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Apparent polar wandering for the Atlantic-bordering continents: Late Carboniferous to Eocene
Earth-Science Reviews, 10(1974) 99--119 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Apparent Polar Wandering for the Atlantic-Bordering Continents: Late Carboniferous to Eocene R. Van der Voo and R.B. French
ABSTRACT Van der Voo, R. and French, R.B., 1974. Apparent polar wandering for the Atlanticbordering continents: Late Carboniferous to Eocene. Earth-Sci. Rev., 10: 99--119. We present a compilation o f reliable paleomagnetic pole positions from five continental plates (North America, Europe, the Iberian Peninsula, Africa, and South America) for ten time intervals ranging from Late Carboniferous to Eocene. Only well-dated results obtained by demagnetization techniques have been used. Paleomagnetic poles are plotted with respect to the paleo-positions of the continents, as reconstructed from correlations of marine magnetic anomalies in the Atlantic Ocean by Pitman and Talwani and from the fit by Bullard et al. The poles from North America, Europe and the younger poles from Africa show a very good grouping for most of the ten intervals considered, and a continuous apparent polar wandering path is obtained. These data have been used to construct paleolatitude maps for most intervals; thus the relative positions of the continents were established from sea-floor spreading data and their absolute positions on the globe were determined from paleomagnetic data. The older data from South America and the other Gondwana continents show a systematic deviation) from those of the northern continents for Late Paleozoic and Early Triassic time periods. An explanation is offered in a different continental reconstruction between Laurasia ai~d Gondwanaland before Middle Triassic times.
INTRODUCTION V i r t u a l p a l e o m a g n e t i c p o l e p o s i t i o n s , in p a r t i c u l a r t h o s e o b t a i n e d f r o m N o r t h A m e r i c a , E u r o p e a n d A f r i c a , r e v i v e d i n t e r e s t in c o n t i n e n t a l d r i f t t h e o r i e s in t h e l a t e 1 9 5 0 ' s (e.g., R u n c o r n , 1 9 5 6 ; T a k e u c h i e t al., 1 9 6 7 ) . Y e t as l a t e as 1 9 6 7 , a r t i c l e s w e r e b e i n g p u b l i s h e d in w h i c h t h e v a l i d i t y o f p a l e o m a g n e t i c d a t a as e v i d e n c e f o r d r i f t w a s s e r i o u s l y q u e s t i o n e d (e.g., H o s p e r s , 1 9 6 7 ) . I t is n o t d i f f i c u l t t o d e t e r m i n e f a c t o r s w h i c h l e d t o t h i s c o n f u s i o n : (1) e a r l y p a l e o m a g n e t i c w o r k w a s n o t s u b j e c t e d t o t h e p r e s e n t - d a y d e m a g netization techniques and therefore was contaminated with secondary magnetic overprinting; (2) many results were obtained from statistically insuffic i e n t q u a n t i t i e s o f s a m p l e s o r o t h e r s u n i t s , so t h a t s h o r t - t i m e f l u c t u a t i o n s o f
100 the geomagnetic field were not adequately averaged out; (3) it was often not realized until later that some results obtained from tectonically disturbed areas could not be used; and (4) some paleomagnetic results were obtained from rocks that were poorly dated, thereby blurring the details of the polar wandering paths unnecessarily. It was not surprising therefore that some earth scientists displayed caution about paleomagnetically derived conclusions (e.g., Meyerhoff and Meyerhoff, 1972). In the last decade, however, most of the above-mentioned difficulties have been remedied, through more sophisticated paleomagnetic analyzing techniques, radiometric age dating methods and also more insight in tectonic problems. We present in this paper a rigorous selection of what one might call "reliable" paleomagnetic data, i.e., data based on sufficient sampling, alternating field or thermal demagnetization, good stratigraphic or radiometric age control, and often supported by conclusive tests about the primary nature of the magnetizations involved, such as the unfolding test (Graham, 1949). Our data selection is more rigorous than those of previous analyses (e.g., Wells and Verhoogen, 1967; Hospers and Van Andel, 1968; Deutsch, 1969; Larson and La Fountain, 1970; and also Roy, 1972, and Phillips and Forsyth, 1972). The improved age control permits us to group our data in shorter time intervals of 20--30 m.y. duration, roughly representing the lower and upper parts of the major periods. Rob van der Voo (Ph.D. 1969, Utrecht) was born in The Netherlands. He was Research Associate in Utrecht for one post-doctoral year, was Visiting Assistant Professor in the Department of Geology and Mineralogy of the University of Michigan in Ann Arbor and is currently Assistant Professor at this Institution. In addition to some fifteen papers on paleomagnetic studies in the Mediterranean area, he has published on the stratigraphy and tectonics of parts of the Pyrenees and on a seismological study of surface waves generated by nuclear explosions. He is currently investigating absolute rates of polar wandering for the Earth's geological past and has several projects in paleomagnetic research. Rowland B. French received his A.B. from Dartm o u t h College in 1969 and his M.S. in Physics from the University of Michigan. He is currently in the Department of Geology and Mineralogy at the University of Michigan working on his doctoral dissertation in paleomagnetics.
101 Our use of the data compiled is also different in t h a t its basic premises are the validity of the reconstructions of the Atlantic bordering continents (Bullard et al., 1965; V0gt et al., 1971; Le Pichon and Fox, 1971) and the subsequent spreading episodes of the Atlantic Ocean as deduced from marine magnetic anomalies and JOIDES deep-sea drilling (Pitman and Talwani, 1972). It is generally believed that the positions of the continents Africa, North America, and Europe are now fairly accurately known for the Mesozoic and the Tertiary, independent of continental paleomagnetic data. With these reconstructions for Mesozoic and Tertiary times, we have plotted the reliable paleomagnetic pole positions from four continental plates: North America, Europe (north of the Alpine fold belt), the Hercynian Meseta of the Iberian Peninsula, and Africa. Paleomagnetic data from South America are used only for the periods preceding the separation from Africa. We will see that the paleomagnetic data are in excellent agreement with the reconstructions, with the exception of the Late Paleozoic data from the Gondwana continents. In the next section the m e t h o d o l o g y of data selection will be discussed. This leads to the paleogeographical maps (Fig.6A--G) of Appendix II, granted the assumption that the geomagnetic field was, on the average, that of a geocentric axial dipole. Finally, it will be discussed how the Late Paleozoic and Early Triassic paleomagnetic data from Africa and South America compare with those from the northern continents. METHODOLOGY The paleomagnetic poles that we have used are shown in Fig.1 and Table I, grouped according to time interval and continent. Fig.1 shows the localities where the samples were collected. We have established three major criteria for their selection. First, all poles are from studies that used effective demagnetization techniques for a substantial a m o u n t of samples to eliminate possible secondary magnetizations. Either ac or thermal demagnetization, or both, were used to obtain each pole position. Second, all poles are from formations with well-established ages. Only poles which could be grouped into a subunit of a geologic period, such as Upper Cretaceous or Lower Triassic were used. Poles dated simply as Permian or Cretaceous were not considered accurately enough dated. This allows us to group the poles into shorter time units than has been done in the past. Such groupings avoid large scatter of the pole positions and yield a more continuous polar wandering path. Our third selection criterion is that paleomagnetic samples from tectonically disturbed regions are not used. Thus, poles from the California Coast Range or Alpine Europe were not utilized (see Irving and Yole, 1972; Zijderveld and Van der Voo, 1973). Table I shows ten time units with the poles from each continent placed in these groupings. Some periods lack data from some continents. The European data are sparse for the Jurassic and Cretaceous, and the African data are almost non-existent before the Upper Triassic. Not only is the selection of the paleomagnetic results important, it
102
Fig.1. World map with the sites of reliable paleomagnetic sample collections as used in this study (Table I), plotted in North America, Europe, the Iberian Peninsula, Africa and South America, respectively. The corresponding virtual paleomagnetic pole positions are given in Fig.2. m i g h t al~o be very subjective. In t h e a p p e n d i x we give an a c c o u n t o f w h y s o m e results have n o t b e e n used. T h e Mesozoic a n d C e n o z o i c p o s i t i o n s of t h e E u r o p e a n , N o r t h A m e r i c a n , a n d A f r i c a n c o n t i n e n t a l plates, relative t o each o t h e r , are t a k e n f r o m P i t m a n a n d T a l w a n i (1972). T h e y have c o m p i l e d a n d m a p p e d t h e m a g n e t i c a n o m alies in t h e N o r t h a n d C e n t r a l A t l a n t i c Ocean. By j u x t a p o s i n g i s o c h r o n o u s a n o m a l i e s on either side of t h e s p r e a d i n g ridge t h e y have d e t e r m i n e d t h e relative p o s i t i o n s o f N o r t h A m e r i c a , E u r o p e a n d A f r i c a at the t i m e w h e n t h o s e a n o m a l i e s w e r e c r e a t e d . We have a s s u m e d u n i f o r m m o t i o n in t h e s h o r t
103
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Fig.2 Plot of reliable paleomagnetic pole positions (Fig.1) obtained from North America, Europe, the Iberian Shield and Africa, plotted with respect to their present-day positions. A. Pole positions ranging in age from Late Carboniferous to Middle Triassic. B. Pole positions ranging in age from Middlt Triassic to Eocene. intervals b e t w e e n the positions o f the c o n t i n e n t s given by P i t m a n and Talwani. We have also assumed t h a t t h e relative positions b e f o r e the o p e n i n g o f the Atlantic were as p r o p o s e d b y Bullard et al. {1965). T h e d i f f e r e n c e bet w e e n this fit and m o s t others, such as those o f Le P i c h o n and F o x {1971) or Vogt et al. ( 1 9 7 1 ) is t o o small to substantially a f f e c t o u r p a l e o m a g n e t i c comparisons. We have r o t a t e d the Iberian Peninsula as p r o p o s e d by Carey ( 1 9 5 8 ) a n d Bullard et al. (1965). Paleogeographic m a p s have been c o n s t r u c t e d , one for each o f the ten t i m e intervals, using t h e c o n t i n e n t a l r e c o n s t r u c t i o n s described above. Thus, the relative positions o f t h e c o n t i n e n t s were established f r o m sea-floor spreading data, whereas t h e a b s o l u t e positions on the globe were d e t e r m i n e d f r o m
104 TABLE I Table of the paleomagnetic pole positions that have been used for our compilation NORTH
IBERIAN
EARLY TERTIARY LATE CRETACEOUS
[ 11012 ] ll.OI3
111.014
M8.33
M12.49
MII.28
MI2.50
SOUTH
AMERICA
EUROPE
If17
M 8.48 e
M9.29
Mlt.31
MI1.52
M 8.48
M 9.56
M 11,55
M 11.37
[ 10,12
[
LATE
-
I00
MY
-
130
MY
-
155
MY
-
185
MY
-
210
MY
-
250MY
-
255
M 9.40
M 9.43
M 10.69
V 16
I 9.50 M 8,59
V 15
M 863 M 8.61
M 12.93
[ 8.42
18.44
M 10.75
M 8.69
M9.49
.,o.~
M 10.89 M 10.90
LATE
I8.o8
TRIASSIC EARLY TRIASSIC
PERMIAN
MY
M 9.42
JURASSIC
EARLY
70
[ 10.15
EARLY
PERMIAN
-
10.17
M It.58
JURASSIC
LATE
MY
M 12.46
M 8.52
CRETACEOUS
40
M 8.38
MII.25
Y 18
EARLY
M 10.46
Mll.29
M 8.35
AMERICA AFRICA
[ 8.07
M8.69 M 10.88
VII
M8.61
v,z
M9,51 M 10.96
M 11.44
M 9.52
M 11.59
.5.8=
M9.85
M 11.56 ")
M 12. II0 v7
M 11.85
M 11.66
M8.88 M 10.106 Y 6
M 10.105 M 11.67
I7,13 M II .70 V4
[7.54
.,=.,,8 Y 5
LATE .=,,o M 9.90 CARBONIFEROUS"'o-'~ iMII,71
M 8.72 M 11.50e
,,8.77
~7.1, 8.87
M 8.87
M 11.46
M 8.1il M9.69 M I0.107 M 10,108I M to..t/.~ M 11,77 V I
M 11.72 M 11.73 M 11.74
M8.85 M8.99 M 8.101 MII.78
M8.96 M 8.100 M9.98
M8.97
M 10,77 M 11.60 Mf2.1O5 V 15
V 14
M ll.6l
M 12.109
V9
V9
"/10
MY
M 12.1t6 M 12.ll7 M 181;" M 9.107 M 12.124e V 2 Y3
M 8.93
-- 275
MY
295
MY
-
The numbers refer to those from Irving (1964), given here as I . . . ; from McElhinny's lists (1968a,b; 1969; 1970 and 1972), given here as M . . . ; or they have been listed below (the poles given as V 1--V 18). The paleomagnetic poles that have not been used are accounted for in Appendix I. Pole V 1 from Kruseman (1962); V 2 from Thompson (1972, pole 6); V 3 from Thompson (1972, pole 5); V 4 from Krs (1968); V 5 from Kruseman (1962); V 6 from Helsley (1971); V 7 from Zijderveld (1967, Est6rel pole); V 8 from Thompson {1972, pole 12); V 9 from Thompson (1972, pole 11); V 10 from Thompson (1972, pole 10); V 11 from Rother (1971); V 12 from Mulder (1973); V 13 from Thompson (1972, pole 13); V 14 from Veldkamp et al. (1971); V 15 from Creer et al. (1972); V 16 from Symons (1973); V 17 from Ade-Hall et al, (1970); and V 18 from Van der Voo and Zijderveld ( 1971 ).
