Beginning of Mesozoic marine overstep of the Mendips: The Rhaetian and its fauna at Hapsford Bridge, Vallis Vale, Somerset, UK

Abstract

One of the most dramatic environmental changes in the Mesozoic history of Europe was the switch from terrestrial to marine deposition marked by the Rhaetian Transgression, 205 Ma. Beginning with this event, the Mendip Hills, composed primarily of uplifted and folded Lower Carboniferous limestones, were flooded in a stepwise manner from the Late Triassic to mid Cretaceous. The basal Rhaetian beds at the eastern end of the Mendips (Hapsford Bridge, Vallis Vale) lie directly on Carboniferous limestone, which was bored, indicating it functioned as a hardground. Bored pebbles were then eroded, transported, encrusted with bivalves, and deposited in marine muds in the lower parts of the Westbury Formation. At certain levels also, suspended mini-conglomerates within finer-grained sediments suggest continuing storm activity. The Hapsford Bridge Rhaetian bone bed includes microvertebrate remains of four species of sharks and two species of bony fishes, all of them typical of Rhaetian-aged bone beds. The invertebrate fauna is especially rich, including bivalves and echinoids, as well as trace fossils. Unusual elements are barnacles and a possible belemnite.

Full text

Beginning
of
Mesozoic
marine
overstep
of
the
Mendips:
The
Rhaetian
and
its
fauna
at
Hapsford
Bridge,
Vallis
Vale,
Somerset,
UK
James
Ronan
a
,
Christopher
J.
Duffin
a,b,c
,
Claudia
Hildebrandt
a
,
Adam
Parker
a
,
Deborah
Hutchinson
d
,
Charles
Copp
d,1
,
Michael
J.
Benton
a,
*
a
School
of
Earth
Sciences,
University
of
Bristol,
Life
Sciences
Building,
Tyndall
Avenue,
Bristol,
BS8
1TQ,
UK
b
146
Church
Hill
Road,
Sutton,
Surrey,
SM3
8NF,
UK
c
Earth
Sciences
Department,
The
Natural
History
Museum,
Cromwell
Road,
London,
SW7
5BD,
UK
d
Bristol
Museum
and
Art
Gallery,
Queen’s
Road,
Bristol,
BS8
1RL,
UK
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
26
November
2019
Received
in
revised
form
24
February
2020
Accepted
26
February
2020
Available
online
29
May
2020
Keywords:
Chondrichthyes
Osteichthyes
Bristol
Rhaetian
Rhaetian
bone
bed
Penarth
Group
Westbury
Formation
A
B
S
T
R
A
C
T
One
of
the
most
dramatic
environmental
changes
in
the
Mesozoic
history
of
Europe
was
the
switch
from
terrestrial
to
marine
deposition
marked
by
the
Rhaetian
Transgression,
205
Ma.
Beginning
with
this
event,
the
Mendip
Hills,
composed
primarily
of
uplifted
and
folded
Lower
Carboniferous
limestones,
were
flooded
in
a
stepwise
manner
from
the
Late
Triassic
to
mid
Cretaceous.
The
basal
Rhaetian
beds
at
the
eastern
end
of
the
Mendips
(Hapsford
Bridge,
Vallis
Vale)
lie
directly
on
Carboniferous
limestone,
which
was
bored,
indicating
it
functioned
as
a
hardground.
Bored
pebbles
were
then
eroded,
transported,
encrusted
with
bivalves,
and
deposited
in
marine
muds
in
the
lower
parts
of
the
Westbury
Formation.
At
certain
levels
also,
suspended
mini-conglomerates
within
finer-grained
sediments
suggest
continuing
storm
activity.
The
Hapsford
Bridge
Rhaetian
bone
bed
includes
microvertebrate
remains
of
four
species
of
sharks
and
two
species
of
bony
fishes,
all
of
them
typical
of
Rhaetian-aged
bone
beds.
The
invertebrate
fauna
is
especially
rich,
including
bivalves
and
echinoids,
as
well
as
trace
fossils.
Unusual
elements
are
barnacles
and
a
possible
belemnite.
©
2020
The
Geologists'
Association.
Published
by
Elsevier
Ltd.
All
rights
reserved.
1.
Introduction
The
Late
Triassic
was
a
time
of
major
environmental
change.
The
Rhaetian
transgression
marks
the
switch
from
primarily
terrestrial
to
marine
conditions
about
205.5
Ma,
and
it
has
been
noted
across
much
of
Europe.
The
event
is
marked
in
the
UK
by
the
switch
from
the
Mercia
Mudstone
Group
to
the
Penarth
Group
(Fig.
1),
starting
with
the
famous
Westbury
Formation
basal
bone
bed,
which
is
made
up
of
a
rich
accumulation
of
disarticulated
vertebrate
fossils
(Storrs,
1994).
The
change
is
evident
at
many
localities,
especially
those
such
as
Aust
Cliff
(Cross
et
al.,
2018)
where
the
Mercia
Mudstone
Group
largely
comprises
red
beds
and
is
conformably
overlain
by
the
black-coloured
shales
of
the
Westbury
Formation.
The
Rhaetian
transgression
was
probably
triggered
by
the
break-up
of
Pangaea,
marked
by
emplacement
of
the
Central
Atlantic
Magmatic
Province
and
major
rifting
on
the
Afro-
European
and
North
American
sides
(Wall
and
Jenkyns,
2004).
In
South
Wales
and
south-west
England,
from
south
Gloucester-
shire
to
Somerset
and
Dorset,
the
Rhaetian
and
other
Mesozoic
sedimentary
units
accumulated
on
top
of
an
exposed
landscape
formed
from
uplifted,
folded
and
subaerially
weathered
Palaeozoic
rocks,
primarily
Lower
Carboniferous
limestones,
but
also
Devoni-
an
sandstones
and
Upper
Carboniferous
coal-bearing
sediments.
These
limestones
have
been
quarried
for
a
long
time
across
the
Mendip
Hills,
south
of
Bristol,
and
the
quarrying
activity
often
cut
down
through
overlying
Mesozoic
sediments.
Much
of
this
geological
story
can
be
seen
in
Vallis
Vale
(Fig.
2A),
a
narrow
valley
in
the
south-eastern
Mendips,
located
between
the
villages
of
Great
Elm
and
Hapsford,
just
north
of
Frome.
By
1890,
the
Vale
was
an
industrial
site,
with
lime
kilns,
iron
workings,
and
woollen
mills,
all
powered
by
the
fast-flowing
waters
of
the
tiny
Mells
River.
But,
when
Buckland
and
Conybeare
(1824,
p.
225)
visited
the
steep-sided
valleys
of
Mells
and
Vallis,
they
were
quiet
and
secluded,
and
they
noted
that
‘[b]eautiful
sections
may
be
seen
in
the
precipitous
sides
of
these
valleys,
exhibiting
the
oolitic
strata
in
an
absolutely
horizontal
position,
reposing
on
the
truncated
edges
of
highly
inclined
strata
of
mountain
limestone
[sic].’
Much
*
Corresponding
author.
E-mail
address:
mike.benton@bristol.ac.uk
(M.J.
Benton).
1
In
honour
of
Charles
Copp
(1949–2009)
who
carried
out
extensive
work
on
the
Hapsford
Bridge
site
in
the
1980s
and
from
whose
unpublished
PhD
Thesis
work
we
have
drawn
upon
throughout
the
paper.
https://doi.org/10.1016/j.pgeola.2020.02.005
0016-7878/©
2020
The
Geologists'
Association.
Published
by
Elsevier
Ltd.
All
rights
reserved.
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
Contents
lists
available
at
ScienceDirect
Proceedings
of
the
Geologists’
Association
journal
homepa
ge:
www.elsev
ier.com/locate
/pgeola

the
same
observations
were
repeated
by
De
la
Beche
(1846,
p.
287),
when
he
wrote
that
Buckland
and
Conybeare
had
observed
how
Vallis
Vale
and
Murdercombe
‘show
the
inferior
oolite
[sic]
in
nearly
horizontal
beds
upon
the
upturned
edges
of
the
carbonifer-
ous
limestone
[sic],
with
occasionally
an
interposed
portion
of
a
conglomerate
referable
to
the
lias
[sic],
and
containing
organic
remains’.
De
la
Beche
(1846,
p.
288)
illustrated
the
Carboniferous-
Middle
Jurassic
unconformity
(now
commonly
referred
to
as
the
De
la
Beche
Unconformity)
in
the
old
quarry
opposite
the
confluence
of
the
Egford
Brook
and
Mells
River
(ST
7557
4918).
Charles
Moore
collected
in
the
area
during
the
early
1860s
and
passed
some
invertebrate
fossils
to
T.
Rupert
Jones,
who
named
Estheria
minuta
var.
brodieana
(now
Euestheria),
based
partly
on
this
material,
and
gave
a
brief
sketch
of
the
geological
succession
at
Vallis
Vale
(Jones
1862).
It
was
Moore
(1867,
pp.
488–491),
however,
who
provided
the
first
detailed
information
on
the
Vallis
Vale
sections,
describing
the
succession
in
several
quarries,
including
that
with
the
De
la
Beche
unconformity,
and
noting
especially
that
the
rocks
either
side
of
the
Carboniferous-Jurassic
contact
could
be
hard
to
distinguish
in
hand
specimen,
so
close
was
the
lithological
similarity
of
the
two
units.
He
described
quarries
along
the
eastern
branch
of
the
Vale,
towards
Hapsford,
where
he
observed
Liassic-age
fissures
in
the
Carboniferous
limestone,
and
made
the
first
mention
of
bedded
Rhaetian-age
sediments.
He
noted
(Moore,
1867,
p.
489)
that
‘A
thin
bed
of
a
waterworn
pebbly
conglomerate,
which
will
be
found
continuous
and
of
greater
thickness
in
succeeding
sections,
makes
its
appearance,
resting
for
a
short
distance
immediately
on
the
Carboniferous
Limestone.’
Moore
(1875)
provided
further
description
of
the
geology
of
Vallis
Vale,
and
later
(Moore,
1881,
pp.
67–68)
commented,
‘At
the
entrance
to
the
Vallis
at
Hapsford
the
first
sections
show
irregularly
bedded
Rhaetic
conglomerates
resting
in
depressions
on
the
edges
of
the
inclined
Carboniferous
limestone.
They
are
separated
by
thin
blue
clays
with
Avicula
contorta
and
also
Discina
Babiana
[sic].
I
have
no
doubt
they
would
yield
important
vertebrate
remains,
as
I
found
a
very
perfect
Dinosaurian
vertebra;
but,
unfortunately,
these
beds
have
not
been
worked
for
some
years.’
Finally,
McMurtrie
(1885,
pp.
103–106 )
repeated
some
of
Moore’s
comments,
but
especially
highlighted
how
the
Carbonif-
erous
limestone
along
the
banks
of
the
Mells
River
was
overlaid
successively
by
Rhaetian,
Lias
and
Middle
Jurassic
rocks,
corre-
sponding
to
an
inferred
steeply
rising
palaeotopography
of
the
eroded
top
of
the
Carboniferous
limestone
(Fig.
1B).
Woodward
(1890)
gave
a
generalised
overview
of
Mendip
geology,
and
provided
(p.
489,
Fig.
2)
a
rather
poorly
redrawn
version
of
the
unconformity
illustrated
by
De
la
Beche
(1846,
p.
288).
The
Rhaetian
sections
of
the
Hapsford
Bridge
end
of
Vallis
Vale
were
mentioned
by
Reynolds
and
Richardson
(1909);
Richardson
(1907,1909,
1911),
Richardson
and
Young
(1909);
Reynolds
(1912);
Cox
(1941);
Savage
(1977),
and
Duff
et
al.
(1985,
pp.
135–139).
Detailed
studies
were
carried
out
in
his
unpublished
thesis
by
Copp
(1980),
who
made
extensive
collections
at
Vallis
Vale
and
his
sedimentary
log
was
published
(Copp
in
Duffin,
1982),
but
none
of
his
other
work.
Orbell
(1973)
and
then
Warrington
(1984)
reported
palynological
investigations
from
the
section
at
Hapsford
Bridge,
comprising
miospores
and
organic-walled
microplankton
that
indicate
Rhaetian
age,
and
equivalence
to
horizons
from
Chil-
compton.
Furthermore,
Hapsford
Bridge
became
the
type
locality
for
the
penaeid
shrimp,
Aeger
gracilis
(Förster
and
Crane,
1984;
Boomer
et
al.,
1999,
pp.
141–14 4 ).
The
Hapsford
Bridge
sections
were
cleared
in
1979–1980
by
Charles
Copp
and
colleagues,
with
funding
from
the
Nature
Conservancy
Council.
The
aim
of
this
paper
is
to
present
a
report
of
the
Rhaetian
at
Hapsford
Bridge
in
Vallis
Vale.
We
present
evidence
that
the
Rhaetian
Transgression
was
accompanied
by
hardground
forma-
tion
and
the
beginning
of
overstep
of
the
Mendip
islands,
as
well
as
evidence
for
several
storm
events
associated
with
deposition
of
various
levels
of
the
Westbury
Formation.
We
also
document
the
Rhaetian
bone
bed
faunas
and
compare
them
with
examples
from
around
Bristol
and
in
South
Wales.
Repository
abbreviations:
BATGM,
Bath
Royal
Literary
and
Scientific
Institution,
geology
collection;
BRSMG,
Bristol
City
Museum
and
Art
Gallery,
geology
collection;
BRSUG,
University
of
Bristol,
School
of
Earth
Sciences,
geology
collection.
2.
Geological
setting
2.1.
Quarrying
in
the
Vallis
Vale
Hapsford
Bridge
is
part
of
the
Vallis
Vale
Site
of
Special
Scientific
Interest
(SSSI),
scheduled
for
conservation
especially
because
of
the
De
la
Beche
unconformity,
where
yellow-coloured
Middle
Jurassic
limestones
sit
horizontally
on
top
of
a
planed-smooth
palaeotopography
of
uplifted
and
steeply
dipping
Carboniferous
limestones
(De
la
Beche,
1846,
pp.
287–288).
Vallis
Vale
is
lined
with
quarry
faces
which
have
been
abandoned
over
time
and
these
have
become
overgrown.
It
is
a
popular
site
for
walkers,
with
a
stream,
car
park
and
footpath
(Prudden,
2006).
Stone
quarrying
was
a
long-established
industry
in
the
Mendip
Hills,
providing
a
diversity
of
building
stones
(Stokes,
1999).
Quarrying
in
Vallis
Vale
began
in
1893
with
the
formation
of
the
Somerset
Quarry
Company
(Foundations
of
the
Mendips,
2017)
to
Fig.
1.
Summary
of
Late
Triassic
and
Early
Jurassic
stratigraphy
in
England
(after
Swift,
1999;
Trueman
and
Benton,
1997 ).
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
579

