|Beaverhead Impact K-T Impact Boundary Crater?|
NEW DISCOVERIES THAT DATE THE BEAVERHEAD IMPACT STRUCTURE AS A K-T BOUNDRY METEORITE IMPACT CRATER
Please proceed to revised paper at http://www.scribd.com/tmcelvain_1
In my research in the literature concerning macroscopic evidence of terrestrial impact structures I read the following paper by Ernston et. al:
Ernstson, K., M. Rampino, and M. Hill, 2001: Cratered cobbles in Triassic Buntsandstein conglomerates in northeastern
And in my travels looking for evidence of impact structures I came across the following articule in Roadside Geology of Montana: Roadside Geology of
TRIASSIC CRATERED COBBLES: SHOCK EFFECTS OR TECTONIC PRESSURE? M. G. Chapman1, M. A. Evans2, and J. F. McHone3; 1U.S. Geological Survey,
After studying the Chapman et. al. document I realized that I probably would not find any evidence of shock metamorphism in the cobbles themselves, but in my experience elsewhere I thought I might find shocked quartz in the sand and sandstone associated with the cobbles. In August 2011 I did some fieldwork in the
Kblc LIMA CONGLOMERATE (UPPER CRETACEOUS) — Limestone pebble to cobble conglomerate derived from erosion of Blacktail-Snowcrest uplift (Nichols and others, 1985). A-5
Kbsn SNOWLINE SANDSTONE (UPPER CRETACEOUS) — Calcareous salt and pepper sandstone; contains limestone fragments (Ryder and Scholten, 1973).
Kbm MONIDA SANDSTONE (UPPER CRETACEOUS) — Clean, calcareous quartz sandstone (Wilson, 1970; Ryder and Scholten, 1973).
And there are several Tertiary and Cretaceous Conglomerate formations in the area:
Tertiary and Cretaceous Formations
TKb BEAVERHEAD GROUP UNDIVIDED (PALEOCENE
TKbq QUARTZITE CLAST CONGLOMERATE – Unit overlies the Red Butte Conglomerate in the
TKbr RED BUTTE CONGLOMERATE (PALEOCENE
Cretaceous conglomerate formations
Kblq LITTLE SHEEP QUARTZITE CONGLOMERATE (UPPER CRETACEOUS) —
Quartzite roundstone conglomerate; Contains large limestone blocks of
Group limestone (Mm) chiefly carried along thrust faults (Perry and others, 1988)
Kblc LIMA CONGLOMERATE (UPPER CRETACEOUS) — Limestone pebble to cobble conglomerate derived from erosion of Blacktail-Snowcrest uplift (Nichols and others, 1985).
All of the above descriptions taken from the downloaded PDF:
Jeffrey D. Lonn, Betty Skipp, Edward T. Ruppel, Susanne U. Janecke, William J. Perry, Jr.,
James W. Sears, Mervin J. Bartholomew, Michael C. Stickney, William J. Fritz, Hugh A. Hurlow,
and Robert C. Thomas
Open File Report MBMG 408
1/05 Correlation Chart symbols; Text, Part A, unit symbols 1/06 Map: faults with Quaternary movement; added Holocene faults in Centennial Valley north of Lima Reservoir; revised location and type of other faults; Text and Correlation Chart units
This report has had preliminary reviews for conformity with Montana Bureau of Mines and Geology’s technical and editorial standards.
Partial support has been provided by the STATEMAP component of the National Cooperative
Geologic Mapping Program of the
And Foemation discriptions in
Paleocene and Cretaceous sandstone and conglomerate (Beaverhead Formation)
Digital Atlas of
Shock metamorphism in quartz
I made grain mounts of sand grains in the Ksbn and Kbm Formation collected near
The above photomicrograph is of a quartz grains with two primary sets of PDF’s and at least two additional sets of PDF’s that are less prominent; the PDF’s are fresher than most I have found so far in this formation, and are different from any others I have ever found.
The above photomicrograph is of a quartz grain with at least two sets of PDF’s.
The above photomicrograph is of a quartz grain with at least 2 sets of highly decorated PDF’s, and the following photomicrograph is of the same grain illuminated with cross polarized light.
The PRELIMINARY GEOLOGIC
The deformation of the Beaverhead Formation sandstones and conglomerates in this area could have been caused by thrust faulting and/or it could be caused by the Beaverhead Impact event.
The above photograph illustrates the near vertical dip, possibly overturned, outcrop of one of the beds in the Kbsn Formation. The photograph was taken on the top of the ridge approximately 1.5 miles north of
Tertiary and Cretaceous Quartzite Cobble Conglomerate
Cratered polished quartzite cobble – all the circular white marks are little impact craters that shattered the cobble with fine hair line fractures.
The above photo is of a polished, quartzite cobble that has three relatively larger impact craters and several lesser impact scars.
The above photograph is of a small cobble illustrating the numerous intersecting hairline fractures.
PThe above hotograph is of a broken cobble illustrating how the rock fractured along hairline fractures caused by the various impacts; notice the curved surface where the rock separated along one of the ring fractures, and other flat surfaces where the rock separated along shear fractures almost like cleavage.
The above photograph is of a sheared, polished, quartzite cobble.
The fact that this formation with the cratered cobbles has been dated at or near the K-T Boundary raises all sorts possibilities for wild speculation one of which is that this impact structure could be coeval with the Chicxulub Impact Crater.
Highly Folded, Faulted, Paleozoic Formations possible Megabreccia
I drove up the
Mississippian and Pennsylvanian
Pl Msr SNOWCREST RANGE GROUP (PENNSYLVANIAN?
The photographs below illustrate how intensely these formations have been deformed.
The above photo is of broken, rotated and displaced blocks of the Snow Crest Range Group at the mouth of Big Sheep Canyon that look like some mega-breccias I have seen.
The above photo is a bed of the Snow Crest Range Group in
I suppose thrust faulting could have caused this deformation but so could a large bolide impact. The fact that the Beaverhead Impact Crater overprints the Sevier Thrust Belt complicates the investigation and interpretation of the impact crater, but may help date the impact as post Sevier. No shatter cones have been found in the Mississippian – Pennsylvanian limestone formations in the area but this does not necessarily mean that the limestone formations were not present when the Beaverhead bolide arrived. There are examples of large impact craters such as the Lockney Impact Crater in
K-T Boundary Impact Event ?
The possibility that the Beaverhead Impact could have happened at the K-T Boundary invites me to indulge myself in wild speculation. The date of this impact at the K-T seems likely to me at this time, but a lot more work needs to be done. One interesting possibility is that the Beaverhead bolide could have been a companion to the Chicxulub bolide, and/or the Beaverhead impact could have been instrumental in the formation of the Yellowstone Hot Spot and/or the Challis Magmatic Episode. The Bouguer gravity map of the region surrounding the proposed thrust detached root to the Beaverhead structure,
It has been my experience researching the Santa Fe Impact Structure, that due to the controversial nature of impact structures on earth, researchers after establishing the fact that the basement rocks are part of an impact structure further geological investigation is stopped and the whole structure swept under the rug so to speak – into the Precambrian – removing the necessity of looking for evidence of the impact in younger rocks. Hopefully if this new evidence proves to be part of the Beaverhead Impact Structure it will help dispel that tendency.