GUILIELMITES FORMED FROM PHOSPHATIZED CONCRETIONS IN THE ASHFIELD OF THE AREA

By J.G. BYRNES, T.D. RICE*, and D. KARAOLIS*

(Manuscript dated January 1976) (Revised July 1977)

ABSTRACT

Guilielmites, 5-30 mm in diameter, have formed by deformation and partial solution of carbonate apatite nodules in the of the . The phosphate is believed to be an early diagenetic replacement of carbonate concretions, probably penecontemporaneous with Ashfield Shale deposition. The U and F content of the phosphate does not support a marine origin for the formation. Where protected from compression within hard sideritic bands, the phosphatic nodules remain spheroidal. Elsewhere, forms transitional to guilielmites are encountered. In all stages of the transition, Mn, Fe, Mg, Ca, P, F, and S are more abundant than in average Ashfield Shale. Ca, P, F, Na, U, and C0 2 decrease from nodule to guilielmites, whilst Pb, Ti, Si, Al, K, Ba, and S increase; the ratio P/F decreases, indicating the relative immobility of F. The geometry of formation of guilielmites is envisaged simply as a sphere reducing by solution, under vertical pressure, to a biconvex lens of equivalent diameter. A fourfold to tenfold volume reduction is involved, compatible with the degree of residual concentration of Ba, s, and perhaps Pb.

INTRODUCTION

Guilielmites is the convenient pseudofossil name for lustrous, dark, slickensided compaction structures found world­ wide in fine-grained sedimentary rocks. They are conical or lenticular, often biconvex, bodies of circular or elliptical plan. They are 2- 50 mm in diameter (usually 5 - 20 mml. The maximum thickness is 0. 2 - 0. 5 times the diameter and is usually perpendicular to enclosing stratification. Parting surfaces, several of which may occur within a single guilielmites body, carry fine striations in radial, bilateral, or slightly spir~l arrangement.

Guilielmites occur frequently in coal measures in France, Belgium, the Saar, Westphalia, Bohemia, Russia, Scotland,

* Chemical Laboratory, Department of Mines, Lidcombe, New South Wales

Rec. geol. Surv. N.S.W. 18(2), 169-200, 3 figs, 5 pls

I1\\111\1\11 \\Ill \\Ill \1\1\1\1\1 \\Ill \1\\\ Ill\\ IIIII \\111\\1 0004984330 170 J .G. BYRNES, T.D. RICE, AND D. KARAOLIS ..

England, Wales, and North America. They a.lso Q;QC'IItt' in South America, Africa, Asia, and Australia, their total recorded range being Carboniferous to Miocene. In Australia, guilielmites are known from and Triassic sequences. . 'l'lll.e .structures known as "Chinese hat nobbies" at the Lightning Ridge opal field are possibly guilielmites (Byrnes 1975).

In the Triassic Ashfield Shale (figure 1), which is the basal formation of the argillaceous of the Sydney Basin (Herbert 1976b) (table 1), both guilielmites and concretionary nodules have been known for many years. A connection between the two has not been proposed previously. The nodules, which are phosphatic, have been referred to as essentially siderite (Lovering 1954, Lovering and McElroy 1969). That the nodules are phosphatic was first demonstrated by one of us in 1966 (Pyle and Rice 1967, table 7 herein). That guilielmites may also consist largely of calcium phosphate is now noted, possibly for the first time. It is anticipated that guilielmites elsewhere will prove to be phosphatic.

Origin of Guilielmites

Guilielmites have been interpreted, inter alia, as burrows, coprolites, body fossils, concretions, compression cones, and as plant bulbs, seeds, or floats. Regarded initially as fruits, they were described under Calvasia and Carpolithes by Sternberg (1820, 1825), transferred to Cardiocarpum by Bronn (1837), and raised to a new genus by Geinitz (1858). After some time they were rejected from palaeobotany (Schenk 1864). Thereafter they have been regarded mainly as inorganic. Carruthers (1871) inter­ preted them as fluid casts. Gothan (1909) and Schmidt (1934) suggested they may be gas rise structures. For some time they have been generally regarded as inorganic structures indicating differential compaction (Elliot 1965). Differential compaction may occur about a relatively incompressible object such as a concretion, shell, vertical plant root, or animal burrow. Guilielmites have been noted enclosing pelecypods within their burrows and have also been found joined vertically along such a 4 burrow (Pruvost 1930). Their formation about roots has been considered by Pruvost (1930) and Renier et al. (1938).

Possibly a feature common to guilielmites of varied origin is reduction in the volume offering resistance. This may take place by solution of concretions, crushing of incompletely filled shells, or removal of decomposed root material. The earliest mention of volume decrease is possibly that of Wood (1935), who explained guilielmites formation as the result of slipping in the rock on the collapse of some central body, generally a shell. Altevogt (1968), however, concluded that such hard bodies acted only as nuclei for rolling clay accretions, and that it was these accretions which were transformed into guilielmites. GUILIELMITES IN THE ASHFIELD SHALE 171

~ Brlnge/ly Shale

0 Mlnchlnbury

~ Ashfield Shale

~ Hawkesbury - Narrabeen ~ Sandstone Group

151"E I Avoca

-34°$

20 0 20 40

10047

Figure 1. Locality map, guilielmites in the Ashfield Shale

0 1 2 3 4 5 em 172 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

TABLE 1

GENERALIZED STRATIGRAPHY OF THE TRIASSIC OF THE SYDNEY BASIN

Bringelly Shale

Wianamatta Group Minchinbury Sandstone

u H Ashfield Shale Ul Ul ..0: H ~ Mittagong Sandstone E-<

Hawkesbury Sandstone

Includes Bulgo Sandstone, Narrabeen Group ---z- Terrigal Formation ..0: H ~ Coal measures: fluvial and rLI p., marine sediments

The principle feature suggesting a genetic relationship between guilielmites and nodules in the Ashfield Shale is their close spatial association, with morphological and mineralogical intergradation. Some major points of evidence are:

1. Guilielmites are concentrated in intervals notable for nodule abundance. 2. The larger guilielmites (>17 mm diameter) occur in mudstone at the surfaces of hard sideritic bands, positions which are other­ wise often occupied by nodules. 3. Mixtures (roughly 2:1) of guilielmites and flattened nodules were obtained from several mudstone and. shale blocks of small size (e.g., 0.3 m across). 4. Guilielmites have been observed with cores of kaolin, chert, barite, and pyrite, greatly resembling those present in nodules. 5. The range of concentration of insoluble elements in guilielmites relative to nodules (x4 - xlO) corresponds to the volume reduction estimated from geo­ metrical considerations. GUILIELMITES IN THE ASHFIELD SHALE 173

6. The depletion of Ca and C0 2 in guilielmites phosphate with respect to nodule phosphate, is in accordance with the preferential removal of these components from carbonate apatite* undergoing solution.

