The coupling control of biological precursors and environmental factors onβ-carotane enrichment in alkaline lacustrine source rocks:A case study from the Fengcheng formation in the western Junggar Basin,NW China

The organic-rich mudstones and dolostones of the Permian Fengcheng Formation(Fm.)are typically alkaline lacustrine source rocks,which are typified by impressively abundantβ-carotane.Abundant β-carotane has been well acknowledged as an effective indicator of biological sources or depositional environments.However,the specific biological sources of β-carotane and the coupling control of biological sources and environmental factors on the enrichment of β-carotane in the Fengcheng Fm.remains obscure.Based on a comprehensive investigation of the bulk,molecular geochemistry,and organic petrology of sedimentary rocks and the biochemistry of phytoplankton in modern alkaline lakes,we proposed a new understanding of the biological precursors of β-carotane and elucidated the enrichment mechanism of β-carotane in the Fengcheng Fm.The results show that the biological precursors crucially control the enrichment of β-carotane in the Fengcheng Fm.The haloalkaliphilic cyanobacteria are the primary biological sources of β-carotane,which is suggested by a good positive correlation between the 2-methylhopane index,7-+8-methyl heptadecanes/C_(max),C_(29%),and β-carotane/C_(max)in sedimentary rocks and the predominance of cyanobacteria with abundantβ-carotene in modern alkaline lakes.The enrichment of β-carotane requires the reducing condition,and the paleoredox state that affects the enrichment of β-carotane appears to have a threshold.The paleoclimate conditions do not considerably impact the enrichment of β-carotane,but they have some influence on the water's paleosalinity by affecting evaporation and precipitation.While it does not directly affect the enrichment of β-carotane in the Fengcheng Fm.,paleosalinity does have an impact on the cyanobacterial precursor supply and the preservation conditions.

Organic matter accumulation in lacustrine shale of the Permian Jimsar Sag,Junggar Basin,NW China

The lacustrine organic-rich shale in the Permian Lucaogou(LCG)Formation of the Jimsar Sag,Junggar Basin,is one of the main shale oil plays in China.In this paper,geological and geochemical research techniques were employed to evaluate the geochemical variability of the lacustrine shale and the pro-duction of organic matter and its preservation conditions.The LcG Formation is characterized by its complex mineral compositions and a wide range of organic matter richness and quality.The presence of high proportions ofβ-carotane and C2g steranes,indicates that the organic matter mainly originated from phytoplankton and aquatic algal-bacterial organisms,especially cyanobacteria.This study found that the productivity of the Lower LCG Member(P2li)was highest,and the Middle LCG Member(P_(2)l_(2))was the lowest.During the deposition of the Lower LCG Member,the lake's bottom water was predominantly a reducing environment,and the degradation of organic matter was largely a result of bacterial sulfate reduction.During the deposition of the Middle and Upper LCG members,the lake's bottom water was mainly oxidizing,and the degradation of organic matter was likely to be caused by aerobic processes.Based on a comprehensive analysis of the origin and production of organic matter,as well as its depo-sitional environment and preservation conditions,two organic matter accumulation models were pro-posed to explain the distribution of the organic-rich shale.In model A,the high influx of volcanic ash released nutrients and brought abundant sulfate into the water,the accumulation of organic matter was mainly controlled by the preservation of organic matter,which was mainly controlled by BsR.In the model B,the influx of volcanic ash was small,organic matter was mainly degraded by oxygen and the accumulation of organic matter is mainly determined by the production of organic matter.

Contralateral pneumothorax in the subacute phase after pacemaker implantation:lead retention and follow-up

An 89-year-old woman[body mass index(BMI)=20.27 kg/m^2)]with hypertension underwent implantation of a dual-chamber pacemaker because of dizziness and syncope due to sick sinus syndrome.Pacemaker implantation via the left subclavian approach was performed on June 3,2017.A right ventricular active lead(TendrilTM STS 2088TC,St Jude Medical,Penang,Malaysia)and an atrial active lead(OptisenseTM 1999,St Jude Medical,Penang,Malaysia)were placed in the right ventricular apex and anterior wall of the right atrium,respectively.

Source and accumulation process of Jurassic biodegraded oil in the Eastern Junggar Basin,NW China

Biodegradation usually obscures or even radically alters the original characteristics of oil biomarkers.The mixing of oil from multiple sources makes each source difficult to trace.Identifying the source of biodegraded oil from multiple sources has always been a hard nut to crack.Rising to this challenge,in this study-we carried out a comprehensive investigation of biodegradation impacts,oil-source correlation,and oil charging history to trace the source and reveal the mixing process of biodegraded oil in the Toutunhe Formation(J_(2)t)in the eastern Junggar Basin,NW China.The oil of this area was biodegraded to different extent,consequently,many commonly used biomarker parameters(e.g.Pr/Ph,Pr/n C_(17))became less powerful for oil-source correlation.To address this problem,the resistance of many biomarkers to biodegradation was analyzed,and those of high bio resistance were selected to generate a more reliable oil-source correlation.The results revealed that biodegraded oil was a mixture of oil sourced from Lucaogou Formation(P_(2)l)and Xiaoquangou Formation(T_(2-3)xq).Core sample observation,microscopic fluorescent analysis and fluid inclusion analysis were combined to analyze comprehensively oil charging history.The analysis of accumulation process exhibited that the existing oil in J_(2)t was a mixture originated from the P_(2)l and T_(2-3)xq source rocks in two separate charging stages when it underwent a complicated process of charging,biodegradation,recharging and mixing.