Proportions Of Clay Minerals Research Articles

Chemistry of the Ordovician and Silurian greywackes of the Snowy Mountains, southeastern Australia: An example of chemical evolution of sediments with time

The Ordovician quartz-rich greywackes of the Snowy Mountains region are essentially mixtures of two components. These are quartz and clay minerals. The chemistry of any rock is largely determined by its proportions of clay minerals so that there is a strong negative correlation between Si and those elements, other than Si, contained in clay minerals. Elements that occur only in feldspar, but not in clay minerals, that is Ca, Na, Sr and Pb, have a low and variable concentration. These four elements have even lower abundances in the Silurian greywackes deposited in basins on a basement of the Ordovician rocks. This is interpreted to have resulted from a further cycle of chemical weathering that acted on Ordovician source rocks to produce the Silurian detritus. In a similar fashion, the Ordovician rocks are thought to have formed by weathering of more feldspar-rich sedimentary rocks at the margins of the Lachlan Fold Belt. Two episodes of chemical weathering are therefore recognised. The first produced the feldspar-poor Ordovician rocks; the second acted on part of these to form the almost feldspar-free Silurian strata. In both cases, Ca, Na, Sr and Pb were lost as feldspars were converted to clay minerals.

Interparticle Action and Rheology of Dispersive Clays

The determination of the various interacting parameters in the phenomenon of clay soil dispersibility needs consideration of pore fluid chemistry, mineralogy and proportions of clay minerals, and resultant particle interaction. The need to develop an appreciation of soil dispersibility in view of the preceding has resulted in the examination of clay particle interaction with respect to the effects and influence of various salts, and in particular, the potential determining anions on the dispersive performance of certain clays. Various concentrations of NaC1, NaHCO3 and 15 meq/L NaOH were used in the preparaton of soils consisting of Kaolinite, ilite, montmorillonite, and mixtures of these clay minerals, with primary attention paid to kaolinite for the development of particle-interaction models for evaluation in terms of a flocculation-deflocculation status through a study of their rheological properties, light transmission, zeta potential, and adsorption-desorption phenomena. (Authors)

Mineralogy and heavy metal contents of soils and stream sediments in a rural region of Western Germany

This paper presents the results of a study of clay mineralogy and Pb, Zn, Cu, Rb, Sr, Y and Zr analyses of soils and stream sediments of the Schwarzach watershed, a drainage system located in a secluded rural region of eastern Bavaria, far removed from major industrial installations. Clay fractions of soils and stream sediments differ significantly in their mineralogy. The soils average 50% secondary chlorite and 40% illite, whereas recent stream sediments average 20% chlorite and 70% illite. These assemblages are possibly interconvertible under the influence, or on withdrawal, of Schwarzach water. Proportions of clay minerals in fossil stream sediments average approximately 30% chlorite, 50% illite, and 20% kaolinite with up to 10% of 10–14 Å interstratified minerals. Surface soil layers have been enriched in Pb, as have recent stream sediments. The latter have also been enriched in Zn and Cu. The increased amounts of Pb plus its close association with organic C indicate atmospheric deposition of Pb and incipient eutrophication of the Schwarzach River.

Sediment sourcing in the Gangetic alluvium, Himalayan Foreland Basin – competition between Himalayan and cratonic hinterland

DOI = 10.3126/hjs.v5i7.1330 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.149

Occurrence, Mineralogy, and Origin of the Lower Golden Valley Kaolinitic Clay Deposits Near Dickinson, North Dakota

Kaolinitic clay deposits occur in the lower member of the Golden Valley Formation of western North Dakota. The Eocene deposits are from 10 to 40 feet thick, flat lying, and stratiform. They consist of three consistent stratigraphic units; sand in the lower part, clay in the middle, and silt in the upper part. Limonite concretions lie in a definite horizon and stain the clay bright orange where weathered. A thin lignite or carbonaceous silt overlies the clay. Poorly crystallized kaolinite is the dominant clay mineral in the deposit, and 2M-type illite, halloysite, montmorillonite, mixed-layered illite-montmorillonite, and montmorillonite-chlorite are present in varying amounts. Chlorite is present in the enclosing sediments but absent in the clay deposits. The clay mineral content is very uniform within the area studied, but a definite stratigraphic variation in clay mineral proportions is indicated. The kaolinite content increases upward within the deposits as does montmorillonite; the illite content decreases. Various theories of genesis are considered, but sedimentary structures and mineralogic and textural characteristics support the theory that the deposits originated detritally. Deposition in a large, freshwater, lake basin in a sub-tropical climate is postulated. The source of the kaolinitic clay may have been pre-Eocene rocks that lay to the west, but a widespread, deep-weathered zone in these rocks has not been established.

