Silurian linguliformean brachiopods and conodonts from the cobra formation, southeastern New South Wales, Australia

2006·13.1 MB·English

Silurian Linguliformean Brachiopods and Conodonts from the
Cobra Formation, Southeastern New South Wales, Australia
James L. Valentine, Damian J. Cole and Andrew J. Simpson
Centre forEcostratigraphy and Palaeobiology, Department ofEarth and Planetary Sciences, Macquarie
NSW
University, 2109,Australia
Valentine, J.L., Cole, D.J. and Simpson,A.J. (2006). Silurianlinguliformeanbrachiopods andconodonts
fromthe CobraFormation, southeasternNew SouthWales,Australia.Proceedings oftheLinnean
SocietyofNewSouth Wales 111, 199-234.
Silurian linguliformean brachiopods and conodonts are documented and described from the type section
throughtheCobraFormation(TaralgaGroup)inMurruinCreek,nearTaralga.Thelinguliformeanbrachiopod
fauna includes linguloids (six taxa), discinoids (three taxa), acrofretoids (four taxa) and a siphonotretoid.
These are the first Late Silurian linguliformean brachiopods to be documented from eastern Ausfralia.
Newtaxa includeAcrotretella dizeugosa sp. nov., uponwhich is basedthe first detaileddescription ofthe
ontogeny ofAcrotretella Ireland, 1961. Elevenmulti-element conodont taxa are recognised, including the
temporally significanttaxon, Kockelella maenniki Serpagli and Corradini, 1998. Based onthese conodont
data,andotherfaunalelements,theCobraFormationinMurruinCreekappearstorangefrommid-Wenlock?
tomid-Ludlow(earlytovcaA-siluricusZone) inage.
Manuscriptreceived23 June2005, acceptedforpublication 7 December2005.
KEYWORDS: Brachiopods, CobraFormation, Conodonts, Linguliformea, Ludlow, New SouthWales,
Silurian.
INTRODUCTION
(Llandovery-Wenlock) Boree Creek Formation of
central-westernNew SouthWales (Dean-Jones 1979;
The Cobra Formation (Taralga Group) crops out Valentine and Brock 2003; Valentine et al. 2003).
in a thin, north-south trending belt east of Taralga These are the first Late Silurian linguliformean
in southeastern New South Wales (Fig. 1). Despite brachiopods to be documented and described from
extensive studies ofanumber ofsections through the
easternAustralia.
Cobra Formation (eg. Jongsma 1968; Roots 1969; Previous accounts of conodonts from the
Scheibner 1973; Morritt 1979; Powell and Fergusson Taralga Group are restricted to the Wombeyan
1979a; Pickett 1982; Matthews 1985), no detailed Limestone(Sherwin 1969;revisedbyPickett 1982), a
accounts or systematic descriptions ofthe numerous biohermalunitinterpretedasLate Silurianinage, and
fossilgroupsfromthesesectionshavebeenpublished. stratigraphically equivalent to the base ofthe Cobra
The present investigation focuses on linguliformean Formation in Murruin Creek (Naylor 1937; Jongsma
brachiopods andconodontsrecoveredfromthe Cobra 1968; Scheibner 1973). Based on a single Pa element
Formation in Murruin Creek, approximately 20 km assigned to Spathognathodus' (= Pandorinella)
'
north ofWombeyan Caves (Fig. 2). exigua (Philip, 1966), Sherwin (1969) suggested that
The only report of linguliformean brachiopods theWombeyanLimestonewasEarlyDevonianinage.
from the Taralga Group is restricted to a single However, in his biostratigraphic review ofAustralian
occurrence of Schizotreta sp. from the base of the Silurian conodonts, Simpson (1995a:339) stated that
Cobra Formation in Murruin Creek (Sherwin 1970). this element could be a morphotype of Ozarkodina
Silurian linguliformean brachiopods from eastern confluens (Branson and Mehl, 1933), a late Silurian
Ausfralia are generally poorly known, with the only species. No conodonts have previouslybeenreported
well-documentedfaunabeing fromthe Early Silurian from the Cobra Formation.
