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NT. A. RUPK.K Department of Geological and Geophysical Sciences, Princeton University, Princeton, Aw Jersey 08540

Sedimentary Evidence for the Allochthonous

Origin of Stigmaria, Carboniferous, Nova Scotia

ABSTRACT The usual mode of occurrence of Stigmaria, sub- fragmentation, (3) filling of stigmarian fragments parallel to the bedding and with Appendices at- with sediment different from the enveloping rock, tached to it in radial arrangement, has long been and (4) evidence of rapid accumulation of beds con- considered unambiguous proof of growth in situ of taining Stigmaria. The Appendices, commonly be- this plant fossil. Four sedimentary features of Stigmaria in the Carboniferous cliff sections of Nova lieved to have been very soft, may in fact have Scotia, Canada, contradict the general validity of been rather stiff. Paleoecological interpretations of this argument and indicate, instead, transportation stigmarian beds, if originally based on the supposed of the stigmarian specimens. These features are: (1) growth in situ of Stigmaria, will require reconsidera- preferred orientation of Stigmaria axes, (2) their tion.

INTRODUCTION The specimens of Stigmaria under considera- tion do not occur in typical underclays. The For the last 150 years, Stigmaria, the root- origin of underclays is therefore not dealt like base of Paleozoic lycopods, has been in- with in this paper. Furthermore, this paper is terpreted as occurring in situ. Stigmaria has sensu stricto not concerned with the paleobotany lateral Appendices which usually are arranged in of Stigmaria for which Williamson's classical a radial position and penetrate into the monograph (1887) is still a useful source of enveloping rock. This radial arrangement has information. been taken to be proof of growth in situ and to be incompatible with transport of Stigmaria, ACKNOWLEDGMENTS Steinhauer (1818, p. 273) apparently was the Thanks go to Professors E. Dorf, A. G. first to describe the radial position of the stig- Fischer, and F. B. Van Houten of Princeton marian appendages and to conclude an autoch- University, and Professor R. G. C. Bathurst, thonous origin from it. Among later authors, of Liverpool University, for valuable discussion Potonie (1893, 1896) laid particular stress and criticism of the manuscript. on the usual mode of occurrence of Stigmaria as proof of autochthony of Carboniferous plants. OBSERVATIONS Since then, few additional studies have been The Carboniferous strata of Nova Scotia, made of the subject in question; the exposition Canada, are well exposed in various cliff by Potonie appears to have been considered sections. Beds containing Stigmaria make it conclusive proof of autochthony, and it has possible to study its mode of occurrence. As been repeated time and again (Potonie and long ago as Dawson's work (1891), Stigmaria Gothan, 1920, p. 115; Kukuk, 1924, p. 1141; in these strata has been interpreted as occurring Stutzer and Noc, 1940, p. 145; Remy and in situ. The features which throw doubt upon Rcmy, 1959, p. 112). the long-claimed autochthony of Stigmaria A re-examination of Stigmaria in the with its Appendices are chiefly the following Carboniferous deposits of Nova Scotia, Canada, four. yielded several features which indicate that its usual mode of occurrence is not necessarily Preferred Orientation proof of autochthony and that allochthony The specimens of Stigmaria in a particular could have played a part. bed usually crop out either longitudinally or

Geological Society of America Bulletin, v. 80, p. 2109-2114, 1 fig., October 1969 2109

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crosswise in the cliff sections; in any one bed tion measurements on the 22 specimens show they do not occur both ways. This appears to a preferred orientation (Table 1, a; Fig. la). indicate a certain alignment. In order to check Sydney Mines, Cape Breton Island. At this, the orientations of the long axes of the Cranberry Point near Sydney Mines, 20 Stigmaria specimens have been measured. Al- suitable Stigmaria specimens occur in a cross- though many scattered single specimens occur, bedded shaly sandstone bed over a length of separate beds containing a fair number of outcrop of about 200 m. Almost all show them suitable for orientation measurements Appendices more or less clearly. The shaly are rather limited. A total number of 70 sandstone bed is several meters thick, and Stigmaria specimens could be measured, Stigmaria is chiefly found in its upper part. The spread over 5 sampling locations (Table 1). majority of the specimens are wholly or partly Point Aconi, Cape Breton Island. Here 22 filled with sandstone; some are flattened. The suitable specimens occur in a cross-bedded complex dips about 8°. The stigmarian bed is sandstone bed, spread over a length of outcrop overlain by an underclay followed by a coal of about 70 m. Almost all show, more or less bed. The 20 measured specimens show a pre- clearly, Appendices, often some 15 cm in ferred orientation (Table 1, b; Fig. lb). length but occasionally as long as 40 cm. The The South Joggins Section. In the classical thickness of the sandstone bed varies from 1.50 cliff section near Joggins, Stigmaria has been m to 2.00 m, and Stigmaria is chiefly found in measured in 3 different beds outcropping its upper half. The length of the specimens between McLarren Brook and Ragged Reef varies from about 10 cm to over 4.00 m. They Point. Almost all specimens clearly show are embedded parallel to the bedding or they radially arranged Appendices. The sequence are gently inclined; the inclination is in the dips about 18°. In the first bed, a sandstone current direction as inferred from the cross- (1.00 m thick) lying between shale beds, 7 bedding. Most Stigmaria specimens are more or specimens have been measured over a length less filled with sandstone and elliptically of outcrop of about 15 m. In the second bed, flattened in shape. The complex dips about 4°, a sandstone (50 cm thick) lying between shales, and the sequence is as follows: (6) thin coal 8 specimens have been measured over a length bed; (5) little underclay, in places hard to of outcrop of about 7 m. The third bed is a find; (4) sandstone, containing Stigmaria; (3) shaly sandstone (1.00 m thick) lying over a shale; (2) coal bed; and (1) underclay. Orienta- sandstone bed and below a carbonaceous seam.

