Inferred Orientations of the Carolina Bays: Do They Triangulate to a Unique Source?

Evaluating Carolina Bays As Surface Features In A Distal Ejecta Blanket: Geophysical Flow Analysis Predicts Bay Orientation,
EnablesTriangulation To Causal Impact Site

Short Tile: Evaluating Carolina Bays As Surface Features In A Distal Ejecta Blanket

Michael E. Davias1 and Jeanette Gilbride2

Corresponding author address: Michael Davias, Cintos Research, 1381 Hope Street, Stamford, CT 06907 e-mail:

1Cintos Research (unaffiliated)

2North Carolina State University

Index Terms: 5420 Impact phenomena, cratering; 6022 & 8136 Impact phenomena; 0933 Remote Sensing; 0550 Model verification and validation; 0530 Data presentation and visualization; 1928 GIS Science; 1944 Markup Languages; 9350 North America; 5416 Glaciation

Abstract

We present a hypothetical solution to the genesis of the Carolina bays, where those enigmatic landforms areevaluated as surface features in a blanket of distal ejecta. A cosmic impact into the Wisconsinan ice shield at the close of the Pleistocene era is considered here as the ejecta source. The characteristic orientations of the bays are proposed to be artifacts of the ejecta’s momentum-driven flow direction at the moment of emplacement. Ananalytical model was heuristically developed to generate ejecta emplacement orientations which reflect large-scale geophysical flow effects, and its results were compared to empirically measured bay orientations at ~150 Carolina bay "fields" (representing many thousands of bays). Our model's predicted results correlatewell with actual bay orientations when the Saginaw area of Michigan is considered as the location of an oblique cosmic impact. The great-circle distances separating the proposed Saginaw impact crater and all identified Carolina bays also correlate well; the bay’s geographic distribution is along a narrow and symmetrical pair of arcs, east and west of the proposed crater. These positive correlations suggest that a unique geospatial relationship exists between the proposed impact location and the Carolina bays of North America. To facilitate independent testing of the hypothesis, a web-based version of the model was made publically available for integration with Google Earth.

Keywords: Carolina bay, distal ejecta, impact catering, GIS, visualization, Google Earth, kml, glaciation, North America, model verification

Inspirational Quotation

“The Goldsboro ridge is a unique feature on the Sunderland surface and requires special explanation whatever its origin. It must be either an erosional remnant of a once more extensive sediment or a depositional feature. ...The Goldsboro sand overlies the Sunderland Formation conformably. The contact is always abrupt but there is no evidence of deep channeling, basal coarse material, and evidence of weathering at the contact. Even the Carolina Bays do not disturb the underlying Sunderland materials.... The sand in the bay rim is not different from the Goldsboro sand. Therefore, these Carolina Bays are merely surface features associated with the formation of the ridge.”

[Citation: Daniels, R.B., and E.E. Gamble, 1970, The Goldsboro Ridge, an Enigma, Southeastern Geology vol.12 (1970) pp151-158]

1

DRAFT

1Introduction

The Carolina bays are perhaps the most enigmatic landforms encountered on the earth. Numbering in the hundred of thousands in North America, these depressions present a unique planform, featuring a well-developed oval circumpheral rim. Their distinct and persistent geometry and their sheer numbers, in combination with their sharing a common alignment in any one area, drove initial recognition of Carolina bays as unique geological landforms. The visual photography available since the bays were observed from the air in the early 1930’s tells only a part of the story. High fidelity digital elevation maps created with today’s Laser Imaging and Range Detection (LiDAR) systems accentuates their stunning planforms (Figure 1). While some of these features are easily seen in sand dunes or wind-oriented paleolakes, such comparisons have been found to be unsatisfactory by us. The genesis of the Carolina bays remains today as an unsolved geological mystery.

Researches have universally considered the bays to be formed within or excised from pre-existing hosting strata, which itself was created by well-understood fluvial and eolian deposition (Prouty, 1952; Eyton & Parkhurst, 1975; Firestone & West, 2008]. In sharp contrast, we propose that the bays are surface imperfections within a blanket of ballistically deposited sand and ice, and propose that the bays were generatedat time of emplacement by the energetic deflation of steam inclusions. The authors feel this interpretation helps explain many of the bays’ physical characteristics, such as localized bays seen at significantly different elevation, and at times intersecting or overlaying one another. Also explained is a mechanism that could create bays on ridges, the ridges themselves being comprised of ejecta deposition, which is our interpretation of the Goldsboro Ridge in NC [Daniels, R.B., and E.E. Gamble, 1970].