SILURIAN BRACHIOPODS AND CONODONTS
GEOLOGYAND STRATIGRAPHY to have originated through post-lithification tectonic
activity (Matthews 1985).
m MU
The Early Silurian (mid-Wenlock?) to Early The first 468 of the section through the
DevonianTaralgaGroup,croppingouteastofTaralga, Cobra Formation consists of well-bedded, grey-
is an upward-shallowing, deepwater sequence black shales (4-25 cm thick) interbedded with pale
deposited along the eastern limb ofthe Cookbundoon coloured, nodular limestone bands (1-6 cm thick)
m
Synclinorium, on the western edge of the Capertee and dark-grey limestone beds (up to 1.8 thick)
High inthe Hill EndTrough (Scheibner 1973; Powell (Fig. 3). However, continuously exposed horizons
m m
and Fergusson 1979b; Matthews 1985) (Fig. 1). The are restricted to 126-171 and 431-468 above
MU
Cobra Formation forms the basal unit ofthe Taralga the base ofthe section (Fig. 3). Between these
m
Group and consists of -670 of interbedded fine- intervals, only sporadic outcrops ofgrey-black shales
grained micrites, siltstones and limestones (Pickett and nodular limestones, identical to those occurring
m MU
1982; Matthews 1985). Based on the fine detrital in the interval 126-171 above the base ofthe
nature of the Cobra Formation, the orientation of section, were observed.
fossil corals, and the occurrence of the calcareous The only linguliformean brachiopod recovered
MU
alga,PseudochaetetesHaug, 1883 inassociationwith fi"om this part of the section was a single
MU
the tabulate coral, Entelophyllum sp., from the base dorsal valve of Orbiculoidea sp. from sample
of the Cobra Formation in Little Wombeyan Creek 21 (174.6 m above the base of the section) (Table
MU
(Fig. 1), Pickett (1985) concluded that the Cobra 1). Conodonts fi^om this part of the section are
Formation was of turbiditic origin. Disarticulated all predominantly long ranging forms and include
rhynchonelliformean brachiopods from the same Panderodus unicostatus (Branson and Mehl,
horizons are all deposited concave side down, 1933), Panderodus recurvatus (Rhodes, 1953) and
suggesting post-mortem transportation via traction Dapsilodus obliquicostatus (Branson and Mehl,
currents (Matthews 1985). 1933) (Table 2). This fauna is broadly suggestive ofa
The Cobra Formation overlies the low grade Wenlock to Pridoli age.
metamorphic shales and greywackes of the Late Jongsma (1968), Roots (1969) and Scheibner
Ordovician to Early Silurian Burra Burra Creek (1973)allrecordedBatocaramitchelli(Foerste, 1888)
m
Formation (uppermost unit of the Triangle Group) within the first 175 of their respective sections
(Figs 1, 2). The contact between the two units is through the Cobra Formation in Murruin Creek. This
widelystatedto faulted, orahighangleunconformity, species ranges fi^om the mid-Wenlockto mid-Ludlow
and a significant time break has been implied to exist inAustralia (Pickett et al. 2000). Corals identified by
betweenthem (Jongsma 1968; Roots 1969; Scheibner Sherwin (1969) and Pickett (1985) from the base of
1973;Talentetal. 1975;Powelletal. 1976;Powelland the Cobra Formation in Little Wombeyan Creek (Fig.
Fergusson 1979a, b; Pickett 1982). In contrast, both 1) belong to the Hatton's Comer coral assemblage
Morritt (1979) and Matthews (1985) have arguedthat (Strusz and Munson 1997; Munson et al. 2000) and
this contact is paraconformable (though sometimes suggests a late Wenlock to Ludlow age. Therefore,
faulted) as in Murruin, Kerrawary, Guineacor and the base ofthe Cobra Formation would appear to be,
Cowhom creeks, orgradational overabout 15 m as in atmost, mid-Wenlock in age.
