JOURNAL OF THE ROYAL SOCIETY OF WESTERN AUSTRALIA Volume 70 • Part 1 • 1987 §ociety of l^estern AostraHo To promote and foster science in Western Australia and counteract the effects of specialization PATRON Her Majesty the Queen VICE— PATRON His Excellency Professor Gordon Reid Governor of Western Australia COUNCIL 1987—1988 President J T Tippett B Sc, Ph D Vice-Presidents J S Pate Ph D, D Sc, FAA, FRS M Candy M Sc, FRAS Past President J S Beard M A, B Sc, D Phil Joint Hon Secretaries K W Dixon B Sc (Hons), Ph D L Thomas M Sc Hon Treasurer V J Hobbs B Sc, Ph D Hon Librarian Vacant Hon Editor I Abbott B Sc (Hons), Ph D Journal Manager J Backhouse M Sc, Ph D Members W A Cowlinc [ B Agric Sc (Hons), B Dell B Sc (Hons), Ph D S J Hallam M A, FAHA E R Hopkins B Sc, Dip For, Ph D L E Koch M Sc, Ph D K McNamara B Sc (Hons), Ph D J Majer B Sc, DIG, Cert Ed, Ph D Journal of ihc Royal Society of Western Australia. Vol. 70. Part 1. 1987. Cainozoic stratigraphy of the Yeelirrie area, northeastern Yilgarn Block, Western Australia D K Glassford 33 Rockett Way. Bull Creek. WA 6155 Manuscripi received IS November 1986; accepted 17 March 1987 Abstract Seven new formations are recognized in the Cainozoic continental cover of the Yeelirrie area, northeastern Yilgarn Block Western Australia. The oldest is the Westonia Formation, a mainly massive, light grey sandy claystone with local silicificalion and basal conglomerate. It iinconformably overlies Precambrian basement and is overlain by the Mulline Formation, a mainly pisolilic. reddish brown to reddish yellow quartz or quartz and kaolin sphcriic sand with a supporting silt-clay matrix of iron and aluminium minerals. Next, the Menzics Formation, consists of variably altered red sandy clay and sandy claystone: within this formation there is the Bungarra Member, a red kaolin mudstone the Volpress Member a sepiolitic kaolin mudstone, and the Yeelirrie Member, a red sandy claystone with secondary calcrete, sparry calcitc and dolomite. The Mulline and Menzics Formations are unconformably overlain by the Gibson Formation, a mainly massive, red to yellow, quartz and kaolin sphcnie clayey sand and sand which forms much of the present land surface throughout major interfluves and \ alley sides and inteiUngcrs with the next three formations. The Wirrawav Formation consists mainly of massive red quartz sand and clayey sand and occurs along major valley bottoms between and bordering playas. The Nuendah Formation consists of gravel, sand and clayey sand, channcl/ovcrbank. ridgc-foot^slopc and breakaway-front deposits. The Darlot Formation consists to stratified pan/playa gypsum and kaolin muds, and contains the Miranda Mernber. a massive to stratified gypsum deposit. This lithostratigraphic framework provides a basis lor lutLire w'ork into the nature and ongjn of the Cainozoic cover in the Yeelirrie area and also throughout other parts of the Yilgarn Block. Introduction A continental cover mainly of Cainozoic age extends throughout much of southwestern Australia, covering more than 70% of the Precambrian bedrock (.lutson 1914. 1934: Siace el al. 1968; Playford cr al- 1975). The cover ranges up to 80 m in thickness but is usually less than 30 m {Australian Groundwater Consultants 1972. Geologi- cal Survey of Western Australia 1975). Many aspects of this cover have been documented in terms of geology, stratigraphy, petrology, physiography, palaeogeography. gcomorphic processes, geomorphic history, pedology, weathering and groundwater (Julson 1914. 1934; Mabbmi da!. 1963; Beard 1973. 1982; Bull ct al. 1977; Churchward 1977; Mann & Deulschcr 1978: Lively et al. 1979: Mann & Horwitz 1979; van de Graaff elai 1979: Butt 1983. 1 985: Bcttenay 1984). How'cver. no formal lithostratigraphic framework has been developed for these materials, and their nature (geometry, structure, texture, composition) and origin are still ’imperfcctlv know'n. This paper divides the C’ainozoic cover in the Yeelirrie area (Fig. 1) into seven new formations and four new members. The units are introduced to provide a framework and basis for later studies into the stratigraphy, geomorphology. lithology, granulometry, mineralogy. geochemistry, petrogencsis and developmental history of the cover in the Yeelirrie area and throughout other parts of the Yilgarn Block (Fig. IB). A formal lithostratigraphic approach is taken because it provides the most objective basis from w'hich origins mav be inferred. This approach follows that adopted elsewhere wherein formal rock unit status has been given to similar clay and claystone (Lowrv cl al. 1972. Barnett 1980), laterite (Lindner & Drew in MeWhae cl al. 1958, de la Flunty 1965. Barnett 1980). sandy clay (Callen and Tedford 1976). calcrete (Maitland 1904. Glauert 1911, .Semcniuk 1 983) and sihciclastic sand (Logan ci al. 1 970. Playford & Low 1972, Semeniuk 198(3, 1983). Methods Stratigraphic sections were examined and sampled from limited natural outcrop, drill core, auger holes, costeans and pits at more than 100 sites. Type, reference and supplcmentarv stratigraphic sections were sampled vertically by collecting samples from a representative portion of all lithic and diagencticaily distinct units. Sketches were made and photographs were taken to record structures and facies a.ssocialions. To extract the sand fraction from indurated specimens selected samples were weighed, broken into chips and boiled in NaOH and/or FICl. Saprolite and sandy claystone chips were repeatedlv boiled in NaOH. Lateritic duricrust chips were boiled in HC 1 and bauxitic duricrust chips were boiled repeatedly in NaOH and then HCl 55715-1 I Figure 1. — Regional setting of Yeclirrie area- A and B. Location in Yilgarn Block, Western Australia. C. Yeelirrie area with location of Figs. 5 and 10. D. Yeelirrie area showing location of type sections. Residues were washed through a 0.045 mm screen, dried, weighed and sieved. Loose sands were air dried, weighed and also sieved at half phi intervals. Terminology and procedures on sieving and grain size statistics are after Folk (1974). Selected samples were processed in the following manner: (1) impregnated with resin and thin sectioned: (2) examined with petrographic, electron and scanning electron microscopes; (3) examined with a microprobe; and (4) X-rayed using CoK-alpha radiation. X-ray diffractograms were interpreted according to JCPDS ( 1 974) and Brindley & Brown ( 1 980). The data are presented, along with inferred origins, in Glassford (1980). 2 • • • Platy sandy lateritic • • • • • Gravel, conglomerate nodules U Pipe structure • • • Coarse sand/ A Labyrinthoid sandy • • sandstone A A lateritic duricrust • • • Trough cross Stratification Medium to fine Equant colour sand/sandstone mottles Crude/faint Stratification Silt-clay/ Silt-claystone Platy colour mottles Unconformity Bimodal coarse and > > Gypsum silt-clay • • • • • medium or fine > dust/mud TTTTTT • • • • • sand/sandstone > > Induration . — . — . Sandy silt-clay/ > > Silt-claystone > > > Gypsum sand a Precambrian basement Silt-clayey sand/ A A Hard, hypidiotopic 1 Sandstone interval < < < to idiotopic gypsum Westonia Formation A A Brecciod sandy . > . > Gypsum and silt-claystone • > • • > • > quartz sand 2 Mulline Formation sparry and ^ * Gypsum crystals, o cryptocrystalline calcite (calcrete) rosettes 3 Menzies Formation T T Calcareous or > T T " T T T calcrete interval > > Gypseous mud 4 Gibson Formation >4. /R Lamellar calcrete s s Silicified or silcrete gravel s s s interval 5 Wirraway Formation I c c I Lamellar Calcrete c Carnotite 6 I c c Nuendah Formation poor and typically confined to breakaways. The Westonia Formation differs from saprolite by being; generally greyer; locally slratified, locally conglomeratic in thin layers; moderately rich in kaolin spherites which are typically free of iron minerals. Saprolite differs from the Westonia Formation by: being generally whiter; occurrence of quartz veins; occurrence of discordant boundaries due to basic dykes; not containing kaolin spherites. Mulline Formation Reddish brown to yellowish brown laterilic/bauxitic duricrusl of quartz and/or kaolin spherile sand supported in a sill-clay matrix of iron and aluminium minerals (mainly goethite, haematite, kaolin, gibbsite). Sheet and blanket to lense form & less than 1 m to over 1 m thick. Pisolilic to nodular to labyrinthoid (root/burrow structured). Overlies unwcalhered granitic rock, saprolite. Westonia Formation and Menzies Formation; overlain by Gibson Formation. Outcrop is poor and typically confined lo breakaways. Pisolites and nodules of quartz and quartz and kaolin spherile sand with a matrix of iron (goeihile. haemalile) and aluminium (kaolin gibbsitc) minerals are diagnostic. Includes primary and secondary (reworked) laterilic/bauxitic duricrusls. Becomes red and more haemaltlic when affected by bush fires. 4 Journal of ihe Royal Society of Western Australia. Vol. 70. Part 1. 1987. Unit Lithology Geometry and dimensions Structure Stratigraphic relationships Comments Menzies Formation Mainly red sandy clay and sandy claystone with some other facies (see members below). Framework sand consists of quartz and kaolin spherites rich in iron minerals. Matrix silt-clay consists mainly of goethite. haematite and kaolin. Basin to broad major valley shaped fill. Typically up to 20 m thick. Massive to weakly stratified Unconformably overlies Precambrian basement; typically overlain by Gibson Formation Outcrop is poor and typically confined to the bottom of major valleys. Red colour plus framework sand supported by a sill-clay matrix are diagnostic features. Bungarra Member of Menzies Formation Red Kaolin mudstone with minor quartz and carnotite. Tabular to lense shaped up to 1 m thick. Locally may have a thin lense of sand at upper boundary. Massive with scattered vesicles. Overlies red sandy claystone facies and is overlain by Volpress Member. Differs from the mud facies of the Darlot Formation by: having vesicles; being hard and brittle and breaking with a subconchoidal fracture; lacks gypsum; and is buried in contrast to Darlot Formation mud facies which may be buried or form modem playa mud flats. Volpress Member of Menzies Formation Black, grey and while sepiolitic kaolin mudstone with minor carnotite. Tabular, lense to pod shaped and from less than 1 m to over 2 m thick. Massive to veined with anastomose sepiolite. Overlies Bungarra Member and is overlain by the Yeelirrie Member. May be confused with calcrete but differs from the Yeelirrie Member by: not containing calcitc; contains sepiolite; has a ‘■mudstone" fabric and does not contain red sandy claystone. Yeelirrie Member of Menzies Formation While to pale brown to while with red. Red sandy clay and sandy claystone variably cemented, brecciated and replaced by calcrete (cryptocryslallinc calcile) and sparry calcile. Mound to pod to lense shaped and up to 5 m thick. Domal to arcuate structured pods of calcrete grading to dispersed nodules, and rhizocon- cretions of calcitc. Overlies Volpress Member locally and iniergrades vertically and laterally with red sandy clay and sandy claystone facies. Locally overlain by Gibson Formation. Outcrop is poor and typically confined to the bottom of major valleys. Calcretizalion of sandy clay and claystone are distinctive features. Gibson