Mozambique and Ruvuma basins development

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ELSEVIER Sedimentary Geology96 (1995) 7-41 
SEDIMENTARY 
GEOLOGY 
Development of the Mozambique and Ruvuma sedimentary 
basins, offshore Mozambique 
G. Salman, I. Abdula 
Empresa Nacional de Hidrocarbonetos de Mozambique, Avenida Fernao de Magalhaes 34, P.O. Box 4787, Maputo, Mozambique 
Received 22 February 1993; revised version accepted 1 February 1994 
A b s t r a c t 
Two major sedimentary basins have been identified on the continental margin of Mozambique--Mozambique 
Basin and Ruvuma Basin. The formation of the basins is related to the break-up of Gondwana and opening of the 
western part of the Indian Ocean. The basins are relatively young, having developed discordantly to the structural 
plan of Gondwana sedimentary basins. 
The history of the formation of the East African continental margin sedimentary basins within Mozambique has 
been studied on the basis of the present-day concept of Gondwana break-up and Madagascar's drift with respect to 
Africa. Two stages in the history of the East African basins can be recognized: late-Gondwana and post-Gondwana. 
The late-Gondwana stage (303-157 Ma) is typified by sedimentary and volcanogenic rocks of the Karoo Group. 
The post-Gondwana stage (157-0 Ma) corresponds to the period of active Gondwana break-up and the formation 
of Indian Ocean marginal basins. 
The Mozambique Basin occupies both central and southern parts of the coastal plain of Mozambique, extending 
onto the continental shelf and slope. The sedimentary fill is composed of Upper Jurassic, Cretaceous and Cenozoic 
rocks which discordantly overly the Karoo basalts. The Upper Jurassic occurs as continental red-beds, mostly 
distributed within buried grabens. Cretaceous rocks occur as terrigenous sediments of continental and marine 
genesis. Cenozoic deposits are of predominantly marine and deltaic origin. 
The Ruvuma Basin, situated in the north of Mozambique, is part of an extended East African marginal basin 
which includes parts of lhe coastal plains and continental margins of Tanzania and Kenya. The basement of the 
basin is composed of crystalline and metamorphic rocks of pre-Cambrian age. The sedimentary fill is represented by 
continental terrigenous Karoo sediments, marine and lagoonal Jurassic deposits, and marine and deltaic rocks of 
Cretaceous and Cenozoic age. 
The main difference between the sedimentary fill of the Mozambique and Ruvuma basins is related to the 
changing sedimentary environment in the period of Gondwana break-up, Jurassic and Early Cretaceous, when the 
drift of Madagascar and sea-floor spreading took place and the marine basin gradually extended southwards 
between the East African margin and Madagascar. 
From the Late Cretaceous on, the sedimentary environment within both basins was similar, the Mozambique and 
Ruvuma basins forming a single system on the East African continental margin. 
The main stages of the; basins' development are illustrated by a series of palaeogeographic reconstruction maps. 
0037-0738/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved 
SSDI 0037-0738(94)00125-1 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
1. Introduction 
The coas ta l a r ea of M o z a m b i q u e s t re tches for 
over 2300 km a long the Eas t Af r i can con t inen ta l 
margin . Two major bas ins have b e e n iden t i f i ed 
h e r e - - t h e M o z a m b i q u e Basin and the R u v u m a 
Basin (Fig. 1). The s e d i m e n t a r y fill wi th in the 
bas ins is r e l a t ed to G o n d w a n a b reak -up , fo rma- 
t ion of the I n d i a n O c e a n and M a d a g a s c a r dr i f t 
with r e spec t to Afr ica . T h e ma in s tages of dr i f t 
a re r e f l ec ted in the s t r a t ig raph ic r ecords of the 
M o z a m b i q u e and R u v u m a basins. 
W h i l e compi l ing the p r e s e n t work, we used the 
resul ts of oil and gas exp lo ra t ion activi t ies ca r r i ed 
out in the M o z a m b i c a n po r t i on of the E a s t e r n 
Af r i ca s e d i m e n t a r y basins, inc luding deep-d r i l l i ng 
da t a and reg iona l se ismic l ines bo th on- and 
of fshore (Fig. 2). Sect ions of all d e e p wells d r i l l ed 
in this r eg ion have b e e n analyzed , and the d a t a 
I ~o • i 5° 
15" 
20' 
25' 
Fig. 1. Marginal basins of East Africa: 1 = basins regarded in 
the present study; 2 = basement; 3 = Karoo sediment out- 
crops; 4 = Karoo volcanics outcrops; 5 = marginal sedimen- 
tary basins. 
Fig. 2. Location of key profiles and wells used in this study: 
1 = Sunray-1; 2 = Sunray-3; 3 = Sunray-7; 4 = Sunray-2; 5 = 
Sunray-4; 6 = Sunray-12; 7 = Xai-Xai West-l; 8 = Palmeira-1; 
9 = Macia-1; 10 = Zandamela-1; I1 = Domo-1; 12 = Mazenga 
Sul-1; 13 = Funhalouro-1; 14 = Nhachengue-1; 15 = Temane- 
1; 16 = Pande-1; 17= Divinhe-1; 18= Buzi-1; 19 =-Nemo-1; 
20 = Sofala-1; 21 = Sengo Marin-1; 22 = Sangussi Marin-1; 23 
= Zambezi-3; 24 =-Zambezi-1; 25 = Micaune-1; 26 = Rio 
Nhanguazi-1; 2 7 = Nhamura-1; 28 = Mocimboa-1; 29 = 
M'Nazi Bay-1. 
on s t r a t ig raphy and l i thology t ied with seismic 
l ines to p r o d u c e a se i smos t ra t ig raph ic f r amework 
of the s tudy area. 
The work desc r ibed he re is the resul t of the 
au thors ' 10-years activity at the Oil and Gas 
Exp lo ra t ion D i r e c t o r a t e of the M o z a m b i q u e Na- 
t ional H y d r o c a r b o n E n t e r p r i s e ( E m p r e s a Na- 
c ional de H i d r o c a r b o n e t o s de M o z a m b i q u e - - 
E N H ) using the ma te r i a l s f rom E N H archives 
(Amoco , Aqu i t a ine , Hun t , Sunray compan ie s ' 
da ta ) as well as m o d e r n reg iona l seismic da t a 
acqu i red by W e s t e r n Geophys ica l , G E C O (off- 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 9 
shore), Esso (onshore), and ENH geophysical sur- 
veys (shallow-water seismic). 
In addition, use was made of drilling and seis- 
mic data from the adjacent Tanzania areas 
(TPDC), as well as schematic cross-sections of 
wells in Kenya, Ethiopia, Somalia, Madagascar 
(Robertson Research, 1986) and the Seychelles 
(Walton and Khanna, 1992). Reconstruction of 
the sedimentary basins formation history was 
made based on the maps of continental block 
drift from Raillard (1990), Coffin (1992), and 
other studies. 
2. Basin history 
The formation of sedimentary basins offshore 
Mozambique is related to the break-up of Gond- 
wana and relative drifting of the Africa and 
Madagascar continental blocks. 
The main factors which determine the geologi- 
cal history of the East African basins are the 
initial location of Madagascar in the Gondwana 
continental plate and the subsequent drift of 
Madagascar with respect to Africa. Until re- 
cently, the palaeoposition of Madagascar as well 
CONTINENTAL FACIES TRANSITIONAL FACIES 
~ . ~ . ~ RED TERRIGENOUS ] DELTAIC 
COAL-BEARING 
A ^ AI 
]^ ^ ,', A A I LAGOONAL 
{ A ^ { 
~ ~ ASSUMED DEVELOPMENT ~ SALT 
SHELF FACIES 
~ ~ COASTAL AND SHALLOW 
WATER TERRIGENOUS 
- - ~ - - ~ BARRIER REEF 
VOLCANOGENIC AND VOLCANOGENIC- 
- SEDIMENTARY FACIES 
ESTABLISHED 
ASSUMED 
I I 
I 
{ J 
DEEP WATER FACIES 
' ' ,J TERR{GE NOUS-CARBO NATE 
] J, OF CONTINENTAL SLOPE I I 
TERRIGENOUS OF CONTINENTAL 
SLOPE AND RISE 
ASSUMED DEEP WATER 
+ + +1 + 4- 
PRE-CAM BRIAN BASEMENT 
AREAS OF SUBSEQUENT EROSION 
Fig. 3. Legend for basin history charts. 
10 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
as its drift have been a matter of discussion. 
Some authors (Forster, 1975; Kamen-Kaye, 1982) 
considered that Madagascar has not changed its 
location at least since Karoo times (Late Car- 
boniferous-Early Jurassic). Flores (1972) ex- 
pressed the opinion that prior to drift, Madagas- 
car was located in the coastal plain area in the 
southern part of Mozambique. 
In the last few years a numberof proofs have 
been presented, including sea-floor spreading 
magnetic anomalies and some geologic similari- 
ties between the margin basins of Tanzania, 
Kenya and Somalia on the one hand, and the 
western margin of Madagascar on the other, sug- 
gesting Madagascar's north-south displacement 
with respect to Africa (Rabinowitz et al., 1983; 
Coffin and Rabinowitz, 1987; Raillard, 1990; Cof- 
fin, 1992). Recent evidence has confirmed that 
Madagascar separated from Africa along with the 
continental blocks of India and Antarctica, thus 
creating the Western Somalia Basin (Lawyer et 
al., 1992; Royer, 1992). 
The discussion on the relative drift of Mada- 
gascar and Africa has been limited to the time of 
beginning and ending of that process: between 
157.6 Ma (Magnetic Anomaly M25) and 118 Ma 
(Magnetic Anomaly M0). The main lineament 
determining the movement of those blocks is the 
Davie Ridge transform fault system. Kejo Kajato 
(1989) suggests that Madagascar began separating 
from the African continental block as early as 
Late Permian when the Western Somalia Basin 
rifts were formed. The presence of a Mesozoic 
series of magnetic anomalies in the Western So- 
malia Basin confirms the assumption that prior to 
the Gondwana break-up Madagascar was located 
in that basin. 
