Environment Of Sedimentary Rocks Research Articles

Identifikasi Sesar dengan Menggunakan Metode Gaya Berat (Studi Kasus: Sulawesi Tengah)

The study of the geological structure of Sulawesi Island, especially the Central Sulawesi region, is very interesting because it has high complexity as a result of the dynamic interactions of the world's three main plates. Indications of high seismic activity and deformation processes in the Central Sulawesi region can be found from the morphological appearance and activity of several existing faults such as the Palu-Koro fault, the Lawanopo fault, and the Matano fault. The data used in this study are secondary data measuring the distribution of gravitational field anomalies (FAA) and topographical data using the Topex application. At CBA values ranging from 31 mGal to 56 mGal. The height anomaly on the CBA contour map is shown in red to light purple which has a value range of 40.7 mGal to 62.7mGal. Low anomaly is shown in light green to blue which has a value range of 27.3 mGal to 3.2 mGal. The regional gravity anomaly values range from 5.1 mGal to 62.8 mGal with a distribution of gravity anomalies from south to north. While in this study it can only be explained that the residual anomaly value is influenced by rock type and density. The high anomaly found in the southern part is thought to be caused by rocks having high density and being in a sedimentary rock environment which has low density.

Sources of Sediment Clasts and Depositional Environment of Sedimentary Rocks of the Daur Series of the Argun Continental Massif

Sources of Sediment Clasts and Depositional Environment of Sedimentary Rocks of the Daur Series of the Argun Continental Massif

Modeling of the pressure propagation due to CO2 injection and the effect of fault permeability in a case study of the Vedsted structure, Northern Denmark

Assessing the pressure buildup in CO2 storage sites and especially the vertical propagation is vital for evaluation of site behavior and security. Vedsted structure in the Northern part of Jylland in Denmark consists of 290m thick Gassum Formation at 2100m depth forming the primary reservoir and is sealed by the 530m thick Fjerritslev Formation which is mainly shale lithology with very low permeability. Overlying the caprock is a number of formations forming secondary reservoirs and seals including a 420m thick Chalk Group which is overlain by 20–50m Quaternary deposits. Seismic profiling of the structure shows the presence of northwest-southeast trending faults of which some originate in the upper layer of the Gassum reservoir and some reach the base Chalk Group layer. Two faults in the upper Gassum reservoir have been interpreted to be connected to the base Chalk Group. In order to evaluate potential risks associated with vertical pressure transmission via the faults through the caprock, a number of simulation cases have been run with various fault permeabilities spanning orders of magnitude to represent both the worst and best case scenarios. Fault rock permeability data were obtained from a literature study and range from 1000mD (maximum value reported from sedimentary rock environment) for the worst case scenario down to 0.001mD (sealing faults in sedimentary rock environment) for the best case scenario. The results show that after injecting 60 million tons (Mt) of CO2 at a rate of 1.5Mt/year for 40 years, overpressure is developed in the reservoir and about 5bar is transmitted to the base Chalk Group for the 1000mD fault permeability (open fault) case, while for the 0.001mD (sealing fault) case the pressure buildup is confined within the primary caprock. The results also show that, approximately 0.3–5.0bar overpressure can be transmitted to the base Chalk Group when the fault permeability is above 1.0mD.

A non-marine depositional setting for the northern Fortescue Group, Pilbara Craton, inferred from trace element geochemistry of stromatolitic carbonates

