DSpace Collection:

First multi-proxy chronostratigraphy of the lower Cambrian Byrd Group, Transantarctic Mountains and correlation within East Gondwana

2024-08-01T00:00:00Z

Title: First multi-proxy chronostratigraphy of the lower Cambrian Byrd Group, Transantarctic Mountains and correlation within East Gondwana Authors: Betts Marissa J.; Claybourn Thomas M.; Holmer Lars E.; Skovsted Christian B.; Myrow Paul M.; Stemmerik Lars; Topper Timothy P.; Park, Tae-Yoon S.; Hughes Nigel C.; Crowley James L.; Jagodzinski Elizabeth A.; Brock Glenn A. Abstract: Antarctica and Australia were sutured together at the equator during the major pulse of animal biodiversification associated with the Cambrian radiation. However, the lack of detailed systematic chemostratigraphic and biostratigraphic sampling of lower Cambrian sedimentary successions from Antarctica has significantly impeded precise age determination and correlation with Cambrian strata on other palaeocontinents. This study is the first to present integrated, simultaneously sampled biostratigraphic and chemostratigraphic (d13C isotopes) data from the same measured stratigraphic sections through the lower Cambrian Byrd Group in the Transantarctic Mountains. Shelly fossil assemblages (brachiopods, tommotiids, molluscs, bradoriids, trilobites) from the Holyoake Range and Churchill Mountains facilitate direct correlation with the Dailyatia odyssei Zone of South Australia (Cambrian Stages 3-4), and trilobites provide strong correlation between the Starshot Formation and the Cymbric Vale Formation in western New South Wales. A new ID-TIMS radiometric date of 514.96 +/- 0.16 Ma from a tuff in the lower Cymbric Vale Formation is similar to dates from tuff beds in the Third Plain Creek Member of the Mernmerna Formation in the Flinders Ranges, providing an important absolute-age tie point between these lower Cambrian successions. Chemostratigraphic data from the upper Shackleton Limestone in the Holyoake Range capture a negative d13C excursion that can be correlated to negative values within the multipeaked MICE (cycles V-VIII in Siberia). Integrated faunal and chemostratigraphic data indicate a Cambrian Stages 3-4 age, giving robust chronostratigraphic context for the upper Shackleton Limestone-Holyoake Formation-Starshot Formation succession for the first time, permitting reconstruction of the depositional history of the lower Cambrian of Antarctica and global correlation of Byrd Group strata. (c) 2024 International Association for Gondwana Research. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

A multi-proxy detrital study from Permian-Triassic fluvial sequences of Victoria Land (Antarctica): Implications for the Gondwanan basin evolution

2024-02-01T00:00:00Z

Title: A multi-proxy detrital study from Permian-Triassic fluvial sequences of Victoria Land (Antarctica): Implications for the Gondwanan basin evolution Authors: Zurli Luca; Liberato Giovanni Pio; Perotti Matteo; Woo Jusun; Lee, Mi Jung; Cornamusini Gianluca Abstract: One of the most complete Permian -Triassic fluvial sequences of the Beacon Supergroup, characterizing the infilling of the Transantarctic Basin, is recorded in the Allan Hills in Victoria Land (Antarctica). The multidisciplinary provenance approach carried out in this study includes UPb analysis on detrital zircons, chemistry on detrital mineral phases (garnet and white mica), and sandstone petrography. These, coupled with the data regarding the stratigraphic/sedimentological framework, provide a reconstruction of the geological history of the Permian -Triassic portion of the Beacon Supergroup, showing shifting clastic provenance from different source rocks. Results obtained from this integrated study support a source for the Permian Weller Coal Measures from the local basement, made up of very low- to high grade metamorphic rocks. A compositional shift is recorded with the Lower Triassic Feather Conglomerate, mainly linked with changes in the fluvial style, likely associated with tectonic activity. The Middle to Upper Triassic Lashly Formation shows the main provenance change, supporting a distal source region: the fluvial system received a volcanoclastic input derived from the PermianTriassic arc located to the east of the basin. The compositional and provenance variations, together with paleocurrent indicators, compared to the coeval units in the central Transantarctic Mountains, allow the reconstruction of the basin evolution and of the changing clastic drainage patterns. Data support the occurrence of articulated sub -basins where alluvial sedimentation settled, in which a morphological -structural divide was represented by the Ross High, separating during the Permian up to the Early Triassic the Victoria Land sub -basin from the main Transantarctic Basin. According to the changed composition of the Lashly Formation sandstones, it appears that in the Middle/Late Triassic, the Ross High was not more a morphological barrier, and that the Victoria Land sub -basin was joined with the Transantarctic foreland Basin.

