Koutsoukos & Bengtson 1993

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TOWARDS AN INTEGRATED BIOSTRATIGRAPHYOF THE UPPER APTIAN-MAASTRICHTIANOF THE SERGIPE BASIN, BRAZIL

Eduardo A. M. KOUTSOUKOS (*) & Peter BENGTSON (**)

(*) Petrobnis - CENPES - DIVEX/SEBIPE, Cidade Universitliria,Quadra 7, Iiha do Fundao, 21949-900 Rio deJaneiro, RJ, Brazil.(**) Geologisch-Palaontologisches Insti tut der Universitat Heidelberg, Im Neuenheimer Feld 234, W-6900Heidelberg, Germany.

Docum. Lab. Geol. Lyon, nO 125, 1993, p. 241-262, 8 fig.

241



(*) Petrobnis - CENPES - DIVEX/SEBIPE, Cidade Universitaria, Quadra 7, Iiha do Fundao, 21949-900 Rio deJaneiro, RJ, Brazil.(**) Geologisch-Palaontologisches Insti tut der Universitat Heidelberg, 1m Neuenheimer Feld 234, W-6900Heidelberg, Germany.


241



(*) Petrobnis - CENPES - DIVEX/SEBIPE, Cidade Universitliria,Quadra 7, Iiha do Fundao, 21949-900 Rio deJaneiro, RJ, Brazil.(**) Geologisch-Palaontologisches Insti tut der Universitat Heidelberg, Im Neuenheimer Feld 234, W-6900Heidelberg, Germany.


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ResumeVers une biostratigraphie integree de I'Aptien superieur-Maastrichtien du bassin de Sergipe, BresilLes echantillons d' age Aptien superieuraMaastrichtien, collectes sur le terrain ou en subsurfacedans le bassin

de Sergipe du Nord-Est bresilien contiennent des associations abondantes et diversifiees de foraminif'eres, radiolaires etostracodes, representant des environnements allant de paralique (estran et lagon)abathyal inferieur. Les ammonites sontabondantes dans la serie carbonatee d'ageaConiacien, et permettant une subdivisionmacrobiostratigraphiquedetailleefacilement applicable sur le terrain. On presente un premier essai d'integration des zonations de foraminif'eres etd'ammonites pour le Cretace de Sergipe, en utilisant la methode d'intercalibration. Les zones de foraminif'eres etd'ammonites sont principalement des zones d'Oppel, dont les lirnites sont marquees, pour les foraminif'eres, par leurapparition ou disparition locale, et pour les ammonites, par leur premiereoccurrence locale. Des zones reposant sur desassociations de foraminif'eres benthiques, localement applicables, et plutOt contrOlees par le milieu, sont proposees pourI' Aptien sup6rieur. Pour I' intervalleAptien-Albien,la zonation integree est encore tresprovisoire. Un grandenombredecorrelations biostratigraphiques de premier ordre reste aetablir, en se basant sur l'echantillonnage integre de coupescontenant ala fois des microfaunes diagnostiques et des ammonites.MOTS-CLES : Aptien, Albien, Cenomien, Turonien, Coniacien, Santonien, Campanien, Maastrichtien, Cretace inferieur, Cretace superieur, biostratigraphie, methode d'intercalibration, methode d'integration totale, zone d'Oppel,paleoenvironnements, foraminiferes, ammonites, echinodermes, inocecames, bassinde Sergipe,Bresil,OceanAtlantiqueSud.

ResumenHacia una bioestratigrafia integradadel Aptiano superior-Maastrkhtiano de la Cuencade Sergipe,Brasll.Muestras de campo y de subsuelo, collectadas en capas del Aptiano superior alMaastrichtiano de la Cuencade

Sergipe en elNordestedeBrasil, contienen asociaciones ricas y diversificadas de foraminiferos, radiolarios y ostra.codos,que representan medios sedimentarios desde el ambiente panilico (llanura mareica y lagon) hastael batial inferior. Losammonites son abundantes en la secuencia mayormente carbonatada de edad Aptiano a Coniaciano, y forman la base deuna zonaci6n macrobioestratignifica detallada facilmente utilisable en el campo. Se propone un primer intento deintegraci6n de las zonaciones de foraminfferos y ammonites para el Cretaceo de Sergipe, utilizando el metodo deintercalibraci6n. Las zonas tanto de foraminfferos como de ammonites sonmayormente zonas de Oppel, cuyos lfmitesestan marcados, para los foraminfferos, por su primera0 ultima ocurrencia local, y para los ammonites, por sus primerasapariciones locales. Zonas de asociaci6n de foraminiferos bent6nicos, localmente aplicables y rolls biencontroladas porelmedio, estanpropuestaspara el Aptiano superior. Parael intervalo Aptiano-Albiano,la zonaci6n integrada estli todavfamuy provisional. Unnumero importante de correlaciones bioestratigraficas deprimer orden quedanpor serestablecidas,basandose sobre el muestro integrado de secciones que contengan a la vezmicrof6siles diagn6sticos y ammonites.PALABRASCLAVE : Aptiano, Albiano, Cenomaniano, Turoniano, Coniaciano, Santoniano, Campaniano, Maastrichtiano, Cretliceo inferior, Cretliceo superior, bioestratigraffa, metodo de intercalibraci6n, metodo de integraci6n total,zonas de Oppel, medios sedimentarios, foraminiferos, ammonites, equinoideos, inoceramideos, Cuenca de Sergipe,Brasil, Oceano Atlantico Sur.

AbstractTowards an integrated biostratigraphy of the upper Aptian-Maastrichtian of the Sergipe Basin, Brazil.Upper Aptian to Maastrichtian surface and subsurface samples from the Sergipe Basin in north-eastern Brazil

yield abundant anddiversified assemblages of foraminiferids, radiolarians andostracods, representing environments thatrange from paralic (tidal flat and lagoon) to lower bathyal settings. Ammonites are abundant in the Aptian toConiaciancarbonate-dominated sequence and form the basis for a detailed macrobiostratigraphical subdivision, which can easilybe applied in the field. A first attempt is made to integrate the foraminiferid and ammonite zonations for the SergipeCretaceous, using the intercalibrationmethod. The foraminiferal and ammonite zones are chieflyOppel zones, theboundaries of which are marked for foraminiferids by local first andIor last appearances and for ammonites by local firstappearances. Locallyapplicable assemblage zones, which aremoreenvironmentally controlled, are proposed forbenthicforaminiferids of the upper Aptian. For the Aptian-Albian interval the integrated biozonation is as yet highly provisional. A considerable amountof first-order biostratigraphical correlation is yet to be done, basedon integratedsamplingofsections that contain both diagnostic microfossils and ammonites.KEYWORDS: Aptian, Albian, Cenomanian, Turonian, Coniacian, Santonian, Campanian, Maastrichtian, LowerCretaceous, Upper Cretaceous, biostratigraphy, total-integration method, intercalibration method, Oppel zones, palaeoenvironrnents, Forarninifera, ammonites, echinoids, inocerarnids, Sergipe Basin, Brazil, South Atlantic Ocean.

242

ResumeVers une biostratigraphie integree de I'Aptien superieur-Maastrichtien du bassin de Sergipe, BresilLes echantillons d' age Aptien superieur IiMaastrichtien, collectes sur Ie terrain ou en subsurface dans Ie bassin

de Sergipe du Nord-Est bresilien contiennent des associations abondantes et diversifiees de foraminif'eres, radiolaires etostracodes, representant des environnements allant de paralique (estran et lagon) Iibathyal inferieur. Les ammonites sontabondantes dans la serie carbonateed'age IiConiacien, et permettant une subdivisionmacrobiostratigraphiquedetailleefacilement applicable sur Ie terrain. On presente un premier essai d'integration des zonations de foraminif'eres etd'ammonites pour Ie Cretace de Sergipe, en utilisant la methode d'intercalibration. Les zones de foraminif'eres etd'ammonites sont principalement des zones d'Oppel, dont les lirnites sont marquees, pour les foraminif'eres, par leurapparition ou disparition locale, et pour les ammonites, par leur premiereoccurrence locale. Des zones reposant sur desassociations de foraminif'eres benthiques, localement applicables, et plutOt contrOlees par Ie milieu, sont proposees pourI'Aptiensuperieur. Pour I'intervalleAptien-Albien,la zonation integree est encore tres provisoire. Un grandenombredecorrelations biostratigraphiques de premier ordre reste Ii etablir, en se basant sur l'echantillonnage integre de coupescontenant Ii la fois des microfaunes diagnostiques et des ammonites.MOTS-CLES : Aptien, Albien, Cenomien, Turonien, Coniacien, Santonien, Campanien, Maastrichtien, Cretace inferieur, Cretace superieur, biostratigraphie, methode d'intercalibration, methode d'integration totale, zone d'Oppel,paleoenvironnements, foraminiferes, ammonites, echinodermes, inocecames, bassinde Sergipe,Bresil,OceanAtlantiqueSud.