105 p a l e o m a g n e t i c data. I n t e r e s t e d readers m a y o b t a i n these m a p s (70 × 60 c m ) f o r a n o m i n a l fee b y writing to t h e a u t h o r s . S o m e o f the m a p s are p r e s e n t e d in t h e a p p e n d i x . T h e p a l e o l a t i t u d e s w e r e d e t e r m i n e d f r o m t h e m e a n paleom a g n e t i c p o l e f o r each 2 0 - - 3 0 m . y . interval. T h e m e r i d i a n s were d r a w n a r b i t r a r i l y in o r d e r t o p r o v i d e s o m e r e f e r e n c e scale. THE PALEOMAGNETIC POLES FOR THE TEN TIME INTERVALS AND THE PALEOGEOGRAPHIC MAPS T e n p a l e o g e o g r a p h i c m a p s h a v e b e e n c o n s t r u c t e d in an e q u i d i s t a n t projection, b a s e d on t h e fit o f t h e c o n t i n e n t s b y Bullard et al. ( 1 9 6 5 ) and the p o s i t i o n s o f t h e c o n t i n e n t s as d e d u c e d f r o m sea-floor s p r e a d i n g episodes in the A t l a n t i c O c e a n ( P i t m a n a n d Talwani, 1972). Seven of these m a p s are p r e s e n t e d in t h e a p p e n d i x ; t h e y are r e p r e s e n t a t i v e o f the m e a n age o f the r e s p e c t i v e 2 0 - - 3 0 m . y . t i m e intervals. T h e p a l e o m a g n e t i c p o l e s f o r t h o s e p e r i o d s have b e e n p l o t t e d o n t h e m a p s ; t h e m e a n p a l e o m a g n e t i c poles have b e e n used to d e t e r m i n e t h e p a l e o l a t i t u d e s . F o r nine o u t o f t h e s e ten t i m e intervals, nearly all p a l e o m a g n e t i c poles lie w i t h i n a circle o f 10 ° a r o u n d t h e m e a n p o l e p o s i t i o n f o r t h a t interval. M o r e o v e r , t h e circles o f c o n f i d e n c e t h a t c o n t a i n with 95% p r o b a b i l i t y the t r u e m e a n pole p o s i t i o n s have radii less t h a n 7 ° f o r t h e s e nine intervals; for t h e L a t e C a r b o n i f e r o u s a n d t h e E a r l y P e r m i a n t h e s e radii or a 9 s'S are as small as 3.25 ° a n d 2.6 ° (Table II, p . l 1 6 ) . It follows t h a t the 95% c o n f i d e n c e limits f o r t h e p o s i t i o n s o f t h e p a l e o l a t i t u d e lines are c o m p a r a b l e t o t h e a9 s ' s o f t h e i r poles. T h e L a t e C a r b o n i f e r o u s , Early a n d L a t e P e r m i a n , a n d E a r l y Triassic d a t a f r o m N o r t h A m e r i c a , E u r o p e a n d t h e I b e r i a n Peninsula agree well and present a c o n t i n u o u s a n d well-defined virtual p o l a r w a n d e r i n g p a t h (Fig.3A). T h e L a t e Triassic d a t a f r o m N o r t h A m e r i c a a n d Africa, s t r e a k i n g b e t w e e n t h e m e a n L o w e r Triassic a n d L o w e r Jurassic poles, o b v i o u s l y reveal relatively rapid a p p a r e n t p o l a r w a n d e r i n g w i t h r e s p e c t to t h e N o r t h A t l a n t i c b o r d e r i n g c o n t i n e n t s (Fig.3B). T w o results f r o m t h e K e u p e r marls of G r e a t Britain Legend to Table I (cont.):
Footnotes to poles (given by *): M 10.111/113": this result includes data not listed by McElhinny (1969), that were reported by Krs (1968). M 10.108": Pole listing by McElhinny (1969) is incorrect, should be given as 38 N 166 E (Mulder, 1971). M 8.86": age given as Cu (pre-Kiaman interval) by Thompson (1972, pole 3). M 12.124": from the Piaui formation, Brazil. Thompson (1972) lists two poles, one from the lower part of the formation (Thompson, 1972, pole 2, given as pole M 8.107) and this one, from the upper part (Thompson, 1972, pole 4) with coordinates 55N 171 E. M 11.58": age may be P1, according to Helsley (1971). M 11.50": pole listed as 77 N 322 E by McElhinny (1970), which, according to Valencio and Vilas (1972) was calculated from undemagnetized directions of magnetizations. After demagnetization analysis the pole becomes: 77 N 29 E (see also McElhinny, 1972, pole 12.102, though with different coordinates). M8.46": pole quoted as 79 N, 158 E by Krs (1969).
106 (stable Europe) are of marginal reliability as far as complete demagnetization analyses are concerned; they seem to agree better with the Lower Triassic group of poles. Two other results from Europe (southern France), on the other hand, agree very well with the results from Africa and North America for this 210--185 m.y. time interval (Fig.3B). A large gap in our knowledge exists for most of the Jurassic, between roughly 165 and 130 m.y. ago. Moreover, the few results published so far come from areas for which the "belonging" to the stable part of the continent has not been established beyond doubt: the western U.S.A. and the Canadian Cordillera and Spitzbergen. The results are widely scattered (c¢9s = 22 °) and may also reflect rapid apparent polar wandering (see Fig.3B). The relative abundance of North American Early and Late Cretaceous poles and European Lower Tertiary poles form the firm basis for the last three paleogeographic maps. The mean paleomagnetic poles have radii of 95% confidence of 6 °, 7 ° and 5 °, respectively. Post-Eocene results (less than 40 m.y. ago) have not been compiled, since they tend to group more or less around the present-day geographic pole with a relatively large scatter (see for instance a compilation of European and African data by Roche and Westphal, 1971). THE LATE PALEOZOIC GONDWANA POLES Reassuring as the small a 9 s's of the groups of paleomagnetic poles may be in the confirmation of our m e t h o d and selection criteria, it is the occasional pole position that does not agree with the rest of the group that presents the more interesting problems. Not mentioned before, and falling into the latter category, is a whole set of results: those from the Gondwana continents, in particular those from South America, India and Australia, for all of the Late Paleozoic and Earliest Triassic. (For a recent review of the internal consistency of the paleomagnetic poles from the Gondwana continents, see Thompson, 1972; or Tarling, 1971.) This is by no means a new conclusion; the cause of the deviation of the Gondwana poles has been discussed by several authors, e.g., due to an alternative fit along the Tethys (Van Hilten, 1964); by inclination error and/or a short period of continental drift (Creer, 1970); and due to long-term non-axially central dipole components of the geomagnetic field (Briden et al., 1970). The South American results are the most numerous amongst the results of the Gondwana continents. Moreover, they appear to be the least ambiguous for our purpose, since the positions of India and Australia are not yet fully agreed upon (e.g., McElhinny and Luck, 1970; Smith and Hallam, 1970; Tarling, 1971). By repositioning the continents according to the fit by Bullard et al. (1965), one can compare the South American results with those from Europe and North America, for the periods that preceded the breakup of
107
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Fig.3. Plot of reliable paleomagnetic pole positions (Fig, l,2) obtained from North America, Europe, the Iberian Shield and Africa, plotted with respect to the continental reconstructions of Bullard et al. (1965) and Pitman and Talwani (1972). Coordinate system assumes North America held fixed. A. Pole positions ranging in age from Late Carboniferous to Middle Triassic. B. Pole positions ranging in age from Middle Triassic to Eocene. G o n d w a n a l a n d / P a n g e a (Fig.4A). T h e S o u t h A m e r i c a n p o l a r w a n d e r i n g p a t h t h u s o b t a i n e d is parallel t o t h a t f r o m t h e n o r t h e r n c o n t i n e n t s , b u t is disp l a c e d s o m e 20 ° e a s t w a r d . This parallelism c o n t i n u e s f r o m t h e L a t e Carbonif e r o u s t o t h e Earliest Triassic, well b e f o r e t h e o p e n i n g o f t h e p r e s e n t Atlantic Ocean. T h e r e is a clear t r e n d in t h e p o s i t i o n s o f the S o u t h A m e r i c a n poles, lying in a distinct p a t h , w h i c h implies t h a t , even w h e n t h e S o u t h A m e r i c a n results are s u b j e c t t o small errors in age d e t e r m i n a t i o n ( V a l e n c i o a n d Vilas, 1 9 7 2 ) t h e pole p o s i t i o n s are still d i s t i n c t l y deviating. A t t e m p t s have b e e n m a d e p r e v i o u s l y t o alleviate this i n c o n s i s t e n c y . T h e a s s u m p t i o n o f a g e o c e n t r i c axial d i p o l e field was i n v e s t i g a t e d r e c e n t l y b y Briden et al. ( 1 9 7 0 ) , Wilson ( 1 9 7 0 ) a n d others. This is o n e of t h e basic
108 assumptions of paleomagnetism (e.g., Irving, 1964) and seems to hold fairly well for the results from the northern continents. We note that a substantial departure from the geocentric dipole model, lasting for some 100 m.y., would be required to account for the South American discrepancies. Another possibility is that the fit of the continents by Bullard et al. (1965) cannot be used for this period. Van Hilten (1964) did note this possibility and proposed an alternative continental reconstruction, implying subsequent dextral shear in the Tethys zone: the " T e t h y s twist". Since then so m a n y data have become available that the Tethys twist concept is no longer tenable; yet, we feel that the paleomagnetic data strongly indicate an alternative reconstruction for the Late Paleozoic. Fig.4B shows the paleomagnetic pole positions of Africa and South America after an additional clockwise rotation of Gondwanaland over some 20 ° about a point in the southern Sahara (27°N 60°W with respect to North America). One can see
PA LEOMAGNE T IC
POL ES :
•
the NORTHERN
[]
AFRICA
CONTINENTS
$
MEAN POLE POSITIONS (see TABLE I )
SOUTH AMERICA
Fig.4. The same pole positions as in Fig.3, with those from South America added, for the time periods that preceded the break-up of the continents. The pole positions from South America and Africa are emphasized in order to provide comparisons of: A. Plotted poles with respect to the continental configuration of Bullard et al. (1965) and B. Plotted poles with respect to a newly proposed continental configuration for Late Paleozoic times; see also Fig. 5.
