Granulometric and facies analysis of Middle–Upper Jurassic rocks of Ler Dome, Kachchh, western India: an attempt to reconstruct the depositional environment

Grain size analysis is an important sedimentological tool used to unravel hydrodynamic conditions, mode of trans- portation and deposition of detrital sediments. For the present study, detailed grain size analysis was carried out in order to decipher the palaeodepositional environment of Middle–Upper Jurassic rocks of the Ler Dome (Kachchh, western India), which is further reinforced by facies analysis. Microtextures were identified as grooves, straight steps and V-shaped pits, curved steps and solution pits suggesting the predominance of chemical solution activity. Grain size statistical parameters (Graphic and Moment parameters) were used to document depositional processes, sedimen- tation mechanisms and conditions of hydrodynamic energy, as well as to discriminate between various depositional environments. The grain size parameters show that most of the sandstones are medium- to coarse-grained, moderately to well sorted, strongly fine skewed to fine skewed and mesokurtic to platykurtic in nature. The abundance of medi- um- to coarse-grained sandstones indicates fluctuating energy levels of the deposition medium and sediment type of the source area. The bivariate plots show that the samples are mostly grouped, except for some samples that show a scattered trend, which is either due to a mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is predominantly indicative of turbidity current de- posits under shallow-marine conditions. The C-M plots indicate that the sediments formed mainly by rolling to bottom suspension and rolling condition in a beach subenvironment. Log probability curves show that the mixing between the suspension and saltation populations is related to variable energy conditions

Diagenetic characteristics and their implications on the reservoir potential of Bajocian Sandstone, Jaisalmer Basin, western Rajasthan, India

Petrography and scanning electron microscopy (SEM) investigations aided by energy dispersive X-ray (EDX) analysis and quantitative measurement of reservoir properties were used to extensively examine the physical and diagenetic characteristics of the Joyan Member Sandstone of Jaisalmer Formation. The Joyan Member Sandstone is fine- to medium-grained, moderate to well sorted, sublitharenite to litharenite. Mechanical compaction, precipitation of calcareous, ferruginous and silica cements, clay minerals, dissolution and alteration of unstable clastic grains such as feldspar and rock fragments, and grain fracturing are the identified diagenetic features. Feldspar and rock fragments underwent significant changes to kaolinite and chlorite while silica cement primarily originated from the dissolution and alteration of these grains and pressure solution. Mechanical compaction and the authigenic cements like calcareous, ferruginous, and silica reduced primary porosity, while secondary porosity was created by dissolution of clastic grains and cements. Compaction reduced porosity from an anticipated original 40% to around 13.4%. Porosity was reduced by cementation to 20.8%. Cementation reduced the porosity of the Joyan Member Sandstone somewhat more than compaction. Calcareous cementation played a major role in the porosity evolution of Joyan Member Sandstone. During early burial, the early calcareous cement occupied most of the pore spaces, leading to a significant reduction in porosity. However, incomplete filling or scattered patches of calcareous cement helped to preserve some primary porosity. In addition to calcareous cement, clay minerals like kaolinite and chlorite also acted as pore-filling and pore-lining cements. Kaolinite had a booklet-like or lamellar pattern contributing to minor porosity loss through pore-occlusion, while pore lining chlorite helped to retain porosity by preventing syntaxial silica overgrowth. Extensive dissolution of calcareous cement significantly increased the secondary porosity. Diagenesis affects reservoir quality by reducing initial porosity through cementation and compaction, and then increasing it through dissolution of early calcareous cement and unstable grains. The diagenesis of the studied sandstone is closely linked to its potential as a reservoir

Granulometric and facies analysis of Middle–Upper Jurassic rocks of Ler Dome, Kachchh, western India: an attempt to reconstruct the depositional environment

