_________________________________________ O_C __ EA_N_O_L_O_G_'_C_A_A_C_T_A_, _1_98_'_,_N_O_S_P_~e-------

Paleoenvironments P .. Jc:ocnvi ronmenl Gulf of Guinea

For:.mÎniferli Transl:fcssions·regn:ssions

Black Sh .. les

of the Gulf of Guinea PaJéoenvironnemenl Golfe de Guinée

For:tminifèrcs Transgressions- régressions

Mnmes noires

ABSTRACT

RÉSUME

S. W. Pellefs Dcpartmenl of Geology. Universi ty of Ibadan, Ibadan. Nigeria.

Foraminireral asse mblages in Ihrec marginal bas ins in the Gulf of Guinea (name] y, the Benue Trough, the Dahomey Embaymenl , the Niger Della) show maximum development during the major marine transgressions which transpircd in the Middle 10 Laie Albian, Late Cenomanhtn 10 Early Turonian , LaIe Turonian 10 Early Sanlonian , Late Campanian 10 Maas trichtian, Middle to LaIe Paleoce ne, M.iddle 10 Laie Eocene , Middle Üligocene , and Early to Middle Miocene . The Oligoccnc and younger transgressions are more pronounced in the Niger Delta where foss ilife rou~ marine sha les a re interealated wi thin delt'l ie sands. Major transgressio ns in the Gulf of Gui nea eoincided with global LaIe Cretaeeous to Tertiary sca level rises. The transgressive sha llow shelf benthonie fo raminife ral assemblages in the exposed pariS of the Benue T rough and Ihe Dahomey Embayme nt show a progressive increase in faunal d iversity from the Albian to the Eocene. This was due 10 improve marine conditions in these margi nal bas ins when oceanic circula tion was es tablished in the Gulf of Guinea . The weil known Mid-Cre taceous oxygen tlef icienc ies in the world 's oceans and epicontinental seas were feh in the Ben ue Trough where anaerobic shales and oxygen.starved bent honic fomm iniferal asse mblages occur in Upper Cenomanian-Lower Turonian and in Upper Turon ian-Lowcr Sanlo nian blac k shalcs.

Oceanol. Ac/(1. 1981. Proceedings 26'h lnte rnation.,l Geologieal Congress, Geology of contÎnenta l margins symposium , Paris, July 7-17. 1980, 81-85 .

Paléocnvi ro nnemen ts du Golfe de Guinée .

Les assemblages de foraminifères de tro is bassins de la marge du Golfe de Guinée (la fo sse de la Bénoué . le bassin Ju Dahomey , le del ta du Niger) montrent un développement maximal pendant les transgressions marines majeures durilnt l'Albien moyen-supérieur , le Cé nomanien supé rieur-Turonien inférieur , le Turonien supérieur·Santonien inférieur , le Campanien supé­r ieur· Miles lrichtien. le Paléocène moyen-supérieur, t'Eocène moye n-supérieur . t'O ligocène moyen e t te Miocène inférieur à moyen. Les transgressions de l'Oligocè ne et celtes pl us récentes sont plus pro noncées dans le delta du Niger où des argiles marines fossilifè res sont interca lées llvec des sables deltaïques. Les transgressions majeures dllns le Golfe de G ui née ont coïnc idé avec les vari,lt ions eus tatiques pos it ives globales du Crétacé supérieur el d u Tert iai re . Les assemblages de foraminifè res benthiques assoc iés aux dépôts. peu profonds, transgress ifs montre nt une augmenlll iion progressive de leur diversité de l'Albie n à J"Eocène. Ceci s'e xplique par l'accent uation des influences marines dans ces bassi ns de marge quand la c irculat io n océanique s'est établie dans le Gol fe de Guinée. Les épisodes anoxiques bien con nus du Crétacé moyen dans les oeéllOS el les mers épicontinentales onl é té ressent is da ns la fosse de la Bénoué. Des argiles e t des assemblages de fo raminifères benthiques ind iquant un milieu appauvri en oxygè ne se trou ve nt dans les marnes noires du Cénomanie n supérie ur. Turonien infé r ieur e t du Turonien supéricur-So:.n tonie n inférieur.

