Control of Aptian palaeobathymetry on turbidite distribution in the Buchan Graben,Outer Moray Firth,Central North Sea

It is widely recognised that palaeobathymetry is a key control on the distribution of turbidite deposits. Thus, the utilisation of palaeobathymetric surfaces as an input for numerical turbidity current modelling offers a potentially powerful method to predict the distribution of deep marine sands in ancient (subsurface or outcrop) successions. Such an approach has been tested on an Aptian turbidite deposit from the Buchan Graben, UK Central North Sea, where modelled sand distributions could be quality controlled against available well data.     

象山港潮波响应和变形研究 Ⅱ.象山港潮波数值研究

通过象山港水域的潮波运动数值模拟,分析了象山港M4分潮的生成和增长机制．结果说明,潮波传播中的非线性底摩擦效应是M4分潮生成和增长的主要控制因子,M4分潮在湾内的共振现象也起着重要的放大作用二平流效应在绝大部分区域中抑制了M4分潮的发展,只有在佛渡水道中一些岛屿周围极小区域内对M4分潮有增强作用．潮滩在湾内对M4分潮的影响极其微弱．     

Elevated biomass of mesozooplankton and enhanced fecal pellet flux in cyclonic and mode-water eddies in the Sargasso Sea

Accumulating evidence points to the importance of mesoscale eddies in supplying nutrients to surface waters in oligotrophic gyres. However, the nature of the biological response and its evolution over time has yet to be elucidated. Changes in mesozooplankton community composition due to eddy perturbation also could affect biogeochemical cycling. Over the course of two summers we sampled seven eddies in the Sargasso Sea. We focused on and followed a post-phytoplankton bloom cyclonic eddy (C1) in 2004 and a blooming mode-water anticyclonic eddy (A4) in 2005. We collected zooplankton in all eddies using a Multiple Opening and Closing Net Environmental Sampling System (MOCNESS) and quantified biomass (>0.15 mm, in five size fractions) from 0 to 700 m over nine discrete depth intervals. Zooplankton biomass (>0.5 mm) in the upper 150 m was similarly enhanced at night for the periphery of C1 and the center of A4 at 0.514 g m⁻² and 0.533 g m⁻², respectively, compared to outside (0.183 g m⁻² outside C1 and 0.197 g m⁻² outside A4). Despite minimal chlorophyll a enhancement and dominance by picoplankton in C1, zooplankton biomass increased most for the largest size class (>5 mm). Gut fluorescence for euphausiids and large copepods was also elevated on the C1 periphery. In A4, peak biomass occurred at eddy center coincident with peak primary production, but was highly variable (changing by >3-fold) over time, perhaps resulting from the dense, but patchy distribution of diatom chains in this region. Shifts in zooplankton community composition and abundance were reflected in enhancement of fecal pellet production and active transport by diel vertical migration in eddies. Inside C1 the flux of zooplankton fecal pellets at 150 m in June 2004 was 1.5-fold higher than outside the eddy, accounting for 9% of total particulate organic carbon (POC) flux. The flux of fecal pellets (mostly from copepods) increased through the summer in eddy A4, matching concurrent increases in zooplankton <2 mm in length, and accounting for up to 12% of total POC flux. Active carbon transport by vertically migrating zooplankton was 37% higher on the periphery of C1 and 74% higher at the center of A4 compared to the summer mean at the Bermuda Atlantic Time-series Study (BATS) station. Despite contrasting responses by the phytoplankton community to cyclonic and mode-water eddies, mesozooplankton biomass was similarly enhanced, possibly due to differential physical and biological aggregation mechanisms, and resulted in important zooplankton-mediated changes in mesoscale biogeochemistry.     

Examining fault architecture and strain distribution using geospatial and geomechanical modelling: An example from the Qaidam basin,NE Tibet

The investigation of complex geological setting is still dominated by traditional geo-data collection and analytical techniques, e.g., stratigraphic logging, dip data measurements, structural ground mapping, seismic interpretation, balance section restoration, forward modelling, etc. Despite the advantages of improving our understanding in structural geometry and fault architecture, the geospatial modelling, applying computer-aided three-dimensional geometric design, visualization and interpretation, has rarely been applied to such complex geological setting. This study used the Lenghu fold-and-thrust belt (in Qaidam basin, NE Tibetan Plateau) to demonstrate that the application of geospatial and geomechanical modelling could improve our understanding and provide an effective technique for investigating the fault architecture and strain distribution. The three-dimensional configuration of the Lenghu fold-and-thrust belt was initially derived from traditional analysis techniques, such as regional stratigraphic logging, cross section construction, meso-scale ground mapping and landsat image interpretation. The high-resolution field data and landsat image were integrated to construct the geospatial model, which was subsequently used to quantitatively investigate the fault throw changes along the Lenghu thrust fault zone and to understand its control on the lateral structural variation. The geospatial model was then restored in three dimensions to reveal the kinematic evolution of the Lenghu fold-and-thrust belt. Geomechanical modelling, using a Mass-Spring algorithm, provided an effective three-dimensional tool for structural strain analysis, which was used to predict the strain distribution throughout the overall structure, e.g., normal faults with throws ranging from meters to tens of meters in the hanging-wall. The strain distribution predicted by geomechanical modelling was then validated by the natural normal faults in the hanging-wall. The high accordance between the strain prediction and statistics of natural normal faults demonstrates good applicability of geospatial and geomechanical modelling in the complex geological setting of the Lenghu fold-and-thrust belt. The geospatial models and geomechanical models, therefore, can provide a robust technique for analyzing and interpreting multi-source data within a three-dimensional environment. We anticipate that the application of three-dimensional geospatial modelling and geomechanical modelling, integrating both multi-source geologic data and three-dimensional analytical techniques, can provide an effective workflow for investigating the fault architecture and strain distribution at different scales (e.g., ranging from regional-to meso-scale).     

