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Brazilian continental cretaceous
Earth-Science Reviews, 17 (1981) 69--85
69
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Brazilian Continental Cretaceous SETEMBRINO PETRI and VILMA A. CAMPANHA Museu Paulista, Universidade de SEo Paulo, SP (Brasil) Paulipetro, S~o Paulo, SP (Brasil) ABSTRACT Petri, S. and Campanha, V.A., 1981. Brazilian continental Cretaceous. Earth-Sci. Rev., 17: 69--85. Cretaceous deposits in Brazil are very well developed, chiefly in continental facies and in thick sequences. Sedimentation occurred essentially in rift-valleys inland and along the coast. Three different sequences can be distinguished: ( 1 ) a lower clastic non-marine section, (2) a middle evaporitic section, (3) an upper marine section with non-marine regressive lithosomes. Continental deposits have been laid down chiefly between the latest Jurassic and Albian. The lower lithostratigraphic unit is represented by red shales with occasional evaporites and fresh-water limestones, dated by ostracods. A series of thick sandstone lithosomes accumulated in the inland rift-valleys. In the coastal basins these sequences are often incompletely preserved. Uplift in the beginning of the Aptian produced a widespread unconformity. In many of the inland rift-valleys sedimentation ceased at that time. A later transgression penetrated far into northeastern Brazil, but shortly after continental sedimentation continued, with the deposition of fluvial sandstones which once covered large areas of the country and which have been preserved in many places. The continental Cretaceous sediments have been laid down in fluvial and lacustrine environments, under warm climatic conditions which were dry from time to time. The fossil record is fairly rich, including besides plants and invertebrates, also reptiles and fishes. As faulting tectonism was rather strong, chiefly during the beginning of the Cretaceous, intercalations of igneous rocks are frequent in some places. Irregular uplift and erosion caused sediments belonging to the remainder of this period to be preserved only in tectonic basins scattered across the country. THE GEOLOGICAL SETTING
The Brazilian continental Cretaceous sediments were laid d o w n in basins of t w o different kinds: (1) coastal and offshore, (2) inland (Fig. 1). The inland sedimentation t o o k place in intracratonic basins and scattered small areas on the Precambrian shield due to episodes of great subsidence during some stage of the Cretaceous. Some of these deposits have surpassed the intracratonic basin borders and rest directly on t o p of Precambrian rocks or more rarely on Paleozoic beds. A fault block tectonism, well displayed in the northeast of the country, was responsible for the preservation o f several small isolated "basins" filled with Cretaceous (or latest Jurassic) sediments. 0012-8252/81/0000--0000/$04.25 © 1981 Elsevier Scientific Publishing Company
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/ Fig. 1. Brazilian s e d i m e n t a r y basins. 1 = T a k a t u ; 2 = A c r e ; 3 = A m a z o n a s ( i n t r a c r a t o n i c ) ; 4 = A m a z o n M o u t h ( M a r a j 6 ) ; 5 = B r a m g a n ~ a - - V i z e u (Pirabas); 6 = S~o L u i s ; 7 = P E nal'ha; 8 = Barreirinhas; 9 = CearA; 1 0 = Potiguar; 11 = Pernambueo--Paral"ba; 1 2 = o t h e r i n l a n d basins o f northeast; 13 = Rio-do-PeJxe; 14 = A r a r i p e ; 15 = Jatob~; 1 6 = T u e a n o ; I 7 = R e c 6 n c a v o ; 18 = Sergipe--Alagoas; 19 = A l m a d a ; 2 0 = J e q u i t i n h o n h a ; 21 = E s p f r i t o S a n t o ; 22 = C a m p o s ; 23 = Santos; 24 = Pelotas; 2 5 = ParanA; 26 = S~o Francisco. A = Sobra] L i n e a m e n t ; B = Parafba L i n e a m e n t ; C = P e r n a m b u c o l , i n e a m e n t .
The three main Brazilian intracratonic basins with thick Paleozoic and thinner Mesozoic deposits, though sometimes occupying rather great extensions, are the Amazonas, Parnafba (or Maranh~o) and Paran~ basins. Besides these three basins one has to consider, only for the Cretaceous, a fourth one called S~o Francisco and a fifth one, called Acre, this latter located in the high Amazon River system and related to the Pastaza Basin in Peru. A Guyanan rift-valley (called Takatu), running east--west, reaches Brazil at its
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72 western tip, in the extreme north of the country. Most of the coastal basins are rift-valleys. Some of t h e m contain latest Jurassic deposits intimately related to the earliest Cretaceous ones. They are distinguished from the intracratonic basins by their intensively faulted nature, smaller areas but thicker deposits. The rift-valleys are closed basins limited by faults whose total slip may attain 2000 to 3000 m. These basins are shown in Fig. 1. A few of them are not rift-valleys; they are areas of sedimentation open towards the ocean with sediments dipping constantly oceanward. The Santos and Cear~i basins are entirely located on the continental shelf. North from the RecSncavo Basin stretches the Tucano rift-valley up to the S~o Francisco River and then, crossing this river, with an ENE trend, the Jatob~ rift-valley continues. These rifts and that of Takatu are the only ones n o t located in the coastal and continental shelf areas. The east--west Precambrian alignments, named Patos (or Paral~a) and Pernambuco, in the projected northeastern tip of the Brazilian territory, as well as the Sobral alignment north of these structures, are important tectonic features allowing a division of the coastal basins into sections, one of them from Pelotas to Sergipe--Alagoas, the second from Pernambuco--Parafba to Potiguar, and the last from Cear~ to Foz-do-Amazonas (Amazon Mouth). This structural framework was built by an Early Cretaceous pre-Aptian tectonism k n o w n as the Wealdenian Reactivation (Almeida, 1967). The tectonic movements were reduced after the Barremian, so that the Brazilian Early Cretaceous is clearly distinguished from the Brazilian Late Cretaceous. The Early Cretaceous sediments of the coastal rift-valleys of the northeast are commonly tilted towards the continent along fault blocks, while the Late Cretaceous ones dip constantly towards the ocean. All pre-Aptian Cretaceous sediments (including the latest Jurassic) are non-marine in origin and even the Aptian bears evidence of restricted seas. The eastern Brazilian coastal and offshore basins have similar Paleozoic stratigraphic columns which, when complete, are of a threefold nature: (1) lower clastic non-marine section, (2) middle evaporitic section, and (3) upper carbonatic and clastic marine section with non-marine regressive lithosomes only in the Early Cenozoic (Ponte and Asmus, 1975). The first section is pre-Aptian in age, the middle one Aptian and the last is postAptian. THE LATEST JURASSIC--EARLIEST CRETACEOUS Occurrences
The lower clastic non-marine section is made up of one sequence in the sense of Sloss (1963), t h a t is, one b o d y of rocks limited above and below by a widespread u n c o n f o r m i t y ; this does n o t mean to say t h a t local unconformities m a y n o t be present. This sequence, however, is subjected to further subdivisions into an older blanket-like unit covered by a younger b o d y of lenti-
