Experimental and Numerical Assessment of the Influence of Bottomhole Pressure Drawdown on Terrigenous Reservoir Permeability and Well Productivity

During oil and gas fields development,a decrease in reservoir and bottomhole pressure has often a detrimental effect on reservoir properties,especially permeability.This study presents the results of laboratory tests conducted to determine the response of terrigenous reservoir core-sample permeability to changes in the effective stresses and a decrease in the reservoir pressure.The considered samples were exposed for a long time to a constant high effective stress for a more reliable assessment of the viscoplastic deformations.According to these experiments,the decrease of the core samples permeability may reach 21%with a decrease in pressure by 9.5 MPa from the initial reservoir conditions.Numerical simulations have been also conducted.These have been based on the finite element modeling of the near-wellbore zone of the terrigenous reservoir using poroelasticity relations.The simulation results show a limited decrease in reservoir permeability in the near-wellbore zone(by 17%,which can lead to a decrease in the well productivity by 13%).

Carboniferous Mixed Terrigenous Clastic, Carbonate and Sulphate Sediments in the Bachu Area, Xinjiang

The Carboniferous system in the Xiaohaizi area, Bachu County, Xinjiang Uygur Autonomous Region, composed of typical mixed terrigenous clastic, carbonate and sulphate sediments, was mainly deposited in the tidal flat and lagoon environments. The mixed sediments occur as the following eleven types: 1. limestone intercalated with siltstone; 2. interbeds of shale and limestone; 3. gypsolyte interbedded with limestone; 4. gypsolyte intercalated with siltstone; 5. gypsolyte interbedded with shale; 6. gypsolyte intercalated with siltstone, limestone and dolomite; 7. siltstone interbedded with gypsolyte and limestone; 8. terrigenous detritus scattered in carbonate matrix; 9. carbonate as cement in clastic rocks; 10. mixed sediments of carbonate and terrigenous mud; 11. mixed sediments of carbonate grains with terrigenous sand. Based on the analysis of the dynamic mechanism of mixed sediments, it is believed that these types of mixed sediments in the study area were controlled by climate, sea level change and sources of sediments.

New Discovery of the Late Triassic Terrigenous Sediments in the Great Xing＇＇an Range Region,NE China and its Geological Significance

Objective The Great Xing＇an Range is located in the eastern section of Central Asian Orogenic Belt（CAOB）.As a superposed position of multiple tectonic domains,its structural evoIlution has always been a focused issue of geological research.

Late Quaternary terrigenous sedimentation in the Western Arctic Ocean as exemplified by a sedimentary record from the Alpha Ridge

Terrigenous components in sediment core B84A from the Alpha Ridge, Western Arctic Ocean, have been investigated to reconstruct Mid to Late Quaternary variations in sedimentation, provenance, and related climate changes. The core stratigraphy, evaluated by a combination of variations in Mn content, color cycles, foraminiferal abundance, and lithological correlation, extends back to estimated Marine Isotope Stage 12. Twelve Ice Rafted Detritus （IRD, 〉250 ttm） events were identified and interpreted to mostly occur during deglaciation. The Canadian Arctic, which was covered by ice sheets during glacial periods, is suggested to be the major source region. The IRD events likely indicate the collapses of ice sheets, possibly in response to abrupt climate changes. Grain size analysis of B84A indicates sedimentologically sensitive components in core B84A in the 4 9 #m and 19 53/~m silt subfractions, which are inferred to be mainly transported by currents and sea ice, respectively. Down core variability of these two fractions may indicate changes in ice drift and current strength. In accordance with previous studies in the central Arctic Ocean, the average sedimentation rate in core B84A is about 0.4 cm.ka-1. Compared with the relatively high sedimentation rates on the margins, sedimentation in the central Arctic Ocean is limited by sea ice cover and the correspondingly low bioproductivity, as well as the long distance from source regions of terrigenous sediment.

