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Geology topics

Gary W. Hill

Publications and source records attributed to Gary W. Hill.

14 recordsLinked to original sources
USGS1981

Composition of tidal flat sediments, Willapa Bay, Washington

The purpose of this study was to characterize the modern sediments of sandy tidal flats in Willapa Bay, Washington based on their composition. Generally, clay comprises less than five percent of the sediment. Clay content increases upslope and up-estuary. Principal clay minerals are montmorillanite, illite, and chlorite; two clay mineral suites are present: (1) muddy flat suite with clay containing 44% montmorillonite, and (2) sandy flat suite with clay composition of 88% montmorillonite. Heavy minerals make up approximately four percent of the tidal flat sediment. Distribution of heavy minerals reflect their source with (1) heavy minerals most abundant near the beach on flats to the north where they were eroded out of terrace deposits, and (2) relatively greater heavy mineral concentrations (supplied by the Naselle River) across the entire flat to the south. The composition of the heavy mineral suite is mainly clinopyroxene, orthopyroxene, hornblende, epidote, and opaque minerals. This mineral suite represents several sources including rivers, ocean and ocean beaches, and reworked local Tertiary and Quaternary deposits. Tidal flat sediments are approximately 90% light minerals, mostly quartz. The light fraction also contains small quantities of lithic fragments, pumice, vegetation, and biogenic shell fragments. Tertiary and Quaternary terrace deposits are the major source of most of the light material. Fossils make up less than one percent of the bottom sediment. Two foram assemblages are present: (1) a modern shallow-water assemblage characterized by Trochammina inflata, found mainly in muddy flats near rivers, and (2) a relic deep-water assemblage (Eocene to Cretaceous) characterized by such species as Bathysiphon and Cyclammina found predominantly on the sandy flats. Macrofossils consists of shells of the modern tidal flat mollusc assemblage. Organic sediments were mostly carbon (1%). The highest concentrations of organic carbon are associated with muddy sediments near the Palix River and Pickernell Creek; overall, organic carbon concentration increased up-estuary. C/N ratios are transitional between open marine environments and marsh deposits of estuaries.

Washington↗
USGS1981

Tidal flat sediments - texture, Willapa Bay, Washington

The purpose of this study was to texturally characterize the sediments of the mid-estuary tidal flats between Goose Point and Pickernell Creek in Willapa Bay, Washington and to compare these flats with other flats in the estuary. The mean grain size of sediments on tidal flats in the mid-estuary are fine sand (2-3 V). Sand shoals at the Bay entrance and erosion of cliffs between Goose Point and Pickernell Creek are the source of the sand. The subordinate mud fraction is supplied by rivers and creeks; little mud is deposited on the tidal flats except for those flats immediately adjacent to the rivers. Gravel is a minor component and is concentrated in sediments near the base of the cliffs high on the tidal flats. Variability in texture within the study area is most pronounced near the Palix River and Pickernell Creek. The average characteristics of mid-estuary tidal flat sediments are best described as poorly sorted, fine-grained sand with strongly-fine skewed leptokurtic distributions. Distribution patterns of textural parameters show consistent trends of hydraulic energy. Locally, textural patterns reflect (1) the coarsing effects of a flood current gyre between Goose Point and Sandy Point, and (2) relatively narrow flats (i.e., greater slopes) have coarser sediments proportionately higher upslope than wider flats. The following comparisons can be made between tide flats in Willapa Bay. Mean grain size varies systematically up-estuary permitting the estuary to be artificially divided into 3 parts: outer estuary = 2-3 Ø ; mid-estuary = 3-4 Ø ; and inner estuary = greater than 4 Ø . Outer estuarine tide flats extend deep into the estuary, particularly to the south. The transition from outer to inner estuarine tide flats based on textural differences is a rapid change (i.e., occurs over a short distance).

Washington↗
USGS1979

Trace element analysis of marine organisms by anodic stripping voltammetry (ASV)

Trace element analysis of marine organisms has generally been conducted by (1) sophisticated instrumentation (e. g., atomic absorption), (2) complicated cookbook laboratory procedures utilizing a host of chemicals and glassware, or (3) a combination of the above. All these procudures present problems to the investigator. For example, analysis by methods other than instrumentation are unable to detect minute amounts of various trace elements and in general are not extremely accurate. Problems common to all procedures are (1) relatively large amounts of sample (2 grams or more) are required for analyses of even the more common trace elements and (2) contamination of samples is almost a certainty due to complicated sample preparation procedures which include large amounts of glassware, chemicals and excessive handling of the sample. The development of new anodic stripping voltammetry (ASV methods (Matson, 1968) has provided investigators with an instrument which (1) is capable of accurately detecting trace elements in minute quantities, (2) utilizes very small amounts of sample (0.01 mg) , (3) works on a simple operating principle which simplifies sample preparation thereby reducing the possibility of contamination, (4) can be used aboard small boats, and (5) is relatively inexpensive (compared to other instruments used for trace element analysis). Recent ASV literature (Matson, 1968, Fitzgerald, 1970; Bradford, 1972) has dealt exclusively with the analysis of salt water and sediments and does not provide an adequate method for analysis of marine organic matter. This paper reports on an investigation designed to develop the methodology necessary for ASV analysis of organic material from the marine environment.

Open-File Report↗
USGS1979

Key to the common marine molluscs of Texas

A dichotomous key is developed which provides the investigator a means for identifying the common marine molluscs on the Texas coast. The key is written as to allow the user to stop or begin at any desired taxonomic level (class, order, superfamily, family, genus, species) depending on prior knowledge or specific need (Table 1). Because of the special importance of bivalves to many studies, species-specific information is provided pertaining to feeding type, relation to substrate, and distribution (Table 2). An illustrated glossary is also provided.

Texas↗
USGS1975

Maps showing drift patterns along the north-central Texas coast, 1973-1974

An investigation of the rates and directions of drift in the northwestern Gulf of Mexico was initiated in January 1970 as part of a program to study depositional processes and sediment movement off the southern Texas coast. The first phase of that program, a study of coastal drift off south Texas, was reported by Hunter and others (1974). They reported on a three-year program of seasonal releases of both bottom and surface drifters on the south Texas shelf; this study confirmed the hypothesis that the yearly cycle of coastwise water movement is largely controlled by seasonally changing winds. They also showed complex convergences of both surface and bottom waters which shift along the coast, as well as a layered drift structure which periodically directs surface and bottom waters in opposite directions. Results of several drift studies in the northwestern Gulf of Mexico which preceded this study are summarized by Hunter and others (1974). The second phase began in July 1973, when the study was shifted to the coast off north-central Texas . This report presents the first year results in the north-central area where studies are continuing.

Texas↗