Viséan Fossil Plants from the Jiujialu Formation in Central Guizhou Province: Implications for Age of Bauxite and Palaeoenvironment

Fossil plants from the carbonaceous shale of upper part of the Lower Carboniferous Jiujialu Formation in Lindai bauxite deposit fill a gap regarding the distribution of Early Carboniferous flora in Central Guizhou Province.Here the Lindai plant assemblage is systematically described,and its composition and geological age are discussed.Research demonstrates that 9 species in 6 genera of the fossil plants are discovered in this study,and they belong to lycopsids,sphenopsids and ferns,respectively.Based on the analysis of the floral composition,the geological age of the Lindai plant assemblage belongs to the Early Carboniferous Viséan.The discovery of Lindai plant assemblage not only provides a new fossil evidence to restrict the age of bauxite deposits in Lower Carboniferous Jiujialu Formation of Central Guizhou Province,but also has great significance to further research the palaeoecological setting and floral evolution during the Early Carboniferous.

Provenance of Lower Carboniferous Bauxite Deposits in Northern Guizhou,China:Constraints from Geochemistry and Detrital Zircon U-Pb Ages

The Lower Carboniferous Jiujialu Formation bauxite deposits of northern Guizhou Province,China,are a Kazakhstan subtype of karst bauxite deposits.The provenance of the Jiujialu Formation has long been debated,with uncertainty about the formation of the bauxite deposits.Here we report new geochemical data that indicate the affinity between the Lower-Middle Ordovician clastic rocks and argillaceous dolostones and the overlying Carboniferous bauxite deposits,all of which are characterized by high Al_(2)0_(3),K2_(O),and∑REE contents,flat post-Archean Australian shale(PAAS)-normalized REE patterns,and uniform immobile element ratios(TiO2/Al_(2)0_(3),Nb/TiO2,and Zr/TiO2).Their similar detrital zircon age distributions further indicate the link between the bauxite deposits and the clastic rocks and argillaceous dolostones.Zircon age spectra of clastic rocks of the Lower Silurian Hanchiatien Formation in northern Guizhou match those of the bauxite deposits,with a maximum age peak at-980 Ma and other secondary age peaks,suggesting these clastic rocks may represent the provenance of the bauxite deposits.The youngest detrital zircons(-445 Ma)occur only in the bauxite deposits and are probably sourced from K-bentonite beds of the Ordovician-Silurian tran-sition.Our analyses indicate that the source materials of the bauxite deposits in the Jiujialu Formation are of mixed provenance:Lower-Middle Ordovician aluminosilicate rocks and argillaceous dolostones of the underlying strata,and Lower Silurian clastic rocks and K-bentonite from adjacent areas.A comparison of Early Carboniferous bauxitic provenances in northern and central Guizhou indicates that paleotopography was the major factor controlling the provenance of these bauxite deposits.