CLAY MINERALS BULLETIN

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1 CLAY MINERALS BULLETIN No. 31 JULY, 1964 Vol. 5 SOME PROBLEMS RELATING TO THE MINERALOGY OF SEDIMENTS*t A. G. SEIDOV Institute of Geology, Fizuli 67, Baku, Azerbaijan SSR Received 9th December 1963 ABSTRACT: After a brief account of the work currently in progress on fine-grained sedimentary rocks in the U.S.S.R., and particularly in Azerbaijan, the concept of finely-dispersed minerals as against clay minerals is considered and some comments made on classification schemes. Conditions of formation and deposition determine whether sedimentation or diagenesis is predominant and hence the mineralogy of the deposit. Methods of mineralogical investigation are as yet ill-developed and much remains to be done. Finally, some of the wider problems in clay mineralogy are discussed and some suggestions made regarding the organization of suitable studies, particularly in the U.S.S.R. INTRODUCTION It is well known that many very valuable mineral resources (such as oil, coal, refractory, bentonitic and other clays, aluminium, manganese and potassium ores, radioactive and rare elements, etc.) are of sedimentary origin and that fine-grained sedimentary minerals are predominantly involved in the formation of rocks containing these substances. In consequence, the mineralogical investigation of sedimentary rocks in a broad geological sense is of great scientific and practical importance. *Translated by R. C. Mackenzie. tsome terms used in the Russian text are very difficult to translate into English in an understandable manner: one of these is dispersnaya poroda which is literally dispersed rock: the best English equivalent is probably sediment or fine-grained sedimentary rock. These terms are therefore used. On the other hand, it has been decided for various reasons to leave in literal translation tonkodispersnye mineraly-- finely-dispersed minerals. This term, or the alternative vysokodispersnye mineraly (highly-dispersed minerals), is currently much used in Soviet literature and it is useful for the reader to become familiar with them and with their significance. R.C.M. 329

2 330 A. G. Seidov In recent years Azerbaijanian mineralogists have undertaken a thorough investigation of Mesozoic, Tertiary and Quaternary finegrained sedimentary rocks (including clays) rich in minerals of economic importance. The reason for this was to rectify the depressed state of raw material development in the Republic and to enable these materials to be more effectively used in various industrial spheres. A laboratory for the physico-chemical investigation of sedimentary rocks has recently been established in the Institute of Geology of the Azerbaijanian Academy of Sciences so that the Meso-Cainozoic rocks of Azerbaijan can be studied by a combination of the most modern techniques (electronoptical, X-ray, thermal, ultrasonic, spectrophotometric, etc.) and their constitution and conditions of formation established. Many problems are being investigated. The structure and genesis of the minerals in sediments are receiving much attention. Bentonitic clays are being investigated with a view to their use as starting materials in the preparation of adsorbents and catalysts for the purification and cracking of petroleum. The relationship between the structural, mechanical and chemical properties of argillaceous dispersions and the mineralogical and colloid-chemical nature of the clays is being studied by the Institute of Chemistry of the Azerbaijanian Academy of Sciences. At the same time it has been established that the mineralogical composition, the content, the chemical composition of the exchange complex and the lyophilic character of the clay determine the type and stability of thixotropic structures formed in aqueous suspensions. The effect of surface active materials that protect colloids and finegrained weighting materials on the kinetics of thixotropic structure formation has been examined for suspensions of Azerbaijanian bentonitic and kaolinitic clays. As a result of these investigations new types of highly effective fine-grained weighting materials and of surface active reagents have been recommended for use in oil-well drilling. Studies are in progress on the finely-dispersed minerals in oil-beating and reputedly oil-producing sediments of Azerbaijan in order to establish the nature of the association between the organic components and the finely-dispersed minerals and the part the latter play in the process of petroleum formation. In a short paper it is impossible to touch on all aspects of a specific problem, and therefore we shall consider only the principal objectives of further investigations into the mineralogy of sediments, and in particular of clays, which are their chief constituents. In a mineralogical examination of sedimentary rocks the main aims must be to elucidate in detail their mineralogical and petrological characteristics and to determine the conditions of their formation, the probable nature of the parent rock and the locality from which they have been transported, as well

