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Geology, with microscopic eye,
Regards thee as a phantom metaphoric; While Chemistry, whose flight is always high,
Claims thee as a production meteoric; But sister Poesy seems half afraid, And wisely keeps her learning in the shade.
Anonymous (To A Fossil Fern, 1836)

Abstract

Organisms that produce traces occupy such a wide range of substrates that it can be said that as long as a sediment is exposed, it may be occupied. This is especially the case in marine settings, where a succession of infaunal communities may inhabit a deposit as it progresses through the successive stages of soupground, softground, firmground and hardground/rockground. The transition of soupy sediment to indurated rock occurs by compaction and diagenesis and thus accompanies the succession of ichnocoenoses in the same deposit. Complex ichnofabrics result from the juxtaposition of trace fossils produced in an ever-lithifying substrate. For example, borings of the Trypanites ichnofacies (i.e., in a rockground) may be superimposed on burrows of the Glossifungites ichnofacies (i.e., in a firmground), which in turn may be juxtaposed upon burrows of the Skolithos ichnofacies (i.e., in a softground), which themselves may have been emplaced in an already thoroughly bioturbated sediment (i.e., in a soupground).

An excellent example of this parallel succession of diagenetic and ichnologic events affecting a sediment can be seen in the Upper Cretaceous chalk of northern Europe. Compaction deformation of trace fossils and sharpness of burrow margins provide information about the character of the original chalk substrate. Zoophycos and Chondrites, for example, occur only in situations where the sediment was firm but uncemented, even though they commonly are overprinted on a background ichnofabric containing indistinct, highly compacted and deformed burrows. Thalassinoides, on the other hand, apparently was produced in a variety of substrate conditions, including soupgrounds, softground, firmgrounds

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