“source to sink” sedimentology and petrology of a …...“source to sink” sedimentology and...

“Source to Sink” Sedimentology and Petrology of a Dryland Fluvial System, and Implications for Reservoir Quality,

Lake Eyre Basin, Central Australia.

Saju Menacherry Bachelor of Science (Geology), University of Calicut, India. Master of Science (Geology), University of Kerala, India.

Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy

Australian School of Petroleum Faculty of Science

The University of Adelaide Australia

March 2008

“Source to Sink” Sedimentology and Petrology Chapter 4: Provenance Lithotype Characterisation

Saju Menacherry - 63 -

CHAPTER 4 PROVENANCE LITHOTYPE CHARACTERISATION

Provenance data can play a critical role in the following:

• assessing palaeogeographic reconstructions

• constraining lateral displacement in orogens

• characterising crust which is no longer exposed

• testing tectonic models for uplift at fault block or orogen scale

• mapping depositional systems

• correlating sub-surface data, and

• reconstructing the evolutionary model of reworked sediments from older basins to younger basins (Johnson and Beaumont, 1995; Tortosa et al., 1991).

• Burial diagenesis and subsequent reservoir quality determinations

The provenance of siliciclastic sediments has been used for over a century to provide important constraints on the sources of siliciclastic sediments in foreland basins and on the relative timing of deformation and depositional events. The first and most important step in understanding sand generation and evolution is the fundamental analysis of tectonic setting (Dickinson and Yarborough, 1978; Dickinson and Suczek, 1979; Dickinson et al., 1983; Ingersoll and Busby, 1995). In this study the twelve isopach thickness maps discussed in the previous chapter form the basis for analysing the tectonic setting and basin evolution.

This involves relating the sediment provenance and sediment’s environmental signal (climate, transport, facies etc.) to sediment composition during the generation of depositional sequences in different basin settings (Basu, 1976; Potter, 1986; Zuffa, 1987; Wilson et al., 2001). This study adopted this methodology (provenance lithotyping) of sandstone composition and evolution can lead to a better understanding of sediment generation from provenances in different geo-tectonic settings to the present day western Lake Eyre Basin setting.



Provenance lithotype characterisation provides a framework in which to make assumptions about the rocks from which sediments are derived, the processes by which sediments are generated and evolved, and how the sediments of the basin reflect the assemblage of provenance lithotypes in the hinterland. Provenance lithotype assemblage can be inferred from the palaeo-tectonic setting details (Dickinson, 1985; Kairo and Heins, 2004). Provenance studies can provide succinct interpretations of the plate tectonic settings of source areas through analysis of the detrital modes of siliciclastic strata in diverse depositional basins (Dickinson, 1985). The tectonic regime of the hinterland setting is the one that assembled and exposed the provenance lithotypes from which sediments were derived, and that determined drainage and basin geometries at the time of the deposition. As the changes in provenance are basin-wide, compositional variations in the sandstones are useful for regional correlation of siliciclastic strata in depositional basins (Ingersoll, 1978).

The sedimentary successions in intracratonic basins record the uplift and unroofing history of their adjacent basement uplifts. Provenance studies, in combination with structural geology and the data derived from isopach thickness maps, can effectively constrain the timing of uplift and erosion of the hinterland and facilitate the reconstruction of palaeodrainage patterns in the intracratonic basins (Zuffa, 1985; Ingersoll and Busby, 1995; Critelli et al., 2003). In addition geometrical relationships of sediment source areas with respect to the ‘receiving’ sedimentary basins can also be established. These principles can also be used to infer sediment generation and sedimentation from basin to basin, and can determine the amount of reworked sediments from older to younger sedimentary basins (Cavazza et al., 1993).

4.1 METHODOLOGY

Forty-three representative provenance lithotype rock samples were collected from the Precambrian (Palaeo-Neoproterozoic) Peake and Denison Inliers (Davenport Ranges) through to the Cenozoic Lake Eyre Basin strata exposed throughout the Umbum Creek catchment. These samples were subsequently used for petrographic thin-section analysis and constitute the bulk of samples used for the provenance lithotype study (Appendix 2). The samples were collected from the Umbum Creek catchment as this region contains the key provenance lithotypes observed in the present day western Lake Eyre Basin. The lithologies of provenance lithotypes include metasediments, volcanics, granites and monzonites of the Peake and Denison Inliers, and sedimentary rocks.



Sedimentary rocks of three sedimentary basins (Arckaringa, Eromanga and Lake Eyre Basins) were also analysed. The provenance lithotype characterisation study focused on the analysis of sandstones in the source rocks as these rocks best reveal the details of provenance (Bokman, 1955; Folk, 1974; Basu, 1985; Arribas et al., 2000).

During the course of this study 72-grain categories were defined in order to assess frame work grains from their origin and depositional setting, which, in turn, provided the information about the provenance and tectonic regime of the depositional environment (Ingersoll and Busby, 1995) (Appendix 3). The 72-grain categories include quartz (monocrystalline and polycrystalline), feldspar (potassium and calcium), and rock fragments (sedimentary, metamorphic, volcanic, silcretes and other undifferentiated grains) (Folk, 1974; Ingersoll et al., 1984). Based on a selected 14 sandstone thin-sections out of the 43 available, a modal analysis of 250 grain counts was made using the 72-grain categories (Appendix 4). The remaining 29 provenance lithotype thin-sections were petrographically analysed in order to establish composition and to get an indication of depositional environment. The sandstone thin-section data throw light on the evolution of sediment source areas and palaeogeographic reconstructions, in reference to the sedimentary basin evolution history of the western Lake Eyre Basin.

In order to develop a better understanding of the tectonic setting of the various provenance regions, more than one sample were studied from different levels of the successions. For the recognition of source rock lithology and tectonic setting of the provenance, the modal QFL (Q-quartz, F-feldspar, L-lithic fragments) data (Table 4.1) were plotted on a ternary diagram (Folk, 1974). In addition, ternary diagrams were plotted for QmFLt (Qm-quartz monocrystalline, F-feldspar, Lt- total lithics), QFkFp (Q-quartz, Fk- K-feldspar, Fp-plagioclase feldspar), and QtFL (Qt-total quartz, F-feldspar, L-lithic fragments) (Dickinson and Suczek, 1979; Dickinson et al., 1983) (Fig. 4.1).



T

able

4.1: M

odal

analy

sis da

ta for

key l

ithos

tratig

raph

ic un

its (Q

FL, Q

tFL a

nd Q

mFLt

terna

ry dia

gram

s).



Figure 4.1: QFL, QtFL and QmFLt ternary diagrams showing the provenance of sandstone thin section data from each formation in the provenance lithotype characterisation. This figure clearly shows that sublitharenite to quartzarenite are the most dominant provenance lithotypes. Overall, these sediments may represent a recycled to craton interior provenance.



4.2 RESULTS

4.2.1 PEAKE AND DENNISON INLIERS: PALAEO-NEOPROTERZOIC

Description

The Peake and Denison Inliers are typically represented by quartzite samples, whereas the sandstone samples represent the younger sedimentary basins. The Palaeo-Neoproterozoic of the Peake and Denison Inliers comprise meta-sediments and meta-volcanics. The composition of these lithologies varies significantly (Table 1.1). The entire sequence is characterised by abundant quartzites with interbedded basalt and minor rhyolite (Flint, 1993). In total, twenty rock thin-sections were analysed from the Peake and Denison Inliers in order to see the relationship between the source rocks and sedimentation.

