The sandstones of the Late miocene–Pliocene Dibdibba Formation in the Najaf–Karbala Plateau and Basra were examined to determine their source rocks and origin. The rare earth elements(REE) and trace elements(Sc, Co,...The sandstones of the Late miocene–Pliocene Dibdibba Formation in the Najaf–Karbala Plateau and Basra were examined to determine their source rocks and origin. The rare earth elements(REE) and trace elements(Sc, Co, V, and Th) concentrations in these sandstones revealed that they likely derived from a single source. The steep light rare earth elements(LREE) and flat, heavy rare earth element(HREE) patterns, negative Eu anomaly, and high ΣREE contents in sandstones suggest its derivation from a suggests that a passive continental margin environment and originated from felsic source rocks. The average concentration of ΣREE is 93.5 ppm, which is lower than that of the average crustal compositions like Upper Continental Crust and Post Archean Australian Shale. The higher proportion of LREE compared to HREE implies that these sandstones were recycled and derived from a distal source. The Th/Co, Th/Sc, La/Sc, La/Co, Eu/Eu*and(La/Lu)cn elemental ratios indicated that these Late Miocene–Pliocene sandstones were derived from felsic rocks located in the marginal region of the Arabian Shield.展开更多
The sedimentary environment, formation conditions, sedimentary characteristics and the basin evolution model of high-frequency oscillatory lake in arid climatic background of the Lower Eocene in the Dongying depressio...The sedimentary environment, formation conditions, sedimentary characteristics and the basin evolution model of high-frequency oscillatory lake in arid climatic background of the Lower Eocene in the Dongying depression were studied through the analysis of drilling cores, sporepollen, geochemistry and geophysics data. During the sedimentary period of the Eocene Ek^3-Es^4x formations, because of the frequent alternation between dry and wet climates in the arid climatic background and the gentle paleo- geomorphology, the lake level and salinity of the Early Eocene Dongying depression frequently and rap- idly increased and decreased, which is referred to as a high-frequency oscillatory lake. The sedimentation and distribution of sediments in this high-frequency oscillatory lake basin were controlled by the fre- quently alternating dry-wet climates. During periods with relatively wet climate, the seasonal floods and unstable rivers led to the formation of over-flooding lake deltas in the gentle slope belt, and fine-grained clastic sediments, with minor thin layers of gypsum-salt rocks in the sag belt. During the relatively arid climatic periods, sedimentation occurred mainly in the limited area of the sag belt with thick gypsum-salt rocks. Because of the impact of the salinity stratification of the lake water, these gypsum-salt rocks exhibit annular structural features. A sedimentary cycle of the oscillatory lake began with isochronous flood channels and ended with relatively thick gypsum rocks and salt rocks. The thickness of one oscillatory cy- cle is generally 4-20 m. The superposition of multiple sedimentary cycles of the oscillatory lake constitutes the overall vertical idling sequence of the high-frequency oscillatory lake basin.展开更多
The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin ...The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin of South India during the Miocene.Indian Summer Monsoon was thought to be initiated in the early Miocene and intensified during the middle Miocene causing major climatic shifts in the Indian subcontinent.In the present work,detailed mineralogical and geochemical studies on the siliciclastic Cuddalore Formation have been carried out to understand the provenance and paleoclimatic conditions during the Miocene.The paleocurrent direction,textural immaturity and framework detrital modes of sandstones suggest rapid uplift of basement and sediment source from nearby Madras Block of SGT.Various diagnostic immobile trace element ratios such as Th/Sc,Co/Th,La/Sc,La/Co suggest a tonalite-trondhjemite-granodiorite-charnockite provenance,and somewhat more felsic composition of source area compared to the present upper continental crust(UCC).Rare earth element mixed model suggests that sediments were dominantly(80%)sourced from felsic charnockite,with a minor contribution(20%)from mafic granulites.Higher abundance of advanced-weathering products like kaolinite,very high(>98)chemical index of alteration(CIA)values,severe depletion of mobile elements(Ca,Na,K,Mg,Ba,Rb)in comparison to UCC,significantly higher a Mg,a Ca,a Na,a K,a Sr and a Ba values(higher than the unity),all suggest the extreme chemical weathering in source terrain and/or in the sedimentary basin.Calculations based on CIA show high average surface temperature between 29.3℃and 29.5℃and high mean annual precipitation ranging from 2339 mm/yr to 2467 mm/yr.The geochemical data are consistent with the paleogeographic position of the depositional basin(Cauvery Basin)and suggest the deposition of Cuddalore sediments(the Cuddalore Formation)in a nearequatorial location under a warm climate condition with abundant monsoonal precipitation.展开更多
文摘The sandstones of the Late miocene–Pliocene Dibdibba Formation in the Najaf–Karbala Plateau and Basra were examined to determine their source rocks and origin. The rare earth elements(REE) and trace elements(Sc, Co, V, and Th) concentrations in these sandstones revealed that they likely derived from a single source. The steep light rare earth elements(LREE) and flat, heavy rare earth element(HREE) patterns, negative Eu anomaly, and high ΣREE contents in sandstones suggest its derivation from a suggests that a passive continental margin environment and originated from felsic source rocks. The average concentration of ΣREE is 93.5 ppm, which is lower than that of the average crustal compositions like Upper Continental Crust and Post Archean Australian Shale. The higher proportion of LREE compared to HREE implies that these sandstones were recycled and derived from a distal source. The Th/Co, Th/Sc, La/Sc, La/Co, Eu/Eu*and(La/Lu)cn elemental ratios indicated that these Late Miocene–Pliocene sandstones were derived from felsic rocks located in the marginal region of the Arabian Shield.
