Geology topics
Research about Maine
Source-linked reports with geographic coverage including Maine.
Exploratory geophysical traverses in the Oakfield Hills area, Smyrna Mills Quadrangle, Maine
Ground magnetic, gravity, and electromagnetic measurements in the Oakfield Hills area have delineated a series of steeply dipping, dikelike rock units with high apparent susceptibility, high density, and often high conductivity. The measurements were made to investigate the source of a 3000-gamma aeromagnetic anomaly. The rock units are apparently a series of lenticular beds of manganese-bearing iron formation which have been thermally metamorphosed by a nearby intrusion. Some of the electromagnetic anomalies are probably caused by the presence of sulfides.
Physical and ecologic features of the Sagadahoc Bay Tidal Flat, Georgetown, Maine
Sagadahoc Bay is open to the ocean at the south and has no significant fresh-water stream entering it. The intertidal zone is roughly a mile long by half a mile wide; most of it is made up of medium to fine sand, but organic-rich mud characterizes the head of the flat and the protected coves. Refraction-seismograph surveys showed that the bedrock surface lies 30 to 200 feet below the surface of the tidal flat and that it is irregular and fluted longitudinally. Repeated surveys indicate that the intertidal flat builds up and cuts down but is apparently in equilibrium with the present sea level. The sediment that fills the bay came from the sea. Waves and tidal currents tend to move it landward; storms accelerate this, or reverse the direction of movement, depending on the characteristics of the storm. Tidal- and wave-generated currents 0.1 foot above the bottom range in velocity from 0.35 to 0.82 foot per second on incoming tides and from 0.20 to 0.58 foot per second on ebbing tides. Incoming tides float large quantities of sand landward; ebbing tides never carry floating sand. Two distinctive and extensive Mya shell-pavement layers were found at depths of roughly 2 and 3 feet below the present surface of the tidal flat. The lower layer is approximately 1,000 years old according to a radiocarbon age determination of its Mya shells. It is suggested that these shell layers formed by sluicing away of a layer of sand about 2 feet thick, which had been thrown into loose packing by an earthquake at high tide. The earth shock induced a submarine slide of the sand in the outer part of the bay, which oversteepened the profile of the sand headward nearly to the head of the bay. Mya and other shells settled through the layer of quicksand while the sand was running out seaward. Living in the intertidal zone is the usual assemblage of clams, gastropods, crustaceans, worms, and seaweeds found on most northern New England tidal flats. The Mya arenaria population is decreasing, but in general myas are more numerous in the muddy areas than in the sandy areas. They grow more rapidly in the sand, though in the past decade there has been no significant renewal of the Mya population in the sandy part of the flat. Macoma balthica inhabits the muddy areas, whereas Ensis, Spisula, and Arctica are restricted to the low-tide zone and the shallow water below. Gemma gemma grows in great abundance in the sandy part of the flat but is rare in the muddy parts. Small shrimp and green crabs are common. The calcareous shells of these animals are all potential fossils, but the shrimp and crab exoskeletons are not, for their tests are rapidly decomposed in this environment. Other potential fossils are wood and bark, acorn caps, conifer cones, leaves of deciduous trees, seeds, and occasionally even grass stems and pieces of eel grass. All these are reasonably well preserved in the constant reducing environment that prevails an inch or two below the surface. An inverse relationship exists between the abundances of Mya arenaria and Gemma gemma. Cores and test pits show that gemmas are more numerous on the Sagadahoc flat now than they have been in the recent past (estimated 10–100 years). Gemmas are the dominant mollusk in the sandy part of the flat now that the myas are so extremely rare. The speculation is that gemmas became dominant largely because the Mya population was greatly reduced by intensive digging during and just after the last war and through depredations by green crabs. Possibly the warming climate has favored the gemmas selectively. The writer infers that the gemmas are a serious competitor of the myas and that the gemmas now starve out Mya spat, which is known to be carried into the bay each spring and fall. Two recommendations are made: (1) determining under controlled laboratory conditions the food requirements of Gemma and the density of Gemma population that will permit survival of Mya larvae from set through a stage that will assure maturation; and (2) killing off a large percentage of the Gemma population and observing whether or not a natural set of Mya occurs. Gemmas can be killed quickly under a flame shield such as is used to soften asphalt-sand mixtures in street paving. Inasmuch as gemmas are ovoviviparous they should not repopulate the flat rapidly.