The initial location of Madagascar is substanti- 
ated by comparing Karoo sequences in the sedi- 
mentary basins of the Tanzania/Somalia conti- 
nental margin and Madagascar. The gravity gra- 
dients from the sides of both Africa and Mada- 
gascar have been adopted as limits of continental 
crust blocks. Proceeding from this assumption, we 
have compiled a number of palaeogeographical 
schemes which illustrate the main stages of devel- 
opment of the marginal basins, as well as sedi- 
mentation types and environment (Fig. 3). The 
relative drift of the Africa and Madagascar conti- 
nental blocks is shown as in Raillard (1990) and 
Coffin (1992). 
The East Africa Basin history is clearly divided 
in two stages: 
(1) Gondwana stage comprising a period be- 
tween 300 and 157 Ma (Late Carboniferous-Mid- 
dle Jurassic). This stage is characterized by devel- 
opment of sedimentary basins within the single 
Gondwana continental mass. 
(2) Post-Gondwana stage beginning in Upper 
Jurassic (157 Ma) and continuing to the present. 
This is a period of an active break-up of Gond- 
wana and formation of the Indian Ocean conti- 
nental margins. 
2.1. Gondwana stage 
The Gondwana stage is subdivided in two 
phases: the Gondwana rifting phase and the final 
phase. 
The Gondwana rifting phase, 300-205 Ma 
(Late Carboniferous-Triassic), includes the last 
period of development of Gondwana. During that 
period, extended rift structures were formed, 
linking to create a broad platform depression, 
and filled by thick sequences of terrigenous and 
carbonate formations. The thick, sedimentary 
basin deposits are known as the Karoo Group. In 
the north, incursion of palaeo-Tethys seawaters 
along the axial part of the depression could have 
taken place (Fig. 4). 
The final phase comprised the period 205-157 
Ma (Early to Middle Jurassic). This phase marked 
the end of the Gondwana continent and the 
beginning of its disintegration into separate 
blocks. Drift and sea-floor spreading had not yet 
been initiated. The period is characterized by the 
appearance of a vast regional depression with 
platform volcanism extending over the southern 
part of Africa and Antarctica. Inheriting Karoo 
depressions, flood basalts developed which can 
be seen within the Mozambique Basin (Great 
Karoo Basin) and Antarctica (Prisme Explora). 
At the same time, in the northern part of the 
study region, a palaeo-Tethys transgression re- 
suited in formation of a narrow marine embay- 
ment with barrier reefs separating a number of 
G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 11 
saline lagoons (Ogaden, Mandawa and possibly 
Ruvuma basins) (Fig. 5). 
As the final period progressed, volcanic activ- 
ity in the Afro-Antarctic part of Gondwana grad- 
ually diminished, while a deep depression formed 
between Africa and Madagascar, along which the 
palaeo-Tethys transgression further developed, 
creating a marine seaway separating the African 
and Indo-Madagascar blocks (Fig. 6), 
2.2. Post-Gondwana stage 
The post-Gondwana stage of the East African 
basin development can be subdivided in three 
+ : y . . . . . . . . , , , + 
\ / + 
Fig. 4. Gondwana rifting phase, 300-205 Ma (Late Carbonif- 
erous-Triassic). The palaeoposition of Madagascar with re- 
spect to Africa has been determined considering continental 
block limits (gravity gradients) and similarity of Karoo sec- 
tions on Madagascar and the Tanzania/Somalia margin. See 
Fig. 3 for legend. 
Fig. 5. Gondwana stage. Final phase, 205-175 Ma (Early 
Jurassic). Basalt flows cover spaces in Southern Africa and 
Antarctica (Great Karoo Basin and Prisme Explora). A 
palaeo-Tethys ingression is initiated between Africa and 
Madagascar. See Fig. 3 for legend. 
phases: (1) the break-up of Gondwana; (2) stabi- 
lization; (3) neorifting. 
2.2.1. Break-up of Gondwana 
The break-up of Gondwana comprised a pe- 
riod of active sea-floor spreading in the western 
Somalia Basin and Mozambique Channel Basin, 
identifiable from a Mesozoic series of magnetic 
anomalies within these basins, between M25 
(157.6 Ma) and M0 (118 Ma). During this period 
Gondwana separated into two major blocks: West 
Gondwana (Africa and South America) and East 
Gondwana (Antarctica, India and Sri Lanka, 
Madagascar, Seychelles and Australia). Drift of 
continental blocks occurred along a series of 
transform faults located parallel to Davie Ridge, 
12 G. Salrnan, L Abdula / Sedimentary Geology 96 (1995) 7-41 
Mozambique Escarpment and Explora Escarp- 
ment (Antarctica) (Lawver et al., 1992). 
Sea-floor spreading was accompanied by a de- 
veloping marine transgression over the eastern 
margin of the African block and western Mada- 
gascar. Palaeogeographic maps for the Gond- 
wana break-up phase have been compiled using 
relative positions of Eastern and Western Gond- 
wana based on sea-floor magnetic anomalies M22, 
M10 and M0. 
Late Jurassic. Drift of Madagascar relative to 
Africa was probably initiated in Oxfordian time 
(magnetic anomaly M25, 157.6 Ma). Fig. 7 shows 
the location of Madagascar in Kimmeridgian time 
(anomaly M22, 152 Ma). In Kimmeridgian and 
Fig. 6. Gondwana stage. Last part of final phase, 175-157 Ma 
(Middle Jurassic). Volcanic activity in southern Africa is re- 
duced. The sea channel separating Africa and Madagascar 
expands; however, there is no drift of continental blocks. See 
Fig. 3 for legend. 
Fig. 7. Post-Gondwana stage. Break-up of Gondwana, 157-118 
Ma. This phase is related to the drift of Africa and the 
India/Madagascar/Antarctica continental blocks. The posi- 
tion of continental blocks and distribution of sedimentary 
facies is shown at the end of the Kimmeridgian (anomaly 
M22, 152 Ma). See Fig. 3 for legend. 
Tithonian times, the Tethyan transgression ex- 
tended widely, resulting in discordant deposition 
of Upper Jurassic marine shale and limestone in 
North-Eastern African basins, including the Ru- 
vuma Basin. The sea was likely also to have 
penetra ted into the northern part of the Mozam- 
bique Basin. In both central and southern parts 
of the Mozambique Basin, a rift system was 
formed and thick syn-rift, red-colored sedimen- 
tary sequences accumulated. 
Neocomian. T h e beginning of the Cretaceous 
was marked by continuing sea-floor spreading in 
the Somali and Mozambique Channel basins. The 
marine transgression reached the southern end of 
the African block. On the southeastern margin of 
Africa, the development of rift structures and 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 13 
Fig. 8. Post-Gondwana stage. Break-up of Gondwana-130 Ma. 
Palaeoposition of Africa and Madagascar at the end of the 
Neocomian (anomaly M10). SeeFig. 3 for legend. 
accumulation of thick sedimentary sequences 
continued, accompanied by a partial regression. 
The relative palaeopositions of Africa and Mada- 
gascar at the end of the Neocomian (anomaly 
M10, 130 Ma) and the sedimentary facies distri- 
bution are shown in Fig. 8. 
Barremian-Aptian-Albian. The second half of 
the Early Cretaceous was characterized by a new 
transgression onto the African continent, proba- 
bly related to the break-up of Western Gond- 
wana, separation of South America and opening 
of the South Atlantic at ~ 130 Ma (Lawver et al., 
1992). At the end of the Early Cretaceous, Mada- 
gascar had virtually stopped drifting with respect 
to Africa, and, by that time (M0, 118 Ma), forma- 
tion of the main structures of the East Africa 
continental margin had been completed (Fig. 9). 
2.2.2. Stabilization 
118 and 35 Ma comprised a period of stabiliza- 
tion of the East African continental margin. Fur- 
ther development of the marginal sedimentary 
basins was limited to progradational extension of 
the sedimentary section towards the ocean and 
development of compensatory depressions. 
The Late Cretaceous was typified by a devel- 
opment of widespread transgression within East- 
ern Africa. Along the whole continental margin, 
rather uniform, marl/clay sequences accumu- 
lated, prograding onto the continental slope (Fig. 
10). In the southern portion of the Madagascar/ 
Indian block and the adjacent Mozambique 
Channel and Mascarene basins, volcanic activity 
was common, with deposition of thick vol- 
Fig. 9. Latest break-up of Gondwana phase. By the end of the 
Early Cretaceous (M0, 118 Ma) drift ceased. The scheme 
shows the position of Africa and Madagascar by the time of 
anomaly M0 and facies distribution during 130-97 Ma (Bar- 
remian, Aptian, Albian). See Fig, 3 for legend. 
14 G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
canogenic and volcanogenic-sedimentary se- 
quences. This was related to the beginning of 
sea-floor spreading within the Mascarene Basin 
in the second half of the Late Cretaceous and the 
separation of India and the Seychelles from 
Madagascar (magnetic anomaly 34, 84 Ma). 
Paleocene and Eocene complete the stabiliza- 
tion phase of the East African continental mar- 
gin. Shallow-water shelf carbonate sediments were 
widespread, with reefal facies along the outer 
edge of the shelf (Fig. 11). 
2.2.3. Neorifting 
The phase of neorifting comprises a 35-mil- 
lion-year period up to the present and is closely 
connected with the inception and development of 
the East African rift system. 
Fig. 10. Phase of stabilization of the Eastern African conti- 
nental margin, Late Cretaceous (97-65 Ma). During this 
period, drift of the India/Seychelles block relative to the 
Africa/Madagascar block is initiated. See Fig. 3 for legend. 
÷ 
+ 
+ 
5 
Fig. 11. End of stabilization phase, Paleocene-Eocene (65-35 
Ma). A widespread shallow-sea marine transgression is devel- 
oped within the African continent, accompanied by an exten- 
sive deposition of carbonate sediments. See Fig. 3 for legend. 
