Beardmore Glacier Area Research Articles

Celebrating Women in Paleobotany: A Tribute to Edith L. Taylor—Introduction and Dedication

Celebrating Women in Paleobotany: A Tribute to Edith L. Taylor—Introduction and Dedication

Ichnology of a Paleopolar, River-Dominated, Shallow Marine Deltaic Succession in the Mackellar Sea: The Mackellar Formation (Lower Permian), Central Transantarctic Mountains, Antarctica

The Lower Permian Mackellar Formation in the Beardmore Glacier Area of the Central Transantarctic Mountains, Antarctica, was deposited between 80 and 85°S paleolatitude. Previous studies suggest that Mackellar Formation strata were deposited in either a large glacial lake or inland sea. Our study identified 30 ichnogenera from Turnabout Ridge and Buckley Island of which: 1) none are exclusively freshwater forms; 2) 20 ichnogenera are found in freshwater, brackish, and marine settings; and 3) 10 ichnogenera are exclusively found in marine settings. Combining ichnologic evidence with sedimentologic observations suggests that the Mackellar Formation was deposited in a river-dominated delta in a fully marine to brackish-marine setting. Trace-fossil associations are grouped into the Arenicolites–Phycodes, Lingulichnus, Arenicolites–Planolites, Kouphichnium, Phycodes–Teichichnus–Arenicolites, and Planolites–Teichichnus–Phycodes ichnocoenoses of a mixed Skolithos–Cruziana ichnofacies. These associations are characteristic of epi- and endobenthic worms arthropods, and mollusks, with the vast majority of the traces being diminutive in diameter and length, and exhibit shallow (≤10mm) penetration depths. These ichnocoenoses occur in paleoenvironments that include the prodelta, distal to proximal delta front including mouth bars, and subaqueous terminal distributary channels. The diminutive morphology, shallow penetration depth, low bed ichnodiversity, high overall ichnodiversity, and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short-lived communities composed of small-bodied organisms stressed by high freshwater input and high sedimentation rates.

Highly productive polar forests from the Permian of Antarctica

Two stratigraphically closely spaced bedding planes exposed at Lamping Peak in the Upper Buckley Formation, Beardmore Glacier area, Antarctica contain abundant in situ stumps (n=53, n=21) and other plant fossils that allow reconstruction of forest structure and biomass of Glossopteris forests that thrived at ~75° S paleolatitude in the Permian. Mean trunk diameter is 14 and 25cm, corresponding to estimated mean maximum heights of 12 and 19m. Basal areas are 65 and 80m2ha-1. The above ground biomass was calculated using allometric equations for Ginkgo biloba, yielding biomasses of 147 and 178Mgha−1. Biomass estimates based on comparison with biomass of modern forests with equivalent basal areas are higher (225–400Mgha−1). The amount of above ground biomass added each year (annual net primary productivity), based on biomass estimates and growth rings in silicified plant material from the Buckley Formation nearby, is poorly constrained, ranging from ~100–2000gm−2yr−1.Compared to modern forests at all latitudes, the Permian forests have high basal areas and high biomass, exceeded in both only by forests of the U.S. Pacific northwest and Sequoia forests. The estimated range of productivity (ANPP) is within that of many very productive modern forests. The Lamping Peak forests' basal areas and calculated biomass are also larger than younger high paleolatitude fossil forests except for Arctic Cenozoic forests.The presence of these highly productive fossil forests at high paleolatitude is consistent with hothouse conditions during the Late Permian, prior to the eruption of the Siberian flood basalts.

