Archer City Formation
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The Archer City Formation is a
geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...
in north-central
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
, preserving
fossils 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 ...
from the
Asselian In the geologic timescale, the Asselian is the earliest geochronologic age or lowermost chronostratigraphic stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Asselian lasted between and million years ago (Ma ...
and early
Sakmarian In the geologic timescale, the Sakmarian is an age or stage of the Permian period. It is a subdivision of the Cisuralian Epoch or Series. The Sakmarian lasted between 293.52 and million years ago (Ma). It was preceded by the Asselian and fo ...
stages Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...
of the
Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...
period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...
. It is the earliest component of the Texas red beds, introducing a tropical ecosystem which will persist in the area through the rest of the
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 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...
. The Archer City Formation is preceded by the cool
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
swamp sediments of the Markley Formation, and succeeded by the equally fossiliferous red beds of the Nocona Formation. The Archer City Formation was not named as a unique geological unit until the late 1980s. Older studies generally labelled its outcrops as the
Moran Moran may refer to: Places Antarctica * Moran Bluff, Marie Byrd Land * Moran Buttress, Marie Byrd Land * Moran Glacier, Alexander Island Asia * Moran Town, Assam, India * Moran, Israel, a kibbutz * Moran Hill, North Korea * Moran Station, a s ...
or Putnam formations, which are age-equivalent marine units to the southwest. The sediments of the Archer City Formation reconstruct a coastal
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
crossed by small meandering rivers and isolated ponds. The climate was hot and
monsoonal A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscill ...
, preserving a variety of
paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...
s and plant assemblages ranging from dry upland forests to moist riverside galleries. "
Seed ferns Pteridospermatophyta, also called pteridosperms or seed ferns, are a polyphyletic grouping of extinct Spermatophyte, seed-producing plants. The earliest fossil evidence for plants of this type are the Lyginopteridales, lyginopterids of late Devon ...
" (''
Sphenopteris ''Sphenopteris'' is a genus of seed ferns containing the foliage of various extinct plants, ranging from the Devonian to Late Cretaceous. One species, ''S. höninghausi'', was transferred to the genus '' Crossotheca'' in 1911. Biology The fro ...
'', '' Autunia'', '' Odontopteris'', etc.) and early conifers (''
Walchia ''Walchia'' is a primitive fossil conifer found in upper Pennsylvanian (geology), Pennsylvanian (Carboniferous) and lower Permian (about 310-290 Mya (unit), Mya) rocks of Europe and North America. A forest of In situ, in-situ Walchia tree-stumps ...
'', etc.) occupied drier soils, while marattialean ferns ('' Pecopteris'', ''
Asterotheca ''Asterotheca'' is a genus of seedless, spore, spore-bearing, Vascular plant, vascularized ferns dating from the Carboniferous of the Paleozoic to the Triassic of the Mesozoic. Description ''Asterotheca sp.'' is a vascularized, seedless fern ...
'', etc.) and horsetails (''
Sphenophyllum ''Sphenophyllum'' is a genus in the order Sphenophyllales. It has been placed in the family Sphenophyllaceae. Species Species that have been described include: *†''Sphenophyllum angustifolium'' *†''Sphenophyllum biarmicum'' Zalessky (1937) ...
'', ''
Annularia ''Annularia'' is a form taxon, applied to fossil foliage belonging to extinct plants of the genus ''Calamites'' in the order Equisetales. Description ''Annularia'' is a form taxon name given to leaves of ''Calamites''. In that species, the leav ...
'', ''
Calamites ''Calamites'' is a genus of Extinction, extinct arborescent (tree-like) horsetails to which the modern horsetails (genus ''Equisetum'') are closely related. Unlike their Herbaceous plant, herbaceous modern cousins, these plants were medium-size ...
'', etc.) were prominent in more humid areas. The Archer City Formation preserves a diverse fauna of fossil
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s in pond bonebeds across
Archer Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In modern ...
and
Clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
counties. Many fossils are rare fragments of species which are better-preserved in younger parts of the red beds. Nevertheless, complete skeletons and important
type specimens In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes t ...
are also known from the formation. Some notable
synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
s include '' Apsisaurus witteri'', ''
Edaphosaurus boanerges ''Edaphosaurus'' (, meaning "pavement lizard" for dense clusters of its teeth) is a genus of extinct edaphosaurid synapsids that lived in what is now North America and Europe around 303.4 to 272.5 million years ago, during the Late Carboniferous ...
'', '' Ophiacodon uniformis'', and '' Dimetrodon milleri''. Early reptiles such as ''
Protorothyris archeri ''Protorothyris'' is an extinct genus of Early Permian protorothyridid known from Texas and West Virginia of the United States. It was first named by Llewellyn Ivor Price in 1937 and the type species is ''Protorothyris archeri''. ''P. archeri'' ...
'' and ''
Romeria Christianity has a strong tradition of pilgrimages, both to sites relevant to the New Testament narrative (especially in the Holy Land) and to sites associated with later saints or miracles. History Christian pilgrimages were first made to sit ...
'' spp. make up a small component of the terrestrial fauna. Amphibians are common in every niche, with examples such as '' Phonerpeton pricei, Neldasaurus wrightei'', ''
Edops craigi ''Edops'' ('swollen face') is an extinct genus of temnospondyl amphibian from the Late Carboniferous - Early Permian periods. Unlike more advanced temnospondyls of the time, such as ''Eryops'', ''Edops'' exhibited an archaic pattern of palatal bo ...
,'' ''
Eryops megacephalus ''Eryops'' (; from Greek , , 'drawn-out' + , , 'face', because most of its skull was in front of its eyes) is a genus of extinct, amphibious temnospondyls. It contains the single species , the fossils of which are found mainly in early Permian (a ...
'', and '' Pantylus cordatus'', just to name a few. The rivers were roamed by '' Orthacanthus texensis'' (a
xenacanth Xenacanthida (or Xenacanthiformes) is an order or superorder of extinct shark-like chondrichthyans (cartilaginous fish) known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. Some xena ...
"shark") and '' Ectosteorhachis nitidus'' (a megalichthyid fish).


