Study Of Quaternary Sediments Research Articles

Integrated 3D modeling of Quaternary sediments in the Beijing Plain, based on a sequential indicator simulation

The study of Quaternary sediments has long been a focus for geologists, primarily because they are closely aligned with urban safety assessment, energy exploitation and sustainable development. The Beijing Plain was selected for this study. Using existing drilling data and knowledge of the sedimentary characteristics in this study area, a geological model was developed with Petrel software using the sequential indicator simulation algorithm. The main aims were firstly, to integrate ArcGIS and Petrel with drilling information, a digital elevation model, a stratum sedimentary thickness plan and other multi-platform data on the same platform. Secondly, establish a lithology variogram model and then construct a quaternary lithology model based on the variogram model and finally, use the established lithology model to preliminarily analyze the lateral and vertical distribution rules of Quaternary lithology in the study area. These results provide new methods for the establishment of geologic modeling during the preliminary stages when studying engineering geology. The results will also provide baseline information for later research.

A comparison of micro-CT and thin section analysis of Lateglacial glaciolacustrine varves from Glen Roy, Scotland

Despite the prevalence of thin section analysis in studies of Quaternary sediments, there are limitations associated with the production of thin sections (sediment modification) and the inherently 2D view that a thin section affords. Non-destructive and rapid scanning technologies such as X-ray computed microtomography (μCT) enable material samples to be visualised and analysed in 3D. In a Quaternary context, however, such techniques are in their infancy. This paper assesses the optimum approach to μCT analysis of Quaternary sediments, applying the method on Lateglacial glaciolacustrine varves from Glen Roy, Scotland. Scan datasets are examined at each stage of the thin section process and comparisons are made between 2D μCT images and thin sections for the recognition of 2D sediment features, with further appraisal of 3D models to identify 3D sediment structures. Comparable sediment features are observed in 2D μCT images and thin sections, however, the μCT imaging resolution determines the precision of microfacies descriptions. Additional 3D structures are distinguished from volumetric models that are otherwise impossible to identify in thin section slides. These 3D structures can locally alter sediment properties (e.g. layer thickness) as seen in 2D thin sections and/or digital images, although such variation cannot be detected with these media. It has been demonstrated that clear benefits exist in understanding the 3D structure of Quaternary sediments, both prior to thin-sectioning to avoid complicating (e.g. deformation) structures, and after thin-sectioning to establish the complex 3D context of 2D datasets. It is recommended that μCT and thin section techniques are applied in parallel in future studies, which will profit from the integration of ‘true’ 3D data. It is also advised that samples are scanned soon after field sampling, due to the significant modification of in situ sediment structures that can occur during thin section processing.

Turbid-layer bypassing model: The Corsican Trough, northwestern Mediterranean

Studies of Quaternary sediments on the Mediterranean margins indicate that: (1) erosion has prevailed on shelves, shallow ridges and upper slopes, while (2) erosional-depositional and resuspension regimes dominate slopes, and (3) ponding characterizes the deep, more distal basinal sectors. A sedimentation model involving gravity-induced transport of fine-grained material and downslope bypassing is developed on the basis of an examination of cores (petrologic and radiocarbon analyses) and a dense network of 3.5-kHz and seismic records in the Corsican Trough and associated margins and deep-sea fans of the northwest Mediterranean. This model emphasizes that silty mud accumulates at higher rates in more distal regions than do coarser grained sediments in more proximal settings. The principles highlighted here should be applicable to other continental margin settings in the Mediterranean and other ocean basins.

Planktonic foraminiferal fauna associated with eastern Mediterranean Quaternary stagnations

Bradley1 predicted, before any evidence from sediment coring in the Mediterranena Sea, that changing late Quaternary climatic conditions would result in periodic stagnations of the eastern basin and with them, accumulations of organic-rich sediments. Such organic-rich layers from the eastern Mediterranean were subsequently observed in sediment cores by Kullenberg2 and later named “sapropelitic layers”3. Since these initial observations, sapropels have been reported in most studies of Quaternary sediments from the Ionian Sea4–14. As a result, there is a great deal of information available concerning the chemical15–18 and sedimentological properties13–14, faunal characteristics19 and temporal9–11 and spatial10,12 distribution of late Quaternary sapropels. In the study reported here we have attempted to characterise the planktonic foraminiferal biogeography of such late Quaternary sapropels in terms of the modern distribution of foraminefara in the Mediterranean Sea.

EARLY DIAGENESIS AND THE PRESERVATION OF POROSITY IN JURASSIC LIMESTONES

The study of Quaternary sediments has shown that carbonates are susceptible to early lithification, or to dissolution, in many different environments. Most of these surface effects, although reducing primary porosity, rarely destroy it completely. Although similar diagenetic phenomena also occur in ancient rocks, the great majority of limestones do not exhibit early diagenetic fabrics; much sparitic cement is possibly related to carbonate liberated by pressure‐solution within the limestone mass. In spite of the fact that carbonate sediments frequently have high initial porosities, most of it is destroyed by sparitic cement. The exceptional circumstances favouring the preservation of effective porosity may be related to the presence of an early diagenetic phase. A number of reservoirs exhibit early diagenetic cements, dissolution and dedolomitisation fabrics. It is concluded that early lithification tends to retard or prevent subsequent pressure‐compaction and thus reduces the volume of carbonate available for porosity destruction. The recognition of early diagenetic phenomena in ancient limestones therefore has important economic implications.