Kalkkop - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 32° 42' 29" S; 24° 25' 56" E
Notes
  1. Eastern Cape Province, South Africa, 50 km SW of Graaf-Reinet.
Country South Africa
Region Eastern Cape
Date Confirmed 1993
Notes
  1. Confirmed by shatter cone-like features and numerous quartz and alkali feldspar grains with PDFs. The suevite also has a record of a meteoric component as evidenced by low 187Os/186Os isotope ratios compared to the high values of the target rocks (Reimold et al., 1993).
Buried? No
Notes
  1. Interior filled with post-impact limestone.
Drilled? Yes
Notes
  1. Drilled previously, new central hole to 0.152 km depth (NRCAN binder).
Target Type Sedimentary
Notes
  1. Sandstone, mudstone, and shale of the 225 Ma Karoo Sequence.
Sub-Type Mudstone, Sandstone, Shale
Apparent Crater Diameter (km) 640 m
Age (Ma) 0.250 ± 0.050
Notes :
  1. Limestone samples from top and bottom of crater-fill were dated to 0.250 ± 0.050 Ma (Reimold et al., 1998).

Method :
  1. (U-Th)/He
Impactor Type Unknown
Notes
  1. Unknown, may have siderophile anomaly (Reimold et al., 1993). The suevite shows low values of 187Os/186Os compared to the high crustal target rock ratios, indicating a meteoric component in the suevite via (Reimold et al., 1993).

Advanced Data Fields

Notes

Erosion
3
  1. Part of rim still present.
Final Rim Diameter
Unknown
Apparent Rim Diameter
640 m
  1. (Reimold et al., 1993)
Rim Reliability Index
1
  1. Circular, saucer-shaped depression with raised rims (Reimold et al., 1992)
Crater Morphology
Simple
Central Uplift Diameter
km
Central Uplift Height
Unknown
Uplift Reliability Index
Structural Uplift
Unknown
Thickness of Seds
Target Age
Cenozoic
Marine
No
Impactor Type
  1. Unknown, may have siderophile anomaly (Reimold et al., 1993). The suevite shows low values of 187Os/186Os compared to the high crustal target rock ratios, indicating a meteoric component in the suevite via (Reimold et al., 1993).
Other Shock Metamorphism
No
Shatter Cones
Yes
  1. Shatter cones (Reimold et al., 1993). Several strongly fractured shale clasts broke on gentle prodding to reveal shatter cone-like fractures (Reimold et al., 1993). **see Fig. 2a and b Fig. 7d: fracture morphology resembles closely a cluster of tiny shatter cones (Reimold et al., 1998). CHECK REIMOLD AND KOEBERL 2014, MAYBE NOT
Planar Fractures
No
  1. Planar deformation features (PDFs) with typical intersections of the symmetrically equivalent lamellae.
Planar Deformation Features
Yes
  1. PDF in quartz grains and feldspars (Reimold et al., 1993). Numerous quartz grains with PDFs in up to 6 orientations per grain were detected. In addition, partially isotropic quartz grains, frequently with relics of densely spaced PDFs, and a few alkali feldspar grains with PDFs were observed (Reimold et al., 1993). Appreciable amounts of quartz clasts, some with single or multiple sets (for example Fig. 8b) of planar deformation features (Reimold et al., 1998).
Diaplectic Glass
Yes
  1. Fully or partially diaplectic quartz glass or partially isotropised quartz (Fig. 8b-d) (Reimold et al., 1998).
Coesite
No
  1. Did not find in literature.
Stisovite
No
  1. Did not find in literature.
Crater Fill
LB, MB
  1. There is an increase in clast size in melt-bearing breccias (referred to as suevites) with increasing depth (Reimold et al., 1998). "A core drilled through the centre of the crater passes through 89 m of variously laminated and massive, carbonates that overlie brecciated sandstone and shale." via (Mthembi et al., 2016) where it was shown in figure 12 to be polymict lithic breccia. This is in reference to (Reimold, 1993). Spherules were mentioned in (Koeberl et al., 1994) as they sampled "a quartz clast and sulfide-spherule-rich limestone from 89. I5 m." (Koeberl et al., 1994) also found glass, as "some sub-millimeter-sized glass fragments, most probably impact glass in melt-bearing breccias". A series of dyke breccias is present in the otherwise coherent Beaufort Group sediments, which form the floor to the Kalkkop Crater. Mostly narrow zones of different breccia types, including injections of lithic impact breccia, a possible pseudotachylite veinlet, and cataclasite, occur predominantly in an approximately 65 m thick zone below the crater floor. " descibes pseudotachylite and lithic breccia veins via (Reimold et al., 1998)
Proximal Ejecta
Distal Ejecta
Dykes
P, LB
Volume of Melt
Depth of Melting

References

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W U Reimold, R A F Grieve, G Levin (1992) Kalkkop Crater in the eastern Cape: A good candidate for an impact structure, Abstracts of Papers Submitted to the Lunar and Planetary Science Conference 23, p. 1141-1142, Lunar and Planetary Science Conference, Houston, TX, url

W U Reimold, F G Le Roux, C Koeberl, S B Shirey, D P Blanchard, D Black (1993) Kalkkop Crater, eastern Cape: A new impact crater in South Africa, Abstracts of Papers Submitted to the Lunar and Planetary Science Conference 24, p. 1197-1198, Lunar and Planetary Science Conference, Houston, TX, url

Christian Koeberl, Wolf Uwe Reimold, Steven B Shirey, F.G le Roux (1994) Kalkkop Crater, Cape Province, South Africa: Confirmation of impact origin using osmium isotope systematics, Geochimica et Cosmochimica Acta 58(3), p. 1229-1234, Pergamon, Oxford, url, doi:10.1016/0016-7037(94)90588-6

W U Reimold, C Koeberl, J S V Reddering (1998) The 1992 drill core from the Kalkkop impact crater, Eastern Cape Province, South Africa: Stratigraphy, petrography, geochemistry and age, Journal of African Earth Sciences 26(4), p. 573-592, Pergamon, London-New York, url