Slopes - Trace Fossils as Indicators of Sedimentary Environments - page 601

4.1.2 Canyon-Floor Fill
The overlying Tirikohua Formation is interpreted to record canyon-floor
deposits that accumulated above the sequence boundary in outer neritic to upper
bathyal environments ( Hayward, 1976 ). The succession consists of proximal,
thick-bedded turbiditic sandstones and siltstones, intercalated with grain-flow
derived conglomerates. Trace fossils are absent from the well-rounded cobble
to pebble conglomerates but are sporadically distributed (BI

0-3) in sand-
stone and siltstone units. The proximal sandy turbidites of the canyon floor con-
tain allochthonous wood fragments with abundant Teredolites , presumably
reflecting basinward transport of bored logs from shallow-water settings
( Fig. 4 E). In-situ trace fossils include fugichnia, Ophiomorpha ( O. rudis ), Sko-
lithos , Thalassinoides , Planolites , Scolicia , and Nereites (=Scalarituba) . Much
of the suite records post-turbidite recolonization rather than bioturbation of the
substrate during persistent periods of quiescence. The predominance of dwell-
ings and deposit-feeding structures indicates that the slope setting was exposed
to a persistent supply of oxygen and food, which was interspersed by periodic
sediment gravity flows as the submarine canyons filled ( Hayward, 1976 ).

¼

4.2 Slope Deposits, Middle Eocene Ainsa-Jaca Basin, Spain
A spectrum of deposits that record deep-water environments is preserved in
Middle Eocene strata in the Ainsa-Jaca Basin of the Spanish Pyrenees
( Heard and Pickering, 2008; Uchman, 2001 ). The sedimentological and archi-
tectural characterization of these deep-water units is well established and pro-
vides a framework for ichnological analyses (e.g., Clark and Pickering, 1996;
Mutti and Normark, 1987 ). Upper basin slope and slope gully through to fan-
fringe and basin-floor deposits have been reported from the succession ( Heard
and Pickering, 2008 ), although only the most proximal of these are discussed
herein: basin slope, slope gully, and canyon fill ( Fig. 5 ).
In general, proximal slope deposits are characterized by low-diversity trace-
fossil suites, dominated by post-depositional forms ( Heard and Pickering,
2008 ). Mudstone- and siltstone-dominated ambient basin-slope deposits are
highly bioturbated (up to BI ¼ 3), with an overall trace-fossil diversity of 14 ich-
nogenera ( Fig. 5 ). Of these, 10 forms constitute the post-depositional elements
associated with the sandstone beds, and two forms are regarded as pre-
depositional graphoglyptids (i.e., Belorhaphe zickzack and Paleodictyon stroz-
zii ). Basin-slope deposits are cross-cut by erosional gullies, filled with sand-
dominated facies characterized by trace-fossil diversities that range from 5 to

into muddy beds of the Nihotupu Formation. (C) Firmground suite consisting of Rhizocorallium
( Rh ) and Thalassinoides ( Th ) marking the same discontinuity as shown in (B). (D) Firmground Tha-
lassinoides ( Th ) marking the same discontinuity as shown in (B) and (C). (E) Burrowed sandstones
of the Tirikohua Formation showing allochthonous wood containing Teredolites ( Ter ) and in-situ
Ophiomorpha rudis ( Or ) and Scolicia ( Sc ).