In the Oligocene, the African Craton rose, 
accompanied by marine regression. Marine sedi- 
mentation on the continental margin continued 
only in some individual depressions, where large 
deltas had formed (Fig. 12). 
In the Miocene transgression, the shallow- 
water marine environment was restored over a 
wide shelf. Active rifting of East Africa was also 
reflected within the continental margin. The 
Davie and Mozambique submarine ridges experi- 
enced tectonic activity, whilst the Kerimbas and 
Laeerda submarine grahens appeared. At the 
same time, large-scale sedimentation took place 
in the Ruvuma and Zambezi river deltas (Fig. 
13). 
In Quaternary time, the shallow-water shelf of 
the Miocene sea underwent regional uplift, and 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 15 
those sediments presently outcrop on the coastal 
plains. 
3. The marginal sedimentary basins of Mozam- 
bique 
The marginal sedimentary basins were formed 
as a result of the break-up of Gondwana and 
formation of the Indian Ocean at the end of the 
Mesozoic. Pre-Cambrian crystalline and meta- 
morphic rocks form a common basement for the 
basins. The sedimentary cover is subdivided into 
two units: the Gondwana and post-Gondwana 
units separated by a major discordance. 
Fig. 12. Neorifting phase. Oligocene (35-23 Ma). The initial 
stage is characterized by a general uplifting of East Africa and 
sea regression. Sedimentation remains only within individual 
delta depresssions. See Fig. 3 for legend. 
Fig. 13. Neorifting phase. Miocene (23-5 Ma). Intensive vol- 
canic activity. Formation of rift structures both onshore and 
on sea floor. See Fig. 3 for legend. 
The Gondwana unit comprises the lower part 
of the basins' sedimentary fill and is related to 
the development of large epicontinental basins 
within the ancient Gondwana continent. The sec- 
tion appears as a sequence of sedimentary and 
volcanogenic rocks of the Karoo Group (Late 
Carboni ferous-Ear ly Jurassic). 
The post-Gondwanan unit is composed of sed- 
imentary sequences of Middle to Upper Jurassic, 
Cretaceous and Cenozoic age which are the typi- 
cal sedimentary fill for the East African marginal 
basins. 
Mozambique has two marginal sedimentary 
basins, the southern Mozambique and the north- 
ern Ruvuma (Fig. 1), which have substantial sedi- 
mentary fill both on- and offshore. 
16 G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
Parts of Basin 
Age, 
S T A G E S o u t h e r n Cen t ra l No r the rn Me 
OFFSHORE ,i ONSHORE = OFFSHORE 
,TERNARY ~ = = : = ~ c = ¢ = ~ = ~ M ; •" • "• ",'.: ." : ' ~ . . . " ~ " ~ 1 . . . . . . . . . . . i 0 
Plioceno 
oz ~1 E,,,~ i - - ~ , ; ~ ~ : : : : = ~ - ~--I 
UJ Early 
z t=to ~ . , - " 
O- ~ Late . . . . . . • _ _ . , . • 
a. Early 
- - = ~ , ~ - - C O W E - ' R GRU-DJA"~M ~ - ' - . . . . 
Campani~n 
- - Sa.10ntan 
- -Con iac l an ~ UPPER r~OMO SHALE FM ~...~:. ' , ' ' " ' "~ ': " 
U') - - Turo~iml ..~...:;..:~......,,~,.IC,...I.DOMOSANDFM:,..~:::~..t~..~';;:;..... ~3 Cenom~nian o , . . . . . . . . ~ " ~ ; . . . . ~ ' ) : - . ~ l 
LU 
Albi=n ~ , -'-': -300 
~ L O W E R DOMO SHALE FM ~ " ~ , _ ~ 
- - L . = L = . , . . . - . . . ~. • • ' . . ' . ' . ~ . : : . ' . . : - ~ . . ~ ' . ' . , , 
Aplian ~ ' "%% . • , - ; - 'T ~ " f" ' " " . ' J i 
¢n ~ ' ' " ' ' . . . . . . ='o - . ~ . . . . . • , ' 
- -K Immet idg i~ - - , ,,. ~ ~ / ~ • . . . . . - 150 
(_~ Bothonton • /~* ' O 
~V) "~ Bojocllln ~ .UMBELUZ / 
Aulenion ~ - . . _ . . - . ~ 
CO 
V V V V V 
LE3"ABA BASALTS EQUIV. " ~ 
V V V V V 
V V V V V 
20(I 
o ~. : 3 
~ .~ . , 
N 0 , . 
= = ~ 0 
== ;~ n- 
0 ~ , . ~ er~(~'s ~ - 30£ 
,,-- -~ \ ~ _ o/ I ~ - ~ ~ ,,,p 
u E " ° S 
i ( ~ LOWER MOVENE FM 
P R E - C A I d B R I A N E ~ 
Fig. ]4 . Regional stratigraphy of the Mozambique Basin. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 17 
3.1. Mozambique Basin 
The Mozambique Basin covers the central and 
southern, on- and offshore parts of Mozambique. 
The sedimentary section is composed of Ceno- 
zoic, Cretaceous and Upper Jurassic rocks, un- 
conformably overlying Karoo basalts. The sedi- 
mentary thickness increases eastwards and north- 
eastwards, reaching its maximum of some 12 km 
in the Zambezi Delta Depression. 
A significant amount of research has been 
done on the shelf, particularly within its shallow 
part. Seismic and aeromagnetic surveys have been 
conducted in the western part of the basins, and 
new information has been obtained concerning 
the depths of the magnetic basement and the 
regional geological structure of this area. By 1975 
some 54 deep exploratory wells had been drilled 
in the basin. Drilling has once again begun in 
recent years with an exploratory well on the shelf 
of the Mozambique Basin, Xai-Xai-1 (British 
Petroleum). 
The new findingsmake it possible to define 
and add detail to earlier ideas about the structure 
of the basin and the stratigraphy of the sedimen- 
tary fill, and to develop a better understanding of 
the less studied areas. The present work takes 
account of information obtained since 1975, and 
a new chart of the stratigraphic division of the 
section, as well as a chart of the structural tec- 
tonic elements of the basin, has been compiled. 
3.1.1. Stratigraphic framework of the Mozambique 
Basin 
Basement. The basement most likely consists of 
crystalline and metamorphic pre-Cambrian rocks 
of the African platform, which occupy extensive 
areas in the central and western areas of the 
country. Within the Mozambique Basin the pre- 
Cambrian is buried at an unknown depth exceed- 
ing several kilometres. 
The Karoo Group. The Karoo Group deposits are 
distributed widely in Southern Africa and extend 
from the Upper Carboniferous to the Lower 
Jurassic. These are primarily continental terrige- 
nous, coal-bearing formations of the Dwyka, Ekka 
and Beaufort series, with a total thickness of over 
3000 m. In the Ekka section there are widely 
developed, commercially viable seams of hard 
coal, while the rocks of the Beaufort series typi- 
cally have a substantial content of dispersed coaly 
material. 
The Karoo Group section is topped by thick 
layers of basalt and rhyolitic tuff of the Storm- 
berg series (Early Jurassic), which are developed 
in an almost continuous band along the periphery 
of the basin and are buried under younger sedi- 
mentary formations. They have been tested by 
deep boreholes under a layer of sedimentary 
rocks, and everywhere show traces of deep ero- 
sion and weathering. 
The post-Karoo sediments, The post-Karoo section 
includes the formations of the Upper Jurassic, 
Cretaceous and Cenozoic which lie on deeply 
eroded rocks of the Karoo Group. We know of 
continental, marine, transitional and deltaic fa- 
cies of post-Karoo sediments. 
The post-Karoo sedimentary section of the 
Mozambique Basin has been probed to its full 
thickness in the southern part where the depth of 
the top Karoo basaltic basement varies between 
1100 and 4500 m. The greatest thickness of post- 
Karoo sediments has been established according 
to seismic data in the central part of the Mozam- 
bique Basin, in the Zambezi Delta Depression, 
where it reaches 11 km and more. 
A stratigraphic scheme for the Mozambique 
sedimentary basin has been compiled based on 
some new well data and seismostratigraphic in- 
terpretation of the seismic lines (Fig. 14). 
Typical for the geological structure of the 
Mozambique Basin is its asymmetry, which is 
characteristic for the marginal sedimentary basins, 
and the regional dip towards the open sea. Since 
the Early Cretaceous, the palaeoshelf outer edge 
has been gradually extended by younger sedimen- 
tation complexes and shifted seawards (Fig. 15). 
Upper Jurassic (?)-Lower Cretaceous. At the 
base of the post-Karoo sedimentary section lies a 
thick (over 900 m) layer of red, continental sedi- 
ments, found in the southern part of the basin 
and known as the "Red Beds" Formation (Fig. 
14). 
18 G, Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
The Red Beds Formation is distributed in the 
Palmeira and Chidenguele grabens and is evi- 
dently developed in the axial zone in the Changani 
graben system to the west. Corresponding to these 
deposits in the northwest part of the basin are 
continental sandstones of the Lupata Formation. 
w LINE S M - 9 ! 
• 28 I~00 900 500 *,o~ soo ~ooo ~oo ~ooo /~oo 3riO0 
30 
.20 
"]0 
~ 0 
~0 
511- 
5ec 
w 
O- 
tO 
20 
Nhachengue-I 
B 
L IN E S M-59 
E 
0 
-1.0 
~20 
-3.0 
r,O 
"~0 
Sec 
L I N E S 1'4-75 
NW SE 
o. sqp ~,o ,s0o 2,0~ 2soo ~ o , o 
i . 
2 
C o ~s V 
V V 
Sg re_ 
Fig. 15. Shelf-edge stratigraphy and morphology along lines SM-9, SM-59, SM-75 across the Mozambique Basin continental margin. 