New insights into the anatomy, development, and affinities of corystosperm trees from the Triassic of Antarctica

Anatomically preserved trunks and young stems of corystosperm seed ferns are described from the Triassic of Fremouw Peak, Beardmore Glacier area, Antarctica. Based on characters of the primary and secondary vascular system, these new specimens are assigned to Kykloxylon, a genus that was established based on young stems with attached Dicroidium leaf bases. The largest specimens illustrate how some secondary growth characters, such as unequal cambial activity, appeared during later development, which enables a better comparison of Kykloxylon with trunks assigned to other corystosperm genera. Jeffersonioxylon from the Gordon Valley, Antarctica, and Cuneumxylon from South America show strong similarities with the newly described larger Kykloxylon trunks from Fremouw Peak, and might be considered congeneric. Our results provide further support for the presence of two anatomically and morphologically distinct kinds of Dicroidium-bearing trees in the Triassic vegetation of Gondwana, one with a palm-like habit and Rhexoxylon stems and the other with a more Ginkgo-like habit and Kykloxylon/Cuneumxylon-type stems.

Carbon and nitrogen trends in soil chronosequences of the Transantarctic Mountains

Determination of carbon and nitrogen levels in soils of ice-free areas of the Transantarctic Mountains, along with their origin, may determine whether these soils serve as a source or sink of carbon with an increasingly warmer climate. Organic and inorganic forms of carbon and nitrogen were measured in five soil chronosequences in the Transantarctic Mountains using flash combustion and spectrometry. Accumulation of coal carbon was significant in the Beardmore Glacier area and was quantified using chemi-thermal oxidation followed by flash combustion. Carbon levels decreased with drift age for two of the sequences. Decreases in carbon in the Hatherton Glacier sequence were due primarily to high levels of carbon in young ice-cored drifts. Carbon content increased with drift age for the Beardmore Glacier sequence due to the presence of coal in older drifts. Nitrogen content increased with age for a majority of the soil chronosequences. Inorganic carbon and all forms of nitrogen were significantly and positively correlated with mean annual precipitation. Our results suggest that carbon levels in similar settings do not significantly change over time; changes in temperature or moisture associated with microclimate likely play a much larger role in carbon and nitrogen levels.

Permo-Triassic arthropod trace fossils from the Beardmore Glacier area, central Transantarctic Mountains, Antarctica

AbstractPermian and Triassic lacustrine and fluvial-system deposits in the Beardmore Glacier area of the Transantarctic Mountains preserve a superb record of continental environments and evidence of life on extensive bedding plane exposures. They yielded the first invertebrate trackways reported from continental Permo-Triassic deposits of Antarctica, here assigned to the ichnogenera Diplichnites and Diplopodichnus, which were probably produced by myriapodous arthropods. A resting trace is compared to Orbiculichnus and interpreted as generated by a jumping insect. Plant life is represented by leaf impressions, fossil forests and peat, vertebrates by body and trace fossils, and invertebrate shallow infauna by near surface burrows. The small number and diversity of trackways recovered from the large bedding plane exposures suggest that trackway-producing arthropods were rare at these high southern palaeolatitudes.

Seed plant diversity in the Triassic of Antarctica: A new anatomically preserved ovule from the Fremouw Formation

A new anatomically preserved ovule is described from the Middle Triassic Fremouw Formation of the Beardmore Glacier area, Antarctica. Probolosperma antarcticum gen. et sp. nov. is bilaterally symmetrical and up to 1 cm long and 6 mm wide. The integument is characterized by a complex sarcotesta with a palisade-like outer layer and a sclerotesta that forms two small lateral wings and elaborations in the chalazal and apical regions. The vascular system consists of a terete strand that enters the pedicel to form a small cup of tracheids at the base of the nucellus, with two strands that extend distally in the inner part of the sclerotesta. Comparisons with other gymnosperm ovules indicate that Probolosperma represents a new taxon, which enhances the diversity of known seed plants from the Triassic of Antarctica.

