Comparing the depositional architecture of basin floor fans and slope fans in the Pab Sandstone, Maastrichtian, Pakistan
R. Eschard, E. Albouy, F. Gaumet, A. Ayub, 2004. "Comparing the depositional architecture of basin floor fans and slope fans in the Pab Sandstone, Maastrichtian, Pakistan", Confined Turbidite Systems, S. A. Lomas, P. Joseph
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Basin-floor fans and slope fans present major differences in their internal architecture related to changes in: (1) margin morphology, (2) relative sea-level change, and (3) sediment supply. These variations are illustrated in the outcrops of the Pab Sandstone in Pakistan. The Pab Sandstone third-order sequence was deposited on the Indo-Pakistani margin during the Upper Maastrichtian. Uplift of the margin induced erosion on the shelf, incision of submarine canyons on the slope and the development of a sand-rich, high-efficiency basin-floor fan extending over hundreds of kilometres on the basin floor. During transgression, sediment accumulated in backstepping shoreface deposits on the shelf, and a minor mud-rich slope fan was deposited in the basin. Finally, a sand-rich braided delta prograded across the shelf, feeding a sand-rich slope fan where it reached the shelf margin. This slope fan was of more limited lateral extent. The Lower Pab basin-floor fan shows the effects of flow funnelling and confinement due to a canyon incised into the slope. It consists mainly of channel complexes deposited by superconcentrated density flows to low-density turbidity currents. In contrast, the Upper Pab slope fan shows little confinement and low transport efficiency. It consists of tabular lobes, aggrading mid-fan channels and conglomeratic channels in the upper fan. The low transport efficiency of the gravity flows probably explains the low degree of organization of the slope fan.