JOURNAL OF THE ROYAL SOCIETY OF WESTERN AUSTRALIA ISSN0035-922X Soyal #octpty of Hiestern Australia 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 J Dodd B A, M Sc, Ph D Hon Librarian M A Triffitt B A, ALAA Hon Editor I Abbott B Sc (Hons), Ph D Journal Manager J Backhouse M Sc, Ph D Members W A Cowling B Agric Sc (Hons), Ph D 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 the Royal Society of Western Australia, 70 (2), 1987, 29-34 Geochronology of the Mons Cupri Archaean Volcanic Centre, Pilbara block, Western Australia G C Sylvester' & J R Dc Laeier- ' Department of Geology. University of Western Australia. Nedlands WA. 6009. ^ School of Physics and Geosciences, Cunin University of Technology. Bentley W.A. 6102. Manuscript received June 1986; accepted December 1986 Abstract The results of Rb-Sr geochronology on four suites of felsic rocks from the vicinity of the Archaean Mons Cupri volcanic centre in the Pilbara Block of Western Australia are presented. The Caines Well Granite, which represents the foliated granitoid basement to the volcanic complex has a mctamorphic age ol 2 713 ± 53 Ma and an intial ratio of 0.7040 ± 0.0006 on a closclv fitted isochron. A primary age of approximately 3 000 Ma can be calculated using a single stage strontium evolution anaivsis for this granite. This age is in good agreement with other published data. The Mons Cupri Granite is a massive intrusive body and has an age of 2 366 2 60 Ma. which is significantly vounger than similar granitoids in the East Pilbara, The Mons Cupri Porphyry gives an age of 2 610 i 80 Ma whereas the Mount Brow n Rhyolite has an age of 2 331 ^ 42 Ma. These Rb-Sr ages represent updated events rather than the primary ages of the rock units. lntr a sequence of fclsic agglomerate containing thin intercalations of felsic lava and luff. The agglomerate is the host rock to the Mons Cupri copper deposit. Above the agglomerate finer pyroclastic rocks, luflaceous sand- stone and minor conglomerate marks the top of the Mons Cupri Volcanics (Hickman 1983). The Rushall Slate is defined by Hickman (1983). and consists of grey slate and phsllite. subordinate Hows of andesite and d’aciie. quartzite, and lenses of felsic tulT. The geologv of the Mons Cupri volcanic centre has been documented *bv Miller & Gair (1975) and Sylvester (1976). Figure 1 shows the volcanic centre geologv as in- terpreted b\ Svlvestcrl 1976). The oldest rocks in the area arc granilofds of the Caines WcW Granite, one of the large granitoid domes which are of granodiorile composition and arc commonly strongly foliated. For this study, samples w'crc collected from exposures in the Sherlock River. 35 km west of Mons Cupri. Resting unconformablv upon these granitoids in the vicinity of Mons Cupri. is a sequence of intermediate to felsic mctavolcanics. the Mons Cupri Volcanics. The lower units are largclv tuflaccous. although amygdaloidal Hows have been recorded and are mostly of rhyodaciic to rhvolitc composition, although some daciics and andesites arc present. This sequence has been intruded by feldspar porphyries of rhyolite composition. These have broken surface to produce agglomerates, and the Mons Cupri base metal deposit is associated with one such agglomcratic unit. The agglomerates are overlain by fclsic tuffs, rhyolitic and andesitic Hows, thin chert horizons and intercalated slates of the Rushall Slate. This sequence is overlain unconformablv by andesitic Hows and luffs of the Negri Volcanics. Intruding all of these rocks is a large plug of sphcrulitic rhyolite, the Mount Brown Rhyolite, which has produced the domal structure present in the area. Mafic intrusive rocks of the Millindina (omplex range in composition from peridolilc to granophyre. and arc wide- spread throughout the area, postdating the Mount Brown Rhyolite. The youngest Archaean rocks in the area arc subvolcanic adamellite imnisivcs which have been called the Mons C'upri Granilc by Sylvester ( 1976). A review of radiometric ages obtained for rock units within the Rilbara Block has been given by Dc Lacier (V a/. (1 98 1 a), and more recently b\ Blake & McNaughton (1984). Compsion & Arriens (1968) reported an age of approximalelv 3 940 Ma foracid lavas from Whim f reck, although Arnens (1975) stated that this age may need to be revised. However Fillon c/ a/. (1975). quoting a per- sonal communication from .Arriens. suggested that the age may be between 3 300 and 3 500 Ma. Two galena samples from the stratiform Salt Greek de- posit. within fclsic volcanics of the Whim Greek Group, give a mode! age of 3 950 * 10 Ma (Richards & Blocklcy. 1984). The authors argued that the base of the Fortcscue Group cannot be younger than 3 800 Ma. (lulson sialli 5 ed biotiic granodioriic 'Light* mineral separate Recrysulhsed biotite granodioriic Recrysiallised biotite granodioritc Recnrstalliscd biotiic granodioriic Recrysiallised biotite hornblende granodioriic Rccrystaliiscd biotite granodioriic 'Light' mineral separate Recrvstallised biotite granodioriic Recrysullised scricilic. chloniic adamellite Senticised and carbonated adamellite Rccrvsialliscd chlorine adamallitc Recrysiallised chlorine adamalliic Recrystallised chlontic adamallitc Sencitised. silicified and chloritiscd adamellilc Scnciuscd. chloiitiscd and carbonated adamellite- granite Chlorine, finc'grancd rhyolite 'Light' mineral separate Massive sphcrulitic rhyolite Slightly scricilised rhyolite Massive, fine-grained rhyolite Massive sphcrulitic rhyolite Scncitised and carbonated sphcrulitic rhyolite Brecciated. chloritiscd and carbonated feldspar porphvrv Silicilied feldspar porphyry Brccciaied. scricilised feldspar porphyry Brecciated. scricilised chloritiscd feldspar porphyry Slightly chlontic feldspar porphyry Senciiiscd feldspar porphyry Table 3 Representative analyses of calc-alkalinc volcanics and associated high level inirusivcs from the Mons Cupri Volcanic Centre Caines Well Granite 83995 84065 84066 Mons Cupn Granite 84000 83996 82998 83999 83987 Mount Brown Rhyolite 83992 83993 83988 83989 Mons Cupri Porphyry 84010 84013 84012 Si 02 73.55 73.37 70.13 72.15 65.57 76.20 76.87 73.88 77.05 75.41 76.39 76.19 70.54 77.39 67.45 TiOi 0.16 0.16 0.17 0.25 0.33 0.32 0.32 0.50 0.45 0.48 0.45 0.45 0.56 0,56 0.68 AI 263 14.66 16.05 16.30 14.13 15.07 11.15 10.99 12.87 12.41 12.67 12.61 11.50 12.67 12.33 13.59 Fe703 FeO 0.30 l.OO 2.39 0.76 0.62 1.42 1.13 0.38 0.30 0.43 0.04 0.71 0.35 0.49 0.71 0.91 0.01 0.01 1.42 3.03 1.66 1.86 1,40 0.71 0.33 0.75 1.56 3.68 0.53 5.93 MnO 0.02 0.03 0.03 0.03 0.06 0.05 0.05 0.05 0.03 0.03 0.04 0.04 0.08 0.04 0.10 MgO 0.41 0.18 0.62 0.63 2.95 0.19 0.18 0.26 0.17 0.16 0.15 0.89 0.80 0.71 1.40 CaO 1.97 1.40 2.17 1.35 1.52 0.70 0.66 1.29 0.31 0.91 1.26 1.34 1.25 0.48 1.07 Na?© 4.75 4.45 4.72 3.90 0.57 3.66 3.39 5.33 4.78 4,74 3.57 0.18 4.14 3.22 1.96 K-ib 2.76 3.94 2.91 4.37 5.36 3.91 4.13 2.95 3.05 3.94 3.62 4.35 3.52 2.52 3.19 P2O5 LOI 0.05 0.04 0.03 0.09 0.13 0.03 0.03 0.13 0.12 0.13 0.1 1 0.12 0.12 0.05 0.14 0.90 0.77 0.74 1.66 4.72 0.67 0.67 1.71 1.03 1.40 1.06 0.34 2.53 2.07 3.62 Total 100.44 101.40 100.22 100.74 99.93 99.96 100.28 100.75 100.41 100.63 100.05 97.67 100.24 100.39 99.84 Sironlium evolution analysis of the data Irom Caines^ Well Granite suggests a mantle evolution age oi approximately 2 975 Ma assuming single stage evolution. This value has been calculated from the measured age of 2 7 1 3 Ma and the initial ratio of 0.7040. assuming a '‘"Rb/ '*'’Sr ratio which is the arithmetic mean of the suite of samples. Mantle Sr evolution was assumed to be linear from 0.6990 at 4 600 Ma to 0.7040 at present (Faurc & Powell 1972). The primary Rb-Sr age of approximately 2 975 Ma is in good agreement with ages determined by more robust gcochronological lechniciucs on Pilbara Block Batholilhs. Six of the seven Mons Cupri Granite samples fall on an isochron shown in Figure 3. The model 1 age and initial ratio is 2 430 ± 25 Ma and 0.7089 t 0.001 7 respectively. However the MSWD of 26 indicates a poor lit, and a model 3 age and initial ratio of 2 366 ± 60 Ma and 0.7 1 56 ± 0.01 1 respectively are to be preferred. 