Geology topics

M. Gordon

Publications and source records attributed to M. Gordon.

5 recordsLinked to original sources

USGS2000

Perturbations to Saturn's F-ring strands at their closest approach to Prometheus

The strange morphology of the F ring of Saturn is thought to be caused by the perturbing effects of two close satellites, Prometheus and Pandora. The F ring and the satellites also experience periodic close encounters as a result of differential precession arising from Saturn's oblateness. Using the orbits of the F-ring strands derived by Murray et al. (1997, Icarus 129, 304-316) the behaviour of the ring particles at their closest approach to Prometheus is analysed using numerical simulations. The results show that a gap and a wave are formed in the ring at each encounter with the satellite. However, the gap is expected to have a short lifetime due to keplerian shear.

Planetary and Space Science↗

USGS1985

Significance of the Goniatite Bilinguites eliasi and Associated Biotas, Parkwood Formation and Bangor Limestone, Northwestern Alabama

The Bangor Limestone contains conodonts, smaller calcareous foraminifers, and a sparse marine macrofauna dating it as late or latest Chesterian (Late Mississippian). The Parkwood Formation, a paralic sequence disconformably overlying the Bangor, has yielded a fauna containing the reticuloceratid ammonoid Bilinguites eliasi Manger and Saunders which permits correlation of the Parkwood Formation in north-western Alabama to the upper part of the Prairie Grove Member of the Hale Formation in the type Morrowan sequence. The macrofauna occurring with the ammonoid, supports this correlation. Bilinguites eliasi also alows correlation with the lower part of the Yeadonian Stage (lowest Namurian 'C') of Europe. Florules collected just below and above the goniatite occurrence in Frankling County correlate with those in the lower two-thirds of the New River Formation, southern West Virgina, and with the upper Namurian of western Europe. -from Authors

Journal of Paleontology↗

USGS1985

Chesterian davidsoniacean and orthotetacean brachiopods, Ozark region of Arkansas and Oklahoma

Three species of orthotetaceans and one species of davidsoniacean are among the strophomenid brachiopods from Chesterian (Upper Mississippian) rocks of northern Arkansas and northeastern Oklahoma. Type material from the Fayetteville Shale, Orthotetes subglobosus and O. subglobosus var. protensus, is figured for the first time. We regard these species, and O. subglobosus var. batesvillensis Girty from the Batesville Sandstone, as distinct species, for which we are selecting lectotypes. We describe a fourth species, O. stenopsis n.sp., from the Pitkin Limestone. Another species, described from the Pitkin as Streptorhynchus suspectum, has an impunctate shell and is thus not an orthotetacean. This bizarre species generally has a long twisted beak, high interarea, and large forked cardinal process; a myophragm may occur in either valve, but more commonly is in the brachial valve alone. We designate a lectotype for this species and propose a new genus Adectorhynchus and a new family Adectorhynchidae, under the Davidsoniacea, for this taxon.

Journal of Paleontology↗

USGS1980

New evidence for the age of the Quantico Formation of Virginia

A new fossil locality within the Quantico Formation of the Virginia Piedmont in Dale City, Virginia, about 40 km south of Washington, D.C., has yielded crinoids and a cephalopod that re-establishes an age younger than Cambrian for this formation. On the basis of regional considerations and the work of investigators in the early 1900s, an Ordovician age for the Quantico seems likely. Also, the Dale City pluton is not intrusive into the Quantico but is unconformable beneath it. Hence, the 560-m.y. zircon age for the Dale City pluton is no longer inconsistent with the temporal and stratigraphic relationships established for the stratigraphic units in the area. © 1980 Geological Society of America.

Virginia↗

USGS1952

Minor elements in Arkansas bauxite

A study of the minor elements in Arkansas bauxite has revealed some striking relationships between their concentration in the parent nepheline syenite rocks as compared with their concentration in the bauxite . The ratios of concentration, in general, follow a pattern predicted by Gold-schmidt (3),2 based upon the ionic radius and ionic charge of each element present. In the Arkansas deposits, Mg, Ca, Ba, La, and Sr were depleted during the change from nepheline syenite to bauxite . The average concentration of Pb remained the same in the samples tested. Y, Mn, Be, V, Sc, Ti, and Zr were concentrated, but not as much as Al; while Mo, Nb (Cb), Ga, Cu, and Cr were concentrated more than Al.' Niobium (columbium) apparently is found in sufficient quantities to warrant search for methods to extract it commercially as a by-product of alumina plants.

Arkansas↗