Benjamin H. Richard

Pre-Mount Simon basin under the Cincinnati Arch

A newly discovered sedimentary basin underlies the Mount Simon Sandstone (Upper Cambrian) below part of the Cincinnati Arch in southwestern Ohio. On the basis of preliminary examination of samples and geophysical data, the basin is tentatively traced for at least 160 km north-south and 48 km east-west in Ohio and adjacent Kentucky and Indiana. The basin is located in an area with sparse control in the deep subsurface, near the boundary of the Grenville and the Eastern granite-rhyolite provinces. Core recovered from the basin consists of a homogeneous, tightly compacted, grayish-red, lithic arenite. A seismic profile across the core site shows a layered sequence containing eastward-dipping seismic reflectors which extend to a depth of at least 5,200 m. Further work is required to determine the basins precise structural history.

Integrated Geophysical Studies of Buried Valley Aquifers

Integrated geophysical studies of three buried valley aquifers in southwestern Ohio were made to compare the effectiveness of various geophysical techniques in outlining the extent and depth of these valleys. All of the areas have been overridden by two or more Pleistocene glaciers and each valley contains sequences of till and outwash. These buried valley deposits are the primary water source for the region. This paper summarizes the results of the geophysical studies and proposes a strategy for geophysical investigations of shallow buried valleys in glaciated areas. The techniques used in the integrated studies were gravity, magnetics, resistivity, ground‐penetrating radar, seismic refraction, and seismic reflection.Gravity, seismic refraction profiling, and seismic refraction fan shooting surveys were far superior to other geophysical methods in delineating buried valleys. Buried valleys show up as gravity lows of -2.7 to -0.7mGal due to the increased porosity of the fill materials relative to bedrock....

Middle Tertiary Unconformity, North Boulder and Jefferson Basins, Southwestern Montana

The middle Tertiary unconformity, mappable throughout the Townsend, Clarkston, and Three Forks basins (Robinson, 1960), can be mapped also throughout the North Boulder and Jefferson basins. In the North Boulder basin, as in the Three Forks basin, the unconformity is erosional; in the other three basins it may be angular as well. The unconformity separates strata as young as middle Oligocene from strata as old as upper Miocene. The topography in the North Boulder and Jefferson basins at the end of the middle Tertiary erosional episode was apparently similar to the present topography, but drainage was probably to the southwest. Then, as now, one or more broad benches rose gently toward the mountain fronts, and at least part of one bench rose from a scarp bordering the floodplain of the ancestral Jefferson River.

GEOPHYSICAL SURVEY TECHNIQUES FOR IDENTIFYING POTENTIAL COLLAPSE FEATURES UNDER HIGHWAYS

An abandoned coal mine under Interstate 70 in eastern Ohio collapsed and created a large crater along the highway a few years ago. A myriad of unmapped features under the States roadways threatens similar localized collapses. These catastrophic failures may cause loss of life and always cause traffic disruption and require extensive repair expenses. Identifying the zones, which are likely to fail, would allow remedial action to prevent future failure. Methods to locate these zones need to be inexpensive enough to allow widespread use but focused enough to target very specific problem areas. Geophysical survey techniques have the potential for meeting these requirements. The principal objective of the present research study was to develop a reconnaissance geophysical survey technique to delineate the zones that can be further investigated by borings or by localized geophysical studies to determine the nature and probability of significant failures. Accordingly, several different geophysical techniques were adopted during the summer of 1998. The results obtained from this study show that seismic refraction, resistivity imaging and surface wave profiling have the most potential for meeting the project objectives and should be studied further in phase two.

Precambrian Structures of Western Ohio

Ten wells in western Ohio, eastern Indiana, and northern Kentucky have penetrated pre-Mount Simon sedimentary rocks and several hundred kilometers of seismic data allow us to map units below the Mount Simon Sandstone in western Ohio. Most of the wells sampled a lithic arenite, the Middle Run Formation, but one well penetrated over 300 m of carbonate rocks. The seismic data reveal pre-Mount Simon basins that are about 25 km wide and are normally about 2000 m deep, but range in depth. They appear to be structural basins that formed primarily after the Middle Run Formation was deposited. Two basins are located on top of the Grenville Front and, therefore, are younger than Grenville rocks and older than Late Cambrian Mount Simon rocks. Thus the basins could be as young as Middle Cambrian, but at least post-date the Grenville Orogeny.