Skip to comments.Terrestrial Evidence of a Nuclear Catastrophe in Paleoindian Times
Posted on 07/24/2006 12:03:03 AM PDT by ForGod'sSake
The Paleoindian occupation of North America, theoretically the point of entry of the first people to the Americas, is traditionally assumed to have occurred within a short time span beginning at about 12,000 yr B.P. This is inconsistent with much older South American dates of around 32,000 yr B.P.1 and the similarity of the Paleoindian toolkit to Mousterian traditions that disappeared about 30,000 years ago.2. A pattern of unusually young radiocarbon dates in the Northeast has been noted by Bonnichsen and Will.3,4
Our research indicates that the entire Great Lakes region (and beyond) was subjected to particle bombardment and a catastrophic nuclear irradiation that produced secondary thermal neutrons from cosmic ray interactions. The neutrons produced unusually large quantities of 239Pu and substantially altered the natural uranium abundance ratios (235U/238U) in artifacts and in other exposed materials including cherts, sediments, and the entire landscape. These neutrons necessarily transmuted residual nitrogen (14N) in the dated charcoals to radiocarbon, thus explaining anomalous dates.
We investigated a cluster of especially young radiocarbon dates concentrated in the north-central area of North America. For example, at the Gainey site in Michigan a 2880 yr B.P. radiocarbon date was reported, while the thermoluminescence date for that site is 12,400 yr B.P.5 Other anomalous dates found at Leavitt in Michigan,6 Zander and Thedford in Ontario,7 Potts in New York,8 Alton in Indiana,9 and Grant Lake in Nunavut10 are summarized in Table 1. The Grant Lake Paleoindian site is most remarkable because its 160 [rc] yr B.P. age is nearly contemporary, while adjacent and deeper samples give ages of 1480-3620 [rc] yr B.P.
Stratigraphic associations place Paleoindian occupations at depth on the prehistoric North American landscape on sediments that form the old C horizon composed of parent material, Wisconsinan deposits that predate Holocene sediment buildup.11,12,13 The young Paleoindian dates cannot be correct, particularly since there are no patterned anomalies noted in later-period prehistoric assemblages relating to higher stratigraphic positions. In a pioneering study of the Paleoindian site at Barnes, Michigan, Wright and Roosa observed that Paleoindian artifacts were deposited before the formation of spodosols ceased in this area about 10,000 yr B.P.14 This conclusion was based on observing that cemented sediments on artifacts, found outside their original context, defines their original stratigraphic position.
Sediment profiles were taken at Paleoindian sites and at numerous widely separated control locations in Michigan. The C sediment horizon is clearly recognized by its transitional color and confirmed by elevated concentrations of potassium and other isotopes. Color and chemistry are key indicators of this very old soil11,12,13,14 derived from parent materials and associated postglacial runoff.15 At Gainey, large quantities of micrometeorite-like particles appear to be concentrated near the boundary between the B and C sediment horizons. They can be separated with a magnet and are identified by the presence of chondrules and by visual evidence of sintering and partial melting. These particles, dissimilar to common magnetites, are found in association with a high frequency of "spherules." The depth profiles for potassium and particles at the Gainey site are compared in Fig. 1. Minor vertical sorting of particles is apparent, with a shallow spike of particles near the surface probably resulting from modern agricultural or industrial activity. Total gamma-ray counting of sediment profiles in the various locations invariably showed increased radioactivity at the B-C boundary consistent with enhanced potassium (40K) and possibly other activities.
Microscopic examination of chert artifacts from several widely separated Paleoindian locations in North America revealed a high density of entrance wounds and particles at depths that are evidence of high-velocity particle bombardment. Chondrules were identified visually; their presence necessarily indicates heating during high-speed entry into the atmosphere. The depth of penetration into the artifacts implies that the particles entered with substantial energy.16 Field simulations with control cherts for large particles (100-200 microns) suggest an entrance velocity greater than 0.4 km/s, and experiments at the National Superconducting Cyclotron Laboratory indicate that the smaller particles left tracks comparable to about 526 MeV iron ions (56Fe) in Gainey artifacts. Similar features are not observed in later-period prehistoric artifacts or in bedrock chert sources. Track angles were estimated visually; track densities were measured with a stage micrometer; track depths were found by adjusting the microscope focus through the track. These data are summarized in Table 1.