Dct'lI/lOl . AC/(j . 1981. Actes 26" Congrès International de Géologie. colloque Géologie des marges contine ntales, Pil ris, 7-17 juil. 1980, 81·85.

81

S . W PETIERS

INTRO DUCTIO N

ln a recent review of the Cretaceous hislory of the South Atlantie Ocean Reyment (1980) highlighted rive principal s tages in the paleo-oceflnographic evolution of the Gulf of Guinea. These s tages were controlled by tectonic-eus tatic and geoidal eustatic sea level maxima and comprised 1) the initial Late Middle Albinn ~ha llow marine connexion between the North and South At lantiç Oçeans and conse­quently the creation of the Gulf of Guinea; 2) a Late Cc nomanian to Early Turonian tra nsgressio n which :.wamp­cd marginal areas ; ]) a Late Turoninn to Early Santonian transgression during which true oceanic conditions were established ; 4) a Late Campanian to Early Maastrichtian transgression; and 5) the circulation of deep and weil oxygenated water during the Paleogene . The approll imate exte nt of marine inUuence in the GuU of Guinea uuring four of these transgressive peaks is shown in Figure 1. This paleogeographie sketch map was compiled from personal field observations and from field a nd borehole data which are available in the fo llowing publications: Adeleye (1974). Carter et al. (196]). De Klasz and Jan Du Chene (1979), Jan Du Chene el al. (1978). Murat (1972). Offodile (1976), Pellers (1 978 a. b : 1979 a : 1980). Re ymen t (1965), Re yre (1966).

Foraminiferal assemblages from mostly outcropping marine beds of Albian to Eocene age (Fig. 1) are used in this :Irt icle to interprete the paleoen vironmental çonditions that pre vail ­cd in Ihe Gul f of Guinea during the major transgressions. Since they are mostly marine organisms foraminifera are more common during the marine transgressions than during regres.) io ns. The tran.)gres~ i ve beds in Ihis stud y are dated u:.in!; the ammonite biochronological framework of Rey· ment (1965) and Re yme nt and Tait (1972), and the microp.'l­leontological correlations recently presented by Pellers (1980). The widely used foramtmferal pa]eoecologtc statlS­tic:. suçh as the planktonicJbentho nic ratio, the alpha diversilY index and the information function (Lipps el al.. 1979) enable qualitative interpretations of the paleobath y­metry , paieoslllinit ies. ollygen content. and nuuient :lVail.l­bilit y in the Gulf of Guinea. Cretaceous marine beds were sampled mostly in the Renue Trou!;h where the sparse benthonic foraminiferal mkrofaunas point to abnormal ~ alini l ies dudng the init ial Albian transgression. Exclusively planktonic foram iniferal assembl:.lges allest to ' IOOXIC bot­tom conditions during the Late Cenomanian to Earl y

G U L ~ " GIUN t A zoo ~.,

82

Turonian transgression. The La te Turonian to Early Sa nto­nian predominantl y planktonic microfaunas wi th low ben­thonic diversities suggest continued oxygen depletion ;tt the bottom of the Benue Sea , while the more di ver:.c L'tte Campanian to Maastrichtian assemblages especiaJJy in the Dahomey Embayment. indîcate improved bollom circula­tion. In the Dahomey Embayment the cool water plank tonic a:.semblages in the Eocene pho:.phatic beds :.ugge~t cOlbtal upwelling.

Planktonic foraminiferal biochronological uli ta from the regional marine sh'lles in the subsurface of the Niger Delta ;tllow the identification of the ma jor rises in se'l level and the cons truction of a complete though genenllized tmn:.­gressive-regressive curve for the Nigerian part of the Gulf of Guinea (Fig. 2).