Geometry of Guilielmites Formation

The guilielmites of the Ashfield Shale are usually biconvex lenses with a distinct, sharp equator (plate 1; plate 2, figure 1). The equatorial area may rarely be flattened to a flange. The guilielmites range from 5 to 30 rom in diameter. For 162 specimens measured, the first, second, and third quartiles of this variation were at 10, 12, and 14 rom. Maximum thickness varies from 1 to 8 rom and is mostly between 0.2 and 0.3 times the diameter. Guilielmites surfaces, darker than both their matrix and interiors, are smooth and ornamented with abundant fine radial striations (>30/mm). Frequently these bodies disaggregate readily along two or more similar surfaces below the outermost one. A small core of barite, kaolin, chert, and pyrite is common, and a central depression on the upper surface is sometimes present.

The geometry of guilielmites formation may be envisaged simply as a sphere reducing to a biconvex lens without change in horizontal diameter. An early stage of plastic deformation, involving little change in volume but an increase in horizontal dimensions, may have occurred but for simplicity this is overlooked. We may approximate each half of the resultant biconvex lens by revolving sections of the curve y = x 2 about y. 2 If the form can be approximated by y = x , then plotting maximum thickness against diameter should give a curve y =ax, where a is equal to the maximum x value attained on the curve y = x 2 (i.e., y=x 2 =ax).

Figure 2 indicates that the maximum x value is x = 1/3. 2 The volume of the solid formed by revolving y = x , between x = o and x = 1/3, about the y-axis .s iven by 1/3 v = 2IT x.x 2 ...-dx r0 3 ITTf/ 3 2] x .d:y.: 0

1 IT _1_ :!-2. • 8 1

* A mineral group, not a mixture of carbonate and apatite. 174 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

This solid is half of a guilielmites body; therefore the volume of a guilielmites,

v g = 11/81. The volume of a sphere of radius l/3 is

V 4/3 IT. 27 s 411/81 i.e., V /V g s

For x

The concentrations of S, Ba, and Pb during guilielmites formation suggest volume reductions between x3 and xlO. Even greater volume reduction in shale matrix, by compaction, is responsible for the slickeusiding of the guilielmites.

ASHFIELD SHALE GUILIELMITES AND NODULES Distribution The Ashfield Shale varies in thickness from 45 to 61.5 m and has been intersected by at least 113 drill holes. Herbert (l973b, 1974) has proposed the succession of four lithological units shown in the left hand column of figure 3. These may be applied over a large area, from Sydney west-southwest to the Razorback Range (61 km) and west-northwest to Plumpton (39 km), although erosion has removed much of Unit 4. The additional horizons shown in the right hand column of figure 3 may be persistent over a more restricted area on the Cumberland Plains and south to Heathcote.

Many guilielmites occur close to hard sideritic bands in Unit 3, mostly between horizons A and D (plate 3, figure l). • Examples were collected below the level of Band D in quarries at Ashbury, Croydon, Greenacre, North Auburn, Granville, Punchbowl, Campsie, and St Peters. The examples analysed are from strata adjoining Band B in a quarry at Trevenar Street, Ashbury. From between Bands A and D at Greenacre, Homebush Bay, and Ashbury, some large blocks (10- 50 kg) of guilielmites-rich shale were obtained. These were disintegrated for yields of 0. 5-2 guilielmi tes per kilogram. A 45 kg block from Homebush Bay State Brickworks yielded forty-one flattened nodules of up to 30 x 35 x 15 rom size, in addition to eighty-three guilielmites. GUILIELMITES IN THE ASHFIELD SHALE 175

n ;. ~ ®

® ®

:1: 4 ® ® ® ® "':1: ;( ® ... ® :1: ® w ... "0: w ® > "' ® ®

I 0 IS 20 25 MEAN DIAMETER (mm)

Figure 2. Plot of average maximum thickness versus mean diameter. Each point is the plot of average maximum thickness for groups of one to sixteen guilielmites of the same mean diameter vers~s that diameter. Based on 162 examples from between hard sideritic bands A and D in quarries at Ashbury and Greenacre.

Sparse guilielmites occur in the upper part of Unit 2. None have been noted in Units 1 and 4, although the latter has not been examined closely. It is anticipated that guilielmites will be found in Unit 1, as sparse nodules occur therein. The stratigraphic position of guilielmites in Ashfield Shale at St Leonards, Eastwood, Thornleigh, and Bowral is not knowrr. Hard bands which may be the four persistent ones of Unit 3 176 J.G. BYRNES, T.D. RICE,AND .D. KARAOLIS

Minchinbury Sandstone

UNIT 4: laminite sand­ stone. dark grey Position of suspected siltstone. and persistent sideritic s ha I e; frequenc 1 horizons and grainsize of sand possibly increasing up­ wards. small burrow and trai I casts common. 17-32 m

1'!-~-!"_!!!"!_!"!_!"!_!'1 0 Hard sideritic band

UNIT 3: ---- black to dark· grey shale a11d jioiii•---~ C Hard sideritic band mudstone with ~~~~~~ B Hard sideritic band hard sideritlc bands 12-21 m ----

Hard sideritic band

UNIT 2: laminite 1-6m UNIT I: dark grey to black sideritic mudstone and shale. slightly carbonaceous 6-15 m or Hawkesbury Sandstone C.A.M. 7608

Figure 3. Lithological units in the Ashfield Shale

0 1 2 3 4 5 em GUILIELMITES IN THE ASHFIELD SHALE 17':1 occur at the Eastwood brickpit (D absent) and at the Thornleigh brickpit.

Occurrence and Form of Nodules

The nodules occur in both shale and sideritic hard bands. Nodules range from 2 to 50 mm in diameter, mostly 5 to 25 mm. Most have stellate central cavities of uncertain origin. These are now filled by late diagenetic minerals. The greatest concentrations of nodules appear to be within, or at the surfaces of, the sideritic hard bands of Unit 3 (plate 3, figure 2; plate 4, figure 1). Coalescence of nodules is not unusual at the top and bottom of hard bands. At Parkhill Avenue, Leumeah, small sideritic lenses up to 250 mm wide contain a peripheral zone, up to 50 mm thick, which consists almost entirely of coalesced nodules. In shale, coalescence is usually limited to between two individual nodules, except in Unit 1. In Unit l near Picton (GR 604776, Camden 1:63,360) the nodules occur as compound bodies, each with a large central cavity filled by diagenetic minerals. The central cavity comprises up to 17 per cent of the body. A typical compound nodule is a weakly botryoidal flat ellipsoid, about 50 mm in diameter, comprising about fifteen conical members. Euhedral barite lines the walls of the central cavity and later linear gashes. Flat compound nodules up to 50 mm across also occur sparsely at Parkhill Avenue.

A second type of nodule occurrence can be observed in the Ashfield Shale. Relatively small (2- 5 mm) nodules are distributed densely and uniformly throughout 50- 100 mm thick sideritic hard bands (plate 5). This type of hard band appears to be confined to the basal 15 m of the Ashfield Shale and is widely distributed. Lovering and McElroy (1969) listed eight areas with known occurrences, to which may be added Leumeah, Picton, Doonside, Minchinbury, Punchbowl, Rydalmere, Eastwood and Parrs Brush.

