Unravelling the burial-deformation history of sedimentary rocks is prerequisite information to understand the regional tectonic, sedimentary, thermal, and fluid-flow evolution of foreland basins. We use a combination of microstructural analysis, stylolites paleopiezometry, and paleofluid geochemistry to reconstruct the burial-deformation history of the Meso-Cenozoic carbonate sequence of the Cingoli Anticline (Northern Apennines, central Italy). Four major sets of mesostructures were linked to the regional deformation sequence: (i) pre-folding foreland flexure/forebulge; (ii) fold-scale layer-parallel shortening under a N045 σ₁; (iii) syn-folding curvature of which the variable trend between the north and the south of the anticline is consistent with the arcuate shape of the anticline; (iv) the late stage of fold tightening. The maximum depth experienced by the strata prior to contraction, up to 1850 m, was quantified by sedimentary stylolite paleopiezometry and projected on the reconstructed burial curve to assess the timing of the contraction. As isotope geochemistry points towards fluid precipitation at thermal equilibrium, the carbonate clumped isotope thermometry (Δ₄₇) considered for each fracture set yields the absolute timing of the development and exhumation of the Cingoli Anticline: layer-parallel shortening occurred from ~6.3 to 5.8 Ma, followed by fold growth that lasted from ~5.8 to 3.9 Ma.

The timing and duration of fold-related deformation - including layer-parallel shortening (LPS) – related to fold growth, are difficult to estimate because of a lack of data in most natural cases. We propose an original combination of direct and indirect dating methods to reconstruct the burial-deformation history of the Mesozoic carbonates that crop out in the Cingoli Anticline in the Umbria-Marche Apennine Ridge.The Cingoli anticline displays an arcuate shape in map view, trending N140 in its northern part and N160 in its southern part). We first study the fracture-stylolite network to characterize the successive stages of deformation. Several sets of mesostructures were discriminated according to their orientation and relative chronology:(i) N-S trending vertical joints (after unfolding), likely related to foreland flexure/forebulge development; (ii) N045 trending vertical, bedding and fold-axis perpendicular joints/veins, associated with early folding stylolites with N045-oriented peaks and reverse faulting associated with a N045 σ1 (after unfolding), reflecting LPS; (iii) bedding-perpendicular and fold axis -parallel joints/veins, e., trending N140 in the northern part and N160 in the southern part of the anticline, reflecting outer-arc extension associated to strata curvature at fold hinge, the variation about 20° in orientation between the northern and southern parts of the fold being consistent with the arcuate shape of the anticline; (iv) tectonic stylolites with horizontal peaks striking N045, along with conjugate vertical strike-slip faults, associated with a horizontal N045 contraction affecting the strata after the fold was locked, corresponding to the late stage of fold tightening (LSFT). These results suggest that the Cingoli anticline developed under a continuous N045 contraction and that its arcuate shape is likely primary and was achieved in relation to the reactivation of an N-S normal fault inherited from the Tethyan rifting, without any vertical-axis rotation of the fold axis.We further reconstructed burial curves considering sedimentary formation thicknesses, corrected from physical and chemical compaction. We also quantified the vertical stress experienced by sedimentary stylolites from a roughness inversion technique, allowing derivation of the maximum depth experienced by the strata prior to contraction (using bedding-parallel sedimentary stylolites) and during exhumation (using horizontal sedimentary stylolites related to a post-folding compaction). Oxygen and carbon isotope ratios measured in tectonic vein cements point towards a locally-sourced fluid system with limited vertical migration at the scale of the carbonate core, enabling the use of the absolute temperatures obtained from CO2 clumped isotope (D47) to reconstruct the depth during layer-parallel shortening and folding. The comparison of reconstructed depth at which each deformation phase occurred with the burial curve provides absolute timing for the development and exhumation of the Cingoli Anticline. Together with U-Pb ages of calcite vein cements and fault coatings from the nearby San Vicino Anticline, located west of the Cingoli Anticline, our data suggest that contraction started by ~8 Ma (LPS) and ended by ~3 Ma (LSFT), and that the growth of the Cingoli anticline lasted from ~5.5 to 4 Ma.  

Picturing the distribution of stress, in term of magnitude and orientation, during the development of a fold-and-thrusts belt is key for many fundamental and applied purposes, e.g., crustal rheology, orogen dynamics, fluid dynamics and prediction of reservoir properties. Specific meso- and micro-structures observed in fold-and-thrust belts and related forelands (i.e., faults, stylolites, veins and calcite twins), on top of being good markers of the deformation sequence that affected the rocks before, during and after folding and thrusting, can be used to access the past stress orientation and/or magnitude. This study reports the result of a paleopiezometric analysis of calcite twins and stylolite roughness documented in Mesozoic carbonates cropping out in the Cingoli anticline, an arcuate fold in the Umbria-Marche Apennine Ridge (UMAR), where a complex fracturing sequence was highlighted in a previously published study. The stylolite roughness inversion technique (SRIT) was applied to tectonic stylolites related to early folding layer-parallel shortening (LPS), and the calcite twin inversion technique (CSIT) was applied to cements from veins related to either foreland flexure or LPS. Both inversion processes require somehow the knowledge of the depth at which deformation occurred, as the vertical stress is an input for SRIT in the case of its application to tectonic stylolites, and as the differential stress magnitudes obtained by CSIT combined to vertical stress magnitude provides access to the absolute principal stress magnitudes. Building on a previously published time-burial path valid for the studied strata at the Cingoli anticline that also predicted the timing of each deformation stage, we quantify differential and principal stress magnitudes at the scale of the anticline. Beyond regional implications, our approach helps improve our knowledge of the past stress magnitudes in folded carbonate reservoirs.