Late Neoproterozoic stromatolites in glacigenic successions of the Kimberley region, Western Australia: evidence for a younger Marinoan glaciation

Precambrian Research 92 (1998) 65–87

Late Neoproterozoic stromatolites in glacigenic successions of the Kimberley region, Western Australia: evidence for a younger Marinoan glaciation K. Grey a,*, M. Corkeron b a Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia b Tectonics Special Research Centre, Department of Geology and Geophysics, The University of Western Australia, Nedlands, WA 6907, Australia Received 5 November 1997; accepted 10 April 1998

Abstract Tungussia julia, a Neoproterozoic III stromatolite, occurs in the Egan Formation (Louisa Downs Group), the uppermost glacigenic unit in the Kimberley region of Western Australia. Identification of this stromatolite is significant because it allows biostratigraphic correlation of the Egan Formation with the Julie Formation of the Amadeus Basin (Supersequence 3 of the Centralian Superbasin) and the upper Wonoka Formation of the Adelaide Geosyncline. Both the Julie and Wonoka Formations are stratigraphically younger than the Marinoan glacial sediments of the Adelaide Geosyncline and Centralian Superbasin. This implies that the Egan Formation records a younger glaciation in the late Neoproterozoic in Australia. © 1998 Geological Survey of Western Australia. Published by Elsevier Science B.V. Keywords: Glaciation; Neoproterozoic; Stromatolites; Western Australia

1. Introduction Global synchroneity of Neoproterozoic ice ages has been the subject of considerable debate for the last two decades. However, attempts to demonstrate that glacial episodes were coeval and widespread have foundered because of the lack of adequate dating and the uncertainties in Proterozoic lithostratigraphic correlation. In recent years considerable advances have been made towards establishing a chronostratigraphic subdivision of the Neoproterozoic ( Knoll and Walter, * Corresponding author. Tel.: +61 9 2223333; Fax: +61 9 2223633; e-mail: [email protected]

1992, 1995; Kaufman et al., 1997), but correlation of local stratigraphic successions needs to be resolved before successful global correlation can be attempted. In this respect, substantial progress has been made using stromatolite biostratigraphy in correlating Neoproterozoic successions in Australia, particularly in the Centralian Superbasin and Adelaide Geosyncline (Fig. 1), (Preiss, 1972, 1973, 1974, 1985, 1987; Walter, 1972; Walter et al., 1979, 1994, 1995; Grey, 1995, K. Grey, unpublished data). This paper reports the presence of the stromatolite Tungussia julia Walter and Krylov in Walter, Krylov and Preiss, 1979 in the Egan Formation (Louisa Downs Group), the uppermost glacigenic

0301-9268/98/$ – See front matter. © 1998 Geological Survey of Western Australia. Published by Elsevier Science B.V. PII S0 3 0 1 -9 2 6 8 ( 9 8 ) 0 0 06 8 - 0

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Fig. 1. Distribution of Neoproterozoic basins in Australia [after Walter et al. (1995) and Powell et al. (1994)].

unit in the Neoproterozoic succession of the central Kimberley region of Western Australia (Mount Ramsay area, Fig. 2). T. julia was previously recorded by Walter et al. (1979) from the Julie Formation of the Amadeus Basin, central Australia, and the upper Wonoka Formation of the Adelaide Geosyncline, South Australia (Fig. 1). In both successions the stromatolite occurs near the top of Supersequence 3 as defined by Walter et al. (1995), well above the glacigenic units at the base of the supersequence. Since environments of deposition differ for each of the three occurrences, the distribution of T. julia appears biostratigraphically significant, and indicates correlation of the Egan Formation with the Julie and upper Wonoka Formations. Examination of type and other material from both the Amadeus Basin and Adelaide Geosyncline

revealed that specimens from the Wonoka Formation, previously assigned to Tungussia cf. julia, fall within the range of variation shown by the species. These specimens are consequently reassigned here to T. julia. Less diagnostic stromatolites from both the Egan Formation and the Boonall Dolomite of the Albert Edward Group in the east Kimberley ( Fig. 2), here designated Stromatolite Form 1, provide limited support for local correlation of these two units.

2. Geological background 2.1. Stratigraphic setting of the glacigenic rocks The oldest successions in the Kimberley region include rocks of the Kimberley Basin and the King

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Fig. 2. Regional geological setting of the Kimberley glacigene successions, showing stromatolite localities in the Boonall Dolomite on Gordon downs 1:250 000 sheet ( localities on Mount Ramsay are shown in Fig. 3.)

Leopold and Halls Creek Orogens ( Fig. 2). The Kimberley Basin comprises a thick succession of Palaeoproterozoic sedimentary and volcanic rocks that is mainly flat lying except where the margins have been deformed by tectonism associated with the neighbouring orogens. The orogens consist of structurally complex metasedimentary rocks, intrusive and extrusive igneous rocks of Palaeoproterozoic age, and sedimentary rocks of Mesoproterozoic and Palaeozoic age. Neoproterozoic sediments in the Kimberley

region unconformably overlie various stratigraphic units of the Kimberley Basin and the adjacent orogenic belts. The glacigenic and associated sedimentary rocks occur in three separate areas: Mount House; Mount Ramsay; and an area extending northeasterly from near Halls Creek to the Auvergne area of the Northern Territory ( East Kimberley area, Fig. 2). Plumb (1981) gave a comprehensive description of the geographic distribution and stratigraphic relationships of the glacigenic strata and adjacent facies.

