Alternate title: Carolina Bays are as antithetical to impact craters as any dents in the ground possibly could be.
Guest essay by David Middleton
In my previous essay, we discussed the differences between uniformitarian geology and drawing cartoons on Google Earth images. Several commentators brought up the “Carolina Bays” in defense of crater hunter cartoonists. Carolina Bays have also been cited as evidence for the Younger Dryas Impact Hypothesis (YDIH). Since I was already in the process of composing a post on Carolina Bays, my second post on uniformitarian
impact craters will focus on Carolina Bays and other obviously wind-oriented geomorphological features.
Please note: This post is not about the pros and cons of the YDIH. Much of the evidence presented supporting the YDIH is interesting and some of it might even be compelling. This post is about one aspect of the evidence put forward on behalf of the YDIH: the Carolina Bays. As “evidence” of the YDIH, the Carolina Bays might even be worse than amateur crater hunters drawing cartoons on Google Earth images. I am happy to entertain questions and even genuine debate about the geomorphology, stratigraphy and other geological/geophysical aspects of the Carolina Bays and related features. Comments that start out with, “But how can you explain [the black mat, nanodiamonds, microspherules, the Terminal Pleistocene extinctions, Clovis culture or the lack thereof, biomass burning, etc.] will receive the following reply:
Non sequitur = Does not follow from. The Carolina Bays being impact craters does not follow from other possible evidence for the YDIH.
Please also note: This is a long post and I just made it longer with the preceding paragraph. If you don’t want to read it… then don’t. If you don’t read it, but insist on commenting, my reply will unlikely be courteous… Particularly if the comment is along the lines of “TL DNR.” These sorts of comments will generally receive this sort of reply:
The Carolina Bays: Not Impact Features
First, the Arm Waving “Science”
Firestone et al. 2007 cited the Carolina Bays as potential evidence for the YDIH.
The other sample sites were in and around 15 Carolina Bays, a group of ≈500,000 elliptical lakes, wetlands, and depressions that are up to ≈10 km long and located on the Atlantic Coastal Plain (SI Fig. 7). We sampled these sites because Melton, Schriever (20), and Prouty (21) proposed linking them to an ET impact in northern North America. However, some Bay dates are reported to be >38 ka (22), older than the proposed date for the YD event.
Pieces up to several cm in diameter (Fig. 4) were found associated with the YDB and Bays, and their glassy texture suggests melting during formation, with some fragments grading into charcoal. Continuous flow isotope ratio MS analysis of the glass-like carbon from Carolina Bay M33 reveals a composition mainly of C (71%) and O (14%). Analysis by 13C NMR of the glass-like carbon from Bay M33 finds it to be 87 at.% (atomic percent) aromatic, 9 at.% aliphatic, 2 at.% carboxyl, and 2 at.% ether, and the same sample contains nanodiamonds, which are inferred to be impact-related material (see SI Fig. 11). Concentrations range from 0.01 to 16 g/kg in 15 of 15 Bays and at nine of nine Clovis-age sites in the YDB, as well as sometimes in the black mat, presumably as reworked material. Somewhat similar pieces were found in four modern forest fires studied (see SI Text, “Research Sites”).
Age of the YDB.
The YDB at the 10 Clovis- and equivalent-age sites has been well dated to ≈12.9 ka, but the reported ages of the Carolina Bays vary. However, the sediment from 15 Carolina Bays studied contain peaks in the same markers (magnetic grains, microspherules, Ir, charcoal, carbon spherules, and glass-like carbon) as in the YDB at the nearby Topper Clovis site, where this assemblage was observed only in the YDB in sediments dating back >55 ka. Therefore, it appears that the Bay markers are identical to those found elsewhere in the YDB layers that date to 12.9 ka. Although the Bays have long been proposed as impact features, they have remained controversial, in part because of a perceived absence of ET-related materials. Although we now report that Bay sediments contain impact-related markers, we cannot yet determine whether any Bays were or were not formed by the YD event.
