Sedimentological Field Research Articles

Granulometric and Mineralogical Characterization of Sands from the Middle Course of the Kasai River (Ilebo Territory, Kasai Province, DRC)

This study addresses sediment dynamics within the fluvial system of the middle Kasai Basin, specifically between Ilebo town (pk605) and the confluence with the Loange River (pk525). The primary aim is to characterize the granulometric and mineralogical evolution of sand bars in the Kasai River, which pose navigational challenges in this section of the basin. The study seeks to answer the following question: How do the granulometric and mineralogical characteristics of sands transported by the middle course of the Kasai River evolve? The research employs laboratory granulometric techniques. Twenty sand samples were collected from sand bars along the middle and navigable course of the Kasai River during the flood recession period, ranging from upstream to downstream. Sieving was conducted using an AFNOR-type sieve column, followed by sedimentometric analyses and the calculation of various Folk & Ward textural parameters using the Excel program Gradistat. Additionally, six samples underwent automated mineralogical analysis using a QEMSCAN FEG Quanta 650. Granulometric analysis revealed that the sands from the middle course of the Kasai River are unimodal, with fine to medium grains in the granulometric fraction ranging from 186.2 µm to 426.8 µm. Most of these sands are moderately to well graded, with grains showing granulometric symmetry and, less commonly, fine asymmetry. Their kurtosis is largely mesokurtic, with occasional leptokurtic and platykurtic characteristics, indicating multiple depositional environments. The study demonstrates that the evolution of these granulometric parameters is uneven along the middle course of the Kasai River, though overall, the parameters exhibit limited variation. This suggests minimal and regular sediment inputs, consistent with the relative regularity of granulometric variations in environments characterized by free sedimentation. Automated mineralogical analysis identified a diverse mineralogical assemblage, dominated by quartz, followed by calcite, iron oxides, orthoclase, plagioclase, and kaolinite. Additionally, a group of minerals that do not exceed the 0.55% threshold—such as illite, apatite, ilmenite, muscovite, chlorite, biotite, montmorillonite, rutile, pyrophyllite, siderite, zircon, and dolomite—was identified. Consequently, the mineralogical evolution is not uniform throughout the middle course of the Kasai River, showing a sawtooth variation. This study clarifies the evolution of the granulometric parameters of Kasai River sands, which are influenced by the river's hydrodynamic regime. It also elucidates the mineralogical evolution, linked to the petrographic nature of source areas, which are distributed based on their mechanical resistance to abrasion, chemical alteration, and the morphology of the riverbed. The findings from this research contribute significantly to the field of sedimentology and integrated river management

Coupling relationship and genetic mechanisms of shelf-edge delta and deep-water fan source-to-sink: A case study in Paleogene Zhuhai Formation in south subsag of Baiyun Sag, Pearl River Mouth Basin, China

The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration. Based on the newly acquired high-resolution 3D seismic, logging and core data of Pearl River Mouth Basin (PRMB), this paper dissected the shelf-edge delta to deep-water fan (SEDDF) depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag, and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms. The results show that during the deposition of the fourth to first members of the Zhuhai Formation, the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing, with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member. Based on the development of SEDDF depositional system along the source direction, three types of coupling relationships are divided, namely, deltas that are linked downdip to fans, deltas that lack downdip fans and fans that lack updip coeval deltas, with different depositional characteristics and genetic mechanisms. (1) Deltas that are linked downdip to fans: with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area, and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink (S2S). The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level. (2) Deltas that lack downdip fans: with the development of shelf edge deltas in shelf area, while deep water fans are not developed in the downdip slope area. The lack of “sources” and “channels”, and fluid transformation are the three main reasons for the formation of this type of S2S system. (3) Fans that lack updip coeval deltas: with the development of deep-water fans in continental slope area and the absence of updip coeval shelf edge deltas, which is jointly controlled by the coupling of fluid transformation at the shelf edge and the “channels” in the continental slope area.