Fig.
2.
The
context
of
Vallis
Vale,
showing
the
Vale
in
1906,
when
the
quarries
and
mineral
railways
were
active.
(A)
The
four
locations
discussed
in
the
paper
are
numbered
(1,
Hapsford
Bridge
Rhaetian
site;
2,
neighbouring
quarryalso
showing
Carboniferous-Rhaetian
unconformity;
3,
the
site
of
the
De
la
Beche
unconformity
between
Carboniferous
and
Inferior
Oolite
(Middle
Jurassic);
4,
Egford
quarry,
comprising
a
great
thickness
of
Carboniferous
limestone).
(B)
The
Rhaetian
overlies
the
Carboniferous
limestone
along
much
of
the
banks
of
the
Mells
River,
from
localities
1
to
3,
but
disappears
between
2
and
3.
For
A,
©
Crown
Copyright
and
Database
Right
2018.
Ordnance
Survey
(Digimap
Licence).
580
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

work
quarries
in
the
valley
of
the
Mells
River
beside
Hapsford
Mill,
on
the
Vallis
Road
(A362).
The
company
worked
four
quarry
faces
along
the
south
bank
of
Vallis
Vale
(Fig.
2A,
localities
1–3),
and
the
41-man
team
produced
over
100
tons
of
rock
a
day
of
which
10
%
was
burnt
for
lime
in
two
quarry
kilns
and
the
rest
was
crushed
for
road
building
(Thornes,
2015,
p.
75).
The
limestone
was
trans-
ported
in
wagons
called
‘tubs’
and
drawn
by
horses
along
narrow-
gauge
rail
lines
to
Hapsford
Mill.
There,
the
full
tubs
of
stone
were
lifted
to
a
higher
level
by
a
wire
system,
and
dumped
into
the
hoppers
of
the
stone-crushing
machinery,
which
was
powered
by
the
water
flow
of
the
Mells
River
or,
when
the
flow
was
insufficient,
by
a
steam
engine
(Anonymous,
1898).
Soon,
these
horse-drawn
wagons
were
replaced
by
steam
engines
on
the
narrow-gauge
rail
lines.
As
the
business
grew,
and
became
a
registered
company
in
1907,
the
operation
expanded
to
quarrying
six
faces
along
the
banks
of
the
Mells
River
and
Egford
Brook,
and
eventually
12,
which
more
or
less
connected
continuously
(Fig.
2A,
between
sites
2–4).
The
stone
was
shipped
out
along
the
narrow-gauge
railway
lines,
which
connected
up
Vallis
Vale
past
Hapsford
Mill
eastwards
to
join
the
standard-
gauge
Radstock–Frome
line
of
the
Great
Western
Railway
which
runs
past
the
Vale
(Atthill,
1984).
The
190 6
and
1936
Ordnance
Survey
maps
show
the
narrow-gauge
railway
running
on
the
south
bank
of
the
Mells
River
at
Hapsford,
right
beside
the
Rhaetian
section,
and
crossing
to
the
north
bank
of
the
river
to
branch
eastwards
beside
Hapsford
Mill
(Fig.
2A).
The
lines
extended
for
some
2
1
/
2
miles
and
were
worked
by
two
small
four-
wheeled
Ruston
Hornsby
diesel
locomotives.
The
Somerset
Quarry
Company
became
Roads
Reconstruction
(1934)
Ltd.,
and
then
Hanson
PLC
in
1989.
The
narrow-gauge
line
was
replaced
in
1943
with
a
standard
gauge
system
(Thornes,
2015).
Quarrying
in
Vallis
Vale
reduced
after
the
war
and
ceased
in
the
1960s.
Meanwhile,
New
Frome
Quarry,
later
renamed
Whatley
Quarry
(UK
National
Grid
Reference,
ST
731479),
opened
in
the
1940s
to
the
west
of
Vallis
Vale,
generated
over
2.5
million
tonnes
yearly
from
the
1980s
onwards,
and
remains
one
of
the
two
largest
quarries
still
in
operation
in
Somerset
(Quarry
Faces,
2019).
The
Somerset
limestones
also
have
a
history
of
being
used
for
lime-
burning
and
other
by-products
including
poultry
grit,
and
concrete
(Loupekine,
1956).
Evidence
of
the
quarrying
still
remains
today,
with
broad
gravel
tracks
beside
the
streams
where
the
mineral
railways
used
to
run.
Remains
of
eight
lime
kilns
can
also
be
found
in
the
Vallis
area.
2.2.
The
quarry
sites
There
are
some
questions
regarding
the
nomenclature
of
the
sites.
Moore
(1867,
pp.
488-490)
describes
his
route
round
Vallis
Vale,
from
‘Eggford’
(Egford),
now
the
visitor
car
park,
heading
north
beside
Egford
Brook
to
the
De
la
Beche
unconformity
quarry,
and
then
northwards
beside
the
Mells
River
through
wooded
slopes.
He
then
turns
east
along
the
other
branch
of
the
Mells
River
‘towards
Hapsford’
and
describes
a
series
of
quarries
on
the
south
side
showing
considerable
thicknesses
of
Carboniferous
lime-
stones,
and
terminating
at
Hapsford
Bridge
(Fig.
2A,
south
bank
of
Vallis
Vale,
including
localities
2
and
1).
McMurtrie
(1885,
p.
104 )
refers
to
the
site
as
the
Vallis,
and
identifies
quarries
A,
B
and
C
along
the
southern
bank
of
the
Mells
River,
of
which
the
last
is
Hapsford.
Richardson
(1911,
p.
64)
mentions
the
site
as
Hapsford-
Mills.
Since
the
mills
at
Hapsford
Bridge
no
longer
exist,
we
follow
other
authors
in
using
the
term
‘Hapsford
Bridge’
instead.
Our
work
focuses
on
the
Rhaetian
bone
beds
at
the
Hapsford
Bridge
roadside
locality
(ST
76057
49507)
which
runs
parallel
to
the
Mells
River
(Fig.
2A,
locality
1).
Other
quarries
in
the
Vallis
area
were
also
examined
(Fig.
2A)
and
these
include
two
further
disused
quarries
(ST
760494,
ST
760493;
location
2),
the
site
of
the
De
la
Beche
unconformity
(ST
7557
4918;
location
3),
and
Egford
Quarry
(ST
7575
4871;
location
4).
The
geology
around
Vallis
Vale
(Fig.
3)
comprises
mainly
Middle
Jurassic
sediments
to
the
east,
with
a
meandering
strip
of
Carboniferous
rocks
exposed
by
the
action
of
the
Mells
River,
and
then
massively
exposed
in
Whatley
Quarry
to
the
west.
Mercia
Mudstone
and
Penarth
Group
sediments
occur
to
the
west,
and
in
small
patches
along
the
Vale.
Fig.
3.
Geological
map
of
Vallis
Vale
and
neighbouring
areas,
with
map
of
Great
Britain
to
show
general
location
(marked
with
star).
The
Hapsford
Bridge
site
is
marked
with
a
hexagon.
©
Crown
Copyright
and
Database
Right
2018.
Ordnance
Survey
(Digimap
Licence),
and
British
Geological
Survey.
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
581