32 Journal of the Royal Society of Western Australia, 70 (2), 1987 Figure 4 — ''’Sr/*'’Sr vs ''^Rb/’'*Sr diagram for samples from Mount Brown Rhyolite. Figure 3 — ''’Sr/'''’Sr vs ''’Rb/'‘'’Sr diagram for samples from Mons Cupri Granite. The Mons Cupri Granite is one of the young massive in- trusive bodies which arc common throughout the Pilbara Block. It dilTcrs from the Caines Well Granite in being of adamellite composition and having higher Rb/Sr ratios. Thcagcor2 366 i 60 Ma is somewhat vounger than simi- lar granitoids in the East Pilbara. where dates of 2 670 ± 95 Ma and 2 606 - 1 28 Ma have been reported (Dc Lacier & Blocklcy 1972. Dc Laeter et al. 1975). The Moolyclla and Coogicgong adamellites arc intermediate level struc- tural types, whereas the chemistry and petrography of the Mons C'upri Granite show it to be of a high level sub- volcanic type. The Mount Brown Rhyolite samples give a Model I age of 2 331 t 27 Ma and an initial ratio ofO.7136 ^ 0.0008 (Figure 4). The MSWD of 3.6 indicates a reasonably good 111 of the seven samples, but a more accurate estimate of the age and initial ratio would be given by the Model 3 values of 2 33 1 ±42 Ma and 0.7136 * 0.0017 respect- ively. The data may reflect the local outpouring of the low- ermost Fortcscue Group volcanics( Mount Roe Basalt), as suggested by Oversby ( 1976). but more likely relates to the D4 or D5 deformations documented by Hickman ( 1 983). The Rb-Sr age is significantly less than the Sm-Nd model age of 3 000 ± 40 Ma reported by Flclchcr(Pers. comm.). Figure 5 — ’'^Sr/’''’Sr vs '‘’Rb/'‘'‘Sr diagram for samples from Mons Cupri Porphyry. The feldspar porphyry samples fit an isochron {Figure 5). which gives a Model 1 ageof2 617 ± 28 Maand initial ratio of 0.7020 j. 0.001 1. However the samples give a MSWD of 9. 1, and a more realistic estimate would be a Model 4 age and initial ratio of 2 610 ^ 80 Maand 0.7023 * 0.0038 respectively. The Rb-Sr age of the porphyry from Mons Cupri is intermediate in value between the ages obtained for the Caines Well and Mount Brown Rhyolite. Although this is consistent with the gcologv of the region, it mu.st be pointed out that since the Rb-Sr isochron ages arc updated ages, the sequence of measured ages do not represent the ages of emplacement of the vari- ous rock units. The calculated primary age of the Caines Well Granite of approximately 3 000 Ma is however, consistent with the other published age data for the Salt Creek deposit and the Millindinna Complex. Acknowledgements The authors thank Dr D I Groves for suggesting this pro- ject and Dr A F Trcndall for help and advice. Mr D J Hosie and Mrs P R Harris provided technical assistance. The project was supported by the Aus- tralian Research Grants Committee. 33 Journal of the Royal Society of Western Australia. 70 (2). 1987 References Arriens P A 1 975 Gcochronological studies of Proterozoic rocks in Australia. Geol Soc Aust Ist Aust Gcol Convention, Adelaide. 63. Bariev M E, Sylvester G C. Groves D I. Boricy G D & Rogers N 1984 Ar- chaean calc-alkaline volcanism in the Pilbara Block. Western Aus- tralia. Precamb Res 24: 285-319. Blake T S & McNaughion N J 1 984 A gcochronological framework for the Pilbara Region. Univ W Aust Extension PubI 9; 1-22. Compsion W & Arnens P A 1968 The Precambrian Geochronology of*Aus- tralia. Can J Earth Sci 5; 561-583. Dc Lacier J R& Blocklcv JG 1972 Granite ages w ithin the Archaean Pilbara Block. J Geol Soc Aust 19; 363-370. De Laeicr J R. Lewis J D & Blockley J G 1975 Granite ages within the Shaw Balholiih of the Pilbara Block Ann Rep Gcol Surv W Aust 1974: 73-79. De Laeier J R. Libby W G & Trcndall A F 198 la the older Precambrian ge- ology of Western Australia. Spec PubI Geol Soc Aust 7; 145-157. Dc Laeier J R. Williams 1 R. Rosman K J R& Libby WG 1981b Adcfinilivc 3350 Ma age from banded gneiss Mount Narrver area. W’estern Gneiss Terrain. Ann Rep Gcol Sun W Aust 1980: 94-98. Faure G & Powell J L 1972 Strontium Isotope Geology Springer Vcriag. Berlin. Filion M J. Horwitz R C & Sylvester G C 1975 Stratigraphy of the Early Precambrian in the Wwt Pilbara. Western Australia. CSIRO Min- erals Research Lab. Rep FPl 1. Gulson B L Vaasjoki M & CarrG R 1 983 Geochronology in deeply weathered terrains. Regolith m Australia; Genesis and economic significance BMR Creol & Geophysics Record 1983/27: 73-74. Hickman A H 1981 Crustal evolution of the Pilbara Block, Spec PubI Geol Soc -Aust 7: 57-69. Hickman A H 1 983 Geology of the Pilbara Block and its Environs Geol Surv W Aust Bull 127. Korsch M J & Gulson B L 1986 Nd and Pb isotopic studies of an Archaean layered mafic-uliramafic complex. W'esltyn .Australia, and impli- cations for mantle heterogeneity. Geochim C'osmochim Acta 50: I-IO. Marsion R J & Groves D I 1981 The metallogencsis of Archaean basc-mctal deposits in Western Australia. Spec PubI Geol Soc Aust 7: 409-420. Mclnivrc G A. Brooks C. Compsion W & Turck A 1 966 The statistical assess- ment of Rb-Sr isochrons. J Gcophys Res 71: 5459-5468. Miller LJ & Oair H S 1975 MonsCupn coppcr-icad-zinc-siKcr deposit. In: Economic Gcologv of Australia and Papua New Guinea-Metals (cd C C Knight) Aust Inst Min Metall. Melbourne. Norrish K & Chappell B 1967 X-ray fluorocscence spccirography. In: Physical methods in Determinative Mineralogy (cd J Zussman), Academic Press. London. 161-214. Oversbv V 1976 Isotopic ages and geochemistry of Archaean and igneous ' rocks from the Pilbara. W'esicrn Australia. Geochim Cosmochim Acta 40: 817-829. Pidgeon R T 1 984 Gcochronological coniraints on early volcanic evolution of the Pilbara Block. Western Australia. Nust J Earth Sci 31: 237-242. R ichards J R. Reichcr I R & Blockley .1 G 1 98 1 Pilbara Galenas: precise iso- topic assay of the oldest Australian leads: model ages and growth- curve implications. Miner Dcposiia 16; 7-30. Richards J R 1983 Lead isotopes as indicaiorsofold stable craion in Western Australia Gcochem J 17:247-255. Richards J R & Blackley J G 1 984 The base of the Fortescue Group. Western Australia: further galena lead isotope evidence on ns age. Aust J Earth Sci 321; 257-268. Sylvester Ci C 1976 CJeochemistrx- of an Archaean Volcanic Centre in the Pilbara Block ofWcMem Australia, Absir 25lh Int Geol Congr 1 : 22. Trcndall A F 1983 The Hamersicy Basin. In; Banded Iron Formation: Facts and Problems (eds A F Trcndall & R C Morris) Elsevier. Amsterdam. 34 Journal of ihc Royal Society of Western Australia, 70 (2), 1987, 35-47 Origin of limestone lenses in Perth Basin yellow sand, southwestern Australia V Scmcniuk' & D K Glassford^ ' 21 Glenmere Road. Warwick WA 6024 ^ 33 Rockett Way. Bull Creek WA 6155 Manuscripi received April 1987. accepted July 1987 Abstract Aeolian limestone lenses are common in thick sections of vellow quartz sand in the Pleistocene sequences of the Perth Basin, southwestern Australia. Previous workers presumed that these lenses are undigested residuals as the coastal limestones purportedly decalcified to quartz sand. Evidence presented here suggests that the limestone lenses are outliers of calcareous dunes that migrated in- land over yellow quartz sand from a Pleistocene coastal zone. Subsequently the lenses were buried by sea-ward influx of yellow quartz sand. This interpretation is based on size, geometry, lithology and stratigraphy of limestone lenses, and their stratigraphic relationships with encompassing yel- low quartz sand, and comparisons with geomctr>'. stratigraphy and lithology of Holocene dune deposits. Introduction Lenses of acolian limestone arc commonly encountered in thick sections of yellow quartz sand in Pleistocene se- quences of the Perth Basin, southwestern Australia. Gen- erally these limestone lenses, also termed ‘'limestone floaters”, have been interpreted as undigested residuals of limestone which have formed as the Pleistocene cal- careous aeolianites of this region purportedly decalcified to form quartz sand sheets and dunes (McArthur & Bettcnay I960. 1974). Probably the first reference to this process of dccalcification is that of Woodward ( 1 890). but subsequent authors have reached similar conclusions or accepted the conclusions of earlier workers (Clark 1926, Crocker 1946. Prider 1948. Fairbridge 1950, 1953, 1954. Fairhridge& Teichert 1953. McArthur & Bettenay I960, 1974. Welch 1964. Lowr\' 1967, 1977. Low 1971, Baxter 1972, Johnstone ei at. 1973. Lissiman & Oxenford 1973, Mulcahy 1973. Mulcahy & Churchward 1973, Wilde & Low 1975. McArthur 1976. Playford ct at. 1976. and W'yrwoll & King 1985). This paper presents an important and radically differ- cni interpretation of the origm of limestone lenses. It is concluded that limestone lenses in Perth Basin yellow sand, are the buried outliers of attenuated parabolic cal- careous dune that have migrated inland from a Pleistocene coastal zone. This interpretation is based on criteria of size, geometry, and stratigraphic relationships ol limestone lenses to the surrounding quartz sand, and comparisons with geometry, stratigraphy and lithology of Holocene dunes. Such an interpretation depicts a very dif- ferent conclusion to the model currently accepted and provides important implications for the stratigraphic re- lationship of limestone and yellow sand. However, it should be stressed that this paper concentrates on the ori- gin of limestone lenses that occur in yellow sand se- quences. and not on the origin of the yellow sand. The ori- gin of the yellow sand as aeolian deposits is discussed later only in the light of the interpretation that limestone lenses are buried Pleistocene calcareous dunes and not undigested residuals. The philosophy of approach in this paper has been to document the geometr\' and stratigraphy of Holocene parabolic dunes and their geomorphic variations and diagenesis. This forms the basic loundation work to understanding the origin of limestone lenses, and the in- formation from the Holocene is applied to interpret the Pleistocene sections. Methods Stratigraphic information from Holocene quaftzose carbonate sand. Pleistocene yellow quartz sand and Pleistocene quartzose limestone (subsequently referred to as limestone) lenses was collected from quarry' exposures, road cuts, from drill holes using reverse circulation air coring techniques, and from back-hoe trenches and pits. The limestone lenses were fully excavated in four of the study sites to expose the contact between a limestone lens and underlying yellow sand. The limestone lenses were ex- cavated in short 2 to 3 m long trenches along their bases at the other study sites with information augmented bv drilling. 