The Niton field is a classic stratigraphic trap caused by the updip migration of hydrocarbons along a gentle southwesterly regional tilt (50 ft/mi, 9.5 m/km) into reservoir sandstones of the Basal Quartz Formation. These reservoir sandstones were deposited during the Late Jurassic to Early Cretaceous transgression over an unconformable surface on Jurassic sediments. As sea level rose, the topography on the unconformity gave rise to a number of tide-dominant estuarine valleys, 3 to 5 mi (5 to 8 km) wide at their mouths.

Two major factors related to this depositional setting exerted the greatest control on the distribution of Basal Quartz reservoir potential sandstones in the Niton field. (1) The topography of the unconformity governed the lateral extent of estuarine sand bodies deposited during the transgression. Maximum thickness of the sand bodies occurs either (a) along the long axes of paleovalleys, or (b) at entrances to the paleovalleys. (2) Diagenetic patterns of cementing were related to the original environments of deposition. The occurrence of swamps on the topographically high areas generated acidic ground waters which leached carbonate and silica from underlying sediments. This leached material was reprecipitated as silica cements in sediments overlying topographic highs and as calcite ce ents in tidal-flat sequences of the estuary fringes. These cements reduced porosities and permeabilities sufficiently to produce updip and capping seals to reservoir sandstones. Open marine sandstones deposited at the mouths of estuaries were only lightly cemented and, therefore, became the primary reservoir sandstones.

By comparing the depositional setting of the Niton area with modern analogs along Holocene transgressive coastlines, it is apparent that similar stratigraphically controlled sandstone bodies should exist along depositional strike in other drowned estuarine river valleys.

Thus, by comprehending the depositional and diagenetic setting of the Basal Quartz Formation, the energy explorationist has a predictive tool that can be used to discover new areas of reservoir potential sandstones.

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