2.3.
Sedimentary
logs
The
first
detailed
account
of
the
Rhaetian
at
Hapsford
Bridge
was
presented
by
Moore
(1867,
p.
490),
who
gave
a
measured
section
from
the
roadside
quarry
(here
reversed,
with
oldest
rocks
lowest):
Richardson
(1911,
pp.
63–65)
benefited
from
larger
exposures
after
excavation
of
the
rail
lines
and
commercial
quarries
and
was
able
to
provide
further
details.
He
reported
what
he
saw
in
McMurtrie’s
(1885)
three
quarries,
with
5
m
of
Carboniferous
limestone
visible
at
the
south-western
end,
succeeded
by
1.2
m
of
Rhaetian
and
3.7
m
of
Inferior
Oolite.
At
Hapsford
Bridge,
he
gave
a
further
measured
section
which
agrees
with
that
by
Moore
(1867),
except
that
he
reports
Euestheria
(under
the
earlier
designation
Estheria)
and
plant
remains
in
his
bed
4,
part
of
the
Cotham
Member,
and
he
confirms
that
the
uppermost
unit
is
indeed
the
“White
Lias”,
part
of
the
Langport
Member
(Boomer
et
al.
1999,
p.
140 ).
During
field
work
in
October
2018,
all
the
Vallis
Vale
sites
mentioned
in
the
earlier
literature
were
identified
(Figs.
2A,
4
),
sedimentary
logs
were
made,
and
bone
bed
samples
collected.
We
compare
the
sections
by
Moore
(1867,
p.
490)
and
Richardson
(1911,
p.
65)
with
our
measured
section
(Fig.
5A–C).
We
found
the
section
was
5–6
m
high,
along
the
bank
of
what
had
been
cut
for
a
railway
siding,
and
now
marks
the
edge
of
the
access
road.
Only
the
lower
half
could
be
logged,
as
the
upper
portion
is
obscured
by
a
cover
of
soil
and
tree
roots
which
was
impossible
to
clear
by
hand
(Fig.
4C).
We
noted
(Fig.
5C)
0.7
m
of
Carboniferous
limestone
(Black
Rock
Limestone
Subgroup)
at
the
base,
overlain
by
2.3
m
of
Westbury
Formation,
comprising
irregularly
bedded
limestones,
separated
by
thin
blue
clays.
The
Carboniferous-Rhaetian
uncon-
formity
is
marked
by
a
bored
hardground,
as
shown
by
reworked
pebbles
(see
Section
5),
succeeded
by
63
cm
of
muddy
limestone
showing
evidence
of
storm-bed
activity
(see
Section
6).
This
is
succeeded
by
a
calcareous
sandy
bone
bed
with
fossil
fragments
(8
cm
thick),
40
cm
above
which
we
located
a
further
bone-bearing
horizon
in
a
33-cm-thick
muddy
limestone.
The
upper
3
m
of
this
Rhaetian
section
thins
southwards
as
the
unconformity
surface
at
the
top
of
the
Carboniferous
Limestone
rises.
3.
Materials
and
methods
Most
of
the
palaeontological
study
is
based
on
samples
of
the
basal
Rhaetian
bone
bed
collected
in
October
2018
(Fig.
4).
Samples
were
taken
from
the
measured
beds
(Fig.
4C),
with
some
1
kg
each
of
potential
bone
beds
sampled
from
Beds
2,
3
4,
5,
6
and
8
and
small
blocks
from
beds
4,
6
and
8
collected
for
slab-cutting
(Fig.13).
The
fossiliferous
sediment
samples
were
processed
in
the
Palae-
obiology
Laboratory
at
the
University
of
Bristol
by
Adam
Parker.
The
method
of
preparation
followed
that
described
by
Landon
et
al.
(2017).
The
material
was
initially
treated
with
a
5%
solution
of
acetic
acid
in
water
(total
volume
of
4
litres)
to
keep
pH
consistent
and
was
left
for
20
min
with
a
buffer
of
calcium
carbonate
and
tri-
calcium
di-orthophosphate
(4
g
and
2
g).
The
material
was
then
left
for
two
days,
by
which
time
the
reactions
had
finished.
After
acid
digestion,
the
large
(>2.0
mm)
undigested
material
was
set
aside,
and
the
remainder
was
washed
through
a
series
of
sieves
with
gauges
of
2.0
mm,
0.5
mm,
and
0.18
mm
to
separate
the
material
into
exact
sediment
fractions.
A
hose
and
a
squirt
bottle
were
used
to
wash
each
of
the
sediment
fractions
into
a
separate
filtration
system
made
of
a
filter-
paper-lined
funnel
in
a
beaker,
where
it
was
left
for
24
h
to
drain
fully.
The
remaining
undigested
sediment
was
placed
in
a
bucket
of
water
for
72
h
and
was
then
sieved
and
filtered
using
the
same
process
as
before.
After
this,
the
residue
was
air
dried
before
being
treated
with
acid
again.
This
process
was
repeated
through
a
number
of
cycles
until
all
the
sediment
matrix
had
been
digested.
The
acid-digested
concentrate
fractions
were
then
hand-picked
under
a
binocular
microscope
and
fossils
classified
and
separated
into
small
collection
boxes.
The
best
examples
of
each
morphotype
were
photographed
using
a
Leica
DFC425
C
camera
on
an
optical
microscope
with
multiple
image-stacking
software.
Usually,
some
20
digital
images
were
taken
and
then
fused,
and
this
minimised
depth-of-field
effects.
The
digital
images
were
cleaned
and
saved
at
600
dpi
and
prepared
as
plates
for
the
systematic
descriptions.
4.
Systematic
palaeontology
4.1.
Introduction
Vallis
Vale
has
been
a
rich
source
of
fossils
from
the
Rhaetian,
Lias
and
Middle
Jurassic.
Here,
we
review
the
microvertebrates
and
invertebrates
found
at
the
Hapsford
Bridge
locality
(Figs.
6–10),
including
fossils
collected
by
Michael
D.
Crane
and
Rosie
H.B.
Crane
in
March
and
April
1978
for
comparison
(BRSMG
collections;
Crane-Copp
correspondence;
Geology
File
No.
CRA
31,
1–34).
In
earlier
accounts,
Moore
(1867)
and
Richardson
(1907,
1911)
reported
extensive
collections
of
invertebrates
from
the
limestone
beds
of
the
Westbury
and
Lilstock
formations,
which
we
do
not
include
here.
Richardson
(1911,
p.
65)
also
reported
many
lycopod
plant
remains,
and
he
identified
the
shark
and
bony
fish
teeth
in
the
basal
bone
bed
as
well
as
fish
scales
in
the
Cotham
Member.
The
German
palaeontologist
Erika
von
Huene
(1933)
reported
the
mammal-like
tooth
Tricuspes
sp.
from
Vallis
Vale,
a
genus
identified
earlier
from
the
German
Rhaetian,
and
possibly
belonging
to
a
cynodont
(Storrs,
1994).
Such
a
find
is
unusual
in
the
British
Rhaetian
bone
beds,
but
much
more
common
at
several
sites
in
continental
Europe,
in
Belgium,
Luxembourg,
and
France
for
example
(Lukic-Walther
et
al.,
2019).
The
specimen
is
probably
BATGM
C108
(Storrs
1994,
p.
246).
In
unpublished
work,
Copp
(1980)
reported
on
all
the
fossils
from
the
different
horizons
at
Hapsford
Bridge,
especially
the
invertebrates,
based
on
collections
now
in
BRSMG.
A
summary
of
his
main
findings
is
as
follows.
In
the
dark-coloured
clays
at
the
base
of
the
Rhaetian,
Copp
(1980,
pp.
24–26)
reported
an
abundant
fauna
including
the
bivalve
Atreta
intusstriata
(common)
and
Lopha
fimbriata
(fragments),
echinoid
spines,
and
neritopsid
gastropod
opercula.
These,
he
noted,
are
rare
in
the
British
Rhaetian.
He
also
noted
rare
Rhaetavicula
contorta,
as
well
as
other
bivalves,
gastropods
and
brachiopods.
Numerous
limestone
pebbles
show
borings
of
Polydorites
(=
Gastrochaenolites)
and
Trypanites
(see
Section
5).
In
the
conglomeratic
limestones
(his
beds
2,
4;
the
basal
582
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

Fig.
5.
Sedimentary
logs
of
the
Rhaetian
beds
at
Hapsford
Bridge,
Vallis
Vale
ST
76057
49507.
Log
A
data
from
Charles
Moore
(1867);
(B)
data
from
Richardson
(1911)
and
(C)
the
log
we
measured
in
2018.
In
(C),
we
indicate
our
bed
numbers
1–8,
and
mark
inferred
storm
beds
on
our
section
(see
Fig.
6).
Thicknesses
in
metres.
Fig.
4.
Hapsford
Bridge
roadside
locality
and
De
La
Beche
unconformity.
(A)
The
roadside
section
being
measured
by
(from
left
to
right)
Jack
Lovegrove,
Mike
Benton,
James
Ronan,
and
Doug
Robinson.
(B)
Jack
Lovegrove
and
James
Ronan
log
the
Westbury
Formation
sequence,
lying
above
Carboniferous
limestone
at
the
base.
(C)
Logging
higher
in
the
section,
and
difficulties
of
clearing
soil
and
vegetation,
with
Jack
Lovegrove,
Joe
Flannery
Sutherland
and
James
Ronan.
(D)
Beds
2–6
of
the
Westbury
Formation,
showing
the
basal
bone
bed,
level
with
the
hammer
head,
overlain
by
muddy
limestone
and
limestone
beds.
(E)
The
De
la
Beche
unconformity,
which
is
slightly
overgrown
by
vegetation,
showing
the
yellow
horizontally
bedded
Jurassic
Inferior
Oolite
lying
unconformably
on
the
steeply
dipping
Carboniferous
limestone
(For
interpretation
of
the
references
to
colour
in
this
figure
legend,
the
reader
is
referred
to
the
web
version
of
this
article).
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
583

bone
bed),
he
noted
the
same
fish
teeth
and
scales,
bivalves
and
echinoid
remains
which
we
report
here,
as
well
as
the
bivalves
Rhaetavicula
contorta
and
Chlamys
valoniensis,
borings
in
pebbles,
and
insects
(although
we
have
been
unable
to
trace
the
specimens
of
insects).
In
the
overlying
Cotham
Member,
Copp
(1980,
p.
27)
noted
earlier
reports
by
Moore
and
Richardson
of
the
conchostracan
Euestheria
minuta,
rare
insects,
and
abundant
plant
remains
(Lycopodites
=
Naiadita).
In
the
Langport
Member,
he
found
only
poorly
preserved
remains
of
the
coral
Montlivaltia
and
crustacean
burrows
in
the
top
bed.
4.2.
Chondrichthyans
Four
species
of
shark
have
been
identified
from
the
Hapsford
Bridge
locality,
but
identifiable
specimens
are
rare,
and
they
include
Vallisia
coppi,
first
described
from
this
location.
4.2.1.
Lissodus
minimus
(Agassiz,
1833-1844)
One
example
of
this
species
was
found
in
the
collection
(Fig.
6A,
B).
The
specimen
is
over
3
mm
in
length
and
is
elongate,
with
a
central
cusp
with
a
rising
vertical
tip
on
the
left
side
which
is
broken.
The
specimen
in
labial
view
displays
some
abrasion,
and
because
of
incompleteness
it
cannot
be
assigned
to
a
particular
region
in
the
jaw.
Lissodus
teeth
are
very
common
at
some
localities,
such
as
Charton
Bay,
Devon
(Korneisel
et
al.,
2015),
and
they
occur
as
anterior,
anterolateral,
lateral
and
posterolateral
forms,
depending
on
their
original
position
in
the
jaws
(Duffin
1999,
pp.
199–201).
These
are
all
long
and
low-crowned,
and
the
different
forms
vary
in
length
and
height
of
the
central
cusp.
4.2.2.
Synechodus
rhaeticus
(Duffin,
1982)
We
identify
five
teeth
of
Synechodus
(Fig.
6C–L)
because
they
bear
small
lateral
cusplets,
a
heavy
ornamentation
comprising
vertical
ridges,
and
a
reticulate
ornament
on
the
crown
shoulders.
When
complete,
the
teeth
are
roughly
symmetrical
around
a
distinctive,
pointed,
upright
central
cusp.
Because
of
abrasion,
this
pointed
central
cusp,
and
the
lateral
cusplets,
have
been
removed.
4.2.3.
Duffinselache
holwellensis
(Duffin,
1998)
We
identify
one
tooth
of
Duffinselache
(Fig.
6M–N),
which
is
elongate,
with
crown
and
root
of
similar
height.
The
crown
may
form
a
single
blade
with
slight
crenulations,
and
there
is
a
definite
major
cusp
as
a
sloping
triangular
structure.
Fig.
6.
Chondrichthyan
teeth
from
Hapsford
Bridge,
beds
4–6.
(A–B)
Lissodus
minimus
(BRUSG
29954-170)
in
lingual
(A)
and
labial
(B)
views.
(C–L)
Synechodus
rhaeticus,
five
teeth
in
lingual
(C,
E,
G,
H,
I)
and
labial
(D,
F,
J,
K,
L)
views:
BRSUG
29954-47,
posterior
tooth
(C,
D);
BRUSG
29954-48
(E,
F);
BRSUG
20054-73
to
75
(G–L),
broken
into
three
pieces,
BRSUG
29954-75
(G,
L);
BRSUG
29954-74
(H,
K);
and
BRSUG
29954-73
(I,
J).
(M–N)
Duffinselache
holwellensis,
BRSUG
29954-72,
posterior
tooth
in
lingual
(M)
and
labial
(N)
views.
Scale
bar
is
1
mm
for
all
specimens.
584
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

