Compositional Variation in Component Layers in Natural Illite/Smectite
Published chemical data for suites of mixed-layer minerals from diagenetic sedimentary rocks, hydrothermally altered tufts, and a metasomatic bentonite bed indicate that the layer charge and composition of the different components of illite/smectite (I/S) differ from one geological environment to another. It appears that the composition of the elemental smectite and illite layers in the I/S is more or less constant for samples within each geologic setting. In the examples considered, the smectite layers are predominantly montmorillonitic in character (i.e., the charge is in the octahedral site), whereas the illite layers show different types of charge sites, depending upon the suite studied. Illite layers appear to have about the same charge in all three suites studied, slightly more than 0.7 per O10(OH)2 unit, whereas the smectite layers in the different suites range in charge from about 0.3 to 0.7 per O10(OH)2 unit. Cation-exchange capacities reflect these differences in charge, although not ideally. The differences in the composition of the component layers in each geologic suite of mixed-layer clays are probably due either to differences in the bulk chemistry of the rocks in the different suites or to differences in intensive variables, such as temperature and pressure, of the regime under which they have formed.
Metasomatic and non-metasomatic low grade metamorphism of Ordovician meta-bentonites in Sweden
Abstract Bulk rock and electron microprobe analyses of two series of meta-bentonite beds one of which was subjected to low grade metamorphic conditions indicate that: 1. (a) K is the most important element in the metasomatic transformation of volcanic ash into bentonite clay mineral assemblages. Al content of the ash beds is closely related to K content 2. (b) Low grade metamorphism of such bentonites does not greatly influence the major element chemistry of the beds 3. (c) Low grade metamorphism does affect Rb-Sr abundances in the beds indicating that while major elements are more or less isochemical during the process of recrystallization, minor elements can behave as mobile elements.
Water Production from Abnormally Pressured Gas Reservoirs in South Louisiana
ABSTRACT The author has had an opportunity over the years to become familiar with a number of cases in which abnormally pressured gas wells have been produced to, or almost to, depletion. In some cases, the pressure declined to or below the economic limit without the appearance of salt water; in others, large quantities of water have appeared after a period of production of gas without water. Since these reservoirs are not artesian but are confined by some type of barrier, there must be some mechanism which causes the water to ascend to the well bore. This paradox is examined and cases of production of water and non-production of water are described with suggestions of possible causative mechanisms.