Pekin Formation | |
---|---|
Stratigraphic range: Late Carnian, ~ | |
Type | Geological formation |
Unit of | Chatham Group |
Underlies | Cumnock Formation |
Thickness | 542–1,240 metres (1,778–4,068 ft) |
Lithology | |
Primary | Sandstone |
Other | Siltstone, shale, conglomerate |
Location | |
Region | North Carolina |
Country | United States |
Extent | Sanford Sub-basin, Deep River Basin |
Type section | |
Named for | The village of Pekin, Montgomery County |
Named by | Campbell & Kimball |
Year defined | 1923 |
The Pekin Formation is a Late Triassic (Carnian) geological formation in North Carolina. The Pekin Formation is specific to the Sanford Sub-Basin of the Deep River Basin of North Carolina, although it may be equivalent to the Stockton Formation of Pennsylvania, New Jersey, and New York. The Pekin Formation was deposited in a rift basin along the Atlantic margin of North America during the breakup of the supercontinent Pangaea during the Late Triassic. The most common rocks in the Pekin Formation are red to brown sandstones, representing a terrestrial fluvial (riverine) and floodplain environment in a hot, humid climate. It has yielded both abundant plant and animal fossils, including some of the oldest potential dinosaur footprints in the world and the large predatory crocodylomorph Carnufex carolinensis .
On the surface, the Pekin Formation is exposed only as a long, narrow strip along the western edge of the Sanford Sub-basin. It is both the oldest and stratigraphically lowest formation in the sub-basin. As such, it unconformably overlies the much older eroded and metamorphosed Proterozoic to Cambrian aged metasediments and metavolcanic rocks of the Piedmont. The upper boundary grades into the overlying Cumnock Formation, distinguished by its fine-grained grey lacustrine sediments. The Pekin Formation was deposited in a half-graben that formed as part of a series of rift basins that make up the Newark Supergroup during the breakup of the supercontinent Pangaea and subsequent opening of the Atlantic Ocean. [1] [2]
As originally defined by Marius R. Campbell and Kent W. Kimball in 1923, the Pekin Formation spanned the entirety of the lower Deep River Basin, encompassing the lowest sedimentary units of the neighbouring Durham and the Wadesboro sub-basins. In fact, the Pekin Formation was named after the village of Pekin located in the Wadesboro Sub-basin, as this was where Campbell and Kimball (1923) considered it to be best exposed. [3] However, although the three sub-basins share a broadly similar three-part stratigraphy, geologists have not been able to accurately correlate those of the Sanford Sub-basin with the other sub-basins due to variations in stratigraphy, lithology and biostratigraphy. Furthermore, the Pekin has a very similar lithology to the Sandford Formation, and are only distinguishable by the presence of the Cumnock Formation between them. [1] As such, the Pekin, Cumnock and Sanford formations have been restricted to just the Sanford Sub-basin where they can be recognised. [2]
In 2016, Robert E. Weems, Lawrence H. Tanner, and Spencer G. Lucas proposed that the Pekin Formation should be subsumed into the Stockton Formation. Rather than dividing the Newark Supergroup into numerous distinct formations localised in single basins, they proposed a system where the disparate formations of local basins were merged into fewer regional-scale formations, based upon overall similar lithologies, biostratigraphy and chronology. Under this scheme, the Pekin Formation is equivalent to and is synonymous with the Stockton Formation. The Pekin Formation could then be considered an informal name for the Stockton Formation exposed in the Sanford Sub-basin. [4]
The base of the formation is composed of a roughly 10 metres (33 ft) thick layer of grey conglomerate, historically referred to as "millstone grit". This unit has been interpreted as alluvial fan deposits made up of material derived from the Piedmont to the west flowing down in a southeasterly direction. The remainder of the Pekin Formation is made up of red to brown and purple sandstones, siltstones and mudstones, along with deposits of conglomerate and shale that altogether support a fluvial and floodplain deposition environment. Unlike the lowest layers, sedimentation for the rest of the Pekin Formation had switched to a source in the highlands to the southeast, with rivers and streams in the upper Pekin flowing towards the north and northwest. The overall climate is interpreted as being warm and humid with highly seasonal rainfall. [3] [5]
Clays from the Pekin Formation have been used extensively for the production of pottery, bricks and tiles, namely the Boren and Pomona pits. These two quarries have historically been the site of fossil discoveries, preserving both plants and animals, as well as trace fossils, although these quarries are now disused and some have filled with water. [6] However, excavations by palaeontologists have been continued in a new brick quarry (Merry Oaks Quarry) by the North Carolina Museum of Natural Sciences (NCMNS) at a site labelled NCPALEO 1902. These excavations have uncovered various new vertebrate fossil discoveries, including the relatively complete remains of new Triassic archosaurs. [7] [8]
The age of the Pekin Formation has been estimated based on biostratigraphy and magnetostratigraphy to the Late Carnian (or Tuvalian), supported by correlations with faunas in western North America. [9] [8] [10]
A variety of plant and vertebrate fossils have been recovered from the Pekin Formation, the including partial skeletons of large vertebrates. The Boren pits preserves abundant plant megafossils, most commonly cycads and bennettitales, as well as horsetails, various ferns and conifers. Some of the most notable finds include an intact specimen of the early palm-like cycad Leptocycas gracilis , as well as a new species of the bennettitale Williamsonia , W. carolinensis, that preserves rare reproductive organs and suggests that it and the leaf Eoginkgoites belong to the same plant. [6] [11]
Invertebrate fossils from the Boren pits include conchostracans (clam shrimps) and clams, as well as numerous Scoyenia burrow trace fossils likely made by a crayfish-like decapod. Vertebrate remains are more common in the Pomona pit, which has preserved the fragmentary remains of archosaurs, phytosaurs, and synapsids, as well as fish bones and scales. Fossil footprints and trackways of tetrapods have also been recorded from the Pomona pit (with a single print from the Boren pit), including bipedal three-toed footprints that may have been made by early dinosaurs. [2] [9]
Only vertebrate fossils are known from the upper Pekin NCPALEO 1902 locality, and include a variety of archosaurs and synapsids typical of Late Triassic North America. The vertebrate fauna of the Pekin Formation has been used to correlate it with strata in western North America, such as the Chinle Formation, with some genera (e.g. Placerias , Coahomasuchus ) being shared between eastern and western North America. [8] [9]
Color key
| Notes Uncertain or tentative taxa are in small text; |
The online collections of the North Carolina Museum of Natural Sciences list tooth fragments of " Archosaurus " sp. and Uatchitodon kroehleri , as well as a humerus fragment of " Rhynchosaurus " sp. [12] Archosaurus and Rhynchosaurus are likely only provisional labels.
Phytosaurs of the Pekin Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
A. lineatus | Pomona pit | Trackways and isolated prints. [9] | Phytosaur footprints. | ||
Phytosauria indet. | Indeterminate | NCPALEO1902 | Currently undescribed. [8] | ||
? Rutiodon | ?R. carolinensis | Rostrum fragment | Originally misidentified as the sacrum of a large fossil bird and named "Palaeonornis struthionoides". [13] |
Pseudosuchians of the Pekin Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
cf. Brachychirotherium isp. | Pomona pit | Numerous isolated tracks. [9] | Tracks similar to Brachychirotherium, but differ in having a functionally tridactyl foot with reduced first digit and fifth digit positioned further back. Lack unequivocal hand impressions. [9] | ||
Crocodylomorpha indet. [7] | Indeterminate | NCPALEO 1902 | A nearly complete articulated skeleton. [14] | A small-bodied basal crocodylomorph, currently undescribed. | |
C. carolinensis | NCPALEO 1902 | A partial skull and fragmentary postcranial skeleton. [7] [10] | A large, possibly bipedal predatory crocodylomorph. | ||