3 Mineralogy of sediments as to devise reasonable uses for these rocks, which constitute valuable raw materials. During recent years Soviet scientists have carried out a number of studies of great theoretical and practical importance in connection with the study of sedimentary formations in general and the mineralogy of fine-grained sediments in particular. Among these one may cite Strakhov (1960), Pustovalov (1940), Chukhrov (1955), Ginzburg & Rukavishnikova (1951), Teodorovich (1958) and others. Definite progress has also been made in the determination of the crystal structure of finely-particulate minerals; a detailed petrological and mineralogical examination has been carried out on Meso-Cainozoic, Quaternary and Recent deposits in different structural zones--i.e, in geosynclinal and platform regions; the fine-grained sediments of the oil-bearing and oilproducing strata of Azerbaijan, the Northern Caucasus, the Ural- Volzhsk region, etc., have been subjected to detailed study; and thorough mineralogical and technological investigations have been made on the refractory and bentonitic clays of the Ukraine, Georgia and Azerbaijan since these are of great importance in the national economy. However, a number of major problems still await solution and among these the main question which is attracting serious attention concerns nomenclature and classification. NOMENCLATURE AND CLASSIFICATION OF MINERALS IN FINE-GRAINED SEDIMENTS In the literature the term clay minerals is usually, but not very successfully, used in classifying minerals of the groups occurring in fine-grained sedimentary rocks. On the basis of textural criteria this term ought to refer only to minerals with particle size less than 0.01 mm----i.e, in the clay fraction--but in the mineralogical sense the same term can also characterize a range of other types of rocks with finely-dispersed particles. Because of this it seems desirable to replace the term clay minerals by the term finely-dispersed minerals. This term indicates silicates with layer and chain lattices and covers the essential constituents not only of typical clay rocks but also of clay slates, argillites, oozes, soils, materials of the weathering crust and the dispersed part of a range of clastic carbonate and other rocks representing in all more than 75% of all sedimentary formations. It should be pointed out, too, that the concept finely-dispersed minerals has a crystalline and textural significance (these minerals are usually very finely particulate, but they can occur in nature in different sizes including those greater than 0.0l ram). Consideration of some of the main physical properties of finelydispersed minerals enables the clay minerals to be correctly distinguished, 33 l

332 A. G. Seidov since by crystallochemical criteria they belong to the phyllosilicates and because of their physical properties they can form monomineralic aggregates.

4 332 A. G. Seidov since by crystallochemical criteria they belong to the phyllosilicates and because of their physical properties they can form monomineralic aggregates. Such are the minerals of the kaolinite, montmorillonite and hydromica groups and a number of others. However, such minerals as biotite, vermiculite, clinochlore, muscovite, pennine, pyrophyllite, talc, chrysotile, sepiolite, etc, cannot be referred to the clay group because their physical properties forbid the formation of clay-like aggregates. Thus the problem of the classification of minerals in fine-grained sediments has not yet been finally solved. At a meeting of the Nomenclature Sub-Committee of Comit6 International pour l'etude des Argiles in Copenhagen in August 1960, several possible classification schemes for the clay minerals were considered, the great majority of these having a crystallochemical and structural basis, Discussion showed that the majority of investigators agreed with the classification scheme of Mackenzie (1957, 1959). In this scheme the clay minerals are divided into two broad structural categories--layer lattice and chain lattice. In the layer-lattice category there are divisions into structural types with two, three and four sheets in the repeat layer and further subdivision, depending on the population of the octahedral sheet, into dioctahedral and trioctahedral. Interstratified minerals are assigned to a special group. Some of the suggested classification schemes also allowed for substitutions (replacements) in tetrahedral and octahedral positions and for the swelling characteristics of the clay minerals. The fact that there are such differences of opinion on the question of the classification of clay minerals leads to the conclusion that, since a considerable proportion of such minerals is not characteristic only of clay and some other rocks, this group should not be termed clay in the strict sense of the word. It is indeed conveniently classified under the name finely-dispersed minerals and related layer silicates. The schemes proposed by Mackenzie (1959), Frank-Kamenetsky (1960) and Zvyagin (1961) could well be used as a basis to develop a classification of such minerals. As a special case it is then necessary to evolve classification schemes based on the textural and physical criteria of the finely-dispersed minerals for the clay minerals sensu strieto. As a basis for this serve the schemes suggested by Grim (1953), Vikulova (1957) and Chukhrov (1961). Despite the number of classification schemes proposed for clay minerals there has, however, been little attempt to classify clay rocks. This' omission has been rectified by Kashkai (1959), who has recognized five genetic types covering rocks of hydrothermal and hydrothermalmetasomatic origin as well as those in the crust of weathering and sediments.

