The Whitehill Formation, alternatively written as White Hill Formation and formerly known as White Band or Whitehill or White Hill Member, is a regional

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 ...

(

Artinskian In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of the ...

Kungurian In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Artin ...

, dating to around 282 to 275 Ma) geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

belonging to the

Ecca Group The Ecca Group is the second of the main subdivisions of the Karoo Supergroup of geological strata in southern Africa. It mainly follows conformably after the Dwyka Group in some sections, but in some localities overlying unconformably over much ...

in the southeastern

ǁKaras Region The ǁKaras Region (pronounced , with a lateral click) is the southernmost and least densely populated of the 14 regions of Namibia; its capital is Keetmanshoop. The name assigned to the region reflects the prominence of the Karas mountain rang ...

of southeastern

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

and

Eastern Eastern may refer to: Transportation *China Eastern Airlines, a current Chinese airline based in Shanghai *Eastern Air, former name of Zambia Skyways *Eastern Air Lines, a defunct American airline that operated from 1926 to 1991 *Eastern Air Li ...

Northern Northern may refer to the following: Geography * North, a point in direction * Northern Europe, the northern part or region of Europe * Northern Highland, a region of Wisconsin, United States * Northern Province, Sri Lanka * Northern Range, a ra ...

and

Western Cape The Western Cape is a province of South Africa, situated on the south-western coast of the country. It is the fourth largest of the nine provinces with an area of , and the third most populous, with an estimated 7 million inhabitants in 2020 ...

provinces of

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

. The formation comprises

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 ...

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

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 ...

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

beds,

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...

and

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

layers and a layer of

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

within the formation. With a thickness between and present in an area of , the formation is considered the primary target for

shale gas Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some a ...

potential in the Southern Karoo.

Total Organic Carbon Total organic carbon (TOC) is the amount of carbon found in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment. TOC may also refer to the amount of organic c ...

(TOC) values average 4.5% with a range from 0.5 to 14.7%, placing the formation in the same range as the well-known

Barnett Shale The Barnett Shale is a geological formation located in the Bend Arch-Fort Worth Basin. It consists of sedimentary rocks dating from the Mississippian period (354–323 million years ago) in Texas. The formation underlies the city of Fort Worth a ...

and

Marcellus Formation The Marcellus Formation or the Marcellus Shale is a Middle Devonian age unit of sedimentary rock found in eastern North America. Named for a distinctive outcrop near the village of Marcellus, New York, in the United States, it extends throughou ...

of the United States. The Whitehill Formation of the

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ext ...

and Nama or Kalahari Basin is contemporaneous with the Huab Formation of the Huab Basin and is correlated with a series of formations in the

Pelotas Pelotas () is a Brazilian city and municipality (''município''), the third most populous in the southern state of Rio Grande do Sul. It is located 270 km (168 mi) from Porto Alegre, the state's capital city, and 130 km (80.8&nb ...

and

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande d ...

s in southeastern Brazil, deposited in a larger basinal area, 150 million years before the break-up of

Pangea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

. The abundance of ''

Glossopteris ''Glossopteris'' tymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")is the largest and best-known genus of the extinct Permian order of seed ferns known as Glossopteridales (also known as Arberia ...

'' and ''

Mesosaurus ''Mesosaurus'' (meaning "middle lizard") is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with it, the genera '' Brazilosaurus'' and ''Stereosternum'', it is a member of the family Mesosauridae a ...

'' fossils are characteristic of the

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 ...

n correlation across present-day South America, Africa, Antarctica and Australia. The Whitehill Formation has provided fossil reptiles,

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s, fish and flora.

Description

The Whitehill Formation is an extensive Lower Permian unit, cropping out in a thin band stretching from the

in South Africa through southeastern Namibia and the

Northern Cape The Northern Cape is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley. It includes the Kalahari Gemsbok National Park, part of the Kgalagadi T ...

in the north to the

Eastern Cape The Eastern Cape is one of the provinces of South Africa. Its capital is Bhisho, but its two largest cities are East London and Gqeberha. The second largest province in the country (at 168,966 km2) after Northern Cape, it was formed in ...

of South Africa in the east.Cole, 2014, p.4 The formation is found at the edge of the Karoo Basin at distances of north to south and east to west.Cole, 2014, p.15 The formation is part of the

Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a perio ...