1 = Quaternary; 2 = Ol igocene-Miocene; 3 = Paleocene-Eocene; 4 = Upper Cretaceous; 5 = Lower Cretaceous; 6 = Red Beds 
Formation; 7 = Karoo volcanics. Cretaceous volcanics are cross-hatched. Red Beds Formation is dotted. See Fig. 2 for location. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 19 
Towards the east the facies change from conti- 
nental sandstones of the Lupata Formation to 
deposits of the ancient delta, a sandy clay layer of 
which has been penetrated by the Nhamura-1 
borehole (Lower Zambezi Graben, Fig. 16). 
Lower Cretaceous-Cenomanian. Deposits of 
this age are marked by considerable variety and 
occur as marine, continental and transitional fa- 
cies. The following formations have been identi- 
fied: Maputo (Neocomian); Sena (Lower Creta- 
ceous-Cenomanian); and Lower Domo Clays 
(Aptian-Cenomanian). The boundaries between 
the formations are not strictly chronostrati- 
graphic, but define a diachronous change in fa- 
cies (Fig. 14). 
A Cretaceous transgressive marine sequence 
begins with the Maputo Formation deposits. The 
Maputo Formation is distributed in the southern 
and central areas of the Mozambique Basin and 
occurs as a layer of glauconitic-quartzose sand- 
stones and arenaceous limestones, interbedded 
with argillites. Shallow-water marine sandstones 
and limestones of the Maputo Formation overlie 
eroded Stormberg basalts or the "Red Beds" 
32"E 36"E 
• : ; " . . ~ O,j~UELIM,aNE 
32°E 36~E 
m's 
22" 
Fig. 16. Mozambique Basin. Development of the Red Beds and Lower Lupata formations. Late Jurassic rift structures: 
1 = Palmeira graben; 2 = Chidenguele graben; 3 = Changani graben system; 4 = Lower Zambezi graben. 
20 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
Formation. In light of recent work (Salman et al., 
1985), deposits of the Maputo Formation may be 
assigned to the Neocomian (Fig. 17). In the 
northern part of the Mozambique Basin, Neoco- 
mian deposits which could be regarded as equiva- 
lent to the Maputo Formation are deeply buried 
and have not been encountered by any of the 
wells drilled to date. The equivalent to the Ma- 
puto Formation has been identified here at the 
base of sedimentary cover on the basis of seis- 
mostratigraphic correlation. 
The Sena Formation occupies the central and 
northern parts of the Mozambique Basin. This is 
a continental rock sequence of variegated fluvial 
and alluvial formations: arkose sandstones, con- 
glomerates and argillites enriched with coaly de- 
tritus. The Sena Formation deposits are widely 
developed in the Lower Zambezi graben and 
have been penetrated by boreholes in the central 
part of the basin. The thickness of this formation 
in the Nhamura-1 well is 2700 m (Fig. 18). The 
Sena Formation continental sediments also in- 
clude deposits of Upper Cretaceous (Cenomani- 
an-Turonian) age. 
The Lower Domo Shales Formation is dis- 
tributed in the southern and central areas of the 
Mozambique Basin, both on- and offshore, where 
it occurs as dark marine argillites with occasional 
bands of arkose sandstones. The thickness varies 
from 700 to 1500 m. The argillites contain Ap- 
tian-Albian and Cenomanian fauna. The Maputo 
Formation and the Lower Domo Shales are the 
FUNHALOURO - 1 DOMO- 1 
BALANE °1 MAZENGA SUL SUNRAY-12 
~050 .1729 
'-:~-~.~: Z156 ".L."-~ Cct~ 
~ . ~ 1921 
• r 1982 
~ LLL 
I'LL 
LLL 
, 5 
"--~___-'. ~SuB°. r- APt 
:'.":5' ~1,0 NeO 
3188 
8 
O 
Z 
8 
._1 
5 
rr" 
LU 
¢:Q 
n,," 
O I.-- 
,J3 
~IOSTRATIGRAPHIC LIMIT 
TION LIMIT 
Fig. 17. Correlation of Lower Cretaceous sediments in the wells in the southern part of the Mozambique Basin. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
S E N G O M A R I N - 1 R I O N H A N G U A Z I - 1 
B U Z 1 - 1 M ICAU N E - 1 N H A M U R A - 1 
o ~._.._. -._-_~ 
0 .... IE " "-2---- Z ~ 
=-~ _ , . . . J 
;~ ...T.,.-1"4aucY - - i 
,....._.--_. _ _~ 
o. ¢ , . 9 
E I ,- ____ / 1 4 ' I -,.__~ 
o - . 4 
o ~ ' ~ , - , - , - -~ /~ I ' / "_-:-~7--,_.=-7 , _ . , 
LU ~" 0 - - - - - ~ / - " 
a -J . . . . . ' 
,_, ,,,,, . - ._ - /~_ - - ~ 
< - . -_ 2oI,~ 7-77 
p-- o C '-%--" ~ ~ 7-.'~ 
(j o , "'7--" -.- 
uJ - - E E " - - "r2170" .' - - "I 
tr OLL ---,- '' 7"--~. 
o _--_ /~ ..-7 
~ ~-~- 
D ~ /4 
o: D _ - - _ # . - -7~. 
LLI -- -- 
O. 
i ca. . ~ - - . . _ ~ 
] ~ "" ~ ' ^ -: :- ' - : ,~ 9~'~ - - 
:~_ - - - 
- - 
r:. ~ E - - - ' ~ - " 
Q ~ (~LL T--L7 .... 
u~ --'-- 3329 F ~ ~ 
Nhomura-I ! ~Micaune-')~// 357. 
Rio Nhanguazimt / ; ~ 
< 
l-- 
"0 
LU 
(D 
<E 
Z (j 
0 n~ 
Ud 
O_ 
-- 0. 
~r to 
0 
Q W 
t~ 
@-- 
rY 
Z L} 
iii t~ 
w 
0 
.J 
'33 57, <[' 
=<E =" 
C H R O N O S T R A T I G R A P H I C L I M I T 
F O R M A T I O N L I M I T 
Fig. 18. Correlation of Cretaceous sediments in the wells of the northern part of the Mozambique Basin. 
2l 
marine equivalent of the Sena Formation. East- 
wards, Lower Domo Shales grade into continen- 
tal slope and continental rise sediments where 
fan complexes are widespread. On the Western 
Geophysical offshore seismic lines, the zone of 
fan development is mapped along the present-day 
shelf edge, indicating the location of the conti- 
nental palaeoslope (Fig. 19). 
Upper Jurassic-Lower Cretaceous volcanics. 
The time at which the "Red Beds", Lupata and 
Sena formations and their equivalents were 
formed is typified by intense volcanic activity. 
Along the faults forming the graben boundaries, 
ancient volcanoes appeared, evidence for which 
are the buried basic and acidic lava flows. Vol- 
canic rocks of Late Jurassic-Early Cretaceous 
age occur as liparites and basalts of the Lupata 
Formation and alkalic lavas in the lower parts of 
the Sena Formation in the Mid-Zambezi grabens, 
basalts of the Lower Movene Formation and li- 
parites and basalts of the Pequenos Libombos 
Formation. Early Cretaceous volcanic rocks have 
been sampled in boreholes Mambone-1 and 
Nemo-1. 
22 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
Upper Cenomanian-Maastrichtian. Deposits of 
the Upper Cenomanian-Maastrichtian form a 
self-contained cycle of sedimentation associated 
with the development of the East African conti- 
nental margin, and are typified by a consistent 
marine transgression. Three formations have been 
identified according to their stratigraphic position 
and lithology: the Domo Sandstones (Upper 
Cenomanian-Turonian); Upper Domo Shales 
(Turonian-Lower Senonian) and Lower Grudja 
(Campanian-Maastrichtian). These formations lie 
on the eroded surface of the underlying deposits. 
The Domo Sandstones Formation is the basal 
unit and occurs primarily as quartzose sandstone, 
interbedded with dark argillite. The sandstones 
are distributed in the central part of the Mozam- 
bique Basin, where their total thickness exceeds 
200-250 m. Towards the south and east the sand- 
stones decrease in importance and the section 
becomes primarily argillaceous. 
32°~ 36"E 
+ + +1 - ^ , ~ \ f + - o + - - - - - . " a " - ' ~ . °. ."T-.'.,:--7~U~" 
, t t I0 | ~ -X~'-O + O-~°~--'~'EU---E~UELIMANE--. +~-~ I 
~+ + + k o - - ~ . . . . . ~ , ~ . ; ~ _ _ ~ + 
,+ + o ~ ~ ~ t 
:. +/' I ~+ ~ ° ~ - ~ ~ / 
,," + ' • 
> o o ~-::'~:':; /g! I t> o o i 
,," o o o ~ q ~ - 
/i" o o o o . ' : - q ' = . r - F - , 
, o o o o X , : : ~ J ~ 
. ~ < , o o o / - . 7 " : " - ' . ' . ' . : ' L : t l 
I ' .o"~ ,% . . . . . 0 0 . . ' . . . .":": ' ." . ' . i . ." ' " ' . ' ~ [~ :ZZ l ~ I 
|0 o • . .. 21~--'.'." 
~ . " ".'_" ." " . " . "...'._'~ ,NHAhtBAN E I 
. . 
I ~ ~ o ~o ,oo ,~o~ 
l ~ 7 : F ~ - - t . . . . . . 
3 2 " E 36"E 
Fig. 19. Mozambique Basin. Chart of Early Cretaceous facies development: 1 = continental clastic sediments; 2 = predominantly 
coastal and shallow-water shelf sediments, sand shallows and bars; 3 = deltaic sediments; 4 = continental slope terrigenous 
sediments--progradational bedding, development of submarine fans; 5 = deep-water shale sediments; 6 = limits of facies zones; 
7 = basement. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 23 
The Upper Domo Shales Formation is a se- 
quence of dense clays, 600-650 m thick• The 
maximum thickness of these has been reported in 
the Sengo Marin-1 well as 1225 m (Fig. 18). 
