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

Palaeoclimatic interprétation of clay minerals in marine deposits : an outlook from the continental origin.

Flocculation and de-flocculation of suspended matter in estuaries

Summary
The results obtained by the author in the study of clay-minerals diagenesis are compared critically with the principal publications in this field, giving a general picture of the transformation of sheet silicates.

Kaolinite minerals are related to the surficial zones of the earth's crust where they are formed. They are characterized by the hexacoordination of aluminium. They furnish paleogeographic indications in ancient sediments. During diagenesis they are very sensitive to the geochemical environment, stable in acid conditions, unstable in alkaline conditions. However, the increase in temperature by burial causes their destruction sooner or later. In the transitional zone to metamorphism (anchizone), kaolinite is not present. Only dickite and nacrite can be observed, provided that the environment is acid.

Montmorillonites are hydrated minerals. The rise in temperature and above all in pressure during burial expels water from the interlayers. Concentrated interstitial solutions of diagenesis provide cations which replace molecules of water between the layers. It is an irreversible reaction which produces 14-A minerals (chlorites) or 10-A minerals (illites), passing generally through mixed-layer structures. The lack of montmorillonite is normal in formations which have undergone a marked burial.

Mixed-layers are intermediate stages which occur during degradation by weathering and during aggradation by deep diagenesis. This aggradation is the result of an incorporation of certain cations taken up from interstitial solutions, and of a rearrangement within the lattice. There are two major pathways: a potassium and sodium pathway, which produces the illites, then the micas, passing possibly by regular mixed-layering of the allevardite-rectorite type; and a magnesium pathway, which produces the chlorites, passing possibly by a regular mixed-layering of the corrensite type. These mixed-layers can remain stable until the border of meta-morphism (anchizone).

Micaceous clay minerals or illites form a very heterogenous group in the sediments which have been hardly diagenetized. Particles of diverse origin are found. They become more regular during burial. In deep diagenesis and the anchizone, crystallo-graphic parameters of the illite are sufficiently well defined to serve as a scale of recrystallization, a zoneographic index. The morphology of the particles changes. Polymorphic types 1Md and 1M are replaced by the 2M-type. The sharpness of the 10-A peak, conventionally called “crystallinity”, is an interesting quantitative criterium, together with the intensity ratio of the 5-A and 10-A peaks, which is related to the chemical composition of the octahedral layer.

Micas in low-grade metamorphism, called sericites by petrographers, replace the illites discussed above. They are different from the true micas by a weaker layer charge, less than 0.9 by half-cell. They often contain sodium (paragonitic muscovites and paragonites). The octahedral charge (zero for the muscovite) is generally high, due to the replacement of Al by Fe2+ and Mg (phengites). These transformations should not obscure the fact that metamorphism is also accompanied by crystalline growth and massive neoformation.

Chlorites are the least well-known clay minerals in diagenesis. Detrital particles can be aggraded to chlorite during early diagenesis by passing through the mixed-layer stage of corrensite. A massive growth of chlorite is observed in late diagenesis and the anchizone. Illite and chlorite slates give place to sericite and chlorite schists. At present, general data are not available on the crystal chemistry of chlorites in the anchizone and the greenschist facies.

The stages in the diagenetic evolution of clay minerals are too little understood to be able to give them precise limits. However, the following provisional scheme can be proposed:

(1) Early diagenesis (= “diagenesis” of Russian authors; = the “shallow-burial stage” of Muller, 1967a). In this stage all the clay minerals are stable; some undergo aggradation by adsorption of Mg, K and Na (various mixed-layers); some are neoformed (montmorillonites).

(2) Middle diagenesis (= “early catagenesis or epigenesis” of Russian authors; the “deep-burial stage” of Muller, 1967a, includes this stage and all the following until metamorphism). In this stage the sediment becomes compact. It has lost at least 50% of its connate water. Porosity is high and circulation still plays an essential part. Some detrital minerals, such as biotite, are unstable. All the clay minerals are still stable, but many types of replacement take place, due to interstitial circulation. Dickitization of kaolinite and illitization of montmorillonite can already be observed.

(3) Deep or late diagenesis (= “late catagenesis or epigenesis” of Russian authors). In this stage the temperature is greater than 100 °C, pressure increases and porosity becomes very weak. Montmorillonites and irregular mixed-layers disappear. Kaolinite recrystallizes as dickite in acid environment. These changes are irreversible.

