The genesis of glaucony in the Oligo–Miocene Torquay Group, southeastern Australia: petrographic and geochemical evidence

ELSEVIER

Sedimentary Geology 125 (1999) 99–114

The genesis of glaucony in the Oligo–Miocene Torquay Group, southeastern Australia: petrographic and geochemical evidence Jonathan C. Kelly Ł , John A. Webb School of Earth Sciences, La Trobe University, Bundoora, Vic. 3083, Australia Received 29 August 1998; accepted 16 November 1998

Abstract The Oligo–Miocene Torquay Group at Bird Rock, in southeastern Australia, comprises a sequence of fine-grained skeletal carbonates and argillaceous and glauconitic sandstones, which were deposited in a cool-water, mid-shelf environment. The Bird Rock glaucony consists predominantly of randomly interstratified glauconitic smectite, which constitutes bioclast infills and faecal pellet replacements. Petrographic and geochemical evidence indicates that the glaucony is autochthonous and comprises chemical components derived primarily from argillaceous matrix material; seawater is unlikely to be a significant source of ions. The glauconitization of the Bird Rock sediments occurred under sub-oxic partially reducing conditions, in the very shallow burial environment, and involved local iron redistribution. Sub-oxic conditions favour glauconitization because iron is stable in the soluble ferrous state and can be fixed in authigenic silicates due to the negligible concentrations of hydrogen sulphide. It is likely that localised acidic conditions were initiated during the glauconitization process; this acidity appears to have been buffered by the dissolution of bioclastic carbonate. The fact that glaucony predominantly occurs as bioclast infills and faecal pellet replacements implies that the physico-chemical conditions appropriate for glauconitization develop preferentially in such biogenic detritus. The development of appropriate micro-environments within such sediments probably relates to their physical confinement and=or high organic matter content. The Bird Rock glaucony developed during intervals of slow sedimentation and environmental quiescence associated with marine flooding events. These conditions facilitated glauconitization by allowing the favoured clay-rich sediments to accumulate and remain in the appropriate physico-chemical regime sufficiently long for the complex glauconitic structures to form.  1999 Elsevier Science B.V. All rights reserved. Keywords: glaucony; diagenesis; sedimentology; mineralogy; geochemistry

1. Introduction The term glaucony refers to the petrographic facies in which glauconitic minerals are abundant, typically as sand-sized, ellipsoidal, green pellets that Ł Corresponding

author. Present address: Santos Ltd., Santos House, 91 King William St., Adelaide, S.A. 5000, Australia. Fax: C61 8 8224 7334; E-mail: [email protected]

have an earthy or lustrous appearance (Odin and Matter, 1981; Odin and Morton, 1988). Glauconitic minerals are iron- and potassium-rich alumino-phyllosilicates, which constitute a continuous family with smectitic and micaceous end members (Odin and Fullagar, 1988). Glaucony occurs in the surficial sediments of every ocean and in marine sedimentary rocks from all parts of the geological column (McRae, 1972; Odin

0037-0738/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 7 - 0 7 3 8 ( 9 8 ) 0 0 1 4 9 - 3

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and Fullagar, 1988). Radiometric dates of glauconies have been widely used to determine the depositional age of sedimentary rocks and have provided numerous age constraints for the calibration of the relative time scale (Odin et al., 1978; Craig et al., 1989). Authigenic glaucony may also bear testament to the physico-chemical, sedimentological and palaeoceanographic conditions that prevailed during its development (Kazakov, 1983; Stille and Clauer, 1994). In addition glaucony is commonly associated with condensed sections, unconformities and transgressive deposits (Loutit et al., 1988; Shanmugam, 1988; Amorosi, 1995), and as such may contribute to an increased understanding of sea-level cyclicity. The successful utilisation of glaucony for geochronological, palaeo-environmental and palaeooceanographic purposes necessitates a thorough understanding of its genesis. Glaucony is generally considered to form by halmyrolytic processes at the sediment–open ocean interface during periods of slow sedimentation. However, the origin of glaucony is imperfectly understood, and there has been considerable debate regarding both the nature of the chemical reactions involved and the parameters that control its development (McRae, 1972; Odom, 1984; Odin and Fullagar, 1988). The aim of this study is to constrain the genesis of glaucony in the Oligo–Miocene Torquay Group of the Torquay Basin, southeastern Australia. The source of the chemical components of glaucony, and the physico-chemical and sedimentological conditions associated with glauconitization will be investigated through detailed petrographic, geochemical and sedimentological analysis of both glauconitic and non-glauconitic lithologies in the Torquay Group. 1.1. Geological setting The Torquay Basin lies on Australia’s southeastern margin, in southern Victoria, and was a major sediment depocentre from at least the Late Paleocene through to the Middle Miocene (Webb et al., 1995). The stratigraphy of the northwestern onshore part of the basin is well exposed in coastal cliffs between Torquay and Airey’s Inlet, and comprises a mixture of terrestrial and marine siliciclastics and

Fig. 1. Map showing the location of the Bird Rock study area.

marine carbonates (Fig. 1; Abele, 1979; Reeckmann, 1979). At Bird Rock, southwest of Torquay (Fig. 1), Oligo–Miocene strata of the marine Torquay Group are exposed. This group comprises the Jan Juc and overlying Puebla Formations (Fig. 2). The Jan Juc Formation at Bird Rock consists of friable, fine to very fine skeletal packstones and argillaceous sandstones, with minor interbeds of highly indurated skeletal grainstone. The Puebla Formation comprises massive mid- to dark-grey calcareous mudstones, which are variably pyritic, and thin horizons of indurated and concretionary limestone. The boundary between the Jan Juc and Puebla Formations is marked by a distinct lithologic change, a significant faunal extinction event, an increase in the proportion of pelagic bioclasts (Raggatt and Crespin, 1954; Carter, 1990) and a thin veneer of richly glauconitic and intensely bioturbated sediment. Carter (1990) attributed the facies change at this boundary to a marine deepening event. Although originally regarded as conformable (Raggatt and Crespin, 1954; Abele, 1979; Darragh, 1985), the contact between the Jan Juc and Puebla Formations has more recently been interpreted as an erosional disconformity (Reeckmann et al., 1986; Reeckmann, 1994; Boreen and James, 1995).

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Fig. 2. The stratigraphic succession at Bird Rock (modified after Van Der Linden, 1997).

There have been several attempts to correlate the interface between the Jan Juc and Puebla Formations with the eustatic sea-level curve of Haq et al. (1988). Reeckmann (1994) equated this surface with the 25.5 Ma global sequence boundary, whilst Boreen and James (1995) correlated the surface with the 21 Ma sequence boundary. The thin glauconitic horizon that occurs at the base of the Puebla Formation has been interpreted as a condensed deposit associated with flooding following the inferred lowstand event (Reeckmann et al., 1986; Reeckmann, 1994). Authigenic glauconitic minerals are disseminated

throughout the Bird Rock section (Raggatt and Crespin, 1954; Abele, 1979; Reeckmann, 1979), and are richly concentrated in several iron-stained and intensely bioturbated horizons. Two of these glauconitic beds were sampled for this study: the ¾40-cm-thick glauconitic layer which lies at the boundary between the Jan Juc and Puebla Formations, and a somewhat recessive horizon of similar thickness which occurs ¾5 m below the top of the Jan Juc Formation, near the base of the Bird Rock cliffs (Fig. 2). In outcrop the former is largely obscured by slumping, but is represented by numerous

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olive-grey burrows which penetrate the uppermost Jan Juc Formation.