Four quartzites from the Peake and Denison Inliers, all with different mineralogical composition, were analysed (Appendix 4). Monocrystalline and polycrystalline quartz comprised the most abundant framework grain type in these samples (Table 4.1). Details of the four quartzites whole rock thin section description are listed below:

1. Baltucoodna Quartzite (Palaeoproterozoic) (Fig. 4.2A) (Table 4.1). This quartzite comprises lithic arkose and is fine- to medium-grained, very angular to sub-angular, with the framework consisting of predominantly monocrystalline quartz grains (55%). K-feldspar (24%) is typically present and there is an absence of polycrystalline quartz and plagioclase. The polycrystalline quartz seems to have recrystallised during metamorphism. Lithic fragments include volcanics (felsic 6% and mafic 8%) and muscovite (8%).

2. Duff Creek Beds sandstone (Neoproterozoic) (Fig. 4.2B) (Table 4.1). This quartzite consists of sublithic arenite and is fine- to medium-grained, very angular to subangular. It is composed of monocrystalline (50%) and polycrystalline (29%) quartz grains, mostly plagioclase feldspar (8%) with a rare appearance of K-feldspar (1%). Lithic fragments include volcanic tuff (4%) and volcanic mafic and dolomite (3%).

3. Mount Margaret Quartzite (Fig. 4.2C) (Table 4.1). This quartzite consists of quartz arenite and is fine- to medium-grained, and angular to sub-rounded. It has an abundance of monocrystalline quartz (96%), very minor polycrystalline quartz (2%)



and < 3% K-feldspar without any other lithic fragments, including volcanic or metasedimentary fragments.

4. Skillogalee Dolomite sandstone (Fig. 4.2D) (Table 4.1). This quartzite is typical of a feldspathic litharenite (Fig. 4.1) according to the scheme of Folk (1974). Clasts are fine- to medium-grained, very angular to subangular and comprise monocrystalline quartz (59%) grains, sedimentary lithic fragments (17%) and chert (>1%), with a relatively high content of K-feldspar (17%). Lithic fragments are predominantly felsic volcanic clasts (6%) and mafics (<1%).

The remaining Peake and Denison Inliers thin section samples analysed related lithologies such as granites, volcanics, volcanic tuff, siltstone, hornfels, dolomite and monzonite. The provenance lithotype thin-sections were also analysed from the Wirriecurrie Granite, Tidnamurkuna Volcanics, Cadlareena Volcanics, Warloan Beds, River Wakefield Formation, Fountain Spring Beds and Kalachalpa Formation (Fig. 4.2E, F, G, H) (Appendix 2).

Interpretation

1. Baltucoodna Quartzite

Palaeoproterozoic rocks (Fig. 4.2) are exposed in the Peake and Denison Inliers immediately adjacent to the northeastern margin of the Gawler Craton (Fig. 2.2). In the Baltucoodna Quartzite the abundance of non-undulatory monocrystalline quartz suggests a plutonic provenance for this sandstone which was then later metamorphosed to a quartzite sequence (Dickinson, 1985; Suttner et al., 1981; Tortosa et al., 1991) (Table 4.1). In addition the high incidence of potassium feldspar further suggests that the detritus was derived from a granitic source (Basu, 1976).

The presence of muscovite mica and angular clasts collectively point to rapid deposition and to a near source (Blair and McPherson, 1994). High-grade metamorphic gneisses of the Gawler Craton are the most likely source for these muscovites. The tectonic setting of the source area for the Baltucoodna Quartzite is recycled orogenic (Valloni, 1985; Potter, 1986). The volcanic fragments observed in the thin sections (Table 4.1) probably originate from erosion of the volcanic province within the Gawler Craton region. Whilst the minor presence of calcsilicates, epidote



Figure 4.2: Thin section photomicrograph of provenance lithotypes from the Proterozoic – Peake and Denison Inliers. A. Baltucoodna Quartzite B. Duff Creek Beds sandstone C. Mount Margaret Quartzite D. Skillogalee Dolomite sandstone E. Wirriecurrie Granite F. Tidnamurkuna Volcanics G. River Wakefield Formation laminated siltstone H. Kalachalpa Formation siltstone.



ellipsoids within some quartzites, rare marble, and fine-grained, well-laminated and well-sorted quartzites in the Palaeoproterozoic, Peake and Denison Inliers are interpreted as indicating a shallow-marine depositional environment with bimodal volcanism (Drexel et al., 1993).

2. Duff Creek Beds sandstone

The Neoproterozoic succession (Fig. 4.2) of the Peake and Denison Inliers commences with coarse clastics followed by volcanics and evaporative deposits such as dolomite and limestone (Krieg, 2000). The abundance of quartz suggests a plutonic provenance for this Duff Creek sample. Poor sorting and angular grains indicate rapid deposition and derivation from a nearby source. The presence of plagioclase feldspar is indicative of a volcanic provenance (Blair and McPherson, 1994; Pittman, 1963). A sandstone unit in the Duff Creek Beds is dominated by angular grains of both monocrystalline quartz and polycrystalline quartz (Table 4.1) suggesting that these were eroded from the adjacent granitic crystalline basement (Basu, 1976; Suttner et al., 1981). Carbonate grains are probably the eroded clasts from previous sequences (reworking) or from the Gawler Craton. Erosion from the Gawler Range Volcanic province is the most likely provenance of the volcanic fragments observed in the sample. These deposits formed under arid to semiarid conditions in shallow, highly saline seas, associated with evaporating lagoons above high tide level, and also in playas farther inland (Krieg, 2000). The tectonic setting of the source area for the sandstone unit of the Duff Creek Beds is a recycled orogenic provenance (Fig. 4.1) (Valloni, 1985; Johnson and Beaumont, 1995). The sedimentation of this sequence was supplied from local provenance regions, mainly the Gawler Craton, but also from the Musgrave Block.

3. Mount Margaret Quartzite

The high percentage of monocrystalline quartz in the Mount Margaret Quartzite sample(Table 4.1) suggests that the detritus was derived from the stable craton (Suttner et al., 1981). The presence of potassium feldspar indicates a source from granitic terrain (Helmold, 1985). The fine- to medium-grained, angular to sub-rounded grains, as well as sparse feldspar, points to a wet tropical or subtropical climate regime. The decreasing feldspar content and decreasing grain size in the succession suggest peneplanation of the stable cratonic provenance (Tortosa et al., 1991). A stable craton continental block provenance (Fig. 4.1) is suggested as the tectonic



setting for the Mount Margaret Quartzite of the Neoproterozoic period in the Peake and Denison Inliers. The Mount Margaret Quartzite sediments were supplied from local provenance regions, mainly the Gawler Craton. During the time of this deposition no sediments were derived from the Musgrave Block, as it was submerged (Drexel et al., 1993).

