Oligocene and early Miocene rocks are reported from coastal Martin 

 and Indian River Counties but apparently do not occur in Brevard County 

 which may have been above sea level during this period (Brown, et al., 

 1962). However, offshore, under the shelf section within the study 

 limits, Oligocene and early Miocene deposits may have been deposited on 

 the downdip slope of the Eocene surface. 



During middle-Miocene time, the entire study area was flooded by the 

 sea, and sediments of the Hawthorn Formation were deposited. This episode 

 was followed by a retreat of the seas - at least from the northern part 

 of the study area - and subsequent erosion of the Hawthorn surface. In 

 late Miocene and possibly Pliocene time the area was again submerged and 

 deposition took place. Parker (1951) included all upper Miocene sedi- 

 ments in southern Florida in the Tamiami Formation; most pre-Pleistocene 

 deposits overlying Hawthorn sediments are probably part of this formation. 



During Pleistocene time, the study area was alternately flooded and 

 exposed to subaerial erosion leaving a variable and sometimes complexly 

 related series of sediments and erosional surfaces. The last major event 

 was the advance of the Holocene Sea across the upper Continental Slope 

 and Shelf, starting about 12,000 years ago and essentially concluded 

 about 4,000 years ago (Curray, 1965; Milliman and Emery, 1968). 



c. Coastal Morphology and Sediment Characteristics - From Palm Beach 

 north to Cape Kennedy, the coast consists of a chain of sandy barrier 

 islands separated infrequently by narrow inlets. A narrow sandy beach 

 continuously borders the ocean sides of the islands, and a marshy lowland 

 fringes the lagoon sides. These islands rarely exceed 1 mile in width or 

 20 feet in elevation. 



North of St. Lucie Inlet, the shallow lagoon (Indian and Banana 

 Rivers) which separates the barrier islands from the mainland is 1 to 3 

 miles wide. Waters of Hobe Sound, Lake Worth, and marshy tidal creeks 

 separate the islands and mainland between St. Lucie Inlet and Palm Beach. 

 Following the coastal classification system of Shepard (1963), a coast, 

 with features as those described, is referred to as a marine depositional 

 coast, and more specifically as a barrier coast. 



Real-estate development of the shorefront has been intensive locally, 

 however, much of the barrier island coast of the study area is still un- 

 developed. Sand on the beaches and on the adjacent nearshore bottom is 

 composed of quartz and shell fragments. The quartz fragments are colorless 

 and vary from subangular to rounded forms. Shell-derived fragments are 

 most commonly well-worn smooth pieces of mollusk shell colored to shades 

 of white, pink, gray, and orange-brown. 



In the high-energy beach and shallow nearshore zone (to about 12 feet 

 MLW) , sediments are characteristically coarse, poorly sorted to moderately 

 well-sorted, calcareous quartzose sand. In this zone, variations in size 

 from place to place along the coast are pronounced and numerous. These 

 variations result from availability of a wide range of particle sizes in 