ResumenHacia una bioestratigrafia integradadel Aptiano superior-Maastrkhtiano de la Cuencade Sergipe,Brasil.Muestras de campo y de subsuelo, collectadas en capas del Aptiano superior alMaastrichtiano de la Cuencade

Sergipe en elNordestedeBrasil, contienen asociaciones ricas y diversificadas de foraminiferos, radiolarios y ostra.codos,que representan medios sedimentarios desde el ambiente panilico (llanuramareica y lagon) hastael batial inferior. Losammonites son abundantes en la secuencia mayormente carbonatada de edad Aptiano a Coniaciano, y forman la base deuna zonaci6n macrobioestratignifica detallada facilmente utilisable en el campo. Se propone un primer intento deintegraci6n de las zonaciones de foraminfferos y ammonites para el Cretaceo de Sergipe, utilizando el metodo deintercalibraci6n. Las zonas tanto de foraminfferos como de ammonites sonmayormente zonas de Oppel, cuyos lfmitesestan marcados, para los foraminfferos, por su primera0 ultima ocurrencia local, y para los ammonites, por sus primerasapariciones locales. Zonas de asociaci6n de foraminiferos bent6nicos, localmente aplicables ymas biencontroladas porelmedio, estanpropuestaspara el Aptiano superior. Parael intervalo Aptiano-Albiano,la zonaci6n integrada estli todavfamuy provisional. Unnumero importante de correlaciones bioestratigraficas deprimer orden quedanpor serestablecidas,basandose sobre el muestro integrado de secciones que contengan al a vez microf6siles diagn6sticos y ammonites.PALABRAS CLAVE: Aptiano, Albiano, Cenomaniano, Turoniano, Coniaciano, Santoniano, Campaniano, Maastrichtiano, Cretliceo inferior, Cretliceo superior, bioestratigrafia, metodo de intercalibraci6n, metodo de integraci6n total,zonas de Oppel, medios sedimentarios, foraminiferos, ammonites, equinoideos, inoceramideos, Cuenca de Sergipe,Brasil, Oceano Atlantico Sur.


yield abundant anddiversified assemblages of foraminiferids, radiolarians andostracods, representing environments thatrange from paralic (tidal flat and lagoon) to lower bathyal settings. Ammonites are abundant in the Aptian toConiaciancarbonate-dominated sequence and form the basis for a detailed macrobiostratigraphical subdivision, which can easilybe applied in the field. A first attempt is made to integrate the foraminiferid and ammonite zonations for the SergipeCretaceous, using the intercalibrationmethod. The foraminiferal and ammonite zones are chieflyOppel zones, theboundaries of which are marked for foraminiferids by local first and/or last appearances and for ammonites by local firstappearances. Locallyapplicable assemblage zones, which aremoreenvironmentally controlled, are proposed forbenthicforaminiferids of the upper Aptian. For the Aptian-Albian interval the integrated biozonation is as yet highly provisional. A considerable amountof first-order biostratigraphical correlation is yet to be done, basedon integratedsamplingofsections that contain both diagnostic microfossils and ammonites.KEYWORDS: Aptian, Albian, Cenomanian, Turonian, Coniacian, Santonian, Campanian, Maastrichtian, LowerCretaceous, Upper Cretaceous, biostratigraphy, total-integration method, intercalibration method, Oppel zones, palaeoenvironments, Foraminifera, ammonites, echinoids, inocerarnids, Sergipe Basin, Brazil, South Atlantic Ocean.

242

ResumeVers une biostratigraphie integree de I'Aptien superieur-Maastrichtien du bassin de Sergipe, BresilLes echantillons d' age Aptien superieuraMaastrichtien, collectes sur le terrain ou en subsurfacedans le bassin

de Sergipe du Nord-Est bresilien contiennent des associations abondantes et diversifiees de foraminif'eres, radiolaires etostracodes, representant des environnements allant de paralique (estran et lagon)abathyal inferieur. Les ammonites sontabondantes dans la serie carbonateed'ageaConiacien, et permettant une subdivisionmacrobiostratigraphiquedetailleefacilement applicable sur le terrain. On presente un premier essai d'integration des zonations de foraminif'eres etd'ammonites pour le Cretace de Sergipe, en utilisant la methode d'intercalibration. Les zones de foraminif'eres etd'ammonites sont principalement des zones d'Oppel, dont les lirnites sont marquees, pour les foraminif'eres, par leurapparition ou disparition locale, et pour les ammonites, par leur premiereoccurrence locale. Des zones reposant sur desassociations de foraminif'eres benthiques, localement applicables, et plutOt contrOlees par le milieu, sont proposees pourI' Aptien sup6rieur. Pour I' intervalleAptien-Albien,la zonation integree est encore tresprovisoire. Un grandenombredecorrelations biostratigraphiques de premier ordre reste aetablir, en se basant sur l'echantillonnage integre de coupescontenant ala fois des microfaunes diagnostiques et des ammonites.MOTS-CLES : Aptien, Albien, Cenomien, Turonien, Coniacien, Santonien, Campanien, Maastrichtien, Cretace inferieur, Cretace superieur, biostratigraphie, methode d'intercalibration, methode d'integration totale, zone d'Oppel,paleoenvironnements, foraminiferes, ammonites, echinodermes, inocecames, bassinde Sergipe,Bresil,OceanAtlantiqueSud.

ResumenHacia una bioestratigrafia integradadel Aptiano superior-Maastrkhtiano de la Cuencade Sergipe,Brasll.Muestras de campo y de subsuelo, collectadas en capas del Aptiano superior alMaastrichtiano de la Cuencade

Sergipe en elNordestedeBrasil, contienen asociaciones ricas y diversificadas de foraminiferos, radiolarios y ostra.codos,que representan medios sedimentarios desde el ambiente panilico (llanuramareica y lagon) hastael batial inferior. Losammonites son abundantes en la secuencia mayormente carbonatada de edad Aptiano a Coniaciano, y forman la base deuna zonaci6n macrobioestratignifica detallada facilmente utilisable en el campo. Se propone un primer intento deintegraci6n de las zonaciones de foraminfferos y ammonites para el Cretaceo de Sergipe, utilizando el metodo deintercalibraci6n. Las zonas tanto de foraminfferos como de ammonites sonmayormente zonas de Oppel, cuyos lfmitesestan marcados, para los foraminfferos, por su primera0 ultima ocurrencia local, y para los ammonites, por sus primerasapariciones locales. Zonas de asociaci6n de foraminiferos bent6nicos, localmente aplicables y rolls biencontroladas porelmedio, estanpropuestaspara el Aptiano superior. Parael intervalo Aptiano-Albiano,la zonaci6n integrada estli todavfamuy provisional. Unnumero importante de correlaciones bioestratigraficas deprimer orden quedanpor serestablecidas,basandose sobre el muestro integrado de secciones que contengan a la vezmicrof6siles diagn6sticos y ammonites.PALABRASCLAVE : Aptiano, Albiano, Cenomaniano, Turoniano, Coniaciano, Santoniano, Campaniano, Maastrichtiano, Cretliceo inferior, Cretliceo superior, bioestratigraffa, metodo de intercalibraci6n, metodo de integraci6n total,zonas de Oppel, medios sedimentarios, foraminiferos, ammonites, equinoideos, inoceramideos, Cuenca de Sergipe,Brasil, Oceano Atlantico Sur.


yield abundant anddiversified assemblages of foraminiferids, radiolarians andostracods, representing environments thatrange from paralic (tidal flat and lagoon) to lower bathyal settings. Ammonites are abundant in the Aptian toConiaciancarbonate-dominated sequence and form the basis for a detailed macrobiostratigraphical subdivision, which can easilybe applied in the field. A first attempt is made to integrate the foraminiferid and ammonite zonations for the SergipeCretaceous, using the intercalibrationmethod. The foraminiferal and ammonite zones are chieflyOppel zones, theboundaries of which are marked for foraminiferids by local first andIor last appearances and for ammonites by local firstappearances. Locallyapplicable assemblage zones, which aremoreenvironmentally controlled, are proposed forbenthicforaminiferids of the upper Aptian. For the Aptian-Albian interval the integrated biozonation is as yet highly provisional. A considerable amountof first-order biostratigraphical correlation is yet to be done, basedon integratedsamplingofsections that contain both diagnostic microfossils and ammonites.KEYWORDS: Aptian, Albian, Cenomanian, Turonian, Coniacian, Santonian, Campanian, Maastrichtian, LowerCretaceous, Upper Cretaceous, biostratigraphy, total-integration method, intercalibration method, Oppel zones, palaeoenvironrnents, Forarninifera, ammonites, echinoids, inocerarnids, Sergipe Basin, Brazil, South Atlantic Ocean.

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INTRODUCTIONThe fonnation of the Brazilian marginal basins is directly related to the rupture of the African-South

American plate. Separation of the two continents took place along a typical, divergent, Atlantic-typecontinental margin extending along nearly 8 000 km. The depositional basins on both sides of the presentSouth Atlantic thus have a commonevolutionary history, which encompasses fourmain tectonosedimentaryphases (Ojeda & Fugita 1976; Ponte & Asmus 1976; Ojeda 1982; Asmus & Baisch 1983): pre-rift [lateJurassic(?) to earliest Cretaceousl, rift [earliest Cretaceous to early(?) Aptianl, transitional, proto-marine,evaporitic (Aptian), and a marine drift phase (late Aptian to Recent).The palaeogeographic setting of theSergipe Basin in north-eastem Brazil (fig. 1) during the mid- and late Cretaceous is a direct consequence ofthe strongtectonic activity thataffected thearea sincethe beginningof the riftingbetween South America andAfrica in the early Cretaceous.The basin consistsof a seriesof half-grabens with a regional dip averaging 1015 to the south-east, resulting from NE-SW trending nonnal faults.

post-Coniacian(piayabuyu Formation)Cenomanian-Coniacian(Cotinguiba Formation)Aptian-Cenomanian(Riachuelo Formation)

POTIGUAR

.::: JEQUITINHONHA.::. CUMURUXATIBA. .... ... MUCURI

o pre-Aptianfault

o 500./ ....---:"k-m ,

Nr50,

km

.. .. .. .. .. .... .. .. .... .. .. .. .. .. .. .. .... .. .. .... .. .. ... .. .. .... .. .. ... .. .. .....

o,

SERGIPEBASIN

11 0

Fig. 1 - Geology of onshore portion of the Sergipe Basin (from Berthou & Bengtson 1988).A =Aracaju, E =Estiincia, I =Itaporanga, J =Japaratuba.

