The stratigraphy and palaeontology of Teapot Creek, MacLaughlin River, NSW

21 Pages·2000·10 MB·

by  L Armand

.
The Stratigraphy and Palaeontology of Teapot
Creek, MacLaughUn River, NSW
LeanneArmand'-^,W. D. L. Ride'and Graham Taylor^
'DepartmentofGeology,AustralianNational University, Canberra,ACT0200;
^Current contactaddress: Institute ofAntarctic and Southern Ocean Studies,
University ofTasmania, GPO Box 252-77, Hobart 7001, Tasmania,Australia
([email protected]);
^CooperativeResearch Centre forLandscape Evolution andMineralExploration,
University ofCanberra,ACT2601
Armand, L., Ride, W.D.L. and Taylor, G. (2000). The stratigraphy and palaeontology of
TeapotCreek,MacLaughlinRiver,NSW.ProceedingsoftheLineanSocietyofNewSouth
Wales 122, 101-121.
ThestratigraphyandtheQuaternarydepositionalhistoryofTeapotCreek,atributary
oftheMacLaughlinRiverintheSouthernMonaro,southeasternNewSouthWales,aregiven
anddiscussed.Otherfossil-mammalbearingdepositsintheMacLaughlinValleyarereported.
ThevalleyofTeapotCreekcontainsasequenceofterraces.Thehighestandoldest
oftheseischaracterisedbypoorlysortedconglomeratedepositstypicalofstream-deposited
longitudinalbars.Palaeomagneticresultsobtainedfromthisterraceareinterpretabletothe
Bruhnesnormalpolarityinterval(<0.78Ma).Asecond,lowerterraceissetintothehighest
terrace.Depositionofthisterracebeganbefore5320±80yrBPandischaracterisedbyoverbank
deposits.Thelowestandyoungestterrace,consistingmostlyoffineclaysandsilts,represents
lateralaccretionsinsidemeanderloopsduringmodemfloodingevents.
The youngest terrace contains the remains ofmodern introduced mammals. The
intermediateterracehasyieldedfossilsofmodemMacropusandanunidentifiedmurid.The
highest terrace contains the remains of fossil mammals found in Plio-Pleistocene fossil
deposits elsewhere inEasternAustralia. Species identifiedfromit areMacropusaltus, M.
ferragus, M. titan, Procoptodongoliah,P.pusio, Protemnodonanak, P. "roechus/brehus",
Sthenurus atlas, S. occidentalis, S. newtonae, Troposodon minor, andPhascolonus gigas,
butnomodemspeciesofMacropuskangaroosorwallabies.
Pleistocenefossilmammalshavebeenlocatedinfourothersitesinthevalleyofthe
MacLaughlinRiver.Afifth site.ChalkPool, is sedimentologicallydifferentandatalower
levelrelativetothemodernriverthantheotherterraces.SpeciesidentifiedintheChalkPool
depositareregardedasPlio/Pleistoceneforms(Macropuspan,Protemnodonchinchillaensis
andP. "roechus/P. brehus"); ofthese,P. chinchillaensisisknownonlyfromthePliocene.
Manuscriptreceived 1 July2000,acceptedforpublication 13 November2000.
KEYWORDS:ChalkPool,Macropodidae,Marsupial,Monaro,Pleistocene,Pliocene,Teapot
Creek,Vombatidae.
INTRODUCTION
Background
The Monaro region is the highest part of the southern tablelands ofNew South
Wales. Workonmammalfossils fromalluvialdeposits in theregionhaspreviouslybeen
confinedtoastudyonthenorthernpartoftheregion (Rideetal. 1989; Davis 1996; Ride
andDavis 1997), althoughinthe 1930'sfossilmammalremainshadbeencollectedfrom
Proc.Linn.Soc.n.s.w., 122.2000
102 MACLAUGHLINRIVERFOSSILDEPOSITS
a gravel pit at Jincumbilly in the southern Monaro (AustraHan Museum specimens and
localpressreports).Morerecently,in 1987,studentsoftheUniversityofCanberra,engaged
in geological mapping in the region, reported finding a large bone fragment (a
diprotodontid)inBungarbyCreekonBrooklynStationandmacropodinefossilsinTeapot
Creek on Sherwood and Boco Stations (Fig. 1). Further studies ofTeapot Creek were
made principally by the first author (Dansie 1992). During these studies a further four
sites were located, close by in the valley of the MacLaughlin River, of which Teapot
Creek is atributary.
