Bryan, W.H. (Walter Heywood)

Jones, O.A. (Owen Arthur).

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University of Queensland 
PAPERS 
DEPARTMENT OF GEOLOGY 
VoL. IV. (New Series) 1955 
Radiolaria as Critical Indicators of 
Deformation 
BY 
W. H. BRYAN AND 0. A. JONES 
Priu: One Shillitsg 
THE UNIVERSITY OF QUEENSLAND PRESS 
BRISBANE 
DATE OF PUBLICATION :  
Uth MAY, 1955 
No. 9 
DEPARTMENT OF GEOLOGY 
VoL. IV. (New Series) 1955 NuMBER 9 
RADIOLA RIA AS CRITICAL INDICATO RS OF 
D EFO RMATION 
BY 
W. H. BRYAN AND 0. A. JONES 
THE UNIVERSITY OF QUEENSLAND PRESS 
BRISBANE 
DATE OF PUBLICATION : 
12th MAY, 1955 
Wholly set up and printed in Australia by 
WATSON, FERGUSON AND COMPANY 
Brisbane, Q. 
1905 
Radiolaria as Critical Indicators of Deformation 
By \V. H. BRYAN AND 0. A. JONES 
The distortion of various spherical and cylindrical bodies, organic and inorganic, has 
been used from time to time as a measure of the stresses to which the containing beds have 
been subjected. The most notable of these studies is that of Emst Cloos ( 1947) who, after 
citing in historical review the earlier efforts, based his own approach to the subject on a study 
of the deformation of oolites. It would appear from Cloos' comprehensive introduction and 
from other literature on the subject that little if any use has hitherto been made of spherical 
radiolaria for this purpose, although Hu�son, McGugan and Morton (1954, p. 135) have 
recently referred to the radiolaria of some of the cherts of Trucial Oman as being "uniformly 
compressed parallel to the bedding." 
Radiolarian-bea�ing rocks have been recorded in south-eastern Queensland by Richards 
and Bryan (1923, 1924, pp. 57, 82, 1925) and by Denmead (1928, pp. 92-95). In all of these 
local examples the radiolarian skeletons are spherical in shape and are preserved as translucent 
chalcedonic casts in cherts, jaspers, quartzites or other very siliceous rocks of Devonian or 
earlier age. 
The only reference to deformed radiolaria in Queensland is a short one by Richards 
and Bryan (1924) where Figure 3 of Plate XI is described as "Banded radiolarian chert found 
as a pebble" in which "as a result of considerable pressure the rounded radiolaria have been 
compressed into lenticular shapes." 
The radiolaria which form the basis of this paper occur at Upper Brookfield, a western, 
outer-suburb of Brisbane. Here they occur as numerous translucent chalcedonic casts set 
in an opaque red jasper of the Neranleigh-Fernvale Group of possibly Silurian age (Bryan 
and Jones 1951, p. 2). The containing rock is remarkably uniform in character and measures 
approximately 150 feet in present thickness, striking \V.::-.l".W. and dipping at 70° to the S.S.W. 
The rock cleaves readily parallel to the bedding which thus becomes a conspicuous feature. 
A well-developed joint set takes a N.E.-s.v.,r direction while another less pronounced is 
approximately parallel to the strike. 
The most notable feature of the radiolaria in these jaspers, and the one which forms 
the basis of this paper is their abnormal shape. But, fortunately for our purpose, the 
individuals on at least one horizon appear to be regular in all respects. These consequently 
provide a useful standard for comparative purposes. The skeletons are very numerous (over 
100,000 to the cubic inch) and must be virtually perfect spheres, for slices in all directions 
are circular in outline (pl. 1, fig. I). These undistorted radiolaria are all pierced by numerous 
evenly distributed circular openings which give them a reticulate appearance. This combined 
with their spherical shape places them in the sub-order Spumellina of the order Porulosida 
which ranges from Cambrian to Recent (Campbell 1954). Cross-sections of a few individuals 
each exhibit a single stout spine with an axial canaL It would seem from this evidence that 
spines were extraordinarily fragile or few in number and possibly limited to one for each 
individual. 
In view of the striking similarity displayed by all these radiolaria and the suggestion 
put forward by Haecker (quoted in Glaessner 1944, p. 8) that only the adults possessed 
skeletons, the possibility was examined of all the circular sections having been derived from 
adults and these of nearly the same dimensions. A histogram was prepared based on a group 
of one hundred individuals in which frequency of occurrence was plotted against diameters. 
This showed clearly that the radiolaria, of which these sections represented random slices, 
could not all have been of the same size. Indeed the histogram showed that the size 
distribution is that to be expected in a normal population. The great majority of the circular 
RADIOLARIA AS CRITICAL INDICATORS OF DEFORMATlO� 