243


American plate. Separation of the two continents took place along a typical, divergent, Atlantic-typecontinental margin extending along nearly 8 000 km. The depositional basins on both sides of the presentSouth Atlantic thus have a commonevolutionary history, which encompasses fourmain tectonosedimentaryphases (Ojeda & Fugita 1976; Ponte & Asmus 1976; Ojeda 1982; Asmus & Baisch 1983): pre-rift [lateJurassic(?) to earliest Cretaceous], rift [earliest Cretaceous to early(?) Aptian], transitional, proto-marine,evaporitic (Aptian), and a marine drift phase (late Aptian to Recent).The palaeogeographic setting of theSergipe Basin in north-eastem Brazil (fig. 1) during the mid- and late Cretaceous is a direct consequence ofthe strongtectonic activity thataffected thearea sincethe beginningof the riftingbetween South America andAfrica in the early Cretaceous.The basin consistsof a seriesof half-grabens with a regional dip averaging 1015 to the south-east, resulting from NE-SW trending nonnal faults.


POTIGUAR


o pre-Aptianfault

o 500./ ....---:"k-m ,

Nr50,

km

.. .. .. .. .. .... .. .. .... .. .. .. .. .. .. .. .... .. .. .... .. .. ... .. .. .... .. .. ... .. .. .....

o,

SERGIPEBASIN

11 0

Fig. 1 - Geology of onshore portion of the Sergipe Basin (from Berthou & Bengtson 1988).A =Aracaju, E =Estancia, I =Itaporanga, J =Japaratuba.

243


American plate. Separation of the two continents took place along a typical, divergent, Atlantic-typecontinental margin extending along nearly 8 000 km. The depositional basins on both sides of the presentSouth Atlantic thus have a commonevolutionary history, which encompasses fourmain tectonosedimentaryphases (Ojeda & Fugita 1976; Ponte & Asmus 1976; Ojeda 1982; Asmus & Baisch 1983): pre-rift [lateJurassic(?) to earliest Cretaceousl, rift [earliest Cretaceous to early(?) Aptianl, transitional, proto-marine,evaporitic (Aptian), and a marine drift phase (late Aptian to Recent).The palaeogeographic setting of theSergipe Basin in north-eastem Brazil (fig. 1) during the mid- and late Cretaceous is a direct consequence ofthe strongtectonic activity thataffected thearea sincethe beginningof the riftingbetween South America andAfrica in the early Cretaceous.The basin consistsof a seriesof half-grabens with a regional dip averaging 1015 to the south-east, resulting from NE-SW trending nonnal faults.


POTIGUAR


o pre-Aptianfault

o 500./ ....---:"k-m ,

Nr50,

km

.. .. .. .. .. .... .. .. .... .. .. .. .. .. .. .. .... .. .. .... .. .. ... .. .. .... .. .. ... .. .. .....

o,

SERGIPEBASIN

11 0

Fig. 1 - Geology of onshore portion of the Sergipe Basin (from Berthou & Bengtson 1988).A =Aracaju, E =Estiincia, I =Itaporanga, J =Japaratuba.

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TheSergipeBasin containsoneof themostextensivemiddleCretaceousmarinecarbonatesuccessionsamong thenorthernSouthAtlantic basins. The sequence, although far from complete,spans the upperAptianto middle Coniacian interval (fig. 2) and can be subdivided into two main depositional systems (cf.Koutsoukos et al., in press) :(1) a mixed carbonate-siliciclastic platform system (latest Aptian to Albian : Riachuelo Formation,normally about 500 m thick, locally up to 1 700 m) ;(2) a carbonate ramp system, chiefly developed as a massive succession of fine-grained deep-waterlimestones (Cenomanian to mid-Coniacian : Cotinguiba Formation, normally about 200 m thick, locallyexceeding 1 000 m).The carbonate-dominated succession is overlain unconformably by a sequence of siliciclastic deposits; these form the P i a ~ a b u ~ u Formation (upper Coniacian or Santonian to Miocene or Pliocene, up to andexceeding 2 000m).

Form.Ulhostratigraphy

Members

Calumbi (Cal)

Sapucari (Sap)Aracaju (Aju)

SE

_ Tq_-_ - _ - _ Aguilhada (Ag)Maruim (Mar)Taquari (Tq)Angico(An)

--------------------------- = = = = = = = = = = = = = ~ = = = - g - = = = ~ =

Facies relationships

----------------------------------------------- - = = ~ = ~ = ~ = ~ = ~ ~ = ~ = ~ = ~ ~ ~ ~ ~ ~ = ~ ~ ~----------------------------------------------------------------------------------- = -= - :Ca l : - = -= : -= -= -= -= -= -= -= -= -= -=-------------------------_._-----------------------------------_._-------------------------

:'cl!i"n"~ : . ; t i l Conglomerates Ma Stages NW

E - - ~ Shales 70 Maastricht.1:::::::::1 Sandstones~ Carbonate- mudstones Campanianm Ooliticloncolitic 80 grainstones orpackstones

~ D o l o m i t i c Sanlonianlimestones c........90 TuronianI::: -:- ::::1 Siltstones CenomanianrV"V' Unconformity

100Albian

110

Fig. 2 - Schematic stratigraphy of the marine Cretaceous sequences of the Sergipe Basin.The stratigraphyand the depositionaland geological history of the marineCretaceousofSergipe have

been described by Schaller (1970), Ojeda& Fugita (1976), Bandeira Jr. (1978), Feij6 (1980), Schaller et al.(1980), Bengtson (1983), Berthou & Bengtson (1988), Lana (1990), and Koutsoukos et al. (in press), amongothers. Biostratigraphical research has until now been focused on individual fossil groups, with onlypreliminary attempts at integrating the different schemes. A systematic survey initiated by P. and S. I.Bengtson in the 1970's (see Bengtson 1983) provides the basis for a detailed integrated biostratigraphycomprising all biostratigraphically important groups. In this paper we report on the results achieved to dateusing chiefly foraminiferids and ammonites. We also discuss the palaeoenvironmental conclusions drawnfrom the occurrences of the faunas, in particular the microfossils.

The paper is a contribution to IGCP Project 242 Cretaceous of Latin America.

244

TheSergipeBasin containsoneof themostextensivemiddleCretaceousmarinecarbonatesuccessionsamong thenorthernSouthAtlantic basins. The sequence, although far from complete,spans the upperAptianto middle Coniacian interval (fig. 2) and can be subdivided into two main depositional systems (cf.Koutsoukos et aI., in press) :(1) a mixed carbonate-siliciclastic platform system (latest Aptian to Albian: Riachuelo Formation,normally about 500 m thick, locally up to 1 700 m) ;(2) a carbonate ramp system, chiefly developed as a massive succession of fine-grained deep-waterlimestones (Cenomanian to mid-Coniacian : Cotinguiba Formation, normally about 200 m thick, locallyexceeding 1 000 m).The carbonate-dominated succession is overlain unconformably by a sequence of siliciclastic deposits; these form the P i a ~ a b u ~ u Formation (upper Coniacian or Santonian to Miocene or Pliocene, up to andexceeding 2 000m).

Form.Uthostratigraphy

Members

Calumbi (Cal)


SE


--------------------------- = = = = = = = = = = = = = ~ = = = - g - = = = ~ =


----------------------------------------------- - = = ~ = ~ = ~ = ~ = ~ ~ = ~ = ~ = ~ ~ ~ ~ ~ ~ = ~ ~ ~----------------------------------------------------------------------------------- = -= - :Ca l : - = -= : -= -= -= -= -= -= -= -= -= -=-------------------------_._-----------------------------------_._-------------------------

:'''!i"n"~ : . ; t i l Conglomerates Ma Stages NW


~ D o l o m i t i c Santonianlimestones c........90 TuronianI::: -:- ::::1 Siltstones CenomanianrV"V' Unconformity

100Albian

110




244

TheSergipeBasin containsoneof themostextensivemiddleCretaceousmarinecarbonatesuccessionsamong thenorthernSouthAtlantic basins. The sequence, although far from complete,spans the upperAptianto middle Coniacian interval (fig. 2) and can be subdivided into two main depositional systems (cf.Koutsoukos et al., in press) :(1) a mixed carbonate-siliciclastic platform system (latest Aptian to Albian : Riachuelo Formation,normally about 500 m thick, locally up to 1 700 m) ;(2) a carbonate ramp system, chiefly developed as a massive succession of fine-grained deep-waterlimestones (Cenomanian to mid-Coniacian : Cotinguiba Formation, normally about 200 m thick, locallyexceeding 1 000 m).The carbonate-dominated succession is overlain unconformably by a sequence of siliciclastic deposits; these form the P i a ~ a b u ~ u Formation (upper Coniacian or Santonian to Miocene or Pliocene, up to andexceeding 2 000m).