“Melton, Schriever (20), and Prouty (21)” are from 1933 and 1952 respectively. Frey (22) is from 1955. No one noticed the Carolina Bays as a distinct morphological feature prior to the advent of aerial photography.
↵ Melton FA, Schriever W (1933) J Geol 41:52–56.Google Scholar
↵ Prouty WF (1952) Bull GSA 63:167–224.CrossRefGoogle Scholar
↵ Frey DJ (1955) Ecology 36(4):762–763.CrossRefGoogle Scholar
When Carolina Bays were observed on aerial photos, the first hypothesis was that they were the result of a series of meteoric impacts, because they kind of look like craters. Subsequent work has found no evidence whatsoever that the shallow depressions were the result of impacts; and all of the age estimates make the Carolina Bays far older than the Younger Dryas. We will revisit the geology and age determinations of the Carolina Bays later in this essay.
This really struck me…
The other sample sites were in and around 15 Carolina Bays…
“In and around”? How about location maps? Lat/Lon or some other location data?
They cite the two papers from 60-80 years ago as a basis to investigate the Carolina Bays as potential impact sites, ignore everything published since 1955 and conclude with:
Although we now report that Bay sediments contain impact-related markers, we cannot yet determine whether any Bays were or were not formed by the YD event.
Of course you can “determine whether any Bays were or were not formed by the YD event, ” because there is no evidence to support this idea. Even if their “impact-related markers” constituted evidence for the YDIH, an air-bursting bolide*, 12,900 years ago would have showered the Carolina Bays with “impact-related” materials.
*Yes, I know that “air-bursting bolide” is redundant.
The cometary impact hypothesis of the origin of the bays was popular among earth scientists of the 1940s and 50s. After considerable debate and research, geologists determined the depressions were both too shallow and lacking in any evidence for them to be impact features. Reports of magnetic anomalies turned out not to show consistency across the sites. There were no meteorite fragments, shatter cones or planar deformation features. None of the necessary evidence for hypervelocity impacts was found. The conclusion was to reject the hypothesis that the Carolina Bays were created by impacts of asteroids or comets (Rajmon 2009).
A new type of extraterrestrial impact hypothesis was proposed as the result of interest by both popular writers and professional geologists in the possibility of a terminal Pleistocene extraterrestrial impacts, including the Younger Dryas impact hypothesis. It said that the Carolina Bays were created by a low density comet exploding above or impacting on the Laurentide ice sheet about 12,900 years ago. However, this idea has been discredited by OSL dating of the rims of the Carolina bays, paleoenvironmental records obtained from cores of Carolina bay sediments, and other research that shows that many of them are as old as, or older than, 60,000 to 140,000 BP.
The Wikipedia entry is surprisingly quite good… Probably because there’s no Gorebal Warming or any other left-wing environmental aspect to the Carolina Bays and/or the YDIH.
From Firestone et al., 2007 SI Text…
Carolina Bays. The Carolina Bays are a group of »500,000 highly elliptical and often overlapping depressions scattered throughout the Atlantic Coastal Plain from New Jersey to Alabama (see SI Fig. 7). They range from ≈50 m to ≈10 km in length (10) and are up to ≈15 m deep with their parallel long axes oriented predominately to the northwest. The Bays have poorly stratified, sandy, elevated rims (up to 7 m) that often are higher to the southeast. All of the Bay rims examined were found to have, throughout their entire 1.5- to 5-m sandy rims, a typical assemblage of YDB markers (magnetic grains, magnetic microspherules, Ir, charcoal, soot, glass-like carbon, nanodiamonds, carbon spherules, and fullerenes with 3He). In Howard Bay, markers were concentrated throughout the rim, as well as in a discrete layer (15 cm thick) located 4 m deep at the base of the basin fill and containing peaks in magnetic microspherules and magnetic grains that are enriched in Ir (15 ppb), along with peaks in charcoal, carbon spherules, and glass-like carbon. In two Bay-lakes, Mattamuskeet and Phelps, glass-like carbon and peaks in magnetic grains (16-17 g/kg) were found ≈4 m below the water surface and 3 m deep in sediment that is younger than a marine shell hash that dates to the ocean highstand of the previous interglacial.