Benthic aquatic ecosystems across the Permian-Triassic transition: record from biogenic structures in fluvial sandstones, central Transantarctic Mountains

The effect of the Permian extinction in communities inhabiting sandy stream bottoms can be evaluated using trace fossils as proxies for body fossils. Permian and Triassic sandstones exposed in the Beardmore and Shackleton Glacier areas (central Transantarctic Mountains) were deposited in sandy braided streams and contain four types of trace fossils (vertical shafts and horizontal, bilobed and chevron traces). These traces were produced by a single type of animal that moved in the top 30 cm of sediment and dominated the benthic community. Evidence for a single producer includes similar size (diameter) of all traces and change within single specimens from one trace type to another. The animal was not affected by the Permian extinction event, as evidenced by its equal abundance within the Permian (Buckley Formation) and Triassic (Fremouw Formation) fluvial sandstones in the Beardmore Glacier area. Based on trace morphology and on domination of modern sandy river ecosystems by insects, the producer most likely was an insect, although its more precise identity is problematic. Although families of insects with modern aquatic burrowers are not known before the Jurassic, these trace fossils may show that these burrowers were present earlier than the insect body-fossil record suggests. Alternatively, archaic insect groups, many of which became extinct at the end-Permian and are known to have been aquatic but not infaunal, may have included some active burrowers that were unscathed by the Permian extinction.

Implications of a Pliocene stand of Nothofagus (southern beech) within 500 kilometres of the South Pole

Branches, stems and roots of Nothofagus (southern beech) were reported from the Beardmore Glacier area (Sirius Formation) some 500 km from the South Pole. The Sirius Formation is a glacially derived unit which is considered Pliocene in age. We considered two scenarios by which a Nothofagus forest could flourish so close to the South Pole during the Pliocene. One scenario calls for the disappearance of this genus from Antarctica during the early Tertiary (Oligocene) and its re-introduction during a warm Pliocene interval. Seeds from modern Nothofagus, however, are not viable after submersion in sea water, are not carried by migrating birds and are not designed for long-distance wind transport. The second scenario involves survival of Nothofagus in Antarctic refugia through middle Tertiary glacial advances and its flourishing during a Pliocene warming. Excluding its occurrence in the Beardmore Glacier area, the known range of this genus in Antarctica is Cretaceous to Oligocene with some questionable occurrences in the early Miocene. The existing data do not support the refugia scenario. We also considered published speculations in which the closest modern analogue to the Beardmore Glacier Region, during the time that the Nothofagus represented by these specimens lived, was the coastal region of southern Chile where average annual temperatures are approximately 5°C and summer temperatures are of the order of 8–10°C. We incorporated these observations and speculations into a palaeoenvironmental model, assuming them to be valid; the results require Pliocene temperatures as warm as, or warmer than, the Cretaceous, a scenario which is not supported by the literature. We conclude, therefore, that the occurrence of Nothofagus in the Beardmore Glacier area is older than Pliocene. Instead, we suggest that it represents a relict assemblage which is probably no younger than Oligocene but which may have persisted into the early Miocene.

A new Triassic vertebrate fauna from Antarctica and its depositional setting

A new fauna of late Early to early Middle Triassic vertebrates has been found in the upper member of the Fremouw Formation in the Beardmore Glacier area of Antarctica. It includes Cynognathus, a kannmeyeriid, and other therapsid (mammal-like) reptiles representing new, more derived genera of carnivorous and gomphodont cynodonts. New genera of temnospondyl amphibians belonging to the capitosauroid evolutionary complex also occur. The unusual abundance of well-preserved amphibians may offer new insights concerning the evolution and distribution patterns of early Mesozoic temnospondyls. These fossils represent only the second terrestrial vertebrate fauna from the mainland of Antarctica. The fossils occur on a prominent sandstone platform, which represents part of the exhumed channel of a braided stream deposit. The platform is over 200 metres above the well-known Lystrosaurus fauna of the lower Fremouw Formation. The locality is near the axis of a major foreland basin that paralleled the present trend of the Transantarctic Mountains. Conditions of rapid subsidence and aggradation of fluvial units were ideal for the preservation of vertebrate faunas.