Although composed originally of fibres (plate 4, figure 2; plate 2, figure 2), none of the nodules, not even the smallest, are of regular radial-fibrous construction. The larger nodules have a mamillary surface and display coalesced or ove~grown discrete growth bundles in section. Fundamental growth aggregates are recognizable, in which the fibres radiate outwards from a common axis and upwards away from the nodule centre. These aggregates may be regarded as outward-growth "spherulites", comparable with the trabeculae of corals. The most regular structure encountered, usually in small nodules, is radial arrangement of such aggregates. In large nodules, curvi-linear arrays of these aggregates commonly extend slightly beyond the general nodule surface. In hard sideritic bands the nodules are often preserved in an incompletely grown state, with matrix between the aggregates and a tendency towards lateral growth parallel to stratification (plate 4, figure 2). Originally fibrous, the nodules are now recrystallized. 178 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

The central stellate cavities, in which barite, chert, kaolin, and pyrite grew, have the appearance of gashes rather than solution products. The cracks taper outwards. The strictures of spherical geometry dictate that uniform shrinkage of an isotropic spheroid should produce cracks which taper outwards, as in a septarian nodule (Boyer et al., 1977). This is possibly the case with the guilielmites - forming nodules, although they perhaps cannot be considered as rheologically isotropic.

Nature and Significance of the Hard Bands

The sideritic hard bands have undergone negligible compression since the formation of their internal nodules. These are still spheroidal, whilst ones at the band surfaces may be flattened. Lack of compression is also evidenced by the modes of fossil preservation. Hollows after the decay of sub-horizontal plant stems may be still perfectly cylindrical, and fusiform have occasionally been preserved upright rather than lying on their sides. Preservation of puckers in the skin of an may also be noteworthy (Fletcher 1962). The hard bands are the least permeable rock type in the formation. Because of their negligible compression and low permeability they are regarded as repositories of nodule phosphate of the most pristine composition available.

The hard sideritic bands have been regarded previously as lenticular and very irregular in vertical and horizontal extent (e.g., Loughnan et al. 1962, Lovering and McElroy 1969). In exposures of Unit 3, up to ten hard bands may be present, most of which are quite restricted or lenticular. The four horizons thought to be continuous between exposures are possibly associated with more nodules than are the very local bands. Band D appears to be the least continuous. It is discontinuous at Auburn and Homebush Bay, and absent at Merrylands, Eastwood, and Heathcote. Of the pair B and C, Band B is usually the thicker and more frequently displays pinch and swell to 170 mm thickness. Full boudinage along hard bands is fairly common.

Environment of Ashfield Shale Deposition

Two formations of the Wianamatta Group, the Minchinbury Sandstone (Chapman 1909, Lovering 1953) and the underlying Ashfield Shale (Herbert 1973a, b, 1974) have been regarded as of at least partial marine origin. Byrnes and Byrnes (1977) re-examined supposed ostracodes, foraminifera, and algae described from the Minchinbury Sandstone by Chapman (1909) and Lovering (1953). These "fossils" proved to be of inorganic origin. The Ashfield Shale had been regarded usually as non-marine until Herbert (1973a, b, 1974) re-interpreted it as a shallow marine to brackish shelf deposit, offshore from a regressive coastline marked by sand barriers (Minchinbury Sandstone). GUILIELMITES IN THE ASHFIELD SHALE 179

Herbert (1976a, b) interpreted the Ashfield Shale as shallow marine or estuarine deposits formed in an embayment along the axis of the Sydney Basin. Sediment was supplied from the north along the axis of the Basin. Most of the sediment was deposited on levees and in backswamps (). Lagoon and marsh deposits (basal Bringelly Shale) accumulated behind sandy barrier islands (Minchinbury Sandstone) , the whole complex prograding seawards. Within the Wianamatta Group, apparent confinement of notable phosphate values to the Ashfield Shale was a factor influencing Herbert (pers. comm.) in assigning a marine origin to the Ashfield Shale.

The fossils of the Ashfield Shale mostly do not support a marine depositional environment. Possible exceptions are Acanthomorphitae acritarchs which occur intermittently throughout the Wianamatta Group (Helby 1969). Plant fossils are present throughout the Ashfield Shale, including the sideritic hard bands. Animal remains have been collected mainly from the hard bands. The fauna comprises thirteen fish species (Woodward 1908), three species of labyrinthodont (Watson 1958), unionid pelecypods (Etheridge 1888, McMichael 1957), an isopod (Chilton 1917), and six species (Tillyard 1916). Of these, the isopod Phreatoicus wianamattensis is of a genus still extant and confined to fresh water. Phosphatic shell fragments have been encountered in the sideritic hard bands, initially suggesting linguloid brachiopods, and hence salinity. Since unionids are the only shells known intact from the Ashfield Shale, such fragments are more likely to be phosphatized pelecypod debris. The fish fauna associated with the hard bands is best known from St Peters (Woodward 1908). There it appears to have been obtained from a band in which phosphatic concretions were rare. This may be of little significance, however, since fish-bearing hard bands near Maroota have abundant phosphate concretions (specimens F 13789 and F 13790, Geological and Mining Museum, Sydney). The fish faunule of the hard bands is distinct from that of the interbedded . Notable in the hard band faunule is the sharklike PZeuracanthus parvidens which attained a length of 1.43 m, and the Ceratodus Zaticeps of about 1 m length.

As correlation of the hard bands appears to be possible over many kilometres, the siderite is thought to have been deposited beneath large areas of open water, in either a lake or a lagoon. The planar stratification within the hard bands is rarel~ disturbed, other than by boudinage formation, and ripples are unknown. Thus deposition was probably below wave base. For DM Plumpton DOH 1, Herbert (1976b) found that the maximum P20s value, for 0.6 m core lengths, occurred exactly at the mid-point of the Ashfield Shale section. As the Ashfield Shale is both underlain and overlain by shallow-water , this finding suggests that P 20 5 content of the formation correlates directly with water depth and bottom stagnancy. Although most abundant in the relatively deep water strata, the nodules probably formed at all depths. Thus guilielmites have been noted (at Eastwood, Homebush Bay, and south of Campbelltown) in laminite sequences with common 180 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

small sand dykes which are 1 - 3 rnrn thick and sometimes ptygmatic. Assuming that these dykes represent desiccation, and that a narrow range of environments gave rise to the phosphate nodules, deep offshore marine deposition appears unlikely. The laminite sequences are probably lake or lagoon marginal facies, partially subaerial. Sets of inclined and slumped laminae, as at St Peters and Artarmon, are interpreted as marking subaerial channels.