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74 cular lithologies. The older one is made up of sediments deposited under conditions of an intense faulting tectonism. The classical standard reference for this latest Jurassic--Early Cretaceous is found in the RecSncavo Basin (Fig. 2). The blanket-like unit belongs to the intracratonic or pre-rift cycle (Sampaio and Northfleet, 1973) and is characterized b y a great continuity of its lithologic bodies with few horizontal variations. It is best developed in the Rec6ncavo and Sergipe--Alagoas basins, occurring also in the Tucano and as scattered remnants in the small basins of the inland of the northeast (Jatob~, Mirandiba, Sgo Jos~ do Belmonte, Araripe). This blanket unit disappears south of the Almada Basin. Lithologically, it is again subdivided into two bodies (Table I). The complex b o d y of sediments that covers the blanket unit, was laid d o w n under strong fault tectonic conditions, so thick wedges of syntectonic conglomerates developed along the major trends of the downfaulted blocks. These sediments vary in thickness from a few hundred to more than 5000 m and show considerable facies changes. Many local unconformities occur due to the syntectonic nature of the sediments but, as a whole, they m a y be considered a continuation of the blanket unit without a major break in the process of sedimentation. This b o d y of lithosomes from the Alianqa and S~o Sebastigo to the Salvador Formation is composed of essentially Conformable lithologies separated from the rocks below and above b y regional unconformities. It is known as the Bahia Supergroup, with thicknesses of more than 6500 m; its thickness increases gradually southward from Jatob~ to Rec6ncavo while its overall coarseness decreases gradually southward. The development of the Sergipe--Alagoas Basin during the same geological time is closely similar to that of the Rec6ncavo. In the Almada Basin, south of RecSncavo, only the Sergi Formation of latest Jurassic age is present, and south of this basin it is entirely absent. The Early Cretaceous units reach the Espirito Santo Basin (Ponte and Asmus, 1975), b u t south of it there is no equivalent to the Bahia Supergroup. The Espirito Santo to Santos basins were the site of intense magmatic activity. No equivalent beds are present in the Pelotas Basin. North of the Sergipe--Alagoas Basin little is known a b o u t possible sequences equivalent to the Bahia Supergroup. The Recife--Jo~o Pessoa Basin has subsided less than the basins to the north and the south, with a sedimentary fill of less than 2000 m (Souza, in Ponte and Asmus, 1975). It is uncertain whether or not an Early Cretaceous tectonism has affected this basin, its formative tectonism being of Turonian age. Early Cretaceous continental terrigenous sediments m a y be present in the offshore part of the Potiguar Basin, according to seismological evidence. Non-marine sedimentary sequences from offshore Cear~ Basin and from Barreirinhas and S~o Luis basins would eventually be time-equivalent of the Early Cretaceous part of the Bahia Supergroup. The Foz-do-Amazonas sedi-
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76 mentary record begins only in the Late Cretaceous. Several small "basins" are scattered in the inland of northeast Brazil on an area of predominantly Precambrian crystalline rocks. The largest and most famous one is the Araripe "basin" (Fig. 3). Its richly fossiliferous fish localities as well as its important gypsum beds are well known. It is unique among these small basins because it stands above the low-lying Precambrian area forming a 180 b y 50 km plateau generally limited by pronounced escarpments. This situation, as well as the presence of inselbergs south of the plateau, attest to a former larger extension. The Araripe Mesozoic sediments constitute two sequences separated by an u n c o n f o r m i t y ; the lower one is correlated to the latest Jurassic of the Bahia Supergroup, and the upper one is of Aptian--Albian age. The other "basins" of the northeast are preserved as downfaulted blocks limited by more elevated areas of Precambrian rocks. A latest Jurassic sequence is present in the small Mirandiba and Sgo Jos~ do Belmonte basins; no pre-Aptian Early Cretaceous sediments are present. The other small basins of the region contain deposits belonging to only one sequence equivalent in time to the Early Cretaceous units of the RecSncavo Basin; no beds equivalent to the latest Jurassic are present there. The principal "basins" are those of Rio
Paleogeography and paleoclimate of the latest Jurassic The evaporites of the Juru~ Mirim red beds from Acre suggest a desert passing westward to coastal environments and farther away, outside of Brazil, to the marine environments of the Andean geosyncline. The anhydrite and halite present in the basal part of the Alianqa Formation of the RecSncavo Basin point also to dry climates. The post-evaporitic latest Jurassic sediments in the RecSncavo and other rift-valleys are made up of clastics with sedimentary structures indicating
77 flood plains of meandering rivers with lakes and o x b o w stagnant waters. Primary red beds were formed in this environment; red argillaceous layers are frequent in the lower part, suggesting derivation from red lateritic clayey soils. The overbank and o x b o w lake facies retain evidence of argillaceous oxydizing conditions whereas reducing circumstances in the larger water bodies imprinted greenish hues on the sediments. Among the lacustrine deposits, limestone beds with concentrations of ostracod shells are found (Alian~a and equivalent formations). Red sandstone beds b e c o m e more and more frequent towards the top, suggesting deep erosion in the source areas, resulting in the denudation of the regolith and erosion of fresh rocks. These sandstones contain rock fragments and their crossbedding is of torrential type, with silicified conifer trunks along some of the foresets in such way as to suggest transport (Sergi and equivalent formations). Red hues are seen only in the matrix of the sandstones. The evidence suggests a change from meandering to braided channels. Latest Jurassic sediments of the rift-valley basins therefore provide evidence of change in climatic conditions from dry to humid with dry and wet seasons. The RecSncavo and Tucano basins formed part of a latest Jurassic fluvial basin which drained southward through rivers with headwaters in the Jatob~ or m a y b e even Araripe areas. The sediments of these areas, now separated from each other, were probably part of a single basin disrupted b y erosion. The thickness of the formations increases gradually from north to south; the coarseness of sandstones, on the other hand, increases from south to north. The greatest subsidence is found in the southern Rec5ncavo Basin in the supposed transport direction. This ancient fluvial basin was broken up b y the Wealdian tectonism (Petri, 1974); it extended apparently south to the Almada Basin. The Sergipe--Alagoas Late Jurassic deposits, though lithologically and paleontologically similar to those of the RecSncavo--Tucano--Jatob~ basins, probably belonged to one or more independent river systems. The formations n o w cover discrete areas separated by erosion according to some geologists. However, the possibility of original discrete areas resulting from separated river systems m a y be considered.
Paleogeography of the Early Cretaceous pre-Aptian The Paran~ Basin was the scene of enormous basaltic and alkaline volcanic activity. A few sandstone lenses occur between the first flows and a rather thin eolian sandstone may cover the last flow. A great number of diabase dykes chronologically correlated to the flows cut through Precambrian rocks b e y o n d the border of the Paran~ Basin. The coastal basins of Santos, Campos and Espfrito Santo were also affected b y this volcanism. Contemporaneous volcanism reached the Parnafba Basin, though on a smaller scale. No sedimentary record is k n o w n in this basin as well as in other intracratonic basins.
78 As tension fractures were developing in the south, a strong fault tectonism was developing in the northeast. The Late Jurassic RecSncavo--Tucano-Jatob~ Valley persisted during the Early Cretaceous but with a change in the disposition of the headwaters which no longer passed through the Mirandiba, S~o Jos~ do Belmonte and Araripe areas, but through those of Rio-doPeixe and Pau
79 TABLE II Brazilian stratotypes, probable age equivalents and characteristic fossils Stage (Brazil)
Stage (international)
Fossils
Alagoas
Late Aptian
Jiqui~
Late Barremian to Early Aptian
Buracica
Early Barremian
Aratu
Late Valanginian to Hauterivian
Rio-da-Serra
Early Valanginian
Dora Jo~o
Purbeckian
sporomorphs: Inapertinopollenites and other forms belonging to ClassopoUis, Gnetales, Araucariacites, Tricolpites, Triletes and Cicatricosiposites; Exesipollenites tumulus (in Campos Basin) point to Late Aptian ostracods: Petrobrasia diversicostata KrSmmelbein, Candona centroimpressa Weber ostracods: Coriscina eoriacea KrSmmelbein, Cypridea (Sebastianites) fida minor Moura ostracods: Paracypridea obovata obovata (Swain), Cypridea ( Morinina? ) bibullata bibullata Wisher ostracods, in following zones, from base to top: Cypridea kegeli Wisher; Theriosynecum varietuberatum Grekoff and KrSmmelbein; Cypridea (Morinoides ) andeiensis KrSmmelbein; Paracypridea brasiliensis KrSmmelbein ostracod: Bisulcocypris pricei Pinto and Sanguinetti
North of the Sergipe--Alagoas Basin, pre-Aptian Cretaceous sediments are of minor importance. T h e y m a y be present on the continental shelf of the Potiguar Basin, filling downfaulted blocks evidenced by seismic reflection lines (Ponte and Asmus, 1975). Brazilian latest Jurassic--earliest Cretaceous chronostratigraphy The exact position of these strata in the world standard column is not yet known due to their non-marine nature, with sediments laid down in restricted seas only at the top. As a result of this difficulty, Brazilian Oil Company (Petrobr~s) geologists advocated a Brazilian time-stratigraphic column with its own stratotypes, based on non-marine ostracod zones and, for the Alagoas Stage, on sporomorphs. The proposed stages and their probable equivalents are shown in Table II (after data from Schaller, 1969; and Viana et al., 1971).
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81 APTIAN AND POST-APTIAN CONTINENTAL DEPOSITS A generalized uplift of the Brazilian territory after the latest Jurassic-earliest Cretaceous sequences resulted in a widespread u n c o n f o r m i t y in the beginning of the Aptian. This u n c o n f o r m i t y separates, in the RecSncavo and Tucano basins, the Bahia Supergroup (Late Jurassic to pre-Aptian Cretaceous) from the Marizal Formation laid d o w n during Alagoas time. The Marizal has a varied lithology from conglomerates to shales and even rare limestone beds. The predominant lithology is a poorly sorted clayey sandstone, c o m m o n l y cross-bedded with cut-and-fill structures. The conglomerates contain boulders of varied lithologies. The thickness of the Marizal Formation shows considerable local variations. The lithological characteristics, distribution and irregular thickness suggest a close association with the uplifted fault blocks with local sources formed b y fault scarps. The transport was torrential or by way of debris flows near the slopes and by laminar flow on the plains away from these slopes. Although no evaporites are known, it is believed that the climate was dry and internal drainage might have occurred at least during part of the time of deposition of the formation. The nature of the Marizal and the geographical proximity to contemporaneous evaporitic deposits of Sergipe--Alagoas and Jequitinhonha favor this interpretation. After the deposition of the Marizal Formation there was a consolidation of the RecSncavo--Jatob~ rift-valley to the Brazilian craton. This formation therefore represents a kind of molasse deposit in a rift-valley basin. In the southern and northeastern coastal basins there are formations correlated to the Marizal which contain evaporites among other lithologies. These sediments were formed initially in lagoonal environments passing later into restricted marine conditions. No such deposits are k n o w n in the northern coastal basins. After a short regressive episode, a new transgression caused the deposition of a Late Aptian--Santonian sequence, with a short regressive fluctuation in the Cenomanian in the northeastern and eastern basins. This sequence is well represented in the basins of Amazonas, S~o Luis, Barreirinhas, P a r n a ~ a (Table III), Araripe and S~o Francisco. A region of maximum subsidence in this time developed in the Barreirinhas coastal basin of the State of Maranh~o, which could then constitute the site of convergence of different fluvial systems. The first sediments of the Albian--Santonian sequence of this basin contains fanglomerates accumulated at the f o o t o f slopes of rising fault blocks. They grade laterally into floodplain and lacustrine deposits. No marine sediments are k n o w n among these basal deposits, which are characterized by abrupt lateral facies changes. Fluvial sediments exhibit high-energy distributary channels and overbank facies, grading northward on the present continental shelf into deltaic plain facies with low-energy distributmT channels. The rivers were of a braidedchannel type, frequently covered b y fine clastics of the floodplain facies and b y swamp deposits in which lignite developed.
