Bloomsburg Formation

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A sample of the Bloomsburg siltstone from Port Clinton, Pennsylvania.
A sample of the Bloomsburg siltstone from Port Clinton, Pennsylvania.

The Silurian Bloomsburg Formation (Sb) is a mapped bedrock unit in Pennsylvania, New Jersey, New York and Maryland. It is named for the Town of Bloomsburg, Pennsylvania for which it was first described.

Contents

[edit] Description

The Bloomsburg is defined as a grayish-red and greenish-gray claystone, argillaceous siltstone, shale, and very fine to fine-grained sandstone,[1] arranged in fining-upward cycles.[2] Although the Bloomsburg can sometimes be green to gray, its most dominant color is red and they are often called "The Bloomsburg Red Beds". This is significant in the Appalachian Basin since it marks the first large scale terrestrial collection of sediemnts in the rock record. Most of the sediments that were deposited before this time were marine, or a small scale terrestrial zone.

[edit] Depositional Environment

The Bloomsburg is mostly molasse resulting from the Taconic orogeny. The red color is often evidence that the sediments were deposited in arid conditions. The upper parts of the Bloomsburg are thought to be a marine transition zone.[3]

[edit] Fossils

There are numerous fossils found in the Bloomsburg, mostly in the upper parts of the formation. There are trace fossils of early land plants and brachiopod fossils in the upper marine transitional zones.[3]

[edit] Age

Relative age dating of the Bloomsburg places it in the Upper Silurian period, being deposited between 417 to 410 (±5) million years ago. It rests conformably a top the Clinton Group[1] and Shawangunk Formation, and has a complex upper contact. In eastern Pennsylvania and New Jersey, the upper part of the Bloomsburg marks the Wallbridge Unconformity. As you move west, the Wills Creek Formation lies conformably atop the Bloomsburg. Further west, the McKenzie Member of the Mifflintown Formation interfingers with the Bloomsburg and eventually, the Bloomsburg pinches out into the Mifflintown.[4]

[edit] Economic uses

The Bloomsburg formation is a source of material for the manufacture of brick and other clay products, as well as a local building stone.[5]

[edit] References

  1. ^ a b Jackson, Margaret S.; Hanley, Peter M.; and Sak, Peter B. (2007). Preliminary Bedrock Geologic Map of the Middle Portion of the Susquehanna River Valley, Cumberland, Dauphin, And Perry Counties, Pennsylvania (pdf). Open File Report OFBM-07-05.0. Pennsylvania Geological Survey. Retrieved on 2008-01-26.
  2. ^ Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.
  3. ^ a b Hoskins, D.M., (1961). Stratigraphy and paleontology of the Bloomsburg Formation of Pennsylvania and adjacent states: G36. Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
  4. ^ Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
  5. ^ Doden, Arnold G. and Gold, David P.. "Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania" (pdf). . Pennsylvania Geological Survey

[edit] See also


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