2. Methods and procedures Six samples were taken from the Bird Rock section: one of the lower glauconitic horizon which lies near the base of the Bird Rock bluff, three of the glauconitic burrows which occur at the boundary between the Jan Juc and Puebla Formations, and two of the uppermost Jan Juc lithology which plays host to the glauconitic burrows (Fig. 2). The uppermost Jan Juc lithology is representative of the bulk of the non-glauconitic Jan Juc Formation at Bird Rock. To facilitate sampling and lithological analysis, a small part of the glauconitic horizon at the boundary between the Jan Juc and Puebla Formations was excavated beneath the steps at Bird Rock. This horizon was also examined in core 17 of the Torquay Drilling Project (a joint venture involving the Sydney and La Trobe Universities, which was undertaken in 1994). Polished thin sections of the samples were prepared and stained using the carbonate staining method of Dickson (1966). A petrographic study, including point counts .n D 500/, was made of the samples to identify and quantify mineralogical and textural components. Cathodoluminescence was used to confirm quartz and feldspar abundance estimates. The bulk chemistry of the samples was determined by X-ray fluorescence (XRF) with a Siemens SRS 303AS X-Ray Fluorescence Spectrometer, using the techniques described by Norrish and Hutton (1969). The precision of the XRF analysis was better than 1% relative for each oxide. FeO was determined by direct titration with standardised ceric sulphate. H2 OC , H2 O , CO2 (carbonate) and CO2 (organic matter) were determined gravimetrically using a multi-stage loss on ignition method modified after Stein (1984). A <2-µm clay fraction was separated from each sample by gravitational settling using Stoke’s Law. Glauconitic minerals were separated from the samples and subdivided into fractions of different evolutionary state using a combination of magnetic, electrostatic and handpicking techniques, following the methods of Odin et al. (1982).

Qualitative X-ray diffraction (XRD) analysis of oriented samples of the clay and glauconitic fractions was conducted using a Siemens D5000 X-Ray Diffractometer, with Cu X-ray tube (40 kV=30 mA) and graphite monochromator .½ D 1:54056/. Oriented samples were prepared by sedimentation from suspension onto a ceramic filter, under vacuum. Each sample was analysed three times: initially untreated, subsequently after glycol solvation (12 h with ethylene glycol at 70ºC) and finally after heat treatment (1 h at 600ºC). Potassium and iron determinations for aliquots of the clay and glauconitic fractions were made by inductively coupled plasma–atomic emission spectrometry (ICP–AES) on a GBC Integra XM, using potassium chloride and ferric chloride standard solutions. Before analysis the clay and glauconitic aliquots were dissolved in Teflon beakers by HF= HNO3 =HCl digestion at 100ºC. The precision of this analysis was better than 2% relative for each element.

3. Petrography The sampled lithologies display strong textural and compositional similarities. They are all poorly sorted and comprise fine to very fine sand-sized grains in a muddy matrix. They also contain the same bioclastic, terrigenous and authigenic components. However, the proportions of these components vary; the uppermost Jan Juc lithology is a very fine skeletal packstone, whilst the glauconitic lithologies are fossiliferous fine to very fine argillaceous sandstones (Table 1). 3.1. Skeletal packstone The skeletal packstone is pale grey-brown and very poorly indurated. It contains abundant and diverse skeletal grains (¾50–60%), which include planktonic and benthonic foraminifera, gastropods, bivalves, irregular echinoids, bryozoa, solitary corals, calcareous sponges, scaphopods, pteropods, ostracods and phosphatic fish debris (bones, teeth and scales), with bivalves, echinoids, gastropods and foraminifera being most abundant. The calcareous bioclasts commonly display evidence of fragmentation and phosphatisation. Never-

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Table 1 Petrographic point count data for the Bird Rock sediments Sample No.

Matrix (%)

Bioclasts (%)

Quartz (%)

Feldspar (%)

Glaucony (%)

Pyrite (%)

Classification

BR1 BR2 GL1 BW2 BW3

23.4 26.2 38.6 44.4 40.2

62.6 53.4 41.4 31.0 38.4

11.3 16.7 6.9 2.0 4.8

0.7 0.7 0.7 3.0 2.0

1.8 3.0 10.0 19.6 14.2

0.2 Trace 2.4 Trace 0.4

Very fine skeletal packstone Very fine skeletal packstone Glauconitic and fossiliferous very fine argillaceous sandstone Glauconitic and fossiliferous very fine argillaceous sandstone Glauconitic and fossiliferous very fine argillaceous sandstone

N.B. Accessory components not recorded during point counting include: biotite, muscovite, siderite, tourmaline, zircon, phosphate, iron oxides and argillaceous faecal pellets. No point counting was completed on sample BW1 due to insufficient sample size.

theless, whole and well-preserved bioclasts, including irregular echinoids and bivalves up to 4 cm in diameter, also occur. Terrigenous grains typically constitute ¾12–18% of the packstone and consist largely of angular to subrounded, fine to very fine quartz sand. Subordinate tabular to sub-rounded feldspar is predominantly orthoclase, with traces of microcline and plagioclase. The feldspars show minor alteration to clay and carbonate; the clay alteration product occasionally shows a pale green colouration which may reflect incipient glauconitization. Accessory terrigenous minerals include biotite, muscovite, tourmaline and zircon. Pale-brown argillaceous matrix is abundant (¾25%), but has a somewhat patchy distribution. XRD analysis indicates that the matrix predominantly consists of smectite with lesser kaolinite. Glaucony is a very minor constituent of the fossiliferous packstone (¾2–3%). Glauconitic minerals are predominantly confined to relatively small bodies (mode 80 µm) infilling the intraparticle porosity of bioclasts; however, faecal pellet replacements and traces of diffuse pigmentary glaucony also occur. The glauconitic component of the Bird Rock lithologies is discussed in detail below. Other authigenic phases are present only in very minor amounts, and include pyrite, siderite, phosphate and iron oxide minerals. Framboidal and cubic pyrite grains are disseminated in the matrix and partially occlude intragranular porosity. Pyrite also occurs rimming and in partial replacement of glauconitic pellets (Fig. 3); these textures indicate that pyrite post-dates the development of glaucony in the Bird Rock lithologies. Siderite occurs as slightly flattened rhombs scattered through the matrix. The siderite has a modal