Sources and Transport of Terrigenous Organic Matters Along the East China Sea Inner Shelf: Insights from Lignin and Alkane Biomarkers

The area of East China Sea(ECS)inner shelf is an important sink of suspended particulates from Yangtze River(YR)and materials originated from YR basin.In this study,the parameters of lignin and alkane biomarkers in surface sediment samples from ECS inner shelf were determined to distinguish the sources and to trace the transport of terrigenous organic matters in the region.Our dataset showed that total alkanes with carbon numbers from 10 to 38(T-alkanes)were significantly correlated to both TAR(terrigenous/aquatic ratio)and HMW/LMW(the ratio of high molecular weight to low molecular weight alkanes)(r=0.88,P<0.05 for both),indicating that the majority of T-alkanes was predominantly originated from terrestrial sources,and T-alkanes are important constituents of terrestrial organic matters in the study area.The area was probably affected by petroleum pollution to a certain degree,as indicated by the values of carbon preference index(CPI),odd-over-even carbon number predominance(OEP)and the ratio of pristane to phytane(Pr/Ph).The values of Pr/n-C_(17) and Ph/n-C_(18) suggested a strong reductive sedimentary condition in the region with no obvious biodegradation.The content of eight lignin phenols(Σ8)decreased from the coast to the open sea,indicative of riverine input and hydrodynamic transport of terrigenous organic matters.Lignin degradation parameters presented an increasing trend from the coastline toward the open sea.The lignin vegetation parameters and alkane index(AI)suggested the predominance of non-woody angiosperms in the YR basin.The obvious correlation betweenΛ8(Σ8 normalized to 100 mg organic carbon),TAR and HMW/LMW reveals the significantly concurrent input of lignin and alkanes from terrestrial sources.

Response of Terrigenous Sediment Input to Sea Level Change and East Asian Monsoon Evolution Since 30kyr in the Southwestern Taiwan Basin

The compositions of grain size,clay minerals,and geochemical elements in core sediments(TS4)from the southwestern Taiwan Basin(South China Sea)were investigated to assess the response of terrigenous sediment input to sea level change and the East Asian monsoon evolution since 30 kyr.The chronology was discussed based on foraminiferal AMS14C dates.Our results indi-cated that rivers in Taiwan have been the major sediment contributors since 30 kyr,followed by the Pearl River;and Luzon Island contribute little sediments to the southwestern Taiwan Basin.In this study,we reconstructed the variations in terrigenous sediment input by using the proxies such as Al2O_(3)(%),F1 score,and TiO_(2)/CaO.The F1 score can be used to indicate the flux of terrigenous sediments.The contribution of Taiwan Residents rivers and the Pearl River were evaluated by using the value of(illite+chlorite)/kaolinite.The variations of Al2O_(3)(%),F1 score,and TiO_(2)/CaO values along the core were clearly correlated to the evolution of the East Asian summer monsoon since 30 kyr.Based on these records,we recognized three evolutionary stages of terrigenous sediment input in the southwestern Taiwan Basin.During stage Ⅰ(29-24kyr),the input of terrigenous sediments continued to increase.During stage Ⅱ(24-11.5 kyr),the sediment input decreased at first and then increased,with the lowest value during the last glacial period(21-17kyr).Terrigenous sediment input during stage Ⅲ(11.5 kyr-)showed the decreasing first and then increasing trends,generally higher than those in the first and second stages.The variations of terrigenous sediment input in the study area corresponded well with the evolu-tion of the East Asian summer monsoon since 30 kyr.Increased terrigenous sediment input during 4-1.8 kyr was suggested to be caused by the enhanced ENSO activity.Sea level change does not alter the overall trend of terrigenous sediment input,but does change the relative contributions of rivers in Taiwan and the Pearl River.