Structural Inheritance in the Eastern Cordillera, NW Argentina: Low‐Temperature Thermochronology of the Cianzo Basin

AbstractThe present‐day deformation style of the Eastern Cordillera in NW Argentina is strongly influenced by the inversion of pre‐existing Paleozoic and Mesozoic structures. In particular, the extensional faults and lithological contrasts resulting from the Cretaceous–Paleogene Salta Rift phase form heterogeneities that were preferentially reactivated during the Andean orogeny. Constraining the timing and characteristics of reactivation is a key to understanding the interplay between tectonics and inherited crustal anisotropies. In this study, we combine structural and sedimentological field data with a low‐temperature thermochronology data set from the area surrounding the fault‐bounded Cianzo basin. The southeastern boundary is formed by the inverted Hornocal fault, which was the basin‐bounding normal fault of the Lomas de Olmedo sub‐basin (Salta Rift basin). Lacustrine deposits of the Yacoraite Formation overspill on the footwall of this fault and mark tectonic quiescence during the post‐rift phase of the Salta Rift. Apatite (U‐Th‐Sm)/He and fission track ages in the Hornocal fault hanging wall show an onset of rapid cooling interpreted to be concomitant with fault inversion between the latest Oligocene and middle Miocene (∼24–15 Ma). Low‐temperature thermochronology data also constrain the timing of major folding in the eastern limb of the Cianzo syncline to pre‐10 Ma, whereas the western limb started tilting post‐10 Ma. Characterization of exhumation patterns related to fault activity surrounding the Cianzo basin emphasizes the influence of the pre‐existing structural framework on deformation in fold‐and‐thrust belts.

Microfacies analysis of marine shale: A case study of the shales of the Wufeng–Longmaxi formation in the western Chongqing, Sichuan Basin, China

Abstract It is a great challenge for sedimentologists to perform the facies analysis of shales due to the lack of macro-structures and high heterogeneity in shale, and thus, conventional research methods are poorly applied in the field of shale sedimentology. To establish a typical depositional model for marine shales, a new method adopted from marine carbonate rocks was employed to perform the microfacies analysis of marine shales of the Wufeng and Longmaxi Formation in Sichuan Basin. This method emphasizes the fact that many skeletal constituents in marine shales have specific bathymetric distributions, allowing for a better understanding of the depositional process of shales. With this approach, a total of nine microfacies were identified and two depositional models for marine shales were proposed. The depositional models show that sea levels were high during the Middle to Late Wufeng period, which was followed by a rapid regression that led to a significant sea-level drop by over 50 m at the topmost of the Wufeng Formation, and consequently, widespread fine-grained sandy shales with large amounts of benthic bioclasts were deposited in the study region. The eustatic sea-level changes recovered by using the method of microfacies analysis are in line with the global trend, indicating that the method has promising applications in the field of marine shale sedimentology.

Fluid evolution and related fluid–rock interactions of the Oligocene Zhuhai sandstones in the Baiyun Sag, northern margin of the South China Sea

Pore fluids control the diagenetic processes and storage spaces of deep clastic rock reservoirs and have become a major area of interest within the fields of sedimentology and petroleum geology. This paper aims to relate the diagenetic processes of the Oligocene Zhuhai sandstones in the Baiyun Sag to pore fluids varying with burial depth. The types and distribution patterns of authigenic minerals are investigated through analysis of petrographic, mineralogical, and geochemical features to illustrate the origin and flow patterns of pore fluids and their influences on reservoir diagenesis. Strong cementation of eogenetic carbonate cement near the sandstone–mudstone interface was a consequence of material migration from adjacent mudstones on a large scale. The pore fluids were mainly affected by microbial methanogenesis and carbonate mineral dissolution in adjacent mudstones during eogenesis. The pore fluids were diffusively transported in a relatively open geochemical system within a local range. Support for this model is provided by the heavier stable isotopic values present in eogenetic calcite and dolomite. Feldspar dissolution during early mesogenesis was spatially accompanied by the precipitation of authigenic quartz and ferroan carbonate cement. Pore fluids in this period were rich in organic acids and CO2, and their migration mechanism was diffusive transport. The obviously lighter carbon and oxygen isotopic compositions of the ferroan calcite support this inference. During late mesogenesis, the input of deep hydrothermal fluid might have been partly responsible for the precipitation of ankerite, barite and authigenic albite. Oil charging may have inhibited carbonate cementation and compaction, accordingly preserving porosity, and together with authigenic kaolinite, might have promoted the transition of the reservoir from water wet to oil wet to the benefit of oil entrapment. The findings reported here shed new light on the evaluation and prediction of sandstone reservoirs that have experienced multiple periods of fluid flow.