Formation Red to reddish yellow to yellow and sometimes locally white framework support siliciclaslic clayey sand to sand. Framework grains mainly include quartz and kaolin spherites which typically contain iron minerals (goethite, haematite). Sheet, inlerdune sheets up to 4 m thick and linear hills or ridges typically up to 10 m thick Overall up to 14 m thick. Massive (ant. termite and root bioturbaled) to rarely cross stratified. Overlies the Mulline Formation and Menzies Formation; may interfinger or be overlain by the Nuendah. Wirraway and Darlol Formations. The upper boundary forms much of the present day landsurface. Distinctive features include: massive structure; silt-clayey coarse and fine sand: minor to co-dominant amounts of nearly perfectly rounded and optimally developed kaolin spherites pigmented with irom minerals; reddish yellow to yellow colour resulting from goethite and haematite pigmenting kaolin coalings on grains; and numerous ant holes and termiiariums. Wirraway Formation Red to reddish yellow quartz sand and clayey sand. Sheets, linear hills, mounds or ridges and lunate hills or ridges up to more than 5 m thick. Massive (ant, termite and root bioturbaled) to locally cross-stratified Overlies the Menzies Formation and interfmgers and overlies the Gibson, Nuendah and Darlol Formations. Occurs along the axis of major valleys Ixnwecn around and on the margins of playas. In handspecimen the Wirraway Formation may be confused with the Gibson Formation. However the Wirraway Formation consists mainly of quartz with no kaolin spherites or minor amounts of very iron-nch kaolin spherites and fragments of kaolin spherites. Nuendah Formation Pale brown lilhic gravels, quartz sands and clayey quartz sands. Ridge-fool-slope channel and fan shaped and breakaway-front ribbons from less than 1 m to more than a few metres in thickness. Massive to bedded to laminated. Bedding may be graded. Overlies and interfmgers with the Gibson and Wirraway Formations; overlies Precambrian basement and the Menzies Formation. Has modern and pre-modern facies. Occurs along Precambrian basement ridge-fooislopes, along breakaway-fronts and along dendritic tributary drainage tracts of major valley sides. 5 Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. Unit Lithology Geometry and dimensions Structure Stratigraphic relationships Comments Darlot Formation Red to brown to yellow to grey gypseous k^aolin mud. with some other facies (see Miranda Member). Varies widely in shape and thickness from tabular to lenticular sheets to filling circular and elongate basins. Ranges from less than 1 m to many metres thick. Massive to laminated to bedded. Overlies and interfingers with the Gibson and Wirraway Formations; overlies Precambrian basement. Occurs intermittently along the axis of the Yeelirrie valley. It has modem and pre-modern facies equivalent to “salt lake” and associated deposits. Miranda Member of Darlot Formalion White to brown gypsum sand and sandstone crystalline gypsum and gypsum silt-clay. Sheets and hills from less than 1 m to over 5 m thick. Massive to laminated to bedded. Commonly overlies the mud facies of the Darlot Formation. Distinctive handspecimen features include white to whitish brown and dominant gypsum composition. Westonia Formation Wcstonia Formation is the name proposed for a unit of light grey sandy claystone plus minor conglomeratic and other facies. The formation overlies unweathered and weathered (saprolite) Precambrian basement and is overlain by the Mullinc Formation. (Tables 1, 2). Derivauem of name. Named after Westonia. a gold mining town several hundred metres south of the type section, lat. 3 r 1 8'S. long. 1 1 8” 4 1'E. Southern Cross I ;250 000 sheet. Type scaion. The designated type section is an escarpment produced b\ the collapse of a portion of the roof of the old Edna May gold mine, lat. 3C 18'S, long. 1 18° 41'E. Southern Cross 1:250 000 sheet (Table 2: Figs 3. Tr. 6 and 4.TS1 ). A new phase of underground gold mining in the vicinity of the type section may progress to open cut mining and thereby endanger the designated type section. Therefore fable 2 General descriplion of lilhology. Wesionia Formalion type scciion. Depth (m) Description Rock unit 0-0.5 Sandy laterite; reddish brown Mulline Formation 0.5-0.75 Sandy claystone; light grey, massive, matrix supported, w ith unimodal. medium to fine, quartz and kaolin spherite sand, reddish bcow'n soft plats mottles. 0.75-1.0 Sandy claystone; as- above but unconsolidated and without colour mottles. 1. 0-2.0 Sandy claystone light grc\. massive and trough stratified, matrix supported, with unimodal, medium to fine quartz and kaolin spherite sand; hard, flint clay fracture. Wesionia Formalion 2.0-4.0 Sandy claystone; light grey massive and pipe-structured, matrix suppotied with unimodal. medium to fine, quart/ and kaolin spherite sand; hard reddish brown nodular and irregular mottles. 4.0-4.2 Pebbly sandy claystone; light grey, massive, with quartz pebbles supported in a matrix of quartz and kaolin spherite sand and kaolin flint clay. 4.2-5.0 + Gneissic saprolite Archaean Basement two reference sections are also designated. The first is in the face of a breakaway, lat. 30° 7'S. long. 120° 14'E. Kalgoorlie 1 :250 000 sheet (Tr. 4-1 ofFig. 3). This section is remote with access by a track which is very poorK defined and difficult to negotiate. Therefore a second readily accessible but incomplete and thinner section is also designated. This section is a low breakaway on the north side of the Perth to Kalgoorlie main road. lat. 31° 16'S. long. 120°'I'E. Boorabbin 1:250 000 sheet (Tr. 5-1 of Fig. 3). Disirihuiion. The Westonia Formation docs not crop out extensively and is poorly represented in the Yeelirrie area. Outcrop is typically confined to interfluve breakaways and outside the study area to valley bottom breakaways which in places border playas (Figs 3.5). Surface features. Where the upper surface of the Westonia Formation crops out the exposure is typically limited to a few square metres and is characterized by an irregular .surface of erosion. Geometry and diincnsions. Although there are only a few clear exposures, extrapolation of discontinuous exposures indicate that the formation is thin and generally tabular, lobate to lenticular to channel-Iike-fill shaped, with maximum thickness up to 5 m (Fig. 3). Lirhic characteristics. The Wesionia Formation is massive to crudely trough bedded. It is usually pale grey with scattered red" to orange mottles. The formalion has vertical pipes filled with sandy claystone similar to the host sandy claystone within which the pipes occur. Pipe structures are usually outlined by red margins, are more mottled, and may contain scattered sesquioxide gravels. The formation has the following facies (Figs 3.4): 1. Sandy claystone and claystone facies. Sandy claystone is massive and at handspecimen scale has a matrix support fabric. .At a microscopic scale it has a grain support fabric with framework grains of quartz and kaolin spherite sand (Killigrew & Giassford 1976) and a matrix of disordered kaolin clay. Claystone is also massive and at a handspecimen scale has a "mudstone" fabric (fabric term after Dunham 1962). and at the microscopic scale it also typically has a grain support fabric with a framework of kaolin spherite sand. Both facies may locally be partly silicificd (Figs 3; 4. TS 1 ). 6 Figure 3. — Regional to medium scale sellings for Wesionia Formation and Mulline Formation type sections. A.B.C. Location of stratigraphic transects (Tr.) in the Yilgarn Block, Western Australia. Tr. 1 ioTr.6, transects showing large to medium scale geomorphic and stratigraphic settings for stratigraphic sec- tions. D. Generalized stratigraphic sections showing that the Weston ia (Tr.6-1) and Mulline (Tr. 3- 1 ) Formations can be correllaied from their respective type sections (Tr.6-1 and Tr.3-I) to the Yeelirrie area (Tr.I-land Tr.2-1). 55715-2 Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. 2. Sandstone to muddy sandstone facies. This facies is massive to locally bedded and has a grain support fabric with a quartz sand framework and a disordered kaolin clay or tlini-day matrix. In the Yeclirrie area this facies IS nearly wholly silicified (Butt 1983, 1985). 3. Conglomeratic facies. This facies varies from clayey conglomerate through sandy and clayey conglomerate to conglomeratic sandstone (Figs 3; 4. TSl). It is commonly a basal unit and massive to crudely layered. Gravels are typically rounded, pebble sized (4 to 64 mm in diameter) quartz. Matrix material is composed of kaolin spherite sand and/or disordered kaolin clay. The (basal) conglomerate facies is sporadic in occurrence. The kaolin clay component of all facies is typically hard, docs not develop plasticity and commonly breaks with an uneven or sub-concKoidai fracture. These properties of the Westonia Formation are also shared by flint clay (Loughnan 1971, 1975. 1978). Fossils. The Westonia Formation generally lacks fossils but in places it contains roughly ellipsoidal casts 2 to 5 cm long and 1 to 2 cm in diameter which have been attributed by Kriewaldt (1969. p. 50-54) to the pupae of Lepwpius sp. (Jackson 1941. p. 72-74). However they are more likely to be the brood cell of soliian native bees, superfamily .Apoidea (T. S. Houston. W.A. Museum, pers. comm. I9'86). Some brood cells are connected to a krotovina. The sandy claystone of the formation is generally light grey but in the vicinity of brood cells it is red to orange for I to 20 mm. The brood cells are usually part to completely filled with relatively more porous quartz and kaolin spherite sand and this fill is typically red or orange. Pipes within the formation may be lap-root casts. Slraiigraphic relationships. .At the type section the Westonia Formation unconformably overlies gneissic saprolite and is itself overlain by the Mulline Formation. The lower boundary of the Westonia Formation is sharp, flat to gently dipping, and near planar, and locally varies to irregular and steeply dipping in the form of V and U-shaped valleys (Fig. 3. Tr. 3). These valleys have amplitudes of a few metres over distances of a few metres. The lower boundary is typically concealed and in places characterised by a thin basal conglomerate. The upper boundary is commonly sharp to abruptly gradational with overlying Mulline Formation, and it is generally flat to gently dipping, and near-planar to broadly iindulose. The Westonia Formation may be laterally equivalent geographically, but not temporally equivalent, to in situ pallid zone (saprolite) for where contacts are discernible the Westonia Formation unconformably overlies saprolite. Discussion. The We.stonia Formation is easily confused with in situ weathered Precambrian basement rock. This applies especially to the sandy claystone facies of the formation because it is similar in handspccimen with granitic saprolite. However sandy claystone and clay.stonc facies typically have kaolin spherites whereas deeply weathered granitic rock docs not contain kaolin spherites (Killigrcw & Glassford 1976). Furthermore. Westonia Formation can be distinguished from saprolite by generally being grey, the presence of stratification, conglomerate layers and sporadic well-rounded quartz pebbles. In addition, saprolite can be distinguished from the Westonia Formation by generally being white, the presence of quartz veins and their truncation at the unconformity between saprolite and Westonia Formation, and by palimpsest gneissic structures and granitic fabrics. In the Yeclirrie area the Westonia Formation has been previously mapped as Falconer and Nuendah landform — regolith systems (modified from land systems of Mabbutt el al. 1963) by Churchward (1977) and as deepi) weathered rock, silcrelc-siliceous rock with angular quartz grains, and sandstone, siltsione. claystone and conglomerate by Bunting and Williams ( 1979). In the Kalgoorlie 1:250 000 sheet area it has been mapped and described as Old Alluvium (Kriewaldt 1969. p. 22-31). Throughout the Yilgarn Block it has been referred to as saprolite derived alluvial sediment (Killigrew &. Glassford 1976). Stratified and kaolin spherite-rich sandy claystone, designated here as Westonia Formation, has been incorrectly identified in the Mcrredin area (Brewer & Beitenay 1973) and in the Westonia area (Webster & Mann 1984) as the mottled and pallid zones of in situ weathered Precambrian basement granitic rock. Mulline Formation The Mulline Formation is the name proposed for a unit of reddish brown to yellowish brown sandy lalcritic to bauxilic duricrust which overlies saprolite and Westonia Formation and typically is overlain by the Gibson Formation (Tables 1. 