The post about the Carolina Bays that I wrote a couple of weeks ago turned out to be relatively popular (as far as this webpage goes, anyway). Carolina bays are elliptical depressions of varying size that occur along the Atlantic Coastal Plain in a band extending from New Jersey to Florida. Their limited geographic distribution and northwest-southeast orientation has given rise to many ideas about how these features were formed. Ongoing debate centers around the question of whether the bays formed as (1) the result of impacts associated with an extraterrestrial object (e.g., debris ejected by a comet strike in Saginaw Bay) or (2) through the actions of wind and water during the Pleistocene. Extraterrestrial or terrestrial?
A new paper by Chris Moore and colleagues (see full reference below) in Southeastern Geology provides more evidence that the bays were formed and modified over long periods of time by natural, terrestrial processes. You can read the paper for yourself here.
The analysis in the paper focuses on Herndon Bay, a 1-km long elliptical depression in Robeson County, North Carolina. Using a combination of detailed surface mapping, ground penetrating radar data, geomorphological analysis, and age estimates obtained using OSL, Moore et al. show that punctuated migration of Herndon Bay to the northwest from about 41 to 24 thousand years ago produced a sequence of sand rims on the southeast side of the basin. The bay held its shape and orientation as it migrated over the course of thousands of years.
A portion of Figure 3 from "The Quaternary Evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): Implications for Paleoclimate and Oriented Lake Genesis." The numbers show locations of dated sand rims left by migration of the bay (4 is the oldest, 1 is the youngest).
The evidence and analysis that Moore et al. present is a pretty strong argument against the idea that the bays were formed by a single event (i.e., an extraterrestrial impact). I encourage you to take a look at the paper. I'll just paste in a paragraph from their conclusion (pg. 168):
"The characteristics of Carolina bays, including basin shape, changes in basin orientation with latitude, and sand rims reflect long-term and pervasive environmental, climatological, and hydrological factors over millennia rather than from sudden or catastrophic events (Kaczorowski, 1977; Thom, 1977; Carver andBrook, 1989; Brooks and others, 1996; Grant and others, 1998; Brooks and others, 2001;Ivester and others, 2007, 2009; Brooks and others, 2010). The fact that practically all Carolina bays in a particular geographic region have nearly identical patterns of shape, orientation,and sand rim composition suggests similar processes working over long periods of time. This study also indicates that Carolina bays can respond rapidly, and appear to become more active during periods of climatic instability. While many nuances of bay evolution remain to be re-fined, the evidence at Herndon Bay clearly supports the concept that Carolina bays represent a regional example of a globally-occurring phenomenon: They are wind-oriented lakes shaped primarily by lacustrine processes."
Moore, Christopher M., Mark J. Brooks, David J. Mallinson, Peter R. Parham, Andrew H. Ivester, and James K. Feathers. 2016. The Quaternary Evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): Implications for Paleoclimate and Oriented Lake Genesis. Southeastern Geology 51(4): 145-171.
Addendum (3/18/2016): Let's start over with the comments. Please keep comments on the topic of the blog post (Carolina bays) or I'll delete them.
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