grainsize of ¾30 µm and is weakly pleochroic from colourless to pale brown. Orange-brown phosphate, with characteristic low birefringence, predominantly occurs replacing calcareous bioclasts. Phosphate also occurs as small irregular patches in the matrix and as traces of intergranular cement. Red-brown iron oxide or oxyhydroxide minerals, with a modal grainsize of 15 µm, are disseminated throughout the matrix. Many of these grains are irregularly shaped; others have rhombic and cubic habits and probably represent oxidised siderite and pyrite respectively. The cores of some glauconitic pellets also show alteration to fine ferric oxides. 3.2. Glauconitic and fossiliferous argillaceous sandstones The glauconitic sandstones are mid to dark greygreen, very poorly lithified and display evidence of intense bioturbation. The burrows at the boundary between the Jan Juc and Puebla Formations are spectacular and consist of large branching Thalassinoides burrows (4–5 cm in diameter) and relatively small columnar Planolites burrows (1–2 cm across). The glauconitic sandstones essentially comprise the same bioclastic, terrigenous and authigenic components as the packstone, but the proportions are significantly different (Table 1). Bioclasts (¾30–40%) and argillaceous matrix (¾40%) are the predominant components of the glauconitic sandstones. Planktonic foraminifera and small gastropods, which include planktonic pteropods, are the most abundant skeletal grains, but echinoids, bivalves, bryozoa, benthonic foraminifera and solitary corals are also common.

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Fig. 3. An aggregate of pyrite crystals ( p) partially replacing a glauconitic faecal pellet (g).

Many of the macrofossils show evidence of fragmentation, particularly in the burrow lithologies; this may to some extent reflect the intense bioturbation evident in the glauconitic sediments. The argillaceous matrix of the glauconitic sediments is brown to dark brown and comprises the same clay minerals as that of the packstone. The relatively dark colour of the matrix probably reflects a diffuse carbonaceous component. Terrigenous clasts constitute ¾5–8% of the glauconitic lithologies. The burrow lithologies contain sub-equal proportions of quartz and alkali feldspar, whilst the terrigenous clasts of the lower glauconitic horizon are predominantly quartz. Dark-brown sub-spherical faecal pellets, which range up to 600 µm in diameter, are a minor constituent of the glauconitic lithologies. These pellets are generally argillaceous with detrital and bioclastic inclusions. Some of the pellets are pale olive-green, probably reflecting incipient glauconitization; others, red-brown in colour and almost isotropic, have evidently been phosphatised. Glaucony constitutes ¾10–20% of the sandstones, and forms comparatively large grains (mode

300 µm). Bioclast moulds are common, but free pellets, including faecal pellet replacements, predominate. The Bird Rock glaucony is described further below. Autochthonous pyrite, phosphate and iron oxide minerals have very similar habits and proportions to those in the packstone. However siderite, which is abundant in the matrix of the packstone, is uncommon in the glauconitic sediments.

4. Environment of deposition The general textural and mineralogical similarity of the sampled lithologies suggests that they accumulated in very similar depositional environments. Their fine-grained, poorly sorted character and the excellent preservation state of many of the fossils indicate deposition in a fairly deep, low-energy regime. Palaeodepth estimates for the Jan Juc and Puebla Formations, based on ostracod and foraminiferal faunas, are mid-shelfal, i.e. probably less than 120 m (Abele, 1979; M. Warne, unpublished data in Webb et al., 1995).

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The diverse benthic fauna of the Bird Rock lithologies suggests that they accumulated under open marine conditions, with oxygenated bottom waters of normal salinity (Abele, 1979; Reeckmann, 1979). The Jan Juc and Puebla Formations contain a characteristic cool water fauna, which includes bryozoans, molluscs, echinoids, solitary corals and tusk shells (see James, 1995). Palaeo-water temperature estimates for the Torquay Group of between 12 and 17ºC have been made on the basis of oxygen isotopes and calcareous nannofossils (Dorman and Gill, 1959; Siesser, 1979). The Bird Rock lithologies constitute a fairly continuous spectrum of compositions. The end-members are represented by the argillaceous glauconitic burrows and the calcareous and glauconite-poor packstone, whilst the lower glauconitic horizon has an intermediate composition. This situation probably reflects deposition in a dynamic sedimentary system in which the balance between carbonate productivity and the influx of terrigenous fines fluctuated in response to changes in sea-level and=or water velocity.

5. Glaucony in the Bird Rock section 5.1. Habit The glaucony of the Bird Rock section ranges in colour from pale to dark-olive green and occurs as grains which range from ¾70 µm to ¾1.2 mm in diameter. The pale-green glaucony has an earthy lustre, whilst the dark green grains have a more shiny or polished appearance. In thin section the glauconitic grains are generally mid-olive green, but show a weak green pleochroism. The glaucony has a random microcrystalline internal texture and displays aggregate polarisation which renders detailed optical work impossible. Much of the glaucony infills the intraparticle porosity of bioclasts such as foraminifera, small gastropods, bryozoa, sponge spicules and finely perforate echinoderms. The bioclastic host structures are often partially or completely dissolved, and are frequently represented by mouldic porosity (Fig. 4). When separated from the sediments, the morphological diversity of the bioclast infills becomes appar-

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ent. Internal moulds of gastropods and foraminifera display distinctive coiled and globular morphologies. Irregularly shaped glaucony with a fine porous structure probably represents moulds of calcareous sponge matter or perforate echinoids. Columnar pellets, which commonly display a fine ornament of raised pimples, are probably internal moulds of bryozoan fragments. Leaf-, kidney- and cap-shaped pellets appear to be internal moulds of individual foraminiferal chambers. Glaucony also occurs as relatively large pellets with lobate, ovoidal, botryoidal, capsule and less regular shapes. The morphology and internal texture of the lobate, ovoidal and capsule-shaped pellets suggests that they are of faecal origin. The origin of the less regular shaped pellets is difficult to determine; many may be fragments of the more distinctive grain types. Many of the glauconitic grains display irregular surface cracks which taper inwards. Such cracks have previously been interpreted as either expansion cracks relating to differential mineral growth in the pellets (Odin and Morton, 1988) or as shrinkage cracks relating to dehydration during the mineralogical evolution of glaucony (McRae, 1972). The average diameter of the glauconitic grains varies according to the host lithology, from 300 µm in the glauconitic sandstones to only 80 µm in the packstone. This reflects the habit of the glaucony, which predominantly occurs as large free pellets in the argillaceous sandstones and as comparatively small bioclast infills in the packstone. The glauconitic pellets commonly contain inclusions of detrital and bioclastic matter analogous to those within the surrounding matrix. Most pellets have distinct physical boundaries; however, some grade almost imperceptibly into argillaceous matrix. Patches of diffuse green glauconitic pigmentation, up to 2 cm in size, occasionally occur in the matrix. This pigmentary glaucony commonly encapsulates terrigenous grains, bioclasts and pelletal glaucony, and is often present in the argillaceous internal sediment of large bivalves and echinoids. Textural features such as patches of diffuse glaucony in the matrix, and gradational boundaries between pelletal glaucony and surrounding matrix, clearly show that the Bird Rock glaucony is autochthonous. The similarity of detrital and bioclastic