The depositional environment of sedimentary rocks from the Neoarchaean Fortescue Group (2.78–2.63 Ga) in the Hamersley Basin, Pilbara Craton, Western Australia, is controversial, with both lacustrine and shallow-marine settings proposed. Stromatolitic carbonates occur throughout the stratigraphic section at various levels, and their trace element geochemistry is used herein to examine ambient water from which these carbonates precipitated. Specifically, rare earth elements (REE) and yttrium were analysed to understand whether: (i) Fortescue carbonates display a marine or lacustrine geochemical signature, and (ii) to identify temporal trends in the geochemistry consistent with a transition in the depositional environment. Detailed inspection reveals that Fortescue stromatolites from the northern part of the Hamersley Basin are devoid of trace element compositions that are characteristic of marine carbonates. For instance, the carbonates lack distinct La (expressed as La/[3Pr–2Nd] in shale-normalised diagrams) and Gd ([Gd/(2Tb–Dy)] shale) anomalies and supra-chondritic Y/Ho ratios, which are well-developed in seawater-derived carbonates formed throughout Earth history. The Neoarchaean Fortescue Group stromatolites also lack depletion of the light REE relative to the middle and heavy REE when shale-normalised, in contrast to modern seawater and marine carbonates, which are typically HREE-enriched. Importantly, the absence of a clear temporal trend in the geochemistry suggests that the depositional environment remained unchanged from 2.8 to 2.6 Ga. It is concluded that Neoarchaean stromatolitic carbonates throughout the Fortescue Group in the northern part of the Hamersley Basin were deposited in a lacustrine environment, or a very shallow lagoonal environment dominated by freshwater influx from rivers. Our study demonstrates that trace element geochemistry is a powerful tool to constrain depositional environments of ancient carbonate rocks. This study is the first to document the geochemical characteristics of carbonates formed through microbial activity in an ancient lake, or shallow lagoonal, setting.

東濃地域における地下水化学と地下微生物の相互作用

The abundance and diversity of groundwater microorganisms were studied in a geochemically defined borehole (TH-6, DH-3) in the Tono area, central Japan. Total cell counts by epifluorescence microscopy were estimated to be approximately 1.6 × 105-5.7 × 106 cells ml -1 and showed little decrease with depth. Cell viability, based on cell membrane integrity, respiration-based metabolism, and esterase activity was estimated to be 0.001% to approximately 100% of the total counts. The distribution of microbial abundance seems to be related to a variety of environmental factors, including fracture numbers, hydrological, and geochemical conditions of the groundwater. The geochemistry of the groundwater suggests that sulfate reducing bacteria play an important role in the sedimentary rock environment. It appears that microbial sulfate reduction occurs at the highest level in the upper part of the Toki Lignite-bearing Formation. This microbial reaction may play an important role in maintaining anaerobic conditions for uranium fixation, that could in turn scavenge soluble and oxidized uranium. On the other hand, in the granite groundwater, iron-oxidizing/reducing bacteria seem to play an important role in iron redox cycling. Iron-oxidizing bacteria may contribute to the formation and deposition of iron colloids in the upper part of Toki granite.

Depositional environment of sedimentary rocks inferred from normal fatty acid compositions

Normal saturated fatty acid (n-fatty acid) in marine sediments from coastal and pelagic environments were analyzed. The coastal sediments contain both short-chained n-fatty acids with carbon numbers from 12 to 18 and long-chained acids from 22 to 32, whereas the pelagic sediments contain predominantly short-chained acids. The relative abundance of short-chained to long-chained n-fatty acids, expressed by the molar ratio C 16=C26, can be an indicator to assess the depositional environment of sedimentary rocks. The ratio of long-chained n-fatty acids (C22‐C32) to the total n-fatty acids also has the potential to discriminate sedimentary environments. The indicators based on the n-fatty acids were applied to the Franciscan bedded cherts. The result shows that the bedded cherts had deposited in continuous environments from the pelagic to the coastal. This is in harmony with the same inference based on major, trace and rare earth elements and normal paraffins. © 1999 Elsevier Science B.V. All rights reserved.

Rehabilitation of a uranium-ore processing residues storage site at Le Bouchet, Paris Region, France

From 1949 to 1971, the French Atomic Energy Commission operated a uranium-ore processing plant in the Paris region. After the plant was dismantled in the 70s, the plot of land that had been used to store the processing residues, and the area covered by the settling basin, were locked up. A study of the site in 1990 showed that the level of radon emissions and radon daughters from these premises was 10 to 100 times greater than the mean level above the ground. In 1992, the local authorities decided to rehabilitate the site. To limit the radon emissions, the land was buried under various materials, including a bed of clay several tens of centimetres thick. The measurements made on the site and in the surroundings of it, after the land was covered, showed clearly that the radon and the radon decay product concentrations were lowered to the same order of magnitude as the representative regional background noise in the Paris basin, typical of a sedimentary rock environment.