Grain size analysis is an important sedimentological tool used to unravel hydrodynamic conditions, mode of transportation and deposition of detrital sediments. For the present study, detailed grain size analysis was carried out in order to decipher the palaeodepositional environment of Middle–Upper Jurassic rocks of the Ler Dome (Kachchh, western India), which is further reinforced by facies analysis. Microtextures were identified as grooves, straight steps and V-shaped pits, curved steps and solution pits suggesting the predominance of chemical solution activity. Grain size statistical parameters (Graphic and Moment parameters) were used to document depositional processes, sedimentation mechanisms and conditions of hydrodynamic energy, as well as to discriminate between various depositional environments. The grain size parameters show that most of the sandstones are medium- to coarse-grained, moderately to well sorted, strongly fine skewed to fine skewed and mesokurtic to platykurtic in nature. The abundance of medium- to coarse-grained sandstones indicates fluctuating energy levels of the deposition medium and sediment type of the source area. The bivariate plots show that the samples are mostly grouped, except for some samples that show a scattered trend, which is either due to a mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is predominantly indicative of turbidity current deposits under shallow-marine conditions. The C-M plots indicate that the sediments formed mainly by rolling to bottom suspension and rolling condition in a beach subenvironment. Log probability curves show that the mixing between the suspension and saltation populations is related to variable energy conditions

Granulometric and facies analysis of Middle–Upper Jurassic rocks of Ler Dome, Kachchh, western India: an attempt to reconstruct the depositional environment

Grain size analysis is an important sedimentological tool used to unravel hydrodynamic conditions, mode of trans- portation and deposition of detrital sediments. For the present study, detailed grain size analysis was carried out in order to decipher the palaeodepositional environment of Middle–Upper Jurassic rocks of the Ler Dome (Kachchh, western India), which is further reinforced by facies analysis. Microtextures were identified as grooves, straight steps and V-shaped pits, curved steps and solution pits suggesting the predominance of chemical solution activity. Grain size statistical parameters (Graphic and Moment parameters) were used to document depositional processes, sedimen- tation mechanisms and conditions of hydrodynamic energy, as well as to discriminate between various depositional environments. The grain size parameters show that most of the sandstones are medium- to coarse-grained, moderately to well sorted, strongly fine skewed to fine skewed and mesokurtic to platykurtic in nature. The abundance of medi- um- to coarse-grained sandstones indicates fluctuating energy levels of the deposition medium and sediment type of the source area. The bivariate plots show that the samples are mostly grouped, except for some samples that show a scattered trend, which is either due to a mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is predominantly indicative of turbidity current de- posits under shallow-marine conditions. The C-M plots indicate that the sediments formed mainly by rolling to bottom suspension and rolling condition in a beach subenvironment. Log probability curves show that the mixing between the suspension and saltation populations is related to variable energy conditions

Facies architecture and textural attributes of the Late Quaternary cliff embankment sections of the Sai River, Central Ganga Plain, India

The cliff embankments are covered as sediments from the floodplain run on both sides of the river. Various sediments transportation and depositional mechanism are contained in these floodplain deposits. For better understanding of depositional history of the floodplain sediments cliff embankments along the Sai River at the villages of Chaukhada and Khatihara in the districts of Pratapgarh and Jaunpur, respectively, were analysed using a laser particle size analyser. The common facies observed in the studied sections are very silty sandy mud, very silty sand, slightly silty sand and very silty slightly sandy mud accordingly. Indurated calcretes are also observed in the very silty sandy mud layer in the Chaukhada section. The Chaukhada section has mean size value ranging from 2.80 phi to 4.98 phi while Khatihara section has these values ranging from 3.80 phi to 4.27 phi, implying coarse silt to very fine sand size range for both the cliff section. The sediments in both of the investigated cliff sections are poorly to very badly sorted, as seen by the sorting (standard deviation) values for the Chaukhada section, which are ranging from 1.12 phi to 2.22 phi, and the Khatihara section, ranging from 1.30 phi to 1.84 phi. The sediment samples displayed the skewness values ranging from 0.23 to 0.34 for the Chaukhada section and 0.09 to 0.32 for the Khatihara section, indicating that the sediments are very finely skewed. The kurtosis value ranging between 1.24 to 1.73 for the Chaukhada section and 1.22 to 1.72 for the Khatihara sections shows that the sediments are leptokurtic to very leptokurtic in nature. Bivariate plots of textural parameters have been also utilized to figure out the depositional environment. The C–M plot indicates that the graded to uniform suspension was the primary mechanism of transportation for all the sediments