AL BIAN TRAN SG RESS ION

Silts tones. shales and limestones referred to as the A~u River Formation in the middle Benue Trough and in the southern part where the Abakaliki Shale is a lso exposed have yielded Late Middle Albian and Late Albian oxytropi. doceratid and diploceratid ammonites in sorne local ities (Reyment. 1955 ; 1965 ; orfodile. Rtyment, 1977). Recause of ilS sparse moJJuscan f<luna Reyment (1965) inferred a sh;IJJow marine environment which was diluted by run-off from land . Albian foraminifera are very flIre in the Benue Trough. About 15 m of allernating lime stone and shale of probably AlbÎlm lige whieh lire exposed in a recenl quarry at Yandev yieldeu onl y one species of Gal'elillella in the shaly limestone beds. This sequence rests directly o n b:lsement roc ks which are exposed nearby. and represent the first marine flood ing of the lI rea during which only Gal'eli'lrllll sp . could survive the probably lower than normal marine sahmtles in the basin. An01 her basat sequence comprising bright green shales are exposed in a recent roadcut near Wukari. These shales. which may be of Albinn age. are barren and probllbly represent the coastal muds o f the Albian transgre:.sio n. Nca r Calabar in southeastern Nigeri .. . the s tromatolitic . oolitic, and karstic JimeslOne uni t of the Odukpani Formation of latest Albian age (Fors ter. 197K) contains a very sparse a~se mblllge of Trocholj,w odllkpa­Iliel1sis. Hyperwll/llinli. Ballly.tif/holl and o ther arcnaceous fontmi nifem which support shaJlow red'II origin fo r Ihe Iimes tone (Fayose, 1978).

Figure l Sktlch /IIUp ul IIrt Gulf QI Gui/lta sho"';nR IlpproX;/IIlllt lill/ils ul muTine inf/llrncr frutti Middle Albilln 10 lht Pl1/tllgt.'nt.

Figure 2

, ~ M , _

••

• • •• D'

'''0_ 1 J>CI'OI,e ,

Slrutigruphic CQrrelmiOIi chan for Cllustu l busins ill SOlltllem Nigeria showillN a 1IllliruliuJ trU/lsgrlssi,'e-regrf'Ssi\'e CUfI' l!.

LATE CENO MAN IAN-EAR L y TURONIAN TRANS­GRESS ION

Cenomanian to Turonian bcds a re known in the subsurface of southwes tern Nigeria (De Klasz, Jan Du C hene , 1979 ; Jan Du Chene et al. , 1979) and a re exposed in the middle and southern Benue Trough as the marine and marginal marine shales. limestones. and subtidal sandstones of the Eze-Aku (correct spelli ng for stralOtype is Eziyiaku) Form<llion (Banerjee . 1980; Offodile, 1976 ; Reyment. 1965). In the vicini ty of Calabar where LaIe Ccnomanian to Early Turo­nian marine beds of the Eze-Aku Formation arc exposcd (Peners, 1980) the foraminifera l assemblages in sorne o f the shales a re excJusively of the neritopelagic type comprisi ng Heterohelix morel/will and Hedbergel/a plO/lispira . The absence of benthonic fO fltminifera from these interyals suggests anaerobic bottom condi tions as in cocyal depos its in the Western rnterior of North America (Eicher , WorSlcl1 , 1970) and in the South Atlantic Ocean (yan Andel el al. , 1977).

Other Lower Turonian deposits in the Benue Trough are the transitio nal Yolde Formation, the marine Duk ul Formation . and the Gongila Formation (Carte r et al. , 1963) which represent the northeastward facies of the widespread I.ale Cenoma nia n to Early Turonian transgression.

• 3

PALEOENVIRONMENTS OF THE GULF OF GUINEA

LATE TURON IA N-EA RLY SANT ON rAN TRA NS­GRESSION

A more extensiye marine transgression transpired in the Gulf of Guinea from Ihe LateTuronian to the Coniacian and waned in the Early Santon ian. T he Awgu Formation (Fig. 2) which is lithologicall y continuous with the Eze-Aku Forma­tion, was deposited in the Dahomey Embaymenl (Uillman. 1976), and in Ihe southern Benue Trough (Reyment , 1965) while the Jessu and Sukuliye Formations were J eposi ted in the northeas tern Benue Trough (Carte r et al., 1963 ; Enu , 1978). Keelcd planktonic foraminifcra such as Margillotrl/lt ­cami rellÛ, M. difformis and M . sigali. which ind icate Laie Turonian to Coniac ia n age as weil as Early Coniacian coccoliths occur in the limesto ne and shale sequence of the Awgu Formation at the Nkalagu quarry (Peners, 1978 a : 1980). On the eyidence of the keeled planktonic species <lnd the high percentage of planktonic fo raminifera (Fig. 3), the Nkalagu succession is the deepes t marine interya! so fa r reported in the Benue Trough , and was assigned a maximum w,lter depth of about 30 m (Peners, 1978 a ), Alpha divers ity yalues for the benthonic fo ramin iferal assemblages in the N kalagu succession are generally less than 2 and with the flood abundances of only Gavelinella sp. a t sorne interyals, sugges t a n oxygen staryed assemblage. This means that the

~W~U .c~ .... 'O" ••• c . ... ou.o.,

._no.o 'COI ~U IOM

. w . .... u Quun

PIon' /S.nt~~.

