The Beacon Supergroup is a geological formation exposed in Antarctica and deposited from the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

to the Triassic (). The unit was originally described as either a formation or sandstone, and upgraded to group and supergroup as time passed. It contains a sandy member known as the Beacon Heights

Orthoquartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

Overview

The base of the Beacon Supergroup is marked by an unconformity and is composed of the

Taylor Group, a

quartzose Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

sandstone sequence; and the Late Carboniferous to Early Jurassic Victoria Group, consisting of glacial beds, sandstone,

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

, and coal. The Beacon Sandstone was named by

Hartley T. Ferrar Hartley Travers Ferrar (28 January 1879 – April 1932) was a geologist who accompanied Captain Scott's first Antarctic expedition. Biography Ferrar was born at 3 Grosvenor Place, Dalkey, near Dublin, in 1879, the son of John Edgar Ferrar, a ba ...

during Scott's Discovery Expedition (1901–1904), using the

Beacon Heights The Beacon Heights () are a small cluster of peaks between Beacon Valley and Arena Valley in Quartermain Mountains, Victoria Land, rising to in West Beacon, and also including East Beacon and South Beacon. They were named by Hartley Ferrar, ...

survey points as reference. '' Glossopteris'' fossils dated the sandstone to the Permian and linked the

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

to similar sequences on neighboring continents. Generally flat lying, the supergroup is up to 3.2 km thick and is fairly continuous from south Victoria Land to the

Beardmore Glacier The Beardmore Glacier in Antarctica is one of the largest valley glaciers in the world, being long and having a width of . It descends about from the Antarctic Plateau to the Ross Ice Shelf and is bordered by the Commonwealth Range of the Queen ...

along the Transantarctic Mountains. The Urfjell Group in Dronning Maud Land and the Neptune Group in the

Pensacola Mountains The Pensacola Mountains are a large group of mountain ranges of the Transantarctic Mountains System, located in the Queen Elizabeth Land region of Antarctica. Geography They extend 450 km (280 mi) in a NE-SW direction. Subranges of the ...

have been correlated with the Taylor Group. Macrofossils and palynomorph assemblages age date Devonian, Late Carboniferous–

Early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), 01'' (Richard Müller album), 2001 * 01 (Son of Dave album), ''01'' (Son of Dave album), 2000 * 01 (Urban ...

, Late Permian and Triassic

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

. The Ferrar Dolerite intrudes at various levels, while the Mawson Formation and Kirkpatrick Basalts within the Ferrar Supergroup cap the Beacon Supergroup. The location of the formation in a cold, desert environment and the lack of nutrients or soil (due to the purity of the sandstone) has led to the Beacon Sandstone being considered the closest analogue on Earth to Martian conditions; therefore, many studies have been performed on life's survival there, mainly focusing on the

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.depositional environment. The well-sorted nature of the unit suggests that it was probably deposited close to the shoreline, in a high-energy environment. Features such as the presence of

coal bed Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

s and

desiccation crack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, ...

s suggest that parts of the unit were deposited subaerially, though ripple marks and cross bedding show that shallow water was also commonly present. Heat from burial is modest, though the rock could have been heated to over 160 °C by intrusion of dolerite sills, dykes and

lenses A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

during the early Jurassic as a consquence of the breakup of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

. The rock is low in phosphorus.

Taylor Group

The Taylor Group is separated from the overlying Victoria Group by a disconformity called the Maya Erosion Surface. Taylor Group formations in the Darwin Mountains region include the Brown Hills Conglomerate (34 m), which overlies pre-Devonian plutonic rocks of igneous and metamorphic nature, with over 30 m of erosional relief, and igneous and metamorphic clasts. The conglomerate is poorly sorted at the base, with influxes of coarser material. Coarseness is laterally variable, with pebbles in places and sands in others at the same horizon. The conglomerate includes planar beds, trough cross-bedding,

flaser bed Flaser beds are a sedimentary, bi-directional, bedding pattern created when a sediment is exposed to intermittent flows, leading to alternating sand and mud layers. While flaser beds typically form in tidal environments, they can (rarely) form in ...

