2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 10
Presentation Time: 8:00 AM-12:00 PM


DENNISON, John M.1, ALLEN, Joseph L.2 and HUNT, Erin B.2, (1)Geological Sciences, Univ of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3315, (2)Geology and Physical Sciences, Concord University, Athens, WV 24712, palteach@mindspring.com

Lower Famennian strata in the Brallier Formation about 100 m above the Famennian/Frasnian boundary display flute casts in excavations at Hardee's restaurant in Bluefield, Virginia. These overturned strata dipping 57°S20°E are in the footwall of the St. Clair fault 0.5 km northwest of the fault. The distal turbidites are approximately 374 million years old. Famennian strata at Bluefield are about 940 m thick.

Rake orientations within 10 m of strata were measured for 500 flutes with random and isolated spacing on three bedding surfaces. These were restored to depositional attitude after removing faulting overturning and a 7° counterclockwise strike direction rotation to yield a vector mean current flowing toward N79°W with a vector magnitude of 99%. This is consistent with paleoslope nearly due west as indicated by regional facies changes and isopachs of the Catskill delta complex in southern West Virginia and southwestern Virginia.

The flutes are mostly simple-parabolic, but about 20% are asymmetrical, of the twisted and corkscrew varieties showing a sense of rotation of the vortex at the flute point. Seventy eight of 98 swirling flutes had clockwise rotation as viewed from the top of bedding and after correction for tilting, and 20 swirled counterclockwise. This is a non-random, Devonian preferred clockwise swirl with greater than 99% confidence.

This preferred swirl suggests a Coriolis force cause, that produces counterclockwise swirl in a northern hemisphere low-pressure vortex, which is reversed in the southern hemisphere. This is consistent with modern vortex swirls noted by traveling scientific friends at various latitudes. The exact cause of Coriolis “mini-tornadoes” in some flutes is not clear.

Scotese and McKerrow (1990) show the Late Devonian north pole for the North American craton about 36°W relative to the modern pole, and paleo-latitude restoration of Bluefield was about 23°S as determined paleomagnetically. Brallier turbidites probably moved a few km/hr oblique to Devonian polar direction. Dominant clockwise rotation in the flutes thus gives an independent verification on the southern hemisphere location of Bluefield in the Devonian, but not a latitude amount.

Perhaps the flute cast method could be used to choose among alternative options for continental fragment restorations.