The origin and occurrence of subaqueous sedimentary cracks

Sean McMahon, Ashleigh van Smeerdijk Hood, Duncan McIlroy
2016 Geological Society Special Publication  
The rock record attests that sediments have cracked at or below the sediment-water interface in strictly subaqueous settings throughout Earth history. In recent decades, a number of hypotheses have been advanced to explain this phenomenon, but these are widely regarded as being mutually exclusive and there is little consensus about which model is correct. In this paper, we first review the geometries, lithologies and range of facies in which subaqueous sedimentary cracks occur in the geological
more » ... r in the geological record, with particular attention to cracks in carbonates. We then evaluate current models for subaqueous cracking, emphasizing that different models may be correct with respect to different sets of cracks, but that cracking is generally a two-step process involving sediment stabilization prior to disruption. We also present the results of some simple new experiments designed to test the dominant models of crack formation. These results demonstrate for the first time that microbial mats can produce thin, shallow cracks at the sediment-water interface. We conclude that the presence of cracks in marine, brackish and lacustrine rocks should not be used uncritically to infer fluctuations in salinity in the depositional environment. *Setting inferred partially from interpretation of cracks as evidence of fluctuating salinity. This is a non-exhaustive list of examples, selected from papers in which they are photographically illustrated. Shape: P ¼ plan; V ¼ vertical cross-section. The inferred depositional settings noted are those provided in the publication cited. Molar tooth structures and septarian cracks are not included. CO 3 , carbonate present as a cement; Fm, Formation; Mb, Member; MISS, putative microbially-induced sedimentary structures in close stratigraphic proximity to cracks; ND, not determined. ORIGIN OF SUBAQUEOUS SEDIMENTARY CRACKS 289 by guest on July 21, 2018
doi:10.1144/sp448.15 fatcat:x7w5aqgspndjbjvj7eyyrjoxte