4. Skillogalee Dolomite sandstone

The Skillogalee Dolomite of the Neoproterozoic consists mainly of dark grey dolomite with interbeds of partly dolomitic sandstone and siltstone (Krieg, 2000). A fine- to medium-grained sandstone in the Skillogalee Dolomite contains very angular to sub-angular clasts derived from the adjacent granitic crystalline basement (Basu, 1985). The abundant monocrystalline quartz and the presence of potassium feldspar (Table 4.1) indicate a plutonic granitic provenance (Suttner et al., 1981). The provenance of the volcanic sediments in the succession suggests erosion from the Gawler Range Volcanic province within the Gawler Craton basement (Marsaglia, 1993). The presence of rare siltstone rock fragments also provides evidence of a sedimentary source area. The mineralogy of this sequence is consistent with a change in depositional environment from a lake to a shallow marine setting within a wet tropical climate (Mack, 1981). A recycled orogenic provenance is suggested as the tectonic setting for the sandstone unit of the Skillogalee Dolomite (Basu, 1985; Tortosa et al., 1991) (Fig. 4.1). The Skillogalee Dolomite sediments in the Peake and Denison Inliers were originally supplied mainly from the Gawler Craton. The submerged Musgrave Block was not a source for the Skillogalee Dolomite deposits (Drexel et al., 1993).

The Qt-F-L diagram (Fig. 4.1) demonstrates a recycled-orogen provenance. The exception is the Mount Margaret Quartzite sample which is shown to be derived from a stable craton interior continental block provenance. In the Qm-F-Lt diagram (Fig. 4.1), the Baltucoodna Quartzite sample plots in the mixed zone (quartzose recycled and transitional continental provenance); the Duff Creek Beds sample plot in the transitional recycled provenance; the Mount Margaret Quartzite plots in the cratonic interior provenance and the Skillogalee Dolomite sample plots in the quartzose recycled provenance. The above four quartzose sandstones show increasing maturity in mineralogy according to the quartz and feldspar diagram (Fig. 4.1).



The difference in detrital composition between the quartzite successions and the sandstone units are thus caused by the change in provenance (Haughton et al., 1991; Arribas et al., 2000). This change may reflect an unroofing sequence related to the progressive erosion of the Gawler Craton, Musgrave Block and the Gawler Range Volcanics. Alternatively, the change in composition may have been caused by a variation in the source area. The final stage of sedimentation in the Peake and Denison Inliers was characterised by two episodes of glacial deposition separated by a warmer interglacial episode, followed by a long period of emergence and erosion, prior to the next cycle of events (Krieg, 2000). The presence of relatively high feldspar percentages in the Baltucoodna Quartzite, Duff Creek Beds and Skillogalee Dolomite samples (Table 4.1) indicates an uplift of the Gawler Craton basement. Increased lithic fragments in the Skillogalee Dolomite sample also suggests basement uplift within Peake and Denison Inliers with unroofing of older formations are the most likely sediment source.

In summary, the petrographic attributes of the sedimentary cycles in the Peake and Denison Inliers strongly suggest that sedimentation in the Palaeo- and Neoproterozoic successions was influenced by tectonic uplift in the basement of the Gawler Craton and Musgrave Block, mainly from granitic sources within a continental tectonic setting. The nearby Gawler Craton is the most probable provenance for the Palaeoproterozoic successions and the combined provenances of Gawler Craton, Musgrave Block and Gawler Range Volcanics are suggested for the Neoproterozoic successions. The influence of plutonic sources is probably related to the erosion of the granitic basement of Gawler Craton, which represents the western limit of the Peake and Denison Inliers. The volcanic rock fragments most probably originated from the Gawler Range Volcanics.

4.2.2 OFFICER BASIN: CAMBRIAN-ORDOVICIAN

Description

Thin section analysis was not possible on any of the sandstones of the Officer Basin due to the lack of exposed outcrops in the Umbum Creek catchment area. Cambrian-Ordovician igneous rocks are represented in this area by the Bungadillina Monzonite (Fig. 4.3) and granitoids from the Peake and Denison Inliers (Davenport Ranges). These range from quartz monzonite to quartz syenites, and feldspathic granitoid rocks (Lindsay and Leven, 1996). No other Cambrian-Ordovician deposits are known in the study area, and if they were ever deposited they have been



subsequently removed by erosion. However, provenance and tectonic setting details of the Officer Basin sediments are available from published literature (Drexel and Preiss, 1995; Gravestock et al., 1995; and Lindsay and Leven, 1996).

Interpretation

According to Lindsay and Leven (1996) the depositional sequences in the Cambrian-Ordovician were deposited in northeast-trending Troughs in the study area. These sequences were originally sourced from a combination of Gawler Craton and Musgrave Block, as well as from the reworking of older sediments (Fig. 2.2). The Officer Basin is only sparsely represented in the subsurface within the study area, but much of the sedimentary record has been lost through deep weathering, erosion and planation in the Palaeozoic (Drexel and Preiss, 1995; Gravestock et al., 1995).

4.2.3 ARCKARINGA BASIN: LATE CARBONIFEROUS-PERMIAN

Description

Thin-section petrographic analysis was not possible on any sandstones from the Arckaringa Basin succession due to the lack of exposure in the Umbum Creek catchment area (modern sand study area). However, existing PIRSA thin-sections were examined from two units of the Arckaringa Basin: the Boorthanna Formation and the Stuart Range Formation (Fig. 4.3), with the resulting interpretations supplemented by published work regarding provenance and tectonic setting from previous published works by Wopfner (1980), Hibbert (1995) and Krieg (2000).

The Arckaringa Basin succession consists of three formations: the Boorthanna Formation (oldest and lowermost), the Stuart Range Formation (middle) and the Mount Toondinna Formation (youngest and uppermost) (Table 1.1).



Figure 4.3: Thin section photomicrographs of provenance lithotype in the Officer and Arckaringa basins. A. Bungadillina Monzonite B. Conglomeritic section of Boorthanna Formation C. Boorthanna Formation sandstone with fine silty matrix D. Stuart Range Formation Shale.



1. The Boorthanna Formation: The formation generally consists of mudstones, conglomerates, sandstones and green-brown shales and siltstones (Krieg, 2000). One thin section plus observations of previous workers is used to characterise this formation. A single thin-section examined shows both siltstone with conglomerate. Quartz is the most abundant framework grain type (Fig. 4.3C). In the conglomerate grain size ranges from a few millimetres to a few centimetres and consist of various rock types including limestone, quartzite, rhyolite (volcanic rocks from the Gawler Ranges volcanic province), ironstone and other crystalline basement rocks.

2. The Stuart Range Formation: Observations of previous workers is used to characterise this formation. The unit consists mainly of pyritic, claystone characterised by randomly scattered quartz grains (Krieg, 2000). The available thin-section shows pyritic shale, with minor silt to very fine-grained arkosic sandstone. Quartz and feldspar are the most abundant framework grain type (Fig. 4.3D).

3. The Mount Toondinna Formation: This formation consists of grey pyritic, micaceous, fine-grained sandstone and silty to sandy shale with abundant carbonaceous laminae (Krieg, 2000).

