Ordovician period

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. 

Ordovician Period Geologic period of the Paleozoic Era after the Cambrian Period between 500 and 435 million years ago. Major advances during this period include the bony fish and possibly land plants (during the late Ordovician). 

The earliest fossil record of fungi in terrestrial ecosystems occurred during the Ordovician period (480 to 460 MYBP) (Heckman et al, 2001). Since that time fungi have been ubiquitous components of the microbial... 

Silurian A geological period of the Palaeozoic era following the Ordovician period and extending until the beginning of the Devonian period. It began about 444 million years ago and lasted for about 28 million years. 

Wade and Cathey (1986) also reported isotopic age determinations of feldspar and biotite of the Hope Granite by the K-Ar and Rb-Sr methods. However, feldspars do not retain radiogenic " Ar and the initial Sr/ Sr ratios used to calculate the Rb-Sr dates were not provided. Therefore, the reliability of these dates is uncertain. However, two Rb-Sr dates of biotite from Longhorn Spurs (84°40 S, 174°4LW) and Den Hartog Peak (84°20 S, 178°52 E) indicate that the granitic rocks at these locations cooled sufficiently to retain radiogenic Sr at 470 25 Ma during the Ordovician Period. 

The largest known trilobite, with a length of 28 inches, is Isotelus rex from the late Ordovician period of Manitoba. 

The Order Siphonotretida is known from the Cambrian and Ordovician periods with numerous and sometimes abundant genera, and is characterised by hollow spines and a ventral pedicle foramen. The Siphonotretidae has been considered to... 

Nevertheless, cellulose has been a slow developer and scholars associate its first clear appearance with the microscopic green seaweeds of the Ordovician period, i.e. celllulose is probably no more than 500 million years old. Prior to this, complex polysaccharides may have played a role in the development of primitive cells walls. One such is the glycolipid or lipopolysaccharide. 

Such interpretations must be approached with great caution As Taylor (3) logically points out, the fossil record (from both structural and morphological perspectives) is far too incomplete to draw any firm conclusions. Indeed, the earliest land plant forms may have appeared in the Ordovician period and Taylor has proposed that Cooksonia plants should be given consideration as the forerunners of early vascular plant forms. But this too is open to question since many of the specimens examined apparently lack any primitive vascular system (6). Given this state of confusion, it is... 

Ordovician 500 Myr Diversification of echinoderms, other invertebrate phyla, jawless fishes. Mass extinction at end of period (ca. 85To of all species disappear)... 

If the asteroid-impact theory is correct, the extinctions should be repetitive and the Ir anomaly should be observed in other geological stratigraphic levels corresponding to known extinctions. About five other massive extinctions (besides the one at the end of the Cretaceous Period) have been noted [25]. These come at the end of the Cambrian ( 500 MY ago), the Ordovician (M35 MY age), the Devonian ( 345 MY ago), the Permian ( 230 MY ago) and the Triassic ( 195 MY ago) Periods. 

The first large mass mortality occurred during the end-Ordovician, 440 My ago (Fig. 16.1). A less extensive loss took place during the late Devonian, followed by the huge mass mortality of the end-Permian, 250 My ago, when the trilobites - marine arthropods that had survived the late Ordovician event - disappeared. Coming after a period of dry cold climate that saw the Appalachian mountains buUd up, the end-Permian mass mortality brought to extinction more than half the families of living species. It paved the way to the scleractinians, which formed the coral reefs (Stanley 2001). 

The Period-averaged mass ratio of calcite to dolomite (Figure 10.29) is relatively high for Cambrian, Permian, and Tertiary System rocks, whereas this ratio is low for Ordovician through Carboniferous age sediments and rises in value from the Triassic through the Recent. The generalized sea level curve of Vail et al. 

Paleozoic Era The period of time beginning 570 million years ago ending 245 million years ago falls between the Proterozoic and Mesozoic Eras and is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods. 

Silurian Period The geological time period of the Paleozoic Era following the Ordovician, between 435 and 395 million years ago, when plants colonized the land. 

A survey has shown that the city of Enshi, Hubei Province, China, has three major Se-enriched deposition periods including the early Cambrian, Late Ordovician, and Permian periods. The stone coal formed during the first two periods has a low Se content of 30 pg g, which is similar to the stone coal formed in Early Paleozoic in Southern Shaanxi. However, the black shale series formed in the Permian period have a Se concentration that is at least threefold higher than that of the former two. There is a cross-cutting low-Se area with brown soil series from northeastern to the southwestern China including more than 10 provinces. Approximately 72% Chinese are deficient in Se, while there are about 1.5 billion people living in Se-deficient areas worldwide (Banuelos, 2009). 

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