Track and particle data in Table 1 suggest that the total track volume (density times depth) is highest at the Michigan, Illinois, and Indiana sites and decreases in all directions from this region, consistent with a widespread catastrophe concentrated over the Great Lakes region. The nearly vertical direction of the tracks left by particle impacts at most sites suggests they came from a distant source.
Natural uranium, which is ubiquitous in cherts, has a 235U/238U isotopic ratio of 0.72 percent, which varies by less than 0.1 percent in natural sources.17 Significant variations in the isotopic ratio do not occur because of chemical processes; however, a thermal neutron bombardment depletes 235U and thus alters the ratio. Solar or galactic cosmic rays interacting with matter produce fast secondary neutrons that become thermalized by scattering from surrounding materials. Thermal neutrons see a target of large cross section (681 barns)A for destroying 235U, compared with a target of only 2.68 barns for neutron capture on 238U. Therefore, despite the low abundance of 235U, about 1.8 times as many 235U atoms are destroyed as 238U atoms by thermal neutrons.
If a large cosmic-ray bombardment impacted the earth and irradiated the prehistoric landscape with thermal neutrons, the 235U/238U ratio would be changed; 239Pu would be produced from neutron capture on 238U, followed by the decay of 239U. Neutrons colliding with nitrogen (1.83 barns) would create 14C in exactly the same way 14C is normally produced in the upper atmosphere, necessarily resetting the radiocarbon dates of any organic materials lying near the surface on the North American prehistoric landscape--including charcoals at Paleoindian sites--to younger values. 239Pu produced during the bombardment will also be partly destroyed by thermal neutrons with 1017 barn cross section. Assuming 239Pu doesn't mobilize, it will decay back to 235U (half-life 24,110 yr), partially restoring the normal abundance.
Paleoindian artifacts from Gainey, Leavitt, and Butler, and two later-period artifacts from the same geographic area of Michigan were analyzed for 235U content by gamma-ray counting at the Phoenix Memorial Laboratory, University of Michigan. They were compared with identical chert types representative of the source materials for the artifacts. Control samples were extracted from the inner core of the purest chert known to be utilized by prehistoric people. The Paleoindian artifacts contained about 78 percent as much 235U as the controls and later-period artifacts, suggesting substantial depletion. Depletion of 235U necessarily indicates that thermal neutrons impacted these artifacts and the surrounding prehistoric landscape.
Various artifacts, cherts, sediments, and a control sample containing about 0.2 percent uranium obtained from uraninite were sent to the McMaster University Centre for Neutron Activation Analysis to determine 235U concentration by delayed neutron counting and 238U concentration by activation analysis. These results are shown in Table 2. The 235U/238U ratios for all samples except the control deviated substantially from the expected ratio. McMaster ran additional calibration standards and has considerable expertise analyzing low-level uranium. This analysis was sensitive to a few ppb for 235U and 0.1-0.3 ppm for 238U, more than sufficient to precisely analyze the uranium-rich chert samples (0.7-163.5 ppm). Most samples were depleted in 235U, depletion increasing geographically from the southwest (Baker, Chuska chert, 17 percent) to the northeast (Upper Mercer, 77 percent), as shown in Table 2. This is consistent with cosmic rays focused towards northern latitudes by Earth's magnetic field. Only a very large thermal neutron flux, greater than 1020 n/cm2, could have depleted 235U at all locations.
Samples of unaltered flakes from Taylor and sediment originally adjacent to Gainey artifacts showed 235U enriched by 30 percent. Both samples were closely associated with the particles described above. The position of these samples appears to be related to the enrichment, which cannot be explained by thermal neutrons from the bombardment. To test this, we bathed another Taylor flake in 48-percent HF at 60°F for ten minutes to remove the outer 70 percent of the sample and the attached particles. Analysis showed the "inner" flake depleted in 235U by 20 percent, consistent with the other depleted cherts.
