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1. I n t r o d u ct i o n

1.1.BACKGROUNDThis

report

presents

the

geomorphology

and

sedimentology

of

the

North

West

Marine

Region

(NWMR)andasectionoftheNorthernMarineRegion(NMR)termedthenominatedareaofthe

(NNMR). The threemain outputs of the report include: 1) a review of previous geological

researchundertakenintheNWMRandNNMR;2)theresultsofaquantitativestudyofseabed

sediment texture and composition for these regions; and 3) a synthesis of this information

characterisingregionaltrendsinsedimentology,geomorphologyandbathymetry.Thestudyis

acollaborationbetweenGeoscienceAustraliaandtheDepartmentoftheEnvironment,Water,

HeritageandtheArts(DEWHA)andisacontinuationofsimilarworkconductedfortheSouth

WestMarineRegion(Potteretal.,2006;Richardsonetal.,2005).

Previoussediment

studies

in

the

NWMR

have

predominantly

produced

qualitative

results

at

localscales.Existingquantitativetexturalandcompositionaldataavailablefortheregionprior

tothistaskwasrelativelysparse.Thestudyhasimprovedthecoverageofquantitativedatafor

theNWMRby procuring and generating quantitative texture and composition data for 200

nominal seabed samples. This data expands the national marine sediment dataset for

Australiasmarinejurisdiction,withanalysesconsistentwiththosecompletedonsamplesfrom

the rest of themargin. By combining results of previous qualitativework and quantitative

information generated from existing and new data, this report provides an improved

understandingofsedimentologyfortheNWMRandtheNNMR.Informationcontainedwithin

thisreportwillcontributetotheDepartmentoftheEnvironment,Water,HeritageandtheArts

MarineBioregional

Planning

work

program

and

will

be

one

information

input

used

for

the

selectionof candidatemarineprotectedareas for theNorthWestandnominated areaof the

NorthernMarineRegion.

Geomorphic,sedimentaryandbiologicalinformationhaspreviouslybeenutilisedtodevelopa

NationalBioregionalisationofAustraliasExclusiveEconomicZone (EEZ)(Departmentofthe

Environment and Heritage (National Oceans Office), 2005; now the Department of the

Environment,Water,HeritageandtheArts)andsubstantivegeomorphicfeaturesofthewest,

northwestandnortherncontinentalmarginshavealreadybeenidentifiedandmapped(Heap

andHarris,inpress).Thisreportaddssignificantlytothesepreviousstudiesbyincorporating

theinformation

in

asedimentological

synthesis

that

includes

adiscussion

of

the

implications

formarineconservationintheNWMRandnominatedareaoftheNMR.

Thephysical characteristicsof the seabed,asdescribedby sediment textureandcomposition

data,canassist indetermining thediversityofbenthicmarinehabitats.Thesedata represent

enduring features which are elements of the physical environment that do not change

considerably(inhumanlifespans),andtheyareknowntoinfluencethediversityofbiological

systems. This is important for marine conservation due to the better definition and

characterisation ofbenthic habitats. Seabed texture and composition are easilymeasurable

parametersthat,whencombinedwithotherphysicalfeaturescanbeusedtocreateseascapes

thatserve

as

broad

surrogates

for

benthic

habitats

and

biota

(Whiteway

et

al.,

2007).

Seascapes

have thepotential tobeused in informing themarinebioregionalplanningprocess and the


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design of a national system of representative Marine Protected Areas (MPA). This data

increases the sediment coverage of theNWMR andNNMR tobeused in the generation of

seascapes.

1.2.SCOPE1.2.1.GenerationandSynthesisofSeabed Information for theNWMRandtheNNMRIn April 2007, Geoscience Australia and the DEWHA agreed to undertake a collaborative

projectto identify,analyseandcollateexisting informationonthetextureandcompositionof

theseabedintheNWMRandtheNNMR.Themainobjectivesofthisprojectwereto:

Identifyandsummariseallpreviousgeological information for theNWMRand

theNNMR;

Procure and analyse sediment samples (nominally 200) from the NWMR,

currentlyheldbyGeoscienceAustraliaandothermarinescienceinstitutions,for

grainsizeandcarbonateconcentrations;

Provide data on the texture and composition of the seabed for theNWMR to

populate Geoscience Australias national marine samples database (MARS;

www.ga.gov.au/oracle/mars)withthedata;and

Produce a report synthesising and summarising the sedimentology and

geomorphology of the seabed for the NWMR and the NNMR in support of

marinebioregionalplanningandcreationofanationalsystemof representative

marineprotected

areas.

