A revised Mississippian lithostratigraphy of County Galway … · 2017-02-08 · non, Co. Leitrim to the northeast (Figure 1). Finally, analysis is made of the carbonate depositional

Journal of Palaeogeography2015, 4(1): 1-26

Lithofacies palaeogeography and sedimentology

DOI: 10.3724/SP.J.1261.2015.00065

A revised Mississippian lithostratigraphy of County Galway (western Ireland) with an analysis of carbonate lithofacies, biostratigraphy, depositional environments

and palaeogeographic reconstructions utilising new borehole data

Markus Pracht1, Ian D. Somerville2, *

1. Geological Survey of Ireland, Beggars Bush, Dublin 4, Ireland*2. UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland

Abstract An integrated study of borehole data and outcrop of Mississippian (late Tour-naisian to late Viséan) rocks in Co. (County) Galway, western Ireland has enabled a more detailed geological map and lithostratigraphy to be constructed for the region. Several car-bonate formations have been distinguished by microfacies analysis and their precise ages established by micropalaeontological investigations using foraminifers and calcareous algae. In addition, palaeogeographic maps have been constructed for the late Tournaisian, and ear-ly to late Viséan intervals in the region. The oldest marine Mississippian (late Tournaisian) deposits are recorded in the south of the study region from the Loughrea/Tynagh area and further south in the Gort Borehole; they belong to the Limerick Province. They comprise the Lower Limestone Shale Group succeeded by the Ballysteen Group, Waulsortian Limestone and Kilbryan Limestone Formations. These rocks were deposited in increasing water depth associated with a transgression that moved northwards across Co. Galway. In the northwest and north of the region, marginal marine and non-marine Tournaisian rocks are developed, with a shoreline located NW of Galway City (Galway High). The central region of Co. Galway has a standard Viséan marine succession that can be directly correlated with the Carrick-on-Shannon succession in counties Leitrim and Roscommon to the northeast and east as far as the River Shannon. It is dominated by shallow-water limestones (Oakport, Ballymore and Croghan Limestone Formations) that formed the Galway-Roscommon Shelf. This facies is lat-erally equivalent to the Tubber Formation to the south which developed on the Clare-Galway Shelf. In the southeast, basinal facies of the Lucan Formation accumulated in the Athenry Ba-sin throughout much of the Viséan. This basin formed during a phase of extensional tectonics in the early Viséan and was probably connected to the Tynagh Basin to the east. In the late Viséan, shallow-water limestones of the Burren Formation extend across much of the south-ern part of the region. They are characterized by the presence of rich concentrations of large brachiopod shells and colonial coral horizons which developed in predominantly high-energy conditions. These limestones also exhibit palaeokarstic surfaces and palaeosols which formed during regressive conditions of glacio-eustatically controlled cyclicity. Locally, slightly deeper

* Corresponding author. E‑mail: [email protected]. Received: 2014-07-29 Accepted: 2014-09-12

2 JOURNAL OF PALAEOGEOGRAPHY Jan. 2015

water, lower energy conditions developed on the shelf with the formation of rare bryozoan-rich mud-mounds. Deep-water basinal facies were maintained in the central and southeastern parts of the region between the two shelves with the persistence of the Lucan Formation. Ac-tive syn-sedimentary faulting influenced deposition in the Viséan and interfingering of basinal sediments with slumps and shallow-water shelf carbonates are recognized.

Key words Carboniferous, Mississippian, western Ireland, carbonate microfacies, biostratigraphy, foraminifers, shelf and basin environments, palaeogeography

1 Introduction and geological setting

The study area includes a large terrane of flat-lying Lower Carboniferous (Mississippian) limestone in Co. Galway, western Ireland, approximately 2000 km2, extending from Lough Corrib in the west to the River Suck (Ballinasloe) in the east, and from Ballymoe and the

Slieve Dart Fault in the north to Craughwell and Loughrea in the south (Figure 1). It represents part of an extensive carbonate platform (“Galway‑Roscommon Shelf ” in Morris et al., 2003; Nagy et al., 2005 or “Tuam Block” in Long et al., 2004), adjacent to the older Precambrian and Lower Paleozoic Connemara Massif to the northwest of Galway city. Exposures are very limited and much of

Figure 1 Geological map of western Ireland (adapted from Long et al., 2004; Pracht et al., 2004). O.R.S. = Old Red Sandstone.

3Vol. 4 No. 1Markus Pracht and Ian D. Somerville:

A revised Mississippian lithostratigraphy of County Galway (western Ireland)

the area is covered by glacial and fluvioglacial sediments; the best sections are in the limestone quarries close to Galway city (Pracht and McConnell, 2012). The most recently published maps of the area (1:100,000; Pracht et al., 2004; Long et al., 2004) show that the majority of the exposed limestones are of Viséan age and mainly depicted as undifferentiated shelf carbonates, with small isolated patches of Viséan basinal limestones.

Recent investigations have attempted to differentiate this >800 m‑thick Viséan carbonate succession into constituent formations, based on analysis of drillcore from several deep boreholes (>300 m thick) and many shorter boreholes (c. 100 m thick) drilled by the Geological Survey of Ireland (GSI). In total, during the period from 2005 to 2012, 30 boreholes have been drilled within this region and logged in detail. Sampling of selected boreholes has been undertaken by the authors to determine the age of different stratigraphic units based on their macrofauna (corals) and microfossils (principally foraminifers and calcareous algae). Correlation between the deeper bore‑holes has recognized several distinct Viséan stratigraphic successions that clearly show lateral facies changes across the region. These comprise in the west the Oughterard‑Headford succession around Lough Corrib, the Dunmore‑Ballymoe succession in the northeast and centre, and further south the Craughwell‑Burren succession (Figure 2). Also, in the southeast of the area, a transition from shelf to basin facies can be recognized, as well as an older Tournaisian succession with Waulsortian mud‑mounds in the Loughrea‑Tynagh area (Figures 1, 2).

The region has been affected by major NE‑ and ENE‑trending Variscan faults with downthrows of hundreds of metres. The Athenry and Craughwell Faults juxtapose shelf and basinal successions, and the Loughrea Fault and Slieve Dart Fault expose inliers of basal Carboniferous siliciclastic rocks and Tournaisian (Courceyan) limestones (Pracht et al., 2004; Long et al., 2004; Pracht and McConnell, 2012; Figures 1, 2).

The main aim of this study is a synthesis of the newly acquired borehole data from the 30 recently drilled GSI boreholes integrated with older borehole data on file in the GSI (28 boreholes; comprising 14 drilled by GSI and 14 non‑GSI commercial drillholes), together with new field data we have collected. The result of collating data from the 58 boreholes is a much improved and detailed geological map and lithostratigraphy of the region (Fig‑ure 2), with an attempt to show the areal distribution of Viséan formations tied to key boreholes and outcrops. Also, a wealth of microfacies and micropalaeontological

data from the limestones has been gathered and used to help characterize and date the various formations, and to correlate them within the region and with other type sections and boreholes outside the study area. These are principally from the Burren region of Co. Clare and Gort Borehole (G-1) in southern Co. Galway in the southwest, and around Boyle, Co. Roscommon and Carrick‑on‑Shan‑non, Co. Leitrim to the northeast (Figure 1). Finally, analysis is made of the carbonate depositional environments and palaeogeographic maps are reconstructed for the region.

2 Lithostratigraphy, biostratigraphy and microfacies

Succeeding the basal Carboniferous siliciclastic units and Tournaisian limestones, four distinct Viséan lithostratigraphic successions have been recognized within the study area (Table 1). In the northeast and central part of the region is the Dunmore-Ballymoe succession, identi‑ fied in the Esker (GSI-12-01), Fartamore (GSI-12-02), Lisna (GSI‑11‑01), Corancarton (GSI‑11‑315) and Bullaun Bridge (GSI‑07‑178) boreholes (Figures 2, 3). The stratigraphic units identified are closely comparable to the succession defined by Caldwell (1959) from the Carrick‑on‑Shannon Syncline, 40 km to the northeast in counties Roscommon and Leitrim (Figure 1, Table 1), which crops out between Boyle and Carrick‑on‑Shannon. In the western part of the region is the Oughterard-Head-ford (Lough Corrib) succession, based on boreholes (HS‑4, GSI‑02‑03, GSI‑92‑09, GSI‑92‑10; Figure 2) and outcrops around the shores of Lough Corrib (Pracht et al., 2004; Long et al., 2004). In the south of the region is the Craughwell-Burren succession, identified in GSI-06-02, GSI‑06‑387, GSI‑07‑179, GSI‑08‑239, GSI‑10‑04 and GSI‑96‑50 boreholes (Figures 2, 5) and comparable to the Burren‑Gort succession in south Co. Galway and north Co. Clare (Pracht et al., 2004; Gallagher et al., 2006). In addition, thick Viséan basinal successions are present in the southeast of the region recognized in GSI‑07‑01 (Cuddoo), GSI‑07‑03 (Gloves), 2099-2 and 01-1798/1 boreholes (Figures 4, 5) (Loughrea succession).

The description of the various Lower Carboniferous formations is from oldest to youngest, beginning with the basal siliciclastic and limestone formations of Tournaisian age. These are only briefly described, as the main focus of this paper is on the younger Viséan formations, which areally account for the majority of the region. More comprehensive descriptions of these Tournaisian units can be found in Pracht et al. (2004). Also, as the Viséan


Figure 2 Geological map of Co. Galway and location of selected boreholes and localities mentioned in the text. The three main stra‑tigraphic successions are also highlighted.



limestone formations defined around the shores of Lough Corrib in the west of the region can be directly equated to the limestone succession further east (see Table 1), only details of the stratigraphy in the Dunmore‑Ballymoe area, which is regarded as the standard succession for most of the Galway‑Roscommon Shelf (see Morris et al., 2003), is documented here. More detailed descriptions of the Lough Corrib succession can be found in Pracht et al. (2004). Biostratigraphic dating of the Tournaisian and Viséan limestones has been achieved principally using foraminifers. The assemblages have been assigned to the standard Mississippian foraminiferal biozones MFZ 6-MFZ 14 of Poty et al. (2006; Table 1) (broadly equivalent to the former Cf2-Cf6ɣ zones and subzones, as used in Jones and Somerville, 1996). Important characteristics of the limestone microfacies are summarized in Table 2, based on an examination of over 400 thin sections.

