Clast Fabric Research Articles

The role of rock and clast fabric in the physical performance of crushed-rock aggregate : Ramsay, DM Univ. Dundee, Scotland, GB Dhir, RK Univ. Dundee, Scotland, GB Spence, IM Univ. Dundee, Scotland, GB 10F, 5T, 17R Engng. Geology, V8, N3, Oct. 1974, P267–285

The role of rock and clast fabric in the physical performance of crushed-rock aggregate : Ramsay, DM Univ. Dundee, Scotland, GB Dhir, RK Univ. Dundee, Scotland, GB Spence, IM Univ. Dundee, Scotland, GB 10F, 5T, 17R Engng. Geology, V8, N3, Oct. 1974, P267–285

Sedimentation of deep water conglomerates in lower Ordovician rocks of Quebec; composite bedding produced by progressive liquefaction of sediment

ABSTRACT A Sequence of Lower Ordovician conglomerates and sandstones outcrops on the south shore of the St. Lawrence River, northeast of the village of Grosses Roches, Quebec. Detailed measurement of a section 100 meters thick shows that the conglomerate facies, which includes conglomerates, conglomeratic sandstones, and sandstones, occurs above a sequence of claystones, and alternates with a sandstone-shale turbidite facies. The conglomerates erode both the claystones and the turbidites. Rip-up structures, channeling of underlying sediments, grading, poor sorting, very large clasts, and chaotic clast fabric in some conglomerates suggest formation by deposition from gravity-controlled slides or flows. The conglomerates display two types of bedding: (1) Beds with no marked internal textural cha ges from top to bottom. These are termed simple beds in the present study. (2) Beds with several thin discontinuous sandstone layers in them. These layers can be traced up to 80 m along strike, but most layers are of limited lateral extent. These conglomerate beds are termed compound beds. Sandstone layers within compound conglomerate beds generally have flat tops and irregular bases. Where they wedge out, they invariably thin from the base upwards. They are not eroded by overlying conglomerate layers, although erosive features are common at the bases of both simple and compound beds. Thin fine-grained turbidites and thick medium to coarse-grained quartzose sandstone beds occur between compound conglomerate beds but not between layers within compound beds. This suggests that deposition of individual compound beds occurred as a series of events which were closely related in time and space, i.e., the beds are composite. It is likely that the development of such a series of events is related to the mechanism of initiation of a slide or flow rather than to the transp rt or depositional mechanism. This implies some type of progressive failure of the sediment mass at source. Recent advances in the field of experimental soil mechanics, and observations during recent earthquakes, suggest that the phenomenon of progressive liquefaction may account for relatively rapid but discontinuous failure of unconsolidated sediment. Considering the grain size of the material involved and the structures in the conglomerates, it is suggested that the composite beds in the Grosses Roches section result from deposition from a submarine slide or flow which was caused by progressive liquefaction of sandy layers in a series of unconsolidated sands and gravels, perhaps during an earthquake.

Clast Fabric Strength of Tillite

A stepwise regression analysis of twenty-four variables measured from beds of tillite from the Permian Pagoda Formation of Antarctica suggests that the strength of long-axis clast fabric in tillite is largely dependent on subglacial conditions at the time of deposition. In particular, fabric strength depends on the distribution of shear stress at the ice-sediment interface at the time of till deposition. The larger particles in till are subjected to greater shear stress at the depositional interface and are more likely to be reoriented. Consequently, when fabric studies are made it may be more important to select smaller clasts and remain within limited grain size range than it is to select clasts on the basis of shape. The strongest fabrics can be expected in thicker beds and in beds with a high clay content. The presence of striae paralleling the prominent edges of clasts indicates that the interaction between clasts and the depositional interface is a powerful reorienting mechanism. However, the proportion of striated clasts observed in a bed of till does not necessarily offer a direct measure of the degree to which clasts have been reoriented, because a proportion of the striated clasts may have been derived by the reworking of underlying beds by subsequent ice advances.

Clast Fabric of Till and its Development

ABSTRACT Long-axis clast fabrics from tillites of the Permian Pagoda Formation in Antarctica can be classified into several morphologic types depending on the strength and orientation of the fabric modes. The fabrics result from a large number of processes which take place both englacially, as the clast is being transported in actively deforming ice, and subglacially at the ice-sediment interface at the time of deposition. A few of the clast fabrics from the Pagoda Formation probably developed englacially and a like number were completely reorganized during deposition. However, the largest proportion of the diagrams are intermediate in character between those of fabrics formed englacially and those formed during deposition. This suggests that the subglacial conditions are such during depositio of most till units that the englacial fabrics are generally only partially reorganized. The degree to which subglacial reorganization of the clast fabric takes place depends in large part on the distribution of shear stress at the ice-sediment interface at the time of deposition which in turn depends on bottom roughness and the rate of deposition. Thus clast fabric not only provides information on paleo-ice flow direction but is also valuable in determining the conditions prevailing at the ice-sediment interface during till deposition.

Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains

Research Article| April 01, 1970 Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains JOHN F LINDSAY JOHN F LINDSAY Institute of Polar Studies, Ohio State University, Columbus, Ohio 43210 AUTHOR'S PRESENT ADDRESS: NASA, MANNED SPACECRAFT CENTER, HOUSTON, TEXAS 77058 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (4): 1149–1172. https://doi.org/10.1130/0016-7606(1970)81[1149:DEOPGR]2.0.CO;2 Article history received: 26 Jun 1969 accepted: 08 Oct 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN F LINDSAY; Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains. GSA Bulletin 1970;; 81 (4): 1149–1172. doi: https://doi.org/10.1130/0016-7606(1970)81[1149:DEOPGR]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Permian glacial sediments of the Pagoda Formation in the central Transantarctic Mountains range from 126 to 395 m in thickness. Grooved sandstone lenses within the tillite beds indicate that they were deposited during retreat phases from active temperate ice which flowed to the southeast. Several interbeds and sedimentary breaks within the formation suggest possibly as many as 13 minor advances and retreats of the ice front. Grooved surfaces and clast fabrics indicate that the ice moved across the area in a direction of 148° ± 19°. The paleo-ice flow directions vary randomly about the mean from bed to bed, probably in response to local conditions. Between ice advances, streams, some of them quite large, flowed across a subdued topography and were locally diverted or dammed by the retreating ice front.The extent and continuity of the Paleozoic glacial deposits and the consistency in paleo-ice flow direction in Antarctica suggest an ice sheet of continental dimensions centered on southern Victoria Land. Dark shales conformably overlying the tillites over much of their known extent appear to have been deposited as the ice retreated prior to isostatic rebound of the depressed subglacial surface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Development of Clast Fabric in Mudflows

ABSTRACT Computer simulation of the motion of particles in a viscous fluid in laminar flow shows that strong long-axis fabrics may develop in mudflows in a short period of time. The rate at which the fabric develops in any one situation depends on the velocity gradient. The viscosity of the mudflow one of the main factors controlling the velocity gradient, is increased considerably by the clasts contained in the matrix Fabric development is cyclical and begins as a vague girdle dipping upstream. At the same time a single mode develops, centered on the girdle, and gradually increases in intensity until a maximum is reached when the plunge of the mode is horizontal. The fabric from this point degenerates in reverse order, first to a weak girdle dipping downstream, and then to a fabric similar to the initial fabric when the particles have completed a half cycle of motion. The process then begins again. The strength of the fabric depends on the instant at which the mudflow is arrested. Even though most mudflows travel in a turbulent manner, the fabric is developed in the final stages as the velocity of the flow decreases, and it passes to a laminar phase before coming to rest. Limited experiments and simulations show that a C-axis fabric should also develop with a single vertical mode and girdle transverse to the flow direction. Settling of the clasts under gravity after the flow has come to rest probably leads to a strengthening of the C-axis fabric, as clasts would tend to reorient themselves with their plane of maximum projection (the A, B plane) normal to the force of gravity. The Permian Pagoda Formation in Antarctica consists largely of tillite but contains a small number of beds deposited from mudflows. Four A-axis fabrics were measured from the mudflow units and were found to be similar to long-axis fabrics produced by the simulations. All four have dipping girdles, and two display a central mode. When compared with till fabrics from the same section the mudflow fabrics can be distinguished because of the girdles. Had the mudflows been arrested at a stage of maximum fabric development, it would be impossible to distinguish them from most till fabrics. In this situation the problem may be clarified by measuring several fabrics at different levels in the flow. Because the velocity gradient decreases upward the strength of the mudflow fabrics should be dif erent at different levels. An attempt to exploit this method in the field met with very limited success, probably because the change in velocity gradient upward through the mudflow was too small. C-axis fabrics developed by mudflows have vertical modes while their counterparts in till fabrics plunge steeply in a downstream direction. It is concluded that clast fabric could be a valuable tool in determining the origin of diamictites, but more field data are needed.

Paleocurrent Patterns in Upper Cretaceous Beds of Marsh Creek Formation of Northern Diablo Range, California: ABSTRACT

Cretaceous turbidite beds that crop out along the northeastern flank of the Diablo Range between Altamont Pass and Mount Diablo exhibit numerous paleocurrent features. More than 400 pieces of paleocurrent data from sole marks, sand grain and conglomerate clast fabrics, carbonaceous fragment orientation, and parting lineations collected from outcrops within a 300-sq-mi area were used to deduce that the trend of the ancient currents which deposited these beds was from northwest to southeast. The majority of the beds studied dip homoclinally northeast into the San Joaquin Valley. Therefore, the paleocurrent analysis was dominantly two dimensional for each time-stratigraphic interval in the section. The sequence studied is more than 20,000 ft thick and ranges in age from Maastrichtian to Turonian, but a few localities may be as old as Aptian. Dating of the beds was based mainly on microfossils, but a few ammonites and other diagnostic Upper Cretaceous megafossils also were found. A change in thickness of the sequence from about 10,000 ft to more than 20,000 ft takes place along the strike of the beds from near Mount Diablo in the northwest corner of the area studied to Altamont Pass in the southeastern part of the area. Current trends observed near the base of the section show little deviation from those noted higher up and, therefore, the pattern of current flow must have remained static in this area for the duration of Late Cretaceous time. Deviations from the general paleocurrent pattern were observed in some of the paleocurrent features studied, but the number of these deviations is minor compared with the majority of the data collected. End_of_Article - Last_Page 561------------