Revista Brasileira de Geociências 16(3) : 311-319, setembro de 1986

LOWER CRETACEOUS SEDIMENTARY SEOUENCES lN THE BASIN, NORTHEASTERN : A REVISION

MARIA AUGUSTA MARTINS DA SILVA'

ABSTRACT The Araripe Basin in northeastern Brazil contain a 700 m-thick succession of Jurassíc-Cretaceous strata. The 200 m-thíck Lower Cretaceous is widely known for lts flsh-bearing concretíons and gypsum deposits. Detailed field studies and core analyses provided data for revision of the Lower Cretaceous stratigraphy in the Araripe Basin. A regional disconfonnity within the Lower Cretaceous succession is described here for the flrst time. This surface divides the Aptian-Albian succession into two parts : I . a lower sequence of black shale, laminated carbonate, algal mat carbonates, and evaporites in ascending stratlgraphic ord er; and 2. an overlyíng sequence contaíning concretionary shale, limestone , and sandstone. These two stratigrapWc divisions are herein defmed as the Ararípína Formation (new name) and the Santana Formation (revísed), respectively . The expressíon of the disconformity varies across the basin. ln the southwest it is marked by caves fonned in the gypsum and a karstic top ograph y. Toward s the northeast, a 50 cm-thick layer of laminar calcareous and siliceous calcrete crust marks the disconformity surface.

RESUMO A Bacia do Araripe no norde ste do Brasil apresenta uma sucessão sedimentar de idade jurássico-cretáci ca de aproximadamente 700 m de espessura. As rochas do Cretá ceo Inferior, com cerca de 200 m de espessura, são bem conhecidas pelos depó sitos de gipsita e concreções contendo peixes. Este artigo apresenta uma revisão da estratigrafia do Cretáceo Inferior com base em trabalho de campo e análise de testemunhos. Verificou-se a existência de uma discordância regional truncando as rochas do Cretáceo Inferior. Esta superfície erosiva divide o pacote Aptiano-Albiano em duas partes: 1. uma seqüência inferior de folhelho s pretos, carbonatos laminado s e carbonatos com esteiras algálicas, e evaporitos no topo da seqüência ; e 2. uma seqüência superior contendo folhelho rico em concreções, calcário e arenito intercalado. Essas duas seqüências sedimentares são aqui formalmente definidas e nomeadas de, respectivamente, Formação Araripina (nome novo) e Formação Santana (revisada). A superfície de discordância se apresenta basicamente de duas formas distintas. Na parte sudoeste da bacia, ela aparece como cavernas e depressões na rocha formada por gipsita definindo uma paleotopo­ grafia kárstica. Na parte nordeste, ela ocorre como uma superfície de cerca de 50 cm de espessura formada por crostas laminares de calcário e sílica (calcrete).

INTRODUCTlON The Araripe Basin is located in northeastern Brazil about 400 km northwest of (Fig, I) . This Mesozoic basin contains a sequence of sedimentary rocks surrounded and underlain by rocks of the Brazilian Shield (Fig. 2). Late Cretaceous-Early Tertiary uplift formed a conspicuous plateau of Mesozoic sedimentary rocks, the Araripe Plateau elevated 600-900 m above sea levei and extending 200 km in an eastwest direction and 70 km (maximurn value) north to south. The Araripe Basin fírst formed in the Jurassic associated with rifting during initial breakup of South Arnerica and Africa. This rifting produoed a series of graben-líke basins along and west of the present Brasilian Margin which were initially filled with Jurassic fluvial and lacustrine deposits. Widening, inundation and later evaporation of this basin in the Early Figure 1 - Location of the Araripe Plateau in the north­ Cretaoeous resulted in deposition of lacustrine evaporites eastern interior ofBrazil. AA' Tine represents section shown and interbedded shales and limestones. Mesozoic sedimenta­ in figure 6 (Modified from DNPM 1974a) tion ended in the Albian and is marked by a fluvial sandstone (Exu Formation) which now cap the Araripe Plateau (Fig. 2). Much controversy surrounds the stratigraphy of the The Lower Cretaceous formations, that is the Santana Araripe Basin; the systerns proposed in the past have been and Araripina Formations, respectively, the subjects of mainly based on paleontological studies of fish and ostracod this work, are well known for the abundant and well assemblages (Figs. 3 and 4). Some additional stratigraphic preserved fossil flsh found in concretions in shale, and for information resulted from field work and sulfide pros­ gypsum deposits (Oliveira et ai. 1979, Scheid et al. 1978, pecting. The formations and members defíned for the Moraes et al: 1975, Munis 1971, Mabesoone 1971, Silva Cretaoeous sucoession have been constantly modified Santos & Valença 1968, Braun 1966, Beurlen 1963, Jordan (Figs. 3 and 4) and a stable and comprehensive system of 1923, Small 1913) . nomenclature based on carefully defined stratigraphic units

• Laboratórcvde Geologia Marinha (Lagemar), Departamento de Geologia, Universidade Federal Fluminense, Av. Bento Maria da Costa, 115-A, CEP 24260, Charitas, Niterói, RJ, Brasil. 312 Revista Brasileira de Geociências, Volume 16, 1986 is necessary before the paleoenvironrnents and evolution and the upper limestone member together in the Santana of lhe Araripe Basin can be interpreted, The purpose of this Formation (Fig. 3). paper is lo clarify lhe slraligraphy of lhe Crelaceous rocks Moraes et al (1963), based on photogeologic interpreta­ of lhe Araripe Basi n. The work is based on field observa­ tíon , divided the Santana Formation into two informal tions carried on during July, 1981, and on the study of members: I. a lower member composed of shale, laminated cores drilled by the brazilian Departamento Nacional da limestone, and gypsum; and 2. an upper member composed Produção Mineral (DNPM) and by the Superintendência de of concretionary marl, clay, and limestone. Desenvolvimento do Nordeste (Sudene). Interpretation Braun (1966) redefined the Santana Formation as a of the depositional environments and evoiution of the sequence of siltites, marls, limestones, and dark shale with Araripe Basin was presented by Silva(198 3) and will not be intercalated layers of gypsum unconformably bounded by here discussed. the two fluvial deposits (Figs. 3 and 4). Braun (op. cil.) did not recognize members and disagreed with Beurlen's (1963) PREV IOUS WORK The first published account on the subdivision of the sequence into two formations, and dated straligraphy of the Araripe Basin was by Small (1913), who the sedimentary rocks of the Araripe Basin on the basis named a sequence of interbedded limestone and marl of rich fossil biotas. He correlated the fresh-water ostracods containing two fluvial deposits the San!'Ana Limestones. of the Sanlana Formation in the Araripe region with those At present, paleontologists and stratigraphers who have of Aptian age in the coastal basins of Brazil described by worked on that area disagree on the definition of the Krommelbein (1965), Krommelbein & Wenger (1966), and Santana Formation (Fig. 3), as follows: Viana (1966), and especially with the assemblage from the Beurlen (1962) defined the Sanlana Formation as a well-studied Sergipe Basin. series of bituminous shales, laminated limestones, gypsite, ln 1968, Silva Santos & Valença conducted a clayey siltites, and marls with calcareous concretions paleontologic and geologic survey in the Araripe Basin in divided into three informal members: I. a lower member conneclion with the study of fossíl-físh assemblage of the consisting of interbedded shale and laminated limestone; Santana Formation. They disagreed with both Braun's 2. a middle member represented by gypsite; and 3. an (1966) and Beurien's (1962) stratigraphic nomenclature upper member including marl, siltite, and limestone (Fig. 3). of the Santana Formation. Instead, they adopted the ln 1963, Beurlen removed the lower limestone member stratigraphic terminoiogy of Moraes et ai. (1963) from lhe Santana Formation and described it as the Crato (Fig. 3) based on the following arguments: I. greal Formation. He then grouped the rníddle gypsite member lithologic and paleontologic sirnilarity between the Crato

Alb ion (sondstonel

Apt ion/Albion (shoíe.corborote, evoporite l Jurossic ( sondstone.shole)

Figure 2 - Geologic map oflhe A raripe Basin showing locations of cores studied in this work (From DNPM 1974a and b) RevistaBrasileira de Geocíénetas, Volume 16. 1986 313