A lacustrine rather than lagoonal depositional site for the phosphatic interval of the Ashfield Shale is favoured here. It might be argued that the freshwater invertebrate fossils could have been introduced into a lagoon during floods. However, in that case one would expect restricted marine arenaceous microfauna to be present. Many samples have been examined for such microfauna, with negative result. The low uranium and fluorine contents of the Ashfield Shale phosphate could suggest a body of fresh water. Comparably low levels of uranium may be found in subaerial cave and island phosphates, formed from the action of meteoric water and excreta on limestone. By contrast, uranium typically comprises 50- 200 ppm (rarely 1000 - 2000 ppm) of marine carbonate apatite (Altschuler et al. 1958). Likewise, terrestrial phosphorites typically contain much less ( 0. OS - 1. 3 per cent) fluorine than do marine phosphorites (3.1-4.2 per cent) (Mansfield · 1940, Altschuler et al. 1958).

Chemical Composition of the Ashfield Shale

Chemical analyses of Ashfield Shale samples carried out in the past (see table 2) are sufficient to provide an overall average against which guilielmites formation may be assessed. Twenty-five analyses carried out by the Department of Mines on "shale" samples, collected mostly from metropolitan brickpits, were assembled by Lovering (1954). Averages from later analyses of drill core, by the Department of Mines and Colonial Sugar Refining Co. Ltd (Herbert 1976b) are also included in table 2.

Both series of analyses (brickpit and drill core) illustrate that the upper Ashfield Shale is poorer in alumina and richer in silica than is the lower portion. This is caused by the upwards increase in quartz. The averages from drill core analyses reptesent material fresher than brickpit shale samples and also less well separated from sideritic bands, phosphatic bodies, and laminite. It is clear from the present study that Fe, Mg, Ca, and P are associated within early diagenetic carbonate apatite and carbonates in the Ashfield Shale. As would be expected, the drill core analyses are higher in these elements than the brickpit shale samples. Oxidation and depletion of iron appears to be quite considerable in the case of the brickpit samples.

It is suspected that carbonate apatite is present in the Ashfield Shale as a matrix phase as well as in nodules. Nodule versus matrix, or guilielmites versus matrix, concentration factors for P and Fare similar (table 4). This suggests that GUILIELMITES IN THE ASHFIELD SHALE 181 matrix P and F occur together, in carbonate apatite. It is quite likely that some undetected nodules contributed to the "matrix" values. However, examination of thin sections does disclose disseminated fine-grained material of very low briefringence, which is presumably phosphate.

Chemical Changes during Guilielmites Formation

Analyses of nodules, guilielmites, and associated matrixes are given in table 3. All oxide ranges in table 3 are wider than those from normal Ashfield Shale samples (table 2). Typical nodules contain more than 60 per cent carbonate apatite, less than 40 per cent included detrital sediment, and 5- 20 per cent siderite. They may be largely replaced by siderite but this is unusual, less than 10 per cent being normal. The composition of the phosphate phase is roughly estimated by calculation from analyses, in accordance with petrographic observations (table 8). In the case of the one analysis not recast, the nodules are significantly replaced by calcite and siderite.

Table 5 shows the concentration and depletion factors associated with the formation of guilielmites, the overall average for the Ashfield Shale (table 2) providing reference values. Mn, Ca, Fe, Mg, P, F, and S are concentrated relative to average Ashfield Shale and are associated with the non-detrital minerals. Si, Al, and Ti, which are associated with the detrital minerals, are depleted because of dilation by diagenetic minerals. Table 4 presents the concentration of components in nodules and guilielmites with respect to their matrixes.

The conclusions regarding element behaviour during guilielmites formation are set out in table 6. Si, Al, Ti, and K decrease regularly with increasing dilation by authigenic minerals. They probably represent detrital phyllosilicates. The apparent positive anomaly in the sequence for Si and Al in the hard sideritic band nodules is not reflected by K and is due to the presence of later stage diagenetic chert and kaolinite filling central cavities. Ca, P, and probably Na, are components of the phosphate phase. Fe, Mn, and Mg appear to be associated with the carbonate phase which dilated the matrix detritus and at the same or later stage invaded the nodules. These elements show little overall decrease through the series taken as representative of guilielmites formation (table 3), but an increase with respect to matrixes (table 4). This is another expression of residual concentrations. The sparser the siderite in the original sediment, the greater was the subsequent compaction and dissolution of the concretions. As only a little of the Fe, Mn, and Mg was lost during this solution, the concentrations of these elements relative to matrixes (table 4) should be inversely proportional to the original matrix siderite content. 182 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

Most of the u, F, and C0 2 originally present has been lost from those nodules transformed into guilielmites. It is not known whether this took place during the transformation or subsequent to it. During guilielmites formation, Ba, S, and .perhaps Pb, concentrate by factors compatible with the volume reduction expected from geometrical considerations. Ba occurs as barite within the central cavities. As the paragenesis of the cavity­ filling minerals is not yet known, Ba is regarded as a less sensitive indicator of volume reduction than is Pb, the latter being depleted in the nodules relative to their matrix.

THE PHOSPHATE Discovery in the Sydney Basin Triassic

Intensive Australia-wide exploration for phosphorite began in 1961 (Howard 1972) • Phosphatic concretions in Triassic strata of the Sydney Basin were recognized independently by several workers in the mid 1960's. Lassak and Golding (1966) noted nodules in the basal Newport Formation at Mona Vale, and concretions near the top of the formation near Gosford (Golding 1955). In the Bulgo Sandstone, Lassak and Golding (1966) and Taylor (1967) noted phosphate in all the abovementioned forms south of Sydney, whilst north of Sydney phosphatic rinds surround siderite in worm tubes at Long Reef (Gibbons and Gordon 1974). Ellipsoidal kaolin nodules with phosphatic cores have been noted from the Bouddi National Park area (E.V. Lassak pers. comm.). Phosphate has been noted widely within the Narrabeen Group in the form of nodules, areas of enrichment in fine sediment, individual grains, or cement in sandstones (Uren 1974). Nonetheless, Retallack (1975) doubted the diagenetic nature of phosphatic nodules reported from Mona Vale, suggesting that the phosphate may be bone or else is redeposited from the . However, the correlative Terrigal Formation has yielded concretions of coarsely crystallized radial apatite from coastal cliffs bordering Bulbararing Bay near Avoca (museum specimens lacking precise locality). The presence of phosphatic :nodules and concretions within the Narrabeen Group is of interest here because G. Retallack (pers. comm.) has noted the occurrence of guilielmites in sideritic and carbonaceous shales of the freshwater Newport Formation.