109
that there is much better agreement between the paleomagnetic poles from the northern and southern continents in the alternative reconstruction (Fig.4B): notably, the paths of polar wandering fall on top of each other. Although there is generally also good agreement between the ages of the two sets of poles, there are a few exceptions: in particular, three of the four Late Permian South American poles are located more than 15 ° away from the Late Permian mean pole of the northern continents. It is conceivable that these data were obtained from redbeds that are younger than the Late Permian redbeds studied in North America and Europe. Fig.5 shows the continental configuration that results from the 20 ° rotation of Gondwanaland. We note that this configuration was proposed previously by Walper and Rowett (1972). There are of course many geologic implications of the reconstruction of Fig.5, notably the overlap of South America and northern Mexico, which 'would force us to relocate not only Central America (Guatemala, the
PALEO_LATITUDE
MAP: EARLY PERMIAN
Fig.5. Equidistant projection of the North American, European, Iberian, African and South American plates in a newly proposed continental configuration for Late Paleozoic times; Early Permian pole positions and an Early Permian paleolatitude pattern are superimposed.
110 Yucatan peninsula, Honduras, etc.), but also the entire Mexican part of the North American continent. The difference between our reconstruction for the Permian and the configuration of Bullard et al. (1965) can be seen by comparing Fig.5 with the Triassic paleolatitude maps of Fig.6, Appendix II. We tentatively suggest, however , that this reconstruction was valid from Late Carboniferous through Late Permian times. Then, in the Latest Permian/Early Triassic, there was a movement of Gondwanaland relative to Laurasia: the above-described counterclockwise rotation over some 20 °. This rotation implies the formation of the Gulf of Mexico in Permo-Triassic times, transcurrent dextral shear movements along Appalachian and Atlas fault systems (e.g., Reed and Bryant, 1964; Mattauer et al., 1972), and narrowing of the eastern part of the Tethys, with consumption of some Tethys ocean floor. In the Late Triassic, after this motion was completed, the continents would be in the positions similar to those proposed by Bullard et al. (1965) and the Atlantic would start opening in the generally accepted fashion as described in detail by Pitman and Talwani {1972). The details of our reconstruction (Fig. 5), and the resulting motions are based only on paleomagnetic data from Africa and South America. The paleomagnetic data from India and Australia were not used in this study, but they generally conform to those from South America (Tarling, 1971; Thompson, 1972). We feel there is enough leeway in this approach to make it a viable alternative to the non-centric dipole field assumption of Briden et al. (1970); the geologic implications, such as the continuity of the Appalachian belt (from the Ouachita mountains and the Marathon uplift (Texas) to the northwestern Venezuelan/Colombian Late Paleozoic fold belt) and the Late Paleozoic paleogeography of Central America and Mexico (e.g., Freeland and Dietz, 1972; Mattson, 1972; Walper and Rowett, 1972) remain to be investigated. ACKNOWLEDGEMENTS
It is our pleasant d u t y to acknowledge the help and criticism of several colleagues. Prof. H.N. Pollack kindly read and criticized the manuscript and offered many helpful suggestions. APPENDIX I
Paleomagnetic poles from formations ( ~ 40 m.y. and ~ 295 m.y.) that have not been used for our compilation, for the reasons given below Several results fall i n t o m o r e t h a n o n e category, b u t t h e y have b e e n listed o n l y once. R e f e r e n c e is m a d e to t h e lists b y Irving ( 1 9 6 4 ) a n d M c E l h i n n y {1968a, b; 1 9 6 9 ; 1970 a n d 1972). (1) Poles t h a t were c o n s i d e r e d to b e u n r e l i a b l e b y t h e original a u t h o r s , b y Irving or M c E l h i n n y , or t h a t were o b t a i n e d w i t h o u t s u f f i c i e n t d e m a g n e t i z a t i o n e x p e r i m e n t s .
Cu: Irving (1964), poles 6.01--6.04; 6.12--6.13; 6.15--6.23; 6.30--6.32; 6.36--6.42; 6.56--6.57; 6.64--6.66; 6.68; 6.69; 6.71; 6.74. McElhinny's lists, poles 8.98; 9.92--9.96; 10.110; 10.116; 12.130--12.132. P: Irving (1964), poles 7.06--7.10; 7.12; 7.14; 7.16--7.17; 7.22--7.41; 7.44--7.52; 7.57--7.60. McElhinny's lists, poles 8.83; 9.64; 9.69--9.75; 9.85--9.87; 10.99--10.103; 11.62; 12.106--12.107; 12.115; 12.118; 12.120--12.123. Tr: Irving (1964}, poles 8.01--8.05; 8.08--8.27; 8.30--8.41; 8.43; 8.46--8.51. McElhinnys's lists, poles 8.66; 8.71; 8.73--8.75; 9.50; 9.53--9.54; 9.59; 10.80; 10.94--10.95; 11.47; 11.51--11.53; 12.94--12.96. J: Irving (1964), poles 9.01--9.20; 9.24--9.27; 9.34--9.35; 9.43; 9.52. McElhinny's lists, poles 9.45; 10.72--10.76; 11.42. K: Irving (1964), poles 10.01--10.06; 10.13--10.14; 10.19. McElhinny's lists, poles 8.50--8.51; 8.53; 9.37; .10.51--10.55; 10.57--10.61; 10.65; 12.60--12.64; 12.74. Te: Irving (1964), poles 11.008--11.010; 11.015--11.017; 11.025; 11.027; 11.033--11.040; 11.044; 11.097; 11.099--11.101; 11.117; 11.125. McElhinny's lists, poles 10.44--10.45. (2) Poles from tectonically disturbed areas (poles from Irving's list (1964) given I . . . ; poles from McElhinny's lists given as M . . . ) Mediterranean (Alpine) mountain belt, poles I 7.19--7.21; I 7.55--7.56; M 8.81; 8.84; M 9.28; M 9.38; M 9.41; M 9.44; M 9.46; M 9.48; M 9.55--9.58; ]VI 9.60; M 9.62; 9.67--9.68; M 9.77--9.84; M 9.88; M 9.91; M 10.41; M 10.49; M 10.56; M 10.62; 10.71; M 10.91 (Italy, not Germany); M 10.97--10.98; M 11.48; M 11.54; 11.68--11.69; M 11.75; M 12.67; M 12.71; M 12.78--12.79; M 12.100--12.101; 12.111--12.113. Western North America (coastal ranges), poles I 11.098; M 10.68; M 11.38--11.40. Alaska: poles M 12.47--12.48. Spitzbergen, poles M 10.67, possibly M 10.69.
as M M M M M
(3) Poles from areas for which the paleogeographic position is ambiguous. South America, post-Jurassic (= post-opening South Atlantic Ocean), poles I 9.36; I 9.53. U.S.S.R. east of the Urals; a whole series of results that are not only internally inconsistent, but also suspect because of metamorphism, tectonic disturbances, inclination -- or declination -- errors, or that were obtained from too few samples. Poles M 8.45; M 8.55; M 8.70; M 8.76; M 8.78; M 12.53--12.57; M 12.65--12.66; M 12.68--12.70; M 12.75--12.77; M 12.81--12.82;M 12.84--12.92;M 12.97--12.99;M 12.103--12.104;M 12.108. (4) Results from formations that were not dated accurately enough. Irving (1964), poles I 7.18; I 10.16; I 11.110--11.113; McElhinny's lists, poles M 8.19--8.23; 8.34; 8.49; 8.94; 8.102; 8.109; 8.112; 8.113; 9.30--9.34; 9.47; 9.76; 10.48; 10.93; 10.104; 10.115; 11.26; 12.51; 12.125--12.129. Poles M 11.49 and M 11.56 have recently been dated by K/Ar methods as 263 _+ 5 m.y. old, by the University of Newcastle, U.K. (Creer et al., 1971); yet, in a review paper submitted more recently than this publication, Thompson from Newcastle, U.K. (1972) did not use these dates and still lists the results as Triassic. (5) Results based on too few samples (~---6). McElhinny's lists, poles M 8.65; M 8.90; M 10.92; M 11.30; (6) Results superseded by later publications. (I . . . . refers to Irving, 1964; M . . . . refers to McElhinny's lists, 1968a,b; 1969; 1970 and 1972; V . . . . refers to Table I.)
