The Shackleton Limestone is a

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

formation of the Byrd Group of the

Ross Dependency The Ross Dependency is a region of Antarctica defined by a circular sector, sector originating at the South Pole, passing along longitudes 160th meridian east, 160° east to 150th meridian west, 150° west, and terminating at latitude 60th para ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

. The age of the formation is established to be

Cambrian Stage 3 Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxima ...

, dated at ranging from 520 to 516 Ma. This period correlates with the End-Botomian mass extinction. Fossils of

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s and '' Marocella mira'' and '' Dailyatia'' have been found in the formation, named after

Ernest Shackleton Sir Ernest Henry Shackleton (15 February 1874 – 5 January 1922) was an Anglo-Irish Antarctic explorer who led three British expeditions to the Antarctic. He was one of the principal figures of the period known as the Heroic Age of Antarcti ...

, who led a failed expedition into Antarctica. At time of deposition, the Antarctic Plate has been established to be just south of the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

as part of the supercontinent

Pannotia Pannotia (from Greek: ''wikt:pan-, pan-'', "all", ''wikt:νότος, -nótos'', "south"; meaning "all southern land"), also known as the Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neo ...

, contrasting with its present position at 82 degrees southern latitude.Shackleton Limestone
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org

Geology

The formation, named by Laird in 1963, crops out in the

Churchill Mountains The Churchill Mountains is a major range of mountains and associated elevations bordering the western side of the Ross Ice Shelf, between Byrd Glacier and Nimrod Glacier. They are south of the Britannia Range and north of the Geologists Range, ...

, part of the

Transantarctic Mountains The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted rock (primarily sedimentary) in Antarctica which extends, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats L ...

of southwestern Antarctica. The most complete exposures are in the Holyoake Range.Myrow et al., 2002, p.1073 Paleontological data and carbon isotope stratigraphy indicate that the Shackleton Limestone ranges from lower

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxi ...

through upper

Botomian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission ...

. The formation is a thick carbonate deposit with a lower unit of unfossiliferous interbedded

quartzite Quartzite is a hard, non- foliated metamorphic rock that 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 tecton ...

and

, overlies the Late Proterozoic

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...

turbidite A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...

Goldie Formation and underlies the

Starshot Formation Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail interstellar probes named ''Starchip'', to be capable of making the journey to the Alpha Centauri star ...

. Other

lithologies 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. Lith ...

noted in the Shackleton Limestone are

marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...

with

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

, conglomerate,

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

.Laird et al., 1971, p.428 The abrupt transition from the Shackleton Limestone to a large-scale, upward coarsening

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclastic rock types include mudrock, sandstone Sandstone is a Clastic ...

succession records deepening of the outer platform and then deposition of an eastward-prograding molassic wedge. The various formations of the upper Byrd Group show general stratigraphic and age equivalence, such that coarse-grained

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

deposits of the Douglas Conglomerate are proximal equivalents of the marginal-marine to shelf deposits of the Starshot Formation.Myrow et al., 2002, p.1070 The sandstone-rich lower member of the Shackleton Limestone is exposed at Cotton Plateau beneath Panorama Point, where it consists of up to of interbedded white- to cream-weathering, vitreous,

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and brown-weathering, white, fine-grained dolomitic

grainstone Under the Dunham classification (Dunham, 1962) system of limestones, a grainstone is defined as a grain-supported carbonate rock that contains less than 1% mud-grade material. This definition has recently been clarified as ''a carbonate-dominated ...

. These beds are in fault contact with the adjacent Goldie Formation.Myrow et al., 2002, p.1075 The formation postdates the Beardmore Orogeny of the

Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...

,Elliot, 1975, p.54 and was deformed by the Ross Orogeny.Stump et al., 2006, p.2

Fossil content

The formation has provided fossils of

s such as '' Holyoakia granulosa'', '' Pagetides (Discomesites) spinosus'', '' Lemdadella antarcticae'', '' Kingaspis (?) convexus'', '' Yunnanocephalus longioccipitalis'', and '' Onchocephalina (?) spinosa''.Palmer & Rowell, 1995 Other fossils found are '' Marocella mira'', and '' Dailyatia odyssei'' and ''D. braddocki''.Skovsted, 2015, p.16

References

Bibliography

* * * * * * {{cite book , last1=Stump , first1=Edmund , last2=Gootee , first2=Brian , last3=Talarico , first3=Franco , title=Antarctica , chapter=Tectonic Model for Development of the Byrd Glacier Discontinuity and Surrounding Regions of the Transantarctic Mountains during the Neoproterozoic — Early Paleozoic , publisher=Springer-Verlag , publication-place=Berlin/Heidelberg , date=2006 , isbn=978-3-540-30673-3 , doi=10.1007/3-540-32934-x_22 , pages=181–190, chapter-url=https://epic.awi.de/17003/1/Stu2006d.pdf Geologic formations of Antarctica Paleozoic Antarctica Limestone formations Sandstone formations Shale formations Conglomerate formations Dolomite formations Shallow marine deposits Cambrian southern paleotropical deposits Paleontology in Antarctica

Geology

Fossil content

See also

References

Bibliography