Channel development in the chalk of the Tor Formation, North Sea: evidence of bottom current activity - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 566

Pebble
floatstone
chalk (PFC)

Matrix: Mudstone
and wackestone
with variable
clay content.
Clasts: cemented
silicified and
dolomitised
chalk intraclasts.

Matrix supported, highly disorganised,
polymictic conglomerate with rounded
clasts of coarse sand to pebble size
showing poor-moderate sorting and
local normal grading. Bedding poorly
developed (cm-m thickness). Sparse
shell fragments. Local evidence of
inclined parallel and crenulated
sedimentary laminations occasionally
cut or disturbed by bioturbations.
Rare cm-thick beds of clast-supported
conglomeratic chalk with clasts as
above showing local imbrication. Base
of the beds is sharp and erosional
while the top is marked by gradual
disappearance of clasts.

Rare bioturbation usually
confined to certain intervals.
Identifiable traces are
Chondrites , Planolites and
Thalassinoides .

Low density/high
porosity signals,
often with sharp
bases and tops.

Resedimented/
allochthonous chalk:
cohesive and non-
cohesive debris flow.

Homogeneous
chalk (HC)

Poor argillaceous
mudstone and
wackestone.

Uniform and massive with rare
laminae or traces of plastic flow. Rare
millimetric chalk grains and shell
fragments. Poorly developed bedding
locally a few decimetres to several
metres thick.

Rare to common bioturbation
usually confined to certain
intervals. Identifiable traces
are Planolite s and Chondrites .

Variable density and
porosity signals
but commonly
similar to PFC
facies, commonly
with sharp bases
and tops.

Pelagic/autochthonous
chalk or resedimented/
allochthonous chalk in
the form of low density
turbidite or turbulent
mud clouds.

Packstone and
grainstone
(PGC)

Poor argillaceous
packstone and
grainstone.

Uniform and massive. Grainstone may
by strongly laminated and with
planar laminations and planar cross-
laminations. Locally associated with
silica cementation. Moderate amount of
shell fragments. Base of beds is sharp
and locally erosional while the top is
marked by the gradual disappearance
of clasts.

Rare to common bioturbation.
Identifiable traces are
Planolite s and Chondrites .

High porosity and
low density
response.

Resedimented/
allochthonous chalk:
tempestite and
turbidite; winnowed
lags by bottom current.