Modern Fires. Four recent modern sites were surface-sampled. Two were taken from forest underbrush fires in North Carolina that burned near Holly Grove in 2006 and Ft. Bragg in 2007. Trees mainly were yellow pine mixed with oak. There was no evidence of carbon spherules and only limited evidence of glass-like carbon, which usually was fused onto much larger pieces of charcoal. The glass-like carbon did not form on oak charcoal, being visible only on pine charcoal, where it appears to have formed by combustion of highly flammable pine resin.
Two surface samples also were taken from recent modern fires in Arizona; they were the Walker fire, which was a forest underbrush fire in 2007 and the Indian Creek Fire near Prescott in 2002, which was an intense crown fire. Trees mainly were Ponderosa pine and other species of yellow pine. Only the crown fire produced carbon spherules, which were abundant (≈200 per kg of surface sediment) and appeared indistinguishable from those at Clovis sample sites. Both sites produced glass-like carbon fused onto pine charcoal.
All told, Firestone et al., 2007 wasn’t batschist crazy. There was a fair amount of arm waving; but they didn’t really drift off into Art Bell land.
Next, the Science Fiction
Cue the theme from Twilight Zone. Firestone 2009 was essentially a variation of Firestone et al., 2007, with a few bits of SyFy tossed in,
West also investigated sediment from 15 Carolina Bays, elliptical depressions found along the Atlantic coast from New England to Florida (Eyton and Parkhurst, 1975), whose parallel major axes point towards either the Great Lakes or Hudson Bay as seen in Fig. 3. Similar bays have tentatively been identified in Texas, New Mexico, Kansas, and Nebraska (Kuzilla, 1988) although they are far less common in this region. Their major axes also point towards the Great Lakes. The formation of the Carolina Bays was originally ascribed to meteor impacts (Melton and Schriever, 1933) but when no meteorites were found they were variously ascribed to marine, eolian, or other terrestrial processes.
West found abundant microspherules, carbon spherules, glass-like carbon, charcoal, Fullerenes, and soot throughout the Carolina Bays but not beneath them as shown in Fig. 4. Outside of the Bays these markers were only found only in the YDB layer as in other Clovis-age sites.
Figure 3. The Carolina Bays are »500,000 elliptical, shallow lakes, wetlands, and depressions, up to »10 km long, with parallel major axes (see inset) pointing toward the Great Lakes or Hudson Bay. Similar features found in fewer numbers in the plains states also point towards the Great Lakes. These bays were not apparent topographical features until the advent of aerial photography.
Figure 4. At two sandy Carolina Bays magnetic grains, carbon spherules and glass-like carbon (vitreous charcoal) are found distributed throughout the Bay sediment.
Glass-like Carbon: Pieces of glass-like carbon, up to several cm in diameter, have been found in the YDB layer at most sites with concentrations in sediment ranging from 0.01- 16 g/kg. Glass-like carbon doesn’t exist naturally and the man-made varieties are shown to have a structure similar to Fullerenes (Harris, 2004). Nanodiamonds were found in a Carolina Bay sample. The PGAA analysis of glass-like carbon sample from the Carolina Bays is shown in Table 2. It is 90 wt.% C and analysis by 13C NMR indicated that it is 87 at.% aromatic, 9 at.% aliphatic, 2 at.% carboxyl, and 2 at.% ether. PGAA shows that the sample contains significant amounts of SiO2 (4.8 wt.%) and Al2O3 (1.0 wt.%), probably from contamination by YDB sediment. A significant quantity of nitrogen (0.66 wt.%) and trace amounts of TiO2 (0.067 wt.%) and FeO (0.08 wt.%) were found. The ratio of TiO2/FeO=0.8 is comparable to that found in magnetic grains and microspherules.