Form.Ulhostratigraphy

Members

Calumbi (Cal)


SE


--------------------------- = = = = = = = = = = = = = ~ = = = - g - = = = ~ =


----------------------------------------------- - = = ~ = ~ = ~ = ~ = ~ ~ = ~ = ~ = ~ ~ ~ ~ ~ ~ = ~ ~ ~----------------------------------------------------------------------------------- = -= - :Ca l : - = -= : -= -= -= -= -= -= -= -= -= -=-------------------------_._-----------------------------------_._-------------------------

:'cl!i"n"~ : . ; t i l Conglomerates Ma Stages NW


~ D o l o m i t i c Sanlonianlimestones c........90 TuronianI::: -:- ::::1 Siltstones CenomanianrV"V' Unconformity

100Albian

110




244


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BIOSTRATIGRAPHYBiostratigraphicaI integrationIntegrated biostratigraphy, in the true sense of the term, is a technique that is still in its infancy.Although it is a well-known fact that all organisms are facies-bound to a varying degree, it is only during the

lastdecades that biostratigraphers seem tohave realisedthatmore preciseand reliable resultscan be achievedif diagnostic fossils from as many different groupsas possible are applied simultaneously insteadofonly onegroup at a time. The term integrated biostratigraphy is in common use today ; however, much ofwhat islabelledas integratedbiostratigraphyconsistsof comparisonsof existing biozonal schemesfordifferent fossilgroups rather than truly integrated biostratigraphy based on detailed integrated sampling. Most of thebiostratigraphicalwork underlying such zonal comparisons dates back to the not-too-distant time when eachfossil group was sampled and studied in isolation. These single-group zonal schemes and biozonalcomparisons must be used with caution when attemptinl!; to establish an integratedbiostratigraphy. An integrated biostratigraphy can be achieved and presented in tW0 nrincipal ways (fig. 3), by using: (1) the total-integration method,bywhich the entire biota is treated as one large fossil group, and byWhICh thediagnostictaxa, irrespective of systematic position, are singled out and used for the definition and characterization ofbiozones; (2) the intercalibration method,by which conventional single-group zonal schemes are used and/or erected but through precise stratigraphical control are fIrmly calibrated to each other (for an exemplarywork of this kind, see, for example, Rasplus et al. 1987). Integrated biostratigraphy based on the totalintegration method can perhapsbe seen as theonly truly integrated biostratigraphy and, indeed, it is temptingto conceive as a final goal an all-embracing biostratigraphical zonation scheme, whereby zones can beidentified usingmembersof virtually any fossil group. However, toestablish an integratedbiostratigraphyofthis kind wouldmean that entirely new zonations had to be produced to replace existing single-group zonalschemes, a huge task that has noprospectsof being completed within the foreseeable future. Anotherdisadvantage of the total-integration method is that zones will be basedon varying properties (first appearances,last appearances, acmes, etc.) of probably several tens of taxa, which will contribute to making zonaldefinitions unclear and of difficult use.

The intercalibrationmethod aims at calibrating existing andnew single-groupzonal schemes throughimproved stratigraphical control. This method utilizes all available biostratigraphical information, old andnew, with its faults and virtues, andmay therefore give less precise results than the total-integration method.However, biozones will be more clearly defined and easier to grasp and apply than those based on the totalintegration method. Also, comparisonswith other areas will beeasier tomake,as biogeographic restraints canbe avoidedwith the selectionof commondiagnostic taxa, andbecause further improvements and refinementscanbemadewithoutupsetting theentireintegratedbiozonal scheme. Inour work onan integratedCretaceousbiostratigraphy of Sergipe we have opted for the intercalibration method.

Review of foraminiferal and ammonite biozonal integration.The current integrated foraminiferal-ammonite biostratigraphical scheme for the Aptian-Maastrich

tian of the Sergipe Basin is shown in fig. 4. Several studies have focused on the palaeontology andbiostratigraphy of this basin (see Bengtson 1983 for a review; also Berthou & Bengtson 1988). The firstattemptat an ammonitezonationwas by Beurlen(1961) for the upperAptian andAlbian, whereasPetri(1962)proposed a foraminiferal zonation for the entire Albian-Maastrichtian interval. Petri also attempted tocorrelate themicrobiostratigraphicalschemewith themacrofossil succession, whichuntil then hadbeen basedchiefly on the work ofMaury (1937). Beurlen (1969,1970) complementedK. Beurlen's (1961) ammonitezonation with a Cenomanian-lower Coniacian subdivision; further additions to this zonation were byReyment&Tait(1972), Reymentetal. (1976), Bengtson (1979, 1983),andSmith& Bengtson (1991). Freitas(1984) discussed the stratigraphy and distribution of calcareous nannofossils in the basin. Lower Turonianinoceramid bivalves and Albian to Coniacian echinoids were subsequently describedby Hessel (1988) andSmith (1991), respectively.

A microbiostratigraphical scheme was proposedby Koutsoukos (1989), basedon foraminiferids; 23planktonic and benthicforaminiferid zoneswere recognized for theupperAptian-Maastrichtian strata. Workis currently in progress to fully integrate and refme the foraminiferid and ammonite biozonal schemes(Koutsoukos & Bengtson, in preparation), based onjoint studies of further field sections. The timing of the

245

BIOSTRATIGRAPHYBiostratigraphical integrationIntegrated biostratigraphy, in the true sense of the term, is a technique that is still in its infancy.Although it is a well-known fact that all organisms are facies-bound to a varying degree, it is only during the

lastdecades that biostratigraphers seem tohave realisedthatmore preciseand reliable resultscan be achievedif diagnostic fossils from as many different groupsas possible are applied simultaneously insteadofonly onegroup at a time. The term integrated biostratigraphy is in common use today ; however, much ofwhat islabelledas integratedbiostratigraphyconsistsof comparisonsof existing biozonal schemesfordifferent fossilgroups rather than truly integrated biostratigraphy based on detailed integrated sampling. Most of thebiostratigraphicalwork underlying such zonal comparisons dates back to the not-tao-distant time when eachfossil group was sampled and studied in isolation. These single-group zonal schemes and biozonalcomparisons must be used with caution when attemptinl!; to establish an integratedbiostratigraphy. An integrated biostratigraphy can be achieved and presented in tW0 nrincipal ways (fig. 3), by using: (1) the total-integration method,bywhich the entire biota is treated as one large fossil group, and byWhICh thediagnostictaxa, irrespective of systematic position, are singled out and used for the definition and characterization ofbiozones; (2) the intercalibrationmethod, by which conventional single-group zonal schemes are used and/or erected but through precise stratigraphical control are fIrmly calibrated to each other (for an exemplarywork of this kind, see, for example, Rasplus et al. 1987). Integrated biostratigraphy based on the totalintegration method can perhapsbe seen as theonly truly integrated biostratigraphy and, indeed, it is temptingto conceive as a final goal an all-embracing biostratigraphical zonation scheme, whereby zones can beidentified usingmembersof virtually any fossil group. However, toestablish an integratedbiostratigraphyofthis kind wouldmean that entirely new zonations had to be produced to replace existing single-group zonalschemes, a huge task that has noprospectsof being completed within the foreseeable future. Anotherdisadvantage of the total-integration method is that zones will be basedon varying properties (first appearances,last appearances, acmes, etc.) of probably several tens of taxa, which will contribute to making zonaldefinitions unclear and of difficult use.





245

BIOSTRATIGRAPHYBiostratigraphicaI integrationIntegrated biostratigraphy, in the true sense of the term, is a technique that is still in its infancy.Although it is a well-known fact that all organisms are facies-bound to a varying degree, it is only during the

lastdecades that biostratigraphers seem tohave realisedthatmore preciseand reliable resultscan be achievedif diagnostic fossils from as many different groupsas possible are applied simultaneously insteadofonly onegroup at a time. The term integrated biostratigraphy is in common use today ; however, much ofwhat islabelledas integratedbiostratigraphyconsistsof comparisonsof existing biozonal schemesfordifferent fossilgroups rather than truly integrated biostratigraphy based on detailed integrated sampling. Most of thebiostratigraphicalwork underlying such zonal comparisons dates back to the not-too-distant time when eachfossil group was sampled and studied in isolation. These single-group zonal schemes and biozonalcomparisons must be used with caution when attemptinl!; to establish an integratedbiostratigraphy. An integrated biostratigraphy can be achieved and presented in tW0 nrincipal ways (fig. 3), by using: (1) the total-integration method,bywhich the entire biota is treated as one large fossil group, and byWhICh thediagnostictaxa, irrespective of systematic position, are singled out and used for the definition and characterization ofbiozones; (2) the intercalibration method,by which conventional single-group zonal schemes are used and/or erected but through precise stratigraphical control are fIrmly calibrated to each other (for an exemplarywork of this kind, see, for example, Rasplus et al. 1987). Integrated biostratigraphy based on the totalintegration method can perhapsbe seen as theonly truly integrated biostratigraphy and, indeed, it is temptingto conceive as a final goal an all-embracing biostratigraphical zonation scheme, whereby zones can beidentified usingmembersof virtually any fossil group. However, toestablish an integratedbiostratigraphyofthis kind wouldmean that entirely new zonations had to be produced to replace existing single-group zonalschemes, a huge task that has noprospectsof being completed within the foreseeable future. Anotherdisadvantage of the total-integration method is that zones will be basedon varying properties (first appearances,last appearances, acmes, etc.) of probably several tens of taxa, which will contribute to making zonaldefinitions unclear and of difficult use.





245


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first marine connection between the central and South Atlantic oceans is indicated by ammonites andmicrofossils contained in the lowermostmarine bedsof the RiachueloFormation (Bengtson & Koutsoukos1992).The sequencehas yielded upperAptian ammonites of theearly douvilleiceratid lineageChelonicerasEodouvilleiceras. The upperAptian is subdivided with planktonic foraminiferids into two zones, theGlobi-gerinelloides barri-Hedbergella (H.) gorbachikae and Globigerinelloides ex. gr. maridalensis-Hedbergella (H.) similis zones. The upper boundary of the latter zone is defined by the last appearance of diagnosticspecies likeG. barri (Bolli,Loeblich& Tappan, 1957),G. exgr.maridalensis(Bolli, 1959),andH.(H.)similisLongoria, 1974, among others, at or near the Aptian-Albian boundary (Koutsoukos 1989, Bengtson &Koutsoukos 1992). The zone correlates with the lower part of theGlobigerinelloidesferreolensis- Ticinellabejaouensis Zone of van Hinte(1976) ; see fig. 5.

TOTAL-INTEGRATION METHOD

Zone 4ammonites, foraminifers,dinoflagellates, pollen,bivalves, echinoids,radiolarians, etc.

Zone 3ammonites, foraminifers,dinoflagellates, pollen,bivalves, eChinoids,radiolarians, etc.Zone 2ammonites, foraminifers,dinoflagellates, pollen,ostracods, bivalves,etc.Zone 1ammonites, foraminifers,dinoflagellates, pollen,bivalves, echinoids,radiolarians, etc.

