The mammilated chert(MC) studied in this paper is a kind of silica-rich concretion(SiO2 93%) occurring in the Upper Devonian argillaceous silicolites(SiO2≈88%)in Mugui,Guangxi.Impurity components in the MC are relati...The mammilated chert(MC) studied in this paper is a kind of silica-rich concretion(SiO2 93%) occurring in the Upper Devonian argillaceous silicolites(SiO2≈88%)in Mugui,Guangxi.Impurity components in the MC are relatively low and show systematic variationhs as compared with the country rocks.Abundances of Mg,Si,Ti,Fe,Mn,U and Th are characteristically similar to those of recent and fossil hot-water sediments,Moreover,the MC is also characterized by low REE baundance,LREE>HREE,apparent negative Ce anomaly and moderate positive Eu anomaly,OXygen isotope data show that the formation temperature of the MC is about 20℃,higher than that of the host rock.The results of geochemical,geological and lithological studies suggest that the MC may have been formed through metasomatism,fillinn and crystallization beneath the sedimentary basin during the Devonian period.展开更多
Power spectral analysis is discussed and an exmple of its application to a geochemical stratigraphic profile is presented.In the Dachang area,all major elements,as well as the maximal sedimentary trend factor(MSTF),de...Power spectral analysis is discussed and an exmple of its application to a geochemical stratigraphic profile is presented.In the Dachang area,all major elements,as well as the maximal sedimentary trend factor(MSTF),demonstrate consistent change periodicity,but are out-of-step with cach other.This can be explained by sedimentogecochemical consideration.The results of power spectral analysis enable geochemists to group elements on the basis of the distribution of their changed periods,and to interpret some special geological and geochemical situations.展开更多
Two positive δ13C excursions are presented in records from the Frasnian-Famennian (F-F) marine carbonate sediments in Europe, America, Africa, and Australia, having been considered as a worldwide pattern, and attribu...Two positive δ13C excursions are presented in records from the Frasnian-Famennian (F-F) marine carbonate sediments in Europe, America, Africa, and Australia, having been considered as a worldwide pattern, and attributed to enhanced organic carbon burial during the F-F biological mass extinction. However, this worldwide pattern has not been revealed from the well-deposited Late Devonian sequences in southern China. In this paper, a detailed investigation has been made on the Late Devonian section at Dongcun, Guilin, southern China to constrain perturbations in δ13C of carbonates in the F-F deposited sequence. The result from this section also indicates two positive δ13C excursions during the F-F transition. The first excursion with an amplitude of 1.5‰ occurred at the bottom of linguiformis Zone, later than the early excursion existing in the Late rhenana Zone of the Late Devonian profiles in other continents, especially, in central Europe. This difference has been expected to be a result as conodont Palmatolepis linguiformis occurred earlier in southern China than other sites. The second excursion with an amplitude of 2.1‰ is located at the F-F boundary, same as the records from other continents. This result strongly supports the view that two carbon isotope positive excursions during the F-F transition are common in carbonate sediments, resulting from worldwide increases of organic carbon burial intensity.展开更多
文摘The mammilated chert(MC) studied in this paper is a kind of silica-rich concretion(SiO2 93%) occurring in the Upper Devonian argillaceous silicolites(SiO2≈88%)in Mugui,Guangxi.Impurity components in the MC are relatively low and show systematic variationhs as compared with the country rocks.Abundances of Mg,Si,Ti,Fe,Mn,U and Th are characteristically similar to those of recent and fossil hot-water sediments,Moreover,the MC is also characterized by low REE baundance,LREE>HREE,apparent negative Ce anomaly and moderate positive Eu anomaly,OXygen isotope data show that the formation temperature of the MC is about 20℃,higher than that of the host rock.The results of geochemical,geological and lithological studies suggest that the MC may have been formed through metasomatism,fillinn and crystallization beneath the sedimentary basin during the Devonian period.
文摘Power spectral analysis is discussed and an exmple of its application to a geochemical stratigraphic profile is presented.In the Dachang area,all major elements,as well as the maximal sedimentary trend factor(MSTF),demonstrate consistent change periodicity,but are out-of-step with cach other.This can be explained by sedimentogecochemical consideration.The results of power spectral analysis enable geochemists to group elements on the basis of the distribution of their changed periods,and to interpret some special geological and geochemical situations.
文摘Two positive δ13C excursions are presented in records from the Frasnian-Famennian (F-F) marine carbonate sediments in Europe, America, Africa, and Australia, having been considered as a worldwide pattern, and attributed to enhanced organic carbon burial during the F-F biological mass extinction. However, this worldwide pattern has not been revealed from the well-deposited Late Devonian sequences in southern China. In this paper, a detailed investigation has been made on the Late Devonian section at Dongcun, Guilin, southern China to constrain perturbations in δ13C of carbonates in the F-F deposited sequence. The result from this section also indicates two positive δ13C excursions during the F-F transition. The first excursion with an amplitude of 1.5‰ occurred at the bottom of linguiformis Zone, later than the early excursion existing in the Late rhenana Zone of the Late Devonian profiles in other continents, especially, in central Europe. This difference has been expected to be a result as conodont Palmatolepis linguiformis occurred earlier in southern China than other sites. The second excursion with an amplitude of 2.1‰ is located at the F-F boundary, same as the records from other continents. This result strongly supports the view that two carbon isotope positive excursions during the F-F transition are common in carbonate sediments, resulting from worldwide increases of organic carbon burial intensity.