History and stratigraphy

Fossil bonebeds in the vicinity of Archer City were first investigated in detail by
Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...
and
Llewellyn Price Llewellyn Ivor Price (October 9, 1905 – June 9, 1980) was one of the first Brazilian paleontologists. His work contributed not only to the development of Brazilian but also to global paleontology. He collected ''Staurikosaurus'' in 1936, th ...
, starting in the late 1920s. At the time, these bonebeds were assigned to the
Pueblo Pueblo refers to the settlements of the Pueblo peoples, Native American tribes in the Southwestern United States, currently in New Mexico, Arizona, and Texas. The permanent communities, including some of the oldest continually occupied settlement ...
,
Moran Moran may refer to: Places Antarctica * Moran Bluff, Marie Byrd Land * Moran Buttress, Marie Byrd Land * Moran Glacier, Alexander Island Asia * Moran Town, Assam, India * Moran, Israel, a kibbutz * Moran Hill, North Korea * Moran Station, a s ...
, or Putnam formations of the Cisco Group. The Archer City Formation was first named in a 1987
geological map A geological map or geologic map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...
seeking to update the stratigraphy of
North Texas North Texas is a term used primarily by residents of the Dallas–Fort Worth metroplex to refer to a geographic area of Texas, generally considered to include the area south of Oklahoma, east of Abilene, Texas, Abilene, west of Paris, Texas, Par ...
. The formation and its stratigraphic placement were formalized in text a year later. The formation outcrops in an arc from Montague County in the east, through
Clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
,
Archer Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In modern ...
, and
Young Young may refer to: * Offspring, the product of reproduction of a new organism produced by one or more parents * Youth, the time of life when one's age is low, often meaning the time between childhood and adulthood Music * The Young, an America ...
counties, as far as Throckmorton County in the west. It is most broadly exposed in Clay and Archer counties, including under its namesake of Archer City. The Archer City Formation is a unit of the Bowie Group, lying above the Markley Formation and below the Nocona Formation of the
Wichita Group The Wichita Group is a geologic group in the Permian Red Beds. It preserves fossils dating back to the Permian period. See also * List of fossiliferous stratigraphic units in Texas * Paleontology in Texas Paleontology in Texas refers to pa ...
. Some publications have labelled the Nocona Formation as the "Upper Archer City Formation", thus considering the Archer City Formation to be a unit of the Wichita Group. This proposal is not widely agreed upon. The Cisco Group and its constituent formations have been restricted to marine strata further south and west. Of these strata, the Archer City Formation is roughly equivalent in time to the uppermost Pueblo Formation, the Moran Formation, the Sedwick Formation, and the Santa Anna Branch shale (= Putnam Formation), from oldest to youngest.