C. chathamensis | NCPALEO 1902 | "Largely articulated, anterior portion of a skeleton". [8] | |||
G. pekinensis | NCPALEO 1902 | 10 articulated rows of osteoderms from the front half of the animal. [15] | A desmatosuchine aetosaur. Unique among aetosaurs for having spines on both its dorsal and lateral osteoderms around the neck. | ||
Longosuchus sp. | Pomona pit | Osteoderms [15] | A desmatosuchine aetosaur. Material referred to it may actually belong to Lucasuchus. | ||
L. hunti | Pomona pit | Osteoderms [15] | A desmatosuchine aetosaur. | ||
| Possibly a herbivorous aetosauriform related to Revueltosaurus . Initially reported from the Pekin Formation, but actually from the overlying Cumnock Formation. [16] | ||||
Revueltosaurus sp. | Teeth | Unpublished, listed in the online collections of the North Carolina Museum of Natural Sciences. [12] |
Synapsids of the Pekin Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
B. jeffersoni | NCPALEO 1902 | A herbivorous traversodontid cynodont, also known from Virginia. | |||
P. hesternus | Pomona pit | Fragmentary cranial and postcranial bones. | Originally identified only on the assumption that Placerias was the only dicynodont from Late Triassic North America, later examination confirmed this assignment. [19] | ||
Stahleckeriidae indet. | Indeterminate | NCPALEO 1902 | A partial complete skeleton preserving the back half of the animal just ahead of the sacrum. [20] | A stahleckeriid dicynodont distinct from Placerias, currently undescribed and so its affinities are unclear. [19] |
Ray-finned fishes of the Pekin Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
Redfieldiiformes indet. | Indeterminate | Undetermined scales and bones. [21] | An indeterminate freshwater redfieldiid fish. |
Crustaceans of the Pekin Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
C. sp. | A clam shrimp. | ||||
Scoyenia | S. sp. | Traces of possible decapod burrows. [21] |
A diverse flora is known from the formation: [21] [22] [23]
Plants of the Pekin Formation | |||
---|---|---|---|
Genus | Species | Notes | Images |
Cladophlebis | C. microphylla | Fronds of an indeterminate leptosporangiate fern. | |
Compsostrobus | C. neotericus | Male & female cones and foliage of a compsostrobacean conifer. [24] | |
Clathopteris | C. sp. | Fronds of a dipterid fern. | |
Cynepteris | C. sp. | Fronds of a cynepterid fern. | |
Danaeopsis | D. sp. | Fronds of a marattiid fern. | |
Eoginkgoites | E. sp. | Leaves of a williamsonacean bennettitale, superficially similar to those of ginkgos. Possibly the foliage of Williamsonia carolinensis. | |
Ischnophyton | I. iconicum | A bennettitale stem. [25] | |
Leptocycas | L. gracilis | Leaves, stems, and cones of a cycad, including intact specimens. [6] [26] Possibly a member of the Zamiaceae. [27] | |
Lonchopteris | L. virginiensis | Fern fronds. The species has sometimes been considered referable to another fern genus, Cynepteris . | |
Matridiostrobus | M. sp. | Female conifer cones. | |
Neocalamites | N. virginiensis | Leaves and stems of a large neocalamitaceous equisetale (horsetail relative). | |
N. knowltoni | |||
Otozamites | O. powelli | Leaves of a williamsonacean bennettitale. | |
O. hespera | |||
Pekinopteris | P. auriculata | Fronds of a schizaealean fern. [28] | |
Pelourdea | P. sp. | Conifer (possibly gnetophyte) leaves. | |
Phlebopteris | P. smithii | Fronds of a matoniaceous fern. | |
Phoenicopsis | P. sp. | Leaves of a czekanowskialean gymnosperm, distantly related to ginkgos. | |
Pseudoctenis | P. sp. | Cycad leaves. | |
Pterophyllum | P. sp. | Leaves of a williamsonacean bennettitale. | |
Voltzia | V. andrewsii | Seed cones of a voltzian conifer. [29] | |
Williamsonia | W. carolinensis | Female reproductive structure of a williamsonacean bennettitale, possibly belonging to the same plant as Eoginkgoites. | |
Wingatea | W. sp. | Fronds of a gleicheniaceous fern. |
Revueltosaurus is an extinct genus of suchian pseudosuchian from Late Triassic deposits of New Mexico, Arizona and North Carolina, United States. Many specimens, mostly teeth, have been assigned to Revueltosaurus over the years. Currently, three species are included in this genus, all of which were originally thought to represent monospecific genera of basal ornithischian dinosaurs. Revueltosaurus was about 1 meter long.
