Evolution of Diagenetic Fluid of the Dawsonite-Bearing Sandstone in the Jiyang Depression,Eastern China

Based on the petrology,isotope geochemistry and fluid inclusions analysis,we established the evolutionary mode of the diagenetic fluid of dawsonite-bearing sandstone in the Jiyang Depression.Dawsonite-bearing sandstone is characterized by double injection of CO_(2)and oil-gas in the Jiyang Depression that have experienced a relatively complex diagenetic fluid evolution process.The diagenetic sequence of secondary minerals involves secondary enlargement of quartz,kaolinite,first-stage calcite,dawsonite,second-stage calcite,ferrocalcite,dolomite and ankerite.Hydrocarbon charging in the dawsonite-bearing sandstone occurred at around 2.6–0 Myr.The CO_(2)charging event occurred during Dongying tectonism,forming the Pingfangwang CO_(2)gas reservoir,which provided an abundant carbon source for dawsonite precipitation.Carbon and oxygen isotopic compositions of dawsonite demonstrate that CO_(2)forming the dawsonite was of an inorganic origin derived from the mantle,and that water mediating the proc-ess during dawsonite precipitation was sequestered brine with a fluid temperature of 82℃.The evolutionary sequence of the diagenetic fluid in the dawsonite-bearing sandstone was:alkaline syngenetic fluids,weak alkaline fluids during organic acid forma-tion,acidic fluids in the early stage of CO_(2)injection,alkaline fluids in the late stage of CO_(2)injection,and weak alkaline fluids during oil and gas charging.The mode indicates an increase in-HCO_(3)because of the CO_(2)injection,and the loss of Ca^(2+)and Mg^(2+)due to the precipitation of carbonate minerals.Therefore,the evolutionary mode of diagenetic fluids is in good agreement with high HCO_(3)^(-),low Ca^(2+)and low Mg^(2+)composition of the present formation water in the dawsonite-bearing sandstone.

Analyzing and quantitatively evaluating the organic matter source at different ecologic zones of tidal salt marsh, North Jiangsu Province, China

In order to explore the effect of different eco-logical zones and their above plants in the organic matter cycling of the whole tidal salt marsh,indicators such as total organic carbon(TOC),total nitrogen(TN),C/N ratio,δ13C and d15N of surface,core sediments,and plants of tidal salt marshes in North Jiangsu Province are analyzed.Subse-quently,distribution regularities of these measurement indi-cators are discussed,and the biogeochemistry processes between sediments and plants are also analyzed.Lastly,the organic matter sources of different ecologic zones in tidal salt marsh are evaluated,and the organic matter accumu-lations in different ecologic zones induced by their plants are also compared.These results indicate that TOC,TN,C/N ratio and δ13C showed obvious zonal distribution.The organic matter sources are dominated by marine input in the silt flat,artemisia schrenkiana flat,and the transition zone between silt and spartina alterniflora flat,and are controlled by terrigenous input in spartina alterniflora flat.Spartina alterniflora plays an important role in the accumulation of organic matter in the whole tidal salt marshes ecosystem.In the study area,the annually increased TOC,organic matter and TN in the spartina alterniflora,artemisia schrenkiana and reed flats reach 6,451,12,043 and 536 t,respectively.The amount of TOC,organic matter and TN accumulated in the spartina alterniflora flat is more than that in other ecological zones,which shows that the spartina alterniflora flat exert a non-replaceable effect on the material cycle and exchange in the whole tidal salt marshes ecosystem.

Mantle-derived magmatic gas releasing features at the Rehai area, Tengchong county, Yunnan Province, China

This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion in shallow crust at this area. Modern mantle-derived mag-matic volatiles are being released currently in a steady stream by way of active faults. The escaped gases are mostly composed of CO2, together with subordinate amounts of H2S, N2, H2, CH4, SO2, CO and He. At the studied area, the north-south directed fault is the deepest, and it may be interlinked with the deep-seated thermal reservoir that would be directly recharged by the mantle-derived magmatic volatile. The He, C isotopic evidence reveals that the modern active magma beneath Rehai area may originate from the historical mantle-derived magma which caused the latest eruptive activity of volcanoes in that region.