Marine Micropaleontology, 15 (1990) 365-378 365 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Significance of Devonian-Carboniferous Radiolarians from Accretionary Terranes of the New England Orogen,

Eastern Australia

JONATHAN AITCHISON Department of Geology and Geophysics, University of New England, Armidale, NSW 2351 (Australia)

(Received August, 1~88; revised and accepted March, 1989)

Abstract

Aitchison, J.C., 1990. Significance of Devonian-Carboniferous radiolarians from accretionary terranes of the New England orogen, eastern Australia. Mar. Micropaleontol., 15: 365-378.

Radiolarians provide age constraints for many previously undated terranes in the New England Orogen (NEO), a tectonic collage developed along the eastern margin of Australia.

Djungati terrane, the age range of which was previously unknown, contains two distinctive siliceous sedimentary lithofacies. The oldest is a thick sequence of red, ribbon-bedded cherts which probably accumulated in a deep ocean- floor setting far from land. Middle Silurian through Late Devonian radiolarians have been recovered from these cherts. Green tuffaceous cherts which contain a latest Devonian (Famennian) radiolarian fauna depositionaUy overlie the lower red ribbon-bedded chert sequence. These cherts are intercalated with volcaniclastic sediments and the fauna which they contain can be used to constrain the timing of accretion of older rocks into a subduction complex.

Anaiwan terrane, which was also previously undated, contains thin ribbon-bedded cherts which are depositionally overlain by tuffaceous chert, siliceous siltstones and volcaniclastic sediments. Latest Devonian (?late Famennian ) and Early Carboniferous radiolarians have been recovered from these cherts and tuffaceous siltstones.

Radiolarians also occur in fine-grained siliceous sediments of the Yarrimie Formation, part of the Gamilaroi terrane. These radiolarians are of Late Devonian (Frasnian) affinity and their presence indicates that blocks of limestone, which contain Givetian conodonts and corals and were previously thought to indicate the age of the Yarrimie For- mation, are allochthonous.

Introduction

The geology of eastern Australia is domi- nated by a tectonic collage of terranes known locally as the New England Orogen (NEO). The detailed geology of the NEO is not well known due to structural complexity and poor expo- sure. Recent detailed work has shown the oro- gen to be a complex collage ofterranes (Fig. 1 ) which were accreted to the eastern margin of Australia at various times during the late Pa- leozoic (Flood and Aitchison, 1988a, b). Early

plate tectonic models for this portion of eastern Australia assumed a relatively simple active plate margin during the Paleozoic (Leitch, 1974, 1975; Cawood, 1983; Harrington and Korsch, 1985; Murray et al., 1987). However, previous models for the tectonic development of the NEO are inconsistent with the available data (Flood, 1988) and the interrelationships of many of the terranes present are unknown. Although some terranes are moderately fossiliferous (e.g., Gamilaroi terrane), macrofossils are generally scarce and previous tectonic models have been based on assumed ages. Recent radiolarian

0377-8398/90/$03.50 © 1990 Elsevier Science Publishers B.V.

366 J. AITCHISON

I ~ Early Permian Successions

OVERLAP SEQUENCES

~ Late P e r m i a n V o l c a n i c s

Successorl Basins

GRANITOIDS

~ Late P e r m i a n - E a r l y Triassic I and A Types

~ L a t e C a r b o n i f e r o u s - Early Permian S Typ~

STITCHING1 D + E PLUTONS !

_ 2 G + H

3 D + I 4 C + D

s A + C i L , . . . . . . . . , L1898 - - - - - - h

L1904 - -

~ 1~2o

E

+ + . . . . + + + +

vvv~vvvvJvvvvvv ~++

vvvvvvvvJvvvvvv

v v v v v v v ~ J v v v , v ~ v v v v J v v : 1 2 1 . . . . . . 24

v v v v , , j I . . . . . . . . . . . , ~

* ÷ ÷ ~ v v v v v . ¢ l . . . . _ . . . . . . . . . ( N

v v v ~ v v v v J I . . . . . . . . . . . . . . . v v v v v v v v ¢ ~ . . . . . . . . . . . . . . v v v v v v v v ~ : ' ' ~ : ' : : '. • ~ v v , v v v v ¢ ~ . : . : . . . . . /