In 1966, T.W. Dickson reviewed phosphate occurrences in the Tasman Fold Belt and Sydney Basin areas. His sample collection included representatives of the two main varieties of phosphatic nodules known from the Ashfield Shale. The small cutting of Parkhill Avenue (formerly Guernsey Road) at the southern side•of Leumeah Road, Leumeah, is the site from which the first published phosphate determinations for Ashfield Shale nodules were made (Pyle and Rice 1967, table 7 herein). Lovering (1954) described Ashfield Shale phosphate nodules but thought they were siderite. As the 1966 discovery of large phosphorite deposits in the Georgina Basin, western Queensland, rendered the New South Wales deposits of TABLE 2

AVERAGES AND KNOWN RANGE OF PERCENTAGE VALUES FOR MAJOR COMPONENTS IN THE ASHFIELD SHALE*

Lower Ashfield Shale Upper Ashfield Shale

<30.5 m >30.5 m c::Gl Units above base above base H Chemical Known 1 to 3 (15 analyses) unit 4 (10 analyses) Overallt t"' H constituent range (6 analyses) (Lovering 1954) (4 analyses) (Lovering 1954) average t:IJ ~ Si0 48.4 - 75.04 55.2 64.12 59.6 65.73 61.16 H 2 o-,3 Ti02 0.48- 1.10 0.8 0.78 0.8 0.74 0.78 t:IJ Al203 13.45- 22.09 19.6 19.59 16.9 16.98 18.27 Ul Fe2o3 <0.1 - 7.6 0.3 1.99 0.1 4.04 1.61 H FeD 0.18- 9.8 8.0 0.54 5.1 0.49 3.53 z MnO 0.00- 0.26 - 0.08 - 0.02 0.05 MgO 0.25- 1.3 1.0 0.56 0.8 0.64 0.75 te CaD 0.00- l. 33 0.7 0.44 1.1 0.40 0.66 t:IJ Na o 0.02- 0.22 0.2 0.51 0..26 2 0.89 0.1 ~ K20 0.52- 3.11 2.8 2.13 2.4 1.48 2.20 ::r: P205 0.02- 0.9 0.5 0.13 0.2 0.05 0.16 ":! 2.91- 7.06 7.0 5.89 5.8 6.33 6.26 H H20+ t:IJ H20- 1.02- 4.79 1.2 1.49 1.1 3.36 l. 79 t"' co 2 2. 73- 6.8 4.1 - 3.8 - 3.95 0 s 0.02- 0.11 - trace - 0.04 0.04 Ul BaD <0. 01- 0.38 - <0.01 - 0.12 0.06 ::r: NaCl 0.15- 0.26 - - - 0.21 0.21 c 0.00- 3.74 0.7 l. 22 0.7 0.5 0.78 i ~ Total 102.0 99.18 98.6 101.5 102.6 I

Based on twenty-five analyses of brickpit shale samples (Lovering 1954) and ten subsequent analyses of drill core by Colonial Sugar Refining Co. Ltd and the Department of Mines (G71/1918 to G71/l921). t These values, in not being weighted averages, favour the drill core analyses; core includes phosphatic bodies, sideritic bands, and laminite, whereas brickpit samples may be hand-picked shale. The average adopted for P2o 5 is thit from ninety-seven analyses of DM Plumpton DDH 1 core (G72/679-728, 1276-1390).

1-' 00 w 1-' ()) TABLE .3 *" ANALYSES OF NODULES FROM UNIT l AND OF EXAMPLES REPRESENTING THE GUILIELMITES FORMATIONAL SERIES AND ASSOCIATED 11ATRIXES FROM UNIT 3 OF THE ASHFIELD SHALE

GUILIELMITES FORMATION Unit 3 at Ashbury quarry, GR 412812 Sydney 1:250,000 Ellipsoidal INITIAL STAGE INTERMEDIATE STAGE TERMINAL STAGE nodules from black Unit 1 siltstone, c., Spheroidal radial GR 604776, aggregates with central Gl Camden 1:63,360 expansion gashes filled by chert and pyrite, Ellipsoidal nodules Typical guilielmites, tr1 firmly embedded in hard easily freed from easily freed ><: sideritic band matrix from fissile matrix ~ {fl Analysis M75/2438 M75/2434 M75/2437 8 by Bureau G76/936 Nodules Hard Ferrugi- of Single imperfectly sideritic no us M75/2433 0 Chemical Mineral compound sawn free of band M75/2436 mudstone 1-175/2435 Shale constituent Guilielmites (matrix) ::0 Resources nodule matrix (matrix) Nodules (matrix) H 0 t<:! Si02 15.2 14.5 19.5 18.4 32.1 42.4 45.8 52.5 ~ Ti02 0. 77 0.14 0.28 0.33 0.34 0.64 0.69 0. 78 0 Al203 10.0 5.58 7.49 6.37 10.89 14.53 16.92 17.81 0 Fe203 (T) 23.0 0.97 12.38 41.5 6.03 12.98 9.70 10.26 MnO 3.4 0.02 0.66 2.87 0.24 0.35 0.15 0.16 MgO 1.5 0.14 1.14 1.83 0.91 1.32 1.28 1.44 5';1 CaO 15.5 41.7 26.3 3.60 25.1 7.34 4.59 0.97 Na20 0.26 0.20 0.31 0.14 0.30 0.19 0.20 0.16 0.1 0.72 0.85 0.89 1.42 2.19 2.39 2.50 ~ K20 H P20s 9.95 30.9 18.1 1.91 16.7 5.04 3.22 0.48 {fl Total H20 4.9 2.35 ------H20(-l05°C) - 0.50 0.54 0.48 1.50 1.05 l. 39 1.10 C02 16.2 0.74 8.19 25.3 4.89 8.21 5.15 5.53 s 0.01 0.05 0.65 0.26 0.07 0.06 1.12 0.08 I F 0.75 2.71 1.15 0.12 1.15 0.35 0.22 0.04 I Organic C 0.3 0.30 ------

- -- _j • TRACE ELEMENTS (ppm) ± 25-50% relative by optical emission spectrography

~ - <100 100 (<100) J. (<100) (<100) 1 100 (<100) I 8 Ba 360 (450) 1000 (2800) 1000 (1830) 750 (900) 500 (750) >10000 1000 (15 00) H - t:"' Be - - (<10) (<10) (<10) (<10) (<10) (<10) H Ce 320 - 100 (<50) 250 100 250 100 t'IJ 0 - 5 10 10 5 10 25 10 ~ r 60 10 25 (<10) 50 50 100 50 H u 60 5 25 10 25 75 100 50 ~ (Jl Ga - - 25 (<20) 25 25 50 25 La 60 - (<50) (<50) (<50) (<50) (<50) (<50) H Nd 210 - 100 (<100) 250 100 250 (<100) z 50 Ni 42 5 10 (<5) 10 10 50 ~ Ph 12 <20 25 100 25 50 100 100 t'IJ Sc - 5 25 (<20) 25 (<20) 25 (<20) Sn - <25 (<10) 25 (<10) (<10) 10 (<10) [;; Sr 675 (630) 1000 (940) 100 (180) 1000 (930) 500 (330) 1000 (630) 100 (14(0) :I: - "l Th - - (<10) - (<10) - (<10) - H 15 (<10) (<10) - t'IJ u -- - - t:"' 280 50 100 100 100 250 100 100 0 100 50 250 100 50 25 ~ 370 - (Jl Zn 120 <25 25 50 10 100 50 100 Zr - 150 100 175 100 250 175 250