Age

Based on correlations with coastal strata further west, the Carboniferous-Permian boundary is positioned near the top of the Markley Formation. This suggests that the Archer City Formation occupies most of the Asselian (299–293 Ma), the first global stage of the Permian Period. The plant fossils of the Archer City Formation also resemble those of Asselian Europe. The upper part of the Archer City Formation may extend into the succeeding
Sakmarian In the geologic timescale, the Sakmarian is an age or stage of the Permian period. It is a subdivision of the Cisuralian Epoch or Series. The Sakmarian lasted between 293.52 and million years ago (Ma). It was preceded by the Asselian and fo ...
stage (293–290 Ma). The Santa Anna Branch Shale and overlying Coleman Junction Limestone both preserve fossils of '' Sweetognathus merrilli'', a
conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
index fossil Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...
of the early Sakmarian. The Asselian and Sakmarian global stages are equivalent to the early-middle parts of the
Wolfcampian The Cisuralian, also known as the Early Permian, is the first series/epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the western slopes of the Ural Mount ...
regional stage.


Paleoenvironment

As with the rest of the Texas red beds, the Archer City Formation was deposited on a
coastal plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...
between an inland marine basin in the west and patches of steadily eroding mountains in the north and east. Some of the mountains are still standing in the present day, such as the
Wichita Mountains The Wichita Mountains are located in the southwestern portion of the U.S. state of Oklahoma. It is the principal relief system in the Southern Oklahoma Aulacogen, being the result of a failed continental rift. The mountains are a northwest-south ...
and
Arbuckle Mountains The Arbuckle Mountains are an ancient mountain range in south-central Oklahoma in the United States. They lie in Murray County, Oklahoma, Murray, Carter County, Oklahoma, Carter, Pontotoc County, Oklahoma, Pontotoc, and Johnston County, Oklahoma, ...
, while others have been fully eroded or buried, such as the Texan portion of the
Ouachita Mountains The Ouachita Mountains (), simply referred to as the Ouachitas, are a mountain range in western Arkansas and southeastern Oklahoma. They are formed by a thick succession of highly deformed Paleozoic strata constituting the Ouachita Fold and Thru ...
. The marine basin is formally known as the Midland Basin, a major component of the Permian Basin oil field. Rising sea levels through the Early Permian allowed the coastline to gradually transgress northward and eastward. The major bonebed sites of the Archer City Formation were probably away from the coast. During the Permian, the area was near 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 ...
, with a
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
of 0° to 5° N. Temperature estimates can be inferred for the Archer City Formation via
δ18O In geochemistry, paleoclimatology and paleoceanography ''δ''18O or delta-O-18 is a measure of the deviation in ratio of stable isotopes oxygen-18 (18O) and oxygen-16 (16O). It is commonly used as a measure of the temperature of precipitation ...
records for
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
and
phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...
minerals in
paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...
s. These data points suggest soil temperatures of , significantly warmer than the cool and wet conditions of the Markley Formation. This fits with climate evidence from rapid sedimentary changes between the formations, as well as an increasingly patchy distribution of high-humidity flora. The Archer City Formation would have had a hot
monsoonal A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscill ...
climate, with moist or swampy areas shrinking to the vicinity of riverbanks and ponds during the dry season.


Geology

In terms of their
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 ...
, the Archer City and Nocona formations are nearly indistinguishable, with equivalent sets of
fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...
and
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
sediments. The vast majority of each formation is homogeneous red
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, ...
with small
calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...
nodules Nodule may refer to: *Nodule (geology), a small rock or mineral cluster *Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, p ...
. Fluvial
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 ...
beds and paleosols are also common. Fossils and other organic debris are concentrated into rare greyish
claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...
bonebeds, which correspond to
perennial In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...
ponds. Most of the pond bonebeds are too small to continuously support an ecosystem of large aquatic vertebrates, suggesting that the carcasses may have been washed in from larger bodies of water.


Sandstone beds

By volume, the most prevalent sandstone beds are upwards-fining stacks of
point bar A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on ...
, scroll-bar, and coarser
channel Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Australia in Queensland and pa ...
fill deposits. These are all hallmarks of small meandering rivers, with channels only a few meters wide. Other common sandstone features include subdued, fine-grained
crevasse splay A crevasse splay is a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain. A breach that forms a crevasse splay deposits sediments in similar pattern to an alluvial ...
deposits. The crevasse splays are often associated with plant fossils which have been remineralized by
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
minerals. Some sandstone beds are isolated straight channel fills, without corresponding riverbank deposits. These straight beds may reach 30 meters in width (though most are much narrower) and several kilometers in length. Coarser beds preserve sinuous
megaripple In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (Ocean current, current or wind wave, waves) or directly by wind. Defining ripple cross-laminae and asymmetric ripples ...
s while finer channels develop small climbing ripples towards the top. Straight channels would have formed during high-energy erosion events, but the climate was probably too moist for frequent flash floods.


