Problems of lithification in carbonate muds

Problems of Lithification in Carbonate Muds by R. G. C. BATHURST Received 18 November 1969

CONTENTS I.

2. 3.

page 429

THE PROBLEM PRIMARY COMPOSITION PROCESSES ...

(a) (b) (c) (d) (e)

Inferences from the Forms of Intercrystalline Boundaries Source of the Cement Experiments of Hathaway & Robertson Significance of the Upper Crystal Size of Calcite Micrites Structure Grumeleuse (f) Fossilised Stages 4. 5.

PROGRESS . GLOSSARY . REFERENCES

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ABSTRACT: The lithification of carbonate muds is examined on the basis of their high primary porosities of 50 to 70 per cent and the characteristic absence of dewatering-compaction structures in the hardened micrite. Some cementation is presumed, therefore, to have been early (pre-compaction), forming a rigid, load-resistant framework. This first generation of cement may have been locally derived, either from marine pore-water or by fresh-water dissolution-precipitation of the more soluble sedimentary particles. The main bulk of the cement is a late second generation and was either allochthonous or produced locally by the development of stylolites. Lithification involved such various processes as loss of water while pores were occluded by cement, the wet transformation of aragonite to calcite, recrystallisation of calcite, dissolution of small supersoluble particles, transfer of Mg2+, the production of secondary voids, influx of allochthonous CaC03 and pressure-solution. Some micrites have been lithified on the sea-floor as hardgrounds during prolonged exposure to sea-water, supersaturated for CaC03, for hundreds of thousands of years. Other micrites have been hardened more rapidly as a result of exposure to meteoric groundwater. The evolution of clotted limestones is considered. Finally, it is emphasised that neomorphic fabrics in micrites were produced not by alteration of the dense micrite as we see it now but by neomorphism of the highly reactive primary mud-porous, wet and multimineralogical.

1. THE PROBLEM IT IS nowadays common knowledge that the lithification of a carbonate mud, like the lithification of carbonate sediments in general, involves a change from a squelchy mixture of solid carbonate phases, bathed liberally in an aqueous pore solution, to a rock composed of low-magnesian calcite with a porosity of, perhaps, 2 or 3 per cent. The problems raised by this transformation are much the same whether we are dealing with a micrite or 429

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a calcarenite. The central difficulty is tantalisingly familiar-how to cement a carbonate mud while it is still largely uncompacted. Holocene carbonate muds have porosities mainly of 50 to 70 per cent (Ginsburg, 1964; Pray & Choquette, 1966). Most ancient micrites- and biomicrites (Dunham's, 1962, mudstones and wackestones) show no sign of having been compacted (Pray, 1960). Delicate tests are uncrushed, thin skeletal structures have not been broken as a result of grain-to-grain movement, the crystal size distribution of micrite is the same inside shells where the overburden load was effectively zero as in the intergranular micrite, cavities in the mud remained open until filled with cement. The conclusion is inevitable-cement was precipitated in the pores in sufficient quantity to form a resistant framework before the overburden was great enough to cause detectable compaction. Presumably some compaction by dewatering took place until the particles were in contact, as in Florida Bay, where the rate of decrease of porosity with depth falls off rapidly at about a porosity of 70 per cent (Ginsburg, 1957). Dewatering compaction of this kind would not, however, have proceeded on the same scale in shell chambers where the overburden load was practically zero, yet their filling of micrite is petrographically indistinguishable from the intergranular micrite. That the load in the shell chamber was zero is particularly obvious where the micrite is geopetal and only partly fills the chamber. Again we must infer that compaction of the sediment was very slight. This early cementation is in dramatic contrast with the situation in terrigenous clays (illite, montmorillonite, etc.). In the Carboniferous Limestone of North Wales, layers of biomicrite containing uncompacted crinoid columnals (circular cross-section) are interbedded with terrigenous shales in which the columnals have been squashed flat. The Inoceramus and White Chalk lithofacies of Northern Ireland, which show 15 to 31 per cent compaction (Wolfe, 1968), are very rare exceptions. As the porosities of most carbonate muds have not been reduced by compaction from initial values of 50 to 70 per cent to their present values of 2 to 3 per cent, then the pores were filled by cement. This conclusion in turn presents difficulties. Where was the source ofsuch an enormous quantity of CaCOa-more than half the volume of the limestone? How was it transported and precipitated? These problems are still unsolved. 2. PRIMARY COMPOSITION The initial composition of past muds is not generally known, although studies with the electron microscope are revealing increasing detail in the less altered muds, particularly coccolith oozes (Honjo & Fischer, 1964; Fischer, Honjo & Garrison, 1967). It is likely that they ranged from 1

A short glossary of terms is given on p. 438.