Early Palaeozoic history of the upper Beardmore Glacier area: implications for a major Antarctic structural boundary within the Transantarctic Mountains

The central and western Transantarctic Mountains appear to be divided longitudinally by one or more terrane boundaries that separate two regions characterized by different Lower Palaeozoic successions. Re-examination of the upper Beardmore Glacier area and reinterpretation of its Early Palaeozoic stratigraphy emphasizes the strong similarity between it and the Byrd Group outcrops in the area between the Byrd and Nimrod glaciers. This similarity demonstrates that for several hundred kilometres the Cambrian succession of an inboard region is largely devoid of volcanic rocks but includes fossiliferous Lower Cambrian platformal limestones that are overlain unconformably by coarse basin-fill deposits. The latter probably include beds of Middle and perhaps early Late Cambrian age that were themselves deformed prior to the Devonian. Erratic blocks indicate that comparable successions may have been developed as far west as the Whichaway Nunataks. The inferred geological history of this part of the continental margin, which is commonly regarded as autochthonous, stands in contrast to that of more outboard regions where thick volcanic sequences occur in expanded stratigraphic sections that include shallow-marine Middle and Late Cambrian deposits. We consider that these regions, predominantly the Queen Maud and Theil mountains and the Neptune Range of the Pensacola Mountains, constitute one or more displaced crustal blocks. The boundary between them and the inboard sequence adjacent to the craton is probably a series of large strike-slip faults that may have been initiated during the Early Palaeozoic and have been active episodically since then.

Glacial advance and retreat sequences in a Permo‐Carboniferous section, central Transantarctic Mountains

ABSTRACTEpisodes of glacial advance and retreat can be recognized through analysis of vertical facies sequences in the Permo‐Carboniferous Pagoda Formation of the Beardmore Glacier area, Antarctica. The formation includes a remarkably complete record of continental sedimentation near the terminus of a temperate glacier. Facies sequence is pre‐eminent for inferring glacial advance and retreat. Other important criteria are abundance and geometry of sandstone interbedded with diamictite, diamictite character and nature of bed contacts. Using these characteristics advance and retreat sequences 5–60 m thick are recognized. A sharp contact, with a striated surface and erosional relief, overlain by structureless diamictite (lodgement till) is typical of grounded ice advance. Grounded ice retreat is characterized by structureless diamictite (lodgement till), overlain by crudely stratified diamictite (melt‐out till) and then by diamictite interbedded with sandstone and conglomerate (flow till and glacio‐fluvial or glacio‐lacustrine deposits). Gradational contacts between shale overlain by diamictite and diamictite overlain by shale characterize advance and retreat, respectively, in subaqueous settings.Pauses in sediment accumulation, minor(?) fluctuations of the ice margin, and/or changes in subglacial dynamics are indicated by specific features within diamictite units such as probable frost‐wedge casts, single layer boulder beds, sharp sedimentary contacts and changes in diamictite character. These minor(?) events are superimposed upon the main advance‐retreat cycles. Study of both the overall facies sequence and of individual diagnostic structures, albeit in an incomplete stratigraphic record, permits a distinction between major and minor advance‐retreat events. As many as six major advance‐retreat cycles exist in some Pagoda sections, but the number of cycles present varies in different sections.

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA III. PERMIAN SEEDS

Small, anatomically preserved gymnospermous seeds are detailed from late Permian age silicified specimens collected in the Beardmore Glacier region of Antarctica. The seeds are platyspermic with prominent, sarcotestal wings and a simple pollen chamber. The integument consists of a narrow endotesta, a two‐parted sclerotesta and a complex sarcotesta. In mature seeds, the nucellus is present as a papery layer, separated from the endotesta by a nucellar and endotestal cuticle. Cellular megagametophytes are present in many of the seeds and commonly contain two archegonia. A multicellular embryo is present within each archegonium. The embryos are at a similar stage of development and provide evidence of simple polyembryony in these seeds. Although the affinities of the seeds are not presently known, they are discussed in the context of other seeds described from Gondwana deposits, as well as the known flora from the Beardmore Glacier area.

