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Straited surfaces and related features, developed by the gondwana ice sheets (state of Paraná, Brazil)
Palaeogeqgraphy, Palaeoclimatology, Palaeoecology Elsevier Publishing C o m p a n y , A m s t e r d a m - Printed in The N e t h e r l a n d s
STRIATED SURFACES A N D R E L A T E D FEATURES, DEVELOPED BY T H E G O N D W A N A ICE SHEETS (STATE OF PARANA, BRAZIL) JOAO JOSI~ BIGARELLAI~ RIAD SALAMUNI 1 AND REINHARDT A. FUCK 2
1 Geological Institute, Federal University ofParan6, Curitiba, Parant~; Commission of the Geological Map of Parand, Curitiba, Paran6 (Brazil) (Received O c t o b e r 10, 1966)
SUMMARY
The occurrence of striated floors, produced by the Gondwana ice sheets, is briefly described in this paper. Several striated localities crop out in the second plateau of the State of Paran~ (Brazil), some of them being unusually well preserved. The striations occur on pre-Gondwana surfaces of the Devonian Furnas Formation, as well as on the periglacial deposits of the Itarar6 Formation (Upper Carboniferous), which also bears the glacial sequences. Many outcrops are directly overlain by typical tillites, making possible a comparison between the direction of the glacial lineations, and the long axis pebble orientation of those rudaceous deposits. The average pebble long axis dip direction for the Cancela Tillite is S 11 ° E, while the glacial striations direction is S 2 ° E, the difference being only 9 °. The ice movement deduced for the Cancela Tillite was toward N 11 ° W. Besides the results obtained from the tillite fabric, additional data were gathered from sedimentary structures of the periglacial deposits. Thus, crossbedding measurements, carried on in the outwash sandstones associated to several Gondwana glaciations, afforded the following average result: N 5 ° W. General results, as compared together, show a reasonable agreement between both the results of glacial deposits and of the periglacial ones. As the present writers are gathering more data, it is assumed that definite and more reliable results may be given in forthcoming papers.
INTRODUCTION
In the literature reference is made to three to five extensive tillites in the Paran~ Basin Gondwana glacial deposits, indicating at least three to five ice advances. Obviously the tillites are indicators of ancient cold climates and, therefore, they characterize glacial conditions over large areas of the basin. Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
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J. J. BIGARELLA, R. SALAMUNI AND R. ,A. FUCK
Periglacial sediments occur between the tillites, with which they are closely associated. Periglacial sediments are relatively good indicators of ice retreat, specially the varvites bearing drift deposits, such as pebbles, cobbles and boulders, dropped from drifting ice. It seems important to note that many rudaceous deposits, interbedded in the Gondwana sequence, have been rather indiscriminately called tillite by several authors. However, owing to recent detailed survey, many questions have been raised about the true nature of such deposits. There is no doubt that some of these sediments can safely be considered as true tillites, while others are of doubtful origin and should be better ascribed to other agents of deposition, rather than glacial activity. On the other hand, as far as ancient glacial deposits are concerned, such as those of southern Brazil, there is not a definite evidence whether the material actually represents a ground moraine or a reworked sediment. Field indications frequently point out that the original till was reworked during the ice retreat, and not rarely removed, being sometimes replaced by structureless mudflows that bear some resemblance with the former till. As it is particularly true with such ancient glacial succession, sometimes because of these similarities confusion often arises as to the understanding of the glacial environmental conditions. It is therefore desirable that other evidence of glacial activity should be considered to aid in the solution of the problem. One of the purposes of this paper is to establish the relation between the striated and grooved surfaces and the tillites, as well as between the inferred direction of those structures and the details of the fabric of these rudaceous deposits.
GENERAL REMARKS
The Gondwana glaciation in Brazil has been recognized for a long time, with its general features relatively well outlined. Nevertheless there is a lack of systematic and detailed studies, as well as of complete geologic mapping and stratigraphic correlations. Another point, still poorly known is that concerning paleogeographical problems. Several authors, at different times, discussed these problems, commonly reaching contradictory conclusions. Much of the information given in this paper was obtained from the QueroQuero, Campo Largo, P6rto Amazonas and Contenda geologic quadrangles as a result of the mapping project performed by the "Comiss~o da Carta Geol6gica do Paran/t". Field work in this area was carried on by A. Muratori, J. A. U. Lopes, E. Trein, J. Palka and by the authors of the present paper. Mapping of the above mentioned areas was concerned mainly with the different lithologic sequences, without regard to a detailed stratigraphy, which is actually being performed. Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACES DEVELOPED BY THE GONDWANA ICE
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Until now, twenty outcrops showing glacially striated surfaces were surveyed. Pebble orientation was measured in six localities, where tillite crops out in a fairly good condition. At the same time, cross-bedding measurements were made wherever the associated periglacial sandstones presented cross-stratification. In the Paran~t Basin, the occurrence of glacial striations and other features related to ice abrasion have been mentioned by some authors in a few localities of the pre-Gondwana surface. However, these features were not studied in detail. References about them are rather scarce and limited to a few outcrops, already destroyed by quarrying. In South America the first striated floor described seems to be that mentioned by Du TOlT (1927) from northern Uruguay, in which the striae are oriented southeast-northwest. Later in the same country WALTER (1931) described striations oriented east-west. Possibly one of the first references to glacial striae in Brazil was that by CARVALHO (1940, p.271), from the km 62 of the old road between Mafra and Sao Bento do Sul (State of Santa Catarina). The scratches were found over a granodiorite surface, underlying Itarar6 sequences of tillite, sandstone and shales. However, no indication on direction was made. The same locality was also studied by BARBOSA(1940, p.272), who indicates a direction of N 32 ° W (magnetic) for the striae. According to Barbosa the sense of the ice movement was probably from southeast to northwest. He also mentions the presence of "roches moutonn6es" in the area and suggests that the scratches were produced by ice movement inside a valley. "Roches moutonn6es" and glacial striations were described by AL~aEIDA (1948, p.115) from Salto, in the State of S~,o Paulo. According to this author the striae were oriented northwest. He also concludes that the ice moved from southeast to northwest. Apparently there are no other references on striated surfaces in the Paran~t Basin. Fig.1 shows the location of twenty new localities in the Ponta Grossa plateau where glacial striae occur. The glacial striations here described are not very conclusive regarding the determination of the sense of ice movement. Related features of the scratched surface, such as crescentic marks and stoss-and-lee forms, are not sufficiently convincing. Their use without any other evidence seemed to be unsafe, in the writers opinion. Concerning similar pleistocenic features, FLINT (1961, p.58) states that "in the majority of instances the actual direction of flow is not determined, and is not determinable, from evidence furnished by the striation itself." In order to know in which direction the glacier moved it is necessary to find out other informations from the glacial or periglacial sediments. LEINZ (1937), MAAC~ (1946), MAtJ (1958) and MARTIN (1964), using different methods and criteria attempted to deduce the ice movement direction in the Paran~ Basin.