112 -
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PALEOMAGNETIC
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PALEO_LATITUDE
MAP:
LATE
NoR'rN AMERICA
PERMIAN
Fig.6A,B (for legend see p.115). PALEO_LATITUDE
MAP:
EARLY TRIASSIC
113
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PALEO_LATITUDE
MAP:
LATE
SOUTH AMERICA
TRIASSIC
PALEOMAGNETIC _
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•
NORTH
•
AFRICA
POLES:
AMERICA
yu" SOUTH AMERICA
PALEO_LATITUDE
MAP:
EARLY
JURASSIC
Fig.6 C,D. (for legend see p.115).
114
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P A L E O M A G N E T I C POLES ~o o
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PALEO_LATITUDE
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MAP:
EARLY
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PALEO_LATITUDE
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NORTH AMERICA
.
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PALEOMAGNETIC POLES. 6
EUROPE
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NORTH AMERICA
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CRETACEOUS
115
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PALEO_LATITUDE MAP:
pALEOMAGNETIC POLES:
•
EUROPE
•
NORTH AMERICA
=
AfRicA
t
IBERIAN SHIELD
EARLY TERTIARY
Fig.6. Paleo-latitude maps (see Appendix II for explanation). A. Late Permian. B. Early Triassic. C. Late Triassic. D. Early Jurassic. E. Early Cretaceous. F. Late Cretaceous. G. Early Tertiary. Poles (superseded by . . .) I 7.01 --7.05 (by V 7) I 7.15 (by M 11.77) I 9.46--9.49 (by I 9.50) I 9.51, M 8.56--8.58 (by M 8.59) I 10.11, M 10.66 (By M 11.36) I 10.18 (by M 8.48) I 11.018--11.24, I 11.026 (by M 12.49) M 8.62, M 8.64 (by M 10.77)'M 8.91, M 8.92 (by M 8.93) M 10.42, M 10.43 (by V 18) M 10.81--10.87 (by M 10.88) M 11.41 (by V 15) M 11.55 (by M 12.105) M 12.102 (see M 11.50", Table I) M 12.114 (by V 2). APPENDIX II Equidistant projections of the positions of the Atlantic-bordering continents, as proposed by Bultard et al. (1965) and Pitman and Talwani (1972), have been drawn in Fig.6 for seven periods, ranging from Late Permian to Early Tertiary, with the exception of the Late Jurassic. Paleomagnetic poles are plotted with respect to the suggested positions of the continents, arid a paleolatitude pattern is drawn as inferred from the mean paleomagnetic pole position. With the exception of the southern Eurasian margin, the continental outlines have been drawn in full for easy reference. It should also be noted, however, that the western coastlines of North and South America are generally younger than the time-span indicated on the maps. The paleomagnetic data are listed in Table I, the mean paleomagnetic pole positions and their statistical parameters are given in Table II.
25.9N 234.6E
40.0N 219.6E 60.2N 132.2E
20.8N 234.6E
35.0N 221.3E 58.3N 141.5E
54.8N 174.7E
Africa (in t h e p o s i t i o n s of the alternative fit, t h i s p a p e r )
Africa (in t h e p o s i t i o n s ofBullardetaL, 1965)
S o u t h A m e r i c a (in t h e p o s i t i o n s o f Bullard et al., 1 9 6 5 )
S o u t h A m e r i c a (in t h e positions of thealternat i r e fit, this p a p e r )
3.3 °
107
2.6 °
206
16
7.0 °
76
7
67.3N 155.3E
61.7N 110.9E
50.0N 215.5E
36.3N 234.5E
51.6N 206.3E
50.0N 151.1E
49.0N 112.7E
Pu*
* Data f r o m S o u t h A m e r i c a a n d Africa n o t i n c l u d e d .
~9s (Fisher, 1 9 5 3 )
K, p r e c i s i o n p a r a m e t e r (Fisher, 1 9 5 3 )
19
41.8N 211.7E
37.0N 213.9E
I b e r i a n Shield
N, n u m b e r o f poles
43.9N 163.5E
40.6N 168.7E
Europe
59.1N 169.9E
43.0N 125.0E
39.7N 130.2N
PI*
North America
Cu*
5.6 °
38
113
5.2 °
18
69.4N 66.1E
69.4N 66.1E
66.4N 236.2E
66.4N 236.2E
69.0N 225.0E
68.2N 136.6E
67.1N 98.5E
Tru
8
74.5N 128.0E
60.9N 87.3E
61.0N 211.1E
47.5N 236.7E
62.3N 199.7E
56.0N 135.0E
54.9N 97.0E
Trl*
5.4 °
152
6
77.7N 32.5E
77.7N 32.5E
62.0N 262.8E
62.0N 262.8E
66.4N 258.7E
79.4N 160.8E
78.4N 120.6E
J1
21.6
19
4
°
75.4N 153.6E
75.4N 153.6E
42.0N 242.0E
42.0N 242.0E
48.0N 242.7E
59.9N 201.8E
59.5N 162.1E
Ju
M e a n p a l e o m a g n e t i c pole p o s i t i o n s , c a l c u l a t e d f r o m all reliable p a l e o m a g n e t i c data, a n d t h e i r statistical p a r a m e t e r s . T h e m e a n poles are listed, for c o n v e n i e n c e , for e a c h c o n t i n e n t , with respect to the present-day coordinate system
T A B L E II
62.0N 231.0E
62.0N 231.0E
72.0N 200.4E
72.0N 200.4E
71.0N 179.0E
Ku
5.6 °
139
6
6.7 °
81
7
post-opening South Atlantic
post-opening South Atlantic
53.9N 253.4E
53.9N 253.4E
65.3N 247.0E
72.6N 221.6E
72.2N 184.5E
Kl
4.8 °
59
16
75.4N 211.7E
75.4N 211.7E
78.6N 172.3E
78.6N 172.3E
75.6N 184.5E
Tpa-e
117
REFERENCES Ade-Hall, J.M., Dagley, P., Wilson, R.L., Smith, P.J., Evans, A. and Riding, A., 1971. A palaeomagnetic study of the Mull dyke swarm. In: S.K. Runcorn (editor), Palaeogeophysics. Academic Press, London, pp. 139--142. Briden, J.C., Smith, A.G. and Sallomy, J.T., 1970. The geomagnetic field in Permo-Triassic time. Geophys. J., 23:101--117. Bullard, E.C., Everett, J. and Smith, A.G., 1965. A symposium on continental drift. Philos. Trans. R. Soc., Lond., Ser. A., 258: 41--51. Carey, S.W., 1958. A tectonic approach to continental drift. Symp. Continental Drift, Hobart, Tasmania 1958, pp.177--355. Creer, K.M., 1970. A review of palaeomagnetism. Earth-Sci. Rev. 6:369--466. Creer, K.M., Mitchell, J.G. and Valencio, D.A., 1971. Evidence for a normal geomagnetic field polarity event at 263 + 5 m.y. BP within the late Palaeozoic reversed interval. Nature Phys. Sci., 233:87--89. Creer, K.M., Mitchell, J.G. and Deeb, J.A., 1972. Paleomagnetism and radiometric age of the Jurassic Chon Aike formation from Santa Cruz Province, Argentina: Implications for the opening of the South Atlantic. Earth Planet. Sci. Lett. 14:131--138. Deutsch, E.R., 1969. Paleomagnetism and North Atlantic paleogeography. In: North Atlantic Geology and Continental Drift. Am. Assoc. Pet. Geologists, Mem., 12:931--954. Fisher, R.A., 1953. Dispersion on a sphere. Proc. R. Soc. Lond. Ser. A. 217:295--305. Freeland, G.L. and Dietz, R.S., 1972. Plate tectonics in the Caribbean: a reply (to P.H. Mattson). Nature, 235:156--157. Graham, J.W., 1949. The stability and significance of magnetism in sedimentary rocks. J. Geophys. Res., 54 :131--167. Helsley, C.E., 1971. Remanent magnetization of the Permian Cutler formation of Western Colorado. J. Geophys. Res., 76:4842--4848. Hospers, J., 1967. Review of palaeomagnetic evidence for the displacement of continents, with particular reference to North America and Europe--northern Asia. I n : S.K. Runcorn (editor), Mantles of the Earth and Terrestrial Planets. Interscience/Wiley, London, pp.331--349. Hospers, J. and van Andel S.I., 1968. Palaeomagnetic data from Europe and North America and their bearing on the origin of the North Atlantic Ocean. Tectonophysics 6:475--490. Irving, E., 1964. Paleomagnetism and its Application to Geological and Geophysical Problems. Wiley, New York, N.Y., 399 pp. Irving, E. and Yole, R.W., 1972. Paleomagnetism and the kinematic history of mafic and ultramafic rocks in fold mountain belts. Publ. Earth Phys. Branch, Dep. Energy, Mines, Res. Ottawa, 42(3): 87--95. Krs, M., 1968. Rheological aspects in paleomagnetism. Proc. Int. 13th Geol. C o n g . , Prague, 1968, 5:87--96. Krs, M., 1969. Paleomagnetismus. Knihovna I:lstrednfho lJstavu Geol., Akad., Prague, 40:202 pp. Kruseman, G.P., 1962. Etude pal4omagn6tique et s6dimentologique du bassin Permien de Lodbve, H6rault, France. Geol. Ultraiectina, 9:66 pp. Larson, E.E. and LaFountain, L., 1970. Timing of the breakup of the continents around the Atlantic as determined by paleomagnetism. Earth. Planet. Sci. Lett., 8: 331--351. Le Pichon, X. and Fox, P.J., 1971. Marginal offsets, fracture zones, and the early opening of the North Atlantic. J. Geophys. Res., 76:6294--6308. Mattauer, M., Proust, F. and Tapponnier, P., 1972. Major strike-slip fault of Late Hercynian age in Morocco. Nature, 237:160--162. Mattson, P.H., 1972. Plate tectonics in the Caribbean. Nature, 235:155--156.
