An official website of the United States government
The Junggar and Turpan basins of Xinjiang, northwest China, host a well-preserved terrestrial Permo-Triassic boundary sequence exposed on the flanks of the Bogda Mountains. During the Permo-Triassic, this region was located in mid-latitude northeast Pangaea (~45°N), making it an important comparison to the higher latitude record preserved in the South African Karoo Basin (~60°S). Broad similarities exist between the tetrapod records of both areas, such as the reported co-occurrence of Dicynodon-grade dicynodontoids and Lystrosaurus in the upper Permian and the high abundance of Lystrosaurus in the Lower Triassic. In the Bogda sections, the Permo-Triassic boundary falls within the upper Guodikeng Formation (= upper Wutonggou low order cycle), but several horizons have been proposed based on biostratigraphy, chemostratigraphy, and paleomagnetic data. A new Bayesian age model calibrated by multiple radiometric dates and tied to detailed litho- and cyclostratigraphic data offers new insight into the location of the Permo-Triassic boundary in Xinjiang and the opportunity to reconsider tetrapod occurrences in a highly resolved chronostratigraphic framework. We investigated the positions of new and historic tetrapod specimens relative to the revised Permo-Triassic boundary, including uncertainties about the locations of key historic specimens. The stratigraphic range of Dicynodon-grade dicynodontoids in Xinjiang is poorly constrained: most specimens, including the holotype of Jimusaria sinkianensis, cannot be precisely placed relative to the Permo-Triassic boundary. A new specimen of Turfanodon sp. for which we have reliable data occurs in the upper Permian. Despite their previous treatment as Permian in age, most Bogda chroniosuchians were collected in strata above the Permo- Triassic boundary and the therocephalian Dalongkoua fuae also may be Triassic. Some prior placements of the Permo- Triassic boundary in Xinjiang imply an upper Permian lowestoccurrence for Lystrosaurus, but all Lystrosaurus specimens that we can precisely locate fall above the Permo-Triassic boundary. The high abundance of Lystrosaurus in the Early Triassic of Xinjiang likely parallels an Early Triassic age for the interval of greatest Lystrosaurus abundance in the Karoo Basin, but additional research is needed to determine whether there was a single, globally synchronous time of highest Lystrosaurus abundance.
more »
« less
The Fremouw Formation of Antarctica: Updated vertebrate fossil record and reevaluation of high-latitude Permian–Triassic paleoenvironments
Permian–Triassic rocks of the Transantarctic Basin provide an unparalleled record of high latitude paleoenvironments and terrestrial vertebrate faunas. Here we summarize the taxonomic and paleoecological implications of the approximately 1300 vertebrate fossils collected since 1968, as well as report on new geologic field observations made during the 2017–18 austral field season. The Fremouw Formation records a vertebrate assemblage taxonomically most similar to that of the Karoo Basin of South Africa, with 10 genera shared in common. However, temnospondyls form a much greater percentage of tetrapod occurrences in the Fremouw Formation, suggesting favorable conditions for these ectothermic fossil amphibians at high latitudes. Lower Triassic small reptiles (viz. Procolophon, Prolacerta) occur in slightly higher proportions than in the Karoo, but their taxonomic diversity is likely undercounted. Seven stratigraphic columns of the upper Buckley and lower–middle Fremouw formations detail fluvial depositional environments in the central Transantarctic region, recording a shift from wet swamp lands to drier floodplains, most similar to Gondwanan basins in Australia. Fremouw Formation paleosols primarily consist of Protosols, which indicate poor soil forming conditions likely due to low precipitation and high sediment supply from crevasse splays. Mineralogy from X-ray diffraction, review of igneous intrusives, and Buckley Formation coal characterization demonstrate post-pedogenic diagenetic alteration that casts doubt on the results of previous stable isotopic studies of these paleosols. Tetrapod fossils first appear in the Fremouw Formation, which has been taken as evidence for immigration to the Antarctic portion of southern Pangea around the time of the end-Permian mass extinction. However, this may be due to higher soil pH, increased base saturation, lower moisture content, and more rapid burial conditions in the Fremouw than the underlying Buckley Formation that favored bone preservation.
