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您的检索式：作者名="JANSA Luba F."
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| 1 | Hydrothermal Dolomite in the Upper Sinian (Upper Proterozoic) Dengying Formation, East Sichuan Basin, China显示文摘Hydrothermal Dolomite(HTD) is present in the Upper Sinian(Upper Proterozoic) Dengying Formation, east Sichuan Basin, China. The strata are comprised by primary dolomite. The HTD has various textures, including zebra dolomite, subhorizontal sheet-like cavities filled by saddle dolomite and breccias cemented by saddle dolomites as well occur as a fill of veins and fractures. Also co-occur MVT type lead-zinc ores in the study area. The δ13C and δ18O isotopes of HTD in the Upper Sinian Dengying Formation are lighter than those of the host rocks, while 87Sr/86 Sr is higher. The apparent difference in carbon, oxygen and strontium isotopes, especially the large difference in 87Sr/86 Sr isotopes ratio indicate crystallization from hot basinal and/or hydrothermal fluids. Saddle dolomite was precipitated at temperatures of 270-320°C. The diagenetic parasequences of mineral assemblage deposited in the Dengying Formation are:(1) dolomite host rock →sphalerite-galena-barite-fluorite;(2) dolomite host rock →saddle dolomite →quartz;(3) dolomite host rock → saddle dolomite→bitumen;(4) dolomite host rock → saddle dolomite → barite. The mean chemical composition of the host dolomite matrix and HTD didn't change much during hydrothermal process. The fluids forming the HTDs in the Dengying Formation were mixtures of freshwater from the unconformity at the top of Sinian, fluids from diagenetic compaction and hydrocarbon generation & expulsion from the Lower Cambrian Niutitang Formation mudstones or the Doushantuo Formation silty mudstones, and hydrothermal fluids from the basement. The hydrocarbon reservoirs associated with the HTD were mostly controlled by the basement faults and fractures and karsting processes at the unconformity separating Sinian and Cambrian strata. The hydrocarbon storage spaces of HTD included dissolved cavities and intercrystalline pores. Dissolution cavities are extensive at the top of Dengying Formation, up to about 46 m below the unconformity between Sinian and Cambrian and were generated mainly during karstification. Hydrothermal alteration enhanced the reservoir property of the Dengying Formation dolomites with 3%-5% increase in porosity. No agreement has been reached why zebra dolomite occurs only in the Upper Sinian strata, which would indicate that HTD mineralization occurred during two different periods, each of them related to major extensional tectonic event. The early one related to the Xingkai taphrogenesis(Z2-?1)and the later one to the Emei taphrogenesis(D2-T2). But, all the data from saddle dolomite suggest that the predominant crystallization occurred during the latter event. | LIU Shugen HUANG Wenming JANSA Luba F. WANG Guozhi SONG Guangyong ZHANG Changjun SUN Wei MA Wenxin | 2014 | Acta Geologica Sinica(English Edition)2014，88，5： | 11 |
| 2 | Biostratigraphy of a Paleocene-Eocene Foreland Basin boundary in southern Tibet显示文摘This study of the Paleocene—Eocene boundary within a foreland basin of southern Tibet, which was dominated by a carbonate ramp depositional environment,documents more complex environmental conditions than can be derived from studies of the deep oceanic environment.Extinction rates for larger foraminiferal species in the Zongpu-1 Section apply to up to 46%of the larger foraminiferal taxa. The extinction rate in southern Tibet is similar to rates elsewhere in the world,but it shows that the Paleocene fauna disappeared stepwise through the Late Paleocene,with Eocene taxa appearing abruptly above the boundary.A foraminifera turnover was identified between Members 3 and 4 of the Zongpu Formation—from the Miscellanea—Daviesina assemblage to an Orbitolites—Alveolina assemblage.The Paleocene and Eocene boundary is between the SBZ 4 and SBZ 5,where it is marked by the extinction of Miscellanea miscella and the first appearance of Alveolina ellipsodalis and a large number of Orbitolites. Chemostratigraphically,theδ^(13)C values from both the Zongpu-1 and Zongpu-2 Sections show three negative excursions in the transitional strata,one in Late Paleocene,one at the boundary,and one in the early Eocene.The second negative excursion ofδ^(13),which is located at the P—E boundary,coincides with larger foraminifera overturn.These faunal changes and the observedδ^(13)C negative excursions provide new evidence on environmental changes across the Paleocene—Eocene boundary in Tibet. | Xiaoqiao Wan Xi Wang Luba F. Jansa | 2010 | Geoscience Frontiers2010，1，1： | 4 |
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