Sara Satolli

Magnetic stratigraphy of Kimmeridgian-Aptian sections from Umbria-Marche (Italy): New details on the M polarity sequence

[1] The magnetic stratigraphy of the Maiolica and Calcari ad Aptici pelagic limestones is documented from four Umbro-Marchean land sections (Italy). The overall biostratigraphic age of the sampled strata encompasses the whole Kimmeridgian–Lower Aptian. The data were gathered from two new sections (Arcevia, Contessa) and by resampling more densely than in the past two additional classical sections (Bosso, Gorgo a Cerbara). A detailed record of the polarity chrons M21n-M14 and M9-M0 was derived, and no difference was observed with respect to the sequence of M polarity chrons inferred from oceanic magnetic anomalies. Barely measurable remanent magnetization from chron M14 to M10n at Contessa concurred with previous evidence from Bosso, indicating that the Maiolica from Umbria-Marche is characterized by a ‘‘recording gap’’ during chrons M14n to M11, possibly due to diagenetic magnetite dissolution related to the Late Valanginian carbon isotope event. At Arcevia and Bosso, the boundary between Maiolica and Calcari ad Aptici occurs at the top of chron M19n and in the upper part of chron M20n, respectively, showing that the onset of Maiolica sedimentation may be diachronous by 1.5–2 Myr along the Umbria-Marche domain. Arcevia is the most expanded Mid-Upper Tithonian land section documented so far. Here, the subchrons M20n-1 and M19n-1 are found to represent 3.2% and 10.1% in time of chrons M20n and M19n, respectively. Evidence is also provided for a reversal excursion occurring within the M20n-1 subchron. At Bosso, an excursion and a reversal excursion were found within chrons M16n and M16, respectively.

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.