The Proterozoic Singhbhum Basin is a distinct litho-tectonic unit of the Singhbhum crustal province of the Eastern Indian shield. The sedimentary cover (ca 2.3 Ga) is a deformed folded sequence of metaclastic units in which records of depositional history are well preserved along the eastern cratonic margin of an unstable foreland trough formed during the early phase of the Singhbhum Orogeny. A total continuity of sedimentation and stratigraphic history from the basin margin towards the north following a slope controlled channelized submarine fan system that originates from the south and opening up towards the north is recorded. The development of submarine fan is related to intra- and extra-basinal factors. Proximal, medial and distal associates of the submarine fan system are well preserved. The proximal sequence is a product of submarine fluidized non-cohesive granular-debris flow, triggered by instability of the basin flank. The medial and distal components of the fan are excellently preserved as sandstone-shale turbidite deposited in overlapping submarine fan system. During basin filling, instability of the basin flank and basin floor strongly influenced the sedimentary character through various scales of turbidity current activities, and intra-basinal contemporaneous flows. This was followed by an ultimate stagnation and onset of post depositional processes.
In
recent years, much interest has centered on the stratigraphic,
structural and sedimentologic aspects of prograding submarine
fan deposits (Middleton, 1993; Haughton, 2000; Piper and Normark,
2001; Sinclair and Tomasso, 2002; and Shanmugam, 2003). Fans
associated with continental slopes are generally incised by
shallow to deep submarine channels, and sediment bypassing
is usually common because most of the coarse-grained sediments
are funneled from the upper shelf to the lower slope and basin,
through a system of anastomosing channels trending down the
dip of the regional basin slope (Shanmugam, 2005). The upper
shelf consists of sediments deposited from debris flow and
the mid-lower slope and basin plain consists of sediments
deposited from turbidity currents (Middleton and Hampton,
1973; Walker, 1975; Bourgeois and Leithold, 1984; Lowe, 1982;
Hein, 1984; Postma, 1986; Tokuhashi, 1996; Boiano, 1997; Viana,
et al., 1998; and Shanmugam, 2003). The sedimentary
environment guided by submarine basinal conditions and tectonic
controls on depositional history of clastics are some of the
aspects which demand due attention (Burke, 1972; Ghibaudo,
1992; and Reading and Richards, 1994).
The
present contribution is based on a detailed study in parts
of the Proterozoic Sedimentary Basin (PSB), 50-60 km in width
and extending for 200 km in roughly EW arcuate trend (³2.4-1.0
Ga) (Gupta and Basu, 2000) in the Singhbhum crustal province
of the Eastern Indian shield and lying in between Singhbhum
Archaean granite craton (³3.4-2.6 Ga) (Saha, 1994), occurring
to the south and high-grade metamorphic-migmatite belt to
the north (Figure 1). It also proposes a model on the mode
and nature of sedimentation on an ancient shelf-slope-base
of slope environment that now exists as a deformed, metamorphosed
lithounit (greenschist-lower amphibolite facies). |