Indian Association of Sedimentologists

The idea to constitute a forum Indian Association of Sedimentologists (IAS) was floated in the valedictory session of a conference hosted by Delhi University, Delhi in 1975, for providing an opportunity to sedimentologists of the country to meet, discuss and extend ideas of mutual interest. The idea was appreciated and got support from veteran geologists and academicians. Soon after, in 1976, the Indian Association of Sedimentologists was formed and duly registered with its headquarters at the Department of Geology, Aligarh Muslim University, Aligarh in recognition of leading research carried out in the Department in the field of sedimentology.

Impact of thermal maturity on the diagenesis and porosity of lacustrine oil-prone shales: Insights from natural shale samples with thermal maturation in the oil generation window

Shale diagenesis controls the generation, migration and accumulation of hydrocarbons through time and has become a frontier area of study in the fields of sedimentology and petroleum geology. There have been only a few studies on the generation of organic pores in lacustrine shale oil reservoirs during the oil generation thermal evolution stage. In this study, lacustrine organic-rich shale samples at various stages of maturity, from the first member of the Songliao Basin Qingshankou Formation were investigated, and a thermal transformation law of macerals was established, based on organic petrology. The diagenetic alteration styles and sequences were investigated using a high-resolution field emission scanning electron microscope, and cathode luminescence. Furthermore, automated pore extraction technology enabled the examination of the characteristics and genetic process of organic and inorganic pores under the influence of thermal maturation. The results indicate that a small quantity of pre-oil bitumen is generated during the early oil mature stage (Ro: 0.7% - 0.9%), and that the generation of a large quantity of post-oil bitumen that occurs following the peak oil generation stage (i.e., late oil mature stage, Ro: 1.1% - 1.4%), is controlled by the unimodal distribution of the activation energy of Type I kerogen. Compaction intensity certainly influences pore volume reduction. Siliceous cementation primarily occurs during peak oil generation maturity and the subsequent thermal evolution stage. The pores formed in the oil generation window primarily arise from mineral dissolution and organic matter polycondensation. Following peak oil generation, the pores undergo iron dolomitization, smectite illitization, and bitumen cracking. The degree of development of inorganic pores, the most common pore type in shale oil reservoirs, appears to have a significant impact on the total porosity of a reservoir shale. During thermal evolution, the inorganic pore volumes show a decreasing trend. There is a secondary pore development stage, reached when Ro exceeds 1.2%, closely related to the transformation of clay minerals. According to the hydrocarbon generation kinetics and compaction model, organic pore volumes increase gradually at 0.7%Ro, reach their peak at 1.1%Ro, and then steadily decrease due to compaction. The organic pores are relatively well developed when Ro is >0.85% (at the start of the oil window). The shale oil reservoir's most favorable thermal evolution stage is late oil maturity stage that follows the oil generation peak.

Eocene Paleoclimate Evolution under the Background of Warmhouse-Hothouse Conditions in the Continental Fushun Basin: Implications from Magnetic Susceptibility and Color Reflectance.

Paleocene–Eocene hyperthermal events are a current research focus in the fields of sedimentology and paleoclimatology. The Fushun Basin in northeast China contains continuous continental Eocene fine-grained rocks, and a series of Eocene hyperthermal events in the Fushun Basin have been identified. Because of the high cost of high-precision isotope data testing, it is necessary to find new and alternative paleoclimate parameters. In this study, Eocene coal and oil shale-bearing layers in the Fushun Basin are used as research objects. The high-precision data of magnetic susceptibility, color reflectance, rock composition, and cluster analyses are used to conduct a vertical comparison in the same category and compare that analysis with the identified Eocene hyperthermal events in the Fushun Basin. The preliminary results show that high-frequency-dependent susceptibility, high color reflectance a* (redness)/L* (lightness) values, and high kaolinite content in the study area have good correspondence with global hyperthermal events and can be used as effective parameters for the identification of continental basin hyperthermal events. The detailed magnetic susceptibility and color reflectance data also reveal that the Eocene strata in the Fushun Basin recorded the Late Lutetian Thermal Maximum (LLTM) and 13 short-term hyperthermal events during the Early Eocene Climatic Optimum (EECO). These results indicate that the parameters of rock physical properties can be used to study the evolution of the paleoclimate in geological history, and it has universal practicability in continental and marine fine-grained sedimentary rocks.