Interpretation

The modal analyses of petrographic attributes of the basal Boorthanna Formation are consistent with a glacigene origin. Hibburt (1995) interpreted a marine depositional environment for the Stuart Range Formation following a deglaciation, whilst Krieg, (2000) concluded that lacustrine depositional environment for the Mount Toondinna Formation was most likely.

The sequences of the Arckaringa Basin, with the exception of sediments from the early Boorthanna Formation, reflect similarity in sediment composition, probably as a result of input from the same provenance (Hibburt, 1995) (Fig. 2.3). The southern part of the basin was strongly influenced the sediment sourced from Gawler Craton provenance. Whilst Officer Basin sediments mainly controlled the sedimentation in the north of the basin (Hibburt, 1995). The minor changes in the provenance and the sand dispersal system for these formations suggest a probable source



derived from plutonic basement, with additional contributions from quartzose sediment and volcanic rocks (Hibburt, 1995).

1. Boorthanna Formation: Krieg (2000) concluded that the frame work grain population was derived from the early Boorthanna Formation is significantly different from that of other successions in the Arckaringa Basin, which all display a similar sediment distribution. The clasts were interpreted as redeposited glacial debris, transported downslope by mudflows (Drexel et al., 1993). Petrographic data supports sediment derivation from a combination of Gawler Craton, Musgrave Block, Gawler Range Volcanics and Officer Basin successions. The occurrence of volcanolithic sandstones and siltstones probably signify individual episodes of unroofing and glacial transportation (Krieg, 2000).

2. Stuart Range Formation: The abundance of polycrystalline quartz suggests either cratonic or continental arc with large outcrops of metamorphic basement as the provenance for these sediments (Tortosa et al., 1991; Johnson and Beaumont, 1995). The source of sediment for the Stuart Range Formation is probably from the Gawler Craton, Musgrave Block, Gawler Range Volcanics and Officer Basin successions (Krieg, 2000).

3. Mount Toondinna Formation: As with the Stuart Range Formation, the inferred provenance for these deposits was from a combination of Gawler Craton, Musgrave Block, Gawler Range Volcanics and Officer Basin successions (Krieg, 2000).

4.2.4 EROMANGA BASIN: EARLY JURASSIC-LATE CRETACEOUS

Description

The Jurassic-Cretaceous sedimentary record is represented mainly by sandstones and mudstones of the Eromanga Basin. These successions can be divided into seven geographically distinct tectonic units (Table 1.1), each which display various, distinctive, sedimentological, heavy mineral and petrographic differences. Pre-Jurassic orogenic folding and faulting, basin development, and epeirogenic movements created many separate geological provenance sources for sediments of the Eromanga Basin (Drexel and Preiss, 1995; Krieg et al., 1995). The Jurassic–Cretaceous successions out-crop in the Umbum Creek catchment area. These formations include the



Algebuckina Sandstone, the Cadna-owie Formation, the Mount Anna Sandstone, the Bulldog Shale, the Coorikiana Sandstone, the Oodnadatta Formation and the Winton Formation. These are all slightly tilted and in the present landscape form erosional remnants and cuesta-type landforms on the present day banks of the Umbum Creek.

Sandstone samples from the Algebuckina Sandstone, Cadna-owie Formation, Bulldog Shale, Coorikiana Sandstone and Oodnadatta Formation were analysed for provenance lithotype characterisation. Samples from Mount Anna Sandstone and Winton Formation were not analysed due to the lack of outcrops in the study area.

1. Algebuckina Sandstones: Three sandstone thin-sections from the Algebuckina Sandstone were analysed (sublitharenite to litharenite) (Fig. 4.1) (Appendix 4):

• Algebuckina Sandstone –1

•

from the lower part of the sequence (Fig. 4.4A) (Table 4.1). This sandstone consists mostly of moderately sorted, medium-grained, angular to sub-rounded grains and clasts. It is a sublitharenite with monocrystalline quartz (76%), and sub-ordinate polycrystalline quartz (10%). There are K-feldspar contents (5%) and more than trace quantities of plagioclase (<1%). Sedimentary recycled lithic fragments (<8%) and traces of heavy minerals (<1%) are also present.

Algebuckina Sandstone –2

•

from the middle part of the sequence (Fig. 4.4B) (Table 4.1). This sandstone sample is moderately sorted, fine- to medium-grained and dominated by angular to sub-rounded grains. The sample has a litharenite with less monocrystalline quartz (65%) compared to the previous sample, but equivalent polycrystalline (10%), and K-feldspar (4%) contents more than trace quantities of plagioclase (<1%). Sedimentary recycled lithic fragments including chert (11%), and muscovite mica (2%) are present as well as both felsic (2%) and mafic (>2%) volcanic fragments. Around 4% of wood fragments are also present.

Algebuckina Sandstone –3 from the upper part of the sequence (Fig. 4.4C) (Table 4.1). This sandstone sample consists mostly moderately sorted, fine-grained angular to sub-rounded frame work grains. Compositionally this sample is a sublitharenite, with a high monocrystalline quartz content (90%), with much less polycrystalline quartz (2%) observed. Also present are K-feldspar contents (>1%),



sedimentary recycled lithic fragments (<1%), muscovite mica (4%) and traces of heavy minerals (>2%).

2. Cadna-owie Formation sandstone (Fig. 4.1 and 4.4D) (Table 4.1) (Early Cretaceous): This sandstone consists of moderately sorted, very fine- to fine-grained, angular to sub-rounded frame work grains. This sample is a litharenite dominated by monocrystalline quartz (72%) with minor polycrystalline (2%). K-feldspar contents (4%) are present with plagioclase (3%). There are also sedimentary recycled lithic fragments (7%), chert (3%), muscovite mica (4%), glauconite clasts (>2%), plants fossils (>1%) and traces of heavy minerals (>2%).

3. Bulldog Shale (Fig. 4.1) (Table 4.1): Two thin-sections were examined:

• Sandstone – 1:

•

This sample consists of poorly sorted, very fine- to fine-grained, very angular to angular grains. This sample consists of feldspathic litharenite dominated by monocrystalline quartz (74%), with no polycrystalline grains. There is less K-feldspar (1%) than plagioclase (6%). There are also sedimentary recycled lithic fragments (8%), carbonate fragments (>2%), mafic volcanic fragments (2%), muscovite mica content (3%), biotite mica (<1%), and heavy minerals (>3%) (Fig. 4.4E).

Sandstone – 2

: This sandstone sample consists mostly of medium-grained, moderately sorted, angular to sub-rounded grains. A feldspathic litharenite, this sample comprises monocrystalline quartz (70%), less polycrystalline (6%), plagioclase (6%), K-feldspar (>2%), sedimentary recycled lithic fragments (6%), chert (6%), carbonate fragments (>1%), mafic volcanic fragments (<1%), metamorphic lithic fragments (>1%), and traces of heavy minerals (<1%) (Fig. 4.4F).

4. Coorikiana Sandstone (Mid Cretaceous) (Fig. 4.4G) (Table 4.1): One thin section was examined from typical Coorikiana Sandstone, consists of moderately sorted, fine-grained, angular to rounded clasts. A litharenite (Fig. 4.1), This sample is less dominated by quartz, and all monocrystalline quartz (57%). Plagioclase (>6%) exceeds K-feldspar (>1%) clasts. Sedimentary lithic fragments are important (17%), with carbonate lithic fragments (8%),



muscovite mica (<1%), glauconite (9%) and traces of heavy minerals (>1%) also observed.