Paleosols

Four different types of paleosol (labelled types E through H) have been identified in the Archer City Formation. Three (F, G, and H) first appear in this formation, while type E paleosols are retained from the underlying Markley Formation. All four continue to persist through the Texas Lower Permian up until an
aridification Aridification is the process of a region becoming increasingly arid, or dry. It refers to long term change, rather than seasonal variation. It is often measured as the reduction of average soil moisture content. It can be caused by reduced preci ...
event in the mid-
Clear Fork Group The Clear Fork Group is a geologic group in the Texas Red Beds. It preserves fossils dating back to the Permian period. See also * List of fossiliferous stratigraphic units in Texas * Paleontology in Texas Paleontology in Texas refers to pa ...
. The paleosols are generally dark red or brown, with only intermittent gleying in the type E variety. The Archer City Formation mostly lacks the high-humidity paleosol varieties of the Markley Formation (types A through D). Type E paleosols are silty or fine sandy soils with persistent mottling, hematite nodules, and few distinct horizons. They are a type of
entisol Entisols are soils, as defined under USDA soil taxonomy, that do not show any profile development other than an A-horizon (or “A” horizon). Entisols have no diagnostic horizons, and are unaltered from their parent material, which could ...
, young soils corresponding to isolated, frequently disturbed areas with a high
water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...
, such as riverbanks. Type F paleosols are
alfisol Alfisols are a soil order in USDA soil taxonomy. Alfisols form in semi-arid to humid areas, typically under a hardwood forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium (Al) and iro ...
s, patterned with deep root casts and numerous horizons, including intermediate layers with calcareous nodules and
smectite A smectite (; ; ) is a mineral mixture of various swelling sheet silicates (phyllosilicates), which have a three-layer 2:1 (TOT) structure and belong to the clay minerals. Smectites mainly consist of montmorillonite, but can often contain secon ...
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
. They develop in stable forested uplands with a low water table and a semi-arid to subhumid climate (~70 cm of annual precipitation). Type G paleosols are similar, with sandy vertical cracks and abundant calcareous nodules. They qualify as
vertisol A vertisol is a Soil Order in the USDA soil taxonomy and a Reference Soil Group in the World Reference Base for Soil Resources (WRB). It is also defined in many other soil classification systems. In the Australian Soil Classification it is c ...
s, inundated and dried at a seasonal frequency along the margins of a floodplain. Type H paleosols have an even greater proportion of calcareous minerals, forming blocky crusts interspersed among
chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...
- and
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...
-rich clay. They could be termed
aridisol Aridisols (or desert soils) are a soil order in USDA soil taxonomy. Aridisols (from the Latin ''aridus'', for "dry", and ''solum'') form in an arid or semi-arid climate. Aridisols dominate the deserts and xeric shrublands, which occupy about on ...
s or (more broadly)
inceptisol Inceptisols are a soil order in USDA soil taxonomy. They form quickly through alteration of parent material. They are more developed than Entisols. They have no accumulation of clays, iron oxide, aluminium oxide or organic matter. They have a ...
s, deposited in dry upland areas free from the influence of
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
.


