DEPOSITIONAL ENVIRONMENT OF THE DEVONIAN-MISSISSIPPIAN SPECHTY KOPF FORMATION

The Devonian-Mississippian Spechty Kopf Formation of northeastern Pennsylvania is a controversial unit based on its origin of deposition. Previous workers have proposed different origins for Spechty Kopf Formation. Costolnick (1987) suggests a transgressive sequence during a basin infilling. Sevon et al. (1997) suggest that the lower portion of the formation represents deposition of sediments after a bolide impact, which is based on the presence of diamicts and laminated sediments. Bjerstedt (1986) places the depositional environment in a near-shore marine environment i.e. barrier bay or estuarine, based on tidal inlet-fill sequences. This abstract proposes that the Spechty Kopf Formation represents a deltaic environment. The study area is located in Lackawanna, Luzerne, and Carbon Counties, in northeastern Pennsylvania. Outcrops were studied along several major highways in the area (I-380, PA Routes 209 and 309). The data collected were then used for facies analysis, petrofacies analysis, Markov Chain analysis, and paleocurrent mapping. The petrofacies analysis shows that there are distinct lithologies representing the delta plain, delta front, and prodelta depositional settings. The prodelta environment is represented by thinly bedded siltstone and mudstone couplets and diamicts to pebbly mudstones. Within the prodelta sequence there are numerous recumbent folds, ball and pillow structures, fluid escape structures, and mud diapirs. The diapirs are approximately seven meters thick and eleven meters in diameter, with the roots not exposed. The presence of these structures suggests rapid sediment loading. The delta front environment is represented by siltstone-shale tidal rhythmites, fine-grained hummocky stratified sandstone units, and medium-grained planar laminated sandstones that make up the delta clinoforms. The delta plain environment is composed of medium to coarse-grained trough cross-bedded sandstones. Some of which show oscillation ripples on the tops of the beds, this would also suggest a tidal influence. The data suggest that the Spechty Kopf Formation represents an ancient delta.