Douglas Impact Crater Strewn Field , Wy , Usa : A Progress Report (original) (raw)
Related papers
2018
More than thirty circular to ellipsoidal possible impact craters have been identified on the northeast facing flank of the Sheep Mountain anticline near Douglas, Wyoming, USA. Rim-to-rim diameters of craters range from 16 to 66 meters. The exposed strewn field has a minimum length of 6.4 kilometer in SE-NW direction. Satellite and drone imagery has revealed crater shape, orientation, and size. Eight of the craters have the compelling geomorphology of a simple impact crater with a raised rim and overturned flap, an apparent continuous ejecta blanket, and an ovoid shape oriented SE to NW coincident with the apparent strike of the strewn field implying an impact from SE towards NW. Some have resistant crescent shaped morphologies, with lowest spill point to northeast caused by strata tilting and erosional processes. Here we present the first proof of the impact origin of one of these craters with a diameter of 60 meters, centered on 42◦39’07.35”N, 105◦26’58.61”W [1]. This crater contai...
Evidence for a large Paleozoic Impact Crater Strewn Field in the Rocky Mountains
Scientific Reports, 2018
The Earth is constantly bombarded by meteoroids of various sizes. During hypervelocity collisions a large amount of energy is coupled to the Earth’s atmosphere leading to disruption of decimeter to hundred meter-sized meteoroids. Smaller meteoroids may form meteorite strewn fields while larger initial bodies and high-strength iron meteoroids may form impact crater strewn fields. Impact crater strewn fields are ephemeral and none documented to date are older than about 63,500 years. Here we report on a newly discovered impact crater strewn field, about 280 Myr old, in tilted strata of the Rocky Mountains near Douglas, Wyoming. It is the oldest and among the largest of impact crater strewn fields discovered to date, extending for a minimum of 7.5 km along a SE-NW trajectory. The apparent width of the strewn field is 1.5 km, but the full extent of the crater strewn field is not yet constrained owing to restricted exposure. We probably see only a small section of the entire crater strew...
Ernstson Claudin Impact Structures Meteorite Craters, 2022
Secondary craters in impacts on moon, planets and their moons are a well known phenomenon, which has been investigated many times. In the article commented by us here, the authors report on a crater strewn field in the American state of Wyoming, which is interpreted as a field of secondary craters of a so far unknown larger primary impact structure and as a first on Earth. We compare the Wyoming crater strewn field with the Chiemgau impact crater strewn field in SE Germany and find that both have nearly identical characteristics of virtually all relevant features, in terms of geometries and petrography. We conclude that the alleged Wyoming secondary crater field is a fiction and the craters attributable to a primary impact. The alleged evidence is very poor to easily refuted. A primary crater does not exist to this day. The negative free-air gravity anomaly referred to, but not even shown, is invalid for this purpose. The Bouguer gravity map shows no indication of a possible large impact structure. Also unsuitable is the use of asymmetries with elongations of assumed secondary craters with a very questionable corridor intersection for the ejecta. Of 31 craters surveyed as proven, 15 are circular (eccentricity 1) and more than half (19) have an eccentricity ≤1.2. Circular and elongated craters are intermixed. The evaluated crater axes may just as well originate in a multiple primary impact. Elongated craters may also result from doublets of overlapping craters that are no longer fresh, as described by the authors themselves. In their paper, the authors do not show a Digital Terrain Model with contour lines for any of the surveyed craters, but only aerial photos blurred by vegetation. A verification of the crater measurements with the deduced eccentricities and strike directions is impossible. Not a single topographic profile over even a single crater in the strewn field is shown, either from DTM data or from an optical leveling, which could have been accomplished in an instant given the relatively small craters. Grave is the misconception that such a large crater field of 90 km length with three separate clusters is not possible according to 20 years old model calculations. A primary impact with multiple projectiles could perhaps be conceivable under rare circumstances, which are described by the authors as not relevant. The alleged impossibility of such a large primary strewn field with referring to the known small impact fields of Morasko, Odessa, Wabar, Henbury, Sikhote Alin, Kaalijärv, and Macha is contradicted by the three larger impact strewn fields of Campo del Cielo, Bajada del Diablo (very likely), and Chiemgau, which are best described in the literature but are not mentioned by Kenkmann et al. with a single word. The comparison of the Wyoming strewn field with the Chiemgau impact crater strewn field of about the same size here in the commentary article proves the scientifically clearly much greater significance of the Chiemgau impact, which must be considered as currently the largest and most significant Holocene impact despite the rejection and ignoring in some parts of the so-called impact community.
