Cambro-Ordovician

Cambro-Ordovician altered meta-rhyolitic pyroclastics are host to the Thalanga Zn, Pb and Cu massive sulfide deposit in Queensland (Govett Atherden 1987). Beyond the sub-outcrop gossan zone mineralization is covered by up to 70 m of Tertiary horizontal terrestrial sandstones, conglomerates and siltstones (Campaspe beds). 

Geological Setting The IRAC is hosted in folded and faulted sedimentary rocks of Cambrian to lower Ordovician age (Currie 1975). These units are the slaty-limestone of the McKay Group (Cambro-Ordovician), massive limestone of the Ottertail Formation (Cambrian), and the sheared argillaceous rocks of the Cambrian Chanceller Formation (Allan 1914, Aitken Norford 1967). 

Orogen (Williams 1995). The Meguma Terrane is made up primarily of Cambro-Ordovician metasedimentary rocks of the Meguma Group and approximately one third of the terrane has been intruded by Late Devonian granitoid batholiths, the largest of which is the South Mountain Batholith (MacDonald 2001). These basement rocks are overlain by the sedimentary rocks of the Maritimes Basin. 

Metallogeny of the gold-enriched Cambro-Ordovician rocks in the Annidale area, south-central New Brunswick, Canada... 

The estimated ultimate recovery is also reported by the geologic age of the reservoir. It is recognized that problems may arise where the geologic age of a reservoir cannot be determined specifically, such as Permo-Pennsylvanian and Cambro-Ordovician, or where production from reservoirs of different geologic age is combined. 

Triplehorn (1967) post-depositional in Cambro-Ordovician sandstone, Algeria. 

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 Glenelg River Complex comprises part of the Cambro-Ordovician Delamerian Orogen... 

He, Z., Gregg, J. M., Shelton, K. L., and Palmer, J. R., 1997, Sedimentary facies control of fluid flow and mineralization in Cambro-Ordovician strata, southern Missouri basin-wide diagenetic patterns in SEPM Conference on Basin-wide diagenetic patterns Integrated petrologic, geochemical, and hydrologic consideration. Lake Ozark, Missouri, United States, p. 81-99. 

In the Tri-State region, the stratigraphic section above the Precambrian basement, consists of Cambrian and Ordovician dolomites and sands, and generally less permeable Devonian, Mississippian, Pennsylvanian and Pleistocene sedimentary rocks. The Cambro-Ordovician section is the source of the... 

The major source of recharge of the Cambro-Ordovician aquifer is the area around the Ozark Mountains of southwestern Missouri. The generalized potentiometric surface for the Cambro-Ordovician aquifer is shown in Fig. 

Freshwater moving westward in the Cambro-Ordovician section encounters saline, H2S-bearing waters near the Kansas—Missouri boundary. The transitional zone between the two water masses serves as the source for various public supply wells in eastern Kansas. West of this zone, water too saline for general public use is encountered. 

Fig. 2. The potentiometric surface of the Cambro-Ordovician aquifer in the Tri-State region with sample locations. (Potentiometric data provided by the Kansas Geological Survey.)...

Macfarlane, P.A., 1980. Distribution of radium-226 in the Cambro-Ordovician ground-water system, Tri-State region, Kansas, Missouri, and Oklahoma. Meet. South-Cent. Sect., Geol. Soc. Am., Rolla, Mo. (abstract). 

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. 

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. 

Fig. 3.6a,b. Mechanical compaction features of Saharan reservoirs, a Contact type plot for sandstones from 1 Cambro-Ordovician, Hassi Messaoud oil field (cement content cement content <12%), 3 Triassic, Hassi R Mel gas field (cement content <16%). b Correlation curves of I reservoirs porosity,2 adjacent shales density,3 montmorillonite/illite proportion in adjacent shales, 4 potassium content in shales also... 

Fig. 3.6c,d. Mechanical compaction features of Saharan res-servoirs. c Correlation curves of contact index with depth for Triassic, Devonian and Cambro-Ordovician reservoirs, Oued el-Mya Basin i sandstones with 20-30% ductile cement, 2 sandstones with 20-10% ductile cement, 3 sandstones with less than 10% ductile cement, d Comparative correlations of tight packing index for Devonian sandstones with 10-15% ductile cement from i Ghadames Basin, 2 Oued el-Mya Basin,... 

It goes without saying that the 150 mg dissolved silica per 1 in the formation waters of the Cambro-Ordovician reservoirs may represent a source for cementation and compaction of the sandstones whereas the 7 mg silica per 1 in the Triassic formation waters will not have any effect on the cementation of sandstones containing 6-12% of secondary silica. We thus still have to locate an important source for the cementation of the sandstones. 

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. 

We present some dissolved silica data here for waters from various environments in northern Algeria subsurface waters 5-10 ppm, thermal waters 5-20 ppm, shallow nearshore water 1-2 ppm, fluvial surface water 11-12 ppm. Meteoric waters with 10-15 ppm dissolved silica are known to circulate to depths of many hundred of meters and therefore could present a cement source (Blatt 1979). Although surface water contains some silica in solution which might promote quartz cementation at shallow depth, it is clear that this silica content is too little to account for the amount of authigenic quartz present in Saharan oil-field sandstones at depths of several thousand meters. In the Hassi Messaoud oil field formation water from the Cambro-Ordo-vician reservoirs contains about 150 ppm dissolved silica, formation water from the Albian reservoirs in the same field contains 15 ppm, while in the Berkaoui oil field Albian formation water contains 10 ppm, Triassic water 3.6 ppm and Hassi R Mel (gas-condensate) Triassic formation water contains 5-7 ppm silica. It is obvious therefore that the 150 ppm of dissolved silica found today in Cambro-Ordovician reservoirs could... 

Naphthene-paraffinic type (saturated cycloalkanes, isoalkanes, more rich in naphthenic and aromatic components than the former type), occurring in the Cambro-Ordovician Hassi Messaoud,El-Gassi, Rhourde el-Baguel, Silurian Oulouga, Triassic Berkaoui and El-Bourma oil pools. 

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