'"m"": ... 00 ~j! .

"'~. ' 0 __ _

"

" l

Figure J

. " ", . .. ..... 0" '"!JIU· ~o.' "uCOU"T U'.[I'W~ •

PoOk/8tnlto %

." o ~o 100

!"" o. ....... :: Sha l.

Limule ... - : Morl no d" l ..

Pionkton!c FOIotn. a..thonie FOfO ....

.... Kt .0 . .. . '00_ ' u ~ o .... u~ .. ~ ON uue,,· ' COIT " •• ~ou.' U ... nl ....

P'<I"'/a.nt~% o "0 100

':I:~~ • :=:'

, ---.p...... ..

" , . •

, ~ V ,

,,/ • ~

•• ,

ri' , C" ~ ~ ~,

"

r

,

'00'

Il,,.,.. Fo"nolkm X (Co"'oeion ) • Nkpe' o SlIal.

(MooI" leMlonl

EWlko,o ,0", • • ''''0 Shol. (Pal.oe ... 1

0. ",,,,.h ,0",.

1 Eo~.n. )

Gtntraliztd fo rumilliftrul papu/miOlt Sialis/les for tlle Coui/ICiUlI /Q

Eocellt of the 8 erlue 'frlJllJ[h IIlId th" Dalwlltt)· Emha)'merll .

S. W. PETTERS

Mid-CreUlceous oceanic anoxie event (Sehlanger. Jenkyns. 1976) was still evide nl in the Benue Trough a t the lime of peak marine transgression. The reappcarance of exclusively neri topclagic foraminife ra wit h only Whilei"el/a baltica in some blac k 5hales a l thc top part of the Awgu Formation near Awg~ town suggeslS complete depletio n of oxygen on the sea boltom duri ng Ihe Early Santonian withdrawal of the sea.

CAMPAN IAN-MAASTRl CHTIAN TR ANSGRESSION

The transgressive N kporo Shale in southern Nigeria, which was deposited after the Santonian fo lding episode in the Be nue Trough. contains Campanian to LaIe Maasl r ichtian heterohelicid, rugoglo-bigerinid . and globotruncanid planktonic species in Ihe subsurface of sou thwe~tern Nige­ria near Okit ipupa, and in reccnt roadcuts near Calabar (Adego ke el al .. 1980: Pelle rs. 1980). AlIho ugh not as ex tensive as the earl ier transgressions. Ihe LaIe Campanian to Maastr ichtÎa n marine transgress io n supported slightly more diverse be nthonic foraminifc ral assem h l llge~ in sou­Ihern Nigerill even at shallow depths (Fig. 3). This was due to ge nerally improved and deeper oceanic c ircul ation in Ihe Gulf of Guinea. The Late Campanian-Maasl r icht ian trans­gression e reated a sha llow embayment into the southern Benue Trough and the Nupe Basin where abundant brackis h marsh a renaceous fom minifera were recorded from near Lokoja (Ja n Du C hene et al .• 1978) and from the Enugu shale in Enugu (l'etiers, 1979 Il).

PALEOCENE

Wilh the outgrowth of Ihe Niger Delta in the Danian (Reyme nt. 1980) Tertiary marine Iran~gress ions in the Gulf of Guinea could not extend as far inland as previously. Ge neraJJy Ihe shoreline of Tertiary marine tra nsgressions migrated progressively southward bccause of lotrong dcllaic progradation. Middle 10 Late Paleocene marine deposits in soulhern Nigeria include the Imo Shale and its Niger Delta eq ui valent. the Aklltll Shale. and the Ewekoro LimeslOne in southwe~tern Ni gerill . Although the low planktonic pcr cent in the Ewc koro Form;H io n a nd in exposures of the Imo Shale in southwestern Nigeria. the low alpha diversity values for benthonic forami nifera (Fig. 3), and the bent ho­nic species composition (Petle rs. 1979 b) suggest sha llow inner nerit ic depths. Ihe occurrence of keeled planktonic species such as MoroWliella allgulalll. M. acutispira, and M. aequa (Pellers, Olsson. 1979) a lle.~ 1 10 the prevlllcnce of fully oceanic condi t ions offshorc. 8arriers 10 deep oceanic circulation broke down in both the South and North Atlantic Oceans d uring the Paleogene and allowed the enuy of deep weil oxygenated waters (Berggren. 1978; Reyment. 1980).

