Shocked quartz grains from the Målingen structure, Sweden-Evidence for a twin crater of the Lockne impact structure

2014 ◽  
Vol 49 (6) ◽  
pp. 1076-1082 ◽  
Author(s):  
C. Alwmark ◽  
S. Alwmark-Holm ◽  
J. Ormö ◽  
E. Sturkell
Keyword(s):  
Impact Structure ◽  
Shocked Quartz ◽  
Quartz Grains

scholarly journals Shocked quartz in distal ejecta from the Ries impact event (Germany) found at ~ 180 km distance, near Bernhardzell, eastern Switzerland

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sanna Holm-Alwmark ◽  
Carl Alwmark ◽  
Ludovic Ferrière ◽  
Matthias M. M. Meier ◽  
Sofie Lindström ◽  
...  
Keyword(s):  
Impact Structure ◽  
Impact Cratering ◽  
Impact Ejecta ◽  
Deformation Features ◽  
Different Depths ◽  
Shocked Quartz ◽  
Depositional Age ◽  
Impact Events ◽  
Planar Deformation Features ◽  
Quartz Grains

AbstractImpact ejecta formation and emplacement is of great importance when it comes to understanding the process of impact cratering and consequences of impact events in general. Here we present a multidisciplinary investigation of a distal impact ejecta layer, the Blockhorizont, that occurs near Bernhardzell in eastern Switzerland. We provide unambiguous evidence that this layer is impact-related by confirming the presence of shocked quartz grains exhibiting multiple sets of planar deformation features. Average shock pressures recorded by the quartz grains are ~ 19 GPa for the investigated sample. U–Pb dating of zircon grains from bentonites in close stratigraphic context allows us to constrain the depositional age of the Blockhorizont to ~ 14.8 Ma. This age, in combination with geochemical and paleontological analysis of ejecta particles, is consistent with deposition of this material as distal impact ejecta from the Ries impact structure, located ~ 180 km away, in Germany. Our observations are important for constraining models of impact ejecta emplacement as ballistically and non-ballistically transported fragments, derived from vastly different depths in the pre-impact target, occur together within the ejecta layer. These observations make the Ries ejecta one of the most completely preserved ejecta deposit on Earth for an impact structure of that size.

Shocked quartz in polymict impact breccia from the Upper Cretaceous Yallalie impact structure in Western Australia

2019 ◽  
Vol 54 (3) ◽  
pp. 621-637 ◽  
Author(s):  
Morgan A. Cox ◽  
Aaron J. Cavosie ◽  
Ludovic Ferrière ◽  
Nicholas E. Timms ◽  
Phil A. Bland ◽  
...  
Keyword(s):  
Western Australia ◽  
Upper Cretaceous ◽  
Impact Structure ◽  
Shocked Quartz

Microscopic planar features in quartz from Scollard Canyon, Alberta, and the Cretaceous–Tertiary boundary event

1988 ◽  
Vol 25 (9) ◽  
pp. 1530-1534 ◽  
Author(s):  
R. A. F. Grieve ◽  
J. Alexopoulos
Keyword(s):  
Continental Margin ◽  
Crystalline Rocks ◽  
Meteorite Impact ◽  
Isotopic Data ◽  
Near Surface ◽  
Deformation Features ◽  
Shocked Quartz ◽  
Quartz Grains ◽  
Geologic Processes ◽  
Basaltic Material

Quartz grains separated from the Cretaceous–Tertiary (K/T) boundary clay at Scollard Canyon, Alberta, have prominent, microscopic planar features. These occur in 15–30% of the grains from the lower 1.5 cm of the boundary clay. They commonly correspond to the ω and π orientations found at known meteorite impact sites and differ from deformation features produced by other dynamic geologic processes. Basal planar features, however, are absent here and at other K/T sites. One possible explanation is that quartz at boundary sites is an incomplete sample of shocked quartz from the postulated K/T impact and unshocked detrital quartz. The source of the shocked quartz most likely was close to the point of impact and near surface. This and previous isotopic data suggest the K/T target site contained a relatively thin upper unit of quartz-bearing crystalline rocks overlying basaltic material, corresponding possibly to thinned continent or a continental margin.

The Cleanskin impact structure, Northern Territory and Queensland, Australia: A reconnaissance study

2021 ◽  
Author(s):  
T. Kenkmann ◽  
P.W. Haines ◽  
I.P. Sweet ◽  
K. Mitchell
Keyword(s):  
Remote Sensing ◽  
Northern Territory ◽  
Impact Structure ◽  
Impact Event ◽  
Deformation Features ◽  
Apparent Diameter ◽  
The Impact ◽  
Planar Deformation Features ◽  
Impact Origin ◽  
Quartz Grains

ABSTRACT We report on the Cleanskin structure (18°10′00″S, 137°56′30″E), situated at the border between the Northern Territory and Queensland, Australia, and present results of preliminary geological fieldwork, microscopic analyses, and remote sensing. The Cleanskin structure is an eroded complex impact structure of ~15 km apparent diameter with a polygonal outline caused by two preexisting regional fault sets. The structure has a central uplift of ~6 km diameter surrounded by a rather shallow ring syncline. Based on stratigraphy, the uplift in the center may not exceed ~1000 m. The documentation of planar deformation features (PDFs), planar fractures (PFs), and feather features (FFs) in quartz grains from sandstone members of the Mesoproterozoic Constance Sandstone confirms the impact origin of the Cleanskin structure, as proposed earlier. The crater was most likely eroded before the Cambrian and later became buried beneath Cretaceous strata. We infer a late Mesoproterozoic to Neoproterozoic age of the impact event. In this chapter, the Cleanskin structure is compared with other midsized crater structures on Earth. Those with sandstone-dominated targets show structural similarities to the Cleanskin structure.

A search for shocked quartz grains and impact ejecta in early Silurian sediments on Gotland, Sweden

1994 ◽  
Vol 131 (3) ◽  
pp. 361-367 ◽  
Author(s):  
Birger Schmitz ◽  
Lennart Jeppsson ◽  
Johan Ekvall
Keyword(s):  
Lateral Spreading ◽  
Asteroid Impact ◽  
The Earth ◽  
Planar Shock ◽  
Impact Ejecta ◽  
Single Grain ◽  
Shocked Quartz ◽  
Impact Events ◽  
Impact Origin ◽  
Quartz Grains

AbstractAll bentonite and bentonite-resembling layers thicker than a few millimetres from a 120m-thick Early Silurian sequence on Gotland, Sweden, were searched for shocked quartz grains of comet or asteroid impact origin. Although more than 200000 quartz grains from 86 bentonite samples were studied, not one single grain with multiple planar shock features was found. The studied sequence represents sedimentation during a period of about 2 million years. Impact frequencies, estimated from the cratering record and astronomical observations, indicate that during a 2-myr- period on average 20 comet or asteroid bodies larger than 0.5 km in diameter strike the Earth. The number of smaller impacting bodies is many times higher. In the light of this high frequency of impacts, the absence of any shocked-quartz-bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small- and medium-scale impact events.The results also show that shocked quartz in general is absent or extremely rare in volcanic ash. This strengthens the case for an impact-related origin of shocked quartz grains in the Cretaceous–Tertiary boundary days.

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