Allochthonous salt in the sub-Alpine fold–thrust belt of Haute Provence, France

Abstract

In the sub-Alpine chains of Haut Provence, SE France, a very well-exposed Mesozoic sequence showing rapid thickness and facies changes associated with Jurassic and Cretaceous extension on the margin of the Ligurian Tethys has been deformed by ‘Alpine’ compression which occurred from the Late Cretaceous to the Pliocene. Although the geology has been very well known for decades, aspects of the structure remain enigmatic and cannot be explained by either Mesozoic extension or Alpine shortening alone. We infer that some deformation resulted from salt tectonics. A completely overturned, highly condensed Jurassic section near Barles village resembles the elevated roof of a Triassic salt body in a deep-marine basin. This carapace became overturned as a flap in the Middle Jurassic when salt broke out at the seafloor and overran the inverted flap as an allochthonous extrusion, comparable to those in the deepwater Gulf of Mexico or Angola. Later, Alpine compression exploited the weakness of the salt sheet as the Digne Thrust moved over the inverted flap. Although the flap is in the footwall of the thrust, evidence of soft-sediment deformation and other anomalous structures within the flap suggest that it did not originate as an overturned footwall syncline.

Salt tectonics in the SW Alps (Italy–France): From rifting to the inversion of the European continental margin in a context of oblique convergence

“…This general picture is in agreement with the proposed interpretation of the western part of the Subalpine chain (e.g. Ford et al, 1999;Graham et al, 2012). However, the Ventimiglia sector presents kinematic data that strongly differ from those of the neighboring areas, particularly in terms of spatial orientation: thrusts and associated folds of the Ventimiglia area show directions of transport (internally variable) ranging from NW to SW (Fig.…”

“…Because of the absence of seismic or gravimetric data, the deep geometry of the diapirs may be only hypothesized on the basis of the better constrained salt structures of the contiguous western Provençe (e.g. Dardeau and De Graciansky, 1990a,b;Ford et al, 1999;Graham et al, 2012) or from the results of analogue-modeling of evaporite layers involved in the fold-and-thrust belt (e.g. Bonini, 2003).…”

“…Since the beginning of the Tethyan rifting cycle, salt diapirs, rising from Triassic evaporites, have deformed the younger deposits (Dardeau and De Graciansky, 1990a,b). The salt displacement and migration continued in the proximal passive margin during the successive steps of the orogenic cycle, also with the local formation of salt nappes that are proved to reach the sea bottom before the Cretaceous (Graham et al, 2012), thus during the oceanization process (Handy et al, 2010). During the subsequent Alpine collision the European passive margin was inverted into a fold-and-thrust belt mainly with a main S-to SW-directed tectonic transport (Fry, 1989;Lickorish and Ford, 1998;Lickorish et al, 2002).…”

Influence of salt in the tectonic development of the frontal thrust belt of the eastern Cordillera (Guatiquía area, Colombian Andes)

“…The model accounts for early layer tilting, diapir squeezing, and the formation of an overturned flap, with similarities to other remarkable recumbent folds in thrust settings recently interpreted as salt related (e.g., Graham et al, 2012;Rowan et al, 2014), and it bears implications for other compressional areas in which the role of salt can be overlooked due to diapir welding and/ or dissolution. Based on seismic lines, maps, the occurrences of salt in old mines, and a detailed analysis of the postdrilling information from the Anaconda-1 well, we propose a new kinematic model for the Guatiquía segment, which emphasizes the influence of long-lived salt tectonics, especially during early deformation stages (Cretaceous extension and early Cenozoic contraction), which has been masked by the later stages of the Andean compression.…”

Enigmatic structures within salt walls of the Santos Basin—Part 1: Geometry and kinematics from 3D seismic reflection and well data

“…Thus we interpret these synclines to be overturned flaps related to the rise and breakout of an intrasalt allochthonous sheet of lower-A1. These structures are geometrically comparable, if not scale equivalent to, overturned flaps in subsalt strata below allochthonous salt bodies in the Gulf of Mexico Jackson, 2006, 2009), Yemen (Davison et al, 1996), France (Graham et al, 2012), Germany (Schachl, 1987), Mexico (Giles and Lawton, 2002;Rowan et al, 2003), Australia (Kernan et al, 2012;Hearon et al, 2015) and Israel (Alsop et al, 2015), as well as to salt sheets generated in physical models (e.g., Dooley et al, 2009Dooley et al, , 2015a. The flaps in the Santos Basin differ from these natural and model examples in that they are found within diapiric salt rather than within flanking country rock.…”