In this paper, a study of the stratigraphy and palaeontology of Teapot Creek is
presented. Two "'C dates arerecordedfortheintermediateterraceofTeapotCreek, anda
palaeomagnetic result for the highest terrace. The other localities and their fossils are
also listed briefly and theirrelationship to theTeapot Creekdeposits is discussed.
General description
Basalts of Paleocene to Oligocene age dominate the valley of the MacLaughlin
River (K-Ar dates of 51±0.3 and 37.2±1.0 Ma, Taylor et al. 1990; Roach et al. 1994).
Theseoverlie lacustrine sediments. The basalts provide theprincipal sourcematerial for
theQuaternaryhillslope (colluvial)andalluvialdepositsofthevalley.Thebasalts, which
are also the basement rocks at the Quaternary and Holocene fossil sites described here,
are considered to have been derived locally from multiple eruption sites. Teapot Hill,
closetothejunctionofTeapotCreekandthe MacLaughlinRiveris one oftheseeruption
sites (Roach 1991; Roach et al. 1994) (Fig. 2).
The lacustrine sediments which underlie the basalts are believed to represent the
western edge ofa palaeolake (Lake Bungarby, Taylor et al. 1990). These sediments are
thoughttobe the sourceofquartz sands andpebbles foundas ararercomponentin some
ofthe post-basaltic deposits.
Similarsub-basalticlacustrinedepositsoccurnearbyinthevalleyoftheMacLaughhn
River. These contain a diverse fossil macroflora (Taylor et al. 1990; Hill 1991; Hill and
Carpenter 1991; Christophel 1994) andonthebasisofcontainedfossilpollen,havebeen
assignedtotheLygistepollenitesbalmeiZoneofthe late Palaeocene (Tayloretal. 1990).
The sediments underlyingthebasaltsinTeapotCreekarethoughttobeextensions ofthe
same deposits.
WeinferthatduringthelateQuaternary (<75 ka)theareawas subjecttoperiglacial
conditionsonseveraloccasions. IntheKosciuszkoregion,recentmoraineexposuredates
haveindicatedanearlyglaciationphaseat-55-65 kaandalateglaciationperiodbewteen
15-35 ka with three progressively less extensive glacial advances occuring at 32,000 ±
2500, 19,100 ± 1600 and 16,800 ± 1400 years ago (Barrows et al. in press). Similar
findings from glacial records are reported from the Tasmanian Highlands (Fitzsimmons
andColhoun 1991; Colhoun2000). SedimentsintheACTreveal severalperiodsofslope
instabilitythatarethoughttoindicateseparateperiodsofperiglacialclimatesinthesouth
eastern highlands (Barrows 1995). In addition, the Monaroregion lies in therainshadow
inducedbytheAustralianAlps(Tulipetal. 1982;Rideetal. 1989).Whiletherainshadow
may have ameliorated the effect ofclimate shifts, the late Quaternary was undoubtedly
cooler and drier than at present with attendant higher sediment mobility. Under these
climatic influences erosion and alluviation have shaped the valleys.
RESULTS
Geomorphology ofTeapot Creek
The TeapotCreek catchment covers 7 km' on Sherwood Station, approximately 12
km south-west of Nimmitabel in the southern Monaro (Fig. 1). Teapot Creek rises as
channels in the steep, hilly terrain ofSherwins Range at an elevation of950 m, and over
its length of4 km, falls to below 780 m to a wide, gently sloping valley at itsjunction
with the southerly flowing MacLaughlin River, the latter being a tributary ofthe Snowy
Proc.Linn.Srx;.n.s.w., 122. 2000
L.ARMAND,W.D.L.RIDEANDG.TAYLOR 103
Figure 1.TopographicmapindicatingfossilsitesandtheTeapotCreekstudyareadescribedinthetext.Sitesare
identified as follows: 1= Bungarby Creek, Brooklyn Station, 2= Chalk Pool, 3=Toppings Creek, 4= Ben's
Bin,5=RailwayCutting,6=TeapotCreekStudyArea,enclosedbybox.Sites2to6arelocatedonSherwood
Station.Mapreferencescale:AustralianMapGrid(U.TM.) intervalsof 1000fromOriginofZone55.
