Big Horn Basin Series
Identification of a proposed ejecta field and downrange/orbital data has allowed this topic to be moved to a Proof Series status.
Engima statement:
The rocks in and around the Absaroka Mountains of northwestern Wyoming, in the Yellowstone country, have puzzled geologists for more than a century. There lie the remains of an enormous sheet of shattered rock, covering some 3400 square kilometers, lying above rocks that are undisturbed. The detachment surface that forms the base of this sheet is unbelievably flat and nearly level, having a slope of less than 2 degrees. The bulk of the rock sheet ends at the side of Dead Indian Hill, but more pieces are found as far as 50 kilometers beyond. One of these pieces is a few miles north of Cody, a fault-bottomed fragment—a klippe—called Heart Mountain that has given its name to the detachment.
Geologic fieldwork has established that the rocks above the Heart Mountain detachment were once a much thicker and less extensive body.Carbonate rocks of Paleozoic age (as old as Ordovician or 400 million years) were overlain by younger ones, topped with a thick pile of volcanic rocks dating from the Eocene, about 50 million years old.
Then something made this pile collapse catastrophically and spread southeast to nearly three times its former extent, like one of those broken Antarctic ice shelves. When it was all over, ancient limestones had slid sideways to sit atop much younger rocks in the Bighorn Basin. Erosion later removed much of the slide but a few klippen remain, including Heart Mountain, to testify how far it once spread. Geology About.com author: Andrew Alden
Investigation into this enigma using the Perigee: Zero hypothesis has yielded a potential solution to this enigma. The area today know as the Bighorn basin is encircled to the East by the Bighorn range, to the South by the Owl Creek Mountains, and to the West by the Absaroka mountains. These structures are interpreted by us as the manifestation of a Perigee: Zero terminal event crater rim. The Bighorn basin is the manifestation of the crater proper. The GE representation is shown here, with the Keyhole file available via the KMZ link.
Bighorn Basin Crater
As a comparison, here is a graphic using a suggested original extent of the Absaroka Mountains in place. When using the GE facility to interpret this data, please turn this overlay off to view the present structure.
PZ Fan Crater outline superimposed on suggested original Absaroka Mountains
The following description of the components of the proposed ejecta layer are excerpted from a paper which presents an entirely different rationale for the emplacement:
Carbonat-rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds (accretionary lapilli) and impact ejecta clouds and in intrusive diatremes. In these settings and also in industrial processing, accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other. Elongate grains in thick microbreccia have strong but diverse shap-preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent flow, and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault. Catastrophic emplacement of the Heart Mountain block slide, Wyoming and Montana, USA by Edward C. Beutner, Gregory P. Gerbi
We interpret the Owl Mountain Range to be a manifestation of both this event and a later PZ trenching event to the immediate south, which effectively pushed them back northward slightly.
The reader should note that we have utilized a variant of the generic PZ fan crater structure in this instance, as the event was a transitional Trenching-to-Terminal event due to the sudden increase in elevation when the trench reached the front range of the Absaroka Mountains. Also indicated on this graphic is a small "companion" trench event, which we interpret to be the manifestation of a successful trenching (i.e., non terminating) event from a smaller comet body which preceded the main body into the area. The longitudinal offset between the two trajectories is read as 0.6372º, which is equivalent to ~2.5 minutes of earth rotation.
The floor of the Bighorn basin contains the common "backwash" structure, which is the manifestation of a tsunaminite wave of material shattered during the impact, but dragged behind the comet body rather than lofted forward. Here are some detailed GE composites. The locations and view snapshot parameters are included in the KMZ file. Both graphics are linked to higher resolution versions.
Backwash Wall A detail
These two graphics depict detail of the tsuamnite debris wall dragged along behind the comet body. Detail A is looking across the wall structure, while B is looking back along the trajectory of the comet body. In the background can be seen the basement-rock surface of the Bighorn Basin, with it's characteristic cleany-scowered and polished surface. black squares are from the GE overlay graphic.
Backwash Wall B detail
The terrestrial material excised from this cratering event was sent on a southerly trajectory, on a bearing of ~156º. This corresponds to an emplacement azimuth of ~336º. The PZ investigation has identified the correlated down range ejecta field across the High Plains of the Texas Panhandle and Eastern New Mexico. The graphic below presents the suggested trajectory path for the ejecta splash. We feel that the alignment and downrange location of these Playas make for a strong case for their being ejecta emplacements from the Big Horn PZ crater.
A keyhole file is available that presents many of these Playa Lakes in Google Earth using the generic PZ ejecta overlay to suggest shape and orientation.
Playa lakes Keyhole File
The Large ejecta field has been discussed in a POST on the Google Earth Keyhole BBS services.
High Plains Playas
More, smaller, Playas
Playa Detail
Our conjecture that the Big Horn Basin impact occurred in the last 15,000 years suggest humans would have witnessed the event and its aftermath. At 9,000 feet elevation, on a ridge of Medicine Mountain with a commanding view of the proposed crater we find the oldest and physically largest of the many "Medicine Wheel" cosmic alignment structures built and revered by the native indians. They consider Big Horn to be one of the great centers of the earth. The site is marked on the Big Horn Basin graphic at the top of this page.
Panorama of the Medicine Wheel looking from the southeast - Steven Dutch photo
As at Stonehenge and Cahokia Mounds, the hypothesis maintains that these alignment structures were constructed to track the Taurid Comet complex members, with the hope of identifying possible reoccurrence of the cosmic disaster.
View into the basin - Steven Dutch photo
PZ Terminal events have demonstrated the possibility that a small component of the cometary body may continue on a suborbital trajectory after such an impact. In the case of the Bighorn event, the inferred body of the companion trench crater would also be a candidate for a suborbital trajectory, given that it seems to have successfully exited its trench. There exists a strong correlation with the comet body implicated in the Katmandu crater event, approximately 2/3 the way around the earth on the outbound orbital ground track. The sizes of both causal comet bodies are also suggestive of correlation, both being relatively small at 6 km (Katmandu) and 10 km (companion here) radius.
The graphic here presents the sub-orbital ground track of the companion trench comet body. The body was actually terminated in the Himalayan front range.
Big Horn to Katmandu Sub-orbital ground track.