Discovery of lacustrine shale deposits in the Yanshan Orogenic Belt, China: Implications for hydrocarbon exploration

The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m3. Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 108 m3, with shale oil geological resources of 3340.152 × 104 t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.

Geochemistry of Surface Sediments From the Emperor Seamount Chain, North Pacific

Investigating the composition and distribution of pelagic marine sediments is fundamental in the field of marine sedimentology. The spatial distributions of surface sediment are unclear due to limited investigation along the Emperor Seamount Chain of the North Pacific. In this study, a suite of sedimentological and geochemical proxies were analyzed, including the sediment grain size, organic carbon, CaCO3, major and rare earth elements of 50 surface sediment samples from the Emperor Seamount Chain, spanning from ∼33°N to ∼52°N. On the basis of sedimentary components, we divide them into three Zones (I, II, and III) spatially with distinct features. Sediments in Zone I (∼33°N–44°N) and Zone III (49.8°N–53°N) are dominated by clayey silt, and mainly consist of sand and silty sand in Zone II. The mean grain size of the sortable silt shows that the hydrodynamic condition in the study area is significantly stronger than that of the abyssal plain, especially at the water depth of 1,000–2,500 m. The CaCO3 contents in sediments above 4,000 m range from 20 to 84% but decrease sharply to less than 1.5% below 4,000 m, confirming that the water depth of 4,000 m is the carbonate compensation depth of the study area. Strong positive correlations between Al2O3 and Fe2O3, TiO2, MgO, and K2O (R > 0.9) in the bulk sediments indicate pronounced contributions of terrigenous materials from surrounding continent mass to the study area. Furthermore, the eolian dust makes contributions to the composition of bulk sediments as confirmed by rare earth elements. There is no significant correlation between grain size and major and minor elements, which indicates that the sedimentary grain size does not exert important effects on terrigenous components. There is significant negative δCe and positive δEu anomalies at all stations. The negative Ce anomaly mainly exists in carbonate-rich sediments, inheriting the signal of seawater. The positive Eu anomaly indicates widespread volcanism contributions to the study area from active volcanic islands arcs around the North Pacific. The relative contributions of terrestrial, volcanic, and biogenic materials vary with latitude and water depth in the study area.

Response of the Dnieper river fluvial system to the river erosion caused by the operation of the Kaniv hydro-electric power plant (Ukraine)

The commission of the Kaniv dam in 1973, as the last of the six dams on the lower Dnieper River cascade, changed the river regime completely. A description of these changes and their impact on the evolution of the fluvial anastomosing system form the aims of the study. The operation of the hydroelectric power plant (HPP) in Kaniv significantly affected the erosion and accumulation of sediment on valley floor and thus changed the fluvial system of the Dnieper River below the dam. The HPP initially operated on a hydropeaking system (until the early 1990s) and then on a run-of-river system. This study used the indicators of hydrologic alteration (IHA), the RB flashiness index, archival topographic and bathymetric maps, hydrological and sedimentological field studies, and satellite images to assess how the magnitude and duration of changes in the flow regime affected erosion and accumulation processes on the river bed and changed the pattern of channels as well as the landforms separating them.Until the commission of the dam in Kaniv, the fluvial system of the Dnieper River in its undisturbed state was a sand-bed channel but was then transformed from a braiding to an anastomosing river system. This was achieved by bars where consolidation of vegetation on fine clastic deposits created interchannel areas and islands. During the operation of the hydropeaking system, characterised by frequent artificial flows of short duration, channels became incised and narrowed. Interchannel areas were divided up into islands. Then, after the HPP switched to working a run-of-river system, the islands began to merge again into interchannel areas. This happened as a result of intensified erosion processes in both the main and the side channels. The operation of the HPP, by changing the flow regime and sedimentation processes in the river valley, modified the natural process of evolution of the fluvial system of the Dnieper River.

