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Shatter cones and planar deformation features confirm Santa Marta in Piauí State, Brazil, as an impact structure
Author(s) -
Oliveira Grace Juliana Gonçalves,
Vasconcelos Marcos Alberto Rodrigues,
Crósta Alvaro Penteado,
Reimold Wolf Uwe,
Góes Ana Maria,
Kowitz Astrid
Publication year - 2014
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12368
Subject(s) - impact structure , impact crater , geology , syncline , plateau (mathematics) , bouguer anomaly , basement , structural basin , seismology , conglomerate , magnetic anomaly , paleontology , geomorphology , geochemistry , gravity anomaly , geography , archaeology , mathematical analysis , physics , mathematics , astronomy , oil field
A total of 184 confirmed impact structures are known on Earth to date, as registered by the Earth Impact Database. The discovery of new impact structures has progressed in recent years at a rather low rate of about two structures per year. Here, we introduce the discovery of the approximately 10 km diameter Santa Marta impact structure in Piauí State in northeastern Brazil. Santa Marta is a moderately sized complex crater structure, with a raised rim and an off‐center, approximately 3.2 km wide central elevated area interpreted to coincide with the central uplift of the impact structure. The Santa Marta structure was first recognized in remote sensing imagery and, later, by distinct gravity and magnetic anomalies. Here, we provide results obtained during the first detailed ground survey. The Bouguer anomaly map shows a transition from a positive to a negative anomaly within the structure along a NE – SW trend, which may be associated with the basement signature and in parts with the signature developed after the crater was formed. Macroscopic evidence for impact in the form of shatter cones has been found in situ at the base around the central elevated plateau, and also in the interior of fractured conglomerate boulders occurring on the floor of the surrounding annular basin. Planar deformation features ( PDF s) are abundant in sandstones of the central elevated plateau and at scattered locations in the inner part of the ring syncline. Together, shatter cones and PDF s provide definitive shock evidence that confirms the impact origin of Santa Marta. Crystallographic orientations of PDF s occurring in multiple sets in quartz grains are indicative of peak shock pressures of 20–25 GPa in the rocks exposed at present in the interior of the crater. In contrast to recent studies that have used additional, and sometimes highly controversial, alleged shock recognition features, Santa Marta was identified based on well‐understood, traditional shock evidence.