Teeth
of
D.
holwellensis
are
known
only
from
the
Rhaetian
(Slater
et
al.,
2016,
p.
470),
but
have
been
widely
reported
from
most
British
Rhaetian
bone
bed
localities.
4.2.4.
Vallisia
coppi
Duffin,
1982
We
did
not
find
any
specimens
of
this
key
species
in
our
2018
collection,
but
there
are
examples
in
the
Crane
1978
collection.
These
specimens
(Fig.
7A–D)
are
1.5
mm
high,
with
three
main
upright
cusps
and
two
tiny
lateral
cusplets
on
a
central
base
forming
the
crown.
The
tooth
overall
is
flattened
labio-lingually.
The
central
cusp
is
tallest,
and
it
shows
symmetrical
faces
anteriorly
and
posteriorly.
The
flanking
cusps
are
smaller,
but
also
show
angled
anterior
and
posterior
faces,
so
all
three
major
cusps
show
ridges
facing
labially
and
lingually.
The
lateral
cusplets
are
small
projections
from
the
two
flanking
cusps.
The
surface
of
the
crown
is
not
ornamented.
The
base
of
the
crown
expands
and
overhangs
the
root,
from
which
it
is
separated
by
a
deeply
incised
groove.
The
root
branches,
with
flat
lobes
pointing
slightly
anteriorly
and
posteriorly
on
either
side
of
a
medial
canal.
The
surface
of
the
root
is
roughened,
and
it
bears
some
large,
circular
pores.
Some
of
the
Hapsford
specimens
are
complete
(Fig.
7A,
B),
but
others
are
broken
(Fig.
7C–F),
as
commonly
seen
in
previously
described
examples
from
Vallis
Vale
(Duffin,
1982),
Manor
Farm
Quarry
(Allard
et
al.,
2015,
Fig.
4B),
Hampstead
Farm
Quarry
(Mears
et
al.,
2016,
Fig.
6k),
and
Belgium
(Duffin
et
al.,
1983).
The
affinities
of
Vallisia
coppi
have
been
debated,
with
Cuny
and
Benton
(1999)
confirming
that
the
ultrastructure
of
the
enameloid
is
not
neoselachian.
In
a
recent
review,
however,
Cappetta
(2012,
p.
327)
classified
the
taxon
as
Neoselachii
incertae
sedis.
4.2.5.
Dermal
denticles
We
identified
19
chondrichthyan
denticles
in
the
Crane
collection
(Fig.
7G–K),
all
of
them
about,
or
less
than,
1
mm
in
diameter.
These
are
hard
to
identify,
even
though
they
are
generally
well
preserved.
Three
small
specimens
(Fig.
7H–J)
are
broken,
and
show
distinct
ridges
and
curved
grooves,
reflecting
their
original
‘hand-shaped’
form.
One
of
these
(Fig.
7G)
is
a
scale,
another
(Fig.
7H)
is
a
ctenacanthid
denticle,
and
another
(Fig.
7I)
looks
like
a
placoid
scale.
Another
(Fig.
7J)
is
just
over
1
mm
in
diameter,
brown
in
colour,
and
with
clear
striations
from
the
base
of
the
denticle
upwards.
A
final
example
(Fig.
7K)
is
under
1
mm
in
diameter,
black
in
colour,
and
with
striations
that
extend
laterally.
4.3.
Actinopterygians
Two
taxa
of
bony
fish
have
been
identified
from
collection
samples
at
the
Hapsford
Bridge
locality
known
from
the
British
Rhaetian.
4.3.1.
Gyrolepis
albertii
Agassiz,
1833-1844
These
are
the
most
common
actinopterygian
teeth,
with
68
being
identified,
15
of
which
are
broken.
There
are
varied
morphologies
(Fig.
8A–G),
but
they
all
share
an
elongate,
sometimes
curved,
conical
shape,
with
circular
cross
section.
All
show
the
translucent
acrodin
tip,
which
is
variably
long
and
sharply
pointed
(Fig.
8C,
F,
G)
or
blunt
ended
(Fig.
8B,
D,
E),
either
as
a
result
of
wear
in
use
or
abrasion
during
transport
and
deposition.
There
is
generally
no
ornament,
although
some
specimens
show
faint
longitudinal
ridges.
Gyrolepis
albertii
is
almost
always
the
most
common
actino-
pterygian
tooth
in
Rhaetian
bone
beds,
and
is
reported
throughout
Europe
(Duffin,
1999,
p.
213).
4.3.2.
Severnichthys
acuminatus
(Agassiz,
184 4 )
There
are
ten
Severnichthys
teeth,
which
show
varied
mor-
phologies
(Fig.
8H–O).
Specimens
of
the
‘Saurichthys’
tooth
type
Fig.
7.
Chondrichthyan
teeth,
dermal
denticles
and
scales.
(A–D)
Vallisia
coppi
teeth.
(A)
The
holotype
tooth
BRSMG
Cc400,
in
lateral
view.
(B)
BRSMG
Cc401,
in
lateral
view.
(C)
BRSMG
Cc402,
in
lateral
view.
(D)
BRSMG
Cc404,
in
lateral
view.
(E,
F)
Fragmentary
teeth
BRSMG
Cd1595
(E)
and
Cd1596
(F).
(G)
Ctencanthid
scale
BRSMG
Cd152.
(H–K)
Dermal
denticles
BRSMG
Cd1526
(H),
BRSMG
Cd1516
(I),
BRSMG
Cd1517
(J),
BRSMG
Cd1520
(K).
Scale
bar
is
1
mm
for
all
specimens.
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
585

(Fig.
8H–L)
are
all
conical,
ranging
in
height
from
1
to
1.5
mm,
and
with
a
small
but
pointed
translucent
cap,
which
in
some
cases
(Fig.
8H,
K)
is
inset
above
a
definite
constriction
of
the
tooth.
The
‘Birgeria’-type
teeth
(Fig.
8M–O)
are
<
1
mm
in
height
and
the
translucent
tip
occupies
more
of
the
tooth
length.
All
Severnichthys
teeth
lack
distinct
ridges,
which
probably
reflects
their
somewhat
abraded
state:
Cross
et
al.
(2018,
Fig.
10b,
c)
shows
unabraded
examples
with
distinct
longitudinal
wrinkles
and
ridges
in
the
Saurichthys-type
teeth.
The
story
of
Severnichthys
has
been
known
for
some
time,
a
genus
that
combines
two
tooth
types
that
were
formerly
ascribed
to
distinct
genera
and
species
(Storrs,
1994).
As
in
most
Rhaetian
bone
bed
sites,
this
was
likely
the
largest
fish
present,
a
large
predatory
fish
that
may
have
fed
as
a
pike-like,
lurking,
ambush
predator
(Duffin,
1999,
pp.
215–216).
4.3.3.
Other
actinopterygian
remains
Osteichthyan
scales
were
the
second
most
abundant
fossils
from
the
Hapsford
locality,
with
594
counted.
Most
of
these
are
fragmentary
and
abraded
quite
heavily.
Twenty-three
of
these
display
the
classic
Gyrolepis
albertii
ganoin,
which
is
preserved
as
a
black/dark
blue
surface,
though
many
are
abraded
and
heavily
worn.
Four
morphotypes
were
identified,
but
the
abraded
condition
of
many
scales
makes
it
hard
to
be
sure,
and
difficult
to
compare
directly
with
the
scale
morphotypes
identified
by
Mears
et
al.
(2016,
pp.
490–491).
The
morphotype
1
scale
(Fig.
8P)
is
over
1
mm
in
length
and
possesses
a
rounded
rhomboidal
shape.
The
ganoin
layer
is
hard
to
distinguish
because
of
abrasion,
though
traces
of
the
longitudinal
ridge-like
pattern
can
be
distinguished.
The
morphotype
2
scale
(Fig.
8Q)
is
around
3
mm
in
length
and
less
abraded.
It
features
a
more
rhomboidal
shape
with
a
thinner
ganoin
layer,
and
the
overlap
facets
are
clearly
defined
at
the
right-hand
end.
The
morphotype
3
scale
(Fig.
8R)
is
just
over
3
mm
in
length.
It
features
a
very
thick
ganoin
layer
with
defined
markings
which
extend
across
the
scale
longitudinally.
The
morphotype
4
scale
(Fig.
8S)
is
around
1.5
mm
in
length,
and
has
a
defined
ganoin
layer
that
is
flat,
smooth
and
much
more
rounded.
There
are
some
better
quality
Gyrolepis
scales
in
the
Crane
collection
(Fig.
9).
Some
show
an
encrusted
cover
of
crystalline
calcite
(Fig.
9A).
Others,
though,
are
in
less
abraded
condition
(Fig.
9C–E),
showing
the
ganoin
cover
and
antero-posterior
longitudinal
wavy
and
branching
ridge-groove
patterns.
These
scales
also
all
show
the
overlap
facets
along
the
posterior
margin.
4.4.
Other
fossils
The
bone
beds
include
a
variety
of
fossils
other
than
fish
remains,
including
some
unusual
invertebrates,
as
well
as
coprolites.
4.4.1.
Barnacle
Eolepas
rhaetica
(Moore,
1861)
We
found
45
barnacle
pieces,
all
of
them
phosphatic,
black
on
the
outer
surface,
likely
to
be
from
Eolepas,
but
they
are
all
broken
(Fig.
10A–D).
One
example
shows
the
classic
pattern
of
horizontal,
parallel
growth
lines,
intersecting
a
vertical
pattern
of
fine
ridges
Fig.
8.
Actinopterygian
teeth
and
scales.
(A–G)
Gyrolepis
albertii
teeth
from
beds
2–3,
all
in
side
profile.
(A)
BRSUG
29954-1.
(B)
BRSUG
29954-2,
very
abraded
tooth.
(C)
BRSUG
29954-25.
(D)
BRSUG
29954-26.
(E)
BRSUG
29954-27.
(F)
BRSUG
29954-28.
(G)
BRSUG
29954-29.
(H–O)
Severnichthys
acuminatus
teeth
from
beds
3–5,
all
in
side
profile,
and
showing
the
two
morphs,
the
‘Saurichthys’
type
(H–L)
and
the
‘Birgeria’
type
(M–O).
(H)
BRSUG
29954-38.
(I)
BRSUG
29954-115.
(J)
BRSUG
29954-116.
(K)
BRSUG
29954-117.
(L)
BRSUG
29954-118,
broken
specimen.
(M)
BRSUG
29954-119.
(N)
BRSUG
29954-120.
(O)
BRSUG
29954-121.
(P–S)
Osteichthyan
scales
with
external
sculpture
beds
4-6.
(P)
Osteichthyan
scale
morphotype
1,
BRSUG
29954-62.
(Q)
Osteichthyan
scale
morphotype
2,
BRSUG
29954-110.
(R)
Osteichthyan
scale
morphotype
3,
BRSUG
29954-111.
(S)
Osteichthyan
scale
morphotype
4,
BRSUG
29954-140.
Scale
bar
is
1
mm
for
all
specimens.
586
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

