Vendian-Cambrian tidal and sabkha facies of the Siberian platform

Summary The Vendian-Cambrian interval on the Siberian Platform contains thick carbonate and evaporite sequences formed in extensive shallow-water basins. The carbonate sequences are characterized by a cyclic composition. Finegrained dolomites, undulated algal dolomites, flat pebble conglomerates, storm breccias and solution-collapse breccias form the base of each cycle. These rocks are characterized by an increased clay content which can be high enough to form argillites. Short sedimentation breaks reflected by mudcracks or silicification horizons are present as well as small cross-bedded tidal channels. Peloidal grainstones with algal overgrowth dominate in the central parts of the cycles. These members are often recrystallized and dolomitized. Micritic dolomites, undulous laminated dolomites, storm breccias and columnar stromatolites with abundant mud cracks form the upper members of the cycles. These sequences are free of clay but contain abundant anhydrite crystals and nodules. In the uppermost parts of some cycles massive layered anhydrite beds are present. The cycles vary in thickness, but usually they are between 15 and 20 m thick. The lower cycle member documents extreme shallow-water deposits. They formed in tidal and partially also supratidal zones not far from the mainland, from where fine clayey material was washed in. These parts of the sequence reflect a slow transgression. The central member of a cycle was deposited during the maximal transgression in a shallow basin with normal salinity and rather active hydrodynamics. Sedimentation of the upper part of the cycles reflects a regression stage (tidal and especially sabkha environments). The final layered anhydrite beds formed most probably in relict lakes on the sabkha plain. During sea-level falls some sequences of the central parts of the cycles were subaerially exposed and underwent partial dolomitization. The Vendian-Cambrian sabkhas are partly comparable with their recent counterparts.     

Definition of the margin of major coronary artery bifurcations during radiotherapy with electrocardiograph-gated 4D-CT

PurposeThe aim was to measure the cardiac motion-induced displacements of major coronary artery bifurcations utilizing electrocardiography (ECG)-gated four-dimensional computed tomography (4D-CT) and to determine the margin of coronary artery bifurcations.MethodsThirty-seven female patients who underwent retrospective ECG-gated 4D-CT in inspiratory breath hold (IBH) were enrolled. The left main coronary artery bifurcation (LM), the obtuse marginal branch bifurcation (OM), the first diagonal branch bifurcation (D₁), the second diagonal branch bifurcation (D₂), the caudal portion of the left anterior descending branch (APX), the first right ventricular artery bifurcation (V) and the acute marginal branch bifurcation (AM) were contoured. The center of the contour of the coronary arterial bifurcations at end systole was defined as the standard, and the margin were then calculated.ResultsThe margin in the left–right (LR), cranio-caudal (CC), and anterior-posterior (AP) coordinates were as follows: LM 3, 3, and 3 mm; D₁ 6, 3, and 3 mm; D₂ 3, 3, and 3 mm; APX 4, 4, and 4 mm; OM 4, 6, and 5 mm; V 6, 8, and 7 mm; and AM 6, 8, and 7 mm, respectively.ConclusionCoronary artery bifurcations should be considered a separate organ at risk (OAR), and different margin should be provided due to the differences resulting from motion displacement. The maximum margin in the LR, CC, and AP coordinates of left coronary artery bifurcations were 6, 6, and 5 mm, and those of the right coronary artery bifurcations were 6, 8, and 7 mm, respectively.     

从肿瘤体积到计划靶体积的三维边缘扩展

在适形放疗中需要在肿瘤体积周围加上三维边缘形成计划靶体积。传统的靶体积到计划体积的扩展方法是在组成靶体积的每层轮廓线外手动勾画一个边缘,费时且结果不准确,本文介绍一种新的三维边缘扩展方法,具有思路简洁,结果准确,节约时间等优点。     

Morphology and sedimentology of (clustered) cold-water coral mounds at the south Rockall Trough margins,NE Atlantic Ocean

Cold-water coral mounds on both margins of the Rockall Trough (NE Atlantic Ocean) have a strongly different morphology. Single, isolated mounds occur on the SE margin and are mainly found on the upper slope between 900 and 650 m water depth, while large mound clusters are found on the SW margin in water depths between 600 and 1,000 m, in a narrow zone almost parallel to the slope. Sedimentation rates on the mounds are higher than on the surrounding seabed as a result of baffling of biogenic carbonate debris and siliciclastic particles by the coral framework covering the mounds. This is confirmed by ²¹⁰Pb measurements. The individual coral growth rate can be three times higher then the vertical growth rate of the coral cover (±10 mm year⁻¹) which in turn is more than an order of magnitude higher then the present-day overall mound growth rate (±0.25 mm year⁻¹). The presence of extensive hardgrounds and firmgrounds and the three-dimensional coral framework are considered to be responsible for the stability of the relatively steep slopes of the mounds. High current velocities in the intramound areas result in local non-sedimentation and erosion, as is shown by the presence of IRD (ice-rafted debris) lag deposits on the seabed and moats around some of the mounds. The morphology and sedimentology of cold-water coral-covered (mainly Lophelia pertusa and Madrepora oculata) mounds on the southern Rockall Trough margins (NE Atlantic Ocean) is discussed and a model describing the development of these mounds is presented.     