TERRANE SYMBOLS

t/ ,ak Gamilaroi ! B Weraerai r

: v Djungati i D Anaiwan i ,m ,

; ~ - - - Keinjan

' - - Gidabal ! ( J Yugambal r

i H Bundjalung Ngaku

~.w Birpai I K Ngamba

INDIFFERENTI

+ + + +

+ + + +

50km

)01~ ~ / ~L1900

)02

l UNDIFFERENTIATED

%

I¢

153 °

Fig. 1. Lithotectonic terrane map of the southern portion of the New England Orogen (after Flood and Aitchison, 1988b) with the areal extent of major terranes discussed in this paper indicated. Radiolarian localities discussed in this paper are indicated by University of New England UNE L numbers.

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 367

studies (Ishiga et al., 1987, 1988; Aitchison, 1988a-e this paper) clearly show that many of these age assumptions are incorrect.

The first description of radiolarians from rocks of the NEO was by Hinds (1899). He de- scribed 53 species in siliceous limestone sam- ples from the Yarrimie Formation exposed at Tamworth Common. Despite this excellent early work no further detailed studies of Aus- tralian radiolarians were made until the 1980's (Gogo Formation, Canning Basin, Western Australia: Nazarov et al., 1982; Nazarov and Ormiston, 1983; Lachlan Fold Belt, NSW: Webby and Blom, 1986). Although the pres- ence of radiolarians, in parts of the NEO, has long been known (David and Pi t tman, 1899; Richards and Bryan, 1924; Bryan and Jones, 1962) studies of these fossils did not commence in this area until the late 1980's.

Utilising HF acid leaching techniques (Pes- sagno and Newport, 1972), well preserved ra- diolarians have been extracted from siliceous rocks of the NEO. These radiolarians can be used to place the first reliable age constraints on the development of some previously undated terranes. When accompanied by detailed map- ping (e.g., Aitchison, 1988e) this work clearly demonstrates that the NEO is much more com- plex than previously thought and illustrates the need for further study.

Details of radiolarian faunas discovered dur- ing preliminary (and continuing) work are de- scribed in this paper. Most radiolarians discov- ered so far are of Late Devonian to Early Carboniferous age and many of the species present are common in radiolarian faunas de- scribed from the northern hemisphere (De- flandre, 1952, 1960; Holdsworth, 1973; Hold- sworth et al., 1978; Holdworth and Jones, 1980; Comble et al., 1985; Cheng, 1986). Fossils illus- trated in this paper are curated at the Austra- lian National Museum, Sydney and corre- sponding AMF numbers are indicated. Fossil localities are assigned University of New Eng- land locality (UNE L) numbers.

G a m i l a r o i t e r r a n e

Gamilaroi terrane is a stratigraphic terrane comprising a discontinuous, Devonian through Permian, sequence of epiclastic and volcanic rocks. Rocks stratigraphically lowermost in the terrane crop out at its eastern edge and are in fault contact with the Weraerai terrane, a dis- membered ophiolite. These strata include tuff, volcaniclastic conglomerate, sandstone, silt- stone, fossiliferous limestone and keratophyre. Cawood (1976) reported Late Cambrian and Middle-Late Ordovician fossils from limestone clasts within conglomerates. More recently Ca- wood (1983) and Leitch and Cawood (1987) have assigned lowermost Gamilaroi terrane sediments a Cambro-Ordovician age. However, the Cambrian and Ordovician fossils are all from clasts redeposited in conglomerates and not in situ. Therefore, they do not necessarily indicate the depositional age of these conglom- erates and there is no a priori reason for this age assignment. Thin section examination of cherts intercalated with these rocks reveals the presence of radiolarian ghosts bearing three- bladed spines which may indicate Late Devon- ian or younger affinities. The oldest well-dated strata in the Gamilaroi terrane are Early De- vonian epiclastic breccias. These sediments are overlain by a diverse sequence of predomi- nantly epiclastic conglomerate, sandstone and siltstone along with interbedded tuffs, lime- stones and spilitic pillow lavas up to 3000 m thick (Crook, 1960a; Cawood, 1983). Cawood and Leitch (1985) suggest that a general t rend towards deeper water deposition is seen upsection.