INTERCALlBRATION METHOD

Fig. 3 -Hypotheticalzonationsto illustrate the total-integration and intercalibration methods.

AMMONITES FORAMINIFERS DINOFLAGELLATES BIVALVESZoneA4 ZoneF4 Zone 04ammonites foraminifers dinoflagellates Zone 83

bivalvesZoneA3 Zone F3 Zone 03

dinoflagellatesammonites foraminifersZone 02 Zone 82ZoneA2 ZoneF2 dinoflagellates bivalves

ammonites foraminifersZone 01ZoneA1 ZoneF1 Zone 81dinoflagellatesammonites foraminifers bivalves

246





INTERCALIBRATION METHOD






246





INTERCALlBRATION METHOD






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FORAMINIFERAL ZONESAGES "STANDARD AMMONITEZONES" ZONES PLANKTONIC BENTHIC

G. contusa-G. aegyptiaca O. clarki-P. kickapooensisMaastrichtian G. gansseri-G. stuartiformis G. loetterlei-a. velascoensis

G. ex gr. fornicata- G. ex gr. beaumontiana-G.finneiana G. nonionoidesG. orientalis-G. ventricosa L. gouskovi-O. clavata

Campanian G. patelliformis-G. elevatal S. bramlettei-stuartiformis plexus R. ex gr. szajnochaeDicarinella asymetrica N. texana-O. clarki

SantonianD. concavata-M. sinuosa L. revoluta-G. spinea

Coniacian Peroniceras tridorsatum S. armatus-P lenti Gavellinella sp. A-B. onilahyense- A. cretacea-D. primitiva Valvulineria s p. AForrester/a (H.) petrocor/ensis ForresteriaSUbprionocyclus Suprionocyclus- Valvulineria sp. B-Dicarinella prim/t/va G. berthelini-plummerae-neptuni Reesidites reussi plexusTuronian Mammites nodosoides M. nodoso/des-K. turon/ense H. aprica- G.levis-

W. amudar/ense- H. (W) baltica N. ex gr. obscuraWatinoceras spp. K.se/tzjV. harttii- H (W) archaeocretacea- G. obesa-G. levisNeocardioceras juddii P. footeanum H. reussi

Meto/coceras E. septemseriatum H. (W) aprica- G. levis-Discammina s p. AG. bentonensisgesfinianum P harpax-T. aft. sornayi H.(W) baltica- Nodosaria ex. gr. obscura-Cenomanian Acanthoceras jukesbrowne/ A. jukesbr.-E. pen/ago H(W) brittonensis Gibicides s p. ATurrilites acutus-costat us A. spathi-Dunveganoc.P. delrioensis- L. (?) cf. thalmanniformis-Mantelliceras G.lozoi- R. appenninica S. cretaceamantelli H. betaitraensis R. brotzeni Gibides sp. A-P. complanata

Mortoniceras H. (H.) gorbachikae- N. subcretacea-Morton/ceras T. raynaudi T. ex gr. excavatainflatum G. texomaensis- N. subcretacea-Elobiceras B. breggiens/s S. cf. crassicostaB. breggiensis- G. berthefini-plummerae-Albian Euhopfites ? T. ex gr. primula reussi plexus-G. cf.gradatalautus Oxytropidoceras T. ex gr. primula- E. spinufifera-E. carpenteriT. bejaouaensisT. bejaouaensis a. schloenbachi-Douvilleiceras P.IS. ex gr. dividensmamillatum Douvilleiceras

----- ? -----.- G. cushmani- E. carpenteri-G. filiformisLeymeriella regularis ? T. bejaouaensisG. ex gr. maridalensis- L. ex gr. sUbangulata-H (H.) similis L. ex gr. nodosa

Late Epicheloniceras- A. cf. copro/ithiformis-Aptian Diadochoceras- B. cf. hedbergi-Eodouvilleiceras G. barri- H.lueckeiH (H.) gorbachikae L. ciryi-L. nodosaria-M. ex gr. aequivoca

Fig. 4 - Integrated foramlnlferid-ammonite blostratlgraphy of the marine Cretaceous of the Serglpe Basin.(Foraminiferids after Koutsoukos 1989 ; Aptian ammonites from Bengtson & Koutsoukos 1992; Albian ammonitesmodifiedafterBeurlen 1969. 1970; Cenomanian-Coniacian ammonites modified afterBengtson1983. Smith& Bengtson1991 and S. I. Bengtson (Uppsala). personal communication 1992; age lengths not to scale).

247


C. contusa-G. aegyptiaca O. clarki-P. kickapooensisMaastrichtian G. gansseri-G. stuartiformis G. loetterlei-a. velascoensis

C. ex gr. fornicata- C. ex gr. beaumontiana-G.linneiana G. nonionoidesG. orienta/is-G. ventricosa L. gouskovi-O. clavata

Campanian G. patelliformis-G. elevata/ S. bramlettei-stuartiformis plexus R. ex gr. szajnochaeDicarinella asymetrica N. texana-O. clarki


Coniacian Peroniceras tridorsatum S. armatus-P lenti Gavellinella sp. A -B. oni/ahyense- A. cretacea-D. primitiva Valvulineria s p. AForrester/a (H.) petrocor/ensis ForresteriaSUbprionocyclus Suprionocyclus- Valvulineria sp. S -Dicarinella prim/t/va G. berthelini-plummerae-neptuni Reesidites reussi plexusTuronian Mammites nodosoides M. nodoso/des-K. turon/ense H. aprica- G.levis-

W. amudar/ense- H. (W) baltica N. ex gr. obscuraWatinoceras spp. K. seitz;V. harttii- H (W) archaeocretacea- G. obesa-G. levisNeocardioceras juddii P. footeanum H. reussi

Meto/coceras E. septemseriatum H. (W) aprica- G. levis-Discammina sp. AG. bentonensisgeslinianum P harpax-T. aft. samayi H.(W) baltica- Nodosaria ex. gr. obscura-Cenomanian Acanthoceras jukesbrowne/ A. jukesbr.-E. pen/ago H(W) brittonensis Cibicides sp. ATurri/ites acutus -cost atus A. spathi-Dunveganac.P. delrioensis- L. (?) ct. thalmanniformis-Mantelliceras G.lozoi- R. appenninica S. cretaceamantelli H. betaitraensis R. brotzeni Cibides sp. A-P. complanata

Mortoniceras H. (H.) gorbachikae- N. subcretacea-Morton/ceras T. raynaudi T. ex gr. excavatainflatum G. texomaensis- N. subcretacea-Elobiceras B. breggiens/s S. ct. crassicostaB. breggiensis- G. berthelini-plummerae-Albian Euhoplites ? T. ex gr. primula reussi plexus-G. ct.gradatalautus Oxytropidoceras T. ex gr. primula- E. spinulifera-E. carpenteriT. bejaouaensisT. bejaouaensis a. schloenbachi-Douvilleiceras P./S. ex gr. dividensmamillatum Douvilleiceras


Late Epicheloniceras- A. ct. copro/ithiformis-Aptian Diadochoceras- B. ct. hedbergi-Eodouvilleiceras G. barri- H.lueckeiH (H.) gorbachikae L. ciryi-L. nodosaria-M. ex gr. aequivoca

Fig. 4 - Integrated foramlnlferid-ammonite biostratigraphy of the marine Cretaceous of the Serglpe Basin.(Foraminiferids after Koutsoukos 1989 ; Aptian ammonites from Bengtson & Koutsoukos 1992; Albian ammonitesmodifiedafterBeurlen1969. 1970; Cenomanian-Coniacianammonitesmodified afterBengtson1983. Smith& Bengtson1991 and S. I. Bengtson (Uppsala). personal communication 1992; age lengths not to scale).

247


G. contusa-G. aegyptiaca O. clarki-P. kickapooensisMaastrichtian G. gansseri-G. stuartiformis G. loetterlei-a. velascoensis

G. ex gr. fornicata- G. ex gr. beaumontiana-G.finneiana G. nonionoidesG. orientalis-G. ventricosa L. gouskovi-O. clavata

Campanian G. patelliformis-G. elevatal S. bramlettei-stuartiformis plexus R. ex gr. szajnochaeDicarinella asymetrica N. texana-O. clarki


Coniacian Peroniceras tridorsatum S. armatus-P lenti Gavellinella sp. A -B. onilahyense- A. cretacea-D. primitiva Valvulineria s p. AForrester/a (H.) petrocor/ensis ForresteriaSUbprionocyclus Suprionocyclus- Valvulineria sp. B -Dicarinella prim/t/va G. berthelini-plummerae-neptuni Reesidites reussi plexusTuronian Mammites nodosoides M. nodoso/des-K. turon/ense H. aprica- G.levis-

W. amudar/ense- H. (W) baltica N. ex gr. obscuraWatinoceras spp. K.se/tzjV. harttii- H (W) archaeocretacea- G. obesa-G. levisNeocardioceras juddii P. footeanum H. reussi

Meto/coceras E. septemseriatum H. (W) aprica- G. levis-Discammina sp. AG. bentonensisgesfinianum Pharpax-T. aft. sornayi H.(W) baltica- Nodosaria ex. gr. obscura-Cenomanian Acanthoceras jukesbrowne/ A. jukesbr.-E. pen/ago H(W) brittonensis Gibicides sp. ATurrilites acutus-costatus A. spathi-Dunveganoc.P. delrioensis- L. (?) cf. thalmanniformis-Mantelliceras G.lozoi- R. appenninica S. cretaceamantelli H. betaitraensis R. brotzeni Gibides sp. A-P. complanata

Mortoniceras H. (H.) gorbachikae- N. subcretacea-Morton/ceras T. raynaudi T. ex gr. excavatainflatum G. texomaensis- N. subcretacea-Elobiceras B. breggiens/s S. cf. crassicostaB. breggiensis- G. berthefini-plummerae-Albian Euhopfites ? T. ex gr. primula reussi plexus-G. cf.gradatalautus Oxytropidoceras T. ex gr. primula- E. spinufifera-E. carpenteriT. bejaouaensisT. bejaouaensis a. schloenbachi-Douvilleiceras P.IS. ex gr. dividensmamillatum Douvilleiceras


Late Epicheloniceras- A. cf. copro/ithiformis-Aptian Diadochoceras- B. cf. hedbergi-Eodouvilleiceras G. barri- H.lueckeiH (H.) gorbachikae L. ciryi-L. nodosaria-M. ex gr. aequivoca

Fig. 4 - Integrated foramlnlferid-ammonite blostratlgraphy of the marine Cretaceous of the Serglpe Basin.(Foraminiferids after Koutsoukos 1989 ; Aptian ammonites from Bengtson & Koutsoukos 1992; Albian ammonitesmodifiedafterBeurlen1969. 1970; Cenomanian-Coniacianammonitesmodified afterBengtson1983. Smith& Bengtson1991 and S. I. Bengtson (Uppsala). personal communication 1992; age lengths not to scale).

