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The University of Maine DigitalCommons@UMaine Earth Science Faculty Scholarship Earth Sciences 6-10-1995 Landscape Evolution of the Dry Valleys, Transantarctic Mountains: Tectonic Implications David E. Sugden George H. Denton University of Maine - Main, [email protected] David R. Marchant Follow this and additional works at: https://digitalcommons.library.umaine.edu/ers_facpub Part of the Earth Sciences Commons Repository Citation Sugden, David E.; Denton, George H.; and Marchant, David R., "Landscape Evolution of the Dry Valleys, Transantarctic Mountains: Tectonic Implications" (1995). Earth Science Faculty Scholarship. 55. https://digitalcommons.library.umaine.edu/ers_facpub/55 This Article is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Earth Science Faculty Scholarship by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. B7, PAGES 9949-9967, JUNE 10, 1995 Landscapeevolution of the Dry Valleys,Transantarctic Mountains: Tectonicimplications David E. Sugden Departmentof Geography,University of Edinburgh,Edinburgh, Scotland GeorgeH. Denton Departmentof GeologicalSciences and Institute for QuaternaryStudies, University of Maine,Orono DavidR. Marchant• Departmentof Geography,University of Edinburgh,Edinburgh, Scotland Abstract. Thereare differentviews about the amount and timing of surfaceuplift in the TransantarcticMountains and the geophysicalmechanisms involved. Our new interpretationof the landscapeevolution and tectonichistory of the Dry Valleysarea of the Transantarctic Mountainsis basedon geomorphic mapping of anarea of 10,000km 2. Thelandforms are dated mainlyby their associationwith volcanicashes and glaciomarine deposits and this permitsa reconsmactionof the stagesand timing of landscapeevolution. Followinga loweringof baselevel about55 m.y. ago,there was a phaseof rapid denudationassociated with planationand escarpmentretreat, probably under semiarid conditions. Eventually, downcutting by rivers,aided in placesby glaciers,graded valleys to nearpresent sea level. The main valleyswere floodedby the seain the Mioceneduring a phaseof subsidencebefore experiencing a final stageof modest upwarpingnear the coast. There hasbeen remarkably little landformchange under the stable, cold,polar conditions of the last 15 m.y. It is difficult to explainthe SiriusGroup deposits, which occurat high elevationsin the area,if they are Pliocenein age. Overall,denudation may have removeda wedgeof rock with a thicknessof over 4 km at the coastdeclining to 1 km at a point 75 km inland,which is in goodagreement with the resultsof existingapatite fission track analyses. It is suggestedthat denudation reflects the differencesin baselevel causedby high elevationat the time of extensiondue to underplatingand the subsequentrole of thermaluplift and flexural isostasy.Most crustaluplift (2-4 km) is inferredto haveoccurred in the early Cenozoicwith 400 m of subsidencein the Miocenefollowed by 300 m of uplift in the Pliocene. Introduction debate,we do not considerthe issuein this paper(but seeDenton et al, [ 1993]). The aim of this paperis to relate geomorphologicalevidence Extending acrossAntarctica, the Transantarctic Mountains of landscapeevolution to the tectonicprocesses in the Dry Valleys rise to over 4000 m in the Royal SocietyRange. The mountains of the Transantarctic Mountains. Like the Drakensberg consistof gentlytilted blocksof sedimentaryrocks (Devonian- Mountains in southernAfrica and the Great Dividing Range in Triassic Beacon Supergroup)overlying Pre-Cambrian-Devonian Australia the Transantarctic Mountains consist of an eroded basementand are intruded and cappedby Jurassicdolerites and plateau edge characteristicof high-elevationpassive continental basalts. The mountainscomprise the uplifted rift flank of the margins [Gilchrist and Summerfield,1990]. Understandingthe West AntarcticRift System[Behrendt et al., 1991], which has landscapeevolution of the mountainsis importantbecause it can been periodicallyactive since the separationof Antarcticaand be used to constrainvarious geophysical models of the tectonic Australia [Tessensohnand Worrier, 1991]. processesassociated withsuch margins. The tectonic history of Thereis considerableuncertainty about the mount and theTransantarctic Mountains isintimately involved ina debatetiming of uplift and the tectonic processes involved. Apafite aboutthe stability ofthe East Antarctic IceSheet. Although our fissiontrack analysis indicates thatthere has been about 5 km of new interpretationof landscapeevolution has implicationsfor the denudationin the Dry Valleys area since the early Cenozoic; denudationrates were high in the early Cenozoicbefore tailing off 1NowatInstitute forQuaternary Studies, University ofMaine, [Gleadowand Fitzgerald, 1987; Fitzgerald, 1992; Brown et al., Orono. 