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and proportions of ichnological elements, and this remains an important area of
future research. The Nereites Ichnofacies is not observed in upper slope or shelf
deposits (cf. MacEachern et al., 2007a ).
4. SLOPE DEPOSITIONAL ENVIRONMENTS—CASE STUDIES
4.1 Submarine Canyon Fill, Early Miocene Tirikohua
Formation, Northland, New Zealand
EarlyMiocene strata of theWaitakere Group crop out on the west coast of North-
land, NewZealand ( Fig. 4 ), and contain two submarine canyons that were cut into
bathyal volcanogenic turbidites of the Nihotupu Formation ( Hayward, 1976 ).
Canyon margins are overlain by outer neritic to upper bathyal canyon-floor
deposits of the Tirikohua Formation. Paleobathymetric assessments have been
made on the basis of molluscan and foraminiferal assemblages ( Murray,
1973 ). The canyon margins are interpreted to have been incised during a relative
base-level fall associated with tectonic uplift and block faulting of the margins of
an inter-arc basin. Some 30 km from these localities, toward Auckland, nearly
time-equivalent deposits of theWaitemata flysch possess suites of the archetypal
Nereites Ichnofacies (including graphoglyptids), consistent with basin-floor depo-
sitional positions (cf. Uchman and Wetzel, 2012; Wetzel and Uchman, 2012 ).
The underlyingNihotupu Formation consists of weakly and sporadically bur-
rowed (BI
0-2) turbiditic mudstones and sandstones, as well
as conglomeratic debris-flow deposits, all of volcanogenic origin. Andesitic
pillow piles also are locally present. Biogenically reworked units are generally
isolated and local. Ichnogenera identified by Hayward (1976) are limited to
Skolithos (called ' Tigillites ' but synonymized with Skolithos by Alpert (1974)
and presently broadly accepted), Thalassinoides , Planolites , and Nereites
(
0-3, mainly BI
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Scalarituba) . In addition, Chondrites occurs at the Tirikohua Point locality.
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4.1.1 Submarine Canyon Margin
The submarine canyons in the area range from 600 to 2000 m wide and 80 to
150 m deep. The canyon margins correspond to a sequence boundary ( Fig. 4 A)
and are commonly demarcated by widespread palimpsest ichnological suites,
representing firmground substrate conditions ( Fig. 4 B-D). No true borings were
identified from the surface ( Hayward, 1976 ). Firmground burrows are present
along overhangs, locally possess bioglyphs (scratch marks), and are passively
infilled with sand from the overlying Tirikohua Formation. The sequence
boundary shows BI
1-3, with firmground Rhizocorallium , Thalassinoides ,
Spongeliomorpha , and Skolithos of the Glossifungites Ichnofacies. A few sim-
ple inclined to horizontal tubes may be attributable to firmground Palaeophy-
cus . Studies of the modern Scripps Submarine Canyon ( Warme et al., 1971 ) and
some New England canyons ( Dillon and Zimmerman, 1970 ) display similar
ichnological expressions (cf. Hayward, 1976 ).
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