S :1 ~LL B[URLL'J BEURLEN BRl\Uíl :IO RAES & OT HERS BEURLEfl 10RÂES & JT:!Ei"{S L!.iA 191; 1962 1953 196G 1963 197J 1976 1979

UP PER EXIl EXIl E'\U ARA J AR A EXU EXU EX U FOR ~ 'lA T FORIAT ION FORIA TIO:, e , " 0 0 ,"" 0 FOR1ATla !1 FOR: IATION FOR:1ATI0'1 ImI rOR 1ATIDrl

UPPER L1IES z: ARG ILO-S IL - ~ o 2i RO'IUALJO g o TOI IE :IE: 18E R A1lTAflA ' IE'IGER TIC & EVA?:l ;:: UPPER ~ ~ ~ o, Forn ATlOiI - - - ~ :;< RiTlC FAC IES ~ SANT AT IA :;< ::; YPSUi l ~ :'lE:IBER ~ :;< ~ o " :IE1BE R ~ ~ IPUBI '"o ~ Ci. o o o o ~ ~ o u; u, 'IE:18ER '"u, '"u, u LL1 ESlJ'IE u, LOOlER LLlES SANT Ai IA CRATO -er TO NE 'IEI8E R ~ ~ ~ FOR:1AT lm; CRATO < ,18, ~ c; ~ :IE:18ER C ARBO~ ~AT IC ~

~ 2: u CAR IRI CAR IRJ fAC A,ATU -~'" BASAL CAR lRI CAR IRI TAC1RATU CAR IRI Õ FO R 1 A T I Q ~! i :OR" 1A T I~~1 N FOR ' ~AT [QI! FOR IAT IDrI FOR'J4 TI0:1 FOR'IAT lml FO R:1AT IO N o CO:IGJ.,1 JERATI: w u u '"w

Figure 3 - Table of stratigraphic names used by previous workers for the Lower Cretaceous sedimentary rocks of the Araripe Basin

and Santana Formations which suggests that they should be facies considered equivalent to th e Crato Member and th e grouped together in one formation; 2. the gypsum layer lower part of th e Member ; 2, an argillo-siltic and represent s a normal part of a carbonate to evaporite evaporitic facies considered to be equivalent to the upper succession in a normal precipitation af salts from a brine, part of the Ipubi and the Romualdo memb ers, and lithogeneticaUy should be grouped with the carbonates Lima (19 79) pointed out the need to reconsider th e at the top of the lower member; and 3, the continuity subdivisions of the Santana Format íon as proposed by and thickness of th e gypsum layer makes it an important Beurl en (19 71), Lima believed that only the Crato Member st ratigraphic horizon which allows easy division of the was c1early distinguishable and should be reta ined; he Santana Formation into two members, Based on th e fossil stated that th e Ipubi and Romualdo Members should either fish assembly in the calcareous concretions of the upper be abandoned or redefined because " I. th ey represent a member of the Santana Fonnation and th eir correlation continuous lithologic sequence and do not represent with European and African species, Silva Santos & Valença distin ct phases in th e depa sition of the Santana Formation ; (1968) assigned a probable Aptian age to th e Santana 2. they show complex contac ts and great faciologic varia­ Formation . tion" (Fig, 3), Based upon biostratigraphic considerations Beurlen (19 71) reconsidered his previous works (1962, and field work, Lima (1979) defined th e Santana Forma­ 1963) abandoning the name Crato Formation and redefining t íon as a cyclic marine-nonma rine sequence of upw ard th e whole sequence as th e Santana Formation (Fig. 3), fining sandsto ne, shale, dark shale, and limestone, which However, he did not follow lhe divisions of Moraes in tum is overlain by ao upward-coarseningshale, sandstone, et ai, (1963) ar Silva Santos & Valença (1968). Based and siltite facies sequence to th e top of the formation . on his 1962 work, Beurlen (1971) divided th e Santana He considered the gypsum to be a lenti cular bod y in th e Formation into three new fo rmal members and argued argillite and siltite layers (Fig. 4), that each represented a disti nct phase of sedimen tation During field work, the aut hor observed that the strat í• during Santana deposition , in ascending stratigraphic order: graphy of the basin as defined by Moraes et al. (1963) on 1. the lower Crato Member characterized by laminated the basis of photogeology helped to identify the sedimentary limestone and siltite ; 2, th e middle Ipubi Member comprised sequences. However, the erosional unconformity truncating ar gypsite, Iimestone, and concretionary marl; and 3. th e th ese sequences prec1uded them from being defined as upp er Romualdo Member containing siltite and argillite, members of th e Santa na Formatio n (as proposed by Mora es According to Beurlen (op, cit.], th e Santana Formation et ai, 1963). As it will be shown below there are two was conformable between the two adjacent fluvial sand­ defined for mations limited by an unconform íty. stone layers. ln the 1970's, the Araripe Basin was intensely prospected PRESENT WORK The figure 5 defines th e stra tigraphic for gypsum, sulfides, and for fossil-fish-bearing concretion sequences for th e Araripe Basin based on the present localities in arder to cont rol their commercial exploration study, Cretace ous rock-stratígraphíc units are her ein (Moraes et al. 1975, Moraes et al: 1976, Scheid et al: 1978, formall y propoded, These are th e Arariplna Fo rmation and Oliveira et al. 1979), These warkers generally followed th e Santana Formatio n (revised) separated by the regional Beurlen's (1971) stra tigraphic nom enclature, but further unconformity. The Jurassic and A1bian nomenc1ature adopted a lithofacies division as follow s: 1. a carbonate shown (Fig, 5) is the most widely accepted in the Brazilian 314 R evista Brasileira de Geoctênctas. Volume 16. 1986

