1 Introduction Numerous studies on the Meso-Neoproterozoic life evolution show that the cyanobacteria which thrived and dominated the biological world in the Proterozoic Era is closely related to the genesis of microb...1 Introduction Numerous studies on the Meso-Neoproterozoic life evolution show that the cyanobacteria which thrived and dominated the biological world in the Proterozoic Era is closely related to the genesis of microbial carbonate rocks.Considerable oil and gas resources can be found in microbial carbonate rocks and many related oil and gas展开更多
Well Lundong-1 is located in the periclinal area on the eastern flank of the Tahe-Lunnan paleo-uplift in the Tarim Basin. A 25-m-high cave fill sequence was observed in the Upper Ordovician interval of the well at 680...Well Lundong-1 is located in the periclinal area on the eastern flank of the Tahe-Lunnan paleo-uplift in the Tarim Basin. A 25-m-high cave fill sequence was observed in the Upper Ordovician interval of the well at 6800-6825m. A third cut of cores was obtained from the top of the cave. The following conclusions were obtained by studying the cave sediments and depositional sequence, and by undertaking paleontological and elemental geochemistry analyses. 1. The cave sediments contain abundant brachiopod, gastropod, echinoderm, ostracod, and acritach fossils, which can be classified into two groups: cave autochthonous and cave allochthonous fossils (from collapse breccia dissolution or transportation by underflow). The fossils indicate that the cave was formed before the Carboniferous and partly-filled and buried during Carboniferous resubsidence. 2. Elemental geochemistry shows that the mud that filled the cave is sourced from calcareous paleo-soil and weathered crust that came from a salty environment with poor water circulation. 3. The formation and evolution of the cave occurred in three stages. The first stage occurred after the deposition of the Late Ordovician Lianglitage Formation, the second stage took place after the deposition of the Late Ordovician Sangtamu Formation, and the last stage happened after Silurian deposition. Major dissolution occurred in the latter two stages as a result of bedding-confined deep underflow karstification. Based on the reconstruction of the cave formation history, favorable paleokarst targets can be predicted and estimated to aid paleogeography and paleokarstology studies.展开更多
文摘1 Introduction Numerous studies on the Meso-Neoproterozoic life evolution show that the cyanobacteria which thrived and dominated the biological world in the Proterozoic Era is closely related to the genesis of microbial carbonate rocks.Considerable oil and gas resources can be found in microbial carbonate rocks and many related oil and gas
基金supported by"Conditions for Giant Marine Carbonate Oil/Gas Fields to Form in Sichuan, Tarim Basins and the Neighboring Regions" a Key National Oil and Gas Program (Grant No. 2008ZX05004-002)
文摘Well Lundong-1 is located in the periclinal area on the eastern flank of the Tahe-Lunnan paleo-uplift in the Tarim Basin. A 25-m-high cave fill sequence was observed in the Upper Ordovician interval of the well at 6800-6825m. A third cut of cores was obtained from the top of the cave. The following conclusions were obtained by studying the cave sediments and depositional sequence, and by undertaking paleontological and elemental geochemistry analyses. 1. The cave sediments contain abundant brachiopod, gastropod, echinoderm, ostracod, and acritach fossils, which can be classified into two groups: cave autochthonous and cave allochthonous fossils (from collapse breccia dissolution or transportation by underflow). The fossils indicate that the cave was formed before the Carboniferous and partly-filled and buried during Carboniferous resubsidence. 2. Elemental geochemistry shows that the mud that filled the cave is sourced from calcareous paleo-soil and weathered crust that came from a salty environment with poor water circulation. 3. The formation and evolution of the cave occurred in three stages. The first stage occurred after the deposition of the Late Ordovician Lianglitage Formation, the second stage took place after the deposition of the Late Ordovician Sangtamu Formation, and the last stage happened after Silurian deposition. Major dissolution occurred in the latter two stages as a result of bedding-confined deep underflow karstification. Based on the reconstruction of the cave formation history, favorable paleokarst targets can be predicted and estimated to aid paleogeography and paleokarstology studies.
