The Kirkwood Formation is a geological formation found in the Eastern and Western Cape provinces in South Africa. It is one of the four formations found within the Uitenhage Group of the Algoa Basin – its type locality – and in the neighbouring Gamtoos Basin. Outcrops of the Kirkwood are also found along the Worcester-Pletmos, Herbertsdale-Riversdale, Heidelberg-Mossel Bay, and Oudtshoorn-Gamtoos basin lines. At these basins the Kirkwood Formation underlies the Buffelskloof Formation and not the Sundays River Formation.John Pether (April 2014) Extension of quarrying on Portion 12 of Farm Hartenbosch 217 (Maandagskop Crusher), Mossel Bay, Western Cape. Brief Palaeontological Assessment (Desktop Study). Link:http://www.phsconsulting.co.za/uploads/7593872PIA%20Brief%20Maandagskop.pdf
Geology The Kirwood Formation was formed along the southern section of South Africa during the break up of Gondwana. Dating it has proven tricky, with some regarding it as a Late Jurassic (~145 Ma) or Early Cretaceous deposit (~135 Ma). However, dating the Kirkwood's abundant volcanic ash layers by U-Pb methods is currently underway.
The Kirkwood Formation is composed of sedimentary rocks deposited under fluvial conditions at or near sea level, such as variegated mudstone (an iconic feature), medium-grained lithic sandstone (often being charcoal-rich), and sporadic conglomerates. At its base, the Kirkwood Formation includes a significant deposit of fine-to-medium grained, poorly-sorted (often quartzitic) estuarine sandstone with subordinate dark grey to brow shale layers. This deposit was described as the Swartkops Member. The lower portion of the remainder of the Formation is composed predominantly of siltstones, but includes a smaller sandstone layer (described as part of the Bethelsdorp Member). The upper portion of the Formation is composed predominantly of fine, clay-rich mudstones, with multiple smaller layers of estuarine sandstone.<
The Kirkwood is the second formation of the Uitenhage Group, positioned between the overlying Sundays River Formation and the underlying Enon Formation. Only three geological members have been described within it: the Swartkops Member which contains estuarine sandstone deposits and lacks fossils. The Colchester Member is the most fossil-rich containing terrestrial and lacustrine fossils and is composed of dark grey shale, siltstones and sandstones. The third, the Bethelsdorp Member, resembles the Colchester in containing dark-grey shales and sandstone, and contains marine microfossils. The upper section of the member is overlain by mudstone and siltstone.
Paleontology
Fragmentary remains of various reptile, frog, insect, and mammal fossils have also been found, including fish scales and freshwater bivalves. In addition several plant species such as bryophytes, ferns, conifers, cycads, and bennettitaleans have been discovered, including silicified fossil tree trunks in the sandstone sections which show evidence of being burned. Amber from possible Araucariaceae tree have been reported.
Actinopterygii +Fishes of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageHolostei indet.indeterminateSite 6Scale fragmentsClosely resembling Lepisosteus, but specific placement unknownTeleostei indet.indeterminateSite 6Partial toothSpecific placement unknown
Lepidosaurs +Lepidosaurs of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageSquamata indet. indeterminateKirkwood Cliffs ‘Lookout’BraincaseSpecific placement unknownSphenodontia indet. indeterminateKirkwood Cliffs ‘Lookout’and Site 6Palatine and dentary remainsDifferent from aff. Opisthias sp. from the same formationaff. Opisthias sp.indeterminateSite 15Jaw fragment
Testudines +Testudines of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageTestudinata indet.indeterminateSite 6 and Site 16Shell fragmentsSpecific placement unknown
Pseudosuchia +Pseudosuchians of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageMesosuchia indet.indeterminateSite 6 and site 15Dental remains, incomplete osteoderms and large (72 mm) centrumSpecific placement unknown
Dinosaurs Theropods +Theropods of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageTheropoda indet. indeterminateUnknownSingle tooth (MB R2352)Specific placement unknown, estimated tooth size large as TyrannosaurusTheropoda indet.indeterminateSite 6Dental remainsMuch smaller than MB R2352, probably represents other group of small or juvenile theropodTetanurae indet.indeterminateKirkwood Cliffs ‘Lookout’Proximal femurProbable basal tetanuranNqwebasaurusN. thwaziAlmost complete skeleton (AM 6040)Basalmost Ornithomimosaur
Sauropods +Sauropods of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageAlgoasaurusA. bauriPort Elizabeth Brick and Tile Company QuarryA cervical vertebra, femur, an ungual phalanx and a scapulaNeosauropod with uncertain placement Brachiosauridae indet.indeterminateUmlilo Game FarmVertebrae remainsDicraeosauridae indet.indeterminateOutskirts of KwaNobuhle Township, 3.3 km south of Uitenhage.Vertebrate remainsDiplodocinae indet.indeterminateKirkwood Cliffs ‘Lookout’Cadual vertebraeEusauropoda indet.indeterminateUmlilo Game FarmVertebrae remainsRepresents either a non-neosauropod eusauropod or a non-titanosauriform macronarianTitanosauriformes indet.indeterminateSite 15Dental remainsInitially reported as Camarasauridae, aff.Pleurocoelus sp., and aff. Astrodon sp., but subsequent research suggested taxonomic assignment anything lower than indeterminate titanosauriform not available.
Ornithischians +Ornithischians of the Kirkwood FormationGenusSpeciesRegionMemberMaterialNotesImageParanthodonP. africanusBushmans River, Woodbury FarmPartial skull and incomplete vertebraA Stegosaurid Stegosaur.IyukuI. raathiKirkwood Cliffs ‘Lookout’Uppermost memberAt least 27 individuals, from juveniles and hatchlings.A Dryosaurid ornithopod.
References