The lack of a correlated impact structure in North America is problematic for any attempt to implicate a cosmic impact in the genesis of the Carolina bays. Our conjecture holds that the impacting object was a massive low-density hydrated silicate object, likely a cometary body, which impacted the earth on a shallow angle, nearly tangential to the earth’s surface. Imaging of the surfaces of solar system terrestrial planets and moons has show that approximately 5% of all craters are created during low angle of incidence – oblique – impacts. These events create a set of recognizable characteristics: oval shape, butterfly ejecta pattern, “no-fly” ejecta area up field, and “blow-out” rim down field. [Herrick, R.R, 2009; Herrick R.R. and K. Hessen, 2003]. Recent studies suggest that impacts into solid surfaces protected by a layer of low impedance materials generate “impact” structures that differ from the classic crater planforms [Schultz, P. H. and A. M. Stickle, 2009]. In our specific case, we invoke the Wisconsinan ice shield as a low-impedance layer protecting the sedimentary strata of the Michigan basin. Excised terrestrial minerals, along with cometary minerals and glacial ice, would be intermixed and distributed as hydrated ejecta in a butterfly flow pattern.

The ejecta curtain wall radiating outward from a cosmic impact should follow a few simple laws of large-scale geophysical flows. If a model could be created to replicate those flows, it may be able to predict the Carolina bays’ orientations. Positive correlations between those predictions and the bays’ actual orientation could be considered strong support for the distal ejecta hypothesis. Once engineered and refined, the model may also be capable of triangulation to the causal crater using actual measured bay orientations.

2Methods

2.1Determining the Geographical Extent of Carolina bay landforms

Using the facilities and satellite imagery of Google Earth’s Geographic Information System (GIS), augmented with high resolution digital elevation mapping (DEM) data from the USGS, a survey was undertaken to catalogue the full extent of Carolina bays, indexed as localized “fields” of bays.

Identifying Carolina bays on the costal plain is straightforward, given their ubiquity and solid identification, but they are rounded in Maryland and in Georgia, presenting challenges. Also challenging is the increasingly rough terrain seen when moving inland from the costal plain. The ejecta blanket hypothesis maintains that the bays can persist through time only under special circumstances. If the landing area is relatively flat and moist, they will be easily stabilized as bays. If the area is level but dry, the blanket will be reworked by the wind into a generic dune field, obliterating any bay formation. When the landing field is in rough terrain, we propose it is sloughed off. In many regions we successfully pursued the search for bays by examining raised plateaus, as identified in color-ramp hinted digital elevation maps (DEMs) as smoother regions. We suspect that more extensive access to higher resolution DEMs (1/9 arc second), currently only available in North Carolina and Maryland, would aid in expanding the bays’ identified range.

While there is a great deal of research discussing Carolina bays in the east, little attention has been paid to the significant quantity of aligned, oval-shaped landforms in the Midwest [Zanner, W., 2001]. We interpret these bays as being aligned towards the north east (Figure 1), intersecting the eastern bay’s north-west orientations, and are therefore considered by us to be vital components of the impact crater triangulation network.

From this survey, we have created a catalogue of ~140 “Fields” of Carolina bay landforms, managed in a spreadsheet database and also in a Keyhole Markup Language (kml) metadata file. The catalogue is available for interactive visualization through the use of the Google Earth GIS, by referencing the kml file available online @ A basic listing of the fields is presented in Appendix A.

2.2Assigning Bay Arrival Bearings

Our hypothesis that a bay’s ovoid shape represents a blemish in a distal ejecta sheet leads to a corollary principal that the direction of arrival is displayed in the planform as a momentum artifact. We propose that the arrival alignment is along the major axis, with the highest rim segment being down-range. To measure and capture this “inferred” alignment, we employ a “Bearing Arrow” with a graticule as an overlay in the Google Earth GIS visualization tool (Figure 1). The overlay is manually rotated so that it aligns with the user’s interpretation of the bay’s orientation and the rotational value is captured in the kml metadata of the element. Since the bays are rarely perfect ellipsoids, the interpretation is better qualified by comparison with numerous companion bays as a “best fit”.

While the bays of North and South Carolina are seen as elongated ellipsoids, many of the bays of Maryland and New Jersey to the north, and Georgia to the south, do not present the elongation necessary for determining an inferred orientation. What is left, significantly, is a predisposition for having a segment of the enclosing rim that is fatter & higher than the opposing side. For the purpose of this discussion, we have assumed the inferred alignment of circular bays to be from the shallow side to the fat “lip”.

2.3Predicting Carolina bay Orientations

Previous attempts by others at triangulation using the bays’ orientations have failed to produce a focus. We propose this to be caused by several large-scale geophysical flow properties not considered. First, that the impact may have been an oblique event, which would infer a chaotic focus. Secondly, the earth rotates during any realistic ejecta loft time. [Wilbur , K.E. and P.H. Schultz, 2002]. A third variable is the proper accounting for the west-to-east ground-velocity difference between the ejection site and the landing site, which will be resolved as the ejecta re-enters the atmosphere and strikes the earth. Also a factor is the interpretation of a given bay’s inferred orientation, as the bays rarely present a geometrically pure ovoid form [Eyton, J.R. and Parkhurst, J.I., 1975]. This is especially true at the northern edge of their eastern range, where we interpret bays as being “squashed” along the arrival bearing.

