Geology Reference
In-Depth Information
Subtidal
Deposits
(1) A mixed assemblage
of trace fossils may be
present, but are
generally dominated
by either horizontal or
vertical trace-fossil
forms in (nearly)
monospecific suites.
Most common vertical
traces include
Slolithos,
Cylindrichus
, as well
as a subordinate
Arenicolites,
Cphiomorpha
and
Polyklodichnus
. Most
common horizontal
forms include
Planolites,
Teichichnus
with
subordinate
Thalassinoides
attenuated, owing to
higher sedimentation
rates. Most commonly,
unburrowed beds are
intercalated with
burrowed beds (B12-3)
(2) In environmentally hostile
conditions, bioturbation is
rare throughout, with B10
to 1 representing the
dominant modes of
bioturbation intensity
(1) Under conditions of
effective larval recruit-
ment and in the presence
of brackish water, regular
heterogeneous distribu-
tions dominate
(2) Where living conditions
are poor (e.g., very low
salinities, persistently
elevated sedimentation
rates, very turbid water,
common fluid muds),
sporadic heterogeneous
distributions are most
common
(2) Rarely, suites of the
Glassifungites
<$$$>
chnofacies may be observed
at the basal contact
(3) Lags may be present, but are
not requisite. Thicker
mud-beds associated with
fluid mud accumulation may
be present near lower
contact
inclined heterolithics
tratification (IHS)
comprising cm-scale
through to <$$$>−scale
sand / mud couplets
(2) In the case of cm-scale
IHS, 3+ to <$$$> dipping
lenticular through wavy
to flaser bedding are
common