Palaeogeography, Palaeoclimatol., Palaeoecol., 3
(1967) 265-276
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J. J. BIGARELLI, R. SALAMUNI AND R. A. FUCK
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Fig.1. Location and orientation of the striated surfaces on the several geologic quadrangles. I = Quero-Quero; H = Campo Largo; I l I = Curitiba; I V = P6rto Amazonas; V = Contenda; VI = Arauc~iria. In Brazil, LEINZ (1937) made the first attempt to determine the directions of ice-flow using tillite fabric, reaching to the conclusion that the ice moved from northeast to southwest. MAACK (1946), also using tillite fabric, came to similar results. MAW (1958) also studied tillite fabric measuring the shape of the pebbles. His results indicated an ice movement from southeast to northwest. An extensive work on the Paranfi Basin Itarar6 Formation sediments was made by MARTIN(1964) using different glacial features as indicators of the direction of ice-flow, such as tillite fabric, direction of preglacial valleys and hills, striated floors and '°folding and imbrication structures". According to this author the general ice movement trend was from southeast to northwest. In the neighbourhood of the area described in this paper, MARTIN (1964, p.36--37) surveyed about ten outcrops on the Curitiba-Palmeira road. His observations were distributed over about 50 km section of the road. Martin concludes '°that the ice-movement was in a west-northwest direction, whilst the asymmetry of many of the fold and imbrication structures shows clearly that the flow was from east-southeast to west-northwest." Martin based his work mostly on the folding, thrusting and imbrication structures. These structures found in sand lenses inside a tillite and those found in sandstone and siltstone underlying a tillite can be attributed to the movement of the Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACES DEVELOPED BY THE GONDWANA ICE
269
ice-sheet. However, not all the folds in the Itarar6 Formation were produced in this way. They may be also the result of solifluction and other phenomena from the periglacial environment.
STRIATED SURFACES
Many outcrops of the Furnas, as well as of the Itarar6 Formation sandstones, show striated surfaces of at least two ages, which were produced by drift-shod-ice during two advances of the Gondwana glaciers. As such abrasive features may be generated by different agents, it seems to be necessary to establish their glacial origin. The most reliable evidence are the sediments, mainly tillites, and the stoss-and-lee forms. In those cases where the striated surfaces are not associated with unequivocal glacial deposits, the striae must be carefully checked, until their association either with glacial or periglacial phenomena can be properly assigned. Usually the striated surfaces produced by glaciers are not of restricted distribution but occur over large areas. Remnants of striations in the surveyed area, document very well the nature and extension of the involved agent. In the case here considered, the striae are associated with continental deposits, and are therefore
Fig.2. A remarkably striated surface, on the Lower Devonian Furnas Sandstone. These striations are overlain by periglacial deposits. Outcrops in the Rio do Salto valley (Quero-Quero Quadrangle), Rio do Salto glaciation.
Palae~Leeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
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J . J . BIGARELLA, R. SALAMUNI AND R. A. FUCK
related to glacier advances. If caused by floating ice of pan ice sea the associated deposit would be marine. However, this is not the case. The abrasion of bed rock surfaces by glaciers caused the sculpturing (modelling) of smooth boss-like forms, through the streamline flowage of the glaciers with its abrassive bed load. Frequently, these swell-like bosses are not symmetrical, ending distally or downstream in small cliffs or hackly surface. The stoss-and-lee form as referred in the literature, are reliable indicators of the direction of ice flowage. The striated pavement, outcropping in the area surveyed does not provide a safe indication of the flow trend. In addition, these small features may have been disturbed by further erosion in the outcrop. Anyway, the lines of the ice movement are well preserved, although they certainly do not indicate the sense of flow of the ice that fashioned them. Two different erosion surfaces in the area have been striated. The older one, represented by the pre-Gondwana surface, is preserved on the Furnas Sandstone of Devonian age. The striae outcrop in the Rio do Salto valley, and were formed during the first advance of the ice, which can be recorded in the local area (Rio do Salto glaciation), being related to the older tillite of the Quero-Quero Geological Quadrangle (Fig.2). The second set of striations were made over an erosion surface that cut both the Furnas Sandstone and the periglacial sediments deposited during the Rio do Salto glaciation ice retreat. The striae crop out in Witmarsum (on the Furnas Sandstone), S~o Luiz do Purun~ (on the Itarar6 Formation periglacial sandstone), and in many other points of the P6rto Amazonas Geological Quadrangle. These striations were produced during the second recorded ice advance (Cancela glaciation) and are related to the second tillite of the Quero-Quero Geological Quadrangle. In all the observed outcrops, the striations were disposed in an almost perfect parallel pattern, without the interference of different age striae. Judging by their exposed parts these glacial lineations may occupy a considerable area under the overlying deposits. Normally, they consist of grooves and crests with irregular dimensions, and extremely variable distances between successive crests. The crests are usually rounded, showing a remarkable convexity in a transverse section. On the other hand, the grooves are more or less concave, being persistently U-shaped. The features associated with the striations, such as chattermarks, crescentic gouges, nailhead striations, and related structures are not very clearly preserved in the outcrops examined. However, some structures that very closely resemble stossand-lee forms were observed in a few outcrops. In Witmarsum the striated Furnas Sandstone surface is directly covered by the tillite of the Cancela glaciation. The average direction of the tillite pebbles coincides with the striae orientation. In this particular case, there is a confirmation regarding the origin of the striae, as well as of the tillite nature (ground moraine). However, in the Rio do Salto valley (a partially exhumed pre-Gondwana valley), most of the
Palaeogeography, Palaeoclimatol.,Palaeoecol., 3 (1967) 265-276
S T R I A T E D SURFACES D E V E L O P E D BY T H E G O N D W A N A ICE
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Rio do Salto glaciation tillite was removed before the subsequent deposition of the periglacial sediments of the ice retreat. The striated surfaces were exposed and were then covered by new sedimentary sequences. In one case, the Itarar6 Formation sandstone, overlying the striae, is texturally similar to the Furnas Sandstone, due to the fact that it is actually a reworking of the latter one. In this example, it is rather difficult to make a distinction between both sandstones.