2.4Systematic by Loft Time Adjustment

The kinematic Coriolis force is applied to an object to “force” it along a great circle path as it proceeds along a trajectory. For example, if an object is launched with sufficient velocity on an azimuth of 90 degrees from latitude 45º north (i.e. due East), it will follow a great circle route as it begins to circle the earth’s surface. The Cartesian coordinate “bearing” of our example object begins to “turn” south, and eventually the object will cross the equator on an azimuth 45 degrees increased, or 135 degrees. During an ejecta loft period the earth would be rotating from the west to the east beneath the ejecta’s trajectory path. The landing location of the ejecta will actually be westward of the initial “target”, although it would be imprinted with the arrival bearing to the initial target site. We consider that imprinted value to be our “baseline” bearing, which is further refined in the model’s next step.

2.5Systematic by Latitude Adjustment

While Coriolis force components are systematic by loft time, there is another factor superimposed on alignment that is systematic by latitude [Prouty, 1952]. Here, we account for ground speed differences between any two particular spots on the earth, which is a function of the cosine of the locations’ latitudes. The end cases are the poles – where the ground velocity w>e due to rotation is negligible – and the equator – where the ground speed w>e is ~1,670 km per hour.

In our specific proposal, a relevant set of w>e velocities would be the Saginaw crater – rotating at 1,270 km/hr – and a generic ejecta field such as Bishopville – rotating at 1,382 km/hr. A droplet of ejecta traveling from the north to the south in its great-circle frame of reference would not be affected by that ground and atmospheric speed difference until it approaches the surface of the earth, where atmospheric breaking effects on terminal velocity would be applied. Figure 2 attempts to explain the adjustments we apply to the Systematic by Loft’s baseline bearing to generate a final bearing prediction for a particular bay.

2.6Spreadsheet-based Analytical Model

We present a model for an ejecta curtain wall radiating outward from an impact site that applies those two geophysical flow adjustments discussed above. Assuming it accurately replicates those flows, it should be able to predict the Carolina bays’ orientations. We maintain that a positive correlation between those predictions and the bays’ actual orientation should be considered strong support for the distal ejecta conjecture.

Our bay field catalogue spreadsheet was extended to generate predictions based on the loft and latitude adjustments discussed above, allowing for a simultaneous solution to all fields in the database against variables such as proposed impact location, average ejecta velocity and terminal velocity. Those variables were adjusted until all empirically measured alignments were within the calculator's predicted values. Charts are generated within the spreadsheet to correlate the predicted values with those measured empirically, offering an opportunity to tune the calculator’s input variables to identify best-fit solutions simultaneously across all bay fields. The spreadsheet also generates catalogue-wide sets of Google Earth KML to visualize the model’s output in the GIS tool. The model is heuristically focused on the latitude and longitude of the proposed Saginaw crater’s three control points (NE, Centroid and SW).

2.7Tool for Independent Testing of Hypothesis

To facilitate independent testing of the hypothesis, a web-based version of the model has been made available for integration with Google Earth’s GIS: ( Using the Google Earth “Placemark” metadata element, a bay’s latitude and longitude are captured and annotated. The analytical model processes the placemark and generates a predicted orientation for visualization in Google Earth. The calculator can also reverse the process, and provide a “walk-back” to a putative crater by processing a user-adjusted Bearing Arrow element as the input datum. In all cases, the data transfer is accomplished by using Google Earth kml metadata.

3Results

3.1Initial Identification of the Cosmic Impact Location

Using the empirically measure arrival bearings of an initial 40 Carolina bay fields, we generated great circle paths for visualization in Google Earth. This yielded a fuzzy triangulation locus at 43.5 north, 89.5 west. Our analysis implies that this simple great circle bearing triangulation would yield an erroneous “surrogate” impact crater location. The Systematic by Loft Time concept places the actual impact crater somewhere along a path extending due east from the surrogate crater location. We heuristically examined various geological depression found along that transit, and selected the Saginaw area of Michigan’s Lower Peninsula (LP) for further analysis. Our proposed impact site represents approximately a 22 minutes loft time offset (equating to 5.5 degrees longitude rotation). Further refinement using the Systematic by Latitude concept in our analytical model is shown to reduce the loft time to a more realistic 4 to 10 minutes.

3.2Correlation of Bay Distribution

The flight lines, distances and bearings of all catalogued Carolina bayfields were analyzed for correlation to the proposed surrogate impact crater site. Our first correlation considered the great circle distance from each field back to the proposed impact site and their symmetrical distribution around it. As shown in figure 3, a very high degree of correlation is seen, suggesting that the bays are geographic distributed along a narrow and highly symmetrical pair of “butterfly” arcs centered on the triangulated Saginaw impact location. Such a distribution is suggested in the current research on oblique impacts. The lack of ejecta directly down-range in the “blow-out” zone is expected. Loft distance to the Midwest are nearly identical to those in Southeastern areas, suggesting a general trend of longer loft distances down range compared to those oblique to the crater’s major axis in the Northeast, where the shortest loft distances are documented. We note that areas north of the impact site’s latitude were covered in glacial ice sheet, prohibiting formation of identifiable bays in those areas.