3). Derivation of name. Named after the abandoned gold mining town of Mulline. lat. 29° 47'S, long. 120° 31'E, Menzics 1:250 000 map sheet. Type section. The designated type section is the face of a breakaway, w'cst of a small playa, lat. 29° 47'S. long. 120° 57'E. Menzies 1:250 000 map sheet (Table 3: Figs 3, Tr.3); 4. TS3). Di.strihiaion. The Mulline Formation is poorly exposed and typically covered by sand of the Gibson Formation throughout much of the Yeclirrie area, including the continental divide (Figs 3. 4, 5 ). Outside the Yeclirrie area outcrop occurs as lateritic gravel plains (Stace et al. 1968) or at the top and in the face of breakaways. The formation occurs throughout the northern interfluve plateau and the southern valley side of the Yeclirrie valley. Surface features. Where the Mulline Formation crops out it has a relict surface. The outcrop is often characterized at a small to fine scale by an irregular morphology and patchy veneers of hard, pisolitic to nodular sandy gravel. (Icomcuy and dimensions. The formation is typically shcct-like and usually less than I m thick over areas of a few lens of square metres to many tens of square kilometres outside the study area. Us geometry is inferred by correlating and extrapolating the discontinuous outcrops. Lithic characteristics. The Mulline Formation consists of reddish to yellowish brown sandy lateritic to bauxitic duricrust materials. It locally exhitits crude bedding, but generally it lacks bedding and is typically characterized by a pisolitic. nodular, plaiv or labyrinthoid structure (Fig. 4). Pisolites, nodules and plates consist of a nucleus (ranging from a few mm to many cm in diameter) and a thin (c. 0. 125 to 5 mm) laminated envelope. The pisolite nucleus typically consists of a framework of quartz or quartz and kaolin spherite sand supported in a silt-clay 8 TS 1 TS 3 TS 5 TS 7 TS 2 TS 4 WIRRAWAY FORMATION 3 TS 6 (— 0 ' — 1m Figure 4.— Type section (TS) stratigraphic sections for the: Westonia Formation (TSl); Mulline Formation (TS2); Menzies Formation (TS3V Gibson Forma- tion (TS4): Wirraway Formation (TS5); Nuendah Formation (TS6); and Darlot Formation (TS7). See Fig. 1 for location. Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. Table 3 General description of lithology. Mulline Formation type section. Depth (m) Description Rock unit 0-0.5 Clayey sand; reddish yellow Gibson Formation 0.5-1.75 Sandy lalerite: yellowish brown, pisolitic; pisolites form a framework supported fabric: pisolites have a nudeu.s of fine skewed, moderately well to poorly sorted, fine to very' fine quartz and kaolin spherile sand supported in a silt and clay matrix of gcoihilc. haematite, kaolin and quartz; pisolites have a thin laminaied envelope or pellicle of sill and clay sized goethite. haematite, kaolin and quartz. Mulline Formation 1.75-3.1 Claystone; light grey, colour mottled. Westonia Formation 3. 1-3.5 + Gneissic saprolite Archaean Basement sized matrix of iron and aluminium minerals {typically goethite. haematite, kaolin and gibbsite) and quartz. Envelopes generally consist of similar sill-clay sized iron and aluminium minerals and quartz. The mler-pisoliie/nodule/platc domain may consist of void space and/or sandy sill-clay or sill-clayey sands. Labyrinthoid structure consists of a tortuous arrangement of vermiform to vesicular voids and labyrinthoid walls. The walls are similar to the nuclei of pisolites in that they consist of quartz and kaolin spheritc sand with, or supported in, a sill-clay sized matrix of iron and aluminium minerals and quartz and the walls may exhibit envelope veneers. Framework quartz and kaolin spherile sand of pisolites and nodules from the type section constitute 15 to 20% by weight of the rock and are fine skewed, moderately well to poorly sorted, fine to very fine sand. The mean size of the size fraction greater than 0.045 mm is 0.078 mm or very fine sand. Mulline Formation kaolin spheritesand matrix sill-clay arc pigmented red and yellow by haematite and goethite. This contrasts with the kaolin spherilcs and most of the silt-clay of the Westonia Formation, w’hich arc essentially free of haematite and goethite. Fossils. The formation in places contains trace fossils which are similar to those previously described in the Westonia Formation. The fossils have also been noted by K.riewa!dl(l967. 1969, 1970) in the same unit, designated here as the Mulline Formation (Fig. 3) throughout much of the Menzies and Kalgoorlie 1:250 000 map areas. Stratigraphic relationships. The Mulline Formation has an abrupt to gradational contact whith underlying Westonia Formation and an abruptly gradational contact with overlying Gibson Formation. Both upper and lower contacts are low angled and near-planar (Figs 3, 4). Discussion. The Mulline Formation can be distinguished from other units mainly by its lateritic or bauxitic duricrust nature; this includes pisolitic. nodular, platy, and labyrinthoid structures; iron and aluminium minerals (c.g. goethite, haematite, kaolin, gibbsite); and silt-clay sized matrix which supports a framework of quartz or quartz and kaolin spherite sand. The unit designated Mulline Formation has been mapped previously in the Yeelirrie area as Falconer and Nuendah landform-regoiilh systems by Churchward (1977). Teniary laleritc (massive and pisolitic hmonite deposits and cemented ironstone gravel) by Bunting and Williams (1979). and described or mapped in the Yeelirrie and surrounding areas as. sandy lalerite or duricrust. and as variously altered, wholly or partly desert aeolian sediment (Killigrew and Glassford 1976, Glassford & Killigrew' 1979. and Glassford 1980). Menzies Formation The Menzies Formation is the name proposed for a unit of red sandy clay and sandy clayslone which encloses lesser amounts of calcite-cemented sandy clay, sepiolite-ccmented mudstone, mudstone, laminated calcitc and clayey sand. The formation typically overlies granitic rock and is overlain by the Gibson Formation. (Tables 1. 4). There are three distinct and spatially inter-related lithologies in the formation which are given member Table 4 General description of lithology, Menzies Formation type section, Depth (m) Description Rock unit 0-0.55 Sandy clay; light to medium reddish brown, massive, matrix .supported, unimodal, fine skewed, moderately sorted, fine, quartz and kaolin spherile sand with a silt and clay matrix of calciie, quartz and kaolin; scattered ofT white calcrete pisolites and rhizoconcrelions, Yeelirrie Member of the Menzies Formation 0.55-0.65 Sandy gypsne; while. •Darlot Formation 0.65-0.75 Laminar calcrete breccia: off white to light brown, angular gravels of laminar calcrete. 0.75-2.50 Sandy clay; light to medium reddish brown, massive, matrix supported unimodal. fine skewed, moderately sorted, fine quartz and kaolin spherile sand with a silt and clay matrix of calciie. quart/ and kaolin; scattered calciie pisolilc.s and rhizoconcretion.s. Yeelirrie Member of the Menzies Formation 2.5-4.S Calcrete: reddish brown and white: red sandy clayslone breccia supported in crypiocrystalline calciie: red sandy clayslone breccia domain.s have a matrix supported fabric: framework grams are unimodal. fine skewed, moderately sorted, quartz, and kaolin spheritc sand; matrix sill and clay is mainly kaolin, minor carnotite: calcrete domains are crypiocrystalline calciie with scattered quartz and kaolin sand; quartz grains in calcrete have ragged edges. 4.5-5. 6 Sepiolilic clayslone; dark grey and while, kaolin mudstone with veins of sepiolite; minor carnotite. Volpress Member of the Menzies Formation 5.6- S.7 5. 7- 6.1 Clayey sand; light reddish brown, unimodal. framework supported, moderately sorted, coarse, quartz sand; soft, unconsolidated. Mudstone; red. vesicular and massive kaolin mudstone; minor carnotite; brittle, subconchoidal fracture. Bungarra Member of the Menzies Formation 6.1-7. 0+ Sandy clayslone; reddish brown, massive, matrix supported fabric; framework grains unimodal. fine skewed, moderately sorted, fine, quartz and kaolin spherite sand. Menzies Formation 10 • • • • 1/2 • • • • WESTONIA AND MULLINE FORMATIONS 5 MENZIES FORMATION 6 . . 4. . GIBSON FORMATION 7 NUENDAH FORMATION DARLOT FORMATION Figure 5. — Map showing distribution of formations in the upper central Yeelirrie valley. See Fig. 1 for locations. Journal of the Royal Society of Western Australia, Vol. 70. Part 1. 1987. status. The members are: Bungarra Member: Voipress Member; and Yeelirrie Member and they are described later. Derivation of name. Named after Menzies townsite. lat. 29°41'S, long. 12r2'E. Menzies 1:250 000 sheet. Type section. The designated type section is a uranium exploration trench, termed by Western Mining Corporation, number 2 slot or bottle-slot lat. 27°1TS. long. 1 19*55'E. Sandstone 1:250 000 sheet (Table 4: Figs 4.TS3;6A). Distribution. The Menzies Formation has been encountered in costeans (Western Mining Corporation’s slots 1 and 2), drill holes, trenches and creek incisions throughout valley side and valley floor landsurface positions of the Yeelirrie area. Outcrop is poor and generally occurs as small patches along the a.xis of the Yeelirrie valle> and along the floors and sides of tributary incisions (Fig. 5). Surface features. Red sandy clay and sandy claystone generally forms the upper part of the formation in valley-side gully locations of the Yeelirrie valley and it usually has a flat to gullied erosional surface. The calcite'-ceniented portion of the formation usually occurs along the axis of the Yeelirrie valley and has a broad hummocky erosional surface, locally with a veneer of gravelly calcrete and calcareous sandy silt-clay. Geometry and dimensions. In the Yeelirrie area the Menzies Formation forms a very broad basin-shaped valley fill. The lower boundary is concealed and has only been noted at a depth of about 18 m (Fig. 7. Site 175). Seismic contour and drilling data suggest the lower boundary is a broad valley form with the thickness of the formation increasing down valley (Australian Groundwater Consultants 1972). Lithic characteristics. The Menzies Formation consists mainly of red sandy clay to red sandy claystone and locally red clayey sand and sandstone which are laterally and vertically interrelated in that they arc inierbedded and intcrgradational over a few metres. These main lithologies are also interlaycred with other diagenelic and allochthonous sediment types such as (Fig. 7): { I ) calcitic sandy clay to calcitc with minor dolomite-cemented red sandy claystone, (2) sepiolite-ccmented kaolin mudstone, (3) red kaolin mudstone. (4) laminar calcitc and (5) very coarse to coarse clayey sand (Fig. 4.TS3): these latter lithologic intercalations however arc minor components within the red sandy clay and sandy claystone which form the bulk of the formation. The red sandy clay and sandy claystone is massive to weakly stratified. Stratification is most apparent where occasional thin calcitc laminae occur. The sediment is composed of quartz, kaolin spherites (pigmented with goethite and haematite) and rare feldspar and sesquioxide (lateritic) framework grains with a goethite and haematite pigmented kaolin silt-clay matrix. Monocrystalline quartz grains predominate, although locally, polycryslalline quartz grains occur in minor amounts. 