, more precisely the

, where it overlies the

Prince Albert Formation A prince is a male ruler (ranked below a king, grand prince, and grand duke) or a male member of a monarch's or former monarch's family. ''Prince'' is also a title of nobility (often highest), often hereditary, in some European states. The ...

and is overlain by the Collingham Formation,Evans & Bender, 1999, p.175 and in the southern Karoo by the Tierberg Formation.Cole, 2014, p.28 Single zircon U- Pb SHRIMP dating yielded an age of 279.1 ± 1.5 Ma for the Uhabis River Tuff present in the upper strata of the underlying Prince Albert Formation.Werner, 2006, p.207 The Khabus Tuff within the Whitehill Formation provided a weighted mean ²⁰⁶Pb/²³⁸U age of 280.5 ± 2.1 Ma.Werner, 2006, p.362 Other authors use an estimated age for the whole formation of around 275 Ma.Geel et al., 2013, p.259 In the central part of the

Karoo Basin The Karoo Supergroup is the most widespread stratigraphy, stratigraphic unit in Africa south of the Kalahari Desert. The group (stratigraphy), supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Pennsylvan ...

, the formation ranges in thickness from and is highly organic with up to 14 weight percent of

(TOC).Branch et al., 2007, p.465 The formation is highly conductive and can be traced in seismic profiles across nearly the whole basin.Branch et al., 2007, p.475

Lithologies

The Whitehill Formation has been subdivided into two major subunits according to their weathering color in outcrops. The lower and thicker part consists mainly of bluish- to greenish-grey

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 ...

s and

s, which grade upward into more light brownish, buff weathering, slightly coarser grained

s. This zone is conformably overlain by white weathering shales, with intermittent

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 ...

lenses and pyritic stringers; the latter rarely exceeding in thickness. The sedimentary structure is generally massive, however laminations do occur that resemble algal lamellae. The formation appears white due to

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

of pyrite (

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

) at surface to

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...

(

).Branch et al., 2007, p.467 This section is grading upward into dark

carbonaceous Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to gro ...

, bluish-grey weathering shales. From a lithological point of view only the upper part of the succession consists of the Whitehill-characteristic carbonaceous

s.Werner, 2006, p.80 A

aceous zone occurs within the Whitehill Formation a few metres below the stratigraphic interval, which contains several dolomitic limestones. This limestone interval forms a mappable unit in all outcrops of the Whitehill Formation in central southern Namibia.Werner, 2006, p.221 In the Northern Cape, the formation is intruded by

dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...

sills.Cole, 2014, p.22 The sediments are considered to be deposited in an anoxic environment. Besides pyrite, the shales contain

lenses near the base. The rocks are highly folded and faulted by the Cape orogeny forming the

Cape Fold Belt The Cape Fold Belt is a fold and thrust belt of late Paleozoic age, which affected the sequence of sedimentary rock layers of the Cape Supergroup in the southwestern corner of South Africa. It was originally continuous with the Ventana Mount ...

, and thus, interpreted as "decollement".Geel et al., 2013, p.258

Depositional environments

The Whitehill Formation was deposited in a shallow

inland sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...

with little to no connection to the open ocean. This sea, stretching from the

in current southeastern Brazil to the Karasberg and

s of southwestern Africa, probably represents the transition from marine to brackish or freshwater conditions, in sediment-starved, stratified and anoxic embayments. From outcrops in southernmost Namibia (Aussenkjer-Noordoewer area) it became evident that the boundary between the Prince Albert and the Whitehill Formation represents the turning point from a progradational to a retrogradational succession.Werner, 2006, p.99 The tuffs within the Whitehill Formation, as well as other tuffaceous beds found in the underlying and overlying formations, were possibly sourced by volcanoes located in present-day South America,Werner, 2006, p.383 although other interpretations of the tuffs of the Dwyka and Ecca Groups propose a general source along the southern Panthalassian margin of current southern Africa.Werner, 2006, p.377

Correlations

The Whitehill Formation is time equivalent with the Pietermaritzburg Formation of the Waterberg Basin of southern Namibia.Werner, 2006, p.373 To the north in the Karoo Basin, the shales of the Whitehill Formation are laterally equivalent with the Vryheid Formation.Cole, 2014, p.7 The upper part of the formation is correlated with the

Irati Formation Irati Formation is the name of a geological formation of the Paraná Basin in Brazil. It has previously been dated as Late Permian using palynomorphs, but is now dated as Early Permian using zircon ages obtained from bentonite layers. The base of ...

of the Paraná and

Pelotas Basin The Pelotas Basin ( pt, Bacia de Pelotas, es, Cuenca de Pelotas) is a mostly offshore sedimentary basin of approximately in the South Atlantic, administratively part of the southern states Santa Catarina and Rio Grande do Sul of Brazil and the ...

s in

Rio Grande do Sul Rio Grande do Sul (, , ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative_units_of_Brazil#List, fifth-most-populous state and the List of Brazilian st ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, the Black Rock Member of the

Falkland Islands The Falkland Islands (; es, Islas Malvinas, link=no ) is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and about from Cape Dubouzet ...

