Geoscience Reference
In-Depth Information
Table 3.
Facies associations (FA) in the upper Are and Tilje formations used to deduce depositional processes and environments.
Ichnology
(FA) Facies
associations
General
Description
Sedimentary
structures
Facies
Internal organisation
Ichnofacies
Trace Fossils
Environmental Interpretation
FA1: Lower-
shoreface
F4, F6.4,
locally
F5.2.2
Light grey
very-fine to
fine-grained
sandstone
and intensely
bioturbated
sandstone.
Local sand/
mud mixed
heterolithics.
HCS, low angle to
planar lamina-
tion, wave ripples,
wavy lamination.
Upward-sanding trend (up to
5 m thick). Basal sandstones
moderately to intensely
bioturbated alternate locally
with wavy-bedded combined-
flow heterolithics. Overlain
sharply by amalgamated HCS
sandstones (up to 3 m thick).
Moderate to
intense, high
diversity. Mixed
Cruziana
and
Skolithos
assemblage.
Paleophycus
,
Skolith-
os
,
Rosselia, Plano-
lites
,
Cylindrichnus
,
Thalassinoides,
Ophiomorpha
Diplocraterion
, and
Rhizocorallium
.
Storm-influenced lower
shoreface. Periods of
low energy succeed by
high-energy oscillatory and
combined-flow conditions
during storm events. Inter-
ruption of fair-weather by
seasonal storms.
FA2: Trans-
gressive
shelf lags
F6.1, and
F2.
Brown to reddish
and/or grey,
poorly sorted,
silty, fine- to
medium-
grained sand-
stones. Locally,
coarse-grained.
Floating
angular bioclas-
tic calcite grains
are common.
Low-angle cross-
bedding, low-angle
lamination, parallel
lamination.
Sharp and erosively based
tabular beds. Occasionally
coarsening- or fining-upward
successions (10 cm to 70 cm).
Homogeneous aspect.
Abundant,
high diver-
sity. Proximal
expressions
of
Cruziana
Ichnofacies.
Rosselia
,
Planolites
,
Cylindrichnus
,
Skolithos
,
Berguae-
ria
,
Paleophycus
,
and rare
Thalas-
inoides
.
Marginal to normal-marine
lags. Reworking processes
by tidal or wave currents
under conditions of slow
sedimentation.
FA3:
Distributary
mouth bars
F2, F3,
F5.1,
locally
F4
Light brown and
grey, well sort-
ed, very-fine
to fine-grained
sandstone.
Local homoge-
neous mud-
stones.
Cross-beds, current-
ripple cross-
lamination (locally
bipolar), low-angle
planar lamination
(HCS). Double
mud-drapes.
Sharp-based. Cleaning and
sandier upward (2 m to
4 m thick). Fluid-mud layers
(3 cm thick) and/or angular
rip-up mud clasts towards
the base of cross-beds. Cross-
bedded sandstone alternates
with ripple-cross-laminated
and double mud- draped
sandstones.
Low to moderate,
low diver-
sity. Proximal
Skolithos
.
Skolithos
,
Arenico-
lites
,
Berguaeria
,
Planolites
, and
Paleophycus
.
Mouth-bar region. Relatively
high energy. Tidally
influenced currents and
sporadic storms.
F5.1,
F5.2.1,
F5.5,
F2,
locally
F5.2.2
Mixed sand-mud
heterolith-
ics. Bimodal,
from coarser
granules to
fine and/
or very-fine
grained sand.
Laminated to
Current-ripple cross-
lamination (locally
bipolar), cross-
bedding, wave
and asymmetric
combined-flow
ripples, small-
scale HCS, wavy
bedding, synaere-
sis cracks.
Stacked coarsening-upward
and thickening-upward suc-
cessions (2 m to 3 m thick),
showing alternation between
bioturbated fine-grained
heterolithics and less bio-
turbated heterolithics with
bimodal sand grain size. The
heterolithics are punctuated
Low to intense.
Mixed
Cru-
ziana
and
Skolithos
assemblage.
Paleophycus
,
Skolithos,
Planolites
,
Cylindrichnus
,
Teichichnus
, and
Diplocraterion
.
Mouth-bar region. Moderate
and high energy. Alternation
between times of low and
high fluvial discharge mod-
ulated by tidal currents and
waves. Mouth-bar deposits
interbedded with terminal
distributary channel cross-
bedded sandstones.
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