26. ALBIAN TO SENONIAN PALYNOLOGY OF SITE 364, .26. ALBIAN TO SENONIAN PALYNOLOGY OF SITE 364, ANGOLA

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26. ALBIAN TO SENONIAN PALYNOLOGY OF SITE 364, ANGOLA BASIN

Roger Morgan, Geological and Mining Museum, 36-64 George Street North, Sydney, New South Wales, Australia

ABSTRACTPalynological processing of 19 samples from Site 364 yielded 11

good assemblages. The frequent spores and pollen provide betterbiostratigraphic data than the useful, but rare, dinoflagellates.Cores 42-46 are considered early Albian, Cores 38-40 middleAlbian, Cores 29-32 late Albian, Core 27 Vraconian orCenomanian, and Cores 23-25 late Turonian to Coniacian, withmany reworked Cenomanian-Turonian elements.

The site was located a considerable distance from shore duringthe Cretaceous, or lacked large runoff from major river systems, asmost spores and pollen are windborne. The climate may have beentropical but semi-arid; the vegetation was certainly very differentfrom that at Site 361. Although restricted, marine influence in theform of dinoflagellates existed from the south.

INTRODUCTION

This shore based post-leg study was undertaken atthe Geological Survey of New South Wales, on samplessupplied by Dr. W. Siesser, of the University of CapeTown, and the Lamont-Doherty sample repository.The aim was to improve the age dating of those periodswhen the basin was restricted and open marine faunaspoor. Palynological analysis is largely restricted tosapropelic lithologies, with four exceptions from graymarly shale. Nineteen samples were studied from 15cores in the Cretaceous part of the section. Four werecompletely barren, and a further four yielded poorassemblages. Palynomorph distribution is presented inTable 1.

GEOLOGICAL BACKGROUND

Site 364 penetrated a Pleistocene to Albian sequence witha probable Cenomanian-early Turonian hiatus (Chapter 4,this volume). The original farget for the hole, late Aptiansalts underlying much of the Angola Basin, was not reachedand the hole at total depth was in early Albian or possiblylate Aptian sediments.

The early and partly middle Albian interbeddeddolomite and sapropelic mudstones are interpreted torepresent cyclic restrictions of the basin. At this timeAfrica and South America were adjacent, and the basinwas restricted by the Walvis Ridge (Figure 1). Themiddle Albian to possibly Cenomanian limestones andmarly limestones represent a period of continuousshallow open marine conditions. In the Turonian andlower Senonian, lithologies deposited include chalks,marly chalks, and sapropelic mudstones, indicating asecond period of cyclic restriction. Middle Senonian toEocene nanno and marly chalk represent open marineto deep-sea conditions, after the final separation ofAfrica and South America and perhaps subsidence ofthe Walvis Ridge. Miocene to Pleistocene lithologies

are typical of the deep-sea conditions prevailing to thisday at Site 364.

PALYNOLOGICAL BACKGROUNDAlthough no established zonations exist in the

literature for areas immediately surrounding Site 364, anumber of zonations from areas to the north haveproved useful. Jardine and Magloire (1965) erected 12spore pollen zones ranging in age from Barremian toMaestrichtian. This zonation was established inSenegal and the Ivory Coast, over 3000 km and 20 oflatitude away. Muller (1966) erected five zones ofAlbian to Senonian age from the Maranhas, Bahia,Sergipe, and Alagoas basins of coastal Brazil.Herngreen (1973, 1975) erected three zones and sixsubzones in the early Albian to late Cenomanian of theBarreirinhas Basin and discussed the Cenomanian tolower Senonian of the Sergipe Basin, both of coastalBrazil. Before the drifting apart of Africa and SouthAmerica, the Sergipe Basin was within 1000 km and 5of latitude of Site 364. In Cenomanian time, separationwas about 1500 km and increasing rapidly.

These spore-pollen zonations were expected to be oflimited use at Site 364, with vegetation changesassociated with latitudinal climatic difference beingreflected in the spore pollen floras. The SouthAmerican zonations were expected to be useful in theEarly Cretaceous, but of decreasing relevance in theLate Cretaceous, as the South Atlantic Ocean widened.

A compilation from the zonations cited is presentedin Figure 2, with additional data from Jardine (1967),Boltenhagen (1965, 1967, 1975), Jardine et al. (1974),and Brenner (in press). Total known ranges are shown,although some palynomorphs are known to be faciesdependent. In particular, Elaterosporites spp. andCretaceiporites spp. do not have the maximum knownrange at Site 364. Some inaccuracy may have beenintroduced into Figure 2 as spore pollen taxa, somefacies controlled, were used to correlate the zonations.

915

R. MORGAN

TABLE 1Palynomorph Distribution Chart

(presentstudy)

(from Bolliet al., 1975)

Depth(m)

Cores andSamples

Examined

PalynologyCollection No.