基金supported by the National Natural Science Foundation of China(Nos.41402095,U1262203)the Chinese Postdoctoral Science Foundation(No.2014M550380)the China National Science and Technology Special Funds(Nos.2011ZX05051-001,2011ZX05006-003)
文摘The sedimentary environment, formation conditions, sedimentary characteristics and the basin evolution model of high-frequency oscillatory lake in arid climatic background of the Lower Eocene in the Dongying depression were studied through the analysis of drilling cores, sporepollen, geochemistry and geophysics data. During the sedimentary period of the Eocene Ek^3-Es^4x formations, because of the frequent alternation between dry and wet climates in the arid climatic background and the gentle paleo- geomorphology, the lake level and salinity of the Early Eocene Dongying depression frequently and rap- idly increased and decreased, which is referred to as a high-frequency oscillatory lake. The sedimentation and distribution of sediments in this high-frequency oscillatory lake basin were controlled by the fre- quently alternating dry-wet climates. During periods with relatively wet climate, the seasonal floods and unstable rivers led to the formation of over-flooding lake deltas in the gentle slope belt, and fine-grained clastic sediments, with minor thin layers of gypsum-salt rocks in the sag belt. During the relatively arid climatic periods, sedimentation occurred mainly in the limited area of the sag belt with thick gypsum-salt rocks. Because of the impact of the salinity stratification of the lake water, these gypsum-salt rocks exhibit annular structural features. A sedimentary cycle of the oscillatory lake began with isochronous flood channels and ended with relatively thick gypsum rocks and salt rocks. The thickness of one oscillatory cy- cle is generally 4-20 m. The superposition of multiple sedimentary cycles of the oscillatory lake constitutes the overall vertical idling sequence of the high-frequency oscillatory lake basin.
文摘The Cuddalore Formation of the Cauvery Basin received siliciclastic detritus from inland areas of the Southern Granulite Terrain(SGT).It represented continental-fluvial sedimentation in the eastern continental margin of South India during the Miocene.Indian Summer Monsoon was thought to be initiated in the early Miocene and intensified during the middle Miocene causing major climatic shifts in the Indian subcontinent.In the present work,detailed mineralogical and geochemical studies on the siliciclastic Cuddalore Formation have been carried out to understand the provenance and paleoclimatic conditions during the Miocene.The paleocurrent direction,textural immaturity and framework detrital modes of sandstones suggest rapid uplift of basement and sediment source from nearby Madras Block of SGT.Various diagnostic immobile trace element ratios such as Th/Sc,Co/Th,La/Sc,La/Co suggest a tonalite-trondhjemite-granodiorite-charnockite provenance,and somewhat more felsic composition of source area compared to the present upper continental crust(UCC).Rare earth element mixed model suggests that sediments were dominantly(80%)sourced from felsic charnockite,with a minor contribution(20%)from mafic granulites.Higher abundance of advanced-weathering products like kaolinite,very high(>98)chemical index of alteration(CIA)values,severe depletion of mobile elements(Ca,Na,K,Mg,Ba,Rb)in comparison to UCC,significantly higher a Mg,a Ca,a Na,a K,a Sr and a Ba values(higher than the unity),all suggest the extreme chemical weathering in source terrain and/or in the sedimentary basin.Calculations based on CIA show high average surface temperature between 29.3℃and 29.5℃and high mean annual precipitation ranging from 2339 mm/yr to 2467 mm/yr.The geochemical data are consistent with the paleogeographic position of the depositional basin(Cauvery Basin)and suggest the deposition of Cuddalore sediments(the Cuddalore Formation)in a nearequatorial location under a warm climate condition with abundant monsoonal precipitation.