1.2.2.ExpectedProjectOutcomesTheexpectedoutcomesofthisprojectare:

To obtain a better understanding of the nature of the seabed for the west,

northwestandnorthernmarginsofAustralia;

ToimprovetheavailableinformationonthesedimentologyoftheNWMRforthe

scientific and planning communities, leading to the development of Marine

BioregionalPlans;

Toimprove

access

to

data

on

the

nature

of

the

seabed

through

continued

populationoftheMARSdatabaseasanationalfundamentalmarinedatasetand

Toprovidetextureandcompositiondataforfutureprojects;forexample,thedata

may be combined with other physical data on the seabed (i.e. depth,

geomorphology,sedimentmobilityetc)tocreateseascapesthatrepresentmajor

ecologicalunitsbasedonmeasurable, recurrent andpredictable features of the

marineenvironment.


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1.2.3.ProductsandOutputsKeyoutputsofthisprojectwillbe:

200 quantitative textural and compositional data points for the NWMR and

associatedmetadataavailableintheMARSdatabase;

A reviewand synthesisofpreviousgeological information for theNWMRand

nominatedareaoftheNMR(Chapter3);

Quantitative analysesof the sedimentology andgeomorphologyof theNWMR

andnominatedareaoftheNMR(Chapters4,5and6);

A synthesis of allprevious andnew sediment information for theNWMR and

nominatedareaoftheNMRatplanningregionandbioregionscales(asdefined

byDEWHA)(Chapters4,5and6);

Aninterpretation

of

sediment

information

and

discussion

of

the

significant

findingsandtheirimplicationsforMarineBioregionalPlanning(Chapter6);and

A series of webaccessible digital maps to standards appropriate for data

coverageandsedimentpropertiesintheNWMRandnominatedareaoftheNMR

(AppendixG).

1.3.DESCRIPTIONOFGEOMORPHOLOGYIn 2004, a collaborative agreement between Geoscience Australia, CSIRO Marine and

AtmosphericResearch,andtheformerDepartmentoftheEnvironmentandHeritage(National

OceansOffice)

created

aNational

Marine

Bioregionalisation

(NMB

2005)

of

Australia

(DepartmentofEnvironment,Water,HeritageandtheArts,2005).TheNMB2005providesan

overarchingmanagementframeworkforalargepartofAustraliasmarinejurisdictionandis

basedon themostuptodateknowledge of thebiophysicalpropertiesofAustraliasmarine

environment,includingseabedgeomorphologyandsedimentology.Definitionsofgeomorphic

provincesandfeaturesincludedintheNMB2005andusedinthespatialanalysesinthisstudy

arelistedinTable2.1.

1.4.MARINEREGIONSThefivemarineregionsofAustraliasExclusiveEconomicZone(EEZ)includetheEastMarine

Region,NorthernMarineRegion,NorthWestMarineRegionandSouthEastMarineRegion.Marinebioregional planswillbe developed for each of thesemarine regions including the

NWMRoutlinedinthisreport.

1.4.1.NWMRandNominatedAreaoftheNMRTheNWMRencompassesCommonwealthWatersbetweenKalbarriinWesternAustraliatothe

WesternAustraliaandNorthernTerritoryborderintheBonaparteGulf(Fig.1.1;Fig.1.2).This

regioncomprises1.1millionkm2ofoceanandseabedandisboundedinshorebytheouterlimit

of statewatersofnorthernWesternAustralia (which generally extendsout to threenautical

miles

from

the

territorial

sea

baseline),

and

bounded

offshore

by

the

edge

of

the

Australian

EEZ

(200 nautical miles from the low water mark) except between Cape Leveque and Cape

Londonderry,wheretheNWMRdoesnotextendtotheEEZboundary.


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Changestothelocationofthemarineplanningregionboundarieshaveresultedinaportionof

the Northern Marine Region (NMR) being excluded from previous geomorphology and

sedimentologyassessmentsbyGeoscienceAustralia(HeapandHarris,inpress).Thisarea,the

nominated area of theNorthernMarine Region herein referred to as theNNMR, hasbeen

includedin

the

present

study.

