Geology topics

S.L. Bressler

Publications and source records attributed to S.L. Bressler.

4 recordsLinked to original sources

USGS1981

Preliminary paleomagnetic poles and correlation of the Proterozoic Uinta Mountain Group, Utah and Colorado

Stable paleomagnetic directions have been obtained from seven sites spanning much of the 7-km-thick middle Proterozoic Uinta Mountain Group. The characteristic magnetization is carried partly by detrital(?) and secondary specularite and partly by hematite pigment. Preliminary paleomagnetic poles for six of the seven sites are closely grouped and their mean pole is 0.6°N, 157.2°E ( N = 6, α 95 = 5.4°). The pole for the seventh and stratigraphically highest site lies to the west, 4.6°N, 140.1°E, and ( n = 8, α 95 = 15.9°). On the basis of the poles, revisions to correlations of the Uinta Mountain Group with other sequences are proposed. The Uinta Mountain Group appears to correlate with the Chuar Group and perhaps the upper member of the underlying Nankoweap Formation, and post-dates the Unkar Group of the Grand Canyon Supergroup. In addition, the upper part of the Uinta Mountain Group appears to correlate with the Little Dal Group of the Northwest Territories, Canada. The Uinta Mountain Group appears to entirely post-date the Belt Supergroup of Montana and Idaho. Correlation of the Uinta Mountain Group with the Chuar and Little Dal Groups is supported by the presence of the fossil Chuaria and by apparently overlapping isotopic ages. A maximum age range for the Uinta Mountain Group, extrapolated from the Grand Canyon Supergroup and the Little Dal Group, extends from <1100 to > 770 m.y.

Colorado, Utah↗

USGS1981

Magneto-stratigraphic studies in Neogene deposits of Taylor Valley and McMurdo Sound, Antarctica

Magnetic polarity and susceptibility zonations obtained from drill cores have served to refine temporal correlations in glaciogenic sections cored in eastern Taylor Valley. The zonations have led to a better understanding of the glacial and structural history for an interval of time that extends from the late Miocene (about 7 m.y. ago) to perhaps near the end of the Pliocene (- 2.4 to 1.8 m.y.). However polarity data from a core drilled in McMurdo Sound (hole MSSTS-I) were found to be less useful. In this core, normal and reverse polarity deposits of Holocene, Pleistocene, and Pliocene age are nearly 40 m thick and appear to unconformably overlie strata assigned to the middle Miocene on the basis of a reworked fauna and flora. Gaps in the stratigraphic coverage of the Miocene strata, and two intervals in which the magnetisation post-dates deposition, however, have made development of a reliable polarity zonation impossible, and no firm correlation could be made with the magnetic polarity time scale.

Journal Royal Society New Zealand↗

USGS1980

Declination and inclination errors in experimentally deposited specularite-bearing sand

Naturally disaggregated specularite-bearing sandstone from the Triassic Moenkopi Formation, artificially deposited in controlled magnetic fields of ∼5 × 10 −2 mT, acquires a stable remanent magnetization that has systematic errors in inclination and declination. Inclinations about 12° shallower than the applied fields are produced by deposition on a horizontal surface in still water. Deposition from flowing water on a surface inclined 6–10° results in inclination errors of as much as 20°. Water flowing obliquely to the applied field results in declination errors of about 10°, with declinations systematically rotated toward the upstream direction of current flow. These experimental results indicate that specularite-bearing sediment responds to the earth's field in a manner similar to magnetite-bearing sediment, and support observational evidence for a primary magnetization of depositional origin in specularite in red beds of the Moenkopi Formation.

Earth and Planetary Science Letters↗

USGS1977

Paleomagnetic poles and polarity zonation from Cambrian and Devonian strata of Arizona

Basal Paleozoic Tapeats Sandstone (Early and Middle Cambrian) in northern and central Arizona exhibits mixed polarity and a low-latitude paleomagnetic pole. Carbonates of Middle and early Late Cambrian age, and directly superposed carbonate and carbonate-cemented strata of latest Middle(?) and early Late Devonian age, are characterized by reversed polarity and high-latitude poles. The high-latitude Middle Cambrian pole, which appears to record a large but brief excursion of the polar wandering path, is considered provisional pending additional work. The Devonian data from Arizona indicate that a shift of the pole to a “late Paleozoic” position had occurred by Middle Devonian time.

Arizona↗