Macro-organisms which may directly affect marine sediments after their deposition are limited to benthonic forms which burrow for shelter or in search of food, and those which ingest sediments for the contained organic material. Changes which are produced by such organisms are: destruction of bedding, destruction of gradation of grain size, trituration and solution of rock masses and fragments, formation of tubes and burrows,addition of faecal debris, initiation of cementation, bleaching or coloration, and destruction of organic material. Since the degree of alteration is directly proportional to the number of benthonic organisms, the greatest changes must occur where the optimum dwelling conditions exist; hence, not in regions of stagnant water, nor where sedimentation is rapid.

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