Samples of Gainey sediment and Taylor flakes were analyzed for plutonium by Nuclear Technology Services, Inc., of Roswell, Georgia, which specializes in radiochemistry using standard methodology. The plutonium, with an aliquot of NIST-traceable 242Pu added, was chemically separated on an anion exchange resin column and counted on an alpha-particle spectrometer. The 239Pu/238U ratios in both samples were approximately 10 ppb, vastly exceeding the expected ratio of 0.003 ppb.18 The results of this analysis are shown in Table 2.
Chert is a glass-like material highly impervious to penetration by any nuclear fallout that might also contribute 239Pu. We analyzed a long-exposed piece of Bayport chert by gamma-ray counting at the LBNL low-background facility for the presence of cesium-137 (137Cs), a key indicator of fallout (from nuclear testing), and found none. The B-C interface typically lies sufficiently deep that contamination by fallout is improbable. It is important to note that fallout cannot explain the depletion of 235U.
Since the depletion of 235U must have resulted from bombardment by thermal neutrons, the presence of 239Pu from irradiation of 238U is expected. The total thermal neutron flux required to produce the observed 239Pu concentration can be calculated from the relative concentrations of 239Pu (corrected for the decay) and 238U, and the thermal neutron-capture cross section for 238U. This neutron flux can then be used to estimate the amount of additional 14C that would have been produced in charcoal by neutrons colliding with 14N (14N cross section = 1.83 barns). The corrected radiocarbon age can then be estimated by comparing the current amount of 14C in the dated charcoals, determined from their measured radiocarbon age, with the amount of 14C that would have been produced by the bombardment. For these calculations we assume that charcoal contains 0.05 percent residual nitrogen19 and that initial 14C concentrations were the same as today (one 14C atom for 1012 12C atoms).
We derive a thermal neutron flux of c. 1017 n/cm2 at Gainey, which corresponds to an approximate date of 39,000 yr B.P. No radiocarbon date is available for the more southerly Taylor site, but for the conventional range of accepted Paleoindian dates the neutron flux would be c. 1016 n/cm2, giving a date of about 40,000 yr B.P. These calculations necessarily neglect differences in the neutron flux experienced by the dated charcoal and the artifacts, the effects of residual 239Pu from previous bombardments, and loss of 239Pu due to leaching from chert over time.
The neutron flux calculated from the 235U/238U ratio is more than 1000 times that implied by the level of 239Pu. Since 239Pu decays to 235U, partly restoring the natural abundance, it appears that substantial quantities of 239Pu have migrated out of the chert. This mobility is demonstrated at the Nevada Test Site, where plutonium, produced in nuclear tests conducted by the U.S. between 1956 and 1992, migrated 1.3 km.20 It has also been shown that atoms produced by radioactive decay or nuclear reaction become weakly bound to the parent material and pass more readily into solution than isotopes not affected.21 Both 239Pu and 235U are thus expected to be mobile, complicating any analysis. This is consistent with the enrichment of 235U in the two external samples where migrating 239Pu or 235U may have been trapped, thus enriching the relatively uranium-poor outer regions. Alternatively, excess 235U may have been carried in by the particles. Radiocarbon produced in situ by irradiation should also be mobile. If 14C is more mobile than 239Pu, then the dates calculated above should be decreased accordingly.
The 39,000 yr B.P. date proposed for the Gainey site is consistent with the prevailing opinion among many archaeologists about when the Americas were populated. It is also commensurate with dates for South American sites and with a Mousterian toolkit tradition that many see as the Paleoindian precursor. The proposed date for the Gainey site also falls closer in line with the radiocarbon date for a Lewisville, Texas, Paleoindian site of 26,610 ± 300 yr B.P.22,23 and radiocarbon dates as early as c. 20,000 yr B.P. for Meadowcroft Rockshelter.24 Since the Lewisville and Meadowcroft sites were likely exposed at the same time to thermal neutrons, we estimate that their dates should be reset to c. 55,000 yr B.P. and c. 45,000 yr B.P., respectively.