A sample from the Carolina Bays shown in Fig.8 was found to grade from glass-like carbon at one end to wood on the other. The wood was identified by Alex Wiedenhoft (private communication) as Yellow Pine, a species native to the Carolinas at the time of the YDB. Glass-like carbon can be produced by the thermal decomposition of cellulose at 3200 °C (Kaburagi et al. 2005) but such high temperatures would normally consume the entire tree. The composition of this sample is consistent with a tree that was impacted by a rapidly moving, high-temperature shockwave that produced glass-like carbon on only one side as it passed. The anoxic conditions following the shock wave would have stopped further burning.
Figure 8. A carbon sample from a Carolina Bay that varies from the shiny, melted appearance of glass-like carbon at the top to Yellow Pine on the bottom. This can occur if the sample were exposed to the 3200 ° shockwave that “melted” one side of a tree but failed to destroy it entirely due to anoxic conditions behind the shockwave.
Radiocarbon dates for six glass-like carbon samples from the Carolina Bays are summarized in Table 2. Dates range from 685-8455 yr BP, much younger than the age inferred from their statigraphic context. The discrepancies are not as large as for the carbon spherules suggesting that these samples are predominantly composed of tree cellulose with additional 14C-rich carbon mixed into the glass-like carbon by the shockwave.
Radiocarbon dates for six glass-like carbon samples from the Carolina Bays are summarized in Table 2 [Table 3?]. Dates range from 685-8455 yr BP, much younger than the age inferred from their statigraphic context. The discrepancies are not as large as for the carbon spherules suggesting that these samples are predominantly composed of tree cellulose with additional 14C-rich carbon mixed into the glass-like carbon by the shockwave.
The 14C dates for the “six glass-like carbon samples from the Carolina Bays” range from 685-8,455 years before present (1950 AD). Even after calibrating the 14C dates to calendar years, the bits of burnt wood are way too young to be evidence for the YDIH.
|14C ky||Calendar ky|
In Firestone et al., 2007 they allowed for the possibility that the glassy bits of burnt wood could have been the product of forest fires. Two years later and flying solo, the glassy bits of wood had been “exposed to the 3200 ° shockwave that “melted” one side of a tree but failed to destroy it entirely due to anoxic conditions behind the shockwave.” °F or °C? Not that it matters.
Even if the glassy bits of wood were the result of some sort of air-bursting bolide, it doesn’t constitute evidence for the Carolina Bays being impact features, much less evidence that they were suddenly created at the Younger Dryas Boundary (YDB). The Bay ridges range from 27 ka to well over 100 ka. The basin fill can be as young as a few hundred years old. Stuff falling out of the sky 12,900 years ago could have easily been buried in Carolina Bays, even in the ridges.
This has become one of the most oft-repeated memes among YDIH proponents:
West also investigated sediment from 15 Carolina Bays, elliptical depressions found along the Atlantic coast from New England to Florida (Eyton and Parkhurst, 1975), whose parallel major axes point towards either the Great Lakes or Hudson Bay as seen in Fig. 3.
It’s often accompanied by variations of this image:
The wrongness of the image above is spectacular.
Carolina Bays and Similar Features Do Not Point at the Great Lakes or Hudson Bay
There are several recent detailed USGS surficial geology quadrangles in which Carolina Bays and comparable features have been mapped in detail. Almost none of the “parallel major axes point towards either the Great Lakes or Hudson Bay.” If the major axes were parallel (as many are in the Carolinas), they couldn’t all point at any common feature.
These examples are from the Surficial Geologic Map of the Elizabethtown 30′ × 60′ Quadrangle, North Carolina (Weems et al., 2011).
Zooming in on one of the more prominent bays:
Big Juniper Bay and cross section B-B’…
LiDAR images yield a similar picture:
The Carolina Bays have a western cousin: Nebraska’s Rainwater Basins; where we have a brand new, detailed map of a series of Rainwater Basins: Surficial Geology of the Fairmont 7.5 Minute Quadrangle, Nebraska (Hanson et al., 2017).