82 The prodelta sediments are 2000 to 3000 m thick and the non-marine sediments up to 5000 m. The accumulation of such thicknesses in such a short time could n o t be accomplished unless at least a major river was actively transporting material. This delta was possibly a composite one, the product of several rivers converging into an area of high subsidence. A transgressive Albian phase followed by a regressive Cenomanian--Santonian phase was superimposed on this constructive delta, causing a transgressive--regressive cycle well displayed in the Parnafba intracratonic basin with the Grajau, Cod5 and Itapecuru Formations (Aguiar, 1971). Similar beds occur in the S~o Luis coastal basin. The correlation of the formations in the S~o Francisco Basin is still controversial. This basin is very much dissected today, so that the Cretaceous crops o u t in isolated spots distributed in a huge area of 1000 km in a N--S direction by 500 km in the E--W direction. The sediments belong to t w o formations, the Areado (the older) and the Mata
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Similar to the S~o Lufs Basin, the Albian to Cenomanian sediments of the Potiguar Basin were formed in non-marine environments. The latest Cretaceous sediments of the coastal basins, except that of the Amazon Mouth, are marine. Table IV presents the characteristics of the deposits in this latter basin. Another area of non-marine Late Cretaceous sedimentation is located in the Acre Basin. Here a continuous conformable sequence spans the Cenomanian--Maastrichtian time. These sediments form a transgressive--regressive cycle b u t the sea never reached the Acre Basin, being restricted more to westward in Peru. During the Late Cretaceous, the so-called Alto Paranaiba uplift (Hasui et al., 1975) separated t w o areas of sedimentation: the S~o Francisco Basin and the Alto Paran~ sub-basin. The intensification of the uplift in this area caused the outburst of several volcanoes. In the S~o Francisco Basin, the alkaline and ultrabasic lavas and the volcanic tufts grade distally into green cross-bedded cineretic sandstones and conglomerates which pass distally into clayey sandstones with montmorillonite i n the matrix (related to the volcanic source) and subordinated conglomerates (Mata
This history of the Cretaceous in Brazil is one of transgressive and regressive fluctuations increasing from the Early Cretaceous to a maximum in the Albian, at least in the northeast, and from then, decreasing in intensity. No marine earliest Cretaceous is k n o w n in Brazil, and since the Albian, the marine occurrences are more and more displaced towards the present ocean. This trend lasted well into the Cenozoic until the Oligocene. The climates during the Cretaceous were probably always tropical. Dry climates were present during the latest Jurassic. The earliest Cretaceous to Barremian witnessed more humid climates at least in the northeast, b u t dry climates returned during the Aptian and evaporites were widespread in the
85 c o a s t a l basins f r o m s o u t h t o t h e n o r t h e a s t . E x t r e m e l y d r y c l i m a t e s p r o b a b l y n e v e r o c c u r r e d again. N o p o s t - A l b i a n e v a p o r i t e s are k n o w n , even t h o u g h L a t e C r e t a c e o u s a n d T e r t i a r y regressive p h a s e s w o u l d set p r o p e r c o n d i t i o n s f o r t h e d e v e l o p m e n t o f t h e s e c h e m i c a l s e d i m e n t s , h a d a suitable c l i m a t e existed. REFERENCES Aguiar, G.A., 1971. Revis~o geol6gica da Bacia Paleoz6ica do Maranh~o. Soc. Bras. Geol., An. X X V Congr., S~o Paulo, SP, 3: 113--122. Almeida, F.F.M., 1967. Origem e evolu~o da plataforma brasileira. Dep. Nacl. Prod. Min., Div. Geol. Min., Bol., 241:36 pp. Braun, O.P.G., 1966. Estratigrafia dos sedimentos da parte interior da regi~o nordeste do Brasil. Dep. Nacl. Prod. Min., Div. Geol. Min., Bol., 236:75 pp. Braun, O.P.G., 1970. A Formaq~o Areado e a Formaq~o Serra Negra. Rev. Escola Minas Ouro Preto, 28 (3). G a m a Jr., E., 1970. Modelo geol6gico das bacias do Rec6ncavo e Tucano. Soc. Bras. Geol., An. X X I V Congr., Brasflia,DF: 191--200. Grossi Sad, J.H., Cardoso, R.N. and Costa, M.T., 1971. Formaq~es Cret~ceas e m Minas Gerais: urea revis~o. Rev. Brasil. Geoci~nc., 1 : 2--12. Hasui, Y., Sadowski, G.R., Suguio, K. and Fuck, G.F., 1975. The Phanerozoic tectonic evolution of the western Minas Gerais State. An. Acad. Brasil.Ci~nc., 47 : 431--438. Mabesoone, J.M. and Tinoco, I.M., 1971. Geologia da faixa sedimentar costeira Pernambuco--Paral'ba. Univ. Federal Pernambuco, Inst. Geoci~nc., Dep. Geol. Paleontol., resumo II Semin~rio Dep., 7 pp. (manuscript). Moura, J.A., 1972. Algumas esp~cies e subesp~cies de ostracodes da Bacia Rec6ncavo-Tucano. Bol. T~c. Petrobr~s, 15 : 245--263. Petri, S., 1974. Sequences and correlations of Brazilian Late Paleozoic and Mesozoic deposits. Soc. Bras. Geol., An. XXVIII Cong., Porto Alegre, RS, 2: 17--29. Ponte, F.C. and Asmus, H.E., 1975. The Brazilian marginal basins: current state of knowledge. An. Acad. Brasil.Ci~nc., 48 (Supl.): 215--240. Sampaio, A.V. and Northfleet, A., 1973. Estratigrafia e correlaq~o das bacias sedimentares brasileiras.Soc. Bras. Geol., An. X X V I I Congr., Aracaju, SE, 3: 189--206. Schaller, H., 1969. Revis~o estratigr~ificada bacia Sergipe--Alagoas, Bol. T~c. Petrobr~s,
12: 21--86. Sloss, L.L., 1963. Sequences in the cratonic interior of North America. Geol. Soc. Am. Bull., 74: 93--104. Tinoco, I.M. and Mabesoone, J.M., 1975. Observaq~es paleoecol6gicas sobre as bacias mesoz6icas de Iguatu, Rio do Peixe e intermediarias. Bol. Nficleo Nordeste Soc. Brasil. Geol., 5-Atas VII Simp. Geol. Nordeste, Fortaleza, pp. 95--107. Viana, C.F., Gama Jr., E.G., Sim~es, I.A., Moura, J.A., Fonseca, J.R. and Alves, R.J., 1971. Revis~o estratigr~fica da Bacia Rec6ncavo--Tucano. Bol. T4c. Petrobr~s, 14: 152--192. [Manuscript received September 4, 1980]
69