A08 L11 hol. Mbr. Form. ~ EVAPORITE L2J 5AND5TONE A08 L11hol. FmI. MARL 5HALE ~ .----- Z G3 EJ----- c( Q. '"Q. '::> ai :::> X ..J I&J ~ CONCRETlON5 ~ CARBONATE c( I ~ '::> X ai I&J . ~ ..J ~. A08 Lilhol. Focie& Form. C/) c( ::> ,, '/'oe O ai 'i/ '::> I&J o ..J X (.) .., c( 'ii: 'o/IK I&J E.-_-_-_-::: o c( i,':'. Lilhol Form . ~ ::J Z Z E c( f-':- - - - - lO I,'.':"':;,:··i:::·:",·.'.·:: I&J E-:.-_-_-_-_ o ~ " ~- - - - - ~ li: I- >.8 c( a: c( ",o fi>- ':-';:- ':-õ- (.) I- z m--....L~ z z ------z .. :...... ;.:,.:...... -. ~ c( 8======>.> \::;::'i·:.:-,~:: :'::: :.~:::~:;'; c( ----- a.. :, C/) oW ~ c( c( :õ ~ ~;i L-- ,\\\\\\\ ~ '- ~\\\W Q. Ü Z S~~.:== z I- : ,_:,;,~, 'c. c( ~;',;'::i'."'''''''.".::-:,' :' c( a.. z o '\: I o c( Õ '" C/) }';;·;·:·::i ~:i ;. ::: t:).·\ ;: :: :·.: : ~ c( o C/) I- ..c f-:' ::: ~ o Z - - - 0 a.. ------c: c( o ·:J/+y:.:::,)j ~F#:; c( ------Mabesoone and o C/) Tinoco I973 z ------=---- :------~ ·;7-;-:;'-;;7:;-;'[ c( :------I------:I: ::":"'::::<;':'::':::.::.::;:' -(l) a.. ..,>. ..J a: ~ c( c: I&J Lima I979 I&J ..J o > 2 C/) a: cn C/) O c( o C/) I&J c( c( Iii:..----- C/) :..:-- --- C\- ~ a: ------c( 50 ., ..,::> o ..~ oti 21 Z I&J c( 100 .. z =~=~=~=~~ :J -~ E------~-.:-.:~~:.. c( I50 Moraes et aI - - -- 1976 Brau n 1966