1'hc quartz grains generally have a haematite and goethite pigmented coating of kaolin. The matrix often has a curv'ilincar laminated structure consistent with flow lines and meniscus lines. These features indicate that much of the matrix is a cement formed after the framework grains were deposited. The fraction of the red sandy claystone and clayey sandstone greater than 0.045 mm is 20 to 80% sand by weight. The sand is bimodal to very' poorly unimodal, strongly fine skewed to near-symmetrical, moderate to poorly sorted, medium to fine sand, in places ranging from coarse to very fine sand. Tossil.s. .Apart from possible algal filaments in the Bungarra Member the formation appears to be devoid of fossils. Stratigraphic relationships. The Menzies Formation has a sharp contact with underlying granitic rock and is unconformably overlain, usually with a sharp contact, by the Gibson. Wirraway and Nuendah formations (Fig. 7). It tends to be laterally equivalent geographically to, but generally docs not overlie the Mullinc Formation. This is because the Mullinc Formation is ty pically confined to upland plateaux and the Menzies Formation is best developed under major valley sides and bottoms. Where the Mullinc Formation has undergone reworking it may overlie the Menzies Formation (Fig. 8. Section 1 38). Bungarra Member of Menzies Formation. Named after Bungarra rockholc, lat. 27"2TS, long. I!9°36'E, Sandstone 1:250 000 sheet. The Bungarra Member is a massive red kaolin mudstone up to 1 m thick which in places has a thin lens of clayey coarse sand at upper levels (Fig. 7, section 1 56). It was’ encountered in two trenches excavated by Western Mining Corporation and in drill cores over a distance of more than 1 0 km. and at a depth of about I to 8 m. This distribution is probably not continuous. Distinguishing features include: tabular shape with approximately straight and parallel upper and lower boundaries: massive structure with scattered millimetre-sized vugs; brittle with a sLib-conchoidal fracture; “mudstone" fabric; red colour and dominantly kaolin clay composition with minor to trace amounts of silt to fine sand sized quartz; moderate amounts of carnotite as vug linings; 0.02% organic carbon: and a sparse network of dark fibres which may be fossilised algal filaments. The Bungarra Member has a sharp near-horizontal contact with underlying and overlying red sandy clay and sandy claystone portions of the Menzies Formation, and in places underlies sepiolitic mudstone of the Voipress Member. Voipress Member of Menzies Formation. Named after Voipress Well. lat.'27°34'S, long, 120°2TE, Sir Samuel 1:250 000 sheet. The Voipress member is a black to grey and white mottled and veined sepiolitic mudstone (Fig. 4.TS3). It is characterised by: tabular to lens to pod shape; •‘mudstone" fabric with trace amounts of silt to fine sand sized quartz; white to black mottled appearance: sepiolitic kaolin composition with white anastomosing veins and blebs of scpiolitc; minor amounts of carnotite; traces of smectite; and 0.12 to 0.36% organic carbon. There is a lower sharp straight contact with red mudstone of the Bungarra Member and a discordant contact with the overlying calcite-cemenled red sandy day and sandy claystone facies of the Yeelirrie Member. The upper contact is gradational and undulating. Yeelirrie Member of the Menzies Formation. Named after Yeelirrie homestead, lat. 27°20'S, long. 120°14'E, Sir Samuel 1 :250 000. 12 Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. The Yeclirrie Member is up to 5 m thick and crops out intermittently as broad mounds and depressions along the bottom of the Yeclirrie valley for over 100 km (Fig. 5). It forms thick lenses to pods tens of metres in diameter. In places pods exhibit a crude domal or arcuate structure which is roughly parallel with their dome surface form and similar to the caliche pscudo-anticlincs of Jennings & Sweeting (1961 ). This member consists of live lithofacies: (a) white and red calciiic sandy claystone breccia; (b) massive white calcitc: (c) massive to cavernous, white and grey pods of calcitc and dolomite; (d) laminar calcite sheets and brcccioid clasts of laminar calcite; and (e) pisolitic to nodular to rhizoconcrelionary calcite supported in sandy clay (Fig. 4.TS.3). The white and red calcitic sandy claystone breccia facies forms a transitional zone between red sandy claystone and massive calcite or calcrete. The massive to cavernous, white and grey pods of calcitc and dolomite form a zone within the red calcitic sandy claystone^ breccia. The lamellar calcite sheets and breccioid clasts of lamellar calcitc plus pisolitic to rhizoconcretionary calcitc in sandy clay lend to overlie the other facies. Minor to trace amounts of carnotitc occurs in association with the calcite and dolomite domains of all facies. Following the digestion of carbonates in HCl. up to 15% by weight of greater than 0.045 mm quartz and kaolin spheriie grains remain. This residue is typically poorly unirnodal, fine skewed, moderately sorted, fine sand. The Yeclirrie Member has a broad gradational lateral contact with red sandy claystone and an irregular discordant contact with the underlying Volpress Member. The Yeclirrie Member is unconformably overlain by the Gibson. Wirraway. Nuendah and Darlot Formations or. in places along the axis of the Yeclirrie valley, it forms the contemporary landsurface. Discussion. The red sandy clay and sandy claystone facies of the Men/ies Formation has a varied provenance. Monocrystalline quartz, polycryslallinc quartz and feldspar indicate contributions from granitic rock, saprolite. metamorphic rock and the Westonia Formation. Kaolin spheriics and laterite clasts indicate contributions from laterite of the Mullinc Formation. Much of the matrix material of the red sandy clay and sandy claystone facies is a cement of kaolin, gocthile and haematite wJiich formed after the framework grains were deposited. This host red sandy clay and sandy claystone has been locally overprinted by calcitc thereby forming the Yeclirrie Member. The red .sandy clay and sandy claystone facies of the Menzies Formation can be distinguished from the Westonia Formation by its redness, goethite and haematite pigmented kaolin spheriics and matrix silt-clay. The matrix material breaks with an uneven fracture rather than a flint-clay sub-conchoidal fracture typical of the Westonia Formation, The red sand> clay and sandy claystone facies may also be superficially confused with the Wiluna Hardpan of Bellenay & Churchward (1974). However at its type section ( !at. 24°3'vS. long. 1I9“34'E. near Bulloo Downs in the Bangcmall Basin, c. 370 km NNW of Yeclirrie) the Wiluna Hardpan is a conglomerate wMth pebbles of laterilic duricrusl. quartzite, silcrelc and shale supported in a red sandy cla> matrix. Thus the Menzies Formation is not conglomeratic and can be distinguished from the Wiluna Hardpan which is conglomeratic. Furthermore the different lithic nature of the Wiluna Hardpan, as defined by Bcttenay & Churchward (1974) at its type section reflects its location in the Bangcmall Basin; in contrast the Menzies Formation type section is located in the Yilgarn Block and reflects that province. The red sandy clay and sandy claystone facies in the Yeclirrie area has been referred to previously as hardpan (Tcaklc 1936, 1950: Mabbutt el al. 1963). Wiluna Hardpan (Beilcnax Sc Churchward 1974). alluvium (Haveraft 1976). mainly altered desert aeolian valley fill (Glassford )98()) and as alluvial/fluvial/colluvial/acolian channel fill (Arakel & McConchic 1982). The Yeclirrie Member has been referred to as; calcrete (Sofoulis 1963. Sanders 1974, Haycrafl 1976. Arakel & McConchie 1 982): valley or groundwater calcrete (Carl isle etal. 1978, Mann & Horwitz 1979); calcrclcd drainage lines (Churchward 1 977): and calcitc and dolomite brccciated. cemented and replaced, desert aeolian valley fill (Glassford 1980). 'I'hc Volpress Member has been referred to as transition calcrete (Haycraft 1976), altered playa-lakc sediment (Glassford 1980) and mottled calcrete (.Arakel & McConchic 1982). The Bungarra Member has been referred to previously as altered playa and playa input fan sediment (Glassford 1980). Gibson Formation Gibson Formation is the name proposed for a unit which forms sand sheets and linear dunes. It is massive to locally weakly stratified red through reddish yellow to yellow and in places w'hite clayey sand and sand. The formation typically overlies the Mullinc and Menzies Formations (Tables 1.5). Derivation oj name. Named after the Gibson Desert the western margin of which includes the Yeclirrie area. Type section. The designated type section is the face of a quarry in a linear dune on the south side of the Agnew to Sandstone road and 1 1 km west of the .Agnew to Wiluna road. lat. 27'’58'S, long. 120"24'E, Sir Samuel 1:250 000 sheet (Table 5: Figs 4. TS5;6B). Distribution. The Gibson Formation is areally the most dominant land surface unit throughout the area. It occurs as a patchwork of large scale sand sheets on interfluve plateaux, valley side plains and on the continental divide between westerly and easterly sloping major valley systems (Figs 5; 6A.B;8). Surface features. The surface of the Gibson Formation has four major expressions in the Yeclirrie area: relict spinifex covered sand flats; relict spinifex covered linear dunes; erosional . Icc/cw-covered sand flats; and crosional and dcpositional dendritic to braided shallow channels. Fable 5 General description of lithology, Gibson Formation type section. Depth (m) Description Rock unit 0-5.0 Sand: yellowish red to red. massive, framework supported: from top to bottom grades uniformly from unirnodal to poorly unimodal and from line to more One skewed, and from well to moderately well sorted, and from fine to medium quart/ and kaolin sphcrite sand. 