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aragonite needle-muds like those on the Bahamas-Florida platform (Purdy, 1963; Cloud, 1962; Ginsburg, 1957) and in the Persian Gulf (Evans, 1966; Kinsman, 1969) through mixed detrital skeletal carbonate muds such as are known off British Honduras (Matthews, 1966), to nearly pure oozes of low-magnesian calcite made of coccoliths, as in the Chalk (Black, 1953; Wolfe, 1968). All muds would have contained a number of solid phases, aragonite, various low-magnesian calcites (MgC03 2 to 3 mole per cent) and high-magnesian calcites (MgC03 12 to 17 mole per cent). Particle size and shape would have varied with the origin (Folk, 1965, 29). The wellknown tendency for organic matter to be concentrated in the finer sediments means that the silt and clay grade carbonates will have been rendered even more complex by the addition not merely of organic matter but of the algae, bacteria, fungi and yeasts that accompany it. The loss of this noncarbonate material from muds by oxidation is not as efficient a process as in sand-grade, relatively well-circulated calcarenitic sediments, and the long-term influence of residual organic products may, therefore, be more important in the lithification of carbonate oozes than of calcarenites. 3. PROCESSES It is plain that, for many calcilutites (lithified muds) the lithification was contrapuntal, a weaving of two melodies, on the one hand the influx and precipitation of externally derived cement, on the other the neomorphism of the original crystals. Not only did the muds undergo early cementation but, associated with this process went extensive development of neomorphic sparry calcite. This is apparent, for example, in the Pleistocene limestones of Guam (Schlanger, 1964) and of Funafuti (Cullis, 1904). The many processes that, it must be assumed, proceeded simultaneously during lithification were certainly wet ones. As the reduction of porosity during cementation continued, the water content fell and it is sensible to expect that the consequent reduction in the availability of solvent was responsible for a logarithmic slowing of the various processes. The relative importance of such processes is something we cannot yet judge. They include the wet transformation of aragonite to calcite, the dissolution of tiny supersoluble particles and prominences on grains, the transfer of Mg2+ from magnesian calcites, dissolution yielding voids, the influx of allochthonous CaC03, pressure-solution, and the precipitation of cement -in fact, all the paraphernalia of aggrading neomorphism (Folk, 1965). The results of these processes are nevertheless clear. The calcilutite consists now of low-magnesian calcite. Many of the smallest primary particles (crystals), with shortest diameters as small as 0.111, have been lost, and the final calcilutite has a new lower limit of crystal diameter probably at about 0.5 II and an upper limit of about 3 to 411 (Bathurst, 1959,367; Folk, 1965,29). There is commonly a mode around I to 211 (Schwarzacher,

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1961; Flugel, 1967). The restricted crystal size-range of the calcilutites is combined with a tendency to equigranular texture, and, surprisingly often, plane intercrystalline boundaries, features that have been amply demonstrated with the aid of the electron microscope. A note of caution is necessary here regarding the description of the crystal mosaics of micrites-and, indeed, of crystal mosaics, in general, which are (1) monomineralic, (2) have no visible porosity and (3) are equigranular. It is obvious, in these circumstances, that any plane interface between two adjoining crystals must be either (a) a face of one of them, or (b) a compromise boundary (Buckley, 1951; Schmidegg, 1928; Bathurst, 1958). Published descriptions of micrites (and commonly of dolomites) as idiomorphic or hypidiomorphic are based, it would seem, on the frequency of plane intercrystalline boundaries and not, as the terms imply, on the frequency of identified crystal faces. A simple arithmetic calculation will show that it is impossible theoretically for more than half the crystals in an equigranular non-porous mosaic to be euhedral. In natural conditions, where the crystals vary somewhat in size, in shape and orientation and are bounded by numerous plane surfaces, the likelihood is that the proportion of euhedral crystals will be much lower, probably less than 10 per cent. Subhedral crystals would not be so rare. The reason for dwelling on this matter of the polygonality of equigranular, monomineralic, non-porous mosaics, is that the exact nature of the intercrystalline boundary is a question of profound importance in diagenetic studies. It matters in fabric analysis whether an intercrystalline boundary is a crystal face or simply an unidentified plane interface. (a) Inferences from the Forms of Intercrysfalline Boundaries