Put it all to together and we have:
I could pull geologic maps all day long, and the results would only get worse for the Carolina Bays being evidence for the YDIH. Which makes me wonder if Firestone ever looked at any geologic maps.
The older, lower resolution Quaternary geologic map of the Savannah 4 degrees x 6 degrees quadrangle (Colquhoun et al., 1987) covers all of South Carolina and much of Georgia and North Carolina. While most of the Carolina Bays trend from NW-SE, some trend from N-S, some aren’t even particularly elliptical.
Why Would Anyone Expect Impact Craters to be Elliptical?
Why are impact craters always round? Most incoming objects must strike at some angle from vertical, so why don’t the majority of impact sites have elongated, teardrop shapes?
Gregory A. Lyzenga, associate professor of physics at Harvey Mudd College, replies:
“When geologists and astronomers first recognized that lunar and terrestrial craters were produced by impacts, they surmised that much of the impacting body might be found still buried beneath the surface of the crater floor. (Much wasted effort was expended to locate a huge, buried nickel-iron meteorite believed to rest under the famous Barringer meteor crater near Winslow, Ariz.) Much later, however, scientists realized that at typical solar system velocities–several to tens of kilometers per second–any impacting body must be completely vaporized when it hits.
“At the moment an asteroid collides with a planet, there is an explosive release of the asteroid’s huge kinetic energy. The energy is very abruptly deposited at what amounts to a single point in the planet’s crust. This sudden, focused release resembles more than anything else the detonation of an extremely powerful bomb. As in the case of a bomb explosion, the shape of the resulting crater is round: ejecta is thrown equally in all directions regardless of the direction from which the bomb may have arrived.
“This behavior may seem at odds with our daily experience of throwing rocks into a sandbox or mud, because in those cases the shape and size of the ‘crater’ is dominated by the physical dimensions of the rigid impactor. In the case of astronomical impacts, though, the physical shape and direction of approach of the meteorite is insignificant compared with the tremendous kinetic energy that it carries.
“Only roughly 5% of all craters (greater than 1 km in diameter) observed on Mars, Venus, and the Moon have elliptical shapes with an ellipticity of 1.1 or greater”…
Planetary and Space Science
Volume 135, January 2017, Pages 27-36
Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon
Tatsuhiro Michikami, Axel Hagermann, Tomokatsu Morota, Junichi Haruyama, Sunao Hasegawa
Only roughly 5% of all craters (greater than 1 km in diameter) observed on Mars, Venus, and the Moon have elliptical shapes with an ellipticity of 1.1 or greater, where the crater’s ellipticity is defined as the ratio of its maximum and minimum rim-to-rim diameters (Bottke et al., 2000). Although elliptical impact craters may be rare on solid-surface planetary bodies, a better understanding of the formation of elliptical craters would contribute to our overall understanding of impact cratering. For instance, it is well-known that crater size depends on impact angle (e.g., Elbeshausen et al., 2009).
Do any of the simulated craters above look even remotely like Carolina Bay features? Many Carolina Bay features are very smooth ellipses, often with ellipticities >1.5.
“Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces.”
The transition from circular to elliptical impact craters
Dirk Elbeshausen, Kai Wünnemann, Gareth S. Collins
First published: 15 October 2013 https://doi.org/10.1002/2013JE004477
 Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three‐dimensional (3‐D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock‐induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum‐controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.
 The vast majority of impact craters on planetary surfaces, moons, and asteroids are circular in plan. Only 5% of the crater record—at least on Mars, Moon, and Venus—shows an elliptical morphology [see e.g., Schultz and Lutz‐Garihan, 1982; Bottke et al., 2000]. Elliptical craters result from impacts that occur at a very shallow angle of incidence. If a cosmic object (projectile) strikes the planetary surface (target) at an angle smaller than a certain threshold angle, the resulting crater shape deviates from a circular symmetry and becomes elongated in the direction of impact. The ellipticity of the crater increases with decreasing impact angle [Gault and Wedekind, 1978]. From the point of view of celestial mechanics, moderately oblique impacts are the norm and the most likely angle of incidence is 45°. Half of all impacts occur at even shallower angles and only ~5% of all impacts strike the target at an angle of 12° or less [see Gilbert, 1893; Shoemaker, 1962]. Accordingly, Bottke et al.  concluded that the threshold angle to form elliptical craters must be 12° in order to match the observational record that 5% of all craters have an elliptical morphology.
