Charles E. Weaver

Potassium, illite and the ocean

Abstract Not only do clays extract material from the ocean but they also contribute. Sufficient clay has passed through the ocean to exert a significant influence on its chemical composition. The extraction of potassium by the formation of illite is considered by some to be one of the more important processes operative in the sea. Some of the assumptions on which this idea is based are critically evaluated. Clay minerals are presently adsorbing from the ocean more Na + and Mg 2+ than K + . Younger sediments have relatively more Na + and montmorillonite and less K and illite than older sediments. This change occurs near the end of the Paleozic and appears to be world wide. The change is believed due to an increase in the Na, and perhaps Mg, content of the oceans, caused by the rapid development of plant life and an increase in soil acidity. Montmorillonite, rather than illite, was formed in the Cenozoic and Mesozoic oceans. Much of the Paleozoic and Precambrian illite was formed on the land rather than in the ocean. Primitive biota may have aided in concentrating K in the early terrestial environment. Less than 10 % of the K + carried to the ocean today is in solution. This value may have been even smaller in the past. Considerably less K, in solution, has been cycled through the ocean than has been assumed. Since the late Paleozoic a major portion of the K removed from the ocean has been removed in the interstitial waters trapped in marine and deltaic muds. Only after deep burial is this K fixed in the illite lattice.

Mössbauer Analysis of Iron in Clay Minerals

M�ssbauer absorption spectrography can be used to establish the presence of Fe2+ and Fe3+ in clay minerals. In the sheet structure silicates, octahedrally coordinated iron can be distinguished from tetrahedrally coordinated iron. Siderite and goethite, common contaminants of the clay minerals, can usually be detected. Goethite has a well-organized structure, though, owing to its fine grain size, it may appear to be amorphous to x-rays. The various families of clay minerals show minor differences in isomer shift and quadrupole splitting values, caused by variations in the character of the octahedral layer.

MINERALOGY AND PETROLOGY OF SOME ORDOVICIAN K-BENTONITES AND RELATED LIMESTONES

Twenty-two samples of Ordovician K-bentonite were examined by the use of size analyses, heavy- and light-mineral separates, thin sections, differential thermal curves, x-ray diffraction patterns, chemical analyses, and electron micrographs. The less than one micron fraction of two typical samples was studied in detail. The K-bentonite consists of randomly interstratified expanded and nonexpanded 2:1 layers in the ratio of 1:4. In addition, many of the samples contain packets of chlorite, the cause of an endothermal peak on the differential thermal curves formerly believed due to illite. Chemical analyses of the two samples indicate a direct correlation between the percentage of K present and the percentage of nonexpanded layers (illite). The nature of the heavy and light minerals shows that the clay altered from a volcanic glass. It is believed the clay formed as an expanded 2:1 mineral (montmorillonite) and later adsorbed K which caused 80 per cent of the layers to become nonexpanded (illite). Twenty-seven samples of the limestone on either side of a series of K-bentonite beds were examined in detail. The heavy and light minerals indicate that the insoluble residue is composed of both volcanic and nonvolcanic material. The nonvolcanic material is largely a nonexpanded dioctahedral 2:1 clay (illite); the volcanic material altered to form chlorite. The chlorite and volcanic heavy minerals increase in abundance as the K-bentonites are approached. It is believed that the ash altered to chlorite because of the availability of Mg, which was probably enhanced by the presence of the calcite ooze. The “Tioga Bentonite”, a thin clay bed in the Middle Devonian, is nearly identical to the Ordovician K-bentonite.

Correlation of the marine Cenozoic formations of western North America

INTRODUCTION By Charles E. Weaver This is Number 11 of the series of correlation charts being prepared by the Committee on Stratigraphy of the National Research Council (Dunbar et al., 1942, p. 429–434.). It has been constructed by stratigraphers and paleontologists actively engaged in both field and laboratory research and is not purely a compilation of information sought for in the literature; it has resulted from continuous scientific investigations by some of the men most active in developing present-day conceptions concerning the classification of Cenozoic formations and the interpretation of the geologic history of the Cenozoic era in this part of the globe. As more critical data are obtained concerning the lithology, distribution, and stratigraphic relations of the rock formations and their contained faunas, the interpretations of the correlation and geologic history will become modified. Two schools of thought exist on the Pacific Coast regarding the classification of Cenozoic . . .

Potassium Content of Illite

The average potassium oxide content of 18 Paleozoic two-layer monoclinic illites is 8.75 percent. There is an excellent linear relation between the ratio of the intensities of the reflections at 10 angstroms and 5 angstroms (10 �/5 �) and the potassium oxide content. The frequency distribution curve of the 10 �/5 � intensity ratio of 249 Paleozoic illite-rich shales is approximately normal. The modal value is 2.0, equivalent to 9.3 percent potassium oxide, and the average ratio is 2.47, equivalent to approximately 8.5 percent potassium oxide. The illite layers of many of the mixed layer illites-montmorillonites have from 8 to 10 percent potassium oxide. With a minimum number of assumptions realistic structural formulas for the two members of a mixed-layer illite-montmorillonite can be calculated.