These deposits are also known in the central part 
of the basin where they grade into continental 
sandstones and become part of the Sena Forma- 
tion sequence towards the northwest• 
The Lower Grudja Formation is spread widely 
in the central part of the basin, where it has been 
encountered in most of the boreholes. In the 
north of the basin the sediments of the Lower 
Grudja Formation are developed along the west- 
ern flank of the Zambezi Delta Depression• The 
formation occurs as a layer of clay with bands of 
glauconitic-quartzose sandstone. Commercial gas 
pools have been found in different layers. The 
thickness of the sandstone layers varies from a 
few metres to as much as 50 m. The overall 
thickness of the sequence in the central part of 
32°E 
+ 
}+ + 
/ + 
i + 
M-I- + 
~:~ + 
.i + + 
, 
' " i+ ++/ 
f + / 
36°E q+ 
+ 
+ + + .4. 
4- + ÷ ~ 
~6~s 
/ ' / ) i j • . ~" 
• # * "o'e - - --"7-" 
I : 
\ • 
\ . 
) 
.32°E ~E 
 -qs 
.... ~ 6 
o so oo, 
Fig. 20. Mozambique Basin. Scheme of Late Cretaceous facies development: 1 = continental and coastal terrigenous sediments; 
2 = shallow-water shelf sediments--interbedding of glauconitic sands and shales (Lower Grudja Formation); 3 = continental slope 
and rise sediments--progradational interbedding of clays and marls; 4 = isopach of the Lower Grudja Formation; 5 = boundaries 
of facies zones; 6 = basement. 
24 G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
the basin reaches 1100-1200 m and decreases at 
the periphery (Fig. 20). 
Because of subsequent erosion, deposits of the 
Lower Grudja Formation are absent from the 
buried elevated areas and horsts in the southern 
parts of the basin. The sandstone beds are buried 
shoals and bars which had formed in a shallow- 
water shelf environment. Towards the east the 
sandy bodies gradually disappear from the sec- 
tion and synchronous deposits occur as a thick 
uniform layer of Upper Cretaceous shale, de- 
posited on a continental palaeoslope (Fig. 21). 
In the western direction the Lower Grudja 
grades into continental sands and conglomerates. 
Cenozoic. The Cenozoic sediments display the 
features characteristic of a passive continental 
margin, the section building by progradation to- 
wards the outer edge of the palaeoshelf and the 
continental slope. Two sedimentary cycles can be 
identified in the section: a Paleocene-Eocene 
and an Oligocene-Neogene cycle, separated by 
an unconformity. 
The Paleocene-Eocene sediments are sepa- 
rated from the underlying rocks by an erosional 
w 
"7 
ua 
- - ~ Ke~y Be( 
~_~--- 
l ~ ~ 
I " ' ~ " ' T ~ ~ 0 - fez ~ , ~ 
. . . ~ 
L i n e A - A ' ~ ~ - -..-. 
I = 
~ ~ 
---B=~'~--fS"__~*~"*" Line B-B' - X- 
W. Temone-l~ TU P 
3¢ ~ e ~ ~ q . n e - 1 Temane I 
35" 
E 
0 
Pg 
>i 
Moo 
-lO00 
~1 S ai- 
I co 1500 
0 
Pg 
Moo 
"500 
Crnp 
qan 000 
Fig. 21. Schematic cross-section of the Lower Grudja Formation in the Mozambique Basin. The Lower Grudja Formation is 
represented by clay with horizons of glauconitic, quartzitic sand deposited in a shallow shelf environment. The sandy/shaly 
character is displaced by Senonian/Maastrichtian marl to the east. The lenticular morphology of the sand beds is inferred from 
well data. 
G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 25 
unconformity. They are basically deposits of the 
shallow-water shelf, which give way towards the 
east to deeper-water formations of the continen- 
tal slope. The following formations in the se- 
quence have been identified in areas where shal- 
low-water facies have developed, distributed 
mainly within the boundaries of the present-day 
coastal plain: the Upper Grudja (Paleocene- 
Lower Eocene)and the Cheringoma (Middle- 
Upper Eocene) (Fig. 22). 
The Upper Grudja Formation is a sequence of 
glauconitic sand, clay and marl with bands of 
limestone. The total thickness of the formation is 
300-400 m. 
The Cheringoma Formation occurs as num- 
mulitic limestones with bands of clay and calcare- 
NW 
BALANE-1 
FUNHALOURO-1 DOMO-1 
SE 
, BED 
'=i o 
I Ch°'7 °l' 
2/41 MazencJ° Su I'~r)Domo4 
,l/,L. 
CHRONOSTRATIG RAPHIC LIMIT 
FORMATION LIMIT 
Fig. 22. Correlation of Cenozoic sediments in the southern part of the Mozambique Basin. 
26 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
ous sandstone. The thickness of the formation is 
250 m. 
Eastwards, the facies of the shallow-water shelf 
are replaced by deeper-water formations, cal- 
carenitic and calcilutitic which formed in condi- 
tions of a continental slope and continental rise. 
Along the outer edge of the shelf, a chain of reef 
massifs is present. 
In the central part of the Mozambique Basin, 
toward the east, a facies change also takes place 
and the Paleocene-Eocene in the area of the 
present-day shelf, comprises rocks deposited in 
outer palaeoshelf and continental slope environ- 
ments. The sediments of the Upper Grudja and 
the Cheringoma formations are replaced by ter- 
rigenous and calcareous rocks which prograda- 
tionally built up the palaeoshelf outer edge. The 
most representative section in this area is the 
sediment deposited in the Zambezi Delta De- 
pression (Fig. 23). 
The section of Paleocene-Eocene sediments 
occurs here as deep-water facies comprising 
marls, shales and calcilutites. A section of the 
Zambezi-3 well which comprises calcarenite, cal- 
cilutite and marl provides an interesting insight 
into the palaeogeographic environment at that 
time. This section is considered to be shelf slope 
or fore reef facies. The string of reefs forms a 
barrier between calcareous and argillaceous fa- 
cies. 
As a result of the detailed correlation of the 
wells and the seismic interpretation, three reef 
levels have been established in the Zambezi De- 
pression: Paleocene, Early Eocene and Middle- 
Late Eocene. The limits of the palaeoshelf outer 
edge gradually shifted westwards accompanying 
the Palaeogene transgression (Fig. 24). 
The Paleocene reef structure has been studied 
in more detail within the central part of the 
Zambezi Delta Depression. A shallow-water shelf 
is represented by interbedded sandstone, arena- 
ceous limestone and marl of the lower part of the 
DIVINHE-1 NEMO-1-X SEN60 MARIN-1 
MARRUPENHE-1 JANGUENE'I SOFALA-1-X SANGUSSI MARIN-1 
. . . . . . . - 92.-------,- ,~=~ 3o ~ -'k-- : - - ' - - " 
o • ' , SHELF "- • - - "7-" u- ! ~ . - - , . _ . 
, . E = , . " , . . . . . . 
~ , - - ~]~o~=:~Du,~up \ 1 ' : : : 1 ~ ~ " X - - - - - 
~o ~= °'~1/'--'-].=. " ' ~ ] ~ 2 0 " " I%---]"~INfUNEO=--~--'~-._-~"~'~'~-- --" X " \ \ \ --'7--" "_-7- 
< ~ ~ - - - ~ BEDS - - "-' 
PEt ~ ==I 13~'7 ~_ -'~,., X~ XX~ "-=~'-"-:'1755 :':':': 
I ~ -oq ~ .=C~U.E-~ " T z " L ' - I ~ ( , 9 ~ ' ~ ..... I-:"-.-I'zo:~6 ~"--....I.---: - I . . . . Pa l , [ ~, 
/ /=] l ~ ZAMBEZI-I ~ ~. ---'--[. """~-~,~] 
I / ~ 1 I 5 SANBUSSI MARIN-I ~ .]'T-L.-1 
• L ~ . _ / ~ I , . I &SEN60 MARIN-1 .'~J_~.z~L,....00_ PQ[ll 
Z O [ ~ " { t ~ ~ 2 1 7 BUZI - 1 F"'T~I"=° " - " - - - - - J 
S ~ g ^ [ IS 8 ZAMBEZI-3 K 2 
j . ~ , u I I 0 SOFALA-I-X 12 DIVINHE-1 
113"-,~.,,. I [ IONEMO-1-X 1'3 M A R R U P E N H E - 1 
11 JANSUENE- 1 1L, MAMBONE- 1 
Fig. 23. A correlation and a palaeo-environmental interpretation of the Paleocene-Eocene sediments on the southwestern flank of 
the Zambezi Delta Depression. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 27 
Upper Grudja Formation. Several small palaeo- 
topographical highs can be outlined within the 
shelf area (Fig. 23). 
The edge of the shelf is limited by carbonate 
buildups with a thickness of 100-150 m. The 
continuity of the barrier reef is interrupted by 
several submarine canyons which cut through the 
outer edge of the shelf. The canyons act as the 
main source of clastic material (i.e. calcarenites 
and calcilutites) for the submarine fans. 
An archipelago of Paleocene reef massifs is 
situated seaward of the reef on the outer edge of 
the shelf. Development of this type of reef is 
associated with the central part of the Zambezi 
Delta Depression. 
The accumulation of the greatest thickness of 
the calcarenite and calcilutite (which make up the 
fan bodies) is related to the inter-reefal lows 
(channels, submarine canyons) and to the outer 
slope of the archipelago. In this part of the se- 
quence underwater slumping processes are 
widespread, making the interpretation of the seis- 
mic data very difficult. 
Eastwards, the reef zone is limited by an abrupt 
80s ~8"s 
22" 
26"s 
32"E 36"E 
-. ~ l lr~..AMBANE 
i ' J o so 1oo ,so~ 
32"E 36 E 
Fig. 24. Scheme of the migration of Paleocene-Eocene shelf margin buildups in the Mozambique Basin. Thick lines show 
successive positions of the carbonate shelf outer edge during the Palaeogene. 
28 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
slope break, where the Palaeogene sequence 
comprises thinner clayey and marly deposits. 