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Brazilian Continental Cretaceous SETEMBRINO PETRI and VILMA A. CAMPANHA Museu Paulista, Universidade de SEo Paulo, SP (Brasil) Paulipetro, S~o Paulo, SP (Brasil) ABSTRACT Petri, S. and Campanha, V.A., 1981. Brazilian continental Cretaceous. Earth-Sci. Rev., 17: 69--85. Cretaceous deposits in Brazil are very well developed, chiefly in continental facies and in thick sequences. Sedimentation occurred essentially in rift-valleys inland and along the coast. Three different sequences can be distinguished: ( 1 ) a lower clastic non-marine section, (2) a middle evaporitic section, (3) an upper marine section with non-marine regressive lithosomes. Continental deposits have been laid down chiefly between the latest Jurassic and Albian. The lower lithostratigraphic unit is represented by red shales with occasional evaporites and fresh-water limestones, dated by ostracods. A series of thick sandstone lithosomes accumulated in the inland rift-valleys. In the coastal basins these sequences are often incompletely preserved. Uplift in the beginning of the Aptian produced a widespread unconformity. In many of the inland rift-valleys sedimentation ceased at that time. A later transgression penetrated far into northeastern Brazil, but shortly after continental sedimentation continued, with the deposition of fluvial sandstones which once covered large areas of the country and which have been preserved in many places. The continental Cretaceous sediments have been laid down in fluvial and lacustrine environments, under warm climatic conditions which were dry from time to time. The fossil record is fairly rich, including besides plants and invertebrates, also reptiles and fishes. As faulting tectonism was rather strong, chiefly during the beginning of the Cretaceous, intercalations of igneous rocks are frequent in some places. Irregular uplift and erosion caused sediments belonging to the remainder of this period to be preserved only in tectonic basins scattered across the country. THE GEOLOGICAL SETTING
The Brazilian continental Cretaceous sediments were laid d o w n in basins of t w o different kinds: (1) coastal and offshore, (2) inland (Fig. 1). The inland sedimentation t o o k place in intracratonic basins and scattered small areas on the Precambrian shield due to episodes of great subsidence during some stage of the Cretaceous. Some of these deposits have surpassed the intracratonic basin borders and rest directly on t o p of Precambrian rocks or more rarely on Paleozoic beds. A fault block tectonism, well displayed in the northeast of the country, was responsible for the preservation o f several small isolated "basins" filled with Cretaceous (or latest Jurassic) sediments. 0012-8252/81/0000--0000/$04.25 © 1981 Elsevier Scientific Publishing Company
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/ Fig. 1. Brazilian s e d i m e n t a r y basins. 1 = T a k a t u ; 2 = A c r e ; 3 = A m a z o n a s ( i n t r a c r a t o n i c ) ; 4 = A m a z o n M o u t h ( M a r a j 6 ) ; 5 = B r a m g a n ~ a - - V i z e u (Pirabas); 6 = S~o L u i s ; 7 = P E nal'ha; 8 = Barreirinhas; 9 = CearA; 1 0 = Potiguar; 11 = Pernambueo--Paral"ba; 1 2 = o t h e r i n l a n d basins o f northeast; 13 = Rio-do-PeJxe; 14 = A r a r i p e ; 15 = Jatob~; 1 6 = T u e a n o ; I 7 = R e c 6 n c a v o ; 18 = Sergipe--Alagoas; 19 = A l m a d a ; 2 0 = J e q u i t i n h o n h a ; 21 = E s p f r i t o S a n t o ; 22 = C a m p o s ; 23 = Santos; 24 = Pelotas; 2 5 = ParanA; 26 = S~o Francisco. A = Sobra] L i n e a m e n t ; B = Parafba L i n e a m e n t ; C = P e r n a m b u c o l , i n e a m e n t .
The three main Brazilian intracratonic basins with thick Paleozoic and thinner Mesozoic deposits, though sometimes occupying rather great extensions, are the Amazonas, Parnafba (or Maranh~o) and Paran~ basins. Besides these three basins one has to consider, only for the Cretaceous, a fourth one called S~o Francisco and a fifth one, called Acre, this latter located in the high Amazon River system and related to the Pastaza Basin in Peru. A Guyanan rift-valley (called Takatu), running east--west, reaches Brazil at its
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72 western tip, in the extreme north of the country. Most of the coastal basins are rift-valleys. Some of t h e m contain latest Jurassic deposits intimately related to the earliest Cretaceous ones. They are distinguished from the intracratonic basins by their intensively faulted nature, smaller areas but thicker deposits. The rift-valleys are closed basins limited by faults whose total slip may attain 2000 to 3000 m. These basins are shown in Fig. 1. A few of them are not rift-valleys; they are areas of sedimentation open towards the ocean with sediments dipping constantly oceanward. The Santos and Cear~i basins are entirely located on the continental shelf. North from the RecSncavo Basin stretches the Tucano rift-valley up to the S~o Francisco River and then, crossing this river, with an ENE trend, the Jatob~ rift-valley continues. These rifts and that of Takatu are the only ones n o t located in the coastal and continental shelf areas. The east--west Precambrian alignments, named Patos (or Paral~a) and Pernambuco, in the projected northeastern tip of the Brazilian territory, as well as the Sobral alignment north of these structures, are important tectonic features allowing a division of the coastal basins into sections, one of them from Pelotas to Sergipe--Alagoas, the second from Pernambuco--Parafba to Potiguar, and the last from Cear~ to Foz-do-Amazonas (Amazon Mouth). This structural framework was built by an Early Cretaceous pre-Aptian tectonism k n o w n as the Wealdenian Reactivation (Almeida, 1967). The tectonic movements were reduced after the Barremian, so that the Brazilian Early Cretaceous is clearly distinguished from the Brazilian Late Cretaceous. The Early Cretaceous sediments of the coastal rift-valleys of the northeast are commonly tilted towards the continent along fault blocks, while the Late Cretaceous ones dip constantly towards the ocean. All pre-Aptian Cretaceous sediments (including the latest Jurassic) are non-marine in origin and even the Aptian bears evidence of restricted seas. The eastern Brazilian coastal and offshore basins have similar Paleozoic stratigraphic columns which, when complete, are of a threefold nature: (1) lower clastic non-marine section, (2) middle evaporitic section, and (3) upper carbonatic and clastic marine section with non-marine regressive lithosomes only in the Early Cenozoic (Ponte and Asmus, 1975). The first section is pre-Aptian in age, the middle one Aptian and the last is postAptian. THE LATEST JURASSIC--EARLIEST CRETACEOUS Occurrences
The lower clastic non-marine section is made up of one sequence in the sense of Sloss (1963), t h a t is, one b o d y of rocks limited above and below by a widespread u n c o n f o r m i t y ; this does n o t mean to say t h a t local unconformities m a y n o t be present. This sequence, however, is subjected to further subdivisions into an older blanket-like unit covered by a younger b o d y of lenti-
