Ordovician sediments

This further emphasizes the importance of sedimentary processes in the development of such fractionated Rb/Sr and Eu/Sr ratios. Second, in the context of the LFB, the Ordovician turbidites have progressively lower Eu/Sr ratios than the feldspathic Cambrian sediments from which they were partly derived. Thus, it also appears that the displacement to higher Eu/Sr is linked to the number of weathering and erosion cycles involved in the formation of particular sedimentary rock suites. In the examples in Figure 20, the reduction in strontium content for the most evolved Ordovician sediments is nearly 10-fold, and this clearly results in an associated increase in Rb/Sr, and hence with time in strontium isotope ratios. 

Hoffmann C. F., Foster C. B., Powell T. G., and Summons R. E. (1987) Hydrocarbon biomarkers from Ordovician sediments and the fossil alga Gloeocapsomorpha prisca Zalessky 1917. Geochim. Cosmochim. Acta 51, 2681-2697. 

Unit C encompasses the basal sediments of a marine transgression. As the sea level continued rising the eroded material coming from the tidal flats, the intertidal zones, the lagoons and the volcanic expanses of the Lower Series was deposited on the coastal sea floors under a shallow water cover. Most of these materials were derived from the reworking of the Cambro-Ordovician sediments and transported along the coast by coastal currents. 

Lower Paleozoic sediments in the Ahnet, Mouydir, Reggane, Tindouf and North Timimoune Basins are characterized by a high level of diagenesis (R = i.2-i.6%). In deeply buried areas in the Tindouf and Reggane Basins, R reaches 2-3% in the Cambro-Ordovician sediments. On the other hand, the Sbaa sub-basin (South Timimoune Basin) is distinguished by relatively moderate thermal gradients and R is somewhat o.9-i.o% in the Silurian and Devonian sediments. 

The crystalline host rocks are covered by Palaeozoic sediments of the Western Interior Basin. These consist of Ordovician... 

Keywords Bathurst, VMS, Ordovician, sedimentary (or sediment) lithogeochemistry... 

Total Carbohydrates. The results of the phenol-sulfuric acid tests for total carbohydrates are listed in Table 1. The Lower and Middle Ordovician dolomites and limestones of this area did not yield detectable total carbohydrates, either because they are absent or because of metamorphic degradation. Palacas (5) and Palacas, Swain, and Smith (6), on the other hand, found traces of glucose and other sugars in Lower and Middle Ordovician rocks of Franklin County, Pa. southeast of the Mt. Union area. It appears that the early and medial Ordovician seas of the Mt. Union area may neither have been receiving much carbohydrate material from the lands nor was much being contributed by organisms to the bottom sediments. 

In invertebrates, collagen is uncalcified, whereas in vertebrates it occurs in the form of soft and hard tissue. Remains of the earliest vertebrates — bony armour — are found in sediments of the Ordovician (ca. 500 million years). At about that time, conodonts appeared in the stratigraphic column mineralogically they are carbonate apatite. Conodonts are small tooth-shaped fossils 0.2 to 3 mm in size whose origin is in doubt they are most likely remains of some unknown chordata that became extinct in Triassic time516. ... 

Triplehorn, D.M., 1967. Occurrence of pure, well-crystallized 1M illite in Cambro-Ordovician sandstone from Rhourde El Baguel Field, Algeria. J. Sediment. Petrol, 37 879-884. 

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. 

Badiozamani K. (1973) The Dorag dolomitization model-application to the Middle Ordovician of Wisconsin. J. Sediment. Petrol. 43, 965-984. 

Efforts to find trace-metal evidence of extraterrestrial impact at the Ordovician-Silurian boundary have been unsuccessful (e.g., Orth et al, 1986 Wang et al, 1992). Peaks in iridium abundance at the boundary have been linked to reductions in sedimentation rate the persistent cosmic source of iridium is otherwise diluted by high terrigenous or biogenic sedimentation. 

Outstanding concentrations of n-Ci, n-Cn, and n-Ci in early Paleozoic rocks Gloeocapsomorpha prisca, marine phytoplankton of uncertain affinity, probably an alga identified in Cambrian-Devonian sediments but most prominent in Ordovician. Estonian kukersite is a typical source. Blokker et al. (2001) and Powler (1992)... 

The Ordos Basin is located about 300 km to the north of Xi an, central China. With an area of 260,000 km it is the second largest sedimentary basin in China. Its central part is characterised by nearly horizontal strata some 4,000 m thick. The sedimentary column can be divided into three major units Lower Palaeozoic marine carbonates Upper Palaeozoic coal-bearing series and Mesozoic terrestrial sediments. Oil and gas fields occur throughout these sediments. The gas is believed to originate from over-matured Ordovician carbonates and coal beds, whilst the source of the oil is thought to be lacustrine sediments of Triassic age. The region is semi-arid and the soils are thin and poorly developed. 

Kupecz, J.A. Land, L.S. (1994) Progressive recrystallization and stabilization of early-stage dolomite Lower Ordovician Ellenburger Group, west Texas. In Dolomites (Eds Purser, B., Tucker, M Zenger, D.), Spec. Publ. int. Ass. Sediment. 21, 255-279. Blackwell Scientific Publications, Oxford. 

Montanez, I.P. Read, J.F. (1992) Fluid-rock interaction history during stabilization of early dolomites. Upper Knox Group (Lower Ordovician), US Appalachians. J. sediment. Petrol., 62, 753-778. 

De Ros, L.F., Morad, S. Paim, P.S.G. (1994) The role of detrital composition and climate on the diagenetic evolution of continental molasses evidence from the Cambro-Ordovician Guaritas Sequence, southern Brazil. Sediment. Geol, 92, 197-228. 

Amthor, J.E. Friedman, G.E. (1992) Early- to late-diagenetic dolomitization of platform carbonates lower Ordovician Ellenburger Group, Permian Basin, West Texas. 7. sediment. Petrol., 62, 131-144. 

Gao, G. Land, L.S. (1991) Early Ordovician Cool Creek dolomite, middle Arbuckle Group, Slick Hills, SW Oklahoma, USA origin and modification. J. sediment. Petrol., 61, 161-173. 

Lee, Y.I. Friedman, G.M. (1987) Deep-burial dolomitization in the Ordovician Ellenburger Group carbonates, west Texas and southeastern New Mexico. J. sediment. Petrol., 57, 544-557. 

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