118
McElhinny, M.W., 1968a. Palaeomagnetic directions and pole p o s i t i o n s - VIII. Geophys. J. 15:409--430. McElhinny, M.W., 1968b. Palaeomagnetic directions and pole positions -- IX. Geophys. J. 16:207--224. McElhinny, M.W., 1969. Palaeomagnetic directions and pole positions -- X. Geophys. d. 19:305--327. McElhinny, M.W., Palaeomagnetic directions and pole positions -- XI. Geophys. d. 20:417--429. McElhinny, M.W., 1972. Palaeomagnetic directions and pole positions -- XII. Geophys. J. 27:237--257. McElhinny, M.W. and Luck, G.R., 1970. Paleomagnetism and Gondwanaland. Science 168:830--832. Meyerhoff, A.A. and Meyerhoff, H.A., 1972. "The New Global Tectonics": major inconsistencies. Bull. Am. Assoc. Pet. Geologists, 56:269--336. Mulder, F.G., 1971. Paleomagnetic research in some parts of central and southern Sweden. Sver. Geol. Unders5kn., C. Nr. 653, Avhand. Uppsatser, 64(10):56 pp. Mulder, F.G., 1973. Paleomagnetic results from Irish Carboniferous and Triassic rocks. Geol. Surv. Ireland, Spec., Pap., in press. Phillips, J.D. and Forsyth, D., 1972. Plate tectonics, paleomagnetism and the opening of the Atlantic. Geol. Soc. Am. Bull., 83:1579--1600. Pitman, W.C. and Talwani, M., 1972. Sea-floor spreading in the North Atlantic. Geol. Soc. Am. Bull., 83:619--646. Reed, J.C. and Bryant, B., 1964. Evidence for strike-slip faulting along the Brevard Zone in North Carolina. Geol. Soc. Am. Bull., 75:1177--1196. Roche, A. and Westphal, M., 1971. Pal6omagn6tisme de l'Europe et de l'Afrique comme jalon de la formation du Golfe de Gascogne. In: J. Debyser, X. Le Pichon and L. Montadert (Editors), Histoire Structurale du Golfe de Gascogne. Editions Technip, Paris, 11--3:21 pp. Rother, K., 1971. Gesteins- und pal/iomagnetische Untersuchungen an Gesteinsproben vom Territorium der DDR. Dtsch. Akad. Wiss. Berlin, VerSffentl. Zentralinst. Phys. Erde, 5:92 pp. ROy, J.L., 1972. A pattern of rupture of the Eastern North American--Western European paleoblock. Earth Planet. Sci. Lett. 14:103--114. Runcorn, S.K., 1956. Palaeomagnetic comparisons between Europe and North America. Geol. Assoc. Can. Proc., 8:77--85. Smith, A.G. and Hallam, A., 1970. The fit of the southern continents. Nature, 225:139--144. Symons, D.T.A., 1973. Paleomagnetic results from Topley intrusions near Endako, British Columbia. Can. J. Earth Sci., 10:1099--1108. Takeuchi, H., Uyeda, S. and Kanamori, H., 1967. Debate about the Earth. Freeman, Cooper, San Francisco, Calif., revised ed., 281 pp. Tarling, D.H., 1971. Gondwanaland, palaeomagnetism and continental drift. Nature, • 229:17--21. Thompson, R., 1972. Palaeomagnetic results from the Paganzo basin of north-west Argentine. Earth Planet. Sci. Lett., 15 : 145--156. Valencio, D.A. and Vilas, J.F., 1972. Palaeomagnetism of Late Paleozoic and Early Mesozoic rocks of South America. Earth Planet Sci. Lett. 15:75--85. Van der Voo, R. and Zijderveld, J.D.A., 1971. Renewed paleomagnetic study of the Lisbon volcanics and implications for the rotation of the Iberian peninsula. J. Geophys. Res., 76:3913--3921. Van Hilten, D., 1964. Evaluation of some geotectonic hypotheses by paleomagnetism, Tectonophysics, 1:3--71. Veldkamp, J., Mulder, F.G. and Zijderveld, J.D.A., 1971. Palaeomagnetism of Surinam dolerites. Phys. Earth. Planet. Int., 4:370--380.
119
Vogt, P.R., Anderson, C.N. and Bracey, D.R., 1971. Mesozoic magnetic anomalies, seafloor spreading, and geomagnetic reversals in the southwestern North Atlantic. J. Geophys. Res., 76 : 4796--4823. Walper, J.L. and Rowett, C.L., 1972. Plate tectonics and the origin of the Caribbean and the Gulf of Mexico. Trans. Gulf Coast Assoc. Geol. Soc., (22nd Ann. Conf. Proc.):105--116. Wells, J.M. and Verhoogen, J. 1967. Late Paleozoic paleomagnetic poles and the opening of the Atlantic Ocean. J. Geophys. Res., 72:1777--1781. Wilson, R.L., 1970. Permanent aspects of the Earth's non-dipole magnetic field over Upper Tertiary times. Geophys. J. 19:417--437. Zijderveld, J.D.A., 1967. The natural remanent magnetizations of the Exeter volcanic traps (Europe). Tectonophysics, 4:121--153. Zijderveld, J.D.A. and Van der Voo, R., 1973. Paleomagnetism in the Mediterranean area: A review. In: D.H. Tarling and S.K. Runcorn (Editors), Implications of Continental Drift to the Earth Sciences. Academic Press, London, 1:133--161. (Accepted for publication September 6, 1973)
Apparent Polar Wandering for the Atlantic-Bordering Continents: Late Carboniferous to Eocene R. Van der Voo and R.B. French
ABSTRACT Van der Voo, R. and French, R.B., 1974. Apparent polar wandering for the Atlanticbordering continents: Late Carboniferous to Eocene. Earth-Sci. Rev., 10: 99--119. We present a compilation o f reliable paleomagnetic pole positions from five continental plates (North America, Europe, the Iberian Peninsula, Africa, and South America) for ten time intervals ranging from Late Carboniferous to Eocene. Only well-dated results obtained by demagnetization techniques have been used. Paleomagnetic poles are plotted with respect to the paleo-positions of the continents, as reconstructed from correlations of marine magnetic anomalies in the Atlantic Ocean by Pitman and Talwani and from the fit by Bullard et al. The poles from North America, Europe and the younger poles from Africa show a very good grouping for most of the ten intervals considered, and a continuous apparent polar wandering path is obtained. These data have been used to construct paleolatitude maps for most intervals; thus the relative positions of the continents were established from sea-floor spreading data and their absolute positions on the globe were determined from paleomagnetic data. The older data from South America and the other Gondwana continents show a systematic deviation) from those of the northern continents for Late Paleozoic and Early Triassic time periods. An explanation is offered in a different continental reconstruction between Laurasia ai~d Gondwanaland before Middle Triassic times.
INTRODUCTION V i r t u a l p a l e o m a g n e t i c p o l e p o s i t i o n s , in p a r t i c u l a r t h o s e o b t a i n e d f r o m N o r t h A m e r i c a , E u r o p e a n d A f r i c a , r e v i v e d i n t e r e s t in c o n t i n e n t a l d r i f t t h e o r i e s in t h e l a t e 1 9 5 0 ' s (e.g., R u n c o r n , 1 9 5 6 ; T a k e u c h i e t al., 1 9 6 7 ) . Y e t as l a t e as 1 9 6 7 , a r t i c l e s w e r e b e i n g p u b l i s h e d in w h i c h t h e v a l i d i t y o f p a l e o m a g n e t i c d a t a as e v i d e n c e f o r d r i f t w a s s e r i o u s l y q u e s t i o n e d (e.g., H o s p e r s , 1 9 6 7 ) . I t is n o t d i f f i c u l t t o d e t e r m i n e f a c t o r s w h i c h l e d t o t h i s c o n f u s i o n : (1) e a r l y p a l e o m a g n e t i c w o r k w a s n o t s u b j e c t e d t o t h e p r e s e n t - d a y d e m a g netization techniques and therefore was contaminated with secondary magnetic overprinting; (2) many results were obtained from statistically insuffic i e n t q u a n t i t i e s o f s a m p l e s o r o t h e r s u n i t s , so t h a t s h o r t - t i m e f l u c t u a t i o n s o f
100 the geomagnetic field were not adequately averaged out; (3) it was often not realized until later that some results obtained from tectonically disturbed areas could not be used; and (4) some paleomagnetic results were obtained from rocks that were poorly dated, thereby blurring the details of the polar wandering paths unnecessarily. It was not surprising therefore that some earth scientists displayed caution about paleomagnetically derived conclusions (e.g., Meyerhoff and Meyerhoff, 1972). In the last decade, however, most of the above-mentioned difficulties have been remedied, through more sophisticated paleomagnetic analyzing techniques, radiometric age dating methods and also more insight in tectonic problems. We present in this paper a rigorous selection of what one might call "reliable" paleomagnetic data, i.e., data based on sufficient sampling, alternating field or thermal demagnetization, good stratigraphic or radiometric age control, and often supported by conclusive tests about the primary nature of the magnetizations involved, such as the unfolding test (Graham, 1949). Our data selection is more rigorous than those of previous analyses (e.g., Wells and Verhoogen, 1967; Hospers and Van Andel, 1968; Deutsch, 1969; Larson and La Fountain, 1970; and also Roy, 1972, and Phillips and Forsyth, 1972). The improved age control permits us to group our data in shorter time intervals of 20--30 m.y. duration, roughly representing the lower and upper parts of the major periods. Rob van der Voo (Ph.D. 1969, Utrecht) was born in The Netherlands. He was Research Associate in Utrecht for one post-doctoral year, was Visiting Assistant Professor in the Department of Geology and Mineralogy of the University of Michigan in Ann Arbor and is currently Assistant Professor at this Institution. In addition to some fifteen papers on paleomagnetic studies in the Mediterranean area, he has published on the stratigraphy and tectonics of parts of the Pyrenees and on a seismological study of surface waves generated by nuclear explosions. He is currently investigating absolute rates of polar wandering for the Earth's geological past and has several projects in paleomagnetic research. Rowland B. French received his A.B. from Dartm o u t h College in 1969 and his M.S. in Physics from the University of Michigan. He is currently in the Department of Geology and Mineralogy at the University of Michigan working on his doctoral dissertation in paleomagnetics.