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A single glacial unit, the Walsh Tillite, is present in the Mount House area. Two tillites, the lower Landrigan Tillite of the Kuniandi Group and the upper Egan Formation of the Louisa Downs Group, crop out in the Mount Ramsay area (Fig. 3). The Kuniandi and Louisa Downs Groups are separated by a regional unconformity (Dow and Gemuts, 1969), so these tillites represent two distinct glacial episodes. By contrast, the Fargoo Tillite and overlying Moonlight Valley Tillite of the Duerdin Group in the east Kimberley represent two stadia within a single glacial episode (Dow and Gemuts, 1969). Detailed descriptions of the successions, together with measured sections, are given by Dow et al. (1964) and Roberts et al. (1965, 1972)

2.2. Age Depositional ages of the Kimberley glacigenic successions are poorly constrained. The successions are separated from underlying early Neoproterozoic sediments by an angular unconformity (Dow and Gemuts, 1969). Southeast of Halls Creek, the glacigenic rocks unconformably overlie a carbonate unit, previously assigned to the Mesoproterozoic Bungle Dolomite but recently identified as Tonian or early Cryogenian (between ca 1000 and 725 Ma, early Neoproterozoic) by Grey and Blake (unpublished data). The glacigene successions are unconformably overlain by the latest Proterozoic or early Cambrian Antrim Plateau Volcanics (Mory and Beere, 1988). The

Fig. 3. Distribution of the Egan Formation in the Mount Ramsay area showing stromatolite localities.

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Antrim Plateau Volcanics are unconformably overlain by the Negri Subgroup in Western Australia and the Daly River Group in the Northern Territory, both of which contain fossils of earliest Middle Cambrian (Ordian) age (Mory and Beere, 1988; Kruse, 1990). Previous geochronological dating of shales by the Rb–Sr method (Bofinger, 1967) is of doubtful value, and critical reviews have questioned the precision of the dates obtained (Coats and Preiss, 1980; Plumb, 1981). More recently, Dickin (1995) expressed reservations about the use of Rb–Sr methods, stating that ‘Rb–Sr dating of shales cannot be considered a reliable technique for dating sedimentary deposition’. The validity of the Kimberley dates is therefore suspect, and correlations at present need to be independent of available geochronology. Attempts to date the successions using other techniques, such as acritarch biostratigraphy ( K. Grey, unpublished data), have been unsuccessful. However, some preliminary results ( Williams, 1979; Kennedy, 1996) indicate that isotope chemostratigraphy may have potential for correlation with isotopic curves recently derived from successions in central and South Australia (Calver, 1995). No convincing fossils have yet been found, although younger parts of the Kimberley successions are presumably coeval with successions containing the Ediacaran fauna. The poor result from other methods of dating means that the recognition of late Supersequence 3 stromatolites in the Kimberley succession is significant because it provides the most reliable method of correlation to date. 2.3. Previous correlations Correlation between the three Neoproterozoic Kimberley successions ( Fig. 4) has been debated for many years (Dow and Gemuts, 1969; Plumb and Gemuts, 1976; Coats and Preiss, 1980; Preiss et al., 1978; Plumb, 1991, 1996). Even more discussion has arisen regarding possible correlations between the Kimberley and other parts of Australia. Correlations were based mainly on lithological comparisons because of the lack of suitable dating.

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The association of ‘cap dolostones’, laminated pink-buff dolostones overlying Neoproterozoic glacial successions, is well recognized worldwide ( Knoll et al., 1996). Dow and Gemuts (1969) based their correlation of Kimberley glacigene successions on comparison of the diamictites and associated cap dolostones in the Landrigan, Walsh and Moonlight Valley Tillites. They also used the lithostratigraphic similarities in overlying successions to verify their correlations (Fig. 4, correlation a). Coats and Preiss (1980) noted a resemblance between carbonates in the type section of the Egan Formation (MRM 101) and the Marinoan cap dolostone in the Adelaide Geosyncline. This led them to propose correlation of the Egan Formation with the Walsh and Moonlight Valley Tillites ( Fig. 4, correlation b). However, it is only in the type section that the Egan Formation resembles a cap dolostone. Elsewhere it comprises a complex suite of dark-grey silty limestone and pink dolostone and includes stromatolitic horizons. More detailed facies investigations of these carbonates are the subject of ongoing study by one of the authors (MC ). Most previous Kimberley Neoproterozoic correlations assumed that, where there were two successive glaciations, the older one was probably Sturtian in age and the younger Marinoan. Coats and Preiss (1980) followed this premise and assigned the Landrigan Tillite to the Sturtian and the others to the Marinoan. Recently, Plumb (1996) supported the earlier correlation of the Landrigan Tillite with the Walsh and Moonlight Valley Tillites by Dow and Gemuts (1969). However, he followed Coats and Preiss (1980) in accepting the cap dolostones as Marinoan in age. The correlation of the Landrigan, Walsh and Moonlight Valley Tillites with basal Marinoan glacigenic sediments elsewhere in Australia, as advocated by Plumb (1996), implies that there is no evidence of Sturtian glaciation in the Kimberley region. The correlation of the Egan Formation with the Julie and upper Wonoka Formations proposed here, and based on the presence of T. julia, indicates that the Egan Formation represents a glacial event younger than the basal Marinoan glaciation. It represents an additional episode that

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Fig. 4. Stratigraphy of the Kimberley glacigenic successions indicating alternative correlations: a, after Dow and Gemuts (1969), Plumb and Gemuts (1976) and Plumb (1996), in which the Walsh, and Landrigan Tillites and the package containing the Fargoo and Moonlight Valley Tillites were considered correlatives. The two earlier sets of authors considered these tillites to be equivalents of the Sturtian glaciation, and the Egan equivalent to the Marinoan glaciation. Plumb (1996) considered the presence of cap dolomites in the Walsh, Landrigan and Moonlight Valley tillites to indicate that they were Marinoan, and that the Egan Formation was younger. b, After Coats and Preiss (1980), in which the Egan Formation, Walsh and Moonlight Valley/Fargoo Tillites were correlated and interpreted as equivalent to the Marinoan glaciation, whereas the Landrigan Tillite was considered equivalent to the Marinoan. - - , Suggested correlation of the Boonall Dolomite with the Egan Formation, otherwise the present correlation is consistent with version a.

is still part of the Marinoan, but which is older than the frondose Ediacaran assemblage which appeared between ca 565 and 543 Ma (Brasier and McIlroy, 1998).

