Carapace Nunatak () is a prominent isolated

nunatak A nunatak (from Inuit language, Inuit ) is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They often form natural pyramidal peaks. Isolated nunataks are also cal ...

, the most westerly near the head of

Mackay Glacier Mackay Glacier () is a large glacier in Victoria Land, descending eastward from the Antarctic Plateau, between the Convoy Range and Clare Range, into the southern part of Granite Harbour. It was discovered by the South magnetic pole party of the B ...

Victoria Land Victoria Land is a region in eastern Antarctica which fronts the western side of the Ross Sea and the Ross Ice Shelf, extending southward from about 70°30'S to 78th parallel south, 78°00'S, and westward from the Ross Sea to the edge of the Ant ...

, standing southwest of

Mount Brooke The Mawson Glacier () is a large glacier on the east coast of Victoria Land, Antarctica, descending eastward from the Antarctic Plateau to the north of Trinity Nunatak and the Kirkwood Range, to enter the Ross Sea, where it forms the Nordenskjöld ...

where it is visible for a considerable distance from many directions. It was so named by the

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

party of the

Commonwealth Trans-Antarctic Expedition The Commonwealth Trans-Antarctic Expedition (CTAE) of 1955–1958 was a Commonwealth-sponsored expedition that successfully completed the first overland crossing of Antarctica, via the South Pole. It was the first expedition to reach the South ...

(1956–1958) because of the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

s of small

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s found in the exposed rocks.Stewart, J., 2011. ''Antarctica: An Encyclopedia,'' 2nd ed. Jefferson, North Carolina and London, McFarland & Company, Inc. 1771 pp.

Geology

The Carapace Nunatak is an erosional

outlier In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

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

, which consists of about of the Ferrar Group. The exact thickness is unknown because the strata is broken up by faults and discontinuous

glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...

s conceal the underlying Jurassic strata.Ballance, P.F. and Watters, W.A., 1971. ''The Mawson Diamictite and the Carapace Sandstone, formations of the Ferrar Group at Allan Hills and Carapace Nunatak, Victoria Land, Antarctica.'' ''New Zealand Journal of Geology and Geophysics'', 14(3), pp.512-527.Bradshaw, M.A., 1987. ''Additional field interpretation of the Jurassic sequence at Carapace Nunatak and Coombs Hills, south Victoria Land Antarctica.'' ''New Zealand Journal of Geology and Geophysics'', 30(1), pp.37-49. At the base of Carapace Nunatak, about of cross-bedded sandstones and fine lithic conglomerates of the Carapace Sandstone

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

s. The

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

fraction of the fine conglomerates consists of

pebble A pebble is a clastic rocks, clast of rock (geology), rock with a grain size, particle size of based on the Particle size (grain size), Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than Granule (geology), gra ...

s of

coal 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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...

, and weathered

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

. Some

beds A bed is a piece of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many be ...

contain

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

debris. The uppermost contains beds of laminated and

fossiliferous A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved i ...

beds of

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

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. Although its permeabil ...

, and

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

. The base of the Carapace Sandstone is not exposed. The Carapace Nunatak is the type locality for the Carapace Sandstone. Conformably overlying the Carapace Sandstone is of Kirkpatrick Basalt. The basalt

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s include a thick layer of hyaloclastite

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 ...

with beds of

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discontinu ...

at its base. About above its base, a thick layer of volcanic breccia lies sandwiched between basaltic lava flows. The lava flows exhibit

columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as Joint (geology), joints, result in the formation of a regular array of polygonal Prism (geometry), prisms, or columns. Columnar join ...

and, at the base of the Kirkpatrick Basalt, contain with very large (up to thick) xenoliths (''rafts'') of fossiliferous, laminated siltstone and chert. The upper surface of the Kirkpatrick Basalt has been long since removed by

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

Fossils

The fossiliferous horizons of the Ferrar Group at Carapace Nunatak contain one of the richest and most diverse

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

Jurassic paleobiota known from Antarctica. Not only are these fossils diverse, except for poorly preserved

petrified wood Petrified wood (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial plant, terrestrial vegetation. ''Petrifaction ...

, the fossils found at Carapace Nunatak are remarkably well preserved to the extent that their source is referred to as a Lagerstätten.Babcock, L.E., Leslie, S.A., Elliot, D.H., Stigall, A.L., Ford, L.A. and Briggs, D.E., 2006. ''The “Preservation Paradox”: microbes as a key to exceptional fossil preservation in the Kirkpatrick Basalt (Jurassic), Antarctica.'' ''The Sedimentary Record'', 4(4), pp.4-8.Ribecai, C., 2007. ''Early jurassic miospores from ferrar group of carapace nunatak, south victoria Land, Antarctica.'' ''Review of Palaeobotany and Palynology'', 144(1-2), pp.3-12. In the laminated, and

silicified In geology, silicification is a process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and abundant com ...

, fine-grained lake deposits of Carapace Sandstone, fossil conchostracans (

clam shrimp Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classif ...

) are the most important in terms of number of individuals and distribution.Yabin, Shen, 1994. ''Jurassic conchostracans from Carapace Nunatak, southern Victoria Land, Antarctica.'' ''Antarctic Science'', 6, pp.105–113. They consist of small, , bivalved spinicaudatan

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s. They are most typical of ephemeral, alkaline ponds. Associated

macrofossil Macrofossils, also known as megafossils, are the preserved remnants of organic beings and their activities that are large enough to be visible without a microscope. The term ''macrofossil'' stands in opposition to the term microfossil. Microfoss ...

s include notostracan branchiopods,

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

es, insect nymphs and wings, and

plant leaves A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...

. Macroscopic

trace fossil A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

s are extremely rare. The lake cherts from the upper part of Carapace Sandstone contain an abundance of fusainized plant material and animal remains. This fine-grained Magadi-type chert preserves abundant plant fossils. These plant fossils include at least three

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

represented by vegetative and reproductive structures, isolated ovules, a diversity of taxa of

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

pinnules A leaflet (occasionally called foliole) in botany is a leaf-like part of a compound leaf. Though it resembles an entire leaf, a leaflet is not borne on a main plant stem or branch, as a leaf is, but rather on a petiole or a branch of the leaf. Co ...

, rachides and

rhizome In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...

s, and cycadophyte foliage. Intermixed with the plant fossils are numerous of shallow-water conchostracans and other ephemeral freshwater crustaceans.Hieger, T.J., Serbet, R., Harper, C.J., Taylor, T.N., Taylor, E.L. and Gulbranson, E.L., 2015. ''Cheirolepidiaceous diversity: an anatomically preserved pollen cone from the Lower Jurassic of southern Victoria Land, Antarctica.'' ''Review of Palaeobotany and Palynology'', 220, pp.78-87.

References

{{Reflist Paleontological sites of Antarctica Nunataks of Oates Land