Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 608

4.5 Lower-Slope Channel Deposits, Cretaceous Tres
Pasos Formation, Chile
Channel deposits in the Tres Pasos Formation are present toward the toe of a
slope clinoform ( Fig. 7 A), first described by Fildani et al. (2009) and
Hubbard et al. (2010) . Individual channels are 300-400 m wide and 15-25 m
thick ( Fig. 8 ). The basal scour surfaces are commonly draped with siltstone,
which record deposition from the tails of high-energy turbulent currents that
largely bypassed the channel setting (cf. Mutti and Normark, 1987 ). The main
FIGURE 8 Slope-channelmodel (top) andphysical and biogenic structure overviewfor theLateCre-
taceous Tres Pasos Formation at Laguna Figueroa, Magallanes Basin, Chile. The low-sinuosity chan-
nels are characterized by approximately symmetric margins, as shown in the strike-oriented cross-
section. Intrachannel subenvironments can be discerned by trace-fossil suites; trace fossils are more
abundant upward and at the edges of channel fills (i.e., most abundant and diverse in distal abandon-
ment deposits). Trace-fossil abbreviations: Ar , Arenicolites ; Ast , Asterosoma ; Co , Cosmorhaphe ; Di h ,
Diplocraterion habichi ; fu, fugichnia; Gyr , Gyrochorte; He, Helminthopsis ;Ne, Neonereites ; Op ,
Ophiomorpha ; Pa t , Palaeophycus tubularis ; Pa h , P. heberti ; Ph , Phycosiphon ; Pl m , Planolites mon-
tanus ; Pl, Planolites ; Rh , Rhizocorallium ; Ro , Rosselia ; Sk , Skolithos ; Sc , Scolicia ; Te , Teichichnus ; Th ,
Thalassinoides .