TILLITE A N D T I L L I T E - L I K E SEDIMENTS
General description As generally accepted the till is the product of mechanical desaggregation of fresh rocks, consisting of fresh mineral chips transported and deposited in the continental glacial environment below the ice. It is characterized by being a nonsorted sediment, containing a wide range of grain sizes and a rather small proportion of pebbles, cobbles and boulders with or without abraded facets or striations (compare, among others, SCHWARZBACH, 1961; FLINT, 1961). The Itarar6 Formation bears many sequences of tillite, tillite-like sediments (directly derived from ancient tills), and diamictite. Fine grain sizes greatly predominate over pebbles and larger particles, in most tillites. Fig.3 illustrates the grain size constitution of the matrix of the Cancela Tillite. The median diameter ranges between 0.047 mm and 0.188 mm. The mean diameter averages 0.066 ram. The sediments as a whole have a low degree of sorting, being chaotic in this respect. The sorting of the matrix is also low. Inman's sorting coefficient tr ~ ranges between 1.96 and 3.18, being 2.65 in average. Trask's sorting coefficient, based on the quartile measures, ranges between 2.7 and 7.8, with a 4.4 average. Grain size distributions have a low asymmetry value (a ~ <0.5) the curves being usually skewed toward the finer grains. In the tiUite, stratification rarely occurs. Sometimes a pseudo-stratification develops, possibly related to the shearing caused by the ice movement. Small sandstone lenses are frequently interbedded within the tillites. These lenticular layers are usually but not always stratified, even though sometimes they don't apparently show any bedding. Such lenticular beds may be interpreted as ice tunnel deposits, or else the infilling of thawed ice lenses or wedges inside the ground moraine. These unsorted sediments with interbedded sandstone lenses may be also interpreted as being a result of reworking of ancient tills. The tillite phenoclasts are usually angular or sub-angular. Nevertheless, some are sub-rounded or even rounded. The provenance of the latter ones seems to be from older gravel deposits either of fluvial origin or from the outwash plain. Striated pebbles may occasionally be found, and "flat iron" pebbles are rather scarce.
Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
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Tillite.fabric
It has long been verified that the phenoclasts within undisturbed till have a tendency to lie with their long axis approximately parallel to the direction of the glacier movement. In this way, HOLMES(1941, p. 1299) refers to the pioneer studies of Miller (1884), Bell (1888) and Upham (1891) that pointed out the existence of an alignment of the long axis of pebbles with the direction of the glacier flow. In the tills of northern Germany, Richter (cited by KRUMBEIN, 1938) also found that the long axes of pebbles are usually aligned parallel to the direction of ice flow. Till fabric analysed by KRUMBEIN (1938) from a deposit at Random Lake Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
273
STRIATED SURFACES DEVELOPED BY THE GONDWANA ICE
indicates, besides an alignment parallel to the ice movement, a transverse disposition of the long axes, which was also verified by Richter. Detailed studies of the attitude of pebbles inbedded in the till of Central New York were made by HOLMES(1941) who has shown that inherent characters in the till stones, such as form, roundness, size and relative axial length predispose a stone to a certain depositional attitude in the rock fabric. Some types of stone have relatively high statistical probability in depositional attitude, with the long axis aligned either parallel to or transverse to the direction of glacier flow. As a general conclusion, Holmes confirmed the preferred arrangement of the stones with their long axes parallel to the direction of glacier flow. Pebble orientation in the Itarar6 tillites has been measured in several outcrops, following the progress of the mapping project of the "Comissfio da Carta Geol6gica do Paranfi". Some measurements have been made outside the area here considered, as for instance those in the tillites of Lapa and Palmeira quadrangles. The tillite of the last quadrangle is supposed to be the third regional tillite of the Gondwana glaciations. Owing to time limitations, among other reasons, the method suggested by HO~UES (1941) was not used in our measurements. Instead, it seemed that a simplification would be desirable. Generally, most of the bibliographic references are
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Fig.4. Pebble long axis dip direction rose diagrams for six localities o f the Cancela Tillite, as well as for the ensemble as a whole. Some localities present a transverse to diagonal pattern, others have the normal pattern, i.e., parallel to the ice flow. The resultant vector is up glacier, therefore opposite to the ice movement. There is clearly a tendency of the pebbles to imbricate up glacier. The table included in the drawing gives the general results obtained from the measurements. The dip directions are referred to true north. Palaeogeography, Palaeoelimatol., Palaeoeeol., 3 (1967) 265-276
274
J.J. BIGARELLA,R. SALAMUNIAND R. A. FUCK TN
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Fig.5. General results of 889 pebble measurements made on three different tillites from the surveyed area. A. Pebble long axis dip direction. The resultant vector is S 20 ° E. Compare this result with the Cancela Tillite average referred in Fig.4. Both results are very close together, being the difference only 9 o. B. Pebble direction (no dip considered). concerned with the measurement of the long axis direction, practically without details as to dip direction or shape of the pebbles. The measurements obtained by the present writers refer to the dip direction of the pebble. In the Cancela Tillite elongated pebbles of different size and shape were used, but as a rule most of them were ovoid, sub-angular to sub-rounded. The number of pebbles measured ranged from 50 to 120 according to the conditions of the locality surveyed. A rose diagram constructed from the dip direction of the pebbles shows that the orientation is partially parallel to the direction of ice flow deduced from the striated floors, as well as partially transverse or diagonal to that direction (Fig.4). Rose diagrams, which only refer to the long axis direction of the pebbles are quite different from those illustrated in the dip direction diagram (Fig.5). Relevant to pebble direction (no dip considered), patterns similar to those usually mentioned in the literature were noticed. Some localities show the "normal pattern" (HOLMES, 1941, p. 1310) parallel to the ice flowage, and others the "transverse pattern" essentially at right angles, to the inferred direction of the glacier flow. The parallel and transverse oriented pebbles occur side by side giving the impression of lack of internal organization. The dip direction rose diagrams show that the pebble long axis has a tendency to dip up glacier. The resultant vector of the dip directions is actually opposite to the sense of the ice flowage. In the Cancela Tillite, 364 measurements Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACESDEVELOPEDBY THE GONDWANA ICE
275
have been made at six different localities. The average dip direction and the consistency ratio (c.r.) were determined according to the following formulas: tan 0 --
~sin 0
ycos 0
c.r.