Current velocities in Sagadahoc Bay, Maine
During the summer of 1953 continuous velocities were obtained through a tidal cycle at each of the 17 stations indicated on the accompanying map. Tidal cycle as used in this report applies to the interval of 4 to 6 hours when the tidal flat at a given station is submerged. The velocities were measured by recording current meters set 0.1ft., 1.0ft, and 3.0ft above the bottom. Velocities at 0.1ft above the bottom are the bottom velocities discussed in this report. Velocities at the other heights were used for comparision.
Preliminary report on the Passamaquoddy bedrock survey, July-August, 1951
In order to understand the results of the Passamaquoddy bedrock survey and the details of the method of obtaining them, it is desirable to have, in outline, a general idea of the methods and their application. In this part of the report a general account of the operation will be developed. The details will be found in subsequent parts of the report. At this point a statement of the general objective and some mention of the plans for reaching it are in order. The purpose of the Passamaquoddy survey was to determine the submarine geology in certain areas of Passamaquoddy and Cobscook Bays--the sea-bottom topography, the bedrock topography, the thickness of sediment overlying the bedrock beneath the sea, and the type of sediment. The information is needed for the planning of major engineering structures that may be built in the area. It developed in planning the study that detailed surveys could be limited to several areas where dams may be located. To determine bottom or bedrock topography, elevations of each were determined by sonic methods at a number of closely spaced locations (about 400 feet apart), evenly distributed on range lines 1,000 or 800 feet apart, in each of eight areas. Contour lines were then drawn to produce the desired topographic maps. Sonic soundings are necessarily referred to the existing water surface. To ascertain specific elevations in an area of large tidal variations is a complex problem. The details are discussed in the section on Vertical Control by Charles E. Knox (part 8). The basic datum is mean low water as determined by the U. S. Coast and Geodetic Survey. Equally important is the accurate positioning horizontally of each sounding location or fix. All such positioning was by the use of the standard three point fix procedure, using sextants. A net of shore points tied to the first-order control net of the Coast and Geodetic Survey was set up for this purpose, and all positions were thus accurately located. These problems are discussed in a section on Horizontal Control by Norman Duckworth (part 7). The general planning was done in conferences held in May 1951 at the Boston office of the Corps of Engineers, and in Eastport, Maine, after a brief reconnaissance of the area. A detailed account of the conferences is given in a memorandum by Herman J. Kropper of the New England Division, Corps of Engineers, reproduced in this report as part 4. Detailed survey procedures were developed on May 18, 1951, at a conference attended by P. J. A. Scott and Norman Duckworth of the Corps of Engineers and W. O. Smith of the Geological Survey. In order to make the necessary geophysical interpretation of the sound records, adequate geologic control had to be established. A preliminary field study of the geology was made by G. G. Parker of the Geological Survey during the period May 15-17, 1951. Subsequently Dr. T. E. Upson of the Geological Survey made the detailed geologic study required for the project. Two sonar units were used for the survey. One was a low-frequency high-power sonar unit developed by the Edo Corp. to meet specifications established by the Geological Survey. It was used to collect the bulk of the bedrock and bottom data. The other, of higher frequency and lower power, was manufactured by Bludworth Marine, Inc., end was required for adequate determination of water depths in shoal areas. The Edo equipment is described by Dr. Charles E. Mongan, Jr., in part 6 of this report.
Reconnaissance of radioactive rocks of Maine
The state of Maine was traversed with car-mounted Geiger-Mueller equipment in the late summer of 1948 and the radioactivity of approximately 4,600 miles of road was logged. All samples were analyzed, both in the field by comparing the radioactivity of each sample to the radioactivity of a stranded measured with a simple scaling modification of a portable counter, and in the Geological Survey’s Trace Elements Section Washington Laboratory. Differences between both types of analyses were negligible. The maximum equivalent uranium content of the most radioactive rocks thus analyzed was 0.008 percent. A 1,400-square-mile abnormally radioactive province in southwestern Maine was outlined. The outcrop data obtained from car traversing are evaluated statistically. Cumulative frequency distribution curves are drawn to show the distribution of outcrops at various levels of radioactivity, and straight-line extensions are made to show to maximum probable grade for various rock types and areas in Maine. A maximum grade of 0.055 percent equivalent uranium is thus predicted for the entire state. This prediction necessarily is a broad generalization because large areas of Main are inaccessible for car traversing. A concept of evaluation of an area for possible mineral deposits is proposed on the basis of lithology, and observed and indicated ranges in grade.
