Debris flow (olistostromes) and slumping on a distal passive continental margin: the Palombini limestone–shale sequence of the northern Apennines

Abstract

An olistostrome accumulation up to 530 m thick occurs in the Casanova area of the northern Apennines. It lies within or above the calciturbiditic Palombini limestone‐shale sequence, and is part of the allochthonous Vara Complex—sediments originally deposited on oceanic crust. The olistostromes are poorly sorted, monomict, matrix‐supported, submarine debris flow deposits with rigid plugs. They have a compactional foliation and a compaction‐modified, planar clast fabric created during flow. Although diachronous in the main part of the area, the olistostromes have a vertical gradational contact with the overlying slumped Palombini, in which recumbent asymmetric fold hinges and trains and slump boudins are present. Many criteria indicate soft‐sediment deformation. Fold asymmetry indicates a uniformly SW‐dipping palaeoslope. The textural gradation from slumps to olistostrome beds, plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps. In vertical sections, variations in limestone petrography, volume percentage and size of clasts confirm that the olistostromes were derived from the Palombini as a series of bed‐by‐bed slumps keeping pace with sedimentation of the Palombini. From olistostrome clast sizes and bed thicknesses, a depositional slope of ∼ 4° is estimated. The olistostromes are not precursor sediments shed from advancing nappes, as in the Bracco ridge model of some authors; rather, they were formed at the foot of a distal, block‐faulted passive continental margin, long before nappe emplacement.

Depositional environments along a carbonate ramp to slope transition in the Silurian of Washington Land, North Greenland

“…This may be the result of non-deposition or post-depositional sliding of the entire section down the paleoslope (cf. Davies 1977;Naylor 1981;Bosellini et al 1981). Conclusive evidence for either possibility is lacking.…”

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

“…Attributing stratal disruption to submarine mass wasting processes or to shallowlevel tectonic deformation is one of the most hotly debated problems in the geology of mélanges and accretionary wedges (Moore, 1973;Page, 1978;Naylor, 1982;Raymond, 1984;Underwood, 1984;Cowan, 1985;Brandon, 1989;Hanamura and Ogawa, 1993;Orange and Underwood, 1995;Pini, 1999;Yamamoto and others, 2000). This discussion focuses on the early stages of sediment-rich mélange formation (Brandon, 1989;Hanamura and Ogawa, 1993) and concerns the deformation of non-consolidated, water-rich sediments (for example, Elliot and Williams, 1988;Maltman, 1994a).…”

“…Folds may indicate the direction of slide movement assuming they verge downslope, with their axes parallel to paleoslope strike (Jones, 1940;Corbett, 1973;Woodcock, 1976;Naylor, 1981;Pickering 1982Pickering , 1987. Rotation of fold hinges, nucleation of oblique and downslope folds and the presence of sheath folds may complicate the picture (Lajoie, 1972;Woodcock, 1979b;Ghosh and Sengupta, 1984;Webb and Cooper, 1988).…”

“…It was introduced by Flores (1955) to indicate sedimentary bodies with a chaotic, block-in-matrix fabric inside layered sequences of normal marine deposits in the Tertiary succession of Sicily. This definition has been extended to similar bodies in the rest of the Apennines (for example, others, 1970, 1981;Elter and Trevisan, 1973;Ricci Lucchi, 1975;Naylor, 1981Naylor, , 1982Pini, 1999). The definitions used do not include size (Abbate and others, 1981), and the accepted broad definition given includes the following different types of sedimentary bodies (Abbate and others, 1981;Pini, 1999;Lucente, ms, 2000;Cowan and Pini, 2001):…”

Controls on Devonian hemi-pelagic limestone deposition analyzed on cephalopod ridge to slope sections, Eastern Anti-Atlas, Morocco

“…A few hundred meters further downslope, these deformed beds pass into conglomerates with imbricated platy clasts, then into poorly sorted conglomerates with a random clast orientation. This lateral association indicates slump movement, where beds become disintegrated and pass downslope into debris Xows (e.g., Naylor 1981;Strachan 2008).…”