Carl
Brett
Comparative Stratinomy and Paleoecology of Ordovician to Devonian Black
and Dark Gray Shale Facies, Appalachian Basin
(funded by ACS-PRF grant 27217-AC8 to C.E. Brett and G.C.Baird; supplemented
with a fellowship to Baird).
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project presently involves intensive mapping and sampling of black shales,
associated K bentonite, and phosphatic lag horizons within the Middle
Ordovician Trenton Group and Upper Ordovician Utica Shale in the Mohawk
Valley of New York. Brett and Baird have been working intensively on the
sequence and event stratigraphy of Middle Ordovician Trenton and Utica
strata in the classic Mohawk Valley area of New York. Collaboration with
Prof. Charles Mitchell (SUNY Buffalo) on graptolite biostratigraphy and
bentonite stratigraphy will establish an integrated stratigraphic framework
for these strata. Over 40 K-bentonite horizons have been recognized, tentatively
correlated, and sampled in the Mohawk Valley. Samples from selected horizons
are being geochemically fingerprinted by Prof. John Delano at SUNY Albany.
Brett and Baird are developing data on stratigraphy and sedimentology
of Ordovician black shales that can be compared with previous observations
on Middle to Upper Devonian shales in the Appalachian basin. A number
of comparable patterns of occurrence have already been recognized; these
include:
(A ) Black shales tend to show sharp contacts with underlying gray mudrocks,
that are marked by lags of erosional phosphatic and conodont enriched
material.
(B) Black shales display a "shingled" pattern of onlap over
older erosion surfaces with upslope equivalents of black shales. Bases
of black shales are scoured unconformity surfaces that were produced by
submarine erosion. This corroborates a model of pycnocline-controlled
erosion and deposition of the suspended muds that was originally developed
for the Upper Devonian in New York State and Ohio (Baird and Brett, 1991).
(C) The occurrence of thin lags and of phosphatic material, and internal
lamination within ash beds suggests that they too are associated with
intervals of non-deposition and/or erosion. Contrary to common belief,
some ash beds may represent condensed sedimentary intervals.
Next phases of this research will a) attempt to extend correlations of
discontinuities and K-bentonites into Ontario and Pennsylvania; b) examine
micro-fabrics of shales and associated K-bentonites; c) examine geochemistry
of black shales. Ultimate aims of this study are to provide a new model
of depositional processes of black shales and associated strata in foreland
basins.
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References
Baird, G. C, and Brett, C. E. 1991. Submarine erosion on the anoxic sea
floor: stratinomic, palaeoenvironmental, and temporal significance of
reworked pyrite-bone deposits. In Tyson, R. V. and Pearson, T. H., eds.,
Modern and ancient Continental Shelf Anoxia. Geological Society Special
Publication , p. 233-257.
Baird, G. C. and Brett, C. E., 1996, Patterns of sedimentary condensation
and submarine erosion in a Middle Ordovician (Caradocian) foreland basin:
evidence of lithospheric flexure and sediment bypass. Geological Society
of America, Abstracts with Programs. v. 28, p. 36.
Brett, C. E., Dick, V. B., and Baird, G. C., 1991, Comparative taphonomy
and paleoecology of Middle Devonian dark gray and black shale facies from
western New York. In Landing, E. and Brett, C. E., eds., Dynamic Stratigraphy
and Depositional Environments of the Hamilton Group (Middle Devonian)
in New York State, Part II. New York State Museum Bulletin 469: 5-36.
Lehmann, D. M., Brett, C. E., and Cole, R. 1994. Tectonic and eustatic
influences upon the sedimentary environments of the Upper Ordovician strata
of New York and Ontario. In Dennison, J. M. and Ettensohn, F. M., eds.,
SEPM Special Publication, Concepts in Sedimentology and Stratigraphy 4:
181-201.
Lehmann, D. M., Brett. C. E., Cole, R. M. and Baird, G. C. 1995. Distal
sedimentation in a peripheral foreland basin: Ordovician black shales
and associated flysch of the western Taconic foreland, New York. Geological
Society of America Bulletin 107: 708-724.
Ver Straeten C. A., Brett, C. E. and Griffing, D. H. 1994. The lower part
of the Marcellus "shale", central to western New York State:
stratigraphy and depositional history. In Brett, C. E. and Scatterday,
J. eds., New York State Geological Association 68th Annual Meeting Guidebook,
Rochester, NY, p. 271-321.
Brett, C.E. and Allison. P.A., 1998, Paleontological approaches to environmental
interpretation of marine mudrocks. In Schieber, J., ed., Sedimentology
of Mudrocks. E. Schweizerbart'sche Verlagsbuchhandlung, p. 391-439.
O'Brien, N. , Brett, C.E., and Woodard, M. 1998. Shale fabric as a clue
to sedimentary processes--Example from the Williamson-Willowvale Shale
(Silurian), New York. In Schieber, J., ed., Sedimentology of Mudrocks.
E. Schweizerbart'sche Verlagsbuchhandlung, p. 349-360.
Ettensohn, F. and Brett, C.E., 1998 Tectonic components in third order
Silurian cycles: Examples from the Appalachian Basin and global implications.
In Landing, E., ed., New York State Museum Bulletin 491, p. 143-162.
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