Silurian rocks

Table I. Bituminous Substances in Ordovician and Silurian Rocks from Mobile Oil Co. No. 1 long Well, Centre County, Pa.a...

Fig. 6.8. a Temperature and b maturation histories of the Silurian source shales in the Takhoukht region computed for the main variant with erosion in Fig. 6.2 solid lines) and for the variant without erosion in Fig. 6.7 dashed lines). The temperature of Silurian rocks did not exceed 85 C during the preerosion period and, therefore, the present-day maturation level does not differ in either variant... 

Fig. 6.14. Hydrocarbon (HC) yields solid line), rates of hydrocarbon generation (dashed line), and expulsion threshold in the geological history of the Silurian source shales of the Oued el-Mya Basin. Calculations used time-temperature history of the Silurian rocks and activation energy spectrum shown in Makhous et al. (1997). Two stages of hydrocarbon generation took place in the basin history in the pre-erosion Carboniferous and during the Greta ceous-Cenezoic...

Fig. 6.16. Burial, thermal, and maturation histories of the sedimentary section of the Akfadou region, Ghadames Basin. The greater volume of sedimentation compared with the variant of Oued el-Mya Basin in Fig. 2 in Makhous et al. (1997) led to the greater level of maturation of organic matter in Silurian rocks, despite a moderate level of Hercynian uplift...

This realm is definitively known exclusively from the southern two-thirds of South America and north-west Africa. The Disa Siltstone fauna of South Africa is now (Boucot, 1999) considered to be of latest Ordovician, Hirnantian age, although an Early Llandovery age was considered earlier. If shallower-water brachiopod faunas of Silurian age are recovered from southern Africa they would be expected to be similar to those of the Afro-South American Realm known from so many South American localities, as is also the case with the Falkland Islands, where Silurian rocks are currently unrecognised. The northernmost occurrence is in the Amazon Basin, with numerous occurrences from the Titicaca region of southern Peru and adjacent Bolivia southerly into northwestern Argentina (in the provinces of Salta and Jujuy). 

The BSC (part of the Dunnage tectonic Zone) formed in Late Ordovician to Early Silurian (i.e., during the Salinic Orogeny), and contains the accreted and subducted remnants of the Middle to Late Ordovician Tetagouche-Exploits back-arc basin. Consequently, the rocks of the BSC have... 

The geology of the area consists of rocks from three time periods (Fig. 1) Silurian (Kingsclear Group), Devonian (Harvey Group) and Carboniferous (Mabou... 

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... 

In the northern part of the TCZ, the Chaleurs Group comprises subaerially deposited. Late Silurian bimodal volcanic rocks that overlie early Silurian shallow marine fine- to coarse-grained clastic and carbonate sedimentary rocks. The Chaleurs Group is overlain disconformably by bimodal volcanic rocks and interlayered sandstones and siltstones of the Dalhousie Group. 

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. 

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. 

Coal deposits, usually called beds or seams, can range from fractions of an inch to hundreds of feet in thickness. Coals are found in all geologic periods from Silurian through Quaternary, but the earliest commercially important coals are found in rocks of Mississippian age (Carboniferous in Europe). Coals generally... 

The reservoir rocks that yield crude oil range in age from Precambrian to Recent geologic time but rocks deposited during the Tertiary, Cretaceous, Permian, Pennsylvanian, Mississippian, Devonian, and Ordovician periods are particularly productive. In contrast, rocks of Jurassic, Triassic, Silurian, and Cambrian age are less productive and rocks of Precambrian age yield petroleum only under exceptional circumstances. 

Figure 8.37. Burial history plot for Helderberg Group rocks and other strata. Helderberg Group is shaded, whereas the base of Ordovician strata, base of Silurian strata and base of Mississippian strata are shown as thin lines marked O, S and M. Dashed lines are time-temperature indices of maturity (TTI see Waples, 1980). The oil generation window represents the necessary conditions of time and temperature for potential oil generation. The 50° oil preservation deadline is the upper TTI limit for occurrence of oil with API gravity of 50°. (Modified from Dorobek, 1987.)...

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