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ichnology ot fluvial systems

ichnofacies socms to prt;vail in floodplain deposits of meander i ng Systems. In any case, with respect to tracę fossil distribution, the most useful distinction is that between channel and overbank deposits (Buatois and Mangano, 2004).

Fluvia! channels are characterized by high to relatively high energy, rapid fluctuations in rates of sedimentation and erosion, and coarser grain sizes than those typically deposited in adjacent environments. Accordingly, channels represent stressful environments for benthic organisms and, therefore, production and/or preservation of biogenic structures is commonly inhibited. Some fluvial channel ichnofaunas seem to record substrate colonization when the channel is still active, while others reflect emplacement within the substrate after channel diversion ('abandonment') or during periods of Iow discharge virtually characterized by nondeposition ('inactive').

The ichnofauna from active channels is characterized by low-diversity, typically monospecific, suiles of simple yertical burrows and escape traces (e.g., Bradshaw, 1981; Zawiskie et al., 1983; Fit/gerald and Barrett, 1986; Woolfe, 1990; Sarkar and Chaudhuri, 1992). Moderately deep to dęep Skulithos, commonly forming dense assemblages, and escape tracę fossils are common components in pebbk* conglomerate and trough cross-bedded, planar cross-bedded, or parallel

Coprinisphaeru Ichnofacies

Scoyenia Ichnofacies

l-TatmiHwn 2* Beaconilet yScaytma yHusopkyau 5- Camhorygma

2' ilirauiairhnium t- Umfistoaa

I - Palmiraichnus

2-    Uruguay

3-    Anaichnus

4-    Coprinisphaera

5-    Rnscllichnus

6-    Ealonichnus

7-    Tacuruichnus

8-    Celliforma

.    • FIGURĘ 17.4 SchemaHc reconstruction of the

FIGURĘ 17.2 Schematic reconstruction of t coye    Coprinisphaera ichnofacies. Based on Buatois et al. (2002).

ichnofacies. Based on Buatois et al. (2002).

Mermia Ichnofacies

\-Mermia

2-    CochlUhnus

3-    (jordia

4-    Helminthoidlchnitet

5-    HelminihopsU (>■ PlannUtet

7- TrepUi hnui tuberrulhhnui '/ Puluetiphyi:ui 10- ( Iri ulii hnut I i - Vanorti:hnu$

Mermia ichnofacies. Based on

reconstruction <»

12 Untlit lma

FIGURĘ 17.3 Schematic Buatois et al. (2002).