Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 μ- and 2–20 μ-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite(?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, feldspars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted:

Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean.

Mineralogical analysis of the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin.

Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface.

Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa.

The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety of pedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation.

In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea arc mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator.

Mineralogy and Sedimentation of Recent Deep-Sea Clay in the Atlantic Ocean and Adjacent Seas and Oceans

The distribution of clay minerals in the World Ocean

Physical chemistry of soil potassium

The study of potassium (K) exchange on clay minerals and soils can be viewed from either a thermodynamic or a kinetic perspective. In pursuing the soil science literature, one will undoubtedly find that most of the studies on K exchange have been of an equilibrial rather than of a dynamic nature. Although the former studies have proved valuable in understanding the often elusive behavior of K in heterogeneous systems, they do not convey information about the rates or mechanisms of K exchange processes. Moreover, thermodynamic investigations on soil K are often not applicable to field conditions. Although a quasi-state equilibrium in K exchange can be achieved in the laboratory, these conditions are seldom if ever attained under field conditions.

Potassium Dynamics in Soils

Clay minerals are classified and non-clay minerals in the clay fraction listed. Chapters follow on: the environment and occurence of clay minerals; various kinds, their structures and diffraction patterns; x-ray diffraction as applied to clay mineralogy; preparation of clays for x-ray examination; quantitative estimation of clay minerals in a mixture.

Clay minerals: A guide to their X-ray identification

Studies were made of several clays of soils and other deposits to clarify the nature of weathering of layer silicates. Data obtained by X-ray diffraction, thermal, R(OH)n sorption, and elemental analyses lead to the proposal of general occurrence of interstratified X-amorphous zones in 2:1 layer silicates. As weathering of true micas proceeds through illite, intermediates, vermiculite, and montmorin, a given K interlayer is rapidly depleted of K along a preferential weathering plane, leading to some degree of expansion. Concurrent hydroxylation by H+ addition to the octohedral layer together with dealumination accounts for loss of some of the mica layer charge. Increasing proportions of such weathered planes leads to various combinations of X-amorphous and X-crystalline zones typical of illite, vermiculite, and montmorin found in soils and other deposits, accounting for their diffraction properties; internal surface; K, H₂O, and OH contents; and exchange properties. Functional continuity of mineral weathering in Great Soil Groups of China through layer silicates (including kaolinite), gibbsite, hematite, and anatase is demonstrated.

R. C. Vanden Heuvel

Papers

Weathering Sequence of Clay-size Minerals in Soils and Sediments