Proc.Linn.Soc.n.s.w., 122.2000
104 MACLAUGHLINRIVERFOSSILDEPOSITS
Trib.p'- / Trib.E
a.
Trib.cVJY^>.,. b.
Trib.F
16#-^17
abandoned
^.^^^
• T^Teapot channels
"MCreek i^^
14i
Jl3
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11
10^
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8
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Trib.B \
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abandoned
#4 channels Teapot /
rZ ,.- Trib.H Creek
>3 ''^<%P!=-a=>^-
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KEY
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_^_^ I
Terrace 1 Basalt
'^c"? Terrace2 Alluvialfan
^ ^0
Alluvium/
Terrace 3
Colluvium
Figure 2a: Teapot Creek fossil localities described in text. 2b: Corresponding generalised cross sections of
TeapotCreek (from 2aj illustrating alluvial terraces. Illustrationsin2barenottoscale.
River. The modem TeapotCreek flows down the north-eastern sideofits valley whereit
incises asequenceofgently sloping alluvial plains. Lateral fansmerge withtheseandare
incisedbysmall tributaries(Figs 1 and2).ThedepthofincisionbyTeapotCreekdecreases
down stream from approximately 15 m to 2 m. Alluvial fans merge laterally with the
alluvial plain along the lower valley, where current entrenchment of the stream shows
some evidence ofmeandering prior to its present incision.
Proc.Linn.Soc.n.s.w., 122. 2000
L.ARMAND,W.D.L. RIDEANDG.TAYLOR 105
Thefossil-bearingsitesarelocatedinbanksexposedbytheentrenchmentofTeapot
Creek.Themoderncreekis confinedto a singlemajorchannel (approximately 1 mwide
and about50 cmdeep). Flooding in the creekraises the waterlevel upto 2 m. Currently,
TeapotCreekisasinuousstreamwhichhaslowpoint-barsandthalwegdepositsofbasalt-
derived gravel, sands and mud, and deep, steep entrenched banks. Basalt crops out in
manyplacesalongthecreek,evenintheupperreaches,whereentrenchmentdowntothis
level has produced well worn surfaces and minorpools.
Sequence and sedimentology oftheAlluvialTerraces
Stratigraphic information forTeapot Creek valley was obtained from exposures in
escarpments, cut stream banks, and four trenches excavated with a back-hoe. From the
information gathered, terrace sequence was determined and an informal stratigraphy
provided (Dansie 1992). There is no formal stratigraphy associated with the deposits of
the Southern Monaro and the description of stratigraphy is hindered by the lack of
superposition.Severalfaciesareobservedineachofthesedimentaryunitswithinexposures
andtheirdescriptionsfollow lithofaciesdefinedbyMiall (1977, 1978), andRust (1978).
Three alluvial benches are identified along the length of Teapot Creek. These
morphological terraces areinset withinone anotheralongtracts ofthecreek(see section
W-XinFig.2b).Relativeelevationsandlithostratigraphicsimilarityoftheexposedterraces
determined correlation of the terraces along the creek. Figure 2b shows a generalised
valley-fillsequenceforTeapotCreekatthreepointsofitslength.Eachterraceiscomposed
of a single alluvial morphostratigraphic unit often overlain by colluvial and alluvial
deposits, which has been derived from the valley sides and during flood events. The
contact between the terrace deposits and the overlying colluvial/alluvial veneer varies
fromdiffuse,incaseswhereintensepedogenesishasoccurred,tosharphiatus.Theterraces
alloverlieabasaltbasement, exceptatone site (Fig. 2a, site5) wheretheterraceoverlies
amixedquartz sand andbasalt-derivedclayey facies, consideredtohavebeenreworked
from the Palaeocene lacustrine deposits and surrounding basalt material.
