Discussion
Features given below are diagnostic to which sedimentary environment ?
Tectonic setting : Mostly found in rifting continental grabens, foreland basin, overthrust mountain belts undergoing rapid uplift.
Geometry : Wedge-shaped, limited in lateral extend upto few meters to kilometers, thickness can be tremendous if subsidence is persistent.
Typical Sequence : Coarsing upward of cross-bedded sandstone channel lag conglomerates, unsorted debris-flow deposits.
Sedimentology : Extreme range in grain size boulders to clay, fanglomerate and cross-bedded sandstone common unsorted debris-flow, reverse grading, sieve deposit, sediment immature and angular with rock fragments and feldspar.
Fossils : Fossils and organic matter are rare.
Answer: C
The features describe Alluvial fans.
Alluvial fans build where steep mountain streams emerge onto a basin floor at fault-bounded margins: rift grabens, foreland basins and rising thrust belts. They form wedge-shaped bodies that thin away from the mountain front, with very poorly sorted, immature deposits from boulders to clay, debris-flow beds, fanglomerates and sieve deposits, and they rarely preserve fossils.
Lacustrine deposits are fine-grained and often fossil-rich. Meandering rivers deposit fining-upward point-bar sequences, and braided rivers, though coarse, lack the debris flows, sieve deposits and extreme sorting range listed here.
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