Little Wombeyan Creek (Fig. 1). Continuously cropping out horizons occur for
No evidence of a high angle unconformity the last 64.2 m ofthe MU section, beginning 605 m
MU
betweenthe BurraBurraCreek andCobra formations above its base (Fig. 3). This part ofthe section
was observed in Murruin Creek. The contact is consistsofwell-bedded,dark-greylimestonehorizons
marked by a prominent, 14 m thick conglomeritic (up to 20 cmthick) interbeddedwiththickerintervals
horizon, whose upper boundary marks the start of of soft, light brown mudstones between 605-623.1
MU m MU
the section (Figs 2, 3). Matthews (1985) argued above the base of the section. Several faults
that this conglomeritic horizon only occurs where also occur in this part ofthe Cobra Formation (Fig.
—
m MU
faulting (parallel and/orsubparalleltobedding) exists 2) one at623.1 abovethebase ofthe section,
betweentheBurraBurraCreekandCobraformations. wheremassiveblacklimestonesreplacethemudstone
The fault, and associated conglomerate, can occur horizons. These limestone horizons continue through
withineitherformation, oras inMurruinCreek, atthe to the top ofthe Cobra Formation (Fig. 3). This part
MU
contact between the two. Where faulting is absent, as of the section has undergone folding as part of
inLittle Wombeyan Creek, the conglomeritic horizon the latest Devonian to early Carboniferous regional
is also absent. Therefore, this horizon would appear deformation event that affected the Hill End Trough
(Powell etal. 1976).
200 Proc. Linn. Soc. N.S.W., 127, 2006
VALENTINE, COLE AND SIMPSON
J.L. D.J. A.J.
34°00'S 34''00'S
20 km
Sydney Basin
Granite Plutons
Late Devonian to Lambie Group
EarlyCarboniferous
Earlyto IVIiddle ^1 > Bindoolc Porphyry
Devonian > V Complexandequivalents
? EarlySilurianto Taralga Group
Early Devonian
? Late Ordovician Triangle Group
to ? EarlySilurian
Anticline
Synclina
Figure 1. Generalised regional geological map ofthe Taralga area showing where the Taralga Group
crops out (modified afterPowell and Fergusson 1979a). Study area in Murruin Creekis indicated by
boxed area and enlarged in Fig. 2.
Proc. Linn. Soc. N.S.W., 127, 2006 201
SILURIAN BRACHIOPODS AND CONODONTS
MU
Figure 2. Detailed geological map ofstudy area in Murruin Creek, showing location of section.
MU
Note that the section runs from right to left.
The change in Hthology to massive black
limestones coincides with a dramatic increase in the
number oflinguliformean brachiopods and conodont FiguMreU3. (OPPOSITE) Stratigraphic column of
elements recovered. The linguliformean brachiopod the section showing lithology and all sam-
fauna is dominated by acrotretoids, particularly pulmend hroerpirzeosnesn.t Nmeutmrbeesrasboovnetthheelbeaftseofofeatchhe McoUl-
Opsiconidion ephemerus (Mergl, 1982) (Table 1).
This species ranges from the upper Ludlow of the section and those on the right, sample numbers.
m
Detail of lithology and sampling for the 47 of
Kopanina Formation to the Pridoli Pozary Formation MU MU
of the Czech Republic and broadly agrees with the section from sample 1 to 21 is enlarged
Ludlow age determination for the upper part of the to the left. Note that due to scale, only those nodu-
MU lar limestone horizons sampled in this interval
section based on conodont data (see below). In
are included. Detail of lithology and sampling
fact, the Murruin Creek linguliformean brachiopod m MU
for the 2.51 of section from sample 25 to
assemblage is similar to that described by Mergl MU m
(2001) from the deepwater Ludlow Kopanina M30U, and foMrUthe 0.9 of section from sam-
ple 32 to 38, are enlarged to the right.
Formation in the Barrandian ofthe Czech Republic.
The Kopanina fauna, also dominatedby acrotretoids,
202 Proc. Linn. Soc. N.S.W., 127, 2006
VALENTINE, COLE AND SIMPSON
J.L. D.J. A.J.