2.1 Basal Carboniferous siliciclastic units

In the north of the region, the basal siliciclastic unit is identified as the Boyle Sandstone Formation, which forms inliers in Slieve Dart and Castlerea and has its

type section near Boyle, Co. Roscommon (Caldwell, 1959; Morris et al., 2003) where it is c. 105 m thick. It is represented in GSI‑12‑01 by >30 m of grey sandstone. Its lateral equivalent in the western Lough Corrib succession (GSI‑92‑10 and HS-4) is the Tonweeroe Formation (>115 m thick) which shows a lower red‑bed sandstone and conglomerate sequence passing up to grey bioturbated sandstones and mudstones (Figure 2). In GSI‑92‑10 borehole the Tonweeroe Formation rests directly on the Silurian-Devonian Galway granite. The age of the Boyle Sandstone Formation has been confirmed as late Tournaisian based on spore data (CM Zone) from the type section (Morris et al., 2003). In GSI‑12‑01 the Boyle Sandstone Formation is followed by marine limestones of the Moathill Formation (Figures 2, 3). In the southern boundary of the study region a thicker and more complete Tournaisian succession is preserved around Craughwell (2099-2) and Loughrea (Figure 1). There, continental red bed sediments pass up to a transitional marine succession (Lower Limestone Shale Group) developed around the margin of the Slieve Aughty Inlier (Figure 1), succeeded by an open marine limestone succession (Ballysteen

Table 1 Revised Mississippian lithostratigraphy for Co. Galway showing lateral equivalence of the main successions (Modified and updated from Morris et al., 2003; Pracht et al., 2004; Pracht and McConnell, 2012). Abbreviations: TOURN. = Tournaisian, COURC. =

Courceyan, CHAD. = Chadian, ARUND. = Arundian, HOLK. = Holkerian, MFZ = Mississippian foraminiferal zone, Mbr. = Member, mb = mud‑mound (bioherm/buildup), O.R.S. = Old Red Sandstone, LST. = limestone, GRP. = Group.

FORMATION FORMATION FORMATION FORMATION

BURRENBURREN

TUBBERTUBBER

LUCAN

mb

TWO MILEDITCH Mbr.

O.R.S. O.R.S.

BALLYSTEEN GRP. BALLYSTEEN GRP.

WAULSORTIANLST.

WAULSORTIAN LST.

LOWER LST. SHALE GRP. LOWER LST. SHALE GRP.

BURREN

CROGHANLIMESTONE

BALLYMORE LIMESTONE

OAKPORT LIMESTONE

KILBRYAN LIMESTONE

BOYLE SANDSTONE

BALLYSTEEN and MOATHILL

TONWEEROE

OUGHTERARD LST.

CREGG LST.

OLDCHAPEL LST.

ILLAUNAGAPPUL

ARDNASILLAGH

CORRANELLISTRUMAUGHNANURE OOLITE

KNOCKMAA

MFZ 12

MFZ 11

MFZ13-14

MFZ9-10

MFZ6-8

MIS

SISS

IPPI

ANVI

SÉAN

(par

t)TO

UR

N.

(par

t)

CO

UR

C.

CH

AD.

ARU

ND

.H

OLK

.AS

BIAN

STAG

E

AGE

SUB-

STAG

E FORAMZONATION(Poty et al.

2006)

LOUGH CORRIBSUCCESSION

(Oughterard andHeadford) (W Galway)

DUNMORE-BALLYMOESUCCESSION

(Central and NE Galway)

CRAUGHWELL-BURRENSUCCESSION

(South and SW Galway)

LOUGHREA SUCCESSION(SE Galway)


Figu

re 3

C

orre

latio

n of

bor

ehol

es fr

om w

est t

o ea

st a

cros

s no

rther

n C

o. G

alw

ay w

ith im

porta

nt c

oral

taxa

(in

red)

and

mic

rofo

ssils

indi

cate

d. A

bbre

viat

ions

: e.o

.h. =

end

of h

ole,

LST

. =

Lim

esto

ne, C

HA

D. =

Cha

dian

, AR

UN

D. =

Aru

ndia

n.



Figu

re 4

C

orre

latio

n of

bor

ehol

es fr

om n

orth

to s

outh

acr

oss

Co.

Gal

way

with

impo

rtant

cor

al ta

xa (i

n re

d) a

nd m

icro

foss

ils in

dica

ted.

Abb

revi

atio

ns: e

.o.h

. = e

nd o

f hol

e, C

OU

RC

. =

Cou

rcey

an, C

HA

D. =

Cha

dian

, AR

UN

D. =

Aru

ndia

n, H

OLK

. = H

olke

rian,

ASB

. = A

sbia

n.


Figu

re 5

C

orre

latio

n of

bor

ehol

es in

sout

hern

and

sout

heas

tern

Co.

Gal

way

to sh

ow p

latfo

rm‑b

asin

tran

sitio

ns w

ith im

porta

nt c

oral

taxa

(in

red)

and

mic

rofo

ssils

indi

cate

d. A

bbre

viat

ions

: e.

o.h.

= e

nd o

f hol

e, A

RU

ND

. = A

rund

ian,

HO

LK. =

Hol

keria

n, A

SB. =

Asb

ian.



Tabl

e 2

Cha

ract

eriz

atio

n (m

acro

faci

es, m

icro

faci

es a

nd in

terp

reta

tion

of d

epos

ition

al fa

cies

) of l

ate

Tour

nais

ian

and

Visé

an li

mes

tone

form

atio

ns in

the

Co.

Gal

way

regi

on, a

rran

ged

in

appr

oxim

atel

y st

ratig

raph

ical

ord

er (o

ldes

t at t

he b

ase)

. The

lim

esto

nes a

re c

lass

ified

acc

ordi

ng to

the

Dun

ham

, 196

2 sc

hem

e (m

odifi

ed b

y Em

bry

and

Klo

van,

197

1).

Form

atio

n (a

ge)

Mac

rofa

cies

(cor

e an

d ou

tcro

p)M

icro

faci

esM

ain

biot

a an

d co

mpo

nent

sD

epos

ition

al se

tting

Luc

an(V

iséa

n)

Thin

bed

ded

mos

tly fi

ne-g

rain

ed la

mi‑

nate

d lim

esto

ne in

terb

edde

d w

ith m

ud‑

ston

e; o

ccas

iona

l th

in c

oars

er g

rain

ed

limes

tone

bed

s; fr

eque

nt c

hert

band

s

Mos

tly

fine-

grai

ned,

po

orly

so

rted

wac

kest

one/

pack

ston

e w

ith c

oars

er s

kele

tal

grai

nsto

ne

band

s

Crin

oids

, sp

onge

spi

cule

s (c

omm

on),

cal

cisp

here

s (a

bund

ant),

for

amin

ifers

(sp

arse

), cy

anob

acte

ria, o

s‑tra

cods

, fen

este

llid

bryo

zoan

s, ka

mae

nids

; pyr

ite, d

e‑tri

tal q

uartz

and

mic

a

Dee

p‑w

ater

, lo

w‑e

nerg

y ou

ter

shel

f to

ba

sina

l fa

cies

w

ith

rede

posi

ted

shel

f‑de

rived

bio

‑cl

astic

mat

eria

l; p

artia

l dy

s‑ae

robi

c en

viro

nmen

t

Tubb

er(E

arly

‑Lat

e Vi

séan

)

Mos

tly l

ight

gre

y m

ediu

m‑

to c

oars

e‑gr

aine

d lim

esto

ne w

ith d

olom

itic

inte

r‑va

ls; c

hert

band

s

Mod

erat

ely

sorte

d fin

e-gr

aine

d sk

elet

al

wac

kest

one/

pack

ston

e an

d w

ell‑s

orte

d co

arse

‑gra

ined

in

tracl

astic

sk

elet

al

pelo

idal

gr

ains

tone

Abu

ndan

t cr

inoi

ds,

dasy

clad

acea

n al

gae,

red

alg

ae,

kam

aeni

ds,

cyan

obac

teria

, pr

oble

mat

ica,

for

amin

i‑fe

rs, c

alci

sphe

res,

fene

stel

lid b

ryoz

oans

, bra

chio

pods

, bi

valv

es, g

astro

pods

, ech

inoi

d sp

ines

, tril

obite

s, os

tra‑

cods

, cor

al f

ragm

ents

; pel

oids

, int

racl

asts

, mic

ritiz

ed

bioc

last

s; o

oids

Pred

omin

antly

sha

llow

‑wat

er

mod

erat

e‑ to

hig

h‑en

ergy

shel

f

Bur

ren

(Lat

e Vi

séan

)

Med

ium

‑ and

coa

rse‑

gra

ined

lig

ht a

nd

dark

gre

y w

ell ‑b

edde

d an

d m

assi

ve

limes

tone

, ra

re c

lay

band

s; f

requ

ent

cora

l co

loni

es a

nd b

rach

iopo

d ba

nds;

ra

re m

assi

ve fi

ne-g

rain

ed li

mes

tone

in‑

terv

als w

ith c

aviti

es; s

ome

parti

al d

olo‑

miti

satio

n

Poor

ly

sorte

d an

d w

ell ‑s

orte

d sk

elet

al,

pelo

idal

, in

tracl

astic

pa

ckst

one

and

grai

nsto

ne;

skel

‑et

al w

acke

ston

e

Abu

ndan

t cr

inoi

ds,

dasy

clad

acea

n al

gae,

red

alg

ae,

kam

aeni

ds, c

yano

bact

eria

, for

amin

ifers

, cal

cisp

here

s, fe

nest

ellid

bry

ozoa

ns,

brac

hiop

ods,

biva

lves

, os

tra‑

cods

, ga

stro

pods

, ec

hino

id s

pine

s, tri

lobi

tes,

cora

l fr

agm

ents

; pe

loid

s, in

tracl

asts

; m

ud m

ound

s w

ith

stro

mat

actid

cav

ities

con

tain

ing

pelo

ids,

trepo

stom

e,

tabu

lipor

id a

nd fe

nest

ellid

shee

ts, o

stra

cods

and

abu

n‑da

nt sp

onge

spic

ules

Pred

omin

antly

sh

allo

w‑w

ater

m

oder

ate‑

to h

igh‑

ener

gy sh

elf

with

occ

asio

nal

suba

eria

l ex

‑po

sure

; loc

alis

ed m

ud‑m

ound

s in

slig

htly

dee

per s

helf

Cro

ghan

Lim

esto

ne(L

ate

Visé

an)