1994]. This implies that significantlocal relief existedaround 55 m.y. ago and that the rift flank was alreadyelevated with respect to base level, either as a consequenceof thermal uplift or Copyright1995 by theAmerican Geophysical Union. underplatingor as a result of the rifting of a preexisting,high- elevation surface. This interpretationagrees with evidenceof Papernumber 94JB02875. 0148-0227/95 / 94JB-02875$05.00 limited recent surface uplift as inferred from the elevation of 9949 9950 SUGDEN ET AL.: DRY VALLEY LANDSCAPE EVOLUTION undisturbedsubaerial Pliocene volcanic cones in Taylor Valley denudationprofiles from the northernsides of Ferrar and Wright [Wilchet al., 1993a]. A differentline of evidencesuggests that valleys[Fitzgerald et al., 1986] imply that the blockhas behaved there has been substantialsurface uplift of parts of the as one unit since the early Tertiary, thus holding constantone TransantarcticMountains of 1-2 km over the past 2-3 m.y. variable in landscapeevolution. Second,the block contains [McKelveyet al., 1991; Webbet al., 1984; Webband Harwood, outcropsof SiriusGroup deposits at high elevations(2650 rn on 1987]. This view is based on the existence of the remains of Mount Feather), critical evidence which must eventually be temperatevegetation of presumedPliocene age (2-3 Ma) in Sirius accommodatedin any explanation. Third, the valleys containa Group depositsat high elevations. There are some 30 Sirius terrestrial record of surface deposits extending back to the Groupoutcrops in theTransantarctic Mountains flanking the Ross Miocene, thus providingan unprecedentedlylong window into Ice Shelfbetween latitudes 86øS and 78øS and further outcrops in mountainevolution. A disadvantageof a studyrestricted to one the highmountains of SouthernVictoria Land in the Dry Valleys blockis that any conclusionscannot necessarily be extrapolatedto and the Prince Albert Mountains [Denton et al., 1993; Verbers other areas of the Transantarctic Mountains. and Van der Wateren,1992]. The datingof the depositsdepends There have been two main phases of interest in the criticallyon the age and origin of reworkeddiatoms thought to geomorphologicalevolution of the Dry Valleys. The first have originatedin marine basinsin East Antarcticaand to have involved geologistsof Scott's and Shackleton'sexpeditions, been subsequentlytransported to the mountainsby ice. The whoseinitial observationson the great age of the landscapeand biostratigraphicage of certainof the diatomshas been confirmed the modestimpact of presentglaciers make relevantreading to by isotopicdating of a volcanicash layer in the offshoreCIROS-2 this day [Ferrar, 1907; David and Priestley,1914; Wright and core [Barrett et al., 1992]. Severalother supportinglines of Priestley,1922; Taylor, 1922]. The secondphase accompanied evidencefor recentsurface uplift have beencollated by Behrendt U.S. and New Zealand activities after the International andCooper [ 1991],including the "youthfulappearance" of the rift GeophysicalYear in 1957. In numerouspapers elaborating the shoulderand the presenceof offshoreHolocene fault scarps. geologicaland glacialhistory of the area, a generalconclusion Thesevarious views were synthesizedby Fitzgerald[1992] who was that the main valleysowed their origin to earlier stagesof suggestedthat crustal uplift of the TransantarcticMountains in glaciationunder more temperateconditions [e.g., Taylor, 1922; the Dry Valleys area has occurredthroughout the Cenozoicbut Bull et al., 1962; Calkin, 1974a; Denton et al., 1971, 1984; with two acceleratedpulses at 55-40 Ma and 10-0 Ma. Nichols,1971; Selbyand Wilson,1971]. This view is consistent In view of the uncertaintyabout the timingof the uplift, it is with the argumentsof Van der Waterenand Verbers[1992] in difficult to relate the tectonic evolution of the mountains to the northernVictoria Land. In addition, there is recognitionof the widerprocesses of platetectonics. At leasttwo periodsof rifting particularrole of cold desertagents of erosion. For example, have been inferred from study of the Ross Sea embayment Selby [1971, 1974] recognized the prevalence of straight [Tessensohnand Worner,1991; Cooperet al., 1991;LeMasurier rectilinearslopes and tentlikeridges which he attributedto salt and Rex, 1991]. The first phasebegan in the Mesozoic(possibly weatheringand wind deflationcharacteristic of this type of frigid, linked to the separationof Antarcticaand Australia) and was arid environment. The characteristicslope angles were also associatedwith widespreadgraben downfaultingand crustal related to rock strengthcharacteristics
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