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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

Abstract– The Omeonga ring structure (D.R. Congo) shows a remarkable drainage pattern encircling an area up to 45 km wide and encompassing a central smoothed relief 20 km wide. This inner circular ridge is elevated about 70 m above the ring depression corresponding to the bed of the Unia River, which flows between the inner ridge and an outer irregular ridge. Landsat 7 ETM and ASTER DEM show that the structural characteristics resemble those of several wide impact structures known on Earth. Other geological modes of origin that could produce ring structures, such as magmatic activity, salt diapirism, and karst dissolution have been considered. However, after evaluating the regional stratigraphy, the distribution of volcanism, and morphometry, these processes seem to be rather unlikely. If of impact origin, the age of the Omeonga structure can be constrained to the Late Cretaceous-Cenozoic according to the youngest units in which the ring structure was formed.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

The terrestrial impact crater record is still largely incomplete, and in many areas suspected impact structures have to be confirmed after field analysis. Considering the known impact craters of Earth, many of the best-studied examples are located on cratons, in landscapes like deserts or prairies. On the other hand, the particularly severe effects of fluvial erosion and transport and vegetation cover in warm climates make it difficult to recognize impact structures in rain forest areas, which therefore lack fully proven impact structures, as testified by several databases (e.g., Earth Impact Database; Impact Database; Terrestrial Impact Craters). Indeed, some structures have been reported also in equatorial areas, but with rare and noteworthy exceptions (Master and Reimold 2000; Reimold et al. 1998, 2006), they still require geological descriptions (Impact Database).

In this article, we have focused on a large ring structure, reported as a suspected impact crater named Omeonga in the Impact Database (Rajmon and Shaulis 2007). This structure is located in the rain forest of Central Africa. The aim of the present study is to evaluate the reliability of an impact origin for the Omeonga structure on the basis of remote sensing interpretation and the stratigraphic, geomorphological, and geological information available for Central Africa.

Geology of the Eastern Kasai and Omeonga Structure

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

Omeonga is a ring structure located in the Eastern Kasai province (D.R. Congo), centered at 3°37′50″ S, 24°31′00″ E near the village of Omeonga, 25 km south of the town of Katako-Kombe (Fig. 1) in the Central African rain forest. The structure is recognizable on satellite images by the perfect roundness of the ring feature corresponding to the flow of the Unia River, a tributary of the Lomami River. The ring formed by the river has a diameter of 36 km. The springs of the Tshuapa and Lukenia rivers, which flow into the main Congo River further to the west, are also located in the outer region of the structure (Fig. 1).

image

Figure 1.  a) Distribution of the African cratons (1: West African Craton, 2: Congo-Kasai Craton, 3: Tanzania Craton, 4: Kaapvaal-Kalahari Craton); b) sketched geological map of Central Africa (modified after Giresse 2005) with the location of the study area in the box; D = Dekese borehole; LH = Lokonia High; c) geological map of the area surrounding the ring formed by the Unia River (red circle) modified after Choubert and Faure–Muret (1986); Lu.R. = Lukenie River; T.R. = Tshuapa R.; Lo.R. = Lomami R.; K-K = Katako-Kombe village; O = Omeonga village; W-N = Wembo-Nyama village.

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The Eastern Kasai province is located in the Cuvette Central of the Congo Basin (Cahen 1954), one of the largest cratonic basins on Earth, with a surface extent of about 1.2 million km2. The structure and stratigraphy of the Congo Basin has been widely described in regional works (Cahen 1954; Daly et al. 1992; Catuneanu et al. 2005; Giresse 2005; Milesi et al. 2006) and recently reinterpreted by Kadima et al. (2011a). The tectonostratigraphic reconstruction of Kadima et al. (2011a) indicates a stack of four different stratigraphic sequences bounded by unconformities recognized in seismic stratigraphy and exploration wells. These sequences lie on the pre-Neoproterozoic basement of the Congo Craton (e.g., Batumike et al. 2009) and extend into the Cenozoic (Fig. 2). The structural interpretation of seismic lines suggests that the area was affected by a compressional phase during the late Paleozoic, which formed an intracratonic thrust belt named the Lokonia High (Daly et al. 1991, 1992; Kadima et al. 2011b). A more detailed stratigraphy can be inferred from the 1860 m deep Dekese well (Cahen et al. 1960), located within the foreland basin of the belt about 300 km west of the Omeonga structure (Fig. 1b).

