Devonian age

Holmes isolated U minerals from a Devonian -age rock. He measured the U contenl by the rate of production of radioactive Rn gas, which is a decay product along the way to Pb. To measure Pb, he fused (Section 28-2) each mineral in borax, dissolved the fused mass in acid, and quantitatively precipitated milligram quantities of PbS04. The nearly constant ratio Pb/U = 0.046 g/g in 15 minerals was consistent with the hypotheses that Pb is the end product of radioactive decay and that little Pb had been present when the minerals crystallized. More importantly, the average age of the minerals was 370 million years. 

Figure 7.4. A sedimentation diagram for a hypothetical Devonian-age carbonate sequence. The curve for the sequence gives its inferred position relative to sea level and land surface elevation since the time of its sedimentation. Schematic subsurface isotherms are also presented based on estimates of crustal thickness and hypothetical heat flow values related to plate movements and igneous activity. [Adapted from Siever s (1979) representation of the Esopus Formation.]...

Studies in Kentucky have shown that soils derived from the same parent rock, a black fissle shale of Devonian age, can differ greatly in their Mo concentrations (Massey and Lowe, 1961). For example, soils from the Colyer series classed as lithosols, which are shallow, with deep broken topography, contain much higher amounts of Mo than do the red-yellow and gray-brown podzolic intergrade soils that have gentle slopes and are moderately well drained. Some soils in the Colyer series, upon liming, produce Mo concentrations in alfalfa that are toxic to livestock (Massey and Lowe, 1961). 

The sandstones of the Alexandra Formation, like those of Beacon Heights Orthoquartzite and the Hatherton Sandstone, contain only a few trace fossils. Nevertheless, the Devonian age of the Alexandra Formation is indicated by its correlation to the Beacon Heights Orthoquartzite which contains impressions of lycopod stems (Plumstead 1962), while the overlying Aztec Siltstone contains abundant fossil fish and plant microfossils which constrain a Devonian age (McKelvey et al. 1970, 1972 Helby and McElroy 1969). 

In summary, the Sr/ Sr ratios of calcite in carbonate rocks of Triassic, Permian, and Devonian age indicate that this mineral did not precipitate from seawater. Instead, the calcite probably precipitated from pore water percolating through the sediment after deposition. The strontium in solution in the pore water originated by incongruent dissolution of detrital grains of K-feldspar, biotite, and other Rb-bearing minerals in the sediment. We conclude that even marine sandstones (e.g., the Alexandra Formation) may contain diagenetic carbonate lenses and concretions that formed after deposition and therefore did not form in a marine environment. 

The former association of Marie Byrd Land (MBL) with northern Victoria Land (NVL) was tested by isotopic age determinations of the Swanson Formation in the Ford Ranges located east of Edward Vn Peninsula in MBL (Adams 1986 Adams et al. 1995). The Swanson Formation consists of folded metasedimen-tary rocks that were intruded by granitoids of Late Devonian age and by leucogranites of Jurassic to Cretaceous age. These plutons are surrounded by contact metamorphic aureoles of biotile homfels that are 100-500 m wide. The pre-Devonian deformation of the Swanson Formation was accompanied by low-grade regional metamorphism of the rocks. 

The third and final hole was completed in 1999 and reached sandstone of the Beacon Supergroup of Devonian age. The final depth of CRP-3 was 934 mbsf. The reports arising from the study of the third... 

The major areas of coal distribution are principally in the Northern Hanisphere with the exception of Australia, the southern continents are relatively deficient in coal deposits. This relatively uneven distribution is the result of the deposition and maturation of the plant at different times in the geological past in predominantly tropical latitudes, and the subseqnent drift of the continents to their present-day positions. The oldest coals of any economic significance date from the Middle Carboniferous Period— the earliest geological strata in which coal has been identified are of Devonian age bnt they are generally of little economic significance. With the exception of parts of the Triassic Period, major coal deposits have been forming somewhere in the world throughout the last 320 million years. Sedimentary sequences of the last 2-3 million years do not contain coal— there has been insufficient time for them to develop from plant debris. 

The Marcellus Shale is the most expansive shale gas play, spanning six states in the northeastern United States. The estimated depth of production for the Marcellus is between 4000 and 8500 feet (Table 5.5). The Marcellus Shale is a Middle Devonian-age shale bounded by shale (Hamilton Group) above and limestone (Tristates Group) below (Figure 5.5). 

The Woodford Shale play is located in south-central Oklahoma it ranges in depth from 6000 to 11,000 feet (Table 5.6). This formation is a Devonian-age shale bounded by limestone (Osage Limestone) above and undifferentiated strata below (Figure 5.6). Natural gas production in the Woodford Shale began in 2003 and 2004 with vertical well completions only (Cardott, 2004) however, horizontal drilling has been adopted in the Woodford Shale, as in... 

The Antrim Shale play is a brown to black, pyritic, and organic-rich shale located in the upper portion of the lower peninsula of Michigan within the Michigan Basin. This Late Devonian-age shale is bounded by shale (Bedford Shale) above and by limestone (Squaw Bay Limestone) below and occurs at... 

Additionally, it can now be suggested that there is a Siberian unit, based on a high level of vertebrate and tracheophyte endemism however, the marine benthos do not show evidence for this, that is, it may be purely a terrestrial and brackish-water unit. The New Zealand Region is recognised only for the Emsian, since both earlier and later Devonian age strata are unknown there, except for the slightly earlier Baton River Formation Tasman Region fauna known in north-west Wellington (Shirley, 1938). 

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