3. Methods and terminology Stromatolites from Kimberley localities were collected during the 1995/96 field seasons (Figs. 2 and 3). Previously collected Kimberley stromatolites were also examined. Comparisons were made with a range of Neoproterozoic stromatolites held in the collections of GSWA, AGSO, Department of Minerals and Energy of South Australia and the University of Adelaide, including type and illustrated material of T. julia. Stromatolite study

methods, serial reconstructions and descriptive terminology follow Krylov (1963), Hofmann (1969, 1976), Preiss (1972, 1976), Walter (1972) and Grey (1989). The ‘Contents’ section for each stromatolite group refers to forms currently attributed, and does not imply critical re-assessment of the contents of the taxon. Linnean (binomial ) nomenclature is adopted for stromatolite names (Grey, 1984). Localities are identified by GSWA fossil locality numbers, consisting of a three-letter 1:250 000 map sheet code and accession number (e.g. MRM 101). More specific locality and specimen details are held by GSWA. Described specimens are stored in the GSWA Fossil Collection under catalogue numbers prefixed by the letter F. Precambrian subdivision follows the IUGS chro-

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nometric subdivision (Plumb, 1991). Following Plumb (1991), the terminal Proterozoic (650 to ca 545 Ma) is referred to informally as ‘Neoproterozoic III’ pending recommendations from the Working Group on the Terminal Precambrian. The Australian Marinoan glaciation is included in Neoproterozoic III because of its assumed age of 610 Ma (Christie-Blick et al., 1995). Stratigraphic subdivisions follow the terminology of Walter et al. (1995) for the Centralian Superbasin, in which four supersequences were recognized in Neoproterozoic rocks. This subdivision can be applied to most Neoproterozoic rocks in Australia, and the Marinoan glacial succession occurs at the base of Supersequence 3.

4. Results 4.1. Stromatolites from the Egan Formation Stromatolites are widespread and present at three horizons in the Egan Formation ( Figs. 3 and 5). The formation,which is ca 80 m thick, comprises a basal unit of shallow lacustrine or marine carbonate rocks overlain by a massive diamictite, meltwater-derived conglomerate and sandstone, and a thick succession of subtidal platform carbonate units ( Fig. 5). Stromatolite horizon 1 is best preserved at locality MRM 106 near the O’Donnell River ( Fig. 3). It forms a prominent bench, up to three metres thick, below the diamictite ( Fig. 6) consisting of contiguous, and in places laterally linked, domes and broad columns ca 0.5 m high and 0.5–1.0 m wide, in a cream-yellow dolostone with sandy lenses. Columns are ovoid or slightly elongate in plan view. Laminae are gently and regularly curved, and have a wrinkled profile. Stromatolites from this horizon are here assigned to Stromatolite Form 1. Similar stromatolites are present at three other localities (Fig. 3, MRM 098, 101 and 110). Complexly branching, tungussiform stromatolites are widespread in the Egan Formation (Fig. 3, MRM 091, 099, 100, 107, 109 and 111; stromatolite horizons 2 and 3 in Fig. 5). Stromatolites from both horizons 2 and 3 are assigned to T. julia (Figs. 7–10) because of their widely divergent

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branching and gnarled habit, and from their laminar characteristics. In stromatolite horizon 3, T. julia forms tabular biostromes with closely spaced, occasionally stacked, fascicles. The thickness of the stromatolitic horizon is variable (up to ca 6 m thick), and the tops of some biostromes are truncated. The association of sandy lenses and pebblesized intraclasts in the stromatolitic dolostone implies that the stromatolites grew in a high energy environment. In stromatolite horizon 2, at MRM 109 and MRM 111 incipient columns of T. julia directly overlie diamictite and even encrust some of the diamictite clasts (Fig. 11). 4.2. Stromatolites from the Boonall Dolomite The Boonall Dolomite of the Albert Edward Group, east Kimberley area, is the only other carbonate unit in the glacigene successions of the Kimberley region. Although stromatolites were recorded in the Boonall Dolomite (Dow and Gemuts, 1969), they consist mainly of stromatolitic lamination and fragments of small domes. However, at localities GDD 010 and 015–017 ( Fig. 2) small domical stromatolites occur in cream-yellow dolostone in rubbly outcrops ( Fig. 12). The domes are simple and ca 0.2 m in diameter. Similar domical forms occur in the Egan Formation, although they are rare, and the same microstructure is seen at MRM 106 in stromatolite horizon 1, although here the stromatolites form large domes and pseudocolumns. The Egan Formation stromatolites have undergone extensive recrystallization, making it difficult to confirm that they belong to the same taxon. However, there are sufficient similarities in microstructure to justify assignment of all specimens to Stromatolite Form 1. This tentative identification supports a correlation between the Boonall Dolomite and Egan Formation.

5. Discussion 5.1. Stromatolite biostratigraphy The stromatolite biostratigraphy of the Australian Neoproterozoic is well documented

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Fig. 5. Composite section of the Egan Formation showing the stratigraphic position of stromatolite horizons. (Detailed lithological and facies description of the Egan Formation will be published by MC elsewhere.)

