Arkell.1956.Jurassic..

TITHONIAN
TANGANYIKA 331
limestone in the upper part, but no fossils. They are arkosic and pass
down into arkoses, probably Triassic in age, which rest on the basement
complex.
The Kilwa-Kiswere-Lindi Hinterland
In general the structure is similar to that of northern Tanganyika, except
that the Tertiary coastal belt is narrower and the Cretaceous plateau is
wider. The Cretaceous overlaps the Jurassic, which is gently folded along
north to south axes and crops out in a network of valleys cut into the
plateau. The capping of the plateau consists of Neocomian and Aptian
beds (variously called the Makonde and Lindi formations) and rises to
heights of about 400 to 600 m. above the sea. The whole country is
thickly covered with bush.
The fullest and most complete Jurassic outcrops occur in the hinterland
of Kiswere, along the Mandawa River and its tributaries. Part of the
area was described by Hennig (1937). During 1951 Mr W. G. Aitken
of the Geological Survey made a reconnaisance of much of the area and
for the first time measured the formations, and Dr P. E. Kent for the
D'Arcy Exploration Company also visited, with him, some of the sections
and made collections and valuable observations. They proved an unsuspectedly
great development of Upper Jurassic marine strata to a total
thickness of about 735 m., lying in a trough of deposition parallel to the
present coast and thinning rapidly inland against the crystalline shield.
It has been my privilege to study the remarkable collections of ammonites
made by the Geological Survey and Dr Kent and to have the use of their
unpublished field data and diagrams. The ammonites prove the presence
of marine faunas ranging from Middle Callovian to Tithonian, the highlight
being a splendid assemblage of the Anceps Zone in pure Cutch
development, hitherto unknown in Africa.
The general succession is as follows (Aitken, 1954, 1955):—
Trigonia smeei Sandstones : up to 165 m. Tithonian and Upper
Kimeridgian
Septarian Marls: up to 390 m. Kimeridgian
Unnamed beds (Nerinella Sandstones pro parte): Oxfordian and Callovian
up to 180 m.
Pindiro Beds (unknown thickness) and coral limestone Supposed Middle Jurassic
of Matumbi plateau (no ammonites)
? Basal sandstones (in north only) ?
The presence of at least a Lower Tithonian fauna comparable with
that of the Lower Umia formation of Cutch is attested by some ammonites
in a coarse pebbly grit. One, from a locality on the Kikundi stream, is a
large Micracanthocer as sp. The remainder, from farther south, are poorlypreserved
Perisphinctids so finely ribbed as to be comparable only to
Virgatosphinctes communis Spath of the Lower Umia.
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