Beacon sandstone

The Beacon sandstone is a geological formation exposed in Antarctica and deposited from the Devonian to the Triassic (~Ma|400|- Ma|225Verify source|date=April 2008). The sandstone was originally described as a formation, and upgraded to group and supergroup as time passed. It contains a sandy member known as the Beacon heights orthoquartzite.

etting in time and space

Named after Beacon Heights.cite journal
first =Duncan, Jr.
last = Stewart
title = The Petrography of the Beacon Sandstone of the South Victoria Land
url = http://www.minsocam.org/ammin/AM19/AM19_351.pdf
journal = Mineralogical Society of America
accessdate = 2008-04-23 ] First named 1907, type section described in 1963.cite journal|author=Hamilton W & Hayes PT|title=Type section of the Beacon Sandstone of Antarctica|url=http://pubs.er.usgs.gov/usgspubs/pp/pp456A|year=1963|journal=US Geol Survey Prof paper|volume=456-A|pages=1–18] Originally dubbed a formation, with scope left (and later used) to expand to group, then supergroup, as better mapped and understood.

Age

*Upper Devonian to Triassic

Exposure

* Antarctica: McMurdo sound, shores of Ross Bay;cite web
title = Scott's Terra Nova Antarctic Expedition
url = http://www.nhm.ac.uk/research-curation/collections/departmental-collections/mineralogy-collections/rocks/scott-collection.html
accessdate = 2008-04-23 ] also southern Victoria land, Ross desert.cite journal
author = Friedmann, E.I.
coauthors = Weed, R.
year = 1987
title = Microbial trace-fossil formation, biogenous, and abiotic weathering in the Antarctic cold desert
journal = Science
volume = 236
issue = 4802
pages = 703–705
doi = 10.1126/science.11536571]
* Described by Scott & team on way to South Pole.cite journal
author = Elliott, R.B.
coauthors = Evans, W.D.
year = 1963
title = A Beacon Sandstone: its Petrology and Hydrocarbon Content
journal = Nature
volume = 199
issue = 4894
pages = 686–687
doi = 10.1038/199686b0]

The series is over 1km thick in places, and extends for over 1,000 miles.

The beds are almost flat lying, dipping at about 3° to the north;cite journal
author = Kamp, P.J.J.
coauthors = Lowe, D.J.
year = 1982
title = Geology and terrestrial age of the Derrick Peak meteorite occurrence, Antarctica
journal = Meteoritics
volume = 17
pages = 119–127
url = http://adsabs.harvard.edu/full/1982Metic..17..119K
accessdate = 2008-04-22] many are interleaved with dolerite sills.

Location

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 focussing on the lichen communities that form the modern inhabitants.e.g. cite journal
author = Derek Pullan, Frances Westall, Beda A. Hofmann, John Parnell, Charles S. Cockell, Howell G.M. Edwards, Susana E. Jorge Villar, Christian Schroder, Gordon Cressey, Lucia Marinangeli, Lutz Richter, Gostar Klingelhofer.
year = 2008
title = Identification of Morphological Biosignatures in Martian Analogue Field Specimens Using "In Situ"v Planetary Instrumentation
journal = ASTROBIOLOGY
volume = 8
issue = 1
doi = 10.1089/ast.2006.0037
pages = 119]

edimentology

The unit is a "Fine grained, arkosic quartz sandstone". It is composed of shales, coals, conglomerates, and in places the occasional thin limestone bed.

Lithofacies

Originally divided into 3 subunits, further refined into five facies, listed below from oldest to youngest:

Brown hills conglomerate

Basal. Grades into Junction sandstone. Variable thickness; (0-5/17/80cite journal
author = Woolfe, K.J.
year = 1993
title = Devonian depositional environments in the Darwin Mountains: Marine or non-marine?
journal = Antarctic Science
volume = 5
issue = 02
pages = 211–220
doi = 10.1017/S0954102093000276] m), overlies pre-Devonian plutonic rocks, of igneous and metamorphic nature, with over 30 m erosional relief. Contains igneous and metamorphic clasts.

Poorly sorted at base, influxes of coarser material. Coarseness is laterally variable - pebbles in places, sands in others, at same horizons. Planar beds, trough cross-bedding, flaser bedding, mud-drapes on some ripples; U-shaped burrows & escape structures; fining up cycles topped by desiccation cracks in places.

Probably alluvial fan. Unidirectional flow & sheet-like deposition point to braided channels.