V ( ~ s i n O) z q- (~cos 0 ) 2
number of measures
Results for the individual localities, as well as the general average for the area, are given in Fig.4. The data for most of the localities are congruent. The consistency ratio, although low, is characteristic for this type of distribution, being therefore significant. The average pebble dip direction is S 11 ° E, while the orientation of the scratches on the striated surfaces differs only by 9 °, being S 2 ° E. Moreover, at locality I where the tillite rests on the striated surface, the scratches and the average direction of the pebbles are almost coincident. This is a good indication that the method based on pebble long axis measurements is very accurate. On the other hand the average pebble direction (no dip concerned) is somewhat different from the average dip direction, but the results are still congruent. The consistency ratio is rather lower than the one obtained for the dip direction analysis. To calculate the direction resultant vector, and the corresponding consistency factor, we followed a procedure similar to that of CURRAY (1956, p.1 19) using the following formulas: tan 2 0 --
c.r. --
~sin 2 0 ~cos 2 0
~¢/( ~sin 20) 2 -c ( ~cos 20) 2 number of measures
CONCLUSIONS The sense of the ice movement could not be definitely inferred by using the striated surfaces and the averages of pebble long axis direction or dip direction, without comparing these results with those concerning periglacial sediments transportation data. As the field work progressed and more data were gathered, we noticed that the resultant vector for the tillite pebbles was opposite to the associated periPalaeogeography, Palaeoclimatol.,Palaeoecol., 3 (1967) 265-276
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J . J . BIGARELLA, R. SALAMUNIAND R. A,. FUCK
glacial s a n d s t o n e vector, d e d u c e d f r o m c r o s s - b e d d i n g studies. This conclusion is i m p o r t a n t , as it indicates t h a t the i m b r i c a t i o n o f the pebbles in the tillite has a tendency to dip up glacial, like the pebble attitude in the rivers. Nevertheless, m a n y m o r e m e a s u r e m e n t s are still needed to confirm the a b o v e statement. C r o s s - b e d d i n g measurements, m a d e in the periglacial sandstones associated to v a r i o u s G o n d w a n a glaciations, give as average t r a n s p o r t a t i o n trend N 5 ° W. T h e a b o v e d a t a can be c o m p a r e d with the following directions, (referred to n o r t h e r n quadrangles) o b t a i n e d up to n o w f r o m the striated floors a n d f r o m several tillites (including the tillite o f the C a n c e l a glaciation): (a) striations: N 2 ° W (or S 2 ° E) (b) pebble long axis direction: N 38 ° W (or S 38 ° E) (c) p e b b l e long axis dip direction: S 20 ° E (d) ice m o v e m e n t d e d u c e d f r o m (c): N 20 ° W These results indicate t h a t there is a g o o d a g r e e m e n t between the m e a s u r e ments p e r f o r m e d in the glacial deposits a n d those o f the periglacial environment.
REFERENCES
ALMEIDA, F. F. M., 1948. A "roche moutonn6e" de Salto, Estado de S~o Paulo. Geol. Met., Bol. (S6o Paulo), 5: 112-118. BARBOSA, O., 1940. Estrias produzidas pot g~lo Permo-Carbonifero. Minera¢6o Met. (Rio de Janeiro), 4 (24): 272-273. BEURLEN, K., 1952. La Pal6ogeographie de la glaciation Gondwaniene au Br6sil m6ridional. Congr. G~ol. Intern., Compt. Rend., 19e, Algiers, 1952, 8: 193-211. CARVALHO,P. F., 1940. Estrias glaciais em granodiorito sobposto ao Gondwana de Santa Catarina. Minera¢6u Met. (Rio de Janeiro), 4(24): 271-272. CtrRRAV, J. R., 1956. The analysis of two-dimensional orientation data. J. Geol., 64(2): 117-131. Do TOIT, A. L., 1927. A geological comparison of South America with South Africa. Carnegie Inst. Wash. Publ., 381:157 pp. FLINT, R. F., 1961. Glacial and Pleistocene Geology. Wiley, New York, N.Y., 533 pp. HOLMES,C. D., 1941. Till fabric. Bull. Geol. Soc. Am., 52(9): 1299-1354. KRUMaEIN, W. C., 1938. Preferred orientation of pebbles in sedimentary deposits. J. Geol., 47: 673-706. LEINZ, V., 1937. Estudos sfbre a glaciaqao Permo-Carbonifera do Sul do Brasil. Dept. Nacl. Prod. Mineral, Div. Fomento Prod. Mineral, Bol., 21 : 47 pp. MAACK, R., 1946. Geologia e Geografia da regi~o de Vila Velha (Est. Paran~i) e considera96es s6bre a glaciag~.o Carbonifera no Brasil. Arquiv. Museu Paranaense, 5:305 pp. MARTIN, H., 1964. The directions of flow of the Itarar6 ice sheets in the Paran~i Basin, Brazil. Bol. Paranaense Geograf., 10/15: 25-76. MAU, H., 1958. Contribuig~o para a geologia de Ibaiti (Paran~i). Bol. Soc. Brasil. Geol., 9(2): 79-82. SALAMUNI,R., BIGARELLA,J. J. and FucK, R. A., 1966. S6bre a ocorr6ncia de estrias glaciais no Segundo Planalto do Paran~c BoL Paranaense Geograf, 18/20: 127-131. SCHWARZBACH,M., 1961. Das Klima der Vorzeit. Enke, Stuttgart, 275 pp. (English translation by R. O. Muir, 1963, Van Nostrand, London). WALTER,K., 1931.1Jber ein Vorkommen von geschrammter Landoberfl/iche aus dem Gondwanaglazial. Zentr. Mineral, Abt. B, 1931: 449-460.
Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACES A N D R E L A T E D FEATURES, DEVELOPED BY T H E G O N D W A N A ICE SHEETS (STATE OF PARANA, BRAZIL) JOAO JOSI~ BIGARELLAI~ RIAD SALAMUNI 1 AND REINHARDT A. FUCK 2
1 Geological Institute, Federal University ofParan6, Curitiba, Parant~; Commission of the Geological Map of Parand, Curitiba, Paran6 (Brazil) (Received O c t o b e r 10, 1966)
SUMMARY
The occurrence of striated floors, produced by the Gondwana ice sheets, is briefly described in this paper. Several striated localities crop out in the second plateau of the State of Paran~ (Brazil), some of them being unusually well preserved. The striations occur on pre-Gondwana surfaces of the Devonian Furnas Formation, as well as on the periglacial deposits of the Itarar6 Formation (Upper Carboniferous), which also bears the glacial sequences. Many outcrops are directly overlain by typical tillites, making possible a comparison between the direction of the glacial lineations, and the long axis pebble orientation of those rudaceous deposits. The average pebble long axis dip direction for the Cancela Tillite is S 11 ° E, while the glacial striations direction is S 2 ° E, the difference being only 9 °. The ice movement deduced for the Cancela Tillite was toward N 11 ° W. Besides the results obtained from the tillite fabric, additional data were gathered from sedimentary structures of the periglacial deposits. Thus, crossbedding measurements, carried on in the outwash sandstones associated to several Gondwana glaciations, afforded the following average result: N 5 ° W. General results, as compared together, show a reasonable agreement between both the results of glacial deposits and of the periglacial ones. As the present writers are gathering more data, it is assumed that definite and more reliable results may be given in forthcoming papers.
INTRODUCTION
In the literature reference is made to three to five extensive tillites in the Paran~ Basin Gondwana glacial deposits, indicating at least three to five ice advances. Obviously the tillites are indicators of ancient cold climates and, therefore, they characterize glacial conditions over large areas of the basin. Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
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Periglacial sediments occur between the tillites, with which they are closely associated. Periglacial sediments are relatively good indicators of ice retreat, specially the varvites bearing drift deposits, such as pebbles, cobbles and boulders, dropped from drifting ice. It seems important to note that many rudaceous deposits, interbedded in the Gondwana sequence, have been rather indiscriminately called tillite by several authors. However, owing to recent detailed survey, many questions have been raised about the true nature of such deposits. There is no doubt that some of these sediments can safely be considered as true tillites, while others are of doubtful origin and should be better ascribed to other agents of deposition, rather than glacial activity. On the other hand, as far as ancient glacial deposits are concerned, such as those of southern Brazil, there is not a definite evidence whether the material actually represents a ground moraine or a reworked sediment. Field indications frequently point out that the original till was reworked during the ice retreat, and not rarely removed, being sometimes replaced by structureless mudflows that bear some resemblance with the former till. As it is particularly true with such ancient glacial succession, sometimes because of these similarities confusion often arises as to the understanding of the glacial environmental conditions. It is therefore desirable that other evidence of glacial activity should be considered to aid in the solution of the problem. One of the purposes of this paper is to establish the relation between the striated and grooved surfaces and the tillites, as well as between the inferred direction of those structures and the details of the fabric of these rudaceous deposits.
GENERAL REMARKS
The Gondwana glaciation in Brazil has been recognized for a long time, with its general features relatively well outlined. Nevertheless there is a lack of systematic and detailed studies, as well as of complete geologic mapping and stratigraphic correlations. Another point, still poorly known is that concerning paleogeographical problems. Several authors, at different times, discussed these problems, commonly reaching contradictory conclusions. Much of the information given in this paper was obtained from the QueroQuero, Campo Largo, P6rto Amazonas and Contenda geologic quadrangles as a result of the mapping project performed by the "Comiss~o da Carta Geol6gica do Paran/t". Field work in this area was carried on by A. Muratori, J. A. U. Lopes, E. Trein, J. Palka and by the authors of the present paper. Mapping of the above mentioned areas was concerned mainly with the different lithologic sequences, without regard to a detailed stratigraphy, which is actually being performed. Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
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Until now, twenty outcrops showing glacially striated surfaces were surveyed. Pebble orientation was measured in six localities, where tillite crops out in a fairly good condition. At the same time, cross-bedding measurements were made wherever the associated periglacial sandstones presented cross-stratification. In the Paran~t Basin, the occurrence of glacial striations and other features related to ice abrasion have been mentioned by some authors in a few localities of the pre-Gondwana surface. However, these features were not studied in detail. References about them are rather scarce and limited to a few outcrops, already destroyed by quarrying. In South America the first striated floor described seems to be that mentioned by Du TOlT (1927) from northern Uruguay, in which the striae are oriented southeast-northwest. Later in the same country WALTER (1931) described striations oriented east-west. Possibly one of the first references to glacial striae in Brazil was that by CARVALHO (1940, p.271), from the km 62 of the old road between Mafra and Sao Bento do Sul (State of Santa Catarina). The scratches were found over a granodiorite surface, underlying Itarar6 sequences of tillite, sandstone and shales. However, no indication on direction was made. The same locality was also studied by BARBOSA(1940, p.272), who indicates a direction of N 32 ° W (magnetic) for the striae. According to Barbosa the sense of the ice movement was probably from southeast to northwest. He also mentions the presence of "roches moutonn6es" in the area and suggests that the scratches were produced by ice movement inside a valley. "Roches moutonn6es" and glacial striations were described by AL~aEIDA (1948, p.115) from Salto, in the State of S~,o Paulo. According to this author the striae were oriented northwest. He also concludes that the ice moved from southeast to northwest. Apparently there are no other references on striated surfaces in the Paran~t Basin. Fig.1 shows the location of twenty new localities in the Ponta Grossa plateau where glacial striae occur. The glacial striations here described are not very conclusive regarding the determination of the sense of ice movement. Related features of the scratched surface, such as crescentic marks and stoss-and-lee forms, are not sufficiently convincing. Their use without any other evidence seemed to be unsafe, in the writers opinion. Concerning similar pleistocenic features, FLINT (1961, p.58) states that "in the majority of instances the actual direction of flow is not determined, and is not determinable, from evidence furnished by the striation itself." In order to know in which direction the glacier moved it is necessary to find out other informations from the glacial or periglacial sediments. LEINZ (1937), MAAC~ (1946), MAtJ (1958) and MARTIN (1964), using different methods and criteria attempted to deduce the ice movement direction in the Paran~ Basin.