Identification of terrigenous and autochthonous organic carbon in sediment cores from cascade reservoirs in the upper stream of Pearl River and Wujiang River,southwest China:lignin phenol as a tracer

Organic carbon(OC)source attribution for cascade reservoir sediments has been identified as a critical gap in understanding the effective carbon sink of inland waters.In this study,nine sediment cores were collected from cascade reservoirs in the Wujiang and Pearl Rivers.We analyzed lignin phenol(Λ8),total organic carbon(TOC)content,and stable carbon isotopic composition(δC)of the sediments,focusing on the changes of terrigenous OC,and the variation of OC source in cascade reservoir sediments after damming.Our results showed that theΣ8 and TOC contents decreased from upstream to downstream reservoirs,indicating the significant interception of terrigenous OC by cascade damming.Additionally,theΛ8 content in the Pearl River reservoir sediments was much higher than that in the Wujiang River.From the three-end-member mixing model,we estimated that OC in reservoir sediments mainly comes from soil and plankton.After damming,the proportion of plankton OC in TOC slightly increased in seasonal and annual regulation reservoirs due to the limnetic evolution of the reservoir.These findings suggest that the cascade damming increases the interception capacity of the river to terrigenous OC and nutrients,and that slowing of water velocity caused by damming affected primary productivity and fluvial carbon cycling.

Formation and distribution of coal measure source rocks in the Eocene Pinghu Formation in the Pinghu Slope of the Xihu Depression,East China Sea Shelf Basin

The Xihu Depression in the East China Sea Shelf Basin is a large petroliferous sedimentary depression,in which oil and gas reservoirs were mainly discovered in the Pinghu Slope and the central inversion zone.The oil-gas source correlation in the Xihu Depression was analyzed by hydrocarbon generating thermal simulation data via gold-tube pyrolysis experiments.The results indicated that the oil and gas in the Xihu Depression were mainly derived from coal measure source rocks of the Eocene Pinghu Formation.Therefore,the identification of coal seams is extremely crucial for evaluating coal measure source rocks in the Pinghu Formation in the Xihu Depression.Geochemical and petrological characterization pointed to input of terrigenous organic matter and redox conditions of the depositional environment as factors that govern the ability of the coal measure source rocks in hydrocarbon generation in the Xihu Depression.In this regard,the sedimentary organic facies in the Pinghu Formation were classified into four predominantly terrigenous and one mixed-source subfacies,which all varied in carbon and hydrogen content.The coal measure source rocks in the carbon-and hydrogen-rich tidal flat-lagoon exhibited the highest hydrocarbon generation potential,whereas the mudstone in the neritic facies was the poorest in its hydrocarbon yield.These results suggested that the coal measure source rocks in the Pinghu Formation likely developed in the Hangzhou Slope and the Tiantai Slope,both representing promising sources for oil and gas exploration.

Source of silica and its implications for organic matter enrichment in the Upper Ordovician-Lower Silurian black shale in western Hubei Province,China:Insights from geochemical and petrological analysis

To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3)w-S_(1)l)black shale in western Hubei Province in the middle Yangtze area,were investigated through geochemical and petrological analyses.The results show that the O_(3)w-S_(1)l black shale is mainly composed of five lithofacies with varying graptolite abundance,total organic carbon(TOC),and silica contents.Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O_(3)w-S_(1)l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes.Moreover,with the increase in biogenic silica content or decrease in terrigenous siliciclastic input,TOC values in black shale initially rise and then fall,which is different from originally expected simple linear relationship.We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence.An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation,rather than one with excessive high sea level and less terrigenous input.

Glacial-interglacial productivity contrasts along the eastern Arabian Sea:Dominance of convective mixing over upwelling