It is likely that Paleoindians occupied low latitudes during the full glacial and migrated to more northerly areas as the ice front retreated. Therefore the pattern of dates makes sense from the archaeologist's point of view. Dates for North American sites should generally be reset by up to 40,000 years, depending on latitude and overburden.
Geologists believe that before c. 15,000 yr B.P. the Wisconsinan glaciation covered the more northerly locations where Paleoindian sites have been found.25 The ice sheet would have shielded the landscape and any artifacts from an irradiation. (The Gainey thermoluminescence date of 12,400 yr B.P. is probably a result of the heat generated by the nuclear bombardment at that time, which would have reset the TL index to zero.) The modified dates for Paleoindian settlements suggest that the timetable for glacial advance sequences, strongly driven by conventional radiocarbon dates, should be revisited in light of the evidence presented here of much older occupations than previously thought."
A large nuclear bombardment should have left evidence elsewhere in the radiocarbon record. It is well known that radiocarbon dates are increasingly too young as we go back in time. The global Carbon Cycle suggests that 14C produced by cosmic rays would be rapidly dispersed in the large carbon reservoirs in the atmosphere, land, and oceans.26 We would expect to see a sudden increase in radiocarbon in the atmosphere that would be incorporated into plants and animals soon after the irradiation; after only a few years, most of the radiocarbon would move into the ocean reservoirs. The 14C level in the fossil record would reset to a higher value. The excess global radiocarbon would then decay with a half-life of 5730 years, which should be seen in the radiocarbon analysis of varved systems.
Fig. 2 plots 14C from the INTCAL98 radiocarbon age calibration data of Stuiver et al. for 15,000-0 yr B.P.27 and Icelandic marine sediment 14C data measured by Voelker et al. for 50,000-11,000 yr B.P.28 Excess 14C is indicated by the difference between the reported radiocarbon dates and actual dates. Sharp increases in 14C are apparent in the marine data at 40,000-43,000, 32,000-34,000 and c. 12,000 yr B.P These increases are coincident with geomagnetic excursionsB that occurred at about 12,000 (Gothenburg), 32,000 (Mono Lake), and 43,000 yr B.P. (Laschamp),29 when the reduced magnetic field would have made Earth especially vulnerable to cosmic ray bombardment. The interstitial radiocarbon data following the three excursions were numerically fit, assuming exponential decay plus a constant cosmic ray-produced component. The fitted half-lives of 5750 yr (37,000-34,000 yr B.P.), 6020 yr (32,000-16,000 yr B.P.), and 6120 yr (12,000-0 yr B.P.) are in good agreement with the expected value.
We also determined that contemporary radiocarbon contains about 7 percent residual 14C left over from the catastrophe. The constant cosmic ray production rate was about 34 percent higher for the Icelandic sediment than the INTCAL98 samples, perhaps implying higher cosmic ray rates farther north. Disregarding fluctuations in the data from variations in ocean temperatures and currents, the results are clearly consistent with the decay of radiocarbon following the three geomagnetic excursions.