K, Ar, Illite Burial

K, Ar, and mineral analyses of montmorillonitic mud samples 4233 ft to 16,450 ft deep from a well in the Mississippi Delta area show that, with depth, the apparent K-Ar ages of the bulk samples decrease 100 m.y.; the >2 μ fraction is relatively constant in apparent age at approximately 400 m.y.; and the apparent age of the μ fraction decreases 40 m.y. with depth. With increasing depth and temperature, K (0.8 percent) appears to be released from the course K-feldspar and mica and to become fixed between the montmorillonite layers. Due to the formation of chloritic layers, fewer illitic layers are formed than is commonly supposed. K-Ar data may be useful in reconstructing the thermal and burial history of shales.

Construction of limpid dolomite

Protodolomite associated with Miocene palygorskite deposits of Georgia and Florida provides a clue as to how some euhedral dolomite crystals are formed. The early dolomite has a frothy texture and is formed of plates, sheets, and fragmental rhombs; with time the number of crystal faces increases, and euhedral dolomite crystals form. The dolomite grew slowly from dilute water in a schizohaline environment. The dolomite crystals were constructed layer by layer and face by face. When the supply of Mg decreased, construction ceased, thus preserving the intermediate morphologic types.

Opaline Spheres: Loosely-packed Aggregates from Silica Nodule in Diatomaceous Miocene Fuller's Earth

ABSTRACT Spheres of opaline silica, 1,000 A to 8,300 A in diameter, occur individually and in small aggregates around cavities of diatom fragments in a silica nodule from the middle Miocene Hawthorne Formation in south Georgia. The spheres are apparently equivalent to the silica spheres of precious opal, except that the spheres in precious opal are imperfectly close-packed and the spheres in this nodule are not close-packed, probably because of lack of sedimentation. The spheres are a high-silica variety of opal and presumably form in voids which are relatively inaccessible to other ions such as Al, Fe, and Mg. These opaline spheres are not present in isolated diatoms in the clay bed.

The illite-phosphate association

Abstract The insoluble (HCl) residues of phosphate grains from the Atlantic Coastal Plain, the Pacific Ocean and other areas, in addition to quartz, organic matter, and iron compounds, consist largely of K-feldspar and K-mica. Though the matrix of the phosphate sands contains a wide variety of clay minerals, only illite is present in the phosphate grains. Apparent K—Ar ages indicate most of the K-silicates are detrital in origin, though thin section studies show a minor amount of authigenic illite and glauconite are present in some phosphate grains. Chemical analyses and electron microscope studies indicate considerable amorphous material is present in the phosphate grains. The observed relations indicate that clay minerals may act as a phosphate reservoir during the formation of phosphorites and that the phosphate eventually destroys the non-K-clay minerals. The environment in which phosphate grains form is apparently similar to that in which glauconite forms.

ELECTRON MICROPROBE STUDY OF KAOLIN

Electron microprobe studies of kaolinite indicate that most of the Fe is evenly distributed throughout the kaolinite and must either be in the structure or occur as very small particles adsorbed on the surface. In addition to Ti the anatase impurities contain Fe and Mg. Fe, Mg, Mn, V, and K are present in biotite. It is necessary to concentrate the fine-grained mineral impurities in order to study them with the electron microprobe.RésuméDes études sur le kaolin, effectuées par microsonde électronique, indiquent que la plupart du Fe est réparti de façon uniforme dans tout le kaolin et doit se trouver soit dans la structure, soit en très petites particules adsorbées à la surface. En plus du Ti, les impuretés d’anatase contiennent du Fe et du Mg. Fe, Mg, Mn, V et K sont présents dans le biotite. Il faut concentrer les impuretés minérales fines pour pouvoir les étudier à la microsonde électronique.KurzreferatUntersuchungen von Kaolinit mit der Elektronenmikrosonde zeigen an, dass der Hauptteil des Fe gleichförmig durch den Kaolinit hindurch verteilt ist und entweder im Gefüge enthalten oder in Form winziger Teilchen an der Oberfläche adsorbiert worden sein muss. Neben Ti enthalten die Verunreinigungen des Anatas Fe und Mg. In Biotit sind Fe, Mg, Mn, V und K gegenwärtig. Die feinkörnigen mineralischen Verunreinigungen müssen konzentriert werden, um der Untersuchung durch die Elektronenmikrosonde zugänglich zu sein.РезюмеИсследования каолинта электронным микрозондом показывают, что большинство Fe равномерно распределено по всему каолиниту и находится в структуре или-же появляется как очень малые, адсорбированные на поверхности частицы. Кроме Ті анатазовые примеси содержат также Fe, и Mg. В биотите присутствуют Fe, Mg, Mn, V и K. Мелкозернистые минеральные загрязнения приходится концентрировать для того, чтобы подвергнуть их исследванию электронным микрозондом.