Junction sandstone

Part of Taylor group. Gradational boundaries at top and bottom. up to 540m thick."Skolithos" abundant.Intermediate between Brown Hills Conglomerate and Hatherton sandstone.

Hatherton sandstone

Part of Taylor group. 250-300m thick. Divided into upper and lower subunits.
* 95% Quartz.
* Abundant: Zircon, limonite. Common: garnet, magnetite. Present in places: Shell fragments (Brachiopod / bivalve)cite journal
author = Angino, E.E.
coauthors = Owen, D.E.
year = 1962
title = Sedimentologic Study of Two Members of the Beacon Formation, Windy Gully, Victoria Land, Antarctica
journal = Transactions of the Kansas Academy of Science (1903-)
volume = 65
issue = 1
pages = 61–69
url = http://links.jstor.org/sici?sici=0022-8443(196221)65%3A1%3C61%3ASSOTMO%3E2.0.CO%3B2-V
accessdate = 2008-04-21
doi = 10.2307/3626470]

Lower: white/yellow sandstone. Layers of grit/conglomerate at base, silt at top, of some beds, which reach 15m thickness. Trough cross beds.

Upper: Similar, but rust-weathering, current rippling.

Dates to late Middle Devonian, by correlation to the well constrained (by fish fossils) Aztec Sandstone nearby.cite journal
author = Woolfe, K.J.
year = 1994
title = Cycles of erosion and deposition during the Permo-Carboniferous glaciation in the Transantarctic Mountains
journal = Antarctic Science
volume = 6
issue = 01
pages = 93–104
doi = 10.1017/S095410209400012X]

Abundant ichnofauna.

Common bedforms: planar beds, bi-modal cross-beds, hummocky cross-stratification (HCS), laminated seds.Drainage to north east.

Presumed marine for a long time on the basis of trace fossils such as "Skolithos", and typically-marine HCS. But sedimentologists kept pointing out subaerial features such as desiccation cracks (polygonal jointing?), rain drop impressions, surface run-off channels, muddy veneers, and redbeds; also, river-like features such as unidirectional currents and small channels.cite journal
author = Woolfe, K.J.
year = 1990
title = Trace fossils as paleoenvironmental indicators in the Taylor Group (Devonian) of Antarctica
journal = Palaeogeography, Palaeoclimatology, Palaeoecology
volume = 80
pages = 301–310
doi = 10.1016/0031-0182(90)90139-X
* Great images of the different trace fossils] The confusion was rectified when it was realised that HCS and the ichnofacies could in fact be marine.

Beacon heights orthoquartzite

Only known in north.

Sometimes just referred to as top 30m of Hatherton sst.

Well sorted and cemented. Grains medium to coarse. Trough cross-beds. "Haplostigma irregulare" - lycopod remnants. Constrain to early Middle Devonian. Contact on Hatherstone sandstone is sharp, irregular, and in places cobbly - so erosional.

Aztec siltstone

The Aztec siltstone bears interbedded sandstones and fish-bearing shales (providing late Mid Devonian age). Palæosols abundant and well developed, implying subaerial periods.

Only known in north. Top 7.5m contains dewatering structures - result of loading by tillites.cite journal
author = Isbell, J.L.
coauthors = Lenaker, P.A.; Askin, R.A.; Miller, M.F.; Babcock, L.E.
year = 2003
title = Reevaluation of the timing and extent of late Paleozoic glaciation in Gondwana: Role of the Transantarctic Mountains
journal = Geology
volume = 31
issue = 11
pages = 977–980
doi = 10.1130/G19810.1
* contains images of dewatering structures] This implies that the sediments were not consolidated in Permian times, and indeed that the area did not undergo glaciation during the Carboniferous ice age.

Minimum thickness 135m. Coarse sands and finer muds; cross-bedded channels up to 12m wide. Small and large roots. Psilophytes, lycopod stems, logs.

Darwin tillite

Base of Victoria group.Also known as Metschel tillite.Overlays Hatherton and Aztec unconformably, resting on "Maya" erosion surface,which has only "slight" relief.cite journal
author = PR Pinet, DB Matz, MO Hayes
year = 1971
journal=Journal of Sedimentary Research
volume =41
title = An Upper Paleozoic Tillite in the Dry Valleys, South Victoria Land, Antarctica: NOTES
doi = 10.1306/74D7236A-2B21-11D7-8648000102C1865D
issue=3
pages=835–838] Underlying sands thumped by granitic clasts, which form load structures.