Rutiodon is an extinct genus of mystriosuchine phytosaurs from the Late Triassic of the eastern United States. The type species of Rutiodon, Rutiodon carolinensis, encompasses a large number of skulls and assorted postcranial fossils discovered in the Cumnock Formation of North Carolina. Fossils referable to the species are also known from Pennsylvania, New Jersey, and Virginia. Rutiodon carolinensis is the most well-described species of phytosaur in eastern North America, though its validity as a natural taxon has been questioned. Some paleontologists also recognize a larger and more robust species, Rutiodon manhattanensis, which is known from teeth and postcranial fossils from New Jersey and Pennsylvania.
The Newark Supergroup, also known as the Newark Group, is an assemblage of Upper Triassic and Lower Jurassic sedimentary and volcanic rocks which outcrop intermittently along the east coast of North America. They were deposited in a series of Triassic basins, the Eastern North American rift basins, approximately 220–190 million years ago. The basins are characterized as aborted rifts, with half-graben geometry, developing parallel to the main rift of the Atlantic Ocean which formed as North America began to separate from Africa. Exposures of the Newark Supergroup extend from South Carolina north to Nova Scotia. Related basins are also found underwater in the Bay of Fundy. The group is named for the city of Newark, New Jersey.
Litargosuchus is a sphenosuchian crocodylomorph, a basal member of the crocodylomorph clade from the Early Jurassic of South Africa. Its genus name Litargosuchus is derived from Greek meaning "fast running crocodile" and its species name leptorhynchus refers to its gracile snout. Litargosuchus, along with all of South Africa's crocodylomorph taxa, are confined to the upper Elliot Formation (UEF) in South Africa.
The Ischigualasto Formation is a Late Triassic geological formation in the Ischigualasto-Villa Unión Basin of southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation dates to the late Carnian and early Norian stages of the Late Triassic, according to radiometric dating of ash beds.
Arganodus is an extinct genus of freshwater lungfish that had a wide global distribution throughout much of the Triassic period, with a single species surviving across Gondwana into the Cretaceous. It is the only member of the family Arganodontidae, although it is sometimes placed in the Ceratodontidae or synonymized with the genus Asiatoceratodus.
The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern Eastern Cape, southern Free State, and in the eastern KwaZulu-Natal provinces of South Africa. Outcrops and exposures are also found in several localities in Lesotho such as Qacha's Neck, Hill Top, Quthing, and near the capital, Maseru. The Elliot Formation is further divided into the lower (LEF) and upper (UEF) Elliot formations to differentiate significant sedimentological differences between these layers. The LEF is dominantly Late Triassic (Norian-Hettangian) in age while the UEF is mainly Early Jurassic (Sinemurian-Pliensbachian) and is tentatively regarded to preserve a continental record of the Triassic-Jurassic boundary in southern Africa. This geological formation is named after the town of Elliot in the Eastern Cape, and its stratotype locality is located on the Barkly Pass, 9 km north of the town.
Coahomasuchus is an extinct genus of aetosaurine aetosaur. Remains of the genus have been found from deposits in Texas and North Carolina that date to the Otischalkian faunachron of the Late Triassic. It was small for an aetosaur, being less than 1.5 metres long. The dorsal plates are distinctively flat and unflexed, and have a faint sub-parallel to radial ornamentation. The genus lacked spines or keels on these plates, features seen in many other aetosaurs. Coahomasuchus was very similar in appearance to the closely related Aetosaurus.
Euscolosuchus is an extinct genus of suchian archosaurs from the Late Triassic of Virginia. It is probably an aetosauriform, as the sister taxon to Acaenasuchus and a relative of aetosaurs.
Notochampsa is an extinct genus of protosuchian crocodyliform. Fossils have been found from the lower Clarens Formation of the Karoo Supergroup in South Africa, dating back to the Pliensbachian stage of the Early Jurassic. Notochampsa comes from a period of relative fossil scarcity, and is the youngest known occurrence of a crocodylomorph from the Karoo Basin of South Africa.
The Cow Branch Formation is a Late Triassic geologic formation in Virginia and North Carolina in the eastern United States. The formation consists of cyclical beds of black and grey lacustrine (lake) mudstone and shale. It is a konservat-lagerstätte renowned for its exceptionally preserved insect fossils, along with small reptiles, fish, and plants. Dinosaur tracks have also been reported from the formation.