The

NNMR

covers

an

area

of

nearly

200,000

km2

and

includes

the

seabedandwatercolumnfromtheboundaryoftheNWMRinthewesttotheAurariBayinthe

east(Fig1.1).

Figure 1.1. Location and extent of the North West Marine Region (NWMR) and nominated area of the North MarineRegion (NNMR) relative to other Marine Regions in the Australian EEZ.

1.5. BIOREGIONSThebenthiccomponentoftheNMB2005managementframeworkconsistsofahierarchicalset

of geographicmanagement units. Below the scale of themajor oceanbasins that comprise

Australiasmarinejurisdiction (i.e., the Indian,SouthernandPacificOceans), theshelf,slope,

rise and abyssal plain/deep ocean floor are designated as Primary Bathymetric Units that

representthe

broadest

scale

planning

unit

and

have

areas

of

several

million

km2.


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Within each of the Primary Bathymetric Units are Provincial Bioregions,which havebeen

definedmainlybythedistributionofdemersalfish,bathymetry,andgeomorphology,andhave

areasofhundredsof thousandsofkm2 (IMCRA 4.0 2005).TheProvincialBioregions are the

principal planning unit forMarine Bioregional Planning.Marinebioregional plans willbe

developedforeachofthesemarineregionsincludingtheNWMR.

1.5.1.BioregionsoftheNWMRTheNWMRcompriseseightbioregions.(Fig,1.2&Table1.2).Onlythreeofthesebioregionsare

containedentirelywithintheNNMRboundary.Theremaindereitheroccupyareaswithwater

depths


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Table 1.2. Summary details of the provincial bioregions contained in the NWMR.

Bioregion% of bioregion

included in NWMRWater type % of total NWMR area

Northwest Shelf Transition 44 Transitional Waters 13

Northwest Shelf Province 88 Tropical Waters 20

Central Western Shelf Transition 76 Transitional Waters 1

Central Western Shelf Province 65 Subtropical Waters 3

Central Western Transition 100 Transitional Waters 15

Timor Province 72 Tropical Waters 15

Northwest Transition 100 Transitional Waters 17

Northwest Province 100 Tropical Waters 17

TheNWMR

contains

the

Northwest

Shelf

Province,

Central

Western

Shelf

Transition,

Central

WesternShelfProvince,andpartoftheNorthwestShelfTransition(Table1.2). Theseprovinces

andtransitionsarelocatedontheshelf.Waterdepthsintheshelfbioregionsarebetween10m

and350mbutaregenerally


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Chapter5.AsfortheNWMR,resultsofthisstudyarediscussedinthecontextoftheProvincial

Bioregions,anddataarepresentedforindividualbioregions.

Theentirearea(179,200km2)ofthetwoshelfprovincesandtransitionsarelocatedontheshelf.

AsmallareaofslopeispresentintheTimorTransitioninthenortheastofthenominatedarea

ofthe

NMR.

Waterdepths in thenominatedareaof theNMRvarybetween10and350m. Deepestareas

occurontheslopealongtheouterboundaryoftheEEZ.Samplecoverageinthenominatedarea

oftheNMR isrelativelyeven,withminordatagapsexistinglocallyatseveral locationonthe

innershelfandonelocationonthemid outershelfinthewestoftheregion.

1.6. REPORTSTRUCTUREThe report provides a regional assessment of the sedimentology and geomorphology of the

NWMR

and

NNMR.

The

report

provides

a

synthesis

of

the

existing

sedimentology

and

geomorphologyoftheNWMRandNNMR(Chapter3)whichprovidesaframeworkinwhich

thenewdata canbeunderstood.This is followedby a regional scale spatial analysis of the

sedimentology and geomorphology for the NWMR and NNMR (Chapter 4) and for each

provincialbioregionoccurringintheNWMR(Chapter5),puttingthenewdataintothecontext

oftheplanningzonesusedbyDEWHA.Lastly,resultsofthisstudyandpreviousworkinthe

NWMRandNNMRare summarisedanddiscussed in termsof their implications formarine

planning(Chapter6).

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