Mos

tly fi

ne-

to m

ediu

m-g

rain

ed,

dark

gr

ey

wel

l ‑bed

ded

argi

llace

ous

lime‑

ston

e

Poor

ly

sorte

d an

d w

ell ‑s

orte

d sk

elet

al

wac

kest

one/

pack

ston

e an

d gr

ains

tone

Abu

ndan

t cr

inoi

ds

and

kam

aeni

ds,

fora

min

ifers

, sp

onge

spi

cule

s, ca

lcis

pher

es, f

enes

telli

d br

yozo

ans,

trilo

bite

s

Low

‑ an

d hi

gh‑e

nerg

y m

id

shel

f

Bal

lym

ore

Lim

esto

ne(E

arly

Vis

éan)

Mos

tly fi

ne-g

rain

ed,

dark

gre

y w

ell-

bedd

ed a

rgill

aceo

us li

mes

tone

alte

rnat

‑in

g w

ith li

ght g

rey

coar

se‑g

rain

ed li

me‑

ston

e; s

hale

int

erbe

ds;

freq

uent

cor

al

colo

nies

Mai

nly

poor

ly

sorte

d sk

elet

al

wac

kest

one/

pack

ston

e with

wel

l‑ so

rted

intra

clas

tic sk

elet

al g

rain

‑st

one

Abu

ndan

t cr

inoi

ds a

nd k

amae

nids

, sp

arse

for

amin

i‑fe

rs a

nd s

pong

e sp

icul

es,

calc

isph

eres

, fe

nest

ellid

br

yozo

ans,

spar

se d

asyc

lada

cean

alg

ae;

rar

e co

ated

gr

ains

and

ooi

ds

Mod

erat

ely

shal

low

‑wat

er lo

w‑

to h

igh‑

ener

gy s

helf;

cor

al b

i‑os

trom

es

Oak

port

Lim

esto

ne(E

arly

Vis

éan)

Fine

‑, m

ediu

m‑

and

coar

se‑g

rain

ed,

light

gre

y lim

esto

ne, t

hick

‑bed

ded

and

mas

sive

; occ

asio

nal i

nter

vals

of

fene

s‑tra

l an

d bu

rrow

ed m

icrit

e; o

ccas

iona

l ch

ert

nodu

les;

bra

chio

pods

; do

lom

itic

inte

rval

s

Mai

nly

wel

l ‑sor

ted

skel

etal

, pe

‑lo

idal

and

intra

clas

tic p

acks

tone

an

d gr

ains

tone

; lim

e m

udst

one

Com

mon

fora

min

ifers

, crin

oids

, das

ycla

dace

an a

lgae

, cy

anob

acte

ria, k

amae

nids

, gas

tropo

ds, p

robl

emat

ica;

pe

loid

s, in

tracl

asts

, spa

rse

ooid

s

Shal

low

‑wat

er m

oder

ate‑

to

high

‑ene

rgy

shel

f; pr

otec

ted

lago

on


Tabl

e 2,

con

tinue

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Group) (Table 1), typical of the Gort borehole (G-1) in the Limerick Province (see Philcox, 1984; Somerville and Jones, 1985; Sleeman and Pracht, 1999; Somerville and Waters, 2011; Somerville et al., 2011).

2.2 Moathill Formation

This formation comprises an alternation of bioclastic limestone, grey calcareous sandstone and mudstone. It is c. 15 m thick in GSI‑12‑01 in the north of the region (Fig‑ure 2). It represents the local transitional unit into the suc‑ceeding limestone‑dominant Ballysteen Formation. The Moathill Formation forms part of the Navan Group which is better developed east of the River Shannon in Co. Long‑ford (Morris et al., 2003; Somerville and Waters, 2011).

Microfacies: The limestones typically comprise mod‑erately well‑sorted, coarse‑grained skeletal grainstone/rudstone (Figure 6A). The main skeletal components are brachiopods, crinoids, fenestellid bryozoans, ostracods, algae (Kamaena), foraminifers and calcispheres.

Depositional setting: The formation was deposited in a nearshore, shallow‑water siliciclastic‑dominant shelf in which both fine- and coarse-grained clastic sediments ac‑cumulated. Periodically, shelf limestones with a rich and diverse benthic biota developed, when siliciclastic input onto the shelf was reduced. High‑energy conditions pre‑vailed during the formation of the limestones, as suggested by the good sorting and rounding of skeletal material.

Age: The Moathill Formation is late Tournaisian in age, based on a sparse foraminiferal assemblage includ‑ing Endothyra, Septatournayella, Earlandia, Eoforschia (MFZ 6), and algal/cyanobacteria and microproblematica (Girvanella, Salebra sibirica).

2.3 Ballysteen Formation

This formation comprises light‑grey and dark‑grey, fine-grained argillaceous bioclastic limestone alternat‑ing with calcareous mudstone. The limestones are often bioturbated and chert nodules are commonly developed. Rare large solitary rugose corals and crinoids are the main macrofaunal elements. Identified taxa include: Canino-phyllum patulum, Sychnoelasma, and Amplexizaphrentis. In the northeast of the region, in GSI‑11‑01, the Ballys‑teen Formation is nearly 100 m thick (Figure 4), but thins westwards around Dunmore (c. 35 m in MGR.82.35 and 20 m in GSI‑12‑01 respectively; Figures 3, 4). In the south of the region near Craughwell (2099-2), the Ballysteen Formation is also thin (c. 56 m), but thickens southeast to Loughrea where it is c. 168 m (Pracht et al., 2004) and contains oolitic and sandy intervals. In the south of the

region near Gort, the Ballysteen Formation together with the Ballymartin Formation form the Ballysteen Group (Somerville et al., 2011).

Microfacies: Typically poorly sorted skeletal wacke‑stone/packstone and grainstone. The main skeletal com‑ponents are crinoids, brachiopods, fenestellid bryozoans, sponge spicules, algae (Kamaena), sparse foraminifers, gastropods and calcispheres. Partial silicification of bio‑clasts is common.

Depositional setting: The Ballysteen Formation was deposited mostly in an offshore shelf/middle ramp, be‑low fairweather wave‑base but above storm wave‑base, in which fine-grained siliciclastic sediment accumulated. The biota is rich and diverse with abundant large crinoids, brachiopods and solitary corals. The lack of sedimentary structures, poor sorting of bioclasts and abundance of bryozoans implies low‑energy, relatively quiet water con‑ditions. Locally, though, in the Loughrea area, shallower water, higher energy conditions developed with the pres‑ence of ooids and better sorting of bioclasts.

Age: The Ballysteen Formation is late Tournaisian in age based on a sparse foraminiferal assemblage includ‑ing Eoforschia, Septatournayella, Earlandia, Eblanaia (MFZ 6), and algal/cyanobacteria and microproblematica (Parachaetetes, Girvanella, Salebra sibirica).

2.4 Waulsortian Limestone Formation

Within the study area, the Waulsortian Limestone For‑mation mainly occurs around Loughrea in the southeast, where it reaches a thickness of c. 500 m (Pracht et al., 2004). Although no boreholes in the recent drilling pro‑gramme encountered this unit, further to the north in the Slieve Dart Borehole (02-3471-01; Figure 2), 45 m of Waulsortian Limestone were recorded (Morris et al., 2003). The dominant Waulsortian lithology is pale‑grey, massive limestone, which, at outcrop in eastern Galway, forms large mud‑mounds several tens of metres in thick‑ness (Lees, 1964, 1994; Lees and Miller, 1985, 1995). There is a sharp basal contact with dark grey argillaceous limestones of the Ballysteen Formation. In the Loughrea area it is succeeded by either the Tubber Formation (see below) or basinal facies (Lucan Formation), but in the northern part of the region it is overlain by and is partly equivalent to the Kilbryan Limestone Formation (Mor‑ris et al., 2003; Table 1). In some boreholes (GSI‑12‑01, GSI‑11‑01, GSI‑11‑315 and MGR.82.35) where typical massive pale‑grey micritic Waulsortian limestone is not developed, a thinly-bedded, fine-grained nodular lime‑stone and shale unit is present and referred to as ‘Waulsor‑


Figure 6 Photomicrographs of carbonate microfacies (all in plane polarized light) of late Tournaisian and early Viséan limesto‑nes. A-Skeletal grainstone with crinoids (C) and brachiopods (B) in sparry calcite cement, Moathill Formation, Esker Borehole (GSI‑12‑01), 300.2 m; B-Spiculitic wackestone, with monaxin and hexactin calcitic spicules in lime mud matrix, Waulsortian equi‑valent, Corancarton Borehole (GSI‑11‑315), 440.9 m; C-Skeletal wackestone with fenestellid bryozoans (F), sponge spicules (S), trilobites (T) and ostracods (O) in lime mud matrix, Waulsortian equivalent, Corancarton Borehole, 440.9 m; D-Skeletal wackestone with kamaenids and ostracods in lime mud matrix, Kilbryan Limestone Formation, Corancarton Borehole (GSI‑11‑315), 379.2 m; E-

Skeletal peloidal intraclastic grainstone with moderately well‑sorted micritized bioclasts in sparry calcite cement, Oakport Limestone Formation, Corancarton Borehole (GSI‑11‑315), 290.1 m; F-Skeletal grainstone with abundant tubular problematicum Luteotubulus in sparry calcite cement, Oakport Limestone Formation, Fartamore Borehole (GSI‑12‑02), 177.1 m; G-Skeletal intraclastic packstone with dasyclad alga Koninckopora (K) sp. (monolaminar) and foraminifers (F) in sparry calcite cement, Oakport Limestone Formation, Fartamore Borehole (GSI‑12‑02), 144.5 m; H-Skeletal packstone with abundant foraminifers and calcispheres in sparry calcite cement and lime mud, Oakport Limestone Formation, Esker Borehole (GSI‑12‑01), 64 m.



tian equivalent’ (Figures 3, 4). The latter unit is differenti‑ated from the Kilbryan Limestone Formation by its higher proportion of limestone to mudstone.