Observations that yield useful evidence of the processes of cementation and neomorphism (= lithification) of carbonate oozes are extremely scarce. Intercrystalline boundaries may be plane surfaces or curved. It is necessary to note that plane crystal interfaces can form either by passive growth of cement at crystal-solution interfaces (i.e. syntaxial cement overgrowths) or by syntaxial growth in situ during neomorphism at the interface between a crystal face and a solution film, as one crystal enlarges at the expense of adjacent crystals. There is here an awkward complication. It is well known that intercrystalline boundaries in metamorphosed rocks have simple forms which tend toward plane surfaces as equilibrium is approached. Illustrations in Fischer and others (1967) are instructive. It is necessary to learn to distinguish, therefore, between the fabrics of a micrite that has only experienced low temperature and pressure and of one that has undergone metamorphism. This should not be too difficult, but the appropriate research is awaited.

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Other intercrystalline boundaries are amoeboid and thus it is probable that some crystal contacts are pressure-welded. Schwarzacher (1961,1500) has investigated the possibility that pressure-solution could have been responsible for the fabric of some silty micrites (low-magnesian calcite) in the Carboniferous Limestone of north-westem Ireland. He made acetate peels of etched, ground surfaces and in this way produced photomicrographs with exceptionally fine detail for light microscope preparations. He measured the longest axis within each crystal (in two dimensions) and found a strong maximum perpendicular to the bedding with a small submaximum in the bedding. This fabric is not what would be expected in a micrite lithified by pressure-solution under a vertically applied load, but it could, Schwarzacher suggested, have evolved in the presence of a pore solution moving vertically, along a hydrostatic pressure gradient. Pressuresolution might, he wrote, account for the submaximum. A difficulty in the way of interpreting any micrite fabric in terms of pressure-solution is the general paucity of compaction structures in these rocks. The early cementation which this implies seems to rule out the possibility of particle-toparticle pressure-solution, at least as a major lithifying process. On the other hand pressure-welded contacts between micrite crystals are apparent in illustrations by Fischer and others (1967), so the process is not unimportant. (b) Source of the Cement

It is obvious that the change from aragonite to calcite, by whatever train of processes, with the accompanying 8 per cent increase of volume, yields a definite but very small amount of surplus CaCOa for precipitation as cement (Harris & Matthews, 1968; Pingitore (l970»-but nothing like enough to fill the porosity of 50 per cent or more. Indeed, even in a purely aragonitic sediment, primary porosities of 60 per cent and 40 per cent would be reduced by polymorphic exchange only to 56.8 and 36.4 per cent. Yet at the moment of writing no one has been able to discover whence the extra quantity of CaCOa was derived. Some light on the source of CaCOa for cementation in general has been shed by the studies of hardgrounds, where submarine cementation of these lithified sea-floors can be demonstrated (for example, Lindstrom, 1963; Bromley, 1967, 1968; Taylor & Illing, 1969; Shinn, 1969). It is becoming increasingly clear that, in the Swedish Arenig sea, the Chalk sea of northern Europe, the Holocene Persian Gulf, very slow rates of sedimentation have allowed grains to lie undisturbed near the sediment surface for vast periods of time while sea-water, supersaturated for CaCOa, has been pumped through the sediment pores by the action of tides and waves. Given this unchanging diagenetic environment for hundreds of thousands of years, while sedimentation is practically zero, the cementation of lime-