The western continental margin of India is one of the highly productive regions in the global ocean.Primary productivity is induced by upwelling and convective mixing during the southwest and northeast monsoons respectively.Realizing the importance of high primary productivity,a sediment core was collected below the current oxygen minimum zone（OMZ） from the southwestern continental margin of India.This was dated by AMS radiocarbon and as many as 60 paleoclimate/paceoceanographic proxies,such as particle size,biogenic components,major,trace and rare earth elements（REEs） which were measured for the first time to determine sources of sediment,biogeochemical processes operating in the water column and their variations since the last glacial cycle.R-mode factor analysis of comprehensive data indicates that the dominant regulator of paleoproductivity is the southwest monsoon wind induced upwelling.Other paleoproductivity related factors identified are the marine biogenic component and biogenic detritus（as an exported component from the water column added to the bottom sediment）.All paleoproductivity components increased significantly during the marine isotope stage-1（MIS-1）compared to those accumulated from MIS-4 to MIS-2.The second group of factors identified are the terrigenous sediments with heavy minerals like zircon and ilmenite.The terrigenous sediment,in particular,increased during MIS-2 when the sea-level was lower;however,the heavy mineral component fluctuated over time implying pulsed inputs of sediment.The diagenetic fraction and reducing component are the third group of factors identified which varied with time with increased accumulation during the MIS transitions.The primary productivity along the southwestern continental margin of India seems to have been controlled principally by the upwelling during the southwest monsoon season that was weaker from MIS-4 to MIS-2,as relative to that during the MIS-1.In contrast,increased glacial productivity noticed in sediments deposited below the current oxygen minimum zone（OMZ） along the north of the study area that can be linked to entrainment of nutrients through the intensified convective mixing of surface water during the northeast monsoon.The sequestration of greenhouse gases by the western continental margin of India was higher during glacial than interglacial cycles.

Sedimentological Study of Caves in the Zemo Imereti Plateau, Georgia, Caucasus Region

The Zemo Imereti Plateau is located in the easternmost part of the limestone region of western Georgia and is Caucasus’ only karst plateau. It is centrally located in a relatively elevated part of the intermountain plain of the country of Georgia. Lithostratigraphical (petrographic, mineralogical, and XRD) research on terrigenous sediments found in caves in the region was conducted in the Upper Cretaceous limestones located at different hypsometric levels (400 - 700 m). This study focused on allochthonous deposits, which, due to sedimentological features, contains significant and complete information for paleogeographic reconstruction as opposed to the autochthonous sediments. Source provinces of the sediments’ origin were determined using petrographic analysis. Lithological study of the terrigenous sediments indicated their origin from the Racha range, as well as their transportation mechanisms, and sedimentation conditions during deposition. Approximate ages (the end of the Middle Pleistocene and the beginning of the Late Pleistocene) of ancient terrestrial sediments in Rganisklde Cave were achieved by taking into account the geological and geomorphological development of the region. Lithostratigraphical analysis of the cave deposits and modern archaeological data indicate that the formation of the caves in the Zemo Imereti plateau took place mainly during the end of the Middle Pleistocene and in the beginning of the Pleistocene;while on the southern slope of the Racha range and in the surrounding area of Ertso-Tsona (Caucasus southern slope), they formed in the Early Pleistocene.

Coral Ba/Ca and Mn/Ca Ratios as Proxies of Precipitation and Terrestrial Input at the Eastern Offshore Area of Hainan Island

Geochemical ratios in coral reef skeletons could be used as proxies to reconstruct past climatological and environmental records in data-poor regions. Using a 103-year data set(1902 to 2005), the annual variations in Ba/Ca and Mn/Ca ratios of Porites lutea skeletons at an eastern offshore area of Hainan Island(19?12'28.4''N, 110?37'38.8''E) were analyzed using inductively coupled plasma-optic emission spectrometry(ICP-OES). The analysis results showed that Ba/Ca ratios varied from a minimum of 3.120 μmol mol^(-1) in 1903 to a maximum of 10.064 μmol mol^(-1) in 1944, with an average of 5.256 μmol mol^(-1). Mn/Ca ratios varied from 0.206 to 5.708 μmol mol^(-1) with an annual average of 1.234 μmol mol^(-1), with peak values in 2001, 1964 and 1932, that correlated with strong rainfall events caused by typhoons. Variation in Ba/Ca and Mn/Ca ratios were compared with available river discharge and precipitation records, providing insight into past climatological events. Human activities and their indirect effects could impact the strength of the relationship between Ba/Ca and Mn/Ca ratios and observed precipitation and terrestrial input in the future.