image

Figure 2.  Stratigraphy of the eastern Kasai Craton inferred from the Dekese borehole (Cahen et al. 1960) and the overall geological interpretation after Kadima et al. (2011a); depth to basement after Kadima et al. (2011b).

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According to these data, as reviewed by Kadima et al. (2011a) (Fig. 2), the thin Cenozoic sedimentary cover, about 22 m thick, is made up of fluviatile-lacustrine loose deposits. The underlying Mesozoic succession can be subdivided into the Bokungu Fm. and the Loia Fm. They are mainly made up of stratified sandstones locally interbedded with mudstones of Early Cretaceous–Late Jurassic age; their overall thickness is approximately 700 m. In the interpretation of Downey and Gurnis (2009), the thickness of the Jurassic-Cenozoic succession increases toward the northwest (reaching a maximum thickness of 1200 m around the Congo Basin depocenter). These sedimentary units lie on an unconformity related to a flexural and faulting deformation phase of Triassic—Early Jurassic age (U3 of Kadima et al. 2011a). The unconformity cuts a 146 m thick sequence of shales and sandstones related to the Lukuga Formation of Permian age (Catuneanu et al. 2005; Kadima et al. 2011a). The underlying sediments (816 m thick) are composed of tillites with interbedding of shales and sandstones attributed to the late Carboniferous expansion of the Gondwana ice-cap (Dwyka stage of the Karoo Supergroup accumulation). The bottom 180 m of the Dekese core is made up of Lower Paleozoic red arkoses and black shales, which lie unconformably on Neoproterozoic sedimentary units. This unconformity (U2 in Kadima et al. 2011a) has been related to Late Pan-African tectonism. According to the stratigraphy constrained by other Congo Basin wells and new seismic profiles, the Neoproterozoic units are composed of limestones and siliciclastic sediments related to the Lokoma Group and are separated by an unconformity from the underlying carbonates and evaporites of the Ituri Group. The average thickness of the Neoproterozoic succession would exceed 2 km (Kadima et al. 2011a). The stratigraphic succession should be the same or even thinner further eastward, as Omeonga is located close to the Loconia Late Pan-African High (Daly et al. 1992; Downey and Gurnis 2009; Kadima et al. 2011b).

The basement of the Congo-Kasai Craton lies at the bottom of the sedimentary succession; it is made of granulites, gneisses, amphibolites, granites, gabbros and migmatites of ages ranging from Archean to Neoproterozoic (Batumike et al. 2009 and references therein). It is worth noting that three alkaline-kimberlitic magmatic events of Archean, Neoproterozoic, and Cretaceous ages have been reported within the basement 500 km south of the study area (Batumike et al. 2009).

Geophysical data showed a wide negative gravity anomaly in the Congo Basin (Sahagian 1993; Hartley and Allen 1994; Downey and Gurnis 2009; Crosby et al. 2010) that Kadima et al. (2011b) related to low-density evaporites of the Ituri Group in the lowermost part of the sedimentary succession at about 2 km depth. The Omeonga structure is at the margin of this negative gravimetric anomaly, which is centered about 300 km to the north-west. By contrast, gravity highs of short wavelength as far as 300 km northwards from the Omeonga structure are assumed to relate to two intrusions buried by 3 km of sedimentary succession (Kadima et al. 2011b).

Remote Sensing Analysis

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

Data Set and Processing

The remote sensing analysis and interpretation were carried out on LANDSAT 7 ETM data and on ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) images and DEM (Digital Elevation Model), by using ENVI and ARC-GIS software packages.