EOCENE

Lower and Middle Eocene depos its in the Gulf of Guinea include the clastic eKposed Ameke and Nanka Fonnations in eastern Nigeria. the subsurface Agbada Formation in the Niger Delta. and the phosphatic Oshmun Formation in the Dahomey Embayment (Fig. 2). Exposures of the top part of the Ameke FormatÎon near Umuahia and subsurface samples of the Oshosun Formation contain abundanl and

84

weil preserved foraminifera, ostracods . and radiolaria. Foraminife ral indicators of shallow inner neri t ic deplhs for . the top part of the Ameke Formation include the low ph:lflktonic foramÎni feral per cent. the low alpha diversity value (Fig. 3). and the low information funct io n of 1.2 to 1.7. However. the common occurrence of radiolarians in the Arneke and Oshosun samples and the abundance of subbolέnid and acarininid planklonic forllminifera in the Oshosun Formation suggesl the infl uence o f the cold Be nguela Currenl and coastal upwelling. In this study. borehole samples of the phosphatie beds in Renin Republic yie lded a bundant plankto nic foraminifera including Acorinino esnaensis. A. pe"tacamerata. A . pseudotopilensis, A. so/dadoensi~· so/dadoensis. G/oborOla/ia wilcoxerr sis , and Subbotina inaequispim. This subbol.inid-acarininid associa­tion characterized Eocene high lati tude regions (Rerggrcn. 1978) and probabl y appeared a t shullow depths in Ihe Gulf of Guinea as a result of coastal upwelling, a process thal favo ured phosphate sedimentation in the Dahomey Embay­me nt.

TERTIARY T RANSG RESS IO NS IN THE NIGER DELTA

Recent foraminiferal biostratigraphic aoal ys is (Pellers, 1979 (..) a nd work in progress h,IVe shown that the Niger Delta offlap sequence conla ins highly fossilife rous mari ne shales which were deposited during major marine tra nsgres­s io ns. T he occurrence of abundan t planktonic foraminifera in these widespread marine shales aJlow the recognition of sorne of the major transgressio ns (Fig. 2) which were reported by Vail el al. (1977) in their account of global episodes of sea level r ises. Diagnostic planktonic foramini­fe ra i associations and markers ha ve e nabled Ihe identifica­tion o f the Middle to Early La tc Paleocene G/oborotlllia pusilla pusilla-Moro1.ollella U/Igulala Zone and the lower part of the PllI/lOrolaliles fJseudomenardii Zone. the Late Eurly Eocene Acarini"(l penlacamerata Zone, Ihe Early Late Eocene Trlmcarotrlioides rohri extinc t ion dat um. the Early to Middle Oligocene Cassigerirrella chipa/e" l·ü­Pseudoha Sligeri"a micra Zone. the Early Miocenc Globo­rol(llill kll~/eri Zone , and the Middle Miocene Gluborotlllia Johsi fohsi Zone.

CONCLUS IONS

Late Cretaceous to Early Tert iary marine transgressions in the Gulf of Guinea are wc!! represented by the r ich forami niferal assemblages in the marginal basins such as the Be nue Trough lInd the Da homey Emlxlymenl. In the Niger Oelta Ihe highly fossiliferous marine shales intercaJated within the thick dellaic sequence were dcpositcd during Late Eocene , Middle OJigocene , and Early to Middle Miocenc sea level riscs.