Lower Carboniferous strata are of similar fa- cies to those of Late Devonian age. Gradual regression led to shallow marine deposition by early Visean time (Crook, 1960b; Evans and Roberts, 1980; Mory, 1982). Close proximity to a contemporaneously active volcanic arc is in- dicated by the presence of andesitic, dacitic and rhyolitic tufts and lavas. Development of shal-

368 J. AITCHISON

low marine oolitic limestones was widespread in the Visean.

Late Carboniferous sedimentation was pre- dominantly terrestrial and includes diamictites associated with the Gondwana glaciation (McKelvey, 1981). Violent silicic plinian and phreatoplinian volcanism was contempora- neous with terrestrial sedimentation (McPhie, 1986).

Permian sediments include non-marine and marginal marine conglomerate, sandstone, silt- stone, oil shale and coal. Silicic tuffs interbed- ded with the clastic sequence provide evidence of penecontemporaneous volcanism (McPhie, 1986).

Gamilaroi terrane has been simply deformed

by faulting and broad open folding. Burial metamorphism to zeolite facies is widespread with slightly higher grade prehnite-pumpel- lyite facies found in stratigraphically lower- most sediments.

Gamilaroi terrane formed on, or in close proximity to, an active oceanic island arc dur- ing the early (Devonian) stage of its develop- ment. Radiolarians are abundant in the Yarri- mie Formation (part of the Tamworth Group of Crook, 1961). Although they are abundant in tuffaceous siltstones, these radiolarians are not always well preserved. Hinde (1899) de- scribed 53 radiolarian species from etched thin- sections of dark colored siliceous limestones of the Yarrimie Formation exposed at Tamworth

Fig. 2. Radiolarians from siliceous limestones and cherts of the Yarrimie Formation (Gamilaroi terrane) localities UNE L1901 [Tamworth Hospital Quarry figs. A, B, H, I] and UNE L1902 [Silver Gully figs. C-G]. Length of scale bar in #m is indicated in parentheses. A: Ceratoikiscum sp. cf. C. avimexpectans Deflandre (75 #m), AMF74482, B: Entactinosphaera sp (90 #m), AMF74483, C: Entactinia additiva? Foreman (120 #m), AMF74484, D: SpongentactineUa corynacantha Na- zarov and Ormiston ( 110 #m ), AMF74485, E: ?Palaeoscenidium cladophorum Deflandre (90 #m ), AMF74486, F: Spongen- tactineUa sp. cf. Spongentactinella sp. 2 of Nazarov and Ormiston 1983 (80 Mm), AMF74487, G: Entactinosphaera grandis Nazarov (90 Hm), AMF74488, H: Entactinosphaera vetusta (Hinde), (110 #m), AMF74489. I: Staurodruppa praelonga (Hinde) (90 Hm), AMF74490.

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 369

Fig. 3. (for exp lana t ion see p. 371 )

370 J. AITCHISON

Fig. 4. (for e x p l a n a t i o n see p. 371 )

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 371

Common. The city of Tamworth has grown considerably since 1899 and the best exposures of these rocks are now found in a quarry behind Tamworth Hospital. The fauna described by Hinde (1899) has been recollected from Tam- worth (UNE L1901 ) and at a new locality, Sil- ver Gully (UNE L1902) in the type section of the formation (Fig. 2). Radiolarians present include: Ceratoikiscum sp. cf. C. avimexpectans Deflandre, Spongentactinella corynacantha Na- zarov and Ormiston, ?Palaeoscenidium clado- phorum Deflandre, Spongentactinella sp. cf. Spongentactinella sp. 2 of Nazarov and Ormis- ton (1983), Entactinia additiva? Foreman, En- tactinia spp., Entactinosphaera grandis Naza- rov, Entactinosphaera vetusta (Hinde), Entactinosphaera spp. and Staurodruppa prae- longa (Hinde ).

