Middle Devonian rocks

The rocks of the TCZ are interpreted to have erupted in a transtensional continental rifting environment in the Late Siiurian to Middle Devonian. In this tectonic environment A-type granites are expected, and indeed the reiativeiy high Zr, Nb, and Y content in these rocks support this. However, many other geochemicai aspects of these rocks, i.e., high Ba, Rb, Th and K, are more typical of the I-type magmas that commonly occur in collisional settings. 

Table IV. Carbohydrate Components of Middle and Upper Devonian Rocks of Central Pennsylvania0...

The relative increase in carbohydrates in the Middle Silurian and Middle Devonian is suggested as resulting from a period of increased organic productivity during the deposition of those rocks. 

Qing, H. Mountjoy, E.W. (1994b) Rare earth element geochemistry of dolomites in the Middle Devonian Presqu ile barrier. Western Canada Sedimentary Basin implications for fluid-rock ratios during dolomitization. Sedimentology, 41, 787-804. 

Ores of antimony sometimes occur m the Devonian rocks of Rhenish Prussia between Wintrop and Meutrop, four miles from Arnsberg, where are found bands of bituminous limestone from 6 inches to 18 inches in thickness, interstratified between clay slates and siliceous shales. Stil)uite penetrates all these strata, which are overlain by Millstone Grit. Tt is-also noticed that the stibnite accumulates more plentifully towards the middle part of the various beds, but gradually thins out near the bedding planes of deposition. Sometimes fragments of the country are included in the more massive portions. (D.)... 

To briefly summarize, the Late (and Middle) Devonian source shales are potentially of commercial interest in the Ghadames, South Timimoune and Reggane, whereas the Silurian source rocks are potentially of commercial interset in the basins of the Triassic Province, North Sbaa and North Timimoune. In these regions, these two source horizons display a similar potential for hydrocarbon generation. 

Whole-rock K-Ar dates of slate and siltstones of the Mariner Group in Appendix 4.8.4.2, reported by Adams et al. (1982), range from 417 3 (Lower Devonian) to 380 3 Ma (Middle Devonian) and are lower than the age indicated by fossils (late Middle to late Late Cambrian), although they do overlap with the K-Ar dates of the Sledgers Group in Fig. 4.20. 

Andesites of the Black Prince Volcanics have whole-rock K-Ar dates of 323 6 and 375 6 Ma (Late Devonian to Early Carboniferous) reported by Adams et al. (1986). These dates are in good agreement with age determinations of the Admiralty Intrusives in Fig. 4.21. The lava flows at Mount Black Prince are interbedded with sedimentary rocks that contain plant fossils of Middle Devonian to Early Carboniferous age (Findlay and Jordan 1984). 

The study area is situated in the Tobique-Chaleurs Zone, (TCZ) which contains early to middle Silurian sedimentary and volcanic rocks (Chaleurs group) that are disconformably overlain by Lower Devonian volcanic and sedimentary rocks of the Dalhousie and Tobique groups (Wilson 2004) and is bounded by the Rocky Brook-Millstream Fault to the northeast and the Mackenzie Gulch Fault to the north (Fig.1). The McCormack Brook Fault (a splay of the Rocky Brook-Millstream Fault) lies to the north of the... 

Bituminous Substances. The distribution of hydrocarbons and other bitumens in some of the Paleozoic rocks of the area is shown in Tables I and II, the latter summarized after Swain (7). The presumed saturated hydrocarbons of the Ordovician, Silurian and Lower Devonian samples are measurably less than in the Middle and Upper Devonian samples. The presumed aromatic hydrocarbons are not as well differentiated. The pyridine-plus-methanol-eluted chromatographic fractions, arbitrarily taken as asphaltic material, also appear, like the aromatic fractions, to be controlled more by local variations than by geologic age. 

Offshore neritic formations in the Paleozoic rock sequence probably include, on faunal and lithologic grounds, the Lower Ordovician Beekmantown dolomites, Middle Ordovician limestones, and Devonian Marcellus and Burket black shales (Table III). The first two are characterized by 0.1-0.4% organic carbons, very low organic nitrogen, and about 20 p.p.m. hydrocarbons but no carbohydrate residues. The Devonian offshore neritic black shales by contrast... 

K-Ar dates of slate and of volcanic rocks of the Sledgers Group in Fig. 4.20 and Appendix 4.8.4.1 range from 332 7 to 467 3 Ma (Adams et al. 1982 Adams 2006). Two whole-rock samples of volcanic rocks yielded K-Ar dates of 328 7 Ma (Lower Carboniferous) and 360 6 Ma (Late Devonian). AU of the K-Ar dates of the Sledgers Group are lower than the late Middle Cambrian age (i.e., -500 Ma, lUGS 2002) indicated by polymerid trilobites. The evident... 

The age of the felsic volcanics at Gallipoli Heights was determined by Faure and Gair (1970) by means of a two-point whole-rock Rb-Sr age determination based on samples collected by S.J. Carryer. The results yielded a Middle-to-Late Devonian date of 370 40 Ma (recalculated to A, = 1.42 x 10 year ) and an initial Sr/ Sr ratio of 0.70548. This value of the initial Sr/ Sr ratio is typical for continental volcanic rocks (e.g., rhyolites of Central America and Mexico Faure 2001), but it is lower than the initial ratio (at360Ma) of most of the 27 specimens of Admiralty Intrusives analyzed by Kreuzer et al. (1987). 

Fig. 8.7 The Patuxent Range forms the most southerly part of the Pensacola Mountains. It consists of nunataks composed of the Patuxent Formation (as revised by RoweU et al. 2001) which forms the local basement complex. The metasedimentary rocks of the Patuxent Formation are isoclinally folded and consist of a repetitious sequence of graywacke and slate. These rocks are younger than the fossiliferous Nelson Limestone which is late Middle Cambrian. The map area also contains outcrops of Devonian sandstone south of the Patuxent Range and of Permian siltstone and shale of the Pecora Formation in the Pecora Excarpment (Adapted from Schmidt and Ford 1969 with information from Rowell et al. 2001)...

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