5. Oodnadatta Formation sandstone (Late Cretaceous) (Fig. 4.4H) (Table 4.1): A thin section of a typical sandstone sample consists mostly of moderately sorted, fine- to medium-grained, angular to sub-rounded grains. It is a sublitharenite (Fig. 4.1) comprising monocrystalline quartz (80%) and polycrystalline grains (10%). There is a complete lack of feldspar. Other components include sedimentary recycled lithic fragments (9%) and traces of heavy minerals (1%).

Interpretation

The provenance of the Eromanga Basin samples is interpreted below for each of the formations examined.

1. Algebuckina Sandstone: (Fig. 4.4). The fluvial Algebuckina Sandstone (Croke et al., 1998) show subtle changes (sorting, grain size, composition ..etc) from the base to the top indicating variation in sediment deposition in the provenance area. The lower sample (Algebuckina Sandstone –1) (Table 4.1) and upper sample (Algebuckina Sandstone –3) (Table 4.1) show a comparatively higher percentage of quartz than the middle sample (Algebuckina Sandstone –2) (Table 4.1).

Compositionally these three samples plot in the ‘recycled-orogen’ in the Qt-F-L diagram. However, according to the Qm-F-Lt diagram (Fig. 4.1), both the bottom and middle samples fall in the ‘quartzose recycled’ field and the upper sample plots in the ‘craton interior’ field (Basu, 1976; Dickinson, 1985; Ingersoll and Busby, 1995). The high incidence of monocrystalline quartz and K-feldspar in the lower sample (Algebuckina Sandstone -1) indicates a granitic provenance which is consistent with the provenance definition of Basu, (1976). In addition, sedimentary lithic fragments suggest reworked grains from an older sedimentary provenance. The lack of volcanic lithic fragments implies no involvement of a volcanic terrain in the sediment source area, or there has been a complete removal of volcanic lithic fragments via intensive chemical weathering transforming into clays.



Figure 4.4: Thin section photomicrographs of provenance lithotypes in the Eromanga Basin. A. Lower Algebuckina Sandstone B. Middle Algebuckina Sandstone C. Upper Algebuckina Sandstone D. Cadna-owie Formation sandstone E. Coarse-grained sandstone in Bulldog Shale F. Medium-to fine-grained sandstone with fine matrix in Bulldog Shale G. Coorikiana Sandstone H. Oodnadatta Formation sandstone.



The nature of the framework grains suggests that the most likely provenance for the lower sample from the Algebuckina Sandstone was a combination of Gawler Craton, Musgrave Block, and older Arckaringa Basin sedimentary deposits. Although the middle sample from the Algebuckina Sandstone (Algebuckina Sandstone -2) has a lower quartz content, the predominance of K-feldspar within the feldspar group, also suggests a granitic terrain source which consistent with provenance definition of Pittman, (1970). The volcanic lithic fragments suggest that a minor part of the detritus was derived from an older volcano-sedimentary succession in the sediment source area. The ‘upper’ sample however has a quartz and K-feldspar content indicative of a granitic source. The muscovite grains are indicative of detritus derived from a nearby source and that less chemical weathering had occurred. The minor amount of sedimentary lithic fragments also suggests minimise reworking and rapid localised deposition. The presence of heavy mineral is consistent with a granitic provenance which agrees with Morton and Hurst, (1995).

In summary, tectonic uplift of a granitic provenance (Gawler Craton) influenced sedimentation in agreement with Valloni, (1985); Ingersoll and Busby, (1995). In addition, the tectonic uplift at the basin margins of the Eromanga Basin was accompanied by adjacent accommodation space creation which led to the deposition of the medium to lower coarse-grained fluvial sediments in during the deposition of the Algebuckina Sandstone.

2. Cadna-owie Formation: (Fig. 4.4). The provenance of the Cadna-owie Formation sandstone sample plots in the recycled-orogen zone as per Qt-F-L ternary diagram, whereas according to Qm-F-Lt ternary diagram (Fig. 4.1), these samples plots in the quartzose recycled provenance area.

The high percentage of monocrystalline quartz and K-feldspar indicates a granitic provenance as per the studies of Dickinson, (1985). Conversely sedimentary lithic fragments indicate some reworking from an older sedimentary provenance. The presence of chert also suggests a sedimentary origin with the reworking of chert grains, most likely from marine Officer Basin sediments. The lack of volcanic lithic fragments indicates the absence of a volcanic terrain in the source area. The muscovite grains indicate a low chemical weathering influence, and that detritus was derived from either a nearby granitic



source area or metamorphic muscovite rocks from adjacent Proterozoic deposits. The presence of zircon heavy minerals is also consistent with a granitic provenance region which agrees with Morton and Hurst, (1995). The presence of glaucony confirms the shallow marine depositional environment for the Cadna-owie Formation.

In summary, the lithology of the various framework grains infer that the provenance of the sandstone sample from the Cadna-owie Formation was most likely from the Gawler Craton and Musgrave Block in combination with an adjacent metamorphosed Proterozoic deposits. Recycled of older sedimentary deposits, from the Officer and early Eromanga Basin successions is also possible. A major tectonic event occurred late in Cadna-owie Formation time, resulting in the uplift of the Gawler Range Massif, leading to the erosion of the uppermost part of the of the Cadna-owie Formation (Krieg, 2000).

3. Bulldog Shale: The Bulldog Shale has been described by Krieg, (2000) as a marine succession composed of dark grey carbonaceous shaley mudstone and claystone, interbedded with pale siltstone and very fine sandstone (Fig. 4.4). Wood fragments and finely disseminated pyrite are also present, and shell debris is common. Shelly limestone concretions and ironstone concretions occur stratigraphically higher in the succession and observed in outcrop within the study area (Croke et al., 1998).

The analysed sandstone samples plot on the Qt-F-L and Qm-F-Lt diagrams (Fig. 4.1), confirm the provenance as recycled-orogen and quartzose recycled field respectively which agrees with provenance definitions of Dickinson, (1985); Potter, (1986). However, the variation in lithology suggests different depositional settings with changes in sediment generation at the sediment source area for each of the two sandstones of this succession.

The samples from the lower succession of the Bulldog Shale have only monocrystalline quartz and have elevated plagioclase and lower K-feldspar proportions, suggestive of a granitic and metamorphic source which is consistent with Pittman, (1970); Helmold, (1985). The presence of sedimentary, metamorphic and volcanic rock fragments in trace amounts suggests that a minor part of the detritus was derived from an older volcano-



sedimentary succession in the source area. The muscovite grains suggest that minimise exposed chemical weathering and those clasts were derived from a near source.

4. Coorikiana Sandstone: This formation was described by Moore and Pitt (1984) as a succession of very fine- to medium-grained clayey to silty sandstone with interbeds of claystone and siltstone (Fig. 4.4). In addition, carbonaceous material, wood fragments and wood impressions are present in unweathered parts of this succession (Moore and Pitt, 1984; Krieg, 2000). This unit represents a period of widespread regression, resulting in a thin extensive lowstand shoreface sand-prone succession (Moore and Pitt, 1984; Krieg et

al., 1995).