ding, mud-drapes on some ripples, U-shaped burrows and escape structures, with fining-up cycles topped by

s in places. The depositional environment is probably that of an alluvial fan, though unidirectional flow and sheet-like deposition point to braided channels. Equivalent strata in South Victoria Land include the Wind Gully Sandstone (80 m), the Terra Cotta

Siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

(82 m), and the New Mountain Sandstone (250 m), which are separated from the overlying Altar Mountain Formation (235 m) and Arena Sandstone (385 m) by a disconformity. Within the Darwin Mountains region, the Junction Sandstone (290 m) overlies the Brown Hills Conglomerate, with abundant '' Skolithos''. This is followed by the Hatherton Sandstone (330 m), with brachiopod and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

shell fragments in places. Trough cross beds and current rippling are present, with abundant

ichnofauna Ichnofauna is the diversity of fauna based on the ichnological ( tracks and footprints) evidences. This term is often used by vertebrate paleontologists.Mateus, O., & Milàn, J. 2010. A diverse Upper Jurassic dinosaur ichnofauna from central‐west ...

. Drainage was to the north east, with the depositional environment presumed to be marine, though also present are subaerial features such as desiccation cracks, rain drop impressions, surface run-off channels, muddy veneers, and redbeds, besides river-like features such as small channels. The Beacon Heights Orthoquartzite (330 m) is found in the South Victoria Land region between the Arena Sandstone and the overlying

Aztec Siltstone. It is well sorted and cemented, with medium to coarse grain sizes and trough cross-beds, with '' Haplostigma'' and ''

Beaconites ''Beaconites'' is an ichnogenus known from the Beacon Supergroup, Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Oce ...

'' remnants. The Aztec Siltstone (125–220 m) is found both in South Victoria Land and the Darwin Mountains. The siltstone includes interbedded sandstones, fish-bearing shales, conchostracans, and paleosols implying subaerial periods within an alluvial plain sequence. Within the Beardmore Glacier region, the Devonian Alexandra Formation (0–320 m), which constitutes the entire Taylor Group, is a quartz sandstone to siltstone.

Victoria Group

The Victoria Group begins with a

diamictite Diamictite (; from Ancient Greek ''δια'' (dia-): ''through'' and ''µεικτός'' (meiktós): ''mixed'') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that ra ...

-bearing unit known as the Metschel Tillite (0–70 m) in South Victoria Land and continues with the Darwin Tillite (82 m) in the Darwin Mountains, the Pagoda Tillite (395 m) at the Beardmore Glacier, the Scott Glacier Formation (93 m) on the

Nilsen Plateau Nilsen Plateau () is a rugged, ice-covered plateau in Antarctica. When including Fram Mesa, the plateau is about 30 nautical miles (60 km) long and 1 to 12 nautical miles (22 km) wide, rising to 3,940 m between the upper reaches of the Amu ...

, and the Buckeye Tillite (140–308 m) in the

Wisconsin Range The Wisconsin Range () is a major mountain range of the Horlick Mountains in Antarctica, comprising the Wisconsin Plateau and numerous glaciers, ridges and peaks bounded by the Reedy Glacier, Shimizu Ice Stream, Horlick Ice Stream and the interior ...

and Ohio Range. The glacial beds are valley fill or occur as sheets. This is followed by the Misthound Coal Measures (150 m) in the Darwin Mountains and the Permian Weller Coal Measures (250 m) in South Victoria Land. A disconformity separates the Misthound Coal Measures from the overlying Ellis Formation (177 m), consisting of conglomerate, sandstone and siltstone. The Pyramid Erosion Surface separates the Mitschell Tillite and the Weller Coal Measures, which are overlain by the Feather Conglomerate (215 m) and the Triassic Lashly Formation (520 m). The Pagoda Tillite is overlain by the MacKellar Formation (140 m) of

interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimen ...

black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...

s and fine sandstones, the Lower Permian Fairchild Formation (220 m) arkosic sandstone, the

Upper Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

Buckley Formation (750 m), the Middle-

Lower Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

Fremouw Formation (650 m), the Upper- Middle Triassic Falla Formation (530 m), and the Jurassic Prebble Formation (0–460 m) volcanic

, tuff and tuffaceous sandstone.

