Foresets – Knowledge and References

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Sedimentary Environments and Facies

Published in Supriya Sengupta, Introduction to Sedimentology, 2017

Forms and magnitudes of dunes of eolian and subaqueous origin overlap to a large extent. These cannot be used as criteria for recognition of ancient eolian dunes, therefore. The presence of lag gravels on avalanche toes, convex foresets, arching either up or down, deformation and reactivation surfaces, and progressive flattening and thinning of cross-bedding surfaces towards the top mark many of the present-day eolian deposits. Modern eolian dunes are also characterised by the absence of trough cross-beds. The upper parts of slip faces are generally steep (29°–34°). A combination of all these features might indicate eolian sedimentation although no single criterion can be taken to be diagnostic.

Gilbert-style Pleistocene fan delta reveals tectonic development of North Island axial ranges, New Zealand

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Journal Information

Published in New Zealand Journal of Geology and Geophysics, 2018

Callum Rees, Julie Palmer, Alan Palmer

Gcn facies is interpreted as bottom sets formed via subaqueous high-density turbidity currents initiated at the fan delta front. As Smith (1986) and Waresback and Turbeville (1990) point out, normal grading and horizontal clast orientation are indicative of clast interactions within fluid rich, cohesionless flows. Sharp to erosive lower contacts are characteristic of turbulent flow that scours the underlying sediments. Flows initiated on the steepened delta foresets fan out from the base of the delta slope forming an apron of sediment radiating out into the receiving basin (Figure 3).