The outer ring of a circular structure in the Marche Region, Central Italy: Evidence of a non-extraterrestrial origin

Abstract

Google Earth images in the Marche Region of Central Italy revealed a circular structure consisting of a ring system made up of concentric hills and valleys. Cartography, DEM, geological, and available geophysical data were used to constrain the possible origin of the structure. Located in the Messinian foredeep deposits of the Central Apennines, it has a rim diameter of 3.75 km and a central uplift connected to its southernmost part. As it was formed in the clays of the Lower Pliocene, and clays are believed to have emerged definitively after the Upper Pliocene, its age might be constrained to the Lower Pleistocene. Similar concentric structures are usually found in impact craters, sedimentary domes, and volcanic landforms. As salt domes and magmatic activity are not found in this region, this study seeks to validate the results of previous work that it was the result of an ancient impact crater, of hydrological, brachy anticline, or clayey diapiric origins. Specifically, an observed second ring portion, with a curvature radius about double the first in size, will be investigated in this work. This second ring portion appears to be concentric to the first one and is visible along the its northern and western parts. Although double concentric rings are usually due to impact craters, the absence of the ring portion in the other two directions, and the probable deviation of a river, deduced by studying hydrography, supports the hypothesis that it might be of a clay diapir origin.