DIAMICTITES OF THE UPPERMOST DEVONIAN-LOWERMOST MISSISSIPPIAN SPECHTY KOPF FORMATION IN NORTHEAST PENNSYLVANIA

Brezinski, et al, (2008)*, hypothesize that diamictites in the Late Devonian Spechty Kopf Fm. of northeast PA and the Rockwell Fm. of southcentral PA and adjacent MD are glacial deposits. Their hypothesis derives largely from the work of Caputo (1985) (and others) which indicates considerable climatic cooling and associated highland glaciation in South America during the Late Devonian. Similar cooling and glaciation have not been positively established for Eastern North America.

We disagree with Brezinski, et al because: (1) They ignore the diamitictes in northeast PA, the type area of the Spechty Kopf Formation and the area where it has been most extensively studied. The many workers who have studied those rocks agree they are the result of subaqueous debris flows, not glaciation. (2) Given the probable distance from the highland sources to the sites of diamictite deposition, attributing the diamictites to glacial deposition requires the equivalent of a continental glaciation, an untenable hypothesis for northeast PA. (3) Our examination of Brezinski, et al’s primary locality, Sideling Hill, MD, indicates the close association there of diamictites with stratigraphically adjacent marine sediments which argues for deposition by subaqueous debris flows, not glaciers.

In addition, we believe that a non-glaciogenic origin for the Spechty Kopf diamictites in northeast PA is clearly indicated by: (1) the lack of evidence there for significant climatic cooling in the Late Devonian, (2) the lack of evidence for glacial erosion on the former Catskill Delta alluvial plain, (3) the sedimentologic character of the diamictites, (4) the sedimentologic character of the stratigraphic package enclosing the diamictites, (5) the irregular regional distribution of diamictite occurrences and (6) clear evidence that the rounding and polishing of quartzite clasts found in the diamictites was not developed by glacial erosion-transport mechanisms, but was the character of the clasts within the parent material prior to riverine erosion and transport.

*Brezinski, D.B., Cecil, C.B.,Skema, V.W.,Stamm, R., 2008, Late Devonian glacial deposits from the eastern United States signal an end of the mid-Paleozoic warm period: Paleogeography, Paleoclimatology, Paleoecology, 280:2-3, p. 143-151.