Optimizing a standard preparation procedure for grain size analysis of marine sediments by laser diffraction (MS-PT4SD: Marine sediments-pretreatment for size distribution)

Grain size distributions are a key physical measurement in marine sediment studies. The introduction of laser diffraction spectrometry analyzers a few decades ago, allowed the differentiating of grain size in higher resolution than before, and led to increased volumes of samples analyzed overall. However, pretreatment of the sediment samples is required for obtaining high quality results by this method. Currently there are different pretreatment methods for different sediments, but no inclusive, standard method that is applicable across many types. Moreover, often the particulars of the methods are not fully described in the literature. A standard simple and effective pretreatment method which is applicable for a large variety of marine sediments is required as it can allow for intra and inter study comparisons. This study systematically tested and compared commonly applied digestion and dispersion pretreatment techniques for particle size analysis by laser diffraction spectrometry. The pretreatments were applied on a wide spectrum of marine sediments to distill a single protocol that produces precise, reliable, and consistent results across all samples. The recommended marine sediment pretreatment protocol (‘PT4SD’) reduces the needed amount of sediment for analysis, reduces handler bias and overall digestion time. We propose that using ‘PT4SD’ as a standard pretreatment protocol will greatly benefit sedimentological laboratories individually, as well as encourage and improve the depth of cross-study comparability, thereby improving the collective field of marine sedimentology and related research as a whole.

Geomorphic response to the Lateglacial–Holocene transition in high Alpine regions (Sanetsch Pass, Swiss Alps)

Several palaeoclimatic archives have documented the pronounced climatic and environmental change associated with the Lateglacial–Holocene transition in the European Alps. However, the geomorphic response to this major environmental transition has only been punctually investigated. In this study, we propose a detailed reconstruction of post‐Last Glacial Maximum palaeoenvironmental conditions and geomorphic connectivity in the Sanetsch Pass area (2252 m a.s.l., western Swiss Alps) based on a multi‐method approach combining geomorphological and sedimentological field investigations with quantitative sedimentology and geochronology. Samples for sediment characterization (grain size, micromorphology and X‐ray diffraction) and geochronology (optically stimulated luminescence and 10Be surface exposure dating) were collected from three representative landforms of the study area: a high‐elevation silty deposit covered by patterned ground, an alluvial fan, and a hummocky moraine covered by rockfall deposits. Our results reveal the geomorphic history of the three deposits and their connectivity through sediment cascade. These results highlight the development of rapid and most probably transient landscape changes in high Alpine regions during the Lateglacial–Holocene transition, with an increase in sediment flux and the establishment of paraglacial and periglacial geomorphic processes.

The concept, characteristics and significance of fluvial fans

Abstract The concept and characteristics of fluvial fan are elucidated through literature review and case analysis. Firstly, the concept and terminology of fluvial fan are introduced. Secondly, the progress and controversy on the formation mechanism, analysis methods and sedimentary models of fluvial fan are elaborated, and fluvial fan is compared with alluvial fan, river and lacustrine delta. Finally, ten identification signs of the fluvial fan are proposed. It is found through the study that development and scale of fluvial fan are affected by external factors such as climate, tectonic, provenance and wind field. The facies and lithofacies association inside the fan are controlled by the activity of the internal channel. It is pointed that fluvial fans are widely distributed in the world not only today but also in the geological history. The occurrence of fluvial fan will change the traditional continental deposition system dominated by alluvial fan-river-lacustrine. Meanwhile, the research of fluvial fan will be of great significance in the fields of sedimentology and oil and gas exploration.

Coupled Andean Growth and Foreland Basin Evolution, Campanian–Cenozoic Bagua Basin, Northern Peru

AbstractCenozoic sedimentary rocks of the intermontane Bagua Basin record the Andean orogenic history of northern Peru at ~4–7°S. The northern Peruvian Andes define the northern termination of the Central Andes and are comprised of a narrow, low‐elevation orogen relative to the rest of the Central Andes. New stratigraphic and sedimentologic field observations, subsidence analysis, and detrital zircon provenance analysis enable reconstruction of the regional tectonic history. Late Cretaceous to Paleocene detrital zircon U‐Pb age spectra from the Fundo El Triunfo and Rentema formations reveal active volcanism in the Western Cordillera as early as ~80 Ma and early exhumation of Mesozoic rocks in a nascent Marañon Fold‐Thrust Belt. Eocene fluvial deposits of the Cajaruro Formation record a progressive increase in shortening and volcanism in the Western Cordillera. The upper Eocene–middle Miocene fluvial succession of the Sambimera Formation records deposition in a proximal foredeep setting. Sambimera deposits contain syndepositional detrital zircon U‐Pb age populations that reveal a major Cenozoic magmatic source in the west. An erosive boundary separates the Sambimera from the overlying San Antonio Formation. The San Antonio Formation was deposited in an intermontane basin associated with uplift of the Eastern Cordillera at these latitudes. These results highlight a foreland progression of fold‐thrust deformation, with shortening concentrated in the Western Cordillera from latest Cretaceous to middle Miocene time. We suggest that the late Miocene transition to intermontane deposition in the Bagua Basin marks initial exhumation during shortening of the Eastern Cordillera in northern Peru.