Paleobiota


Synapsids


Reptiles


Temnospondyls


Other amphibians


Fish

Scales of indeterminate
palaeoniscoid The Palaeonisciformes, commonly known as "palaeoniscoids" (also spelled "paleoniscoid", or alternatively "paleoniscids") are an extinct grouping of primitive ray-finned fish (Actinopterygii), spanning from the Silurian/Devonian to the Cretaceous. ...
s, spines of ''
Xenacanthus ''Xenacanthus'' (from Ancient Greek wikt:ξένος, ξένος, xénos, 'foreign, alien' + wikt:ἄκανθος, ἄκανθος, akanthos, 'spine') is an extinct genus of Xenacanthida, xenacanth cartilaginous fish. It lived in freshwater environ ...
'', ''
Hybodus ''Hybodus'' (from , 'crooked' and 'tooth') is an extinct genus of Hybodontiformes, hybodont. Species closely related to the type species ''Hybodus reticulatus'' lived during the Early Jurassic epoch. Numerous species have been assigned to ''Hyb ...
'', ''
Ctenacanthus ''Ctenacanthus'' (from , 'comb' and , 'spine') is an extinct genus of ctenacanthiform chondrichthyan. Remains have been found in the Bloyd Formation (Carboniferous Period) of Arkansas and the Cleveland Shale (Devonian Period) of Ohio in the U ...
'', and "'' Anodontacanthus americanus''" (= '' Platyacanthus''), and teeth of '' Barbclabornia luederensis'', '' Helodus'', '' Gnathorhiza'', petalodonts, and
cladodont This is a typical Cladodont tooth, of a Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a common category of early Devoni ...
s have also been reported from bonebeds of the Archer City Formation.


Plants

Plant fossils in the Archer City Formation are concentrated at two sites in Clay County: Kola Switch and Sanzenbacher Ranch. Both sites were discovered in 1940–1941 by Adolph H. Witte, a local geologist working for the WPA. Though Witte's original collections have been lost, he sampled the sites further in 1961, along with
USGS The United States Geological Survey (USGS), founded as the Geological Survey, is an government agency, agency of the United States Department of the Interior, U.S. Department of the Interior whose work spans the disciplines of biology, geograp ...
geologists Sergius H. Mamay and Arthur D. Watt. On behalf of the
USNM The National Museum of Natural History (NMNH) is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. With 4.4 ...
, Mamay led another expedition in 1990–1991. The floral diversity of the Archer City Formation strongly overlaps with other Asselian-Sakmarian formations in the southwestern United States. These include the Bursum and
Abo The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes (red blood cells). For human blood transfusions, it is the most important of the 47 different blood type (or group) cla ...
formations of New Mexico and the Neal Ranch Formation of
West Texas West Texas is a loosely defined region in the U.S. state of Texas, generally encompassing the desert climate, arid and semiarid climate, semiarid lands west of a line drawn between the cities of Wichita Falls, Texas, Wichita Falls, Abilene, Texa ...
. There are some notable differences, such as a lack of marattialean ferns in the Bursum Formation and a greater variety of swamp foliage in the Neal Ranch Formation. Many of the broader groups prevalent in these formations are equally abundant in the
Rotliegend The Rotliegend, Rotliegend Group or Rotliegendes () is a lithostratigraphic unit (a sequence of rock strata) of latest Carboniferous to Guadalupian (middle Permian) age that is found in the subsurface of large areas in western and central Europe ...
of Europe, even if only a few specific species (such as '' Autunia conferta'') are common in both regions. Conversely, there is little similarity with swampy coal-bearing areas such as the Dunkard Group of the
Appalachian Basin The geology of the Appalachians dates back more than 1.2 billion years to the Mesoproterozoic era when two continental cratons collided to form the supercontinent Rodinia, 500 million years prior to the development of the range during the form ...
. This is most likely a consequence of local environmental factors rather than a turnover of plant diversity at the Permo-Carboniferous boundary.


