Geoscience Reference
In-Depth Information
Table 2.
Summary of lithofacies observed in the Tor Formation.
Lithology and
texture
Facies and code
Sedimentary and diagenetic features
Biogenic structures
Well log signature
Interpretation
Bioturbated
argillaceous
chalks (BAC)
Mudstone and
wackestone with
intermediate
to high clay
content.
Interbedded clay-poor and clay-rich chalk
beds. Clay-rich beds are commonly
well laminated, but also show wispy
to flasery clay-rich laminations and
solutions seams. Clay-poor intervals are
intensively bioturbated with numerous
horizontal to sub-vertical burrows.
Pyrite grains and pyritised shell
fragments appear occasionally. Bedding
marked by changes in the clay content.
Common to abundant
bioturbation induced
mottling with indeterminate
burrows. Identifiable traces
are
Chondrites
,
Planolite
s and
Thalassinoides
.
Broad and poorly
delineated
signals with low
porosity and high
density showing
high gamma ray
response.
Pelagic/autochthonous
chalk.
Laminated
chalk (LC)
Mudstone and
wackestone
with low to
intermediate
clay content.
Weakly to well defined and undisturbed
planar-parallel to sometimes wavy-
parallel sedimentary laminations
with bedding well developed and
bed thickness varying from several
centimetres to 50 centimetres.
Laminations are usually well defined,
but occasionally disturbed or cut by
bioturbation and bioturbation induce
mottling. Common and sparse shell
fragments.
Rare bioturbation and
bioturbation induced
mottling with poorly defined
horizontal and vertical
burrows. Identifiable traces
are
Chondrites
,
Planolite
s and
Zoophycos
.
Broad and poorly
delineated
signals with low
porosity and high
density showing
intermediate to
low gamma ray
response.
Pelagic/autochthonous
chalk periodically
interrupted by
deposition of low
density turbidity
currents.
Bioturbated
homogeneous
chalk (BHC)
Mudstone and
wackestone
with low to
intermediate
clay content.
Homogeneous to indistinct lamination.
Bedding poorly to moderately
developed with beds varying from
10 cm to 100 cm thick.
Abundant bioturbation induced
mottling. Traces include
Chondrites
,
Planolite
s and
Zoophycos
.
Broad and poorly
delineated
signals with low
porosity and high
density showing
intermediate to
low gamma ray
response.
Pelagic/autochthonous or
biogenically reworked
allochthonous chalk if
relatively thin (<1 m).
Deformed chalk
(DC)
Mudstone and
wackestone with
variable clay
content.
Convoluted, crenulated, folded and
shredded steeply dipping laminae with
common changes of dip direction.
Laminae may be variably argillaceous
or cemented. Bedding moderately
developed with thickness varying from
few decimetres to several metres.
Very rare bioturbation; highly
deformed if present.
Broad interval
characterised by
low density/high
porosity but with
a gradual decrease
of porosity and
increase in density
towards the top.
Resedimented/
allochthonous chalk:
slide, slump and creep.
Search WWH ::
Custom Search