The exact age of the Yarrimie Formation fauna has not yet been established, however ra- diolarians present in the formation include spe- cies which show closest affinity to faunas de- scribed from Late Devonian rocks of West Australia (Nazarov et al., 1982; Nazarov and

Ormiston, 1983) and Ohio (Foreman, 1963). An abundant conodont fauna has been used to es- tablish a late Eifelian age for lenses of Moore Creek Limestone, a member of the Yarrimie Formation, which are present at the Tamworth locality (Philip and Pedder, 1966; Philip, 1967). However, bedding relationships are uncertain and if, as indicated by the radiolarian faunas, the Yarrimie Formation is Frasnian then it is likely that these limestones blocks are allochthonous.

Djungati terrane

Djungati terrane comprises of a disrupted ba- salt, chert, tuffaceous chert, volcaniclastic silt- stone and sandstone succession interpreted to have accumulated in a subduction complex which developed in association with an intra- oceanic volcanic island arc. Previous attempts at dating this terrane have relied on ages ob- tained from faunas within allochthonous lime- stone blocks. These ages do not necessarily cor- respond to that of the rest of the terrane or to

Fig. 3. Radiolarians from the Djungati terrane. Length of scale bar in/lm is indicated in parentheses. A-F: from red ribbon- bedded chert at locality UNE L1903 [Middle Crossing]: radiolarians figured are of probable Middle Silurian age. G-J and M-T from green tuffaceous cherts at locality UNE L1904 [Burnima], K, L and P-S from locality UNE L1905 [Windi] radiolarians figured are of probable Late Devonian (Famennian) age. A: spheroidal radiolarian (90/~m) AMF74491, B: spheroidal radiolarian (120/lm) AMF74492, C: spheroidal radiolarian (140 pm) AMF 74493, D: spheroidal radiolarian (120 /~m) AMF74494, E: spheroidal radiolarian (120/lm) AMF74495, F: spheroidal radiolarian (100 gm) AMF74496, G: Entac- tinosphaera sp. (60/lm ), AMF74497, H: Entactinosphaera sp. (90/zm ), AMF74498, I: Entactinia sp. (80/Lm ), AMF74499, J: Entactinia sp. (65/~m), AMF74500, K: Entactinosphaera sp. (35/~m), AMF74501, L: Entactinosphaera sp. (90 pm), AMF74501, M: ?Palaeoscenidium cladophorum Deflandre (75/~m), AMF74502, N: Holoeciscus sp. (110/~m), AMF74503, O: Holoeciscus sp. ( 110/lm), AMF74503, P: Entactinosphaera sp. (30/lm), AMF74504, Q: Entactinosphaera sp. (50/lm ), AMF74505, R: Entactinia sp. (140 #m), AMF74506, S: Entactinia sp. (80 pm), AMF74507, T: Entactinia sp. (160/~m), AMF74508.

Fig. 4. Radiolarians from the western part of the Anaiwan terrane: A-J from ribbon bedded red, brown and grey cherts of probable (late Famennian) age locality UNE L1898 [Warrawee] (lower Cara Formation). K-V from tuffaceous, siliceous red mudstones of Early Carboniferous age at locality UNE L1896 [Braeside]. Length of scale bar in pm is indicated in parentheses. A: Holoeciscus [ormanae Cheng (80/zm), AMF74509, B: Holoeciscus formanae Cheng (80 pro), AMF74510, C: Ceratoikiscum sp. (110/~m), AMF74511, D: Cyrtentactinia sp. (70 #m), AMF74512, E: Cyrtentactinia sp. (50 pln), AMF74513, F: Entactiniid gen. et sp. indet. (120 pm), AMF74514, G: Archocyrtium sp. B (40 #m), AMF74515, H: Archo- cyrtium sp. (60 #m), AMF74516, I: ?Palaeoscenidium cladophorum Deflandre (110 pm), AMF74517, J: ?Palaeoscenidium cladophorum Deflandre (70/~m), AMF74519, L: Staurodruppa sp. aff. S. prolata Foreman, (100 pm), AMF74520, M: Archocyrtium sp. (70/~m), AMF74521, N: Cerarchocyrtium sp. ( 115/lm), AMF74522, O: Cyrtisphaeractenium sp. (65 pln ), AMF74523, P: Cerarchocyrtium sp. (70/Lm), AMF74524, Q: Cerarchocyrtium sp. (80 tim), AMF74525, R: Cyrtisphaerac- tenium sp. (40 pm), AMF74526, S: Entactinosphaera sp. (90 #m), AMF74527, T: Cerarchocyrtium sp. (40/Lm ), AMF74528, U: Archocyrtium sp. (70 pm), AMF74529, V: Archocyrtium coronoaesimile Won (65 pm), AMF74530.