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Fig. 4. A photomicrograph of a glauconitic internal mould of a foram test ( f ); the foram has been almost completely removed by dissolution and is represented by mouldic porosity ( p).

inclusions in the glaucony to those of the matrix also suggests that the glaucony is authigenic. In addition, the poorly sorted character of the glauconitic Bird Rock sediments implies that the glaucony formed in situ; if the glauconitic grains had been transported it is likely that they would have been concentrated in sediments with a greater textural maturity as a result of hydraulic sorting processes. 5.2. Mineralogy and chemistry XRD analyses of green pellets separated from the Bird Rock suite of samples display the characteristic (001), (020) and (003) reflections of glauconitic minerals (Bayliss et al., 1986). The (001) reflection of the glauconitic phase lies ˚ in untreated samples and has a subdued at 10 A intensity, broad base and slightly asymmetric appearance. With glycol solvation the (001) reflection shows some evidence of expansion and peak separa˚ and becomes tion, but upon heating collapses to 10 A much more intense and symmetrical. The peak shifts evident upon glycolation and subsequent heat treat-

ment reflect the interstratification of expandable and non-expandable layers within the glauconitic phase (Thompson and Hower, 1975). Glauconitic structures which contain an expandable component are described as randomly interstratified glauconitic smectite (Odom, 1984). Minor admixed kaolinite is ˚ which collapses indicated by a small peak of 7.15 A with heat treatment (Hardy and Tucker, 1988). Glauconitic structures evolve from smectitic (expandable) to micaceous (non-expandable) end-members through the progressive incorporation of potassium and iron (Thompson and Hower, 1975; Odin and Matter, 1981). The total iron content of the glauconitic pellets of the Bird Rock sediments (expressed as Fe2 O3 ) ranges from 17.8 to 24.9 wt.%, whilst potassium varies from 3.5 to 4.9 wt.% K2 O (Table 2). This range of potassium values is consistent with the identification of the glauconitic phase as randomly interstratified glauconitic smectite (McRae, 1972; Odom, 1984). On the basis of potassium content the Bird Rock glaucony equates with the nascent and slightly evolved glauconies of Odin and Morton (1988).

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Table 2 Potassium and iron compositional data for the Bird Rock glaucony and clay fractions (sample BW3) a Sample No.

K2 O (wt.%)

Fe2 O3 (wt.%)

Glaucony (0.40) Glaucony (0.45) Glaucony (0.50) Glaucony (0.55) <2 µm clay

4.90 4.31 3.84 3.46 2.30

24.85 21.89 19.57 17.83 9.92

The numbers in brackets denote the current (A) required to attract the glaucony on a magnetic separator set with a lateral inclination of 15º and a longitudinal inclination of 20º. a Data obtained using the ICP–AES technique.

The variation in the chemistry of the Bird Rock glaucony is accompanied by systematic variation in its colour, lustre and paramagnetic properties; the more potassic and ferroan glaucony is darker in colour, has a more lustrous appearance and shows a greater paramagnetic susceptibility on a horizontal magnetic separator (Table 2). However, the XRD characteristics of the glaucony show no obvious variation as a function of chemistry.

Fig. 5. Variation in the modal abundance of matrix and glaucony in the Bird Rock sediments.

6. Sedimentary environment of glauconitization The textural and compositional differences between the glauconitic and non-glauconitic lithologies, although subtle, are very significant. The glauconitic sandstones are texturally and mineralogically less mature than the glauconite-poor packstone. They are relatively poorly sorted, contain fewer terrigenous and bioclastic grains and more argillaceous matrix, and have lower quartz to feldspar ratios (Table 1; Figs. 5 and 6). These characteristics suggest that the glauconitic lithologies accumulated under more quiescent conditions than the packstones. In addition, the relative abundance of pelagic forams and gastropods, and paucity of terrigenous framework grains in the glauconitic sediments indicates that they were deposited in deeper-water environments, further from the palaeoshoreline, during marine flooding events. It is noteworthy that the uppermost glauconitic horizon is coincident with the boundary between the Jan Juc and Puebla Formations; the facies change at this

Fig. 6. Variation in the modal abundance of glaucony and the quartz=feldspar ratio in the Bird Rock sediments.

boundary has been attributed to a marine transgressional event (as previously discussed). Furthermore, the comparative abundance of planktonic bioclasts and muddy sediment in the glauconitic lithologies, together with their highly bioturbated character, suggests that they accumulated during periods of relatively slow sedimentation. Slowly accumulated sediments commonly contain relatively large amounts of pelagic to hemipelagic detritus (Loutit et al., 1988; Shanmugam, 1988), and the intensity of biological mixing in marine sediments

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shows an inverse correlation with sedimentation rate (Boudreau, 1994). The uppermost glauconitic horizon has been previously interpreted as a condensed interval relating to marine flooding (as described above). The positive correlation between the proportions of argillaceous matrix and authigenic glaucony (Fig. 5) suggests that slow sedimentation rates and low-energy sedimentological conditions were conducive to the development of glaucony, and may also have a more direct genetic significance, which is discussed further below.

potassium and iron largely reflect the proportions of matrix and glaucony. Silica mainly correlates with clay mineral abundance, but framework quartz is also significant. When compared with geochemical averages for common sedimentary rocks, the Bird Rock lithologies have compositions that are intermediate between typical limestone and shale (Table 3). This provides additional support of the inference that the Bird Rock glaucony is autochthonous (see above); glauconitic greensands which contain abundant allochthonous glaucony typically display much higher relative proportions of potassium and iron (Fig. 7). The Fe2 O3 content of the Bird Rock sediments shows a positive correlation with the abundance of glaucony; FeO displays an antipathic trend (Fig. 8; Tables 1 and 3). The preponderance of ferric iron in the glauconitic sediments reflects the fact that glauconitic minerals mainly contain iron in the trivalent state; the Fe3C =Fe2C ratio in glauconitic minerals varies between 2 and 10 (Weaver and Pollard, 1973). The predominance of divalent iron in the non-glau-

7. Bulk chemistry of the Bird Rock lithologies The bulk chemistry of the Bird Rock lithologies shows significant variability in the amounts of calcium, silica, alumina, iron and potassium (Table 3), largely reflecting the relative proportions of bioclastic grains and clay minerals. Calcium correlates with skeletal carbonate content, whilst alumina,

Table 3 Bulk chemical data for the Bird Rock sediments and selected sedimentary rock averages (wt.%) Sample No.