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74 cular lithologies. The older one is made up of sediments deposited under conditions of an intense faulting tectonism. The classical standard reference for this latest Jurassic--Early Cretaceous is found in the RecSncavo Basin (Fig. 2). The blanket-like unit belongs to the intracratonic or pre-rift cycle (Sampaio and Northfleet, 1973) and is characterized b y a great continuity of its lithologic bodies with few horizontal variations. It is best developed in the Rec6ncavo and Sergipe--Alagoas basins, occurring also in the Tucano and as scattered remnants in the small basins of the inland of the northeast (Jatob~, Mirandiba, Sgo Jos~ do Belmonte, Araripe). This blanket unit disappears south of the Almada Basin. Lithologically, it is again subdivided into two bodies (Table I). The complex b o d y of sediments that covers the blanket unit, was laid d o w n under strong fault tectonic conditions, so thick wedges of syntectonic conglomerates developed along the major trends of the downfaulted blocks. These sediments vary in thickness from a few hundred to more than 5000 m and show considerable facies changes. Many local unconformities occur due to the syntectonic nature of the sediments but, as a whole, they m a y be considered a continuation of the blanket unit without a major break in the process of sedimentation. This b o d y of lithosomes from the Alianqa and S~o Sebastigo to the Salvador Formation is composed of essentially Conformable lithologies separated from the rocks below and above b y regional unconformities. It is known as the Bahia Supergroup, with thicknesses of more than 6500 m; its thickness increases gradually southward from Jatob~ to Rec6ncavo while its overall coarseness decreases gradually southward. The development of the Sergipe--Alagoas Basin during the same geological time is closely similar to that of the Rec6ncavo. In the Almada Basin, south of RecSncavo, only the Sergi Formation of latest Jurassic age is present, and south of this basin it is entirely absent. The Early Cretaceous units reach the Espirito Santo Basin (Ponte and Asmus, 1975), b u t south of it there is no equivalent to the Bahia Supergroup. The Espirito Santo to Santos basins were the site of intense magmatic activity. No equivalent beds are present in the Pelotas Basin. North of the Sergipe--Alagoas Basin little is known a b o u t possible sequences equivalent to the Bahia Supergroup. The Recife--Jo~o Pessoa Basin has subsided less than the basins to the north and the south, with a sedimentary fill of less than 2000 m (Souza, in Ponte and Asmus, 1975). It is uncertain whether or not an Early Cretaceous tectonism has affected this basin, its formative tectonism being of Turonian age. Early Cretaceous continental terrigenous sediments m a y be present in the offshore part of the Potiguar Basin, according to seismological evidence. Non-marine sedimentary sequences from offshore Cear~ Basin and from Barreirinhas and S~o Luis basins would eventually be time-equivalent of the Early Cretaceous part of the Bahia Supergroup. The Foz-do-Amazonas sedi-
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76 mentary record begins only in the Late Cretaceous. Several small "basins" are scattered in the inland of northeast Brazil on an area of predominantly Precambrian crystalline rocks. The largest and most famous one is the Araripe "basin" (Fig. 3). Its richly fossiliferous fish localities as well as its important gypsum beds are well known. It is unique among these small basins because it stands above the low-lying Precambrian area forming a 180 b y 50 km plateau generally limited by pronounced escarpments. This situation, as well as the presence of inselbergs south of the plateau, attest to a former larger extension. The Araripe Mesozoic sediments constitute two sequences separated by an u n c o n f o r m i t y ; the lower one is correlated to the latest Jurassic of the Bahia Supergroup, and the upper one is of Aptian--Albian age. The other "basins" of the northeast are preserved as downfaulted blocks limited by more elevated areas of Precambrian rocks. A latest Jurassic sequence is present in the small Mirandiba and Sgo Jos~ do Belmonte basins; no pre-Aptian Early Cretaceous sediments are present. The other small basins of the region contain deposits belonging to only one sequence equivalent in time to the Early Cretaceous units of the RecSncavo Basin; no beds equivalent to the latest Jurassic are present there. The principal "basins" are those of Rio
Paleogeography and paleoclimate of the latest Jurassic The evaporites of the Juru~ Mirim red beds from Acre suggest a desert passing westward to coastal environments and farther away, outside of Brazil, to the marine environments of the Andean geosyncline. The anhydrite and halite present in the basal part of the Alianqa Formation of the RecSncavo Basin point also to dry climates. The post-evaporitic latest Jurassic sediments in the RecSncavo and other rift-valleys are made up of clastics with sedimentary structures indicating
77 flood plains of meandering rivers with lakes and o x b o w stagnant waters. Primary red beds were formed in this environment; red argillaceous layers are frequent in the lower part, suggesting derivation from red lateritic clayey soils. The overbank and o x b o w lake facies retain evidence of argillaceous oxydizing conditions whereas reducing circumstances in the larger water bodies imprinted greenish hues on the sediments. Among the lacustrine deposits, limestone beds with concentrations of ostracod shells are found (Alian~a and equivalent formations). Red sandstone beds b e c o m e more and more frequent towards the top, suggesting deep erosion in the source areas, resulting in the denudation of the regolith and erosion of fresh rocks. These sandstones contain rock fragments and their crossbedding is of torrential type, with silicified conifer trunks along some of the foresets in such way as to suggest transport (Sergi and equivalent formations). Red hues are seen only in the matrix of the sandstones. The evidence suggests a change from meandering to braided channels. Latest Jurassic sediments of the rift-valley basins therefore provide evidence of change in climatic conditions from dry to humid with dry and wet seasons. The RecSncavo and Tucano basins formed part of a latest Jurassic fluvial basin which drained southward through rivers with headwaters in the Jatob~ or m a y b e even Araripe areas. The sediments of these areas, now separated from each other, were probably part of a single basin disrupted b y erosion. The thickness of the formations increases gradually from north to south; the coarseness of sandstones, on the other hand, increases from south to north. The greatest subsidence is found in the southern Rec5ncavo Basin in the supposed transport direction. This ancient fluvial basin was broken up b y the Wealdian tectonism (Petri, 1974); it extended apparently south to the Almada Basin. The Sergipe--Alagoas Late Jurassic deposits, though lithologically and paleontologically similar to those of the RecSncavo--Tucano--Jatob~ basins, probably belonged to one or more independent river systems. The formations n o w cover discrete areas separated by erosion according to some geologists. However, the possibility of original discrete areas resulting from separated river systems m a y be considered.