101 Our use of the data compiled is also different in t h a t its basic premises are the validity of the reconstructions of the Atlantic bordering continents (Bullard et al., 1965; V0gt et al., 1971; Le Pichon and Fox, 1971) and the subsequent spreading episodes of the Atlantic Ocean as deduced from marine magnetic anomalies and JOIDES deep-sea drilling (Pitman and Talwani, 1972). It is generally believed that the positions of the continents Africa, North America, and Europe are now fairly accurately known for the Mesozoic and the Tertiary, independent of continental paleomagnetic data. With these reconstructions for Mesozoic and Tertiary times, we have plotted the reliable paleomagnetic pole positions from four continental plates: North America, Europe (north of the Alpine fold belt), the Hercynian Meseta of the Iberian Peninsula, and Africa. Paleomagnetic data from South America are used only for the periods preceding the separation from Africa. We will see that the paleomagnetic data are in excellent agreement with the reconstructions, with the exception of the Late Paleozoic data from the Gondwana continents. In the next section the m e t h o d o l o g y of data selection will be discussed. This leads to the paleogeographical maps (Fig.6A--G) of Appendix II, granted the assumption that the geomagnetic field was, on the average, that of a geocentric axial dipole. Finally, it will be discussed how the Late Paleozoic and Early Triassic paleomagnetic data from Africa and South America compare with those from the northern continents. METHODOLOGY The paleomagnetic poles that we have used are shown in Fig.1 and Table I, grouped according to time interval and continent. Fig.1 shows the localities where the samples were collected. We have established three major criteria for their selection. First, all poles are from studies that used effective demagnetization techniques for a substantial a m o u n t of samples to eliminate possible secondary magnetizations. Either ac or thermal demagnetization, or both, were used to obtain each pole position. Second, all poles are from formations with well-established ages. Only poles which could be grouped into a subunit of a geologic period, such as Upper Cretaceous or Lower Triassic were used. Poles dated simply as Permian or Cretaceous were not considered accurately enough dated. This allows us to group the poles into shorter time units than has been done in the past. Such groupings avoid large scatter of the pole positions and yield a more continuous polar wandering path. Our third selection criterion is that paleomagnetic samples from tectonically disturbed regions are not used. Thus, poles from the California Coast Range or Alpine Europe were not utilized (see Irving and Yole, 1972; Zijderveld and Van der Voo, 1973). Table I shows ten time units with the poles from each continent placed in these groupings. Some periods lack data from some continents. The European data are sparse for the Jurassic and Cretaceous, and the African data are almost non-existent before the Upper Triassic. Not only is the selection of the paleomagnetic results important, it
102
Fig.1. World map with the sites of reliable paleomagnetic sample collections as used in this study (Table I), plotted in North America, Europe, the Iberian Peninsula, Africa and South America, respectively. The corresponding virtual paleomagnetic pole positions are given in Fig.2. m i g h t al~o be very subjective. In t h e a p p e n d i x we give an a c c o u n t o f w h y s o m e results have n o t b e e n used. T h e Mesozoic a n d C e n o z o i c p o s i t i o n s of t h e E u r o p e a n , N o r t h A m e r i c a n , a n d A f r i c a n c o n t i n e n t a l plates, relative t o each o t h e r , are t a k e n f r o m P i t m a n a n d T a l w a n i (1972). T h e y have c o m p i l e d a n d m a p p e d t h e m a g n e t i c a n o m alies in t h e N o r t h a n d C e n t r a l A t l a n t i c Ocean. By j u x t a p o s i n g i s o c h r o n o u s a n o m a l i e s on either side of t h e s p r e a d i n g ridge t h e y have d e t e r m i n e d t h e relative p o s i t i o n s o f N o r t h A m e r i c a , E u r o p e a n d A f r i c a at the t i m e w h e n t h o s e a n o m a l i e s w e r e c r e a t e d . We have a s s u m e d u n i f o r m m o t i o n in t h e s h o r t
103
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Fig.2 Plot of reliable paleomagnetic pole positions (Fig.1) obtained from North America, Europe, the Iberian Shield and Africa, plotted with respect to their present-day positions. A. Pole positions ranging in age from Late Carboniferous to Middle Triassic. B. Pole positions ranging in age from Middlt Triassic to Eocene. intervals b e t w e e n the positions o f the c o n t i n e n t s given by P i t m a n and Talwani. We have also assumed t h a t t h e relative positions b e f o r e the o p e n i n g o f the Atlantic were as p r o p o s e d b y Bullard et al. {1965). T h e d i f f e r e n c e bet w e e n this fit and m o s t others, such as those o f Le P i c h o n and F o x {1971) or Vogt et al. ( 1 9 7 1 ) is t o o small to substantially a f f e c t o u r p a l e o m a g n e t i c comparisons. We have r o t a t e d the Iberian Peninsula as p r o p o s e d by Carey ( 1 9 5 8 ) a n d Bullard et al. (1965). Paleogeographic m a p s have been c o n s t r u c t e d , one for each o f the ten t i m e intervals, using t h e c o n t i n e n t a l r e c o n s t r u c t i o n s described above. Thus, the relative positions o f t h e c o n t i n e n t s were established f r o m sea-floor spreading data, whereas t h e a b s o l u t e positions on the globe were d e t e r m i n e d f r o m
104 TABLE I Table of the paleomagnetic pole positions that have been used for our compilation NORTH
IBERIAN
EARLY TERTIARY LATE CRETACEOUS
[ 11012 ] ll.OI3
111.014
M8.33
M12.49
MII.28
MI2.50
SOUTH
AMERICA
EUROPE
If17
M 8.48 e
M9.29
Mlt.31
MI1.52
M 8.48
M 9.56
M 11,55
M 11.37
[ 10,12
[
LATE
-
I00
MY
-
130
MY
-
155
MY
-
185
MY
-
210
MY
-
250MY
-
255
M 9.40
M 9.43
M 10.69
V 16
I 9.50 M 8,59
V 15
M 863 M 8.61
M 12.93
[ 8.42
18.44
M 10.75
M 8.69
M9.49
.,o.~
M 10.89 M 10.90
LATE
I8.o8
TRIASSIC EARLY TRIASSIC
PERMIAN
MY
M 9.42
JURASSIC
EARLY
70
[ 10.15
EARLY
PERMIAN
-
10.17
M It.58
JURASSIC
LATE
MY
M 12.46
M 8.52
CRETACEOUS
40
M 8.38
MII.25
Y 18
EARLY
M 10.46
Mll.29
M 8.35
AMERICA AFRICA
[ 8.07
M8.69 M 10.88
VII
M8.61
v,z
M9,51 M 10.96
M 11.44
M 9.52
M 11.59
.5.8=
M9.85
M 11.56 ")
M 12. II0 v7
M 11.85
M 11.66
M8.88 M 10.106 Y 6
M 10.105 M 11.67
I7,13 M II .70 V4
[7.54
.,=.,,8 Y 5
LATE .=,,o M 9.90 CARBONIFEROUS"'o-'~ iMII,71
M 8.72 M 11.50e
,,8.77
~7.1, 8.87
M 8.87
M 11.46
M 8.1il M9.69 M I0.107 M 10,108I M to..t/.~ M 11,77 V I
M 11.72 M 11.73 M 11.74
M8.85 M8.99 M 8.101 MII.78
M8.96 M 8.100 M9.98
M8.97
M 10,77 M 11.60 Mf2.1O5 V 15
V 14
M ll.6l
M 12.109
V9
V9
"/10
MY
M 12.1t6 M 12.ll7 M 181;" M 9.107 M 12.124e V 2 Y3
M 8.93
-- 275
MY
295
MY
-
The numbers refer to those from Irving (1964), given here as I . . . ; from McElhinny's lists (1968a,b; 1969; 1970 and 1972), given here as M . . . ; or they have been listed below (the poles given as V 1--V 18). The paleomagnetic poles that have not been used are accounted for in Appendix I. Pole V 1 from Kruseman (1962); V 2 from Thompson (1972, pole 6); V 3 from Thompson (1972, pole 5); V 4 from Krs (1968); V 5 from Kruseman (1962); V 6 from Helsley (1971); V 7 from Zijderveld (1967, Est6rel pole); V 8 from Thompson {1972, pole 12); V 9 from Thompson (1972, pole 11); V 10 from Thompson (1972, pole 10); V 11 from Rother (1971); V 12 from Mulder (1973); V 13 from Thompson (1972, pole 13); V 14 from Veldkamp et al. (1971); V 15 from Creer et al. (1972); V 16 from Symons (1973); V 17 from Ade-Hall et al, (1970); and V 18 from Van der Voo and Zijderveld ( 1971 ).
105 p a l e o m a g n e t i c data. I n t e r e s t e d readers m a y o b t a i n these m a p s (70 × 60 c m ) f o r a n o m i n a l fee b y writing to t h e a u t h o r s . S o m e o f the m a p s are p r e s e n t e d in t h e a p p e n d i x . T h e p a l e o l a t i t u d e s w e r e d e t e r m i n e d f r o m t h e m e a n paleom a g n e t i c p o l e f o r each 2 0 - - 3 0 m . y . interval. T h e m e r i d i a n s were d r a w n a r b i t r a r i l y in o r d e r t o p r o v i d e s o m e r e f e r e n c e scale. THE PALEOMAGNETIC POLES FOR THE TEN TIME INTERVALS AND THE PALEOGEOGRAPHIC MAPS T e n p a l e o g e o g r a p h i c m a p s h a v e b e e n c o n s t r u c t e d in an e q u i d i s t a n t projection, b a s e d on t h e fit o f t h e c o n t i n e n t s b y Bullard et al. ( 1 9 6 5 ) and the p o s i t i o n s o f t h e c o n t i n e n t s as d e d u c e d f r o m sea-floor s p r e a d i n g episodes in the A t l a n t i c O c e a n ( P i t m a n a n d Talwani, 1972). Seven of these m a p s are p r e s e n t e d in t h e a p p e n d i x ; t h e y are r e p r e s e n t a t i v e o f the m e a n age o f the r e s p e c t i v e 2 0 - - 3 0 m . y . t i m e intervals. T h e p a l e o m a g n e t i c p o l e s f o r t h o s e p e r i o d s have b e e n p l o t t e d o n t h e m a p s ; t h e m e a n p a l e o m a g n e t i c poles have b e e n used to d e t e r m i n e t h e p a l e o l a t i t u d e s . F o r nine o u t o f t h e s e ten t i m e intervals, nearly all p a l e o m a g n e t i c poles lie w i t h i n a circle o f 10 ° a r o u n d t h e m e a n p o l e p o s i t i o n f o r t h a t interval. M o r e o v e r , t h e circles o f c o n f i d e n c e t h a t c o n t a i n with 95% p r o b a b i l i t y the t r u e m e a n pole p o s i t i o n s have radii less t h a n 7 ° f o r t h e s e nine intervals; for t h e L a t e C a r b o n i f e r o u s a n d t h e E a r l y P e r m i a n t h e s e radii or a 9 s'S are as small as 3.25 ° a n d 2.6 ° (Table II, p . l 1 6 ) . It follows t h a t the 95% c o n f i d e n c e limits f o r t h e p o s i t i o n s o f t h e p a l e o l a t i t u d e lines are c o m p a r a b l e t o t h e a9 s ' s o f t h e i r poles. T h e L a t e C a r b o n i f e r o u s , Early a n d L a t e P e r m i a n , a n d E a r l y Triassic d a t a f r o m N o r t h A m e r i c a , E u r o p e a n d t h e I b e r i a n Peninsula agree well and present a c o n t i n u o u s a n d well-defined virtual p o l a r w a n d e r i n g p a t h (Fig.3A). T h e L a t e Triassic d a t a f r o m N o r t h A m e r i c a a n d Africa, s t r e a k i n g b e t w e e n t h e m e a n L o w e r Triassic a n d L o w e r Jurassic poles, o b v i o u s l y reveal relatively rapid a p p a r e n t p o l a r w a n d e r i n g w i t h r e s p e c t to t h e N o r t h A t l a n t i c b o r d e r i n g c o n t i n e n t s (Fig.3B). T w o results f r o m t h e K e u p e r marls of G r e a t Britain Legend to Table I (cont.):
Footnotes to poles (given by *): M 10.111/113": this result includes data not listed by McElhinny (1969), that were reported by Krs (1968). M 10.108": Pole listing by McElhinny (1969) is incorrect, should be given as 38 N 166 E (Mulder, 1971). M 8.86": age given as Cu (pre-Kiaman interval) by Thompson (1972, pole 3). M 12.124": from the Piaui formation, Brazil. Thompson (1972) lists two poles, one from the lower part of the formation (Thompson, 1972, pole 2, given as pole M 8.107) and this one, from the upper part (Thompson, 1972, pole 4) with coordinates 55N 171 E. M 11.58": age may be P1, according to Helsley (1971). M 11.50": pole listed as 77 N 322 E by McElhinny (1970), which, according to Valencio and Vilas (1972) was calculated from undemagnetized directions of magnetizations. After demagnetization analysis the pole becomes: 77 N 29 E (see also McElhinny, 1972, pole 12.102, though with different coordinates). M8.46": pole quoted as 79 N, 158 E by Krs (1969).