Figure 4 - Columnar sections iIlustrating /ighology and stratigraphic nomes used by previous workers in the AraripeBasin literature, and is adopled here. The Aplian sedimenlary An erosional surface was observed on top ofthe evaporile rocks in questíon lie unconfonnably belween Ihese Iwo layer, as evidenced by dissolution features resembling fluvial deposils. The Aplian sequence of black shale aI lhe karsl lopography, a hard calcareous and siliceous-cemenled base passing upwards lo límestone, Ihen algal laminaled surface (calerele) and a conglomerale layer presenl aI shale, and on lop , an evaporile layer is herein defined as differenl localilies. This unconformity could be Iraced lhe Araripina Fonnation . This sequence corresponds wilh regionally in outcrop and quarries and fonn s a key marker lhe Crato Member and lhe lower parI of lhe Ipubi Member horizon which divides lhe sedimenlary sequence inlo lhe of Beurlen (1971). The upper unil of lhe Aptian sequence Iwo distinct formalions described above (Fig. 5). is represenled by alternating layers of concrelionary shale and limeslone with inlertonguing sandslone and is herein EVIDENCE FDR UNCONFORMITY The expressiono f redefined as lhe Sanlana Fonnation. This sequence lhe dísconforrnity surface (Dunbar & Roger 1957, p. 119) corresponds with lhe upper parI of lhe Ipubi Member and varies across lhe basin (Fig. 6).To lhe south, lhe erosion lhe Romualdo Member ofBeurlen (op. cit.). surface is a paleokarsl landscape whereas lo lhe northeasl, R evista Brasileira de Geoci éncias, Volume 16, 1986 315

it is a calcrete layer. At the extreme southwest of the area, as pipes connecting lhe overlying sedimentary rocks with it is an erosional surface separating Cretaceous rocks from lhe paleokarstic surface are not presen!. Consequent1 y, underlying Paleozoic rocks. caves and sinks formed in the gypsum are inferred to have resulted from subaerial dissolution. ln the northeast part of the basin, around Crato and Missão Velha, this paleokarst surface dísappears and is L1THOlOGV FORMATION GROUP replaced by a calcrete layer (Fig. 6), probably due to BARREI , variations in the moisture distribution ln the region (Silva CENOZOIC ":::: :: :: ::: RAS 1983). This layer is best displayed at IBACIP Quarry as 20 cm-thick caicareous and siliceous laminar crusts on top : : :: : :::: : ::: of the algal laminated shale (photo IB). Chert nodules, drusy caleite, and slight brecciation were observed along this surface. The results of petrographic work confirm the presence of calcrete-related featur es and vadose diagenesis (Silva 1983). Overlying the calcrete layer is a 50 cm-thíck layer of conglomerate (Photo IB). UJ o, , The calerete layer at IBACIP occurs as a protruding hard a: surface in the middle part of the exposure (photo IB); lhe -c beds above and below it are essentiaUy parallel. The a: recognition of such a surface as a disconfonnity can be

sw NE

conglomerate :~;..~::::~'.~~: :' I, • • , j I calcrete I II I II I

Not to Scete

A

Rancharia

~ SM~tÃNÃ _ "o " õ ------FORMATION ~~ ", - - - -Discontormity ------~- -- '- ARARIPINA FORMATION

.... o -, ------tij~T;~;\ -~ -- -- Jurassic 8-"~;;:'- -- __ •..ent - - - -_ Mlfu marl LJ sandst one 1;:=,"::'-, concretionary evaporite - shoie = ~ carbonate I" -_I algae-rich - stiale 1---1 shale 1:"'('/'1 Imetamorohic/SrOCKS

Figure 6 - Diagram il/ustrating the variable expression of the unconform ity surface between the Araripina and Santana Formations across the Araripe Basin. Location ofline AA' is shown in figure 1. The schematic (not to scale) drawing on the upper part of the figure il/ustrate the different deposits associated with this disconformity

The type seetio n is the Casa de Pedra Quarry where Petrographically, the limesta nes exhibit a variety af cores SE- 2, - 19, and - 22 are located (Fig. 8). The small compasitians and textures (see Silva1983 for more informa­ town of Trindade, the closest to Casa de Pedra, is cansidered tion). Predominantly they are micritic and dolomicritic, the type locality. ln Casa de Pedra , the formation attains ranging to pelmicrite and biomicrite . Diagenet ic imprint s a thickness of 70 m (Fig. 7). Core SE- 22 reaehed gnaisses and stylolites are abundant. and schists of the basement, and recovered organic-rich ln quarries, the evaparites farm white, tab ular layers af black shale at a position corr esponding to the base of the secondary gypsum exhibiting a variety of crystalline types form ation overlain by 40 m of carbonate. A layer of (alabaster, satin spar, selenite crystals, and ro sette s). algae-rich laminat ed shale overlies the carbonate and , in Petrographically, the evaporites are predominantly secondary tum, is overlain by a 30 rn-thick layer of gypsum and gypsum with some relict anhydrite. Diagenesis has anhyd rite. extensively modified these evaporites, but core SE-2 still The kerogen-rich shales recovered by these thr ee cores displays textures and varietie s of primary anhydrite and contain abundant ostracods, gastro pods, plant fragments, gypsum. The study af thi s core provides additiona l informa­ and algae; in places they are stro mato litic or micritic­ t íon for the facies interpretation and environrnental

