Depositional Environments of Sunniland Formation and Diagenetic Characteristics of Productive Facies, Lehigh Park Field, Florida: ABSTRACT

Abstract

The Sunniland formation in the subsurface of Lehigh Park field, south Florida, consists of 11 carbonate facies deposited during a transgressive and regressive cycle in five major depositional systems: shallow-water shelf, shoal-water carbonate complex, restricted and open lagoon, tidal flat, and sabkha. The shallow-water shelf facies consist of northwest-southeast-trending caprinid-chondrodontid patch reefs that overlie chondrodontid mounds. Caprinid-chondrodontid rudstones, grainstones, and packstones form a talus debris apron surrounding the patch reefs with abundant carbonate mud in more protected areas. Mollusk, gastropod, peloidal packstones and/or grainstones flank the shallow areas adjacent to the patch reefs. Sea grass probably grew in a mud-rich, protected, back-reef lagoon. In protected shallow-water areas between and behind the patch reefs, chondrodontid and requieniid wackestones and mudstones were deposited. Orbitolina(?) sp. and Coskinolina sunnilandensis are found in the higher energy shallow-water shelf deposits with miliolids prevalent in the more protected areas. Th productive shoal-water complex overlies the shallow-water shelf facies and consists of porous mollusk, echinoid, intraclast, orbitolinid packstones, and grainstones. Impermeable lagoonal deposits of low-energy, burrowed, miliolid mudstone or wackestone and nodular anhydrite in dolomitic mud provided the trap rock for the productive shoal-water sequence. Requieniid, miliolid wackestones accumulated in the shallow-water protected lagoon on the lee side of the shoals. Broad colonies of chrondrodontids inhabited the transitional lagoon-tidal flat areas. Oolitic-coated grainstones composed End_Page 1420------------------------------ of miliolids, gastropods, and dasyclads occur in tidal channels, banks, and bars. The lagoonal facies are overlain by tidal-flat deposits composed of an algally laminated, miliolid, pycnodont, gastropod, intraclastal, dolomitic mudstone and wackestone. Sabkha deposits of nodular or nodular-mosaic anhydrite overlie and are interbedded with the tidal-flat sediments. The time of lower Sunniland deposition was characterized by a gradual transgression over the underlying Punta Gorda anhydrite resulting in an open, shallow-water shelf environment in which the patch reefs formed. Progradation of the open-marine and landward facies during a rapid eustatic fall in sea level probably resulted in this evolution of facies and eventually led to the anhydrites of the overlying Lake Trafford Formation (upper massive anhydrite). Subaerial exposure and freshwater phreatic diagenesis preserved high, primary interparticle porosity and resulted in good secondary moldic porosity in the grainstones and packstones of the shoal-water complex and shallow-water shelf sediments. Diagenetic similarities exist with four other producing facies identified from Sunniland fields. Other high-energy facies deposited and subaerially exposed during Sunniland deposition may also provide attractive exploration targets. End_of_Article - Last_Page 1421------------