BR1

BR2

GL1

BW1

BW2

BW3

Shale (277)

Limestone (93)

Sandstone (253)

SiO2 TiO2 Al2 O3 Fe2 O3 FeO MnO MgO CaO Na2 O K2 O P2 O5 H2 OC H2 O CO2 (organic) CO2 (carbonate) S Total (–O S) Total

28.80 0.28 3.33 1.22 2.37 0.03 1.97 28.61 1.27 0.82 0.00 2.80 2.08 4.81 20.90 0.65 99.94 0.33 99.62

29.88 0.30 3.46 1.17 2.38 0.03 2.00 27.40 1.64 0.82 0.00 2.87 2.08 2.95 22.77 0.66 100.41 0.33 100.08

30.02 0.34 5.83 2.19 1.75 0.01 2.10 25.58 1.31 1.23 0.00 3.64 3.52 2.61 20.23 0.48 100.83 0.24 100.59

43.52 0.57 11.13 5.37 1.40 0.01 2.30 10.70 1.75 2.26 0.03 5.56 5.56 3.04 7.15 0.57 100.93 0.29 100.65

36.68 0.47 7.57 3.26 0.72 0.01 1.98 15.01 2.07 1.54 0.10 3.97 4.65 4.55 12.81 1.25 96.65 0.63 96.02

35.14 0.40 7.59 3.68 1.04 0.01 2.48 16.15 3.07 1.50 0.00 4.21 5.37 4.96 15.81 0.61 102.01 0.31 101.71

58.90 0.78 16.70 2.80 3.70 0.09 2.60 2.20 1.60 3.60 0.16 5.00 nd 1.30 nd 0.24 99.67 nd 99.67

6.90 0.05 1.70 0.98 1.30 0.08 0.97 47.60 0.08 0.57 0.16 0.84 nd 38.30 nd 0.11 99.64 nd 99.64

78.70 0.25 4.80 1.10 0.30 0.03 1.20 5.50 0.45 1.30 0.08 1.30 nd 5.00 nd nd 100.01 nd 100.01

3.85 0.51

3.81 0.49

4.13 1.25

6.93 3.84

4.06 4.53

4.84 3.54

6.91 0.76

2.42 0.75

1.43 3.67

Total iron (as Fe2 O3 ) Fe2 O3 =FeO

Sandstone, shale and limestone averages after Wedepohl (1969). No. of samples used for average in brackets. N.B. CO2 and H2 O figures for the sedimentary rock averages represent total values.

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Fig. 7. Comparison of the abundance of iron and potassium in the Bird Rock sediments with average shale, average limestone, and greensands which contain abundant allochthonous glaucony. BR, Average of the BR packstone analyses (this paper); GL, Glauconitic sandstone sample GL1 (this paper); BW, Average of the BW glauconitic sandstone analyses (this paper); A–D, Paleocene-Eocene greensands, New Jersey (Mansfield, 1920); E, Eocene greensand, Texas (James, 1966); F, Eocene greensand marl, Texas (James, 1966); G, Recent greensand, South Africa (James, 1966); H, Eocene greensand, New Zealand (Pettijohn, 1975); I, Recent greensand, New Zealand (Stoffers et al., 1984). Limestone and shale averages after Wedepohl (1969).

conitic sediments reflects the paucity of glauconitic minerals and the relative abundance of siderite. The ferric=ferrous ratio in the glauconitic sandstones is much higher than that of the packstone (which contains little glaucony), and is also high in relation to global sedimentary rock averages (Table 3). This suggests that the development of glaucony involved unusual redox conditions and processes that converted most of the sedimentary iron to the trivalent state. The importance of redox reactions to the genesis of glaucony is investigated below.

8. Source of chemical constituents of glauconitic minerals Several different models of the glauconitization process have been developed, including the layer lattice theory of Burst (1958) and Hower (1961), the verdissement theory of Odin and Matter (1981) and the two-stage evolutionary model of Clauer et

Fig. 8. Variation in the modal abundance of glaucony and the iron content of the Bird Rock sediments. (A) Fe2 O3 variation. (B) FeO variation.

al. (1992). The systematics of the different models vary, nevertheless each involves the derivation of constituent ions from both parent sediment and seawater. Normal seawater contains very low concentrations of aluminium, silica and iron, but contains appreciable potassium (399 ppm; Drever, 1988). Therefore, oceanic water is unlikely to contribute significant Al, Si and Fe to the glauconitization process, but may be a viable source of K. However, the iron, aluminium, silica, and potassium contents of the glauconitic Bird Rock sediments are intermediate between those of the limestone and

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shale averages (Table 3; Fig. 7), suggesting that it is unnecessary to invoke chemical enrichment from seawater to explain the development of glaucony. The chemical constituents of glaucony may be derived entirely from primary detrital phases as suggested by Stille and Clauer (1994) in their modification of the original two-stage glauconitization model of Clauer et al. (1992). The positive correlation between the proportions of autochthonous glaucony and argillaceous matrix in the Bird Rock sediments suggests that detrital clay plays an important role in the genesis of glaucony (Fig. 5). Textural features such as diffuse patches of glaucony within the matrix, terrigenous and bioclastic inclusions in glaucony, and gradational boundaries between pelletal glaucony and surrounding matrix (described above) indicate that glauconitic minerals have replaced argillaceous matrix material. This hypothesis is supported by the fact that the glaucony predominantly occurs in faecal pellets and bioclast pores, which otherwise contain argillaceous matter. Furthermore argillaceous matrix, which consists of smectite and kaolinite and constitutes 20–40% of total rock volumes, is the principal primary sink of aluminium and silica in the Bird Rock sediments and is therefore likely to be the predominant source of Al and Si for the glauconitization process. Argillaceous matrix is also the main primary iron- and potassium-bearing component of the Bird Rock sediments (Table 2), and probably supplied much of the Fe and K necessary for glauconitization. The iron in the matrix is presumably present largely as a structural component of the smectitic clay; ferric coatings on the clay minerals and microcrystalline inclusions of iron-bearing phases may also be present (Carroll, 1958). Other primary iron-, aluminium-, potassium-, and silica-bearing minerals in the sediments include biotite, muscovite and feldspar. Biotite and muscovite are present in only trace amounts; feldspar is slightly more abundant (Table 1), but generally displays the bright blue cathodoluminescence characteristic of pristine alkali feldspar, and only occasionally show pale-green alteration. Therefore any contribution of K, Fe, Al and Si to the glauconitization process from these minerals would have been small. Quartz is relatively abundant in the Bird Rock

sediments (2–17%) and constitutes a potential source of Si for glauconitization. Quartz generally has a very low solubility under sedimentary conditions (Drever, 1988); however, redox reactions involving iron can enhance quartz dissolution (Morris and Fletcher, 1987). Nevertheless, the quartz in the Bird Rock sediments shows no evidence of etching or replacement in thin section, and is therefore unlikely to have contributed significant silica to glauconitization.