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stone crusts can be achieved. Other relatively early cementation results from the early exposure of carbonate sediments to the subaerial meteoric environment: this type of early lithification has been demonstrated on Eniwetok and Guam (Schlanger, 1963, 1964), on Bermuda (Friedman, 1964; Land, 1967) and on Barbados (Matthews, 1968; Pingitore (1970). Recent work on the evolution of stylolites gives the impression that these structures may have played a much greater part in releasing CaCOa for cementation than has generally been realised. Porosity tends to increase upward and downward, away from the stylolite, as if CaCOa had moved outward from the stylolitic seam (Harms & Choquette, 1965; Dunnington, 1967). Many stylolites have certainly been syndiagenetic in origin, developing gradually during the process of lithification (park & Schot, 1968). The release of CaCOa for cementation during pressure-solution has also been estimated by Barrett (1964) and Oldershaw & Scoffin (1967), in a loosely quantitative manner. (c) Experiments of Hathaway & Robertson

The experiments of Hathaway & Robertson (1961, 301) are of uncerta in relevance to the problem of the lithification of micrite-despite their inevitable fascination-because they imply a degree of compaction not generally found in nature. These authors subjected wet aragonite mud from the Bahamas to various temperatures and pressures , in a cylinder from which surplus pore water could escape as the mud compacted. Temperatures ranged up to 400 C. (equivalent to a depth of about 20 km.) and pressure to 3450 bars (equivalent to an overburden of about IO km. of average crust) . Times ranged up to sixty-three days. Their series of electron photomicrographs (the mineralogy checked by X-ray diffraction) shows a change from aragonite to calcite, accompanied by rounding of needles and the appearance of increasingly larger globular-shaped masses of calcite. With their maximum pressure and time an equigranular mosaic of crystals was formed , with many plane intercrystalIine boundaries. Photographs of the end-product (fracture surface) are embarrassingly like those of natural micrites, such as tho se from the famous Upper Jurassic Solnhofen Limestone of Bavaria, the Triassic Halstatter Limestone of Austria and the Carboniferous Limestone of the British Isles. Nevertheless, it is inconceivable that micrites in general were constructed with the heat and violence lavished upon the Bahamian muds by Hathaway & Robertson, but it is significant, as they point out, that an artificial calcite micrite can be produced in this way. Transformation of the aragonite was completed early in the process, so the remainder of the evolution consisted of wet recrystallisation of calcite, dissolution and cementation (the pore filling) of an accumulation of calcite crystals, giving a final specific gravity for the artificial rocks of 1.9 (Solnhofen Limestone has sp. gr. of 2.6). The 0

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end-product retains, therefore, a porosity of about 30 per cent , so that, to complete the lithification, a further 30 per cent of CaCOa would have to be exotic in origin. (d) Significance of the Upper Crystal Size of Calcite Micrites

The widespread upper crystal diameter for the groundmass of lithified micrites at 3 to 4 u, ignoring the included coarser skeletal debris, is intriguing. As I wrote earlier (1959, 366), this 'points to the existence of a universal threshold state at which fabric evolution stops and beyond which it can, but need not , continue'. A possible reason for this , which would bear further investigation, is that a stage is reached in the combined neomorphism and cementation, when the porosity and permeability are so reduced that the transport of Ca 2 + and COa 2 - from one crystal face to another becomes slow even on a geological time-scale. Th is stage would represent virtual stability. Some new driving force would be needed to induce further progress in neomorphism, such as elastic strain induced during deformation. Probably a more plausible explanation has been made by Folk (1965, 36). He suggested that the crystal size of the micrite represents the long axes of the original crystals which 'have mainly expanded in volume by fattening out rather than lengthening'. This , of course, implies the introduction of allochthonous CaCOa. (e) Structure Grumeleuse In connex ion with the question of micrite lithification it is useful to glance for a moment at this clotted limestone, named and lucidly described by Cayeux (1935, 271) thus: ' ... elle montre de tout petits elements calcaires, it pate extremement fine, se detachant en gris sombre, de forme generale globuleuse ou irreguliere , dont les contours ne sont jamais franchement arretes, et sans differenciation d'aucune sorte. Ces materiaux, dont la microstructure est invariablement cryptocrystalline, sont plonges dans une gangue de calcite incolore et grenue.' The fabric studied by Cayeux in the Carboniferous Limestone of France and, above all, of Belgium is known in limestones of many other places and ages. The twocomponent fabric, consisting of patches of micrite embedded in a matrix of microspar (Folk, 1965), occupies a central position in a spectrum of limestone fabrics. In one direction, from the classificational point of view this clotted limestone passes into micrite, as the proportion of microspar falls and the boundaries between micrite patches and matrix become less obvious. In the other, it passes into structure pseudoolithique (Cayeux, 1935), the familiar pelsparite of Folk (1959). Cayeux noted particularly that the grumeaux are of silt grade. (Grumeau = clot or lump = peloid = grain of micritic composition with no special origin implied .) The passage from structure grumeleuse to micrite, again from a purely classificational PROC. GEOL. ASS., VOL. 81, PART 3,1970