Mineralogy of sediments 333 CONDITIONS OF FORMATION OF MINERALS IN SEDIMENTS It is well known that the processes of weathering of sedimentary, igneous and metamorphic rocks play an important part in

5 Mineralogy of sediments 333 CONDITIONS OF FORMATION OF MINERALS IN SEDIMENTS It is well known that the processes of weathering of sedimentary, igneous and metamorphic rocks play an important part in the formation of minerals in sedimentary rocks, and particularly in argillaceous rocks, the products of weathering collecting in accumulation areas both as terrigenic particles and as colloidal material. Minerals can also be formed authigenically: by precipitation of minerals from aqueous solution (chemogenic), by biochemical reactions (soil processes), as a result of alteration deep in the basin during the diagenesis of vitroclastic ashy material and other crystalline silicate minerals, or by diagenetic and epigenetic alteration of finely-dispersed minerals. It has been established that usually the mineral-forming processes for sediments, and in particular for clay deposits, are reasonably constant for a particular geological period. Differences observed in the mineralogical composition of sedimentary rocks from different regions and strata are related to the character of the facies and the physico-chemical conditions of sediment accumulation and diagenesis. The results of studies on clay rocks of different age from various regions of the U.S.S.R. have shown that unusual mineral associations can arise from the presence of general sources of supply provinces in different structural zones--platform and geosynclinal. The effect of different factors on the formation of fine-grained sedimentary rocks is shown by the results of complex s~udies on Meso-Cainozoic deposits in the geosynclinal region of the Caucasus and in the Russian platform (Grossgeim, 1961 ; Seidov, 1962) and by investigations on Mesozoic and Upper Palaeozoic sediments of different structural zones--platform in the Lena-Vilyui depression and geosynclinal on the Verkhoyansk ridge (Kossovskaya, Shutov & Muravev 1960). The results have demonstrated that the mineral composition of clays of platform regions depends on the conditions under which the sediment accumulates and hence their mineral composition is relatively complex, whereas in the geosynclinal zone clays, irrespective of the character of the facies, are usually distinguished by the simplicity of their mineralogy. At the same time the type of finely-dispersed mineral likely to occur in any particular instance is governed by the mineral-forming factor that is predominant--i.e, the predominance of sedimentation (geosynclinal area) over diagenesis (platform area) or vice versa. Detailed study of the clays of the Tertiary complex of Azerbaijan have shown them to contain mainly hydromica with isomeric lamellar particles indicative of a detrital origin. Within the Tertiary complex, however, occur individual stratigraphical horizons (Kounsk strata, etc.)

334 A. G. Seidov where the clays are montmorillonitic because of diagenetic transformation of introduced ash under marine reducing and alkaline conditions.