9. Physico-chemical environment of glauconitization 9.1. Redox Overall, the glauconitic lithologies are not significantly iron-enriched relative to the non-glauconitic packestone (Table 3), particularly when compared on a carbonate-free basis. However, the glaucony of the Bird Rock sediments contains more iron than its argillaceous progenitor (Table 2); therefore the redistribution of iron must be a fundamental feature of the glauconitization process, at least on the scale of millimetres to centimetres. The solubility of iron in sedimentary systems is largely controlled by redox. During early diagenesis marine sediments show a general trend of decreasing Eh with increasing burial depth, which relates to the microbial degradation of organic matter (Claypool and Kaplan, 1974; Froelich et al., 1979). In oxic conditions and neutral to alkaline pH, iron has very low solubility and is stable in the ferric trivalent state in minerals such as haematite, goethite and smectite; under more reducing conditions iron is stable in the soluble ferrous state and the dissolution of iron-bearing minerals is possible (Garrels and Christ, 1965; James, 1966; Harder, 1980). Dissolved iron may be incorporated into a variety of diagenetic minerals, including ferrous carbonates (e.g. siderite and ankerite), ferrous sulphides (e.g pyrite) and iron-rich silicates such as glauconitic minerals (Curtis and Spears, 1968; Froelich et al., 1979; Burdige, 1993). The stability of these diagenetic phases is largely controlled by the activities of hydrogen sulphide and bicarbonate, which are in turn controlled by redox processes (Curtis and

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Spears, 1968; Claypool and Kaplan, 1974; Froelich et al., 1979). Several lines of evidence indicate that the glauconitization of the Bird Rock sediments occurred under sub-oxic, partially reducing conditions. First, the environment cannot have been oxidising, as iron was clearly mobile; the pH would have been close to neutral, buffered by the abundant calcite present (see discussion below). Second, textural relationships in the Bird Rock sediments indicate that pyrite post-dates glauconitization, as pyrite often rims and partially replaces glauconitic pellets (Fig. 3). Pyrite precipitates under reducing conditions, when the sulphate in pore waters is reduced to sulphide (Curtis and Spears, 1968; Berner, 1981; Burdige, 1993). Thus, glauconitization occurred earlier than pyrite formation, under less reducing conditions, before the onset of significant sulphate reduction. Once pyrite became the stable iron-bearing phase glauconitic minerals could not continue to form. The theory that the glauconitization process occurs under partially reducing conditions appears at odds with the fact that glaucony mainly contains iron in the oxidised ferric state. However, several authors suggest that this situation reflects the oxidation of iron within glauconitic minerals in response to structural requirements, rather than being a true indication of the redox conditions in the genetic environment (Weaver and Pollard, 1973; McConchie et al., 1979). Additional evidence which indicates that glaucony develops under partially reducing conditions can be drawn from several sources. Harder (1980) concluded that layer silicates which contain both ferrous and ferric iron, such as glauconitic minerals, can only be synthesised under slightly reducing conditions. McConchie et al. (1979) found that artificially leached iron-depleted glauconies absorbed both ferric and ferrous iron when placed in a solution containing only Fe2C . Thermodynamic studies show that magnetite, which like glauconitic minerals contains both ferrous and ferric iron, is only stable under partially reducing conditions at circum-neutral pH (Garrels and Christ, 1965; Taylor and Curtis, 1995). Berner (1981) stated that glauconitic minerals weather to ferric oxides under oxic conditions and readily react with hydrogen sulphide to form iron-

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sulphides under strongly reducing conditions; it may therefore be inferred that glaucony is only stable under sub-oxic, partially reducing conditions. The diverse benthic fauna and intense bioturbation of the glauconitic Bird Rock sediments suggest that oxic bottom water conditions prevailed during their accumulation (Byers, 1977; Wignall and Myers, 1988). The inference that the glaucony developed under sub-oxic conditions suggests that glauconitization occurred in isolation from the open ocean, in the shallow burial environment. The variation of Eh with depth in marine sediments is controlled by a large number of variables, such as sedimentation rate, bioturbation rate, bottom water oxygen content, sediment porosity and permeability, the amount and reactivity of organic matter, and the amount and type of manganese and iron-bearing detritus (Froelich et al., 1979; Van Der Loeff, 1990; Burdige, 1993). As a result the depth at which the required sub-oxic conditions develop in modern marine sediments varies from a few millimetres to several metres (Van Der Loeff, 1990; Canfield et al., 1993). Organic carbon is the principal agent of iron reduction in sediments and plays an important role in most diagenetic processes (Froelich et al., 1979; Burdige, 1993; Canfield et al., 1993). The overall organic carbon content of the Bird Rock sediments shows no obvious correlation with either the abundance of glaucony or the ratio of ferric to ferrous iron (Tables 1 and 3). However, glaucony predominantly occurs as bioclast infills and faecal pellet replacements, and these micro-environments may have contained relatively large amounts of organic matter. It is noteworthy that pyrite is more common in the bioclasts and faecal pellets than in the surrounding matrix, suggesting that conditions at these sites were more reducing than in the bulk of the sediment. The physical confinement of the bioclast cavities and faecal pellet interiors may also have contributed to the preferential distribution of glaucony. These micro-environments could have provided the degree of chemical isolation required to allow unusual chemical conditions to occur, while being sufficiently open to permit ionic exchange with pore fluids (see Odin and Matter, 1981; Odin and Fullagar, 1988).

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9.2. pH Many of the carbonate bioclasts which host glauconitic minerals show evidence of dissolution (see above), whilst the bioclasts which are not closely associated with glauconitic minerals display no obvious dissolution features. This suggests that localised acidic conditions were initiated by the glauconitization process. Nascent glauconitic structures may release hydrogen ions during the fixation of potassium, in a fashion analogous to the proton release associated with the conversion of smectite to illite (reaction 1; Lundegard and Land, 1986). This production of acidity could be buffered by the dissolution of bioclastic carbonate intimately associated with the developing glaucony (reaction 2). Glauconitic smectite C KC > Glauconitic mica C HC 2H C CaCO3 > CO2 C H2 O C Ca C

(1) 2C

(2)

10. Significance of slow sedimentation to glauconitization The glauconitic lithologies in the Bird Rock sequence probably accumulated during periods of relatively slow sedimentation, as previously discussed. Indeed, authigenic glaucony is regarded as a characteristic indicator of slow sedimentation in marine deposits, and is commonly associated with condensed sections and unconformities (Amorosi, 1995). In addition, the results of the present study suggest that low-energy conditions are conducive to the development of glaucony. Slow sedimentation and environmental quiescence probably facilitate the glauconitization process as they permit the favoured clay-rich sediments to accumulate. Furthermore, slow sedimentation rates and low-energy conditions may contribute to glauconitization by allowing sediments to remain in the appropriate physico-chemical regime sufficiently long for the complex glauconitic structures to form. Rapid sedimentation and vigorous wave and current activity would inhibit the development of glaucony by quickly removing the sediments from the environment of glauconitization, through burial and reworking processes, respectively.

