Stratigraphic framework and sedimentary evolution during the Cryogenian-Ediacaran transition in northeastern Sichuan Basin,South China

The northeastern Sichuan area in the northern Yangtze margin has unique Ediacaran geological records,especially the Doushantuo Formation(DST),and become a hot research area in recent years.However,the Cryogenian-Ediacaran(C-E)boundary has not been precisely identified,which restricts the in-depth study of geological information during this crucial transitional period and is unfavorable for a systematic and complete understanding of the Yangtze Block and even the global paleogeographic pattern.This study conducted stratigraphy,sedimentology,and chronostratigraphy to establish the stratigraphic framework and sedimentary evolution of the C-E transition strata in northeastern Sichuan.The results showed that the Ediacaran sediments,without the cap dolomite,unconformably overlaid the Cryogenian sediments in the studied area.The Member II of the DST,characterized by 50-160 m of red-green sandstone(approximately equivalent to the original Chengkou“Guanyinya Formation”),directly overlaid the Cryogenian sediments and displayed a 623±2.3 Ma maximum depositional age from the detrital zircon U-Pb dating.Regional stratigraphic correlations indicate that the C-E transition strata in northeastern Sichuan had a consistent lithological association and sedimentary sequence characteristics but differed from the Three Gorges.Typically,the upper Nantuo massive glacial diamictites transition to the icebergs rafted lonestone-bearing mudstones at the top,then change upward to DST barrier coast sandstones.The proposed DST of the northeastern Sichuan Basin was divided into three lithostratigraphic members without the regional Member I cap dolomite:(i)Member II purple-red,gray-green sandstone strata,(ii)MemberⅢblack mudstone strata,and(iii)Member IV P-Mn bearing strata.During the C-E transition,the study area experienced(i)the global deglaciation stage in the terminal Marinoan glaciation and(ii)the filling-leveling up stage with clastic rocks in the early Ediacaran.Overall,the early Ediacaran of northeastern Sichuan succeeded the paleogeographic features of the late Cryogenian.

Keyhole Foraminotomy via a Percutaneous Posterior Full-endoscopic Approach for Cervical Radiculopathy:An Advanced Procedure and Clinical Study

Endoscopic cervical foraminotomy is increasingly used for cervical spondylotic radiculopathy(CSR),but there is great concern about radiation exposure because of the heavy dependence of this surgical method on fluoroscopy.The objective of this study was to introduce in detail an advanced surgical technique of keyhole foraminotomy via a percutaneous posterior full-endoscopic approach as a treatment for CSR and investigate its clinical outcomes.We retrospectively reviewed 33 consecutive patients with CSR who underwent keyhole foraminotomy via a percutaneous posterior full-endoscopic approach from October 2015 to April 2017.The patients’general characteristics,including operative time,blood loss,hospital stay,complications,and recurrence,were obtained.Clinical outcomes were evaluated using the visual analogue scale(VAS)for radicular pain,the neck disability index(NDI)for functional assessment,and the modified MacNab criteria for patient satisfaction.All operations were successfully performed(mean operation time,62 min),with no measurable blood loss or severe related complications.The mean follow-up was 25 months.The VAS and NDI scores were significantly improved as compared with those in the preoperative period(preoperative vs.final follow-up:7.6±1.6 vs.3.83±7.34 for VAS,P<0.01;69.5%±10.5%vs.17.54%±13.40%for NDI,P<0.01).Of the 33 patients,32(97.0%)had good-to-excellent global outcomes and all patients obtained symptomatic improvement.In conclusion,keyhole foraminotomy via a percutaneous posterior full-endoscopic approach is an efficient,safe,and feasible procedure for the treatment of CSR.Its simplified single-step blunt incision for localization appears to decrease radiation exposure risks.

Geochemistry of upper Permian siliceous rocks from the Lower Yangtze region, southeastern China:implications for the origin of chert and Permian ocean chemistry

The Permian Chert Event is of great significance to understanding the geological evolution of the entire Permian; however,the origin of widespread chert formation is debated. We report new geochemical data from deep-marine siliceous rocks of the upper Permian Da-long Formation, Lower Yangtze region, southeastern China. Their geochemical results show that these thin-bedded siliceous rocks have a clear biologic origin, with rare to no evidence of hydrothermal influence. The values of Al/(Al + Fe + Mn) and Eu/Eu~* are 0.60-0.84(mean = 0.72) and 0.45-1.08(mean = 0.77), respectively, and Mn/Ti ratios are relatively low(mean = 0.72). The correlations of LaN/CeN, LaN/YbN, and Fe203/Ti02 with Al_2 O_3/(Al_2 O_3 + Fe_2 O_3), along with the Ce anomaly, indicate that the Da-long siliceous rocks were deposited at a transitional zone between a continental margin and the open ocean; i.e., relatively close to terrestrial sediment input and far from hydrothermal activity. The accumulation of chert is related to its unique paleogeographic location in an equatorial setting with many submarine paleo-highlands.Intense upwelling and frequent local volcanism are the main factors that promoted the development of siliceous rocks in the studied area. Ocean acidification triggered by large-scale volcanism(Large Igneous Province) during the late Permian led to extensive silica precipitation and preservation.