Late Pleistocene tectonic tilting of the Frasassi anticline from offset stalagmites in the Grotta Grande del Vento (Marche, Italy)
Published:September 11, 2019
David Bice, Michael Lacroce, David McGee, Alessandro Montanari, 2019. "Late Pleistocene tectonic tilting of the Frasassi anticline from offset stalagmites in the Grotta Grande del Vento (Marche, Italy)", 250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco, Christian Koeberl, David M. Bice
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The massive Jurassic limestone making up the core of the Frasassi-Valmontagnana blind thrust anticline hosts a large sulfidic cave complex, which, due to Pleistocene tectonic uplift, has been incised by the Sentino River, forming the deep Frasassi Gorge. The Frasassi cave complex is organized into seven horizontal levels, with the youngest and presently active one at river level, and the oldest (ca. 1.2 Ma) one some 200 m above the Sentino River. Therefore, the Frasassi cave complex records the river incision history of this still-active Apennine mountain belt. In addition to an uplift rate of ~0.55 mm/yr for the Holocene, previous radioisotopic dating and surveying of phreatic calcite deposits revealed an overall tilting of the Frasassi anticline of ~0.2° toward N60E for the past 9000 or so years. Our study adds to this history of tectonic tilting by focusing on a group of 30 tilted stalagmites found at the bottom of the Abisso Ancona of the Grotta Grande del Vento (the largest room in the Frasassi complex). These stalagmites have a fairly uniform plunge of ~81° trending toward N30W, and we interpret this to record a tilt of the cave toward S30E during the formation of the stalagmites. From U-Th dating of these paleotiltmeters, we deduce that the Frasassi anticline was tilted by ~0.3° from 32 to 7 k.y. B.P., and the tilt rate gradually increased during this period. The 60° (NE) direction of oblique-slip faults in this area and the local focal mechanisms of recent seismic activity suggest that the tilting is caused by movement along a listric oblique strike-slip zone south of the Frasassi anticline. Our findings also demonstrate that given the right conditions, stalagmites can be used as paleotiltmeters that provide insight into recent crustal deformation.
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250 Million Years of Earth History in Central Italy: Celebrating 25 Years of the Geological Observatory of Coldigioco
Central Italy has been a cradle of geology for centuries. For more than 100 years, studies at the Umbria and Marche Apennines have led to new ideas and a better understanding of the past, such as the Cretaceous-Paleogene (K-Pg) boundary event, or the events across the Eocene-Oligocene transition from a greenhouse to an icehouse world. The Umbria-Marche Apennines are entirely made of marine sedimentary rocks, representing a continuous record of the geotectonic evolution of an epeiric sea from the Early Triassic to the Pleistocene. The book includes reviews and original research works accomplished with the support of the Geological Observatory of Coldigioco, an independent research and educational center, which was founded in an abandoned medieval hamlet near Apiro in 1992.