42-10 Geographic Extent of the Spechty Kopf Formation Diamictites Extended by Core Observations: An Example of the Utility of Measured Sections and Core Drilling during Geologic Mapping

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

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Abstract:

While mapping the Catawissa quadrangle in Columbia County, Pennsylvania, cores were drilled on Catawissa Mountain to characterize the regional stratigraphy. The Spechty Kopf Formation was of particular interest, since exposure is limited within the quadrangle. Furthermore, the exposures that do exist are typically composed of resistant sandstone outcrops along the crest of the mountain and within water gaps. This results in a natural outcrop-bias where the sandstones are exposed more readily than the softer mud-lithologies which are concealed under colluvium. The mudstone facies within the Spechty Kopf Formation provide critical insight into the depositional environment for the unit and insight into paleoclimate during a critical point in the geologic past.

Two diamictite intervals were identified within the core at the base of the Spechty Kopf Formation. These diamicitites are composed of a grayish-red mudstone with mud matrix-supported sand grains, granules, and pebbles. Pebbles are well rounded and composed of quartz and lithic fragments. The basal diamictite rests sharply on a mottled grayish-red and medium-gray mudstone (paleosol) of the underlying Catskill Formation.

The presence of the diamictites and thickness of the Spechty Kopf Formation in core were a surprise in the context of observed outcrop. Less than seven miles south of the core site a road cut exposure along State Route 42 has the diamictite missing from the formation and the entire Spechty Kopf Formation is 115 feet thinner. This outcrop site also features the basal contact at the base of a thick package of quartz-pebble conglomerate and sandstone. The absence of the diamictite at the State Route 42 outcrop is interpreted as the result of younger fluvial channels within the Spechty Kopf Formation eroding out the diamictite. This explains in part some of the section loss between the State Route 42 exposure and the Catawissa Mountain core.

The geologic context provided by both the Catawissa Mountain core and the State Route 42 measured section was necessary for accurate mapping of the contacts. Similarly, both sources of data were paramount to understanding the geographic extent and lateral facies changes. In fact, the presence of the diamictite and variation in formation thickness would have been missed entirely without both sources of information. This reinforces the utility of rock cores and measured sections in geologic mapping.

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