An impact crater in northeast South Carolina inferred from potential field data

Abstract

A comparison of recently acquired gravity data with aeromagnetic data for northeastern South Carolina revealed the presence of coincident circular anomalies near Johnsonville. These ∼11 km diameter circular lows meet the geophysical criteria for those associated with buried complex impact craters. Within the magnetic low is a northwest‐southeast structure enclosed by two concentric “moat‐like” lows to its northeast and southwest. The pattern of surface streams passing above the structure is also consistent with the interpretation of a buried impact crater. Fortuitously, a drill core was available from a borehole drilled within these lows. The core includes ∼10 m of Paleozoic crystalline Piedmont basement. Petrographic analysis of basement samples from the core revealed indications of shock metamorphic texture.

Magnetic Anomalies of Impact Craters at Low Magnetic Latitudes

“…In other instances, simple craters appear because they disturb the magnetic pattern in the surrounding bedrock by their absence of magnetic material. Figure 4 shows this type of simple crater in magnetic data from northeast South Carolina (Talwani et al, 2003).…”

Aeromagnetic interpretation in the south-central Zimbabwe Craton: (reappraisal of) crustal structure and tectonic implications

“…However, for the purpose of regional crustal structure, intermediate or medium to long wavelength anomalies are useful (e.g., Gibson and Millegan 1998). In this case, pseudo-depth slicing (depth ensemble filtering) and an upward continuation filter (e.g., Blakely 1995;Talwani et al 2003;Nabighian et al 2005) were used to attenuate the high frequency anomalies, leaving responses from larger scale and/or deeper features. Pseudo-depth slicing is a filtering technique used to isolate anomalies based on wavelength criteria by calculating the contribution of selected depth intervals to the total magnetic field (Spector and Grant 1970).…”

“…These depth intervals are related to slope segments in the energy spectrum for any given data set. Interpretation of different depth-slice images can be used to determine the thickness of different magnetic bodies and establish their progressive changes with depth (Talwani et al 2003). Available regional gravity data are used to help achieve this objective; they provide additional depth information.…”

“…Based on the grid power spectra (e.g., Spector and Grant 1970;Talwani et al 2003), shallow and deep depth slices of the magnetic field were able to separate the high frequency anomalies from the low frequency ones. Figure 8 shows the filtered RTP magnetic data due to a depth-slice of ~1600m (corresponding to a layer with a maximum depth of 1.3 km) where several high frequency anomalies are now absent on the filtered magnetic map, indicating that their sources lie in the top ~1000 m. However, most major faults, greenstone belts and mafic-ultramafic horizons are still present on this map, which implies that they are deep crustal structures; mafic-ultramafic intrusives are signs of deeply-rooted magma (e.g., Bauer et al 2003;Ferraccioli et al 2005;Allek and Hamoudi 2008).…”