This erosion surface was formed by downcutting streams, later scoured by glacial ice. Permian in age. Erosion surface covered with pebbly mudstone.Features rhythmic, varved layers, with some channel and sheet sandstones. Main unit is diamictite.

Misthound coal measure

Part of Victoria group.Overlays tillite unconformably, resting on "Pyramid" erosion surface which was formed by reworking of the tillite.Dominated by "Gangamopteris".Cross-bedded sandstones, with some mudstones, carbonaceous shales, and of course coal.

Ellis formation

Comprises a conglomerate, sand- and silt-stone.

Palæontology

Body fossils

The Aztec sandstone contains units bearing body fossils of Fish: Phyllolepid placoderms, [Allowing dating to late Mid Devonian] cite journal
author = Woolfe, K.J.
year = 2004
title = Cycles of erosion and deposition during the Permo-Carboniferous glaciation in the Transantarctic Mountains
journal = Antarctic Science
volume = 6
issue = 01
pages = 93–104
doi = 10.1017/S095410209400012X] and thelodonts;cite journal
author = Turner, S.
coauthors = Young, G.C.
year = 2004
title = Thelodont scales from the Middle-Late Devonian Aztec Siltstone, southern Victoria Land, Antarctica
journal = Antarctic Science
volume = 4
issue = 01
pages = 89–105
doi = 10.1017/S0954102092000142] abundant in fish beds; and conchostracans.

Also: Charred wood remnants, and the plants "Glossopteris" and "Haplostigma".

Wood bears clear rings, so environment must have been very seasonal. Large enough to represent temperate climate, at least. Glacial just before Beacon deposition.

Nothing else though.

Trace fossils

Sparse below, but become common in Hatherton Sandstone. Changes from Skolithos-dominated facies to wide diversity and abundance, including vertical and horizontal burrows, and huge arthropod trackways. Size of arthropod tracks (<91cm!) taken to imply that water must have been required for support. In Hatlerton, "Skolithos" density decreases.

Present include:

*Fodinichnia: feeding burrows, probably of marine polychaetes, featuring evidence of rhythmic defecation.
**Narrow, sinuous, near-surface forms on flat bedding surfaces
**Longer, larger forms, reaching 13cm across and 1 m in length.
*Walking trackways of arthropods (Repichnia).cite journal
author = Gevers, T.W.
coauthors = Frakes, L.A.; Edwards, L.N.; Marzolf, J.E.
year = 1971
title = Trace Fossils in the Lower Beacon Sediments (Devonian), Darwin Mountains, Southern Victoria Land, Antarctica
journal = Journal of Paleontology
volume = 45
issue = 1
pages = 81–94
url = http://links.jstor.org/sici?sici=0022-3360(197101)45%3A1%3C81%3ATFITLB%3E2.0.CO%3B2-J
accessdate = 2008-04-21]
**"Beaconites 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.
**Wider spaced grooves (~3cm); small footprints visible. Implies many walking limbs and an approximately rectangular shape - reminiscent of the Trilobites. "B. barretti"? Extend laterally up to 1.7m; burrow "deeply" into sediment.cite journal
author = Bradshaw, M.A.
coauthors = Harmsen, F.J.
year = 2007
title = The paleoenvironmental significance of trace fossils in Devonian sediments (Taylor Group), Darwin Mountains to the Dry Valleys, southern Victoria Land
journal = Antarctica: A Keystone in a Changing World--Online Proceedings of the 10 thISAES X, edited by AK Cooper and CR Raymond et al., USGS Open-File Report
volume = 1047
url = http://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea133.pdf
accessdate = 2008-04-22] Probably produced by a very different arthropod to "B. antarcticus".
**Large (~30cm 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 but aren't a perfect match to known eurypterid trails; they may also have been formed by Xiphosurans

*"Diplichnites" trackways - double rows of fossils - previously attributed to marine trilobites. Clearly not - so perhaps annelids / myriapods? Here appear on metre-scale crossbeds: sub-fluvial dunes?

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.

*"Cruziana" & "Rusophycus": thought to be formed by trilobites, whose body fossils are only found in marine assemblages. Could they also be made by other arthropods, or could the lower parts of the Beacon sandstone have been marine? They have been found in many other non-marine instances.

*"Skolithos" - again, traditionally thought to be marine, but there are lots of examples where it isn't.

Ichnofacies

*"Scoyenia" ichnofacies implies freshwater aquatic nature.