Terrace 3 is the highest alluvial deposit in the area. It is predominantly a fluvial
deposit, containingcrudelybeddedconglomeratic units withweaklyimbricatedgravels.
EachexposureofTeixace3 (Sites3 to7,9to 12, and 14to 17)hasauniqueinternalfacies
sequence, but at all sites examined there is a comparable mix of facies consisting of:
matrixsupported,poorlybedded,medium-tocoarse-grainedwellsortedchannelgravels;
andpebbly muds and very fine sands ofoverbankdeposits. Theconglomerate facies are
%
predominantlybasaltderivedbutincluderare(< 1 ofconglomeratecomposition)quartz
andjasperpebblesindicatinganOrdovicianprovenanceforsomematerial.Granitepebbles
found at Site 7 indicate that material possibly derived from the Silurian aged Berridale
Batholith, was available at the time ofdeposition. However, source areas for such older
rocks are unknown in the present catchment. It is possible they are recycled from pre-
andintra-basaltic alluvial deposits, which are common throughoutthe Monaro. Soils on
Terrace3 varyfrom5 cmto370cminthickness,andhaveanaveragethicknessof60cm
They comprise a dark, yellowish brown clay with discrete calcrete nodule layers. In
instanceswherethesoilshavebeeneroded,thesecalcretebandsareexposedonthesurface.
Multiple channel deposits are common within Terrace 3, indicating that they
representalongperiodofdeposition.Terrace 3 sitesincludethebulkofthe stratigraphic
sections investigated (Fig. 2). Site 13 is thoughtto representTerrace 3, but it occurs out
m
ofstratigraphic context on top ofa 15 high escarpment, and in addition its sediment
characters remain undetermined due to its inaccessibility.
AtthetimeTerrace3wasdeposited.TeapotCreekwasabraidedstreamcomparable
totheScotttype(proximalbraidedstream)ofMiall(1977, 1978, 1982),whichisindicative
ofscour-based,massiveconglomeratebedsoverlainbysandyfaciesthatarethenscoured
by superimposingbars.Thecyclicity intheTerrace 3 deposits is interpretedasrecording
rapidaggradationfromfloodingevents.Thebraidedstreamisestimatedtohavebeen40-
m
50 wideintheupperreachesofthecreek(Sites 15 and 11,Fig. 2a),whichhaddecreased
Proc.Linn.Soc.n.s.w., 122.2000
106 MACLAUGHLINRIVERFOSSILDEPOSITS
m
inbreadth to around 15-20 at Site 7 (Fig. 2a).
Terrace 2 is distinguished from Terrace 3 by its lower elevation and by black-
coloured fine-grained sediments and conglomeratic channel deposits. The colour is the
resultofahighorganiccontent.Atsites 1 and2 (Fig. 2a),Terrace2showsfiningupward
sequencesoffinelylaminatedclays,siltsandsands,andlowangledcross-beddedcoarse-
to fine-grained sands. Both facies indicate a stream that developed a significant flood
plain with waning flow. The overbank deposits increase in thickness up-sequence, and
contain charcoal deposits, and evidence of bioturbation. Conglomeratic deposits are
generally ofwell-rounded and sorted basalt clasts. The area ofdeposition ofTerrace 2
decreases upstream in Teapot Creek as the valley decreases in width and depth and the
entrenchment of the creek increases. The terrace is also found in tributaries ofTeapot
Creekbut similarlydisappears upstream. Soildevelopmentonthe surfaceis upto 37 cm
deep and is composed ofbasalt-derivedblackclays.