on
the
outer
face
(Fig.
10A),
but
with
a
smooth
inner
face
(Fig.
10B).
Another
specimen
shows
the
same
external
sculpture
(Fig.
10C)
and
a
platform
and
concave
shape
internally
(Fig.
10D).
All
of
the
fragments
seem
to
be
partial
scutum
and
carina
plates.
Eolepas
rhaetica
was
named
by
Moore
(1861),
initially
as
a
species
of
Pollicepes,
from
the
Vallis
Vale
Rhaetian
limestones,
based
on
fragmentary
and
more
complete
specimens
showing
entire
valves
(Boomer
et
al.,
1999,
pl.
20,
Figs.
5–9).
These
show
the
same
sculpture
patterns
as
our
specimens.
In
life,
Eolepas
looked
something
like
a
modern
gooseneck
barnacle,
with
six
rhomboid
valves
of
varying
sizes
enclosing
the
body,
and
all
ending
with
a
rounded
point
distally
(Gale
and
Schweigert,
2016).
The
genus
Eolepas
ranges
from
the
Late
Triassic
to
Early
Cretaceous,
so
E.
rhaetica
is
one
of
the
first
members
of
the
genus
and
is
indeed
the
oldest
recorded
scalpellid
barnacle
(Boomer
et
al.,
1999).
4.4.2.
Bivalve
Atreta
intusstriata
(Emmrich,
1853)
Ten
examples
of
bivalves
were
identified.
Some
are
broken
portions
of
large
oysters
with
heavy
zig-zag
commissure
line,
like
Lopha
haidingeriana
(cf.
Ivimey-Cook
et
al.,
1999,
pl.
13,
Fig.
8).
Two
(Fig.
10E–F)
show
the
general
shape,
irregular
layering,
and
radiating
pattern
of
fine
ridges
seen
in
Atreta
intusstriata
(cf.
Ivimey-Cook,
et
al.,
1999,
pl.
13,
Figs.
3,
4).
Both
are
5–6
mm
in
size,
and
represent
incomplete
fragments
from
near
the
hinge
line,
showing
irregular
folds
in
the
shell,
and
radiating
striations.
Atreta
intusstriata
is
commonly
found
in
other
Rhaetian
shallow
water
deposits
of
north-western
Europe
including
Germany
and
the
Tethys,
but
is
rare
in
the
Westbury
Formation,
occurring
more
commonly
in
the
Lilstock
Formation.
It
is
a
dimyoid
oyster
(Order
Ostreoida),
typically
small
(maximum
height
12
mm,
and
width
9
mm)
and
the
right
valve
was
cemented
to
the
rock,
presumably
close
to
shore.
We
identified
it
also
as
one
of
the
encrusting
bivalves
on
the
uprooted
Carboniferous
pebbles
(Fig.
12D).
4.4.3.
Echinoid
spines
We
identified14
echinoidspines,
possibly
those
of
cidaroids,
all
of
which
are
elongate
and
cylindrical,
and
range
in
size
from
2
mm
to
over
9
mm
in
length,
and
1–2
mm
in
diameter.
They
are
all
preserved
differently,
one
(Fig.
10G)
being
grey-coloured
and
mottled,
8
mm
long,
another
(Fig.
10H)
orange,
and
6
mm
long,
and
showing
some
tapering,
and
a
further
one
(Fig.
10I)
grey
and
tapering,
8
mm
long.
Cidaroid
spines
are
frequently
reported
in
sieved
residues
of
the
Rhaetian
bone
beds
(Swift,
1999).
Our
examples
are
rather
featureless
when
compared
to
those
reported
from
Hampstead
Farm
Quarry
(Mears
et
al.,
2016,
Fig.
17h),
which
show
the
basal
boss
or
acetabulum
by
which
they
attach
to
the
echinoid
test
and
short
pines
on
longitudinal
ridges
along
the
length
of
the
spine.
4.4.4.
Possible
belemnite
One
specimen,
originally
identified
as
a
cidaroid
spine
(Fig.10J),
is
composed
of
crystalline
calcite
which
shows
a
radiating
pattern
on
the
broken
end.
It
is
hard
to
identify
definitively
as
either
cidaroid
or
belemnite
because
of
considerable
abrasion
of
the
outer
surface.
Its
size
(9
mm
long)
tends
to
favour
interpretation
as
a
cidaroid
spine,
but
the
radiating
breakage
of
the
calcite
looks
belemnite-like.
If
it
is
a
belemnite,
however,
it
would
be
the
first
from
the
British
Rhaetian,
and
one
of
only
a
few
recorded
from
the
Late
Triassic.
4.4.5.
Coprolites
We
identified
only
four
coprolites
in
our
collection
(Fig.
10K–N).
They
measure
1–2
mm
in
diameter
and
3–7
mm
long,
but
all
are
broken
and
incomplete.
All
coprolites
are
light
brown/grey
in
colour
and
show
the
usual
spiral
structure.
None
of
them
show
identifiable
remains
of
plants
or
fish
scales
on
the
surface.
Coprolites
such
as
these
are
common
components
of
the
Rhaetian
bone
beds
(Swift
and
Duffin,
1999;
Mears
et
al.,
2016,
p.
496;
Slater
etal.,
2016, pp.
473–474).Previously,
a
numberof
classes
ofcoprolites
Fig.
9.
Bony
fish
fossils
from
the
Crane
collection.
(A)
Small
block
(BRSMG
CD1588)
containing
ganoid
scales
with
calcite
cement.
(B–E)
Examples
of
Gyrolepis
albertii
scales,
showing
various
morphotypes
in
external
(B,
C,
E)
and
internal
(D)
views;
BRSMG
Cf7846.1
(B)
Cf7846.4
(C),
Cf7846.2
(D),
Cf7846.3
(E).
Scale
bar
is
1
mm
for
all
specimens.
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
587

Fig.
10.
Invertebrate
fossils
from
beds
3–5.
(A–D)
Barnacle
Eolepas
rhaetica
(BRSUG
29954-14-
29954-171).
(A–B)
Specimen
BRSUG
29954-14,
in
outer
(A)
and
inner
(B)
views,
showing
external
sculpture,
and
white
colour
of
phosphate
internally.
(C–D)
Specimen
BRSUG
29954-171,
in
outer
(C)
and
inner
(D)
views,
showing
external
sculpture,
and
black
colour
of
phosphate
internally.
(E–F)
Bivalves
Atreta
intusstriata,
partial
specimens
BRSUG
29954-17
(E)
and
BRSUG
29954-175
(F).
(G–I)
Cidarid
spines,
BRSUG
29954-17
(G),
BRSUG
29954-76
(H),
BRSUG
29954-77
(I).
(J)
Small
belemnite
or
cidaroid
spine,
BRSUG
29954-78.
(K–N)
Coprolites,
all
incomplete
and
missing
their
ends,
BRSUG
29954-49
(K),
BRSUG
29954-89
(L),
BRSUG
29954-90
(M),
BRSUG
29954-91
(N);
coprolites
L–N
show
spiral
ornament
at
different
sizes.
Scale
bar
equals
1
mm
for
(A–N)
and
2
mm
for
(E–J).
588
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

have
been
identified,
but
ours
all
appear
to
be
similar,
being
cylindrical
in
shape
and
marked
by
closely
spaced
spiral
structures.
They
are
likely
the
ejecta
of
one
of
the
fishes,
possibly
a
shark.
4.5.
Faunal
composition
and
comparison
Our
2018
collection
from
Hapsford
Bridge
comprises
1740
specimens.
Of
these,
763
are
identifiable
as
non-bone
fragments,
including
76
teeth
and
687
other
fossil
elements.
Of
the
chon-
drichthyan
remains,
five
teeth
belong
to
Synechodus
rhaeticus,
and
one
tooth
each
to
Lissodus
minimus
and
Duffinselache
holwellensis.
Of
the
osteichthyan
remains,
68
teeth
belong
to
Gyrolepis
albertii
and
10
to
Severnichthys
acuminatus.
Eolepas
rhaetica
barnacles
are
common,
with
45
valve
pieces
being
identified.
The
remaining
977
unidentifiable
fossils
comprise
scales,
denticles,
and
teeth.
In
comparing
the
six
samples,
the
first
(bed
2)
did
not
yield
any
fossils,
the
second
yielded
only
32,
but
third
to
sixth
were
much
richer,
with
542,
161,
835
and
170
individual
microvertebrate
fossils
in
each.
The
most
abundant
categories
were
unidentified
fish
remains
(899
specimens)
and
osteichthyan
scales
(594
specimens),
followed
by
Gyrolepis
teeth
(68),
barnacle
pieces
(45),
unidentified
teeth
(44)
and
denticles
(29).
Identifiable
shark
and
bony
fish
teeth
were
overall
quite
rare,
with
generally
<10
specimens
each.
Therefore,
comparing
the
relative
proportions
of
the
different
categories
between
the
five
fossiliferous
horizons
was
less
useful
than
we
had
expected,
unlike
in
the
case
of
the
Hampstead
Farm
Rhaetian
where
substantial
differences
were
found
in
faunal
composition
up
through
the
section
(Mears
et
al.,
2016).
Here
(Fig.
11 ),
we
can
say
that
Gyrolepis
teeth
are
generally
the
most
common
fossils
at
all
levels,
then
with
main
occurrences
of
Synechodus
and
Duffinselache
in
bed
5,
Synechodus
and
Lissodus
in
bed
8,
and
Severnichthys
in
beds
4–8.
When
compared
with
other
Rhaetian
bone
bed
sites,
the
ranges
and
proportions
of
species
differ,
but
our
sample
sizes
are
small,
and
many
specimens
are
abraded.
A
common
feature
is
the
relative
abundance
of
Gyrolepis
teeth
and
scales,
as
here,
but
Severnichthys
is
usually
relatively
more
abundant.
The
occurrence
of
Lissodus
confirms
these
are
basal
Westbury
Formation
bone
beds,
based
on
its
temporally
confined
occurrence
at
Hampstead
Farm
Quarry
(Mears
et
al.
2016,
Fig.
20).
Among
the
sharks,
the
absence
of
Rhomphaiodon
is
surprising,
as
it
is
usually
the
most
common
shark
tooth
in
other
British
Rhaetian
bone
beds
(Allard
et
al.,
2015;
Norden
et
al.,
2015;
Cross
et
al.,
2018).
Further
differences
are
the
occurrence
of
the
shark
Vallisia
coppi
and
the
barnacle
Eolepas
rhaetica
at
Hapsford
Bridge,
taxa
that
occur
only
rarely
elsewhere;
Vallisia
was
reported
from
Hampstead
Farm
Quarry
(Mears
et
al.
2016,
p.
487)
and
Manor
Farm
(Allard
et
al.,
2015,
p.
768).
Finally,
unlike
most
other
Rhaetian
bone
bed
sites,
we
do
not
find
teeth
of
the
durophagous
actinopterygians
Sargodon
and
Lepidotes.
Of
the
sharks,
Lissodus
was
likely
adapted
to
crushing
hard-
shelled
prey
with
its
long,
low
teeth.
The
other
sharks,
with
sharp
cusps
on
their
teeth,
were
presumably
predators
that
fed
on
other,
smaller
fishes.
The
actinopterygians
Gyrolepis
and
Severnichthys
were
also
predatory,
feeding
on
small
to
medium-sized
prey
respectively.
As
in
previous
Rhaetian
bone
bed
food
web
recon-
structions
(e.g.,
Cross
et
al.
2018,
Fig.15),
Gyrolepis
is
in
the
middle
of
the
food
chain,
probably
preying
on
invertebrates
and
smaller
fishes,
and
preyed
upon
by
Severnichthys
and
the
sharks.
The
durophagous
Lissodus
fed
on
molluscs
and
other
hard-shelled
prey.
5.
The
sub-Rhaetian
hardground
The
planed
upper
surface
of
the
Carboniferous
limestone
around
Vallis
Vale
forms
a
remarkable
hiatus
in
the
stratigraphic
column.
Not
only
does
it
mark
an
important
unconformity,
but
it
also
records
evidence
that
this
surface
was
a
hardground
in
the
Triassic
and
Jurassic.
Reynolds
(1912)
described
the
top-Carboniferous
surface
as
uneven
and
bored
in
places,
and
sometimes
colonised
by
oysters.
In
other
places,
the
surface
is
simply
flat,
described
by
Winwood
(1890)
as
‘planed
off
almost
as
level
as
a
billiard
table.’
Copp
(1980,
pp.
318–
327)
emphasized
how
the
surface
was
smooth
and
generally
not
bored
or
encrusted
over
most
of
the
Mendips.
However,
Tedbury
Camp
Quarry
(ST
747489),
west
of
Vallis
Vale,
shows
an
extensive,
cleared
surface
of
the
top
of
Carboniferous
limestone,
with
bivalve
encrustation
and
intensive
borings
assigned
to
three
ichnotaxa,
Gastrochaenolites
and
two
species
of
Trypanites,
the
smaller
being
T.
Fig.
11.
Relative
proportions
of
key
fossils
in
six
fossiliferous
samples
from
beds
2,
3,
4,
5,
6,
and
8
(Fig.
4C)
respectively.
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Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
589