5.0-6.5 Sand, slightly clayey; red. massive to faintly slraiilk’d. framework supported, line skewed, moderately .soricd. medium sand: courser sand consists of quart/, liner sand consists of quart/ and kaolin spheriics. Gibson Formation 6.5-7.0 Sandy laterite: brownish red. Mullinc Formation 13 Journal of the Royal Society of Western Australia, Vol. 70. Part I, 1987. Figure 6. — Geomorphic and stratigraphic setting for the respective type and supplementary sections. A. Regional scale schematic section of the Yeelirrie valley showing location of smaller scale settings or sections. B, C, D. E. F, G. Medium scale geomorphic and stratigraphic settings for type sections of Fig. 4. The surface of linear dunes is generally loose sand, however the surface of interdunes and spinifex covered sand sheets generally consists of a thin {c. < 1 cm) coherent crust overlain by a thin {c. < 1 cm) veneer of loose coarse sand. The coherent crust is formed by the packing of fines between larger grains, probably by rain-drop impact, and the binding action of Chara sp. filaments. Geometry and dimensions. The Gibson Formation is a sand sheet w h ich has been reworked i nio few to numerous linear dunes. The sand sheet in the Yeelirrie area is typically about 1 to 4 m thick and the linear sand dunes are generally about 5 to 10 m high (Figs 4;6b). Linear dunes are 0.5 to 3.5 km long, and 0.25 to 2 km apart. Dune orientation on average is 1 29'’ or NW to SE and ranges from 100“ to 1 56^ Some dunes are symmetrical or asymmetreal in cross-section, others exhibit complex cross-sectional asymmetry. That is crest to mid-flanks may be symmetrical and lower flanks on the same dune may be asymmetrical and vice versa. Thus the dunes are termed linear rather than the genetic terms longitudinal or transverse. Lilhic characteristics. Sands of the Gibson Formation range from red to yellowish red to reddish yellow to yellow and in places white. Sand sheets and linear sand dunes of the formation are usually massive, but relatively rare very faint cross-stratification occurs in some wind-exposed quarry faces. The formation has two primary facies, a sand sheet facies (which includes interdune sand sheet) and a linear sand dune facies. Sand sheet facies typically consist of sand which is bimodal to poorly unimodal. fine skewed, moderately well 10 poorly sorted, coarse to fine sand with dust (silt-clay). The “coarse” mode ranges from very coarse to medium sand (2.0 to 0.25 mm) and the “fine” mode ranges from medium to ver>' fine sand (0.25 to 0.125 mm). Sand sheet facies have approximately 2 to 20% fines (less than 0.09 mm fraction). The sand-dune facies contain sand which is bimodal to unimodal, fine skewed, moderate to well sorted and medium to fine. Sand dune facies have approximately 0.5 to 8% fines (less than 0.09 mm fraction). 14 Journal of the Royal Society of Western Australia. Vol. 70, Part 1, 1987. All fades have two major framework grain types, quartz grains and kaolin spherites. Quartz grains have a characteristic coaling of haematite and goethite- pignienlcd (disordered) kaolin in addition to silt-sized quartz. Quartz sand may range from about 60 to over 90% and kaolin spherites range from a few per cent to over 30%. Kaolin spherites are best developed and most abundant in fine sand-sized material (0.25 to 0.125 mm) of sand sheet, interdune sand sheet and linear dune facies. The spherites are unimodal. fine skewed, well to moderately sorted fine sand. They arc extremely well rounded and pigmented red, reddish brown, reddish yellow or yellow by haematite and gocthiie. Kaolin spherites usually have a nucleus of pclletal to crudely oriented kaolin which is typically free of haematite and goethite and less commonly, quartz, opaque minerals or smaller spherites. The nucleus is encapsulated by a haematite and goethite pigmented oolitic kaolin envelope. Locally (e.g. some leeward dune flanks) sand to silt sized microcline may occur in minor amounts. The sill-clay fraction of sand sheet and sand dune facies usually consists of quartz, disordered kaolin, haematite, goethite and minor feldspar and anatase. Fossils. No fossils have been found in the formation. Stratigraphic relationships. The Gibson Formation overlies the Mullinc Formation and the Menzies Formation and in places is overlain by the Wirraway and Nuendah Formations. The lower boundary of the formation is sharp, flat to gently dipping and planar. The upper boundary is typically the present day land surface (Figs 3, 4. 6, 8). Discussion. The occurrence, size, shape, roundness, internal structure, colour and composition of kaolin spherites in the Gibson Formation are consistent with it being mainly derived from the Menzies, Mulline and Westonia Formations. The surface of the unit designated Gibson Formation has been mapped previously in the Yeelirrie area as: (1) Bullimorc land system, sand plain or aeolian sand and described as red sand consisting of reworked and residua! lateritic soils by Mabbutt ei af. (1963); (2) Quaternary aeolian deposits described as unconsolidated sheets and dunes of sand by Australian Groundwater Consultants (1972); (3) Bullimore landform-regolilh system (modified from Bullimorc land system of Mabbutt et ai (1963): (4) depositional sand plains of aeolian and tluviaiile deep sands, grits and clays by Churchward (1977); (5) Quaternary' aeolian deposits (Qps), red and yellow quartz sand in dunes and sheets; and (6) Quaternary colluvium and alluvium (Qpz). dark red to brown clay to sandy loam by Bunting and Williams (1979): (7) spinifex sand plain with longitudinal dunes and acacia sand plain and described as relict desert aeolian sand sheet and dunes by Glassford (1980k and (8) aeolian sand plains with few or weak dunes by Beard (1984). Wirraway Formation The Wirraway Formation is the name proposed for a sheet to dune unit of massive to stratified, mainly red to reddish yellow quartz sand to quartz clayey sand. The formation typically overlies the Menzies and Gibson Formations and intcrfingcrs with the Nuendah and Darlot Formations (Tables 1,6). Derivation of name. Named after Wirraway Bore, lat. IT 5'S, long. 1 19°45'E, Sandstone 1:250 000 sheet. Type section. The designated type section is a low, broad, linear dune south of Lake Darlot. lat. 27°56'S, long. 12T 13' E, Sir Samuel 1:250 000 sheet Table 6; Figs 4. TS5; 6A,C,D). Distribution. The Wirraway Formation occurs disconlinuously along the axis of the Yeelirrie valley. It occurs near and between playas (extra-playa) as low broad linear channel-border dunes, around and on the edges of playas and pans (playa-bordcr) as pan or playa-contiguous sheets and sinuous to lunate dunes, and within playas (intra-playa) as sheets and dunes (Figs 9.10). Surface features. The surface is usually relict to crosional and vegetated. It also may be bare of vegitation as a reworked or primary depositional surface with sand ripples produced by the wind. Geometry and dimensions. The Wirraway Formation occurs as thin sheets, low broad linear dunes and as sinuous to lunate dunes. It ranges from 1 to over 5 m thick (Figs 4; 6 A,C,D;9). Lithic characteristics. The Wirraway Formation is a sheet 10 dune unit which consists typically of masive to locally stratified, red to reddish yellow to yellow quartz sand to quartz clayey sand. Outside the study area it has scattered rhizoconcretions at depth. On the basis of geometry and location relative to playas it may be divided into facies (Table 7). Channel-border dune facies tend to be red to reddish brown whereas other facies tend to be yellowish red to reddish yellow because of goethite and haematite pigmented kaolin clay coatings on quartz sand grains. The formation is typically massive but some lunate and modern dune facies arc stratified. Overall. Wirraway Formation sand is positively skewed, moderately well to poorly sorted, locally very coarse but usually medium to fine quartz with 0.5 to 26% lines (Table 7). The crests of channel-border dunes are relatively coarser than the flanks. This is similar to some lunate dunes and contrasts with linear dunes of the Gibson Formation which have dune crests which are relatively finer than flanks. Fossils. Apart from rhizoconcretions at depth in channel-border dunes located outside the Yeelirrie area, no fossils have been obseiwed in the Wirraway Formation. Stratigraphic relationships. The Wirraway Formation overlies the Menzies and Gibson Formations with a sharp, near-planar contact and locally interfingcrs with the Darlot Formation (Figs 4:6A.C,D;9). Discussion. Apart from its different land surface position, geometry, grain size properties and stratigraphic relationships the Wirraway Formation can be distinguished from the Gibson Formation because the Gibson Formation typically has moderate amounts of Table 6 General de.scnption of lithology. Wirraway Formation type section. Depth (m) Description Rock unit 0-1.5 Sand; red. masive, framework supported. Wirraway unimodal, fine skewed, modcratciy to poorly sorted, medium quartz sand: fines (less than 0.09 mm) are 5.5% (top) to 6.8% (bottom). Formation 1. 5-2.0 + Sandy clayslone; reddish brown. Menzies Formation 15 A Wiluna ■ 175 156 ^ TS3 ^72 .176 Yeelirrie ■ Ol CO o> 126 • (25km east) ► TS4^ TS5-. N Legend for A 0 40km i 50km approx V =. 250H approx 126 Cainozoic 175 /cover 72 \156 ■'^6 0 20km approx 1 I V - 100H approx D 175 156 72 176 15 86 126 T ■ T T 15 16- 17- 18 3a< t_T _ T _ J_T __ T_ T_T _ T _ T_T _ T _ T ’ T + + rO Lim 20 - • • • • ^6 ^5 /5 • • • • • • ^ * • . — . \ / T \ / T T _ . — \ \ / t ■ \ / / _T T_ T — 1 T T T 1 T T T 1 T T T I 1 T T T I 1 T I 1 jr . j_ . . I 3c 1 1 T T T — I I l T n I I 1 T T I I 1 T I 1 T T I 1 T I 1 T T I 1 T I 1 T T I 1 T I 1 T T I 1 T I 1 T T I 1 t 1 . _L . . I I 1 1 1 J_ . _ — ■ — I I I 1 1 1 1 _ T_ — ■ — I I I I 1 1 10- — — 10- — . — I I I 1 1 . . 13- -I 1 r -47- I I 1 15[ . — . -4>- I 14- I 1 . . 1R- MENZIES FORMATION t 4=Gibson Formation SnWirraway Formation 6:rNuendah Formation Figure 7. — Regional stratigraphy of the Menzies Formation in the Yeelirrie area. A,B. Location and geomorphic and stratigraphic settings of stratigraphic sec- tions. D. Stratigraphic sections. Note: The Menzies Formation also occurs at the base of TS5 (see Fig. 4). Journal of the Royal Society of Western Australia, Vol. 70. Part 1. 1987. Figure 8. — Regional stratigraphy of the Gibson Formation in the Yeelirrie area. A. Location of sections. B, C, D, E, F, G, H. Geomorphic and stratigraphic settings of stratigraphic sections. I. Stratigraphic sections. 