Palæontology

Body fossils

The Aztec sandstone contains units bearing body fossils of fish:

Phyllolepid Phyllolepida ("leaf scales") is an extinct taxon of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. ...

placoderms Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally 'Plate (animal anatomy), plate-skinned') is a Class (biology), class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devoni ...

,Allowing dating to late Mid Devonian and thelodonts, abundant in fish beds, and conchostracans. The presence of ''Scoyenia''

ichnofacies An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited. Concept Trace fossil assemblages are far from random; the range of fossils recorded in association is constra ...

implies freshwater. Also present are charred wood remnants and the plants '' Glossopteris'' and '' Haplostigma''. The wood bears clear growth rings, indicating a seasonal environment, and is large enough to represent a temperate climate, though glacial just before Beacon deposition.

Trace fossils

Trace fossils are sparse below, but become common in the Hatherton Sandstone. They change from ''Skolithos''-dominated facies to wide diversity and abundance, including vertical and horizontal burrows and huge arthropod trackways. The size of the arthropod tracks (less than 91 cm) is taken to imply that water must have been required for support. *

Fodinichnia Fodinichnia (singular fodinichnion) are trace fossils formed by deposit feeders as they excavate the sediment in search of food.Allaby A & Allaby M (1999) Oxford Dictionary of Earth Sciences. They tend to have repeated patterns (e.g. '' Chondrit ...

: feeding burrows, probably of marine polychaetes, featuring evidence of rhythmic defecation. **Narrow, sinuous, near-surface forms on flat bedding surfaces **Longer, larger forms, reaching 13 cm across and 1 m in length. *Walking trackways of arthropods ( Repichnia). The presence of crawling traces in such well sorted sands is problematic. The arthropod trackways are thought to have been formed in shallow water, and supersaturated sand has a shallow angle of repose. Thus either a layer of organic matter, perhaps in the form of an algal slime, must have supported the sediment, or the sediment must have been partially dry. In the context of subaerial features such as raindrop marks and desiccation cracks on associated horizons, the best explanation is that the trackways were formed on bedforms produced on a river bed, but while they were exposed by a low-flow period. **''

antarcticus'': narrow, parallel grooves, about an inch apart, disappearing into elliptical pits; created by shovelling the surface sediment aside before burrowing into the sediment. Occasionally branch. **Perhaps ''B. barretti'': more widely spaced grooves (~3 cm); small footprints visible. Implies many walking limbs and an approximately rectangular shape — reminiscent of trilobites. Extend laterally up to ; burrow deeply into sediment. Probably produced by a very different arthropod to ''B. antarcticus''. **Large (~30 cm wide) trails with a scrape mark from a central tail. Three to four footprint pits diverge from these tracks at a high angle. The feet making the footprints had spines on their rears. These may have been formed by

eurypterids Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is l ...

but are not a perfect match to known eurypterid trails; they may also have been formed by xiphosurans *''

Diplichnites ''Diplichnites'' are arthropod Fossil trackway, trackways with two parallel rows of blunt to elongate, closely spaced tracks oriented approximately perpendicularly to the mid-line of the trackway. The term is more often used for the ichnofossils ...

'' trackways: double rows of fossils previously attributed to marine trilobites but now thought to perhaps be formed by annelids or myriapods. Here they appear on metre-scale crossbeds that may represent sub-fluvial dunes. *'' Cruziana'' and ''

Rusophycus ''Rusophycus'' is a trace fossil ichnogenus allied to ''Cruziana''. ''Rusophycus'' is the resting trace, recording the outline of the tracemaker; ''Cruziana'' is made when the organism moved. The sculpture of ''Rusophycus'' may reveal the approx ...

'': thought to be formed by trilobites, whose body fossils are found only in marine assemblages. Could also have been made by other arthropods, or the lower parts of the Beacon Sandstone may have been marine. They have been found in many other non-marine instances. *''Skolithos'': traditionally thought to be marine; however, there are many counterexamples.