Chiara Caricchi

Reconstruction of maximum burial along the Northern Apennines thrust wedge (Italy) by indicators of thermal exposure and modeling

A new data set of temperature-dependent clay mineral parameters and vitrinite reflectance of the Tuscan successions in the Northern Apennines (Italy) displays decreasing levels of thermal maturity from hinterland to foreland, and abrupt changes parallel to the strike of the chain which are structurally controlled by northeast-southwest–trending faults (e.g., Marecchia valley lineament). To the southeast of the Marecchia valley lineament, paleothermal indicators show deep diagenetic conditions in the hinterland and early diagenetic conditions in the foreland (R o % ranges from 0.80% to 0.30%; illite content in mixed-layer illite-smectite [I-S] from 86% to 38%). To the northwest of the Marecchia valley lineament, in the hinterland, R o % is up to 0.95% and mixed-layer I-S have an illite content of ~87%–88%, both gradually decreasing toward the northeast (to R o % of 0.33%, and illite in I-S of 50%). Thermal models allowed us to constrain the geometry of the Miocene thrust wedge with special regard to the original thickness and distribution of its allochthonous uppermost structural unit (Ligurian unit) across northeast-southwest–trending tectonic lineaments. The thickness of the Ligurian unit ranges from 1 to 1.5 km to the south of the Marecchia valley lineament, to 3 km to the north-northwest. This tectonic lineament affected wedge geometry, amounts of tectonic transport, and thickness of the uppermost structural unit, and, possibly, Neogene–Quaternary levels of exhumation.

Paleomagnetic evidence for a post-Eocene 90° CCW rotation of internal Apennine units: A linkage with Corsica-Sardinia rotation?

We report on an extensive paleomagnetic study (36 sites) of the Tuscan Nappe succession from the Northern Apennines Arc, aimed to reconstruct the tectonic evolution of the internal sector of this chain. We analyzed Eocene pelagic foreland ramp deposits (Scaglia Toscana Formation) and Oligocene–lower Miocene siliciclastic turbidites (Macigno and Falterona Formations). Paleomagnetic results show that the internal sector of the Northern Apennines underwent large counterclockwise (CCW) rotations with respect to the Adria-Africa foreland. A decrease in the rotation magnitude was observed from the southern to the northern sector of the arc (from 91 to 36°). This trend is opposite to that observed in the more external units of Northern Apennines and demonstrates that the oroclinal bending model, which has been proposed for the external units of the chain, is not appropriate to explain the evolution of the internal sector of the arc. On the basis of the observed paleomagnetic pattern, we propose a new tectonic model in which the Tuscan and Falterona-Cervarola units in the southern area were first rotated CCW along with the Corsica-Sardinia block during its lower Miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector (Umbria domain), thus yielding the final curved shape of the Northern Apennines chain. Data from this study represent the first paleomagnetic evidence of the influence of the Corsica-Sardinia CCW rotation in the Apennines orogenic wedge deformation, in the general framework of the geodynamic evolution of the Central Mediterranean subduction system.

Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)

Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (including structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and paleomagnetism, and paleothermometry) is used to define thrusting conditions, deformation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150xa0km of outcropping length, 30xa0km of maximum horizontal displacement, and 5xa0km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside striations) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the kmax/kint plane in sites with strong shear deformation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong deformation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels.

Thermal maturity of Silurian deposits in the Baltic Syneclise (on-shore Polish Baltic Basin): contribution to unconventional resources assessment

Shale gas is envisaged to contribute in the next future to the European energy mix in the prospective of lowering CO2 emissions. Poland is by far one of the most perspective countries in Europe. In the “Golden Belt”, potential productive levels are Early Paleozoic in age and the reliable assessment of their thermal maturity is crucial for evaluating hydrocarbon generation/expulsion scenarios. When exploring Lower Paleozoic targets that are devoid of vitrinite macerals, uncertainties in thermal maturity evaluation can occur according to commonly adopted parameters (e.g., vitrinite reflectance). These uncertainties can negatively influence targets assessment.nnWe adopted a multi-method approach to assess thermal maturity of the Silurian sections encountered in three wells deep between 2.9 and 3.3 km, recently drilled in the Polish Baltic Basin. The methodological strategy consists of: ( i ) measurement of organoclasts (mainly graptolites) reflectance; ( ii ) FT-IR spectroscopy on bulk dispersed organic matter; ( iii ) X-ray diffraction on <2 µm grain-size fraction of sedimentary core samples. Organoclasts reflectance is between 0.6 and 1.4% indicating a large range of thermal maturity spanning from early to late mature stages of hydrocarbon generation. Mixed layers illite-smectite and FT-IR indexes (e.g. CH2/CH3, A and C) allowed us to improve the definition of thermal maturity of Lower Paleozoic rocks (Roeq between 0.8 and 1.1%).nnThis original dataset indicates lower levels of thermal maturity than those predicted in pre-existing thermal maturity maps, suggesting that the Silurian sections experienced thermal maturity conditions equivalent to the oil window more than the gas window.

Formation of arc-shaped orogenic belts in the Western and Central Mediterranean: a palaeomagnetic review

Abstract During the past few decades, palaeomagnetism has been used as a powerful tool for constraining kinematic models of curved orogenic systems, because of its great potential in quantifying vertical axis rotations and in discriminating between primary and secondary (orocline s.l.) arcs. The Mediterranean area has represented an attractive region to apply palaeomagnetic analysis, as it shows a large number of narrow arcs, defining an irregular and rather diffuse plate boundary. This paper is intended to be an updated review on the contribution of palaeomagnetism to the reconstruction of the Neogene geodynamic evolution of the arc-shaped orogenic belts in the Western and Central Mediterranean Basin. The Gibraltar Arc, the Northern Apennines and the Calabria Arc are here described, underlining the common and the different features that characterize these arcuate mountain chains. In particular, the mechanisms that lead to the present-day shape of these arcs (the subduction process) will be discussed, in the general framework of the geometry and space–time evolution of the Mediterranean subduction system.

Distinct magnetic fabric in weakly deformed sediments from extensional basins and fold-and-thrust structures in the Northern Apennine orogenic belt (Italy)

We report on results from anisotropy of magnetic susceptibility (AMS) analyses carried out on weakly deformed fine-grained sediments from the Northern Apennine orogenic system (Italy). We sampled 63 sites from preorogenic, synorogenic, and postorogenic sequences, which differ in age, composition, depositional environment, degrees of deformation, and tectonic regimes. The magnetic fabric is typical of weakly deformed sediments, with a magnetic foliation subparallel to the bedding plane and a magnetic lineation well defined in this plane. Northern Apennine chain deposits are characterized by strongly oblate magnetic susceptibility ellipsoids, indicating that the magnetic fabric is the result of both compaction process and tectonic load experienced by the sediments during diagenesis and orogenic events. The orientation of magnetic lineation is significantly different depending whether the studied sites underwent extensional or compressional tectonic regimes. In the Northern Apennine chain, the magnetic lineation is mostly oriented NNW-SSE, parallel to the main compressional structures. It suggests a tectonic origin of the magnetic lineation with an acquisition related to the Apennines compressional phases. In the extensional Tuscan Tyrrhenian margin, magnetic lineation is oriented ENE-WSW, almost perpendicular to the main extensional faults, which represent the main deformation elements of the area. Our results demonstrate a close relationship between the shape and orientation of magnetic fabric and the tectonic history of rocks, confirming that AMS represents a valuable tool to investigate the tectonic history of weakly deformed sedimentary rocks.