weisei
and
the
larger
T.
fosteryeomani
(Cole
and
Palmer,
1999).
The
Gastrochaenolites
boring
is
a
living
crypt
of
a
rock-boring
bivalve
much
like
that
of
modern
Lithophaga,
and
the
Trypanites
borings
are
usually
ascribed
to
worms
(Kelly
and
Bromley,
1984).
The
planing,
boring
and
encrustation
of
the
surface
were
dated
to
the
Middle
Jurassic
by
those
authors
based
on
the
age
of
the
immediately
overlying
Inferior
Oolite,
which
also
infills
the
borings.
Other
such
exposures
with
bored
hardground
surfaces
are
seen
in
Torr
Works
and
on
the
road
near
Holwell.
The
Vallis
Vale
Rhaetian
is
also
a
source
of
bored
and
encrusted
pebbles
of
Carboniferous
limestone,
which
occur
in
the
basal
mudstones
and
in
the
bone
bed.
Richardson
(1911)
noted
these
at
several
locations,
and
Copp
(1980,
pp.
327–340)
reported
several
examples
from
Vallis
Vale. One specimen
(Fig.12A,B)
shows
numerous
borings
of
two
size
classes,
0.8–0.9
mm
and
3–4
mm
in
diameter,
and
both
up
to
10
mm
long.
Two
or
three
shallow
borings,
4–6
mm
in
diameter
and
6–10
mm
deep,
have
a
flask-like
shape,
broader
at
the
rounded
base
and
with
a
narrower
neck
(the
‘clavate’
shape).
Note
that
the
borings
occur
on
one
side
only
of
the
flat
pebbles,
suggesting
that
the
boring
happened
before
the
clasts
were
uplifted.
These
three
borings
are
the
two
species
of
Trypanites
and
the
one
species
of
Gastrochaenolites
identified
by
Cole
and
Palmer
(1999)
at
Tedbury
Camp,
confirming
the
temporal
longevity
of
these
trace
fossils.
Some
of
the
pebbles
(e.g.,
Fig.
12C,
D)
are
also
encrusted
with
examples
of
two
bivalves,
Atreta
intusstriata
and
the
oyster
Liostrea,
both
typical
of
the
Rhaetian
(Swift,
1999).
This
confirms
that
uplift
and
tumbling
of
the
pebbles
happened
in
the
Rhaetian,
when
they
became
encrusted
as
they
lay
on
the
sea
floor
and
before
burial.
These
pebbles
confirm
that
the
Carboniferous
limestone
top
surface
formed
a
hardground
under
the
advancing
Rhaetian
sea,
and
here
and
there
the
energy
of
the
Rhaetian
waters
tore
up
chunks
of
that
hardground,
retaining
the
borings,
but
tumbling
and
abrading
the
pebbles
before
they
were
redeposited
(Fig.
11 E,
F).
Then,
some
of
them
became
encrusted
by
oysters
in
the
shallow
Fig.12.
Reworkedpebblesof Carboniferouslimestonefrom the basalbeds
of
theWestburyFormation.(A,B)One pebble (BRSMGCd384), inupper (A)
and
lateral(B)
views,showing
Trypanites
and
Gastrochaenolites
borings.
(C,
D)
A
larger
pebble
(BRSMG
Cd382),
in
upper
(C)
and
lower
(D)
views,
showing
Trypanites
and
Gastrochaenolites
borings,
overlaid
by
encrusting
bivalves
Liostreaand
Atreta.Note
the
Rhaetian
greyclay infilling
Gastrochaenolites
borings
(C).
(EG)
Inferredhistory,
as
encrusting
worms
and
bivalves
make
Trypanites
and
Gastrochaenolites
borings,
respectively,
presumably
in
earliest
Rhaetian
times
(E),
and
then
some
surface
layers
of
the
Carboniferous
pavement
is
stripped
off,
and
the
fragments
tumbled
and
abraded,
before
settling
on
the
seabed
and
becoming
encrusted
by
bivalves
(F),
and
finally
burial
in
basal
Westbury
Formation
sediments
(G).
590
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

marine
waters
of
the
Rhaetian.
In
detail,
the
assumed
sequence
of
events,
based
on
our
evidence
of
bored
pebbles
in
the
basal
units
of
the
Westbury
Formation,
is:
1
uplift
and
subaerial
erosion
of
the
Carboniferous
limestone;
2
flooding
by
the
latest
Norian
or
earliest
Rhaetian
sea;
3
development
of
hardground
in
which
bivalves,
worms,
and
others
bored
into
the
limestone
for
protection
and
to
recycle
calcium
carbonate
ions
into
their
own
skeletons;
4
influx
of
rough
waters,
perhaps
associated
with
the
formation
of
the
first
conglomeratic
bone
bed,
and
tearing
of
pebbles
from
the
seabed;
5
transport
of
debris,
including
pieces
of
the
hardground
surface,
and
deposition
together
with
other
debris;
6
encrusting
of
some
pebbles
by
oysters
and
other
bivalves
before
eventual
burial.
6.
Rhaetian
storm
beds
We
identified
putative
storm
bed
sediments
at
three
levels
in
the
Westbury
Formation
(Fig.
5C),
in
the
muddy
limestone
containing
the
‘basal’
bone
bed
(Fig.
13A,
B),
in
the
calcareous
mudstone
60
cm
above
(Fig.
13C,
D),
and
in
the
muddy
limestone
a
further
43
cm
above
(Fig.
13E,
F).
When
cut
vertically,
these
muddy
limestone
blocks
show
suspended
conglomerates.
The
first
example
(Fig.
13A,
B)
shows
a
limited
intraformational
conglom-
eratic
layer
comprising
some
mudstone
clasts,
and
abundant
shelly
debris
in
an
otherwise
fine-grained
limestone.
The
second
and
third
examples
(Fig.
13C–F)
show
some
large
(up
to
10
cm
diameter),
well-rounded
clasts
of
grey
brown
and
yellow-coloured
mudstone,
all
of
which
match
bedded
sediments
in
the
Westbury
Formation
succession.
Around
these
larger
clasts,
there
is
a
finer
mush
of
1–3
cm
rounded
pebbles
and
debris
of
<
10
mm
diameter.
The
sediment
above
and
below
is
fine-
to
medium-grained
muddy
and
silty
limestone.
We
interpret
these
as
suspended
conglomerates
as
they
are
located
in
the
middle
of
sedimentary
beds
that
lack
all
sign
of
grading.
Further,
they
include
largely
reworked
autochthonous
debris,
and
some
of
it
relatively
soft
sediment
that
has
evidently
not
been
transported
far,
presumably
eroded
and
deposited
from
underlying
Rhaetian-aged
sediments.
There
are
two
kinds
of
conglomerates
at
Hapsford
Bridge,
both
indicating
storm
bed
deposition.
First,
the
flat
pebbles
(Fig.
12)
presumably
formed
part
of
a
flat-pebble
conglomerate,
a
kind
of
deposit
long
interpreted
as
direct
evidence
of
storm
wave
activity
(Bourgeois
and
Leithold,
1984;
Myrow
et
al.,
2004),
indicating
high
energy,
churning
currents
that
ripped
up
pebbles
from
the
seabed
and
dumped
them,
often
chaotically
in
basal
storm
deposits.
Second,
the
intraformational
suspended
conglomerate
layers
(Fig.
13)
also
indicate
storm
activity.
Conglomerates
usually
show
grading,
as
water
currents
diminish
or
increase
in
energy,
but
here,
Fig.
13.
Inferred
storm
beds
from
different
levels
in
the
Westbury
Formation.
(A,
B)
Bed
4
muddy
limestone,
(C,
D)
Bed
6
limestone,
and
(E,
F)
Bed
8
conglomeratic
mudstone,
showing
photographs
of
slabbed
sections
(A,
C,
E)
and
interpretive
sketches
(B,
D,
F).
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
591