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Fig. 6. Stromatolite Form 1 from the Egan Formation, locality MRM 106. (A) Large, contiguous bioherms in outcrop. Bioherms are ca 1 m in diameter. (B) Thick section of sample F49875 showing poorly preserved, moderately steeply inclined lamination. Scale bar in centimetres. (C ) Detail of lamination and (D) detail of microstructure.

(Preiss, 1972, 1973, 1974, 1985, 1987; Walter, 1972; Grey, 1978, 1995; Walter et al., 1994). Stromatolite time distributions are becoming more tightly constrained as correlation of the Australian Neoproterozoic is refined, and are in accord with results from lithostratigraphy, sequence stratigraphy, isotope chemostratigraphy, acritarch biostratigraphy and, in the latest Neoproterozoic, trace fossils and macrofossils ( Walter et al., 1995). Neoproterozoic stromatolite taxa show non-repetition through time, and many appear to have restricted ranges (Fig. 13). Several forms have wide geographic distributions. This has already enabled correlations to be made for the Tonian or early Cryogenian (early Neoproterozoic) part of the succession (Grey, 1995). Stromatolite correlations in the later Cryogenian and Neoproterozoic III successions (middle and late Neoproterozoic)

are less certain because occurrences are generally less well documented in this part of the succession. In the Amadeus Basin, T. julia occurs at the top of the Supersequence 3 in the Julie Formation ( Fig. 14). The Julie Formation is a succession of oolitic dolostone, limestone, and siltstone with lenses of sandstone that forms the upper part of a single major shallowing-upward succession. The depositional environment is interpreted as a shallow marine environment containing oolitic platform carbonates ( Walter et al., 1979). In the Wonoka Formation of the Adelaide Geosyncline, T. julia occurs near the top of the formation in a very shallow-water facies comprising ooid grainstone, small stromatolite bioherms and intertonguing shallow-water sandstone (Haines, 1990). Both of these environments contrast with the periglacial succession of the Egan Formation. Thus,

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Fig. 7. T. julia from the Egan Formation at locality MRM 100. (A) Series of bioherms in a large biostrome. Bioherms ca 1 m in diameter. (B) Fascicle showing bushy branching habit. Note eroded top. Bottom left column is ca 7 cm wide. (C ) and (D) Fascicles showing branching habit. Lens cap is 52 mm wide. ( E ) Large bioherm showing radiating branching (bottom left). Hammer is 33 cm long.

T. julia has been recorded in different paleodepositional environments, suggesting that the main control on its distribution is probably an evolutionary one. The precise range of T. julia is not known because it is confined to carbonate horizons in predominantly siliciclastic successions. Carbonate

horizons lower in the Neoproterozoic, however, do not contain T. julia, even though some formed in shallow water, high energy environments similar to either the platform carbonates of the Julie Formation or the lagoonal carbonates of the Wonoka Formation. Various Forms of Tungussia are present in these older carbonates ( Fig. 12), but

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Fig. 8. T. julia from the Egan Formation from locality MRM 100. (A and B) Thick sections of sample F49857 showing branching pattern and column shape. Scale bars in centimetres. (C ) Detail of lamination showing streaky microstructure and (D) detail of microstructure showing discontinuous dark laminae.

all are readily distinguished from T. julia (see comparisons in the Systematic Descriptions). Because the stromatolite record is well established below the first known occurrence of T. julia, and because the taxon appears to be independent of facies control, its time-range seems to be restricted to the uppermost part of Supersequence 3. This means that it is still Marinoan in age, but that it occurs in the late Marinoan, rather than the basal Marinoan. The restriction in time distribution allows a correlation to be made between the Egan, Julie and upper Wonoka Formations (Fig. 14). If this correlation is correct, the Egan Formation cannot be equivalent in age to the Marinoan glaciation at the base of Supersequence 3 as previously proposed (Coats and Preiss, 1980), but must lie near the top of Supersequence 3. This also implies that the

Egan Formation records a glacial episode younger than the widespread basal Marinoan event. The other stromatolites in the Egan Formation and Boonall Dolomite (Stromatolite Form 1) have simple morphology and are too poorly preserved to merit formal description. However, they appear to indicate a correlation between the Boonall Dolomite and the Egan Formation. Previously, correlation between the Boonall Dolomite and the Julie and Wonoka Formations had been suggested, based on their equivalent stratigraphic positions and lithological similarities (Coats and Preiss, 1980; Preiss and Forbes, 1981; Plumb, 1996). The present tentative correlation based on stromatolites is consistent with this. There are several records globally of tillites that may be younger than the basal Marinoan ( Kaufman et al., 1997; Brasier and McIlroy, 1998)

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Fig. 9. Serial reconstruction of T. julia. Various views of sample F49859 from MRM 100, showing development of base of columns.

and extending into the Early Cambrian (BertrandSarfati et al., 1995). At present there is insufficient evidence to correlate the Egan Formation globally, but this correlation indicates that the Egan

Formation is older than the frondose Ediacaran fauna of the Pound Subgroup and younger Arumbera Sandstone ( Figs. 13 and 14) which was documented by Walter et al. (1995) and considered

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Fig. 10. Serial reconstruction of T. julia. Sample F49860 from MRM 100, showing development of columns and branching patterns. (A) Selected column showing laminations and tuberous shape. (B) Numerous columns showing complexity of branching.

to have appeared between 565 and 543 Ma by Brasier and McIlroy (1998). 5.2. Diamictite–stromatolite relationships The co-occurrence of diamictite and stromatolites has been interpreted as indicating rapid climatic warming (e.g. Schermerhorn, 1976; Williams, 1979; Preiss, 1987). At two localities in the Egan Formation, T. julia encrusts diamictite

clasts in stromatolite horizon 2 (Fig. 11). The diamictite matrix of fine-grained ferruginous dolomite with lenses of poorly sorted sand grains persists upwards, and is incorporated in the stromatolites, both as lenses within the columns, and in the column interspaces. There is no evidence of a major hiatus between the diamictite and the stromatolites, and it appears that T. julia was actively growing in an environment similar to that of modern saline Antarctic lakes ( Walter and

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Fig. 11. (A) T. julia encrusting mixed boulder clasts in Stromatolite horizon 2 at locality MRM 109. (B) Sample F49865 from MRM 109, polished face showing T. julia encrusting sandstone clasts. Note the intercalation of ferruginous micritic matrix and incipient stromatolite columns. Scale bars in centimetres.