The high planktonic for,lminiferal pcrcenlages and exclus i­vely planklOnic assemblages in some black shales in the Upper Cenomanillfl to Lower Santonian of thc Benuc Trough :lIIest to nerilOpelagic habi tats for the heterohelicids and globigerine taxa which dominatc these microfaullas. Benthonic foraminifera are either completely absent from SOffie of these shales duc to anaerobic bottom conditions or hilvc very low divers ities on account of insufficient oxygen

at the sea bottom. Oceanic circulation amelioraled in the GuU of Guinea {rom Laie Campania n onwards and cau~ed slightly higher benl honÎc diversities at sha llow deplh~. T he lower planktonic percentages in Tertiary shallow waler assemblages in Ihe Gulf of Guinea wa~ due 10 the preference of Tertiary pJanktonic foraminife ra for ocennic habitats. The prevalence of cool watcr planktonic foraminifcra in Eocene phosphatic beds in the Dahomey Embayment was

RE FERENCES

Adegok~ O. S., P~llen S. W., Enu K I., Ako 8 . O. , Adf'gok~. Anthony C. W., Qdebode M. O., Cok~r S. L.. Emofurleta W. E., 1980. Thf biluminous sands af Ondo Imd Ogun S/atu of Nigeria. Spec. Pub!. 2, Nigerian Mining and Geosciences Society. 27-37.

Adel~y~ D. R., 1974. A fauna from Ihe ironsloneof the midd!e Niger v:J lley, Nigeria, Niger. J. Minu. Geol.. 8, 45-48.

Harnejee 1., 19110. A subtidal bar model for the Eze-Aku saBdsto­nes, Nigeria. Sediment. Geul.. 25, 291 -309.

IkrggN:n W. A., 1978. Rece nt advance~ in Cenozoic planktonic foraminiferal biosl ra ligraphy. biochronol08Y, IInd biolleography : Atlanlic Ocean. MicmpalronfOlogy, 24, 337-370.

BlIlman H. G., 1976. Offshore stratigraphy of tM: Dahomey Embayment, West Africa, AbSlraclS. 7" African Micropal. Collo­quillnl. lie-Ife, Nigeria, 16-17.

Carter J. D., Bar ber W " Tll i! E . A., JOIIC:!! G. P ., 1963 . The geology of pariS of Adamawa, Bauchi and Bornu Provinces in North­eaSlern Nil,'Cria, Geai. SUT\'. Niger. Bull .. 2, 108 p.

De Klan L , Jan Du Cbene R. E. , 1979. Presence of Albian­Cenomanian in soulhwes tern Nigeria and iL~ paleolleogr«phic implications, C. R. Séances Soc. Ph ys. Hisl. Nat. Genil,t, N.S .. J, 10-1 5. Elcber D. L .. WorsteJl P. , 1970. Ce nomanian and Turon; .. n forami ­nifera from the Great Plains , United 51111es. Micmpaleantology. 16, 269-324. Enu E. J., 1978. Contribution à l'l:ttide sédimentologiqLle des formations c rétacées de la région de Cham (Vallée de la Bénoue. Nigeria nord-oriental ). unpublished Pli. D. Thelis, Uni". Nice. Fllyœe E. A., 1978. Depositional e nvi/onments of carbonates Cala­bar flank . soulheastern Nigeria. Niger. J . Miner. Geol .. 15, 1-13.

Fonder R. , 1978. Evidenee for an open seaway belween northern aBd SOUlhern proto-Atlantic in Albian limes, Natu", 272, 158-159.

Jan Du Cbene R. E., De KllI$z 1., Ar~hibung E. E., 1979. Biostrali­graphic s iudy of Ihe borehote Ojo-l, S W Nigeria . with spe~ial emphasis 0 .. the Cretaceous microflora , Rel'. MicrQpaltQntal.. 21, 123-139. l iln Du Cbene R. E., Adegoke O. S., Adedira n S. A., Pe ller~ 5. W., 1978. Palyno logy and for .. minife ra of Ihe l.oknja Sandstone (Maas· tricht;an), Bida Basin. Nigeria. Re". Esp. Micmpaleonwl.. 10, 379-393.

LippsJ. 11. , ~~r W. H., Buzas M. A., Doulll.~ R. G. , K ...... C. A., 1979. Foraminiferal ecology aBd paleoecology, SEPM Short Course, 6, 198 p. MUni t R. C., 1972. Stratigr .. phy and paleolleography of the Crela­ccous and lower Tertiary in SOUlhern Nigeria, in : African ge%g,.. ediled by T. F. J. Dessauvagie and C . A. J . Whileman, 1b;ldan Universily Press, Ibadan, 251-266.

