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G. L. Shideler

Publications and source records attributed to G. L. Shideler.

9 recordsLinked to original sources
USGS1994

Sedimentological indicators of paleoenvironments and siliciclastic stratigraphic sequences in some Miocene deposits of the Calvert Cliffs, southern Maryland

Middle Miocene siliciclastic deposits comprising the Calvert Cliffs section at the Baltimore Gas and Electric Company's (BG&E) nuclear power plant site in southern Maryland were analyzed in terms of lithostratigraphy, sedimentary structures, and granulometric parameters, to interprete paleo-environments within a sequence-stratigraphic framework. In terms of sequence-stratigraphic models, the BG&E section can be interpreted as consisting of two genetic stratigraphic sequences (Galloway model), namely, a shelf sequence and an overlying deltaic sequence. Using the Exxon model, the section consists of two third-order (1-5 m.y. duration) depositional sequences. The stratigraphic sequences of the BG&E section reflect both relatively short-term eustatic transgressive events, as well as a long-term regressive trend with associated local deltation and coastal progradation. The regression probably signified a regional basinward shift of depocenters within the Salisbury embayment during Miocene time. -from Author

Southeastern Geology↗
USGS1978

A sediment-dispersal model for the South Texas continental shelf, northwest Gulf of Mexico

Textural-distribution patterns of sea-floor sediments on the South Texas continental shelf between Matagorda Bay and the U.S.-Mexico international boundary were evaluated as part of a regional environmental-studies program. Sediment textural gradients support a conceptual model for the regional sediment-dispersal system, which is characterized by both net offshore transport and net south-trending coastwise transport components on a wind-dominated shelf. Coastwise transport results in the net southward migration of both palimpsest sandy mud composing the ancestral Brazos-Colorado delta flank in the northern sector, and modern mud composing the central sector; these migrating sediments are encroaching southward onto immobile relict muddy sands composing the ancestral Rio Grande delta in the southern sector. In the proposed model, the suspension transport of modern silt-enriched mud derived mainly from coastal sources is the dominant dispersal mechanism. Net offshore transport is attributed both to diffusion, and to the advective ebb-tide discharge of turbid lagoonal-estuarine waters from coastal inlets. Net southward transport is attributed mainly to advection by seasonally residual coastwise drift currents reflecting a winter-dominated hydraulic regime. Frequent winter storms characterized by relatively high-speed northerly winds that accompany the passage of cold fronts appear to be dominant regional dispersal agents.

Texas↗
USGS1978

Factors controlling heavy-mineral variations on the South Texas outer continental shelf, Gulf of Mexico

Heavy-mineral distribution on the outer continental shelf off the southern coast of Texas shows regional variability induced by provenance and local variability reflecting genetic differences in sea-floor sediments. Q-mode factor analysis showed that three suites of heavy minerals are present. The southern ancestral Rio Grande delta sediments contain a distinct opaque-pyroxene-garnet suite, whereas the northern ancestral Brazes-Colorado delta sediments contain a tourmaline-green hornblende suite. An interdelta region contains a heavy mineral suite that is mixed owing to contributions from both ancestral deltas. Analysis of variance, correlation, and regression methods indicate that heavy-mineral variations in each sedimentary province have been significantly influenced by hydraulic fractionation by size, shape, and density, and by a selective chemical decomposition of unstable minerals. These factors have operated at varying degrees on the relict, palimpsest, and modern sediment populations of the sedimentary provinces since the end of Pleistocene time. The differential effects of these processes on the sediments have resulted in local variations that contribute to the total mineralogical variability. A comparison of the heavy mineral suites of the modern and relict Rio Grande delta sediments, which are derived from a common provenance, also shows mineral variations resulting from factors other than provenance.

Texas↗
USGS1977

Heavy-mineral variability in bottom sediments of the lower Chesapeake Bay, Virginia

Heavy minerals in bottom-sediment samples of the lower Chesapeake Bay show distribution patterns and interrelationships that denote characteristic mineral suites associated with defined geographic provinces. The Baymouth province has a garnet-hornblende-pyroxene suite, which is largely attributed to the influx of littoral and shelf sediments; the Eastern Shore province has a similar suite, derived largely from coastal erosion of the Eastern Shore peninsula. The Northern and Combined River provinces have a zircon-tourmaline-staurolite assemblage, which reflects derivation from an Appalachian Piedmont-Atlantic Coastal Plain sourceland. The Western Shore province is associated with a zircon-epidote-staurolite assemblage, apparently derived jointly from tributary influx and coastal erosion of the western shore. Factor analysis identified two major factors that account for 63% of the total variation in the relative amounts of the seven most common heavy minerals. The dominant factor (44%) is based on a zircon-hornblende-staurolite-pyroxene relationship, which indicates that mineral stability, as influenced by sediment maturity, is a major contributing factor. The second factor (19%) based on a tourmaline-epidote-staurolite-garnet relationship indicates that provenance is another major cause of heavy-mineral variability within the lower bay.

Virginia↗