Terrace 1 is the lowest terrace and occurs on the inside bends ofmeander loops,
where it forms lateral accretion deposits of fine clays and silts. It is very young by
comparison with Terrace 2 and contains remains of modern species introduced by
Europeans. Terrace 1 occurs upstreamofSite 8 (Terrace 2) and along mosttributaries in
the study area. Itis coveredinplacesbyrecently depositedflooddebris. Chutechannels
often cross some ofthe Terrace 1 benches down stream in the open valley (abandoned
channels in Fig. 2b.) Minimal black clayey soil development occurs at the surface of
theseterraces,havingamaximumdepthof10cm,whichisfrequentlydisturbedbymodem
flooding events. Such development is termed stratic: a low alluvial bench frequently
flooded, ofraw, pedologicallyunmodifiedalluiviumthatisencompassedbyalluvialsoil
classification (Walker and Coventry 1976: 307).
Terrace chronology
Terraces 1 and 2 both occur close to the stream bed. Terrace 1 in the downstream
reachandTerrace 2 fartherupstream. Terrace 3 occurs well aboveTerraces 1 and2 (Fig.
2b).Progressiveloweringofthealluviallandscape,producingtheseyoungerinsetterraces,
relates to the reduction of stream discharge due to late Quaternary change in climate.
Charcoal and sediment from one stratigraphic 'bed' (Fig 2a, site 2) were obtained and
senttoBetaAnalyticInc. (Florida,U.S.A.)fordating.Twocarbondatesataapproximate
depth of 550 cm and 560 cm, provided ages of 4940±140 BP (TPC/B/1- Beta-50156,
charcoal) and 5320±80 BP (TPC/B/2-Beta-50157, sediment) respectively.
ThermoluminescencedateswerenotobtainablefromthefluvialdepositsofTeapotCreek
because the deposits lack sufficient quartz material and no molluscan remains were
encountered, thus eliminating the possibility ofdelta'^0 analysis.
Terrace 3 is predominantly composed ofchannel deposits and occurs high in the
landscape relative to Terrace 2. Palaeomagnetic samples were taken from fine-grained
facies within fossil-bearing Terrace 3 conglomerate beds at Sites 4 and 15 (Fig. 2a).
These samples were then step-wise alternate field demagnetised and measured on a
MolspinspinnermagnetometeratthejointAGSO/ANUPalaeomagneticLaboratory,Black
Mountain, Canberra. Palaeomagnetic results indicate a normal polarity for fine-grained
facies from these sites, which although not conclusive, is interpretable to the Brunhes
normal polarity interval (<0.78 Ma) (B. Pillans pers. comm. 1996).
Teapot Creek fossil mammals: identification and physical condition
From the Teapot Creek study area (Fig. 1, no. 6) 244 fragmentary specimens of
fossil mammals were collected between 1988 and 1995. Ofthis total only 62 specimens
have been identified to family, and only 42 to species. Of the latter, all but Macropus
titan are sparsely represented (in some cases only by a few parts ofbroken molars).
The probable causes of the fragmentation include transport by water and post-
depositional weathering by episodic clay expansion and contraction, and also calcrete
impregnation. There does not seem to be any evidence ofbite marks on the bone. There
Prcx;.Linn. Soc.n.s.w., 122. 2000
.
L.ARMAND,W.D.L. RIDEANDG.TAYLOR 107
is little evidence ofbone mineralisation, butpartial 'opalisation' is noted in some ofthe
teethrecovered.
Species identifications ofthe fragmentary material are presentedhere on the basis
thateachspecimenisnotmorphologicallyseparablefromanequivalentpartofasecurely
identified specimen of the species named (preferably the holotype or a topotypical
specimen). To enable the identifications to be evaluated by subsequent workers, each
species listed is accompanied by the number and a briefdescription ofthe specimen(s)
on which the species identification principally depends (the voucher specimens), the
collection number of the museum specimen with which it was compared, and a
bibliographic reference to adescription ofthe diagnostic characters. Voucher specimens
forall taxa identified are deposited in theAustralian Museum, Sydney.
All taxa listed above were identified by the senior author and Ride; the latterthen
visitedmuseumcollections andmadedirectcomparisons with identified specimens (and
whereverpossiblewithtypesandtopotypicalspecimens). ComparisonswithSthenurinae
were confirmed forus by Dr G. Prideaux.
