Distinguishing microbially induced sedimentary structures from flow-induced interfacial deformation structures (MISS v. FIDS)

Flow-induced interfacial deformation structures (FIDS) are both diverse and common in turbidite successions where they form in soft, cohesive substrates beneath sediment gravity flows, but their significance has only recently been recognized. Their range of forms encompasses most of the morphological types attributed to microbially induced sedimentary structures (MISS) and the two have probably been widely conflated. Variants of FIDS include longitudinal ridges and furrows, polygonal networks and mamillated forms that are identical to structures assigned to MISS. A distinctive MISS form with flat-topped ridges and furrows called ‘Kinneyia’ is also found within the FIDS spectrum. Some FIDS may have also been assigned to Ediacaran taxa, notably the controversial Arumberia. Distinguishing FIDS from MISS in hand specimen is difficult, but their environmental context is important. Intertidal MISS occurrences are unlikely to be FIDS because the sediment gravity flows that produce deformation of the substrate are unlikely in such settings. However, MISS (mis)reported from turbidite settings are likely to be FIDS. One of the few distinctions between MISS and FIDS occurs when textured surfaces are developed on the upper surfaces of sandstone beds and they are overlain by fine-grained sediments; in this case a microbial origin is likely.