The ROSS SEA DEPENDENCY including VICTORIA-LAND
This will be third time I have made some attempt to summarise the geology of the Ross Sea Dependency and adjoining areas, eg Geological Structure and Stratigraphic Correlation in Antarctica; N.Z.J.Geol.Geophys. 6,(3),1963, also see N.Z.Geol.Surv.Bull.71, 1972). More information has become available, more age dates and more fossils, so many corners have been filled in. However many crucial lithological contacts remain buried under snow, and many critical formations have been stripped by the grinding ice, so the subject is still far from complete.
A great many names have been applied not only geographically but also to purely local rock formations and the descriptions are often far from adequate. My own hands on (hammer on?) experience is limited to the Cape Hallet region, the Mawson Glacier to Mulock Inlet sector and the Shackleton (or Nimrod) Glacier to the Beardmore. For the rest we have to rely on other accounts.
Unfortunately there is little relationship between the geography and the persons for whom geographic features are named. Beardmore was a Scottish manufacturer (he built engines for the well-known Fe2B fighter in WW1), the "James Caird", (perhaps the best-known ships lifeboat ever built) was named after another financial supporter of Shackleton. Mountain ranges are cursed with names of politicians and bureaucrats applied by those currying favour, the worst all perhaps being the naming of the "Royal Society Range" after members who did their level-best to prevent the appointment of Capt. Scott to the 1901 Expedition, and were able to block him being awarded a knighthood afterwards. Scott was one of the few that cared about really exploring and mapping this new continent (and was also the most successful) but has remarkably little named after him, people who came (and still come) with the avowed intention of earning notoriety are much better known to this day, people who have sat of committees are even better known.
The man to whom we owe most of our knowledge of the depth and volume of the Antarctic ice sheet is Dr Albert Crary, known to his friends and admirers as "Bloody Bert". For years he crisscrossed the continent on seismic traverses, but I do not know of any features named for him, except perhaps the "Crary Laboratory" in Mac Town, and an obscure nunatak. The committee for Geographic Place Names includes a "Crary" range in Marie Byrd Land which includes at least one volcano, which are already given several names. The worst thing about history is that we have to live with it.
Scott et al in 1901-03, Shackleton in 1907-08 and Scott again in 1910-12 and their followers, especially Hartley Ferrar, Sir Edgeworth David, Charles Wright, Raymond Priestley, Frank Debenham and their helpers, found virtually every rock type known to this day in the Ross Dependency region. I spent about 7 years, in the field and on the study of the petrography and geochemistry of Antarctic rocks but seldom found something that had not been to some degree described by Professor Benson of Otago University who had been given the 1907 collections to work on, or by Sir Frank Debenham and others. However, the samples they collected including the famous 35lbs of sample brought back from the head of the Beardmore by Scott, Wilson, Bowers and Oates on their death march, were almost all picked up as erratics from moraines. It can take many hours to battle through crevasses to reach the valley walls and it was seldom done, in fact when I sampled granites, aplites, marbles, calc-schists, dolerites etc up the Ferrar-Taylor Glaciers in 1955-56 I believe these were among the first rock samples ever collected in place with the exception of certain of those collected by Hartley Ferrar himself (Ferrar, H.T., 1924, 'The Geological History of the Ross Dependency', N.Z.Jour.Sci.Tech., 354-361.)
The main contribution Guyon Warren and I made in 1956-58 was to collect several thousand samples which were positively located in place, to locate the Devonian and the Permo-carboniferous in situ, and in addition the plant beds of the Triassic and Jurassic Beacon Sandstone and this enabled us to produce the first real geological map. (Gunn and Warren, 1962, "The Geology of Victoria Land from Mawson Glacier to Mulock Inlet", (NZ Geol.Surv.Bull.71, 1-157). We were also the first to locate the Ferrar Volcanics and establish the differentiation processes in the dolerites. This was all written up by the end of 1958 but there were innumerable delays in printing, the bulletin sat for a year on the desk of a Survey geologist who was supposed to proof read it. Finally Dr Larry Harrington, a senior Survey geologist suggested that as many more geological people were pouring into Antarctica in the wake of our publicising the existence of more dry valleys, that we should put out a summary of the stratigraphic nomenclature before others superseded it and duplicated it. We agreed and he put out a short summary of our main formation names, but under his own name, (Harrington, H.J. 1958, Nomenclature of Rock Units in the Ross Sea Region, Antarctica, Nature, Lond. 182,(4631):290) However the original definitions are to be found in the Survey Bulletin 71.