Microfacies: The characteristic lithology of the Waul‑sortian equivalent is wackestone with crinoids, fenestrate bryozoans, sponge spicules, trilobites, brachiopods and molluscs (Figure 6B, 6C). In the lime mudstone of the mud-mounds, large spar-filled cavity structures (stroma‑tactis), ranging up to many centimetres across, are com‑monly developed (Lees, 1964, 1994; Lees and Miller, 1985, 1995; Somerville, 2003), and foraminifers are rare.

Depositional setting: The mud mounds characteristic of this formation developed in a deep‑water distal ramp set‑ting below storm wave‑base. Low‑energy conditions pre‑vailed during the formation of the massive limestones and their laterally equivalent bedded limestones dominated by crinoids, sponges and bryozoans.

Age: The Waulsortian Limestone is late Tournaisian in age based on very limited foraminiferal and conodont data (Sevastopulo, 1982; Pracht et al., 2004).

2.5 Kilbryan Limestone Formation

The Kilbryan Limestone Formation (Caldwell, 1959; Morris et al., 2003) consists of dark-grey, fine-grained argillaceous bioclastic limestone alternating with mi‑nor mudstone and some chert nodules. The lower part of the formation shows a nodular bedding, bioturbation, geopetals and dewatering structures. It also contains two thin green clay bands in GSI‑12‑02 (at 262.7 m and 267.2 m) in GSI‑12‑01 (at 202.6 m and 223 m) and in GSI‑11‑315 (at 365.0 m and 389.5 m) (Figures 3, 4). One of these may possibly correlate to the clay band in HS-4 (at c.75 m; Figure 3) and the one in MGR.82.35 (at c. 33 m; Figure 4). These clay bands have been interpreted elsewhere as decomposed volcanic ashes (tuffs) (Philcox, 1984; Morris et al., 2003). The upper boundary to the overlying Oakport Limestone Formation is transitional, with light‑grey lime‑stone increasing in proportion to argillaceous limestone for tens of metres. The Formation is 108 m thick in GSI‑12‑01 compared to c. 185 m in MGR.82.35. Further west near Headford (Long et al., 2004), the Kilbryan Limestone For‑mation is laterally correlated to the Oughterard Limestone Formation of the Lough Corrib succession and is 166 m in HS-4 (Figure 3, Table 1). The macrofauna comprises rare large solitary rugose corals (Amplexus coralloides) and tabulates (Syringopora).

Microfacies: Typically moderate to well‑sorted skel‑etal wackestone (commonly with microsparite matrix) and poorly sorted skeletal packstone. The main skeletal

components are crinoids, fenestellid bryozoans, sponge spicules, algae (Kamaena)(Figure 6D), foraminifers, cya‑nobacteria coating shells, trilobites and calcispheres.

Depositional setting: The formation was deposited in a moderately deep‑water shelf/mid ramp, below storm wave-base, in which both fine-grained clastic mud and carbonate mud accumulated. Low‑energy conditions pre‑vailed during the deposition of the fine-grained muddy limestones. The benthic biota is quite rich and diverse and locally kamaenid algae and ostracods can be abundant.

Age: The Kilbryan Limestone Formation lacks diag‑nostic microfossils. Based on its stratigraphic position between the older Tournaisian‑aged Ballysteen Formation (or Waulsortian Limestone Formation) and the overly‑ing lower Viséan Oakport Limestone Formation, it is late Tournaisian to earliest Viséan in age.

2.6 Oakport Limestone Formation

The Oakport Limestone Formation (Caldwell, 1959; Morris et al., 2003) consists of light‑grey, massive, coarse‑grained bioclastic limestone with occasional intervals of dark-grey fine-grained fenestral lime mudstone; rare black shales and very rare green clay bands occur in the lower part. Chert nodules and bioturbation are occasionally de‑veloped. Large solitary rugose corals, tabulate corals, gas‑tropods, brachiopods and crinoids are the main macrofau‑nal elements. Identified coral taxa include: Siphonophyllia cylindrica, Michelinia megastoma, and Clisiophyllum sp.

The base of the Formation has been placed at the first appearance of light‑grey bioclastic limestone above the underlying Kilbryan Limestone Formation. The top, also gradational, is placed at the incoming of argillaceous li‑thologies. The thickest interval of Oakport Limestone (140 m) is recorded in GSI‑11‑01 and GSI‑12‑01, similar to that in the Slieve Dart Borehole (02-3471-01; 137 m) (Figures 2, 3, 4; Morris et al., 2003). The Formation no‑tably thickens and becomes more argillaceous from west (GSI‑12‑02) to east (GSI‑12‑01) (Figure 3). The Oakport Limestone Formation is laterally correlated to the Cregg Limestone and Oldchapel Limestone Formations in the Lough Corrib succession (Figure 3, Table 1). In HS-4, only the lower 28 m of Oakport Limestone Formation was drilled. In the central region near Tuam, the Oakport Lime‑stone Formation thins to 110 m (GSI‑11‑315; Figure 4) but was not intersected in boreholes further to the south.

Microfacies: Typically moderate to well‑sorted, intra‑clastic, skeletal peloidal wackestone and packstone with occasional intraclastic skeletal grainstone (Figure 6E) and rare ooids in the upper beds. The main skeletal compo‑


nents are locally abundant problematica (Luteotubulus, Figure 6F), dasycladacaean algae (Koninckopora (Figure 6G) and Kamaena), endothyroid foraminifers (rich and di‑verse in the lower beds, Figure 6H), cyanobacteria coating shells, calcispheres, crinoids and micritized bioclasts.

Depositional setting: The Oakport Limestone For‑mation was deposited in a shallow‑water shelf setting above fairweather wave‑base. The presence of rounded intraclasts, ooids, micritized bioclasts and peloids in well‑sorted coarse‑grained limestones attests to high‑energy conditions. However, the formation also contains fenestral and burrowed lime mudstones, which indicate deposition in low‑energy intertidal lagoonal environments protected by ooid and skeletal grainstone shoals. The biota is rich and diverse with abundant crinoids, foraminifers and dasy‑cladacean algae, the latter suggesting growth in a shallow photic zone.

Age: The Oakport Limestone Formation is early Viséan (Chadian) in age, based on the presence of the key fora‑minifers: Eoparastaffella simplex, Pseuodolituotubella, Brunsia, Pseudoammodiscus, Eblanaia michoti, Eostaffel-la (an assemblage characteristic of MFZ 9), as well as the alga Koninckopora sp. (monolaminar wall) and abundant Luteotubulus.

2.7 Ballymore Limestone Formation

The Ballymore Limestone Formation (Caldwell, 1959; Morris et al., 2003) attains its greatest thickness (225 m) in GSI‑11‑315 (Figure 4), which is thicker than in the type section (c. 170 m) at Ballymore House near Boyle (Caldwell, 1959). It consists predominantly of dark‑grey well-bedded and nodular fine-grained argillaceous lime‑stone showing common bioturbation, with occasional in‑tervals of massive, light‑grey, coarse‑grained limestone. The middle of the formation includes thicker calcareous shale intervals. Chert nodules are commonly developed. Large solitary rugose corals, fasciculate rugose and tabu‑late coral colonies, bellerophontid gastropods, brachio‑pods and sparse crinoids are the main macrofaunal ele‑ments. Identified taxa include: Siphonophyllia garwoodi, Michelinia megastoma, Siphonodendron martini, S. soci-ale, Palaeosmilia murchisoni, and Amplexus coralloides. The Ballymore Limestone Formation is laterally corre‑lated to the Ardnasillagh Formation in the Lough Corrib succession and differs mainly in having less chert (Table 1). It is succeeded conformably by the Croghan Limestone Formation.

Microfacies: Comprises poorly sorted intraclastic skel‑etal wackestone/packstone/grainstone (Figure 7A, 7D),

moderate to well‑sorted skeletal peloidal packstone/grain‑stone, and spiculitic wackestone (Figure 7B). The main skeletal components include: crinoids, fenestellid bryozo‑ans, sponge spicules, sparse dasycladacaean algae (mono‑laminar and bilaminar Koninckopora and Kamaena), mostly sparse foraminifers, although small archaediscids can be locally abundant (Figure 7C), rare red algae (aouj‑ galiids), calcispheres, problematica (salebrids) and very rare ooids/coated bioclasts.

Depositional setting: The Ballymore Limestone Forma‑tion was deposited in a moderately deep‑water shelf below fairweather wave‑base but above storm wave‑base. Also, the formation comprises mainly fine-grained limestones interbedded with thick mudstone intervals which would have accumulated in a low‑energy shelf setting. The biota is rich and diverse with crinoids, fenestellid bryozoans and sponge spicules, suggesting mainly quiet water, low‑en‑ergy conditions. However, the development of occasional coral biostromes and sparse dasyclad green and red algae implies more turbulent conditions in a shallower photic zone.

Age: The Ballymore Limestone Formation is early Vi‑séan (Arundian) in age, based on the presence of the key foraminifers: Uralodiscus, Paraarchaediscus at involutus stage, Glomodiscus, Valvulinella, and Forschia (typical of MFZ 10-11), as well as the dasyclad alga Koninckopora tenuiramosa, and species of the rugose coral Siphonoden-dron. At its type locality, the age of the Ballymore Lime‑stone Formation is Arundian to Holkerian (Morris et al., 2003).

