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Geologic columns for the ICDP-USGS Eyreville A and B cores, Chesapeake Bay impact structure: Sediment-clast breccias, 1096 to 444 m depth

Special Paper of the Geological Society of America
By: , , , and 
https://doi.org/10.1130/2009.2458(03)

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Abstract

The Eyreville A and B cores, recovered from the “moat” of the Chesapeake Bay impact structure, provide a thick section of sediment-clast breccias and minor stratified sediments from 1095.74 to 443.90 m. This paper discusses the components of these breccias, presents a geologic column and descriptive lithologic framework for them, and formalizes the Exmore Formation. From 1095.74 to ~867 m, the cores consist of nonmarine sediment boulders and sand (rare blocks up to 15.3 m intersected diameter). A sharp contact in both cores at ~867 m marks the lowest clayey, silty, glauconitic quartz sand that constitutes the base of the Exmore Formation and its lower diamicton member. Here, material derived from the upper sediment target layers, as well as some impact ejecta, occurs. The block-dominated member of the Exmore Formation, from ~855–618.23 m, consists of nonmarine sediment blocks and boulders (up to 45.5 m) that are juxtaposed complexly. Blocks of oxidized clay are an important component. Above 618.23 m, which is the base of the informal upper diamicton member of the Exmore Formation, the glauconitic matrix is a consistent component in diamicton layers between nonmarine sediment clasts that decrease in size upward in the section. Crystalline-rock clasts are not randomly distributed but rather form local concentrations. The upper part of the Exmore Formation consists of crudely fining-upward sandy packages capped by laminated silt and clay. The overlap interval of Eyreville A and B (940–~760 m) allows recognition of local similarities and differences in the breccias.

Suggested Citation

Edwards, L.E., Powars, D.S., Gohn, G., Dypvik, H., 2009, Geologic columns for the ICDP-USGS Eyreville A and B cores, Chesapeake Bay impact structure: Sediment-clast breccias, 1096 to 444 m depth: Special Paper of the Geological Society of America, no. 458, p. 51-89, https://doi.org/10.1130/2009.2458(03).

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Publication type Article
Publication Subtype Journal Article
Title Geologic columns for the ICDP-USGS Eyreville A and B cores, Chesapeake Bay impact structure: Sediment-clast breccias, 1096 to 444 m depth
Series title Special Paper of the Geological Society of America
DOI 10.1130/2009.2458(03)
Issue 458
Year Published 2009
Language English
Publisher Geological Society of America
Contributing office(s) Eastern Geology and Paleoclimate Science Center, Florence Bascom Geoscience Center
Description 39 p.
First page 51
Last page 89
Country United States
Other Geospatial Chesapeake Bay
Additional publication details