SPE542-11 1st pgs page 1 1 The Geological Society of America Special Paper 542 Synsedimentary deformation in Upper Cretaceous– Lower Paleogene limestones within a thrust anticline of the Umbria-Marche Apennines, Italy Sofia Tognaccini Department of Earth Sciences, University of Florence, 50121 Florence, Italy, and Department of Physics, Earth and Environmental Sciences, University of Siena, 53100 Siena, Italy Enrico Tavarnelli Department of Physics, Earth and Environmental Sciences, University of Siena, 53100 Siena, Italy Alessandro Montanari Osservatorio Geologico di Coldigioco, Contrada Coldigioco 4, 62021 Apiro, Italy ABSTRACT The geometry of collisional mountain belts, which were formed at the expense of passive continental margins, is often complex because orogenic structures, such as thrusts and related folds, commonly interfere with pre-orogenic extensional struc- tures, namely, normal faults, resulting in kinematically complex, composite struc- tural assemblages. In these settings, analysis of the relationships between depositional and structural features may provide very useful tools to correctly unravel the local sedimentary and deformational history and relative ages of structures. Analysis of the relationships between minor normal faults and slumps near Frontale in the Umbria- Marche Apennines of Italy made it possible to correctly unravel the local chronology of events and hence to infer the depositional and deformation history of a part of the Upper Cretaceous–Paleogene Scaglia Rossa Formation pelagic basin. The results of this investigation made it possible to ascribe the normal faults to events that predate the construction of the Umbria-Marche mountain belt. Therefore, the normal faults at Frontale are distinct from those that overprint the main compressional structures responsible for the present-day seismicity of central Italy. Tognaccini, S., Tavarnelli, E., and Alessandro Montanari, A., 2019, Synsedimentary deformation in Upper Cretaceous–Lower Paleogene limestones within a thrust anticline of the Umbria-Marche Apennines, Italy, in Koeberl, C., and Bice, D.M., eds., 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco: Geological Society of America Special Paper 542, p. 1–16, https://doi.org/10.1130/2019.2542(11). © 2019 The Geological Society of America. All rights reserved. For permission to copy, contact editing@geosociety.org. INTRODUCTION The geometry of most collisional mountain belts resulting from continental breakup and reassembly (a sequence known amongst geologists as the Wilson cycle: Wilson, 1968; Dewey and Bird, 1970), often followed by renewed breakup, due to fre- quent switches in tectonic regime from contractional to exten- sional, is usually quite complex because compressive structures, like folds and thrusts, frequently interfere with and overprint pre- and late- or postorogenic normal faults (Butler et al., 2006). In these situations, it may be difficult to unequivocally define and correctly establish the chronological development of extensional