Thirty-seven tephra beds, primarily from coal partings in the Sterling and Beluga formations, were successfully dated by the 40Ar/39Ar method providing a new and revised understanding of the chronostratigraphy of late Tertiary strata within Cook Inlet Basin. Meticulous sample preparation, multiple analyses, and statistical evaluation of the data were required for these low-K, plagioclase- and hornblende-bearing tephras. Dating of subsurface core material provides the first subsurface-to-outcrop tie in Cook Inlet between well 212-24 in the Beluga River Unit and deposits in the Clam Gulch, Diamond Creek, and Fox Creek areas. The new 40Ar/39Ar chronostratigraphic framework place the age of upper part of the Kenai Group strata between 4.6 and 9.4 Ma and support the 8-Ma interpretation of the boundary between the Homerian and Clamgulchian paleobotanical stages. The 49-Ma age from core data in Pioneer Unit suggests the Tyonek Formation is older than previously thought or that these units belong to an older formation. The chronostratigraphic framework demonstrates significant offset on faults along the Kenai Peninsula, the presence of faults in slumps and vegetated areas, disconformities in the stratigraphic succession, and that parts of the Sterling and Beluga formations are time-equivalent strata representing lateral facies variations. Based on crosscutting relations and structural folding, the established chronohorizons indicate that much of the structural deformation in Cook Inlet is no older than early Pliocene in age. The repeated section, due to faulting and the coeval nature of the formations, could significantly affect previous resource assessments of coal and hydrocarbon distributions.
We have updated a simple polyvinyl chloride plastic canister design by adding internal headspace temperature measurement, and redesigned it so it is made with mostly offthe-shelf components for ease of construction. Using self-closing quick connects, this basic canister is mated to a zero-head manometer to make a simple coalbed methane desorption system that is easily transported in small aircraft to remote localities. This equipment is used to gather timed measurements of pressure, volume and temperature data that are corrected to standard pressure and temperature (STP) and graphically analyzed using an Excel based spreadsheet. Used together these elements form an effective, practical canister desorption method. Introduction: This paper presents a system for coal core and drill cuttings desorption that is simplified from existing custom made designs (McLennan et al., 1995; Mavor and Nelson, 1997). This system emphasizes simpler desorption canisters and manometers constructed with off-the-shelf materials and parts. This construction is used because our field areas are usually in remote, sparsely developed areas, our concept is to keep the method and equipment as simple yet light as practical and still have robust equipment that can stand up to unattended air or road transport to remote localities. Further, because the equipment is adapted from widely available, off the shelf equipment, it has proven possible to buy materials and construct canisters in rural locations. Our system, with 10 to 20 three-inch canisters to desorb and sample gases, can fit in three 20 to 40 gallon plastic household storage containers. At the well site, the storage containers also serve as tanks for the constant temperature baths. Construction of Basic Desorption Equipment: Canisters The canister body is made from polyvinyl chloride (PVC) plastic pipe and fittings that are all commercially available schedule 40 grade materials (Appendix 1). The canister body diameter is determined by two factors, the core diameter, and the need to fit the core piece length and diameter as closely as possible to minimize headspace. For core diameters in the 2 to 2.75 inch range, we use 3 inch internal diameter schedule 40 PVC pipe. For cores in the 3 to 3.75 in range, we use 4 inch internal diameter schedule 40 PVC pipe. We cut this material in a 14 inch length (Figure 1) for a 12 inch core piece. The extra two inches are to allow one inch for pressure plug insertion and one inch for the inefficient packing of inadvertently broken core pieces. We find that the 14 inch length and 3-and 4 inch pipe diameters cover the common range of coal core pieces available to us. While intermediate PVC pipe diameters may fit core diameters more closely, the pipe fittings for these sizes can be harder to find and even less commonly found in rural field areas. Other sizes are possible based on a scaled version of our design, but we have found that the three and four inch pipe diameters fit most of the common core sizes used on exploration wells. Core pieces of less than ...
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