17 Journal of the Royal Society of Western Australia. Vol. 70, Part 1, 1987. Wiluna 69 Yeelirrie 147,148 73,76 145 /TS7 iK 24,16,25 131,133,134,135,136 B Continental divide n r' E Lake Darlot 0 50km approx ‘ ■ V = 250H approx Legend for A 0 40km ! I i 69^/145 0 t •f] ' • -_/yV=30H -.UZ^ZTTi/ approx 50m approx. ^ Lunate playa-border sand dune NW 24 i p; / Linear channel-dune SE / 25 0 200 m approx V = 100H approx Selenothamnus SE 1 ^ •8 147 1 M/ \ V N. 1 '■ 0 100 m approx \ j V = 25H approx Sinuous playa-border sand dune 133 136 ISS 134 Samphire 'V V 200m approx. —I V = 40H approx Playa surface 147 148 7 73 r--v. ■ yj. 24 ^ J>0 > 0 > > > > > > > > > > 7a / A A A > > A A A A A > > r^TH— 7 — — / / / rr-i . ■ 145 69 76 / 7a 3 \ > > > —5 * • • • \ • • . A . — . • \ • • 3 16 25 5 131 133 7a 7 134 135 > > > > i> > > — 7a N. S. .7' > > > > > > 7a 7 = Darlot Formation 7a = Miranda Member 6 r Nuendah Formation 5 = Wirraway Formation 3 = Menzies Formation a r Precambrian basement > > 136 \5^ \ \ N . rO Lim Figure 9. — Regional stratigraphy of the Wirraway, Nuendah and Darlot Formations in the Yeelirrie area. A. Location of stratigraphic sections. B,C.D.E,F. Geomorphic and stratigraphic selitngs of stratigraphic sections. G. Stratigraphic sections. Optimally developed kaolin spherites whereas the Wirraway Formation typically has no kaolin spherites or very few iron-rich kaolin spherites and fragments of kaolin spherites. The surface of the unit designated Wirraway Formation has been mapped previously in the Yeelirrie area as: (1) Bullimore and Albany landform-rcgolith systems and described as aeolian and fluviatile deep sands, grits and clays and deep fluviatile and aeolian deposits respectively by Churchward {1977); (2) Quaternary aeolian deposits (Qrs), white to yellow quartz sand, red brown silty sand, in sheets and dunes marginal to sail lakes and calcrete by 18 Journal of the Royal Society of Western Australia, Vol. 70. Part 1, 1987. Table 7 General outline of grain size properties for facies of the Wirraway Formation. Grain size terminology after Folk (1974). Facies General outline of grain size properties Extra-playa Channel-border dunes Poorly unimodal to unimodal, strongly fine to fine-skewed, moderately to poorly sorted, fine sand with 4 to 26% fines (<0.09 mm) Playa-border Sheets Poorly unimodal to unimodal, near-symmetrical, moderately to poorly sorted, medium to fine sand with 8 to 14% fines (<0.09 mm) Sinuous dunes Poorly unimodal to unimodal, strongly fine to fine-skewed, moderately well to moderately sorted, medium to fine sand with 3 to 7% fines (<0.09 mm) Lunate dunes Poorly unimodal to unimodal. strongly fine to coarse-skewed. moderately well to poorly sorted, very coarse to fine sand with 4 to 20% fines (<0.09 mm) Intra-playa Sheets Poorly unimodal to unimodal. near-symmetrical, moderately sorted fine sand with up to 20% fines (<0.09 mm) Dunes (modern) Poorly unimodal to unimodal. strongly fine-skewed to symmetrical, moderately well to moderately sorted, medium to fine sand with 0.5 to 3% fines (<0.09 mm) Bunting and Williams ( 1 979); and (3) channel-border and playa-border aeolian clayey sand and sand (Glassford 1980). Nuendah Formation The Nuendah Formation is the name proposed for pale brown gravels, .sands and clayey sands which occur along Precambrian basement ridge-footslopes. breakaway- fronts and dendritic tributary' drainage tracts of major valley sides. The formation typically overlies Precambrian basement and the Menzics and Gibson Formations (Tables 1,8). Derivation of name. Named after Nuendah, lat. 27°2'S. long. 120*’2I'E, Sir Samuel 1:250 000 sheet. Type section. The designated type section is the south bank of the Jones Creek, 47.5 km SE of Yeelirrie homestead where a telegraph line crosses Jones Creek, lat. Table 8 General description of lithology. Nuendah Formation type section. Depth (m) Description Rock unit 0-0.9 Sand: light brown, faintly stratified, framework supported, poorly unimodal. near symmetrical, poorly .sorted, medium, quartz sand. 0.9-1.75 Sand; light brown, faintly straufied. framework supported, poorly unimodal, fine skewed, coarse, quartz sand. 1.75-2.75 Gravelly sand; light brown, faintly stratified, framework supported, poorly unimodal. .strongly fine skewed, poorly sorted, coarse, quartz sand Neundah Formation 2.75-5.0 Sandy gravel; light brown, massive, poorly unimodal. near symmetrical, poorly sorted, granule quartz and lithoclast gravel. 5.0-6.0-r Sandy claystone; reddish brown. Menzies Formation 27“29'S, long. 120^^3 FE, Sir Samuel 1:250 000 sheet (Table 8; Figs 4,TS6:6A,E,F). One supplementary reference section west of the Yeelirrie to Community Bore road, lat. 27'^4'S. long. 1 20‘^8'E. Sir Samuel 1:250 000 sheet (Fig. 9, site 169) is designated to include a facies not evident in the type section. This supplementary section exposes light brown clayey sand 50 m from the base of the breakaways. Distribution. The Nuendah Formation occurs on valley sides of the Yeelirrie valley. At this scale it occurs as narrow bells along the base of NW to SE and west to east trending breakaways, along the footslopes of NNW trending Precambrian basement ridges and in dendritic tracts along tributary drainage lines which extend from breakaway-fronts and ridge-footslopes to major valley bottoms (Fig. 10). Surface features. Breakaway-front facies have relict dcpositional surfaces to locally modern depositional and erosinal surfaces. Ridge-footslope facies have relict and crosional surfaces. Dendritic tributary facies have modern dcpositional surfaces. Geometry and dimensiotn. The Nuendah Formation has a variable geometry'. It occurs at the base of breakaways as a thin ribbon-like fringe or incipient bajada up to a few metres thick, a few hundred metres wide and up to many kilmetres long. It occurs along the footslopes of Precambrian basement ridges as gullied fans and also extends as thin, braided to discontinuous veneers, a few millimetres to a few decimetres thick, along intermittent tributary drainage lines (Figs 6.A,E.F:9). Lithic characteristics. The Nuendah Formation contains the following facies: (1 ) coarse to fine sand: (2) gravel to fine sand; (3) medium to fine clayey sand, and (4) gravel to coarse sand. The coarse to fine sand facies occurs in ridge-footslope overbank locations. Along the footslopes drained by the Jones Creek it consists of two major beds. A basal upward fining graded bed of light brown, moderate to poorly sorted coarse quartz with minor amounts of basement lithoclast granule gravel to coarse quartz sand, and an upper, upward fining graded bed of light brown, coarse skewed, poorly sorted, medium to fine quartz sand. The gravel to fine sand facies occurs in channels draining ridges and dendritic tributary channels which drain breakaway-fronts and major valley sides. It consists of basement lithoclast and quartz gravels and sands. The haematite and goethite pigmented kaolin grain-coatings are generally less on overbank and channel sands when compared with similar coalings on Gibson Formation sands. The medium to fine clayey sand facies occurs along breakaway-fronts as bajada and pediment deposits. This facies is massive, light brown to light reddish brown, poorly sorted, medium to fine, clayey sand. It is composed of quartz and kaolin with minor kaolin spherites. The gravel to coarse sand facies occurs at the base of breakaways as a scattered pebble to granule float or talus over the medium to fine clayey sand facies and is derived from the breakaways. E'urlhcr from the breakaways the clayey sand is covered by a patchy , millimetre-thin veneer of while, moderate to poorly sorted, very coarse to coarse quartz sand. Fossils. No fossils have been found in the formation. 19 Journal of the Royal Society of Western Australia, Vol. 70. Part 1. 1987. Stratigraphic relationships. Along the front of breakaways the Nuendah Formation overlies granitic rock and interfingers downslopc with the Gibson Formation. Along the footslope of basement ridges it overlies the Menzies Formation. In upper tracts of tributary’ drainage lines it overlies the Gibson Formation. In lower tracts of tributaries it overlies the Menzies Formation and interfingers with the Wirraway Formation (Figs 4,TS6; 6A.E,F:9). The upper boundary of the Nuendah Formation is typically the modern land surface. The surface alternates intermittently from one dominated by deposition to one dominated by erosion. Thus the upper bounding surface is commonly devoid of vegetation. The facies of the Nuendah Formation are laterally equivalent because firstly they are still being formed at the present day land surface: secondly they are laterally intergradational in pit and outcrop profiles; and thirdly they all lend predominantly to overlie the Menzies and Gibson Formations. Discussion. Along breakaway-fronts the Nuendah Formation is derived mainly from Gibson and Weslonia Formations at the lop of breakaways, and from deepl\ weathered granitic rocks which comprise much of the lower pan of breakaways. Near basement ridge-fooislopes it is derived from basement rocks and the Wiluna Formation. Along the lower tracts of tributary drainage lines it is derived mainly from the Gibson and Wiluna Formations. The unit designated Nuendah Formation has been mapped in the Yeelirric area as: Nuendah. Marloo, Keith and Yakabindie landform — regolith systems by Churchw'ard (1977): Quaternary alluvium (Qpv), and colluvium (Qqc. Qpm) by Bunting & Williams (1979): and as footslope channel, overbank and fan alluvial deposits (Glassford 1980). Darlot Formation The Daiiol Formation is the name proposed for a unit of pan silt-clay, playa (“salt lake”) gypseous muds and playa border gypsum deposits w'hich overlie Precambrian basement the Menzies and Gibson Formations and interfingers with the Wirraway and Nuendah Formations (Tables 1,9). The Darlot Formation contains a lithologically distinct and mappable unit and it is proposed to name this unit the Miranda Member (see later). Derivation of name. Named after Lake Darlot. lai. IT 45'S, long. 12rE to lat. 27M5'S, long. I2l°30'E, Sir Samuel 1:250 000 sheet. Type Section. The designated type section is a NE facing escarpment in an island within Lake Miranda, lat. 27° 40'S, long. 1 20°33'E. Sir Samuel 1 :250 000 sheet (Table 9; Figs 4.TS7;6A.E.G). Distribution. The Darlot Formation occurs intermittently along the axis of the Yeelirrie valley as a discontinuous series of foci or sumps for surface and subsurface drainage. It extends down valley as a chain of pan, playa and playa-border deposits (Figs 4,6.9,10). Surface features. All lilhofacies have ancient buried and relict surfaces in addition to modern dcpositional surfaces. Modern mud Oats and sand-dune surfaces have no vegetation. Relict gypsum surfaces have a very sparse to negligible vegetation typically Selenothamnus sp.. Table 9 General description of lithology. Darlot Formation type section. Depth (m) Description Rock unit 0-0.01 Mudstone; white, massive, hard, sill and clay sized gypsum. 0.01-1.25 Sandy sill-clay; white, soft, powden'. massive, silt and clay gypsum with minor unimodal. fine skewed, well sorted, very fine, quartz sand. 1.25-1.26 Crystalline gypsum; while to light brown. Miranda hard, massive. Member of the Darlot Formation 1.26-2.0 Sandy gypsum; while to light brown, poorly consolidated. 2.0-2.01 Crystalline gypsum, while to light brown, hard massive. 2.01-3.1 Sandy gypsum, white lo light brown, poorly consolidaied. 3.1-3.45 Sandy gypsum; white lo light brown, cross-stratified quartz and gypsum sand. 3.45-3.46 Crystalline gypsum; light brown, hard. 3.46-4.25 Crystalline gypsum; white to greenish grey, hypidiomorphic gyp.sum. 4.25-5.0 Crystalline gypsum; pink to red. hypidiomorplVic gypsum. 5. 0-5. 6 Mud; red masivo gvpseous kaolin mud with gypsum ro.scttcs. 5. 6-7.0 Concealed section. Formation 7.0-8.0 + Gypseous mud; reddish brown gypseous kaolin mud. .