Uatchitodon is an extinct genus of Late Triassic reptile known only from isolated teeth. Based on the structure of the teeth, Uatchitodon was probably a carnivorous archosauromorph. Folded grooves on the teeth indicate that the animal was likely venomous, with the grooves being channels for salivary venom. The teeth are similar to those of living venomous squamates such as Heloderma and venomous snakes. Uatchitodon is the earliest known venomous reptile.
Boreogomphodon is an extinct genus of traversodontid cynodonts from the Late Triassic of the eastern United States. Fossils have been found from the Turkey Branch Formation in Virginia and the Pekin Formation of North Carolina.
The Cumnock Formation is a Late Triassic-age geologic formation in North Carolina. It is found in the Sanford sub-basin of the Deep River Basin, the southernmost of the large Mesozoic basins forming the Newark Supergroup. It is the middle unit of the Chatham Group, overlying the Pekin Formation and underlying the Sanford Formation. Both of these encompassing formations are primarily red sandstone. The Cumnock Formation, on the other hand, represents a sequence of darker lacustrine (lake) or paludal (swampy/marshy) sediments deposited in a tropical climate. These primarily include shales and coal, with some thin layers of coarser sediment such as siltstone and sandstone.
The Chatham Group is a Triassic-age geologic group in the eastern United States. It is one of the most fossiliferous sections of the Newark Supergroup, preserving much of the Late Triassic up until the Triassic-Jurassic mass extinction. The group was originally named to refer to Triassic rocks specifically within the Deep River Basin of North Carolina. Later studies have utilized it to encompass Late Triassic strata in most other sedimentary basins in the Newark Supergroup.
Lindsay E. Zanno is an American vertebrate paleontologist and a leading expert on theropod dinosaurs and Cretaceous paleoecosystems. She is the Head of Paleontology at the North Carolina Museum of Natural Sciences and an Associate Research Professor in the Department of Biological Sciences at North Carolina State University.
Carnufex is an extinct genus of crocodylomorph suchian from the Late Triassic of North America. The genus was first described in 2015 by Zanno et al., who named the binomial Carnufex carolinensis, meaning "Carolina butcher". Two specimens are known, the holotype skull and skeleton NCSM 21558, and the referred humerus NCSM 21623. The specimens are from the Carnian-age Pekin Formation, which dates to 231 million years ago. Based on the holotype, Carnufex would have been about 3 m (9.8 ft) long and 1.5 m (4.9 ft) tall, although it may have gotten larger due to the holotype not being fully grown.
The Sanford Formation is a Late Triassic (Norian)-age geologic formation in North Carolina. It is mainly found in the Sanford sub-basin of the Deep River Basin, the southernmost of the large Mesozoic basins forming the Newark Supergroup. It is the highest unit of the Chatham Group, overlying the dark lake and swamp sediments of the Cumnock Formation. The Sanford Formation is composed primarily of coarse red sediments such as conglomerates, sandstones, and mudstones. The conglomerate layers contain pebbles of schist and slate, with the occasional large boulders of granite.
The Timezgadiouine Formation, sometimes spelled as the Timesgadiouine Formation, is a Triassic geological formation in the Argana Basin of Morocco. It is a succession of red bed sediments spanning from the Olenekian to at least the Carnian, encompassing members T3 to T5 of the Argana Group. It is preceded by the Permian Ikakern Formation and succeeded by the Late Triassic Bigoudine Formation.
Eoginkgoites is an extinct form genus of bennettitalean leaves from the Late Triassic of North America. Despite its palmate (hand-shaped) appearance similar to some early ginkgo species, it belongs to a different gymnosperm order, the Bennettitales. The leaf is deeply segmented into five to seven narrow, club-shaped lobes which twist around a very short rhachis. This leads to an overall fan-shaped leaf situated at the end of a long petiole. The leaf has paracytic stomata and veins which strongly branch and lead to a marginal vein at the edge of each leaflet. These structural traits are all shared with benettitaleans. Williamsonia carolinensis, an ovule-bearing bennettitalean cone, has been found closely associated with Eoginkgoites leaves, seemingly confirming its benettitalean identity.
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