The subsurface Appalachians beneath the Atlantic and Gulf Coastal Plains

Thomas, William A.; Chowns, Timothy M.; Daniels, David L.; Neathery, Thornton L.; Glover, Lynn; Gleason, Richard J.

doi:10.1130/dnag-gna-f2.445

Cited by 21 publications

(9 citation statements)

References 26 publications

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“…The youngest (late Paleozoic; Table 1) zircons likely reflect derivation from the Appalachian-Ouachita-Marathon magmatic arc ( Fig. 1; Thomas et al, 1989;Wilson, 1990). Both of these source terranes reflect an easterly or southeasterly source direction.…”

Section: Wolfcampian Samplesmentioning

confidence: 99%

Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea

Soreghan

Hamilton

2002

Geol

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U-Pb geochronology of detrital zircons from upper Paleozoic loessite (western United States) provides data bearing on atmospheric circulation within western equatorial Pangea. Zircon age spectra of four loessites from three localities representing middle Pennsylvanian (Desmoinesian) and Early Permian (Wolfcampian) time vary significantly, reflecting changing provenances attributable to temporal and spatial shifts in winds. Zircons from two Desmoinesian samples (from Arizona and Utah) show a dominant mode between 1800 and 1600 Ma, reflecting the Yavapai-Mazatzal terranes that cored the Ancestral Rockies uplifts and suggesting northeasterly winds. Both samples also contain a secondary cluster of Grenvillian grains (1300-1000 Ma), reflecting a south-southeasterly source. Ages for Wolfcampian samples (from New Mexico and Utah) differ from one another; the New Mexico loessite contains a large mode at 1700 Ma, missing in the Utah sample, reflecting their locations on opposing sides of the Ancestral Rocky Mountains, within a westerly wind regime. Inferred easterly winds for middle Pennsylvanian time match model predictions, and the presence of both northerly and southerly directions might reflect time-averaged fluctuation of the Inter-Tropical Convergence Zone. In contrast, monsoonal circulation and attendant westerly winds appear to have been well established by earliest Permian time.Figure 1. Basement provinces and other important age domains of North America. Dots refer to sample localities: PRB-Paradox basin, Utah; PDB-Pedregosa basin, Arizona; BD-Bravo dome, New Mexico. Two samples are Desmoinesian age (PDB and PRB-lower) and two are Wolfcampian age (BD and PRB-upper). Basement provinces are simplified from Hoffman (1989) and Van Schmus et al. (1993). Other ages are from references cited in text.

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Section: Wolfcampian Samplesmentioning

confidence: 99%

Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea

Soreghan

Hamilton

2002

Geol

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“…A few short, straight, high-amplitude reflections scattered within the Exmore breccia may represent megaclasts. The high-amplitude basement reflector (Proterozoic and Paleozoic crystalline rocks; Thomas et al, 1989) remains nearly horizontal at -0.89 s (-890 m depth) beneath the Lower Cretaceous sedimentary sequence and the slumped megablocks.…”

mentioning

confidence: 98%

Structural outer rim of Chesapeake Bay impact crater: Seismic and bore hole evidence

Poag

1996

Meteorit & Planetary Scien

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Abstract— Nine seismic‐reflection profiles and four continuous core holes define the gross structural and stratigraphic framework of the outer rim of the Chesapeake Bay impact crater. The rim is manifested as a 90 km diameter ring of terraced normal‐fault blocks, which forms a ∼320 m–1200 m high rim escarpment. The top of the rim escarpment is covered by a 20 m–30 m thick ejecta blanket. The escarpment encircles a flat‐floored annular trough, which is partly filled with an ∼250 m thick breccia lens (Exmore breccia). The Exmore breccia overlies a 200 m–800 m thick interval of slumped sedimentary megablocks, which, in turn, rests on crystalline basement rocks. All postimpact strata (upper Eocene to Quaternary) sag structurally into the annular trough, and most units also thicken as they cross the rim into the crater. Postimpact compaction and subsidence of the Exmore breccia have created extensive normal faulting in overlying strata.

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“…It contains a variety of rock and mineral clasts, melt particles, as well as secondary minerals. The lithic clasts in the suevite comprise abundant clasts of pre-impact sediments of the Atlantic coastal plain (e.g., sandstones, siltstones, and mudstones), as well as clasts from the crystalline basement (e.g., granite, gneiss, and schist; Bartosova et al 2009a), which is a distal part of the Appalachian orogen (Thomas et al 1989;Gibson et al 2009). The melt-poor bottom part of the impact breccia sequence with larger basement-derived clasts and gneiss blocks, and generally scarce melt particles, with no evidence of aerial transport, is thought to be of ground-surge origin (Bartosova et al 2009a;Horton et al 2009b).…”

Section: Petrography Of the Impact Breccia Sectionmentioning

confidence: 99%

“…The lithic clasts in the suevite comprise abundant clasts of pre‐impact sediments of the Atlantic coastal plain (e.g., sandstones, siltstones, and mudstones), as well as clasts from the crystalline basement (e.g., granite, gneiss, and schist; Bartosova et al. 2009a), which is a distal part of the Appalachian orogen (Thomas et al. 1989; Gibson et al.…”

Section: Introductionmentioning

confidence: 99%

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

Bartošová

Hecht

Koeberl

et al. 2011

Meteorit & Planetary Scien

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Abstract– The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP–USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397–1551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile‐rich targets, because no large melt body exists, in which homogenization would have taken place.

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The subsurface Appalachians beneath the Atlantic and Gulf Coastal Plains

Cited by 21 publications

References 26 publications

Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea

Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea

Structural outer rim of Chesapeake Bay impact crater: Seismic and bore hole evidence

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

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