Discussion Paper - Part A - Victorian Environmental Assessment ...

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et al. 2000). This Selwyn Block is thought to underlie theMelbourne Zone and extend from similar rocks inTasmania (Fergusson & VandenBerg 2003).The Benambran Orogeny had variable effects across theLachlan Fold Belt and occurred in several pulses between460 and 420 Ma. This orogeny affected rocks on bothsides of the Selwyn Block but not the Selwyn Block itself,which by that time was overlain by the sediments of theMelbourne Zone. Older sedimentary rocks of theBendigo and Stawell Zones were folded and faulted in asingle short-lived but major event during this period. Ineastern Victoria the Benambran Orogeny folded andfaulted Cambrian, Ordovician and Early Siluriansedimentary rocks, and is associated with graniteintrusion and regional metamorphism. Elsewhere,especially in the Bendigo Zone, regional metamorphismwas very low and the orogeny is associated with goldand quartz mineralisation within Ordovician sedimentarysequences.The regional differences between western, central andeastern Victoria that first appeared in the Ordovicianbecame more pronounced after the Benambran Orogeny(450–425 Ma). These differences divide the Lachlan FoldBelt into two belts of different structural evolution fromthe Ordovician to the Middle Devonian—the Benambraand Whitelaw terranes (VandenBerg et al. 2000). TheBenambra Terrane of eastern Victoria comprises theLachlan Fold Belt east of the Selwyn Block and GovernorFault (Tabberabbera zone and those to the east) and wassubject to two episodes of rifting, one in the LateSilurian and the other in the Early Devonian, with anintervening orogeny at about the Silurian–Devonianboundary (Bindian Orogeny described below). TheWhitelaw Terrane comprises the Lachlan Fold Belt thatlies west of the Governor Fault including the SelwynBlock (Stawell, Bendigo and Melbourne zones). Unlikethe Benambra Terrane, the Whitelaw Terrane shows onlymild effects from the Bindian Orogeny. The Whitelawterrane contains the richest gold deposits in the TasmanFold Belt.A major episode of granite intrusion occurred in theBenambra Terrane, and also in the Stawell Zone inwestern Victoria during the Bindian Orogeny (405–415Ma). In the Stawell Zone this was associated with amajor phase of gold mineralisation, and a second phaseof gold mineralisation occurred in the adjacent BendigoZone. The Melbourne Zone is characterised bycontinuing deep-marine sedimentation with conditionsgradually becoming shallower in the western part of thezone.Thick and diverse sediments characterise the LachlanFold Belt from the Cambrian until the Middle Devonian.Deformation and faulting of these thick sediments, andthe later intrusion of granites and eruption of volcanics,forms Victoria’s basement geology. In the MelbourneZone, the Silurian to Middle Devonian sedimentary rockslie conformably upon Ordovician rocks, as is the case inthe Tabberaberra Zone.In the Silurian to early Devonian, magmatism and graniteintrusion occurred in the Grampians–Stavely Zone and inthe eastern and western portions of the Lachlan FoldBelt, but not in the central area. This was reversed in theLate Devonian when central Victoria became the focuswith several large granitic bodies intruded during thattime (e.g. Cobaw, Harcourt, Strathbogie).The Tabberabberan Orogeny (385 Ma) affected thewhole of Victoria, although its expression varied strongly.The most pronounced effects are observed in thepreviously undeformed Melbourne Zone, where the thickOrdovician to Devonian sediment succession wasstrongly folded and faulted. Kilometre-scale movementoccurred along the two bounding faults of theMelbourne Zone. West of the Melbourne Zone its effectswere very mild, limited to rejuvenation of older faultsand generation of strike-slip faults (‘cross-courses’) in theBendigo and Stawell zones. Gold mineralisation occurredin the Melbourne Zone, and in the Bendigo Zone to thewest, where it was the third phase of mineralisation. Thetwo terranes were amalgamated in the MiddleDevonian.The Kanimblan Orogeny (~340 Ma) was the last of thedeformation episodes that built the Lachlan Fold Belt inVictoria. Its effects were mild in Victoria, as the crustacross the state had already been deformed and was, bythat time, quite strong (VandenBerg et al. 2000). Aperiod of tectonic stability followed that lasted throughthe Permian until the onset of the break-up ofGondwana in the late Jurassic and Cretaceous.Deposition during this stable interval is most extensive inlows or troughs some of which are preserved below thecover of more recent sediments in the Murray Basin(Figure 2.3).During the Permian, Victoria lay on the edge of an icesheetextending south. Sediments from this time arepreserved as a marine and glacial sequence at BacchusMarsh and Lake Eppalock and smaller scattered patcheselsewhere, and marine black mudstone (UranaFormation) within the Numurkah Trough of the MurrayBasin (Figure 2.3). The periglacial sediments includefluvial (river-borne) sandstone and mudstone, as well aslacustrine (lake-bed) sediments with ‘drop stones’.Within the River Red Gum Forests study area, basementrocks rarely appear above the largely flat riverine plain,with notable exceptions at Pyramid Hill, Terrick Terrick,Lake Boga, and along the river valleys that extend intothe Eastern Highlands.MesozoicThe rock record of the Triassic through Jurassic is poorlyrepresented in Victoria and not known from the studyarea. Triassic granites and volcanics occur in thehighlands near Benambra, and a small isolatedsedimentary sequence at Bacchus Marsh has also beenidentified as Triassic (Webb & Mitchell in prep). Theabsence of Mesozoic deposition may be due to Victoriabeing an elevated area at the time. Very little definitiveJurassic material has been identified within Victoria—perhaps only limited volcanics and intrusives from theCasterton and Bendigo areas could be reasonablyattributed to this time period.Early Cretaceous age (145–95 Ma) rocks are wellrepresented across southern Victoria with extensive<strong>Discussion</strong> <strong>Paper</strong>13
outcropping and subsurface sequences of volcanogenicand fluvial sandstones and siltstones (Otway, Bass andGippsland basins) and minor occurrences within theMurray Basin at depth. During the Late Cretaceous(95–65 Ma), the mountains of the Great Dividing Rangerose as the rift between Australian and Antarcticaspread. Downwarping on the northwestern side of therange enhanced the broad depression of the MurrayBasin which rests upon basement rocks with a hillytopography much like the adjoining landscape. Streamdeposits on both sides of the Great Dividing Rangecontain rich alluvial gold deposits accumulated duringthe prolonged erosion following the Permian glaciation.Subsequent basalt eruption, especially south of theDivide during the Cainozoic, buried the river sedimentsand gold-rich gravels that are now known as ‘deepleads’.CainozoicSedimentation in the Murray Basin and the riversdraining into it was largely regulated by sea levelchanges with fault movements throughout theCainozoic influencing deposition patterns and hydrologymore generally (Figure 2.3). For example, movement onthe Tawonga Fault influenced the development of theOvens and King Rivers in the eastern part of the studyarea. Across much of the study area only small tectonicmovement has occurred in the Cainozoic, although evensmall vertical offsets have resulted in major deflections ofdrainage lines on the flat land of northern Victoria. Themost significant of these is the Cadell Fault near Echucawhere the fault block diverted both the Murray andGoulburn rivers prior to 35,000 years ago (see chapter 3Geomorphology and Land Systems).Cainozoic sediments, of both marine and terrestrialorigin, blanket and infill the basement surface acrossnearly the entire study area (Map 2.1). Conditions foraccumulation of sediments were favourable during threemajor episodes of the Cainozoic era (65–0 Ma) reflectedin three layers comprising the Renmark, Murray andWunghnu groups. These sediments consist of fluviallacustrinesandstones, claystones and minor coals of theRenmark Group (Palaeocene–Early Oligocene), thepredominantly marine carbonate Murray Group(Oligocene–Middle Miocene), overlain unconformably bythe Late Miocene–Pliocene marine to fluvial WunghnuGroup. In the eastern part of the basin the marineMurray Group is replaced by non-marine sediments.In general, Palaeocene to Pliocene sediments havelimited outcrop in the study area and are largelyblanketed by the younger Quaternary sediments of theriverine plains, and the aeolian (wind-blown) sequencesof the dunefields and sand plains (Map 2.1).Renmark GroupThe Palaeocene to Oligocene Renmark Group restsunconformably on older basement rocks, infilling thepre-existing topography. The sequence has variablethicknesses up to a maximum of 300 m in the Milduraarea, and up to 60 m in the palaeo-drainage systems ofthe Loddon, Campaspe and Goulburn rivers but less overthe palaeo-topographic highs. Renmark Group sandunits are important groundwater recharge sources foroverlying aquifers. Brown coal seams occur at the top ofthe Renmark Group, especially in the Kerang,Torrumbarry and Echuca areas (see chapter 16 EarthResources). The Renmark Group is overlain by the marineOligocene–Miocene Murray Group or its non-marineequivalents and does not outcrop in the study area.Murray GroupThe Murray Group refers to all marine carbonatesediments between the top of the Renmark Group andthe base of the Late Miocene or Early Pliocene WunghnuGroup. The limited Murray Group outcrop consistspredominantly of exposures along river incisions andover the Gredgwin Ridge south of Kerang. It is notpresent in the Kerang–Cohuna and Goulburn areas ofthe Murray Basin and non-marine sediment equivalentsoccur to the east of this region. A complex mix ofmarine and non-marine sediments occurs across a poorlydefined boundary between these areas. The MurrayGroup comprises a mixture of marine muds, clays andlimestones (Ettrick