A great many papers were published in the 1960s era but many of them were simply recapitulation of what had been described in detail by Wright and Priestley, 1922, (Glaciology. Brit. Terra Nova Exped.1910-13, 581pp) and by Ferrar, Debenham, Taylor, David, Campbell Smith, Prior and others. These and many other early publications are referred to in the Survey Bulletin 71 which is fairly readily available still and so will not be repeated here.
The Geology of Victoria Land at a Single Glance.
This view taken at the head of the Wright Valleys shows most of the geology of Victoria land in a single section.
A great deal of geology is visible so set screen to max resolution, say
We stand on a litter of retreatal moraine of a mixture of dolerite and sandstone, occasionally some granite, on a valley shoulder immediately above the top of the Peneplain Sill and gazing north-west. There is a sharp change in slope above the hard dolerite which lies below the easily-eroded sandstone which underlies the foreground.
The Labyrinth (centre) consists of narrow (fluviatile?) channels cut in the Peneplain Sill of the Ferrar Dolerites of mid-Jurassic (165 myr) age, the upper margin of which forms a shadow on the far side. Originally resting on the peneplained surface of the granites, (now below the sill) are about 5000ft of flat-lying, mainly terrestrial, sandstones, arkoses, orthoquartzites and minor shales of the Devonian to Jurassic Beacon Sandstone. Middle Devonian armoured fish, and even 9ft sharks are found elsewhere about 1000ft above the base. A little above the base of the Beacon opposite is a very well defined horizon of what??? Permian tillite?? Has the Devonian been identified here? Then in cliffs of small dolerite-capped cirques directly towards Mt. Shapeless are prominent black bands. These OUGHT to be PermoCarb Glossopteris-Gangamopteris coal measures as some Triassic carbonaceous beds with plentiful plant fossils occurs at the summit at about 10,000ft.
Notice strong lithological control of glacial topography due to the extreme durability of the Ferrar Dolerite compared to the easily abraded, weakly cemented Beacon Sandstone. The Wrights Cascades as I called them in 1956 (also called Air Devron Six Icefalls, may God save us all) cascade over a dolerite sill. The upper Wright Glacier is wasted by ablation but no recent sign of retreat. Down out of sight on right is the ice of the cutoff toe of the ancient glacier covered by ablation moraine.
Similar fossil ice in the Beacon Valley has been estimated at 2myr. On the extreme left is Mt Fleming, with the most extensive Triassic sequence of plant beds known, though Triassic is also found at Mt Feather and in the Queen Maud Ranges. In some restricted area, above the Triassic lie Jurassic plant beds and coals, and fresh-water beds including Jurassic Ostracods. The intrusion in the Jurassic of enormous volumes of continental flood basalts as sills completely disrupted the sequence, and not far off are the tholeiitic lava flows which reached the Jurassic surface
We came off the Ice Cap to camp on the skyline right of centre on Xmas Eve, 1957 and leaving the dogs to yelp in frustration, we shot off up Shapeless for a good ski run home, but the snow was like sand!
Notice the abrupt change in topography at the top of the truncated spurs. So we can assume that at the height of the Last Glaciation (the age of which we will discuss later) the ice levels stood 500 2000ft above the present valley floors. If it ever stood higher all signs have been removed by cirque sapping. Notice also that it would take very little rise in the height of the ice cap to bring this about, probably a mere 200ft would do it.
Some of this lowering of the local Ice Cap surface has been brought about by Ice Capture by the large, fast moving Mawson, Mulock, Barne and glaciers moving at up to 800m a year which could easily deepen their beds by 1 mm/yr, = 20m only in 20,000yr for dolerite but ten or twenty times as much if the glacier bed is of Beacon Sandstone.