644m
170m-
160m
150m-:
Flaggysandstonesandshales
140m-
Massiveblacklimestones
Calcltebands
Nooutcrop
Dark-greytoblacklimestonebeds
130m-i
Lightcoloured nodularlimestone
bands
Grey-blackshalesandmudstones
Grey-blackshalesinterbeddedwith
lightcolourednodularlimestonebands
Sporadicallycropping outhorizonsof
grey-blackshalesinterbeddedwith
lightcolourednodularlimestonebands
i_
o o o
Burra Burra o o o o Conglomerate
Creek $^
Formation Black,thinlybeddedshales
27 Samplenumbers
Proc. Linn. Soc. N.S.W., 127, 2006 203
SILURIAN BRACHIOPODS AND CONODONTS
0^
MU
Metres above base of section od
C/3
Sample Numbers
e2
21 31 32 34 35 36
Brachiopod Taxa
w
1 1 2
pseudolingulid gen. et sp. indet. 1
dv 1 2 2 5
w
Kosagittellal sp. 1 1 2
w?
1 1
Rowellellal sp. dv? 2 2
frag 1 19 20
w
1 1
Paterula sp. dv 2 2
CO 1 1
linguloid gen. et sp. indet. 1 frag 8 8
linguloid gen. et sp. indet. 2 dv 1 1
w
2 2
Orbiculoidea sp. dv 1 2 1 2 2 6 14
frag 22 1 6 4 7 40
w
2 1 3
Schizotreta sp. dv 3 4 3 6 16
frag 4 2 12 21 39
discinoid gen. et sp. indet. 1 dv 1 1 2
dv 29 9 1 5 19 63
Artiotreta sp. cf. A. longisepta
CO 1 1 1 3
w
25 6 3 2 36
Acrotretella dizeugosa sp. nov.
dv 23 7 5 4 39
w
4 8 8 14 34
Opsiconidion sp. cf. O. ephemerus
dv 19 24 16 20 79
Opsiconidion sp. dv 8 2 3 3 16
siphonotretid gen. et sp. indet. 1 dv 2 1 3
Table 1. Distribution and abundance ofeach linguliformean brachiopod species recovered
MU
from productive samples along the section through the Cobra Formation in Murruin
w
Creek.Abbreviations: = ventral valve(s); dv = dorsal valve(s); frag = fragment(s); co =
conjoined specimen(s).
204 Proc. Linn. Soc. N.S.W., 127, 2006
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VALENTINE, COLE AND SIMPSON
J.L. D.J. A.J.
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Proc. Linn. Soc. N.S.W., 127, 2006 205
SILURIAN BRACHIOPODS AND CONODONTS
agreement with the Ludlow age
Abbreviation Explanation
L valve length determination for this part ofthe
W MU
valve width section.
H
valve height Conformably overlying
WI width ofpseudointerarea the Cobra Formation in
LI maximum length ofpseudointerarea
Cowhom, Kerrawary, Guineacor
Fa length ofpedicle foramen
F'w width ofpedicle foramen and Little Wombeyan creeks
Fp point oforigin ofpedicle foramen (Fig. 1), are thinly bedded (<1
LS length ofdorsal valve median septum m thick), deep-water, turbiditic
MBHSS mpaoxiintmoufmohriegiignhtofofdodrosraslalvavlavlevememdeidainansespetputmum arenites, lutites and siltstones of
OSP point oforigin ofsurmounting plate theArgyle Formation (Scheibner
LSP length ofsui-iiiounting plate 1973; Pickett 1982; Matthews
WSP width ofsurmounting plate 1985). In Murruin Creek, the
WLPP length oflarval shell CobraFormation is conformably
width oflarval shell
overlain by the Whipbird Creek
HP height oflarval shell
N number ofmeasurements Formation (Fig. 2), a turbiditic
MEAN average value sequence of interbedded
SD standard deviation sandstones and shales that may
MAX maximum value
represent a distal facies of the
MIN minimum value
Argyle Formation. Matthews
Table 3.Abbreviations used for measurements (in |am) oflinguli (1985) reported rare boundary
formean brachiopods. Abbreviations based on those ofPopov and faulting between the Cobra
Holmer (1994:35, fig. 39). Where applicable, all measurements are and Argyle formations in Little
made from the posterior margin. Wombeyan Creek and similar
faulting occurs in the upper
includes numerous small discinids and rarer part of the Cobra Formation in
occurrences of larger discinids, obolids, linguloids Murruin Creek (Fig. 2). The contact between the
m
and a siphonotretoid (Mergl 2001). Cobra and Whipbird Creek formations lies -670
MU
The majority of the conodonts recovered from above the base ofthe section (Fig. 3), compared
thispartoftheMUsectionwerethesamelongranging to only 550 m reported by Scheibner (1973), Pickett
forms occurring in the lower part ofthe MU section (1982) and Matthews (1985). Given the folding and
(Table 2). The lenticular and triangular elements of faulting occurring inthispartofthe CobraFormation,
MU
Belodella anomalis Cooper, 1974 recovered from the possibility ofrepeatedhorizons inthe section
Murruin Creek (Table 2) are all broad-based (Fig. carmot be dismissed.
