ABSTRACT

Salient structural features of the Sunniland oil field are discussed and illustrated by structure maps drawn on the top of a sand in the Miocene, on top of the Crystal River formation, the Avon Park limestone, the Lake City limestone, the Oldsmar unconformity, the Oldsmar anhydrite, the Cedar Keys formation, the Cedar Keys anhydrite, the Upper Cretaceous, the Lower Cretaceous, near the top of the Fredericksburg, near the top of the Trinity, and on top of an anhydrite near the Sunniland producing zone. Isopach maps of the Cedar Keys formation, the Upper Cretaceous, and the Lower Cretaceous (between the top of the Lower Cretaceous and the top of an anhydrite near the Sunniland producing zone) illustrate the lateral variations in thickness of these stratigraphic units.

There is a gradual localization and a gradual increase in relief of the producing fold from the tilted but nearly planar beds of the Paleocene Cedar Keys at a depth near 3,400 feet down to the top of the Sunniland producing zone at a depth near 11,500 feet. At about 11,500 feet, near the Sunniland pay zone, the producing fold has 150 feet of relief. However, tilting to the northeast by 50 feet per mile has reduced the closure to where the producing fold shows only 36 feet of proved closure. Poor symmetry and the presence of two high points suggest that the producing fold is a depositional feature.

The local relief on top of the hard cavernous dolomite (Oldsmar limestone) is about 650 feet; this feature is thought to have been a topographic low in karst topography and is mapped as a large unconformity. Above this feature, beds of the Lake City limestone (Claiborne), the Avon Park limestone and the Crystal River formation filled in the low and restored a nearly level surface of deposition above which a few hundred feet of Miocene to recent sediments occur.