The two LANDSAT 7 ETM scenes (176-062 and 176-063, Fig. 3) were acquired on February 5, 2003 and April 7, 2002, respectively. They were downloaded from the website http://glovis.usgs.gov/. These two images were orthorectified and superimposed onto the ASTER DEM by applying the WGS84-UTM projection. They have not been atmospherically corrected because the atmosphere was clear enough and the area was covered by so much vegetation that spectral analysis would not have been useful to infer the geological composition of the substratum.

image

Figure 3.  a) Landsat 7 ETM composite image of the study area (Panchromatic band 8). b) Line-drawing of the drainage network in the study area. Thin dashed circle: interpolation of the outer ring elevation; thick dashed circle: interpolation of the assumed peak-ring.

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The adopted ASTER DEM was downloaded from the Global DEM site (http://www.gdem.aster.ersdac.or.jp/), which collects DEM derived from ASTER stereopair images. These DEM have a grid resolution of about 29 m per pixel and an estimated accuracy of 20 m at 95% confidence for elevation and 30 m at 95% confidence for horizontal coordinates.

Most of the geological interpretation was performed on LANDSAT RGB 7-4-2 false color composites sharpened using the panchromatic band 8, which is characterized by a higher ground-resolution with respect to the visible and short wave infrared bands of the ETM sensor (15 m per pixel versus 30 m per pixel).

The morphological analysis was carried out on topographic profiles, hill-shades and perspective views derived from the ASTER DEM (Fig. 4a). The topographic profiles were obtained from the ASTER DEM product, which was previously smoothed through a mean filter applied using a 15 × 15 kernel. The shaded reliefs were produced, under a simulated sun-elevation of 20° and different sun-azimuths, to emphasize the minor radial drainage. In addition, the circular sun shading algorithm developed by Cooper (2003) was applied with a sun elevation of 20° and an origin chosen at the center of the Omeonga ring structure. This filter provided images with sunshades both radial and tangential to the circular structure, enhancing features respectively parallel or perpendicular to radial vectors passing through the chosen origin (Figs. 4b and 4c). The adopted method requires hypothesizing the position of the circle center only. In particular, no hypothesis as to the circle radius is necessary, in contrast to the Hough transform-based method (Wang and Howarth 1990), often used in crater detection. This is an advantage of the chosen method because the computation time is significantly less (Cooper 2003).

image

Figure 4.  a) ASTER DEM of the study area in which the traces of the profiles of Fig. 5 are shown. b) color coded DEM superimposed onto the radially sun-shaded image and c) tangentially sun-shaded image.

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Geological-Geomorphological Interpretation

ASTER DEM topography indicates a 36 km diameter ring structure, continuous for about 280°, except for the northeastern sector, where a series of small tributaries complete the circular flow (Fig. 3).

The morphology within the ring corresponding to the circular Unia River flow is quite irregular, with an average elevation of 550 m a.s.l., which is 60–70 m higher than the ring depression, whereas the highest hill reaches 624 m a.s.l. (Fig. 4). Both radial sun-shade and topographic profiles (Fig. 5) show an inner discontinuous circular ridge. Its diameter is estimated at 13–20 km, depending on whether the ridge crest or the external slope is considered (Fig. 4). Small water courses have curved shapes within this inner ridge, whose central part is cut by a tributary of the Unia River; this marks the central depressed area in the profiles of Fig. 5. Many small radial tributaries flow from the inner ridge to the main river in a centrifugal pattern (Fig. 3b). This annular ridge could be a secondary erosional feature of the above-mentioned tributary of the Unia River, but the recurrence of at least two somewhat circular morphologies strongly suggests some kind of structural control.

image

Figure 5.  Topographic profiles across the ring structure with the location of the Unia River and the positions of the inferred rim and peak-ring (see profile traces in Fig. 4a).