106 (stable Europe) are of marginal reliability as far as complete demagnetization analyses are concerned; they seem to agree better with the Lower Triassic group of poles. Two other results from Europe (southern France), on the other hand, agree very well with the results from Africa and North America for this 210--185 m.y. time interval (Fig.3B). A large gap in our knowledge exists for most of the Jurassic, between roughly 165 and 130 m.y. ago. Moreover, the few results published so far come from areas for which the "belonging" to the stable part of the continent has not been established beyond doubt: the western U.S.A. and the Canadian Cordillera and Spitzbergen. The results are widely scattered (c¢9s = 22 °) and may also reflect rapid apparent polar wandering (see Fig.3B). The relative abundance of North American Early and Late Cretaceous poles and European Lower Tertiary poles form the firm basis for the last three paleogeographic maps. The mean paleomagnetic poles have radii of 95% confidence of 6 °, 7 ° and 5 °, respectively. Post-Eocene results (less than 40 m.y. ago) have not been compiled, since they tend to group more or less around the present-day geographic pole with a relatively large scatter (see for instance a compilation of European and African data by Roche and Westphal, 1971). THE LATE PALEOZOIC GONDWANA POLES Reassuring as the small a 9 s's of the groups of paleomagnetic poles may be in the confirmation of our m e t h o d and selection criteria, it is the occasional pole position that does not agree with the rest of the group that presents the more interesting problems. Not mentioned before, and falling into the latter category, is a whole set of results: those from the Gondwana continents, in particular those from South America, India and Australia, for all of the Late Paleozoic and Earliest Triassic. (For a recent review of the internal consistency of the paleomagnetic poles from the Gondwana continents, see Thompson, 1972; or Tarling, 1971.) This is by no means a new conclusion; the cause of the deviation of the Gondwana poles has been discussed by several authors, e.g., due to an alternative fit along the Tethys (Van Hilten, 1964); by inclination error and/or a short period of continental drift (Creer, 1970); and due to long-term non-axially central dipole components of the geomagnetic field (Briden et al., 1970). The South American results are the most numerous amongst the results of the Gondwana continents. Moreover, they appear to be the least ambiguous for our purpose, since the positions of India and Australia are not yet fully agreed upon (e.g., McElhinny and Luck, 1970; Smith and Hallam, 1970; Tarling, 1971). By repositioning the continents according to the fit by Bullard et al. (1965), one can compare the South American results with those from Europe and North America, for the periods that preceded the breakup of
107
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Fig.3. Plot of reliable paleomagnetic pole positions (Fig, l,2) obtained from North America, Europe, the Iberian Shield and Africa, plotted with respect to the continental reconstructions of Bullard et al. (1965) and Pitman and Talwani (1972). Coordinate system assumes North America held fixed. A. Pole positions ranging in age from Late Carboniferous to Middle Triassic. B. Pole positions ranging in age from Middle Triassic to Eocene. G o n d w a n a l a n d / P a n g e a (Fig.4A). T h e S o u t h A m e r i c a n p o l a r w a n d e r i n g p a t h t h u s o b t a i n e d is parallel t o t h a t f r o m t h e n o r t h e r n c o n t i n e n t s , b u t is disp l a c e d s o m e 20 ° e a s t w a r d . This parallelism c o n t i n u e s f r o m t h e L a t e Carbonif e r o u s t o t h e Earliest Triassic, well b e f o r e t h e o p e n i n g o f t h e p r e s e n t Atlantic Ocean. T h e r e is a clear t r e n d in t h e p o s i t i o n s o f the S o u t h A m e r i c a n poles, lying in a distinct p a t h , w h i c h implies t h a t , even w h e n t h e S o u t h A m e r i c a n results are s u b j e c t t o small errors in age d e t e r m i n a t i o n ( V a l e n c i o a n d Vilas, 1 9 7 2 ) t h e pole p o s i t i o n s are still d i s t i n c t l y deviating. A t t e m p t s have b e e n m a d e p r e v i o u s l y t o alleviate this i n c o n s i s t e n c y . T h e a s s u m p t i o n o f a g e o c e n t r i c axial d i p o l e field was i n v e s t i g a t e d r e c e n t l y b y Briden et al. ( 1 9 7 0 ) , Wilson ( 1 9 7 0 ) a n d others. This is o n e of t h e basic
108 assumptions of paleomagnetism (e.g., Irving, 1964) and seems to hold fairly well for the results from the northern continents. We note that a substantial departure from the geocentric dipole model, lasting for some 100 m.y., would be required to account for the South American discrepancies. Another possibility is that the fit of the continents by Bullard et al. (1965) cannot be used for this period. Van Hilten (1964) did note this possibility and proposed an alternative continental reconstruction, implying subsequent dextral shear in the Tethys zone: the " T e t h y s twist". Since then so m a n y data have become available that the Tethys twist concept is no longer tenable; yet, we feel that the paleomagnetic data strongly indicate an alternative reconstruction for the Late Paleozoic. Fig.4B shows the paleomagnetic pole positions of Africa and South America after an additional clockwise rotation of Gondwanaland over some 20 ° about a point in the southern Sahara (27°N 60°W with respect to North America). One can see
PA LEOMAGNE T IC
POL ES :
•
the NORTHERN
[]
AFRICA
CONTINENTS
$
MEAN POLE POSITIONS (see TABLE I )
SOUTH AMERICA
Fig.4. The same pole positions as in Fig.3, with those from South America added, for the time periods that preceded the break-up of the continents. The pole positions from South America and Africa are emphasized in order to provide comparisons of: A. Plotted poles with respect to the continental configuration of Bullard et al. (1965) and B. Plotted poles with respect to a newly proposed continental configuration for Late Paleozoic times; see also Fig. 5.
109
that there is much better agreement between the paleomagnetic poles from the northern and southern continents in the alternative reconstruction (Fig.4B): notably, the paths of polar wandering fall on top of each other. Although there is generally also good agreement between the ages of the two sets of poles, there are a few exceptions: in particular, three of the four Late Permian South American poles are located more than 15 ° away from the Late Permian mean pole of the northern continents. It is conceivable that these data were obtained from redbeds that are younger than the Late Permian redbeds studied in North America and Europe. Fig.5 shows the continental configuration that results from the 20 ° rotation of Gondwanaland. We note that this configuration was proposed previously by Walper and Rowett (1972). There are of course many geologic implications of the reconstruction of Fig.5, notably the overlap of South America and northern Mexico, which 'would force us to relocate not only Central America (Guatemala, the
PALEO_LATITUDE
MAP: EARLY PERMIAN
Fig.5. Equidistant projection of the North American, European, Iberian, African and South American plates in a newly proposed continental configuration for Late Paleozoic times; Early Permian pole positions and an Early Permian paleolatitude pattern are superimposed.
110 Yucatan peninsula, Honduras, etc.), but also the entire Mexican part of the North American continent. The difference between our reconstruction for the Permian and the configuration of Bullard et al. (1965) can be seen by comparing Fig.5 with the Triassic paleolatitude maps of Fig.6, Appendix II. We tentatively suggest, however , that this reconstruction was valid from Late Carboniferous through Late Permian times. Then, in the Latest Permian/Early Triassic, there was a movement of Gondwanaland relative to Laurasia: the above-described counterclockwise rotation over some 20 °. This rotation implies the formation of the Gulf of Mexico in Permo-Triassic times, transcurrent dextral shear movements along Appalachian and Atlas fault systems (e.g., Reed and Bryant, 1964; Mattauer et al., 1972), and narrowing of the eastern part of the Tethys, with consumption of some Tethys ocean floor. In the Late Triassic, after this motion was completed, the continents would be in the positions similar to those proposed by Bullard et al. (1965) and the Atlantic would start opening in the generally accepted fashion as described in detail by Pitman and Talwani {1972). The details of our reconstruction (Fig. 5), and the resulting motions are based only on paleomagnetic data from Africa and South America. The paleomagnetic data from India and Australia were not used in this study, but they generally conform to those from South America (Tarling, 1971; Thompson, 1972). We feel there is enough leeway in this approach to make it a viable alternative to the non-centric dipole field assumption of Briden et al. (1970); the geologic implications, such as the continuity of the Appalachian belt (from the Ouachita mountains and the Marathon uplift (Texas) to the northwestern Venezuelan/Colombian Late Paleozoic fold belt) and the Late Paleozoic paleogeography of Central America and Mexico (e.g., Freeland and Dietz, 1972; Mattson, 1972; Walper and Rowett, 1972) remain to be investigated. ACKNOWLEDGEMENTS
It is our pleasant d u t y to acknowledge the help and criticism of several colleagues. Prof. H.N. Pollack kindly read and criticized the manuscript and offered many helpful suggestions. APPENDIX I
Paleomagnetic poles from formations ( ~ 40 m.y. and ~ 295 m.y.) that have not been used for our compilation, for the reasons given below Several results fall i n t o m o r e t h a n o n e category, b u t t h e y have b e e n listed o n l y once. R e f e r e n c e is m a d e to t h e lists b y Irving ( 1 9 6 4 ) a n d M c E l h i n n y {1968a, b; 1 9 6 9 ; 1970 a n d 1972). (1) Poles t h a t were c o n s i d e r e d to b e u n r e l i a b l e b y t h e original a u t h o r s , b y Irving or M c E l h i n n y , or t h a t were o b t a i n e d w i t h o u t s u f f i c i e n t d e m a g n e t i z a t i o n e x p e r i m e n t s .
