The Karla impact structure (Russia) explored by potential-field investigations

1Yoann Quesnel,2Natalia S. Bezaeva,3Dilyara M. Kuzina,1Pierre Rochette,1Jérôme Gattacceca,1Minoru Uehara,2Dmitry D. Badyukov,3Bulat M. Nasyrtdinov,4,5,6Dmitry A. Chareev,7Cedric Champollion
Meteoritics & Planetary Science (in Press) Link to Article []
1Aix-Marseille Université, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
2V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin str, 119991 Moscow, Russia
3Institute of Geology and Petroleum Technologies, Kazan Federal University, 4/5 Kremlyovskaya Str, 420008 Kazan, Russia
4Institute Experimental Mineralogy, Russian Academy of Science, 4 Academician Osipyan Str, 142432 Chernogolovka, Moscow Region, Russia
5Institute of Physics and Technology, Ural Federal University, 19 Mira Str, 620002 Ekaterinburg, Russia
6National University of Science and Technology “MISiS”, 4 Leninsky Prospekt, 119049 Moscow, Russia
7Géosciences Montpellier, CNRS, Université de Montpellier, Montpellier, France
Published by arrangement with John Wiley & Sons

With no significant topographic expression and limited bedrock exposure, the ~10 km diameter Karla impact structure (Tatarstan, Russia) is poorly known. The age of the impact is also poorly constrained stratigraphically to between 4 and 60 Ma, even if an upper Miocene age is more likely. Targeted gravity and magnetic field surveys were conducted over Karla to explore its size and structure in 2019. Bouguer gravity anomaly data reveal a central positive (+2 mGal) peak ~2 km in diameter surrounded by a concentric negative (−1 mGal) anomaly extending to ~3 km radius; a more irregular, outward-decreasing (+1 to −1 mGal) positive anomaly extends to 6–8 km radius. A complex impact structure with diameter of 8–10 km is consistent with the Bouguer anomalies. Magnetic field data show 1 to several km-wavelength anomalies with amplitude variation from +150 to −150 nT and little concentric structure, although the impact feature broadly corresponds to a magnetic low with a weak central high. A 2-D numerical model of the structure was built using these potential-field data and petrophysical properties measured on collected samples. It confirms a central uplift composed of Paleozoic sediments and Archean crystalline basement up to 1 km of depth. A 500 m deep collapsed disruption cavity filled by breccia and lacustrine deposits accounts for the Bouguer negative ring. The reversely polarized and weak central magnetic anomalies are controlled by the geometry of the crystalline basement associated with the deformation during the central uplift.


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