Miogeosynclinal Metasedimentary rocks of the Ross System
It must be understood that the oldest sedimentary rocks which predate the folding of the Ross Orogeny (an orogeny being the process by which rocks are folded and deformed by intense lateral compressive stress caused by crustal spreading taking place along spreading axes often thousands of miles away) appear to be a direct continuation to the south of the Adelaide Miogeosyncline in South Australia. Being originally a sedimentary basin located within a continental environment and not formed at a continental margin where extensive underthrusting may occur, the usual arc-andesites are missing though there is report of some in Northern Victoria Land. The sediments are more calcareous and often include limestone, not seen in eugeosynclines, and while extensive plutonic rocks may form along the crustal keel (as seen at the base of the modern Himalayas), the chains of superficial andesite volcanoes as seen along the Andean chain are largely missing. Ignimbrites, rhyolites and rhyodacites may form but andesites are insignificant and in fact detrital andesite fragments are not seen in any Ross System rocks I have studied in thin section as they invariably are in the Alpine greywackes of New Zealand for example which are eugeosynclinal.
Ross System rocks are of upper Precambrian to lower Paleozoic age and are always strongly folded about usually NW/SE axes ( or what is the NW direction in Victoria Land), not as one might expect, parallel to the coast line. This means that one group of Ross System rocks are not directly along the strike of another group but lie on an en-echelon pattern, possibly as a result of dextral faulting.
The Robertson Bay Group
These are comprised of a great thickness of isoclinally folded felsite-greywacke-argillite beds well seen on the north facing cliffs of Roberston Bay west of Cape Adare. They extend for 150 Km in a south-westerly direction across the strike.
The area covered by GS Bulletin 80 stopped at the southern side of the Tucker Glacier but the German GANOVEX expedition of 1979-80 have produced a map extending the Robertson Bay Group somewhat further south to Lat 73 deg and Dallai etal, 2003,(Lithos 67, 135-151) show the "Robertson Bay Terrane" so-called, to extend a little to opposite Coulman Island. To the west they extend to the mid point of the Bowers Range between the Lillie and Rennick Glaciers 240 km WNW of Cape Adare.
The Robertson Bay Group have been intruded by the Lower Paleozoic Post-Tectonic Tucker Granodiorite and Edisto Granite with the same contact metamorphic effects as seen in other greywacke-argillite sequences of the Ross system such as at Skelton Glacier and the Beardmore Glacier region for example (below), producing biotite hornfelses and coarse cordierite hornfelses ( see Harrington etal, 1967). Rocks are sometimes current bedded and cross bedded on a fine scale, and as in other members, frequently included interstitial calcite. Chemically they range from 56 to 76% silica and compare closely with other Ross System members.
Note on the pic of Mt Herschel, the face of which is composed of Robertson Bay Group greywackes that the peak appears to be the apex of an anticlinal fold while a syncline appears in the col to the left. See map in Harrington et al, (1967).
In 1963, John Ricker (Outline of Geology between Mawson and Priestley Glaciers, Victoria Land, Antarctic Geology, SCAR Proceedings.) described similar rocks to the Robertson Bay Group from the sides of the Priestley Glacier NW of Terra Nova Bay. They crop out for 60 km between Mt Ogden and Timber Peak, these rocks being previously only known from erratics. They include dark slates, argillites, siltstones, fine sandstones and limestones. All are contact metamorphosed to some degree by post-tectonic granites, the strike direction is again northwest with a vertical cleavage.
The limestones are saccharoidal, contain thin bands of argillite and are also contact metamorphosed. As well as flattened calcite grains they include some quartz, feldspar, tremolite, biotite and extreme cases, diopside and idocrase. Microcline and graphite may also be found. Such rocks form a link to the higher grade schists and paragneisses found in the Koettlitz Ferrar Granite Harbour, Terra Nova Bay and the Wilson Group Schists.
A somewhat disastrous foray in 1959 did result in the mapping of the region between the lower Beardmore Glacier and the lower Shackelton Glacier (which we rather mistakenly decided in 1958 to rename the "Nimrod Glacier" in view of the fact that a small "Shackleton Glacier" already existed somewhere else. I now regret this as I feel Shackles deserves to have the largest glacier in the area named after him.)