Kola Switch

The Kola Switch site is divided into three different layers in a thick interval, each with a different set of fossils. The lower bed is pale upwards-fining siltstone, the middle bed is dark shale with carbonaceous impressions, and the upper bed is greenish claystone. The
seed fern In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the ...
'' Sphenopteris germanica'' is the most abundant plant fossil in the lower bed. The
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 ...
''
Walchia ''Walchia'' is a primitive fossil conifer found in upper Pennsylvanian (geology), Pennsylvanian (Carboniferous) and lower Permian (about 310-290 Mya (unit), Mya) rocks of Europe and North America. A forest of In situ, in-situ Walchia tree-stumps ...
'' (''W.'' cf''. schneideri, W. piniformis'') is also common, followed by the seed ferns '' Odontopteris'' (''O. subcrenulata, O. osmundaeformis, O.'' cf''. readii''), and ''Autunia'' (''A. conferta, A. naumannii''). The plants tend to be adapted to low humidity;
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 of moisture-loving plants such as
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 ...
s and sphenophytes (horsetails) are very rare, despite the evidence for deposition in a slow stream channel. The most common
palynomorphs Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...
are '' Columinisporites ovalis'' ( sphenophyll
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s), '' Potonieisporites'' spp. (conifer
pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...
), '' Colatisporites decorus'' (indeterminate pollen), and '' Vesicaspora'' (seed fern pollen). Conversely, the middle bed is almost entirely marattialean ferns. These include ''Pecopteris'' cf. ''jongmansii'', '' Aphlebia erdmannii'', ''
Asterotheca ''Asterotheca'' is a genus of seedless, spore, spore-bearing, Vascular plant, vascularized ferns dating from the Carboniferous of the Paleozoic to the Triassic of the Mesozoic. Description ''Asterotheca sp.'' is a vascularized, seedless fern ...
'' sp, and several more unnamed species. Sphenophytes such as ''
Sphenophyllum ''Sphenophyllum'' is a genus in the order Sphenophyllales. It has been placed in the family Sphenophyllaceae. Species Species that have been described include: *†''Sphenophyllum angustifolium'' *†''Sphenophyllum biarmicum'' Zalessky (1937) ...
'' are also present. ''Vesicaspora'' and ''Potonieisporites'' continue to make up a significant portion of the palynomorphs, though ''Knoxisporites'' cf. ''ruhlandii'' (indeterminate spores), '' Cyclogranisporites'' spp. (marattialean spores), and '' Punctatisporites'' spp. (marattialean spores) are even more dominant. The middle bed represents foliage washed into a nearby stagnant pond. The upper bed has the greatest portion of sphenophytes, not just sphenophylls (''Sphenophyllum'' cf. ''thonii'') but also calamitaleans ('' Annularia carinata'', ''
Calamites ''Calamites'' is a genus of Extinction, extinct arborescent (tree-like) horsetails to which the modern horsetails (genus ''Equisetum'') are closely related. Unlike their Herbaceous plant, herbaceous modern cousins, these plants were medium-size ...
''). Otherwise, the floral diversity of the upper bed encompasses the same species as the other Kola Switch beds. The upper bed palynoflora is mostly ''Columinisporites ovalis'', ''Colatisporites decorus'', ''Vesicaspora'', ''Potonieisporites'', and the bisaccate pollen '' Platysaccus'' cf''. saarensis''. The combination of fossils from the lower and middle bed is peculiar considering their strongly different depositional environments.


Sanzenbacher Ranch

The Sanzenbacher flora occupies a narrow layer of greyish claystone coarsening upwards to buff-colored siltstone. The most abundant plants are dry-soil species of seed ferns and conifers. Seed fern species include ''Autunia conferta'', ''Sphenopteris germanica'', '' Neurodontopteris auriculata'', ''Odontopteris subcrenulata'', and '' Rhachiphyllum schenkii'', among others. ''Walchia'' is the most common conifer, followed by ''
Cordaites ''Cordaites'' is a genus of extinct gymnosperms, related to or actually representing the earliest conifers. These trees grew up to tall and stood in dry areas as well as wetlands. Brackish water mussels and crustacea are found frequently betwee ...
''.
Riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...
plants are less common but far from rare, giving Sanzenbacher a 'mixed' ecosystem character similar to, but drier than, the upper bed of Kola Switch. Marattialean ferns such as ''Pecopteris'' and ''Asterotheca'' are occasionally prevalent. Sphenophytes include ''Calamites'', ''Annularia spicata'', and to a lesser extent species of ''Sphenophyllum''. The most common palynomorphs are seed fern pollen (''Vesicaspora'', '' Wilsonites'', '' Anguisporites''), while conifer pollen (''Potonieisporites'') and spores are rarer. Still, the palynomorph diversity of Sanzenbacher is much greater than at Kola Switch.


See also

*
Red Beds of Texas and Oklahoma The Red Beds of Texas and Oklahoma are a group of Early Permian-age geologic strata in the southwestern United States cropping out in north-central Texas and south-central Oklahoma. They comprise several stratigraphic groups, including the Clear ...
*
List of fossiliferous stratigraphic units in Texas This article contains a list of fossil-bearing stratigraphic units in the state of Texas, U.S. Sites See also * Paleontology in Texas References * * {{DEFAULTSORT:Fossiliferous stratigraphic units in Texas Fossil Texas Tex ...
*
Paleontology in Texas Paleontology in Texas refers to paleontological research occurring within or conducted by people from the U.S. state of Texas. Author Marian Murray has said that "Texas is as big for fossils as it is for everything else." Some of the most import ...
*
Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...


References

* {{cite web, title= Fossilworks: Gateway to the Paleobiology Database, author= ((Various Contributors to the Paleobiology Database)), url= https://www.fossilworks.org, access-date= 17 December 2021 Permian geology of Texas