Northeastern Section–41st Annual Meeting (20–22 March 2006)

Paper No. 4
Presentation Time: 9:05 AM




About 15-20 of us working over the past 30 years cannot agree on the origin of a diamictite-bearing sequence (DBS) in the Spechty Kopf Formation of Pennsylvania. Included in the DBS are diamictite, laminite and quartz-rich sandstone. Why is agreement about origin so elusive?

The DBS facts are these: 1. it lies wholly within a part of the penultimate late Devonian palynozone, 2) it is developed from place-to-place between Scranton, PA and Sideling, Hill, MD, 3) its thickness varies from 150 m to about 10 m and it is absent at many locations, 4) the diamictite contains sedimentary, igneous and metamorphic clasts, 5) the DBS is found in both red and gray facies, 6) it contains neither body- nor trace-fossils, 7) some diamictite clasts are thought to exhibit glacial striae, 8) iridium values in the DBS hover around or are slightly above background, 9) supposed DBS correlatives in the Appalachian Plateau are quartz-rich sandstones marked by water-release structures and a brachiopod-bearing conglomerate, and 10) the DBS formed during a time of sea level rise and fall in response to southern-hemisphere glaciation.

The diamictite itself has been interpreted as a debris-flow deposit, a subaqueous mudflow deposit formed in a marine, estuarine or lacustrine environment, as part of a deltaic sequence, as a deposit formed by valley-wall collapse, a deposit related to valley glaciation, and, most outrageously, as the result of a bolide-related tsunami. The latter interpretation accounts for more of the data than do any of the others.