Marl, Duddo Limestone, Geera Clay)and their non-marine equivalents such as the CalivilFormation. The Geera Clay is an important barrier togroundwater and provides a salt source to underlyingRenmark Group aquifers, as well as restricting upwardsmovinggroundwater.Wunghnu GroupThe deposition of the Late Miocene to PlioceneWunghnu Group commenced with a short-lived marinetransgression followed by a slower regression of the sea.Sediments deposited during this time include marineunits such as the green micaceous glauconitic marls ofthe Bookpurnong Beds, marginal marine units such asthe Parilla Sand and non-marine equivalents such as theShepparton Formation. These units are allunconformable on the underlying rocks. Theunconformity is likely to represent a LateMiocene–Pliocene tectonic event similar to thatidentified in other areas of Victoria. This sequencecomprises the majority of outcropping rocks throughoutthe study area and is therefore described in detail below.The Wunghnu Group is highly variable with both marineand non-marine units from changing conditions of theMurray Basin including increasing climate variability(which affected both drainage and sediment derivedfrom the Eastern Highlands) and changing sea levels.Sandstone aquifers and claystone units within thissequence have varying degrees of groundwaterinterconnection, both vertically and horizontally,providing significant groundwater resources in theeastern part of the Murray Basin.The Pliocene Parilla Sand forms a series of sub-parallelridges separated by swales across the western half of theMurray Basin in Victoria. It extends into the subsurfaceforming widespread sheet sandstones. These variablyferruginous quartz sands are cross-bedded, medium tofine-grained, and contain some bands of heavy minerals.Individual ridges can be up to 50 m high and severalkilometres wide and extend for several hundredkilometres in a north-northwest direction. Beneath theLoddon Plains the formation is subdivided into theKerang Sand (which laterally replaces the BookpurnongBeds), an intermediate Tragowel Clay Member and theupper Wandella Sandstone, which is the mainoutcropping unit.14 River Red Gum Forests Investigation 2006
Page 3 and 4: 2 GeologyGeology underpins the dive
Page 5 and 6: Figure 2.2 Schematic diagram of fol
Page 12 and 13: Figure 2.4 Murray Basin during the
Page 14 and 15: quartz sand and gravel beds, carbon
Page 17 and 18: Box 3.1 River MeandersRivers rarely
Page 19 and 20: lakes by flooding from Chalka Creek
Page 21 and 22: major valleys. The large, older fan
Page 23: ecommending representative areas fo
Page 26 and 27: Box 3.2 Barmah Area GeomorphologyTh
Page 28: 4 Climate andHydrological SystemsAu
Page 31 and 32: Figure 4.1 Annual anomalies (based
Page 33: such as messmate have a thick prote
Page 36: Natural Hydrology of the River Murr
Page 39: Table 4.3 Stream flow in major Vict
Page 42 and 43: GroundwaterHydrology also relates t
Page 44 and 45: FloodplainsThe floodplains of the R
Page 46 and 47: 5 BiodiversityBiodiversity is impor
Page 48 and 49: Ecosystem Assessment 2005). Species
Page 51: Figure 5.2 Hairy darling-pea on a r
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Figure 5.5 A common blue-tongued li
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Threatened VertebratesBased on cons
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Figure 5.8 Mature river red gum on
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Figure 5.12 Tangled lignum at Mulcr
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Egrets generally only breed in livi
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which is essential habitat for some
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dependent species including darling
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Table 5.7 Summary of risk levels to
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Figure 5.22 Koala in a river red gu
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Examples include the larvae of leaf
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Figure 5.27 Cattle on the bank of t
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Table 5.8 Comments on fire from exp
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6 Indigenous LandAssociationsThis c
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Table 6.1 Summary of area in Victor
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waters. The Joint Body is funded to
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Consultative ManagementConsultative
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7 Non-IndigenousHistoryThe resource
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Figure 7.2 Murray Downs homestead (
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Reception Centre established in 194
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and rural water supply became the r
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FisheriesThe collapse of the Murray
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