Paleogeography of the Early Cretaceous pre-Aptian The Paran~ Basin was the scene of enormous basaltic and alkaline volcanic activity. A few sandstone lenses occur between the first flows and a rather thin eolian sandstone may cover the last flow. A great number of diabase dykes chronologically correlated to the flows cut through Precambrian rocks b e y o n d the border of the Paran~ Basin. The coastal basins of Santos, Campos and Espfrito Santo were also affected b y this volcanism. Contemporaneous volcanism reached the Parnafba Basin, though on a smaller scale. No sedimentary record is k n o w n in this basin as well as in other intracratonic basins.
78 As tension fractures were developing in the south, a strong fault tectonism was developing in the northeast. The Late Jurassic RecSncavo--Tucano-Jatob~ Valley persisted during the Early Cretaceous but with a change in the disposition of the headwaters which no longer passed through the Mirandiba, S~o Jos~ do Belmonte and Araripe areas, but through those of Rio-doPeixe and Pau
79 TABLE II Brazilian stratotypes, probable age equivalents and characteristic fossils Stage (Brazil)
Stage (international)
Fossils
Alagoas
Late Aptian
Jiqui~
Late Barremian to Early Aptian
Buracica
Early Barremian
Aratu
Late Valanginian to Hauterivian
Rio-da-Serra
Early Valanginian
Dora Jo~o
Purbeckian
sporomorphs: Inapertinopollenites and other forms belonging to ClassopoUis, Gnetales, Araucariacites, Tricolpites, Triletes and Cicatricosiposites; Exesipollenites tumulus (in Campos Basin) point to Late Aptian ostracods: Petrobrasia diversicostata KrSmmelbein, Candona centroimpressa Weber ostracods: Coriscina eoriacea KrSmmelbein, Cypridea (Sebastianites) fida minor Moura ostracods: Paracypridea obovata obovata (Swain), Cypridea ( Morinina? ) bibullata bibullata Wisher ostracods, in following zones, from base to top: Cypridea kegeli Wisher; Theriosynecum varietuberatum Grekoff and KrSmmelbein; Cypridea (Morinoides ) andeiensis KrSmmelbein; Paracypridea brasiliensis KrSmmelbein ostracod: Bisulcocypris pricei Pinto and Sanguinetti
North of the Sergipe--Alagoas Basin, pre-Aptian Cretaceous sediments are of minor importance. T h e y m a y be present on the continental shelf of the Potiguar Basin, filling downfaulted blocks evidenced by seismic reflection lines (Ponte and Asmus, 1975). Brazilian latest Jurassic--earliest Cretaceous chronostratigraphy The exact position of these strata in the world standard column is not yet known due to their non-marine nature, with sediments laid down in restricted seas only at the top. As a result of this difficulty, Brazilian Oil Company (Petrobr~s) geologists advocated a Brazilian time-stratigraphic column with its own stratotypes, based on non-marine ostracod zones and, for the Alagoas Stage, on sporomorphs. The proposed stages and their probable equivalents are shown in Table II (after data from Schaller, 1969; and Viana et al., 1971).
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81 APTIAN AND POST-APTIAN CONTINENTAL DEPOSITS A generalized uplift of the Brazilian territory after the latest Jurassic-earliest Cretaceous sequences resulted in a widespread u n c o n f o r m i t y in the beginning of the Aptian. This u n c o n f o r m i t y separates, in the RecSncavo and Tucano basins, the Bahia Supergroup (Late Jurassic to pre-Aptian Cretaceous) from the Marizal Formation laid d o w n during Alagoas time. The Marizal has a varied lithology from conglomerates to shales and even rare limestone beds. The predominant lithology is a poorly sorted clayey sandstone, c o m m o n l y cross-bedded with cut-and-fill structures. The conglomerates contain boulders of varied lithologies. The thickness of the Marizal Formation shows considerable local variations. The lithological characteristics, distribution and irregular thickness suggest a close association with the uplifted fault blocks with local sources formed b y fault scarps. The transport was torrential or by way of debris flows near the slopes and by laminar flow on the plains away from these slopes. Although no evaporites are known, it is believed that the climate was dry and internal drainage might have occurred at least during part of the time of deposition of the formation. The nature of the Marizal and the geographical proximity to contemporaneous evaporitic deposits of Sergipe--Alagoas and Jequitinhonha favor this interpretation. After the deposition of the Marizal Formation there was a consolidation of the RecSncavo--Jatob~ rift-valley to the Brazilian craton. This formation therefore represents a kind of molasse deposit in a rift-valley basin. In the southern and northeastern coastal basins there are formations correlated to the Marizal which contain evaporites among other lithologies. These sediments were formed initially in lagoonal environments passing later into restricted marine conditions. No such deposits are k n o w n in the northern coastal basins. After a short regressive episode, a new transgression caused the deposition of a Late Aptian--Santonian sequence, with a short regressive fluctuation in the Cenomanian in the northeastern and eastern basins. This sequence is well represented in the basins of Amazonas, S~o Luis, Barreirinhas, P a r n a ~ a (Table III), Araripe and S~o Francisco. A region of maximum subsidence in this time developed in the Barreirinhas coastal basin of the State of Maranh~o, which could then constitute the site of convergence of different fluvial systems. The first sediments of the Albian--Santonian sequence of this basin contains fanglomerates accumulated at the f o o t o f slopes of rising fault blocks. They grade laterally into floodplain and lacustrine deposits. No marine sediments are k n o w n among these basal deposits, which are characterized by abrupt lateral facies changes. Fluvial sediments exhibit high-energy distributary channels and overbank facies, grading northward on the present continental shelf into deltaic plain facies with low-energy distributmT channels. The rivers were of a braidedchannel type, frequently covered b y fine clastics of the floodplain facies and b y swamp deposits in which lignite developed.