Petrographic studies of Coorikiana Sandstones revealed both clastic and carbonate sedimentary lithic fragments, glauconite, quartz and feldspar in a clayey to silty matrix. Compositionally the provenance of this sandstone plots in the recycled-orogen in the Qt-F-L diagram, and in the quartzose-recycled field in the Qm-F-Lt diagram which agrees with provenance definition of Dickinson, (1985) (Fig. 4.1).

The apparent decrease in quartz percentage in comparison with the other formations and the relative increased sedimentary lithics suggest additional input of lithic sediments from the cannibalization of bedrock and exposed sedimentary basin deposits. Increased plagioclase content and decreased K-feldspar indicates a metamorphic and plutonic terrain source. The presence of both clastic and carbonate lithic fragments without volcanic rock fragments, and the presence of heavy minerals indicate that the Coorikiana detritus was derived from an older clastic and carbonate sedimentary succession. Although the presence of monocrystalline quartz suggest a granitic hinterland source area retained its influence on sediment supply. In contrast, however the glauconite clasts were observed are typically of those generated in a shallow marine depositional environment. In summary, the Coorikiana Sandstone sediments were generated mainly from an uplifted Proterozoic Gawler Craton as well as from erosion of older Officer Basin sediments.

5. Oodnadatta Formation: This formation was described by (Krieg et al., 1995) as consisting of laminated, thin-bedded claystones and siltstones with interbeds of fine-



grained sandstone (Fig. 4.4) deposited in a low-energy, shallow marine environment. The Oodnadatta Formation samples plot on Qt-F-L, and Qm-F-Lt diagrams (Fig. 4.1), in the ‘recycled-orogen’ and ‘quartzose recycled’ provenance. The high percentage of monocrystalline quartz and slightly increased polycrystalline quartz indicates a sediment source from both a granitic and metamorphic gneissic terrain which is consistent with the observations of Critelli et al., (2003); Johnson and Beaumont, (1995). The absence of feldspar clasts is notable and indicates either less influence from the granitic provenance region, or complete removal of feldspar by chemical weathering. In addition, the sedimentary lithic fragments suggest reworking from an older sedimentary provenance. The presence of heavy minerals also supports the reworking of grains from an older sedimentary provenance or a granitic provenance which agrees with conclusions of Morton and Hurst, (1995).

These framework grains suggest that the most likely provenance for the sandstone sample from the Oodnadatta Formation is a combination of Gawler Craton dominates in the hinterland, as well as older sedimentary deposits around the margin of the basin (possibly of Eromanga Basin origin).

4.2.5 LAKE EYRE BASIN: PALAEOGENE AND NEOGENE

Description

The Lake Eyre Basin represents the Palaeogene and Neogene sedimentary record in the basin evolution study area and is divided into four geographically distinct tectonic units (Table 1.1), each with clear distinctions in sedimentology, petrology and heavy mineral content.

1. Palaeogene—Eyre Formation (latest Palaeocene to the Middle Eocene 56.5 – 42 Ma). The Eyre Formation unconformably overlies Eromanga Basin rocks and is overlain unconformably by the Etadunna Formation. The Eyre Formation comprises sandstone, carbonaceous clastics and conglomerates, and consists largely of mature, pyritic, carbonaceous sand, silt and gravel (Callen et al., 1995; Croke et al., 1998).



2. Palaeogene to Neogene—Etadunna Formation (Late Oligocene to Miocene, 27.9 – 10 Ma). The Etadunna Formation overlies the Eyre Formation and is disconformably overlain by Neogene units. The Etadunna Formation comprises very fine-grained sand and silt with calcareous intervals (Callen et al., 1986; Callen et al., 1995).

3. Neogene (5.3 – 1.6 Ma, Pliocene to Pleistocene). The third phase of sedimentation in the Lake Eyre Basin is characterised by the deposition of red-brown arenites and dark, fine-grained lacustrine sediments. Aeolian and evaporitic facies are common and dense horizons of calcrete and gypcrete have developed in the soils (Alley, 1998).

4. Neogene (1.2 – 0.0 Ma, Pleistocene to Holocene). The fourth phase of Lake Eyre Basin sedimentation is marked by a series of five depositional episodes recorded in the western Lake Eyre Basin (Callen et al., 1995). The sedimentary records of these episodes suggest early fluvial, then lacustrine and finally aeolian dominated influences (Krapf and Lang, 2005).

Sandstone from the Eyre and Etadunna Formations, which represent the first two phases of Lake Eyre Basin development, were used in the provenance lithotype characterisation phase of this study. In addition, the study obtained information about the provenance and tectonic setting of the third and fourth phases of the Lake Eyre Basin sediment formations as described earlier works by Johns (1989), Callen et al. (1995), Magee et al. (1995), Alley (1998), Croke et al. (1998), Lang et al (2004) and Krapf and Lang (2005) were also incorporated into this study. Sediments from the third phase and fourth phases of Lake Eyre Basin development are the main sediment source for the modern sand sediments present in the western Lake Eyre Basin and are the subject of Part 2 of this thesis.

Thin-sections from sandstone samples of the Eyre and Etadunna Formations were analysed as follows (Appendix 4).

1. Eyre Formation: This sandstone is a sublitharenite (Fig. 4.1) dominated by moderately to well-sorted, fine- to medium-grained, angular to rounded clasts. Quartz is the most abundant component (82%) within the Eyre Formation (Table 4.1) and all quartz is monocrystalline. The quartz grains are more rounded than the other clasts. There is comparatively less feldspar (2%); and plagioclase (>1%) slightly exceeds K-feldspar (<1%). Sedimentary recycled lithic fragments (11%) are predominantly clastic lithic fragments and there is increased heavy mineral content (5%).



2. Etadunna Formation: This sandstone is a sublitharenite (Fig. 4.1) dominated by moderately sorted, fine- to coarse-grained, angular to rounded grains. Quartz makes up the highest proportion of the framework grain assemblage (Table 4.1). Monocrystalline quartz (79%) is far more abundant than polycrystalline quartz (7%). Monocrystalline quartz with straight extinction is markedly more abundant than the undulose extinction grains. Feldspar grains comprise 6%, with plagioclase feldspar (3%) slightly more dominant than K-feldspar (>2%) grains. Sedimentary lithic fragments comprise around 5% of the whole rock, in which chert grains make up >1%, clastic sedimentary clasts 3% and carbonate detritus only less than 1%. The heavy mineral content constitutes around 3% in this sandstone.

Interpretation

1. Eyre Formation: Compositionally the provenance for this sandstone plots in the ‘recycled-orogen’ according to the Qt-F-L diagram, and in the ‘quartzose-recycled’ field of the Qm-F-Lt diagram (Fig. 4.1). The high occurrence of monocrystalline quartz and feldspar, both plagioclase and K-feldspar, indicates a granitic and metamorphic source. However, the presence of sedimentary lithic fragments suggests the reworking of grains from an older sedimentary provenance which agrees the observations by Ingersoll and Busby, (1995); Critelli et al., (2003). The lack of volcanic lithic fragments suggests little or no influence of volcanic terrain in the source area. The presence of zircon heavy minerals (Fig. 4.5) also suggests a granitic provenance or, alternatively, the reworking of sediments from older deposits.

