Occurrence of anatase in reworking altered ash beds (K-bentonites and tonsteins) and discrimination of source magmas: a case study of terrestrial Permian–Triassic boundary successions in China

Clay Minerals ◽  
2021 ◽  
pp. 1-13
Author(s):  
Hanlie Hong ◽  
Xiaoxue Jin ◽  
Miao Wan ◽  
Kaipeng Ji ◽  
Chen Liu ◽  
...  
Keyword(s):  
Clay Fraction ◽  
Igneous Rocks ◽  
Stratigraphic Correlation ◽  
Triassic Boundary ◽  
Source Discrimination ◽  
Sediment Reworking ◽  
Volcanic Source ◽  
Marine Facies ◽  
Permian Triassic Boundary

Abstract Potential secondary influences on titanium distribution should be evaluated when using ash beds as volcanic source indicators and for correlation purposes. In this study, well-correlated altered ash beds in Permian–Triassic boundary (PTB) successions of various facies in South China were investigated to better understand their use in source discrimination and stratigraphic correlation. The ash beds deposited in lacustrine and paludal facies contain significantly more Ti relative to deposits in marine facies. Neoformed anatase grains nanometres to micrometres in size are associated closely with clay minerals, whereas detrital anatase was observed in the remnants of altered ash beds of terrestrial facies. Extraction of the clay fraction of altered ash beds may exclude significantly detrital accessory minerals such as anatase and rutile added during sediment reworking, and the concentrations of immobile elements in the clay fraction may therefore be used to interpret more effectively their source igneous rocks.

scholarly journals The Permian-Triassic boundary in Wyoming: the case of the disappearing paraconformity

1992 ◽  
Vol 6 ◽  
pp. 242-242
Author(s):  
James M. Renner ◽  
Donald W. Boyd
Keyword(s):  
Depositional Environment ◽  
Depositional Environments ◽  
Compelling Evidence ◽  
Carbonate Facies ◽  
Triassic Boundary ◽  
Physical Evidence ◽  
Depositional Processes ◽  
Marine Facies ◽  
Permian Triassic Boundary ◽  
Continuous Deposition

Long-standing interpretations of paleontologic, sedimentologic, and stratigraphic evidence from Permian-Triassic marine sequences in western Wyoming have suggested an interruption in deposition of several million years' duration between the two systems, even though physical evidence of unconformity is subtle and somewhat equivocal. We postulated that an unconformity of this duration should be more pronounced in paralic and non-marine facies in central and southeast Wyoming than in adjacent inner-shelf marine facies in westcentral Wyoming. Therefore, we correlated an erathem boundary-bearing sequence from westcentral Wyoming (where it is faunally controlled) to southeast Wyoming (where it is non-fossiliferous) and studied this sequence for evidence of hiatus. The correlations were made using surface sections, surface gamma-radiation logs, and subsurface log suites.In southeast Wyoming, the lithostratigraphic equivalent to the systemic boundary in westcentral Wyoming is located within a redbed-evaporite sequence traditionally interpreted as having accumulated in paralic and/or terrestrial depositional environments. Physical evidence of disconformity at this surface in southeast Wyoming is no greater, and is in places less, than at several other horizons within the boundary-bearing sequence. Also, petrologic examination of the terrigenous clastic units below, through, and above the boundary-bearing sequence in central and southeast Wyoming suggests notable stability of the depositional environment. Southeastward stratigraphic thinning of various units within this boundary-bearing sequence is demonstrable; however, compelling evidence of regional truncation is not evident, and the stratigraphic thinning appears to be due to primary depositional processes rather than post-depositional erosion during hiatus.We interpret slow, episodic, yet generally continuous deposition of evaporite and siliciclastic units in southeast Wyoming across the Permian-Triassic boundary. If true, then conventional biostratigraphic estimates of the duration of a hiatus separating Permian inner and middle-shelf carbonate facies from overlying Triassic siliciclastics in western Wyoming appear to be overly long, and may need re-evaluation.

scholarly journals Hg Isotopes and Enhanced Hg Concentration in the Meishan and Guryul Ravine Successions: Proxies for Volcanism Across the Permian-Triassic Boundary

2021 ◽  
Vol 9 ◽  
Author(s):  
Alcides Nóbrega Sial ◽  
Jiubin Chen ◽  
Christoph Korte ◽  
Manoj Kumar Pandit ◽  
Jorge E. Spangenberg ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Mass Extinction ◽  
Environmental Changes ◽  
Large Igneous Province ◽  
Stratigraphic Correlation ◽  
Mercury Deposition ◽  
Triassic Boundary ◽  
Framboidal Pyrite ◽  
Rare Earth Element Distribution ◽  
Permian Triassic Boundary

High-resolution organic carbon isotope (δ13C), Hg concentration and Hg isotopes curves are presented for the Permian-Triassic boundary (PTB) sections at Guryul Ravine (India) and Meishan D (China). The total organic carbon (TOC)-normalized Hg concentrations reveal more intense environmental changes at the Latest Permian Mass Extinction (LPME) and the earliest Triassic Mass Extinction (ETME) horizons coinciding with major δ13C shifts. To highlight palaeoredox conditions we used redox-sensitive elements and Rare Earth Element distribution. At Meishan, three Hg/TOC spikes (I, II, and III) are observed. Spike I remains after normalization by total aluminum (Al), but disappears when normalized by total sulfur (TS). Spike III, at the base of Bed 26, corresponds with excursions in the Hg/TS and Hg/Al curves, indicating a change in paleoredox conditions from anoxic/euxinic in the framboidal pyrite-bearing sediments (Bed 26) to oxygenated sediments (Bed 27). At Guryul Ravine, four Hg/TOC spikes were observed: a clear spike I in Bed 46, spike II at the base of the framboidal pyrite-rich Bed 49, spike III at the PTB, and spike IV at the LPME horizon. Some of these Hg/TOC spikes disappear when TS or Al normalization is applied. The spike I remains in the Hg/TS and Hg/Al curves (oxic conditions), spike II only in the Hg/TS curve (anoxic/euxinic), and spikes III and IV only in Hg/Al curves (oxic). In both sections, Hg deposition was organic-matter bound, the role of sulfides being minor and locally restricted to framboidal pyrite-bearing horizons. Positive mass-independent fractionation (MIF) for Hg odd isotopes (odd-MIF) was observed in pre-LPME samples, negative values in the LPME–PTB interval, and positive values above the ETME horizon. Most Hg-isotope patterns are probably controlled by the bathymetry of atmospheric Hg-bearing deposits. The source of Hg can be attributed to the Siberian Traps Large Igneous Province (STLIP). In the LPME-PTB interval, a complex of STLIP sills (Stage 2) intruded coal-bearing sediments. The negative δ202Hg, the mercury odd-MIF Δ201Hg patterns, and the Δ199Hg–Hg plot in both sections are compatible with volcanic mercury deposition. Our study shows the strength of Hg/TOC ratios as paleoenvironmental proxy and as a tool for stratigraphic correlation.

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