Fig. 12. Stromatolite Form 1 from the Boonall Dolomite. (A) Plan view of domes at locality GDG016. Hammer is 33 cm long. (B–D) Thick section of specimen F49867 from locality GDD 010. (B) Showing moderately steeply inclined lamination; area outlined is shown in more detail in (C ). (C ) Detail of lamination. (D) Detail of microstructure.

Bauld, 1983). The intermingling of stromatolites and a diamictite matrix in the Egan Formation supports the view that stromatolitic cap dolostones may have formed in a periglacial environment.

6. Conclusions The discovery of T. julia in the Egan Formation means that this particular stromatolite is now

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Fig. 13. Distribution of stromatolite taxa in the Neoproterozoic of Australia [after Preiss (1987)], and incorporating data from Preiss (1972, 1973, 1974, 1985), Walter (1972), Walter et al. (1979, 1994, 1995) and Grey (1995) and (Grey, unpublished data). Widespread distribution within a basin or geographical area is indicated by ‘B’, distribution in more than one Australian basin by ‘Aus’, and distribution in basins elsewhere in the world by ‘G’ for global. Stromatolite distributions are occurrences rather than ranges, and are constrained by interpretation of all available stratigraphic data. Each numbered column represents a formation, or a grouping of formations deemed to be lateral time-equivalents based on data from comparative lithostratigraphy and/or acritarch biostratigraphy, isotope chemostratigraphy, seismic interpretation, and sequence stratigraphy ( Walter et al., 1995; Grey, unpublished data). Columns are as follows: 1, Paralana Quartzite (AG); 2, Gillen Member of Bitter Springs Fm (AB); 3, Loves Creek Member of Bitter Springs Fm (AB), Coominaree Dolomite (AG), Skates Hills Fm (S), Browne Fm (O), Yackah Fm (G), Eliot Range Fm ( K ); 4, ? Dunns Mine Limestone (AG); 5, Waraco Limestone (AG); 6, Paratoo Diapir xenoclast (AG); 7, River Wakefield Subgroup (AG); 8, Skillogalee Dolomite (AG), Neale Fm and Kanpa Fm (O), Tarcunyah Group (S); 9, Sturtian glacials (AG), Julius River Member (diamictite) of Black River Dolomite ( T ); 10, Tapley Hill Formation (AG); 11, Brighton Limestone/Balcanoona Formation (AG); 12, Tarcowie Siltstone (AG); 13, Aralka Fm (AB); 14, Etina Fm (AG); 15, Trezona Fm (AG); 16, basal Pioneer Fm and Winnall beds (AB); 17, upper Pioneer Fm (AB); 18, Pioneer Fm ‘cap dolostone’ (AB), Wonapi Dolomite Member of Mount Doreen Fm (N ); 19, Wonoka Fm (AG); 20, upper Boondawari Fm (S), Boord Fm (AB); 21, Julie Fm (AB), Wonoka Fm ‘unit 11’ (AG), Egan Fm and Boonall Dolomite ( K ); 22, Elkera Fm (G). AB, Amadeus Basin; AG, Adelaide Geosyncline; G, Georgina Basin; K, Kimberley; N, Ngalia Basin; O, Officer Basin; S, Savory Basin; T, Tasmania. $, In situ occurrence; Ω, occurrence as clast; · · · , presumed reworking; - - -, time range between occurrences.

known from three widely separated areas of Australia, and in each it occurs in a different environment, indicating that the main control

on its distribution was an evolutionary one. The known stromatolite distributions in the Neoproterozoic suggests that T. julia had a time

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Fig. 14. Revised correlation of Kimberley glacigenic successions with the Amadeus Basin and Adelaide Geosyncline. The Egan Formation is correlated with the Julie and upper Wonoka Formations by the occurrence of T. julia. The Egan Formation is correlated with the Boonall Dolomite based on lithostratigraphy and the presence of Stromatolite Form 1. The Boonall Dolomite has been lithologically correlated with the Julie and Wonoka Formations by Coats and Preiss (1980), and the T. julia occurrences are older than the frondose Ediacara fauna of the Pound Subgroup and Arumbera Sandstone. The Walsh, Landrigan and Moonlight Valley/Fargoo Tillites are interpreted as correlates of the Marinoan glaciation, and the Egan formation as a younger glaciation.

range, restricted to near the top of Supersequence 3. From this it is concluded that the Egan Formation correlates with the Julie and upper Wonoka Formations of central and South Australia. This correlation indicates that diamictites in the Egan Formation represent a glacial episode younger than the glacial episodes at the base of the Marinoan.