The paucity of glaucony in the Bird Rock packstone probably reflects relatively rapid sedimentation under comparatively energetic conditions. It is likely that energetic conditions restricted the accumulation of the favoured argillaceaous sediment, whilst rapid burial limited sediment residence time in the appropriate sub-oxic redox regime. The sediments moved quickly into strongly reducing conditions where iron-bearing minerals like pyrite and siderite are stable, therefore glaucony could not form. The correlation between textural immaturity and the proportion of authigenic glaucony can be used to identify allochthonous glauconitic deposits. A wellsorted greensand, which consists almost entirely of glauconitic pellets and lacks matrix, is unlikely to comprise autochthonous glaucony. The glauconitic pellets in such lithologies have probably been reworked, through wave or current action, and may therefore have no direct sequence stratigraphic or environmental significance. Absolute ages of sediments and sedimentary rocks obtained from such allochthonous glaucony should be treated with caution.

11. Conclusions (1) The Bird Rock glaucony is autochthonous and developed in a low-energy, mid-shelf environment during periods of slow sedimentation associated with marine flooding events. Environmental quiescence and slow sedimentation rates facilitated the glauconitization process by allowing clay-rich sediments to accumulate and remain in the appropriate physicochemical regime sufficiently long for the complex glauconitic structures to form. (2) Glauconitization occurred under sub-oxic partially reducing conditions, in the very shallow burial environment, and involved local redistribution of detrital iron. Sub-oxic conditions favour glauconitization because iron occurs in the soluble ferrous state and can be fixed in authigenic silicates due to the negligible concentrations of hydrogen sulphide. (3) Glauconitic minerals are preferentially developed in the clay-rich sediments of the Bird Rock section. Clay-rich sediments favour glauconitization, as argillaceous matrix material is the principal source of the chemical components of glaucony; seawater

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is unlikely to be a significant source of ions for glauconitization. (4) The physico-chemical conditions appropriate for glauconitization develop preferentially within faecal pellets and bioclast cavities. The development of appropriate micro-environments within such sediments may relate to their physical confinement and=or high organic matter content. (5) It is likely that localised acidic conditions are initiated during the chemical evolution of glauconitic minerals. This acidity may be buffered by the dissolution of bioclastic carbonate.

Acknowledgements This research was conducted using the technical resources of the Victorian Institute of Earth and Planetary Sciences, and was supported by a La Trobe University Postgraduate Research Scholarship. The authors wish to thank J. Metz and A. Jacka for their technical assistance, and M. Warne and T. Van Der Linden for helpful discussions during the preparation of this paper. This manuscript has benefited from reviews by C.D. Curtis and P.S. Stille.

References Abele, C., 1979. Geology of the Anglesea area, central coastal Victoria. Geol. Surv. Vic. Mem. 31, 71 pp. Amorosi, A., 1995. Glaucony and sequence stratigraphy: a conceptual framework of distribution in siliciclastic sequences. J. Sediment. Res. B65 (4), 419–425. Bayliss, P., Erd, D.C., Mrose, M.E., Sabina, A.P., Smith, D.K., 1986. Mineral Powder Diffraction File: Data Book. International Centre for Diffraction Data, Pennsylvania, 1396 pp. Berner, R.A., 1981. A new geochemical classification of sedimentary environments. J. Sediment. Petrol. 51 (2), 359–365. Boreen, T.D., James, N.P., 1995. stratigraphic sedimentology of Tertiary cool-water limestones, SE Australia. J. Sediment. Res. B65 (1), 142–159. Boudreau, B.P., 1994. Is burial velocity a master parameter for bioturbation? Geochim. Cosmochim. Acta 58 (4), 1243–1249. Burdige, D.J., 1993. The Biogeochemistry of manganese and iron reduction in marine sediments. Earth Sci. Rev. 35, 249– 284. Burst, J.F., 1958. ‘Glauconite’ pellets: their mineral nature and applications to stratigraphic interpretations. Bull. Am. Assoc. Pet. Geol. 42 (2), 310–327. Byers, C.W., 1977. Biofacies patterns in euxinic basins: a general model. In: Cook, H.E., Enos, P. (Eds.), Deep Water Carbonate

113

Environments. Soc. Econ. Paleontol. Mineral. Spec. Publ. 25, 5–17. Canfield, D.E., Jorgensen, B.B., Fossing, H., Glud, R., Gundersen, J., Ramsing, N.B., Thamdrup, B., Hansen, J.W., Nielsen, L.P., Hall, P.O.J., 1993. Pathways of organic carbon oxidation in three continental margin sediments. Mar. Geol. 113, 27–40. Carroll, D., 1958. Role of clay minerals in the transportation of iron. Geochim. Cosmochim. Acta 14, 1–27. Carter, A.N., 1990. Time and space events in the Neogene of south-eastern Australia. In: Tsuchi, R. (Ed.), Pacific Neogene Events; Their Timing Nature and Interrelationship. University of Tokyo Press, Tokyo, pp. 183–193. Clauer, N., Keppens, E., Stille, P., 1992. Sr isotopic constraints on the process of glauconitization. Geology 20, 133–136. Claypool, G.E., Kaplan, I.R., 1974. The origin and distribution of methane in marine sediments. In: Kaplin, I.R. (Ed.), Natural Gases in Marine Sediments. Plenum Press, New York, pp. 99– 139. Craig, L.E., Smith, A.G., Armstrong, R.L., 1989. Calibration of the geologic time scale: Cenozoic and Late Cretaceous glauconite and non-glauconite dates compared. Geology 17, 830–832. Curtis, C.D., Spears, D.A., 1968. The formation of sedimentary iron minerals. Econ. Geol. 63, 257–270. Darragh, T.A., 1985. Molluscan biogeography and biostratigraphy of the Tertiary of southeastern Australia. Alcheringa 9, 83–116. Dickson, J.A.D., 1966. Carbonate identification and genesis as revealed by staining. J. Sediment. Petrol. 49, 501–516. Dorman, F.H., Gill, E.D., 1959. Oxygen isotope palaeotemperature measurements on Australian fossils. Proc. R. Soc. Vic. 71 (1), 73–98. Drever, J.I., 1988. The Geochemistry of Natural Waters. Prentice Hall, Englewood Cliffs, N.J., 437 pp. Froelich, P.N., Klinkhammer, G.P., Bender, M.L., Luedtke, N.A., Heath, G.R., Cullen, D., Dauphin, P., Hammond, D., Hartman, B., Maynard, V., 1979. Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis. Geochim. Cosmochim. Acta 43, 1075–1090. Garrels, R.M., Christ, C.L., 1965. Solutions, Minerals, and Equilibria. Harper and Row, and John Weatherhill, Japan, 450 pp. Haq, B.U., Hardenbol, J., Vail, P.R., 1988. Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea-Level Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ. 42, 71–109. Harder, H., 1980. Synthesis of glauconite at surface temperatures. Clays Clay Miner. 28 (3), 217–222. Hardy, R., Tucker, M., 1988. X-ray powder diffraction of sediments. In: Tucker, M. (Ed.), Techniques in Sedimentology. Blackwell, Oxford, pp. 191–228. Hower, J., 1961. Some factors concerning the nature and origin of glauconite. Am. Mineral. 46, 313–334. James, H.L., 1966. Chemistry of the iron-rich sedimentary rocks.