- ~

1--' ro V1 TABLE 4

1-' CONCENTRATION OR DEPLETION OF MAJOR OXIDES AND SIGNIFICANT TRACE ELEMENTS ro IN NODULES AND GUILIELMITES WITH RESPECT TO THEIR MATRIXES* 0'1

Guilielmites formation

Initial Intermediate Terminal stage stage Stage

(Sideritic (Ferruginous Chemical hard band) mudstone) y constituent nodules nodules Guilielmites Gl to ><: Si02 1.1 0.8 0.9 0.9 Ti02 0.9 0.5 Cfl~ Al203 1.2 0.8 1.0 Fe203T 0.3 0.5 0.9 1-3 MnO 0.2 0.7 0.9 0 MgO 0.6 0.7 0.9 ~ cao 7.3 3.4 4.7 () Na20 2.2 1.6 1.3 _t>J K20 1.0 0.7 1.0 § P20s 9.5 3.3 6.7 C02 0.3 0.6 0.9 0 s 2.5 1.2 14.0 F 9.6 3.3 5.5 ~ $l Bat 1.0 (1. 5) 1.5 (l. 2) >10.0 (6.6) Q_ 2.5 t:"' Ce >2.0 2.5 H Co 1.0 0.5 2.5 Cfl Cr >2.5 1.0 2.0 Nd >1.0 2.5 >2.5 Pb 0.3 0.5 1.0 sr+ 10.0 (5.2) 2.0 (2.8) 10.0 (4.5) y 2.0 2.5 2.0

* Calculated as ratio of value for nodules or guilielmites to that for surrounding matrix. t Ba and Sr were also determined by atomic absorption (bracketed figures). TABLE 5 RATIO OF MAJOR OXIDE VALUES IN NODULES, GUILIELMITES, AND ASSOCIATED MATRIXES TO THOSE IN THE OVERALL AVERAGE ADOPTEDFORASHFIELD SHALE 8 H t:"' H Sideritic Sideritic Ferruginous Ferruginous Guilielmites- t7J Chemical hard band hard band mudstone mudstone bearing shale ~ H constituent nodules (matrix) nodules (matrix) Guilielmites (matrix) til {fl Si02 0.3 0.3 0.5 0.7 0.8 0.9 Hz Ti02 0.4 0.4 0.4 0.8 0.9 1.0 f-,3 ~ Al203 0.4 0.4 0.6 0.8 0.9 1.0 t7J

Fe203T 2.2 7.5 1.1 2.4 1.8 1.9 :~" {fl MnO 13.2 57.4 4.8 7.0 3.0 3.2 ~ 'Tj MgO 1.5 2.4 1.2 1.8 1.7 1.9 H t7J cao 39.8 5.5 38.0 11.1 7.0 1.5 t:"' Na20 1.2 0.5 1.2 0.7 0.8 0.6 0 {fl K20 0.4 0.4 0.6 1.0 1.1 1.1 I ~ :~" P20s 113.1 11.9 104.4 31.5 20.1 3.0 t:"' C02 2.1 6.4 1.2 2.1 1.3 1.4 t7J s 14.8 5.9 1.6 1.4 25.5 1.8

I

..

I-' 00 --J 188 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS

TABLE 6

CONCLUSIONS REGAROING BEHAVIOUR OF ELEMENTS DURING GUILIELM!TES FORMATION

Relationship Relationship Behaviour relative to between nodules Behaviour to Ashfield serial dilation of or guilielmites during Shale overall Behavioural detritus by authigenic and their matrixes guilielmites average (see groups minerals (see table 4) formation table 3)

Si Decreases regularly with Less in nodules Residual Less than in increasing phosphate and and guilielmites concentration the case of Al carbonate; ratio between than in matrixes Si, Al, and nodules or guilielmites Ti; K spans Ti and their matrixes remains the average fairly constant (apparent but remains K si, Al anomalies in hard within the sideritic band nodules normal shale is discussed in text) range

Fe Irregular Less in nodules Overall deGt:.rease Greater than Mn and guilielmites but may concen­ average Mg than in matrixes trate relative C02 'to matrix

Ca Regular, interrelated as More in nodules Decrease, Greater than p components of phosphate and guilielmites absolutely as average F phase than in matrixes well as relative (Na?) Na to matrix

Ce Irregular More in nodules Constant, residual Greater than Nd and guilielmites concentration, average Sr than in matrixes or irregular s

Pb Irregular Less in nodules and Residual Probably less guilielmi tes than concentration than average in matrixes, con­ centrating to equal during guilielmites formation

Ba Irregular concentrating to Residual Probably become greater in concentration greater than nodules and guilielmites than in matrixes (initially equal) GUILIELMITES IN THE ASHFIELD SHALE 189

TABLE 7 PHOSPHATE ANALYSES FOR SAMPLES COLLECTED FROM THE ASHFIELD SHALE*

Analysis number ' P2Ds Sample Location

66/763 0.4 Shale Maroota area, centred on GR 394861, Sydney 764 2.5 Limonite concretion 1:250,000 (the outliers of basal 765 0.3 Shale Wianamatta Group in this area are 766 3.8 Limonite considerably weathered). 924 2.4 Shale 1658 1.7 Hard shale 1659 1.4 Hard shale 1660 2.6 Hard shale 1661 4.0 Hard shale 1662 5.6 Hard shale 1663 1.3 Hard shale 4718 21.5 Shale with small nodules

4312 24.6 Phosphate nodules Cutting at Parkhill Avenue, Leumeah. in shale GR 384794, Wollongong 1:250,000. 4313 26.7 Separated nodules

4479 0.4 Shale Council quarry, Leumeah Road, Leumeah. GR 384794, Wollongong 1:250,000.

4063 30.3 tHard band (?) packed 2.4 km west of Picton. GR 359779 with small nodules Wollongong 1:250,000.

4064 18.9 Hard band (?) with Doonside area, GR 387828 Sydney small nodules 1:250,000.

4199 3. 7 Sideritic nodules 1.6 km east of Leppington on road towards Min to. GR 382801 Sydney 1:250,000.

77/1090 20.5 15 mm diameter Austral Brick quarry, Cowper St, I nodules (·2.21% St Peters. GR 4198ll Sydney carbonate C02, 1:250,000. o. 93% organic C) • 77/1326 15.3 Hard sideritic band, GR 374877 Sydney 1:250,000 near 30 - 50% pea-sized Parrs Brush. nodules

Samples mostly collected by T.W. Dickson in 1966 (Pyle and Rice 1967). t The locality and \P205 suggest that a compound nodule was analysed. 190 J.G. BYRNES, T.D. RICE 1 AND D. KARAOLIS no further economic interest, Dickson did not prepare a report. After the 1966 discovery of the Duchess deposits in Queensland (Russell and Trueman 1971), prospecting was soon abandoned in the Narrabeen Group sediments (Continental Oil Co. (Australia) Ltd 1967, Taylor 1967). Interest in the more prospective Wianamatta Group continued to 1969 (Pacminex Pty Ltd 1969).