4a-g). Simpson (1995b: 310) and Jeppsson (1989)
noted a general morphological trend in this taxon
SYSTEMATIC PALAEONTOLOGY
ofbroad-based elements in the Ludlow (eg. Cooper
1974:pl. 1, figs 1-10; Simpson et al. 1993:fig. 4G-
I; Simpson 1995b:pl. 16, fig. 15) and narrower- Discussion
based elements in the Pridoli (eg. Jeppsson 1989: All type, paratype and figured materials are
pi. 1, fig. 15; Simpson 1995b:pl. 16, fig. 21). Farrell lodged in the palaeontological collections of the
(2004), however, documented a relatively broad- Australian Museum, Sydney (AM F).
based population of elements from the Camelford
Limestone and interpreted this sequence as Pridoli in Phylum Brachiopoda Dumeril, 1806
MU m
age. Sample 34 (642.6 above the base ofthe
M
section) also yielded a single Pa and element of Measurements
the temporally significanttaxon,Kockelellamaenniki Measurements (in jiim) of linguliformean
Serpagli and Corradini, 1998 (Table 2). This species brachiopods are based on those of Popov and
is restricted to the early to rmdi-siluricus Zone (mid- Holmer (1994:35, fig. 39). Abbreviations used for
Ludlow) of Europe and North America (Corradini the measurement of all taxa are listed in Table 3.
and Serpagli 1999; Serpagli and Corradini 1999). In Note that the width of some incomplete specimens
addition, a pygidium, possibly of B. mitchelli, was was determined by measuring half the width
MU m
recovered from sample 28 (624.6 above the and multiplying by two, assuming a bilaterally
base of the section) (Fig. 3). This is also in general symmetrical organism.
206 Proc. Linn. Soc. N.S.W., 127, 2006
VALENTINE, COLE AND SIMPSON
J.L. D.J. A.J.
OrderLingulidaWaagen, 1885 that continues forward ofthe pseudointerarea a short
Superfamily Linguloidea Menke, 1828 distanceasashallowgroove(Fig.4n). Thesubcircular
Family Pseudolingulidae Holmer, 1991 larval shell is smooth and located marginally. The
post-larval shell ornament consists ofwidely spaced
pseudolingulid gen. et sp. indet. 1 concentric lamellae that are best developed on the
Fig. 4a-f lateral slopes (Fig. 4m). These characteristics recall
Kosagittella, and in particular, Kosagittella pinguis
Figured material Mergl,2001 fi-omtheLochkovianLochkovFormation
AM AM
F328314 (Fig. 4a-c): ventral valve; of the Czech Republic. However, the ventral valve
AM
F128315 (Fig. 4d): dorsal valve; F128316 (Fig. pseudointerarea of the Murruin Creek specimens
MU
4e, f): dorsal valve, sample 36. All from sample differ fi"om Kosagittella in lacking laterally inclined
MU
35 unless otherwise mentioned (Table 1). propareas (Fig. 4o).
Discussion Family Zhantellidae Koneva, 1986
The ventral valve pseudointerarea has a well- RowellellaWright, 1963
developed pedicle notch and small, subtriangular
propareas (Fig. 4b, c). The posterior margin of the Type species
dorsal valve is thickened and has an undivided, Rowellella minuta Wright, 1963.
anacline pseudointerarea (Fig. 4d). The larval shell is
smooth and the post larval shell ornament consists of Rowellellal sp.
fine concentric filae (five per 10 |j.m) (Fig. 4a, e, f). Fig. 4p-r
'Lingula' lewisii Sowerby, 1839, from the
lower Ludlow Aymestry Limestone of Wales, was Figured material
AM AM
questionablyreferredtothepseudolingulidsbyHolmer F128322 (Fig. 4p): dorsal? valve;
(1991) based on similarities in vascular impressions F128323 (Fig. 4q, r): ventral? valve. Both firom
MU
and muscle scars with PseudoUngula quadrata (von sample 36 (Table 1).