114

J.C. Kelly, J.A. Webb / Sedimentary Geology 125 (1999) 99–114

In: Data of Geochemistry (6th ed.). U.S. Geol. Surv. Prof. Pap. 440-W, W1–W59. James, N.P., 1995. Paleozoic cryocarbonates: charlatans in the mist? In: Abstracts of the Cool and Cold-Water Carbonate Conference, Geelong, Victoria, Australia, 14th–19th January 1995. Geological Society of Australia, Sedimentology Studies Group, 43 pp. Kazakov, G.A., 1983. Glauconites as indicators for geochemical sediment formation conditions. Geochem. Int. 20, 129–139. Loutit, T.S., Hardenbol, J., Vail, P.R., Baum, G.R., 1988. Condensed sections: the key to age determination and correlation of continental margin sequences. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea-Level Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral., Spec. Publ. 42, 183– 213. Lundegard, P.D., Land, L.S., 1986. Carbon dioxide and organic acids: their role in porosity enhancement and cementation, Paleogene of the Texas Gulf coast. In: Gautier, D.L. (Ed.), Roles of Organic Matter in Sediment Diagenesis. Soc. Econ. Paleontol. Mineral., Spec. Publ. 38, 129–146. Mansfield, G.R., 1920. The physical and chemical character of New Jersey Greensand. Econ. Geol. 15 (7), 547–566. McConchie, D.M., Ward, J.B., McCann, V.H., Lewis, D.W., 1979. A Mossbauer investigation of glauconite and its geological significance. Clays Clay Miner. 27 (5), 339–348. McRae, S.G., 1972. Glauconite. Earth Sci. Rev. 8, 397–440. Morris, R.C., Fletcher, A.B., 1987. Increased solubility of quartz following ferrous–ferric iron reactions. Nature 330, 558–561. Norrish, K., Hutton, J.T., 1969. An accurate X-ray spectrographic method for the analysis of a wide range of geological samples. Geochim. Cosmochim. Acta 33, 431–453. Odin, G.S., Fullagar, P.D., 1988. The geological significance of the glaucony facies. In: Odin, G.S. (Ed.), Green Marine Clays. Elsevier, Amsterdam, pp. 295–332. Odin, G.S., Matter, A., 1981. De Glauconiarum Origine. Sedimentology 28, 611–641. Odin, G.S., Morton, A.C., 1988. Authigenic green particles from marine environments. In: Chilingarian, G.V., Wolf, K.H. (Eds.), Diagenesis II. Developments in Sedimentology 43, Elsevier, Amsterdam, pp. 213–264. Odin, G.S., Curry, D., Hunziker, J.C., 1978. Radiometric dates from NW European glauconites and the Palaeogene timescale. J. Geol. Soc. London 135, 481–497. Odin, G.S., and 35 Collaborators, 1982. Interlaboratory standards for dating purposes. In: Odin, G.S. (Ed.), Numerical Dating in Stratigraphy. Wiley, Chichester, pp. 123–150. Odom, E., 1984. Glauconite and celadonite minerals. In: Bailey, S.W. (Ed.), Reviews in Mineralogy, 13. Micas. Mineralogical Society of America, pp. 545–572. Pettijohn, F.J., 1975. Sedimentary Rocks. Harper and Row, New York, 3rd ed., 628 pp. Raggatt, H.G., Crespin, I., 1954. Stratigraphy of Tertiary rocks

between Torquay and Eastern View, Victoria. Proc. R. Soc. Vic. 67, 75–142. Reeckmann, S.A., 1979. Detailed Stratigraphy of the Tertiary Sequence, Torquay, Victoria — Facies Environment and Diagenesis. Ph.D. thesis, University of Melbourne (unpubl.). Reeckmann, S.A., 1994. Geology of the onshore Torquay Subbasin: a sequence stratigraphic approach. In: Finlayson, D.M. (Compiler), NGMA=PESA Otway Basin Symposium, Melbourne, 20 April 1994, Extended Abstracts. Australian Geological Survey Organisation, Record 1994 (14), pp. 3–6. Reeckmann, S.A., Loutit, T.S., Rahmanian, V.D., Vail, P.R., 1986. Sequence stratigraphy of the Oligocene–Miocene Strata of the Torquay Embayment, Victoria, Australia. 12th Int. Sedimentol. Congr., Abstr., p. 215. Shanmugam, G., 1988. Origin, recognition, and importance of erosional unconformities in sedimentary basins. In: Kleinspehn, K.L., Paola, C. (Eds.), New Perspectives in Basin Analysis. Springer, New York, pp. 83–108. Siesser, W.G., 1979. Oligocene–Miocene calcareous nannofossils from the Torquay Basin, Victoria, Australia. Alcheringa 3, 159–170. Stein, J.K., 1984. Organic matter and carbonates in archaeological samples. J. Field Archaeol. 11, 239–246. Stille, P.S., Clauer, N., 1994. The process of glauconitization: chemical and isotopic evidence. Contrib. Mineral. Petrol. 117, 253–262. Stoffers, P., Pluger, W., Walter, P., 1984. Geochemistry and mineralogy of continental margin sediments from Westland, New Zealand. N.Z. J. Geol. Geophys. 27, 351–365. Taylor, K.G., Curtis, C.D., 1995. Stability and facies association of early diagenetic mineral assemblages: an example from a Jurassic ironstone–mudstone succession, U.K. J. Sediment. Res. A65 (2), 358–368. Thompson, G.R., Hower, J., 1975. The mineralogy of glauconite. Clays Clay Miner. 23, 289–300. Van Der Linden, T.E., 1997. Depositional Facies, Cyclicity, and Sequence Stratigraphy of the Oligo–Miocene Torquay Group, Torquay Embayment, Southeastern Australia. M.Sc. Thesis, Sydney University, New South Wales (unpubl.). Van Der Loeff, M.M.R., 1990. Oxygen in pore waters of deepsea sediments. Philos. Trans. R. Soc. London A331, 69–84. Weaver, C.E., Pollard, L.D., 1973. The Chemistry of Clay Minerals. Developments in Sedimentology 15, Elsevier, Amsterdam, 213 pp. Webb, J.A., Nicolaides, S., Kelly, J., 1995. Cool Water Carbonates of the Northeastern Otway Basin, Southeastern Australia. Australasian Sedimentologists Group Field Guide Series 6, Geological Society of Australia, 60 pp. Wedepohl, K.H., 1969. Composition and abundance of common sedimentary rocks. In: Wedepohl, K.H. (Ed.), Handbook of Geochemistry, Vol. 1. Springer, Berlin, pp. 250–271. Wignall, P.B., Myers, K.J., 1988. Interpreting benthic oxygen levels in mudrocks: a new approach. Geology 16, 452–455.