372 J. AITCHISON

the timing of the amalgamation of these blocks into the terrane. Comparisons of detrital sand- stone petrography have also been used based on the assumption that sandstones of the Djungati terrane were derived from a concomitant and closely associated Gamilaroi terrane (Cawood, 1983). There are major problems with this ap- proach, as the Gamilaroi terrane is not neces- sarily related to the Djungati terrane. Detrital sandstone petrography is not a valid basis for dating these rocks, it merely provides an indi- cation of the nature the eroding source terrane. Recent radiolarian biostratigraphy clearly in- dicates that all ages thus inferred are incorrect.

Radiolarian chert is a dominant lithology in the Djungati terrane. Discoveries of radiolarian faunas facilitate the determination of the orig- inal stratigraphic succession within this now intensely disrupted terrane. Thick, red ribbon- bedded cherts which locally overlie basaltic rocks dominate the lower Woolomin Group (Aitchison et al., 1988). These rocks are inter- preted to have developed some distance from an island arc or continent as part of an ocean floor sequence. The age range of these cherts is not well constrained as radiolarians present are re- crystallised and deformed in many areas; at some localities deformed radiolarian ghosts de- fine an axial planar cleavage. However, pres- ervation is sufficient in some areas to indicate that basal sections of these red cherts accumu- lated prior to the Middle Devonian. Radiolari- ans found near the base of the chert sequence have simple rod-like spines. Incipient grooves on some of these spines are similar to Middle

Silurian forms (B. B. Nazarov, pers. com- mun.). Notably spheroids with three-bladed spines are absent (Fig. 3 A-F) in these assem- blages. Radiolarian faunas dominated by sphe- roidal forms with strongly developed three- bladed spines occur near the top of the red rib- bon-bedded chert sequence and indicate that accumulation of these cherts continued until Late Devonian time.

Green tuffaceous cherts and volcaniclastic sediments overlie the red ribbon-bedded chert sequence (Aitchison and Flood, in prep). Well preserved radiolarians have recently been re- covered from tuffaceous cherts in the northern part of the terrane and indicate a latest Devon- ian (Famennian) age. Radiolarians present (Fig. 3) include Holoeciscus sp. Palaeosceni- dium cladophorum Deflandre variants, Entac- tinia spp., Entactinosphaera spp. and the pres- ence of spheroidal radiolarians with sinistrally twisted three bladed spines may indicate that these strata are of latest Famennian age (Hold- sworth and Jones, 1980).

Volcaniclastic sediments of the Djungati ter- rane are interpreted to have accumulated in, or near, a trench associated with an intraoceanic island-arc subduction complex. Therefore it is likely that the ages of in situ fossils within these sediments will indicate of the timing of the de- veloping subduction complex.

A n a i w a n t e r r a n e

Anaiwan terrane is a regionally extensive terrane which may prove to be composite. This

