THE ROLE OF WAVE REWORKING ON THE ARCHITECTURE OF STORM SANDSTONE FACIES, BELL ISLAND GROUP (LOWER ORDOVICIAN), EASTERN NEWFOUNDLAND

Stacked shallow marine cycles in the Lower Ordovician, Bell Island Gro up, of Bell Island, Newfoundland, show upward thickening and upward co arsening sequences which were deposited on a storm-affected shelf. In the Beach Formation each cycle has a facies sequence comprised, from b ase to top, of dark grey mudstones, light grey mudstones, tabular sand stones and mudstones, lenticular sandstones and mudstones, and thick b edded lenticular sandstones, reflecting a progressive increase of wave orbital velocities at the sediment surface. The mudstones and tabular sandstones reflect an environment in which the sea floor lay in the l ower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents. The lenticular sandstones in the succeeding facies are wave reworked s ands, commonly lying in erosional hollows and having erosional tops an d internal hummocky cross-stratification. Planar lamination is relativ ely uncommon and sole marks are mainly absent. In this facies oscillat ory currents were dominant and accumulated sand in patches generally 1 0-30 m in diameter. The facies formed on the inner shelf where the osc illatory currents generated by storm waves had powerful erosional effe cts and also determined the depositional bedforms. Mud partings and se cond-order set boundaries within sandstone beds are believed to separa te the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds. This interpret ation has important implications for attempts to estimate event freque ncy by counting sandstone beds within a sequence and for estimates of sand budgets during storm events. The thick bedded lenticular facies a ppears to have been formed by erosion of the mud beds between the lent icular sands, leading to nearly complete amalgamation of several lenti cular sand bodies except for residual mud partings. In the overlying R edmans Formation the process of amalgamation progressed even further s o that nearly all the mud partings were removed, resulting in the form ation of thick bedded tabular sandstones. Sequence stratigraphic analy sis of the cyclical sequence suggests that the cycles were eustaticall y controlled. The rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb. There is a gradational but rapid f acies transition from the tabular to the lenticular sandstone facies w hich is interpreted as occurring at the inflexion point on the falling limb. The thick bedded facies of the Beach Formation and the thick be dded tabular facies of the Redmans Formation represent periods of maxi mum sea level fall. The stacked cycles in the Beach Formation are inte rpreted as an aggradational, high frequency sequence or parasequence s et bounded at the top by a sequence boundary and succeeded by the thre e aggradational parasequences of the Redmans Formation. The recognitio n of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies.