Glacial Sedimentary Processes Research Articles

Late Ordovician ice-marginal processes and sea-level change from the north Gondwana platform: Evidence from the Valongo Anticline (northern Portugal)

In the Valongo Anticline, northern Portugal, the Upper Ordovician-age Sobrido Formation records glacioeustatic sea-level changes and glacially-influenced depositional environments on the north Gondwana platform associated with the Hirnantian glaciation. New stratigraphic data from the Sobrido Formation, taking into account lateral facies variations not exposed in the type section, allow for a better understanding of Hirnantian glacial sedimentary processes, sea-level changes and palaeogeography. The lower member of the Sobrido Formation is composed of quartzites alternating with siltstones and mudstones. The transition to the upper member is most commonly an erosional contact marked by a ferruginous horizon. The lowermost part of the upper member contains a thinly laminated and rhythmically-bedded mudstone that is capped by a thin (mm-scale) shelly bed and overlain by massive diamictites. Laterally, conglomerate beds that have erosion bases are rhythmically interbedded with slates and diamictites that sometimes contain outsized mudstone clasts. The uppermost part of the upper member is very variable in thickness laterally and contains massive to laminated diamictite beds intercalated with quartzites, conglomerates and slates. Massive diamictites commonly exhibit thin horizons with Fe-oxides and occasionally manganese, phosphate and oolitic chamosite. The lower member of the Sobrido Formation is interpreted as ice-proximal outwash that is transitional laterally to subaqueous ice-contact fans formed by debris and mass flows. Erosion followed by chemical weathering of the lower member and variably within the lowermost part of the upper member is interpreted as a response to sea-level fluctuations and development of spatially-variable anoxic conditions and groundwater migration within isolated marine basins. Facies within the upper member of the Sobrido Formation are interpreted as ice-distal (laminated diamictites) and ice-proximal deposits (massive diamictites, quartzites and conglomerates). Groove casts and hummocky cross-stratification within quartzite beds suggest deposition in a shallow shelf setting. The Upper Ordovician–Lower Silurian transition is locally marked by a ferruginous horizon. Black basal quartzites are interpreted to record development of an erosional unconformity during Silurian sea-level rise. In other areas a chloritoid layer indicates proximity to dry land. These palaeoenvironmental interpretations suggest dynamic changes in sedimentary and geochemical processes in response to sea level and related palaeogeographic changes during the Upper Ordovician and transitional to the Lower Silurian on the north Gondwana platform.

Glacial Sedimentary Processes and Products

Research in the field of glacial sediments and sedimentary processes increasingly involves a range of different approaches including investigations of modern glacial processes, the paleoglacial record, and numerical ice sheet modeling. This diversity of approaches is reflected in this International Association of Sedimentologists special publication edited by Michael Hambrey et al., which stems from the 2005 “Conference on Glacial Sedimentary Processes and Products,” held at the University of Wales, Aberystwyth. Following a foreword about geologist Brian Harland (to whom the volume is dedicated) and the Neoproterozoic Snowball Earth theory, and an introduction by the editors, the book has four parts.Part 1, “Glacier dynamics and sedimentation,” focuses on modern glacier and ice sheet processes. It includes three very diverse papers. A paper by Siegert et al. explores the possibility of hydrological links between Antarctic subglacial lakes and the consequences of rapid drainage events for subglacial erosion and deposition. This is followed by a paper (Midgley et al.) on moraine geomorphology and sedimentology in Svalbard, Norway, and a final paper (Rousselot et al.) on the description of a laboratory apparatus for investigating clast ploughing in sediments.

Holocene book review: Glacial sedimentary processes and products (IAS Special Publication 39)

Holocene book review: Glacial sedimentary processes and products (IAS Special Publication 39)

Fabric analysis of till clasts in the upper Urumqi River, Tian Shan, China

In-situ measurement of clast fabric within till and other sediment was performed at locations in Hayisa (HY), Upper-Wangfeng (UW), Lower-Wangfeng (LW) and Balatigou (BL), in the upper Urumqi River in the Tian Shan of NW China. Subglacial tills have stronger fabric of both a-axis and a– b-plane than supraglacial till. This can be explained as a result from the different stress and transport histories of till clasts. The preferred orientation of a-axes of till fabrics intersect the former ice-flow direction at a sharp angle (62±16°); whereas the a– b-plane, with its normal intersecting the former ice-flow at 84±4°, is oriented approximately parallel to the ice flow direction. Thereby, subglacial relief appears to strongly influence the till fabric. In particular, the a-axis fabric is more sensitive to landforms than that of the a– b plane. In simple straight troughs, such as the Wangfeng Valley, fabric varies little. In the complex section of the trough, such as the Hayisa Lipolith, fabric characteristics are different at different sites of the Hayisa Drumlin. The fabric data can be used to understand glacial sedimentary processes in the study area.

Weathered bedrock as a source of sand and gravel aggregate in north-eastern New South Wales, Australia

The most commonly recognized sources of sand and gravel aggregate are the deposits of coastal, fluvial and glacial sedimentary processes. It is not commonly recognized that weathered bedrock is also an important source of sand and gravel aggregate. In the case of weathered sedimentary bedrock the product may be indistinguishable from modern sedimentary materials and deposits may be misidentified. Batson's quarry is a major sand and gravel aggregate resource for the rapidly developing region of north-eastern New South Wales. The deposit has previously been assumed to be a young sedimentary deposit, but detailed field examination and comparison with surrounding rock types indicates that it has formed from weathered Mesozoic sandstone bedrock. The extraction of weathered bedrock aggregate deposits has distinctive environmental implications because, unlike sedimentary aggregates, they are not restricted by the geometry of sedimentary environments and do not necessarily interfere with surface drainage systems. This study shows that the recognition of the geological origin of a resource is essential in order to determine its potential geographical extent, and thereby maximize its utilization and minimize land use conflict.

Glacial sedimentary processes and environmental reconstruction based on lithofacies

ABSTRACTGlacigenic sediments exposed in pits around Villeneuve, near Edmonton, Alberta, are subdivided into facies based on grain size, sedimentary structure, glacially‐induced deformation and faulting, and groove marks. Two diamicton facies are recognised, one of which is interpreted as a primary till, deposited directly from glacier ice, and the other as a product of mass‐movement. The diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits. The stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities. At any one place the glacier appears to have alternated between being attached to the bed, causing thrusting and sole marking, and being separated from the bed by a cavity in which fluvial and mass‐movement sediments accumulated. The net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance. The correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history. In addition, the interpretations presented here have implications regarding the formation of soft zones in ‘till’. They indicate that the soft zones are beds of sorted sediment redeposited by mass‐movement.