2.8 Croghan Limestone Formation

The Croghan Limestone Formation (Caldwell, 1959; Morris et al., 2003) is thickest in Gort Na Garrow Bore‑hole (>77 m) (GSI‑07‑06), near Dunmore and is also pres‑ent in GSI‑11‑315 (Figure 4) in the north of the region. In the type section at Cavetown Lough near Boyle c. 107 m are recorded (Caldwell, 1959; Morris et al., 2003). The formation comprises dark-grey, well-bedded, fine-grained argillaceous limestone showing frequent bioturbation, with occasional intervals of massive, light‑grey, coarse‑grained limestone. Chert nodules are commonly developed. The main macrofaunal elements are large solitary rugose cor‑als, fasciculate rugose and tabulate coral colonies, bel‑lerophontid gastropods, brachiopods and sparse crinoids. Identified taxa include: Siphonophyllia garwoodi, Mi-chelinia sp., Siphonodendron martini, and Cravenia sp. The Croghan Limestone Formation is laterally correlated to the Corranellistrum Formation in the Lough Corrib suc‑



Figure 7 Photomicrographs of carbonate microfacies (all in plane polarized light) of early to late Viséan limestones. A-Skeletal packstone with closely packed bioclasts, mostly fenestellid bryozoans (F) and crinoids (C) in sparry calcite cement, Ballymore Lime‑stone Formation, Corancarton Borehole (GSI‑11‑315), 256.5 m; B-Spiculitic wackestone, with monaxon calcitic spicules and ostra‑cods in lime mud matrix, Ballymore Limestone Formation, Corancarton Borehole (GSI‑11‑315), 208.6 m; C-Skeletal packstone with crinoids (C) and archaediscid foraminifers (A) in sparry calcite cement, Ballymore Limestone Formation, Lisna Borehole (GSI‑11‑01), 2.5 m; D-Intraclastic‑skeletal grainstone with intraclasts (I), foraminifers (F) and cyanobacterial coating on shells in sparry calcite cement, Ardnasillagh Limestone (Ballymore Limestone) Formation, Fartamore Borehole (GSI‑12‑02), 133.1 m; E-Skeletal packstone/grainstone with bilaminar palaeotextulariid foraminifers (F) in sparry calcite cement, Burren Formation, Keekil Borehole (GSI‑10‑03), 99.7 m; F-Bryozoan‑rich boundstone with trepostomes (Tr), encrusting tabuliporids (Ta) and fenestellids (F) in lime mud matrix with patches of sparry calcite cement, Burren Formation, Keekil Borehole (GSI‑10‑03), 129.75 m; G-Poorly sorted skeletal, intraclastic grainstone with crinoids, brachiopods, micritized bioclasts and peloids in sparry calcite cement, Tubber Formation, Killsolan Borehole (GSI‑10‑01), 109.8 m; H-Fine‑grained spiculitic wackestone, with dense nework of spicules in lime mud matrix, Lucan Formation, Monivea Borehole (GSI‑06‑387), 152.5 m.


cession and succeeded conformably by the Burren Forma‑tion (Table 1).

Microfacies: Comprises poorly sorted skeletal wacke‑stone and packstone (with microspar matrix), and rare skeletal grainstone. The main skeletal components are cri‑noids, fenestellid bryozoans, sponge spicules, trilobites, rare red algae (aoujgaliids), foraminifers, (small archae‑discids can be locally abundant), calcispheres, problem‑atica (Draffania and salebrids) and kamaenids.

Depositional setting: The Croghan Limestone Forma‑tion was deposited in a moderately deep‑water shelf set‑ting, similar to that of the Ballymore Limestone. Also, the formation comprises mainly fine-grained argillaceous limestones which would have accumulated in a low‑energy shelf. The biota is rich and diverse with crinoids, fenestel‑lid bryozoans, sponge spicules, solitary corals, algae and foraminifers.

Age: The Croghan Limestone Formation is middle Vi‑séan (Holkerian) in age, based on the presence of the key foraminifers: Paraarchaediscus at concavus stage, Eo-staffella, Valvulinella, Forschia (MFZ 12), the dasyclad alga Koninckopora tenuiramosa, and Draffania biloba. At its type locality the age of the Ballymore Limestone For‑mation is Holkerian to Asbian (Morris et al., 2003).

2.9 Burren Formation

The Burren Formation (Pracht et al., 2004; Gallagher et al., 2006) is present in boreholes GSI‑10‑03, GSI‑10‑04, GSI‑10‑05, GSI‑07‑05, GSI‑07‑06 and GSI‑07‑179 with its greatest thickness (>244 m) in Castlequarter Bore‑hole (GSI‑08‑239). The formation occupies most of the low‑lying ground north of Galway city towards Tuam. It was formerly quarried around Angliham and Men‑lough on the southern shores of Lough Corrib, and is cur‑rently well exposed in the working quarries at Two Mile Ditch (GR 132870/229237), Harrington’s Quarry (GR 138281/240201), Mortimer’s Quarry (GR 137553/248535) and Esker Readymix Quarry (GR 153450/224105) (Figure 2). As a result of the recent drilling programme, it is now recognized that the Burren Formation, although in places more argillaceous than in its type locality in the Burren region in Co. Clare, can be extended northwards into south and central Co. Galway (Pracht and McConnell, 2012). Furthermore, it is also recognized that the Two Mile Ditch Member, representing the upper part of the Burren For‑mation, with a type section in Two Mile Ditch Quarry, is laterally equivalent to the Aillwee Member of the Burren region (Pracht et al., 2004; Gallagher et al., 2006). In the type section, the Burren Formation is c. 400 m thick and

the Aillwee Member is c. 150 m thick (Gallagher, 1992). The Burren Formation was previously referred to as the Knockma Formation (Long et al., 2004), but is here incor‑porated in the Burren Formation. In the type area and much of south Co. Galway (e.g. Kiltullagh Borehole GSI‑06‑02; Figure 5) the Burren Formation succeeds the Tubber For‑mation (Pracht et al., 2004; Gallagher et al., 2006), but over much of north Co. Galway it rests conformably on the Croghan Limestone Formation (as in GSI‑07‑06, Figure 4). However, in the southeast of the region it interfingers with and succeeds the basinal facies of the Lucan Forma‑tion, as in Monivea Borehole (GSI‑06‑387) (Figure 5; see Table 1). The top of the Burren Formation and its contact with the overlying Slievenaglasha Formation are not pres‑ent in the study area.

Typically, the limestones of the Burren Formation are pale grey and thickly‑bedded to massive, but there are also intervals that are darker grey, medium‑bedded and cherty. The Formation also comprises black calcareous shales in‑terbedded with bioclastic limestone in the lower part. In the Two Mile Ditch Member, there are a number of clay bands that can be observed in quarry sections resting of‑ten on an irregular palaeokarstic surface (Figure 8A, 8B). In two boreholes (GSI‑07‑05 and GSI‑10‑03, Figure 2) mud‑mound facies lithologies >35 m thick have been en‑countered, but these mounds are not exposed at outcrop. The macrofauna in the Burren Formation is dominated by numerous coral colonies of Siphonodendron sociale, S. pauciradiale and Lithostrotion vorticale (Figure 9A), with crinoids and large gigantoproductid brachiopods of‑ten concentrated in bands at the base and near the top of beds. These brachiopods often occur in a convex‑upward orientation, especially near the top of beds (Figure 9B).

Microfacies: The bedded limestones comprise skeletal wackestone, packstone and grainstone (Figure 7E). The mud-mounds are composed of fine-grained wackestone and have stromatactid cavities with radiaxial fibrous cal‑cite (RFC) cement and peloidal mud. Locally the mounds are rich in trepostome (Leioclema), fistuliporid (Tabu-lipora) and fenestellid bryozoans and form boundstone fabrics (Figure 7F). The main skeletal components in the non‑mound facies are crinoids, dasycladacean green algae (Koninckopora), red algae (aoujgaliids and ungdarellids), fenestellid bryozoans, foraminifers (palaeotextulariids (Figure 7E) and small archaediscids can be locally abun‑dant), sponge spicules, calcispheres, problematica (Draf-fania and salebrids) and kamaenids.

Depositional setting: The Burren Formation was depos‑ited in a shallow‑water shelf setting, mainly between fair‑



A

B

P

PP

PP

P PP

A

Figure 8 Well‑bedded grey limestones of the Asbian Burren Formation (Two Mile Ditch Member) showing: A-An irregular pa‑laeokarstic horizon (arrowed) with green clay wayboard (palaeosol, P) above infilling the topography; B-The palaeokarstic horizon is horizontal (arrowed) with conspicuous orange staining of limestones below the clay band (palaeosol, P). Two Mile Ditch Quarry. Scale: hammer is 40 cm long.


Figure 9 A-Right way up and inverted colonies of Lithostrotion vorticale (L) with overturned convex‑up gigantoproductid bra‑chiopods (G); B-Band of overturned convex‑up gigantoproductid brachiopods (G). Burren Formation (Harrington’s Quarry). Scale: hammer head is 20 cm long; coin is 2.5 cm in diameter.

weather‑ and storm wave‑base, but with periodic shallow‑ing events leading to temporary subaerial exposure. The latter is indicated by the developments of palaeokarstic surfaces and palaeosols, particularly in the upper part of the formation. The rich concentration of large brachio‑pods near the top and base of beds implies more turbulent higher energy conditions, especially when overturned in the hydrodynamically stable position. Abundant coral col‑onies suggest relatively shallow water within the photic zone, confirmed by the abundance of dasyclad algae and large robust thick‑walled foraminifers. The occasional de‑

velopment of bryozoan‑rich mud‑mounds (buildups) sug‑gests a quieter deeper water setting on the shelf.

Age: The Burren Formation is late Viséan (Asbian) in age (MFZ 13-14), and the Two Mile Ditch Member is late Asbian in age (MFZ 14) based on the presence of the diag‑nostic foraminifers: Paraarchaediscus at angulatus stage, Koskinotextularia cribriformis, Cribrostomum lecomptei, Palaeotextularia longiseptata, Lituotubella, Vissariotaxis, Pseudoendothyra and the red alga Ungdarella uralica. At its type locality the age of the Burren Formation is Asbian and is succeeded conformably by the Brigantian Slievena‑



glasha Formation (Gallagher et al., 2006).

2.10 Tubber Formation

The Tubber Formation (Gallagher, 1996; Pracht et al., 2004), attains a maximum thickness of >292 m in Kill‑asolan Borehole (GSI‑10‑01) in the east of the region near Mount Bellew Bridge (Figure 1), and is c. 102 m thick near Craughwell (2099-2) in the south (Figure 4). It ex‑tends from the top of the Ballysteen Formation (or Waul‑sortian Limestone Formation if present) up to the base of the Burren Formation. It is well exposed in the type area around Tubber (c. 8 km SSW of Gort) where it is c. 300 m thick (Pracht et al., 2004). It represents most of the Vi‑séan Burren‑Gort succession below the Burren Formation and occurs mostly in the central and southern part of the region, south of Harrington’s Quarry. Further north it is probably laterally equivalent to the combined Oakport to Croghan Limestone Formations of the Dunmore‑Bally‑moe succession (Table 1).

The Tubber Formation is characterized by medium‑grey, crinoidal‑rich limestone, with shaly partings at some levels and several chert horizons. Fasciculate colonies of Siphonodendron are abundant in the upper part of the Tub‑ber Formation (Pracht et al., 2004).

