One explanation for the occurrence of morphotypes characteristic of more than one ichnofacies
but present in a single ichnocoenosis is that the host sediment body was subject to a change in environmental conditions while still at the surface.
Ichnological analysis indicates that the Las Hoyas invertebrate ichnofauna (Mermia ichnofacies
)displays evidence, such as dominance of superficial structures, the paucity of infaunal traces and a small size that indicate environmental stress due to lack of oxygen, (Buatois et al., 2000) consistent with an environment with short periods of oxygenated bottom waters, but permanently anoxic interstitial waters.
A Nereites ichnofacies
from the Ordovician-Silurian Welsh basin.
The trace assemblage characterizes the Scoyenia ichnofacies
redefined by Buatois and Mangano (1995).
The association of "S-O-T group", Spongeliomorpha, Ophiomorpha and Thalassinoides (Fursich, 1973) with Asterosoma and Rhizocorallium irregulare is well known in Jurassic shallow water environments (Farrow, 1966; Fursich, 1981; Heinberg and Birkelund, 1984; Gaillard et al., 1994), being indicative of the Cruziana ichnofacies
(sensu Pemberton et al., 1992).
This assemblage represents the Scoyenia ichnofacies
, which corresponds to a shallow lacustrine environment with a tendency to near total water loss.
Abundant vertical burrows in Skolithos ichnofacies
are commonly called 'pipe-rock'.
The lack of stratigraphic control makes inferring trace fossil associations and establishing ichnofacies
difficult, especially since most of the fossil-bearing slabs are small and consequently preserve only a few traces each.
The materials are constituted by alternations of highly bioturbated fine sands (Skolithos ichnofacies
) and bioclast-rich cemented coarse sands.
Marine Cretaceous and Paleogene biofacies and ichnofacies
in Southern Tibet, China and their sedimentary significance.
Gordia, Helminthopsis, and Planolites are widespread and common in three ichnofacies
: Cruziana, Mermia, and Nereites.