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)

Abstract

This is an author version of the contribution published on:Questa è la versione dell'autore dell'opera: Review, v. 57, no. 5-8, 540-562. Doi: 10.1080/00206814.2014. Festa et al. (2015) -International GeologyThe definitive version is available at:La versione definitiva è disponibile alla URL:http://www.tandfonline.com/loi/tigr20 AbstractIn the Northern Apennines of Italy, mud-rich olistostromes (sedimentary mélanges) occur at different stratigraphic levels within late Oligocene -early Miocene sedimentary record of episutural/wedge-top basins. They are widely distributed along the exhumed outer part of the Ligurian accretionary complex, atop of the outer Apenninic prowedge, over an area of about 300 km long and 10-15 km wide. Olistostromes represent excellent examples of ancient submarine mass-transport complexes (MTCs), consisting of stacked cohesive debris flows that can be directly compared with some of those observed in modern accretionary wedges. We describe the internal arrangement of olistostrome occurrences in the sector between Voghera and the Monferrato, analyzing their relationships with mesoscale liquefaction features, which are commonly difficult to observe in modern MTCs. Slope failures occurred in isolated sectors along the wedge front, where out-of-sequence thrusting, seismicity and different pulses of overpressured tectonically-induced fluid flows acted concomitantly. Referring to the Northern Apennines regional geology, we also point out a gradual lateral rejuvenation (from late Oligocene to early Miocene) toward the SE and an increasing in size and thickness of the olistostromes along the strike of the frontal Apenninic prowedge. This suggests that morphological reshaping of the outer prowedge via mass transport processes balanced with different pulses in a short time span the SE-ward migration and segmentation of the accretionary processes. The latter have been probably favored by the occurrence in the northwestern part of the Northern Apennines of major, inherited paleogeographic features controlling the northward propagation of the prowedge. The detailed knowledge of olistostromes, as ancient examples of MTCs related to syn-sedimentary tectonics and shale diapirism, and of their lateral variations in term of age and size, provides useful information for better understanding both the tectono-stratigraphic evolution of the Apenninic prowedge and the submarine slope failures in modern accretionary wedges.

Tectonic significance of different block-in-matrix structures in exhumed convergent plate margins: examples from oceanic and continental HP rocks in Inner Western Alps (northwest Italy)

“…), and the strain rate (e.g. Hsü 1968;Cloos 1982;Raymond 1984;Cowan 1985;Cloos andShreve 1988a, 1988b;Festa et al 2012Festa et al , 2015Ukar and Cloos 2013;Wassmann and Stöckhert 2013). Hence, systematic and process-oriented, inter-disciplinary studies of chaotic rock units with block-in-matrix structure may provide much-needed information about convergent plate margin evolution (e.g.…”

Development of an Intrawedge Tectonic Mélange by Out‐of‐Sequence Thrusting, Buttressing, and Intraformational Rheological Contrast, Mt. Massico Ridge, Apennines, Italy

“…A mélange is a mappable, fragmented, and mixed rock body containing a variety of blocks commonly embedded in a matrix (Silver & Beutner, ). Based on mélange‐forming processes, mélanges can be divided into three main categories: sedimentary, tectonic, and diapiric (e.g., Festa, Pini, Dilek, & Codegone, ; Festa, Pini, Dilek, Codegone, Vezzani, et al, ; Vannucchi & Bettelli, ; Vannucchi et al, ; for a review see Festa et al, ).…”

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

“…2), showing lateral and vertical changes in the facies of its block-in-matrix fabric. It consists of three types of broken formation (sensu Hsü, 1968), BrFm1, BrFm2, and BrFm3, and a sedimentary mélange/olistostrome (sensu Raymond, 1984;Festa et al, 2012Festa et al, , 2015b, called here SedMé. The contact between the different types of chaotic rock units is transitional and does not show any traces of Alpine-related mylonitic deformation, even if folded and deformed by the Alpine tectonics.…”