A schematic block diagram of Paleocene- 
Eocene barrier reef structures is shown in Fig. 25. 
The Early Eocene reef is characterized by the 
shifting of the shelf outer margin in a westerly 
direction. The shallow-water shelf section is rep- 
resented by interbedded, stacked arenaceous 
limestone, sandstone and marl of the upper half 
of the Upper Grudja Formation. The outer limit 
of the shelf is traced as a chain of small fiat reefs 
with a characteristic progradational stratification 
at the reef slope (Fig. 23). Some reefs and small 
fan bodies are located in the fore-reefal zone. 
The fore-reefal zone gradually grades into the 
continental slope with the accumulation of shaley 
and calcilutite sediments. 
The Middle-Late Eocene reef is characterized 
by shallow-water carbonate shelf deposits 
(Cheringoma Formation) which are developed 
over a large area, and it is represented mainly by 
stacked nummulitic limestone and marl. The 
margin barrier reef is shifted westward with re- 
spect to those of the Paleocene and the Early 
Eocene. A characteristic feature of the margin 
reef is the development of progradational stratifi- 
cation of Eocene sediments on its outer slope 
(Fig. 23). The thickness of reefal buildups is sig- 
nificant when compared to the thickness of car- 
bonate shelf deposits totaling some 500-600 m. 
Oligocene-Neogene deposits occur as sedi- 
ments of the Limpopo and Zambezi palaeodeltas. 
The Zambezi Deltaic complex is the largest 
Cenozoic deltaic complex on the east coast of 
Africa. It reaches a thickness of 4000 m. The 
delta fan here also incorporates deposits of the 
palaeodeltas of the Punge and Buzi rivers. The 
section is formed of interbedded conglomerate, 
sand and clay with characteristic deltaic superpo- 
sition of layers and numerous intraformational 
interruptions and erosional inlets. During the 
Oligocene, Neogene and Quaternary the depres- 
sion was filled with terrigenous sediments. The 
rate of deposition was higher than the rate of 
subsidence and as a result the delta plain pro- 
graded towards the east. Features of the deltaic 
complex are illustrated in Fig. 26. 
The Limpopo River deltaic complex is marked 
by a considerable reduction in the amount of 
terrigenous material deposited in the marine 
basin. Deposition is mainly concentrated in the 
coastal plain with the formation of a sub-aerial 
delta. 
The Neogene deposits in the central part of 
the basin occupy the space between the Zambezi 
and Limpopo palaeodeltas, and occur as 
shallow-water shelf deposits. The most widely 
distributed deposits are Miocene in age and are 
subdivided into the following formations (from 
the bottom of the section upwards): Inharrime, 
Temane and Jofane. 
The Inharrime Formation unconformablyoverlies the Cheringoma deposits and occurs as a 
layer of red dolomite, red clay and sandstone 
with individual bands of anhydrite. The thickness 
of the formation is 100-350 m. These sediments 
CARBONATE BAR CARBONATE BUILDUP ARCHIPELABO 
COASTAL REEF ~ S H E L . . F MARGIN BUILDUP"'- 
COASTAL UNE f~L~".,..,cvc~,'..-'-~ ~ ./... - " ~ - - 
~ "" "~ L SLOPE 
i ,o ~SUBMABINE CANYON 
PRE-REEF ~v "~RINNACLE 
UNITS 
Fig. 25. Schematic block diagram of the Paleocene-Eocene reef complex in the Zambezi Delta Depression. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 29 
were deposited in a restricted lagoonal environ- 
ment, whose central part comprises a thick, gyp- 
sum-bearing sequence identified as the Temane 
Formation. 
The Jofane Formation occurs primarily as ma- 
rine carbonate: limestone, calcarinite and arena- 
ceous limestone, which are distributed practically 
everywhere within the coastal plain. Thickness is 
up to 200 m. 
The Pliocene deposits were formed at a period 
of extensive marine regression and occur over the 
greater part of the Mozambique Basin as conti- 
nental deposits of ancient dunes, river terraces 
and lakes. The Pliocene marine sediments are 
distributed within the modern shelf and reach 
their maximum thickness in the Zambezi Delta. 
3.2. Ruvuma Basin 
The Ruvuma sedimentary basin is the south- 
ern end of the great East African marginal basin, 
which comprises the coastal plains of Tanzania, 
Kenya and Somalia. 
Commercial discoveries of gas have recently 
been obtained from Oligocene deposits in the 
Ruvuma Delta in Tanzania, from the M'Nazi Bay 
borehole, close to the Mozambique border. Indi- 
cations of gas have also been found in the 
Mocimboa-1 borehole in the central part of the 
basin, in Mozambique. An ingress of water con- 
taining gas has been obtained from Albian de- 
posits. 
The regional structure of the basin has been 
studied by seismic survey both on land and in the 
Mozambique Channel. 
3.2.1. Stratigraphic framework of the Ruvuma 
Basin 
The Ruvuma Basin straddles Mozambique's 
northern border with Tanzania. The sedimentary 
section possibly contains Karoo rocks, overlain by 
Jurassic, Cretaceous and Cenozoic sediments. 
Maximum sedimentary thickness, as shown by the 
results of aeromagnetic and regional seismic sur- 
veys, is on the order of 10 km. 
The sedimentary section in the Ruvuma Basin 
has been tested by drilling to a depth of 3492 m. 
The oldest sediment encountered was Aptian- 
-6 
.o 
.=_ 
z~ 
~'~ 0 
© .r.~ 
0 
e q 
© 
o-6 
¢-q 
E~ 
~ u d 
30 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
S T A G E 
O U A R T E r l N A F I Y 
Z • Pli°c~mLe 
Late _% 
LU O E/ i r ly 
z "Lu-r~ 
E~(ly 
L.~IO 
tL Ea l l y 
Mo.'lsttichli0n 
Aolot ~iarl ' 
tu 
f t . 
(9 tu 
~- 0 [12 
I-- 
; ee 
5 
_~ o 
D 
g~ 
P a r t s o f B a s i n 
AO( 
S o u t h e r n N o r t h e r n M~ 
O F F S H O R E ~: O N S H O R E m O F F S H O R E 
-- - - . ~ ~ . . . . . . ~ . . . . . . . . ~ . ,u 
- ~ . - .-.~.~.7 . - ,5~q 
. - . - . . . - . - . . . . - . - . . . - : ~ . , ~ _ ~ 
i ~ _ _ - - = , " : ' " "" " 2 ---,--,~ - - 
A A A 
I". / C m ~ p n n i a n A ~ A A ~ I~I.~BOTRUNC,,~_ MARLS ~ ~ ~ " 
1 : 5 = - - s~,,to,,~n - - ~ - ,z~ " " 
- - Con i~c ian - - ~ / J ~ S S : " - ' - 
03 - - T iror l i~n - - ' . . . . . ' ~ • • ~ * ~ 130MO SANDS FM EOUIV. - - - - - - - - I~ . . . . . . . - '¢- 
o - ~ ~ "" - - ~ i 
Albi~lll - fO0 
(~ ~ Aptian ~ - - - - 
. . . . . . . . . ___ f : ,.,..,,,,,,~,,,,,,,,""'"°'"""° . . . . . . . . ,,,,, . ~ ~ " - ' ~ . ' - : . . . . . . - e : . ' . , ' "." • "." '..'- • 
I~Orli~tslar i 
' - - ~ . : ' . ' . . . ~ . . - L _ , ' , " , , ' - ¢ _ _ 
- -K im l l l o r i ( l ( l i ~ l ~ - ~ * • • . ' . " . . . . . ~ - m , ' ' 150 
Col lov i ; 3n - ] ~ • , ~ ~XIZIMOANISHALEEQUIV. . n i l r ..a,~,,-,',,~: 
Ua lhon ian , _ _ , . . .r--.pj , . ' ~;" - - ~ I [ '~ /"1~ MIIDOkl¢~-I-I~ J 1:3 • , i i > MTUMBEI I.ST EQUIV_,,~..j~ ~ - " - " 
. . . . . . :- . . . . - :r ,- ~ - . ' " , - ' ~ . ~ a = - 
03 '~" IJaJ Oci:~n ~ M A C A ~ W E FM E Q U I V . - - ~ h i -~pF 
. . . . . . . . . . . . . . . "L'- N<~ ERE N ~ "-S---, 
i 
~ ~ ~ ~ o , EQUIV. ----~ 
T,~C~ O~OS EOtnV~ 
- 200 
- 250 
PnE-CAM~AN + ~_ 
Fig. 27. R e g i o n a l s trat igraphy o f the R u v u m a Basin. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 31 
Albian argillite. The lower portion of the sedi- 
mentary cover, comprising Lower Cretaceous, 
Jurassic and Karoo sediments, has not been pen- 
etrated by the wells, and the composite cross-sec- 
tion was compiled using data from boreholes 
drilled in contiguous areas of Tanzania, and also 
from seismostratigraphic studies in the Ruvuma 
Basin (Fig. 27). 
Basement. Late Proterozoic rocks of the Mozam- 
bique metamorphic belt form the basement of the 
Ruvuma Basin. Those rocks step down by faults 
L 
~1 ~ ~ ' ~ " ~ ~ ~ ~ t 
x I ~ e • - i . . ' " i . : . . ! . 
~" + ,~ x x x " . • " . ' ' . " . ' . ~ ' . ' . " " . "- • , ' 
- 
Fig. 28. Development of Karoo (Permian-Triassic) sediments in the Ruvuma Basin: 1 = terrigenous Karoo sediments; 2 = basement 
outcrops on the surface; 3 = basements outcrops under the post Karoo sediments; 4 = major faults. 
32 G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
to depths exceeding 10 km. Seismic data allow a 
basement surface to be traced with a high degree 
of confidence. 
The Karoo Group. Deposits of the Karoo group in 
the Ruvuma Basin are not exposed at the surface. 