sections were found to be between 0.06 and 0.12 mm. across. The maximum of 0.15 mm. 
reached by about 5 per cent. of the radiolaria probably represented great-circle sections of 
Ja.r9e individuals. A few very rare individuals, none of which was present in the group from 
which the histogram was made, are larger than all the others, have larger pores ·and, since 
th�se are less effective filters, are filled with an opaque red material similar to the groundmass. 
Apart from these rare exceptions, each spherical skeleton is completely filled with 
radially arranged fibres of chalcedony which give a characteristic black-cross extinction pattern 
(pl. Ill, fig. !h). 
By contrast with the above, the radiolaria which provide the subject of this paper are 
all triaxial ellipsoids {pl. I, fig. 2). The axial proportions, while similar for the individuals of 
any one horizon may differ markedly in adjoining horizons. On every horizon examined the 
individual ellipsoids are in strictly parallel alignment. 
A band. not much more than one inch in thickness, was selected for more detailed 
examination and numerOus thin sections prepared. These showed that the ellipsoidal skeletons 
cl..id not represent the original shape of the radiolaria, for the resembl�wce of these to the truly 
spherical skeletons in every thing but external shape is very striking and in shape itself, as 
the field evidence shows, there is an almost perfect gradation from strongly ellipsoidal 
assemblages in some bands, to nearly spherical assemblages in others. 
It is true that one group of radiolaria, the Larcoidca of Glaessner (1944, p. 9) form 
triaxial ellipsoid skeletons, but that group is not found earlier than the Tetirary and figured 
specimens of it are quite unlike those under consideration (Piveteau, 1952, p. 309). 
We conclude therefore that the ellipsoidal skeletons have been produced by the 
deformation of normally spherical individuals such as those already referred to. This 
conclusion is reinforced by the observation that while the spherical radiolaria show no 
disturbance of the radially arranged cbalcedonic fibres with which they are filled, the ellipsoidal 
skeletons invariably show infillings of finely cataclastic aggregates patently produced by 
micro-brecciation of the brittle chalcedony (pl. III, cf. fig. 2a with fig. 2b). 
In order to study the degree of deformation of the radiolaria, microslides were prepared 
in various directions through the parent rock, but all on the same horizon and within a few 
centimeters of each other. 
A study of these slides showed that the dir�tion of maximum elongation of each 
ellipsoid makes an angle of 20o with the direction of dip but lies in the bedding plane and is 
parallel to the more important joint set. The minimum diameter is at right angles to the 
bedding planes or nearly so. 
This arrangement produces a lineation of the type assigned by Cloos (1946, p. 16) to 
the third of his ten categories, namely, "Lineation due to secondary flowage." 
In an attempt to arrive at a quantitative estimate of the amount of distortion that 
had been suffered it was assumed that the largest individuals in any particular micro-section 
could be compared directly with the largest in closely adjacent sections, in whatever direction 
such sections were cut. 
Measurements on this basis indicated that the ellipsoidal diameters of these large 
individuals · were in the approximate ratio of 10 : 7 : 3. A simple calculation gives the 
diameter of a sphere of equal volume as almost exactly 6 and indicates that the maximum 
diameter of the ellipsoid represents an extension of the "a" axis by two-thirds and the minimum 
a reduction of the "c'' axis by one half. The intermediate "b" axis has increased by one-sixth. 
It is of interest and significance to note that this calculated diameter of the undistorted 
sphere {in the scale adopted here six which is equivalent to 0.2 mm.) is considerably larger 
than that of any of the undistorted spheres which we are using as a standard of reference 
and whi_ch reach only .15 mm. iri diameter. From this we may conclude that the ellipsoidal radiolaria have experienced a notable increase in volume during and as a result of their 
deformation. Such an increase of volume could have been anticipated, especially in view 
of the brittle nature of the material. {See :Kt:vin, 1949, pp. 32-33). 
RADIOLARIA AS CRITICAL INDICATORS OF DEFORMATION 
This increase in volume indicates that _ the force which brought about the distortion 
was not a simple compression. In particular the special case of vertical compression due 
to the weight of overlying sediments, even if it be admitted as theoretically possible, is ruled 
out not only by increase in volume but by the occurrence of quite undeformed radiolaria in 