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Externally, the landscape has an average elevation of about 560 m a.s.l., forming a continuous arched ridge (approximately 45 km in diameter) toward the southwest and an irregular topography to the north (Fig. 4a). Indeed, a centripetal drainage network is clearly visible all around the circle of the Unia River (Fig. 3b). The tangential sun shade clearly shows an uneven distribution of the external radial features that are of limited length in the NW and SE quadrants, but reach an extent up to 27 km from the Unia River annular trend in the NE and SW quadrants (Fig. 4c). The enhanced erosion associated with the large Lomami River has partly obliterated the eastern external sector leaving just small and discontinuous hills (maximum elevation of 521 m a.s.l.) still displaying an arched trend (Fig. 4a).

The geological framework of the Eastern Kasai Craton, where the Omeonga structure is located (Choubert and Faure–Muret 1986), is characterized by a thin cover unit of loose deposits with an average thickness of a few tens of meters. This means that the erosion may be heavily controlled by the underlying geological units of Mesozoic age. More specifically, according to the available geological maps (Cahen 1954; Choubert and Faure–Muret 1986; Milesi et al. 2006) (Fig. 1c), the boundary between the Upper Jurassic marls and the Cretaceous red sandstones crosses the eastern part of the ring structure, whereas outside of the structure, the Lomami River flows northwards following the basal boundary of the Upper Jurassic succession, one of the main unconformities of the whole sedimentary stack (U3 in Kadima et al. 2011a). The differential erosion, triggered by the presence of the Jurassic marls, more erodible than the Cretaceous sandstones, seems to have strongly influenced the drainage network of the area.

Discussion: An Impact Origin for the Large-Size Omeonga Structure?

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

The Occurrence of a Circular Structure in the Congo Basin

Circular structures can be generated by different geological mechanisms such as volcanic and intrusive processes, diapirism, and sinkholes in areas of karstification. However, the diameter for most of these morphologies in many cases does not reach more than ten kilometers. Ring structures larger than 36 km, the diameter estimated for Omeonga within the Unia River flow, are not common in geological records.

Volcanic calderas or batholiths can display or exceed dimensions similar to those of Omeonga (≥36 km) (e.g., Johnson et al. 2002), as for example, the Meugueur–Meugueur ring structure of the Aïr Massif, which reaches 65 km in diameter (Moreau et al. 1986; Ritz et al. 1996) or the 40 km wide Richat structure (Mauretania) interpreted as updoming induced by a Cretaceous alkaline intrusion (Matton et al. 2005). In the latter case, the structure is marked by regular hogback geometry of the folded beds easily detectable from remote sensing; whereas in Omeonga none of these morphologies is visible. In addition, volcanic activity does not seem to have affected the eastern Kasai Craton, where the Omeonga structure is located. The East African Rift System extends 300 km to the east of the study area (Cahen 1954; Morgan 1983; Choubert and Faure–Muret 1986). On the other hand, volcanism produced by hotspot migration is located further to the northwest (Morgan 1983; Ngako et al. 2005), outside of the Congo cratonic area (Fig. 6). Young or active volcanism in this region is extremely unlikely (Master 2010) and undocumented by seismic or geophysical analyses (Kadima et al. 2011b). Deep-seated magmatic bodies should be detectable in the geophysical maps as suggested by Kadima et al. (2011b); however, in the area, no short wavelength gravity highs were recorded.

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Figure 6.  Distribution of volcanism on and around the African continent and track of the hotspots; age in brackets; modified after Ngako et al. (2005). Black square: location of the Omeonga structure. (1: West African Craton, 2: Congo-Kasai Craton. 3: Tanzania Craton, 4: Kaapvaal-Kalahari Craton)

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Kimberlitic pipes (Cox 1978) have roundish shapes and have been detected to the south of the study area (Milesi et al. 2006). However, they are relatively small (about 4 km in diameter; Jacques 1998) and are characterized by a wide central depression not visible over the Omeonga structure. Therefore, this morphology can be ruled out in the case of Omeonga.

Karst sinkholes can be excluded because carbonate and/or sulfate successions in the area are negligible close to the surface, and sinkholes normally do not display a central ring feature like the one found within the Omeonga ring.