Palaeogeography, Palaeoclimatol., Palaeoecol., 3
(1967) 265-276
268 ~Oo
J. J. BIGARELLI, R. SALAMUNI AND R. A. FUCK
49"30 ~
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~5o
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,
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Fig.1. Location and orientation of the striated surfaces on the several geologic quadrangles. I = Quero-Quero; H = Campo Largo; I l I = Curitiba; I V = P6rto Amazonas; V = Contenda; VI = Arauc~iria. In Brazil, LEINZ (1937) made the first attempt to determine the directions of ice-flow using tillite fabric, reaching to the conclusion that the ice moved from northeast to southwest. MAACK (1946), also using tillite fabric, came to similar results. MAW (1958) also studied tillite fabric measuring the shape of the pebbles. His results indicated an ice movement from southeast to northwest. An extensive work on the Paranfi Basin Itarar6 Formation sediments was made by MARTIN(1964) using different glacial features as indicators of the direction of ice-flow, such as tillite fabric, direction of preglacial valleys and hills, striated floors and '°folding and imbrication structures". According to this author the general ice movement trend was from southeast to northwest. In the neighbourhood of the area described in this paper, MARTIN (1964, p.36--37) surveyed about ten outcrops on the Curitiba-Palmeira road. His observations were distributed over about 50 km section of the road. Martin concludes '°that the ice-movement was in a west-northwest direction, whilst the asymmetry of many of the fold and imbrication structures shows clearly that the flow was from east-southeast to west-northwest." Martin based his work mostly on the folding, thrusting and imbrication structures. These structures found in sand lenses inside a tillite and those found in sandstone and siltstone underlying a tillite can be attributed to the movement of the Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACES DEVELOPED BY THE GONDWANA ICE
269
ice-sheet. However, not all the folds in the Itarar6 Formation were produced in this way. They may be also the result of solifluction and other phenomena from the periglacial environment.
STRIATED SURFACES
Many outcrops of the Furnas, as well as of the Itarar6 Formation sandstones, show striated surfaces of at least two ages, which were produced by drift-shod-ice during two advances of the Gondwana glaciers. As such abrasive features may be generated by different agents, it seems to be necessary to establish their glacial origin. The most reliable evidence are the sediments, mainly tillites, and the stoss-and-lee forms. In those cases where the striated surfaces are not associated with unequivocal glacial deposits, the striae must be carefully checked, until their association either with glacial or periglacial phenomena can be properly assigned. Usually the striated surfaces produced by glaciers are not of restricted distribution but occur over large areas. Remnants of striations in the surveyed area, document very well the nature and extension of the involved agent. In the case here considered, the striae are associated with continental deposits, and are therefore
Fig.2. A remarkably striated surface, on the Lower Devonian Furnas Sandstone. These striations are overlain by periglacial deposits. Outcrops in the Rio do Salto valley (Quero-Quero Quadrangle), Rio do Salto glaciation.
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J . J . BIGARELLA, R. SALAMUNI AND R. A. FUCK
related to glacier advances. If caused by floating ice of pan ice sea the associated deposit would be marine. However, this is not the case. The abrasion of bed rock surfaces by glaciers caused the sculpturing (modelling) of smooth boss-like forms, through the streamline flowage of the glaciers with its abrassive bed load. Frequently, these swell-like bosses are not symmetrical, ending distally or downstream in small cliffs or hackly surface. The stoss-and-lee form as referred in the literature, are reliable indicators of the direction of ice flowage. The striated pavement, outcropping in the area surveyed does not provide a safe indication of the flow trend. In addition, these small features may have been disturbed by further erosion in the outcrop. Anyway, the lines of the ice movement are well preserved, although they certainly do not indicate the sense of flow of the ice that fashioned them. Two different erosion surfaces in the area have been striated. The older one, represented by the pre-Gondwana surface, is preserved on the Furnas Sandstone of Devonian age. The striae outcrop in the Rio do Salto valley, and were formed during the first advance of the ice, which can be recorded in the local area (Rio do Salto glaciation), being related to the older tillite of the Quero-Quero Geological Quadrangle (Fig.2). The second set of striations were made over an erosion surface that cut both the Furnas Sandstone and the periglacial sediments deposited during the Rio do Salto glaciation ice retreat. The striae crop out in Witmarsum (on the Furnas Sandstone), S~o Luiz do Purun~ (on the Itarar6 Formation periglacial sandstone), and in many other points of the P6rto Amazonas Geological Quadrangle. These striations were produced during the second recorded ice advance (Cancela glaciation) and are related to the second tillite of the Quero-Quero Geological Quadrangle. In all the observed outcrops, the striations were disposed in an almost perfect parallel pattern, without the interference of different age striae. Judging by their exposed parts these glacial lineations may occupy a considerable area under the overlying deposits. Normally, they consist of grooves and crests with irregular dimensions, and extremely variable distances between successive crests. The crests are usually rounded, showing a remarkable convexity in a transverse section. On the other hand, the grooves are more or less concave, being persistently U-shaped. The features associated with the striations, such as chattermarks, crescentic gouges, nailhead striations, and related structures are not very clearly preserved in the outcrops examined. However, some structures that very closely resemble stossand-lee forms were observed in a few outcrops. In Witmarsum the striated Furnas Sandstone surface is directly covered by the tillite of the Cancela glaciation. The average direction of the tillite pebbles coincides with the striae orientation. In this particular case, there is a confirmation regarding the origin of the striae, as well as of the tillite nature (ground moraine). However, in the Rio do Salto valley (a partially exhumed pre-Gondwana valley), most of the
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S T R I A T E D SURFACES D E V E L O P E D BY T H E G O N D W A N A ICE
271
Rio do Salto glaciation tillite was removed before the subsequent deposition of the periglacial sediments of the ice retreat. The striated surfaces were exposed and were then covered by new sedimentary sequences. In one case, the Itarar6 Formation sandstone, overlying the striae, is texturally similar to the Furnas Sandstone, due to the fact that it is actually a reworking of the latter one. In this example, it is rather difficult to make a distinction between both sandstones.