Noformalfaunisticnameis given in this workto the species assemblagesreported
fromthethreeterraces(thespeciesassemblageofTerrace3 depositshaspreviouslybeen
referred to by Dansie (1992) as theTeapotLocal Fauna).
TaxonomicattributionstogeneraarethoseadoptedinRideetal. (1989).Macwpus
titan andM. altus are both morphologically distinctfromM. giganteus andM. robustus
and are conventionally treated as full species. The use ofthe names Procoptodon and P.
pusio are maintained as cases under consideration by the International Commission on
Zoological Nomenclature, in accordance withArticle 82.1 ofthe International Code of
Zoological Nomenclature (Davis andRide 2000).
Fossil occurrences in theTeapot Creek Terraces.
Fossil mammals recovered from each of the three Terraces are listed in Table 1
Terrace 1 contained only the remains ofmodern introduced species. Terrace 2 deposits
(Site 2)haveyieldedthreefossils only. Ofthese, only partofapelvishasbeenidentified
to agenus (Macwpus). The presence ofaspecies ofthe modernkangaroo (M. giganteus
orM. robustus) inthe deposit, which has aprobable minimum age ofbetween4660 and
5480 BP (see above), is consistent with the presence ofmodem species ofMacwpus in
similarly dated deposits in the northern Monaro (Ride et al. 1989; Davis 1996).
AllotherfossilsintheTeapotCreekvalleywererecoveredfromTerrace3 deposits.
Many fossils werecollectedat sites fromwhich theyhadweatheredout, butothers were
excavated directly fromwithin the deposits; those excavated were foundpredominantly
withinconglomeraticfacies and, less frequently, inoverbankandsandypoint-barfacies.
The overbank and sandy point bar facies yielded the least damaged fossils, yet such
facieswererareinTerrace3 deposits (beingconfinedto Site4) and,eveninthosefacies,
the bone structure was crackedby clay expansion and desiccation. As aresult, itis very
unlikelythatfossilmaterialwouldhavebeenreworkedfromTerrace3toTerrace2deposits
without disintegrating. No fossils in that condition were found inTerrace 2.
Specimenscollectedfromthe surfaceinthevalleyofTeapotCreekby students and
others mapping in the area are all attributed by us to Terrace 3 deposits. Information
given by the donors satisfied us that all came from upstream ofthe Site 2 (Terrace 2).
Identifications ofthese arerecordedafterthe siterecords underthe heading "Terrace 3 -
unlocalized".
Otherfossil sites in the valley ofthe MacLaughlin River
Five otheralluvial sites in the valley ofthe MacLaughlin River, southern Monaro,
haveyieldedfossilmammals(Fig. 1: Ben'sBin,RailwayCutting,ToppingsCreek,Chalk
Pool, and Bungarby Creek-the firstfourare within Sherwood Station andthe lastis on
Brooklyn Station).
At Ben's Bin, Railway Cutting and Toppings Creek sites the fossils are eroding
fromcutbanks.Thefossilsareveryfragmentedanddisassociated, andallidentifications
Proc.Linn.Soc.n.s.w., 122.2000
108 MACLAUGHLINRIVERFOSSILDEPOSITS
Table 1.SpecieslistsofTeapotCreekSitesbyTerraceandsiteaffiliation.Thenumberofspecimens,
whetheridentifiableornot,fromeachsiteisprovidedin column2 andincludesbundledcollectionsofbone
shardsrecoveredfromthesites.Acompleteindexofthespecimensandmaterial collectedisfoundin
Dansie(1992). Speciestaxonomy (authorship anddates)ofthespecieslistedinTaMe 1 isformallytreated
intheAppendix.
