Table 7.28.

Additional specialist techniques in the assessment of glacial and periglacial deposits

Geomorphological mapping: Use of glacial geomorphologists for large- to small-scale terrain assessment; mapping and interpretation of glacial and periglacial landforms and interpretation of likely sediment-landform assemblages.Predictive assessment of deposits and ground conditions across a site. Useful in the development of a CSM; can be incorporated with desk-studies. Can be accomplished by site walkover, review of stereo aerial photography, digital elevation models and LIDAR, and bathymetry in the offshore environment. Excellent cost-benefit ratio; can reduce the scope of intrusive investigations by identifying zones of interest.
Detailed logging by a specialist in glacial geology: Use a geologist with experience of glacial and periglacial sediments to log recovered core and samples and interpret depositional process.The geotechnical engineer may be unfamiliar with many of the textural and structural features in glacial and periglacial deposits. This can lead to misinterpretation of depositional processes, lithofacies boundaries and subsequently the selection of appropriate samples and testing for the engineering assessment of the site. A detailed assessment of such deposits should be undertaken by a qualified glacial geologist to avoid this. Good cost-benefit ratio.
Lithological analysis and provenance studiesTill can often be preserved in multiple layers, reflecting either successive periods of glaciation or major fluctuations in ice margin, from dynamic changes in glaciers and ice sheets during a single phase of glaciation. Different tills, particularly where incorporation of older deposits has occurred, may be difficult to distinguish based on visual assessment and basic classification testing. Those tills may however exhibit very different strength, consolidation and other engineering properties as a response to their individual depositional environment and strain response. Differentiating those separate till layers may therefore be of importance. Lithological analysis (visual and geochemical if required) identifies the provenance of clasts in glacial deposits and, through statistical analysis, can demonstrate flow directions of former glaciers and ice sheets allowing the differentiation of separate depositional events. Time-consuming and potentially expensive process.
Clast fabric analysisAnalysis of clast orientation in tills and other deposits. Comparison to modern analogues allows indication of depositional processes, strain response and ice-flow directions. Provides information on the depositional processes and history of a site or sediment unit. Time-consuming but otherwise inexpensive.
Micromorphological analysisPreparation of thin-section subsamples from recovered Class 1 samples. Observation under polarizing light microscope by a specialist in glacial sediments allows identification of microscopic sediment structures and particle orientation. Comparison to modern analogues allows interpretation of deposition processes and strain response of the sediment. May be the only technique suitable for differentiating subglacial, glaciomarine and flow tills in both the onshore and offshore environment. Moderately expensive, time-consuming, requires highly specialist knowledge.
Paleontological/palaeoecological analysisAnalysis of fossilized or preserved fauna and flora (macro- and microorganisms) in glacial or periglacial deposits, peats, lake, river and marine sediment. Constraining environmental conditions at, before or after depositional events. Useful for the interpretation of terrain evolution.
May be a requirement of landscape surveys (Section 7.2.3) where these form a component of a larger site investigation.
May require large sample volumes. Requires very specialized knowledge. Potentially expensive and time-consuming.
Geochronology studiesUse of radiocarbon, luminescence and other radio-isotope ratio dating techniques to constrain the ages of depositional units. May allow differentiation of depositional and erosional events. May be a requirement of landscape archaeological surveys where these form a component of a larger site investigation.
May require specialist sampling. Requires very specialized knowledge. Expensive and time-consuming.