Turtle Bay field, about 40 miles due east of Houston, produces oil and gas from upper Frio and Marginulina sands (Oligocene). Structurally, the field is an anticline formed not by uplift but by subsidence of its north flank into rim synclines around the Moss Bluff, Lost Lake, and Hankamer salt domes, plus regional tilting toward the southeast. The area of the field remained stable as the southerly regional dip was reversed by subsidence into the rim synclines on the north. A thicker than normal Heterostegina limestone is observed on the electric logs of wells drilled in the area, showing reversal of regional dip, and may be used as a criterion to localize the search for more such fields in the district.

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