-irthrocnemum sp. and related genera whilst relict sand-dune surfaces have a variety of grasses, scattered shrubs and trees (Beard 1976). Geometry and dimensions. The formation varies markedly in geometry and thickness. It occurs as discrete tabular to lenticular sheets and ribbons, discrete circular to elongate to irregular basins, or as irregular to sinuous to lunate hills. It ranges from less than I m thick (e.g. small clay pans)' to 7 m thick at the type section and to perhaps tens of metres thick (e.g. large playas). Lithic characteristics. The Darlot Formation has the following facies: (a) gypseous mud; (b) white quartz sand: and (c) a variel\ of gypsum deposits, which will be described under the Miranda Member (Figs 4.TS7;9). Gypseous mud facies occurs as modern playa mud flats at the surface. It ranges from red to reddish brown to locally grey, is massive to flat bedded and laritinatcd and ranges from gypseous kaolin mud to kaolinitic gypsum mud. usually with up to 5% \cr>' tine sand lo silt sized quartz. Near the water table this facies generally consists of large ciystals of authigcnic euhedral gypsum, often in rosettes, with moderate to minor kaolin mud matrix. Relict equivalents of this facies may be either buried with little alteration, or truncated with the upper gypseous kaolin mud removed to leave underlying kaolinitic ciystalline gypsum. Playa deposits arc commonly buried under sheets and dunes of gypsum sill-clay and dunes of gypseous quartz sand and quartzose-gypsum sand. White quartz sand facies occur as shoestring beach deposits around the margins of playa mud flats. It varies from a few millmetres to several decimetres thick and from a few ccniimclres to a few metres wide. The sand commonly contains loose plant debris, algal filaments in patchy mats and sometimes bivalve and Cuxiella shells. Fossils. A few Coxielia shells are locally buried in playa-border dunes. 20 PRECAMBRIAN BASEMENT GIBSON FORMATION a 4 7 WESTONIA AND MULLINE FORMATIONS 1/2 ■ 5 /. WIRRAWAY FORMATION ///^// wy/. 3 WILUNA FORMATION • • • • . 6 . • • • • NUENDAH FORMATION 6/4 DARLOT Breakaways FORMATION MIRANDA MEMBER Dendritic veneers of 6 over 4 1 N 5km I Figure 10. — Map showing distribution of formations in the lower central Yeelirrie valley. See Fig. 1 for location. Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. Stratigraphic relationships. The Darlot Formation occurs in the lowest part of the landsurface and therefore its lower boundary is nearly always concealed. However coslean and pit excavations indicate that occasionally, clay pans of the Darlot Formation develop within, and therefore overlie the Gibson and Wirraway Formations, in addition to the Menzies Formation and* Precambrian basement, with a sharp straight contact (Fig. 9). Miranda Member of Darlot Formation. This unit is named after Lake Miranda, lat. 27®40'S, long. 120°33'E. Sir Samuel 1:250 000 sheet. The Miranda Member consists of sheets and hills of gypsum, over 5 m thick at the type section (Fig. 4.TS7), The unit interfingers with relict play muds and also channel-border dunes of the Wirraway Formation. At the type section it consists of three main facies: (a) gypsum sand and sandstone; (b) crystalline gypsum; and (c) gypsum sill-clay. Gypsum sand and sandstone facies occurs as sheets and dunes ovcrlving and marginal to playa flats. It is loose to weakly lithifled. crudely stratified and consists of brownish to off-white gypsum, and minor to moderate amounts of quartz. The quartz is essentially clean, that is, it is white with no goethite or haematite pigmented kaolin clay coatings. Crystalline gypsum facies consists of tightly-fitted crystals of idiotopic gypsum. The primary' gypsum has probable been modified by ground-water precipitation of secondare- gypsum. Gypsum silt-clay facies occurs as dunes and sheets marginal to modern playas or completely covering former playa mud flats. It is nearly evere^where massie^e. commonly while, and in places brownish white to grey. When dr>f the gypsum is a dusty powder. With increasing moisture content it grades to a soft plasticine-like consistency. This facies is commonly vegetated by Arthrocneminn and related samphire genera plus the peculiar candelabrum-shaped Selenothamnus helmsii (Beard 1976). Discussion. The Darlot Formation has a varied provenance. Sedimenlaiy materials have been derived from both clastic and soluble components of Precambrian basement rocks in addition to all the previously described formations. Furthermore, the playa facies and playa-border facies have both acted intermittently as source materials for each other. However playa facies appear to be the dominant source for playa margin deposits, whereas the latter facies appear to be a minor source for playa facies. Table 10 Summary of main lithology for Cainozoic lilhoslraligraphic units of the Yeelirrie area. ’ 7 6 5 4 3 T Name Main lithology Darlot Formation Gypseous sands and muds Nuendah Formation Lilhoclasi and quartz gravel and sand and light brown clayey quartz sand Wirraway Formation Red quartz sand Gibson Formation Red to yellow quartz and kaolin spherile sand Menzies Formation Red sandy day/ciaysione Mulline Formation Reddish to yellowish brown, sandy lateritic to bauxitic pisolilic duricrust. Westonia Formation Grey sandy claystone (in places silicified) ^ Units arc listed from youngest at top to oldest at bottom. It should be noted that the Darlot, Nuendah and Wirraway Formations intcrfingcr with each other and to a small extent with the Gibson Formation. Also the Gibson Formation typically, unconformably overlies the Mulline and Menzies Formations and the Mulline and Menzies Formations typically, unconformably overlay the Westonia Formation which in turn typically, unconformably overlies saprolne which has developed in Precambrian basement. I he Mulline Formation includes pnmary and secondary (reworked) duncrust materials and in the Ycdirne area the Westoma Formation has been silicified. Discussion The stratigraphic details presented herein show that the Cainozoic cover of the Yeelirrie area consists of seven main lithologic units (Table 1 0): ( I ) Westonia Formation (mainly grey sandy claystone with silicification): (2) Mulline Formation (mainly reddish to yellowish brown sandy latcrite): (3) Menzies Formation (mainly red sandy clay and sandy claystone); (4) Gibson Formation (mainly reddish yellow sificidastic sand, that is composed of quartz and kaolin sphcrilcs); (5) Wirraway Formation {mainly red quartz sand); (6) Nuendah Formation (mainly gravel to gravelly sand to light brown clayey sand); and (7) Darlot Formation (mainly gypseous sands and muds). In terms of landsurface occurrence, geomorphic expression, surface features, geometr>'. structure, fabric, texture (e.g. modality, modal size, mean size, size sorting, size skewmess and fines), composition (c.g. mineralogy of grains, grain coatings), stratigraphic relationships and diagenetic/pcdogenctic overprints (Tabic 1) these formations arc distinctive and readily recognizable rock units. These units arc sufficiently distinctive and consistently distinguishable in the attributes outlined above to be mapped as separate discrete entities (Figs. 5,10), thereby satisfying the requirements for formation status (Hedberg 1976, North .American Commission on Stratigraphic Nomenclature 1983. Staines 1985). Kaolin spherites become pitted and fragmented and coatings ofelav on quartz grains are removed when these grains arc immersed in water. Consequently the presence of these grains in minor trace amounts in concert with their relative degree of preservation can be used to distinguish between sands of the Nuendah or Darlot Formations which have themselves been derived from the Gibson and Menzies Formations. The surface of the unit designated Darlot Formation has been mapped by previous authors as; Miranda landform — regolilh system and described as deep fluvialilc. lacustrine and aeolian deposits of saline clays and gypseous and calcareous earths by Churchward (1977); Quaternary lacustrine (Qra). lacustrine and alluvial (Qrm), aeolian (Qpk) deposits by Bunting & Williams (1979): and playa and associated sub-aqueous and aeolian deposits (Glassford 1980). The proposed lilhoslraligraphic framew^ork provides a relatively objective basis for more detailed future work into the nature and origin of the cover in the Yeelirrie area and also throughout other parts of the Yilgarn Block (Fig. 3). This is because the recognition and description of Hthostratigraphic units is based on observable non-gcnelic physical features (Hedberg 1976. p.3I). In contrast to most previous work, a priori assumptions of genesis or developmental hislor>-, essentially play no pari in the framework presented here. Consequently interpretations of origin for the units of this study have not been made. Such interpretations arc considered premature at present because of the paucity of any integrated and thorough documentation of the major genetically critical atlibutes (c.g. stratigraphy, geometry, structure, texture and composition) of these or any other Cainozoic deposits of the Yilgarn Block. Interpretations Journal of the Royal Society of Western Australia. Vol. 70. Pan 1. 1987. of origin will be presented at a later dale after all the genetically critical attributes have been described for the respective units. Acknowledgements: This paper is based on research initially carried out for a PhD dissertation in the Department of Soil Science and Plant Nutrition. University of Western Australia, with the financial support of a Commonwealth Postgraduate Rcseardt Award and subscquenliy additional private research. 1 thank Western Mining Corporation for logistic support and drill core: Australian Groundwater f'onsuitants Cor drill core samples; the Biggs family for Ihcir support at Ycdirric; L P Killigrew and M J B Kricwaldt for discussions and collaboration on one (M K) and many (L K) field trips; Dr .\ ECockbain, Dr J E Glover and M J B Kricwaldt for critically review'ing one draft and Dr V Semeniuk for discussions and critically reviewing many drafts of the manuscript; O Edwards for typing; and P V D Glassford. far' constant support and encouragement during field work through to manuscript preparation. 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Surveys and Mapping 1 980 Western Australia 1 :2 500 000 map. Dept Mines Penh. Teakle L J H 1936 The red and brown hardpan soils ofthe Acacia semi-desen scrub of Western Australia. J Dept Agric W Aust 13: 48-499. Teakle LJ H 1950 Red and brown hardpan soils of Western Australia. J Aust Inst Agric Set 16: 15-17. TingeyRJ 1 985 Sandstone. W. A. Geol Surv W Aust 1:250 000 Ser Explan Notes. van der Graaff W J E. Crowe R W A. Bunting J A & Jackson M J 1 979 Relict early Cainozoic drainages in arid Western .Australia. Zeit Geomorph 21; 379-400. Webster J G & Mann A W 1 984 The influence of climate, geomorphology and primary geology on the supergene migration of gold and silver. J Gcochem Exploration 22: 21-42. Williams 1 R 1975 Eastern Goldfields Province, in Geology of Western Australia. W ,Ausi Geol Survey Mem 2: 33-54. 