6 334 A. G. Seidov where the clays are montmorillonitic because of diagenetic transformation of introduced ash under marine reducing and alkaline conditions. From the above examples it is clear that within a single facies the mineralogy of the clays of different regions can be quite different depending on the nature of the primary detrital material and the conditions of formation. Analysis of the available data shows that the mineralogical composition of fine-grained sedimentary rocks depends chiefly on the following factors: (a) the petrological nature of the primary material entering the basin; (b) the sedimentation facies; (c) diagenetic and secondary transformation of finely-dispersed materials. Furthermore, the dual nature of the minerals (including the clay minerals sensu stricto) in sediments if now established--i.e, allothigenesis and authigenesis are mutually related as processes of mineral formation and are complementary to each other. STATUS OF AND PROSPECTS FOR DEVELOPING INVESTIGATIONAL METHODS The properties of the minerals in fine-grained sediments are such that their study requires the use of several investigational methods. But limiting factors are operative in view of defects in the methods. The investigation of the minerals in any sediment, including argillaceous sediments, has usually to be commenced by particle size fractionation so as to obtain the fraction with particles < 1 tz, since this consists largely of particles of the dispersed minerals including the clay minerals sensu stricto. The method most widely used for separation is granulometric analysis (particularly elutriation), but several inherent defects ought to be noted. Thus, not only is the process rather timeconsuming but it involves the use of certain processes, such as mechanical disintegration of the specimen, destruction of carbonates and other cementing materials, etc., which might well have a fundamental effect on the minerals being investigated. Furthermore, it should be mentioned that existing methods for granulometric analysis cannot be readily applied in the study of argillites, clay slates and other fine-grained metamorphic rocks, and oil-producing strata containing large amounts of organic materials. These deficiencies may however be overcome and stable suspensions successfully obtained from consolidated rocks by the use of an ultrasonic generator. Results of experiments at the Institute of Geology of the Azerbaijanian Academy of Sciences have shown that, without any preliminary treatment, samples of sedimentary rocks and even strongly metamorphosed rocks can be quickly disintegrated by ultrasonics into

Mineralogy of sediments 335 finely dispersed particles suitable for further mineralogical investigation by various determinative techniques.

7 Mineralogy of sediments 335 finely dispersed particles suitable for further mineralogical investigation by various determinative techniques. Another deficiency in investigational methods for sediments concerns the current lack of any method which will enable quantitative determination of the constituent minerals. Intensive attempts at quantitative determination of the minerals present in sediments using X-ray and thermal techniques are, unfortunately, only isolated. Despite the marked progress made by Soviet scientists in the mineralogical study of sediments as a whole, there is still a considerable lag in structural and crystallochemical investigations on the minerals present in fine-grained sedimentary rocks, including true clay rocks. Finally, finely-particulate oil-bearing, coal-bearing and oil-producing strata rich in organic materials present great difficulties as regards investigational methods, but since clays play an essential part in oil formation the development of suitable mineralogical methods is of paramount theoretical and practical importance. SALIENT PROBLEMS IN THE INVESTIGATION OF SEDIMENTS Our country has large reserves of mineral resources of sedimentary origin which are finding increasing practical use in the national economy in connection with the rapidly growing demands of the chemical, petroleum, fertilizer, etc., industries and also with the annually increasing requirements of the building industry. In order to use the minerals in fine-grained sediments more rationally it is primarily essential to encourage theoretical investigations since these at present are not sufficiently developed to supply answers to the questions posed by the practical man. It must be conceded that there exists as yet no major theoretical generalized work which provides a scientific analysis of and quotes results from investigations on the sediments of the U.S.S.R. Yet an intensive study of their physical and technological characteristics is essential. From the practical aspect it is important to investigate the origin of plasticity in rocks and measuring methods, the processes of deformation and growth of structure in suspensions and pastes, the phenomenon of electroosmosis, change in the structure of dispersed minerals under the influence of prolonged loading, and many other questions. In a wider context, methods must be developed for the beneficiation of kaolinitic, bentonitic and other types of clay. Investigations on the colloid-chemical nature of sediments are of great importance. At the same time there must be a search for rules governing such processes as the effect of different liquid and gaseous media on solid phases, the influence of media of different polarity on the nature of