(4) Anchizone (= “metagenesis” of Russian authors; = “zone anchimetamorphique” of Kubler, 1964). This is the transitional zone to metamorphism. It agrees with temperatures around 200 °C. Illite and chlorite are almost the only sheet silicates. However, dickite can be observed as well as pyrophyllite generally associated with allevardite. The crystallographic parameters of illite define the limit of the following zone, the metamorphic epizone or greenschist facies.

The crystallochemical processes that take place during the diagenetic evolution of clay minerals are schematically the following:

(1) Gradual tetracoordination of aluminium.

(2) Filling of octahedral sites either by interlayer cations, either by cations derived from outside the lattice, without the distinction dioctahedral-trioctahedral becoming very clear.

(3) Interlayer exchange between crystal lattice and interstitial solution. Gradual closing of the layers by alkaline cations or octahedral brucite-like sheets.

(4) Massive crystalline growth in the anchizone and the epizone.

These processes are roughly symmetrical with those which occur during weathering.

This review is a summary of the conclusions drawn in a Docteur-es-Sciences thesis (G. Dunoyer de Segonzac, 1969: Les Mineraux argileux dans la Diagenese. Passage au Metamorphisme, 339 p., 45 tables, 110 illus.) to be published as part of the series Memoires du Service de la Carte Geologique d'Alsace et de Lorraine. Most of the evidence on which these conclusions have been based is not cited directly in this article, but can be found in the thesis mentioned above, to which the reader is referred.

The transformation of clay minerals during diagenesis and low-grade metamorphism: a review

The paleoclimatic interpretation of clay minerals in sediments — a review

Differential settling velocities of individual clay mineral types and clay mineral mixtures in quiet saline water are reported for ocean water chlorinity range 0–18‰, brackish water ionic strength range 0.0–0.686 moles-(unit charge)2/kg, temperature range 6–26°C, clay mineral concentration range 0.01–3.6 g/1., and pH range 6.5–9.8. The materials employed included natural deposit clay minerals and clay minerals extracted from marine sedimentary matter and from terrestrial soils. Settling velocities at 26°C for illitic and kaolinitic materials reached values of 15.8 and 11.8 m/day, respectively, at an ocean water chlorinity of 18‰ and exhibited little dependence upon chlorinity above a chlorinity of 2‰. Settling velocities for montmorillonites were found to be functions of chlorinity over the entire chlorinity range 0–18‰ and to increase exponentially to a limit of 1.3 m/day at 26°C. The settling velocities were determined by pipette analysis, Oden balance techniques, Kelley-Wiegner manometer methods, and spectrophotometric methods, using artificial sea-water and filtered Gulf of Mexico water. In quiet brackish water, variations in ionic ratio composition alter the settling rates of illites and kaolinites less than 15 percent from such rates in ocean water, at constant, brackish water, ionic strength of 14 or greater. In contrast, montmorillonitic settling rates in such water varied by 40 percent or more from ocean water rates, at constant ionic strength unless the magnesium—potassium or magnesiun-strontium ionic ratios of the brackish water were kept constant. These induced variations were not sufficient in magnitude, however, to change the general relative order of settling rates for the clay minerals. Decreasing temperatures over the range 26°-6°C decreased settling rates (of all clay types) progressively up to about 40 percent in accordance with temperature-induced changes in the viscosity and density of the saline water medium. The influences of fifty-seven different organic compounds or materials (carbohydrates and proteins dissolved or dispersed in the water) upon the settling velocities are cited. In general, carbohydrates increased the settling rates of montmorillonitic materials as much as 25 percent, and proteins decreased such rates a maximum of 1–5 percent. Kaolinitic materials suffered a 30–40 percent decrease in settling velocity under the influence of some proteins. So-called “humic acids,” derived from quinone and soil fractions, decreased kaolinitic and montmorillonitic settling rates to lesser extent. No significant alterations of illitic settling rates by organic materials were noted. Chlorite-montmorillonites were found to settle slightly faster than sodium and calcium montmorillonites. Potassium-saturated montmorillonites settled from two to three times as rapidly as the reference montmorillonites. Chlorite settling rates, of magnitude comparable to rates found for kaolinites, and vermiculite settling rates, comparable at higher chlorinities to illite settling rates, are also reported. The apparent interaction of illite and montmorillonite to form illitic-montmorillonitic settling entities in some clay mineral mixtures was noted. Other mixtures, exposed to artificial sea-water for 3–6 years, exhibited a tendency to transport 5–20 percent kaolinite within a developed illitic-chloritic mix, when reagitated. Evidence is also presented to support the argument that clay minerals do not settle in single solid particulate units in saline waters. The effective settling unit, after flocculation, is described as a coacervate, i.e. as a thermodynamically reversible assembly of solid clay particles or strands within a settling solid-rich liquid unit phase. Settling rate increases are thereby not a consequence of any irreversible formation of larger solid particles or solid aggregates by coalescence of fresh water particles at or beyond the fresh-water-saline-water interface. Differential transport of clay minerals by the turbulent flow of saline water in a pipe is quantitatively described. Flow rates of about 6 miles/hr were required to eliminate differential transport of the clay minerals. Clay mineral concentrations over the range 0.01–15.0 g/l. were considered. Chemical data, electron and x-ray diffraction data, base exchange data, and electron micrographs support the settling velocity information.

