scholarly journals Origin of pyrite nodules at the top of the nantuo diamictites, Southern China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Changjie Liu ◽  
Ying Lin
Keyword(s):  
Southern China ◽  
Nodule Formation ◽  
Doushantuo Formation ◽  
Isotopic Compositions ◽  
Pyrite Formation ◽  
Sampling Scale ◽  
Closed Environment

AbstractPyrite nodules up to 20 cm in diameter are found at the top of the Marinoan (~ 635 Ma) Nantuo glacial diamictite as well as in the cap dolostones and shale/siltstones in the lower Doushantuo Formation in eastern Guizhou, southern China. Field occurrences, petrography, and stable sulfur isotopic compositions of pyrite nodules were studied from a section at Taoying, eastern Guizhou, China. Pyrite δ34S values from different nodules varied from 7.3 to 60.5‰ at different stratigraphic levels. No stratigraphic trend existed for the δ34S, supporting the scenario of pyrite formation in sediments before the precipitation of the cap dolostone. Pyrite δ34S values were also homogeneous within individual nodules at a 0.3 to 1 cm sampling scale, but were more heterogeneous at a 2 mm sampling scale. Homogeneity was not expected from the particular model for pyrite nodule formation in a largely closed or semi-closed environment. Thus, differential cementation and compaction of the pyrite-bearing sediments may have produced the nodular shape of the pyrite deposit.

High-Resolution Chronostratigraphy for Sedimentary Rocks using Rock Magnetics

2021 ◽  
Author(s):  
Kenneth Kodama
Keyword(s):  
Magnetic Susceptibility ◽  
High Resolution ◽  
Sedimentary Rock ◽  
Southern China ◽  
Global Climate ◽  
Death Valley ◽  
Milankovitch Cycles ◽  
Doushantuo Formation ◽  
Climate Signal ◽  
Rock Magnetics

<p>Rock magnetics can be used to identify orbitally-forced global climate cycles in sedimentary rock sequences. The identification of Milankovitch cycles with nominal periods of 20, 40, 100 and 400 ka can be used to construct a high-resolution chronostratigraphy for a rock sequence that can have a variety of important geologic applications. Several examples will be presented. The rock magnetic cyclostratigraphy of Eocene marine, deltaic mudstones and marls of the Arguis Formation illustrates how rock magnetics can be used to determine the deformation rates of a salt tectonics growth fold in the Pyrenees. The duration of the Ediacaran Shuram carbon-isotope excursion was determined to be 8-9 Ma from rock magnetic cyclostratigraphy studies of marine rocks from Death Valley, California (Rainstorm member of the Johnnie Formation), southern Australia (Wonoka Formation), and in central and southern China (Doushantuo Formation).  Further cyclostratigraphic study of the Rainstorm member in the Desert Range, Nevada, allowed the construction of a high-resolution magnetostratigraphy by combining and calibrating magnetostratigraphic results from Death Valley and Nevada to reveal a high reversal rate of 12.7 reversals/Ma in the Ediacaran. More detailed study of the Doushantuo Formation at Huangliaba, China indicated that even though its ferromagnetic minerals were predominately secondary pyrrhotite, magnetic susceptibility measurements could still detect a depositional, orbitally-forced cyclostratigraphy carried by paramagnetic minerals. Finally, the Carboniferous Mauch Chunk Formation red beds from Pottsville, Pennsylvania yielded a magnetic susceptibility cyclostratigraphy in terrestrial, fluvial sediments despite their discontinuous sedimentation. This study showed that both portable susceptibility meter measurements and lab-based measurement of rock samples could discern the same period cycles. Detailed low and high temperature magnetic susceptibility measurements indicate that the ferromagnetic mineral hematite, rather than paramagnetic clays, is the predominant carrier of the orbitally-forced global climate signal. All these studies show the power of rock magnetics for constructing a high-resolution chronostratigraphy for sedimentary rock sequences.</p>

Variation in solvent-extractable lipids and n-alkane compound-specific carbon isotopic compositions with depth in a southern China karst area soil

2010 ◽  
Vol 21 (4) ◽  
pp. 382-391 ◽  
Author(s):  
Jingwei Cui ◽  
Junhua Huang ◽  
Philip A. Meyers ◽  
Xianyu Huang ◽  
Jingjing Li ◽  
...  
Keyword(s):  
Southern China ◽  
Karst Area ◽  
Isotopic Compositions ◽  
Carbon Isotopic

Stabilizing pyritic material

1989 ◽  
Vol 4 ◽  
pp. 244-248 ◽  
Author(s):  
Donald L. Wolberg
Keyword(s):  
Significant Contribution ◽  
Organic Materials ◽  
Sedimentary Rocks ◽  
Iron Sulfides ◽  
Decomposition Products ◽  
Iron Minerals ◽  
Pyrite Formation ◽  
Organic Sediments ◽  
Freshwater Environments

The minerals pyrite and marcasite (broadly termed pyritic minerals) are iron sulfides that are common if not ubiquitous in sedimentary rocks, especially in association with organic materials (Berner, 1970). In most marine sedimentary associations, pyrite and marcasite are associated with organic sediments rich in dissolved sulfate and iron minerals. Because of the rapid consumption of sulfate in freshwater environments, however, pyrite formation is more restricted in nonmarine sediments (Berner, 1983). The origin of the sulfur in nonmarine environments must lie within pre-existing rocks or volcanic detritus; a relatively small, but significant contribution may derive from plant and animal decomposition products.

Sign in / Sign up

Export Citation Format

Share Document