First Research on Marine and Nonmarine Sedimentary Sequences and Micropaleontologic Significance across Permian/Triassic Boundary in Iran (Isfahan and Abadeh)

Abundant ichthyoid remains, conodonts and holothurians sclerites were recovered near the Permian/Triassic boundary from a section south of Isfahan. Recovered ichthyoid remains include shark micro teeth and scales. The ichthyolith material is similar to a Fasanian ichthyolith from the Zakazane area in the Slovak karst of the Western Carpathians, which represents a subspecies of Acodina triassica . Conodont species are mostly neogondolellids. This fauna indicates that the sedimentary environment was marine, while to the north of localities near Isfahan and Zagross, terrestrial deposition was dominant at that time. Aluminasilicate and kaolin are present in a continental unit in Dopolan refractory main (Shahid Nilchian mine) and a section south of Chahriseh Village, north of Isfahan. Pisolitie, ironstone facies and bauxite clay are common near the Permian/Triassic boundary in the Chahriseh region.

Main Controlling Factors on Hydrocarbon Accumulation and Distribution in Marine Sedimentary Sequences in South China

Multiple source rock assemblages were deposited in the sedimentary provinces in South China in geologic history, and some of them were destructed by and some survived against multiple tectonic movements. Therefore, multiple sources, mixed sources, and uneven distribution of sources occurred in the marine sedimentary basins in South China during the late stage of hydrocarbon pooling. Epidiagenesis of the marine carbonate reservoirs and its modification to reservoir poroperm characteristics determined the formation and the scale of natural gas pools. The exploration practices show that the large to medium gas fields mainly occur in areas with high-quality reservoirs. Detailed study of the paleo-oil accumulations and typical oil and gas reservoirs reveals that the basins experienced multiphase superimposition and modification, leading to the distribution of the Paleozoic paleo-oil accumulations and bitumen in the peripheral areas. The phenomenon that oil and gas production concentrates in the Sichuan basin indicates that the overall sealing conditions of a basin determine the oil/gas potentials and the scale of oil and gas production. This is a critical factor controlling the accumulation and distribution of gas in the marine sequences in South China. The early oil and gas pools in the Yangtze platform left billions of bitumen in the peripheral areas due to the destruction of seals. Since the Himalayan, ＂late-generation and late-accumulation＂ gas pools represented by the gas pools in the Sichuan （四川） basin were formed in the marine sedimentary sequences in South China as a result of the change of the sealing conditions. Current gas discoveries appear to be ＂paleo-generation and paleoaccumulation＂ gas pools but actually are ＂late-generation and late-accumulation＂ gas pools. These patterns of hydrocarbon pooling clearly depict themselves in western Sichuan basin and Weiyuan （威远） gas field. It is revealed that the gas pools in the Sichuan basin were mainly formed as a result of hydrocarbon phase change （thermal cracking of oil to gas）, miscible migration, and dynamic equilibration since the Himalayan. A large number of gas pools were formed in the Himalayan and the gas pools in the marine sequences are characterized by late pooling; this kind of gas fields/pools are controlled by： （1） effectiveness of modification and superimposition of the marine basins, （2） effectiveness of the source rocks, （3） effectiveness of the overall preservation conditions, and （4） effectiveness of plays.

Characteristics analysis and model prediction of sea-salt water intrusion in lower reaches of the Weihe River,Shandong Province,China

Marine sedimentary strata are widely distributed in the coastal zone of the study area, and are rich in brine resources. The exploitation of underground water resources often first caused the intrusion of salt water in the marine strata. Based on the analysis of sea-salt water intrusion feature, the sea-salt water intrusion is divided into four stages: The occurrence and development stage(1976–1985), the rapid development stage(1986–1990), the slow development stage(1990–2000) and the stable development stage(2000–2015). Based on the comparative analysis of the relationship between seawater intrusion and influencing factors, this paper presents that the groundwater exploitation and the brine resources mining are the main control factors of sea-salt water intrusion. On this basis, we have established a numerical model of the sea-salt water intrusion. Using this model, we predicted the development trend of the sea-salt water intrusion. The results show that if the current development of groundwater and brine is maintained, the sea-salt water intrusion will gradually withdraw; once development of brine stops, sea-salt water will invade again. This provides the scientific basis for the rational exploitation of groundwater and the prevention of sea-salt water intrusion.

The effect of iron on the preservation of organic carbon in marine sediments and its implications for carbon sequestration

Marine sediments are the most significant reservoir of organic carbon(OC)in Earth′s surface system.Iron,a crucial component of the marine biogeochemical cycle,has a considerable impact on marine ecology and carbon cycling.Understanding the effect of iron on the preservation of OC in marine sediments is essential for comprehending biogeochemical processes of carbon and climate change.This review summarizes the methods for characterizing the content and structure of iron-bound OC and explores the influencing mechanism of iron on OC preservation in marine sediments from two aspects:the selective preservation of OC by reactive iron minerals(iron oxides and iron sulfides)and iron redox processes.The selective preservation of sedimentary OC is influenced by different types of reactive iron minerals,OC reactivity,and functional groups.The iron redox process has dual effects on the preservation and degradation of OC.By considering sedimentary records of iron-bound OC across diverse marine environments,the role of iron in long-term preservation of OC and its significance for carbon sequestration are illustrated.Future research should focus on identifying effective methods for extracting reactive iron,the effect of diverse functional groups and marine sedimentary environments on the selective preservation of OC,and the mediation of microorganisms.Such work will help elucidate the influencing mechanisms of iron on the long-term burial and preservation of OC and explore its potential application in marine carbon sequestration to maximize its role in achieving carbon neutrality.

The sedimentological characteristics of microbialites of the Cambrian in the vicinity of Beijing,China

With oil and gas exploration transferring to deeper and more ancient marine strata,more researches have been conducted about the Meso—Neoproterozoic and Cambrian microbial carbonate rocks by petroleum geologists.The Cambrian deposits experienced the first transgression of the Paleozoic,with shallow marine facies depositing in most areas,which are favorable for different kinds of biological reproduction.The Lower Cambrian in Beijing area is lithologically dominated by purple red shales interbedded with limestones,the Middle Cambrian is mainly composed of thick oolitic limestones,and the Upper Cambrian consists of thin limestones and flat-pebble conglomerates.Two beds of microbial carbonate rocks were discovered in the Cambrian outcrops in the vicinity of Beijing.One is from the Zhangxia Formation of Middle Cambrian,and the other is from the Gushan Formation of Upper Cambrian.The microbialites are characterized by combination of multiple stromatolites forming different bioherms.The bioherms are mostly in oval shape and with different sizes,which are 3-4 m long,and 1-3 m high.The surrounding strata beneath the bioherms are oolitic limestones.A central core of flat-pebble conglomerates occurred within each bioherm.Wavy or columnar stromatolites grow on the basis of flat-pebble conglomerates,with dentate erosional surfaces.The bioherm carbonate rocks are interpreted as products from a deep ramp sedimentary environment where potential oil and gas reservoirs can be found.The analysis of sedimentological characteristics of bioherm carbonate rocks and its lithofacies palaeogeography has significant implication for petroleum exploration.Research on geological record of microbialites is beneficial to investigating the Earth evolution,biodiversity,palaeoenvironment and palaeoclimate change,as well as biological extinction event during geological transitions.It also gives warning to human beings of modern biological crisis.