Sites No. specimens Specimens identified tospecies
recovered level
Terrace 1
Between Sites 1 and8 not recorded Vulpesvulpes
Bostaurus
Ovisaries
Terrace2
Sitel
Site2 3 Macropus (eithergiganteus
orrobustus)
Terrace3
Site3 1
Site4 to6 28 Macropus titan
Protemnodonanak
Protemnodon "roechus/brehus"
Procoptodon goliah
Sthenurusoccidentalis
Troposodonminor
Site? 21 Phascolonusgigas
Protemnodonanak
Procoptodonpusio
Macropus titan
Macropusferragus
Site9 5 Macropus titan
Site 10 3
Site 11 3 Macropus titan
Site 12 10 Sthenurusnewtonae
Site 14 12 Macropus titan
Site 15 8 Macropus titan
Macropusferragus
Site 16 13 Macropus titan
Site 17 2 Macropus titan
MacropusaItus
Terrace3 - unlocalised 35 Protemnodon "roechus/brehus"
Macropus titan
Macropusferragus
Sthenurusatlas
Proc. Linn. Soc.n.s.w., 122.2000
L.ARMAND,W.D.L. RIDEANDG.TAYLOR 109
are based on isolated teeth or fragments of teeth and a few more complete dentitions
(suchas several fromToppings Creek). On thebasis ofthefossils the ages ofthesethree
sites are not different from Terrace 3 sites in Teapot Creek and the deposits are either
remnantpoint-bar sequences orconglomeratic thalweg deposits.
An exposure at Chalk Pool, on the MacLaughlin River, close below its junction
with Teapot Creek (Fig. 1), is significantly different from other sites in the region. The
site occurs at lowerelevations (between 750 and 760 m) than any otherfossil site in the
MacLaughlinRivervalley.Herethefossilsarealsocontainedinpointbarorconglomerate
facies. Materialfromthepointbarisencasedina2-4cmthickcalcareous shelloforange
coloured,medium-sizedsandgrains.Jawsthatcontainportionsofmolarrowsandpartial
longboneshavebeenrecovered. Fossils ofatleastthree speciesareidentifiedandall are
known fromthe Plio-Pleistocene elsewhere (one only from the Pliocene).
Two fossil post-cranial fragments have been recovered from a site in Bungarby
Creek, onBrooklyn Station- also alargelyconglomeratic deposit. Neitherspecimen has
been identified to species, although one is certainly a large diprotodontid. Although
attemptsatlocatingotherfossil-bearingdepositsinthevicinityonBrooklynStationhave
beenmade,nootherfossilsorlikely siteshavebeenlocated.Thespeciesfromthese sites
are listed inTable 2.
DISCUSSION
Interpretation offossils
All but one species of fossil mammal {Phascolonus gigas, the giant wombat),
recovered so farfrom Terrace 3 deposits ofTeapotCreek are Macropodidae (kangaroos
andwallabies,andshort-facedkangaroos). Elevenspeciesoffourmacropodidgeneraare
represented. The most common is Macropus titan; the other species comprise less than
35% ofindividuals identified (i.e., Macropusaltus, M.ferragus, Procoptodon goliah, P.
pusio, Protemnodon anak, P. "roechus/brehus", Sthenurus andersoni, S. atlas, S.
occidentalis, S. newtonae, Troposodon minor). From Murray's estimates ofweights of
fossil mammals (Murray 1991:1155 - 56, tables 16, 17) most, when adult, would have
beenbetween50and 100kginweight. BecauseallotherPleistocenefossildepositsinthe
EasternHighlands(includingthenorthernMonaro-seeRideetal. 1989)containnumbers
of smaller species, the composition of the fossil sample indicates that the processes
responsibleforits accumulation in theTerrace 3 deposits werehighly selective, eitherat
death orpost-mortem (orboth); itis notpossible, atthisjuncture, to determine which of
thetwo (orboth) occurred.
The condition of the specimens indicates that they are derived from earlier
accumulations. No specimens are articulated and all are fractured, probably the resultof
theirhavingbeentransported. Butnothingindicatesthatthey are significantlyolderthan
the sediments, orthat more than a short period oftime is represented by them. We have
been unsuccessful in obtaining any dates from the fossils themselves. We attempted to
have collagen dated from fossil bone collected from Terrace 3 (Site 7), but the dating
laboratoryfoundthat"thecollagenfraction(basalboneprotein),whichisverysusceptible
to decay when exposed to nature's weathering mechanisms, has decayed away entirely
.(oralmost entirely)" (in litt. BetaAnalytic Inc., 2April 1993).