A layered sequence has however been identified 
in seismic sections which can be compared with 
the Karoo deposits in southern Tanzania. The 
sequence wedges out towards the west on the 
flank of the trough, having been truncated by 
overlying strata (Fig. 28). This system of deposits 
forms a self-contained structural cycle. Lying at 
the base of the Ruvuma Basin sedimentary sec- 
tion, these deposits compare with the Karoo se- 
quence in southern Tanzania, where they display 
° 
Sec. 
&O'30' ~1"00' 
13" ~e.mbo 
,,, / 
i 
13 ° I 
~ 0 " ~ 41"00" 
13" 
Line {3MR-30? 
10 k m 
I I 
See.. 
Fig. 29. Assumed Middle Jurassic reef massif (line GMR-307). Reef-type seismic anomaly: clinoform reflectors, presence of 
enveloping structure, deterioration of sub-reef reflection quality, abnormally high velocity inside the reef body. 
G. Salman, i Abdula / Sedimentary Geology 96 (1995) 7-41 33 
two facies, developed within the Selous and Man- 
dawa basins (TPDC, 1992). 
The Selous Basin contains the western facies 
zone of the Karoo palaeobasin. The sedimentary 
sequence is mainly represented by syn-rift conti- 
nental sediments of Permo-Triassic age overlying 
the grabens. The basin deposits are composed of 
continental conglomerate and sand with shale 
bands. The thickness reaches 3000 m. 
The Mandawa basin lies further eastwards, in 
o o t incl~ Z ~ j ~ l 
o o o o 
Norunyu-I I 
o o o o 
o 
o Lake Kilere-I "O- 
0 0 0 0 
o o o o 
o o o o 
o o o o 
o o o c 
o o o . 
o o 
o o 
o o o 
o~u [0~ o 
~" + o 
~o 
+ + @ 
°ol 
°1 
o 
o 
o 
o 
o 
I,m ?o 0 20 c o r m 
Fig. 30. Deve lopment of Early and Middle Jurassic facies in the Ruvuma Basin: 1 = deep-water sediments; 2 = shallow-lagoon 
evaporite sediments; 3 = salt domes; 4 = salt ridges; 5 ~ reef massifs; 6 = carbonate- terr igenous shelf sediments; 7 = continental 
terrigenous sediments; 8 = basement outcrops. 
34 G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 
W Line MZ4A-8 E 
2200 2400 
0 I K ~ - 
/ u (^/) ~2"~5' 5km 
% ' / , ' S ~ C . Fig, 31 
t~'90' 
Fig. 31. Correlation of reef and salt facies of the Middle and Lower Jurassic (line MZ4A-8). 
0 
-1.0 
~2.0 
-3.0 
-,i.O 
southern Tanzania. The sedimentary cover ex- 
ceeds 4-5 km in thickness. Development of the 
basin began in Permo-Triassic and Early Jurassic 
times, as riftingresulted in differential subsi- 
dence and the formation of a semi-enclosed basin. 
The Mandawa Basin is a major Jurassic salt basin 
in the central part of the East African continental 
margin. Halogenetic deposits are likely to extend 
further southwards penetrating into the Mozam- 
bican part of the Ruvuma Basin where seismic 
w E 
2250 2300 2350 2400 2450 
0 i t i t ~ 0 
/ - ~ - - - ~ - ~ ~ - . . ~ ~ - - - - - - - - - ~ ~ . - - - - - - . - ~ 
L ~ ~ - - - ~ - - - ~ - - - ~ _ ~ - ~ ' - ~ - - - - - . ~ I 
II" 11" 5,0 
$ec. 
Fig. 32. Sand bar facies in Lower Cretaceous sediments (line MZ4A-56). 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 35 
data suggest salt domes interrupting lower hori- 
zons of the sedimentary sequence. 
One can assume that in the Ruvuma Basin 
both types of Karoo facies are also found, their 
distribution related to buried rifts: on the west, 
continental syn-rift sediments similar to the 
Selous Basin; and on the east, lagoonal-evaporitic 
sediments of semi-enclosed basins similar to the 
Mandawa Basin (Fig. 30). 
Post-Karoo sediments. The post-Karoo sequence 
occurs as predominantly marine sediments of 
Middle to Upper Jurassic, Cretaceous and Ter- 
tiary age, whose deposition is associated with the 
formation of the East African continental margin 
(Fig. 27). 
Middle Jurassic. Sediments of Middle Jurassic 
age are unknown in the Mozambican part of the 
Ruvuma Basin. Based on seismic correlation with 
the adjacent Tanzanian areas, a thick sequence 
can be identified at the base of the sedimentary 
section which is likely to be correlatable with 
Middle Jurassic sediments in Tanzania. These 
sediments are widespread in the central, deepest 
part of the basin and are probably related to the 
beginning of Middle-Late Jurassic marine trans- 
gression. 
The seismic pattern suggests the existence of 
barrier and single reef massifs in the Middle 
Jurassic (Fig. 29). 
Based on seismic data, a palaeofacies chart for 
the Early and Middle Jurassic has been con- 
structed which shows a development zone of shal- 
low-water, lagoonal and reefal sediments, and a 
number of salt ridges and salt diapirs (Fig. 30). 
Upper Jurassic. Upper Jurassic deposits identi- 
fied biostratigraphically in Mozambique have 
been found only in the southern part of the 
Ruvuma Basin. They occur here on top of the 
pre-Cambrian basement as arenaceous bioclastic 
limestone containing a Kimmeridgian-Tithonian 
fauna (Afonso, 1978). In the northern part of the 
Ruvuma Basin within Mozambique, variegated 
sandstone and conglomerate have been identified 
at the base of the section of Lower Cretaceous 
continental deposits (Maconde facies), as a self- 
contained sequence of Jurassic age. The Jurassic 
deposits in the northern basin may reflect the 
continental conditions in the ancient basin, while 
the bioclastic limestone may outline a zone of 
coastal sedimentation (Fig. 31). In contiguous ar- 
eas of Tanzania, the Upper Jurassic has been 
encountered in several boreholes and occurs as 
deeper-water deposits--argillaceous limestone 
and marl. It may be supposed that similar sec- 
tions of Upper Jurassic deposits are also dis- 
tributed in the central part of the Ruvuma Basin 
in Mozambique. 
Lower Cretaceous. Lower Cretaceous deposits 
occur on the western flank of the Ruvuma Basin 
directly on top of the pre-Cambrian basement. 
The Lower Cretaceous deposits occur in expo- 
sures as continental conglomerate and quartz- 
felspathic sandstone of the Maconde Formation. 
The Maconde continental deposits evidently are 
replaced in the east by a sequence of marine 
SW NE 
MOCIMBOA-I 
2 8 0 0 2 8 1 5 0 2 9 p 0 0 
~ ~ ~ M i o ~ - _ 
~S,~-I- ~< , - ~ - - 
/ / f . - ~ - - ~ ~ l J ~ - ~ ~ - - ~ . - - ~ - 
~ . - - - - - [ e n - T u r ------ ~--- ao 
-- ~-- ~-----~---_~ -- ~ ~ : -as 
&O'15 
5 k m 
1 
/,0"15' 
Fig. 33. Fan complex in Aptian-Cenomanian sediments in the 
area of Mocimboa-1 well (line MZ4A-25). 
36 G. Salman, 1. Abdula / Sedimentary Geology 96 (1995) 7-41 
terrigenous formations• Sand bars are widespread 
within a shallow-water shelf zone (Fig. 32). 
Southwards, the continental red sandstones of 
the Lower Cretaceous pass laterally into progra- 
dational facies of conglomerate and sandstone, 
overlain by an arenaceous-marly belemnite se- 
quence which can be ascribed to the Barremian- 
Albian (Civitelli, 1990). The Mocimboa-1 well has 
penetrated deep-water argillites of Aptian-Al- 
bian age with lenses of sandstone, which are 
o / ~:"° 
o ° I • : \ - 
0 LQ~e K l l e r 
o l - . 
° ° \ 
o o • 
o o . \T 
o o O o \ . F a 
o o o 
o o O~ 
t o o 
oMu~o~ o 
+ t ~" ÷ + - ÷ R °. 
o l 
4- 
I 
+1 
Fig. 34. Development of Lower Cretaceous facies, Ruvuma Basin: 1 = continental rise sediments; 2, 3 = continental slope 
sediments; 3 ~ fan complex; 4-6 = shallow shelf terrigenous sediments, inclusive: 5 = coastal conglomerates and sandstones, 
6 = sand bars; 7 = continental terrigenous sediments; 8 = basement outcrops. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 3 7 
interpreted to be associated with submarine allu- 
vial fans on a continental slope ("fan complex") 
(Fig. 33). Facies variations in Lower Cretaceous 
sediments in the Ruvuma Basin are shown on 
Fig. 34. 
Upper Cretaceous. Upper Cretaceous deposits 
occur in the Ruvuma Basin as a sequence of marl 
and argillite (Condusia Formation--marl with 
Globotruncana). Civitelli (1990) points to a con- 
siderable gypsum content in this formation. The 
i 39 ~ FC-~ 
Na~unyu- 1 ~'f 
L~ke Kirere 
t t - t - 
.~. 
I 
 --13 1- 6 + 
I ,~O 0 ,ra 40kin 
_ _ ° _ _ 
L _ _ _ . _ _ 
, i - 
Fig. 35. Development of Upper Cretaceous facies, Ruvuma Basin: 1 = terrigenous sediments of continental rise; 2 ~ terrigenous 
sediments continental slop(;, inclusive: 3 = fan complex, 4 = shelf terrigenous sediments, 5 = basement outcrops; 6 = limits of 
development of Upper Cretaceous rocks. 
38 G. Salrnan, L Abdula / Sedimentary Geology 96 (1995) 7-41 
Upper Cretaceous on the west flank of the basin 
is about 200 m thick and reaches 915 m thick in 
the Mocimboa-1 borehole (Fig. 35). 
Cenozoic. The Cenozoic is characterized by 
shallow-water facies of Paleocene to Miocene age, 
of which the Miocene is the most widespread 
deposit. As in the Mozambique Basin, two sedi- 
mentary cycles can be identified within the Ceno- 
zoic sequence, separated by an unconformity, Pa- 
leocene-Eocene and Oligocene-Neogene. 