56029-3 35 Journal of ihc Royal Society of Western Australia. 70 (2). 1987 The relationships between Holocene dune sand and Pleistocene units were studied by utilising aerial photo- graphs of the region between Bunbury and Dongara. by topographic levelling lo determine cross-sectional relief of Holocene dunes, and by air core drilling, augcring and trenching to ascertain thickness, gcomeirs and underlying contact relationships of the Holocene dune deposits. Samples also were collected for petrographic analyses. This material included in situ yellow sand, rhizoconcrciions in the yellow sand, calcrcied pipes in yel- low sand, general samples of friable lo indurated Pleistocene limestone, and indurated (sparry calcite cemented) Holocene dune sand. Geological Setting The study area is the Swan Coastal Plain which is the coastal lowland stretching from CJeographe Bay to Dongara (Fig. 1 ). The plain is bordered to the east by the Darling Plateau or by the Dandaragan Plateau and Eneabba Plain (Playford d al. 1976. Biggs ct ai 1980). The seaward portion of the Swan Coastal Plain is of rel- evance lo this study because in these locations ridges of the Pleistocene Tamala Limestone ( - Spearwood Dunes of McArthur & Beltenay I960)ma\ interfingerwilh orlic juxtaposed against Pleistocene yellow quartz sand to the east, and adjoin Holocene dunes of the modern coast to the west (Fig. 1 ). The Holocene coastal dune sands, referred to as Safely Bav Sand (Passmore 1970. Playford tV a/. 1 976. Semeniuk & Scarle 1985). typically arc a ’short-parallel unit of white to cream calcareous quartz sand variable in width and thickness dependent upon coastal type and supply of sand. In many areas the coastal dunes form massive in- land migrators parabolic systems that transgress over cither earlier Holocene sand sequences or Pleistocene units such as Tamala Limestone and yellow sand. From a subconlinenlal perspective it is apparent that the number, aitenualion and extent of inland ingress of the Holocene parabolic dunes increase from south lo north in response to a more arid climate and more intense wand system (sec Fig. 2 of Scarle & Semeniuk 1985). Ad- ditionally the direction of the parabolic dune axis changes progressively from approximately cast-west in southern areas to north-south in northern areas (Fig. I). The belt of Tamala Limestone has a shore-parallel trend. The limestone may crop out at the coast, or may be buried by Holocene littoral and coastal dune deposits. The eastern margin of the Tamala Limestone at its con- tact with Bassendean Sand is more complicated, and is locally sharp, or marked by inicrfingcring. or marked by a zone of lenses. The lilhofacies referred lo herein as yellow sand, although typically >cllow. also includes sands varying from white to orange to locally red. Yellow' sand is predominantly quartz with moderate to trace amounts ol feldspar, and minor kaolin, goethile. and heav\ minerals (Prider 1948. Baxter 1972. Lissiman & Oxenford 1973. Glassford & Kiiligrew 1976. Glassford 1980). The term yellow sand as used here is strictly a lithologic term, with no implication as lo stratigraphic occurrence. That is. yel- low sand does not necessarily belong to any one of the cur- rently defined Quaternarx formations. As such it includes the yellow sand portions of the Tamala Limestone (or Spearwood Dunes), the Basssendean Sand, and the Yoganup Formation. Gcomorphic, Stratigraphic & Lithologic Features of Holocene Parabolic Dunes The gcomorphic and slaiigraphic relationships between Holocene parabolic dunes of the Safely Bay Sand and underlying Pleistocene units were investigated in 5 lo- calilie.s: 1) Mandurah. 2) Trigg Island. 3) Whilfords. 4) Cervantes. 5) Juricn Bay. and 6) Dongara (Fig. I ). The re- sults of the investigations arc show n in Fig. 2. The key el- ements of the Holocene stratigraphic information are summarised in Fig. 3. The coastal zone of the study areas, encompassing the shoreline and the subaenal strip up to several kilometres inland, consists of an overlapping bell ofdune-sand ridges developed as adjacent parabolic dunes have formed and accumulated under the inlluencc of prevailing strong on- shore winds. However, distal from the coastal zone there are isolated parabolic dunes extending up to several kilo- metres inland- The amount of overlap between adjacent parabolic dunes also decreases to landward (Fig. 2). In many areas the ailcnuated parabolic dunes have become detached from their coastal ridge source lo become iso- lated curved ribbons/shoesirings and conical hills of acolian sand. Cross-sectional stratigraphic profiles indicate that in near coastal zones the acolian ridge consists of overlap- ping and adjacent parabolic dunes. 1 lowevcr to landward, as the overall inland extent of parabolic dune encroach- ment diminishes, individual isolated parabolic dunes are recognisable with distinct migrating rim. arms and bowl. In cross-section the individual arms of these isolated parabolic dunes appear as low sand mounds with cither fiat bases, or al least gently undulating bases, or gently in- clined bases, corresponding lo the buried topography of a broadly undulating yellow sand plain. In sonic areas the cross-sections show Safely Bay .Sand as a thin sheet with mound-Iikc thickenings indicating local coalesccnsc of the parabolic dunes. Older degraded solilai'y parabolic dunes maN be reduced to low conical sand hills (the re- sidual parabolic dune front) with loss of the trailing arms (Fig. 4). The final product of this type of gcomorphic degradation is an isolated low-relief concial mound of cal- careous sand. In most areas humic soil had developed on yellow sand and the contact of the soil with overlying white Safely Bay Sand is sharp. In some local areas however, the white Safely Bay Sand may he directly on yellow sand without an inicnening soil sheet. In pits and trenches cut into the Safely Bay Sand large scale cross layering is evident and inclined to landward indicating the direction of migration of the ad\ ancing face of the parabolic dune. Locally, the Holocene dune sands are weakly indurated bv sparry calcite cement similar to the induration de- scribed in aeolian sands elsewhere in the world (^'aaion 1967. Bathurst 1975). These cements arc thin epitaxial growths on grains and are thickest al grain contacts. The cements arc forming in modern vadose environments in the southwestern coastal zone (Semeniuk 1983). In the vellow sand beneath ihe base of the Holocene dune sands there may be local development of rhi/oconcreiions where calcium carbonate from solutions derived Irom the calcareous dunes has precipitated around plant roots lodged in the nun calcareous yellow' sand. These rhizoconcreiions are lypically enveloped by a halo of bleached while quartz sand. Thus i n the vicinity ol its con- tact with carbonate sand yellow quartz sand is being trans- formed inloa quarizose limestone. There also may be root 36 Figure 1 -^Geological Selling A Penh Basin (after Playford el al. ! 976). B Swan Coastal Plain and study sites. C Geomorphic units and shore-parallel extent 01 the Spi^rwood Dunes (aUcr McArthur & Betlenay 1 960). D Orientation of Holocene parabolic dune axes along the coastal zone (wind directions from Searle & Semcniuk 1985). E. Schematic section showing regional stratigraphic framework of the Swan Coastal Plain. 37 Figure 2.— Plan view and cross seclions of Holocene coastal parabolic dunes showing alienualed dune forms, isolated parabolic arms, and stratigraphic profiles. pipes which descend from the unlithified Holocene calcerous aeolian sand through the interface between the Holocene sand and yellow sand and into the yellow sand. These pipes are up to 20 cm diameter and are filled with calcareous aeolian sand infiltrated from above (Fig. 5). Pleistocene Limestone Lenses in yellow sand Limestone lenses have been studied in detail at 7 lo- calities. The essential information on these lenses is sum- marized below (Figs. 6. 7 & 8); 1 )Thc lenses arc usually 2-5 m thick and up to 10 m thick: in cross-section they arc up to 20-30 m wide and in places up to 150 m wide, tapering at their margins. 