The group of Macha craters in western Yakutia

Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz‐rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high‐pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s−1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.

“…(); (13) Gibbons et al. (); (14) Taylor (); (15) Smith and Hodge (); (16) Hodge and Wright (); (17) Gurov and Gurova (); (18) Koeberl et al. (); (19) McHone et al.…”

Section: Discussionmentioning

confidence: 99%

Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt

Fazio

Folco

D’Orazio

et al. 2014

“…), Wabar in Saudi Arabia (Wynn and Shoemaker ; Gnos et al. ), and Macha in Russia (Gurov and Gurova ). Thus, in order to identify and confirm small impact structures developed in unconsolidated cohesive sediments (e.g., muds and clays), the circular shape of the structures, presence of meteorites, and identification of possible impactites such as, for example, ejecta, are useful.…”

Section: Introductionmentioning

confidence: 99%

Geology of the Morasko craters, Poznań, Poland—Small impact craters in unconsolidated sediments

Szokaluk

Jagodziński

Muszyński

et al. 2019

Confirmed small impact craters in unconsolidated deposits are rare on Earth, and only a few have been the subjects of detailed investigations. Consequently, our knowledge of indicators permitting unambiguous identification of such structures is limited. In this work, detailed geological mapping was performed in the area of the Morasko craters, of which the largest crater is of about 96 m diameter. These craters were formed in the mid‐Holocene (~5000 yr ago) in unconsolidated sediments of a glacial terminal moraine. Fragments of the impactor—an iron meteorite—have been found in the craters’ vicinity for many decades. Despite numerous studies of the meteorite, no detailed research concerning the geological structure around the craters and of the ejecta deposits has been undertaken. The new data, including evaluation of over 52 sediment cores and 260 shallow drillings, permit the identification of four main sediment types: Neogene clays, diamicton with Neogene clay clasts containing charcoal pieces, diamicton without clasts, and sand with locally preserved paleosoil and charcoal pieces. Based on sedimentological properties, the ejecta deposits are mainly identified as diamicton with Neogene clay clasts, described as lithic impact breccia, covering locally preserved pre‐impact soil. Moreover, crater sections characterized by inverse stratigraphy of sediments are identified as belonging to overturned flaps.

“…Most commonly, organic material from within the crater is used. Samples from within the crater can reveal only a minimum age of the structure (e.g., Macha: Gurov and Gurova ; Morasko: Stankowski et al. ), which often is significantly different from the real age, because datable material can start forming long after the crater formation, and the extent of the time lag is hard to estimate.…”

Section: Introductionmentioning

confidence: 99%

“…A maximum estimate of the age of a crater can be obtained by 14 C dating of the paleosol that is covered by proximal ejecta (e.g., Whitecourt: Herd et al. ; Macha: Gurov and Gurova ). Dating paleosols, however, tends to be problematic because different fractions of soil may yield dissimilar ages (e.g., Pessenda et al.…”

Section: Introductionmentioning

confidence: 99%

Dating a small impact crater: An age of Kaali crater (Estonia) based on charcoal emplaced within proximal ejecta

Łosiak

Wild

Geppert

et al. 2016