Simulation of paleotectonic stress fields and quantitative prediction of multi-period fractures in shale reservoirs: A case study of the Niutitang Formation in the Lower Cambrian in the Cen'gong block,South China

Reservoirs where tectonic fractures significantly impact fluid flow are widespread. Industrial-level shale gas production has been established from the Lower Cambrian Niutitang Formation in the Cen'gong block, South China; the practice of exploration and development of shale gas in the Cen'gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures. In this study, the data obtained from outcrop, cores, and logs were used to determine the developmental characteristics of such tectonic fractures. By doing an analysis of structural evolution, acoustic emission, burial history, logging evaluation, seismic inversion, and rock mechanics tests, 3-D heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Late Hercynian—Early Indo-Chinese and Middle-Late Yanshanian periods. The effects of faulting, folding, and variations of mechanical parameters on the development of fractures could then be identified. A fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers. Favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells. The simulation results indicate the magnitude of minimum principal stress during the Late Hercynian — Early Indo-Chinese period within the Cen'gong block is −100 ∼ −110 MPa with a direction of SE-NW (140°–320°), and the magnitude of the maximum principal stress during the Middle-Late Yanshanian period within the Cen'gong block is 150–170 MPa with a direction of NNW-SSE (345°–165°). During the Late Hercynian — Early Indo-Chinese period, the mechanical parameters and faults play an important role in the development of fractures, and fractures at the downthrown side of the fault are more developed than those at the uplifted side; folding plays an important role in the development of fractures in the Middle-Late Yanshanian period, and faulting is a secondary control. This 3-D heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas, but also have a practical significance for the prediction of other reservoir fractures.     

Complementing coal seam gas facies modelling workflows with decompaction based processes

Differential compaction plays a key role in influencing the palaeogeographic organisation of many depositional systems. In the Jurassic Walloon Subgroup, Surat Basin, Eastern Australia, the process of compensational stacking contributes significantly to the complex coal layer architecture and is documented in mine exposure, borehole and seismic datasets. Despite this understanding, current best-practices do not formally consider the mechanics of compensational stacking when populating palaeogeography facies in coal seam gas (CSG) reservoir models. To address this limitation, a hybrid modelling workflow was developed in which numerical rules representing the process of differential compaction are used explicitly to condition an iterative workflow containing traditional geostatistical facies modelling algorithms. The workflow is facilitated by a newly developed open source plugin which allows grid decompaction in Schlumberger PETREL™ 2015. Application of the workflow was tested in a CSG production area containing closely spaced wellbores and a 3D seismic survey. In this area, facies models were constructed using both traditional geostatistical approaches and the newly developed hybrid methodology. Comparison of these models suggests that facies models constructed via unconstrained geostatistical approaches often result in unrepresentative realisations, inconsistent with coal seam architectures as observed in seismic and outcrop. The hybrid geostatistical-forward modelling approach developed during this study was better able to reproduce complex alluvial stacking patterns, particularly with respect to coal seam amalgamation, bifurcation and washout.     

Does compaction-induced subsidence control accommodation space at the top of prograding carbonate platforms? Constraints from the numerical modelling of the Triassic Esino Limestone (Southern Alps,Italy)

The demise of the high-relief, steep-slope, prograding Ladinian-Early Carnian carbonate platforms of the Esino Limestone (Central Southern Alps of Italy) is marked by subaerial exposure of the platform top associated with different erosional (mainly karst-related), depositional and diagenetic processes (Calcare Rosso). The exposure-related deposits consist of three major facies associations: 1) residual soils with thin lenses of conglomerates with black pebbles, and, locally, weathered vulcanites; 2) chaotic breccia lenses irregularly distributed in the uppermost part of the Esino Limestone carbonate platform, interpreted as collapse breccias in karstic setting: 3) inter-supratidal carbonate cycles with dissolution and development of paleosols and tepee structures.Facies distribution follows the sub-environments of the underlying Esino Limestone. Facies 1 and 2 typically characterize the core of the platform, covering the underlying inner platform facies. Facies 3 instead develops toward the edge of the platform, above reef-upper slope facies of the prograding facies of the Esino Limestone. The thickness of facies 3 decreases toward the core of the platform. Facies distribution reflects differences in the accommodation space and sedimentary processes from the rim (highest accommodation, favouring the deposition of peritidal-supratidal carbonates) to the core (reduced accommodation, causing pedogenesis and karstification) of the carbonate system.The observed thickness changes may be controlled by different factors: 1) syndepositional tectonics, 2) subsidence induced by magmatic activity or 3) differential subsidence controlled by the stratigraphic architecture of the Esino Limestone platform and adjoining basins. As evidence of tectonics was not observed and the presence of volcanic bodies is only documented tens of km away from the study area, the scenario involving the creation of accommodation space by compaction of the basinal sediments (resedimented, fine-grained calciturbidites) during the progradation of the carbonate platform is here investigated. Numerical modelling was performed to verify the compatibility of compaction-induced subsidence with the observed depositional architecture. The models were built to simulate the architectural evolution of the platform by progressively adding layers from deepest to shallowest, while compacting the underlying sediments, in order to evaluate compaction-induced subsidence (and accommodation space for the Calcare Rosso) after the deposition of the youngest platform strata. Modelling results allow us to conclude that the wedge geometry of the Calcare Rosso, deposited on top of the extinct Esino carbonate platform, can be explained by subsidence controlled by compaction of the basinal sediments present below the early-cemented, fast prograding platform slope deposits.     

Abundance and degree of residency of humpback dolphins Sousa plumbea in Mossel Bay,South Africa

Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140?km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.