2) The limestone of the lens is typically aeolianile: it is cross laminated at the large scale with cross layering dip- ping to northeast, east and southeast, and contains abun- dant to common rhizoconcrctions. This is important in that it is not a marine limestone that occurs as lenses. The limestone typically is medium sand-sized quartz skeletal grainstone cemented by sparry calcitc typical of vadose environments. 3) The top of a lens, as defined by an enveloping surface, is convex, but in detail the top surface is sculptured by ■'solution" pipes and karren structures and impregnated with massivc/laminar calcrete: these features are absent along the basal limcstone/ycllow sand interface. 4) Some of the larger lenses and lens margins have been segmented by karren structures. 5) Overall, the base of a lens is flat or semi-planar, but it is not necessarily horizontal: in detail it is flat or slightly hummocky with hummocks < 10 cm amplitude over a length of a metre: the basal contact may be modified (pen- etrated) by calcareous sand-fillcd root pipes and by yellow quartz sand-lllled termite burrows. 6) The contact of limestone with underlying yellow sand is sharp and planar. 39 2. Aeolianite. cross-layered and with rhizoconcretions 4 Segmentation 1. Lens shape 7. Clift margin may be present K 8. Apron of flanking detritus 5. Flat base 6- Sharp planar contact 1 1. Interface upon which the lens rests may be unconformity within yellow sand 9. Rhizoconcretions in yellow sand 3. Convex upper enveloping surface impregnated by calcrete and dissected by karren structures 12. Soil may be developed on yellow sand at this interface o* * 10. Root and pipe structures •; % c | penetrating the base Figure 6.— Summary of key features of Pleistocene limestone lenses. Numbered annotations relate to the obscrsations listed on pp 39-43 of text, 40 41 Figure 8 —Tracings from photographs showing details ofstraiigraphyat the contact between limestone lenses and encompassing yellow ^nd. A, B&G Planar sharp contact of base of limestone lens and underlying yellow sand. G Rhizoconcretions in underlying yellow sand. C & D Details of pipe structures pen- etrating the interface between limestone lens and underlying yellow sand. E & F Laminated apron deposit flanking a limestone lens. 42 Journal of the Royal Society of Western Australia, 70 (2), 1987 7) Some lenses have cliff margins with the adjoining and up to 1 m)by root casts and root pipes emanating from the encompassing yellow sand. limestone and they may be 1 cm. 10 cm or 20 cm in diam- 8) Laminated and cross laminated wedges and sheets of tilled with calcareous sand infiltrated from calcareous quartz sand interlayered with coarse and me- dium quartz sand form Hanking aprons, 30-50 cm thick n) jhc limestone lens mav dircctlv overlie an and several metres wide, around some lenses. unconformity, or bounding surface (see Talbot 1985), 9) Calcareous rhizoconcretions cementing the yellow within the vellow sand marked by an extensive horizon of quartz sand may occur immediately below the limestone; leached white sand, or coarse sand, ora pedogcnic surface these rhizoconcretions. consisting of calcrete and sparry ol clayey yellow sand or lateritic yellow sand. calcite, impregnate a grain-supported vellow quartz sand: ,, .u i . i . i. • ^ i goclhite pigmenicd (>® How) kaolin codlings on the yellow quartz grains are enveloped by the calcite cements. opca on ye lo sand. 10) The yellow sand immediately below the limestone The significance of each of the above observations on lens may be penetrated for a limited distance (20-50 cm Pleistocene limestone lenses is presented in Table 1. Table 1 Siginficance of the geological information on the limestone lenses Observation Interpretation Significance 1. lens shape of limited size mound-like sand body which, after lithification to limestone, would have resembled a limestone knoll eeometry of body reflects geometry of dcpositional form 2. internal structure of cross layering and rhizoconcretions. aeolianilc lithology typical aeolian accumulation and post Jcpositional diagenesis aeolian origin of the body and normal post- depositional diagcnctic processes have operated 3. top of lens with pipes, karren structures and calcrete solution modification of exposed surface or shallowly buried surface; root penetration to de- velop pip>es; subaerial calcrctization of surface of limestone limestone lens had undergone alteration in subaerial environment, the top surface not the basal surface, has been modified subaerially 4. segmentation by karren structures karren structures propagating downwards locally dissected the lenses dissection results in steep-sided hollows and ultimately can result in cliff edges to the limestone lenses 5. flat base aeolianite body encroached onto a sand plain the contact between the limestone and underlying sand is dcpositional not solutional 6. sharp planar contact between limestone and underlying yellow quartz aeolianiie body encroached onto asand plain with subsequent modification of contact by bioturbation the contact is not solutional; small scale irregularities arc due to vegetation and fauna effects 7. clifT margins to lenses during wealhering/erosion in the subaerial en- vironment the lenses were undercut on their mar- gins: undercutting may be due to solution at the quartz sand/timeslonc contact or to wind removal of adjoming/undcrlying quartz sand typical expression of upstanding limestone bodies (or knolls) when underlain by non-calcareous materials, i.e. sharp vertical small to large cliff edge, not thinly tapering 8. aprons of detritus residual quartz from subaerial solution and the more resistant carbonate grians accumulated as aprons around the limestone knoll the mai^ins of the lenses were subaerially exposed and the lenses (knolls) were exposed; only subsequently was the entire knoll and apron system buried by later influx of yellow quartz sand; overlying sand emplaced by transportation and is not ihc’produci of in situ decalcification. 9. calcareous rhizoconcretions in underly- ing quartz sand carbonate dissolved from the limestone perco- lated through the vadosc zone located in the lime- stone and underlying yellow quartz sand: plant roots utilising the vadosc water precipitated rhizoconcretions in the limestone and in the underlying quartz sand source of carbonate in the quartz sand is from overlying limestone: rhizoconcretions post-date em- placement of limestone onto yellow quartz sand. 10. penetration of the basal limestone/ yellow sand contact by plant root struc- tures and pipes filled with quartz carbon- ate sand vegetation inhabiting the knolls emplaced their roots through the limestone, through the limcsionc/vcllow sand interface, and into the yel- low sand; later infiltration of calcareous quartz sand into the rotted roots developed ihc various sized pipes; the calcareous structures were subsequently calcrctised the limcstone/yellow sand contact can be modified by plant root activity, however the overall lower contact between limestone and yellow sand is essentially planar 1 1. limestone rests on an unconformity aeolianite body encroached onto quartz sand plain whose surtacc was pcdogenically altered (i.e. bounding surface) the lower limcstone/yellow sand contact is dcpositional and not solutional 12. limestone rests on humic soil aeolianite body encroached onto quartz sand plain whose surface was pedogcnically altered the lower limesione/ycllow sand contact is depositional and not solutional •Observations numbered 1-12 follow that in the text pp 39-43. 43 Journal of the Royal Society of Western Australia. 70 (2). 1987 The cross-scciions illustrated in the figures represent opportunistic profiles through lenses as exposed in quarries and deierniined by coring. Thus the cross- sections may represent only the margin ot larger lenses, or may represent oblique profiles through elongate lenses {e.