Download BASIN TYPES ACCORDING TO TECTONIC by Prof. Dr. Abbas

SEDIMENTARY BASINS
BASIN TYPES
ACCORDING TO TECTONIC
by
Prof. Dr. Abbas Mansour
B. Convergent plate margins
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10. STABLE CONTINENTAL INTERIOR BASIN
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E.g. Lake Eyre Basin
Intracratonic (= within stable continental crustal mass)
Long term stability
Flat topography
River, desert, lake environments & facies
Mature basement derived sed. ± evaporites
Intracratonic Basins
• Simple basins are divisible into two groups.
Intracratonic basins lie within the continental
crust. Epicratonic basins lie on continental
crust but are partially open to an ocean basin.
These two types often occur adjacent to one
another with little fundamental difference in
genesis or fill
• Intracratonic basins are the classic type of
sedimentary basin. Notable examples include
the Williston, Michigan and Illinois basins of
North America, the Maranhao basin of Brazil,
and the Murzuk and Kufra
Intracratonic Basins
Intracratonic Basins
• The Williston basin is the classic example
of an intracratonic basin. It contains some
three kilometres of rocks of all periods from
Cambrian to Tertiary, with notable gaps
only in the Permian and Triassic.
Sedimentation spanned a range of
environments including fluvial and marine
sands, reefal carbonates, evaporites and
subwave- base pelagic muds. Deep-sea,
turbidite and deltaic fades, igneous activity
and shallow syndepositional faulting are all
absent.
Intracratonic Basins
Intracratonic Basins
Intracratonic Basins
• The lengthy history, diverse facies and
structural simplicity of the Williston basin
are also found in the other basins cited as
examples of intracratonic basins. It is
important to note that the sedimentary
facies, though diverse in lithology and
environment, are seldom indicative of deep
water or abrupt subsidence of the basin
floor. Deposition took place close to sea
level. Subsidence was thus a gradual, if
erratic event, with sedimentation being
sufficiently rapid to keep the basin nearly
Filled at any point in time.
Intracratonic Basins
• Basins of this type are found well within the
present limit of the continental margins, but
it is obvious that they were frequently
connected to the sea. This is shown by their
intermittent phases of marine carbonate and
evaporite sedimentation. During these
periods they might, therefore, be more
truly termed embayments rather than
basins.
Intracratonic Basins
• Modem analogues include the Hudson Bay
and the Baltic Sea, which lie on the
Canadian and Scandinavian shields
respectively. Intermittent uplift of the open
rim of the embayment closes the basin off
from oceanic influence. Evaporite or
continental sedimentation follows. An
interesting example of this is provided by
the Murzuk basin of Libya.
Intracratonic Basins
• An interesting example of this is provided by
the Murzuk basin of Libya. The northern rim
of this basin was separated from the Tethyan
Ocean by the Gargaf arch, a tectonic feature
which controlled deposition through much of
Palaeozoic and Mesozoic time. Nevertheless,
palacocurrent analysis of fluvial CambroOrdovician and Mesozoic strata indicate a
northerly palacoslope over the Gargaf arch
(Fig. 140). These data show that the Murzuk
basin alternately fluctuated from embayment
to basin until attaining its present structurallyclosed intracratonic basin shape.
Intracratonic Basins
Epicratonic basins
• Epicratonic basins are those which lie on the
edge of continental crust. Though subcircular
in plan, by definition, they tend to be embayed
and open towards the adjacent ocean basin.
The axis of an epicratonic basin may plunge to
the floor of the ocean or be interrupted by a
sill-like feature at the rim of the continental
margin. Examples of epicratonic basins
include those of the Mississippi Gulf coast, the
Niger basin and the Sirte basin of North Africa
Epicratonic basins
• The Mississippi and Niger basins are very
similar. Both originated towards the end of
the Mesozoic and continued to be sites of
active sedimentation until the present day.
• Both basins contain a basal layer of salt,
which diapirically intrudes younger
sedimentary rocks. The Louann salt of the
Gulf basin is of Jurassic age. The basal salt
of the Niger basin is believed to be of
Albian-Aptian age (Mascle et at., 1973).
Epicratonic basins
• The basins are infilled by prisms of terrigenous
elastics which were deposited in a range of
environments. On the landward sides of the
embayments alluvial deposits predominate. These
pass basinward into diverse shoreline facies,
which include both barrier and deltaic deposits.
These thin and grade seawards into marine slope
muds, with some development of turbidite sand
facies at the base of the slope. Geo- physical data
suggest a gradual seaward thinning of the
continental crust beneath both the Mississippi Gulf
coast and Niger basins
Epicratonic basins
• The Sirte basin of North Africa shares many
features with the Gulf coast and Niger
basins. It too is essentially an embayment
which opens out to an oceanic basin (the
Mediterranean). The Sirte basin originated
in the end of the Cretaceous and was
infilled more or less continuously
throughout the Tertiary.
Epicratonic basins
• By contrast with the previous, two examples, the Sirte
basin was predominantly a site of carbonate sedimentation.
Basal sands and thin evaporites are overlain by deep-water
Upper Cretaceous and Palaeocene shales. These are
thickest in intrabasinal troughs, while reefal carbonates
were deposited on adjacent horsts. Throughout the Eocene
the Sirte embayment was infilled by nearly a kilometre of
interbedded carbonates and evaporites. The final phase of
basin infilling during the Oligocene and Miocene involved
terrigenous and carbonate sedimentation in both marine
and continental environments. The active history of the
basin was concluded by a bout of basaltic volcanism in the
Pleistocene.
Comparison between both types
• These brief reviews of three epicratonic basins show
how they differ from the previously described
intracratonic examples. Epicratonic basins tend to be
much less stable than intracratonic ones, due to their
situation at continent margins. Initial basin subsidence
can be rapid, resulting in an early phase of deep-water
sedimentation. The floor of the Sirte basin was
extensively faulted and there was some igneous
activity. Like intracratonic basins, however,
epicratonic embayments can be infilled by both
carbonates
and
terrigenous
sediment.
This
differentiation is a function of the degree of uplift of
the adjacent crust.