Clays of Deep Shale Zone, Caillou Island, Louisiana

The shales in the thick Tertiary section of southern Louisiana are largely uniform and lack lithologic contrasts, with the result that conventional logging methods and geophysical surveys often yield inconclusive data. In an effort to provide useful supplementary information, a program of mineralogical study has been conducted for several years at Columbia University on clays from a significant southern Louisiana locality, Caillou Island. Materials available for study have included a few conventional cores, numerous side-wall cores and extensive suites of cuttings. The principal techniques applied have been bulk density measurement by flotation and indentation as an indication of compaction. In addition, core textures have been examined on polished surfaces and mineralogical identifications have been made by means of the X-ray diffractometer, X-ray fluorescence, and optical examination. Likewise optical data have been supplemented by index determinations on fused clays. Clay mineral constituents of the section are almost entirely illite, montmorillonite, and kaolinite, normally in about the same relative amounts, but on the south flank of the dome an important change in distribution ranges is recognized at the top of a deep shale zone. Purified Caillou Island illite has been pressed to form a series of small briquettes at regular intervals in the range 0-50,000 psi. to provide reference material compacted under known static load. The briquettes have been tested for bulk density and relative indentation numbers and the resultant curves have been found to show straight-line relationships. These curves have been used as reference lines in examining bulk densities and indentation numbers of well samples in the range 5,000-18,000 ft. Abnormal deviation from the reference curves in certain wells is believed to indicate differential domal compaction in excess of compaction from the gravitational component. The distribution of the anomalies may be structurally significant. A deep shale zone south of the Caillou Island dome yields an unexpected reduction in indentation numbers and bulk densities with some redistribution of clay mineral proportions. The break in bulk density and indentation curves at the top of this zone in a local area suggests low-angle fault movement associated with the domal intrusion.

Compaction of Sediments

An attempt is made to explore the theoretical relations between compaction of sediments and depth of burial. On the basis of available data and assumptions that seem to be reasonable, a porosity-depth curve for mud and shale is constructed and overburden pressure is calculated. From these data, other relations of interest in stratigraphy are derived. Mud and shale are compacted in several stages that involve: (1) squeezing out of interstitial water until the sedimentary grains come in contact with each other; (2) rearrangement of grains and development of closer packing; (3) soft clay minerals are forced into the interstices between the more resistant minerals; (4) the latter are deformed until all porosity is eliminated. The colloidal properties of clay are very important in this process whose results appear to be predictable for sediments with different proportions of clay minerals. Much less compaction is possible in sand and sandstone because initial porosity is much lower. Colloidal effects are negligible. Most compaction appears to result from intergranular solution but the results are unpredictable because intergranular cement strengthens structure. No consistent relations exist between porosity and depth of burial. The consolidation of limestone is not understood. The initial porosity of most calcareous sediments is greater than that of sand but most limestones show little evidence of compaction. Their consolidation appears to have been accomplished by the deposition of intergranular cement at an early stage before the sediment was subjected to the pressure of much overburden. The source of the cementing calcium carbonate is not known. Organic material, of which coal is presented as an example, is reduced in volume by (1) compression and elimination of pore space, and (2) the loss of substance resulting from, first, biochemical decay and, later, dynamochemical metamorphism. Coal is essentially non-porous and its volume is reduced also by dehydration and increase in specific density. The degradation of organic matter follows one or the other of two paths: (1) carbonaceous (coal), leading to development of larger and more complex molecules (polymerization), or (2) bituminous (oil and natural gas), leading to the development of smaller and simpler molecules (cracking). The difference probably is related to the type of decay that occurs very soon after organic material is deposited as a sediment. Compaction data probably can be applied to the solution of some stratigraphic and structural problems but serious difficulties will remain until the lithification of limestone is more adequately understood. The study of diagenesis has been greatly neglected and it deserves much increased attention from geologists. End_Page 273------------------------------