Microfacies: The Tubber Formation consists mostly of fine- to medium-grained, moderately well-sorted, skeletal and peloidal packstone and grainstone (Figure 7G) with some coarse‑grained bioclastic grainstone intervals. The main skeletal components are crinoids, brachiopods, rare red algae (aoujgaliids), foraminifers, (small archaedisc‑ids can be locally abundant), calcispheres, problematica (Draffania and salebrids) and kamaenids.

Depositional setting: The Tubber Formation was depos‑ited in a moderately shallow‑water shelf, below fairweath‑er wave‑base but above storm wave‑base. The presence of coarser‑grained limestones with intraclasts and rounded bioclasts implies higher energy conditions. The biota is rich and diverse with abundant crinoids and common fora‑minifers, and elsewhere in the upper part of the formation are recorded coral biostromes.

Age: The Tubber Formation ranges in age from latest Tournaisian? to late Viséan (Chadian to Asbian substages). In the lower part of the formation the presence of Kon-inckopora sp. (monolaminar alga) and Eotextularia di-versa suggests a latest Courceyan to Chadian age (MFZ 8-9). Higher in the formation the presence of Eoparas-taffella simplex, Pseuodolituotubella, Brunsia, Pseudoam-modiscus, Eostaffella and absence of archaediscids imply a Chadian age (MFZ 9). Important foraminiferal taxa re‑

corded in boreholes GSI‑09‑381, GSI‑96‑51, GSI‑05‑152 and GSI‑10‑01 include Paraarchaediscus at involutus stage, Uralodiscus rotundus, U. settlensis, Glomodiscus, Planoarchaediscus and Paraarchaediscus at concavus stage, which establish a late Arundian to Holkerian age (MFZ 10-12). In the highest beds of the formation below the Burren Formation in boreholes GSI‑06‑02, GSI‑07‑179 and GSI‑08‑239, the presence of Paraarchaediscus at an-gulatus stage, Paraarchaediscus at concavus stage, and Nodosoarchaediscus, as well as Koskinotextularia, Lituo-tubella and the problematicum Draffania biloba imply a Holkerian to early Asbian age (MFZ 12-13).

2.11 Lucan Formation

The Lucan Formation represents rocks of basinal fa‑cies that are recorded in boreholes in the southeast of the region (GSI‑06‑02, GSI‑06‑387, GSI‑07‑01, GSI‑07‑03, GSI‑95‑113, 2099-2 and 01-1798-1). The greatest thick‑ness (>733 m) is recorded in 01-1798-1. In Kiltullagh Borehole (GSI‑06‑02) 195 m of the Lucan Formation is recorded with rocks of the Tubber Formation above and below (Figure 5). In the Monivea Borehole (GSI‑06‑387), >200 m of the Lucan Formation is recorded below the Burren Formation. The Lucan Formation consists mainly of well-bedded, fine-grained, weakly laminated and bio‑turbated argillaceous limestone alternating with dark grey to black calcareous mudstone. Some limestone beds con‑tain siliceous bands and pyrite is common. Rare slumped intervals are present.

Microfacies: Limestones comprise mainly wackestone and packstone with rare thin beds of grainstone. The main skeletal components are spicules (Figure 7H) and calci‑spheres, with crinoids, fenestellid bryozoans, ostracods and rare foraminifers, with an absence of algae, apart from kamaenids.

Depositional setting: The Lucan Formation was depos‑ited in a deep‑water, low‑energy basinal setting. The pres‑ence of fine-grained limestones with abundant spicules and calcispheres, sparse foraminifers and absence of dasy‑clad algae confirms a depositional setting below the photic zone in quiet water, low‑energy conditions. The presence of detrital quartz and feldspar indicate a terrigenous input, and pyrite suggests dysphotic to anaerobic conditions on the basin floor. Much of the skeletal material has likely been derived from a neighbouring shelf.

Age: The Lucan Formation ranges in age from Arundian to Asbian. In GSI‑07‑01 a suite of archaediscid foramini‑fers of Arundian age (MFZ 11) was recorded including Paraarchaediscus at involutus stage, Planoarchaediscus


and Uralodiscus. In GSI‑07‑03 foraminifers of Asbian age (MFZ 13-14) are recorded, characterized by small archae‑discids of Paraarchaediscus at angulatus stage.

3 Evolution of the depositional setting of Mississippian limestones in west-ern Ireland

The oldest Mississippian marine rocks in the study area are known from boreholes in southern Co. Galway, the Burren and Loughrea in southeastern Galway. The Gort Borehole (G-1) and boreholes around Loughrea contain a transitional succession of sandstone, limestone and shale (Lower Limestone Shale Group) identified as belong‑ing to the Limerick Province — a province recognized throughout most of Munster (Philcox, 1984; Somerville and Jones, 1985; Sleeman and Pracht, 1999). It marks a marine transgression which advanced northwards across the region during the Courceyan (Pracht et al., 2004; Sev‑astopulo and Wyse Jackson, 2009; Somerville and Waters, 2011; Somerville et al., 2011). The succeeding Ballysteen Formation represents widespread, uniform, limestone sedimentation with a rich and diverse open‑marine fauna in the late Tournaisian, that developed as far north as Ba‑ llymoe (Figure 2). The area around Dunmore was desig‑nated by Philcox (1984) as a separate Tournaisian province (Dunmore Province), distinct from the Limerick Province to the south, but similar to the North Midlands Province to the east (Figure 10), although forming a much thinner succession.

The Ballysteen Formation is followed in the later Tour‑naisian by localized development of deeper water Waulsor‑tian mud‑mounds, which typically can be around 200-300 m thick in local complexes, surrounded by bedded cherty limestone (Lees, 1964, 1994; Lees and Miller, 1985, 1995; Devuyst and Lees, 2001; Somerville, 2003). However, in the Ballinasloe area in eastern Galway (Figure 1), the complexes amalgamated to form an interval >700 m thick (Gatley et al., 2005). In the north of the region, around the Slieve Dart Inlier and Mount Bellew Bridge (Figure 2), thinner developments of Waulsortian mud‑mound facies occur (Morris et al., 2003). These interfinger with rocks of the Kilbryan Limestone Formation. The latter formation is characterized by the presence of thin decomposed vol‑canic ash bands (tuffs) which form regional isochronous marker horizons between boreholes. In western Galway, around Lough Corrib, the laterally equivalent Oughterard Limestone Formation contains much siliciclastic detri‑tus derived from the local basal clastics and the exposed

Oughterard granite. It also contains a tuff band which may correlate with one in the Kilbryan Limestone Formation farther east. Microfossil data in the Oughterard Limestone suggest that the tuff band lies close to the chronostrati‑graphic Tournaisian‑Viséan boundary (Sevastopulo and Wyse Jackson, 2009).

In the early Viséan (Chadian) there was the initiation of shallow‑water platform sedimentation with bioclas‑tic limestones, oolites and fenestral limestones (Oakport Limestone Formation). This was followed in the Arun‑dian by more argillaceous bioclastic limestones rich in crinoids and fenestellid bryozoans with abundant colonies of Siphonodendron (Ballymore Limestone Formation). Further to the south, bioclastic limestones of the laterally equivalent Tubber Formation developed, which have oc‑casional oolitic grainstone intervals. In the southeast of the region, deep‑water basinal facies were deposited (Lu‑can Formation) and over 700 m of mainly fine-grained, spiculitic, laminated limestone and mudstone, devoid of algae, accumulated during the Arundian to Asbian. East of Athenry there are rapid changes in thickness and facies changes recorded in the boreholes to suggest that syn‑sed‑imentary faulting on the NE‑trending Athenry Fault and ENE‑trending Craughwell Fault (Figure 1) was probably partly controlling carbonate sedimentation (Figure 5).

Shallow‑water limestone sedimentation continued over most of the region (Croghan Limestone and Tubber Lime‑stone Formations) during the Holkerian, and in the Asbian, a uniform carbonate facies up to 400 m thick was devel‑oped throughout much of the region (Burren Formation). It is characterized by rich faunal bands of brachiopods and corals and abundant dasycladacean green alage. Most cor‑al colonies are in situ but some are overturned. Many ho‑rizons of brachiopod contain concentrations of overturned Gigantoproductus implying periodic strong storm currents sweeping across the shallow water shelf. The upper part of the formation (Two Mile Ditch Member) is also distinc‑tive, as it contains clay wayboards, interpreted as palaeo‑sols, which rest on irregular limestone surfaces considered to be palaeokarsts and comparable to those well‑exposed in the Burren region in the Aillwee Member (Pracht et al., 2004; Gallagher et al., 2006). This unit shows a glacio‑eustatically controlled shallowing‑upward cyclicity lead‑ing to subaerial emergence and karstification of exposed limestones, with terrestrial accumulation of soils. These features are typical of many late Asbian successions in southern Ireland (Gallagher, 1996; Gallagher and Somer‑ville, 1997, 2003; Cózar and Somerville, 2005; Waters et al., 2011). Locally, the Burren Formation contains mud‑



mounds, over 35 m thick, which are only recognized in boreholes. They are like the older, larger Waulsortian mud‑mounds, which contain cavities with peloidal mud and radiaxial fibrous marine cements. However, locally, the Asbian mounds contain a boundstone framework provided by bryozoans. These are similar to bryozoan‑rich mounds (buildups) described from coeval rocks in North Wales (Bancroft et al., 1988; Wyse Jackson et al., 1991) in which the trepostome Leioclema and Tabulipora were important framework components of the buildup. Nevertheless, the absence of light‑requiring algae and a sparse foraminiferal content suggest a quieter and probably deeper water shelf setting than most limestones of the Burren Formation.

The youngest Mississipian limestone rocks exposed in the Burren type section (Slievenaglasha Formation of Brigantian age) are not developed in the Galway area, and if ever deposited were subsequently eroded.

4 Palaeogeographic reconstructions

4.1 Tournaisian

The Lower Paleozoic and Precambrian rocks which lie to the west and northwest of Galway city would have formed a prominent high (Galway High) during the early Tournaisian, with lowland continental sedimentation oc‑curing in the Oughterard area (Cope et al., 1992; Figure 10). This facies is recognized in boreholes, where red‑bed sediments rest unconformably on the Oughterard granite. The Oughterard area forms part of the Connemara Massif (Figure 1), which was the source of much of the siliciclas‑tic detritus brought into the west of the region, although its contribution diminished east of Lough Corrib (Figure 10). In the southeast of the region, however, marine sedimenta‑tion occurred, associated with a trangression that moved northwards across Co. Galway during the early Tournai‑sian (Ivorian) (Sevastopulo and Wyse Jackson, 2009; Fig‑ure 10).

