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Palaeohydrological Reconstructions From a Holocene Valley Fill
At the head of Ekalugad Fjord, eastern Baffin Island, a sequence of outwash deposits preserves a 6,000 year history of Holocene fluvial activity. Four depositional phases occurred:
1. deposits of sublateral drainage under glacial ice prior to 6,000 years BP (referred to as T1);
2. major outwash deposits in front of retreating ice before 4,300 years BP (T2) followed by an erosional interval;
3. aggradation correlated with Neoglacial events at 2,500 years ± BP (T3) followed by an erosional interval;
4. aggradation associated with recent Neoglacial activity (300 to 100 years BP) (T4).
Equivalent effects are found in many other east coast valleys in Baffin Island.
The T2 sediments are mainly foreset deltaic beds, deposited into the sea. Beds vary from cobbles with little matrix to fine, laminated sands. About 2,000 beds, comprising 30% of the total thickness, were sampled to determine grain size. These results form the basis for palaeoflow calculations using tractive force theory. The assumptions underlying the calculations are critically examined and several alternative calculations are made. The relative frequency distribution of the high flows is presented: discharges were about 10x larger than present-day ones, with a maximum of about 300 m3s−1, against an observed maximum of 200 m3s−1. It is concluded that present knowledge of sediment transport mechanics constrains palaeohydrological reconstructions from sediment textural information to be at best an order-of-magnitude exercise.
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