Glacial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 308

Bhattacharya, 2007; Sarkar et al., 2009 ; see Supplementary Table 2 in http://
booksite.elsevier.com/9780444538130 ) . Despite high ichnodiversity, the
trace fossils are sporadically distributed, and the overall small size of the bur-
rows, the absence of body fossils, and the dominance of worms as tracemakers
suggest brackish-water conditions, probably due to influx of glacial meltwater
during climatic amelioration (e.g., Fielding et al., 2006; Virtasalo et al., 2006 ).
Deep glaciomarine bioturbated deposits have been reported only from the
Cenozoic record, both in offshore and deep turbidite deposits. Phymatoderma ,
Thalassinoides ,? Nereites ,and Planolites were reported by Uchman and
Ga´dzicki (2010) in offshore and deeper-water deposits of the Early Miocene
Cape Melville Formation (King George Island, Antarctica), while a more
diverse assemblage composed of Arenicolites , Chondrites , Diplocraterion ,
Ophiomorpha , Rhizocorallium , Thalassinoides ,and Zoophycos had been
reported in the deep-water active-margin turbidites and debris-flow deposits
and prograding continental slope mass-flow deposits from the Late Miocene
Yakataga Formation (Gulf of Alaska; Armentrout, 1979; Eyles et al., 1992 ;
see Supplementary Table 2 in http://booksite.elsevier.com/9780444538130 ).
Shallow-marine deposits are also present in the Yataga Formation, accumu-
lated in a broad shelf with a high sedimentation rate (including abundant coarse
ice-raft debris), but the Skolithos Ichnofaciesisabsentdue to the predominance
of unstable, muddy substrates ( Eyles et al., 1992 ). Trace fossils from theYataga
Formation were grouped in nine assemblages that were referred to particular
depositional settings and types of substrate in submarine channel, slope, shelf
boulder pavement, coquina, storm sands, and shelf postglacial muds. Schatz
et al. (2011b) analyzed biogenic structures in Holocene cores from three fjords
(Maktak, Coronation, and North Pangnirtung) of Baffin Island (Arctic Can-
ada), comparing this information with photos taken from bottom camera sta-
tions. The abundance and diversity of biogenic structures was controlled by
the proximity to the ice, physical disturbances (e.g., turbidity flows), and ice
drift. Sediments have been extremely reworked, especially further away from
the fjord head.
Polychaete borings also occur in Quaternary glaciomarine environments.
Caulostrepsis and Maeandropolydora were recorded in early Holocene marine
terrace boulders of NE Spitsbergen by Hanken et al. (2012) . Earlier, Aitken and
Risk (1988) presented borings in Pleistocene-recent shells and limestone clasts
from the Arctic Canada. Research on microbioerosion along the Swedish coast
(e.g., Wisshak and R¨ggeberg, 2006; Wisshak et al., 2005 ) suggested that some
ichnotaxa (e.g., Flagrichnus baiulus ) occur only in non-tropical settings
( Wisshak and Porter, 2006 ).
3.5 Ichnocoenoses and Ichnofacies of Glaciomarine Rhythmites
Trace fossils reported from tidally influenced and shallow, wave-dominated to
deep glaciomarine settings generally compose suites representative of the Cruzi-
ana and (to a lesser degree) Glossifungites Ichnofacies (see Supplementary