The "Goldie Formation", (Gunn and Walcott, 1962, The Geology of the Mt Markham Region, Ross Dependency, Antarctica, N.Z.J.Geol.Geophys. 5,(3), 407-26) reveals along the western side of the Lowery Glacier the same thin-bedded greywacke-argillite in isoclinal folds which, by stereographic projection have NNW-SSE axes with a plunge of not more than + - 15 deg. Arkoses and subordinate limestone is included. Again contact metamorphism with post tectonic granites has produced spotted slates, albite-epidote-muscovite-biotite hornfelses and hornblende hornfelses which include hornblende, plagioclase, diopside, andalusite and cordierite. Microcline, clinozoisite and sphene may also be present. George Grindley ( 1962, NZJGG,6) found more Goldie Formation grewackes on the sides of the Beardmore Glacier at Mt Kyffin, Wedge Pk, and The Cloudmaker and Cambrian limestone at Mt Buckley, which he called the "Shackleton Fm" . Facing the Nimrod Glacier below the junction with the Marsh Glacier Grindley shows a bluff showing obvious contact of the Goldie Fm greywackes with a thick sequence of limestone.
Unfortunately I was never south-east of the Beardmore and for those rocks we must rely on descriptions of others.
North of the Nimrod Glacier are four block faulted ranges. Near the coast on the flat-topped Nash Range the rocks are Goldie Fm greywackes intruded by post-tectonic Hope Granite.
Queen Maud Group
Vic Macgregor in 1963-4 spent the summer mapping in the area beyond the Beardmore Glacier to the Liv (flown up by Byrd on his first flight to the Pole) and the Axel Heiberg made famous by Amundsen using it as a route on his route to the pole.
Vic named two formations one of greywacke-argillite (= Goldie Fm) and the other of marble. Metamorphism in this, as might be expected in sedimentary rocks occurring only as remnants in a plutonic complex is extreme, being migmatised, shredded into xenoliths, and often partially absorbed. All the usual secondary minerals are present but also wollastonite, grossular garnet and sillimanite.
In some regions, eg west of mcMurdo Sound between the Upper Koettlitz Glacier and Terra Nova Bay, In the lower regions north of Terra Nova Bay, in the Miller Range in the Upper Nimrod there are calcareous schists of garnet amphibolite rank, more strongly altered than, say the Robertson Bay Group. They occur with pre-tectonic gneisses an have coarse 1 cm diopsides, vesuviante and garnet. They seem to be the same as the other Ross System rocks but are more regionally metamorphosed.
We do not yet have enough detail on the Horlick Mts, Pensacola Range, Patuxent Mts and other scattered nunataks occurring towards Dronning Maud Land but we can quote Stump 1995 who show a recurrence of the same tightly folded greywackes and limestones. The constancy and extent of the major antarctic formations is phenomenal.
The Ross Orogeny and the Granite Harbour Intrusives
Under compressive stresses directed in a general NE-SW direction, the eugeosynclinal sediments were isoclinally folded, the generally younger L. Cambrian limestones, being more plastic, are usually crumpled and complexly deformed. Early intrusion of generally sodic hornblende granodiorites formed gneisses, which are segregationally banded, and foliated. A large number of Rb87/86 and Pb/Pb ages show a spread of ages from 550 450 myr in the main, of which we will later show diagrams. The older gneisses were affected by the younger granites and do not all give older ages. The main syntectonic intrusion in the McMurdo region is the weakly foliated Larsen Granodiorite, found at intervals all the way to Terra Nova Bay.
The density of the Post-tectonic granites, granodiorites and diorites varies greatly. In the Granite Harbour region, no sedimentary rock is found, only overlapping granite stocks. In The Robertson Bay - Cape Hallett area, the Admiralty Intrusives are minor in volume and contact metamorphism is local. From Koettlitz Glacier to Terra Nova Bay, the intensity and duration of igneous intrusion has resulted in the Ross sediments being metamorphosed to a higher degree of Upper Amphibolite zone metamorphism, with coarse diopside, scapolite, vesuviantite, garnet etc.
Granitic rocks giving 350-500 myr age dates occur sporadically around the periphery of the whole continent, so while the Ross Orogeny affected all of the basement rocks of the Victoria Mountains, some effects may have occurred at far distances removed from the main axis of deformation.
Complete stability had been achieved by Late Ordovician-Lower Devonian time and a long period of peneplanation ensued. We hope to be able to show pix of the "Kukri Peneplain" at intervals from NVL (Northern Victoria Land) to the Queen Maud Mts, the Horlick Mts, the Thiel Mnts and even further, but when we suggest some benevolent organisation supply us with a plane to take them, we get squawks of outrage. Requests for copies of pix already taken are greeted with the chilliest of silences, so our illustrations may have to be limited. Stump shows Beacon Sandstone resting on truncated, tightly folded Robertson Bay Group without any intervening dolerite. Truncated mountain tops and summit concordance suggests that the Kukri peneplain extended to Cape Adare.