TABLE 1. ORIENTATION (IN DEGREES) OF THE LONG AXES OF Stigmaria SPECIMENS FROM 5 LOCATIONS IN THE CARBONIFEROUS DEPOSITS OF NOVA SCOTIA, CANADA

a b c d e Point Aconi Sydney Mines Joggins Joggins Joggins

1. 75 140 165 125 95 2. 65 80 145 110 125 3. 68 180 165 80 100 4. 95 180 170 120 115 5. 65 180 160 130 180 6. 40 180 155 150 60 7. 60 220 140 125 60 8. 20 140 115 60 9. 20 140 55 10. 50 135 90 11. 45 110 65 12. 50 120 50 13. 20 220 60 14. 25 180 15. 45 180 16. 150 190 17. 120 170 18. 20 180 19. 60 160 20. 40 140 21. 40 22. 65

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In it, 13 specimens, mostly small fragments of seated by rose diagrams because of the com- about 10 cm in length, distributed over a paratively small number of specimens in each length of outcrop of about 15 m, have been bed. measured. In any one bed, the Stigmaria speci- It follows that specimens of Stigmaria from mens show a preferred orientation (Table 1, a particular bed are not distributed at random c, d, e). The orientation data are not repre- but show a preferred orientation. A shale bed was found in which almost all Stigmaria specimens occur crosswise, suggesting preferred orientation. However, poor preserva- N tion of the specimens prevented taking accurate orientation measurements. In another shale bed, Stigmaria appeared rather randomly distributed; here too, poor preservation made accurate measurements impossible. Fragmentation In most cases, it was quite difficult to trace a Stigmaria specimen over its entire length through the enveloping rock, especially when it was cropping out in cross section. Never- theless, for a good many specimens, it could be established that they were but fragments, that is, no longer connected with a tree stem a and quite often with the finer end broken off. Therefore, in the third bed from the South N Joggins section, many of the specimens appeared to be small fragments of about 10 cm in length; yet, radially arranged Appendices were clearly perceptible. t Filling Different from Enveloping Sediment It is not uncommon to find Stigmaria specimens filled with sediment different from the surrounding rock. The filling may be sandstone and the bed may be shale, or the reverse. These specimens often have radially arranged Ap- pendices. As an example, an elliptically flattened specimen, 10 cm wide and 4 cm thick, with Appendices of about 30 cm long, occurred in the middle of a shale bed, 1.70 m thick. Significantly, in several cases it was found that the specimens were fragmented, no longer connected with a tree trunk. Upright Trees in Stigmarian Beds Figure 1. Rose diagrams based on orientation mea- For a long time, the Carboniferous sequence surements for (a) 22 specimens of Stigmaria from a of Nova Scotia has been known for its upright cross-bedded sandstone bed and (b) 20 specimens of Lepidodendrales. Fossil upright Calamitaceae Stigmaria from a cross-bedded shaly sandstone, Carbon- are also present. The fossil upright trees are iferous, Cape Breton Island. The orientation of Stig- found in both sandstone and shale beds, al- maria axes is represented as indicating a direction rather than a line. This is based on the fact that the average though more commonly in the former. Oc- orientation of the specimens in each bed roughly casionally, an upright tree may pass through an coincides with respective current directions inferred alternating sandstone-shale series. Usually, the from a small number of cross-bedded units. Therefore, trunks are in a state of excellent preservation. of the two possible directions, the one indicated by Their height varies from less than a meter to cross-bedding is depicted. as much as several meters. The beds with up-