24 Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. The Bridport Calcilutite V Semeniuk* & D .1 Searle- ^ 21 Glenmere Road. Warwick. WA 6024 ^ 108 Dalkeith Road, Nedlands, WA 6009 Manuscript received 14 April 1987; accepted 16 June 1987. Abstract The term Bridport Calcilutite is proposed for the sequence of Holocene sediments consisting predominantly of homogeneous to biolurbated carbonate mud and shelly carbonate mud. These sedi- ments occur in the contemporary marine environment and in the subsurface of the coastal zone of the Swan Coastal Plain. The sediments have formed as submarine basin deposits in deep water quiescent environments in proximity to seagrass banks. introduction The Holocene coastal zone of the Perth Basin presents a variable suite of facies and sedimentary deposition sys- tems that include aeolian sands, beach deposits, seagrass bank accumulations, deltas, estuarine accumulations and sediments of the nearshore shelf and coastal rocky reefs. Generally each of these depositional systems are distinct in their mode of sedimentation, and they generate sedi- ment accumulations which arc of sufficient size and ex- tent to be recognised as formations. Indeed, the various major types of Holocene coastal sediment accumulations already have been formally recognised as formations: e.g. the Safety Ba\ Sand, the Becher Sand, the Leschenault Formation (Passmore 1970; Playford et al. 1976; Semeniuk 1983; Semeniuk and Searlc 1985). Additional stratigraphic studies along the coastal and marine environments of southwestern .Australia have further delineated a suite of coastal sediments, that have distinct lithologic characteristics, which should be for- mally assigned formation status. It is the purpose of this paper therefore to establish a new formation, the Bridport Calcilutite, fora sequence of Holocene deep water marine carbonate muds and shelly muds in the coastal region of southwestern Australia. Data for this paper were obtained from coastal plain and submarine environments by reverse air core drilling, air-lift drilling and intact cores. Locations of drill sites that intersected the Bridport Calcilutite are shown in Fig. Regional Setting The study area is set along the coastal zone and nearshore marine environment of the Rottnest Shelf of southwestern Australia (Carrigy and Fairbridge 1954). This coastal system is comprised of Holocene sediments as well as crosional surfaces cut into Pleistocene ma- terials, and encompasses the seaward extremity of the Swan Coastal Plain, a Quaternary' sedimentary system of the Phancrozoic Perth Basin (Playford ei a!. 1976). The most important sites of sediment accumulation along the southwestern coast occur in the Cape Bouvard- Trigg Island sector of Searle and Semeniuk (1985). This sector is characterised by shore-parallel limestone ridges, in various stages of erosional degradation, with interven- ing deeper water marine depressions (Searle 1984). Holocene sedimentation, mainly restricted to loci termed accretionary cells (Searle 1984). has formed platforms, east-west oriented banks and subaerial promontories that span and segment the most eastern marine depression (the Cockburn-Warnbro Depression) to form a series of basins (Searle and Semeniuk 1985). The shallow water submarine banks and platforms are seagrass-covered and arc sites where seagrass-derived sediments (bioburbated to shelly quartzo-skeleial sand and muddy sand) accumulate to form deposits referred to as Becher Sand (Semeniuk and Searle 1985). In the deeper water marine basins, where depths are >18 m and sedi- ment floors are extensive, flat and featureless, there is ac- cumulation of carbonate mud and shelly mud. These car- bonate mud deposits have been described sedimcntologically by Carrigy (1956) and Searle (1984), and arc the lithotope of the Bridport Calcilutite, the sub- ject matter of this paper. Definition of the Bridport Calcilutite The Bridport Calcilutite is the formation name pro- posed for the sequence of grey, structureless to bioturbated. calcareous (carbonate) mud with lesser shelly carbonate mud. The formation forms the floors and underlies modern (contemporary) deep water marine basins, and also occurs in the subsurface, typically under- lying the Becher Sand. The formation name is derived from Bridport Point, in the southern part of Warnbro 25 Figure 1. — A and B. Locality diagram and setting within the Perth Basin. C. Location of study area. D. Location of drill sites where Bridport Calcilulilc has been intersected. E. Stratigraphic cross-section showing extent, thickness and east-west geometry of the Bridport Calcilulite along a transect situated near Rockingham. Radiocarbon ages within the Bridport Calcilulite at the type section are samples GX 12904 and GX 12903; both have been corrected for Cl 3. Journal of the Royal Society of Western Australia. Vol. 70. Part 1. 1987. Sound, which is a basin where the Bridporl Calcilutite is accumulating. The lithologic term calcilutite is aptly ap- plied in that the proposed formation consists of cal- careous lutaceous sediment (Bates and Jackson 1980). Type Section: The core site on the west shore of Lake Richmond, in the Rockingham area, is designated as the type section (Fig. 1). Material from the core has been lodged with the Geological Survey of Western Australia. The sequence within the type section is described as follows: Top (Becher Sand): fine to very coarse grey carbonate/quarlz sand, locally shelly 10.5m Bridport Calcilutite: homogeneous, grey/fawn, car- bonate mud with seagrass fibre 6.0 m homogeneous, grey, carbonate mud with shell 0.5 m homogeneous, light grey, carbonate mud ... 3.0 m Base (Tamala Limestone): calcretcd aeolianite lime- stone 2.0 m Distribution: The Bridport Calcilutite has been inter- sected in numerous cores and its distribution, both con- temporaiA' and subsurface, is widespread (Fig. 1). Geometry and Thickness: The formation is up to 10 m thick under the coastal plain in the Rockingham area. Elsewhere the formation is generally 2-6 m thick. In lo- calities where it is contemporary', the unit forms a sheet- like to lens-like body on basin floors. In the subsurface where it has been buried by the Becher Sand, as in the Becher Point-Rockingham Plain area, it forms a seaward thickening wedge body, or a thick prism. Lithology: The dominant sediment in the formation is grey, structureless to bioturbated, calcium carbonate mud composed of clay-sized and silt-sized carbonate material. Locally there are layers with marine shells, layers of lami- nated calcareous mud, and horizons of seagrass fibre and seagrass peat. Stratigraphic relationships: The formation overlies the following units: 1. Tamala Limestone (sharp unconformable contact). 2. Cooloongup Sand (bioturbated to gradational un- conformable contact), 3. Mud of the Leschcnault Formation (bioturbated, gradational, conformable contact). The formation may be overlain by the bioturbated, grey sediments of the Becher Sand, and the contact is conform- able and mostly sharp. Age and fossils: The Bridport Calcilutite is wholly Holocene. Radiocarbon ages from shells in the unit are less than 7 000 C14 yrs BP (Fig. I). The Bridport Calcilutite is locally shelly and mollusc shells predomi- nate. Molluscs include Bittium granarium and Chlamys sp. with less common Clancidus Iplebejns. Cantharidus lepidiis, Cantharidus irisodontes. Ethminolia 'hitiliginea, Diala sp, Nassarius pauperatus, and Brachidontes ustulatus. Discussion The sediments referred here to the Bridport Calcilutite originally were considered part of the basal portion of the Becher Sand (see “unit of fawn coloured mud with seagrass fibre". Table 2 of Semcniuk and Searle 1985: “marine mud unit" in figure 2 of Semeniuk and Searle 1985: and “mud" in Figure 3 of Semcniuk and Searle 1986). How'ever, the extensive drilling in the Rockingham-Becher Plain area has shown that the dis- tinctive carbonate mud unit underlying the Becher Sand is up to 6 m thick, and that it is substantial enough in thickness and extent to be recognised as a separate forma- tion. Drilling elsewhere, such as at Preston and Whitfords-Quinns Rock area, also has shown that the for- mation is not restricted just to the Cape Bouvard-Trigg I. coastal sector. The occurrence of the unit has palaeo-enviromental im- plications. In the modern environment the formation is accumulating in quiescienl, protected, deep water marine basins such as Warnbro Sound and Cockburn Sound. The mud is derived from adjoining seagrass bank environ- ments where wave agitation and reworking entrains fine carbonate sediment into the water column. The sus- pended mud finds its way into the basins and settles out as a suspension deposit. Periodically, the substrates of the basin are inhabited by a mollusc fauna which contribute their remains to the sediment to form shell layers. The Bridport Calcilutite thus represents deposits of quiescent deep water marine basins that adjoin, or are protected by. seagrass bank environments. References Bates J A & Jackson R L 1980 Glossary of Geology (2nd Ed). AGl. Carrigy M A 1956 Organic sedimentalion in Warnbro Sound. Western Aus- tralia. J Sed Petrol 26: 228-239. Carrigy M A & Fairbridge R W 1954 Recent sedimentalion. physiography and structure of the continenilal shelves of Western Australia. J R Soc W Ausi 38: 65-95. Passmore J R 1970 Shallow coastal aquifers in the Rockingham District, Western Australia. WalerResearch Foundation Australia Bull ik Playford P E. Cockbain A E Lo^»’ G H 1976 Geology of the Perth Basin. Western Australia. Aust Gcol Surv Bull 124. ' Searle D J 1984 Sediment transport system. Perth Sector Rottnest Shelf, Western Australia. PhD thesis, Univ of WA. Searle DJ & Semcniuk V 1985 The natural sectors ofthc inner Rottnest Shelf coast adjoining the Swan Coastal Plain. J R Soc W Aust 67: 116-1 36. Semeniuk V 1983 The OLtariemar>' history and geological history of the Ausiralind-Leschcnault Inlet area. J R Soc W' Aust 66: 71-83. Semeniuk V & Searle D J 1985 The Becher Sand, a new stratigraphic unit for the Holocene of the Perth Basin. J R Soc W Aust 67: 109-115. Semeniuk V & Searle D J 1986 The Whitfords Cusp — its geomorphology stratigraphy and age structure. J R Soc W Aust 68: 29-36. 27 1 INSTRUCTIONS TO AUTHORS The Journal publishes (after refereeing) • papers dealing with original research done in Western Australia into any branch of the natural sciences; • papers concerning some biological or geological aspect of Western Australia; • authoritative overviews of any subject in the natural sciences, integrating research already largely published in the more specialized national or international journals, and Interpreting such studies with the general membership of the Society in mind; • analyses of controversial issues of great scientific moment in Western Australia. Prospective authors of papers in the last two categories should consult the Hon. Editor for further advice. 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JOURNAL OF THE ROYAL SOCIETY OF WESTERN AUSTRALIA CONTENTS VOLUME 70 PART 1 1987 Page Cainozoic stratigraphy of the Yeelirrie area, northeastern Yilgarn Block, 1 Western Australia D K Glassford The Bridport Calcilutite V Semeniuk & D J Searle 25 Edited by I Abbott & B Dell Registered by Australia Post — Publication No WBG 0351 No claim for non-receipt of the Journal will be entertained unless it is received within 12 months after publication of Part 4 ofeach Volume The Royal Society of Western Australia, Western Australian Museum, Perth 65716/7/87-700 WILLIAM BENBOW, Acting Government Printer. Western Australia VOLUME 70 PART 1