The Pre-tectonic Gneisses
In 1957 we were confronted with doing what no one had really attempted to do before on a large scale, ie, how to map in and make sense ultimately of about 100,000 square miles of a complex of intrusions of massive granites of different ages and compositions.
Some were banded, deformed and gneissic, some slightly so, some were undeformed. Some were fine grained, some had feldspars 3 inches long, and quartz crystals 3 in across, some were dark hornblende diorites, some black and white granodiorites and some were grey granites and some with large pink potash feldspars or were light pink aplites. Most of the intrusions seemed to be individual plutons or possibly cupolas a few miles across, some seemed to occur intermitently for scores of miles. Some changed in texture as you walked across a well exposed outcrop, dark margins became lighter and coarser grained, light colored bands a few scores of feet wide crossed darker hornblende-bearing rock, some were fairly homogenous, other highly variable.
Once one has seen granites being formed by the melting of sedimentary layers that happen to be of a low average melting composition, as may be seem in the deep valleys of the Himalayas, it becomes obvious why granites are so variable.
First this horizon melts and moves upward in a diapir, then perhaps another more basic but at greater depth. The most obvious characteritic was the degree of deformation, some gneisses were obviously magmatic but had been deformed just as much as the schists and para-gneisses so we called these "Pre-tectonic" though "Early Tectonic" might have been better.
The "Syntetctonic" rocks were slightly sheared and banded but had been intruded after the main period of deformation had passed. The majority are quite undeformed and must have been emplaced after tectonism had ceased, so these were called "Post-Tectonic. Later in in the Canadian Archaea and in Peru the same sequence was seen, early pre-tectonic sodic granodiorites and post-tectonic, always more potassic, granites and last of all pegamitites and alkaline rocks more like monzonites and syenites.
The Kukri Peneplain
This is an almost horizontal erosion surface cut across the Granite Harbour Intrusives of Ordvician age and has the Beacon Sandtone laying on it. The exact age of the base of the Beacon is not known, Devonian fossils lie about a thousand feet above the base but the underlying peneplaned granites give Ordovician (~450myr) ages. Although mentioned in almost every geological paper published in the last 35 years the amount of detailed information on this erosion surface does not seem to have increased that much but an ongoing search will be made for key facts. The peneplain surface is well marked by either yellow-grey-white sandstone resting on a basement of granites, gneisses and schists, or by a chocolate coloured dolerite sill about 1000 1200ft thick which has intruded in Jurassic time between the sandstone and the basement. This is called the "Peneplain Sill". Conglomerates are often found near the contact.
The peneplain surface is not only well seen in the Kukri Hills, in the Dry Valleys and Granite Harbour, it shows along the coastal mountains all the way to Nova Bay and to Nrthern Victoria Land. Dolerites and sandstone are known from Northern Victoria Land, and the continued existence of the Kukri Peneplain is probable and the accordance of summits seen in the Roberson Bay Group greywackes suggests it might have extended north-east to the Ross Sea and north to the Cape Hallet region. It can also be followed down the mountains south to the region of the Beardmore Glacier and to the Horlick Mountains, and probably much further, possibly right into the Indian Ocean coast in Queen Maud Land, but it does not seem to be well documented.
The Karoo of South Africa consists of sandstones lying on basement intruded by sills and overlain by flows, but whether any equivalent of the peneplain exists we do not know though it should.
It is a great puzzle that the Ross Orogeny rocks should be peneplained so quickly, where did all the sediments go? It has occasional water channels in it, as though tidal. Below the Beaufort Sandstones (=Beacon) in the Karoo is an older formation, the Dwyka Tillites, and in South Africa at least, the land was peneplained by glaciation. However the McMurdo region was at least 2,500 miles away from the Karoo, even when the southern continents were still united in the Gondwana super continent. Then quite suddenly enormous amounts of sandstone and arkose, sometimes water laid but mainly aeolian arrive. From where? Was the land peneplaned near the coast while high granitic mountains still stood further inland? Was the Beacon deposition progressive? There is simply not enough exposure to say.