Acknowledgment Substantial contributions to discussions on the geological setting and implications of these inter-

pretations were made by Ken Plumb, Chris Powell, Ian Tyler, Alan Thorne and Annette George. Malcolm Walter and Wolfgang Preiss provided information about T. julia. K. Grey publishes with the permission of the Director of the Geological Survey of Western Australia, and her work contributes to remapping of Proterozoic rocks in the Kimberley area undertaken by GSWA as part of the National Geoscience Mapping Accord. She wishes to thank AGSO, the University of Adelaide and the Department of Mines and Energy of South Australia for arranging access to collections of type specimens and other comparative material. The assistance of Des Strusz, Richard Jenkins and

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Wolfgang Preiss in making material available is gratefully acknowledged. M. Corkeron was supported by ARC Grant No. A39332240 to C. McA. Powell and Z.-X. Li. This paper is publication No. 10 of the Tectonics Special Research Centre, University of Western Australia, and is a contribution to IGCP 320-Terminal Proterozoic.

Appendix A Systematic palaeontology

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T. wilkatanna Preiss 1974 from the Skillogalee Dolomite, Burra Group (Supersequence 1 equivalent), Adelaide Geosyncline. Distribution and age. Mesoproterozoic and Neoproterozoic. Only a few forms are from the Mesoproterozoic, the majority are from the Neoproterozoic (Bertrand-Sarfati and Awramik, 1992). All forms recorded so far from Australia are from the Neoproterozoic. T. julia Walter and Krylov in Walter, Krylov and Preiss 1979 (Figs 7-10)

Group Tungussia Semikhatov 1962 $ $

$

1960 Collenia suchotungusica Semikhatov, p. 1481 (Semikhatov, 1960) 1962 Tungussia Semikhatov, p. 205

Type form. Tungussia nodosa Semikhatov 1962, pp. 205–207, Pl VI, Pl. VII, 1,2 from the Sukhotungusin Suite, Yenisei Mountains. Diagnosis. As in Semikhatov (1962) (p. 1481). For a translation of the diagnosis see Walter et al. (1979) (p. 299). Content. At least 32 forms have been recorded and a detailed list is given in Bertrand-Sarfati and Awramik 1992. Only forms previously recorded as occurring in Australia are listed here: T. erecta Walter 1972, from the Gillen Member, Bitter Springs Formation, (Supersequence 1), Amadeus Basin; T. etina Preiss 1974, from the Brighton Limestone and Etina Formation, Umberatana Group (Supersequence 2 equivalent), Adelaide Geosyncline; T. inna Walter 1972, Ringwood Member, Aralka Formation, (Supersequence 2), Amadeus Basin; T. julia Walter and Krylov in Walter, Krylov and Preiss 1979 from the Julie Formation (Supersequence 3) Amadeus Basin; T. cf julia of Preiss in Walter, Krylov and Preiss 1979 (here transferred to T. julia) from the upper Wonoka Formation, Wilpena Group (Supersequence 3 equivalent), Adelaide Geosyncline;

$

1979 T. julia Walter and Krylov in Walter, Krylov and Preiss 1979 (pp. 299–302, Figs 11 and 12) 1979 T. cf julia Walter and Krylov in Walter, Krylov and Preiss 1979 (pp. 302–304, Figs 13–16)

Material Holotype. T. julia Walter and Krylov in Walter et al. 1979 [Fig. 11(B–E)], CPC 19006, from ‘south of the road from Alice Springs to Ross River Tourist Chalet, 0.5 km east of Acacia Well and south of the turnoff to Trephina Gorge’ Walter et al. (1979). The holotype was illustrated as Fig. 11(B–E), but this information was omitted from the figure caption (M.R. Walter, personal communication, 1994) Paratypes. locality.

CPC 19007–19009, from the type

Other material. T. cf. julia, South Australian Department of Mines and Energy Sample No. 6635RS194, from near the top of the Wonoka Formation, Bunyeroo Gorge, central Flinders Ranges ( Walter et al., 1979); here assigned to T. julia. New material includes GSWA F49855 and F49856 from MRM 099, F49857 to F49860 from MRM 100, F49861 to F49863 from MRM 107, F49864 from MRM 108, F49865 and F49866 from MRM 109. T. julia is also present at MRM 091 and 111. All new specimens are from the Louisa

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Downs area, Mount Ramsay, Kimberley, WA. Locality details are given in Table 1. Diagnosis.

As in Walter et al. (1979) (p. 299).

Description. New specimens conform closely to the diagnosis of T. julia, although laminae are slightly better preserved than in the type and previously described material. Mode of occurrence. T. julia occurs at several outcrops and is commonly visible in vertical section, and occasionally in plan view. It occurs in tabular biostromes consisting of contiguous fascicles, commonly single layered but occasionally stacked en echelon. Bioherms are commonly 50 cm high, but may be up to 1 m high. Individual fascicles are usually ca 50 cm high and 50 cm wide, but can be larger. Where stromatolites encrust erratic boulders, only small, incipient columns are present, but they have similar microstructure to better developed columns. These stromatolitic patches increase in size upwards, and may develop into columns, but they rarely become established as true fascicles. Elsewhere, biostromes are at least 30 m in diameter, and are sometimes more extensive. Fascicles grew on a variety of substrates ranging from fine micritic mudstone to grainstone,

and erratic cobbles and boulders. They are interbedded with micritic mudstone, grainstone, sparry calcite and rare ooid grainstone. The upper contacts of the bioherms tend to be erosional. Fascicle morphology. Fascicles are generally slightly flattened spheroids with a diameter of ca 50 cm to 1 m wide and ca 50–75 cm high. Not all fascicles reached these dimensions, many were truncated before they were properly established. Each fully developed fascicle consists of a complexly branching individual with a bushy habit. Branches radiate from a complex core that consists of small domes and incipient branches, and which has commonly undergone several periods of truncation and regrowth. Branching development is erratic and irregular. Towards the core of the fascicle the structure is generally domical to pseudocolumnar, but some short branches may be present. Away from the core, branching is more common, and once established, branches are persistent, and further branching is infrequent. Branches in general radiate away from the core, but are often highly sinuous. In plan view the structure gives rise to a highly complex pattern of overlapping lobes near the core of the fascicle, and discrete spherical, ovoid, or lobate cross sections around the outer margin of the fascicle.