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right trees often contain Stigmaria, sometimes of upright Lepidodendrales in stigmarian beds spread through the entire thickness of the bed. is related to the fact that the upright trunks In both stigmarian beds on Cape Breton are indicative of a rapid accumulation of the Island, well-preserved upright trunks have surrounding sediment. The Lepidodendrales been found. were chiefly fragile, hollow bark tubes, subject to comparatively rapid decay. None the less, DISCUSSION the upright trunks are mostly well preserved, The preferred orientation of specimens of their top parts as well as their lower parts. Stigmaria in a particular bed can only be ex- From this, it follows that the trunks must have plained by transportation. Significantly, a been buried before decay of their tissues. For a reconnaissance study of cross-bedding in the long time, it has been recognized that the stigmarian beds on Cape Breton Island ap- good preservation of both Lepidodendrales and peared to indicate that the average orientation Calamitaceae required very rapid sedimenta- of the Stigmaria axes coincides with current tion. Bakewell (1828, p. 168) appears to have directions as inferred from cross-bedding. The been the first to conclude from the phenomenon number of measured cross-stratified units, of fossil upright trees "that the strata were however, was rather limited. deposited rapidly, before the decomposition In the Carboniferous of South Limbourg, of the stem could be effected." Reference to The Netherlands, Kimpe and Thiadens (1951) the literature shows that a fair number of found preferred orientation among rhizome geologists have reached this conclusion. Boulay fragments in a coal bed. They explained the (1878, p. 261) estimated that the upright phenomenon in terms of transportation. In trunks must have been entombed within a few their paper, no mention is made of Appendices months. De Lapparent (1883, p. 784) sup- attached to the rhizome fragments. ported this estimation. Geikie (1903, p. 654) The fragmentation of Stigmaria becomes was of the opinion that the burial of these explicable if it is assumed that Lepidodendrales trunks could not have lasted many years. have been uprooted, that their root system Klusemann and Teichmuller (1954, p. 379) has been broken off, and that the individual assume that the entombment took only a few root fragments could have been cut into smaller months or a few years at most. Ruhkin (1959, fragments while transported. The fact that p. 717) comes to the same conclusion. Other Stigmaria fragments occur wholly or partly authors conclude, less specifically, that the rate devoid of Appendices fits this picture well. It of sedimentation around the upright trunks would indicate that during transport many of must have been high (Stutzer and Noe, 1940, the Appendices were rubbed off, probably p. 168; Shrock, 1948, p. 295; Broadhurst and roughly proportional to the distance of trans- Magraw, 1959, p. 157-158; Broadhurst, 1964, portation. This is also supported by the fact p. 865). that Appendices attached to Stigmaria are Stigmaria in the beds containing upright sometimes found to be cracked, broken, or Lepidodendrales is often found on different twisted in a way difficult to explain from a levels. In the case of autochthony, this would functional point of view. imply the growth of several successive forests The filling of Stigmaria with sediment which normally would have involved a con- different from the surrounding rock could be siderable lapse of time. Thus the rapid ac- explained in an autochthonous way by as- cumulation of the stigmarian beds in a short suming that Stigmaria was filled with sediment time interval, as indicated by the well-pre- conveyed from above through a hollow served upright trunks, rules out the pos- lycopod trunk to which it was attached in situ. sibility of forest growth in situ. Consequently, However, since many of the relevant speci- Stigmaria cannot be in situ either and, al- mens are fragments, this autochthonous ex- ternatively, must have been transported like planation does not apply. The phenomenon the sediment which encloses the specimens. could be understood if Stigmaria fragments The four features discussed, each per se got their sedimentary filling during transport incompatible with autochthony, are found (Kimpe and Thiadens, 1951, p. 173) or in situ together for the most part, thus strengthening before they were uprooted, transported, and their individual significance. Other less com- deposited in a different environment. mon features also suggest that Stigmaria, in The discrepancy between the claimed spite of its radially arranged appendages, is autochthony of Stigmaria and the occurrence not in situ. (1) Some specimens of Stigmaria in