Most of the Eyre Formation sediments were derived from a mixture of uplifted sedimentary and meta-sedimentary source rocks. The sediment generation of the Eyre Formation has been interpreted by many workers as the product of a multi-channelled or braided river system during the epeirogenic uplift of the Stuart Range and Peake and Denison Inliers, accompanied by subsidence in the Lake Eyre Basin (Krieg et al., 1990; Alley, 1998; Croke

et al., 1998). The rounded and coarse grains common in Lake Eyre Basin sediments represent reworked second or third-cycle clasts derived from Permian and Mesozoic rocks (Callen et al., 1995). According to Cavazza et al., (1993) the grain size and lack of metamorphic and volcanic clasts suggest slow sedimentation, with more time for chemical weathering possible.



The Eyre Formation is similar to the Algebuckina Sandstone, but shows evidence of lower flow energy, based on shallow channel incision. This according to Krieg, (2000) suggests a landscape of fairly low gradients and only mild uplift in the Eyre Formation sediment source region.

The analysis of the framework grains suggest that the most likely provenance for the Eyre Formation sediments was a combination of Gawler Craton, uplifted metamorphosed Proterozoic deposits from the Peake and Denison Inliers (Davenport Ranges), and older sedimentary deposits, most probably of Eromanga Basin origin.

Following deposition of the Eyre Formation, 14 Ma elapsed before the next sedimentary cycle began. During this time three major concurrent processes took place: weathering, tectonism (folding and faulting) and climate change (Krieg, 2000). There is a significant hiatus in the Palaeogene sedimentary succession within the study area between the Eyre and Etadunna Formations. This sedimentation hiatus was attributed to the regional silcrete and ferricrete development over the Eyre Formation (Wopfner, 1978; Alley, 1998).

2. Etadunna Formation: This sandstone sample composition plots in the ‘recycled-orogen’ of the Qt-F-L diagram, and in the ‘quartzose-recycled’ field according to the Qm-F-Lt diagram (Fig. 4.1).

The high percentage of monocrystalline quartz and the increased polycrystalline quartz is indicative of an uplifted metamorphic terrain. The feldspar content of this sample indicates a granitic and/or a metamorphic source. Both of these interpretations support the work of earlier workers such as Suttner, et al. (1985) and Helmold, (1985). The various sedimentary lithic fragments provide evidence of the presence of reworked

grains from the older sedimentary provenances. Carbonate grains (Fig. 4.5) are probably derived from uplifted Proterozoic metasediments. There is no volcanic influence in the source area, as evidenced by the lack of volcanic lithic fragments, suggesting insignificant influence from Gawler Craton. The presence of heavy minerals also suggests a granitic provenance or the reworking of grains from the older sedimentary deposits. The chert



clasts (Fig. 4.5) represent the reworking of the metasedimentary deposits of the Peake and Denison Inliers.

The petrographic attributes of the Etadunna Formation suggest that these sediments were probably derived from a combination of uplifted metamorphosed Proterozoic deposits from the Peake and Denison Inliers (dominant) and older sedimentary deposits from the Eromanga and Arckaringa Basins (minor).. The sediment style of the Etadunna Formation is interpreted to be the product of fluvial systems which evolved during the epeirogenic uplift of the Peake and Denison Inliers (Davenport ranges) and the uplifted Eromanga Basin sedimentary deposits during the Late Eocene to Mid Oligocene, accompanied by subsidence in the Lake Eyre Basin (Croke et al., 1998; Krieg, 2000).

The siliceous iron-oxide coating around the well-rounded Etadunna Formation grains strongly suggests that precipitation of iron-oxide post-dated the grain rounding, and represents the earliest authigenic event. The Oligocene-Middle Miocene climate remained significantly wetter than today while the extensive dolomite contents of the Etadunna Formation indicates evaporative but warm conditions and permanent water in the Lake Eyre Basin (Alley, 1988). Warm shallow water is farther suggested by the presence of stromatolites (Krieg, 2000). Grain size (fine to coarse) and lithology, especially the presence of feldspar, indicates that the Etadunna Formation is most probably fluvial sand rapidly deposited in large low-sinuosity meandering to braided streams and restricted swamps and lagoons with intermittent wet and dry climatic conditions.

The third and fourth phase of Neogene deposits represents the sediment generation from a combination of uplifted metamorphosed Proterozoic (Peake and Denison Inliers) deposits with sediment contributed from the older sedimentary deposits such as Eromanga and Arckaringa Basins and even sediments from reworked Lake Eyre Basin sediments. According to Krapf and Lang, (2005) the sedimentary records of the Neogene episodes suggest sedimentation in lacustrine to aeolian and evaporitic, then to fluvial and lacustrine, and finally to aeolian dominated settings.



Figure 4.5: Thin section photomicrographs of provenance lithotype in the Lake Eyre Basin. A. Eyre Formation sandstone B. Etadunna Formation sandstone C. Heavy mineral (epidote) in Eyre Formation D. Calcrete in Etadunna Formation.



4.3 WESTERN LAKE EYRE BASIN EVOLUTION

The development of the modern western Lake Eyre Basin was directly influenced both structurally and lithologicaly, by the Arckaringa, Eromanga and Lake Eyre Basins. The Officer Basin was also involved, but indirectly, due to its impact on the development of younger basins. The modern western Lake Eyre Basin provides an excellent example for the evolution of different intracratonic basins adjacent to basement uplifts through various stages of deformation associated with different tectonic settings and eustatic levels.

The developments of modern western Lake Eyre Basin evolution are described as follows using isopach thickness maps and provenance of sediments. The Cenozoic doming and faulting was caused by reactivation of pre-existing structures in the Officer, Warburton, Arckaringa and Eromanga Basins. The tectonic setting and the climatic factors are of major importance in sediment generation and accommodation of continental basins (Weltje et al., 1998), and are interpreted from the isopach thickness maps and provenance of the sediments. Structural settings, and sedimentation and erosional patterns since the Precambrian were interpreted from the isopach thickness maps. These demonstrated the strong influence of pre-existing structural elements on the basin evolution (Fig. 4.6). It was observed that the development and shifting of each basin was controlled by northeast and northwest-trending structures (Fig. 4.7). These tectonically active structures played a prominent role in sedimentation over Troughs and erosion from palaeohighs until the Late Palaeogene (Table 4.2).

Petrographic studies confirmed that the provenance for the depositional successions in the Officer, Arckaringa and Eromanga Basins remained similar. Sediments were sourced from the stripping off Gawler Craton and Musgrave Block along with reworked sediments from older basin successions. Variations in sediment generation from these provenances were due to changing tectonic settings and palaeoclimatic conditions. However, the sediment sources of the Lake Eyre Basin sediments are dramatically different as a result of the early Palaeocene uplift of the Peake and Denison Inliers. The variations of the compositional trends from the Peake and Denison Inliers through to the Lake Eyre Basin are shown in Figure 4.8. Proportions of quartz, feldspar and lithic framework grains as illustrated in QFL diagrams for each study interval are shown in Figure 4.9.