 More detailed studies both by laboratory experiments [Gault and Wedekind, 1978; Christiansen et al., 1993; Burchell and Mackay, 1998] and numerical simulations [Collins et al., 2011] revealed that the angle below which elliptical craters form, the so‐called critical angle, depends on the properties of the target material. Based on numerical models of oblique crater formation and results from laboratory experiments, Collins et al.  proposed that the critical angle for the formation of elliptical craters is a function of cratering efficiency, here defined as the ratio of crater and projectile diameter.
 Ellipticity ε is defined as the length of a crater divided by its width. To distinguish a circular from an elliptical shape, some sort of threshold value has to be defined for ε. This is a relatively arbitrary choice; however, to stay in line with previous studies on this subject, we follow the definition by Bottke et al. , who consider craters as elliptical if the ellipticity ε is larger or equal to 1.1.
The Pleistocene substratum of Carolina Bays and Rainwater Basins is largely unconsolidated sand. Even Pleistocene “sandstone” buried at depths of 20,000′ in the Gulf of Mexico tends to be poorly consolidated (friable in geologeese). Sand control is a major well completion issue in the Gulf of Mexico: Producing the oil & gas without filling up the wellbore with sand is often a challenge.
Herndon Bay is particularly elliptical. If we assume that the substratum is poorly consolidated sand, we find:
- Cohesion of sand = 0.0 MPa
- Herndon Bay ellipticity = 1.8
The impact angle would have had to have been about 1-2° and the meteoric object would have had to have impacted intact to generate such an elliptical crater. I don’t think there is an adequate adjective to tack onto “unlikely” to cover this bit. The next bit gets better.
There are 190 documented, confirmed impact craters on Earth (well, 189 if you don’t count Upheaval Dome). There are possibly 500,000 Carolina Bay type features on Earth, probably many more.
If only 5% of craters on Mars, the Moon, and Venus exhibit an elliptical morphology, generally defined as an ellipticity >1.1… What are the odds that 99.96% of the craters on Earth would be elliptical, with ellipticities often exceeding 1.5?
Now that we’ve demonstrated that Carolina Bays and similar features aren’t mysteriously pointing at the Great Lakes or Hudson Bay, were formed thousands of years prior to the YDB, that elliptical craters are rare and that it would be almost impossible for Carolina Bays to be elliptical impact craters, let’s look at one of the most well-documented Carolina Bays.
I highly recommend that you read THE_QUATERNARY_EVOLUTION_OF_HERNDON_BAY.
The full text is available. It’s the most thorough geological and geophysical investigation of a Carolina Bay feature I have been able to locate.
Geological investigations of Herndon Bay, a Carolina bay in the Coastal Plain of North Carolina (USA), provide evidence for rapid basin scour and migration during Marine Isotope Stage (MIS) 3 of the late Pleistocene. LiDAR data show a regressive sequence of sand rims that partially backfill the remnant older portions of the bay, with evidence for basin migration more than 600 meters to the northwest. Basin migration was punctuated by periods of stability and construction of a regressive sequence of sand rims with basal muddy sands incorporated into the oldest rims. Single grain OSL ages place the initial formation of each sand rim from oldest to most recent as ca. 36.7 +/- 4.1, 29.6 +/- 3.1, and 27.2 +/- 2.8 ka. These ages indicate that migration and rim construction was coincident with MIS 3 through early MIS 2, a time of rapid oscillations in climate. The fact that Carolina bay basins can migrate, yet maintain their characteristic shape and orientation, demonstrates that Carolina bays are oriented lakes that evolved over time through lacustrine and eolian processes. This research also indicates that Carolina bays can respond rapidly during periods of climatic transition such as Dansgaard-Oeschger or Heinrich events.