Table 1 Details of sample localities Locality code

Latitude

Longitude

Location

Formation

Identification

GDD 010 GDD 015 GDD 016 GDD 017 MRM 091 MRM 098 MRM 099 MRM 100 MRM 101 MRM 106 MRM 107 MRM 108 MRM 109 MRM 110 MRM 111

18°17∞47◊S 18°27∞23◊S 18°26∞09◊S 18°15∞30◊S 18°22∞01◊S 18°33∞55◊S 18°33∞56◊S 18°23∞40◊S 18°34∞18◊S 18°18∞13◊S 18°19∞03◊S 18°15∞43◊S 18°14∞56◊S 18°29∞09◊S 18°34∞32◊S

127°58∞41◊E 127°57∞40◊E 127°51∞12◊E 127°00∞30◊E 126°35∞06◊E 126°36∞34◊E 126°36∞10◊E 126°36∞53◊E 127°06∞11◊E 126°42∞55◊E 126°35∞59◊E 126°37∞54◊E 126°40∞07◊E 126°56∞21◊E 126°34∞55◊E

SE end Elvire R. gorge 4 km WNW Mt Timperley 1.8 km SE Palm Spring 9 km NE Mt Flora 5 km SW Junction Yard 3 km ESE Lily Hole Bore 2.8 km SE Lily Hole Bore 2 km NE Pavement Hill 1.5 km S Stockyard Crossing 10.6 km ESE Mt Cummings 7.5 km ENE Mt Dent 10 km SW Mt Cummings 5.8 km SW Mt Cummings 12 km SW Mt Amhurst Hstd 1.8 km S Lily Hole Bore

Boonall Dol Boonall Dol Boonall Dol Boonall Dol Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm Egan Fm

Stromatolite Stromatolite Stromatolite Stromatolite T. julia Stromatolite T. julia T. julia Stromatolite Stromatolite T. julia T. julia T. julia Stromatolite T. julia

Form Form Form Form

1 1 1 1

Form 1

Form 1 Form 1

Form 1

Stromatolite localities in the Mount Ramsay and east Kimberley areas. Localities are identified by a GSWA Locality Code that consists of a three letter code for the relevant 1:250 000 map sheet, followed by an accession number (e.g. MRM 101).

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Branching pattern and column arrangement. Branching is frequent adjacent to the domical core of the fascicle and tends to be sub-parallel or slightly divergent. Branching decreases in frequency, and becomes more markedly divergent outwards from the core. It may be dichotomous or multiple. Branching is highly variable; it is predominantly a, occasionally b and less frequently c in style. Columns frequently coalesce after branching, particularly in the core of the bioherm, and bridging is common. Away from the core bridging and coalescence is less common, and individual, subcylindrical columns develop. Column inclination is very variable; in the centre of the bioherm columns are more or less vertical, those around the margins and at the base are horizontal or frequently recumbent, and between these two extremes columns are gently to steeply inclined. The attitude of a column may change along its length, particularly near the base of the fascicle, where columns flex upwards around the outer margin. Column shape. Columns are highly tuberous, irregular and rarely sub-cylindrical. In plan view they are irregularly lobate to elongate, rarely circular. Column margins are bumpy with numerous protrusions up to 2 cm wide. These sometimes develop into small lateral branches. Some laminae overhang column margins to form small peaks and cornices. Columns may be constringed near the fascicle core, but become more uniform towards the margins. They are generally ca 5 cm wide, but are broader near the fascicle core. Laminae. Laminae vary widely from steeply convex to almost flat lying, and most are wavy and multicrested. Degree of inheritance is low and lateral continuity is variable. Most laminae are persistent across the column, but some are discontinuous. Flexures range from 1 to 20 mm with an amplitude of up to 5 mm, but more commonly of 2 mm. Wall-development is patchy. Some laminae are downturned at column margins and form walls that extend for up to 2 cm. Walls are rarely more than two or three laminae thick, and are often indistinct because of poor preservation. In other parts of the column, particularly towards the core

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of the fascicle, laminae abut against the column margin without downturning. Microstructure and texture. In general the microstructure is streaky, but details are poorly preserved and only visible in patches. In some areas laminae are replaced by secondary recrystallization. Where preserved, the microstructure consists of thin, lensoid, streaky, dark laminae preserved in a pinkish cream matrix [Fig. 8(C and D)]. The matrix consists of poorly defined light laminae, but these are difficult to distinguish where they are stacked directly on each other and not separated by a dark lamina. Dark laminae are quite variable in thickness, for example, a lamina with a thickness of ca 150 mm may thicken suddenly to nearly 400 mm. Thicknesses of dark laminae range from ca 50 mm to ca 400 mm; most are between 100 and 200 mm in thickness and most are micritic. They have a gradational lower boundary, but commonly have a sharper upper contact. They gradually darken upwards. The boundaries are irregular but generally lensoid, and taper rapidly towards the column margin. Few dark laminae extend across the column width. Many laminae are wavy and discontinuous, and the few that turn down at the margins are very thin. Light laminae are more uniform in nature, and thicknesses range from ca 300 mm to over 1000 mm. Where light laminae are stacked directly on light laminae, the boundaries can rarely be discerned. Most grains and peloids are hypidiotopic and are <20 mm in diameter. Both light and dark laminae have palimpsest structures that may represent degraded filament tubes. In most cases these are sub-parallel to the laminae, but in some dark laminae they are vertical and have an indistinct radiating pattern. Some dark laminae also have an indistinct spheroidal texture that is too poorly preserved to allow the original nature to be properly determined, but which resembles poorly preserved coccoid microfossils. Interspace filling. Spacing is variable; columns can be up to 1–2 cm apart, or sometimes less depending on the position in the fascicle. No ooids