The sediments and physical environment of the Sagadahoc Bay tidal flat, Georgetown, Maine
This investigation of the sediments of the Sagadohoc Bay tidal flat was undertaken at the suggestion of the State Geologist of Maine, Dr. Joseph Thefethen, in the hope that the results might be helpful to the biologists of the Maine Department of Sear and Shore Fisheries in their studies of clam productivity and the biologists of the U.S. Fish and Wildlife Service who are making a systematic study of the ecology and potential yields of the soft-shelled clam (Mya arenaria) in Sagadohoc and neighboring bays. The field stage of the investigation lasted from early July to the end of August 1949, during which time I was assisted by W. H. Condon of the U.S. Geological Survey. This report and the accompanying map were prepared in Washington, where the laboratory studies of the sediments were made by T. Woodward of the U.S. Geological Survey.
Occurrence of manganese in eastern Aroostook County, Maine
Manganiferous rocks are found in two areas in eastern Aroostook County, Maine, one west and northwest of Presque Isle and the other south of Houlton. The manganiferous deposits are sedimentary lenses, up to 150 feet thick and half a mile long, in middle Silurian argilllte. The rocks of both areas are much deformed, but the deformation is less intense and the continuity of the deposits therefore greater in the Presque Isle area than in the Houlton area. The dip of the rocks at most deposits is steep to vertical. Below the zone of oxidation the manganese occurs as carbonate and as the silicates braunite and bementite. These minerals are primary constituents of the shales and should continue downward to the limits of the sedimentary units that contain them. One deposit, which has been explored by drill- ing to an average depth of 130 feet, contains about 11 percent of manganese, but most of the deposits probably contain be- tween 6.5 and 9 percent. There are many millions of tons of these manganiferOus shales in the county. Some of the deposits contain 20 percent or more of iron., mostly as hematite and limonite, and magnetite is abundant in the Houlton area. In parts of the deposits above the water table about 30 percent of the manganese occurs as a heavy stain of secondary oxides along joints and parting planes. . The manganese oxides partly replace the primary rock minerals for a distance of 1 to 3 millimeters from cracks in the rock. At the one deposit from which drilling data are available, manganese oxides are found on only a few fractures below the water table, which is at a depth of 20 feet, and none were seen in rocks from below 45 feet. It is estimated that there may be over 1,700,000 tons of partly oxidized manganiferous shale in the region. Some of the deposits are overlain by a thin zone, probably about a foot thick, that is richer in manganese than the underlying oxidized rocks. At the deposit explored by drill- ing, the average manganese content of the deposit as a whole is 76.4 percent of the average as determined from surface sam- ples. The surface enrichment is believed to have taken place before the last advance of the Pleistocene ice, which may have scraped off the enriched part of many deposits. There are probably less than 100,000 tons of enriched rock in all the scattered deposits of the region. There is a very much greater tonnage of low-grade unenriched manganlferous rock in Aroostook County, but it cannot be utilized until methods of extraction have been improved.
Strategic minerals investigations, preliminary map: Black Mountain area, Rumford, Maine
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Water resources of the Penobscot River basin, Maine
This report on the Penobscot River drainage system, the largest and one of the most important in Maine, has been compiled chiefly from the records, reports, and maps of the United States Geological Survey and from the results of surveys made in cooperation with the Maine State Survey Commission. The report includes all data on precipitation, stream flow, water storage, and water power that were available at the end of the calendar year 1909 and is accompanied by plans and profiles of the principal rivers, lakes, and ponds in the basin (Pis. XIII-XIX, at end of volume). Stream-flow data for 1910 and 1911 will be published in Water-Supply Papers 281 and 301, respectively.
Geology of the pegmatites and associated rocks of Maine, including feldspar, quartz, mica, and gem deposits
No abstract available.