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The earliest indications of Ohio’s geological history were found in igneous Precambrian rocks that emerged from the deep subsurface. The land had undergone great changes, as mountains, hills, riverbeds, and lakebeds were appearing and disappearing due to changes in climate and movements of the landmass. It is possible to see spectacular examples of Pennsylvanian landmass in large cuts along Interstate Route 77, south to Marietta, and along Interstate Route 70 from Cambridge to Bridgeport, which present a variety of Pennsylvanian and Permian rocks. The purpose of this paper is to analyze several strata exposed on the outskirts of Marietta and make conclusions about the type of depositional environments that took part in their formation.
Locality and General Geological Information
The location of the outcrop was near Marietta, with township coordinates being South-West 1/4, T2N, R9W. The excavation took place in the Marietta durance loti, West Virginia topographic quadrangle. The excavation site is located 4.6 miles away from Marietta. It can be found on the Washington County OH bedrock geological map. The elevation of the outcrop is 640’’, with each line approximately 20’’ above the other.
The exposure is approximately 9350 meters long and is presented by shale, sandstone, and siltstone geological patterns. According to Ohio’s surface rocks and sediments map, the bedrock geology of Washington County was formed during the Pennsylvanian-Permian period (320-245). The groups presented in the strata include the Upper-Pennsylvanian – Lower Permian Dunkard Groups, which display a more terrestrial and environmental form of fossil deposition, associated with the formation of the Pangaea supercontinent.
Previous Work Background on Possible Environments
There are two types of depositional environments prevalent in Ohio during the Pennsylvanian – Lower Permian period. These are the coastal marine environments and rivers (fluvial environments). Fluvial environments are formed by rivers, which affect their riverbeds by washing out finer sediments and collecting the coarser sediments at the bottom of the riverbed. They are typically represented by sandstone, siltstone, and shale, surrounded by layers of floodplain deposits. The colors of the deposits range from gray to red and green. Bed geometry is typically rippled and uneven (Collins & Smith 134).
Coastal marine deposits are characterized by well-rounded and well-sorted sandstone, as the waves wash out silt and clay. The sand surface is often found in ripples because of the back-and-forth motion of the waves. These ripples are typically symmetrical. The sandstones are almost entirely composed out of quartz. The color of deposits ranges between gray and dark gray (Collins & Smith 134).
The findings are presented in the following layers:
Basal layer: Sandstone and silt, gray color, scoured.
- Layer 1: Silt-shale, gray-green color, gradational.
- Layer 2: Greywacke sandstone, gray-green color, cross-post bed, sharp-undulatory forms.
- Layer 3: Silt-shale, gray-green color, brows, no cover-up.
- Layer 4: Greywacke sandstone, gray-green color, cross-post, sharp undulatory forms.
- Layer 5: Shale, gray-red color, remnants of plant life, no cover-up.
- Layer 6: Silt-sandstone, gray color, thin towards the end, scoured.
- Layer 7: Shale, green color, signs of plant life, and iron deposits.
The most prominent indications of the nature of the depositional environment are the colors of the sediments as well as the presence of plant life remnants. These indicate a fluvial environment, which is characterized by red and green colors (which stand for ancient soil horizons) as well as the rippled, scoured, and uneven structure of bed geometry. The fossils were most likely influenced by the presence of the Ohio River.
The purpose of this field trip was to investigate the depositional environment found 4.6 miles away from Marietta. The layers investigated contained deposits of sandstone, silt, and shale, of gray, green, and red colors, with remains of plant life in them. Based on these findings, it was concluded that the layers were likely formed in a fluvial environment. A subsequent essay will be written that will give interpretations about the likelihood of these sediments contributing to slope instability and landslides in the region.
Collins, Horace R., and Bradley E. Smith. “Geology and Mineral Resources of Washington County, Ohio.” Ohio Geological Survey Bulletin, vol. 66, 1977, p. 134.