Eichwald, 1829). 'Lingula' lewisii differs by being
more rectangular with sharper cardinal angles and Discussion
is larger (average length 11.5 mm) (Chems 1979; Although incomplete, these specimens appear
Bassett 1986). IWadiglossa perlonga (Barrande, to be elongately subrectangular to subtriangular
1879) from the Ludlow Kopanina Formation of in outline (Fig. 4p). The post-larval shell ornament
the Czech Republic, is distinguished by its acutely consists ofdistinct concentric lamellae (six to seven
pointed beak and post-larval shell ornament of low, per 100 |im) separatedbyflatinterspacesbearingfilae
poorly developed concentric growth lines (Mergl that are initially discontinues laterally, but become
2001). concentric during latergrowth stages (Fig. 4q, r). The
post-larval shell microomament ofRowellella cf. R.
Family Obolidae King, 1846 lamellosa Popov, 1976 (inNazarov and Popov 1976)
Subfamily Obolinae King, 1846 fi^om Middle Ordovician strata in Sweden (Holmer
Kosagittella Mergl, 2001 1989) consists of similar sets of discontinuous
filae, but these are developed over the entire shell.
Type species Rowellella distincta Bednarczyk and Biemat, 1978
Kosagittella claraMergl, 2001. from the lowerArenig ofthe Holy Cross Mountains
in Poland (Bednarczyk and Biemat 1978) and the
Kosagittella'? sp. Arenig Klabava Formation of the Czech Republic
Fig. 4m-o (Mergl 1995, 2002), also has a similar post-larval
shell microomament, but has more prominent and
Figured material widely spaced concentric lamellae. The post-larval
AM
F128321 (Fig. 4m-o): ventral valve, sample shell microomament ofRowellella sp. firom the Early
MU
32 (Table 1). Ordovician Bjorkasholmen Limestone of Sweden
and Norway (Popov and Holmer 1994) also consists
Discussion ofdiscontinuous sets ofconcentricfilae, butthese are
The ventral valve has a thickened posterior wall only developed anteriorly.
andaweakly apsacline to orthoclinepseudointerarea, The dorsal? valve interior of the Murruin
medially divided by a parallel sided pedicle groove Creek specimens has an elongate muscle field that
Proc. Linn. Soc. N.S.W., 127, 2006 207
SILURIAN BRACHIOPODS AND CONODONTS
MU
Figure 4. a-f. Pseudolingulid gen. et sp. indet. 1 all from sample 35 unless otherwise mentioned, a-
AM AM
c. Ventral valve F328314; a, exterior; b, interior; c, detail ofpseudointerarea. d. Dorsal valve
AM MU
F128315, interior, e, f. Dorsal valve F128316, sample 36; e, exterior; f, detail oflarval shell, g, h.
MU AM AM
Paterulasp.bothfromsample 36g.Ventralvalve F128317; interior, h.Dorsalvalve F128318;
AM MU
exterior,i-k.Linguloidgen.etsp.indet.2.Dorsalvalve F128319,sample 35; i,exterior;j,interior;
AM
k, detail ofpseudointerarea. 1. Linguloid gen. et sp. indet. 1. Fragment ofpost-larval shell F128320,
MU AM MU
sample 36; exterior, m-o. Kosagittella? sp. Ventral valve F128321, sample 32; m, exterior;
MU AM
n, interior; o, anteriorview. p-r. Rowellellal sp. both from sample 36 p. Dorsal? valve F128322;
AM
interior (scale bar equals 1000 |j^m). q, r. Ventral? valve F128323; q, exterior; r, detail ofpost-larval
shell microornament (scale bar equals 10 jam). Unless otherwise mentioned all scale bars equal 100 \x\a.
208 Proc. Linn. Soc. N.S.W., 127, 2006