Sedimentary rocks structure

On a time series of Quaternary marine terraces in northern California, Brimhall et al. (1992) conducted the first mass balance analysis of soil formation over geologic time spans. This analysis provided quantitative data on well-known qualitative observations of soil formation (i) the earliest stages of soil formation (on timescales of 10 -10 yr) are visually characterized by loss of sedimentary/rock structure, the accumulation of roots and organic matter, and the reduction of bulk density and (ii) the later stages of soil development (>10 yr) are characterized by the accumulation of weathering products (iron oxides, silicate clays, and carbonates) and the loss of many products of weathering. 

Of interest is the detailed structural configurations that can form in sedimentary rock formations, because hydrocarbons are nearly always found in sedimentary rocks. The structural features of interest are faults and folds [26]. 

Fractures, fissures, and joints are openings in sedimentary rocks formed by the structural (mechanical) failure of the rock under loacls caused by earth crust tectonics. This form of porosity is extremely hard to evaluate quantitatively due to its irregularity. 

The Yamizo Mountains are mostly occupied by Paleozoic-Mesozoic sedimentary rocks, mainly of Jurassic age (e.g., Sashida et al., 1982) with a small amount of intrusive granitoids of unknown ages. The Paleozoic-Mesozoic sedimentary rocks have been called the Yamizo Formation (Kanomata, 1961). It is composed chiefly of shale, sandstone, alternating beds of shale and sandstone, and a small amount of limestone and chert. The succession of the geologic units and geologic structure of the Yamizo Formation have been left pending due to complex structure such as upturned beds (Kasai, 1978) and submarine land sliding (Aono et al., 1985). 

Sedimentary rocks from oil reservoirs exhibit significant porosity where crude oils and water often coexist to share the pore space. The characterization of the pore structure and the fluids in situ is essential in the development of oilfields and specifically in the design of the production strategy and the facility. NMR has become an increasingly important well-logging and laboratory technique to quantify rock and fluid properties. 2D NMR has recently been introduced to the petroleum industry as a commercial well-logging service [58]. We will first review a few examples of the 2D NMR experiments on the sedimentary rocks in laboratory and well-logging applications. 

The isotopic composition of carbon in carbonaceous organic material (kerogen) from ancient sedimentary rocks gives information on whether photosynthetic organisms were present during rock formation or not. It can also provide information on biological activities if cellular structures had already been destroyed. Sulphur can be used in a similar way (Schopf, 1999). 

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

Strucmral trap Geological structures, such as diapirs, that retard the migration of petroleum through marine sediments and sedimentary rock. 

The Pinguino veins, occupy more than 30 fault controlled structures. They have a NW and ENE strike and are hosted in Triassic continental sedimentary rocks and lower Jurassic epiclastic and volcaniclastic rocks, and are spatially related to lower Jurassic subvolcanic dioritic intrusions, basaltic sills and andesitic porphyries (Jovic etal. 2005). 

It is interesting to note that the 1M polymorph represents an ordered form while lMd structures are disordered (Guven and Burnham, 1967) and that the typical sequence in the process of glauconitization is lMd to 1M (Burst, 1958). Illite remains, for the most part, disordered even in Paleozoic sedimentary rocks (Velde and Hower, 1963). This would suggest that the glauconite structure, being more symmetric, might be more stable than illite, a point which will be discussed when experimental studies are considered. 

Microprobe analyses of some berthierine pellets from sedimentary rocks (Velde, e t al., 1974, and new data, Figure 30) indicate that these minerals have compositions close to those of 7 8 chlorites delimited by synthesis studies and here there is a more restricted range of silica substitution in the structure than is found in 14 8 chlorites. Thus the two polymorphs have at least different limits in tetrahedral substitutions. 

Another type of analcime concentrations in sedimentary rocks are analcimolites. These are rocks composed almost entirely of granular, spherulitic analcime. Beds up to 1 to 2 m thick have been described in Jurassic formations of Georgia (9). Similar rocks have been found by Buryanova (10) among analcime tuffs and tuffaceous sandstones of early Carboniferous deposits of Tuva. Analcimolites are structurally similar to the rocks described by Vanderstappen and Verbeek (11) in Cretaceous and Jurassic rocks of the Congo. These authors assumed a sedimentary... 

Treibs isolated the first porphyrin coordination complex from a Swiss marl,265 and showed that it (or at least a structurally related derivative) occurred in a wide variety of sedimentary rocks and asphalts. He showed it to contain vanadium and subsequently the involvement of the vanadyl ion was proved.266 Treibs also described a second chelate from the same original source, which he proposed to be an iron complex. Somewhat later it was shown that the complex contained the Ni" ion. It is thus appropriate, and in view of much of the foregoing discussion, to focus attention on the detailed structure of the few fully characterized geoporphyrin complexes recently reported, since their elucidation crowns some five decades of intense activity in this area of coordination geochemistry. 

Compared to bone material, the composition and structure of flint is much simpler. Flint takes part in the big family of silicon-containing sedimentary rocks. It is basically composed of homogeneous microcrystalline silica grains, which give it a homogeneous macroscopic aspect. The name flint especially defines rocks where the cortex is thin and the heart of the stone is characterised by the absence of calcite. The majority of flint is found dispersed in sediments or as subcontinuous... 

Figure 17.2 Geologic index map showing major structural and tectonic features, sedimentary rock-hosted gold deposits, and the three study areas. The area lies between 24 25110" and 26 32 00" N latitude and 104 14,00,/ and 106o07,00, E longitude. Adapted from Peters (2002).

The effect of gravitational compaction in the structure of sedimentary rocks. Bull. Am. Assoc. Petroleum Geol., 10 1035-1072. 

When a portion of the rock is well-cemented while the material around it is not, this can result in differential erosion as the weaker material is worn away. Concretions are masses of well-cemented sediment that often form around a core, sometimes a fossil or a fragment of rock. These structures are often spherical or rounded and occur in many different types of sedimentary rocks. 

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