In Fig. 2, the sharp drop in 14C activity before 41,000 yr B.P. suggests that global radiocarbon increased by about 45 percent at that time and by about 20 percent at 33,000 and 12,000 yr B.P The results are remarkably consistent with Vogel's comparison of 14C and U-Th dates of a stalagmite that indicates global radiocarbon increased about 75 percent from 30,000 to 40,000 yr B.P. and about 30 percent around 18,000 yr B.P.30
McHargue et al. found high levels of 10Be in Gulf of California marine sediments at 32,000 and 43,000 yr B.P.C that could not be explained by magnetic reversal alone and were attributed to cosmic rays, possibly from a supernova.29 The geomagnetic excursion at 12,500 yr B.P. coincides with the thermoluminescence date from Gainey, and additional evidence for a cosmic ray bombardment at that time is found in the increases of 10Be,31 Ca,32 and Mg32 in Greenland ice cores around 12,500 yr B.P. Similar increases are also seen in the data for NO3-, SO4-, Mg+, Cl-, K+, and Na+ ions in Greenland ice cores.33 This occurrence can be dated precisely to 12,500 ± 500 yr B.P., an average of the remarkably consistent concentration peak centroids in the Greenland ice core data. Significant increases at that time are not found in comparable data for the Antarctic, which indicates that the cosmic ray irradiation was centered in the Northern Hemisphere. Weak evidence of an occurrence at 12,500 yr B.P. is seen in the radiocarbon record for marine sediments near Venezuela,34 confirming that the cosmic ray bombardment was most severe in northern latitudes.
Lunar cosmogenic data also show evidence of increased solar cosmic ray activity at or before 20,000 yr B.P.35,36 although these data are not sensitive to earlier irradiation.
Sonett suggests that a single supernova would produce two or three shock waves, an initial forward shock and a pair of reverse shocks from the initial expansion and a reflected wave from the shell boundary of a more ancient supernova.39,40 Fig. 2 shows that each episode in a series produced a similar amount of atmospheric radiocarbon. The sun lies almost exactly in the center41 of the Local Bubble, believed to be the result of a past nearby supernova event. A candidate for the reverse shock wave is the supernova remnant North Polar Spur, with an estimated age of 75,000 years and a distance of 130 ± 75 parsecs (424 light years),42 conveniently located in the north sky from where it would have preferentially irradiated the Northern Hemisphere. Assuming the Taylor flux is average and 1,000 neutrons are produced per erg of gamma-ray energy,43 the catastrophe would have released about 1016 erg/cm2 (2 x 108 cal/cm2), corresponding to a solar flare of 1043 ergs or a gamma-flash of 1054 ergs from a supernova about 1 parsec away.
The geographical distribution of particle tracks, 235U depletion, and 239Pu concentration shown in Fig. 3 are quite consistent, although the particle tracks seem to be confined to a smaller geographic area. They indicate energy released over the northeastern sector of the U.S., with maximum energy at about 43° N, 85° W, the Michigan area of the Great Lakes region.
Wdowczyk and Wolfendale44 and Zook36 propose, based on the existing record of solar flare intensities, that solar flares as large as 3 x 1038 ergs should be expected every 100,000 years. Clark et al. estimate that supernovas release 1047-1050 ergs within 10 parsecs of Earth every 100 million years.45 Brackenridge suggests that a supernova impacted the earth in Paleoindian times.46 Damon et al. report evidence from the 14C tree ring record that SN1006, which occurred at a distance of 1300 parsecs, produced a neutron shower of 2 x 108 n/cm2.47 Castagnoli et al. report evidence of the past six nearby supernovae from the thermoluminescence record of Tyrrhenian sea sediments.48 Dar et al. suggest that a cosmic ray jet within 1000 parsec would produce 1012 muons/cm2 (greater than 3 x 109 eV) and 1010 protons and neutrons/cm 2 (greater than 106 eV) and deposit over 1012 erg/cm2 in the atmosphere every 100 million years.49 A cosmic ray jet is also predicted to produce heavy elements via the r-process and could be a source of 235U enriched up to 60 percent in uranium.
The Paleoindian catastrophe was large by standards of all suspected cosmic occurrences. Normal geomagnetic conditions would focus cosmic rays towards the magnetic poles, concentrating their severity in those regions. However, low magnetic field intensity during a geomagnetic excursion may have allowed excessive cosmic rays to strike northeastern North America. (Whether the geomagnetic excursion admitted cosmic radiation, or the radiation caused the excursion, is uncertain. Given our present state of knowledge, cause and effect in this instance are unclear.) The presence of a nearby small and dense interstellar cloud may explain the origin of the particle bombardment.50 The size of the initial catastrophe may be too large for a solar flare, but a sufficiently powerful nearby supernova or cosmic ray jet could account for it. It appears that the catastrophe initiated a sequence of events that may have included solar flares, impacts, and secondary cosmic ray bombardments.