Differential Settling Tendencies of Clay Minerals in Saline Waters1

Analyses of samples of kaolinitic, illitic, and montmorillonitic clay materials exposed to artificial sea water for periods of six months to five years have yielded some evidence to support the contention that chloritic and illitic clay types may ultimately develop from montmorillonitic material in the marine environment. However, no indications of the initiation or induction of any major lattice alteration of the original kaolinite and illitic type structures have been recognized on the basis of the data collected. The techniques of electron diffraction, electron microscopy, x-ray diffraction, and chemical analysis were employed to detect and measure the extent of modification of the clay materials at selected time intervals during the five year period. Actual separations of illitic-like and chloritic-like materials from treated montmorillonitic material were accomplished by gravitational settling methods. Relative weight percents of 18.2 for chloritic clay separates and 4.4 for illitic clay separates were obtained after more than four years of treatment. Chemical analysis and electron microscopy data suggest that lattice alteration preceded the development of forty to seventy percent of the chloritic and illitic material separated. The chloritic material apparently developed by initial formation of a magnesium-enriched montmorillonite having a hectoritic appearance. Subsequent development of threadlike extensions from the magnesium montmorillonite is shown by electron micrographs. These threads were observed to decrease or equilibrate in apparent amount within the chloritic separates as platelike forms began to appear after three years. The illitic separates were characterized by fine granulai material with increasing occurrence of larger platelike forms as exposure time increased. The modification of montmorillonitic clay was observed to be more dependent upon the magnesium-potassium ratio in the sea water than upon the total salt concentration levels. The limiting magnesium-potassium ratio was found to be approximately 9.4 with a limiting low potassium concentration of 0.005 moles per liter for montmorillonitic material of less than 0.5 micron settling diameter. The alteration of the montmorillonitic material was noted only for material that was initially settled through the artificial sea water media. As the potassium concentration level of these media dropped by extraction below 0.005 molar, a bulk effect of the settling material became operative and the relative percent of altered material decreased. Further, the relative amounts of modified material detected were decreased by the introduction of carbohydrate material into the sea water media. The amounts present after a definite time interval were also observed to be dependent upon the distributive tendencies of the source materials and the physical disturbance of the sea water media. Resuspension of the material by reagitation of the system decreased and significantly governed the rate of diagenetic modification. Special electron micrographs are presented to illustrate relative stages of flocculation of montmorillonitic material as the ionic concentration of sea water increases. It is suggested that these stages govern to an appreciable extent the extent and rate of initiation of any ionic exchange and lattice changes that occur.

Diagenetic modification of clay mineral types in artificial sea water

Differential settling velocities of individual clay mineral types and clay mineral mixtures in quiet saline water are reported for ocean water chlorinity range 0-18%0, brackish water ionic strength range 0.0-0.686 moles—(unit charge)2/kg, temperature range 6-26°, clay mineral concentration range 0.01-3.6 g/1., and pH range 6.5-9.8. The materials employed included natural deposit clay minerals and clay minerals extracted from marine sedimentary matter and from terrestrial soils.

Settling velocities at 26° for illitic and kaolinitic materials reached values of 15.8 and 11.8 m/day, respectively, at an ocean water chlorinity of 18%0 and exhibited little dependence upon chlorinity above a chlorinity of 2%0. Settling velocities for montmorillonites were found to be functions of chlorinity over the entire chlorinity range 0-18%0 and to increase exponentially to a limit of 1.3 m/day at 26°. The settling velocities were determined by pipette analysis, Oden balance techniques, Kelley-Wiegner manometer methods, and spectrophotometric methods, using artificial sea-water and filtered Gulf of Mexico water.

In quiet brackish water, variations in ionic ratio composition alter the settling rates of illites and kaolinites less than 15 percent from such rates in ocean water, at constant, brackish water, ionic strength of 14 or greater. In contrast, montmorillonitic settling rates in such water varied by 40 percent or more from ocean water rates, at constant ionic strength unless the magnesium-potassium or magnesiun-strontium ionic ratios of the brackish water were kept constant. These induced variations were not sufficient in magnitude, however, to change the general relative order of settling rates for the clay minerals.