Burial dolomitization, the genesis of dolomite in the Dapu Formation (Upper Carboniferous), Guixinan area, Youjiang basin, Southwest China: petrologic and geochemical evidence

The genesis of dolomite is an intensively debated and extensively studied problem in the field of carbonate sedimentology. This study focuses on the dolomite of the Dapu Formation in the Guixinan area, with the aim of deciphering the mechanism of dolomitization in the Dapu Formation. Three types of sedimentary environment, including the open marine of inner ramp, the restricted marine of inner ramp, and the shoal of inner ramp, have been identified. Three types of dolostone (DI, DII and DIII) identified in the study area with massive structure had close relationship with fault structures, and contacted with limestone in curved diffuse way on the outcrop. Both of the above points indicated diagenetic dolomite. Three types of dolomite (D1, D2 and D3) displayed similar dark—light purple red luminescence, indicating that the characteristics of their diagenetic fluids were similar. The planar-s to nonplanar dolomite crystals indicated that the temperature was more than 50 °C. The mineral assemblage including D2, D3, and silicate minerals (feldspar, tremolite and actinolite) suggested contact metamorphism and tht the diagenetic fluid was rich in silicon and magnesium. The dolomitization process was not influenced by the leaching of meteoric water in surface or shallow buried environment and hydrothermal fluids, based on the corrected REE characteristics. The range of the δ18O of dolostone samples showed that the burial dolomitization had taken place in high-temperature environment. The lower 87Sr/86Sr ratio of the dolostone samples than the coeval seawater meant that the diagenetic fluid was derived from the alteration of mid-ocean ridge basalt. Based on the geologic setting, it was speculated that the burial dolomitization was driven by the hydro-tectonic processes in the passive margin burial diagenesis hydrologic realm. In brief, magnesium came from the low-temperature alteration of ocean basalts, the thermohaline and compactional flow supplied hydrodynamic condition, and the synsedimentary fault zones-supplied channels.

Image based Particle Shape Analysis Toolbox (IPSAT)

Shape analysis can provide vital information regarding the origin, transport and deposition history of grains. Particle shape measurement has been an active area of research for sedimentologists since the 20th century. With advancement in the field of computation and image analysis, shape analysis can be done in a faster and much more accurate way compared to manual measurements. The results obtained are reproducible as compared to visual qualitative analysis. However, there is a lack of image analysis software tools aimed at the field of sedimentology where the fine details of a particle boundaries are required. Image based Particle Shape Analysis Toolbox (IPSAT) developed in the Mathematica environment for the quantitative characterisation of sedimentary grains in 2-dimensions is presented here. This image analysis toolbox can be used to analyse consolidated as well as loose sediment samples. A total of 12 parameters are available for shape measurement comprising conventional shape parameters (roundness, angularity, circularity and irregularity), mathematically complex shape parameters (fractal dimension and Fourier descriptors) and common geometrical shape parameters (aspect ratio, convexity, solidity, mod ratio, rectangularity and compactness). Additionally, IPSAT offers to compute 6 particle size measurement parameters. Furthermore, 2-D particle size distribution can be transformed to a 3-D size distribution for thin section analysis. Example analyses have been carried out on a sandstone and a loose sediment sample. The toolbox presented here aims to establish a textural analysis methodology to be used by geologists and sedimentologists in particular. It will allow users to quantitatively characterise a large set of grains with a fast, cheap and robust methodology.