Coal-bearing Beacon appear 1500 miles away in the Prince Charles Mts near the Australian base of Mawson. Deep drilling has revealed Beacon down-faulted into McMurdo Sound at Roberts Point. How far towards Marie Byrdland does it occur? We do not know as yet. Does it occur under the centre of the Ice cap? Under the South Pole? One would think that examination of the peripheral continental marine sediments should show where the ice has passed over the easily eroded Beacon.
The final truth is we still know very little about the total extent of either the Kukri Peneplain nor the Beacon Sandstone. Both extend 2000 miles and can be seen occasionally for as much as 100 miles in width. Perhaps both are 2000 miles in width. They continue into the similar Karoo series of South Africa and into a small area of eastern Tasmania or, rather, did continue before the late Jurassic breakup of Gondwana. Coal-bearing sandstones of the beacon type continue up the East coast of New South Wales and southern Queensland.
Though the Beaufort formation in South Africa includes cross bedded sandstone, there seem to be more mudstone than is seen in the Beacon. Both have been intruded by almost identical dolerites sills of the same 165 myr (Jurassic) age.
In Jurassic time, the whole pattern on plate tectonics underwent a massive change and new spreading centres which cut completely across the Gondwana super continent were activated. It appears that initially the massive volumes of magma formed by pressure release as crustal plates separated were in places trapped under crustal slabs. Perhaps at 165Myr, there was a short era of crustal compression. At least 100,000 cubic km of magma was forced up into the sundered crust, at first forming sills in the basement granites, then intruding along the Kukri Peneplain, then higher and sucessively higher in the Beacon Sandstones, finally errupting as lava flows and tuff on the surface. The lower sills may be 1200ft in thickness, those lying higher in the sandstone sometimes only a hundred or so. Feeder dikes washed away enormous blocks of light sandstone, forming linear masses of dolerite a mile or more wide, 30 miles long with 3-5000 vertical feet now exposed. See below.
The Kukri Hills as seen from Ferrar-Taylor medial Moraine
This is the type area for the Ferrar Dolerites. View to east, taken 1955-6 summer. We see about 6-8 miles away the western end of the Kukri Hill Range, the Ferrar Glacier ice splits in two, half flows to the right down the Lower Ferrar Glacier, half swing left and join the Taylor Glacier to perish in the Taylor Dry Valley. We are camped on the medial moraine.
This was a very basic excursion, we had the clothes we stood up in, the two plastic banana-boat sleds, an awful little Ronne-type tent which slatted abominably in wind and had to be held down by brute force, and tropical army concentrate rations with no reserves beyond the 3 weeks we were away! Dinner would be a quarter sized can of spaghetti and sausage! Neither of the two men shown had been on snow before!
In the upper Beacon Dry Valley, ancient ice is obviously still preserved
below thick ablation moraine. Esimates of it's age run all the way up
to about 2 myr. Table Mtn on left, Mt Feather rear left, Beacon Heights
to the right but well out of view.
The main, present day block-faulted Victoria Mountains (sometimes called the "Trans-Arctarctic Mountains" were formed, possibly by a rejuvenation of the Ross Orogeny in the Tertiary "Victoria Orogeny". As is usual while further folding may take place a depth, the surface expresson is one of block faulting. Parallel horst and graben structures are seen for 2000 miles across the continent. The main down thrown block lying immedately east of the Victoria Land coast allowed the accumulation of thousands of feet of glacial detritus being explored by the Cape Roberts Drilling project. Another effect was the eruption of large volumes of alkali-basalt, basanite finding access to the surface along the fault fractures.
Massive volcanoes of Pliocene-Recent age dated from 14.7 Myr to the present (Thomas Wilch) resulted extending from Cape Adare in the north, to Mt Discovery which lies about 20 miles south of McMurdo Sound. About 72 minor monogenetic centres have now been recorded from the Dry Valley area as well.
We will list all of the larger main centres from north to south and add pix when and if any become available. All seem to include both ankaramite, alkali basalt, hawaiite, mugearite, benmoreiite, trachyte and lesser amounts of basanite, trachybasalt, phonolite so we will not individually describe them chemically. There may be inaccuracies in this initial summary. Please correct us.