a closely adjacent bed and by the variation in amount of deformation from bed to bed. 
On the other hand, the increase in the length of the intermediate "b" axis indicates 
that the deforming force was not tensional (Fairbairn, 1949, pp. 199 and 202). But as Cloos 
(1946, p. 42) has shown "lineation accompanied by elongation of fossils, pebbles, ooids, and 
other shapes can well be recognised as secondary flowage," such as may occur in the forward 
motion of rock masses in folding and thrusting. 
In an earlier publication (Bryan and Jones, 1954) we have shown that a large area 
including that under discussion has been subjected to the powerful Hamilton Thrust and been 
pushed forward some seven miles in a south-westerly direction. Such a thrust would be 
capable of producing the effects observed in the distorted radiolaria, nainely, the differential 
effects in neighbouring bands, the direction of lineation, the pronounced elongation of the 
"a" axes, the comparable shortening of the "c" axes, the minor extension of the "b" axes, 
the cataclasis of the chalcedonic infillings and the increase in volume of the deformed 
individuals. 
One important feature that is not in harmony with such a simple thrust from the 
N.E. is the present attitude of the containing beds which dip very steeply to the S.S.\-V. ,  that 
is in a direction away from the thrust and diverging some 20° from it. · But this apparent 
discrepancy is in agreement with other evidence that the Hamilton Thrust proper was not 
the final episode in the complex orogenic movement of which it was a part. 
REFERENCES 
BRYAN, W. H. AND JoNES, 0. A. (1951). Explanatory Notes to Accompany a Geological Map of Brisbane. 
Univ. of Qld. Papers, Dept. of Geol., III (N.S.), No. 13. 
-- (1954-). Contributions to the Geology of Brisbane No. 2. The Structural History of th� Brisbane 
Metamorphlcs. Proc. Roy. Soc. Qld., 65, pp. 25-50, pis. I-VII, geol. map and section. 
CAMPBELL, A. S. (1954-). Treatise on Invertebrate Palaeontology. Edited by R. C. Moore. Geol. Soc. 
Amer. and Univ. Kansas Press. 
CLOOS, ERNST (1946). Lineation, A Critical Review and Annotated Bibliography. Geot. Soc. A mer., Mem. 18. 
--· (1947). Oolite Deformation in the South Mountain Fold, Maryland. Bull. Geol. Soc. Amer., 58, 
pp. 843-917, 6 pis., 21 text figs .. map. 
DENMEAD, A. K. (1928). "A Survey of the Brisbane Schists." Proc. Roy. Soc. Qld., 39, pp. 71-106, pis. 
VI-IX, map and section. 
FAIRBAIRN, H. W. (1949). Structural Petrology of Deformed Rocks, 344 pp. Addison-Wesley Press, 
Cambridge, U.S.A. 
GLAESSNER, M. F. (1944). "Principles of Micropalaeontology." Melbourne University Press. 
HUDSON, R. G. S., McGUGAN, A., AND MORTON, D. M. (1954}. "The Structure of the Jebel Hagab Area, 
Trucial Oman." Q.j.G.S., 110, pp. 121-152, pls. V-VIII. 
NEVIN, C. M. (1949). "Principles of Structural Geology," 4th ed., 410 pp. + 250 figs. John Wiley & Sons, 
New York. 
PrvETEAU, J. (1952). "Traite de Palaeontologie, Masson et Cie." 
RICHARDS, H. C. AND B.RYAN_, W. H. (1923). "Radio�rian Rocks in Southern Queensland." A.A.A.S. [Wellington meetmg], 16, pp. 296-316, 1 sectJ.ou, 3 tables. 
-- (1924). "The Geology of the Silverwood-Lucky Valley Area." Prac. Roy. Soc. Qld., 36, pp. 44-108, 
pls. VII-XX, section, block diagram, map. 
- (1925). "Radiolarian Jaspers in the Brisbane Schist Series." Proc. Roy. Soc. Qld., 36, pp. 131-136, 
pl. XXVI. 
WILLIS, BAIL��
2 
�� W��c::
�w
�:!Tl�NB�t2��., ��o����-Structures," 2nd edit., 518 pp. + pls. A-K and 
RADIOLARIA AS CRITICAL INDICATORS OF DEFORMATION 
EXPLANATION OF PLATES 
PLATE I 
Fig. !-Spherical {undeformed) radiolaria in ml jasper. Ord. light X 34. Univ. of Qld. Slide !'fo. 4.7211. 
Fig. !!-Ellipsoidal {deformed) radiolaria in rro jasper. Elongation is in dirK;tion of bedding. Onl. light 
X 34. Univ. of Qld. Slide No. 4723. 
The two specimens were collected from within a few feet of .one another. 
PLATE II  
Three Pho�omicrographs taken from slides cut in three plane� at right angles and assembled in the 
form of a block d1agram to show the relative amounts of deformation in the three principal directions. Ord. 
light X 34. Univ. of Qld. Slides Nos. 4724-6. 
PLATE III 
Fig. 1-Undefofmed radiola.ria-
lbJ �U�3hn\c�l:;g·17�ni�;� ��1·����� � ���94729. 
Fig. 2-Deformed radiolaria-
fbi g;:�hn\�1; �-�7�ni'{j����1·0��S1�� ���5472/S. 
RADIOLARIA :\S CRITICAL I�DICATORS OF DEFOIUIATIOX 
2 
PLATE: T 

RADIOLARIA AS CRITIC:\L IKDlCATOHS OF DEFOH.MATIOX 
l m m .  
1 ' 1 . \ ll 1 1  

RAD10LARIA AS CRITICAL INDICATORS OF DEFORMATION 11 
1o. ' 1b. 
2o. 2b. 
PLATE Ill 


Radiolaria as critical indicators of deformation

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Radiolaria as critical indicators of deformation

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