waterloo bay, larne, northern ireland: a potential global
TRANSCRIPT
Michael J. SimmsDepartment of Geology, Ulster Museum, Botanic Gardens, Belfast BT9 5AB, Northern Ireland. [email protected]
Andrew J. Jeram, Mullaghdubh House, 27 Gobbins Path, Islandmagee, Co. Antrim BT40 3SP, Northern Ireland. [email protected]
amm
onite
s ab
sent
Pla
norb
is S
ubzo
ne
Lils
tock
Fm
Lang
port
Mem
ber
29
Blu
e Li
as F
orm
atio
n
25
16
12
8
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432
1
14
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24
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LIA
S
GR
OU
PP
EN
AR
TH
GR
OU
P
m s fs
123
45a5b67
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9
8
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cm
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SB
TST
SB
HST
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22a
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1716
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FSST
echinoid horizon
mudcracked horizon
gutter casts
gutter casts
ripples
? 3rd order cycles ? 4th order cycles
CYCLOSTRATIGRAPHY
pale grey mudstone/shale
dark grey mudstone/shale
medium grey mudstone/shale
very dark grey mudstone/shale
limestone
marl
heterolith, mm-cm scale
shale
KEY
articulated ichthyosaur
bone bed
bivalve bed with Cardinia in life position
? 2nd order
rise fall > >
continues up to Bucklandi Zone
continues down to MerciaMudstone Group (Norian)
LO conodonts(England)
dysaerobic?
FO - crinoids (Isocrinus sp. nov.)
Psiloceras erugatum
Neophyllites imitans
Neophyllites antecedens
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28c
28b
28a
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25
24
23b
23a
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33a
33b
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33c
33d
33e
33f
33g
TST
HST
MFS
FSST
22b
22c
22d
recovery fauna
top
Cot
ham
Mem
ber
Lang
port
Mem
ber
HS
T/R
egre
ssio
n A
sym
met
ric B
undl
eM
FS
Con
dens
ed B
undl
eT
rans
gres
sive
Bun
dle
Ero
sion
al tr
unca
tion
TC
TC?
TC
biva
lve
conc
entr
atio
nsM
odio
lus
horiz
ons
Lios
trea
ban
dsab
unda
nt tr
ace
foss
ils
SEQUENCESTRATIGRAPHY
turb
idite
s
Psiloceras planorbis
Psiloceras sampsoniand cf. sampsoni
Psiloceras plicatulumand cf. plicatulum
Caloceras spp.
on this poster
What has the Larne section to offer as a potential GSSP?
Exceptional stratigraphic thicknessThe Triassic-Jurassic boundary succession at Larne is significantly thicker, and experienced more continuous deposition, than correlative strata at St Audrie’s Bay or at any other site in NW Europe. It offers potential for refining the isotope curve of Hesselbo et al. (2002; Geology, 30, 251-254) to a significantly higher resolution.
Diverse macro- and microfauna and floraThe fossil macro- and microfauna (ammonites, bivalves, gastropods, echinoids, crinoids, trace-fossils, vertebrates, ostracods, foraminifera) are abundant and diverse. Data for the nearby Larne borehole are already published. The diversity and preservation of the earliest Jurassic ammonite fauna in the Larne Basin is superior to that at St. Audrie’s Bay or at any other UK site (see poster below).
Potential for global correlationTwo orders of sedimentary cycles, largely unaffected by diagenetic limestones, can be recognised at this site (this poster, far right). Analysis, combining sequence stratigraphy and cyclostratigraphy, indicates that these cycles reflect eustatic fluctuations and hence have significant potential for global correlation (see website for more detailed discussion). �
The foreshore at Waterloo Bay, Larne, on the east coast of Northern Ireland, exposes an almost uninterrupted succession from the upper part of the Mercia Mudstone Group (Triassic, Norian) through to the Bucklandi Zone of the Lias Group (Jurassic, Sinemurian).
The Triassic-Jurassic boundary succession at Waterloo Bay is proving to be superior in many respects to that at St. Audrie’s Bay, in south-west Britain, which, for decades, has been cited as a candidate Global Stratotype Section and Point (GSSP) for the base of the Jurassic System.
Waterloo Bay, Larne, Northern Ireland: A potential Global Stratotype Section and Point (GSSP) for the base of the Jurassic System
early diagenetic carbonate nodule
Hig
hsta
nd B
undl
e
Dublin
Belfast
Cork
Galway
Larne
Waterloo Bay fault
fault
Langport MemberLangport Member
Lias GroupLias Group
(first amm
onites)
(first amm
onites)
upper upper Cotham Cotham MemberMember
upper upper PlanorbisPlanorbisSubzoneSubzone
Penarth GroupPenarth GroupBed 24
Bed 24
Location of Waterloo Bay, Larne, and a view from the adjacent cliff-top of part of the foreshore section at low tide. Strata dip at about 25o to the north-west. Access to the site is exceptionally good via the promenade in the foreground. Figure for scale at the seaward end of the top of the Langport Member.
Triassic-Jurassic boundary stratigraphy (preliminary results)
Log and analysis by A.J.Jeram and M.J.Simms
July 2006
Pla
norb
is S
ubzo
neJo
hnst
oni S
ubzo
ne
Correlative section at St Audrie’s Bay for comparison (after Hesselbo et al. 2002, Geology, 30, 251-254).