scholarly journals Revisiting stepwise ocean oxygenation with authigenic barium enrichments in marine mudrocks

Geology ◽  
2021 ◽  
Author(s):  
Guang-Yi Wei ◽  
Hong-Fei Ling ◽  
Graham A. Shields ◽  
Simon V. Hohl ◽  
Tao Yang ◽  
...  
Keyword(s):  
Temporal Trend ◽  
Global Ocean ◽  
Early Cambrian ◽  
Early Paleozoic ◽  
Secular Changes ◽  
Oxygenation Level ◽  
Geochemical Indices ◽  
Late Neoproterozoic ◽  
Redox Evolution

There are current debates around the extent of global ocean oxygenation, particularly from the late Neoproterozoic to the early Paleozoic, based on analyses of various geochemical indices. We present a temporal trend in excess barium (Baexcess) contents in marine organic-rich mudrocks (ORMs) to provide an independent constraint on global ocean redox evolution. The absence of remarkable Baexcess enrichments in Precambrian (>ca. 541 Ma) ORMs suggests limited authigenic Ba formation in oxygen- and sulfate-deficient oceans. By contrast, in the Paleozoic, particularly the early Cambrian, ORMs are marked by significant Baexcess enrichments, corresponding to substantial increases in the marine sulfate reservoir and oxygenation level. Analogous to modern sediments, the Mesozoic and Cenozoic ORMs exhibit no prominent Baexcess enrichments. We suggest that variations in Baexcess concentrations of ORMs through time are linked to secular changes in the marine dissolved Ba reservoir associated with elevated marine sulfate levels and global ocean oxygenation. Further, unlike Mo, U, and Re abundances, significant Baexcess enrichments in ORMs indicate that the overall ocean oxygenation level in the early Paleozoic was substantially lower than at present.

Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation

2019 ◽  
Vol 484 (1) ◽  
pp. 61-65
Author(s):  
R. M. Antonuk ◽  
A. A. Tretyakov ◽  
K. E. Degtyarev ◽  
A. B. Kotov
Keyword(s):  
Complex Formation ◽  
Central Asian Orogenic Belt ◽  
Early Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Central Asian ◽  
Geochronological Study ◽  
Three Stages ◽  
Late Neoproterozoic ◽  
Quartz Monzodiorites

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

Challenging the dipolar paradigm for Proterozoic Earth

2022 ◽  
Author(s):  
James W. Sears
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Inner Core ◽  
Ultraviolet B ◽  
Late Permian ◽  
Early Paleozoic ◽  
Thin Spherical Shell ◽  
Late Neoproterozoic ◽  
Geocentric Axial Dipole ◽  
Drift Path

ABSTRACT A robust, geology-based Proterozoic continental assembly places the northern and eastern margins of the Siberian craton against the southwestern margins of Laurentia in a tight, spoon-in-spoon conjugate fit. The proposed assembly began to break apart in late Neoproterozoic and early Paleozoic time. Siberia then drifted clockwise along the Laurussian margin on coast-parallel transforms until suturing with Europe in late Permian time. The proposed drift path is permitted by a geocentric axial dipole (GAD) magnetic field from Silurian to Permian time. However, the Proterozoic reconstruction itself is not permitted by GAD. Rather, site-mean paleomagnetic data plot ted on the reconstruction suggest a multipolar Proterozoic dynamo dominated by a quadrupole. The field may have resembled that of present-day Neptune, where, in the absence of a large solid inner core, a quadrupolar magnetic field may be generated within a thin spherical shell near the core-mantle boundary. The quadrupole may have dominated Earth’s geomagnetic field until early Paleozoic time, when the field became erratic and transitioned to a dipole, which overwhelmed the weaker quadrupole. The dipole then established a strong magnetosphere, effectively shielding Earth from ultraviolet-B (UV-B) radiation and making the planet habitable for Cambrian fauna.