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Stages This studyContusotruncana contusa-Globotruncana aegyptiacaZone

Gansserina gansseri -GJobotruncanda stuartiformisZone

Caron1985A. mayaroensis

van Hint.1976A. msyafOBns;S

G. contusa

MaastrIChtlanl- _

ContU50truncana ex gr. fornicataGlobotruncana linneianaZone

GlobotruncanaorientalisGlobotruncana ventricosaZoneCampanlan

Contusotruncana patelliformisGlobotruncanita elevata/stuartiformisplexusZone

Dicarinella asymetricaZone

G. gansseri

G. aegyptiaca

G. havanensis

G, ca/carata

G. ventricosa

G. elevara

D. asymetrica

G.stuar1i

G. gansseri

G. scutilla

G, calcarata

G. 5ubspinosaG. stuartiformis

G, elevata

G. concavataG. elevataSantonian

Coniacian

Turonian

Ciear/nella conCBvataMarginorruncana sinuosaZone

ArchaeoglobigerinacretaceaCiearinellsprimitivaZoneDlc,Wile/la primitivilZone

Hedbecge"" (W) apcica-b e I 1 l 1 ~ ; ~ ; ' 5 j S

Hedbergella (W ) balt icaHedb, (W) brittonensJsZone

D, conC8vata

D. prirnilivB

M sigal i

H. helvetica

W archaeocretacea

R. cushmani

G. sigaliG. concavata

G. renziG, siga/i

"G. " helvetica

H.lehmani

R, cushmani

Cenomanian f - - - - :- - . . . , . . , - - - - - Praecglobotruncanadelrioensis-Rotalipora appenninicaZoneRotalipora brotzeniZone

H e d b e 1 ; ~ f ~ a e f ~ ) r ~ ; ~ ~ ~ ~ 7 i k a e - -Zone

GlobigerinelloidestexomaensisBiticine/labreggiensisZoneAlblan

aiticinelJa breggiensisTlcmella ex gr. primulaZoneTic. ex gr, primulaTicineJ1a beJaouaensis Zone

R reichel i

R. brotzeni

R. appenninica

R. ticinensisR. subticiensisa, breggiensis

T primula

R. gandolfii-R. greenhornensis

R. a p ' b ~ ~ ~ ~ a -f - - - - - - - - -P ticinensisP. buxtorfi

T (a.) breggiensis

T. praeticinensis

Ticinella bejaouaensis ZoneG ~ b i g e r i n e l l o i d e s cushmaniTlcmelfa be]aousensis Zone

UpperAptlan

Globigerinelloides ex gr,m a r i d a l e ~ ~ i i i s H r o ~ e : g e J l a (H)

Globigerinelloldes barriHedbergelJai ~ j e gorbachikae

T bejaouaensis

H. gorbachikae

G. algerians

T bejaouaensis1 - - - - - - - - -G. ferffJOJensis-T. bejaouaensis

H.trocoidelt-G. ferreolensis

248

Fig.5 -Correlationofplanktonlc foramlnlferal zonal schemes proposed for the AptianMaastrlchtlan (stage thicknesses not to scale).





G. contusa

MaastrIChtlanl- _


GlobotruncanaorientalisGlobotruncana ventricosaZoneCampanian Contusotruncana patelliformisGlobotruncanita elevata!stuartiformisplexusZone

Oiearinella asymetricaZone

G. gansseri

G. aegyptiaca

G. havanensis

G, calcarata

G. ventricosa

G. elevars

D. asymetrica

G. stuarti

G. gansseri

G. scutilla

G, calcarata

G. 5ubspinosaG.stuartiformis

G, elevata


Coniacian

Turonian

Oicar/nella conCBvataMarginorruncana sinuosaZone

ArchaeoglobigerinacretaceaOiearinella primitivaZoneolc,wile/la primitivilZone

Hedbecge"" (Wi apcica-b e I 1 l 1 ~ ; ~ ; ' 5 j S

Hedbergella (W ) balt icaHedb, (W) brittonenSJSZone

D, COnC8vata

D. primiliv8

M s igal i

H. helvetica

W archaeocretacea

R. cushmani


G. renziG,siga/i

"G. " helvetica

H.lehmani

R, cushmani



GlobigerinelloidestexomaensisBiticinella breggiensisZoneAlbian

aiticinelJa breggiensisTlcmella ex gr. primulaZoneTic. ex gr, primulaTicineJ1a beJsousensis Zone

R reichel i

R. brotzeni

R. appenninica


T primula

R. gandolfi i-R. greenhornensis


T (a.) breggiensis

T. praeticinensis

Ticinella bejaouaensis ZoneG ~ b i g e r i n e l l o i d e s cushmaniTlcmelfa be]sousensis Zone

UpperAptian


GlobigerinelloidesbarriHedbergelJai ~ j e gorbachikae

T bejaouaensis

H. gorbachikae

G. algerians



248

Fig.5 -Correlationofplanktonle foraminiferal zonal schemes proposed for the AptianMaastrichtian (stage thicknesses not to scale).





G. contusa

MaastrIChtlanl- _


GlobotruncanaorientalisGlobotruncana ventricosaZoneCampanlan

Contusotruncana patelliformisGlobotruncanita elevata/stuartiformisplexusZone

Dicarinella asymetricaZone

G. gansseri

G. aegyptiaca

G. havanensis

G, ca/carata

G. ventricosa

G. elevara

D. asymetrica

G.stuar1i

G. gansseri

G. scutilla

G, calcarata

G. 5ubspinosaG. stuartiformis

G, elevata


Coniacian

Turonian

Ciear/nella conCBvataMarginorruncana sinuosaZone

ArchaeoglobigerinacretaceaCiearinellsprimitivaZoneDlc,Wile/la primitivilZone

Hedbecge"" (W) apcica-b e I 1 l 1 ~ ; ~ ; ' 5 j S

Hedbergella (W ) balt icaHedb, (W) brittonensJsZone

D, conC8vata

D. prirnilivB

M sigal i

H. helvetica

W archaeocretacea

R. cushmani


G. renziG, siga/i

"G. " helvetica

H.lehmani

R, cushmani



GlobigerinelloidestexomaensisBiticine/labreggiensisZoneAlblan

aiticinelJa breggiensisTlcmella ex gr. primulaZoneTic. ex gr, primulaTicineJ1a beJaouaensis Zone

R reichel i

R. brotzeni

R. appenninica


T primula

R. gandolfii-R. greenhornensis


T (a.) breggiensis

T. praeticinensis

Ticinella bejaouaensis ZoneG ~ b i g e r i n e l l o i d e s cushmaniTlcmelfa be]aousensis Zone

UpperAptlan


Globigerinelloldes barriHedbergelJai ~ j e gorbachikae

T bejaouaensis

H. gorbachikae

G. algerians



248

Fig.5 -Correlationofplanktonlc foramlnlferal zonal schemes proposed for the AptianMaastrlchtlan (stage thicknesses not to scale).


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Thepositionof the Aptian-Albian boundaryin Sergipeis difficultto determine in termsof theso-calledstandard zonation. The upperAptianHypaeanthoplitesjaeobiand thelowerAlbianLeymeriella tardefureatazones of north-westEurope (Hancock 1991) are not recognizable in Sergipe, if at all present in the TethyanRealm. Indirect correlation, based on theCheloniceras-Eodouvilleieeras lineage representatives, points to abroadly lateAptian age for the lowermostmarinebeds. Theabsence of thegenusDouvilleieeras in these bedsis also significant. Because of the limited geographical distribution of the L. tardefureata Zone, Hancock(1991) suggested that the first appearance of species ofDouvilleieeras should be used instead to define thebase of the Albian. This would mean a shift to a slightly higherboundary, although with the advantage of itsbeing globally recognizable.

Above the upper Aptian fauna in Sergipe there occurs Douvilleieeras sp., which we interpret aslowermostAlbian. This species is followed byDouvilleieeras exgr.mammillatum(Schlotheim, 1813),whichcan be correlated with the upper lowerAlbianDouvilleieeras mammillatum Zone of north-westEurope. Thelower and middle AlbianDouvilleieeras and Oxytropidoeeras ammonite zones of Sergipe are each subdivided into two planktonic foraminiferal zones, the Globigerinelloides eushmani-Ticinella bejaouaensis andTicinella bejaouaensis zones, .and the T,icinella ex gr. primula-Ticinella bejaouaensis and Bitieinellabreggiensis-Tieinella ex gr. primula zones, respectively. These are based chiefly on abundances of Ticinellabejaouaensis Sigal, 1966, as well as on occurrences of species of Globigerinelloides and Hedbergella. Forcorrelation with other areas, see figs. 4 and 5.