Fig. 5. Early Carboniferous (Tournaisian) radiolarians from ribbon-bedded cherts in the eastern part of the Anaiwan terrane at locality UNE L1899 [Jackadgery]. Length of scale bar in ftm is indicated in parentheses. A: Mostlerium sp. (120/lm), AMF74531, B: Mostlerium sp. (80/~m), AMF74532 C: Cyrtisphaeractenium sp. aff. Cyrtisphaeractenium spinosum Cheng (100 l~m), AMF74533, D: Cyrtisphaeractenium sp. (80/lm), AMF74534, E: DeflandreUium sp. (80 pm), AMF74535, F: Cyrtisphaeractenium sp. aff. Cyrtisphaeractenium spinosum Cheng ( 140/lm ), AMF74536, G: Archocyrtium sp. ( 105 pm ), AMF74537, H: Archocyrtium sp (65/Ira), AMF74538, I: Archocyrtium sp. (75 ]tm), AMF74539, J: Archocyrtium sp. (100 pro), AMF74540, K: Archocyrtiurn riedeli Deflandre (100 ttm), AMF74541, L: Archocyrtium riedeli Deflandre (120/zm), AMF74542, M: Archocyrtium sp. cf. A. castuligerum Deflandre, (110 ttm), AMF74543, N: Pylentonema sp. (90 ]~m), AMF74544, O: Ceratoikiscum avimexpectans Deflandre group (65/lm), AMF74545, P: Ceratoikiscum sp. (80 ttm ), AMF74546, Q: Palaeoscenidium cladophorum Deflandre ( 100/lm ), AMF74547, R: Quadrapesus sp. ( 100 zm ), AMF74548, S: Pylento- nema sp. (75 Itm), AMF74549, T: ProtoalbaiUeUa sp. (65/lm), AMF74550, U: Albaillella paradoxa Deflandre group (90 pm), AMF74551.

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 373

Fig. 5.

~ii~, i~i ~ ~~ ' ~

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 375

terrane consists of minor ocean floor basalt ov- erlain by thin ribbon-bedded chert, tuffaceous siltstones and volcaniclastic sandstones. These lithologies are thought to have accumulated in a subduction complex. Volcaniclastic sand- stones are the dominant lithology. The age of Anaiwan terrane strata was previously poorly defined. The presence of detrital ooliths in greywackes was cited as an indication of a Vi- sean age. This assumption was based on the presence of ooolitic limestones of Visean age in other terranes of eastern Australia (Fergusson, 1984; Cross et al., 1987). However oolites are not restricted to Visean strata elsewhere in eastern Australia and the development of var- ious terranes is not necessarily related. The presence of oolites merely provides an indica- tion of paleoenvironment in the source area.

Four different radiolarian assemblages have been identified so far in the Anaiwan terrane. The ages of these assemblages range from latest Famennian to late Tournaisian. The oldest as- semblage (Fig. 4 A-J) is probably of late Fa- mennian age and is known from "Warrawee" farm property (UNE L1898) in the northwest- ern part of the terrane. Radiolarians present in- clude Holoeciscus formanae Cheng, Ceratoikis- cum sp., Archocyrtium spp., Cyrtentactinia spp., Palaeoscenidium cladophorum Deflandre var- iants and spheroidal radiolarians with three- bladed spines.

At "Braeside" farm property (UNE L1896) in the same area the following radiolarians are present (Fig. 4 K-V): Ceratoikiscum avimex- pectans Deflandre group, Palaeoscendium cla- dophorum Deflandre variants, Cyrtisphaerac- tenium spp., Archocyrtium spp., Cerarchocyr- tium spp., Entactinosphaera sp. and Staurod- ruppa sp. aff. S. prolata Foreman. This assem- blage is most probably of Early Carboniferous age and contains forms similar to those in Early Carboniferous rocks of the Webb Formation, Nevada, USA.

At Jackadgery (UNE L1899), in the eastern part of the terrane, a diverse fauna containing spicules and conodonts as well as radiolarians

(Figs. 5, 6) is present and includes: Protoal- baiUella sp., AlbaiUella paradoxa Deflandre group, Ceratoikiscum avimexpectans Deflandre group and Palaeoscendium cladophorum De- flandre variants. Pylentonemids are both aun- dant and diverse and include: Pylentonema spp., Quadrapesus sp., Archocyrtium spp., Cyrtis- phaeractenium spp., DeflandreUium spp. and Mostlerium spp. Spheroidal radiolarians are also abundant with several new species present (Aitchison, in prep) and include forms with either sinistrally or dextrally twisted three- bladed spines. The "Jackadgery" assemblage is most probably of Tournaisian (Tn2) age.

