., Lucente and Pini, 2003;Mienert 2004;Codegone et al 2012a;Ogata et al 2012aOgata et al , 2014Pini et al 2012).…”

Chaos and geodynamics: Mélanges, mélange-forming processes and their significance in the geological record

“…The term olistostrome describes a sedimentary deposit comprised of a chaotic mass of rock blocks and mud, put together by gravity mass flows of unconsolidated sediments in submarine environments (Abbate et al, 1981;Lucente and Pini, 2003). These deposits accumulate in a semifluid condition and hence generally lack bedding structures.…”