Constraints on the Timing of the Saginaw Impact Manifold
If our conjecture were true, all the bulk of the material making up the bay would have been delivered during a one hour period, sometime in the last 100,000 years. Geochronology techniques are available to place constraints on the timing of recent events, including carbon dating, thermo-stimulated luminescence (TSL), optically stimulated luminescence (OSL), and thermally transferred OSL (TT-OSL). Identification of a wide date range for elements of the bays’ underlying basin structure would falsify any impact hypothesis, and other workers have reported such results (Ivester, A.H, et al, 2007) using OSL techniques.
Our proposal that the bays are composed of distal ejecta presents a challenge to such dating exercises.
Our position on OSL dating is that it does support our hypothesis if properly applied. In numerous bay examples, we suggest the energetic formation of the burst-bubble rim was accomplished with little or no “bottom”, allowing core samples to progress through the deposition horizon and into the hosting strata with no discernable transition. This allows for a continuum of dating back 100 ka or more. OSL technology, with its dependence on exposure to sunlight for multiple hours, has applicability to gradualistic sedimentary processes and may hold no relevance within the context of a mass deposition of ejecta, while TSL may hold more promise given a superheated ejecta regimen. Obviously, the environs around and within the basins were subject to reworking and the infilling of newer sediment over the intervening millennia. Attempts at applying dating techniques must discriminate between the two depositional sequences, and we propose that constraints imposed by dating depositional surfaces immediately below and above the bay stratum may be more appropriate. Our LiDAR images show numerous situations where true wind-driven dune systems are overriding bay structures, at angles totally unrelated to the bays’ orientations; see Bay Planforms.
We call attention to geological anomalies that may correlate with the Carolina bays and which offer support for dating the event ca 40 ka:
Collateral Damage
Ejecta deposition on the scale proposed would have created collateral damage to the North American environment. Burials of fauna, flora and paleosols would be evident beneath the blanket. One example of this may be the ancient Baldcypress trees buried within a 10-meter deposit of white sand near Pee Dee, SC, which are dated at ca 40 ka. (Stahle, D.H., 2005, available on line at http://www.uark.edu/misc/dendro/subfossil.pdf). Stahle, et al, make an interesting observation:
Barrier Island Deposits
Research addressing the mean sea level (MSL) history along the NC coast suggest that barrier island deposits were created during MIS-3 (ca 40 ka), during a high stand above the present-day MSL, and - significantly - stratigraphically above MIS-5 high-stand shoreline deposits (Parham, Peter R., et al, 2006, Mallinson, D., et al, 2008, Scott, T.E., 2010), which is in contradiction to MSL sequences elsewhere across the globe. While many workers invoke complex glacioisotatic regimens across the southeastern US coastline, the hypothesis proposes a 10 to 20 meter ejecta blanket deposits across the continental shelf as an alternative mechanism.
Mississippi Outflows
An analysis of the sea levels during the most recent Wisconsinian Ice age suggest that a strengthening of Mississippi River outflow at 39 ka and an increase in sel level seen in four independent measurement methodologies occurred at a time of decreasing temperatures in the Northern Hemisphere. (Siddall, M, et al, 2008)
Radiocarbon Dates
The finite radiocarbon dates range in age from 440 ± 50 to 27,700 ±2,600 BP radiocarbon in age Whitehead 1981, Gaiser et al. 2001. Some samples are so old, they contained insufficient radiocarbon for dating, which results in "greater than" dates. For example, samples from sediments filling Carolina bays have been dated at greater than 38,000 to 49,550 BP radiocarbon years Frey 1955, Brooks et al. 2001. Ivester has identified two individual samples of sand which fall well outside this range of under 50,000 years.
Nebraska Antecedent Basins
An examination of oriented Nebraska basins (Kuzila, M.S., 1994) has shown that late Wisconsinian loess deposits dated at ca 27 ka are draped evenly over hundreds of antecedent basin structures, smoothing the basins’ sharp rim relief, however not affecting their oval planform. Onset of similar loess deposition over an antecedent basin at Bignell Table, NE has been dated at ca 40 ka. These results suggest the structural basins were deposited prior to 40 ka.
Saginaw Lobe Removal
The Saginaw Lobe retreated prior to 15 ka, as indicated by dated flows into the area from adjacent lobes (Brown, S. E., et al, 2006), a time inconsistent with the general advance of other lobes.
Laschamp Event
An expected outcome of a significant oblique impact would be the initiation of a Geomagnetic Excursion event (R. A. Muller, 2002,10.1029/2002GL015938) where the magnetic pole of the earth either wanders or flips, usually accompanied by a weakening of the overall geomagnetic intensity. Perhaps the strongest and most enigmatic excursion in the last 790,000 years (which was the age of the last full reversal) is the much-studied, intense, yet short-lived Laschamp event, dated at 40.5 kya. There is intriguing evidence linking reversals directly to impacts. The 24-km Ries impact crater in Germany (age 14.8 ± 1 Ma) has reversed polarity in the fall-back breccias but normal polarity in the first crater sediments; thus a reversal took place immediately following the impact (Pohl, 1978).
Graphic from Guilou, et al 2004 D 2004 Elsevier B.V. doi:10.1016/j.epsl.2004.09.018
Additional graphic from Lund, s, et al 2007 doi:10.1016/j.pepi.2005.10.009 , caption references increased sedimentation rate.
