Boundary Strata Research Articles

Trace element geochemistry of the Permian/Triassic boundary section in the Selong-Xishan area, Nyalam County, southern Tibet, China

Samples were collected from the Selong-Xishan Permian/Triassic boundary strata, Nyalam County in southern Tibet and systematically analyzed for their rare-earth elements (REE)and trace elements such as U, Th, Sr, Ba, Sc, Ta, Hf, Rb, Cs, Co, Ni, Cr, As and others with emphasis put on the distribution patterns of rare-earth elements and the variation of trace element contents along the Permian/Triassic boundary section. On this basis a discussion will be made of the paleo-ocean depositional environment.

Comment on “Fossil charcoal in Cretaceous-Tertiary boundary strata: Evidence for catastrophic firestorm and megawave” by M.A. Kruge,

Comment on “Fossil charcoal in Cretaceous-Tertiary boundary strata: Evidence for catastrophic firestorm and megawave” by M.A. Kruge,

Microfossils from the Chert in the Lower Cambrian Shuijingtuo Formation at Miaohe, Zigui, Hubei Province1

Abstract This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2‐3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian‐Cambrian boundary strata with those of the adjacent areas.

A Potential Candidate For the Middle‐Upper Cambrian Boundary Stratotype — An Introduction to the Paibi Section in Huayuan, Hunan

Abstract The Middle‐Upper Cambrian boundary is one of the current stratigraphical problems which remain open in the geological world, since there have been no universally acknowledged delimiting standard and stratotype. Acting on the instruction of Profs. Lu Yanhao and An Taixiang the author studied in details the Paibi Section, which is well exposed as a continuous sequence at an easily accessible locality. The Middle‐Upper Cambrian boundary strata are composed of biocalcimicrosparite, indicating the sedimentary environment of an underwater upheaval on the gentle slope along the frontal margin of the Yangtze carbonate platform.For the upper Middle and lower Upper Cambrian agnostid trilobite zones and conodont zones are erected, and a more accurate correlation between the trilobite and conodont sequences is established. Based on these, the Middle‐Upper Cambrian boundary is drawn more reasonably and precisely than what was done before. In short, the section studied is superior to other known sections of Middle‐Upper Cambrian, and it will probably be an ideal candidate for the Middle‐Upper Cambrian boundary stratotype.

Evolutionary Stages of the Earliest Skeletal Fauna and Division and Correlation of the Precambrian‐Cambrian Boundary Strata

Abstract Through an analysis of the earliest fossils in the Precambrian‐Cambrian boundary beds in various parts of the world, especially in the Yangtze and Siberia platforms, the author has found that the evolution of the earliest skeletal animals may be divided from older to younger into three stages. The first stage (the Anabarites‐Protohertzina fauna) is represented by the Anabarites‐Protohertzina zone of the Meishucunian Stage in the Yangtze platform and the A. trisulcatus and P. cristata zones of the Manykayn Stage in Siberia. The second stage (the earliest orthothecimorphid and mollusc fauna) is represented by the Paragloborilus‐Siphogonuchites zone of the Meishucunian Stage and the Aldanocyathus sunnaginicus zone of the Tommotian Stage. The third stage (the earliest hyolithimorphid and lapworthellid fauna) is represented by the Sinosachites zone of the Meishucunian Stage and the D.regularis and D.lenaicus zones of the Tommotian Stage. The three evolutionary stages can be used as a criterion for worldwide correlation.

State-of-the-Art Summary for Underground Coal Gasification

Distinguished Author Seriesarticles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleum engineering. Introduction Process Chemistry Underground coal gasification Process Chemistry. Underground coal gasification (UCG) process chemistry has been studied extensively through physical and mathematical simulations. The basic chemistryis the same as for surface gasifiers although the reaction sequences arc lesswell defined. The primary reactions include: Oxidation: C + O2 = CO2 + 94.05 kcal/mol 2C+01=2CO + 26.42 kcal/mol Gasification: C+H2O=CO+H,-31.4 kcal/mol C+Co2 =2CO - 41.2 kcal/mol Pyrolysis: Pyrolysis: coal+heat=char+tar+water+gases Secondary reactions involving, gasification products include: Water gas shift: CO + H2O=CO,+H,+9.8 kcal/mol Methanation: C + 2H2 = CH4 + 17.9 kcal/mol CO + 3H2 =CH4 + H4O + 49.3 kcal/mol 2CO + 2H2 =CH4 + C + CO2 + 59.0 kcal/mol During the process all of these reactions can contribute to the finalproduct composition. Both thermodynamic and kinetic effects are significant. Residence times and temperature gradients in the reactor determine the degreeto which these effects are significant for a given coal seam. Process Mechanics Three distinctively different Process Mechanics. Three distinctively different activities must be completed to ensure a successful UCGoperation.Preparation of the process reactor. This includes selection anddetailed characterization of the geologic domain that will be affected by theprocess, as well as installation of process wells and preparation of the seamfor gasification.Gasification of the coal. This entails in-situ conversionof the coal to a gaseous mixture of CO, CO2, H2, CH4, and higher-molecular-weight compounds. The operation should be maintained so thatinflux of boundary strata and water and loss of product gas are minimal. product gas are minimal.Site restoration. Before a site can be abandoned, restoration of the facility to its original-use value must be demonstrated. After an acceptable site is chosen the process reactor is installed by drilling two wells into process reactor is installed by drilling two wells into the coatseam and establishing a highly permeable zone or link between the well pair. Wells should be completed into the lower third of the coal seam. JPT P. 15