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the cross-bedded sandstones from Cape Breton (2) Most writers involved claim that the Island are inclined parallel to the forest beds Appendices consisted chiefly of soft tissues and of cross-bedded units in which they occur; that, when pulled out of the soil, they must this position suggests transport rather than have hung down "like wet rags" (Stutzer and growth in situ. (2) On top of a Stigmaria organ Noe, 1940, p. 145). Although the morphology still attached to its stump, longitudinal and histology of Stigmaria are not considered grooves have been observed (Kukuk, 1939, p. in the present paper, the sedimentary evi- 797). These grooves also occur on isolated dence of transport taken in conjunction with fragments. However, some of these fragments the fact that the Appendices often still have a are found with the groove on their bottom radial position suggests that the stigmarian side, thus suggesting being upside down. This appendages were presumably tougher and fact also points to allochthony. stiffer than commonly supposed. Unfortunately, no Stigmaria specimens could (3) Stigmaria is still a poorly evaluated be found which were both well preserved and paleoecological tool. But usually its presence genuinely in situ. Thus it has been impossible is assumed to reflect the growth in situ of to compare the mode of occurrence of the swamp forests and the formation of a soil. Its transported specimens with that of the presence in the south Joggins section is taken autochthonous ones. by Way (1968, p. 430-431) as indicative of a break or disconformity within the sedimentary CONCLUSIONS record. In view of the present evidence of transportation, however, the presence of (1) The usual mode of occurrence of Stigmaria does not necessarily indicate a Stigmaria in the Carboniferous cliff sections diastem or breaks of greater magnitude and of Nova Scotia cannot be taken as proof of can be consistent with continuous deposition. autochthony, in spite of the radial arrange- Where the paleoecological interpretation of ment of its Appendices. Stigmaria shows con- these stigmarian beds is based only on the clusive evidence of having been transported supposed growth in situ of Stigmaria, recon- in several occurrences. sideration is required.

REFERENCES CITED Bakewell, R., 1828, An introduction to geology: Begrabene Wa'lder im Ruhrkohlenbecken: London, Longman, 540 p. Natur u. Volk, v. 84, p. 373-382. Boulay, N., 1878, Bibliographic: Revue des ques- Kukuk, P., 1924, Das Nebengestein der Stein- tions scientifiques, v. 1, p. 248-262. kohlenfloze im Ruhrbezirk: Gliickauf, v. 60, Broadhurst, F. M., 1964, Some aspects of the p. 1139-1144. paleoecology of non-marine faunas and rates of 1939, Ein Riesenfossil aus dem Karbon des sedimentation in the Lancashire Coal Mea- Piesberges: Gliickauf, v. 75, p. 793-797. sures: Am. Jour. Sci., v. 262, p. 858-869. Potonie, H., 1893, Eine gewohnliche Art der Broadhurst, F. M., and Magraw, D., 1959, On a Erhaltung von Stigmaria als Beweis fur die fossil tree found in an opencast coal site near Autochthonie von Carbon-Pflanzen: Deutsch. Wigan, Lancashire: Liverpool and Manchester Geol. Gesell. Zeitschr., v. 45, p. 97-102. Geol. Jour., v. 2, p. 155-158. 1896, Ueber Autochthonie von Carbonkohlen- Dawson, J. W., 1891, Acadian geology: London, Flotzen und des Senftenberger Braunkoh- Macmillan, 693 p. lenflotzes: Konigl. Preuss. geol. Landesanstalt De Lapparent, A., 1883, Traite de geologic: Paris, u. Bergakademie Jahrb., Berlin, v. 16 (2), p. Savy, 1280 p. 1-31. Geikie, A., 1903, Text-book of geology: London Potonie, H., and Gothan, W., 1920, Die Entsteh- and New York, Macmillan, 1472 p. ung der Steinkohle und der Kaustobiolithe Kimpe, W. F. M., and Thiadens, A. A., 1951, On iiberhaupt: Berlin, Borntraeger, 233 p. the occurrence of coal rafts above and rhizome Remy, W., and Remy, R., 1959, Pflanzenfossilien: inclusions in searn Finefrau B, South Lim- Berlin, Akademie Verlag, 285 p. bourg, Holland: 3rd Internat. Congr. Sedi- Ruhkin, L. B., 1959, The rate of accumulation of mentology, Groningen-Wageningen, Proc., p. sedimentary deposits and duration of breaks 167-173. ' in them: Eclogae Geol. Helvetiae, v. 51 (3), Rlusemann, H., and Teichmuller, R., 1954, p. 716-721.

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Shrock, R. R., 1948, Sequence in layered rocks: Way, J. H., 1968, Bed thickness analysis of some New York, McGraw-Hill, 507 p. Carboniferous fluvial sedimentary rocks near Steinhauer, H., 1818, On fossil reliquia of unknown Joggins, Nova Scotia: Jour. Sed. Petrology, vegetables in the coal strata: Am. Philos. Soc. v. 38, p. 424-433. Trans., n.s., v. 1, p. 265-297. Williamson, W. C., 1887, A monograph on the Stutzcr, O., and Noe, A. C., 1940, Geology of morphology and histology of Stigmaria coal: Chicago, University of Chicago Press, ficoides: London, Palaeontographical Society, 461 p. 1886, 62 p.

MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 1, 1969

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