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were observed in the interspaces, and in this respect the Kimberley specimens differ from those in central and south Australia. Interspace filling is variable and ranges from patches of khaki micrite, pelloidal grains similar to the texture of the columns and neomorphic spar, intermixed with rip-up clasts. Recrystallization is extensive, and replacement by goethite or limonite common. In less recrystallized patches a crude layering can be recognized. Secondary alteration. There has been a considerable degree of secondary alteration. Some laminae have been replaced by limonite and goethite; patches of manganese are present; and parts of the light laminae have poikilotopic cement, and patches of neospar occur. Stylolites occur parallel to some laminae. Thin, sub-parallel quartz veins cross-cut some columns. Comparisons. The specimens can be assigned to Tungussia on the basis of their divergent branching and horizontal to recumbent columns. The stromatolite has highly variable, wavy laminae, a streaky microstructure, and only a thin wall, features characteristic of T. julia. These features distinguish T. julia from most other forms of Tungussia (Bertrand-Sarfati and Awramik, 1992). Tungussia f. indet Preiss 1985 from the Waraco Limestone in the Callanna Group has continuous laminae and tuberous columns. Tungussia wilkatanna Preiss 1974 (recorded from Supersequence 1) has smooth to gently bumpy columns that are tuberous and frequently walled and has continuous, thinly banded laminae. Tungussia erecta Walter 1972 has gnarled, tuberous columns that are mostly erect and sub-parallel, and has walled columns. Tungussia etina Preiss 1974 (from Supersequence 2) shows a wide variation of branching style, and has much thicker, wavy, laminae that pinch and swell. Tungussia inna Walter 1972 (also from Supersequence 2) has crooked, bumpy columns that branch and coalesce frequently, and has an almost continuous multilaminate wall and bridging. Remarks. Although T. julia has been affected by recrystallization at all known localities, it can

still be readily identified by its streaky microstructure and wavy laminae, and forms from all three localities are very similar. Preiss [in Walter et al. (1979)] only tentatively assigned specimens from the Wonoka Formation to the species, but comparisons with the type material from the Julie Formation show that all have the diagnostic characteristics of the species, and T. cf. julia is here transferred to T. julia. Several species of Tungussia occur in the late Neoproterozoic of Australia, but all are quite distinctive, and seem characteristic of specific time horizons. T. julia appears to be restricted in range to the top of Supersequence 3. Distribution and age. Middle to late Ediacarian (Neoproterozoic III ) of Australia. Julie Formation, upper part of Supersequence 3, Amadeus Basin, Centralian Superbasin, Northern Territory. Unit 11 of Haines (1990), topmost Wonoka Formation, Wilpena Group, Adelaide Geosyncline, South Australia. Egan Formation, Louisa Downs Group, Kimberley area, Western Australia. Stromatolite form 1 (Figs. 6 and 12) Material. GSWA F49867 to F49873 from GDD 010, and F49874 from GDD 015, Boonall Dolomite, Gordon Downs, and F49875 and F49876 from MRM 106, Egan Formation, Mount Ramsay; Kimberley, WA. Locality details are given in Table 1. Description. Most specimens are poorly preserved as a result of recrystallization. Stromatolites occur either as small rounded domes or develop upwards into rounded columns. Domes commonly range from 10 to 50 cm in diameter and are about the same in height. Where more columnar forms are present these may be ca 50 cm high, and up to 1 m wide. Columns are usually contiguous and overgrow more domical structures. Column tops are gently rounded. Domes appear to develop on flat-laminated carbonate, but the basal contact is rarely seen. The upper contacts of the bioherms tend to be erosional. Column structure is generally very simple, domi-

K. Grey, M. Corkeron / Precambrian Research 92 (1998) 65–87

cal to pseudocolumnar, and no branching has been observed. In plan view columns are spherical or ovoid, and adjacent columns often merge. Laminae vary widely from steeply convex to almost flat lying in the upper parts of columns. Steeply convex laminae may have a slight crest near the apex, but this never develops into an axial zone. Laminae are regularly curved, and they are generally smooth and persist across the column. Most are wavy, and flexures range up to ca 5 mm with an amplitude of ca 2 mm. A finer scale wrinkling is also present, with wrinkles 0.2 mm high and 1 mm wide. Some laminae are downturned at column margins and form impersistent walls, but the true nature of wall structure is difficult to determine because of poor preservation. The degree of inheritance is high. In general the microstructure is banded, but details are often poorly preserved. Specimens from the Egan Formation are especially poorly preserved because of extensive recrystallization, and only a few patches demonstrate that the microstructure is similar to that observed in the Boonall Dolomite. When well-preserved, the microstructure consists of slightly irregular, occasionally lensoid, dark laminae alternating with more persistent and regular light laminae. The boundary between light and dark laminae is commonly gradational, whereas the upper boundary of dark laminae is often sharp. Thicknesses of dark laminae range from ca 30 mm to ca 60 mm, and they are micritic. Light laminae range from ca 85 mm to over 200 mm. They are formed of rounded grains 10–20 mm in diameter. Details of interspace filling are uncertain and there has been a considerable degree of secondary alteration.

Remarks. Poor preservation prevents identification and more detailed systematic analysis at present. Open nomenclature is preferred until better preserved material is available.

Distribution and age. Boonall Dolomite, Albert Edward Group and Egan Formation, Louisa Downs Group, Kimberley area, Western Australia.

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