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Lower Miocene sediments in the southeast Texas coastal area can be divided into 2 distinct trends. The basal Miocene interval from the top of the Oligocene Discorbis upward to the Robulus chambersi is a predominantly regressive-marine sequence that reflects the gradual progradation of Miocene sands into this area. The overlying sequence from Robulus chambersi to Amphistegina (B) consists of deltaic and delta-related sediments that reflect continued marine regression and seaward progradation of a large early Miocene delta system.
In the nearshore Galveston and High Island areas, the basal Miocene interval contains a series of potential reservoir sandstones, most of which are above the abnormally pressured zones and occur at depths of less than 9,500 ft. Farther offshore, the younger Amphistegina (B) sandstones become favorable exploration objectives.
Several lower Miocene biostratigraphic zones are identifiable throughout the area and an attempt has been made to relate each zone to particular lithologic conditions or depositional environments. Because of the general southward movement of the shoreline during the Miocene and a relatively limited supply of sand, prospective Miocene sandstone trends in the southeast Texas offshore occur in narrow "belts" approximately parallel with the present coastline. Identification of these favorable trends is essential to a successful exploration program in this area.
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