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aspect, is also marked by a merging of the micrite patches. Cayeux's words cannot be improved: 'Dans un stade de differenciation moins prononce, les grumeaux, toujours, separes par de la calcite pure, contractent entre eux des adherences multiples' (1935, 271). These various types of clotted calcilutites have been described and illustrated by Beales (1958) from the Palaeozoic limestones of Alberta. The existence of a range of petrographic types, from micrite through structure grumeleuse, or clotted limestone, to pelsparite, does not by itself mean that this variation represents the different stages in a continuous diagenetic evolution. Indeed, the two leading writers on the question have expressed opposing views on the course of the diagenetic evolution. Cayeux believed that structure grumeleuse evolved by the growth of calcite crystals throughout the mass of an originally homogeneous micrite, and the gradual differentiation, thereby, of a more coarsely crystalline, continuous matrix separating residual clots of microcrystalline (micritic) calcite. Beales, on the other hand, whose extensive researches into pellet limestones are an indispensable introduction to this field (1956, 1958, 1965), thought that the processes operated the other way about, in that 'Many closely packed grains [peloids] appear to have merged on recrystallization into a homogeneous microcrystalline rock differentiated with difficultyfrom calcilutite'. The outstanding characteristic, and the most puzzling aspect, of this fabric, is the merged patches of micrite, with 'des adherences multiples'. This obviously cannot be a primary fabric of mechanically deposited peloids: it must be a secondary feature. Once this is granted, the field is open to speculation on the diagenetic evolution. A factor that must have an important bearing on the development of any working hypothesis is the universality of clotted texture, the widespread occurrence of some degree of clotting in micrites of many ages and localities, despite differences of both depositional and diagenetic environments. Two additional factors also need to be kept in view. One is the ubiquitous formation of faecal pellets in modern carbonate sediments allied to the common occurrence of heavily micritised skeletal debris (Bathurst, 1966). The other is the well-known nature of crystal growth fabrics. Where crystal growth starts at a number ofpoints in a homogeneous crystal mosaic and spreads outward from these points (Folk's 'porphyroid aggrading neomorphism', 1965,22), the resultant fabric is likely to contain radial elements (radial fibres or centrifugal increase in crystal size) and to yield, in ideal cases, a spherical growth front. An obvious example is the growth of spherulitic, radial-fibrous ooids, or needle bundles. Having regard to these three factors, my own, purely intuitive, conclusion as to the origin of structure grumeleuse runs thus: the growth of sparry calcite, beginning at a number of points in a homogeneous carbonate mud (or mudstone) would produce a collection of relatively coarsely crystalline