Introduction: The mechanisms of rock deformation and strength softening during the failure of a transient cavity of large impact craters are not well understood. Hydrodynamics do not describe the material behavior in an appropriate way, since large-scale motions occur along discrete fault zones. With conventional strength properties of rocks and debris one either cannot explain the collapse of a transient cavity. Phenomenological models suggest that rocks beneath a collapsing crater behave like a Bingham plastic, that is, deformation starts at a critical cohesion and from that point on the rock sustain increasing stress with increasing strain rate. The cohesion is in the order of 5 MPa. The most reliable physical model so far which accounts to this mechanical behavior and which provides an adequate explanation of crater collapse is the theory of "acoustic fluidization" [2]. In order to draw nearer to the high strain ratemechanics of target rocks after passage of shock and rarefaction waves, structural and microstructural investigations are required to characterize active deformation mechanisms and to grade the role acoustic fluidization and other softening mechanisms play for the apparent strength reduction of the target material. With this intention a single impact-induced fold within Cambrian rocks of the Crooked Creek impact crater is investigated (Fig.1). From numerical models a period of about 20 s at velocities of 50-100 ms-1 is determined for the whole collapse of this crater. This gives an upper limit for the formation time of the fold. The Crooked Creek Impact structure, Missouri, USA has a diameter of about 7 km and is situated at 37°50' N and 91°23'W in Crawford County, Missouri. A long debate about its origin [3], [4] was solved in favour of the impact hypothesis when [5] found shatter cones and PDF in quartz of Lamotte sandstone. The sediments of Cambrian to Ordovician age are intensely folded, faulted, and brecciated within the partly collapsed central uplift of the crater. The oldest beds exposed along the ring anticline of the central uplift are more than 300 m above their normal position [3]. The ring anticline is encircled by a peripheral ring syncline. Outside the crater rocks are nearly flat-lying. The sample locality (UTM 4188.750 N/641.750 E) is located at the inner limb of the central ring anticline. Analytical Technique: The analysis focused on a single fold. The sample has a size of 20x15x10 cm. Cuttings were prepared normal to the fold hinge. The
Cloud Creek structure, central Wyoming, USA: Impact origin confirmed
Meteoritics & Planetary Science, 2003
available online at http://meteoritics.org 445 Abstract-The circular Cloud Creek structure in central Wyoming, USA is buried beneath ~1200 m of Mesozoic sedimentary rocks and has a current diameter of ~7 km. The morphology/morphometry of the structure, as defined by borehole, seismic, and gravity data, is similar to that of other buried terrestrial complex impact structures in sedimentary target rocks, e.g., Red Wing Creek in North Dakota, USA. The structure has a fault-bordered central peak with minimum diameter of ~1.4 km, composed predominantly of Paleozoic carbonates thickened by thrust faulting and brecciation, and is elevated some 520 m above equivalent strata beyond the outer rim of the structure. There is a ~1.6 km wide annular trough sloping away from the central peak (maximum structural relief, 300 m) and terminated by a detached, fault-bounded, rim anticline. The youngest rocks within the structure are Late Triassic (Norian?) clastics and these are overlain unconformably by post-impact Middle Jurassic (Bathonian?) sandstones and shales. Thus, the formation of the Cloud Creek structure is dated chronostratigraphicly as ~190 ± 20 Ma.
Meteoritics & Planetary Science, 2004
available online at http://meteoritics.org 31 Abstract-The Crow Creek Member is one of several marl units recognized within the Upper Cretaceous Pierre Shale Formation of eastern South Dakota and northeastern Nebraska, but it is the only unit that contains shock-metamorphosed minerals. The shocked minerals represent impact ejecta from the 74-Ma Manson impact structure (MIS). This study was aimed at determining the bulk chemical compositions and analysis of planar deformation features (PDFs) of shocked quartz; for the basal and marly units of the Crow Creek Member. We studied samples from the Gregory 84-21 core, Iroquois core and Wakonda lime quarry.
The Structural Inventory of Mid-Sized Complex Impact Craters Formed in Sedimentary Targets
Introduction: This abstract provides a review of the macro-scale structural inventory of mid-sized complex craters (5-15 km ∅) formed in sedimentary targets. The analysis is mainly based on terrestrial crater studies but also includes structural analysis of martian craters [1]. A comprehensive review is given in [2]. Crater rim: The crater rim of pristine complex craters usually shows a pronounced morphological elevation with a scarp at the inner side. The elevated rim is formed by the ejecta blanket plus uplifted bedrock. Recent analyses of complex lunar and martian craters indicate that target uplift plays the dominant role for the elevation. The circumferential crater rim escarpement is the outermost fault visible on the uneroded target surface and usually forms one of the major terrace steps in the crater rim region. On Earth, where the original morphology of craters is often barely visible and the ejecta blanket is removed, the outermost continuous concentric normal fault usually defines the final crater diameter of a complex impact crater. However, [3] stated that these outermost faults visible in eroded craters can lie further outwards than the main escarpments of uneroded structures. They suggest the terms "rim diameter" for uneroded craters and "apparent diameter" for eroded structures. The main faults are often associated with synthetic or antithetic faults. Pre-existing faults and joints can be reactivated during crater modification. Such craters often appear as polygonal craters with straight rim segments that run along the pre-existing joints [4]. Very deeply eroded impact structures are typically not defined by concentric normal faults. Instead circumferential monoclines or a combination of inward dipping normal faults and monoclines are common, particularly if the target is a sedimentary and stratified one (Fig. 1). The inner limb of a crater rim monocline usually dips downward towards the crater, and the crater rim can be defined by the trace of the monocline's hinge. Crater moat: In pristine craters the moat between the crater rim and the central uplift is buried under a variety of breccias (talus breccias, crater floor breccias, airborne breccias) as well as impact melt. Beneath this crater fill a complex ring syncline exist that is mostly asymmetric in radial cross section, with a steeply dipping or even overturned inner limb and a more gently dipping outer limb that is often segmented by normal faulting. The syncline is radially and concentrically subdivided into numerous fault-bounded segments or disintegrated into blocks. Between the crater rim and
2001
The Wolfe Creek Meteorite Crater is an impact structure 880 m in diameter, located in the Tanami Desert near Halls Creek, Western Australia. The crater formed< 300 000 years ago, and is the second largest crater from which fragments of the impacting meteorite (a medium octahedrite) have been recovered. We present the results of new ground-based geophysical (magnetics and gravity) surveys conducted over the structure in July–August 2003.