Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 634

bioturbated ( Fig. 5 A) and it occupies the uppermost part of a turbidite, commonly
corresponding to Bouma's T d

T e intervals ( Fig. 4 ; Uchman, 1999 ). Oval spots of
different color and sharpness of contours are visible against the indistinctly mot-
tled background. The spots are cross sections of trace fossils, commonly Plano-
lites and Thalassinoides . In some layers, the color contrast is so low that the layer
seems to be structureless. This picture can be altered in thin-bedded turbidites, if
some deep-tier trace fossils of the so-called multilayer colonizers sensu Uchman
(1995b) or crossichnia sensu Monaco and Caracuel (2007) ,suchas Chondrites
and Ophiomorpha , penetrate from the overlying bed to the spotty layer of the
underlying bed ( Rajchel and Uchman, 1998 ). Their sections are visible as last-
generation spots ( Fig. 5 A), having very distinct margins, strong color contrast,
and commonly different lithology from the host rock. The lithology of the spotty
layer differs from that of the underlying sediment; it is more fine-grained and
shows a different color or tint. In sediments deposited below the Calcite Compen-
sation Depth (CCD), it is free of carbonate, at least in the upper part. Above the
CCD, the CaCO 3 content in the spotty layer can be higher than in the underlying

FIGURE 4 Model of ichnofabrics in turbidite/hemipelagite couplets (modified after Uchman, 1999 ).