L i t 
L i n d l - 2 ~ P 
N o r u ~ ¥ t J r I 
Loke K i t e r e - I 
4- "t- 4 - 
-I- " t- -I- 
1:::~1 [-~-13 
. . . . . . ~ 4 "~- 
I = r - l = ~ ,-.~ 7 " i 
I 
i + 
I 
i 
i 
-I 
t.rJ ° 
Fig. 36. Development of Pa l eocene -Eocene and Ol igocene-Miocene deltaic complex, Ruvuma Basin: 1 = terrigenous sediments of 
non-compensated continental slope depression; 2 = shelf terrigenous-carbonate sediments; 3 = limit of development of Paleo- 
c e n e - E o c e n e sediments; 4 = limit of O l igocene -Neogene deltaic complex; 5 = basement outcrops. 
G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 39 
(1) Paleocene-Eocene. On the western flank 
of the Ruvuma Basin, a sequence of fossiliferous 
marl is present, with interbeds of quartzose sand- 
stone and coarse bioclastic calcarenite with a 
nummulitic Eocene fauna in the upper part of 
the section. Total thickness is in excess of 200 m. 
Civitelli (1990) assumes that this type of sediment 
is typical for shallow-water and coastal facies. 
The Mocimboa-1 well penetrated the Pale- 
ocene-Eocene sediments. In the central part of 
the basin, deeper-water carbonate shales are de- 
veloped with a thickness of 130 m which have 
been exposed by the Mocimboa-1 well (Fig. 36). 
(2) Oligocene. Oligocene deposits appear 
within the Ruvuma Basin in two facies types: 
shallow-water and deltaic. Shallow-water marine 
sediments of Oligocene age are widespread in the 
southern part of the basinwhere they were first 
identified by Civitelli (1990). They occur as a 30 
to 70 m sequence of interbedded quartzose sand- 
stone and marl with large Oligocene foraminifera, 
which overlies the eroded surface of the Upper 
Cretaceous sand and marl. 
Oligocene deltaic sediments are widespread in 
the central and northern parts of the basin where 
they have been penetrated by the Mocimboa-1 
and M'Nazi Bay-1 (Tanzania) boreholes. The se- 
quence occurs as an interbedding of shale and 
sand with typical deltaic stratification. The 
Oligocene, along with deposits of Miocene and 
Pliocene age, forms a single deltaic complex of 
the Ruvuma River palaeodelta which can also be 
traced in the neighbouring areas of Tanzania 
(Fig. 36). 
Oblique progradational bedding, which is 
characteristic of deltaic formations, can clearly be 
observed on seismic sections. The deltaic sedi- 
ments are subject to intensive plastic deforma- 
tion, slump structures, shale diapirs and nappes 
(Fig. 37). 
(3) Neogene. Miocene sediments discordantly 
overlie the older rocks. They occur as two facies: 
shallow-water and deltaic. 
Shallow-water Miocene sediments are devel- 
oped in the basin's southern part. The sequence 
of interbedded shallow-water marl and calcaren- 
ite with abundant fauna reaches a thickness of 50 
m. 
0 
l.O 
2.0 
3.0 
4.0 
50 
MZ 4A-56 
2200 2/~00 2600 2800 3000 3200 
B ~ e m ~ ~ 
MCR89-M]5 6RM-312A E 
60o 2oo I 8oo 600 ~00 0 
~ A Sen Bottom -10 
-3.0 
J l -2 Sec. 
251 50kmm 
Fig. 37. Ruvuma Basin. Schematic cross-section along lines MZ4A-56, MCR-M15, GMR-312A. Assumed salt deposits are 
cross-hatched. See Fig. 2 for location. 
40 G. Salman, I. Abdula / Sedimentary Geology 96 (1995) 7-41 
Miocene deltaic sediments form the central 
part of the section in the Ruvuma River 
palaeodelta, where they discordantly overlie the 
Oligocene (Fig. 37). 
Neogene deposits occur in the northern Ru- 
vuma Basin as variegated sand and sandstone of 
the Mikindani Formation, which forms the upper 
part of the delta system. 
An upper section of the delta system has been 
penetrated by the M'Nazi Bay borehole in Tanza- 
nia. Here the sandy clay deposits of the Pliocene 
reach a thickness of 1000 m. 
The marine transgression in the Middle 
Miocene was probably followed by a wide regres- 
sion related to both major elevation of the East 
African continental margin and Cenozoic rifting. 
4. Conclusions 
Analyzing the history of sedimentary depres- 
sions offshore Mozambique makes it possible to 
explain the main differences between the Ru- 
vuma and Mozambique basins' geology. 
(1) Both the Ruvuma and Mozambique basins 
are relatively young structures which developed 
discordantly to the structural plan of the Gond- 
wana sedimentary basins. Their formation is re- 
lated to the break-up of Gondwana and the ap- 
pearance of the East African continental margin. 
This explains the fact that Karoo buried rifts 
serve as a base of the Ruvuma Basin sedimentary 
fill, while in the Mozambique Basin the sedimen- 
tary section is underlain by thick Karoo basalt 
sequences which form the basement. 
(2) The Ruvuma Basin sedimentary section is 
more complete and includes Jurassic marine sedi- 
ments. In the Mozambique Basin, marine sedi- 
ments begin only with the Early Cretaceous, whilst 
the Jurassic deposits are either absent or occur in 
continental facies. This is related to the initial 
phase of the Gondwana break-up and a gradual 
penetration of the marine conditions southward 
along Africa's eastern margin. 
(3) In the Late Cretaceous, during the phase 
of stabilization, the sedimentary environments 
became similar and both the Ruvuma and 
Mozambique basins form a single system of East 
African continental margin sedimentary basins. 
Acknowledgements 
The present study has received the complete 
and unconditional support of the management of 
the Empresa Nacional de Hidrocarbonetos de 
Mozambique (ENH) and its general director, 
Mario Marques. ENH made available to the au- 
thors both the data contained in its geological 
files and the results of research carried out by 
ENH in recent years. ENH employees were in- 
volved in producing graphic illustrations (Elvira 
Boutaeva) and electronic text preparation of the 
English version of the text (Yuri Diudin). 
Considerable assistance has been provided by 
the experts of Tanzania Petroleum Development 
Corporation and its Deputy Managing Director, 
Salvator J. Mtomola. 
The authors wish to express their gratitude to 
M.F. Coffin and Thomas A. Davies, editors, from 
the Institute for Geophysics of the University of 
Texas at Austin, as well as to anonymous review- 
ers whose helpful remarks and comments on the 
paper resulted in considerable improvements in 
the final version. 
References 
Afonso, R.S., 1978. A Geologia de Mozambique. Imprensa 
Nacional de Mozambique, 181 pp. 
Civitelli, G., 1990. The Meso-Cenozoic sedimentary sequence 
of the Cabo Delgado Province, Mozambique. Inst. Nacl. 
Geol., Bull. Geol., 42: 39-66. 
Coffin, M.F., 1992. The East African and Madagascar mar- 
gins: stratigraphy, structure and tectonics. First Indian 
Ocean Petroleum Seminar, pp. 325-343. 
Coffin, M.F. and Rabinowitz, P.D., 1987. Reconstruction of 
Madagascar and Africa: evidence from the Davie Fracture 
Zone and Western Somalia Basin. J. Geophys. Res, 92: 
9385 -9406. 
Flores, G., 1972. The SE Africa triple junction and the drift of 
Madagascar. J. Pet. Geol, 7(4): 403-418. 
F6rster, R., 1975. The geological history of the sedimentary 
basins of Southern Mozambique and some aspects of the 
origin of the Mozambique Channel. Palaeogeogr., Palaeo- 
climatol., Palaeoecol., 17: 267-287. 
G. Salman, L Abdula / Sedimentary Geology 96 (1995) 7-41 41 
Kamen-Kaye, M., 1982. Mozambique-Madagascar Geosyn- 
cline, I. Deposition and architecture. J. Pet. Geol, 5(1): 
3-30. 
Kejo Kajato, H., 1989. Evolution of Sedimentary Basins in 
Tanzania. Tanzania Petroleum Development Corporation, 
ENH Archives, Maputo. 
Lawver, L.A., Coffin, M.F. and Gahagan, L. 1992. The Meso- 
zoic break-up of Gondwana. First Indian Ocean Petroleum 
Seminar, pp. 345-356. 
Rabinowitz, P.D., Coffin, M.F. and Falvey, D.A., 1983. The 
separation of Madagascar and Africa. Science, 220(4592): 
67-69. 
Raillard, S., 1990. Les Marges de l'Afrique de l'Est et les 
Zones de Fracture Associ6s: Chaine Davie et Ride du 
Mozambique. Univ. Pierre et Marie Curie, Paris, 272 pp. 
Robertson Research International, 1986. The Source Rock 
Potential of East Africa, Vol. 3. Maps and Diagrams. 
ENH Archives, Maputo. 
Royer, J.Y., 1992. The opening of the Indian Ocean since the 
Late Jurassic: an overview. First Indian Ocean Petroleum 
Seminar, pp. 169-185. 
Salman, G.B., Vissotski, N.I. and Vedrintsev, A.B., 1985. The 
Geology and Petroleum Potential of Mozambique. ENH 
Archives, Maputo. 
Salman, G.B., Ziubko, A.K. and Sheremetiev, Yu.F., 1990. 
Recursos Potenciais de Petr61eo e Gfis das Bacias Sedi- 
mentares de Mozambique. ENH Archives, Maputo. 
TPDC (Tanzania Petroleum Development Corporation), 1992. 
Tanzania: Petroleum Exploration Potential. ENH 
Archives, Maputo. 
Walton, E.K. and Khanna, M., 1992. The Karroo succession, 
western shelf, Seychelles, First Indian Ocean Petroleum 
Seminar, pp. 245-259.