82 The prodelta sediments are 2000 to 3000 m thick and the non-marine sediments up to 5000 m. The accumulation of such thicknesses in such a short time could n o t be accomplished unless at least a major river was actively transporting material. This delta was possibly a composite one, the product of several rivers converging into an area of high subsidence. A transgressive Albian phase followed by a regressive Cenomanian--Santonian phase was superimposed on this constructive delta, causing a transgressive--regressive cycle well displayed in the Parnafba intracratonic basin with the Grajau, Cod5 and Itapecuru Formations (Aguiar, 1971). Similar beds occur in the S~o Luis coastal basin. The correlation of the formations in the S~o Francisco Basin is still controversial. This basin is very much dissected today, so that the Cretaceous crops o u t in isolated spots distributed in a huge area of 1000 km in a N--S direction by 500 km in the E--W direction. The sediments belong to t w o formations, the Areado (the older) and the Mata
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Similar to the S~o Lufs Basin, the Albian to Cenomanian sediments of the Potiguar Basin were formed in non-marine environments. The latest Cretaceous sediments of the coastal basins, except that of the Amazon Mouth, are marine. Table IV presents the characteristics of the deposits in this latter basin. Another area of non-marine Late Cretaceous sedimentation is located in the Acre Basin. Here a continuous conformable sequence spans the Cenomanian--Maastrichtian time. These sediments form a transgressive--regressive cycle b u t the sea never reached the Acre Basin, being restricted more to westward in Peru. During the Late Cretaceous, the so-called Alto Paranaiba uplift (Hasui et al., 1975) separated t w o areas of sedimentation: the S~o Francisco Basin and the Alto Paran~ sub-basin. The intensification of the uplift in this area caused the outburst of several volcanoes. In the S~o Francisco Basin, the alkaline and ultrabasic lavas and the volcanic tufts grade distally into green cross-bedded cineretic sandstones and conglomerates which pass distally into clayey sandstones with montmorillonite i n the matrix (related to the volcanic source) and subordinated conglomerates (Mata
This history of the Cretaceous in Brazil is one of transgressive and regressive fluctuations increasing from the Early Cretaceous to a maximum in the Albian, at least in the northeast, and from then, decreasing in intensity. No marine earliest Cretaceous is k n o w n in Brazil, and since the Albian, the marine occurrences are more and more displaced towards the present ocean. This trend lasted well into the Cenozoic until the Oligocene. The climates during the Cretaceous were probably always tropical. Dry climates were present during the latest Jurassic. The earliest Cretaceous to Barremian witnessed more humid climates at least in the northeast, b u t dry climates returned during the Aptian and evaporites were widespread in the
85 c o a s t a l basins f r o m s o u t h t o t h e n o r t h e a s t . E x t r e m e l y d r y c l i m a t e s p r o b a b l y n e v e r o c c u r r e d again. N o p o s t - A l b i a n e v a p o r i t e s are k n o w n , even t h o u g h L a t e C r e t a c e o u s a n d T e r t i a r y regressive p h a s e s w o u l d set p r o p e r c o n d i t i o n s f o r t h e d e v e l o p m e n t o f t h e s e c h e m i c a l s e d i m e n t s , h a d a suitable c l i m a t e existed. REFERENCES Aguiar, G.A., 1971. Revis~o geol6gica da Bacia Paleoz6ica do Maranh~o. Soc. Bras. Geol., An. X X V Congr., S~o Paulo, SP, 3: 113--122. Almeida, F.F.M., 1967. Origem e evolu~o da plataforma brasileira. Dep. Nacl. Prod. Min., Div. Geol. Min., Bol., 241:36 pp. Braun, O.P.G., 1966. Estratigrafia dos sedimentos da parte interior da regi~o nordeste do Brasil. Dep. Nacl. Prod. Min., Div. Geol. Min., Bol., 236:75 pp. Braun, O.P.G., 1970. A Formaq~o Areado e a Formaq~o Serra Negra. Rev. Escola Minas Ouro Preto, 28 (3). G a m a Jr., E., 1970. Modelo geol6gico das bacias do Rec6ncavo e Tucano. Soc. Bras. Geol., An. X X I V Congr., Brasflia,DF: 191--200. Grossi Sad, J.H., Cardoso, R.N. and Costa, M.T., 1971. Formaq~es Cret~ceas e m Minas Gerais: urea revis~o. Rev. Brasil. Geoci~nc., 1 : 2--12. Hasui, Y., Sadowski, G.R., Suguio, K. and Fuck, G.F., 1975. The Phanerozoic tectonic evolution of the western Minas Gerais State. An. Acad. Brasil.Ci~nc., 47 : 431--438. Mabesoone, J.M. and Tinoco, I.M., 1971. Geologia da faixa sedimentar costeira Pernambuco--Paral'ba. Univ. Federal Pernambuco, Inst. Geoci~nc., Dep. Geol. Paleontol., resumo II Semin~rio Dep., 7 pp. (manuscript). Moura, J.A., 1972. Algumas esp~cies e subesp~cies de ostracodes da Bacia Rec6ncavo-Tucano. Bol. T~c. Petrobr~s, 15 : 245--263. Petri, S., 1974. Sequences and correlations of Brazilian Late Paleozoic and Mesozoic deposits. Soc. Bras. Geol., An. XXVIII Cong., Porto Alegre, RS, 2: 17--29. Ponte, F.C. and Asmus, H.E., 1975. The Brazilian marginal basins: current state of knowledge. An. Acad. Brasil.Ci~nc., 48 (Supl.): 215--240. Sampaio, A.V. and Northfleet, A., 1973. Estratigrafia e correlaq~o das bacias sedimentares brasileiras.Soc. Bras. Geol., An. X X V I I Congr., Aracaju, SE, 3: 189--206. Schaller, H., 1969. Revis~o estratigr~ificada bacia Sergipe--Alagoas, Bol. T~c. Petrobr~s,
12: 21--86. Sloss, L.L., 1963. Sequences in the cratonic interior of North America. Geol. Soc. Am. Bull., 74: 93--104. Tinoco, I.M. and Mabesoone, J.M., 1975. Observaq~es paleoecol6gicas sobre as bacias mesoz6icas de Iguatu, Rio do Peixe e intermediarias. Bol. Nficleo Nordeste Soc. Brasil. Geol., 5-Atas VII Simp. Geol. Nordeste, Fortaleza, pp. 95--107. Viana, C.F., Gama Jr., E.G., Sim~es, I.A., Moura, J.A., Fonseca, J.R. and Alves, R.J., 1971. Revis~o estratigr~fica da Bacia Rec6ncavo--Tucano. Bol. T4c. Petrobr~s, 14: 152--192. [Manuscript received September 4, 1980]