Sedimentary sources and processes in the eastern Arabian Sea:Insights from environmental magnetism,geochemistry and clay mineralogy

The spatial distribution patterns of surficial sediment samples from different sedimentary domains （shallow to deep-sea regions） of the eastern Arabian Sea were studied using sediment proxies viz. environmental magnetism, geochemistry, particle size and clay mineralogy. Higher concentrations of magnetic minerals （high Xlf） were recorded in the deep-water sediments when compared with the shallow water sediments. The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the XARM/Xlf VS. XARM/Xfd biplot. However, the other samples are catchment-derived. The high correlation documented for Xlf, anhysteretic remanent mag- netisation （XARM） and isothermal remanent magnetisation （IRM） with Al indicates that the deep-sea surflcial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers, the Sindhu （the Indus） and the Narmada-Tapti rivers. A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone （OMZ） but a higher Mn/AI ratio is documented in the lower slope and deep-sea sediments. Clay minerals such as illite （24-48.5%）, chlorite （14.1-34.9%）, smectite （10.6-28.7%） and kaolinite （11.9-27.5%） dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents. Organic carbon （OC） data indicate a low concentration in the shallow/shelf region （well oxygenated water conditions） and deeper basins （increased bottom-water oxygen concentration and low sedimentation rate）. High OC concentrations were documented in the OMZ （very low bottom-water oxygen concentration with high sedimentation rate）. The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions （〈 1800 m） up to the Chagos-Laccadive Ridge show higher concentrations （average - 58%） when compared to deep basin sediments （average - 44%）. Our study demonstrates that particle size as well as magnetic grain size, magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.

Distributions of pigments in reef sediments, contribution of phytoplankton to organic matter budget in coral reef

The temporal distributions of pigment on bio-genic calcareous and terrigenic reef sediments, chlorophyll a, chlorophyll b, chlorophyll c, fuco- xanthin, and porphine concentrations were mea- sured monthly in two sediment columns (0 - 15 cm) for one year. Pigment concentrations in-creased significantly during winter (Novem-ber-April) in both sediment types particularly in the upper layers of the sediments. Phytoplankton contributions to organic matter were found to be 8 ± 3 and 6 ± 2% in calcareous and terrigenous sediments respectively. The accumulation and the successive degradation of phytoplankton detritus to inorganic nutrients in calcareous sand may partly sustain the productivity of the coral reef communities which live in nutrient-poor environments.

Current Situation and Application in Coal-Generated Hydrocarbons

The characteristics and research methods of terrigenous organic hydrocarbon-generated source rock in coal measures are studied in this thesis. After abundance of organic matters, pyrolysis parameter of rocks and hydrocarbon generated capacity of macerals are basically discussed in coal measures of the Cretaceous Muleng-Chengzihe formation in Suibin depression in Sanjang basin, the hydrocarbon generated grade in coal-genera^ted source rock is ascertained in this depression. At last, we think that it is a main attack prospect in coal-genera^ted hydrocarbons study in the future to research the macerals of coal measures organic source rock and to build a criterion to classify the coal-generated hydrocarbons in Northeast region.

Global and regional controls on carbon-sulfur isotope cycling during SPICE event in south China