The enormous energy released by the catastrophe at 12,500 yr B.P. could have heated the atmosphere to over 1000°C over Michigan, and the neutron flux at more northern locations would have melted considerable glacial ice. Radiation effects on plants and animals exposed to the cosmic rays would have been lethal, comparable to being irradiated in a 5-megawatt reactor more than 100 seconds.
The overall pattern of the catastrophe matches the pattern of mass extinction before Holocene times. The Western Hemisphere was more affected than the Eastern, North America more than South America, and eastern North America more than western North America.51,52,53 Extinction in the Great Lakes area was more rapid and pronounced than elsewhere. Larger animals were more affected than smaller ones, a pattern that conforms to the expectation that radiation exposure affects large bodies more than smaller ones.54,55 Sharp fluctuations of 14C in the Icelandic marine sediments at each geomagnetic excursion are interesting; because global carbon deposits in the ocean sediments at a rate of only about 0.0005 percent a year, a sudden increase in sediment 14C may reflect the rapid die-off of organisms that incorporated radiocarbon shortly after bombardment.
Massive radiation would be expected to cause major mutations in plant life. Maize probably evolved by macro-mutation at that time,55,56 and plant domestication of possibly mutated forms appears worldwide after the Late Glacial period. For example, there was a rapid transition from wild to domesticated grains in the Near East after the catastrophe.57
Much of what we assume about the Paleoindian period and the peopling of the Americas has been inferred from conventional radiocarbon chronology, which often conflicts with archaeological evidence. This work mandates that conventional radiocarbon dates be reinterpreted in light of hard terrestrial evidence of exposure of the radiocarbon samples to a cosmological catastrophe that affected vast areas of North America and beyond. A nuclear catastrophe can reset a group of unrelated artifacts to a common younger date, creating gaps and false episodes in the fossil record. Geographical variation and complicated overburdens may further confuse the interpretation. Scrutiny of Paleoindian artifacts and the North American paleolandscape, associated stratigraphic sediments, coupled with continued radiological investigations, may provide more evidence for the cosmic catastrophe and new clues to the origin of Paleoindians.
A good try I suspect but, ahem, I probably need to go find a better graphic. I'll work on that tomorrow; the toothpicks holding the eyelids open are starting weaken...
Ah, yes. Toothpicks for night owls, a great product. I too need to put my toothpicks away and get some sleep. Goodnight.
I'm a soil scientist, not a geologist, and when the subject turns to tectonism, we're venturing out of my field of competence. That's why I wanted to direct you to Helaine Markewich.
I can tell you -- and in this case I am very competent to answer -- that the sediments in the portions of the Wando formation that I worked on in Darlington, Marlboro, and Dillon Counties, in South Carolina, were deposited in a tidal-marsh enviroment. Those sediments are silty and very uniform, and the geomorphic surface there has virtually no topographic relief. In that part of the world, there isn't any other means of deposition that could produce such sediments. A terrestrial riverine system wouldn't do it..there would be too much spatial variation in soil texture, and there would be oxbow/paleochannel scars, splay deposits, lag deposits, etc. So the only question is the date of deposition, and that question is best answered by a geologist.
OOPS! After reviewing Owen's map, I realize I was confusing the Wando and the Soccastee formations. Owens gives a date of 200,000 ka for the Socastee. Your blue-line graph shows sea level at that date being lower than it is today, so the same conundrum still applies. (The Wando in that area of the Pee Dee is riverine).
There is a marine (littoral) facies of the Socastee formation that stretches to about 30 km inland from the present coastline that exhibits bays. The area I referenced earlier does not exhibit them. I think Owens interprets that area as a backswamp; I do not, for reasons I posted previously. But let us not lose sight of the original purpose of this discussion. Extrapolating from your sea-level graph, the Socastee must have been exposed subaerially somewhere between 200,000 and 180,000 years ago. That upper portion of the Socastee (in the Pee Dee region) does not exhibit bays, while immediately adjacent areas of the older Duplin formation do. If meteor or cometary impact at any time in the last 180,000 years had caused the bays, then bays should exist on the aforementioned area; but they do not.