Figure 3 from Moore et al., 2016:Cores were taken from the the four ridges (HB1, HB2, HB3 and HB4). The latitude and longitude of each core is clearly identified and the depth from which the three Optically-Stimulated Luminescence (OSL) samples were extracted are clearly documented. The sandy rims become progressively younger as the bay migrated from SE to NW. It’s kind of difficult for impact craters to migrate.
The youngest sandy rim, HB1, was deposited about 15,000 years before the Younger Dryas.It’s funny… Since the mid-1990’s, Optically-Stimulated Luminescence (OSL) has literally revolutionized Quaternary geology and geoarchaeology.
What is OSL?
OSL is an acronym for Optically-Stimulated Luminescence.
Optically-Stimulated Luminescence is a late Quaternary dating technique used to date the last time quartz sediment was exposed to light. As sediment is transported by wind, water, or ice, it is exposed to sunlight and zeroed of any previous luminescence signal. Once this sediment is deposited and subsequently buried, it is removed from light and is exposed to low levels of natural radiation in the surrounding sediment. Through geologic time, quartz minerals accumulate a luminescence signal as ionizing radiation excites electrons within parent nuclei in the crystal lattice. A certain percent of the freed electrons become trapped in defects or holes in the crystal lattice of the quartz sand grain (referred to as luminescent centers) and accumulate over time (Aitken, 1998).
I wonder how many detractors of uniformitarianism also reject OSL… hmmm?
Oriented Lakes and Other Wind-Oriented Features
Maybe these impact craters are pointing at Tunguska? (/Sarc)
The oriented lakes of Tuktoyaktuk Peninsula, Western Arctic Coast, Canada: a GIS‐based analysis
M. M. Côté C. R. Burn
First published: 25 March 2002
The orientation, size and shape of 578 lakes on Tuktoyaktuk Peninsula were obtained from 1 : 250 000 Canadian National Topographic Survey map sheets, using ArcView geographic information system. These lakes are outside the glacial limits in a tundra plain with <15m relief. The lakes range from 20 to 1900 ha, and have mean orientation N07 °E, with standard error 1.6°. The maps show 145 former lake basins, with lakes inset in 130 of these. The mean orientations of the basins and inset lakes are not statistically different from each other or the general population. Several theories have been proposed for the origin of the oriented lakes, and one theory attributes the orientation to cross winds establishing currents that preferentially erode the ends of the lakes.
Or, maybe, oriented lacustrine features are fairly common occurrences…
Growth Secrets of Alaska’s Mysterious Field of Lakes
Mari N. Jensen
June 27, 2005
The thousands of oval lakes that dot Alaska’s North Slope are some of the fastest-growing lakes on the planet. Ranging in size from puddles to more than 15 miles in length, the lakes have expanded at rates up to 15 feet per year, year in and year out for thousands of years. The lakes are shaped like elongated eggs with the skinny ends pointing northwest.
How the lakes grow so fast, why they’re oriented in the same direction and what gives them their odd shape has puzzled geologists for decades. The field of lakes covers an area twice the size of Massachusetts, and the lakes are unusual enough to have their own name: oriented thaw lakes.
“Lakes come in all sizes and shapes, but they’re rarely oriented in the same direction,” said Jon Pelletier, an assistant professor of geosciences at The University of Arizona in Tucson.
Now Pelletier has proposed a new explanation for the orientation, shape and speed of growth of oriented thaw lakes. The lakes’ unusual characteristics result from seasonal slumping of the banks when the permafrost thaws abruptly, he said. The lakes grow when rapid warming melts a lake’s frozen bank, and the soggy soil loses its strength and slides into the water. Such lakes are found in the permafrost zone in Alaska, northern Canada and northern Russia.
