Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 641

For this purpose, the diversity of trace fossils per formation was analyzed;
Seilacher (1974, 1977b) compared 16 formations; Crimes (1974) did so for
a similar number; McCann (1990) studied 34 formations, Orr (2001) 50
Ordovician-Carboniferous formations, and Uchman (2004a) 151 Phanerozoic
flysch formations ( Fig. 7 ).
A sharp increase in the number of ichnogenera in Cretaceous-Neogene
flysch was described by Crimes (1974) , but he emphasized that “more detailed
studies” were needed. An increasing diversity of deep-sea trace fossils during
the Phanerozoic, with a rapid acceleration in the Cretaceous, was found by
Seilacher (1974, 1976) , who subsequently mentioned a gradual increase in
the diversity of “flysch ichnocoenoses” through the Phanerozoic ( Seilacher,
1977b ), but then returned to his previous idea and proposed a “mid-Cretaceous
diversity burst” ( Seilacher, 1978 ). These findings and hypotheses were tested by
McCann (1990) , who concluded that the increase of diversity was neither grad-
ual during most of the Phanerozoic nor rapid in the Cretaceous; in addition, he
drew attention to a methodological problem. For instance, the Jurassic-Tertiary
flysch of the Polish Carpathians had been taken as one formation, although it
includes different units deposited in a number of basins ( Ksi˛ ˙ kiewicz,
1977 ). According to Orr (2001: 270) , the diversity of deep-sea trace-fossil
FIGURE 7 Diversity through time of deep-sea ichnogenera (the dashed line shows some less
well-documented portions of the curve). The graphs show the contribution of graphoglyptids in
trace-fossil assemblages and the relative abundance of new graphoglyptid ichnospecies, whereas
the chart shows the number of graphoglyptid ichnogenera in the Phanerozoic (upper portions of
the columns express ichnogenera tentatively included in the graphoglyptids). Based on Uchman
(2003, 2004a) , with complementary data by Uchman (2007c) and Wetzel et al. (2007) , updated.