Pre-folding fracturing in a foredeep environment: insights from the Carseolani Mountains (central Apennines, Italy)

Abstract

Bedding-perpendicular joints striking parallel (longitudinal) and perpendicular (transverse) to both the axis of the hosting anticline and the trend of the foredeep-belt system are widely recognized in fold-and-thrust belts. Their occurrence has been commonly attributed to folding-related processes, such as syn-folding outer-arc extension, although they can also be consistent with a pre-folding foredeep-related fracturing stage. Here we report the pre-folding fracture pattern affecting the Pietrasecca Anticline, in the central Apennines (Italy), resolved by a detailed field structural analysis. Field observations, scan-lines and interpretation of virtual outcrops were used to study the intensity, distribution and the orientations of fracture pattern along the anticline. The fracture pattern of the Pietrasecca Anticline consists of longitudinal and transverse joints, oriented approximately perpendicular to bedding, and of a pre-folding longitudinal pressure-solution cleavage set, which is oblique to bedding regardless of the bedding dip. Cross-cutting relationships show that joints predated the development of the pressure-solution cleavage. Furthermore, joint intensity does not relate to the structural position along the anticline. Taken together, these observations suggest that jointing occurred in a foredeep environment before the Pietrasecca Anticline growth. Our work further demonstrates that joints striking parallel and orthogonal to the main fold axis do not necessarily represent syn-folding deformation structures.

Regional Scale, Fault‐Related Fluid Circulation in the Ionian Zone of the External Hellenides Fold‐And‐Thrust Belt, Western Greece: Clues for Fluid Flow in Fractured Carbonate Reservoirs

“…In addition, we highlight that bed-perpendicular joints commonly formed during foreland flexuring can remain barren during the whole fold-and-thrust belt evolution and can be still barren in surface exposure after post-orogenic exhumation (e.g., Carminati et al, 2014;Mercuri et al, 2022;Tavani et al, 2019).…”

“…Peculiar structural features in the Hellenides and in many other fold and-thrust belts worldwide are the bed-perpendicular, hairline calcite veins or joints (see point 1 above; Agosta & Aydin, 2006;Ahmadhadi et al, 2008;Beaudoin et al, 2012;Branellec et al, 2015;Carminati et al, 2014;De Graaf et al, 2019;Graham Wall et al, 2006;Hernández & Franzese, 2017;La Bruna et al, 2018;Mercuri et al, 2022;Swennen et al, 2000;Tavani et al, 2018Tavani et al, , 2019Van Geet et al, 2002;Vilasi et al, 2006Vilasi et al, , 2009. It is worth noting that, if not cemented, these features could generate a relevant portion of the storage fracture porosity in fractured carbonate reservoirs; for instances, in the Albanides fold-and-thrust belt, pre-orogenic bed-perpendicular joints and veins were re-sheared, opened, and filled with oil during contractional deformation (Graham Wall et al, 2006).…”