Lithology(after Bolli

et al., 1975)

PLEISTOCENE

PLIOCENE

MIOCENEOLIGOCENE

EOCENE

PALEOCENE

MAESTRICHTIAN

CAMPANIAN

CONIACIAN

SANTONIAN

Late Turon-ianConiacian

Cenomanian

LateAlbian

MiddleAlbian

EarlyAlbian

TURONIAN

ALBIAN

100-

:

300-

400-

500-

600-

700-

800-

900-

1000

" .2,101-1032" 3, 144-146; ' ^ 4 , 115-1191x^*3, 128-130Z J V M, 123-12524-2, 138-14025-3,67-692627-3,91-922829-2, 43-44303132-3,29-31333 4 - 1 , 146-148

APTIAN

2528253625372530253925382510

2580

2511

2585

2582

25842534253525092533254125322512

Calcareousmud and clay

Marly nannoooze and mud

Pelagic clayand greenishgray rad mud

Nanno chalkand marlychalk

Chalks, marlychalks, andmudstoneswith sapropel

Limestoneand marlylimestone

Dolomiteand

sapropelicmudstone

1 | ~ bo

- s . S &

S- a. a, a. aB S B S S

JC c s: s:ra. .a. .a. .a, .a.Lq ti) k; Lq j

/ i oo , . .

a, a. a. a,

I l l l^ : : S S:

~* -is

MICROFOSSILS EXTREMELY SPARSE

< a8 I S.. a. JJ"? ~ "S iff

HI

As the spore pollen zonations are based on largelynon-marine deposits, little attention has been paid tothe associated dinoflagellates. Only Herngreen (1975)has discussed upper Senonian dinoflagellates asbiostratigraphic markers.

The age of the palynological zones rests on somewhatcontradictory evidence, chiefly from microfaunas.Jardine and Magloire (1965) rely on foraminifer andmegafaunal evidence which they discuss in detail.Muller (1966) and Herngreen (1973) rely onunpublished foraminifer evidence, but Herngreen(1975) includes discussion of megafaunas andforaminifers. The ages used here are shown on Figure 2,and are only a compilation of the other authors, andshould be used with caution. Errors in correlation ofthe zonations, caused by facies control of the sporesand pollen, may also make the ages less precise.

BIOSTRATIGRAPHIC ANALYSIS

Cores 42 to 46 are considered early Albian, Cores 38-40 middle Albian, Cores 29-32 late Albian, Core 27Vraconian or Cenomanian, and Cores 23-25 lateTuronian to Coniacian.

Greatest similarity over the whole section is with thezonation of Jardine and Magloire (1965), and sosamples are assigned to those zones Figure 2 shows thecorrelated zones of the other authors.

Core 46I did not examine this core, but S. Jardine(personal communication) has observed dinoflagellatespecies typical of the early Albian (Madiela Series) ofthe Gabon and Congo basins.

Core 45Only few nondiagnostic pollen wereobserved. S. Jardine (personal communication)observed a nondiagnostic assemblage of spores and

916

PALYNOLOGY OF SITE 364

TABLE 1 - Continued

Spore and Pollen Taxa

5 C ~ c)Jt 3 to "3

5 -a. S | SHit!ii HI

BARREN

< ln.

SS

i= Sa.^

11

S S

R. MORGAN

TABLE 1 - Continued

Age(presentstudy)

(from Bolliet al., 1975)

Depth(m)

Cores andSamplesExamined

PalynologyCollection No.

Lithology(after Bolliet al., 1975)

Microplankton Taxa

PLEISTOCENE

PLIOCENE

MIOCENEOLIGOCENE

EOCENE

PALEOCENE

MAESTRICHTIAN

CAMPANIAN

100-

200-

300-

400

CONIACIAN

SANTONIAN

Late Turon-ianConiacian

Cenomanian

LateAlbian

MiddleAlbian

EarlyAlbian

TURONIAN

700

2, 101-1033, 144-1464, 115-1193, 128-1304, 123-125

24-2 , 138-14025-3,67-692627-3,91-92

ALBIAN

APTIAN

1000

2528253625372530253925382510

2580

2511

2585

2582

25842534253525092533

25322512

Calcareousmud and clay

Marly nannoooze and mud

Pelagic clayand greenishgray rad mud

Nanno chalkand marlychalk

Chalks, marlychalks, andmudstoneswith sapropel

Limestoneand marlylimestone

Dolomiteand

sapropelicmudstone

S f iS .3 S1.1 ft

i a

I I

3"I ao M CS S C

ft? o I d

S Si ^

> "^ 'C "5 * "

a. l> S .8 f>

t^Siifi

fl it" .

> S i "B111 11Illll

2 K ^3 ;

suggested. The presence of Striatopollis dubius (Cores39, 40), Tricolporites S. CI. 260 (Cores 39, 40), andElaterosporites protensus (Core 38) indicate a middleAlbian Zone X or younger assignment. Jardine (1967)dates the oldest occurrence of S. dubius as within themiddle Albian on foraminifer evidence.

Dinoflagellates from Cores 39, 40 includeHystrichosphaeridium arundum, recorded from theearly to late Albian (pre