Depositional environment

Sedimentological and palæontological data point to a shallow marine depositional environment.

The well-sorted nature of the unit suggests that it was probably deposited close to the shoreline, in a high energy environment. This is backed up by the absence of clay-sized particles, and the rounded, spherical shape of quartz grains.

Features, such as the presence of coal beds and desiccation cracks, suggest that parts of the unit were deposited subaerially. Ripple marks and cross bedding show that shallow water was also commonly present.

ource rock

* Too few minerals to come from local granites and schists, unless a long period of subaerial weathering preceded deposition.
* Could have been transported; would have to be a long distance to produce such a clean sandstone.

Thermal history

* Heat from burial modest.cite journal
author = Bernet, M.
coauthors = Gaupp, R.
year = 2005
title = Diagenetic history of Triassic sandstone from the Beacon Supergroup in central Victoria Land, Antarctica
journal = New Zealand Journal of Geology and Geophysics
volume = 48
pages = 447–458
url = http://www.rsnz.org/publish/nzjgg/2005/032-lo.pdf
accessdate = 2008-04-22]
* Heated to 160+° by intrusion of dolerite sills, dykes and lenses during the early Jurassic, related to break up of Gondwana Ma|180. - the Ferrar Dolerite. Reached T of 200-300°C in places.cite journal
author = Bernet, M.
coauthors = Gaupp, R.
year = 2005
title = Diagenetic history of Triassic sandstone from the Beacon Supergroup in central Victoria Land, Antarctica
journal = New Zealand Journal of Geology and Geophysics
volume = 48
pages = 447–458
url = http://www.rsnz.org/publish/nzjgg/2005/032-lo.pdf
accessdate = 2008-04-22]
* Volatiles would have migrated outwards from the hot aureole, condensing when they reached rock cooler than their boiling point. This results in the "steam distillation" of the volatiles.

Utility

Biology

* The rock is low in phosphorous,cite journal
author = Banerjee, M.
year = 2000
title = Phosphatase Activities of Endolithic Communities in Rocks of the Antarctic Dry Valleys
journal = Microbial Ecology
volume = 39
issue = 1
pages = 80–91
doi = 10.1007/s002489900188] creating difficulties for organisms living on it.
* Mostly supports lichens; has its own endogenous community

Hydrocarbon potential

*Great source: but nothing to trap oil.

Further reading

cite book
author = Plume, R.W.
year = 1982
title = Sedimentology and palaeocurrent analysis of the basal part of the Beacon Supergroup (Devonian (and older?) to Triassic) in south Victoria Land, Antarctica
editor = Craddock, C
publisher =University of Wisconsin Press,
location = Madison
booktitle= Antarctic Geoscience
isbn = ] cite book
author = Geevers TW & Twomey
year = 1982
title = Sedimentology and palaeocurrent analysis of the basal part of the Beacon Supergroup (Devonian (and older?) to Triassic) in south Victoria Land, Antarctica
editor = Craddock, C
publisher =University of Wisconsin Press,
location = Madison
booktitle= Antarctic Geoscience
pages = 639-648
isbn = ] cite journal
author = Sherwood, A.M.
coauthors = Woolfe, K.J.; Kirk, P.A.
year = 1988
title = Geological mapping and preliminary paleoenvironmental interpretations of the Taylor Group in the knobhead area, Southern Victoria Land
journal = New Zealand Antarctic record
volume = 8
issue = 2
pages = 60–61] cite journal|last=Plume |first=RW|date=1978|journal=New Zealand Journal of Geology & Geophysics |volume=21|pages=167–173] [cite book
author=Barrett PJ; Kohn BP
year=1975
pages=15-35
editor=Campbell KSW
booktitle=Gondwana Geology
publisher=ANU Press
location=Canberra]

[cite journal|author=Barrett, PJ|year=1979|journal=Proceedings of the 4th International Gondwana Symposium Calcutta 1977|pages= 478–480] [cite journal|author=Bradshaw MA|year=1981 |journal=New Zealand Journal Geology & Geophysics |volume=24|pages=615–652]

References

External links

* cite web
url = http://www.ngsprints.co.uk/m13/Maria-Stenzel/p120398/Layers-of-beacon-sandstone-and-Ferrar-dolerite-on-Finger-Mountai/product_info.html
title = Layers of beacon sandstone and Ferrar dolerite on Finger Mountain
publisher = National Geographics
accessdate = 2008-04-23