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R.C. Circe

Publications and source records attributed to R.C. Circe.

11 recordsLinked to original sources
USGS1995

Seafloor environments within the Boston Harbor- Massachusetts Bay sedimentary system: A regional synthesis

Modern seafloor sedimentary environments within the glaciated, topographically complex Boston Harbor and Massachusetts Bay area have been interpreted and mapped from an extensive collection of sidescan sonar records and supplemental marine geologic data. Three categories of environments are present that reflect the dominant long-term processes of erosion or nondeposition, deposition, and sediment reworking. (1) Environments of erosion or nondeposition comprise exposures of bedrock, glacial drift, coarse lag deposits, and possibly coastal plain rocks that contain sediments (where present) ranging from boulder fields to gravelly sands and occur in areas of relatively strong currents. (2) Environments of deposition contain fine-grained sediments ranging from muddy sands to muds that have accumulated in areas of predominantly weak bottom currents. (3) Environments of sediment reworking contain patches with textures ranging from sandy gravels to muds that have been produced by a combination of erosion and deposition in areas with variable bottom currents. The distribution of sedimentary environments across the Boston Harbor-Massachusetts Bay area is extremely patchy. Locally, this patchiness is due either to modifications of bottom-current strength (caused by the irregular topography and differences in water depth) or to small-scale changes in the supply of fine-grained sediments. Regional patchiness, however, reflects differences in geologic and oceanographic conditions among the estuarine, inner shelf, and basinal parts of the sedimentary system. The estuarine part of the system (Boston Harbor) is a depositional trap for fine-grained sediments because it is protected from large waves, has generally weak and variable tidal currents, and receives a large supply of fine grained detritus from natural and anthropogenic sources. The inner shelf, on the other hand, is largely an area of erosion or nondeposition due to sediment removal and redistribution during past sea-level changes, to sediment resuspension and winnowing by modern waves and currents, and to an inadequate supply of fine-grained sediments. The basinal part of the system (Stellwagen Basin) is mainly a tranquil depositional environment in which fine-grained sediments from several potential sources settle through the water column and accumulate under weak bottom currents. This study indicates areas within the Boston Harbor-Massachusetts Bay sedimentary system where fine-grained sediments and associated contaminants are likely to be either moved or deposited. It also provides a guide to the locations and variability of benthic habitats.

Massachusetts Bay↗
USGS1990

A dolomitized shelfedge hardground in the northern Gulf of Mexico

An elongated calcareous hardground occurs on the shelfedge northeast of the Mississippi Trough. High-resolution seismic reflection profiles show that the hardground is in 90-110 m of water, is 70-250 m wide, at least 2.3 km long, and of low relief (5-10 m). The hardground is composed of dolostone and coquinoid limestone, and exhibits a dead biofacies of nodular and encrusting calcium carbonate-secreting organisms that are significantly different from those forms living in the adjacent unconsolidated sediments. Cementation of the hardground substrate by primary dolomite was initiated during early diagenesis close to the sea floor and progressed by concretionary growth under an interstitial environment partially open to marine molecular fluxes. The bicarbonate necessary to form the dolomite came from an admixture of isotopically light thermogenic and sedimentary organic carbon sources and an isotopically heavier marine source. Exposed surfaces of the dolostone, which have been heavily bioeroded, are covered by an oxidized, goethite-rich, reddish-brown rind. The coquina is primarily composed of whole and fragmented mollusk shells and was deposited in a higher-energy environment than the precursor sediments of the dolostone. The hardground was preserved during the Holocene transgression because of its lithified nature and the top has been intermittently swept free of finer detritus by current action.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS1982

Determination and analysis of bearing capacity of calcarenites off the Florida Keys

A specially designed instrument was used to determine the in situ bearing capacity at 12 sites in the carbonate sand seaward of the Florida Keys. The resulting data set not only represents unique information in such an environment, but also provided an opportunity to determine whether bearing capacity is controlled by any specific property of the calcarenites, or, conversely, whether the bearing-capacity value could be used as an index of a particular substrate characteristic. The in sltu measurements were made in several subenvironments in order to bracket the variability of sediment properties throughout the area. Samples were collected at each bearing-capacity test site and w .ere analyzed for selected geological and geotechnical properties, including texture, grain shapes, and biological constituents. No relationship was found between bearing capacity and any of the analyzed properties of the sediment. Although many salient characteristics of calcarenites exist, at the stress levels used in this study their influence is either masked owing to the complex interaction of properties that leads to a specific bearing-capacity value or, at least in these sediments, is absent.

Open-File Report↗