镜泊湖岩溶台地不同植被类型土壤微生物群落特征

为了探讨不同演替阶段植被类型土壤微生物群落特征,分别选取镜泊湖岩溶台地草本、矮灌木、高灌木、小乔木与灌木混生(简称混生)群落、落叶阔叶林及针阔混交林6种典型植被类型,进行植物群落调查和对土壤微生物生物量、群落结构和多样性指标、土壤物理化学性质的测定。结果表明：从土壤微生物量、土壤微生物群落组成、土壤微生物代谢动力学过程和代谢功能多样性的角度来看,各种植被类型土壤微生物群落具有明显的差异。演替前期的草本群落土壤微生物量碳氮、细菌生物量、真菌生物量,代谢活性及丰富度指数均最低,但Shannon-Wiener多样性指数和均匀度指数显著(P<0.05)高于其他植被类型。矮灌木土壤微生物群落组成显著受植被类型的影响。高灌木群落和混生(小乔木与灌木混生)群落具有极强的相似性, 但在碳源利用类型上两者表现出一定的差异。落叶阔叶林代谢活性最高,碳源利用能力最强,能利用BIOLOG微孔板中的所有31种碳源,这与其具有较高的微生物量碳氮和细菌生物量一致,其代谢功能丰富度最高。演替后期的针阔混交林下的土壤pH最低,真菌比例升高,在碳源丰富的条件下具有极强的竞争优势(仅次于落叶阔叶林),但在碳源贫瘠的条件下其利用碳源能力较弱(仅高于草本)。植被可能主要通过土壤全磷和有机质影响土壤微生物代谢功能多样性。     

基于学习通平台的生物化学线上教学模式的探索与实践

为适应新型冠状病毒肺炎时期线上教学的需求,本文结合生物化学课程特点,对生物化学线上教学模式进行了探索与实践。依托学习通平台创建网络课程,整合、优化线上教学资源,利用学习通同步课堂实时互动,及时进行形成性评价及反馈,保证教学质量。在此总结线上教学经验,希望为生物化学线上教学提供参考。     

Enigmatic dinosaur trackways from the lower jurassic (Pliensbachian) of the Sarca valley,Northeast Italy

Four large limestone blocks with dinosaur footprints have been discovered in a large landslide situated in the Sarca Valley (northeast Italy). The trampled sediments have been ascribed to the upper part (Pliensbachian) of the Lower Jurassic Calcari Grigi Formation, which in the Sarca Valley consists of oolitic‐bioclastic limestones. These carbonates were originally deposited on the western margin of the Trento Platform, a paleogeographic structural high that was located in the northern tropical belt at the westernmost end of Tethys. Several footprints form trackways of quadrupedal dinosaurs. The data suggest the presence, within the ichnoassociation, of possible prosauropods and basal Thyrephora. This inference is consistent with the chronological and geographical distribution of both prosauropods and Thyreophora.     

New upper permian superfamily compositelasmatoidea (Brachiopoda, Terebratulida) from the east of the Russian platform: The specificity of ontogenetic transformations

A previously unknown type of ontogeny is discussed that unites features of two different types of loop development: the ancient dielasmoid type, which is typical of Upper Paleozoic terebratulids, and the angustothyridid type, which is typical of the Lower Mesozoic terebratulids. A new superfamily, Compositelasmatoidea, and a new family, Compositelasmatidae, with its type genus Compositelasma gen. nov., are established based on their unique ontogenetic changes.     

Productivity events of the marine diatom Thalassiosira tumida (Janisch) Hasle recorded in deglacial varves from the East Antarctic Margin

During the last deglaciation calving bay reentrants formed over several deep inner shelf basins around Antarctica as the ice sheets retreated. Marine diatoms flourished in spring and summer within the bays, providing exceptionally high silica flux rates to the basins on an annual basis. As a result, several hundred years of the late deglaciation are archived in many of these deep basins as continuously laminated diatom-rich marine sediments. The laminae are excellently preserved and offer a unique opportunity to study deglacial processes over the Antarctic shelf at very high resolution (subseasonal to seasonal at best). Annual palaeoenvironments from these sediments have been recently reconstructed. However, finer sedimentary detail is also apparent by the preservation of sublaminae of single diatom species, which represent discrete productivity events (blooms). In this paper, we focus on Thalassiosira tumida (Janisch) Hasle sublaminae preserved in the  5 m thick deglacial laminated sequence of NBP01-01 Jumbo Piston Core (JPC) 43B from Iceberg Alley ( 67°S, 63°E) on the Mac.Robertson Shelf, East Antarctic Margin. These T. tumida sublaminae are distinctive, occur several times throughout the deglacial sequence and are always preserved within summer laminae. Importantly they carry ecological and paleoceanographic information for deglacial Iceberg Alley and possibly the entire East Antarctic Margin. We describe and illustrate the T. tumida sublaminae using scanning electron microscope backscattered electron imagery of highly polished thin sections and secondary electron imagery of sublamina fracture surfaces. T. tumida sublaminae range in thickness from 0.57 to 21.07 mm (mean = 5.12; σ = 4.49) and are defined as discrete sedimentary intervals within a summer lamination where T. tumida is the dominant diatom species (abundance > 50%; but frequently > 80%) or is very abundant (abundance 40% to 49%). Based on the stratigraphic position of these sublaminae in the annual/seasonal succession and on published morphological, ecological and distributional data of living specimens in culture and in the field, we surmise an open-water, late summer bloom for T. tumida in deglacial Iceberg Alley, at sea-surface temperatures of 0 to − 1.69 °C, under low or fading light levels just prior to significant sea-ice formation. We suggest that the sublaminae formed by a combination of episodic T. tumida blooms (surface concentration), followed by rapid deposition (high flux) and optimal frustule preservation on the sea floor. Increased sublaminae frequency upcore suggests a lengthening of the summer season, while their complete cessation 43 years prior to the end of lamination deposition in outer Iceberg Alley (JPC43B) may be due to a coastward population shift.