The 'Sirente crater field,' Italy, revisited

摘要

A scientific debate has developed in the last few years as to whether a 130 m diameter sag pond surrounded by a saddle-shaped rim and neighboring smaller sags from the Sirente Plain (Abruzzi, Italy) represent the only known Italian meteoritic crater field, a mud volcano, or an anthropogenic feature. To decipher the nature of the Sirente landforms, we carried out geophysical and geochemical investigations. Geoelectric profiles document two karstified shelf carbonate ridges lying at 10-40 m depth below calcareous lacustrine silts (and deeper more conductive sediments, likely soils/tephra) filling the plain. The smaller sags lie just above the ridges, implying a karstic origin, whereas the main sag (also resting above a carbonate ridge) shows no roots in excess of 10-20 m depth, in contrast to the "crater" interpretation. High-resolution magnetic surveys reveal negative/positive anomaly stripes in correspondence with the buried ridges/ valleys, respectively. The smaller sags, as well as the main crater are located in the domain of negative residuals. The positive long-wavelength magnetic signature is likely due to the strongly susceptive soils/tephra filling the buried valleys. Magnetic modeling shows that the field observed over the crater is incompatible with the field generated by a buried meteorite with realistic characteristics. The smaller sags are characterized by small magnetic anomaly couplets, perfectly reproducible considering the susceptibility contrast between the fill-in soil and the surrounding silts. Our data show that the Sirente crater and the minor depressions are simply the results of human activity and karstic processes, respectively.