|2010 GSA Denver Annual Meeting (31 October –3 November 2010)|
|Paper No. 116-13|
|Presentation Time: 8:00 AM-6:00 PM|
CORRELATING AN IMPACT STRUCTURE WITH THE CAROLINA BAYS
DAVIAS, Michael, Stamford, CT 06907, email@example.com and GILBRIDE, Jeanette L., North Carolina State University, Raleigh, NC 27695|
We propose that the Carolina bays are depositional artifacts in the surface of a ~10 meter-thick sheet of distal ejecta, spread differentially from a cosmic impact. The lack of a correlated impact structure in North America is challenging, however.
Using the alignments of 40 fields of Carolina bays in the East and the Mid-West, we generated great circle paths for visualization in Google Earth. This yielded a fuzzy triangulation locus centered at 43.5 N, 89.5 W. Our analysis implies this triangulation would yield an erroneous impact location, offset to the west due to Earth rotation of .25 degrees of arc every clock minute of flight time. Adjustment of the crater eastward along the 43.5º N Parallel should direct us towards the actual impact site. We examined geological depressions found along that transit, selecting the Saginaw area of Michigan.
It is generally understood that glacial activity removed vast quantities of softer strata from around the Michigan Basin’s periphery (i.e., Lakes Michigan, Huron and Erie), however the ice sheet was unsuccessful in breaching proximal cuestas encircling the basin with one major exception: Saginaw Bay.
We propose a low-density hydrated silicate impactor, likely cometary, impacting the Earth on a shallow angle. Remote sensing shows that approximately 5% of all craters are created during such oblique impacts, creating an oval shaped crater and a butterfly ejecta pattern. The mechanism for removal of terrestrial material is seen as shearing rather than compression, thus many of the classic impact markers (such as shocked quartz) are not expected. We note that the Saginaw region exhibits a geometrically oval shaped depression, oriented SW to NE, which correlates well with the Carolina bay distribution seen across North America as an ejecta butterfly pattern.
Recent studies suggest that oblique impacts into solid surfaces protected by a layer of low impedance materials produces structures that differ from classic crater planforms. In our specific case, we invoke the Wisconsinan ice shield as a low-impedance layer protecting the sedimentary strata of the Michigan basin. The ice sheet offers a rationale for the relatively shallow “crater” seen in the area today. Implicating the ice sheet also provides a vehicle to re-distribute the local crater ejecta across a wide area as "glacial till".
2010 GSA Denver Annual Meeting (31 October –3 November 2010)
General Information for this Meeting
|Presentation Handout (.pdf format, 0 kb)|
|Session No. 116--Booth# 388|
Impact Cratering: From the Lab to the Field; from the Earth to the Planets (Posters)
Colorado Convention Center: Hall B
8:00 AM-6:00 PM, Monday, 1 November 2010
Geological Society of America Abstracts with Programs, Vol. 42, No. 5, p. 306
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