Mechanism of Biomineralization Induced by Bacillus subtilis J2 and Characteristics of the Biominerals

Biomineralization induced by microorganisms has become a hot spot in the field of carbonate sedimentology; however, the mechanisms involved still need to be explored. In this study, the bacterium Bacillus subtilis J2 (GenBank MG575432) was used to induce the precipitation of calcium carbonate minerals at Mg/Ca molar ratios of 0, 3, 6, 9, and 12. Bacillus subtilis J2 bacteria released ammonia to increase pH, but the ammonia released only made the pH increase to 8.25. Carbonic anhydrase was also produced to catalyze the hydration of carbon dioxide, and this process released carbonate and bicarbonate ions that not only increased pH but also elevated carbonate supersaturation. The biominerals formed at a Mg/Ca molar ratio of 0 were spherulitic, elongated, dumbbell-shaped, and irregularly rhombohedral calcite; at a Mg/Ca molar ratio of 3, the biominerals were calcite and aragonite, the weight ratio of calcite decreased from 26.7% to 15.6%, and that of aragonite increased from 73.3% to 84.4% with increasing incubation time. At higher Mg/Ca molar ratios, the biominerals were aragonite, and the crystallinity and thermal stability of aragonite decreased with increasing Mg/Ca molar ratios. FTIR results showed that many organic functional groups were present on/within the biominerals, such as C–O–C, N–H, C=O, O–H, and C–H. HRTEM-SAED examination of the ultra-thin slices of B. subtilis J2 bacteria showed that nano-sized minerals with poor crystal structure had grown or been adsorbed on the EPS coating. The EPS of the B. subtilis J2 strain contained abundant glutamic acid and aspartic acid, which could be deprotonated in an alkaline condition to adsorb Ca2+ and Mg2+ ions; this made EPS act as the nucleation sites. This study may provide some references for further understanding of the mechanism of biomineralization induced by microorganisms.

The Significant Roles of Mg/Ca Ratio, Cl− and SO42− in Carbonate Mineral Precipitation by the Halophile Staphylococcus epidermis Y2

Carbonate precipitation induced by microorganisms has become a hot topic in the field of carbonate sedimentology, although the effects of magnesium on biomineral formation have rarely been studied. In experiments described here, magnesium sulfate and magnesium chloride were used to investigate the significant role played by Mg2+ on carbonate precipitation. In this study, Staphylococcus epidermidis Y2 was isolated and identified by 16S ribosomal DNA (rDNA) homology comparison and ammonia, pH, carbonic anhydrase, carbonate, and bicarbonate ions were monitored during laboratory experiments. The mineral phase, morphology, and elemental composition of precipitates were analyzed by XRD and SEM-EDS. Ultrathin slices of bacteria were analyzed by HRTEM-SAED and STEM. The results show that this bacterium releases ammonia and carbonic anhydrase to increase pH, and raise supersaturation via the large number of carbonate and bicarbonate ions that are released through carbon dioxide hydration catalyzed by carbonic anhydrase. The crystal cell density of monohydrocalcite is lower in a magnesium chloride medium, compared to one of magnesium sulfate. Crystals grow in the mode of a spiral staircase in a magnesium sulfate medium, but in a concentric circular pattern in a magnesium chloride medium. There was no obvious intracellular biomineralization taking place. The results presented here contribute to our understanding of the mechanisms of biomineralization, and to the role of Mg2+ in crystal form.

Extracellular and Intracellular Biomineralization Induced by Bacillus licheniformis DB1-9 at Different Mg/Ca Molar Ratios

Biomineralization has become a research hotspot and attracted widespread attention in the field of carbonate sedimentology. In this study, precipitation of carbonate minerals was induced by Bacillus licheniformis DB1-9 bacteria, (identity confirmed with its phylogenetic tree), to further explore the biomineralization mechanisms. During experiments, lasting up to 24 days with varying Mg/Ca molar ratios and regular monitoring of conditions, ammonia and carbonic anhydrase are released by the bacteria, resulting in a pH increase. Carbonic anhydrase could have promoted carbon dioxide hydration to produce bicarbonate and carbonate ions, and so promoted supersaturation to facilitate the precipitation of carbonate minerals. These include rhombohedral, dumbbell-shaped, and elongated calcite crystals; aragonite appears in the form of mineral aggregates. In addition, spheroidal and fusiform minerals are precipitated. FTIR results show there are organic functional groups, such as C–O–C and C=O, as well as the characteristic peaks of calcite and aragonite; these indicate that there is a close relationship between the bacteria and the minerals. Ultrathin slices of the bacteria analyzed by HRTEM, SAED, EDS, and STEM show that precipitate within the extracellular polymeric substances (EPS) has a poor crystal structure, and intracellular granular areas have no crystal structure. Fluorescence intensity and STEM results show that calcium ions can be transported from the outside to the inside of the cells. This study provides further insights to our understanding of biomineralization mechanisms induced by microorganisms.