Cu: Irving (1964), poles 6.01--6.04; 6.12--6.13; 6.15--6.23; 6.30--6.32; 6.36--6.42; 6.56--6.57; 6.64--6.66; 6.68; 6.69; 6.71; 6.74. McElhinny's lists, poles 8.98; 9.92--9.96; 10.110; 10.116; 12.130--12.132. P: Irving (1964), poles 7.06--7.10; 7.12; 7.14; 7.16--7.17; 7.22--7.41; 7.44--7.52; 7.57--7.60. McElhinny's lists, poles 8.83; 9.64; 9.69--9.75; 9.85--9.87; 10.99--10.103; 11.62; 12.106--12.107; 12.115; 12.118; 12.120--12.123. Tr: Irving (1964}, poles 8.01--8.05; 8.08--8.27; 8.30--8.41; 8.43; 8.46--8.51. McElhinnys's lists, poles 8.66; 8.71; 8.73--8.75; 9.50; 9.53--9.54; 9.59; 10.80; 10.94--10.95; 11.47; 11.51--11.53; 12.94--12.96. J: Irving (1964), poles 9.01--9.20; 9.24--9.27; 9.34--9.35; 9.43; 9.52. McElhinny's lists, poles 9.45; 10.72--10.76; 11.42. K: Irving (1964), poles 10.01--10.06; 10.13--10.14; 10.19. McElhinny's lists, poles 8.50--8.51; 8.53; 9.37; .10.51--10.55; 10.57--10.61; 10.65; 12.60--12.64; 12.74. Te: Irving (1964), poles 11.008--11.010; 11.015--11.017; 11.025; 11.027; 11.033--11.040; 11.044; 11.097; 11.099--11.101; 11.117; 11.125. McElhinny's lists, poles 10.44--10.45. (2) Poles from tectonically disturbed areas (poles from Irving's list (1964) given I . . . ; poles from McElhinny's lists given as M . . . ) Mediterranean (Alpine) mountain belt, poles I 7.19--7.21; I 7.55--7.56; M 8.81; 8.84; M 9.28; M 9.38; M 9.41; M 9.44; M 9.46; M 9.48; M 9.55--9.58; ]VI 9.60; M 9.62; 9.67--9.68; M 9.77--9.84; M 9.88; M 9.91; M 10.41; M 10.49; M 10.56; M 10.62; 10.71; M 10.91 (Italy, not Germany); M 10.97--10.98; M 11.48; M 11.54; 11.68--11.69; M 11.75; M 12.67; M 12.71; M 12.78--12.79; M 12.100--12.101; 12.111--12.113. Western North America (coastal ranges), poles I 11.098; M 10.68; M 11.38--11.40. Alaska: poles M 12.47--12.48. Spitzbergen, poles M 10.67, possibly M 10.69.
as M M M M M
(3) Poles from areas for which the paleogeographic position is ambiguous. South America, post-Jurassic (= post-opening South Atlantic Ocean), poles I 9.36; I 9.53. U.S.S.R. east of the Urals; a whole series of results that are not only internally inconsistent, but also suspect because of metamorphism, tectonic disturbances, inclination -- or declination -- errors, or that were obtained from too few samples. Poles M 8.45; M 8.55; M 8.70; M 8.76; M 8.78; M 12.53--12.57; M 12.65--12.66; M 12.68--12.70; M 12.75--12.77; M 12.81--12.82;M 12.84--12.92;M 12.97--12.99;M 12.103--12.104;M 12.108. (4) Results from formations that were not dated accurately enough. Irving (1964), poles I 7.18; I 10.16; I 11.110--11.113; McElhinny's lists, poles M 8.19--8.23; 8.34; 8.49; 8.94; 8.102; 8.109; 8.112; 8.113; 9.30--9.34; 9.47; 9.76; 10.48; 10.93; 10.104; 10.115; 11.26; 12.51; 12.125--12.129. Poles M 11.49 and M 11.56 have recently been dated by K/Ar methods as 263 _+ 5 m.y. old, by the University of Newcastle, U.K. (Creer et al., 1971); yet, in a review paper submitted more recently than this publication, Thompson from Newcastle, U.K. (1972) did not use these dates and still lists the results as Triassic. (5) Results based on too few samples (~---6). McElhinny's lists, poles M 8.65; M 8.90; M 10.92; M 11.30; (6) Results superseded by later publications. (I . . . . refers to Irving, 1964; M . . . . refers to McElhinny's lists, 1968a,b; 1969; 1970 and 1972; V . . . . refers to Table I.)
112 -
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PERMIAN
Fig.6A,B (for legend see p.115). PALEO_LATITUDE
MAP:
EARLY TRIASSIC
113
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PALEO_LATITUDE
MAP:
LATE
SOUTH AMERICA
TRIASSIC
PALEOMAGNETIC _
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AFRICA
POLES:
AMERICA
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PALEO_LATITUDE
MAP:
EARLY
JURASSIC
Fig.6 C,D. (for legend see p.115).
114
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CRETACEOUS
115
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PALEO_LATITUDE MAP:
pALEOMAGNETIC POLES:
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EUROPE
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NORTH AMERICA
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IBERIAN SHIELD
EARLY TERTIARY
Fig.6. Paleo-latitude maps (see Appendix II for explanation). A. Late Permian. B. Early Triassic. C. Late Triassic. D. Early Jurassic. E. Early Cretaceous. F. Late Cretaceous. G. Early Tertiary. Poles (superseded by . . .) I 7.01 --7.05 (by V 7) I 7.15 (by M 11.77) I 9.46--9.49 (by I 9.50) I 9.51, M 8.56--8.58 (by M 8.59) I 10.11, M 10.66 (By M 11.36) I 10.18 (by M 8.48) I 11.018--11.24, I 11.026 (by M 12.49) M 8.62, M 8.64 (by M 10.77)'M 8.91, M 8.92 (by M 8.93) M 10.42, M 10.43 (by V 18) M 10.81--10.87 (by M 10.88) M 11.41 (by V 15) M 11.55 (by M 12.105) M 12.102 (see M 11.50", Table I) M 12.114 (by V 2). APPENDIX II Equidistant projections of the positions of the Atlantic-bordering continents, as proposed by Bultard et al. (1965) and Pitman and Talwani (1972), have been drawn in Fig.6 for seven periods, ranging from Late Permian to Early Tertiary, with the exception of the Late Jurassic. Paleomagnetic poles are plotted with respect to the suggested positions of the continents, arid a paleolatitude pattern is drawn as inferred from the mean paleomagnetic pole position. With the exception of the southern Eurasian margin, the continental outlines have been drawn in full for easy reference. It should also be noted, however, that the western coastlines of North and South America are generally younger than the time-span indicated on the maps. The paleomagnetic data are listed in Table I, the mean paleomagnetic pole positions and their statistical parameters are given in Table II.
25.9N 234.6E
40.0N 219.6E 60.2N 132.2E
20.8N 234.6E
35.0N 221.3E 58.3N 141.5E
54.8N 174.7E
Africa (in t h e p o s i t i o n s of the alternative fit, t h i s p a p e r )
Africa (in t h e p o s i t i o n s ofBullardetaL, 1965)
S o u t h A m e r i c a (in t h e p o s i t i o n s o f Bullard et al., 1 9 6 5 )
S o u t h A m e r i c a (in t h e positions of thealternat i r e fit, this p a p e r )
3.3 °
107
2.6 °
206
16
7.0 °
76
7
67.3N 155.3E
61.7N 110.9E
50.0N 215.5E
36.3N 234.5E
51.6N 206.3E
50.0N 151.1E
49.0N 112.7E
Pu*
* Data f r o m S o u t h A m e r i c a a n d Africa n o t i n c l u d e d .
~9s (Fisher, 1 9 5 3 )
K, p r e c i s i o n p a r a m e t e r (Fisher, 1 9 5 3 )
19
41.8N 211.7E
37.0N 213.9E
I b e r i a n Shield
N, n u m b e r o f poles
43.9N 163.5E
40.6N 168.7E
Europe
59.1N 169.9E
43.0N 125.0E
39.7N 130.2N
PI*
North America
Cu*
5.6 °
38
113
5.2 °
18
69.4N 66.1E
69.4N 66.1E
66.4N 236.2E
66.4N 236.2E
69.0N 225.0E
68.2N 136.6E
67.1N 98.5E
Tru
8
74.5N 128.0E
60.9N 87.3E
61.0N 211.1E
47.5N 236.7E
62.3N 199.7E
56.0N 135.0E
54.9N 97.0E
Trl*
5.4 °
152
6
77.7N 32.5E
77.7N 32.5E
62.0N 262.8E
62.0N 262.8E
66.4N 258.7E
79.4N 160.8E
78.4N 120.6E
J1
21.6
19
4
°
75.4N 153.6E
75.4N 153.6E
42.0N 242.0E
42.0N 242.0E
48.0N 242.7E
59.9N 201.8E
59.5N 162.1E
Ju
M e a n p a l e o m a g n e t i c pole p o s i t i o n s , c a l c u l a t e d f r o m all reliable p a l e o m a g n e t i c data, a n d t h e i r statistical p a r a m e t e r s . T h e m e a n poles are listed, for c o n v e n i e n c e , for e a c h c o n t i n e n t , with respect to the present-day coordinate system
T A B L E II
62.0N 231.0E
62.0N 231.0E
72.0N 200.4E
72.0N 200.4E
71.0N 179.0E
Ku
5.6 °
139
6
6.7 °
81
7
post-opening South Atlantic
post-opening South Atlantic
53.9N 253.4E
53.9N 253.4E
65.3N 247.0E
72.6N 221.6E
72.2N 184.5E
Kl
4.8 °
59
16
75.4N 211.7E
75.4N 211.7E
78.6N 172.3E
78.6N 172.3E
75.6N 184.5E
Tpa-e
117
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118
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