OPEN FILE REPORT NO. 80


 Middle Miocene-Lower Pliocene, Serravalian Zanclean Stage

 Thp Peace River Formation The Peace River Formation crops out or is beneath a thin
overburden on the southern part of the Ocala Platform extending into the Okeechobee Basin.
These sediments were mapped from Hillsborough County southward to Charlotte County.
Within this area, the Peace River Formation is composed of interbedded sands, clays and
carbonates. The sands are generally light gray to olive gray, poorly consolidated, clayey,
variably dolomitic, very fine to medium grained and phosphatic. The clays are yellowish gray to
olive gray, poorly to moderately consolidated, sandy, silty, phosphatic and dolomitic. The
carbonates are usually dolostone in the outcrop area. The dolostones are light gray to yellowish
gray, poorly to well indurated, variably sandy and clayey, and phosphatic. Opaline chert is often
found in these sediments. The phosphate content of the Peace River Formation sands is
frequently high enough to be economically mined. Fossil mollusks occur as reworked casts,
molds, and limited original shell material. Silicified corals and wood, and vertebrate fossils are
also present. The Peace River Formation is widespread in southern Florida. It is part of the
intermediate confining unit/aquifer system.

 Thpb Bone Valley Member, Peace River Formation The Bone Valley Member
(originally the Bone Valley Formation of Matson and Clapp, 1909), Peace River Formation
occurs in a limited area on the southern part of the Ocala Platform in Hillsborough, Polk and
Hardee Counties. Throughout its extent, the Bone Valley Member is a plastic unit consisting of
sand-sized and larger phosphate grains in a matrix of quartz sand, silt and clay. The lithology is
highly variable, ranging from sandy, silty, phosphatic clays and relatively pure clays to clayey,
phosphatic sands to sandy, clayey phosphorites (Webb and Crissinger, 1983). In general,
consolidation is poor and colors range from white, light brown and yellowish gray to olive gray
and blue green. Mollusks are found as reworked, often phosphatized casts. Vertebrate fossils
occur in many of the beds within the Bone Valley Member. Shark's teeth are often abundant.
Silicified corals and wood are occasionally present as well.
 The Bone Valley Member is an extremely important, unique phosphate deposit and has
provided much of the phosphate production in the United States during the twentieth century.
Mining of phosphate in the outcrop area began in 1888 (Cathcart, 1985) and continues to the
present.

 Pliocene Series
 Lower Pliocene to Upper Pliocene Zanclean to Piacenzian Stage

 Florida's Pliocene sediments have been the focus of numerous, primarily paleontologic,
investigations due to abundant and diverse molluscan faunas. Although the majority of the
Pliocene sediments are unfossiliferous siliciclastics, well preserved shell beds in southern
Florida have attracted much attention (see papers in Scott and Allmon [1992]; Zullo et al.[1993];
Missimer [1997]). Despite the attention to these units, the lithostratigraphy of the Pliocene units
remains poorly understood.
 Pliocene sediments are distributed widely in Florida. In the panhandle and northern two-
thirds of the peninsula the Pliocene sediments are predominantly unfossiliferous siliciclastics. In
the southern one-third of the peninsula, the Pliocene sediments are often fossiliferous