otherwise
fine-grained
sediments
are
suddenly
visited
by
a
pulse
of
large
clasts
from
local
sources.
These
are
analogous
to
suspended
coquinas,
shell
beds
that
unexpectedly
occur
in
the
midst
of
otherwise
low-energy,
fine-grained
sediment
beds
(e.g.,
Benton
and
Gray,
1981;
Puga-Bernabéu
and
Aguirre,
2017),
where
the
storm
surge
ebb
current
deposits
clasts
that
had
been
picked
up
during
the
earlier
storm
surge.
This
is
why
clasts
are
intraforma-
tional,
sometimes
from
unconsolidated
underlying
beds,
often
heterogeneous
and
generally
a
sudden
layer,
with
no
sign
of
grading.
Storm
bed
deposition
within
the
Westbury
Formation
has
long
been
accepted
(Suan
et
al.,
2012).
Indeed,
Short
(1904,
p.
181)
was
first
to
propose
this
model.
He
noted
that
the
Rhaetian
basal
bone
bed
must
have
been
laid
down
in
shallow
seas,
but
that
it
could
not
be
a
strandline
conglomerate
because
it
is
laterally
extensive,
although
discontinuous.
He
then
proposed
that
the
bone
bed
is
a
storm
deposit
for
three
reasons:
it
is
not
always
basal
and
so
is
not
caused
by
the
‘first
inrush
of
the
Rhaetic
sea’;
the
causes
must
have
been
similar
over
England
and
much
of
Europe;
the
water
movements
were
sufficient
to
transport
debris
of
various
sizes,
and;
it
was
associated
with
the
death
of
many
fishes
and
marine
reptiles.
Short
(1904,
p.
182)
goes
on
to
cite
modern
analogues
where
violent
storms
rushed
onshore
killing
many
fishes,
and
then
the
ebb
current
dragged
carcasses
back
down
to
below
wave
base.
The
storm
model
for
the
basal
bone
bed
was
elaborated
by
Macquaker
(1994,
1999)
particularly
to
explain
the
jumbled
nature
of
the
fossil
bones,
in
many
cases
bringing
heavily
abraded
larger
bone
clasts
into
contact
with
smaller,
and
unabraded
material.
He
presented
evidence
that
storm
beds
with
shells
or
lacking
fossils,
as
here,
correspond
to
times
of
shallow
water,
whereas
storm-
deposited
bone
beds
correspond
to
times
of
water-deepening,
where
they
mark
the
final
phase
of
a
coarsening-upward
sequence,
when
a
high-energy
flow
erodes
into
pre-existing
sediment
and
the
often
heavily
abraded
bone
debris
is
finally
dumped.
Rhaetian
bone
beds
may
be
mixed
in
this
way,
comprising
phosphatic
bones,
teeth
and
coprolites
that
represent
multiple
cycles
of
erosion
and
deposition,
as
at
Aust
(Trueman
and
Benton,
1997;
Cross
et
al.,
2018),
or
they
may
comprise
elements
that
all
show
similar
amounts
of
abrasion,
as
at
Hapsford
Bridge.
Further,
as
Korneisel
et
al.
(2015)
noted,
the
base
of
the
basal
Rhaetian
bone
bed
is
often
heavily
burrowed,
and
those
burrows
may
be
filled
with
bone
bed
debris
which
even
shows
meniscate
structures
as
evidence
that
the
crustaceans
that
made
the
burrows
were
scrambling
through
and
packing
the
bone
bed
debris
in
them.
7.
Discussion
The
Hapsford
Bridge
Penarth
Group
succession
shows
the
usual
marine
characteristics
as
widely
seen
in
the
Rhaetian.
The
lower
portions
of
the
Westbury
Formation
were
deposited
presumably
close
to
shore,
and
our
evidence
(Fig.
13)
suggests
that
storm
activity
was
frequent.
Suan
et
al.
(2012)
noted
five
cycles
of
climate
change
throughout
the
time
of
deposition
of
the
Westbury
Formation,
each
marked
by
a
pulse
of
organic
carbon
enrichment.
At
times
of
water
deepening,
abundant
phosphate
was
generated,
corresponding
to
successions
of
black,
anoxic
mudstones
and
rich
bone
beds,
and
the
phosphate
drove
enhanced
productivity
in
the
oxygenated
ocean
above.
The
pale-coloured
limestones
and
mudstones
represent
shallower
waters,
often
with
abundant
invertebrate
life
living
on
the
seabed.
Sharp
changes
in
climate,
sea
level
and
carbon
cycling
through
the
1–2
Myr
duration
of
deposition
of
the
Westbury
Formation
may
have
been
triggered
by
eruptions
of
the
Central
Atlantic
Magmatic
Province,
changing
topography
of
land
and
seabed,
and
altering
runoff
and
phosphorus
input
to
the
oceans
(Suan
et
al.,
2012).
Storm
beds
produced
both
within
the
phosphate-rich
black
anoxic
sediments
and
the
oxygenated
shell-rich
pale-coloured
limestones
and
mudsbysurge
ebb
currentsare
evidence
for
the
sharplychanging
climates
triggered
by
the
first
phases
of
opening
of
the
North
Atlantic.
Higher
portions
of
the
Westbury
Formation
may
have
been
deposited
under
lower
energy
conditions,
represented
by
fine-
grained
sediments.
These
sediments
might
have
been
near-shore,
as
suggested
by
fossils
such
as
the
liverwort
Naiadita
and
the
conchostracan
Euestheria,
as
well
as
reported
terrestrial
insect
remains
(BRSMG
collections).
The
Hapsford
Bridge
locality
provides
new
evidence
about
the
palaeotopography
of
the
Mendips
area.
Farrant
et
al.
(2014)
noted
a
series
of
unconformities
in
the
Mendips,
starting
with
the
Late
Triassic
Dolomitic
Conglomerate,
which
erodes
and
recycles
Carboniferous
limestone
fragments,
and
fills
fissures
at
many
localities.
Further
incursions
of
the
sea
in
the
Early
and
Middle
Jurassic
created
substantial
unconformities,
including
the
De
la
Beche
unconformity
and
Tedbury
Camp,
as
well
as
sediment-filled
fissures
(‘Neptunean
dykes’)
formed
in
the
Carboniferous
lime-
stone
by
tectonic
extension.
Farrant
et
al.
(2014)
report
Cretaceous
sediment
unconformably
in
contact
with
Silurian
and
Devonian
rocks,
and
evidence
for
progressive
westward
overstep
of
the
Mendip
Island,
from
Frome
to
Tadhill,
the
site
of
the
Cretaceous
level.
Our
evidence
from
Hapsford
Bridge
provides
an
older
line
of
overstep
that
reached
a
point
between
Hapsford
Bridge
and
the
De
la
Beche
unconformity.
There
may
have
been
two
or
three
Late
Triassic
overstep
phases
as
sea
levels
rose,
depending
on
the
age
of
the
“Dolomitic
Conglomerate”,
a
Triassic
terrestrial
red
bed
lithology
containing
reworked
Carboniferous
(Farrant
et
al.,
2014)
as
well
as
two
Rhaetian-aged
overstep
phases,
the
one
reported
here
at
the
base
of
the
Westbury
Beds,
and
a
second
one
at
the
Triassic-Jurassic
boundary.
There
was
a
younger
hardground,
reported
from
the
top
of
the
Langport
Member
(uppermost
Rhaetian),
on
the
upper
surface
of
the
“Sun
Bed”,
at
localities
near
Bristol,
Radstock,
and
Wells.
Copp
(1980,
pp.
343–357)
provides
a
detailed
account
of
this
hardground
at
Hapsford
Bridge,
on
top
of
a
bed
that
is
8
cm
thick,
and
bored
through
by
abundant
slender
Trypanites,
clavate
Gastrochaenolites,
and
burrows
and
borings
that
are
broader
and
may
penetrate
the
entire
thickness.
Sea
levels
around
the
Mendips
rose
episodically,
perhaps
interspersed
with
sea-level
falls,
throughout
the
Mesozoic,
from
the
Late
Triassic
to
mid-Cretaceous.
The
sequential
overstep
from
east
to
west
up
the
flanks
of
the
Mendip
island
chain
is
marked
by
littoral
facies
and
hardgrounds
of
Bajocian,
Bathonian,
Callovian,
and
Albian
age
stretching
along
a
10
km
east-west
transect
from
Frome
to
Tadhill(Farrant
et
al.,
2014,
Fig.
8).
We
nowadd two
Rhaetianlevels to
the
east,
both
of
them
lying
lower
topographically.
At
each
of
the
hardground
levels,
whatever
the
age,
the
same
Carboniferous
limestone
basement
was
eroded
and
planed
(‘trimmed’
by
the
waves),
bored
by
various
animals
living
in
shallow
sea
waters,
and
then
inundated
by
high-energy
sediment-laden
currents,
that
at
times
(e.g.,
Hapsford
Bridge,
Tedbury
Camp)
eroded
the
surface
layers
and
redeposited
pebbles
of
the
hardground.
Further
work
in
and
around
Vallis
Vale
is
likely
to
shed
light
on
the
nature
of
the
Rhaetian
Transgression
and
how
it
reshaped
the
landscape
over
south-western
England.
It
is
remarkable
that
this
area
provides
evidence
for
five
or
more
stages
in
the
inundation
of
the
landscape,
spanning
some
100
Myr
(35
Myr
from
Rhaetian
to
Bathonian,
and
then
60
Myr
from
Bathonian
to
Albian)
and
all
located
geographically
so
close
together.
Declaration
of
Competing
Interest
The
authors
declare
that
they
have
no
known
competing
financial
interests
or
personal
relationships
that
could
have
appeared
to
influence
the
work
reported
in
this
paper.
592
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594