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patches in a matrix of unaltered finely crystalline ooze. This is the reverse of what we find in structure grumeleuse, Furthermore, because of the ubiquitous occurrence of primary peloids, diagenetic processes are more likely to take the form of a reduction of the individuality of peloids rather than a fabrication of new ones. Such reduction may follow the merging of soft faecal pellets or the action of pressure-solution. Structure grumeleuse is common in algal stromatolites and it may well be that, in a peloidal calcarenite or calcisiltite trapped by algal filaments, photosynthesis can lead to the precipitation of additional aragonitic micrite which, attaching itself to the existing peloids, will obscure their boundaries and cause merging. Grapestone (Illing, 1954; Purdy, 1963), in which calcarenite peloids, intensely bored by algae, are cemented by micrite (Bathurst, 1966, 21), may have formed in this way. These are, nevertheless, only tentative conclusions, and the elucidation of individual cases remains a matter of extraordinary difficulty, requiring patience and, maybe, the virtue for the time being of suspended judgment. (f) Fossilised Stages In micrites which have been partly replaced by neomorphic sparry calcite, it is important that we should not mistake the micrite as it is now for the oozy stuff that was originally altered to spar. In diagenetically immature limestones (e.g. the Cainozoic limestones of Guam (Schlanger, 1964) or Funafuti (Cullis, 1904», the present fabric and mineralogy of the unaltered, barely consolidated, micrite may truly reflect the condition normally obtaining while neomorphism is active. However, in diagenetically mature limestones (e.g. Carboniferous of Europe, Pennsylvanian of the United States), which are low-magnesian calcite, the present micrite must be different from its mineralogically heterogeneous precursor which existed at the time when neomorphism was operating. In other words, when we see, in a thin section, patches of secondary, sparry low-magnesian calcite associated with residual low-magnesian micritic calcite, we cannot logically infer that the spar is simply a product of recrystallisation of the micrite. I think we are bound to assume, in view of the foregoing discussion, that the spar is the neomorphic product of a material that no longer exists, and that the original micrite (more finely crystalline, more porous, mineralogically heterogeneous) has since changed to low-magnesian calcite with porosity 2 to 3 per cent. This is, of course, another way of saying that neomorphism goes on in some rocks during lithification. 4. PROGRESS In the last fifteen years much has been discovered about the diagenesis of carbonate sediments. We have, first of all, learned how to look at them, to take advantage of the fabric evidence they display. In 1947 Professor Read

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spoke to me before I went into the field to do my independent mapping. He urged me to bring back a map-s-even if it were only the size of a postage stamp! Since then much of my work and that of others in the field of carbonate sedimentology has, indeed, been concerned with the 'mapping' of areas of philatelic dimensions-as observed with the light and electron microscopes. More recently the introduction of quantitative chemical and isotopic data has deepened our conception of diagenesis. The effects of biological agents are only now beginning to be widely appreciated. Yet the situation is profoundly different from that of, say, ten years ago. We are at last in a position to pose many of the critical questions which future research workers should be able to answer. 5. GLOSSARY Biomicrite. A limestone composed of skeletal grains in a matrix of micrite (Folk, 1959). Cement. A non-skeletal void-filling, precipitated on an intragranular or intrasedimentary free surface. This convenient working definition, necessarily a compromise, was informally adopted by the Bermuda Seminar on Carbonate Cementation, September 1969. Compromise boundary. A plane interface between two crystals which evolved by mutual interference of their respective growing faces. This interface is a face of neither crystal (Buckley, 1951). Micrite. An abbreviation of 'microcrystalline ooze', it refers to finely crystalline carbonate sediments with upper crystal diameter of 4 fJ, (Folk, 1959). Microspar. Carbonate crystal mosaic with crystal diameters from 4 to 10 fJ" or even higher, to about 50 fJ, (Folk, 1959). Mudstone. A micrite containing less than 10 per cent grains (Dunham, 1962). Neomorphism. More strictly 'aggrading neomorphism' as used here. A complex of processes whereby a mosaic of finely crystalline carbonate is replaced by a coarser (sparry) mosaic without the development of visible porosity (Folk, 1965). Dominant reactions are the wet transformation of aragonite to calcite and recrystallisation. The process is 'porphyroid' where some of the neomorphic crystals are conspicuously larger than those which surround them. Peloid. A sedimentary grain formed of micritic carbonate irrespective of origin (McKee & Gutschick, 1969). Pelsparite. A limestone composed of pellets (peloids) in a matrix of cement (Folk, 1959). Wackestone. A micrite containing more than 10 per cent of grains: these grains are not in three-dimensional contact with each other. They are 'mud-supported' (Dunham, 1962).