The transitional limestone, shale and sandstone suc‑cession of the Lower Limestone Shale Group, comprises cross‑bedded sandstones, oolitic and skeletal grainstones and mudstones with desiccation cracks (Somerville and Jones, 1985). These indicate an alternation of intervals of sedimentation during low‑ and high‑energy conditions with periodic exposure. They represent a marginal marine to shallow‑water open shelf succession that developed on the Clare‑Galway Shelf which extended south into the Limerick Province (Sevastopulo and Wyse Jackson, 2009). It was succeeded by a predominantly limestone‑

rich deeper water shelf succession of the Ballysteen Group (Somerville and Waters, 2011). The latter, including the Ballymartin and Ballysteen Formations, represents more open‑marine conditions with a richer and more diverse fauna. It is recognized as far north as the Dunmore‑Bally‑moe area. In the late Tournaisian, the deepest water facies was developed in the Loughrea area in the southeast (Fig‑ure 10), where thick accumulations of Waulsortian Lime‑stone are recorded (Lees and Miller, 1995). These would have formed prominent mud‑mounds with substantial top‑ographic sea-floor relief of several hundred metres, most of which was below the photic zone, as dasycladacean al‑gae are absent (Lees and Miller, 1995; Somerville, 2003). Low‑energy sedimentation continued, in part coevally, with the deposition of the Kilbryan Limestone Formation in the northern part of the region, although probably in shallower water, with an abundance of sponge spicules, fenestellid bryozoans and ostracods, with occasional cor‑als. This formation is also characterized by rare thin green clay bands considered to be decomposed volcanic ash bands (tuffs), which can act as isochronous surfaces. Simi‑lar horizons are recorded in the Oughterard Limestone in the west and the equivalent Argillaceous Limestone in Co. Longford, east of the River Shannon (Morris et al., 2003), marking a distinct episode of volcanicity throughout cen‑tral Ireland in the latest Tournaisian.

4.2 Early-Middle Viséan

In the early Viséan (Chadian), a marked shallowing event occurred which led to the development of a wide‑spread shallow‑water platform in the northern part of the region. This was the initiation of the Galway‑Roscommon Shelf (Figure 11), which is known to extend as far north as Boyle and Carrick‑on‑Shannon (Morris et al., 2003; Sevastopulo and Wyse Jackson, 2009; Figure 1). It repre‑sents the accumulation of high‑energy bioclastic and oo‑litic grainstones rich in dasycladacean algae, alternating with low‑energy lagoonal fenestral micrites of the Oakport Limestone Formation. In the Arundian, slightly deeper water shelf facies developed (Ballymore Limestone For‑mation) with more argillaceous bioclastic limestones and coral biostromes. This facies is known throughout the northern part of Co. Galway, but is laterally equivalent to the more variable Tubber Formation, which is known from the Craughwell area in the south and contains oolites, de‑veloped on the Clare‑Galway Shelf (Figure 11). In the east of the region, east of Athenry, deep‑water basinal condi‑tions are recorded with the deposition of the Lucan Forma‑tion in the Athenry Basin (Figure 11). This facies is known


to extend farther east and probably forms the western mar‑gin of the Tynagh Basin (Sevastopulo and Wyse Jackson, 2009) which lies south of Ballinasloe (Gatley et al., 2005; Figure 1). The initiation of these subsiding basins in the early Viséan (Chadian) where substantial thicknesses of sediment accumulated, was probably related to a phase of extensional tectonics which is known throughout the re‑gion (e.g. Tynagh; Philcox, 1984) and the Curlew Fault, north of the Curlew Mountains (Figure 1; Philcox, 1989; Philcox et al., 1992), and eastwards into the Dublin Basin (Nolan, 1989; Strogen et al., 1996).

4.3 Late Viséan

In the late Viséan, shallow‑water shelf facies is well‑developed in the south and southwest of the region with the

deposition of the Burren Formation on the Clare‑Galway Shelf (Figures 1, 11). This limestone facies has a rich and diverse fauna and flora with abundant foraminifers and red and green algae. Coral biostromes are also well developed, as well as concentrations of large brachiopod bands. The presence of palaeokarstic surfaces and overlying palaeo‑sols is an indication of periodic subaerial exposure of the carbonates. A similar shallow‑water carbonate shelf is de‑veloped in the northeast of the region near Mount Bellew Bridge. However, the two shelves are separated by deeper water basinal facies of the Athenry Basin marking a con‑tinuation of the Lucan Formation (Figure 11). In some in‑stances, though, there is clear evidence in long borehole sections (GSI‑06‑387, GSI‑06‑02) to demonstrate that the two facies interfinger.

Figure 10 Palaeogeographic reconstruction of Co. Galway region for the late Tournaisian (based on Cope et al., 1992).



South of Galway City and around Lough Corrib, rare bryozoan‑rich mud‑mounds occur within the bedded lime‑stones of the Burren Formation (Figure 11). These build‑ups probably represent a slightly deeper water shelf setting but are surrounded by algal‑rich bioclastic limestones that clearly formed in shallow water. These mounds are similar to the Waulsortian‑type mounds in possessing stromatac‑tis cavities with radiaxial fibrous marine cements, that are known west of Lough Ree at Lecarrow (30 km northeast of Mount Bellew Bridge) (Morris et al., 2003) close to the northwestern margin of the Dublin Basin between Athen‑ry, Ballinasloe and Athlone (Figure 1). They are also simi‑lar to the Asbian mounds of Co. Sligo (Somerville, 2003; Somerville et al., 2009). They have affinity with shelf

margin mounds described from the northern margin of the Dublin Basin near Loughshinny (Somerville et al., 1992; Somerville, 2003) which have locally developed bound‑stone frameworks.

5 Conclusions

1) Analysis of new borehole data integrated with older borehole records and combined with outcrop study has en‑abled a more detailed comprehensive geological map and lithostratigraphy to be constructed for the Mississippian rocks of Co. Galway in western Ireland.

2) Micropalaeontological investigations using fora‑minifers and microfacies analysis of the limestones has

Figure 11 Palaeogeographic reconstruction of Co. Galway region for the Viséan (Chadian-Asbian) (based on Cope et al., 1992).


enabled them to be precisely dated and their components, textures and fabrics documented. In addition, palaeogeo‑graphic map reconstructions have been achieved for the late Tournaisian, and early to late Viséan intervals in the region.

3) In the southeast of the region the oldest marine Mi‑ ssissippian deposits are associated with a transgression that moved northwards across Co. Galway. These Tour‑naisian rocks belong to the Limerick Province, and are represented by the Lower Limestone Shale and Ballysteen Groups followed by Waulsortian Limestone Formation, as part of an overall deepening‑upward trend. In the north‑west and north of the region, marine Tournaisian rocks are much thinner with a shoreline located northwest of Gal‑way City (Galway High).

4) The central region of Co. Galway has a standard Viséan succession that can be directly correlated with the Carrick‑on‑Shannon succession in counties Roscommon and Leitrim to the northeast and east as far as the River Shannon. It is dominated by shallow‑water limestones (Oakport, Ballymore and Croghan Limestone Formations) that formed the Galway‑Roscommon Shelf. This succ‑ ession is laterally equivalent to the Tubber Formation to the south. In the southeast of the region basinal facies of the Lucan Formation accumulated in the Athenry Basin, which was probably connected to the Tynagh Basin to the east (Figure 1) and persisted throughout most of the Viséan.

5) In the late Viséan, shallow‑water limestones of the Burren Formation extended across much of the southern part of the region on the Clare‑Galway Shelf. These lime‑stones exhibit distinctive palaeokarstic surfaces overlain by terrestrial accumulations of palaeosols which formed during prolonged regressive conditions of glacio‑eustati‑cally controlled cyclicity. They also are characterized by the presence of rich concentrations of large brachiopod shells and colonial coral horizons which developed in pre‑dominantly high‑energy conditions, along with abundant foraminifers and calcareous algae. Locally, bryozoan‑rich mud‑mounds developed in slightly deeper water, lower en‑ergy conditions on the shelf.

Acknowledgements

Markus Pracht publishes with permission provided by the Director of the Geological Survey of Ireland. Brian McConnell is thanked for his insightful comments on an earlier draft of the paper. The reviewers Markus Aretz, Tadeusz Peryt and Colin Waters, and the Editor‑in‑Chief, Prof. Zeng‑Zhao Feng are thanked for their constructive

comments which helped improve the final version.

References

Bancroft, A. J., Somerville, I. D., Strank, A. R. E., 1988. A bryozoan buildup from the Lower Carboniferous of North Wales. Lethaia, 21: 51-65.

Caldwell, W. G. E., 1959. The Lower Carboniferous rocks of the Carrick‑on‑Shannon Syncline. Quarterly Journal of the Geologi‑cal Society of London, 115: 163-187.

Cope, J. C. W., Guion, P. D., Sevastopulo, G. D., Swan, A. R. H., 1992. Carboniferous. In: Cope, J. C. W., Ingham, J. K., Rawson, P. F. (eds). Atlas of Palaeogeography and Lithofacies. Geological Society, London, Memoir, 13: 67-86.

Cózar, P., Somerville, I. D., 2005. Stratigraphy of upper Viséan car‑bonate platform rocks in the Carlow area, southeast Ireland. Geo‑logical Journal, 40: 35-64.

Devuyst, F. X., Lees, A., 2001. The initiation of Waulsortian buildups in western Ireland. Sedimentology, 48: 1121-1148.

Dunham, R. J., 1962. Classification of carbonate rocks according to depositional texture. In: Ham, W. E. (ed). Classification of Car‑bonate Rocks. AAPG Memoir, 1: 108-121.

Embry, A. F., Klovan, J. E., 1971. A Late Devonian reef tract on northeastern Banks Island, Northwest Territories. Bulletin of Canadian Petroleum Geologists, 19: 730-781.

Gallagher, S. J., 1992. Lithostratigraphy, Biostratigraphy and Pa‑laeoecology of the Late Dinantian Platform Carbonates in parts of Southern and Western Ireland. Unpublished Ph. D thesis, Na‑tional University of Ireland.