The overlying upper Albian Elobieeras and Mortonieeras ammonite wnes are represented by theGlobigerinelloides texomaensis-BiticinellabreggiensisandHedbergella (H.) gorbaehikae-Ticinella raynaudi planktonic foraminiferal zones, respectively. Correlationwith thenorth-westEuropean ammonitezonation(Hancock 1991) is hampered by increased ammonite provincialism in the late Albian, and only a broadassignment to theMortonieeras (M.) inflatum Zone is possible. The Stoliezkaia dispar standard zone hasnot been identified in Sergipe and may be missing.

The lowerCenomanian, i. e. the baseof theCotinguibaFormation, is represented by two foraminiferalzones,Rotalipora brotzeni and Praeglobotruneana delrioensis-Rotalipora appenniniea zones, respectively,in part corresponding to theGraysonites lozoi-Hypoturrilitesbetaitraensisammonite wne. This zone correlates with the broaderMantellieeras mantelli Zone of north-west Europe, although its exact vertiCal extension in relation to thiswne is as yet uncertain. The Albian-Cenomanian boundary is not exposed in Sergipe,but is recorded in well-sections at the boundary between the foraminiferid zones of Hedbergella (H.)gorbaehikae-Tieinella raynaudi and Rotalipora brotzeni. The middle-upper Cenomanian Hedbergella(Whiteinella) baltiea-Hedbergella (W.) brittonensis Zone appears to be subdivisible into three zones on thebasisofammonites.The lowertwo, theAeompsoeeras spathi-DunveganoeerasandAeanthoeerasjukesbrowneiEuealyeoeeraspentagonum zones, correspondbroadly to themiddleCenomanian Turrilites eostatus-aeutusand Aeanthoeeras jukesbrowni subzones of north-west Europe (Hancock 1991), respectively. The upperCenomanianHedbergella (Whiteinella) apriea-Globigerinelloides bentonensis foraminiferal zone containSthe globally distributed ammoniteEuomphaloeeras septemseriatum (Cragin, 1893), which is diagnostic fortheMetoieoeeras geslinianumstandard wne [M. geslinianum (d'Orbigny, 1850) is withdoubtrecorded inSergipe from the underlying Pseudoealyeoeeras harpax-Thomelites aff. sornayi Zone].

Above the apriea-bentonensis/septemseriatum zones correlation becomes difficult; in particular theposition of the Cenomanian-Turonian boundary is uncertain. Smith & Bengtson (1991, p. 9) tentativelycorrelated the Vaseoeeras harttii-Pseudaspidoeerasfooteanum ammonite zone with the Neoeardioeerasjuddii Zone of north-west Europe, i. e. uppermostCenomanian. This is in agreementwith the succession in,for example, Portugal, whereP.footeanum (Stoliczka, 1864) occurs in the N. juddii Zone (Berthou 1984).Hancock (1991, p. 273-274) discussed the varying defmitions of the Cenomanian-Turonian boundary, andKennedy & Cobban (1991) proposed that the boundary should be drawn at the base of a Watinoeerasdevonense Zone, which is recognizable in Europe and in theU.S. Western Interior. W. devonense Wright&Kennedy, 1981, itself does not occur in Sergipe, but the faunal association of theWatinoeeras amudarienseKamerunoeeras seitzi ammonite zone places this zone firmly in the lower Turonian, and at least partialcontemporaneity with theW. devonense Zone appears probable. The underlying problematic V. harttii-P.footeanum Zone contains pseudotissotiids known from other areas, where they have consistently beenreferred to the Turonian. Other elements of this zone, for example, Euomphaloeeras aff. septemseriatum,point rather toa Cenomanian age (cf. also the Cenomanian occurrenceofP.footeanum in Portugal (Berthou1984, which suggests a mixed assemblage. Occurrences in this zone of the inocerarnid bivalveMytiloides

249

Thepositionof theAptian-Albian boundary in Sergipeis difficultto determinein terms of theso-calledstandard zonation.The upperAptianHypaeanthoplitesjaeobi and thelowerAlbianLeymeriella tardefureatazones of north-west Europe (Hancock 1991) are not recognizable in Sergipe, if at all present in the TethyanRealm. Indirectcorrelation, based on the Cheloniceras-Eodouvilleieeras lineage representatives, points to abroadly lateAptian age for the lowermostmarine beds.The absence of thegenusDouvilleieeras in these bedsis also significant. Because of the limited geographical distribution of the L. tardefureata Zone, Hancock(1991) suggested that the first appearance of species ofDouvilleieeras should be used instead to define thebase of the Albian. This wouldmean a shift to a slightly higher boundary, although with the advantage of itsbeing globally recognizable.

Above the upper Aptian fauna in Sergipe there occurs Douvilleieeras sp., which we interpret aslowermost Albian. This species is followedbyDouvilleieerasexgr.mammillatum (Schlotheim, 1813),whichcan be correlatedwith the upper lower AlbianDouvilleieerasmammillatum Zone of north-westEurope. Thelower and middle AlbianDouvilleieeras and Oxytropidoeeras ammonite zones of Sergipe are each subdivided into two planktonic foraminiferal zones, the Globigerinelloides eushmani-Ticinella bejaouaensis andTicinella bejaouaensis zones, .and the T,icinella ex gr. primula-Ticinella bejaouaensis and Bitieinellabreggiensis-Tieinellaex gr. primula zones, respectively. These are based chiefly on abundances of Ticinellabejaouaensis Sigal, 1966, as well as on occurrences of species of Globigerinelloides and Hedbergella. Forcorrelation with other areas, see figs. 4 and 5.

The overlying upper Albian Elobieeras and Mortonieeras ammonite wnes are represented by theGlobigerinelloides texomaensis-BiticinellabreggiensisandHedbergella (H.) gorbaehikae-Ticinella raynaudi planktonic foraminiferal zones, respectively. Correlation withthe north-westEuropeanammonite zonation(Hancock 1991) is hampered by increased ammonite provincialism in the late Albian, and only a broadassignment to theMortonieeras (M.) inflatum Zone is possible. The Stoliezkaia dispar standard zone hasnot been identified in Sergipe and may be missing.

The lowerCenomanian, i. e. the baseof theCotinguibaFormation, is representedby two foraminiferalzones,Rotaliporabrotzeni and Praeglobotruneanadelrioensis-Rotaliporaappenniniea zones, respectively,in part corresponding to theGraysonites lozoi-Hypoturrilites betaitraensis ammonite wne. This zone correlates with the broaderMantellieeras mantelli Zone of north-west Europe, although its exact vertiCal extension in relation to thiswne is as yet uncertain. The Albian-Cenomanian boundary is not exposed in Sergipe,but is recorded in well-sections at the boundary between the foraminiferid zones of Hedbergella (H.)gorbaehikae-Tieinella raynaudi and Rotalipora brotzeni. The middle-upper Cenomanian Hedbergella(Whiteinella) baltiea-Hedbergella (W.) brittonensis Zone appears to be subdivisible into three zones on thebasisofammonites. The lower two, theAeompsoeeras spathi-DunveganoeerasandAeanthoeerasjukesbrowneiEuealyeoeeraspentagonum zones, correspond broadly to themiddleCenomanian Turrilites eostatus-aeutusand Aeanthoeeras jukesbrowni subzones of north-west Europe (Hancock 1991), respectively. The upperCenomanian Hedbergella (Whiteinella) apriea-Globigerinelloides bentonensis foraminiferal zone containsthe globally distributed ammonite Euomphaloeeras septemseriatum (Cragin, 1893), which is diagnostic fortheMetoieoeerasgeslinianum standard wne [M. geslinianum (d'Orbigny, 1850) is with doubtrecorded inSergipe from the underlying Pseudoealyeoeeras harpax-Thomelites aff. sornayi Zone].

Above the apriea-bentonensis/septemseriatum zones correlation becomes difficult; in particular theposition of the Cenomanian-Turonian boundary is uncertain. Smith & Bengtson (1991, p. 9) tentativelycorrelated the Vaseoeeras harttii-Pseudaspidoeerasfooteanum ammonite zone with the Neoeardioeerasjuddii Zone of north-west Europe, i. e. uppermost Cenomanian. This is in agreement with the succession in,for example, Portugal, whereP.footeanum (Stoliczka, 1864) occurs in the N. juddii Zone (Berthou 1984).Hancock (1991, p. 273-274) discussed the varying defmitions of the Cenomanian-Turonian boundary, andKennedy & Cobban (1991) proposed that the boundary should be drawn at the base of a Watinoeerasdevonense Zone, which is recognizable in Europe and in the U.S. Western Interior. W. devonense Wright&Kennedy, 1981, itself does not occur in Sergipe, butthe faunal associationof theWatinoeeras amudarienseKamerunoeeras seitzi ammonite zone places this zone firmly in the lower Turonian, and at least partialcontemporaneitywith theW. devonense Zone appears probable. The underlying problematic V. harttii-P.footeanum Zone contains pseudotissotiids known from other areas, where they have consistently beenreferred to the Turonian. Other elements of this zone, for example, Euomphaloeeras aff. septemseriatum,point rather to a Cenomanian age (cf. also the Cenomanian occurrenceofP.footeanum in Portugal (Berthou1984, which suggests a mixed assemblage. Occurrences in this zone of the inoceramid bivalveMytiloides

249

Thepositionof theAptian-Albian boundary in Sergipeis difficultto determinein terms of theso-calledstandard zonation.The upperAptianHypaeanthoplitesjaeobi andthelower AlbianLeymeriella tardefureatazones of north-west Europe (Hancock 1991) are not recognizable in Sergipe, if at all present in the TethyanRealm. Indirectcorrelation, based on the Cheloniceras-Eodouvilleieeras lineage representatives, points to abroadly lateAptian age for the lowermostmarine beds.The absence of thegenusDouvilleieeras in these bedsis also significant. Because of the limited geographical distribution of the L. tardefureata Zone, Hancock(1991) suggested that the first appearance of species ofDouvilleieeras should be used instead to define thebase of the Albian. This wouldmean a shift to a slightly higher boundary, although with the advantage of itsbeing globally recognizable.