£ sites D& G). However in some locations (site C, E & H) the lenses were observed in entirely and the sections represent maximum width and thickness of a lens. Interpretation of Pleistocene sequences Many of the features described from Pleistocene se- quences are direct equivalents of lenses of aeolian coastal sand (arms or rims of isolated parabolic dunes) overlying quartz sand sheets as described in the modern coastal selling. Local pa/aeo-environnwntal intcrpretaiion The Pleistocene limestone lenses arc interpreted as geomorphic residuals of calcareous parabolic dune fronts and as cross-sections of the arms of parabolic dunes, or locally developed barchan dune bodies resting on a for- mer \V‘llow sand plain. Generally it appears that during the Pleistocene the aeolian sand encroached onto a yellow sand plain but locally, particularly in more humid southern areas, the aeolian sand encroached onto a yellow sand plain which had a soil profile. The calcareous dunes migrated from the coastal zone as attenuated parabolic forms and locallv became detached from their source. At this stage a detached dune could develop into a small barchan. As such in a cross-section parallel to the coast the detached dunes now appear as fiat-based lenses. Intern- ally, the large scale cross layering in the lenses indicates gross landward migration. Vadose zone cementation transformed the calcareous aeolian sand to limestone. Small scale (grain to grain) sol- ution of calcium carbonate by meteoric water (Yaalon 1%7* Bathurst 1975). the translocation of dissolved car- bonate to levels lower in the vadose profile, and the utilis- ation of vadose water by plants resulted in the develop- ment of carbonate rhizoconcreiions in the aeolian sand and hH'ally in the undcrlyinK quartz sand. stage 1 Ancestral yellow quartz sand plain with weak pedogenic surface Stage 2 Emplacement of aeolian calcareous sand body Stage 3 Fixation by vegetation and diagenetic alteration Rfiizoconcretions and vadose zona cementation A pipes I Stage 4 Transformation to limestone Stage 5 Calcretisation. erosion and weathering Stage 6 Continued calcretisation. erosion and weathering leading to segmentation and development of "towers* Segmented lenT| Stage 7 Burial by yellow quartz sand aeolian drifts .Present land surface Fio.irr. Q — Mndt-l dcoiciinE oncin and staecs in the aUcraiion of limestone lenses. Note that burial by aeolian yellow quartz sand can take place at any stage ® and consequently term^inate any further development of alteration stages. In addition, aeolian erosion may also exhume the limestone lenses and thus reinitiate the alteration sequence. 44 Journal of ihc Royal Society of Western Australia. 70 (2). 1987 The limestone lenses have undergone subaerial weath- ering. subaerial solution, erosion and impregnation with calcrete. This resulted in a general overall cross-sectional volume reduction of the lens, in development of solution features such as karren and lapies structures (Bogli 1960. 1 96 1 . Jennings & Sweeting 1963. Sweeting 1972. Jakucs ! 977. Eslaban & Klappa 1 983). and in development of a calcrete capstone. Larger scale subaerial solution and de- velopment of karren structure markedly modified the convex upper surface of the limestone to a scries of sleep- sided pinnacles and locally dissected the limestone lenses to an extent that the lenses become segmented. The segmented components would resemble miniature karst lowers as described by Jakucs (1977). The inferred wcathenng/erosion history of the lenses is illustrated in Fig. 9. The features of the upper contact between lime- stone and yellow sand will be the subject of another paper. Locally. clitT margins and perhaps flanking boulder/ block deposits were developed where the limestone lens was undercut by w ind deflation or rain wash of yellow sand, and collapsed along a cliffline. Weathering and sheet wash also resulted in the development of aprons, composed of quart/- sand and resistant carbonate grains, both derived in part from the limestone, flanking the mar- gins of lenses. Similar solution structures in subaerially exposed limestone and flanking detrital deposits derived from limestone outcrops, occur in semiarid to arid regions elsewhere (Jakucs 1979). At all stages of weathering and erosion, the basal con- tact of the calcareous sand/limesione lens with underlying yellow sand was continually modified by vegetation roots and burrow ing fauna such as termites. This resulted in in- filtration of calcareous sediment down into the yellow sand via plant root holes and animal burrows, and in the translocation of yellow sand up into the calcareous sand or limestone via termite activities. Coastal sett ini' interpretation The relationship between the major limestone ridges of the Spearwood Dunes and the outliers of limestone lenses represents a transition from a coastal /one to inland, es- sentially a coastal to continental transition. The Pleistocene coastal environment generated massive aeolian sand accumulations that developed as a large ridge. The ridge consisted ofan overlapping series of para- bolic dunes. This coastal dune ridge overlies an unconformity on limestone or on yellow sand (see Fig. 5 in Allen 1981). Further to landward the ancestral terrain would have consisted of limestone or yellow sand plain. Staggered advances of discrete parabolic dunes ema- nated from the coastal /one and encroached onto the ad- joining ancestral hinterland terrain. These parabolic dunes extended up to several kilometres from their source and locally became detached. As such they represent the extremities of the influence of coastal environment sedimentation. Cross straU^ruphie interpretation I he stratigraphic relationship of limestone lenses in a regional setting represents a transition /one between two major lithofacies. a marine derived coastal carbonate facies, and a land derived continental yellow quart/ sand facies. Such a setting is not unusual in the geological re- cord; as Cilenme ( ! 970: 121) points out "it is important to realise that continental (desert) shoreline and marine facies may all occur in close proximity". The gross stratigraphic setting of this coastal region is interpreted as one of periodic yellow sand incursions from the cast by aeolian transport during glacial periods associ- ated with aridity tuid lower sea levels, alternating with coastal aeolian building during interglacial periods (fol- lowing Fairbridge 1964. Kukla 1977. Sarnthein 1978. Sprigg 1979. Glassford 1980) associated with wetter cli- mates and elevated sealevels. Thus during glacial-age des- ert phases yellow sand incursions w'ould have extended onto the exposed continental shelf. During an interglacial the sediments of the shoreline environment were composed of sand derived from reworking of the former sand plain (quart/ and some fel- spar). reworking of pre-exisiing lime.slonc ridges (lilhoclasts) and contribution of rcsideni/nearby fauna (skeletons). The quart/ose calcareous sand was piled into a dune ridge along the Pleistocene shoreline. From this main ridge parabolic dunes extended inland forming iso- lated arms and mounds of quarizosc calcareous sand. Later, induration by calcile cementation converted these aeolian sands to limestone. During the ensuing glacial period yellow sand aeolian drills blanketed Ihe entire coastal /one bury ing the lime- stone lenses and the main limestone ridge. Since its last major mobilisation the yellow sand has been variously pod/oli/ed. biolurbaied and locally reworked by aeolian. fluvial, lacustrine and marine processes. The stratigraphic array and the dynamics of the gross system is interpreted as an interacting and alternating sys- tem of desert aeolian sand influx (following Killigrew^ & Glassford 1976. Glassford & Killigrcw 1976. Glassford 198(J) and marine (coastal) reworking. The model is sum- mari/cd in Fig. 10. Successive alternating episodes of des- ert aeolian influx and marine reworking would result in a thick section of yellow quartz sand on the cast portion of the -Spearwood (lime.slonc) ridges with scattered lime- stone lenses within the yellow sand body. 1 he zone of limestone lenses in a given time interval would represent the transitional zone between coastal dunes and ancestral hinterland w here local coastal aeolian incursions penetrated a limited extent to inland (for anal- ogous topographic and coastal settings see Glennie 1 970. Fryberger & Ahibrandl 1979 and Fryl-icrgcr ei a/. 1983). As such the contact between limestone ridges and hinter- land yellow sand (i.e. between Tamala Lime.slone and Bassendean Sand) may not necessarily be a straight north- south junction. Rather, it will be an irregular to disjointed contact, and in many places the contact will be a tran- sitional zone of lenses. References Allen A D 1981 Oroundwaicr resources of the Swan Coastal Plain, near Perth. W'estern Australia. In; Groundwater resources of the Swan Coastal Plain cd B R W'helan. CSIKO. 29-80. Bathurst R G C 1975 Carbonate sediments and their diagenesis (2nd cd). Elsevier. .Amsterdam. Baxter. J L 1972 The gcologs of the Eneabba area. Western Australia. Gcol Sup. W Xusl Ann Rep 1971. 61-62. Biggs. E R, Leech R E J & Wilde S .A 1980 Geology, mineral resources and hydrogeology of the Darling System. W'cslcrn Australia. In: Atlas of Natural Resources. Darling System. Western .Australia. Dept Conserv' &. Envir. 5-20. Bogli A I960 Kalklosung und Karrenbildung. Zeit f Geomorph Supp 2. In- tern Bcitragc Zur Karstmorphologic. 4-21. Bogli A 1961 karrentischc. cm Bcilrag zur Karstmorphologic. Zcii f (icotnorph 5: 185-193. Clark E dc C 1926 Natural regions of Western Australia. J Roy Soc W Ausi 12:117-132. 