Geology Reports⌕ Search

Geology topics

James V. A. Trumbull

Publications and source records attributed to James V. A. Trumbull.

7 recordsLinked to original sources
USGS2003

Geology and biology of the sea floor as deduced from simulaneous photographs and samples

During 1963, 260 paired photographs and large bottom samples were taken on the continental shelf and slope off northeastern United States. The photographs revealed surface characteristics of the sediments and natural attitudes of benthic animals; the samples retrieved specimens for geological and biological examination and identification. Samples are the best source materials for making textural studies of sediments consisting mostly of sand, silt, or clay, but photographs are better than samples for bottoms too bouldery for proper sampling. Ripple marks and other surface irregularities revealed by the photographs supplement textural studies of the samples in deducing effects of wave movements and currents upon bottom materials. For biological studies, the photographs yield much information on relationships of the benthic fauna to bottom materials, but they fail to provide useful data on biomasses. Biomasses and accurate taxonomic identifications are far better made upon samples. Thus, a combination of photographs and accompanying samples provides maximum information for biological as well as geological purposes.

Limnology and Oceanography↗
USGS1979

Relationship between physical condition of the carbonate fraction and sediment environments: Northern Puerto Rico shelf

Each of three sediment types recognizable on the northern Puerto Rico shelf and beaches is characterized by calcareous material in different physical condition. Dark terrigenous sand is accumulating at a relatively rapid rate and has a carbonate fraction containing fresh-appearing angular particles. The pure-carbonate skeletal-sand sediment type has a much lower rate of deposition, and its old-appearing calcareous particles have a dull surface luster. The third sediment type, a mixture of the first two, is largely from beaches and is characterized by highly polished, very well-rounded grains. Differences in length of sea-floor exposure and intensity of abrasion appear to be responsible for the variable physical condition of the carbonate fractions. We suggest that on other shelves having less distinctive sedimentary regimes, the physical condition of the carbonate grains could be used to interpret present shelf processes.

Puerto Rico↗
USGS1974

Tectonic transition zone in the northeastern Caribbean

Seismic reflection data indicate that the Atlantic plate has been underthrust beneath the Caribbean plate east of the Lesser Antilles. The data further reveal that the transition from underthrust to strike-slip plate motion occurs near lat 19.3° N. and long 62° W. in alinement with the Anegada Trough. Oceanic basement and reflectors above basement have not been detected beneath the landward wall of the Puerto Rico Trench west of the transition zone. Southeast of the zone, the horizontal distance over which the reflectors and basement can be traced beneath the landward wall (outer part of the Lesser Antilles rise) systematically increases from a few kilometers in the north to as much as 37 km near lat 16.5° N. If a thrust fault emerges at the landward trench wall, the data suggest that a decollement exists between reflectors above basement and an overlying acoustically transparent zone. Gravity and seismic refraction data indicate a thick accumulation of low-density, low-velocity material beneath the Lesser Antilles rise, possibly sediments scraped off the underthrusting Atlantic plate, although massive slumping might cause a similar low-density configuration. The magmatic history of the Lesser Antilles arc suggests two periods of underthrusting, one in the Mesozoic or early Cenozoic and a second in the late Cenozoic. Although the magmatic history of the Lesser Antilles apparently began in the Mesozoic, its Cenozoic history is remarkably similar to the Cenozoic histories of circum-Pacific arcs. Magmatic histories in both areas suggest that island arc evolution in the Cenozoic may have worldwide synchroneity.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Geology of a system of submarine canyons south of Puerto Rico

A strongly dendritic submarine canyon system with four major canyons occupies a 30-km indentation in the insular shelf off the south coast of Puerto Rico between Guanica and Ponce. Each canyon has several headward branches at depths of 100 to 1,100 m. Each of the five major rivers that reach the coast between Guanica and Ponce is opposite a canyon head, and off each of the rivers a channel 20 to 30 m deep is incised into the insular shelf. The entire canyon system is 40 km long and terminates at a depth of about 3.3 km; no fan or other constructional feature appears to have been formed. A 410-km continuous seismic profiling survey shows that three unconformable stratigraphic units underlie the canyon area. One sample of indurated clay of probable Miocene age was dredged from a canyon-wall outcrop of the middle stratigraphic unit. The three stratigraphic units may be roughly correlative with (in ascending order) the Juana Diaz Formation, the Ponce Limestone, and an unnamed upper section found in a nearby drill hole ashore. Canyon-axis sediment at depths of 700 to 2,200 m is entirely of pelagic origin, indicating that sediment is not now being transported down the canyons.

Guanica, Ponce↗