Mode of Nodule Formation Lovering (1954) regarded the nodules as epigenetic to the sideritic hard bands. The nodules are here viewed as syngenetic with, if not antecedent to, the matrix siderite. At the centres of the phosphate nodules occurs a suite of cavity-filling minerals~ microquartz (chert), barite, kaolinite, pyrite, and marcasite (Lovering 1954). Rarely, macroscopic barite crystals reach 5 mm length, as at Parkhill Avenue, Leumeah. Lovering regarded the concretion cores as nuclei for the later growth of radiating "siderite" (carbonate apatite). Conversely, the cores are now thought of as the fillings of cavities, which are early diagenetic, preceeding the formation of guilielmites by pressure solution.

The fibrous texture of the nodules is dissimilar to previously described habits of francolite (see Hutton and Steelye 1942) but does resemble concretionary carbonates. There is meagre evidence for replacement~ however, the experimental work of Ames (1959) strongly suggests that carbonate apatite forms under natural aqueous conditions only by replacement of calcium carbonate. It also seems unlikely that an unusually high concentration of phosphate, sufficient to precipitate carbonate apatite, could have arisen in such different environments as represented by hard bands, laminite, and shale. Certainly, the nodules were not formed at the sediment surface, as stratification is clearly preserved within some. Were the nodules syngenetic, some enrichment in uranium might be expected in the hard band nodules. The hard sideritic bands represent a reducing environ- ment, and tetravalent uranium is preferentially incorporated in phosphate, its ionic radius (0.97ft) beingclosetothatofcalcium (0.99A). Although there are many procedures for synthesis of members of the apatite group, it has not proved possible to precipitate carbonate apatite directly from aqueous solutions. Carbonate apatite has been formed only by phosphatization of carbonates, a process known since Irvine and Anderson (1891). Bone growth may be an exception as it appears to involve the reverse case, the carbonation of' apatite or at least progressive carbonation of carbonate apatite (there is commonly a phase of rapid increase in C0 2 content and Ca/P ratio in bone during the early life of an animal) (Neuman and Neuman 1953) . Because of the initial difficulty in forming apatite, such a process is not attractive when considering phosphate in sediment, nor does it appear to have been demonstrated in inorganic systems at low pressure and temperature. Textural evidence would require the GUILIELMITES IN THE ASHFIELD SHALE 191 prior existence of well-crystallized apatite. Hydroxyapatite has been formed at room temperature in the laboratory only as amorphous fine grains which are probably poorly crystalline and analogous to opal (Skinner 1974).

Source of Phosphorus

Because animal and plant fossils are well known from the sideritic hard bands, the phosphorus is considered to have been derived from the decomposition of organic material. As sediment­ ation was very slow, decomposition may have greatly affected the bottom sediment chemistry. In seawater, struvite (NH4MgP0 4.6H 2 0) can be formed artificially by a reaction between phosphate and ammonia from decomposing organic material with magnesium in the water (Malone and Towe 1970) . If the environment is anaerobic, monohydrocalcite may be co-precipitated. The association of the Ashfield Shale phosphate with Fe, Pb, and Ba is reminescent of the terrestrial behaviour of P. Thus the nature of the soils within the drainage basin may have been significant as regards supply of phosphorus. Introduction of phosphate grains from soils might relate to the common presence of barite in the Ashfield Shale, as the barian phosphate gorceixite is the main end member phosphate in Australian soils (Norrish 1968). The terrestrial association of P and Fe is well known. Soil P is highest (1. 2 - 1. 6 per cent) in laterites with over 40 per cent free iron oxides (Norrish 1968). Likewise, from an extant alluvial system near Cobargo, New South Wales, Koch (1956) has recorded beds with 40-70% Fez03 and

3.2-5.6% P 2 0 5 • This is similar to the iron and phosphorus content of Ashfield Shale hard bands. With the exception of krasnozems (mean P = 0.13 per cent) , Australian soils generally contain little phosphorus (e.g., 0. 007- 0. 08 per cent) (Wild 1958 in Norrish 1968).

Time of Phosphatization

For reasons already discussed, phosphate nodules in the Ashfield Shale are believed to be neither syngenetic nor late diagenitic. They are chronologically of bi-partite formation. They are probably phosphatized calcium carbonate nodules which were of syngenetic or very early diagenetic (pre-lithfication) origin. From analogy with marine phosphorite, early diagenetic phosphatization of the nodules appears likely, probably prior to guilielmites formation. The impermeability of the hard bands seems a formidable obstacle to late-diagenetic phosphatization. Ames (1959) demonstrated the possibility of phosphate replacement of calcite in alkaline solution at low temperature for phosphate concentrations about ten times that of normal sea or river water. That of sea water is about 0.1 mg Po~- per litre. The biotic concentration of phosphate, as in marshes or estuaries, maintains sufficiently high values, up to 0.4 mg PO~- per litre (Peaver 1966). Such concentrations are not likely to be maintained in groundwater or cognate water but might occasionally be available for early 192 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS diagenesis. A possible early diagenetic source could be the destruction of an unstable syngenetic phosphate. At normal high phosphate concentrations, phosphatization time for nodules the size of these in the .Ashfield Shale does not seem likely to be less than a millenium. Phosphatization seems likely to have occurred still within the time span of Ashfield Shale deposition.

Diagenesis

If a syngenetic magnesian phosphate phase such as struvite were involved, its early destruction would supply the phosphate necessary to convert carbonate nodules to carbonate apatite. The liberated Mg would be available for incorporation in still-growing or recrystallizing siderite.

If carbonate apatite formation is confined to the early stage of diagenesis, then considerable time remains for subsequent alterations. The low content of U and F in Ashfield Shale phosphate may indicate leaching rather than offer evidence of freshwater formation. The depletion of U and F in guilielmites, compared to hard band nodules, supports leaching of the guilielmites but not necessarily of the nodules in the rather impervious hard bands. It is not known whether the depletion of u, F, Ca, and C02 in guilielmites has been a long-continuing process or was mainly achieved during generation of the guilielmites form. The latter alternative is supported by the preferential removal of Ca and C0 2 from carbonate apatite during solution, and observations that enrichment of buried phosphate in U and F is a more usual reaction with groundwater than is depletion (Altschuler et al. 1958). The relative insolubility ofF is supported by observed decrease of the P/F ratio from spheroidal nodules to guilielmites.

Reactions involving carbonate apatite, and applicable to diagenesis, are best known for bone. The ability of living bone to lose C0 2 or, less often, absorb it is well known. When bone is held in water or acid, carbon dioxide is removed faster than phosphate, fossil bone being commonly depleted in C0 2 (Brophy and Nash 1968). Calcium is also removed and the net loss durin~ acidosis may be equivalent to CaC0 3 (Neuman and Neuman 1953). More than sufficient phosphate has been dissolved during the formation of guilielmites for complete decarbonation by preferential solution.