45 Journal of the Royal Society of Western Australia, 70 (2), 1987 Stage 1 : Influx of continental desert aeolian sediment Desert aeolian influx Former shelf sub-aerialiy exposed during low sea level and burled by desert aeolian influx Stage 3 : Further influx of desert aeolian sediment Former shelf sub'aerially exposed during low sea level and buried by desert aeolian influx Section A - B Pleistocene parabolic carbonate dunes Regional boundary surface Relict desert aeolian quartz sand P . B a »<*O-C*>0.0°P-P°P^0 oVo «>>.0 °r,0 Ob” I stage 2 : Influx of coastal/marine derived aeolian sediment (pleistocene) Pleistocene carbonate parabolic dunes moving over quartz sand Higher sea level stage 4 : Further influx of coastal/marine derived aeolian sediment (Holocene) Plei.locene Lns, Holocene carbonate parabolic dunes moving over quartz sand Present day higher sea level Section C - D Holocene unconsolidated parabolic carbonate dunes Former regional boundary surface now an unconformity within quartz sand Limestone lenses Relict desert aeolian quartz sand QUARTZ SAND CALCAREOUS SAND/LIMESTONE FiRure I O.-Modd dcpiclingaliernaling phases of desen aeolian influx during glacial penodsand coastal dune accumulation during interglacial periods. Lime- Stone lenses reflect the transition zone between coastal aeolian accumulations and the continental aeolian tacies. 46 Journal of ihe Royal Society of Western Australia. 70 (2), 1987 Crocker R L 1946 f‘osi-Miocenccltmauc and geologic hisiory and iis signifi- cance in relation to the genesis of the major soil types of South Aus- tralia. CSIRO Bull 193. Esiaban M & Klanpa C F IV83 Subaerial exposure. In: Carbonate deposiiional environments ed P A Schollc. D G Beboui & C H Moore. Am Assoc Petr Geol 33: 1-54. Fairbridge R W 1950 The geology and geomorphologv of Point Peron, West- ern Australia. J R Soc W Aust 34: 35-72. Fairbridge R W 1953 Australian stratigraphy. Univ W Aust Text Book Board. Fairbridge R W 1 954 Quatemar> eusiatic data for Western Australia and ad- jacent states. Pan Indian Ocean Sci Congr Proc sect F. 64-84. Fairbridge R W 1964 African icc-agc aridity. In: Problems m Palaeoclimaiology ed A E M Nairn. Inicrscicnce. London, 356-363. Fairbridge R W & Teicheri C 1953 Soil horizons and marine bands in the Coastal limestones of Western Australia, between Cape Naturalisic and Cape Leeuwin. J Proc R 5ioc NSW 86; 68-87. Fry berger S G Al-San A M & Clisham T J 1983 Eolian dune, inierdune, sand sheet, and siliciclastic Sebkha sediments of an offshore prograding, sand sea. Dhahran area, 5iaudi Arabia. Am Assoc Petr Geol Bull 67; 280-312. Fryberger SG & Ahibrandt TS 1979 Meehan isms for the formation of eolian sand seas. Zeit Gcomorph 23: 440-460. Glassford D K 1 980 Late Cainozoic desert eolian sedimentation in Western Australia. Univ. West Australia Ph D Thesis. Reid Library. Univ W Aust Nedlandv Glassford D K & Killigrew L P 1976 Evidence for Quaternary westward ex- tension of the Australian Desert into south-western Australia. Search 7: 394-396. Glennie K W 1970 Desert sedimentary environments. Developments in sedimeniology 14. Elsevier. Jakucs L 1977 Morphogcnctics of karst regions. Hilger. Bristol. Jennings J N& Sweeting M M 1 963 The limestone ranges of the Fiizroy Basin Western Australia. Bonner Geographische Abh 32. Johnstone M H Lowr\ D C & Quiliy P G 1973 The Geology of southwestern Australia — a review. J R Soc W Aust 56: 5-15. Killigrew L P & Glassford D K 1976 Origin and significance of kaolin sphcnics in sediments of southwestern Australia. Search?: 393-394. Kukla G J 1977 Pleistocene land-sca correlations. I Europe. Earth Sci Re- views 1 3; 307-374. Lissiman J C & Oxenford R J 1973 The Allied Minerals N.L. Heavy mineral sand deposit in Encabba. Western Australia. Aust Inst Mining Mclall Conf 1973. Penh WA. 153-161. Low G H 1971 Definition of two Quaternary formations in the Perth Basin. Geol Surv W Aust Ann Rep 1970. 33-34. Lowry. D C 1 967 Busselton and Augusta . W^ A. Geol Surv Aust 1 ;250 000. Geol Senes Explan Notes. Lowry D C 1977 Perth Basin yellow sand. Search 8: 54-55. McArthur W M «& Bctienay E ! 960 The development and distribution of soils of the Swan Coastal Plain, Western Australia. CSIRO Soil Publ 1 6. McArthur W' M & Bctienay E 1 974 The development and distribution of soils of the Swan Coastal Plain, W'csiem Australia. CSIRO Soil Publ 16 (2nd edition). McArthur W M 1 976 The Swan Coastal Plain. In: Groundwater Resources of the Swan Coastal Plain (ed. B A Carbon). CSIRO Division of Land Resources Management. 7-1 1. Mulcahy M J 1973 Landforms and soils of southwestern Australia. J R Soc W Aust 56: 16-22. Mulcahy M J & Churchward H M 1973 Quaternary' environments and soils in .Australia. Soil Sci 116: 156-169. Passmore J R 1970 Shallow coastal aquifiers in the Rockingham district. Western Australia. Water Research Foundation Aust Bull 18. Playford P E Cockbam A E & Low G H 1976 Geology of the Perth Basin. Western Australia. Geol Surv W Aust Bull 1^4. Pridcr R T 1948 The geology of the Darling Scarp at Ridge Hill. J R Soc W Aust 32: 105-129. Sarnthein M 1978 Sand deserts during glacial maximum and climatic opti- mum. Nature 272: 43-46. Searle D J<&Semeniuk V 1985 The natural sectors ofihe inner Roiinest Shelf coast adjoining the Swan Coastal Plain. J R Soc W Aust 67: 1 16-136. Semeniuk V 1983 The Quaternary history and geological history of the Auslralind-Lcschcnauli Inlet area. J R Soc W Aust 66: 71-83. Semeniuk V & Searle D J 1985 The BccherSand. a new stratigraphic unit for the Holocene of the Perth Basin. J R Soc W Aust 67, Sprigg R C 1979 .Stranded and submerged sea-beach systems of southeast South Australia on the aeolian desert cycle. Sedimentary Geol 22: 53-96. Sweeting M M 1972 Karst Landforms. MacMillan. London. Talbot M R 1985 Major bounding surfaces in aeohan sandstones — a climate model. Sedimeniology 32: 257-265, Welch B K 1964 The ilmeniie deposits of Geographe Bay. Aust Inst Mining Mctall Proc 211; 25-48. Wilde S A & Low G H 1975 Explanatory notes on the Perth 1:250 000 geo- logical sheet. Western Australia. Geol Surv W Aust Record 1 975/6. Woodward H P 1890 Geol Surv W Aust Ann Gen Rep 1888-1889. WvTwoll K H & King P D 1985 A criticism of the proposed regional extent of Late Cainozoic arid zone advances into south-western Australia. Catena 1 1: 273-288. Yaalon D H 1 967 Factors affecting the lilhificaiion of eolianiie an interprei- aiion of its environmental significance in the coastal plain of Israel. J Sedim Petrol 37: 1189-1 199. 47 ■ >*ll‘ ' ■ ''■'■'ii’ir iu^-y A. . ^ . X .% * ' . . U . ,.' . . - - ^^• ; -■ v ■ - %.... _ V , v ‘k., . ■ . i . . j — /i*. •- ■•-'V S. ' JgV .-wjumr *J5fi\’- ••**■ -lo * . ■jr. :-..., • , " 4 ^ W»=- I ■’4^ ^ ^ ' *5 .« • • ‘ * • ' ^E'jcr “ -'■;. “I .-- - V-f. . ■-.’' “ •^n.r • Ml 7 *^ ' V^^ ^ F *', , I’ll V.. I :r • t;- aXMa ^ i.f*- ji' (4 r ■-r‘- ' vi'.*t'i»7 « ;*i » ' »* ’ • S 4 ’' 3 ® 3 ''^ * • ** , ..V> --^ ^ - • V iT - ? i I . I* • . “ i ; ,'V' « • • '.j-..- - - r* i. :• . ;■ ^,.v .-i .n ‘/f . *■ •' 7 A v-_Mc , . ' : V 7 ' .V ' -.t. Journal of the Royal Society of Western Australia. 70 (2), 1987, 49-53 The Unconformity in the Kelly Belt, east Pilbara Craton R C Horwilz CSIRO Division of Minerals & Gcochcmistr>’ Floreai Park. W A 6014 Atanuscripi received April I9H7: accepted July 1987 Abstract The approximately 3 Ga year old unconformity of the Whim Greek Group and other pre-Mt Roe Basalt sequences on older rocks, in particular on banded iron formations (BIFs) of the Gorge Creek Group. IS now generally accepted, being recorded in most of the greenstone belts of the Pilbara Craton. However, recent studies indicate that it occurs onlv as far south and cast as the Marble Bar and C oongan Belts which Hank the Corunna Downs and Mt Edgar batholiths. In the Kelly Belt, to the cast of these batholiths. the unit previously mapped as the Lalla Rookh Sandstone (inel. Budjan Creek For- mation) equates instead to the Corboy Formation, w hich is at the base of the Gorge Creek Group in the East Pilbara. These clastic sediments grade up into, and form an unbroken sequence with, the BIFs of the Paddy Market (('Icavcrxille) Formation of the Kelly Belt. Thev are thus assigned to the Soansville Subgroup, which can now be used synonymously with the term Gorge Creek Group. The basal elastics are also tcnlalively correlated, because of similarities in the sequence, to parts at least of the Mosquito Creek Formation further to the east. Mafic volcanics do occur elsewhere in this grouping but the choice of the tvpc section for a basalt in the Soansville Subgroup, near ('harteris ('reck in the Kcllv Belt, is inappropViate because there this basalt underlies the unconformity and is part of an unbroken sequence of pillowed volcanics. cherts and thin tuffaccous sediment bands, frequent in the Salgash and the Taiga Taiga subgroups. Introduction fable I Stratigraphic subdivisions of the Marble Bar area where established by Lippic (1975) and partly revised and ex- tended by Hickman (1983) to the whole of the northern exposed part of the Pilbara Craton. Following earlier workers such as Maitland (1908) and Noldari & Wyatt (1962). Lipple (1975) had subdivided the layered se- quence into a lower, Warrawoona Group, dominantly of volcanic origin and an upper. Gorge Creek Group, essentially ofsedimentary rocks. The latter wassubdivided into a lower, Soansville Subgroup and an upper, un- named