Reservoir characteristics and formation model of Upper Carboniferous bauxite series in eastern Ordos Basin,NW China

Through core observation,thin section identification,X-ray diffraction analysis,scanning electron microscopy,and low-temperature nitrogen adsorption and isothermal adsorption experiments,the lithology and pore characteristics of the Upper Carboniferous bauxite series in eastern Ordos Basin were analyzed to reveal the formation and evolution process of the bauxite reservoirs.A petrological nomenclature and classification scheme for bauxitic rocks based on three units(aluminum hydroxides,iron minerals and clay minerals)is proposed.It is found that bauxitic mudstone is in the form of dense massive and clastic structures,while the(clayey)bauxite is of dense massive,pisolite,oolite,porous soil and clastic structures.Both bauxitic mudstone and bauxite reservoirs develop dissolution pores,intercrystalline pores,and microfractures as the dominant gas storage space,with the porosity less than 10% and mesopores in dominance.The bauxite series in the North China Craton can be divided into five sections,i.e.,ferrilite(Shanxi-style iron ore,section A),bauxitic mudstone(section B),bauxite(section C),bauxite mudstone(debris-containing,section D)and dark mudstone-coal section(section E).The burrow/funnel filling,lenticular,layered/massive bauxite deposits occur separately in the karst platforms,gentle slopes and low-lying areas.The karst platforms and gentle slopes are conducive to surface water leaching,with strong karstification,well-developed pores,large reservoir thickness and good physical properties,but poor strata continuity.The low-lying areas have poor physical properties but relatively continuous and stable reservoirs.The gas enrichment in bauxites is jointly controlled by source rock,reservoir rock and fractures.This recognition provides geological basis for the exploration and development of natural gas in the Upper Carboniferous in the study area and similar bauxite systems.

Effects of Volcanic Activity on Organic Matter Sources and the Paleoenvironment:Geochemical Evidence from Upper Carboniferous Source Rocks(Batamayineishan Formation)in Eastern Junggar,NW China

The mudstone,gray tuffite and carbonaceous shale in the Upper Carboniferous Batamayineishan Formation(Bashan Formation)are essential source rocks for the volcanic reservoir in eastern Junggar,northwestern China.The kerogen components,vitrinite reflectance,Rock-Eval pyrolysis,lipid biomarkers and isotope compositions were measured to understand the provenance and depositional environment of Bashan Formation under the background of volcanic activities.There were 10 and 4 periods of volcanic eruptions identified in the wells CS and DZ,respectively.The source rocks developed in the late or intermittent phase of volcanic activity.The original island arcs of the Early Carboniferous evolved into the Wucaiwan sag and the Dishuiquan sag in the Bashan Formation.The Wucaiwan sag inherited the restricted,closed residual sea,which had a slightly anoxic and hypersaline environment.The Dishuiquan sag was generally an oxidizing lacustrine environment,influenced by a marine transgression that may have occurred at the end of the DZ_(Ⅲ)period during the Late Carboniferous.Although the total organic matter decreased due to the volcanic eruption,ash could cause an increase of aquatic organisms,coinciding with increases in salinity and reducibility in the Dishuiquan sag.

Cycle-Sequences,Carbon Isotope Features and Glacio-Eustasy of the Triticites Zone in Southern Guizhou

In light of the principle of sequence stratigraphy, detailed analysis of depositionalsequences and systematical carbon isotope measurements were done for the Triticites zone ofthe typical Late Carboniferous section in the Dushan area of southern Guizhou. Two sequencesand seventeen parasequences, which can be correlated with the two sequences and seventeensubsequences in the North American Midcontinent, are distinguished in the Gzhelian, whichprovides convincing evidence of the global synchroneity of the depositional records. The inter-nal relations between carbon isotope evolution and eustasy were studied and the evolutionarycharacteristics of carbon isotopes in depositional sequences have been summarized.

Sumixam maximus gen.and sp.nov.,a New Pennsylvanian Species of Archaeorthoptera(Neoptera;Indiana,USA)

A new Mazon-Creek-type fossil specimen is described as Sumixam maximus gen.and sp.nov., assigned to the taxon Archaeorthoptera Bethoux and Nel,2002(composed of Orthoptera and some fossil relatives):it exhibits one of the diagnostic character states of this taxon,which is the fusion of CuA(emerging from M+CuA)with CuP,or a branch of it.A more precise taxonomic assignment is out of reach.The new taxon exhibits a fusion of the anterior branch of MA with RP,and a point of divergence of MA and MP located near the point of divergence of CuA(from M + CuA),but lack a branching of CuPa.This unique combination of character states is probably derived with respect to a number of contemporaneous species.Sumixam maximus gen.and sp.nov.is most likely the closest known relative of the panorthopterans,which include all the recent Archaeorthoptera.