Early Cambrian Seismic Events and Their Tectonic Significance in Western Zhejiang

2012 ◽  
Vol 524-527 ◽  
pp. 42-48
Author(s):  
Fu Sheng Guo ◽  
Zhao Bin Yan ◽  
Liu Qin Chen
Keyword(s):  
Seismic Event ◽  
Regional Distribution ◽  
Sedimentary Rocks ◽  
Seismic Events ◽  
Time Interval ◽  
Early Cambrian ◽  
Distribution Characteristics ◽  
Early Paleozoic ◽  
Tectonic Events ◽  
Tectonic Significance

The two early Cambrian seismic events could be found from sedimentary rocks at Peilingjiao section of Kaihua County, Baishi and Fangcun sections of Changshan County in western Zhejiang, except for Jiangshan area. The seismic event at Baishi outcrop can be correlated to the second seismic event at Peilingjiao section. Taking Fangcun as epicenter of the second seismic event, the magnitude of paleoseism in western Zhejiang is about 7~7.6. According to investigation on regional distribution of seismic events, the two seismic activities should be regulated by large Kaihua-Chun’an fault, but unrelated with Jiangshan-Shaoxing fault or Changshan-Xiaoshan fault. However, the formation time of Kaihua-Chun’an fault has not yet been determinate. Based on controlling on Silurian, the possible formation age was inferred to early Paleozoic. The distribution characteristics of seismites indicate that the Kaihua-Chun’an fault was already being active during early Cambrian and seismic activities may be response to Sinian tectonic events in western Zhejiang. By the way of analysis on paleoseismic rhythm, the time interval of the two seismic events in western Zhejiang is less than 5.0 Ma, which may be the result of early frequent activities of Kaihua-Chun’an fault.

Occurrence of the siliceous sponge spicule Konyrium (Hexactinellida) in the upper Cambrian of the Mackenzie Mountains, northwestern Canada

2002 ◽  
Vol 76 (3) ◽  
pp. 565-569 ◽  
Author(s):  
Brian R. Pratt
Keyword(s):  
Fossil Record ◽  
Southern China ◽  
South Australia ◽  
Early Cambrian ◽  
Siliceous Sponge ◽  
Sponge Spicule ◽  
Animal Phyla ◽  
Sponge Diversity ◽  
Siliceous Sponges ◽  
Late Neoproterozoic

The fossil record of siliceous sponges—Hexactinellida and demosponge “Lithistida”—hinges upon both body fossils plus isolated spicules mostly recovered from limestones by acid digestion. The earliest record of siliceous sponge spicules extends back to the late Neoproterozoic of Hubei, southern China (Steiner et al., 1993) and Mongolia (Brasier et al., 1997), and body fossils attributed to the hexactinellids have been described from the Ediacaran of South Australia (Gehling and Rigby, 1996); thus they are the oldest-known definite representatives of extant animal phyla. The Early Cambrian saw a remarkable diversification in spicule morphology, with the appearance of an essentially “modern” array of forms (Zhang and Pratt, 1994). While a diversity decline may have occurred with the late Early Cambrian extinction(s), the subsequent Paleozoic and Mesozoic fossil record of spicules shows a relatively consistent range of morphologies (e.g., Mostler, 1986; Bengtson et al., 1990; Webby and Trotter, 1993; Kozur et al., 1996; Zhang and Pratt, 2000). However, because spicule form is not restricted to individual taxa and many sponge species secrete a variety of spicule shapes, it is difficult to gauge true siliceous sponge diversity and to explore their biostratigraphic utility using only isolated spicules.

Early Cambrian multiple-sourced plutonism in the Eastern Sierras Pampeanas, Córdoba, Argentina: Implications for the evolution of the early Paleozoic Gondwana margin

2021 ◽  
Vol 106 ◽  
pp. 103048
Author(s):  
Alina M. Tibaldi ◽  
Juan E. Otamendi ◽  
Alejandro H. Demichelis ◽  
Matías G. Barzola ◽  
Fernando Barra ◽  
...  
Keyword(s):  
Early Cambrian ◽  
Early Paleozoic ◽  
Sierras Pampeanas ◽  
Eastern Sierras Pampeanas ◽  
Gondwana Margin
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