part which included the Lalla Rookh Sandstone, the Bunjan Creek formation, and the Mosquito Creek Formation. Like previous authors, Lipple recorded unconformities at the base of these three formations in some localities though Hickman (1983, p. 105) con- sidered these to be ol local significance only. Filton et af. ( 1 975). from studies in the West Pilbara be- tween Rocbourncand Wodgina, restricted the term Gorge Creek Group to what would appear to equate to Lipple's Paddy Market Formation (or the ('Icavcrville Formation of Ryan & Kricwaldt 1 964) which is part of the Soansville Subgroup (see Table I). This formation is characterised by the developments of thick cherts, chenified sediments, BIFs (banded iron formations), and in places shales. Fition ef al. recognized a hiatus and regional unconformity between this unit and the overlying se- quences which they estimated (1975, figure I ) from avail- able gcochronological data to have occurred about 3 Ga Archaean lavered succession of ihe Pilbara (names referred lo in text). Amended after Fition et at. (1975). Lippic (1975). and Hickman (1983). (Geochronology, see Blake & McNaughion 1984 and Trendall 1983). Ml Bruce Supergroup Ml Roe Basali Regional unconformity (about 2.8 Ga) Negri Volcanics^- ■( (including un-named sediments and the Loudon Volcanics) •• ’) Basalt (Yarrie Sheet area) — (?) Lalla Rookh I .Sandstone Whim Creek Group Lwal uncon/ormiiv I I Mallina Formation (includes the Rushal! .Slate and un- named acid volcanics) Constantine Formation Mons Cupn Volcanics Warrambi Basalt Regional unconformity (about 3 Ga) Gorge Creek Group - Soansville Subgroup Mosquito Creek Formation Honeyeaicr Basalt (excluding units mapped on Yarric Sheet area) Paddy Market (CIcavcrville) Formation Charlcns Basalt (Excluding type section area) t'orboy (Budjan C'rcck) Formation Regional unconformity Warrawoona Group Salgash Subgroup Duffer Formation (3.4 to 3.5 Ga) Taiga Taiga Subgroup 49 Journal of the Royal Society of Western Australia, 70 (2), 1987 years ago. Available geochronological results for the whole of the Pilbara Craion are now summarized by Blake & McNaughion ( 1 984) and by Trcndall ( 1 984). Fillon a al. named the sequences above the hiatus, the Whim Creek Group and the Negri Volcanics. The Whim Creek Group contained a volcanic province and a clastic prov- ince. Sediments of the latter (the Constantine Sandstone and the Mallina Formation) were equated, although not always specifically by name, to the upper, un-named pari of Lipple's Gorge* Creek Group; the unconformity in the West Pilbara was equaled to those recorded at the base o( the Laila Rookh Sandstone, the Bunjan Formation, and the Mosquito Creek Formation. Hickman(l977; 1983, pp. I9& I05)denied the validity of the regional hiatus and unconformity but this was how- ever reUited bv Horwitz (1979) and Horwitz & Guj (1986). Also, both Wilhelmij & Dunlop (1984) and Krapez (1984) have mapped in detail, and recorded breaks with angular relationships, basal to the Lalla Rookh Sandstone or its equivalent, in pans of the Sirclley area and in the Lalla Rookh Syncline. Horwitz Sc Guj (1986) pointed out that this break exists throughout the Goldsworthv and the Shay Gap belts, between what Hickman ( 1 983) assigned to the cleaverville (Paddy mar- ket) Formation and to the Lalla Rookh Sandstone, justify- ing it thus as a regional feature. In these areas as well as in the syncline 3 km cast of Coppin Gap in the Marble Bar Belt.' Hickman (1983. p. I & 2) did not recognize the unconformity and interpreted volcanics and sediments above the unconformity for the Honeyealcr Basalt, which, in the tvpc section of Lipple ( 1 975. Table 1 ). is below the unconformity. In elTcct. all these units of the Yarri and northern Port Hedland sheet areas compare well with sec- tions above the unconformity in the Whim Creek Belt, for instance with those of the north flank of the Ml Ada-Mt Wilgie inlicr. 15 km south of Roebourne (correctly mapped bv Archer, 1 979. although this author incorrectly placed these units below the Cleaver\'ille Formation in his legend). I have since also recognized the unconformity above the Soansville Subgroup in the Coongan Belt, south of Glen Herring, and in the Marble Bar Bell, south of Eginbah. Boulter e( al. (1987) record its presence in the Tambina complex. Yarrie LOCALITY DIAGRAM Western Australia OCEAN INDIAN 100 Exposed Archaean Yarrie 1:250.000 Geological Sheet area MB Marble Bar N Nullagine R Roebourne W Wodgina C Coppin Gap MC Mosquito Creek 1. Kelly Belt 2. Corunna Downs Batholith 3. Mt. Edgar Batholith 4. MePhee Dome 5 Marble Bar Belt 6. Coongan Belt 7. Goldsworthy Belt 8 Shay Gap Belt 9- Pilgangoora Synclme lO.Strelley Area 11. Whim Creek Belt 12. Lalla Rookh Belt 13. Soansville Belt l4.Tambina Complex Legend B Mt. Bruce Supergroup and Younger rocks 1 to2II Lithostratigraphic columnar sections of Figure 3. Figure 1 Structural units of the northern (exposed) Pilbara Craion (amended after Hickman 1 983). and localities mentioned in the text. 50 Journal of the Royal Society of Western Australia. 70 (2). 1987 In conclusion, the Soansvillc Subgroup is characterised in parts b\ the presence of thick units of cherts, chertified sediments. BIFs and shale which have been \ ariously re- ferred to as the Clcavervillc Formation (Ryan & Kriewaldt 1964. Hickman 1983). the Paddy Market For- mation (Lipple 1975. Hickman & Lipple 1978). and the Ciorge Creek Ciroup ( Fillon (VrtA 1975. Horwii/ 1979). An unconformits, or disconformity. estimated at about 3 Ga years, above the Soansvillc Subgroup, is recorded nearly everywhere west and north of the Corunna Downs and Ml Edgar Batholilhs (Figure 3). An unconformit> at a lower stratigraphic level was also noted by Lipple { i975) at the base of the Corboy Formation (the basal unit of the Soansvillc Subgroup): but this feature was also considered to be of localized extent by Hickman & Lipple ( 1973. p. 3). An unconformilN is however recorded by Krapez (1984) in the Lalla Rookh Syncline and by Wilhclmij & Dunlop ( 1984) in both the Pilgangoora Synclinc and the Strciley area at. what these authors consider to be. the base of the Soansvillc Subgroup equivalent. Figure 3 records most sections where an uncomformity ordiscomformiiy. basal to the Soansvillc Subgroup, was obserxed. I he unconformity of the Kell> Belt The Kelly Belt passes some 25 km west of Nullagine in the East Pilbara. It flanks the Corunna Downs and Ml Edgar batholilhs to the cast and southeast. The belt is split in two by a svncline of overlying Ml Bruce Supergroup units (Figs 1 i 2). oblique to the greenstone bell, and the overlap of these rocks also limits the belt at both ends. The northern part is bound in the southeast by a faulted con- tact against Warrawoona Group units of the MePhee Dome. Most of the southern half of the bell is on the Marble Bar Geological Sheet area, mapped b> Hickman & Lipple (1978). and the northern half is on the Nullagine Geological Sheet area, mapped by R Thom. A H Hickman ing Warrawoona Group volcanics. confirming subdivisions and mapping by Barley (1980, 1981). Hickman (op.cit.) and Lipple (1975) accordingly named the overlying unit “Charlcris Basalt". (Tabic 1 ). and it is unfortunate that this area (marked (2) on Fig. 2A). was chosen as the type section for this formation, because basalts do exist* in the Soansville Subgroup below the Paddy Market Formation in other areas aboul 100 km to the west. The overlying sediments, above the basal conglomer- ate. in traverses a & b (Fig. 2B) arc turbidites and grade from pscphvies to pellites. They contain rare acid volcanics. Discordant chert veins occur (as indicated by Thom cf < 3 /.. and recorded b\ Hickman 1 983, p. 82) as well as large and small olistolilhs of chertified sediment. As in- dicated on the geological sheet the unit grades up (but 52 Journal of ihc Royal Society of Western Australia, 70 (2), 1987 with considerable interbedding) into cherts, chcriiried sediments and BIFs. in relationships, compatible with typical section of the Archaean illustrated by Anhaeusser (1971). and with genetic models described by Eriksson (1983) for BIFs in the Archaean of Southern Africa and Northern Western Australia. In agreement with Thom ct al. most units were found to becheriified in section c (Fig. 2B). Wherever observed, the younging persisted to be east- wards. right up to the boundary fault against the Warrawoona Group, thus avoiding the introduction of recumbant overfolds made by Hickman (1973. Fig. 3). Traverses were later run across the unconformity of the southern pan of the Kelly Bell, where a medium grained granitic rock intrudes the sequence in several sills. Our observations indicate that the sedimentary sequence is the same as the one in the north. Indeed, although inter- rupted, the sequences arc of similar rocks and in strike c.x- lension along the whole bell, both contain rare acid vol- canic rocks, and both show the same relationships to BIFs