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REFERENCES BARRETT, P. J. 1964. Residual Seams and Cementation in Oligocene Shell Calcarenites, Te Kuiti Group. J. sedim. Petrol. 34, 524-31. BATHURST, R. G. C. 1958. Diagenetic Fabrics in Some British Dinantian Limestones. Lpool Manchr geol. J., 2, 11-36. - - - - , . 1959. Diagenesis in Mississippian Calcilutites and Pseudobreccias. J. sedim. Petrol., 29, 365-76. - - - - . 1966. Boring Algae, Micrite Envelopes and Lithification of Molluscan Biosparites. Geo!.J.,5,15-32. BEALES, F. W. 1956. Conditions of Deposition of Palliser (Devonian) Limestone of Southwestern Alberta. Bull. Am. Ass. Petrol. Geol., 40,848-70. - - - - . 1958. Ancient Sediments of Bahaman Type. Bull. Am. Ass. Petrol. Geol., 42, 1845-80. - - - - . 1965. Diagenesis in Pelletted Limestones. In L. C. PRAY & R. C. MURRAY (Editors): Dolomitization and Limestone Diagenesis: a Symposium. Soc. Econ. Paleontologists Mineralogists, Spec. Publ., 13,49-70. BLACK, M. 1953. The Constitution of the Chalk. Proc. geol. Soc., Lond. 1499, lxxxi-Ixxxii. BROMLEY, R. G. 1967. Some Observations on Burrows of Thalassinidean Crustacea in Chalk Hardgrounds. Q. Jl geol. Soc. Lond., 123, 157-77. - - - - . 1968. Burrows and Borings in Hardgrounds. Meddr dansk geol. Foren., 18, 247-50. BUCKLEY, H. E. 1951. Crystal Growth. Wiley, New York, 571 pp. CAYEUX, L. 1935. Les Roches Sedimentaires: Roches Carbonatees. Masson, Paris, 463 pp. CLOUD, P. E. 1962. Environment of Calcium Carbonate Deposition West of Andros Island, Bahamas. U.S. Geol. SUTV. Profess. Paper, 350, 1-138. CULLlS, C. G. 1904. The Mineralogical Changes Observed in the Cores of the Funafuti Boring. In T. G. BONNEY (Editor): The Atoll of Funafuti. Royal Society, London, 392-420. DUNHAM, R. J. 1962. Classification of Carbonate Rocks According to Depositional Texture. In W. E. HAM (Editor): Classification of Carbonate Rocks. Am. Assoc. Petro!. Geologists, Tulsa, Okla., 108-121. DUNNINGTON, H. V. 1967. Aspects of Diagenesis and Shape Change in Stylolitic Limestone Reservoirs. World Petrol. Congo Proc. 7th Mexico, 2, 339-52. EVANS, G. 1966. Persian Gulf. In R. W. FAIRBRIDGE (Editor); The Encyclopedia of Oceanography. 1. Reinhold, New York, 689-95. FISCHER, A. G., S. HONJO & R. E. GARRISON. 1967. Electron Micrographs ofLimestones. Princeton Univ. Press, 141 pp. FLUGEL, E. 1967. Elektronenmikroskopische Untersuchungen an mikritischen Kalken, Geol. Rdsch., 56, 341-58. FOLK, R. L. 1959. Practical Petrographic Classification of Limestones. Bull. Am. Ass. Petrol. Geol. ,43, 1-38. - - - - . 1965. Some Aspects of Recrystallization in Ancient Limestones. In L. C. PRAY & P. C. MURRAY (Editors); Dolomitization and Limestone Diagenesis: a Symposium. Soc. Econ. Paleontologists Mineralogists, Spec. Publ., 13, 14-48. FRIEDMAN, G. M. 1964. Early Diagenesis and Lithification in Carbonate Sediments. J. sedim. Petrol., 34, 777-813. GINSBURG, R. N. 1957. Early Diagenesis and Lithification of Shallow-water Carbonate Sediments in South Florida. In R. J. LEBLANC & J. G. BREEDING (Editors); Regional Aspects of Carbonate Deposition. Soc. Econ. Paleontologists Mineralogists, Spec. Publ. 5, 80-99. - - - - . 1964. South Florida Carbonate Sediments. Guidebook for Field Trip No. I. Geol. Soc. Am. Convention, 1-72. HARMS, J. C. & P W. CHOQUETTE. 1965. Geologic Evaluation of a Gamma-Ray Porosity Device. Trans. Soc. Profess. Well Log Analysts, 6th Annual Logging Symposium, Dallas. Texas, 1-37.

