A study of coral reef resilience and implications of adaptive management and rehabilitation in Khanh Hoa Province, Vietnam

The Province of Khanh Hoa, Vietnam, is located in the western South China Sea and boasts a shoreline of 385 km and many islands. Previous studies have indicated the extreme diversity and abundance of coral reefs in its waters as compared with other coastal provinces of Vietnam. A study on the resilience of coral reefs against increased surface water temperature and anthropogenic impact is conducted at 19 reef sites in 2015. At each site, a series of parameters (e.g., coral covers, genus diversity, and coral recruitment, substratum heterogeneity, depth, water exchange level, and sediment deposit and water temperature) are measured quantitatively or semi-quantitatively. The measured data are rated based on the relationship between the parameter values and coral susceptibility; the consideration that reef health reflects the biological capability to adapt to environmental changes and the recruitment potential if bleached; and positive or negative influences of physical factors in the mitigation of thermal stress and protecting corals from bleaching. A cumulative analysis enables researchers to divide the studied reefs into four categories based on varying levels of reef health to support resilience, recovery, and vulnerability in the case of increased water temperature. Relevant management interventions for each category and other supporting activities are suggested to enhance management effectiveness and to plan the rehabilitation of coral reefs for biodiversity conservation and touristic development, taking into account the involvement of related stakeholders.     

Models of the REE distribution in the black shale Bazhenov Formation of the West Siberian marine basin,Russia

Rare-earth elements abundance in black shales of the Upper Jurassic (Tithonian Stage)–Lower Cretaceous (Berriassian Stage) Bazhenov Formation is discussed. This formation is the principal oil source rocks of West Siberia. The deposits within the formation can be subdivided into two main marine groups: (a) moderately hemipelagic deposits (clayey-siliceous, including phosphatic and carbonate rocks) and low-density distal clayey turbidites (argillites), both are considered as normal and (b) silty argillites and clayey-silt rocks, which are channel deposits and considered as anomalous. The hemipelagic rocks of normal sections, which are enriched in the rare-earth elements (REE), accumulated under both slow rates of sedimentation (clayey-siliceous rocks) and faster rates of sedimentation (argillites). The channel deposits of anomalous sections, which are impoverished in the REE, accumulated exclusively under fast rates of sedimentation.Within the hemipelagic group the rate of sedimentation of the argillites was faster than of the clayey-siliceous rocks, but the REE concentration in the former rocks (140.4 ppm) is higher than in the latter group (97.4 ppm). The argillites are more than twice enriched in clayey material than clayey-siliceous rocks. It is likely that the clay fraction was the main carrier of REE in these rocks. In the channel group of rocks, the REE abundance in clayey-silt rocks (21.2 ppm) is lower than in the silty argillite (84.6 ppm), in which the clay content is elevated.With respect to redox potential the Bazhenov Formation rocks can be subdivided further into three groups, based on the degree of pyritization index (DOP): (1) the highly reducing clayey-siliceous rocks of normal sections, with high DOP; (2) the substantially reducing argillites and carbonate rocks of normal sections, with intermediate DOP; (3) the moderately reducing rocks of anomalous sections with low DOP. The rocks with the high DOP (group 1) are characterized by ΣLREE/Σ(M+H)REE ratios between 7.37 and 7.5, whereas the rocks with the lower DOP (group 2 and 3) are characterized by ΣLREE/Σ(M+H)REE ratios between 12.8 and 13.5. Negative Ce anomalies are either small or absent in all deposits, which is typical for reducing conditions.Thus, the Bazhenov Formation exemplifies the complex depositional conditions that influence the REE concentration in black shale. However, it is this very complexity that has contributed to the development of six separate depositional models (REE contents in ppm are given in brackets). (1) Phosphatic clayey-siliceous rocks of normal sections (367.95); (2) argillites of normal sections (130.73); (3) clayey-siliceous rocks of normal sections (85.97); (4) carbonate rocks, largely dolomites of normal sections (23.23); (5) silty argillites of anomalous sections (78.7) and (6) clayey-silt rocks of anomalous sections (19.66).     

Catagenesis of organic matter at the top and base of the Jurassic complex in the West Siberian megabasin

Thermal maturation for the top and base of the Jurassic in the West Siberian megabasin was modeled on the basis of the vitrinite reflectance (R_vt⁰) data using mathematical modeling and computer simulations. The values of thermal maturation are found to vary within substages PC₃-MC₃² for the top (or being equivalent to PC₃-MC₁² on the periphery and southern part of the basin, or to MC₂-MC₃² in the north) and PC₃-AC₃ for the base of the Jurassic (or being equivalent to PC₃-MC₂ on the periphery and southern part of the basin or MC₃¹-AC₃ in the north). Thermal maturity levels of the Jurassic in West Siberia are controlled by depths of burial and peak temperatures which the source rocks were subjected to during this period. The situation is further complicated by high heat flows superimposed on the regional background, which are observed in deep fault zones and in the proximity of numerous igneous bodies.     

Computer simulation of Neocomian clinoform reservoirs in northern and arctic West Siberia

Neocomian reservoirs in the Mesozoic sedimentary cover of West Siberia have a complex geological structure. Their wedge-like (clinoform) geometry, with abrupt thickness changes and facies diversity (continental, shoreface, and pelagic deposits), causes difficulty in correlation between drilling- and seismics-based sand formations and clay caps. East-wedging (west-dipping) clinoforms consisting of interbedded clay and sand have the greatest reservoir potential in the West Siberian basin. Prediction of new oil and gas plays and their reservoir potential assessment require regional reconstructions in addition to local contour maps of individual zones and fields. However, the simulation technology which has been applied for years to Jurassic regional reservoirs is not fully applicable to the Neocomian clinoform sequences. Therefore we have adapted it correspondingly and suggest new tools to make due regard for the clinoform reservoir structure. The new approach has been tested through computing several structure and thickness contour maps of clinoform sequences for three largest regional Neocomian reservoirs (sub-Sarman, sub-Pim, and sub-Alymka) in northern and arctic West Siberia.     

Organic Carbon versus Major Elements Relationship in Rocks of the Bazhenov Formation,Western Siberia

A close relation of the organic carbon (C_org) content with major has been established for rocks of the Upper Jurassic–Lower Cretaceous Bazhenov Formation. Applying the method of multiple linear regression, it has been demonstrated that the C_orgcontent in rocks of the Bazhenov Formation is stringently controlled by its bulk chemical composition. This inference is consistent with the existing ideas regarding a close interrelation between the following main components of rocks: organic carbon and authigenic quartz formed on remains of Radiolaria; pyrite formed in a highly reducing medium of C_org-rich sediments; and terrigenous clayey material diluting the authigenic siliceous–carbonaceous–pyritic matrix. These components chiefly determine the spectrum of major elements in the Bazhenov Formation. The establishment of the close relation between the C_orgcontent and the group of major elements refutes the suggestion of some authors that siliceous material was supplied to nonlithified sediments of the Bazhenov sea by hydrothermal solutions, because this mechanism would have inevitably upset geochemical relations between elements in the studied rocks.