-pelmicritic. Detrita l minerais, such as quartz, feldspar I reconstru ction af the basin duri ng the evaporitic stage and micas, and heavy minerais are very abundant in the shale. the results are sha wn in Silva (1983). Opaque minerais, mostly nodular or disseminated pyrit e specks are also abundant, The limestones are THE SANTANA FORMATION (REVISED) The San­ cream, light gray and pink in color, very fine grained and tan a Formation, as revised here, occurs continuously fassiliferou s (ostracods, gastropads, and algae). They throughout the basin as a conspicuous sequence of alter­ contain conspicuous, fine-scale, paraUel laminae, and nat ing layers of concretionary-calcareous shale, limestone, small sets of cross laminae (rippl e marks, sca ur and fill). and sandstone (photo 2). 1t is unconformably overlain by Revista Brasileira de Geociências, Volume 16, 1986 317

lhe Exu Sandstone (A1b ian) and unconformably overlies lhe Araripina Formalion. The Santana Formation locally resls uneonformably on algal larninated shale of lhe Arari­ pina Formation as in IBAC IP (Photo 2); iI may also overlie the gypsum layer as in Araripina, or it may rest direetly upon Paleozoie and Preeambrian roeks (as at Raneharia). Its average thickness is about 50 rn. This formation reflects conlinuous deposilion of 1 lo 2 m-thíck Iayers ofcaleareous shale and limestone. Towards lhe northeasl side of lhe basin, an inlertonguing Iayer of whíte, loosely cemenled sandslone occurs (Fig. 6). The shale presenls Iess organie content than those in lhe Araripina Formation, but is also rieh in oslracods and espeeially in calcareous concrelions in whieh abundanl remains of fish and reptiles are found. The carbonales are very fossiliferous mieriles and dolomicriles conlaining ostracods, gastropods, and plant remains.

A w SE· o2 E Photo IA - Dissolution cavity on the top of I ii .

5HALE '"2 ~ 2 UNCONFORMITY V>'" TOP

EVAPORITES

5E·19 2 ~ ...o . o§------:::;'" =~- "- a: ALGALSHALE ------o ... Photo IR - Calcareous and siliceous laminar crusts forming r- .-----...... SE·22 a calcrete layer, IRA CIP Quarry (f igure I sho ws location ) ALGAl ? ~ ------,7

_ __CARBONATE______S______='9é=:= _

LAM1NATED CARBON ATE '"2 Q. a: BCÃcit ... -...... '"a: _r ,: ~A LE ...... 5AND5TONE - '" ------~~ ~~ " ~ " , -, ..~. L .... ? ...... 400 M. ? BA5EMENT ... Pho to I C - Santana Formation resting unconformab/y Ull Figure 7 - Ty pe 'oÇetion of the Arar/p ina Formation: cores Paleozotclrrecambrian rocks. Rancharia Quarry (figure 1 SE - 2, SE-19 and SE - 22 drilled by Sudene in Casa de shows location]. SF =Santana Formation; N =No ncon­ Pedra Quarry, S WAraripe Plateau (Figure 2 shows location ) fo rmity; DR = Basement Rocks 318 Revista Brasileira de Geoct éncias, Volume 16, 1986

Photo 2 - Type section fo r the revised Santana Formation: IBACIP Quarry near Vila Caldas, northeast Araripe Plateau [figure 1 shows Iocation). Gypsum lay er has been removed by erosion; shales and limestones of the Araripina Formation appearin the basal section ofthe quarry. Unconformity marked by black Un e