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HARRIS, W. H. & R. K. MATTHEWS. 1968. Subaerial Diagenesis of Carbonate Sediments: Efficiency of the Solution-Precipitation Process. Science, 160, 77-9. HATHAWAY, J. C. & E. C. ROBERTSON. 1961. Microtexture of Artificially Consolidated Aragonite Mud. U.S. Geol. Surv. Profess. Paper, 424-C, 301-4. HONJO, S. & A. G. FISCHER. 1964. Fossil Coccoliths in Limestone Examined by Electron Microscopy. Science, 144, 837-9. ILUNG, L. V. 1954. Bahaman Calcareous Sands. Bull. Am. Ass. Petrol. Geol., 38,1-95. KINSMAN, D. J. J. 1969. Interpretation of Sr H Concentrations in Carbonate Minerals and Rocks. J. sedim. Petrol., 39, 486-508. LAND, L. S. 1967. Diagenesis of Skeletal Carbonates.J. sedim. Petrol., 37, 914-30. LINDSTROM, M. 1963. Sedimentary Folds and the Development of Limestone in an Early Ordovician Sea. Sedimentology, 2, 243-75. McKEE, E, D. & R. C. GUTSCHICK, 1969. History of the Redwall Limestone of Northern Arizona. Mem. geol. Soc. Am., 114, 726 pp. MATTHEWS, R. K. 1966. Genesis of Recent Lime Mud in Southern British Honduras. J. sedim. Petrol., 36, 428-54. - - - - . 1968. Carbonate Diagenesis: Equilibration of Sedimentary Mineralogy to the Subaerial Environment; Coral Cap of Barbados, West Indies. J. sedim. Petrol., 38,1110-19. OLDERSHAW, A. E. & T. P. SCOFFIN. 1967. The Source of Ferroan and Non-Ferroan Calcite Cements in the Halkin and Wenlock Limestones. Geol. J., 5, 309-20. PARK, W. C. & E. H. SCHOT. 1968. Stylolites: Their Nature and Origin. J. sedim. Petrol., 38, 175-91. PINGITORE, N. E. 1970. Diagenesis and Porosity Modification in Acropora palmata: Pleistocene of Barbados, West Indies. J. sedim. Petrol., 40, 712-21. PRAY, L. C. 1960. Compaction in Calcilutites. Bull. geol. Soc. Am., 71, 1946 (abstract). - - - - & P. W. CHOQUETTE. 1966. Genesis of Carbonate Reservoir Facies. Bull. Am. Ass. Petrol. Geol., 50, 632 (abstract). PURDY, E. G. 1963. Recent Calcium Carbonate Facies of the Great Bahama Bank 1 and 2. J. Geol., 71, 334-55,472-97. SCHLANGER, S. O. 1963. Subsurface Geology of Eniwetok Atoll. U.S. Geol. Surv. Profess. Paper, 260 BB, 991-1066. - - - - . 1964. Petrology of the Limestones of Guam. U.S. Geol. Surv. Profess. Paper, 403-D, I-52. SCHMIDEGG, O. 1928. Ober geregelte Wachstumsgefuge, Jb. geol. Bundesanst., Wien., 78,1-52. SCHWARZACHER, W. 1961. Petrology and Structure of Some Lower Carboniferous Reefs in Northwestern Ireland. Bull. Am. Ass. Petrol. Geol., 45, l481-503. SHINN, E. A. 1969. Submarine Lithification of Holocene Carbonate Sediments in the Persian Gulf. Sedimentology, 12,109-44. TAYLOR, J. M. C. & L. V. ILUNG. 1969. Holocene Intertidal Calcium Carbonate Cementation, Qatar, Persian Gulf. Sedimentology, 12, 69-107. WOLFE, M. J, 1968, Lithification of a Carbonate Mud: Senonian Chalk in Northern Ireland. Sediment. Geol., 2, 263-90,

R. G. Bathurst The Jane Herdman Laboratories of Geology The University of Liverpool Brownlow Street, P.O. Box 147 Liverpool L69 3BX