Above the upper Aptian fauna in Sergipe there occurs Douvilleieeras sp., which we interpret aslowermost Albian. This species is followedbyDouvilleieerasexgr.mammillatum (Schlotheim, 1813),whichcan be correlatedwith the upper lower AlbianDouvilleieerasmammillatum Zone of north-westEurope. Thelower and middle AlbianDouvilleieeras and Oxytropidoeeras ammonite zones of Sergipe are each subdivided into two planktonic foraminiferal zones, the Globigerinelloides eushmani-Ticinella bejaouaensis andTicinella bejaouaensis zones, .and the T,icinella ex gr. primula-Ticinella bejaouaensis and Bitieinellabreggiensis-Tieinellaex gr. primula zones, respectively. These are based chiefly on abundances of Ticinellabejaouaensis Sigal, 1966, as well as on occurrences of species of Globigerinelloides and Hedbergella. Forcorrelation with other areas, see figs. 4 and 5.

The overlying upper Albian Elobieeras and Mortonieeras ammonite wnes are represented by theGlobigerinelloides texomaensis-BiticinellabreggiensisandHedbergella (H.) gorbaehikae-Ticinella raynaudi planktonic foraminiferal zones, respectively. Correlation withthe north-westEuropeanammonite zonation(Hancock 1991) is hampered by increased ammonite provincialism in the late Albian, and only a broadassignment to theMortonieeras (M.) inflatum Zone is possible. The Stoliezkaia dispar standard zone hasnot been identified in Sergipe and may be missing.

The lowerCenomanian, i. e. the baseof theCotinguibaFormation, is representedby two foraminiferalzones,Rotaliporabrotzeni and Praeglobotruneanadelrioensis-Rotaliporaappenniniea zones, respectively,in part corresponding to theGraysonites lozoi-Hypoturrilites betaitraensis ammonite wne. This zone correlates with the broaderMantellieeras mantelli Zone of north-west Europe, although its exact vertiCal extension in relation to thiswne is as yet uncertain. The Albian-Cenomanian boundary is not exposed in Sergipe,but is recorded in well-sections at the boundary between the foraminiferid zones of Hedbergella (H.)gorbaehikae-Tieinella raynaudi and Rotalipora brotzeni. The middle-upper Cenomanian Hedbergella(Whiteinella) baltiea-Hedbergella (W.) brittonensis Zone appears to be subdivisible into three zones on thebasisofammonites. The lower two, theAeompsoeeras spathi-DunveganoeerasandAeanthoeerasjukesbrowneiEuealyeoeeraspentagonum zones, correspond broadly to themiddleCenomanian Turrilites eostatus-aeutusand Aeanthoeeras jukesbrowni subzones of north-west Europe (Hancock 1991), respectively. The upperCenomanian Hedbergella (Whiteinella) apriea-Globigerinelloides bentonensis foraminiferal zone containSthe globally distributed ammonite Euomphaloeeras septemseriatum (Cragin, 1893), which is diagnostic fortheMetoieoeerasgeslinianum standard wne [M. geslinianum (d'Orbigny, 1850) is with doubtrecorded inSergipe from the underlying Pseudoealyeoeeras harpax-Thomelites aff. sornayi Zone].

Above the apriea-bentonensis/septemseriatum zones correlation becomes difficult; in particular theposition of the Cenomanian-Turonian boundary is uncertain. Smith & Bengtson (1991, p. 9) tentativelycorrelated the Vaseoeeras harttii-Pseudaspidoeerasfooteanum ammonite zone with the Neoeardioeerasjuddii Zone of north-west Europe, i. e. uppermost Cenomanian. This is in agreement with the succession in,for example, Portugal, whereP.footeanum (Stoliczka, 1864) occurs in the N. juddii Zone (Berthou 1984).Hancock (1991, p. 273-274) discussed the varying defmitions of the Cenomanian-Turonian boundary, andKennedy & Cobban (1991) proposed that the boundary should be drawn at the base of a Watinoeerasdevonense Zone, which is recognizable in Europe and in the U.S. Western Interior. W. devonense Wright&Kennedy, 1981, itself does not occur in Sergipe, butthe faunal associationof theWatinoeeras amudarienseKamerunoeeras seitzi ammonite zone places this zone firmly in the lower Turonian, and at least partialcontemporaneitywith theW. devonense Zone appears probable. The underlying problematic V. harttii-P.footeanum Zone contains pseudotissotiids known from other areas, where they have consistently beenreferred to the Turonian. Other elements of this zone, for example, Euomphaloeeras aff. septemseriatum,point rather to a Cenomanian age (cf. also the Cenomanian occurrenceofP.footeanum in Portugal (Berthou1984, which suggests a mixed assemblage. Occurrences in this zone of the inocerarnid bivalveMytiloides

249


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(cf. Kauffman & Bengtson 1985) are as yet to be evaluated. The coeval Hedbergella (Whiteinella)archaeocretacea-Heterohelix reussi foraminiferal zone lacks diagnostic elements for interregional correlation. The H. (W.) archaeocretacea-H. reussi and V. harttii-P.footeanum zones are thus here interpreted asstraddling theCenomanian-Turonian boundary, using the defmition of Kennedy & Cobban (1991).The lower-middle Turonian is represented by the planktonic foraminiferal zone of Hedbergella(Whiteinella) aprica-Hedbergella (Whiteinella) baltica and the two ammonite zones of Watinocerasamudariense-Kamerunoceras seitzi and Mammites nodosoides-Kamerunoceras turoniense. These zonescorrelatewell with theWatinoceras spp. andMammites nodosoides zonesofnorth-westEurope,respectively.The middle Turonian Collignoniceras woollgari standard zone has not been recognized in Sergipe,probably in part owing to significantdepositional breaks in the present onshore part of the basin (Bengtson1983). The upper Turonian is represented by the approximately coeval Dicarinella primitiva andSubprionocyclus-Reesiditeszones, which correlatewellwith the SubprionocyclusneptuniZoneofnorth-westEurope.The lower-middleConiacian interval is represented by theArchaeoglobigerina cretacea-Dicarinellaprimitiva foraminiferal zone and the Barroisiceras onilahyense-Forr;esteria and Solgerites armatusPrionocycloceras lenti ammonite zones, respectively. Coniacian international zonation is in a state of flux,and the Sergipe sequences cannot as yet be firmly tied to the European or other schemes. It is possible thatthe lowerConiacian is partlymissing in Sergipe, at least in the present onshore areas.TheSolgerites armatusPrionocycloceras lentiZonemarks the endof the carbonate-dominateddepositional cyclein Sergipe. In mostonshore areas there follows a significanthiatus,whereas locally offshore the sequence is morecomplete.Theforaminiferal zone of Dicarinella concavata-Marginotruncana sinuosa spans the Coniacian-Santonianboundary.Only a few ammonites have as yetbeen found in the clasticdeposits formed during thepost-Coniaciancycle, the Pial;abul;u Formation (Bengtson et al., in prep.). The biostratigraphy is based on planktonic foraminiferids, supported by benthic foraminiferal assemblages.

Zonal definitions and characterizationsIn the following, zones are defined and characterized in chronostratigraphical order, using the mostdiagnostic taxa. Additional, stratigraphically less useful taxa, are not listed.Some zones are sharply defined, others are more vaguely characterized, many (especially forammonites) are based on recorded assemblages. For several fossil groupsonly isolated observations of taxaare available (e. g. echinoids, inoceramids, non-inoceramid bivalves, gastropods) ; these arecurrently beingintegrated into the scheme.Because of caving and sample mixing that commonly occurs in oil-well cuttings, normally only thetop down-hole occurrences (the evolutionary extinction datum level or the local last appearance in thestratigraphical section due to major environmental changes) of microfossils and their peaks of abundanceshave biostratigraphical significance. However, with the careful examination of all the assemblages anddifferentiation of caved and/or reworked specimens (e. g., decrease in abundance and stray occurrences, differentiation in colour and preservation) itwas alsopossible to record the first appearances of several taxa (see

figs. 6-7), thereby allowing the establishment of a more refined microbiostratigraphical framework.The benthic microfaunas are depth-related and biostratigraphically less useful than the planktonic

ones. However, facies-constant stratigraphical sequences, where no major environmental change has takenplace over a long time-interval, occur within the thick succession of the Pial;abul;u Formation (CalumbiMember) in the offshore south-eastern part of the basin (Mosqueiro Low). The study of these strata allowsthe selection of benthic zonal markers and the precise recognition of their first appearance and extinctionlevels, which provide potentially isochronous zonal boundaries for the post-Coniacian deposits within thebasin. Unless otherwise indicated the foraminiferal and ammonite zones are Oppelzones (Hedberg 1976,p. 58), the boundariesofwhich aremarked for ammoniteschieflyby first appearances and for foraminiferidsby first and/or last appearances. The zones are named after one ormore characteristic taxa that occur in thezone, although not necessarily confined to the zone. More environmentally controlled, locally applicableassemblage zones (sensu Hedberg 1976, p. 50-52) are proposed for thebenthic foraminiferids of the upperAptian.

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(cf. Kauffman & Bengtson 1985) are as yet to be evaluated. The coeval Hedbergella (Whiteinella)archaeocretacea-Heterohelix reussi foraminiferal zone lacks diagnostic elements for interregional correlation. The H. (W.) archaeocretacea-H. reussi and V. harttii-P.footeanum zones are thus here interpreted asstraddl

Koutsoukos & Bengtson 1993

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