Sandstones sampled from Patti Formation,Southern Bida Basin,were studied geochemically using Inductively Coupled Plasma Atomic Emission Spectrophotometer(ICP-AES)and an Inductively Coupled Plasma Mass Spectrometry(ICP...Sandstones sampled from Patti Formation,Southern Bida Basin,were studied geochemically using Inductively Coupled Plasma Atomic Emission Spectrophotometer(ICP-AES)and an Inductively Coupled Plasma Mass Spectrometry(ICP-MS)technique to evaluate their weathering and tectonic setting as well as to deduce the paleo-climatic conditions that existed during their deposition.Geochemically,SiO_(2)range from 73.9%to 86.2%,Al_(2)O_(3)(6.7%~17.1%),Fe_(2)O_(3)(1.1%~1.9%),K_(2)O(0.1%~0.7%)while MgO,CaO,Na_(2)O,P_(2)O_(5),MnO and TiO_(2)were<1%.Enriched in Ba(Av.622.94),Sr(Av.153.63),Rb(Av.55.08)and Zr(Av.51.86)relatively similar in composition to UCC.High SiO_(2)but low other major oxides signify high mobility during processes of weathering.This was confirmed by high value(>80%)for indices like chemical index of alteration,chemical index of weathering,plagioclase index of alteration,mineralogical index of alteration and relatively lower values for weathering index of parker,recently used alpha indices(α^(Al)_(E))of sodium(326.17α^(Al)_(Na)<344.40),magnesium(100.54α^(Al)_(mg)<398.55),calcium(12.07α^(Al)_(Ca)<198.99),potassium(4.43α^(Al)_(K)<64.33),strontium(0.84α^(Al)_(E)<21.40),barium(0.45α^(Al)_(Ba)<10.52)and rubidium(0.0008α^(Al)_(Rb)<0.06),supported by AI_(2)O_(3)-(CaO^(*)+Na_(2)O)-K_(2)O and CIA vs.SiO_(2)plots that imply intense weathering in the source area.The obtained high CIA values(>80)indicates a steady-state of weathering under a warm/humid climate as confirmed by the SiO_(2)vs.Al_(2)O_(3)+K_(2)O+Na_(2)O plot.High average SiO_(2)(75.41wt%)with K_(2)O/Na_(2)O ratio>1(15.63),low Fe_(2)O_(3)(1.27wt%),Al_(2)O_(3)(15.82wt%)and TiO_(2)(0.46)suggest passive margin tectonic setting.This is supported by enrichedΣREE(209.64 ppm),ΣLREE(195.78),LREE/HREE(27.78)and negative Eu/Eu^(*)(0.68),plots of log(K_(2)O/Na_(2)O)vs.SiO_(2)and SiO_(2)/Al_(2)O_(3)vs.K_(2)O/Na_(2)O.Major elements discriminant-function multi-dimensional diagram,DF1(arcrift-col)vs.DF2(arc-rift-col),for high-silica sediments revealed a continental rift tectonic setting.Thus,the Patti Formation sandstone underwent a high degree of weathering under a humid climatic condition within a continental rift tectonic setting.展开更多
文摘Sandstones sampled from Patti Formation,Southern Bida Basin,were studied geochemically using Inductively Coupled Plasma Atomic Emission Spectrophotometer(ICP-AES)and an Inductively Coupled Plasma Mass Spectrometry(ICP-MS)technique to evaluate their weathering and tectonic setting as well as to deduce the paleo-climatic conditions that existed during their deposition.Geochemically,SiO_(2)range from 73.9%to 86.2%,Al_(2)O_(3)(6.7%~17.1%),Fe_(2)O_(3)(1.1%~1.9%),K_(2)O(0.1%~0.7%)while MgO,CaO,Na_(2)O,P_(2)O_(5),MnO and TiO_(2)were<1%.Enriched in Ba(Av.622.94),Sr(Av.153.63),Rb(Av.55.08)and Zr(Av.51.86)relatively similar in composition to UCC.High SiO_(2)but low other major oxides signify high mobility during processes of weathering.This was confirmed by high value(>80%)for indices like chemical index of alteration,chemical index of weathering,plagioclase index of alteration,mineralogical index of alteration and relatively lower values for weathering index of parker,recently used alpha indices(α^(Al)_(E))of sodium(326.17α^(Al)_(Na)<344.40),magnesium(100.54α^(Al)_(mg)<398.55),calcium(12.07α^(Al)_(Ca)<198.99),potassium(4.43α^(Al)_(K)<64.33),strontium(0.84α^(Al)_(E)<21.40),barium(0.45α^(Al)_(Ba)<10.52)and rubidium(0.0008α^(Al)_(Rb)<0.06),supported by AI_(2)O_(3)-(CaO^(*)+Na_(2)O)-K_(2)O and CIA vs.SiO_(2)plots that imply intense weathering in the source area.The obtained high CIA values(>80)indicates a steady-state of weathering under a warm/humid climate as confirmed by the SiO_(2)vs.Al_(2)O_(3)+K_(2)O+Na_(2)O plot.High average SiO_(2)(75.41wt%)with K_(2)O/Na_(2)O ratio>1(15.63),low Fe_(2)O_(3)(1.27wt%),Al_(2)O_(3)(15.82wt%)and TiO_(2)(0.46)suggest passive margin tectonic setting.This is supported by enrichedΣREE(209.64 ppm),ΣLREE(195.78),LREE/HREE(27.78)and negative Eu/Eu^(*)(0.68),plots of log(K_(2)O/Na_(2)O)vs.SiO_(2)and SiO_(2)/Al_(2)O_(3)vs.K_(2)O/Na_(2)O.Major elements discriminant-function multi-dimensional diagram,DF1(arcrift-col)vs.DF2(arc-rift-col),for high-silica sediments revealed a continental rift tectonic setting.Thus,the Patti Formation sandstone underwent a high degree of weathering under a humid climatic condition within a continental rift tectonic setting.