This morning I pulled some old soil surveys to look for pre-Holocene surfaces on the Coastal Plain of SC that do not harbor Carolina Bays, or upon which they are exceedingly rare. I found such areas to be extensive; the lower (seaward) half of Dorchester County, most of Georgetown County, etc. Other areas (such as the lower portion of Marion County, for example) that presumably are of the same geologic age, have bays that are well expressed. This gave me an idea. I don't know exactly how I'll do it, or how long it will take, but I think I'll construct a map of the CP of SC that shows those surfaces, with a data overlay showing the geologic formations and their ages. I think it would be revealing.
Maybe not. I went back to have another look at the abstract(?) of the study I posted in #225. Ran across this little jewel I recall reading but dismissed(?) because I had found what I was looking for in the previous sentence. From that abstract:
It follows that the present elevation of the substage 5a shoreline cannot be explained by uplift or subsidence, and that relative sea-level positions for substage 5a along the South Carolina coast were approximately the same as MIS 5e or the present day.
You'll need to reread #225 to get the whole picture but essentially what this 2005 study concluded, amongst other things, is the 5a layer(ca. 82 ka.) and the 5e(ca. 130-116 ka.), were virtually the same. I don't quite know what to make of that given the "blue line" graph indicating otherwise, except that the blue line graph is possibly/likely wrong? IOW, your arguments are holding up, at least under this layman's scrutiny. Bravo........so far.
I think it would be revealing.
Can you post that this evening.......heh,heh. Seriously, I would love to see what you're able to come up with. I'm a novice graphic artiste so if I can be of assistance, please let me know. This is actually exciting............ahem.
"....Can you post that this evening...."
I think a very optimistic date for completion of this map might be 12-18 months. I do this sort of thing for a living (only with maps of much, much smaller area). I know what it entails. It might have to wait until I go back to grad school...if I decide to do so.
I think a very optimistic date for completion of this map might be 12-18 months.
Well gawrsh! I suppose yesterday is out of the question???
My computin' time is limited for a couple of days by grandbabies' visit, but I intend to go searching for additional maps/charts to see if I can come up with anything better than what I've posted.
"given the blue line graph indicating otherwise"
Actually it doesn't appear to me that the blue line graph does indicate otherwise. At 82ka the sea level was about -45m, from 130-116ya sea level was rising rapidly and passed through the -45m level, so depending on the precise date of the deposition of the 5e, or the area analyzed, they both could have been at the -45m level. If you have the graphic skills, perhaps you could stretch out the blue line graph on the horizontal to get a more precise fix on when the 130-116ya line crossed the same level as the -82ka line.
However, the point I was trying to make was, given the information I had, the bays could not have been formed by sea level fluctations prior to the present because they would now be under water. They would have to be exceptionally old otherwise; like something approaching ~120,000 years. BUT, the information I sortof bypassed in the study I posted indicates sea levels may have been approximately the same ~80,000 years ago as they are now. If I'm missing something(entirely possible), please point it out.
That said, I haven't been able to find any corroboration of that ~80,000 year old sea level, so who's to say??? This particular study is very recent(2005?) and may in fact be on the mark. I suppose time will tell.
This paper is the best I've seen on Carolina Bays. It mirrors my own thinking on the formation being due to hydrologic discharge, wave action loosening sands, and subsequent aeolian deflation during seasonal water level drop.
Price: US $ 30.00
What are you talking about? I just cliked on the link, and it opened up. I even copied it to my hard drive. If you'll PM me with your e-mail address, I'll send it to you as an attachment. It's a PDF file.