Maskelynite- as seen in shocked Lonar target basalt, India, and martian and lunar meteorites

2024-01-01T00:00:00Z

Title: Maskelynite- as seen in shocked Lonar target basalt, India, and martian and lunar meteorites Authors: Ray Dwijesh; Misra Saumitra; Park, Changkun; Newsom Horton E.; Peterson Eric J. Abstract: In this study, we investigate the mineralogical and petrochemical characteristics of maskelynite occurring in a shocked basalt boulder from a terrestrial impact crater on a basaltic target - the Lonar impact crater in India, and the martian and lunar meteorites. The majority of Lonar maskelynite experienced solid-state transformation and maintained almost a uniform chemical composition, consistent with the unshocked feldspar. The locally flow-like texture and marginal vesiculation in feldspathic glass are needed in interaction with the impact-melt. The vesiculated melt occasionally occurring at the margins of maskelynite is characterised by Na-loss due to the shock-induced volatility. A shock pressure of <= 42 GPa and at a temperature of <= 1000 degrees C appear consistent for the formation of Lonar vesiculated melt/feldspathic glass. Under the impact-induced shock metamorphism, maskelynite samples from the moon retain both the crystalline and amorphous domains with a distinct chemical heterogeneity attributed to different shock metamorphism effects of the plagioclase. In contrast, the martian maskelynites exhibit a smooth, homogeneous composition. The estimated shock pressure is relatively higher at similar to 42-45 GPa based on experiments and models. The difference in Si/Al ratio in lunar (1-1.3) and martian maskelynite (1.5-1.9) suggests its inherent difference in composition of the crust, whereas the Lonar maskelynite shows overlapping composition with the martian maskelynite contending Lonar basalt as a potential terrestrial analogue to the martian crust.

Spreading rate, opening time, and kinematic history of the Ayu Trough

2023-01-01T00:00:00Z

Title: Spreading rate, opening time, and kinematic history of the Ayu Trough Authors: 최학겸; Kim Seung-Sep; Park, Sung Hyun; Lee Sang-Mook Abstract: The Ayu Trough, located in the equatorial western Pacific, is the only divergent boundary surrounding the Philippine Sea Plate. A mid-ocean ridge spreading in the N-S direction near low-latitude regions presents low geomagnetic anomalies, thereby complicating the constraining of the trough's spreading rate based on the geomagnetic signal from the magnetized seafloor. According to previous studies, the Ayu Trough has been open since & SIM;25 Ma, with a half-spreading rate of 4.1-8.1 mm/yr. This implies that the trough belongs to the ultraslow-spreading mid-ocean ridge category with a full-spreading rate below 20 mm/yr. However, the geochemical signatures of the rock samples from the Ayu Trough do not exhibit the unique characteristics of ultraslow-spreading ridges, including the enriched mid-ocean ridge basalts (E-MORB) with high rare earth element (REE) concentrations and abundant light rare earth elements (LREE). Rather, the sampled rocks from the entire trough-axis exhibit the typical features of the normal mid-ocean ridge basalts (N-MORB) with low REE concentrations. The contradictory inferences made from geochemical results suggest that the Ayu Trough did not undergo an ultraslow-spreading but rather a considerably rapid spreading over a short period compared to the estimates made by previous studies. The modified interpretation for the spreading rate of the Ayu Trough can be associated with the global plate reconstruction model, considering the major plate reorganization in East Asia. Around 15 Ma, a series of significant tectonic events occurred in East Asia and the western Pacific. The global models for East Asia imply that the spreading of the Ayu Trough could have been initiated afterwards. Based on our geochemical analysis of the MORB on the Ayu Trough and the global plate model, we argue that the spreading of the Ayu Trough was initiated after & SIM;15 Ma during the major plate reorganization in East Asia, and not in & SIM;25 Ma as reported by previous studies. Therefore, the spreading occurred only for a period of about 10 Myr at a relatively rapid full-spreading rate of >20 mm/yr. The massive sediments with a thickness of approximately 50-70 m on the spreading-axis of the Ayu Trough reinforce the estimated cessation time of the trough. In addition, the V-shaped seafloor of the Ayu Trough and the unclear transform fault may be interpreted as topography formed by a propagation of rift or mantle melting. Therefore, the trough does not have to be simultaneously opened throughout the axis, and its spreading rate could be higher than previously estimated.