Petrographic analysis suggests that Peake and Denison Inlier sedimentation was derived mainly from the Gawler Craton for the Palaeoproterozoic successions and from a combination of Gawler Craton, Musgrave Block and Gawler Range Volcanics for the Neoproterozoic successions. The unroofing of sediments from the Peake and Denison Inliers, as a result of uplift during the Palaeogene and Neogene periods, contributed to sedimentation in the western Lake Eyre Basin. Peake and Denison Inlier sediments have not been identified as a source of any other earlier basin sediments.

The thickness variations of the Officer Basin sediments in the basin evolution study area reveals that maximum syn-depositional subsidence took place in the Wintinna, Manya and Boorthanna Troughs (Fig. 3.2). Whilst Middle Bore Ridge and Mabel Creek Ridge regions represent areas of non-deposition or erosion (Lindsay and Leven, 1996). Isopach thickness maps and provenance lithotype studies suggest that the older Officer Basin sediments were stripped off during the Late Palaeozoic era as a result of glacial erosion and were deposited in the younger sedimentary successions of the Arckaringa and Eromanga Basins. However, Officer Basin sediments are not directly evident in the modern sediments of the western Lake Eyre Basin in the basin evolution study area.



Figure 4.6: Synoptic display of isopach maps showing the sedimentation patterns of the Officer Basin (oldest) to Lake Eyre Basin (youngest) in the study area. Note the changing distribution of sediment patterns from older to younger deposits and shifting of sediment depocentres.



Figur

e 4.7:

Figu

re sh

owing

the m

igrati

on an

d shif

ting o

f dep

ocen

tres (

Offic

er B

asin

to La

ke E

yre B

asin)

in th

e stud

y are

a.

Note

the si

gnific

ance

of th

e Kar

ari F

ault z

ones

and D

eniso

n-W

illour

an D

ivide

regio

ns ha

ve fo

cuse

d the

loca

tion o

f dep

ocen

tres t

hrou

ghou

t time

.



Table 4.2: Summary of the tectonic setting of Troughs and palaeohighs in the study area, relative to depositional environment with respect to isopach map thickness (Fig 4.6).



F

igure

4.8:

Prov

enan

ce lit

hotyp

e com

posit

ional

trend

s of s

edim

ents

from

the P

eake

and D

eniso

n Inli

ers t

o Lak

e Eyre

Bas

ins. N

ote th

at La

ke E

yre B

asin

s

ample

s are

mor

e com

posit

ionall

y matu

re th

an th

ose f

rom

the E

roma

nga B

asin

and P

eake

and D

eniso

n Inli

ers.



Figure 4.9: Proportions of quartz, feldspar and lithic framework grains illustrated in QFL diagrams for each study interval. Showing increasing compositional maturity.



The isopach maps demonstrate that during Arckaringa Basin sedimentation, deposition of each succession was followed by a period of erosion and non-deposition. The four major Troughs, the Boorthanna, Mount Furner, Wallira and Karkaro Troughs controlled Arckaringa Basin sedimentation (Figs. 3.4, 3.5, and 3.6). The depositional environment changed throughout Arckaringa deposition from widespread glaciation, to marine transgression and finally to crustal isostatic recovery and fresh water depositional conditions (Hibburt, 1995). A series of linear basins, present in the study area, were filled mostly with detritus derived from the Gawler Craton, Musgrave Block and reworked Officer Basin sediments. The depositional Troughs remained unchanged throughout deposition despite the changing depositional environments. A strong Officer Basin sediment source was noted in the early Arckaringa Basin successions.

Structurally, the Eromanga Basin in the basin evolution study area is divided into northeastern and southwestern parts by the northwest-trending Denison-Willouran Divide. Throughout time sediment depocentres changed laterally to the centre of the study area as result of structural movements and the appearance of Karari faulting zones (Moore and Pitt, 1984) (Fig. 3.15). During the Jurassic, crustal instability increased. Epeirogenic down-warp in the area was accompanied by deposition of a widespread fluvial and lacustrine clastic blanket (Krieg et al., 1995). During Algebuckina Sandstone deposition, the basin margin was spasmodically uplifted supplying large volumes of terrigenous clastics from the Gawler Craton.

Furthermore a major Early Cretaceous epicontinental marine transgression flooded the down-warped region, depositing a blanket of mudstone and siltstone with intermittent sandstones over the older non-marine clastics. The Early Cretaceous subsidence patterns are also reflected in the Bulldog Shale. By the Mid-Late Cretaceous marine conditions had regressed and a terrestrial environment characterised by low-energy fluvial to lacustrine conditions marked the end of widespread deposition.



Provenance analysis of the Eromanga Basin successions highlights the importance of reworked glaciogene sediments from the Officer Basin. Other sources of Eromanga Basin sediments were the Gawler Craton, Musgrave Block and reworked sediments of the Officer and Arckaringa Basins.

The isopach map of Palaeogene sediments shows subsidence of the Lake Eyre region along a major north – south-oriented fault, while simultaneously the Peake and Denison Inliers were gradually uplifted (Williams et al., 1975) (Fig. 3.18). Eromanga sediments are thin or lacking over these structures (Alley, 1998), indicating that the degree of uplift and associated erosion was moderate to high. A final, very pronounced subsidence occurred during late Miocene, creating the enclosed Lake Eyre margin.

Subsidence of the Lake Eyre Basin continued slowly along the main fault zones along the western side of the basin, during the Holocene (Croke et al., 1998). The Neogene isopach map shows wide-spread thin deposition. Conversely the alluvial deposits on either side of the Peake and Denison Inliers are thicker than in other areas (Fig. 3.19). These latter deposits were highly influenced by climatic and sea-level changes. The provenance regions for the Lake Eyre Basin successions include the Gawler Craton, Musgrave Block and reworked sediments of the Officer, Arckaringa and Eromanga Basins.

In summary, petrographic and isopach thickness map data indicates that the evolution of the western Lake Eyre Basin was controlled predominantly by the northeast and northwest-trending structural elements. These same elements were influential in the development of the older basins in the area. This study confirms that there were no major changes in the sand dispersal system and the provenance for early basin sediments. However, the uplift of Peake and Denison Inliers during the Early Palaeogene represented a major structural development through these northwest and northeast structures. This resulted in an abrupt change in hinterland tectonic uplift and provenance for the western Lake Eyre Basin sediments. These younger sediments include ‘long lived’ meta-sedimentary grains having been derived from earlier Precambrian deposits.



This section of this study has demonstrated the concept of multiple provenances. This concept of multiple provenances for younger deposits can be derived from more than one primary source and also include the reworking of meta-sedimentary and sedimentary sources, which is applicable to the modern sediments in the western Lake Eyre Basin. Studies of the sedimentary basin evolution based on provenance and isopach thickness maps provided important constraints regarding the source and age of Umbum Creek sediment. The story however is incomplete without a detailed analysis of the modern sediments of the Umbum Creek catchment and in particular fingerprinting of these sediments to their original provenances. This is the subject of Part 2 of this study.

“source to sink” sedimentology and petrology of a …...“source to sink” sedimentology and...

Documents