8 336 A. G. Seidov the dispersed silicate minerals, the dielectric and electrokinetic behaviour of dispersed minerals in polar and non-polar solvents, the ion-exchange processes and their effect on the technical properties of finely-dispersed minerals, etc. From the mineralogical-geochemical viewpoint much experimental work is necessary, especially on the synthesis of aluminosilicates and ferrosilicates and the clay minerals sensu stricto. It would also be valuable to conduct experiments on the decomposition of such silicates as felspars, micas, chlorites, amphiboles, pyroxenes, and volcanic glass with particular emphasis on determination of the mechanism of decomposition. But for further developments in the mineralogy of sediments to be successful, some organizational problems must also be overcome. The All-Union Committee on Clays established by the Division of Geological and Geographical Sciences of the Academy of Sciences of the U.S.S.R. has played a very valuable r61e in co-ordinating scientific research work and in improving relationships with foreign scientists. In order that these activities should continue to expand the Academy of Sciences of the U.S.S.R. should consider setting up an independent body to be permanently concerned with the co-ordination and direction of work in the field of the mineralogy of sedimentary rocks. It is also necessary to consider seriously the training of young specialists in the mineralogy and petrology of sediments. This could best be ensured by the inclusion of special courses on these subjects in the syllabus of geological and chemical faculties at Universities. REFERENCES CHUKHROV F.V. (1955) Kolloidy v zemnoi kore [Colloids in the Earth's Crust]. Izd. Akad. Nauk SSSR, Moscow. CmJKi-mov F.V. (1961) In the book : Materialy k klassifikatsii glinistykh mineralov [Data on the Classification of Clay Minerals]. lzd. Akad. Nauk SSSR, Moscow. FRANK-KAMENETS~Y V.A. (1960) Clay Min. Bull. 4, 161. GINZBtTRG I.I. & RUKAVISHNIKOVA I.A. (1951) Mineraly drevnei kory vyvetrivaniya Urala [Minerals of the Ancient Weathering Crust of the Urals]. Izd. Akad. Nauk SSSR, Moscow. GRIM R.E. (1953) Clay Mineralogy. McGraw-Hill, New York. GROSS6EIM V.A. (1961) lstoriya terrigennykh mineralov v mezozoe i kainozoe Severnogo Kavkaza i Predkavkazya [ The History of Terrigenie Minerals in the Mesozoic and Cainozoic Deposits of the Northern Caucasus and Near Caucasus]. Gostoptekhizdat, Leningrad. KASHI(AI M.A. (1959) Clay Min. Bull. 4, 44. KOSSOVSKAYA A.G., SI~UTOV V.S. & MURAVEV V.P. (1960) Trudy geol. lint., No. 34. MACKENZIE R.C. (1957) Agroehimiea 1,308. MACKENZI~ R.C. (1959) Clay Min. Bull. 4, 52. PUSTOVALOV L.V. (1940) Teoriya differentsiatsii i geokhimieheskie fatsii osadochnykh porod [Theory of Differentiation and the Geochemical Facies of Sedimentary Rocks]. Gostoptekhizdat, Moscow.

9 Mineralogy of sediments 337 SEIDOV A.G. (1962) Litologo-mineralogicheskaya kharakteristika i asloviya obrazovaniya otlozhenii Maikopskoi svity Azerbaidzhana [Lithological and Mineralogical Characteristics and Conditions of Formation of Deposits of the Maikop Suite in Azerba~jan]. Izd. Akad. Nauk Azerb. SSR, Baku. STRAKHOV N.M. (1960) Osnovy teorii litogeneza [Principles of the Theory of Lithogenesis]. Izd. Akad. Nauk SSSR, Moscow. TEODOROV~CH G.L (1958) Autigennye mineraly osadochnykh porod [The Authigenie Minerals of Sedimentary Rocks]. Izd. Akad. Nauk SSSR, Moscow. VIKULOVA M.F. ( 1957) Metodicheskoe rako vodstvo petrograficheskogo-mineralogicheskogo izucheniya glin [Handbook of Methods for the Petrological and Mineralogical Study of Clays]. Truly Vsesoyuz. Nauch.-issled. Geol. Inst., Leningrad. ZVYAGIN B.B. (1961) In the book: Materialy k klassifikatsii glinistykh mineralov [Data on the Classification of Clay Minerals]. Izd. Akad. Nauk SSSR, Moscow.

THE CLAY MINERALOGY OF THE MOLASSE FORMATIONS OF AZERBAIJAN AND ITS CORREI,ATION WITH PALEOGEOGRAPHY

THE CLAY MINERALOGY OF THE MOLASSE FORMATIONS OF AZERBAIJAN AND ITS CORREI,ATION WITH PALEOGEOGRAPHY Clay Minerals (1968) 7, 441. THE CLAY MNERALOGY OF THE MOLASSE FORMATONS OF AZERBAJAN AND TS CORRE,ATON WTH PALEOGEOGRAPHY A. G. SEDOV AND N. V. PASHALY The nstitute o[ Geology o[ the Academy o] Sciences