Analysis Of Sedimentary Rocks Research Articles

Geochemical constraints on the element enrichments of microbially mediated manganese and iron ores – An overview

The role of biogenicity in the mineral world is larger than many might assume. Biological processes interact with physical and chemical processes at the Earth’s surface and far below underground, leading to the formation, for instance, of banded iron formations and manganese deposits. Microbial mats can form giant sedimentary ore deposits, which also include enrichment of further elements. Microorganisms play a basic role in catalyzing geochemical processes of the Earth and in the control, regularization and leading of cycles of elements. Microbial mats and other biosignatures can be used as indicators for environmental reconstruction in geological samples. This article reviews the many ways that microbially controlled or mediated processes contribute to mineralization and examines some published case studies for clues of what might have been missed in the analysis of sedimentary rocks when biogenicity was not taken into account. Suggestions are made for tests and analyses that will allow the potential role of biomineralization to be investigated in order to obtain a more complete view of formation processes and their implications.

Abstract: Solid-state NMR Analysis of Sedimentary Rocks From Different Laramide Basins of North America

Abstract: Solid-state NMR Analysis of Sedimentary Rocks From Different Laramide Basins of North America

Sandstones of arc and ophiolite provenance in backarc basin, Halmahera, eastern Indonesia

Abstract Analyses of sedimentary rocks from a late Neogene backarc basin on the island of Halmahera in eastern Indonesia show that the detrital mineral assemblages in the sandstones have distinctive characteristics. Quartz is extremely rare in the entire sequence of up to 4 km of basin sediments, clearly indicating that there has been no input from continental sources throughout the basin history. Sediments derived from two distinct provenance areas are recognized: sandstones dominated by volcanic rocks occur in the western half of the basin and in the eastern part there are black sands composed largely of ultrabasic debris interbedded with carbonate mudstones. These sandstone petrographies reflect the nature of the terrains which have bordered the Halmahera Basin throughout its history and other small basins formed in an ‘oceanic’ setting may show similar characteristics. Temporal changes in the volcaniclastic components are attributed to stages in the evolution of the adjacent volcanic arc and do not reflect the degree of dissection of an arc massif.

Anomalous Boron Content of Two Continental Shales in Eastern Colorado

ABSTRACT Boron content and clay mineralogy were determined on samples from a continental facies of the Fountain Formation of Permo-Pennsylvanian age and a pre-Fountain fossil soil developed during late Mississippian time. All samples from both units were found to contain far more boron than amounts previously proposed as indicative of shales deposited in continental environments. The results of the study cast doubt on the reliability of boron analyses of sedimentary rocks as an index of their depositional salinity.

Aliphatic Hydrocarbons in Pre-Cambrian Rocks

Analyses of sedimentary rocks from the Pre-Cambrian of South Africa show that they contain a variety of alkanes. Were these hydrocarbons incorporated into the sediments at the time of sedimentary deposition, and are they biogenic in origin ?

Lithologic Analysis of Sedimentary Rocks

The role of the subsurface stratigrapher increases in importance as the number of unexplored structural traps decreases, but little detailed information regarding the descriptions and interpretations of sample cuttings has been made available in one publication. Rocks may be described in sample cuttings as to rock type, color, grain or crystal size, cement or matrix, impurities, porosity, stain, luster, fossils, associated material, and subordinate features. Clastic rocks are divided into non-carbonate clastics, which include sandstone, siltstone, and clay, or shale, and carbonate clastics which include most types of limestone and dolomite. Non-clastic carbonate rocks (reefs and bioherms) can be composed to a great extent of clastic material, but they originate from and are retained by non-clastic organisms. Evaporites compose a third major rock type. Sedimentary rocks may have interstitial and fracture porosity and in addition carbonate rocks may have solution porosity. Insoluble residues and paleontology are supplemental aids in establishing time surfaces and in indicating environments. Several simple tests for determining mineralogy and oil shows can be made by a stratigrapher. He can also identify in sample cuttings several criteria for the recognition of unconformities.

Operator Variation in Experimental Research

The presence of operator variation is shown to be a common feature of all experimental procedures. This variation arises from two important factors, the one due to differences arising from a constant bias characteristic of each operator and the other due to inconsistent differences within one operator and among a group of operators. The first factor can be resolved by means of suitable experimental design and analysis of variance. The second determines the level of sensitivity of the experiment. These two factors associated with operator variation are shown to increase as the experimental procedure changes from simple measurements through objective to subjective assessment. The effects of these two kinds of operator variation are illustrated from experiments in the analysis of sedimentary rocks, field mapping, and various other aspects of scientific investigation.