to the east. Barley (1981. p. 265) records local unconformities, lower in the sequence, between rhyolite lava flows and basalts. Hickman & Lipplc(1976)and Hickman (1983. p. 105) record an unconformity within the Warrawoona Group, at the base of their Duffer Formation. These unconformities in the volcanic piles arc not relevant to this discussion. No younger Archaean sequence, other than the basal unit of the Ml Bruce Supergroup, was rccognized any- where within the Kelly Bell. Some unconformable outliers of conglomerates and breccias, adjacent to fault line scarps, do occur, but they are considered to be associated with the development of the much later Hamersley Land- scapes of Twidale ct al. ( 1 985). Relationships to the Mosquito ( reek area Relationships of the Soansvilic Subgroup to the units of the Mosquito ('reek area are not yet fully confirmed by field traverses. However, observations in the Brunette Hill general area, to the south of Mosquito ( reek, clearly indicate that Bl Fs arc pan of the lurbiditc sequence of the Mosquito Creek Formation of Thom ct al. (in Hickman 1978). Their mapping around the McFhee Dome indi- cates that nowhere docs the Formation rest upon units comparable to the Paddy Market Formation. The domi- nance of lurbidilcs in both, the Mosquito ('reek Forma- tion and the Soansville Subgroup of the Kelly Bell, argues in favour of their correlation, rather than equating one or the other to the Younger sequences, in which similar facies only occur in the Mallina Trough area some 200 km to the northwest. The Mosquito Creek Formation, or part of it al least, is thus tentatively assigned to the Soansvilic Subgroup and unless it is a \ er\ complex sequence composed of two un- conformable formations, it would appear that the Whim Creek CJroup. and other young Archaean sequences such as the Lalla Rookh Sandstone, are not preserved, or did not extend, as far east and south as the Kelly Beit. AcknuHledKonienis I thank D R Hudson and R C Morris for initially reading the manuscript and M E Barley. T S Blake. S L tipple and A L Meakins for discussions or information pertaining to the subject of the paper. Construc- tive criticism was given by an anonymous referee. References Anhaeusser C R 197 1 Cyclic volcaniciiy and sedimentation in the evolution- ary development of .Archaean greenstone belts of shield areas Pub Geo! Soc Aust. 3: 57-70. .Archer R H 1979 Urban Geology. I:500(X). Sheet Roebourne No 2356 III W Aust Geol .Survey PubL Barley M E 1980 The evolution of Archaean calc-alkaline volcanics: a study of the Kelly Greenstone Belt and McPhcc Dome, eastern Pilbara Block. W’e.siern Australia. Ph.D. Thesis. Univ W Aust. Barley ME 1981 Relations between volcanic rocks in the Warawoona Group; continuous or cyclic evolution? Spec PubGcol Soc Aust 7; 263-273. Blake T S & McNaughion N J 1984 A Geochronological Framework for the Pilbara region In; Archaean and Proterozoic Basins of the Pilbara. Western Australia; Evolution and Mineralization Potential (Ed J R Muhling. D 1 Groves & T S Blake) Ckrol Dept & Univ W .Aust Exten- sion. 1-22. Boulter L A, Bickle M J. Gibson B & Wright R K 198^ Horizontal tectonics predating Upper Gorge Creek Group sedimentation Pilbara Block W Aust. Precambrian Res 36: 241-258. Eriksson K A 1 983 Siliciclastic-hosicd iron-formations in the early Archaean Barberton and Pilbara sequences. J Gcol Soc .Ausi 30; 433-482. Fiiton M J. Horwiu R C & Sylvester G 1975 Stratigraphy of the Early Precambrian in the West Pilbara. Western Australia. CSIRO Min- erals Res Lab FP Rep 11. Hickman A H 1977 Stratigraphic relations of rocks within the W'him Creek Belt. W Aust Gcol Survey Ann Rep 1976; 53-56. Hickman A H 1978 Nullagine. WA W Aust Gcol Survey 1:250000 Geol Series Explan Notes. Hickman A H 1983 Geology of the Pilbara Block and its environs. W Aust Gcol Sursey Bull Ml. Hickman A H & Lipple S L 1978 Marble Bar. WA W' Aust Geol Survev 1 :250000 Gcol Senes Explan Notes. Morwiiz R C 1 979 The Whim Creek Group, a discussion. J R Soc W Aust 61 : 67-72. Horwitz R ( & Guj P 1986 Rc-accreditalion of the Whim ('reek Group ( SIRG Div. Mm Geochem Research Rev 1985: 6-7 Krape/ B 1984 Sedimentation in a Small, fault-bounded basin; The Lalla Rookh Sandstone, East Pilbara Block. In: Archaean and Proterozoic Basins of the Pilbara. Western Australia: Evolution and Mineraliz- ation Potential (cd J R Muhling. D I Groves& T S Blake). Geol Dept & Univ W' AuM Extension 89-1 10. Lipple S L 1975 Definitions of new and revised stratigraphic units of the east- ern Pilbara region W .Aust Gcol Survey Ann Rep 1974: 58-63. Maitland A G 1908 The geological features and mineral resources of the Pilbara Goldfield: w ith an appendix by A Monigomcrs- W Aust Geol Survey Bull 40. Noldan A J & W yatt J D 1 962 The geology of portion of the Pilbara Goldfield covering the Marble Bar and Nullagine 4-milc map sheets W ,Ausi Geol Survey Bull 1 15, Ryan G R &, KnewaUll M J B 1963 Archaean stratigraphy in the Roebourne area. West Pilbara Goldfield. W Aust Gcol Survey .Ann Rep 1962: Trendall A F 1983 The Hamersley Basin. In: Iron-formations: Facts and problems (ed A 1* Trendall & R C Morris), Elsevier. Amsterdam. 69-129. Twidalc ( R. Horwiiz R C & Campbell E M 1985 Hamersley landscapes of the Northwest of Western Australia. Revue Geologic Dynamique Geographic Physique 26: 173-186. Wilhclmij H R !r?/r ' - ■ '.4^' " ' /.A^. ,. . ’• ^ ’ , -■'“r ' - .>‘«i ^ vU ■ ... v.-T^' , , vir:-’ . ... >,_*•:.. . V ^ : V- jM . ■ *■:.. .^r . ' ^ - ■ ■■ • ■ ■ -■' '•-^^-^■'*V^^‘*,■■.‘-''.'(^ S' ‘•' t. ’ -'•l.* ..'' . .^ _. *»* . J>»'' » *' ' _ L N « ' r « W ' (W - ; •; -f^V* . .V ■'■•'*. ,^'V' ■ -5;n . ■ • «:J %-.^ - ♦. - * ^''1*1. - • I . -I k- . . ■ 'i2 ■1;. I- 4?- -. . V, *■ ' . ‘ » ■•4i- - V -8 ^iszt <► -. />• '•. ^ ' -■^:- 1- .■ .J-* XV • - , '/■ ■ ■' . - • * ‘ ■ . :.: ' '^^■■:'’ , -iA ^- *’ - "r r’.’r -'.v.^■ < -yfl. :'^- * • • *^ » '.f .-,*** ' ’<1 “. . '"' •'’. ;-■• Vn»T»r?rA»A . • I . x* ’ ' ' ‘ X'-* »»•, i ^ . r. - # i» ^ \ ■ t ■ • ^■^ 2 ' ^ ^ I?* ''T* . - ... J. -<* ' ’ '' ’i.r ' - -^J J***- ‘*~K - f «“.. ^#.*i ■ t V- .fC^Tbr *■ -'- :^.M -> , I »**••• *^ 2^3 4 *yi*4#f ,- X.1* WV ■ ^ . ^ k'.V.T* V • ’ » ’■• I t V / # xl n» *; r ' • - , ; Journal of ihc Royal Society of Western Australia. 70 (2), 1987, 55 Addendum Two Tables referred to the paper by De Laeter & Baxter were inadvertently omitted from the paper (J R Soc VV Aust 69: 113-1 16). Table 1. Rb/Sr data for the Mulgine Granite Rb Sr Sample (ppm) (ppm) Rb/Sr ^^RW^Sr »’Sr/«'>Sr 216 - . 0.878 i 0.009 2.54 ± 0.03 0.79823 ± 0.0005 215 - - 0.99 ± 0.01 2.89 ± 0.03 0.81304 ± 0.0005 175 - - 1.48 ± 0.02 4.34 ± 0.04 0.87017 ± 0.0006 173 - - 1.70 t 0.02 5.05 ± 0.05 0.90001 ± 0.0007 228 - - 2.00 ± 0.02 5.91 ± 0.06 0.92796 ± 0.0006 214 - - 2.25 ± 0.03 6.69 ± 0.07 0.95964 t 0.0007 219 - - 2.43 ± 0.03 7.22 ± 0.07 0.98121 ± 0.0008 •E295 456 187 2.44 ± 0.03 7.24 ± 0.07 0.98993 ± 0.00071 *E42I 313 96 3.29 ± 0.03 9.82 I 0.09 1.06126 ± 0.00031 *A 344 74 4.64 ± 0.05 I4.I ±0.1 1.22000 ± 0.00023 *E294 514 54 9.48 ± 0.09 30.6 ± 0.3 1.91480 ± 0.00090 •296 410 20 20.0 ± 0.2 73.4 ± 0.7 3.47467 ± 0.00080 255 - - 26.1 ± 0.3 100 ± I 4.1102 ±0.0035 247 - - 49.5 ± 0.6 264 ± 3 9.3947 ± 0.0071 *Drill-core samples Table 2. Rb/Sr data for the porphyritic biotite granitoid from Mount Mulgine Sample Rb (ppm) Sr (ppm) Rb/Sr '''Rb/'‘'’Sr “’Sr/^'-Sr 272 . 1.80 ± 0.02 5.27 ± 0.07 0.90180 ± 0.0004 264 - 2.63 ± 0.03 7.78 ± 0.09 0.99558 ± 0.0005 268 - 2.68 ± 0.03 7.96 ± 0.09 1 .00562 ± 0.0004 273 - 3.12 ± 0.03 9.31 ± 0.10 1.04884 1 0.0003 265 - 3.24 t 0.03 9.68 ± 0.1 1 1.06809 ± 0.0005 270 - 3.43 ± 0.03 10.25 ± 0.12 1.06323 1 0.0005 ' 275 - 3.53 ± 0.04 10.58 ± 0.13 1.10013 ±0.0004 266 - 3.58 ± 0.04 10.71 ± 0.13 1.08032 ± 0.0005 *5001 325 87 3.71 ± 0.04 11. 1 ±0.1 1.125.34 - 0.00026 267 - 4.09 ± 0.05 12.28 ± 0.15 1.1 1395 ± 0.0005 *5005 319 73 4.34 ± 0.04 13.1 ±0.1 1.19641 ± 0.00046 *E29l 364 65 5.56 ± 0.06 17.1 ±0.2 1.34592 ± 0.00081 271 * - 7.88 ± 0.09 24.5 ± 0.3 1.54009 ± 0.0006 *Drill-core samples 55 !A'>. -^^ , - *-•1 F ‘'■^ '’'iSi ^■' ' ' A‘- ^ .'*• •' ■' ■ A\ ^ •'’"* s' '-• -- , •* , f -. - ■*. ir. •. '-J ■i s' . ■f*. • O'-'^ , k %-**» %» '. n. ,• . “ * '» I - ‘iw« ti s '*»"*%*' jjHhi, ■ ■'* • ■“” •• ► ' I- ' “#i*V^ •• ' •‘■. ■ ^ - -^It' ’ ‘.: .-A.: ':t’ ' . r'- IL ^ fVi :‘V??'-'^^r V I f •. . ' =• ;. ■* ?• - -- : -' ',. • ,:;» - V^C.*- -.s. I&jinaaf^ ’ ■^T' --;-:/v ■ •* Si- ' , ■ ^ i-*, > • ,»■ '• - ■ -r^r • >■ !i'-««i; -i .. <» Ip - 5 •■ ■■ .'^ I i-' - ^ ... . i; >-■■ Jl- ' .• - - ” ‘-*-r *“ \ ■' "- ,*; . . - ■ ■ '/ ■ ' '. ■■ , '^ii' *■ '■ ■ ■“ li 'i' ■'. ■''■ ■ -■ d '' , ' 'j'‘-^ .-\ - 'f * ^ '* , » ■ m,. V- V«i] *• 1 ^ • -‘^ --, -r .JJ-, J' ' ■'■ . *■ -* ^ ,* , •' ' ft' ftV ‘ • ■' ■ .- '''•■■ k V.’^- ... J' -’ ■** . * - ^ ■ ” » • • V v..^;;.'-...;.,V;i.^- 4 ^-V “j" li *>- r- • r. ^ \L;V r <1 V’V- .' ■ ■ •? , - • t * . ^ i»^^J ift-*’ -*• » i . M ^ ^ ^ .e ... , : "r^'i ^2 - ■' .'i j-, fc".. £. ■*** •' ‘iJil ,i-- > i\ * .»■ » ^*.1 -. *’*.■ .V- l---'ft