OffodUe M. E. , 1976. The geolagy of the middlt Benue Nigeria, Publ. Palaeo. 10SI. Univ. UppSll la. Spec. 4 , 166 p.

85

PALEOENVIRONMENTS OF THE GULF OF GUI NEA

due 10 the coastal upwelling of deep nutrient-rich waters, a process Ihal favo ured phosphatizalion.

Acknowledgem ents

I lhank Shell Pelroleum Company of Nigeria Lld ., and Gulf Oil Company of Nigeria Ltd. for supplying samples from the Niger Delta.

Offodile M. E. , Reymcnt R. A., 1977. 51ratigraph y of Ihe Keana­Awe area of the middle Benue region of Nigeria, Bull . Geai. Ins/ . Uni". Uppsala. N.S .. 7, 37-66. ~lIers S. W., 19711 a. Mid-Cretaceous paleoenv;ronmenls IInd biostratigl"J.phy of Ihe Senue Trough , Nigeria. Bull. Geol. Soc. Am., 89, 151-154.

" ellers S. W., 19711 b. SlratigrJ.phic evolUlion of the Henue Troullb and ils implie:llions for lhe Upper Cretaceoos paleogcography of West Mriea. J. Gtol.. 86, 311-322.

~turs S. W., 1979 a. PaulÎe arenaceous foraminifera from tbe Upper Cretaceous of Ihe Senile Trough. Nigeria. A cra Paleonro/. Pol.. tA, 451-471 .

Pellel'l!l S. W. , 1979 b. Nigerian Paleocene benthoni~ forJ.minifer .. 1 biostra tigrapby, paleoecology. and paleobiogeography. Mor. Micmpaleuntul .. 4, 85-99.

Peller! S. W., 1979 c. Some LaIe Tertiary foraminifera from Parabe·1. Western Niger Deha. Rt,·. Esp. Micropoleonlol .. Il, 119·133.

Penen S. W., 1980. Biostratigraphy of Upper CrelaceoLis fonuTlini ­fera of the Benue Trough. Nigeria. J . For(Jminiftral Ru .. 10, 3.

P~Uen S. W., Olsson R. K., 1979. Pllmktonic foraminifera from the Ewekoro I,.pe sec tion (Pllleocene) Nigeria. Micropaltolliology, 25, 206-213.

Reymenl R. A. , 1955. The Crelaceous Ammonoidea of Soulhern Nigeria and the Southern Cameroons. Geo/. Sun'. Niger. 8ull .• 25 , 112 p.

Reymenl R. A., 1965. Aspects of the geology of Nigeria. Ibadan Univers ily Press. Ibadan, 145 p .

R~ym~nl R. A., 1980. l'aleo-oceanology and paleobiogeogrnphy of lM: Cretil ceOUS South At lantic Ocean. Deeanol. Ac/a. 3, 1. 127-133.

Keyment R. A., Ta it E. A., 1972. Biostrat igraph ical d .. ting of the early his lory of lhe Soulh Atl"ntic. Philos. Trans. R. Soc. London. Ser. B .. 264, 55-95.

Reyre D., 1%6. H istoÎre géol08ique du bassin de Douala (Came­roun), in: Sedimenlary ba.fins of the Afrieon coasts. 1. Allantie coasl. ediled by D. Reyre , Assoc. Afr. Geol. Surv., Paris. 143-161 .

!Khlanger S. O., lenkyns Il . C., 1976. Cre laceous an"",ic events : c"uses and consequences. Geol. Mijnbou"', 55, 179·HI4.

V.U P. K., Mi tcbum R. M. J r ., T hompson S. III , 1977. Seismic stra ligmphy and global cbanges of sea level, Pa rt 4: g lnb:J1 cycles of relative ehanges of sea level , in: Seismic slrarilvaphy­applications 19 hydrocarbOIl txploralion. ediled by C. E. Payton, Am. Assoc. Pet. Geol.. M .• 26, 113-97.

~Iln Andel T. H_, T bledt J., !Kta ter J . G., " ay W. W., 1977. Deposi l ional history of Ihe South At lantic ()cean during the last 125 mill ion years, J. GeaI.. 85, 651·698.

86