TILLITE A N D T I L L I T E - L I K E SEDIMENTS
General description As generally accepted the till is the product of mechanical desaggregation of fresh rocks, consisting of fresh mineral chips transported and deposited in the continental glacial environment below the ice. It is characterized by being a nonsorted sediment, containing a wide range of grain sizes and a rather small proportion of pebbles, cobbles and boulders with or without abraded facets or striations (compare, among others, SCHWARZBACH, 1961; FLINT, 1961). The Itarar6 Formation bears many sequences of tillite, tillite-like sediments (directly derived from ancient tills), and diamictite. Fine grain sizes greatly predominate over pebbles and larger particles, in most tillites. Fig.3 illustrates the grain size constitution of the matrix of the Cancela Tillite. The median diameter ranges between 0.047 mm and 0.188 mm. The mean diameter averages 0.066 ram. The sediments as a whole have a low degree of sorting, being chaotic in this respect. The sorting of the matrix is also low. Inman's sorting coefficient tr ~ ranges between 1.96 and 3.18, being 2.65 in average. Trask's sorting coefficient, based on the quartile measures, ranges between 2.7 and 7.8, with a 4.4 average. Grain size distributions have a low asymmetry value (a ~ <0.5) the curves being usually skewed toward the finer grains. In the tiUite, stratification rarely occurs. Sometimes a pseudo-stratification develops, possibly related to the shearing caused by the ice movement. Small sandstone lenses are frequently interbedded within the tillites. These lenticular layers are usually but not always stratified, even though sometimes they don't apparently show any bedding. Such lenticular beds may be interpreted as ice tunnel deposits, or else the infilling of thawed ice lenses or wedges inside the ground moraine. These unsorted sediments with interbedded sandstone lenses may be also interpreted as being a result of reworking of ancient tills. The tillite phenoclasts are usually angular or sub-angular. Nevertheless, some are sub-rounded or even rounded. The provenance of the latter ones seems to be from older gravel deposits either of fluvial origin or from the outwash plain. Striated pebbles may occasionally be found, and "flat iron" pebbles are rather scarce.
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J. J. BIGARELLA,R. SALAMUNIAND R. A. FUCK
272
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Tillite.fabric
It has long been verified that the phenoclasts within undisturbed till have a tendency to lie with their long axis approximately parallel to the direction of the glacier movement. In this way, HOLMES(1941, p. 1299) refers to the pioneer studies of Miller (1884), Bell (1888) and Upham (1891) that pointed out the existence of an alignment of the long axis of pebbles with the direction of the glacier flow. In the tills of northern Germany, Richter (cited by KRUMBEIN, 1938) also found that the long axes of pebbles are usually aligned parallel to the direction of ice flow. Till fabric analysed by KRUMBEIN (1938) from a deposit at Random Lake Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
273
STRIATED SURFACES DEVELOPED BY THE GONDWANA ICE
indicates, besides an alignment parallel to the ice movement, a transverse disposition of the long axes, which was also verified by Richter. Detailed studies of the attitude of pebbles inbedded in the till of Central New York were made by HOLMES(1941) who has shown that inherent characters in the till stones, such as form, roundness, size and relative axial length predispose a stone to a certain depositional attitude in the rock fabric. Some types of stone have relatively high statistical probability in depositional attitude, with the long axis aligned either parallel to or transverse to the direction of glacier flow. As a general conclusion, Holmes confirmed the preferred arrangement of the stones with their long axes parallel to the direction of glacier flow. Pebble orientation in the Itarar6 tillites has been measured in several outcrops, following the progress of the mapping project of the "Comissfio da Carta Geol6gica do Paranfi". Some measurements have been made outside the area here considered, as for instance those in the tillites of Lapa and Palmeira quadrangles. The tillite of the last quadrangle is supposed to be the third regional tillite of the Gondwana glaciations. Owing to time limitations, among other reasons, the method suggested by HO~UES (1941) was not used in our measurements. Instead, it seemed that a simplification would be desirable. Generally, most of the bibliographic references are
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Fig.4. Pebble long axis dip direction rose diagrams for six localities o f the Cancela Tillite, as well as for the ensemble as a whole. Some localities present a transverse to diagonal pattern, others have the normal pattern, i.e., parallel to the ice flow. The resultant vector is up glacier, therefore opposite to the ice movement. There is clearly a tendency of the pebbles to imbricate up glacier. The table included in the drawing gives the general results obtained from the measurements. The dip directions are referred to true north. Palaeogeography, Palaeoelimatol., Palaeoeeol., 3 (1967) 265-276
274
J.J. BIGARELLA,R. SALAMUNIAND R. A. FUCK TN
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Fig.5. General results of 889 pebble measurements made on three different tillites from the surveyed area. A. Pebble long axis dip direction. The resultant vector is S 20 ° E. Compare this result with the Cancela Tillite average referred in Fig.4. Both results are very close together, being the difference only 9 o. B. Pebble direction (no dip considered). concerned with the measurement of the long axis direction, practically without details as to dip direction or shape of the pebbles. The measurements obtained by the present writers refer to the dip direction of the pebble. In the Cancela Tillite elongated pebbles of different size and shape were used, but as a rule most of them were ovoid, sub-angular to sub-rounded. The number of pebbles measured ranged from 50 to 120 according to the conditions of the locality surveyed. A rose diagram constructed from the dip direction of the pebbles shows that the orientation is partially parallel to the direction of ice flow deduced from the striated floors, as well as partially transverse or diagonal to that direction (Fig.4). Rose diagrams, which only refer to the long axis direction of the pebbles are quite different from those illustrated in the dip direction diagram (Fig.5). Relevant to pebble direction (no dip considered), patterns similar to those usually mentioned in the literature were noticed. Some localities show the "normal pattern" (HOLMES, 1941, p. 1310) parallel to the ice flowage, and others the "transverse pattern" essentially at right angles, to the inferred direction of the glacier flow. The parallel and transverse oriented pebbles occur side by side giving the impression of lack of internal organization. The dip direction rose diagrams show that the pebble long axis has a tendency to dip up glacier. The resultant vector of the dip directions is actually opposite to the sense of the ice flowage. In the Cancela Tillite, 364 measurements Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276
STRIATED SURFACESDEVELOPEDBY THE GONDWANA ICE
275
have been made at six different localities. The average dip direction and the consistency ratio (c.r.) were determined according to the following formulas: tan 0 --
~sin 0
ycos 0
c.r.