Along Dangarsleigh Road (UNE L1900), near Armidale, an assemblage thought to be slightly younger than the "Jackadgery" assem- blage has been discovered. Radiolarians in this assemblage include: Archocyrtium spp., Cerar- chocyrtium spp., Cyrtisphaeractenium spp., Kantollum undulatum Cheng, Palaeoscenidium cladophorum Deflandre variants, Staurodruppa prolata Foreman and Albaillella paradoxa De- flandre group.

D i s c u s s i o n

The presence of radiolarians in other parts of the NEO is well documented (e.g., Richards and Bryan, 1924; Bryan and Jones, 1962). Prelim- inary work has also begun in the Brisbane area on ribbon-bedded radiolarian cherts of the Ner- anleigh-Fernvale beds where previous age es- timates have ranged from Pre-Cambrian to Carboniferous. An Early Carboniferous fauna which includes Albaillella paradoxa Deflandre group has recently been discovered (Aitchison, 1988b).

An interesting comparison can be made be- tween Early Carboniferous radiolarians of the NEO and other known occurrences worldwide. All radiolarian faunas of this age contain a sim- ilar mix of genera. Similar faunas are known from U.S.S.R., Poland (M. Pazkowski, pers. commun.), France (Deflandre, 1952, 1960; Comble et al., 1985; Gourmelon, 1987), Ger-

376 J. AITCHISON

Fig. 7. Paleogeographic reconstruct ion for earliest Carboniferous t ime prepared on an Apple Macin tosh using T E R R A MOB- ILIS (Scotese and Denham, 1988). Known radiolarian localities are indicated by a star.

many (Won, 1983), Turkey (Holdsworth, 1973), Yunnan, China (Wu and Li, 1988), Alaska and continental U.S.A. All faunas known from northern hemisphere localities oc- cur in rocks which are currently situated at lat- itudes higher than 30 ° N. The Australian faunas all occur in allochthonous terranes which are currently situated at approximately 30 °S lati- tude. Most localities containing this Early Car- boniferous radiolarian fauna are situated at low latitudes as depicted on a paleogeographic re- construction for 360 Ma (Fig. 7) which corre- sponds approximately to the Devonian/Car- boniferous boundary (Harland et al., 1982). Localities which do not plot in equatorial re- gions occur in allochthonous terranes (e.g., Alaskan localities). These terranes possibly lay at much lower latitudes than those shown in Fig. 7 but their paleolatitudes are presently indeter- minate. It is possible that the Carboniferous ra- diolarian faunas described herein represent some form of equatorial assemblage. However, no data are available from areas of high paleo- latitude and further work is necessary before

any paleogeographic realms for Carboniferous radiolarians can be accurately delineated.

Studies of radiolarians which are abundant in the NEO, in what are otherwise sparsely fos- siliferous terranes, are vital to the understand- ing of the tectonic development of eastern Aus- tralia. Future work will result in an improved understanding to the geotectonic evolution of elements of this tectonic collage. Additional data on global occurrences of Carboniferous ra- diolarians may allow the determination of pa- leogeographic realms.

Acknowledgements

This study was made possible through the fi- nancial support of an Australian Common- wealth Post Graduate Research Award, BHP Minerals and the Australian Research Council. Peter Garlick and Barbara Ward of the Elec- tron Microscope Unit, UNE assisted with SEM photography. I am grateful to A. Braun, B. Murchey and J. Blueford for their reviews of this manuscript.

SIGNIFICANCE OF DEVONIAN-CARBONIFEROUS RADIOLARIANS 377

R e f e r e n c e s

Aitchison, J.C., 1988a. Late Paleozoic radiolarian ages from the Gwydir terrane, New England orogen, eastern Aus- tralia. Geology, 16: 793-795.

Aitchison, J.C., 1988b. Early Carboniferous (Tournaisian) Radiolaria from the Neranleigh-Fernvale beds, Lake Manchester, Queensland, Australia. Queensl. Gov. Min. J., 89: 240-241.

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