Previous explanations for the water bodies’ shape and orientation invoked wind-driven lake circulation and erosion by waves.
Even though the “thousands of oval lakes that dot Alaska’s North Slope” are oriented perpendicular to the prevailing wind direction, Pelletier’s model indicates that the cause is seasonal permafrost melting. Whether wind-driven or permafrost driven, they aren’t impact driven.
The fact is that the cause of oriented lake features is not known with any degree of certainty. However, meteoric impacts don’t fit any of the observations. It does appear that wind patterns play a significant role; but other local factors are also very important.
Just for grins, here’s another wind-oriented feature:
Pointing at the Great Lakes? Unfortunately, no. The Norphlet points at Minneapolis…
The Norphlet is an Upper Jurassic formation deposited under very arid conditions. The Upper Norphlet is eolian and characterized by “Seif” dunes. Under Mobile Bay, the Norphlet is at a depth of about 20,000’… Yet, through the miracle of uniformitarian geology, it was relatively easy to characterize the Norphlet as an eolian sequence, rather than impact craters or Gulf of Mexican Ignimbrites.
Addendum 1: Herndon Bay GPR Transect
Moore et al., 2016 included a ground penetrating radar (GPR) transect. I did not discuss this in detail in the post largely because I was trying to directly reproduce as little of their paper as I could. There has been some confusion in the comments about what GPR transects are and what they reveal about Herndon Bay.
GPR data are acquired in time, not depth. The data are recorded and processed relative to the ground surface. In order to present the GPR transect as something resembling a geologic cross section, it has to be surface normalized or topographically corrected.
Topographic Correction of GPR Profiles Based on Laser Data
Data obtained by GPR (Ground Penetrating Radar) are displayed as a continuous cross-sectional profile. Surface, generally, is not flat. As a result, the image becomes distorted and the depth calculated from the surface no longer represents the true and exact position of electrically distinctive layers and objects in materials. In order to get real geologic cross section, GPR data must be corrected. This is paper discusses a new method using the color point cloud data obtained by a Vehicle-borne laser scanning system to compensate for elevation fluctuate. Elevation profile can be extracted from topographic data of survey site acquired using laser scanner, which can then be used to offset the error of GPR data. Through the discrete points in the survey line, each trace of the profile has its own elevation value showing a vertical difference from the reference profile with maximum elevation, then time shifts value of traces vertical offset versus the reference trace of profile can be obtained. At last, the results of topographic correction for radargrams that look extremely like the real geologic cross section are presented, which allows us to get a better profile interpretation and position of the objects and layers in the subsurface.
The GPR transect in Moore et al., was also corrected for terrain (surface normalization) using LiDAR.
The data were acquired with a 300 ns recording window. This is approximately 5-9 m. The depths on the GPR transect are gross approximations due to the variability of the velocity field. While a surface normalized GRP transect looks like a geologic cross section, it is not. It is a geophysical approximation of a geologic cross section.
On depth sections, the top of the Black Creek Group mud facies is essentially flat from the extant basin to second oldest rim. The mud facies under the oldest rim is about 1 m higher than the rest of the rims and basin.
Geoprobe core data reveal wave ravinement into the underlying Cretaceous muds, with muddy sand incorporated throughout the oldest sand rims during the initial period of high-energy lacustrine processes (Figure 4). Coring of sand rims demonstrates the scoured nature of the underlying mud facies, with an elevation drop between the older remnant basin surface to the east and the more recent basin due to scour associated with the initial period of migration and sand rim construction (Figures 3c and 4).
The fact that Carolina bays can migrate, yet maintain their characteristic oval shape, orientation, and rim sequences demonstrates that these landforms are oriented lakes shaped by lacustrine and eolian processes. Clear evidence of basin scour into the underlying Cretaceous sandy mud, reveals that Carolina bays are capable of migrating while backfilling remnant basins with a regressive sequence of paleoshoreline deposits as the position of the basin margin changes through time.
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