Decreasing temperatures over the range 26°-6° decreased settling rates (of all clay types) progressively up to about 40 percent in accordance with temperature-induced changes in the viscosity and density of the saline water medium.

The influences of fifty-seven different organic compounds or materials (carbohydrates and proteins dissolved or dispersed in the water) upon the settling velocities are cited. In general, carbohydrates increased the settling rates of montmorillonitic materials as much as 25 percent, and proteins decreased such rates a maximum of 1-5 percent. Kaolinitic materials suffered a 30-40 percent decrease in settling velocity under the influence of some proteins. So-called “ humic acids,” derived from quinone and soil fractions, decreased kaolinitic and montmorillonitic settling rates to lesser extent. No significant alterations of illitic settling rates by organic materials were noted.

Chlorite-montmorillonites were found to settle slightly faster than sodium and calcium montmorillonites. Potassium-saturated montmorillonites settled from two to three times as rapidly as the reference montmorillonites. Chlorite settling rates, of magnitude comparable to rates found for kaolinites, and vermiculite settling rates, comparable at higher chlorinities to illite settling rates, are also reported.

The apparent interaction of illite and montmorillonite to form illitic-montmorillonitic settling entities in some clay mineral mixtures was noted. Other mixtures, exposed to artificial sea-water for 3-6 years, exhibited a tendency to transport 5-20 percent kaolinite within a developed illitic-chloritic mix, when reagitated.

Evidence is also presented to support the argument that clay minerals do not settle in single solid particulate units in saline waters. The effective settling unit, after flocculation, is described as a coacervate, i.e. as a thermodynamically reversible assembly of solid clay particles or strands within a settling solid-rich liquid unit phase. Settling rate increases are thereby not a consequence of any irreversible formation of larger solid particles or solid aggregates by coalescence of fresh water particles at or beyond the fresh-water-saline-water interface.

Differential transport of clay minerals by the turbulent flow of saline water in a pipe is quantitatively described. Flow rates of about 6 miles/hr were required to eliminate differential transport of the clay minerals. Clay mineral concentrations over the range 0.01-15.0 g/1. were considered.

Chemical data, electron and x-ray diffraction data, base exchange data, and electron micrographs support the settling velocity information.

Differential settling tendencies of clay minerals in saline waters1

Variations in the peptization resistance of selected samples of clay mineralogical materials toward alkaline dispersing agents are discussed from a quantitative point of view. Clay samples, collected from South Carolina, Wyoming, Illinois, New Mexico, South Wales, Great Britain and Cornwall, England were subjected to the action of solutions of Calgon (“sodium hexametaphosphate”), ammonia, sodium hydroxide, sodium carbonate, sodium pyrophosphate, and “sodium lignosulfonate.” The resulting apparent dispersion, in each case, was expressed as a function of the employed concentration and chemical nature of the dispersing agent. Pipette analysis and Oden balance techniques at constant temperature were used to measure the degree of dispersion. All clay samples employed were identified as to type by X-ray diffraction, chemical analysis, thermal analysis, and electron microscopy. All samples examined exhibited a maximum in apparent dispersion (suspension stability) at a specific concentration of dispersing agent. Such maximum was followed by a sudden decrease in apparent dispersion, i.e., flocculation, at higher concentrations of dispersing agent. Concentrations of dispersing agent were varied in steps of one part per thousand. One hundred and twenty experimental runs were made on each type of material examined. Differences in the degree of apparent dispersion attained by use of different dispersing agents were expressed in terms of a threshold concentration which altered “equivalent diameter” one tenth of a phi unit. Among dispersing agents employed, “sodium lignosulfonate” was found to be least selective of clay mineral type in its peptizing action. An equation for the calculation of a “peptization resistance factor” is presented. Results obtained by application of this equation indicate that differences in the response of the same clay material to different alkaline dispersing agents may be attributed, in part, to differences in degree of peptization achieved by “threshold mechanisms” of peptization and by “adjustment mechanisms” along the peptization path. Such equation may have future value in the differentiation of marine and terrestrial clay deposits.

U. Grant Whitehouse

Papers

Differential Settling Tendencies of Clay Minerals in Saline Waters1

Diagenetic modification of clay mineral types in artificial sea water

Differential settling tendencies of clay minerals in saline waters1

Peptization Resistance of Selected Samples of Kaolinitic, Montmorillonitic, and Illitic Clay Materials