The estimated phosphate composition of the compound nodule G76/936 (table 8) from Unit l is of special interest. It is high in F, and low in Ca and C0 2 . It thus resembles the guilielmites phosphate which is regarded as decarbonated carbonate apatite. The nodules from St Peters (table 7) are also decarbonated somewhat. This decarbonation may be related to freshening of the groundwater and lowering of the pH around the periphery of the Wianamatta Group preservational basin. The groundwater salinity TABLE 8

ESTIMATED COMPOSITION OF THE PHOSPHATE PHASE IN NODULES AND GUILIELMITES OF THE ASHFIELD SHALE (Analytical values from table 3 recast using mineral grain counts)

Nodules from shale Nodules from hard band Guilielmi tes I Francolite G) Whole sample Phosphate average (Deer Bone average c as 100% as 100% et al. 1962} (Brophy H Whole sample Phosphate Whole sample Phosphate (Brophy and and Nash 1968) t"' Constl. tuent Partition G76/936 M75/2436 G76/936 M75/2436 as 100% as 100% as 100% as 100% Nash 1968) (mostly fossils) H tl:J

cao Phosphate 41.7 25.1 48.7 54.7 26.3 54.4 4.59 50.4 53.7 50.3 ~ H Whole sample 0.14 0.91 1.14 1.28 ~ MgO Ul Phosphate 0.14 0. 7 0.2 1.5 0. 7 1.5 0.3 3. 3 0.5 1.1 Hz Na20 Phosphate 0.20 0.30 0.2 0. 7 0. 31 0.6 0.1 1.1 0. 3 1.2 :e Whole sample 0.72 1.42 0.85 2.39 tl:J KzO Phosphate o. 72 0.1 0.8 0. 2 0.1 0. 2 0.05 0.6 0.1 2.0 !1:' ::r:Ul P20s Phosphate 30.9 16.7 36.1 36.4 18.1 37.4 3.22 35.4 37.9 36.1 '"':1 H tl:J Whole sample 0.02 5.43 11.15 8. 73 t"' FeO(T) 0 (Siderite (0.03) (8. 76) (17.99) (14.08) equivalent) Ul

Whole sample o. 74 4.89 8.19 5.15 C02 ~ Siderite 0.01 3. 33 6.84 5. 35

Phosphate 0. 73 1. 56 0.9 3.4 1. 35 2.8 0.00 0.0 3.1 3. 7 *

F Phosphate 2. 71 o. 75 3.2 1.6 0.83 1.7 1.14 1.5 4.0 1.5

HzO Phqsphate 0. 7(?) - 1.5 (?) 0. 7 (?) 1.4 (?) 0. 7 (?) 7. 7 (?) 0.9 5. 2 (uncertain}

* Fresh bone phosphate contains more co 2 , about 5% (Neuman and Neuman 1953) . ..

t-' 1.0 w 194 J.G. BYRNES, T.D. RICE,AND D. KARAOLIS at Ashbury is about six times that near Picton (Old 1942) .

Replacement of phosphate by siderite and lesser calcite destroys the fibrous fabric and proceeds inwards from the nodule periphery. Such replacement is probably late diagenetic.

Notes on Analyses

The major and minor elements were determined by a variety of wet chemical techniques (T.D.R.): carbonate C, by evolution of C0 2 with HCl and collection in a weighed Ascarite tube; F, spectrophotometrically by a procedure similar to that of Hall and Walsh (1969); totalS, by Leco analyser with automatic titration of evolved S0 2 with iodate; in suitable aliquots of solutions prepared after fusion of samples with lithium metaborate, Si, P, and Ti were determined spectrophotometrically, Al by complexometric titration, and Fe, Mn, Mg, Ca, Na, and K by atomic absorption spectrometry. The fluorine values were corrected for the effect of P upon lanthanum alizarin fluorine blue colour development.

Trace elements, other than U and Th for which X-ray fluorescence spectrography was used, were determined by optical emission spectrography (D.K.). Spectrograms covered the range 232.7-482.7 nm, in the first order, with a reciprocal linear dispersion of 0.54 nm/mm, allowing more than fifty elements to be sought. Accuracy ranges from ±25- ±50 per cent of the amount present. It is generally ±30 per cent, with sensitivity usually better than 5 ppm.

The nodules had previously been described by Lovering (1954) as sideritic, without mention of phosphate. Only after the present chemical analyses had been commenced was it realized that the nodules and guilielmites are apatitic. In retrospect, it is clear that more informative results could be expected if only the purified phosphate fractions of the nodules and guilielmites were taken for analysis. Some degree of correction for impurities, b~ microscopic means, has been attempted (table 6). However, knowledge of the partition of certain elements, such as Mg or Mn, between the impurities and the carbonate apatite lattice must await physical separation or electron probe work. Repetition of the comparisons made herein, using drill core materials rather than quarry specimens, might also be useful, particularly with respect to determining if u and F have been leached from nodules and guilielmites during weathering. GUILIELMITES IN THE ASHFIELD SHALE 195 CONCLUSIONS

Guilielmites in the Ashfield Shale probably formed from phosphatized carbonate concretions by solution during compaction. The carbonate concretions formed in greatest abundance within ferruginous anaerobic lake floor mud, at times of very low sediment influx. Phosphorus was derived from decomposition of organic matter. Regional events, such as the stripping of extensive laterite or krasnozem, could have increased phosphorus supply. Phosphorus was transferred to the carbonate nodules during early ~iagenesis, probably within the time span of Ashfield Shale deposition. The following sequence is proposed: a) growth of carbonate concretions; b) phosphatization; c) formation of central cavities (possibly coeval with b); d) cavity-filling; and e) solution during compaction, causing a reduction in length of the vertical axis accompanied by surficial and internal slickensiding in response to the greater compaction of the shale matrix.

Several possibilities, from hypotheses which do not integrate the evidence satisfactorily, cannot be disproved individually. Those considered unlikely include the fo~lowing: a) phosphatization postdates conversion of nodules to guilielmites; b) formation of the central cavities postdates guilielmites formation; c) core minerals formed nuclei for outward growth by replacement (Lovering 1954) or displacement; and d) both guilielmites and nodules are growth forms, the former being distinguished by growth against compaction.

Where the Wianamatta Group is being invaded by relatively fresh groundwater around the periphery of the preservational basin, the nodular carbonate apatite has been decarbonated. In peripheral areas the compositional contrast between nodules and guilielmites may be less than in the central basinal area.

ACKNOWLEDGMENTS

We thank the managements of metropolitan brickworks for access to their quarries and several of our colleagues for~their help; David Barnes for photography, Chris Herbert, David Hilyard, and John Pickett for criticism of the manuscript. As noted in table 3, one of the analyses was supplied by the Bureau of Mineral Resources, Canberra. Messrs A. Pierce and F. Thompson are thanked for supplying specimens. 196 J.G. BYRNES, T.D. RICE, AND D. KARAOLIS SELECTED BIBLIOGRAPHY

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Guilielmites in plan and profile . Examples from shale above hard sideriti c Band A. Enfield Brickworks quarry , Juno Parade, Greenacre . (X2 . 4 ) (whitened with a mmonium chlo ride) .

4 5 0 1 2 3 J I em