No species inTerrace 3 deposits is representedby sufficient individuals toprovide
areliable statementofthe distributionofmortality inthe population. However, themost
numerous species, Macropus titan (26 identified individuals), allows some tentative
interpretation of, at least, whether it represents a random sample of a stable breeding
population. In the probably closely-related species, M. giganteus, the age ofindividuals
may be established from molar progression (molar index; Kirkpatrick 1964, 1965a). In
thesampleofM. titan,nospecimensaresufficientlycompletetoenablemolarprogression
stages to be measured directly by Kirkpatrick's method, but the crown wear ofmolars
enables stages of dental eruption and dental progression to be inferred assuming that
Proc.Linn. Soc.n.s.w., 122. 2000
no MACLAUGHLINRIVERFOSSILDEPOSITS
1-100 «
(0
-80
(0
">O Macropus giganteus -60
percentage breeding
9-
1-40 -^
0)
0)
E 6-
03
20 0)
3- (0
—————— — —
0-' II r^-
-i I I I I I r^-T I
1.39 2.42 3.01 3.44 3.77 4.04 4.27 4.47 4.64
Kirkpatrick molar index
Figure 3. Histogram ofmolar indexes ofindividuals ofMacropus titan in theTeapot Creek, Terrace 3
deposit, shownagainstagraphindicatingthepercentageofbreedingfemalesatthesamemolarindexes
in the closely related species, M. giganteus (data ofM giganteus from Kirkpatrick, 1965b; 50% of
wearfollowsthepatternobservedinM. giganteus(detailsofthemethod,andjustification
forit, are tobepublishedby RideandA.C. Davis in aworkonthe Quaternary vertebrate
faunaofPilotCreek, nearCooma, N.S.W.). Estimates canbe made ofmolarindex from
17 ofthe 24 specimens.
ThepatterninferredfromtheMacropustitansamplefromTerrace3 (Fig.3)indicates
thatmostindividualsdiedafterM2haderupted, andbeforethedentinewasfullyexposed
across both lophs (-ids) ofM4. In the case ofmodern M. giganteus, individuals ofthat
age are activelybreeding adults (Kirkpatrick 1965b - i.e., individuals with amolarindex
between 1.39and4.6).ThisconclusioniscomparablewiththoserecordedbyGillespieet
al. (1978:1046); and Flannery and Gott (1984:413) for samples obtained from the
PleistoceneLancefieldSwampandSpringCreekdeposits.Althoughtheseauthorsconclude
that a more aged part of the adult population is represented in their samples compared
with thatfromPilotCreek. Weareunabletocommentonthedifference,butsuchnarrow
andunimodaldistributionsofdeathsrevealedbyallthreepopulationswouldbeunexpected
iftheywere stablemammalpopulations withlongbreedinglivesundergoingprogressive
mortality. In such cases, the remains of juvenile and aged animals are expected to
predominate in samples (especiallyjuveniles - for the interpretation ofage distribution
from similar samples, see Ride and Tyndale-Biscoe 1962; Hughes 1965; Flannery and
Gott 1984; Turnbull and Martill 1988). Since the sample reveals neither a distribution
pattern suggesting progressive mortality in a stable population, norone resulting from a
catastrophic occurrence (such as aflash flood), eitherthe age structure ofthe population
was disti:rbed irregularly as to annual increments, or some selective agent resulted in
juvenileandagedclasses(particularlythejuvenile)tobeunder-representedinthesample.
The Teapot Creek accumulation also displays a strong bias in favour of the
representation of larger mammal species as does the Lancefield deposit (see Van Huet
1999:338-9). At Lancefield, the remains of small mammal species are present but they
are comparatively rare (there, only 24 of317 individuals are of species smaller than M.
titan which isrepresented by263 individuals; othermegafaunaintheLancefielddeposit,
comparable with or larger than M. titan, are Diprotodon, Zygomaturus, Procoptodon,
Sthenurus and Protemnndon).
Proc.Lln.\.Soc.N.S.W.. 122. 2000