V ( ~ s i n O) z q- (~cos 0 ) 2
number of measures
Results for the individual localities, as well as the general average for the area, are given in Fig.4. The data for most of the localities are congruent. The consistency ratio, although low, is characteristic for this type of distribution, being therefore significant. The average pebble dip direction is S 11 ° E, while the orientation of the scratches on the striated surfaces differs only by 9 °, being S 2 ° E. Moreover, at locality I where the tillite rests on the striated surface, the scratches and the average direction of the pebbles are almost coincident. This is a good indication that the method based on pebble long axis measurements is very accurate. On the other hand the average pebble direction (no dip concerned) is somewhat different from the average dip direction, but the results are still congruent. The consistency ratio is rather lower than the one obtained for the dip direction analysis. To calculate the direction resultant vector, and the corresponding consistency factor, we followed a procedure similar to that of CURRAY (1956, p.1 19) using the following formulas: tan 2 0 --
c.r. --
~sin 2 0 ~cos 2 0
~¢/( ~sin 20) 2 -c ( ~cos 20) 2 number of measures
CONCLUSIONS The sense of the ice movement could not be definitely inferred by using the striated surfaces and the averages of pebble long axis direction or dip direction, without comparing these results with those concerning periglacial sediments transportation data. As the field work progressed and more data were gathered, we noticed that the resultant vector for the tillite pebbles was opposite to the associated periPalaeogeography, Palaeoclimatol.,Palaeoecol., 3 (1967) 265-276
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J . J . BIGARELLA, R. SALAMUNIAND R. A,. FUCK
glacial s a n d s t o n e vector, d e d u c e d f r o m c r o s s - b e d d i n g studies. This conclusion is i m p o r t a n t , as it indicates t h a t the i m b r i c a t i o n o f the pebbles in the tillite has a tendency to dip up glacial, like the pebble attitude in the rivers. Nevertheless, m a n y m o r e m e a s u r e m e n t s are still needed to confirm the a b o v e statement. C r o s s - b e d d i n g measurements, m a d e in the periglacial sandstones associated to v a r i o u s G o n d w a n a glaciations, give as average t r a n s p o r t a t i o n trend N 5 ° W. T h e a b o v e d a t a can be c o m p a r e d with the following directions, (referred to n o r t h e r n quadrangles) o b t a i n e d up to n o w f r o m the striated floors a n d f r o m several tillites (including the tillite o f the C a n c e l a glaciation): (a) striations: N 2 ° W (or S 2 ° E) (b) pebble long axis direction: N 38 ° W (or S 38 ° E) (c) p e b b l e long axis dip direction: S 20 ° E (d) ice m o v e m e n t d e d u c e d f r o m (c): N 20 ° W These results indicate t h a t there is a g o o d a g r e e m e n t between the m e a s u r e ments p e r f o r m e d in the glacial deposits a n d those o f the periglacial environment.
REFERENCES
ALMEIDA, F. F. M., 1948. A "roche moutonn6e" de Salto, Estado de S~o Paulo. Geol. Met., Bol. (S6o Paulo), 5: 112-118. BARBOSA, O., 1940. Estrias produzidas pot g~lo Permo-Carbonifero. Minera¢6o Met. (Rio de Janeiro), 4 (24): 272-273. BEURLEN, K., 1952. La Pal6ogeographie de la glaciation Gondwaniene au Br6sil m6ridional. Congr. G~ol. Intern., Compt. Rend., 19e, Algiers, 1952, 8: 193-211. CARVALHO,P. F., 1940. Estrias glaciais em granodiorito sobposto ao Gondwana de Santa Catarina. Minera¢6u Met. (Rio de Janeiro), 4(24): 271-272. CtrRRAV, J. R., 1956. The analysis of two-dimensional orientation data. J. Geol., 64(2): 117-131. Do TOIT, A. L., 1927. A geological comparison of South America with South Africa. Carnegie Inst. Wash. Publ., 381:157 pp. FLINT, R. F., 1961. Glacial and Pleistocene Geology. Wiley, New York, N.Y., 533 pp. HOLMES,C. D., 1941. Till fabric. Bull. Geol. Soc. Am., 52(9): 1299-1354. KRUMaEIN, W. C., 1938. Preferred orientation of pebbles in sedimentary deposits. J. Geol., 47: 673-706. LEINZ, V., 1937. Estudos sfbre a glaciaqao Permo-Carbonifera do Sul do Brasil. Dept. Nacl. Prod. Mineral, Div. Fomento Prod. Mineral, Bol., 21 : 47 pp. MAACK, R., 1946. Geologia e Geografia da regi~o de Vila Velha (Est. Paran~i) e considera96es s6bre a glaciag~.o Carbonifera no Brasil. Arquiv. Museu Paranaense, 5:305 pp. MARTIN, H., 1964. The directions of flow of the Itarar6 ice sheets in the Paran~i Basin, Brazil. Bol. Paranaense Geograf., 10/15: 25-76. MAU, H., 1958. Contribuig~o para a geologia de Ibaiti (Paran~i). Bol. Soc. Brasil. Geol., 9(2): 79-82. SALAMUNI,R., BIGARELLA,J. J. and FucK, R. A., 1966. S6bre a ocorr6ncia de estrias glaciais no Segundo Planalto do Paran~c BoL Paranaense Geograf, 18/20: 127-131. SCHWARZBACH,M., 1961. Das Klima der Vorzeit. Enke, Stuttgart, 275 pp. (English translation by R. O. Muir, 1963, Van Nostrand, London). WALTER,K., 1931.1Jber ein Vorkommen von geschrammter Landoberfl/iche aus dem Gondwanaglazial. Zentr. Mineral, Abt. B, 1931: 449-460.
Palaeogeography, Palaeoclimatol., Palaeoecol., 3 (1967) 265-276