USGS Science⌕ Search

Geology topics

T. D. Fouch

Publications and source records attributed to T. D. Fouch.

11 recordsLinked to original sources
USGS1994

Miocene and Pliocene lacustrine and fluvial sequences, Upper Ramparts and Canyon village, Porcupine river, east-central Alaska

Cenozoic strata exposed along the Porcupine River between the Upper Ramparts and Canyon Village, Alaska, can be divided into five unconformity-bounded units (sequences) which are: lower and middle Miocene unit A, the white sandy fluvial sequence with peat beds; middle Miocene unit B, the basalt sequence-part B1 is basalt, and part B2 is organic-rich sedimentary beds; upper Miocene unit C, mudrock-dominated lake sequence; late Miocene or Pliocene to Pleistocene unit D, terrace gravels, detrital organic matter and associated sediments, and Holocene unit E, mixed sand and gravel-rich sediment and other sedimentary material including peat and eolian silt. The sequence (unit A) of lower and middle Miocene fluvial deposits formed in streams and on flood plains, just before the inception of local volanism. Fossil pollen from unit A suggests conifer-dominated regional forests and cool temperate climates. Peat beds and lake deposits from unit B contain pollen that indicates a warmer temperate climate coinciding with the middle Miocene thermal maximum. The lake deposits (unit C) downstream from the basalts accumulated in a small basin which resulted from a hydrologic system that was dammed in the late Miocene but breached soon thereafter. The lower part of the terrace gravels (unit D) expresses breaching of the dammed hydrologic system (of unit C). The Porcupine River became a major tributary of the Yukon River in late Pleistocene time when Laurentide ice blocked drainage from the Yukon interior basins causing meltwater to spill over the low divide separating it from the Porcupine River drainage initiating erosion and capture of the Yukon interior basins. ?? 1994.

Quaternary International↗
USGS1994

40Ar 39Ar age constraints on neogene sedimentary beds, Upper Ramparts, half-way Pillar and Canyon village sites, Porcupine river, east-central Alaska

40 Ar/ 39 Ar ages of volcanic rocks are used to provide numerical constraints on the age of middle and upper Miocene sedimentary strata collected along the Porcupine River. Intercalated sedimentary rocks north of latitude 67°10′N in the Porcupine terrane of east-central Alaska contain a rich record of plant fossils. The fossils are valuable indicators of this interior region's paleoclimate during the time of their deposition. Integration of the 40 Ar/ 39 Ar 40 Ar 39 Ar "> results with paleomagnetic and sedimentological data allows for refinements in estimating the timing of deposition and duration of selected sedimentary intervals. 40 Ar 39 Ar "> 40Ar39Ar plateau age spectra, from whole rock basalt samples, collected along the Upper Ramparts and near Half-way Pillar on the Porcupine River, range from 15.7 ± 0.1 Ma at site 90-6 to 14.4 ± 0.1 Ma at site 90-2. With exception of the youngest basalt flow at site 90-2, all of the samples are of reversed magnetic polarity, and all 40 Ar/ 39 Ar age spectrum results are consistent with the deposition of the entire stratigraphic section during a single interval of reversed magnetic polarity. The youngest flow at site 90-2 was emplaced during an interval of normal polarity. With age, paleomagnetic and sedimentological data, the ages of the Middle Miocene sedimentary rocks between the basalt flows at sites 90-1 and 90-2 can be assigned to an interval within the limits of analytical precision of 15.2 ± 0.1 Ma; thus, the sediments were deposited during the peak of the Middle Miocene thermal maximum. Sediments in the upper parts of sites 90-1 and 90-2 were probably deposited during cooling from the Middle Miocene thermal maximum. 40 Ar/ 39 Ar results of plagioclase and biotite from a single tephra, collected at sites 90-7 and 90-8 along the Canyon Village section of the Porcupine River, indicate an age of 6.57 ± 0.02 Ma for its time of eruption and deposition. These results, together with sedimentological and paleomagnetic data, suggest that all of the Upper Miocene lacustrine sedimentary rocks at these sites were deposited during a single interval of reversed magnetic polarity and may represent a duration of only about 40,000 years. The age of this tephra corresponds with a late late Miocene warm climatic interval. The results from the Upper Ramparts and Half-way Pillar sites are used to estimate a minimum interval of continental flood basalt activity of 1.1–1.5 million years, and to set limits for the timing and duration of Tertiary extensional tectonic activity in the Porcupine terrane. Our data indicate that the oroclinal flexure that formed before the deposition of the basalts at the eastern end of the Brooks Range was created prior to 15.7 ± 0.1 Ma.

Alaska↗
USGS1994

Simulations of the origin of fluid pressure, fracture gen­ eration, and the movement of fluids in the Uinta Basin, Utah

The Altamont oil field in the deep Uinta basin is known to have reservoir fluid pressures that approach lithostatic. One explanation for this high pore-fluid pressure is the generation of oil from kerogen in the Green River oil shale at depth. A three-dimensional simulation of flow in the basin was done to test this hypothesis. In the flow simulation, oil generation is included as a fluid source. The kinetics of oil generation from oil shale is a function of temperature. The temperature is controlled by (1) the depth of sediment burial and (2) the geothermal gradient. Using this conceptual model, the pressure buildup results from the trade-off between the rate of oil generation and the flow away from the source volume. The pressure increase depends primarily on (1) the rate of the oil-generation reaction and (2) the permeability of the reservoir rocks. A sensitivity analysis was performed in which both of these parameters were systematically varied. The reservoir permeability must be lower than most of the observed data for the pressure to build up to near lithostatic. The results of the simulations indicated that once oil generation was initiated, the pore pressure built up rapidly to near lithostatic. We simulated hydrofractures in that part of the system in which the pressures approach lithostatic by increasing both the horizontal and the vertical permeability by an order of magnitude. Because the simulated hydrofractures were produced by the high pore pressure, they were restricted to the Altamont field. A new flow system was established in the vicinity of the reservoir; the maximum pore pressure was limited by the least principal stress. Fluids moved vertically up and down and laterally outward away from the source of oil generation. The analysis indicated that, assuming that one is willing to accept the low values of permeability, oil generati n can account for the observed high pressures at Altamont field.

AAPG Bulletin↗