more »
« less
- Award ID(s):
- 1947094
- PAR ID:
- 10504952
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Earth-Science Reviews
- Volume:
- 246
- Issue:
- C
- ISSN:
- 0012-8252
- Page Range / eLocation ID:
- 104587
- Subject(s) / Keyword(s):
- Antarctica Fremouw Formation, Triassic
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Global temperatures significantly changed from the late Permian to the Early Triassic: the Earth transformed from a cool world to a hothouse climate. This transition undoubtedly had a strong impact on tetrapod physiology and distribution. During the global cooling, tetrapods generally increased their size; and the currently recognized late Permian tetrapod extinction, exemplified by the record preserved in the South African Karoo Basin, occurred in the late stage of cooling. Rapid warming in the Early Triassic is predicted to have resulted in extinctions and/or local extirpation of low latitude tetrapods, but the very limited fossil record from this region makes testing this hypothesis difficult. Warming is predicted to have had less negative impacts on the tetrapod diversity of mid-latitudes, and promoted the success of tetrapods in the high latitudes. Based on the known fossil record, a tetrapod gap could have existed in central Pangea between ~30◦ N and ~ 40◦S, and lasting from the Induan to the early Spathian. However, the exact boundaries of this gap likely varied over time, and it could have encompassed a larger area during the hottest phases (Griesbachian and near the Smithian–Spathain boundary).more » « less
-
null (Ed.)ABSTRACT A distinctive burrow form, Reniformichnus australis n. isp., is described from strata immediately overlying and transecting the end-Permian extinction (EPE) horizon in the Sydney Basin, eastern Australia. Although a unique excavator cannot be identified, these burrows were probably produced by small cynodonts based on comparisons with burrows elsewhere that contain body fossils of the tracemakers. The primary host strata are devoid of plant remains apart from wood and charcoal fragments, sparse fungal spores, and rare invertebrate traces indicative of a very simplified terrestrial ecosystem characterizing a ‘dead zone' in the aftermath of the EPE. The high-paleolatitude (∼ 65–75°S) setting of the Sydney Basin, together with its higher paleoprecipitation levels and less favorable preservational potential, is reflected by a lower diversity of vertebrate fossil burrows and body fossils compared with coeval continental interior deposits of the mid-paleolatitude Karoo Basin, South Africa. Nevertheless, these burrows reveal the survivorship of small tetrapods in considerable numbers in the Sydney Basin immediately following the EPE. A fossorial lifestyle appears to have provided a selective advantage for tetrapods enduring the harsh environmental conditions that arose during the EPE. Moreover, high-paleolatitude and maritime settings may have provided important refugia for terrestrial vertebrates at a time of lethal temperatures at low-latitudes and aridification of continental interiors.more » « less
-
We report U-Pb age determinations of carbonate nodules from an in situ paleosol horizon in the Upper Permian Balfour Formation and from several horizons of pedogenic nodule conglomerate (PNC) in the Triassic Katberg Formation, Karoo Basin, South Africa, using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). The paleosol sample yields an age of 252 ± 3 Ma, which overlaps with a previous high-precision U-Pb zircon date from a volcanic ash deposit 2 m above the paleosol. This relationship demonstrates the reliability of using LA-ICP-MS dating techniques on terrestrial pedogenic calcite. Two PNC samples collected at the base of the Katberg Formation within the same sandstone unit yield ages of 255 ± 3 Ma and 251 ± 3 Ma. The age of 251 ± 3 Ma overlaps with the high-precision U-Pb zircon date below the PNC and is a maximum age estimate of deposition for the base of the Katberg Formation. Our results show that reworked nodules in the same concentrated conglomerate lag can be of different ages, but that similarly aged nodules are spatially associated. In addition, two PNC samples collected higher in the section yield ages of 249 ± 3 Ma and 241 ± 3 Ma, providing maximum depositional ages for the lower to middle Katberg Formation for the first time. We demonstrate that pedogenic carbonate nodules can be dated with meaningful precision, providing another mechanism for constraining the age of sedimentary sequences and studying events associated with the Permian−Triassic transition in the central Karoo Basin, even though the extinction boundary may not be preserved in this area.more » « less
-
The geology of the Schroeder Hill region near the head of the Shackleton Glacier, central Transantarctic Mountains, consists of Triassic Fremouw Formation and overlying Falla Formation strata intruded by Jurassic Ferrar Dolerite sills. At ‘Alfie’s Elbow', south-east of Schroeder Hill, upper Fremouw strata are overlain by Upper Cenozoic Sirius Group deposits. These upper Fremouw beds differ from all other examined upper Fremouw strata in the Shackleton Glacier region in being carbonaceous. Quartz-pebble conglomerate characterizes the basal Falla beds, emphasizing a change in provenance. Sirius Group beds occur as a stratigraphic succession draped on modern topography and as structureless sand wedged in modern microtopography. Fremouw beds locally are arched with the fold axis approximately parallel to regional normal faulting related to the uplift and formation of the Transantarctic Mountains.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.earscirev.2023.104587