Now, I ran across another graphic I had to do some work on to get it sized to fit a standard(800 X 600 resolution) window. You'll notice re our previous discussion a possible(?) sea level "spike" at ~80,000ya. This more or less coincides with a previous argument about the age(s) of the bays being ~70,000ya. HOWEVER, the sea level indicated at that time was only ~30' above present level(s).
I know you have stated you believe the bays were formed within a marine environment, and if you're correct, something is amiss. What are the chances these marine sediments could have been deposited in existing bays by something like a "mega" tsunami? Or possibly some other process??? Or are there actual sediments deposited over a long period of time?
Anyway, getting late, so here's the graphic witout further comment. Original found HERE.
Is that anything like being formed by "hydrologic" processes???
I forwarded the paper on to you. Read it carefully, especially the last section wherein the authors propose a mechanism for bay formation.
Well, they offer up several possibilites(so I'm not sure which one you refer to), while excluding only one: a metorite/asteroid impact. Maybe they overlooked the possibility of a really big snowball. Some excerpts from the paper I found interesting as they relate to the discussion re bay formation:
Comparison between surface topography and expression of the Upland Unit surface using coring and elevation data reveal that the surface of the Upland Unit generally lies above the level of the basin interiors. The Upland Unit is typically flat-lying beneath the east and south portions of the bay rims and often rises to the west-northwest of the basins.I think they've nailed it.
Well, ok; this isn't speculation, opinion or conjecture, but some hard data apparently. It's not altogether clear from this statement, but it seems to imply there's a "bulge" towards the NW and a "depression" towards the SE in the Upland Unit layer within the bays. But it doesn't appear to help in the how or when department.
The bays themselves may occupy pre-existing depressions in the Upland Unit surface, but also reflect at least some erosion of the Upland Unit surface. Moreover, the regional sand sheet thickens towards the southeast sides of the bays, but is largely absent from within bays. It is possible, therefore, that excavation of the sand sheet after emplacement of the Upland Unit created the present bay depressions and that subsequent deposition of the excavated sands formed the observed bay rims. This statement is supported by significant differences in the age and degree of pedogenic development between the Upland Unit and bay rim and interior deposits that have been cored/excavated and dated (Brooks et al., 1996).
The point of this statement was lost on me. In fact, it doesn't make any sense to me.
Processes including dissolution, meteorite impact, and eolian deflation have been proposed to account for initial formation of the depressions (e.g., Johnson, 1942; Prouty, 1952; Thorn, 1970; Kaczorowski, 1977; Colquhoun, 1982; Blair, 1986) sometime during the period ~ 10-100 ka (Schalles et al., 1989). Investigations have been impeded, however, by the subdued topographic expression of the bays, the dense vegetative cover (e.g., Knight et al., 1989; Richardson and Gibbons, 1993), typically extensive historic era modification (Van Doren, 1928; Brooks et al., 1996; Kirkman et al., 1996), and a paucity of preserved organic material for accurately dating the formation. As a result, it remains uncertain whether some or all bays share a common age or how the present expression reflects the processes responsible for initial formation of the depressions versus subsequent modification. The GPR and supporting data presented herein provide clues to the subsequent modification of the bays that resulted in a common topographic expression, but does not specifically address the initial formation of the depressions.
Although not specifically addressed in the current study, a number of processes could account for generation of the initial basin that eventually evolves into a Carolina Bay. These processes might include, among others, spring activity, solution, deflation, abandonment of channel segments, and/or excavation of original relief on the surface of the Upland Unit. No evidence was found to support basin formation by meteorite impact as suggested by Johnson(1942), and others.
Stratigraphy from the surface down in the vicinity of all four bays is similar (to first-order) and begins with a thin, regional, medium-to-coarse-grained sand sheet (typically ~ 1-3 m thick) that exhibits minimal pedogenic alteration, but whose emplacement likely predates bay formation (Willoughby, 1997).
So, the sand was there before the bays formed??? How long? If the bays are of differing ages(thousands of years even?), it just seems odd to me there's still a certain consistency to it all.
Maybe for you ;^)
placemarker, just a marker