,Werner, 2006, p.373 and with the Huab Formation in the Huab Basin of northwestern Namibia. The lower section correlates with the

Palermo Palermo ( , ; scn, Palermu , locally also or ) is a city in southern Italy, the capital (political), capital of both the autonomous area, autonomous region of Sicily and the Metropolitan City of Palermo, the city's surrounding metropolitan ...

and

Rio Bonito Formation The Rio Bonito Formation is a Formation (stratigraphy), geological formation of the Paraná Basin, Paraná and Pelotas Basins of Permian age. It is represented by a succession of cyclic sedimentary packages of sandstones, siltstones and shales whi ...

s of the Paraná Basin and the

of the Karoo.Horsthemke et al., 1990, p.74 The Permian sequence in the Huab Basin is much thinner than those of the Paraná and Karoo Basins.Holzförster et al., 2000, p.255 The fossil assemblages of ''

'' and ''Mesosaurus'' are known from other parts of

; the Vryheid Formation of South Africa and coal deposits of the Lower Permian in Australia.Horsthemke et al., 1990, p.69

Fossil content

The Whitehill Formation has provided a variety of fossil insects, rare flora and ''

'' fossils, typical for the Permian of Gondwana. The mesosaurids are preserved as molds filled with gypsum crystals; they are commonly disarticulated. More rarely, casts of mesosaurids are found. Plant stems are similarly rare, and most commonly occur as chloritized fragments floating in the pink lower, more massive mudstone succession of the Whitehill Formation, while

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...

s containing either palaeoniscoid scales or fragmentary

crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

n carapaces are preserved on bedding planes.Evans & Bender, 1999, p.177 The following fossils have been reported from the Whitehill Formation:District of Albania, Griqualand West
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org ;Reptiles * ''

Mesosaurus tenuidens ''Mesosaurus'' (meaning "middle lizard") is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with it, the genera '' Brazilosaurus'' and ''Stereosternum'', it is a member of the family Mesosauridae a ...

'' * '' Noteosaurus africanus'' * ''

Stereosternum tumidum ''Stereosternum tumidum'' (meaning "rigid chest") (Stereos, Greek: “solid, firm”; Sternon, Greek: “chest, breastbone”) is an extinct genus of mesosaur marine reptile from the Early Permian of Brazil and also the Great Karoo Basin of South ...

'' ;Fish * '' Palaeoniscum capensis'' * '' Watsonichthys lotzi''Evans & Bender, 1999, p.176 ;Insects * '' Afrochoristella maclachlani'' * '' Afrocupes firmae'' * '' Sharovia permiafricana'' ;Flora * '' Lepidodendron whitehillianum''

Economic geology

The high concentration of organic matter in the

s of the Whitehill Formation make it an interesting target for

exploration. The formation is considered the prime focus for potential shale gas prospects in the Southern Karoo.Geel et al., 2013, p.263 TOC levels average at 4.5% TOC,Geel et al., 2013, p.260 and range from 0.5 to 14.7%, comparable to known shale gas producing formations as the

and the

.Cole, 2014, p.5 The formation is considered to have economic potential in an area around

Beaufort West Beaufort West (Afrikaans: ''Beaufort-Wes''; Xhosa: ''eBhofolo'') is a town in the Western Cape province in South Africa. It is the largest town in the arid Great Karoo region, and is known as the "Capital of the Karoo". It forms part of the Beauf ...

Graaff-Reinet Graaff-Reinet is a town in the Eastern Cape Province of South Africa. It is the oldest town in the province. It is also the sixth-oldest town in South Africa, after Cape Town, Stellenbosch, Simon's Town, Paarl and Swellendam. The town was the c ...

.Cole, 2014, p.31 Results from Rock-Eval pyrolysis,

vitrinite reflectance Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling gla ...

measurements, open pyrolysis and thermovaporization analyses carried out on core samples drilled through the formation show that organic matter has reached an advanced stage of kerogen development. These rocks can therefore be classified as overmature, likely because of the thermotectonic processes related to the Cape orogeny forming the

overprint on lower Karoo rocks in the study area. It is possible that the maturity of the shales decreases farther north in the Karoo basin.Geel et al., 2013, p.264

References

Bibliography

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