Paléokarst paléozoïque en Antarctique

Paleozoic karst in Antarctica Karst features in Antarctica have been rarely observed. In their study on the geology of the Beardmore Glacier area in the Transantarctic Mountains (south of Ross Ice Shelf), Barret and al., (1968) describe a preglacial karst topography (Mt. Counts) and especially a former cave (Ø 10 m) 10 m below the erosion surface and filled with coarse green sandstone. Shaped in the «Shackleton limestone» (Low to Middle Cambrian) probably during the Permo-Carboniferous (hercynian cycle), this karst is fossilized by the «Pagoda formation», permian tillite of the «Beacon sequence» (Devonian-Permian-Triassic).

Structurally Preserved Fossil Plants from Antarctica. I. Antarcticycas, gen. nov., a Triassic Cycad Stem from the Beardmore Glacier Area

Structurally Preserved Fossil Plants from Antarctica. I. Antarcticycas, gen. nov., a Triassic Cycad Stem from the Beardmore Glacier Area

Beardmore Glacier proposals wanted

Proposals for research projects to be conducted in the upper Beardmore Glacier area of Antarctica during the 1985–1986 field season are being accepted by t h e National Science Foundation (NSF) through August 15. Later proposal submissions should be discussed with the appropriate program managers (see below).A temporary camp with helicopter support will be established in the region. Occupation by scientific parties will likely be between mid‐November 1985 and mid‐January 1986. Transportation in the field will be by UH1‐N twin‐engine Huey helicopters (with a range of approximately 185 km) and by motor toboggans. Satellite tent camps will be established within the range of the helicopters. The exact position of the main camp will be determined in November. Likely candidates, however, are Buckley Island Quadrangle, in the area of the Walcott Névé or the Bowden Névé, near Coalsack Bluff or Mount Sirius.

Paleocurrent Analysis of the Mainly Fluviatile Permian and Triassic Beacon Rocks, Beardmore Glacier Area, Antarctica

ABSTRACT The postglacial Beacon sequence in the Beardmore Glacier area comprises 2000 m of nonmarine clastic sediments. Approximately 3000 paleocurrent measurements were taken in sets of about six from stratigraphic intervals less than 30 m thick from the Mackellar, Fairchild, and Buckley Formations of Permian age and the Fremouw and Falla Formations of Triassic age. These data yielded 432 current directions, 168 from small-scale cross-bedding, 162 from medium-scale cross-bedding, 69 from parting lineation, and 33 from logs, ripple marks, and slump folds. Analysis of variance, using vector rather than arithmetic means, was used to indicate the likelihood that differences in current direction for different areas, formations, or types of sedimentary structures are due to variations in a normally distributed population. Four formations have essentially a unimodal current pattern, while the Buckley Formation has a centripetal pattern. There is no significant difference (F.10) between mean directions to the southeast for the three Permian formations, or to the northwest for the two Triassic formations. This reversal implies a laterally constraint of both Permian and Triassic paleocurrent systems. Mean current directions for small- and medium-scale cross-bedding and parting lineation within each formation are not significantly different, and for the Fairchild and Buckley Formations, values for standard deviation are also similar. For these two units, each structure is an equally reliable indicator of paleocurrent direction, and a hierarchy of bedforms like that proposed by Allen (1966) is not indicated. However, such a hierarchy might exist for the Fremouw Formation, where parting lineation is significantly less variable than medium-scale cross-bedding, and medium-scale cross-bedding is significantly less variable than small-scale cross-bedding.

Triassic amphibian from Antarctica.

A fossil bone fragment-the first record of tetrapod life from Antarctica-was found near Graphite Peak in the upper Beardmore Glacier area (85 degrees 3.3'S; 172 degrees 19'E). The fragment was embedded in a pebbly quartzose sandstone, probably of fluvial origin, in the lower part of the Triassic Fremouw Formation (as yet undefined), which contains Dicroidium in the upper part. The fossil horizon is only 76 meters, stratigraphically, above the Glossopteris-bearing Buckley Formation, a coal-bearing sequence of Permian age. The bone fragment is the back portion of a left mandibular ramus of a labyrinthodont amphibian. This identification is based on the characteristic labyrinthodont external surface sculpturing, with indications of "mucous grooves," as well as on other osteological features.