Morphostratigraphy/allostratigraphy

Morphostratigraphy is the subdivision of sedimentary units primarily on the basis of surface form. Morphostratigraphy is an integral component of Quaternary Science, since environmental changes are often imprinted on the Earth's surface as landforms. While surface form is often used as a criterion for separating sedimentary units, morphostratigraphy usually incorporates lithological criteria to aid stratigraphical subdivision. However, unlike lithostratigraphy, morphostratigraphy has traditionally not received formal status. Allostratigraphy uses discontinuities to subdivide sedimentary successions. Since surface landforms essentially represent depositional discontinuities, morphostratigraphical units can also be defined as allostratigraphical units. However, allostratigraphy has the power to deal with buried sediment units as well as surface forms. Allostratigraphy enables lateral variations in lithology to be included within the same stratigraphical unit. Furthermore, it enables lithologically-similar sediments stacked on top of each other to be separated into separate units based on discontinuities. This chapter discusses the applications of morphostratigraphy and allostratigraphy in a range of environmental settings and the practical and philosophical issues concerning both, building on previous editions of this volume (Hughes, 2007, Hughes, 2013).