Salt diapirs or domes are frequently circular and are characterized generally by moderate dimensions (up to 15 km in diameter—Aslop et al. 2000), as for example, the salt diapirs of the Great Kavir (Jackson et al. 1990). On the other hand, the stratigraphy of the sedimentary succession of the Eastern Kasai craton shows indeed the occurrence of evaporite beds in the Ituri Group (Daly et al. 1992; Kadima et al. 2011a). According to recent seismostratigraphy, salt diapirism, generating structures of 15–20 km in size, is located at least 2 km below the topographic surface and is related to the Pan-African tectonism (Early Palaeozoic) and, possibly, to Triassic-Early Jurassic tectonic events (Kadima et al. 2011a). Indeed, the sedimentary succession above the Triassic-Early Jurassic U3 unconformity has not been influenced by diapir tectonics (Kadima et al. 2011a). In addition, each evaporite pillow creates negative gravity and magnetic anomalies (Kadima et al. 2011b), which have not been recorded at the Omeonga structure. Hence, although the Omeonga ring is located close to the Loconia High, where the evaporites of the Ituri Group could be shallower by some hundred meters, the geophysical data (Kadima et al. 2011b) allow the exclusion of a near-surface salt diapir.

In the Congo-Kasai Craton, the undulations of the basement floor related to regional deformations, and recorded by the geophysical prospecting (Kadima et al. 2011b), have wavelengths (at least 100 km) too long to fit the Omeonga structure. In addition, they display a clear NW-SE trend (Daly et al. 1992; Kadima et al. 2011b) and a circular shape as the one of the Omeonga structure is unlikely even in the case of dome and basin fold interference pattern (type 1 of Ramsey 1967), which, however, would imply a recurrence of similar structures at a regional scale.

All these geological arguments suggest that igneous intrusion, volcanic activity, salt diapirism, or karst dissolution are not likely mechanisms for the Omeonga structure, highlighting the possibility of an impact origin (French and Koeberl 2010). Indeed, the concentric path of the river, together with the tributary river networks of Omeonga, is similar to the drainage pattern found in many confirmed large impact structures (Mihályi et al. 2008). Examples of a concentric path of a main river are Popigai (Siberia) (e.g., Deutsch et al. 2000) and Carswell (Canada) (e.g., Pagel et al. 1985), whereas an example of drainage around a pronounced peak-ring structure is Gosses Bluff (Australia) (e.g., Milton et al. 1996). Finally, examples of tributary river networks are Manicouagan (Canada) (e.g., Floran et al. 1978) and West Clearwater (Canada) (e.g., Grieve 1978). Complex drainage patterns with both centripetal and concentric small rivers draining from a central uplift and external rim have been found also in the Brazilian tropical region (e.g., Engelhardt et al. 1992; Romano and Crósta 2004; Reimold et al. 2006).

Omeonga as a Peak-Ring Impact Structure

Based on the rejection of seemingly unsupported alternative modes of origin for Omeonga, a possible origin by impact needs to be evaluated.

According to an impact perspective, the continuous depressed arch formed by the 85 km long Unia River and its northern tributaries can be interpreted as a rim basin encircled by an arched rim (Fig. 3b). The rim is discontinuous, but still detectable throughout the basin, indicating a total diameter of about 45 km (Figs. 3b and 5). The centripetal tributaries flowing from the outer rim, better developed in the southwestern and northeastern parts of the structure, may reflect radial structure originating from an impact and then partly obliterated by subsequent erosion. The inner drainage network has probably been conditioned by the main structure within the impact basin rim, a peak-ring whose remnant is the arch-shaped ridge with a diameter of approximately 13–20 km within the Omeonga main structure (Figs. 4b and 5).