The positive S-isotopic excursion of carbonate-associated sulfate(δ34S_(CAS))is generally in phase with the Steptoean positive carbon isotope excursion(SPICE),which may reflect widespread,global,transient increases in the burial of organic carbon and pyrite sulfate in sediments deposited under large-scale anoxic and sulphidic conditions.However,carbon-sulfur isotope cycling of the global SPICE event,which may be controlled by global and regional events,is still poorly understood,especially in south China.Therefore,theδ13CPDB,δ18OPDBδ34S_(CAS),total carbon(TC),total organic carbon(TOC)and total sulfate(TS)of Cambrian carbonate of Waergang section of Hunan Province were analyzed to unravel global and regional controls on carbon-sulfur cycling during SPICE event in south China.Theδ34S_(CAS)values in the onset and rising limb are not obviously higher than that in the preceding SPICE,meanwhile sulfate(δ34S_(CAS))isotope values increase slightly with increasingδ13CPDB in rising limb and near peak of SPICE(130–160 m).The sulfate(δ34S_(CAS))isotope values gradually decrease from 48.6‰to 18‰in the peak part of SPICE and even increase from 18%to 38.5%in the descending limb of SPICE.The abnormal asynchronous C−S isotope excursion during SPICE event in the south China was mainly controlled by the global events including sea level change and marine sulfate reduction,and it was also influenced by regional events such as enhanced siliciclastic provenance input(sulfate),weathering of a carbonate platform and sedimentary environment.Sedimentary environment and lithology are not the main reason for global SPICE event but influence theδ13CPDB excursion-amplitude of SPICE.Sea level eustacy and carbonate platform weathering probably made a major contribution to theδ13CPDB excursion during the SPICE,in particularly,near peak of SPICE.Besides,the trilobite extinctions,anoxia,organic-matter burial and siliciclastic provenance input also play an important role in the onset,early and late stage of SPICE event.

Genesis and Implications of the Composition and Sedimentary Structure of Fine-Grained Carbonate Rocks in the Shulu Sag

Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.

REEs fractionation and sedimentary implication in surface sediments from eastern South China Sea

To get features of rare earth elements （REEs） fractionation, 106 surface sediment samples from eastern South China Sea were determined for REEs combined with major and trace elements by ICP-MS. The distribution pattern of REEs, strong correlation between REEs and Al, North American shale composite （NASC） normalization all suggest a dominant crustal source for REEs in the research area. However distinct fractionation among REEs was observed in surface sediment from area with water depth over 2000 m, confirmed by the strong positive correlation among light rare earth elements （LREEs） and among heavy rare earth elements （HREEs） but weaker relationship between LREEs and HREEs. Eluviation by Cl- might be a key role on the fiactionation of REEs, comparing with factors such as grain size, co-precipitation with Fe and Mn hydroxide, calcareous and siliceous biogenic precipitation. The fractionation among REEs could be used as index to illustrate the sedimentary environment in reverse.

Novel Tetracyclic Terpanes in Crude Oils and Source Rock Extracts in Pearl River Mouth Basin and Their Geological Significance

Novel tetracyclic terpanes X and Y namely C24-des-A-oleanane and C27 tetracyclic terpane were detected in crude oils and source rock extracts in Zhu 1 depression in Pearl River Mouth Basin by GC-MS analysis technology. These compounds are similar to oleanane in the structure, and their relative abundance in m/z 191 partial mass cbromatogram has a good correlation with oleanane. Here compounds X and Y are considered to be derived from the des-A degradation of oleanoid precursor. The ratio of X/（X-I-C24） and Y/（Y-I-C24） increase with the increasing inputs of terrigenous organic matter in crude oils. Wenchang Formation middle-deep lacustrine source rocks with planktonic algae organic matter inputs and oil generating from it contain low abundance of compounds X and Y, while Enping Formation coal measures source rocks with terrigenous higher plants organic matter inputs and oil generating from it usually have higher compounds X and Y. In general when two terrigenous compounds C19 tricyclic terpane and bicadinane-T are high in crude oils, there are also a corresponding high abundant compounds X and Y. Relative abundance of compounds X and Y is closely related to the source of organic matter and it can indicate the input of terrigenous organic matter.

Devonian ichnofossils and their environmental significance of northern belt of Western Qinling Mountains

It is beheved that the Shujiaba Formation belongs to a series of thick turbidites. 20 ichnogenera have been found in the formation, of which 14 genera were found in the Devonian System of China for the first time The ichnogenera are mostly of typical deep-water ones and belong to the Nereites ichnofacies A detailed study of morphology and behaviour of the trace fossils indicates that the Shujiaba Formation was deposited in a bathyal-abyssal environment.