Gallagher, S. J., 1996. The stratigraphy and cyclicity of the late Dinantian platform carbonates in parts of southern and western Ireland. In: Strogen, P., Somerville, I. D., Jones, G. L. L. (eds). Recent Advances in Lower Carboniferous Geology. Geological Society Special Publications, 107: 239-251.

Gallagher, S. J., Somerville, I. D., 1997. Late Dinantian (Lower Car‑boniferous) platform carbonate stratigraphy of the Buttevant area North Co. Cork, Ireland. Geological Journal, 32: 313-335.

Gallagher, S. J., Somerville, I. D., 2003. Lower Carboniferous (Late Viséan) platform development and cyclicity in southern Ireland: Foraminiferal biofacies and lithofacies evidence. Rivista Italiana di Paleontologia e Stratigrafia, 109 (2): 152-165.

Gallagher, S. J., McDermot, C. V., Somerville, I. D., Pracht, M., Sleeman, A. G., 2006. Biostratigraphy, microfacies and deposi‑tional environments of Upper Viséan limestones from the Burren region, County Clare, Ireland. Geological Journal, 41: 61-91.

Gatley, S., Somerville, I. D., Morris, J. H., Sleeman, A. G., Emo, G., 2005. Geology of Galway and Offaly: A geological description of Galway‑Offaly, and adjacent parts of Westmeath, Tipperary, Laois, Clare and Roscommon to accompany the bedrock geology 1:100,000 Scale Map Series, Sheet 15 with contributions by W. Cox, T. Hunter‑Williams, R. van den Berg and E. Sweeney; A. G. Sleeman (ed.). Geological Survey of Ireland, 90pp.

Jones, G. L. L., Somerville, I. D., 1996. Irish Dinantian biostratig‑



raphy: Practical applications. In: Strogen, P., Somerville, I. D., Jones, G. L. L. (eds). Recent Advances in Lower Carboniferous Geology. Geological Society Special Publication, 107: 371-385.

Lees, A., 1964. The structure and origin of the Waulsortian (Lower Carboniferous) “reefs” of west‑central Eire. Philosophical Trans‑actions of the Royal Society of London, B 247: 483-531.

Lees, A., 1994. Growth‑forms of Waulsortian banks: A reappraisal based on new sections in County Galway. Irish Journal of Earth Sciences, 13: 31-48.

Lees, A., Miller, J., 1985. Facies variation in Waulsortian buildups. Part 2: Mid‑Dinantian buildups from Europe and North America. Geological Journal, 20: 159-180.

Lees, A., Miller, J., 1995. Waulsortian banks. In: Monty, C. L. V., Bosence, D. W. J., Bridges, P. H., Pratt, B. R., (eds). Carbonate mud‑mounds: Their origin and evolution. International Associa‑tion of Sedimentologists Special Publication, 23: 191-271.

Lees, A., Philcox, M. E., 2006. The Lower Carboniferous rocks of G.S.I. map sheets 11 and 14.- A dossier of source materials, mainly unpublished used in the preparation of the booklets to accompanying the map sheets, with contributions from: MacDer‑mot, C. V., Conil, R., F. X., Devuyst, F. X., Hance, L.

Long, C. B., McConnell, B. J., Philcox, M. E., 2004. Geology of South Mayo: A geological description to accompany the bedrock geology, 1:100,000 scale map series, Sheet 11, South Mayo. Geo‑logical Survey of Ireland.

Morris, J. H., Somerville, I. D., McDermot, C. V., 2003. Geology of Longford and Roscommon: A geological description of Long‑ford, Roscommon and part of Westmeath to accompany the bed‑rock Geology 1:100,000 Scale Map Series, Sheet 12. Geological Survey of Ireland, Dublin, 99p.

Nagy, Z. R., Somerville, I. D., Gregg , J. M., Becker, S. P., Shelton, K. L., 2005. Lower Carboniferous peritidal carbonates and asso‑ciated evaporites adjacent to the Leinster Massif, southeast Irish Midlands. Geological Journal, 40 (2): 173-192.

Nolan, S. C., 1989. The style and timing of Dinantian syn‑sedimen‑tary tectonics in the eastern part of the Dublin Basin, Ireland. In: Arthurton, R. S., Gutteridge, P., Nolan, S. C. (eds).The Role of Tectonics in Devonian and Carboniferous Sedimentation in the British Isles. Yorkshire Geological Society Occasional Publica‑tion, 6: 83-97.

Philcox, M. E., 1984. Lower Carboniferous Lithostratigraphy of the Irish Midlands. Irish Association for Economic Geology, Dublin, 1-89.

Philcox, M. E., 1989. Intra‑Dinantian tectonic activity on the Curlew Fault, north‑west Ireland. In: Arthurton, R. S., Gutteridge, P. , Nolan, S. C. (eds). The Role of Tectonics in Devonian and Car‑boniferous Sedimentation in the British Isles. Yorkshire Geologi‑cal Society Occasional Publication, 6: 55-66.

Philcox, M. E., Baily, H., Clayton, G., Sevastopulo, G. D., 1992. Evolution of the Carboniferous Lough Allen Basin, Northwest Ireland. In: Parnell, J. (ed). Basins on the Atlantic Seaboard: Pe‑troleum Geology, Sedimentology and Basin Evolution. Geologi‑cal Society, London, Special Publications, 62: 203-215.

Poty, E., Devuyst, F. X., Hance, L., 2006. Upper Devonian and Mis‑sissippian foraminiferal and rugose coral zonations of Belgium and northern France: A tool for Eurasian correlations. Geological Magazine, 143: 829-857.

Pracht, M., Lees, A., Leake, B., Feely, M., Long, C. B., Morris, J., McConnell, B. J., 2004. Geology of Galway Bay: A geological description to accompany the bedrock geology, 1:100,000 scale map series, Sheet 14, Galway Bay. Geological Survey of Ireland, 76pp.

Pracht, M., McConnell, B., (eds)., 2012. The bedrock geology of geourban project area Galway to accompany the 1:50,000 scale bedrock map parts of sheets 45, 46, 51 and 52, Galway. Geologi‑cal Survey of Ireland.

Sevastopulo, G. D., 1982. The age and depositional setting of Waul‑sortian limestones in Ireland. In: Bolton, K., Lane, H. R., LeMo‑ne, D.V., (eds). Symposium on the Environmental Setting and Distribution of the Waulsortian Facies. El Paso Geological So‑ciety and University of Texas at El Paso, 65-79.

Sevastopulo, G. D., Wyse Jackson, P. N., 2009. Chapter 10. Carbo‑niferous: Mississippian (Tournaisian and Viséan) In: Holland, C. H., Sanders, I. S., (eds). The Geology of Ireland (2nd Ed). Dune‑din Academic Press, Edinburgh, 215-268.

Sleeman, A. G., Pracht, M., 1999. Geology of the Shannon Estuary: A geological description of the Shannon Estuary region including parts of Clare, Limerick and Kerry, to accompany the Bedrock Geology 1:100,000 Scale Map Series, Sheet 17, Shannon Estua‑ry, with contributions by K. Claringbold and G. Stanley (Mine‑rals), J. Deakin and G. Wright (Groundwater), and O. Bloetjes and R. Creighton (Quaternary). Geological Survey of Ireland, 77pp.

Somerville, I. D., 2003. Review of Irish Lower Carboniferous (Mis‑sissippian) mud‑mounds: Depositional setting, biota, facies and evolution. In: Ahr, W., Harris, A. P., Morgan, W. A., Somerville, I. D. (eds). Permo‑Carboniferous Carbonate Platforms and Reefs. Society for Economic Paleontologists and Mineralogists, Special Publication 78 & AAPG Memoir, 83: 239-252.

Somerville, I. D., Cózar, P., Aretz, M., Herbig, H.‑G., Medina‑Varea, P., 2009. Carbonate facies distribution in a tectonically controlled platform in northwest Ireland during the late Viséan (Mississip‑pian). Proceedings of the Yorkshire Geological Society, 57 (3-

4): 173-200.Somerville, I. D., Jones, G. L. L., 1985. The Courceyan stratigraphy

of the Pallaskenry Borehole, Co. Limerick, Ireland. Geological Journal, 20: 377-400.

Somerville, I. D., Pickard, N. A. H., Strogen, P., Jones, G. L. L., 1992. Early to mid‑Viséan shallow‑water platform buildups north Co. Dublin Ireland. Geological Journal, 27: 151-172.

Somerville, I. D., Waters, C. N., 2011. Western Ireland, Chapter 20. In: Waters, C. N., Somerville, I. D., et al. (eds). A Revised Cor‑relation of Carboniferous Rocks in the British Isles. Geological Society Special Report, 26: 133-137.

Somerville, I. D., Waters, C. N., Collinson, J. D., 2011. South Cen‑tral Ireland, Chapter 22. In: Waters, C. N., Somerville, I. D., et


al. (eds). A Revised Correlation of Carboniferous Rocks in the British Isles. Geological Society Special Report, 26: 144-152.

Strogen, P., Somerville, I. D., Pickard, N. A. H., Jones, G. L. L., Fleming, M., 1996. Controls on ramp, platform and basin sed‑imentation in the Dinantian of the Dublin Basin and Shannon Trough, Ireland. In: Strogen, P., Somerville, I. D., Jones, G. L. L. (eds). Recent Advances in Lower Carboniferous Geology. Geo‑logical Society, London, Special Publications 107: 263-279.

Waters, C. N., Somerville, I. D. et al., (eds). 2011. A Revised Cor‑

relation of Carboniferous Rocks in the British Isles. Geological Society Special Report, 26: 186pp.

Wyse‑Jackson, P. N., Bancroft, A. J., Somerville, I. D., 1991. Bryo‑zoan zonation in a trepostome‑dominated buildup from the Low‑er Carboniferous of North Wales. In: Bryozoa Living and Fossil (Ed.Bigney), F. P. Bulletin de la Societé des Sciences Naturelles de l’Ouest de la France Mem. HS1, Nantes, 1991, 551- 559.

(Edited by Yuan Wang)

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A revised Mississippian lithostratigraphy of County Galway … · 2017-02-08 · non, Co. Leitrim to the northeast (Figure 1). Finally, analysis is made of the carbonate depositional