The Laga Basin: Stratigraphic and Structural Setting. Geological Field trip.

The field trip area comprises one of the most studied syn-orogenic basins of Apennines, developed during Messinian time: the Laga Basin. Due to the period of its geological evolution, it represents a link between the internal, uplifted, Lower Miocene fold-and-thrust-belt of the Apennines in the west and the external and more recent part of the chain buried below a thick pile of syn-orogenic, Plio-Pleistocene clastic deposits, in the east. The Laga basin is filled by siliciclastic sedimentary succession which indicates a general eastward migration of the depositional systems, strongly control by thrusting. The basin is the footwall of two regional thrusts cropping out respectively to the west and to the south: the Mts. Sibillini thrust (trending SE-NE) and the Gran Sasso thrust (trending E-W). Other thrust-related-anticlines, trending N-S, developed in the basin during Messinian, are characterized by high angle thrust planes and reduced amount of shortening. The geometric and chronological relationship between the N-S and E-W trending structures is one of the most debated topics regarding this area. The contractional structural building is offset by Upper Pliocene – Pleistocene normal faults, that border the main quaternary basins in the area. The focus of the field trip will be upon the structural and stratigraphic setting of the basin. The stratigraphic architecture of the Laga deposits will be analyzed through some key outcrops (about five or six stops), where is possible to see the main sedimentological features of the different depositional environments. The geometric setting of the Laga deposits with respect to the growing anticlines, the regional monocline and the Gran Sasso thrust will be also shown. Afterward, moving southward, attendees will be given a tour following a section across the Gran Sasso thrust, which includes (in about 4 stops): i) the younger Pliocene deposits that post-dated the main deformation of this regional thrust (Rigopiano Conglomerate Fm in angular unconformity on the Gran Sasso unit); ii) the relationships between the contractional structure and the younger extensional normal faults (Campo Imperatore).