Acknowledgements
We
thank
Tom
Davies
for
assistance
with
photomicroscopy,
and
Doug
Robinson,
Jack
Lovegrove
and
Joseph
Flannery
Sutherland
who
assisted
with
the
fieldwork
and
photos
at
the
Hapsford
Bridge
locality.
We
thank
Judy
Copp
for
providing
us
with
a
copy
of
Charles
Copp’s
unpublished
thesis,
and
Derrick
Hunt
and
Simon
Bowditch
for
providing
supporting
information
and
historical
perspectives
on
Vallis
Vale.
The
paper
arises
from
a
summer
undergraduate
internship
by
J.R.
in
the
Bristol
Paleobiology
laboratories
in
2018–2019.
We
thank
Andy
Farrant
(BGS)
and
one
anonymous
referee
for
immensely
helpful
comments
that
led
to
widespread
revisions
of
the
MS.
Appendix
A.
Supplementary
data
Supplementary
material
related
to
this
article
can
be
found,
in
the
online
version,
at
doi:https://doi.org/10.1016/j.
pgeola.2020.02.005.
References
Agassiz,
J.L.R.,
1833–1844 .
Recherches
sur
les
Poissons
Fossiles.
Tome
3
concernant
l’histoire
de
l’ordre
des
Placoïdes.
Imprimerie
Petitpierre,
Neuchâtel
390
+
34
pp.
Allard,
H.,
Carpenter,
S.C.,
Duffin,
C.J.,
Benton,
M.J.,
2015.
Microvertebrates
from
the
classic
Rhaetian
bone
beds
of
Manor
Farm
Quarry,
near
Aust
(Bristol,
UK).
Proceedings
of
the
Geologists’
Association
126,
762–776.
Anonymous,
1898.
Vallis
Vale
Limestone
Quarries.
The
Quarry
1898,
153–156.
Atthill,
R.,
1984.
Old
Mendip.
Bran’s
Head,
Frome
164
pp..
Benton,
M.J.,
Gray,
D.I.,
1981.
Lower
Silurian
distal
shelf
storm-induced
turbidites
in
the
Welsh
Borders:
sediments,
tool
marks
and
trace
fossils.
Journal
of
the
Geological
Society,
London
138,
675–694.
Boomer,
I.D.,
Duffin,
C.J.,
Swift,
A.,
1999.
Arthropods
1:
crustaceans.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group.
Palaeontological
Association
Field
Guide
to
Fossils,
9.
Palaeontological
Association,
London,
pp.
129–14 8.
Bourgeois,
J.,
Leithold,
E.L.,
1984.
Wave-worked
conglomerates
–
depositional
processes
and
criteria
for
recognition.
Memoirs
of
the
Canadian
Society
of
Petroleum
Geologists
10,
331–343.
Buckland,
W.,
Conybeare,
W.D.,
1824.
Observations
on
the
south-western
coal
district
of
England.
Transactions
of
the
Geological
Society
of
London
2,
210–316.
Cappetta,
H.,
2012.
Volume
3E:
Chondrichthyes.
Mesozoic
and
Cenozoic
Elasmobranchii:
Teeth.
In:
Schultze,
H.-P.
(Ed.),
Handbook
of
Paleoichthyology.
Verlag
Dr
Friedrich
Pfeil,
München.
Cole,
A.R.,
Palmer,
T.J.,
1999.
Middle
Jurassic
worm
borings,
and
a
new
giant
ichnospecies
of
Trypanites
from
the
Bajocian/Dinantian
unconformity,
southern
England.
Proceedings
of
the
Geologists’
Association
110 ,
203–209.
Copp,
C.,
1980.
Fissure
deposits
and
early
Mesozoic
paleogeography
of
the
Eastern
Mendips.
Unpublished
PhD
Thesis.
University
of
Keele
668
pp..
Cox,
L.R.,
1941.
Easter
Field
Meeting.
Proceedings
of
the
Geologists
Association
52,
16–35.
Cross,
S.R.R.,
Ivanovski,
N.,
Duffin,
C.J.,
Hildebrandt,
C.,
Parker,
A.,
Benton,
M.J.,
2018.
Microvertebrates
from
the
basal
Rhaetian
Bone
Bed
(latest
Triassic)
at
Aust
Cliff,
S.W.
England.
Proceedings
of
the
Geologists’
Association
129,
635–653.
Cuny,
G.,
Benton,
M.J.,
1999.
Early
radiation
of
the
neoselachian
sharks
in
Western
Europe.
Geobios
32,
193 –204.
De
la
Beche,
H.T.,
1846.
On
the
Formation
of
the
Rocks
of
South
Wales
and
South
Western
England.
Memoirs
of
the
Geological
Survey
of
Great
Britain
1,
1–296.
Duff,
K.L.,
McKirdy,
A.P.,
Harley,
M.J.,
1985.
New
Sites
for
Old;
A
Students’
Guide
to
the
Geology
of
the
East
Mendips.
Nature
Conservancy
Council,
Peterborough
189
pp..
Duffin,
C.J.,
1982.
Teeth
of
a
new
selachian
from
the
Upper
Triassic
of
England.
Neues
Jahrbuch
für
Geologie
und
Paläontologie,
Monatshefte
1982,
156 –166.
Duffin,
C.J.,
1998.
New
shark
remains
from
the
British
Rhaetian
(latest
Triassic).
2.
Hybodonts
and
palaeospinacids.
Neues
Jahrbuch
für
Geologie
und
Palaöntologie,
Monatshefte
1998,
pp.
240–256.
Duffin,
C.J.,
1999.
Fish.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group.
Palaeontological
Association
Field
Guide
to
Fossils,
9.
Palaeontological
Association,
London,
pp.
215–216.
Duffin,
C.J.,
Coupatez,
P.,
Lepage,
J.-C.,
Wouters,
G.,
1983.
Rhaetian
(Upper
Triassic)
marine
faunas
from
“Le
golfe
du
Luxembourg”
in
Belgium
(preliminary
note).
Bulletin
de
la
Société
Belge
de
Géologie
92,
311–315.
Emmrich,
H.F.,
1853.
Geognostische
Beobachtungen
aus
den
östlichen
bayerischen
und
den
angrenzenden
österreichischen
Alpen.
Jahrbuch
der
Kaiserlich-
Königlichen
Geologischen
Reichsanstalt
4,
326–394.
Farrant,
A.R.,
Vranch,
R.D.,
Ensom,
P.C.,
Wilkinson,
I.P.,
Woods,
M.A.,
2014.
New
evidence
of
the
Cretaceous
overstep
of
the
Mendip
Hills,
Somerset,
UK.
Proceedings
of
the
Geologists’
Association
125,
63–73.
Förster,
R.,
Crane,
M.,
1984.
A
new
species
of
the
penaeid
shrimp
AegerMunster
Crustacea,
Decapoda
from
the
Upper
Triassic
of
Somerset,
England.
Neues
Jahrbuch
für
Geologie
und
Palaeontologie,
Monatshefte
1984,
455–462.
Foundations
of
the
Mendips,
2017.
British
Geological
Survey
website.
.
(accessed
June
2019)
https://www.bgs.ac.uk/mendips/home.htm.
Gale,
A.,
Schweigert,
G.,
2016.
A
new
phosphatic-shelled
cirripede
(Crustacea,
Thoracica)
from
the
Lower
Jurassic
(Toarcian)
of
Germany
–
the
oldest
epiplanktonic
barnacle.
Palaeontology
59,
58–70.
Ivimey-Cook,
H.C.,
Hodges,
P.,
Swift,
A.,
Radley,
J.D.,
1999.
Bivalves.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group.
Palaeontological
Association
Field
Guide
to
Fossils,
9.
Palaeontological
Association,
London,
pp.
83–127.
Jones,
T.R.,
1862.
A
monograph
of
the
fossil
Estheriae.
Monograph
of
the
Palaeontographical
Society
134
pp..
Kelly,
S.R.A.,
Bromley,
R.G.,
1984.
Ichnological
nomenclature
of
clavate
borings.
Palaeontology
27,
793–807.
Korneisel,
D.,
Gallois,
R.W.,
Duffin,
C.J.,
Benton,
M.J.,
2015.
Latest
Triassic
marine
sharks
and
bony
fishes
from
a
bone
bed
preserved
in
a
burrow
system
from
Devon,
UK.
Proceedings
of
the
Geologist’s
Association
126,
130–14 2.
Landon,
E.N.,
Duffin,
C.J.,
Hildebrandt,
C.,
Davies,
T.G.,
Simms,
M.J.,
Benton,
M.J.,
2017.
The
first
discovery
of
crinoids
and
cephalopod
hooklets
in
the
British
Triassic.
Proceedings
of
the
Geologists’
Association
128,
360–373.
Loupekine,
I.S.,
1956.
Mining
and
quarrying
in
the
Bristol
district,
1955.
Proceedings
of
the
Bristol
Naturalists’
Society
29,
155–16 1.
Lukic-Walther,
M.,
Brocklehurst,
N.,
Kammerer,
C.F.,
Fröbisch,
J.,
2019.
Diversity
patterns
of
nonmammalian
cynodonts
(Synapsida,
Therapsida)
and
the
impact
of
taxonomic
practice
and
research
history
on
diversity
estimates.
Paleobiology
45,
56–69.
MacQuaker,
J.H.S.,
1994.
Palaeoenvironmental
significance
of
‘bone-beds’
in
organic-rich
mudstone
successions:
an
example
from
the
Upper
Triassic
of
south
west
Britain.
Zoological
Journal
of
the
Linnean
Society
112 ,
285–308.
MacQuaker,
J.H.S.,
1999.
Aspects
of
the
sedimentology
of
the
Westbury
Formation.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group.
The
Palaeontological
Association,
London,
pp.
39–48.
McMurtrie,
J.,
1885.
Notes
of
Autumn
excursions
on
the
Mendips.
Proceedings
of
the
Bath
Natural
History
and
Antiquarian
Field
Club
5,
98–111.
Mears,
E.,
Rossi,
V.,
MacDonald,
E.,
Coleman,
G.,
Davies,
T.G.,
Riesgo,
C.,
Hildebrandt,
C.,
Thiel,
H.,
Duffin,
C.J.,
Whiteside,
D.I.,
Benton,
M.J.,
2016.
The
Rhaetian
vertebrates
of
Hampstead
Farm
Quarry,
Gloucestershire,
UK.
Proceedings
of
the
Geologists’
Association
127,
478–505.
Moore,
C.,
1861.
On
the
zones
of
the
Lower
Lias
and
the
Avicula
contorta
Zone.
Quarterly
Journal
of
the
Geological
Society
17,
483–517.
Moore,
C.,
1867.
On
abnormal
conditions
of
secondary
deposits
when
connected
with
the
Somersetshire
and
South
Wales
Coal
Basin;
and
on
the
age
of
the
Sutton
and
Southerndown
Series.
Quarterly
Journal
of
the
Geological
Society
of
London
23,
449–568.
Moore,
C.,
1875.
Geological
characteristics
of
Vallis.
Proceedings
of
the
Somerset
Archaeological
and
Natural
History
Society
21,
31–39.
Moore,
C.,
1881.
On
abnormal
geological
deposits
in
the
Bristol
district.
Quarterly
Journal
of
the
Geological
Society
of
London
37,
67–82.
Myrow,
P.M.,
Tice,
L.,
Archuleta,
B.,
Clark,
B.,
Taylor,
J.F.,
Ripperdan,
R.L.,
2004.
Flat-
pebble
conglomerate:
its
multiple
origins
and
relationship
to
meter-scale
depositional
cycles.
Sedimentology
51,
973–996.
Orbell,
G.,
1973 .
Palynology
of
the
British
Rhaeto-Liassic.
Bulletin
of
the
Geological
Survey
of
Great
Britain
44,
1–44.
Prudden,
H.C.,
2006.
New
uses
for
former
mineral
workings
in
Somerset.
Geoscience
in
south-west
England.
Proceedings
of
the
Ussher
Society
11,
249–251.
Puga-Bernabéu,
A.,
Aguirre,
J.,
2017.
Contrasting
storm
versus
tsunami-related
shell
beds
in
shallow-water
ramps.
Palaeogeography,
Palaeoclimatology,
Palaeoecology
471,
1–14.
Quarry
Faces
website,
2019.
Whatley
Quarry
available
from:.
.
www.quarryfaces.
org.uk/siteDetails.php?siteID=7.
Reynolds,
S.,
1912.
A
Geological
Excursion
Handbook
for
the
Bristol
District.
J.W.
Arrowsmith,
Bristol
224
pp..
Reynolds,
S.H.,
Richardson,
L.,
1909.
Excursion
to
Shepton
Mallet
and
Frome
district.
Proceedings
of
the
Cotteswold
Naturalist
Field
Club
16,
223–230.
Richardson,
L.,
1907.
Inferior
Oolite
and
contiguous
deposits
of
the
Bath
Doulting-
district.
Quarterly
Journal
of
the
Geological
Society
of
London
63,
383–423.
Richardson,
L.,
1909.
Excursion
to
the
Frome
district.
Proceedings
of
the
Geologists’
Association
21,
209–228.
Richardson,
L.,
1911.
The
Rhaetic
and
contiguous
deposits
of
West,
Mid,
and
part
of
East
Somerset.
Quarterly
Journal
of
the
Geological
Society
of
London
67,
1–74.
Richardson,
L.,
Young,
G.,
1909.
Excursion
to
the
Frome
district,
Somerset
May
28
th
to
June
1
st
.
Proceedings
of
the
Geologists’
Association
21,
209–228.
Savage,
R.J.G.,
1977.
The
Mesozoic
strata
of
the
Mendip
Hills.
In:
Savage,
R.J.G.
(Ed.),
Geological
Excursions
in
the
Bristol
District.
University
of
Bristol,
Bristol,
pp.
85–100.
Short,
A.R.,
1904.
A
description
of
some
Rhaetic
sections
in
the
Bristol
district,
with
considerations
on
the
mode
of
deposition
of
the
Rhaetic
Series.
Quarterly
Journal
of
the
Geological
Society
60,
170 –193 .
Slater,
T.,
Duffin,
C.,
Hildebrandt,
C.,
Davies,
T.,
Benton,
M.,
2016.
Microvertebrates
from
multiple
bone
beds
in
the
Rhaetian
of
the
M4–M5
motorway
junction,
South
Gloucestershire,
U.K.
Proceedings
of
the
Geologists’
Association
127,
464–477.
Stokes,
P.,
1999.
Yesterday’s
Mendip.
Mendip’s
Past:
A
Shared
Inheritance.
Mendip
District
Council.
Doveton
Press,
Bristol
61
pp..
Storrs,
G.W.,
1994.
Fossil
vertebrate
faunas
of
the
British
Rhaetian
(latest
Triassic).
Zoological
Journal
of
the
Linnean
Society
112 ,
217–259.
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594
593

Suan,
G.,
Föllmi,
K.B.,
Adatte,
T.,
Bormou,
B.,
Spangenberg,
J.E.,
Van
De
Schootbrugge,
B.,
2012.
Major
environmental
change
and
bone
bed
genesis
prior
to
the
Triassic–Jurassic
mass
extinction.
Journal
of
the
Geological
Society,
London
169,
191–200.
Swift,
A.,
1999.
Echinoderms.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group,
Palaeontological
Association
Field
Guide
to
Fossils,
9.
Palaeontological
Association,
London,
pp.
161–16 7.
Swift,
A.,
Duffin,
C.J.,
1999.
Trace
fossils.
In:
Swift,
A.,
Martill,
D.M.
(Eds.),
Fossils
of
the
Rhaetian
Penarth
Group.
Palaeontological
Association
Field
Guide
to
Fossils,
9.
Palaeontological
Association,
London,
pp.
239–250.
Thornes,
R.,
2015.
Quarry
Faces:
The
Story
of
Mendip
Stone.
Ash
Tree
Publications,
Newton
Abbot
215
pp..
Trueman,
C.N.,
Benton,
M.J.,
1997.
A
geochemical
method
to
trace
the
taphonomic
history
of
reworked
bones
in
sedimentary
settings.
Geology
25,
263–266.
von
Huene,
E.,
1933.
Zur
Kenntnis
der
württemburgischen
Rhätbonebeds
mit
Zahnfunden
neuer
Säuger
und
säugerähnlichen
Reptilien.
Jahreshefte
des
Vereins
für
väterländische
Naturkunde
in
Württemberg
1933,
65–128.
Wall ,
G.,
Jenkyns,
H.,
2004.
The
age,
origin
and
tectonic
significance
of
Mesozoic
sediment-filled
fissures
in
the
Mendip
Hills
(SW
England):
implications
for
extension
models
and
Jurassic
sea-level
curves.
Geological
Magazine
141,
471–504.
Warrington,
G.,
1984.
Late
Triassic
palynomorph
records
from
Somerset.
Proceedings
of
the
Ussher
Society
6,
29–34.
Winwood,
H.H.,
1890.
Rhaetic
section
at
Luckington
and
additional
notes
on
the
Vobster
Quarry.
Proceedings
of
the
Bath
Natural
History
and
Antiquarian
Field
Club
7,
45–49.
Woodward,
H.,
1890.
Brief
notes
on
the
geology
of
the
Mendip
Hills
with
reference
to
the
long
excursion,
August
4
th
to
9
th
1890.
Proceedings
of
the
Geologists’
Association
11,
481–494.
594
J.
Ronan
et
al.
/
Proceedings
of
the
Geologists’
Association
131
(2020)
578–594