Mass Extinctions, Volcanism, and Impacts: New Developments
This volume covers new developments and research on mass extinctions, volcanism, and impacts, ranging from the ancient Central Iapetus magmatic province linked with the Gaskiers glaciation to thermogenic degassing in large igneous provinces, the global mercury enrichment in Valanginian sediments, and the Guerrero-Morelos carbonate platform response to the Caribbean-Colombian Cretaceous large igneous province. This section is followed by a series of end-Cretaceous studies, including the implications for the Cretaceous-Paleogene boundary event in shallow platform environments and correlation to the deep sea; the role of wildfires linked to Deccan volcanism on ecosystems from the Indian subcontinent; rock magnetic and mineralogical study of Deccan red boles; and factors leading to the collapse of producers during Deccan Traps eruptions and the Chicxulub impact.
Integrated mineralogical and rock magnetic study of Deccan red boles
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Published:March 06, 2020
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CiteCitation
Eric Font*, Thierry Adatte, Alexandra Abrajevitch, José Mirão, Nikhil Sharma, Valentin Sordet, Mariana Andrade, 2020. "Integrated mineralogical and rock magnetic study of Deccan red boles", Mass Extinctions, Volcanism, and Impacts: New Developments, Thierry Adatte, David P.G. Bond, Gerta Keller
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ABSTRACT
We conducted a detailed rock magnetic and mineralogical study of bole beds from the Deccan magmatic province, India. Magnetic susceptibility of 15 bole beds showed two contrasting patterns, with susceptibility values either increasing or decreasing up the profile. We then focused on two representatives red boles located in the Western Ghats, the RBB and RBAN profiles, to unravel the nature and origin of these contrasting magnetic susceptibility patterns. The presence of smectite argues against significant secondary thermal alterations. Major-elemental compositions obtained by X-ray fluorescence spectrometry of RBB and RBAN red boles are comparable to the parent basalt and show significant and typical depletion of mobile elements such as sodium and calcium compared to the parent basalt. The Ti/Al ratio of both the red boles and their overlying clay layers is close to the typical value of Deccan basalt (0.2), suggesting that the material of the red boles has been derived from weathering of the parent basalt. The chemical index of alteration varies from 40–50 in the parent basalt to 80–90 at the top of the bole beds, consistent with moderate to intense weathering of the bole beds. However, similar to other Deccan bole beds, indices of lateritization below 50 suggest that the state of lateritization has not been reached. Although the RBB and RBAN profiles share similar mineralogical signatures, their magnetic mineral assemblages are distinctly different. In the RBB profile, magnetic susceptibility decreases up-profile as a result of oxidation/dissolution of primary titanomagnetite inherited from the parent basalt, with subsequent formation of pedogenic hematite and superparamagnetic particles. In contrast, magnetic susceptibility in the RBAN profile, which contains magnetite, some hematite, and goethite, increases up-profile. The increase in the magnetic signal is mainly due to the increasing amounts of phyllosilicate and goethite, while the content of magnetite and hematite remains constant along the profile. We attribute the variation in the magnetic mineral assemblage to contrasting humid and dry environments during weathering, leading to the preferential formation of goethite or hematite, respectively. The combined mineralogical and rock magnetic data suggest the existence of a single weathering profile involving soil formation in the two studied red boles, with few or no contributions from an external source.
- alkali metals
- alkaline earth metals
- alteration
- Asia
- basalts
- calcium
- Cenozoic
- clay minerals
- Cretaceous
- Deccan Plateau
- feldspar group
- framework silicates
- Ghats
- goethite
- hematite
- humid environment
- igneous rocks
- India
- Indian Peninsula
- isothermal remanent magnetization
- kaolinite
- lower Paleocene
- magnetic properties
- magnetic susceptibility
- magnetite
- magnetization
- major elements
- Mesozoic
- metals
- mineral assemblages
- mineral composition
- oxidation
- oxides
- Paleocene
- Paleogene
- paleomagnetism
- paleosols
- parent materials
- patterns
- pedogenesis
- plagioclase
- quartz
- remanent magnetization
- reversals
- sheet silicates
- silica minerals
- silicates
- smectite
- sodium
- soils
- solution
- spectra
- stratigraphic boundary
- terrestrial environment
- Tertiary
- titanomagnetite
- Upper Cretaceous
- volcanic rocks
- volcanism
- weathering
- Western Ghats
- whole rock
- X-ray diffraction data
- X-ray fluorescence spectra
- zeolite group
- lateritization
- K-Pg boundary