, I·~~l\ ( I I I I \ I \ I I I 7°20' I,' I 1 , , I

Figure 8 - Location of the type section for the Araripina Formation. Market by crosses are the quarries in whicb the upper part of the Araripina Formation is seen. Arrow indicates the approximate Iocation of drillings SE-2, SE- /9 and SE-22 (Sudene), Araripina region (southwest Araripe Plateau}: Quarries Iocated on the Trindade-Ipubi road (figure 1 shows location). From Topographic Map, Quadrangle SB-24-Y-D-IV, 1:1,000,000 by the Figure 9 - Location of the type section for the revised Serviço Geográfico do Exercito (1969) Santana Formation: IBACIP Quarry near Vila Caldas, on the Barbalha-Jardim road, northeast Araripe Plateau (figure 1 shows Iocation). From Topographic Map, Crato Figure 9 shows the locatily here proposed for the Quadrangle SB-24-V-II, 1:/00,000 Serviço Geográfico neotype seetion of the revised Santana Formation, the do Exército (1969) IBACIP Quarry near the town of Barbalha in the north­ eastern parl of the basin, which preserves the most complete seetion of 'this formation. The IBACIP Quarry also shows the best example of the under!ying conglomerate layer assoeiated with lhe erosional surface. ln this quarry The reason for relaining this name is thal lhe name (photo 2), lhe upper sequence uneonforma bly rests on top Santana Formation has long been attaehed lo the fos­ of lhe shale and limestone of lhe Araripina Formation. The silíferous mar! and limestone of the Araripe Plateau (The evaporite layer is nol presenl here. Sant' Anna Limestone of Small 1913). R evista Brasileira de Geociências, Volume 16, 1986 319

CONCLUSIONS The Lower Cretaceous sedimentary Cretaeeous sequenee is placed in a revised Santana Forma­ sequenee of the Araripe Basin is divided into two forma­ tion. The revised Santana Formation Iies uneonformably tions bounded by unconformites: 1. the lower Araripina between the Exu Formation and the Araripina Formation. Fonnation (Aptian/A lbian), and 2. the upper Santana For­ The neoty pe seetion for the Santana Formatio n, the mation (revised). A newly deteeted regional unconfonnity IBACIP Quarry located near Vila Caldas, Barbalha, in separates them. the nort heastern part of the plateau best displays the The Araripina Fonnation Iies uneonfonnably on Jurassie uneonformity separating the two formati ons. strata or noneonfonnably overlies the Paleozoie and Laek of reeogoition of the disconformity separating Preeambrian basement roeks. This formation includes, in these two rock fonnations prevent ed their stratigraphie aseending order, blaek shale, laminated Iimestone and relationship from being cleary understood, and eonsequently dolostone, algal-larninated shale, and evaporites (gypsum­ the depositional history of these distinet sedimentary -anhydrite) . The type seetion for this formation is in sequences have been misinterpreted. The depositional Casa de Pedra, southwest of the plateau, near Araripina, history of the Cretaeeous sedimentary roeks in the Araripe a major town in that vieinity. Cores SE-2, SE- 19, and Basin is presented by Silva (1983). SE-22 drilled in Casa de Pedra represent the Araripina Formation. The upper part ofth e fonn ation whieh outerops Acknowledgements Financial support for this work in the region is seen at Ponta da Serra, São Severino, Alto was provided by the Conselho Nacional de Desenvolvi­ Bonito, and Lagoa de Dentro Quarries. The Araripina mento Científico e Tecnológico (CNPq) (proe. 402402/80) Formatio n is truncated by a regional disconfonnity whieh and by Dr. J. Sanders. 1 thank Drs. J. Sanders, L. Gambôa, has variable expression aeross the basin: a paleokarst R. Schweickert, L. Burekle, and J. Damuth for eriticaUy surface to the south and a calcrete Iayer to the north reviewing this text . Mrs. Gabriella M. Kerty and Ana Maria and easl. Alvarez provided teehnical assistanee, whieh was very mueh The upper alternating layers of eoneretionary-ealeareous appreeiated. 1 am grateful to Mrs. Neusa N. da Costa who shale, Iimestone, and intertonguing sandstone of the Lower typed the manuseripl.

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