Hence, Omeonga could be considered a complex crater structure of “peak-ring basin” type, as expected from its diameter of about 45 km (e.g., Melosh 1989; French 1998). The principal mechanisms that lead to the development of such a structure relate to the collapse of the initial bowl-shaped transient crater, achieved mainly by uplift of the rocks underlying the crater center and flow of material from the wall of the transient crater inward (Melosh 1989). The result is a shallower structure, with a well-developed wall terrace and an inner peak-ring diameter roughly half the rim-to-rim diameter (Melosh 1989).

However, the geographical and climatic position must be taken into consideration. In fact, the Congo Basin has been a tropical region since the Cretaceous, and, therefore, the sedimentary cover has been affected by intense weathering as well as the strong erosion by rainforest rivers. For this reason, the assumed impact structure must have been heavily affected by weathering and erosion, which determined the rather flat morphology of the area (the differences in elevation do not reach 100 m). However, the dendrite morphology, quite common in a mature fluvial environment, here shows an anomalous circular shape compared with the rest of the Congo River catchment; this anomaly indicates that the differential erosion and the drainage affected a circular depression. This, as argued above, may be ascribed to the depression between the peak-ring and rim-to-rim ridges, whose diameters are approximately 20 km and 45 km, respectively.

The Omeonga structure is formed within an Upper Jurassic-Lower Cretaceous sedimentary succession overlaid by Quaternary loose deposits (Fig. 1) included in the seismostratigraphic unit C of Kadima et al. (2011a). Hence, the postulated impact may have occurred as early as the Late Cretaceous. However, the instability of an impact structure in a region of such climatic conditions points to a rapid flattening of the structure and may suggest a younger age, as topography seems to still preserve a morphology akin to a peak-ring basin. However, this may be solved only by future field analysis.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

The investigation of the Omeonga structure (D.R. Congo), based on remote sensing geomorphological analysis and stratigraphic review, suggests the following:

  • 1
     The remarkable drainage pattern of the Omeonga ring structure in the central Congo Basin encircles circular feature up to 45 km wide encompassing a central ridge of approximately 13–20 km.
  • 2
     A geological origin, such as magmatic activity, salt diapirism, and karst dissolution, is unlikely for several reasons including regional stratigraphy, distribution of volcanism, and morphometric considerations.
  • 3
     On the other hand, the whole structure exhibits characteristics similar to several large impact structures known on Earth (e.g., West Clearwater, Carswell, and Popigai).
  • 4
     Morphological evidence points to a complex crater with a “peak-ring-basin structure.” The floor between the rim and the peak-ring is now almost entirely occupied by the Unia River, whereas the central peak-ring is at present an arched ridge 70 m higher than the river thalweg. The rim is discontinuous because of erosion and weathering, but still easily distinguishable. The pattern formed by several centrifugal tributaries of the Unia River may be conditioned by the concentric rim slope as well as radial fractures, whereas the centripetal drainage within the ring is more likely controlled by the inner peak-ring structure.
  • 5
     The Eastern Kasai stratigraphy suggests that the possible impact event should have happened as early as the Late Cretaceous. However, the area has been affected by strong weathering related to tropical climate since the Cretaceous, and rapid topographic flattening is expected; hence, the presence of a morphology that, despite the low elevation differences, still recalls that of a peak-ring basin suggests that the impact may have happened even as late as during the Tertiary.

Although geomorphological and stratigraphic analyses are not sufficient to constrain an impact origin for the Omeonga ring structure, all the above arguments indicate that this structure highly deserves detailed field investigation to provide petrographic evidence that could confirm an impact origin.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References

Acknowledgments— We thank Lydia H. Gulick for the revision of the English text. We acknowledge D. Rajmon, S. Master, K. M. A. Walemba, and the Editor W. U. Reimold for scientific reviews. We are grateful to D. Delvaux for useful suggestions.

Editorial Handling— Dr. Uwe Reimold

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Geology of the Eastern Kasai and Omeonga Structure
  5. Remote Sensing Analysis
  6. Discussion: An Impact Origin for the Large-Size Omeonga Structure?
  7. Conclusions
  8. Acknowledgments
  9. References
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