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Hurricane Andrew, one of the strongest storms of the century, crossed the southern part of the Florida peninsula on 24 August 1992. Its path crossed the Florida Everglades and exited in the national park across a mangrove-dominated coast onto the shallow, low-energy, inner shelf. The storm caused extensive breakage and defoliation in the mangrove community; full recovery will take decades. It produced no extensive sedimentation unit; only local and ephemeral ebb-surge deposits. The discontinuous shelly storm beach ridge was breached at multiple locations, and it moved landward a few meters. After seven months, there was little geologic indication that the storm had passed. It is likely that the stratigraphic record in this area will not contain any recognizable features of the passage of Hurricane Andrew.

The complex barrier/inlet system on the Gulf Coast of the Florida peninsula includes 30 barrier islands and a like number of tidal inlets. The diverse morphology of these elements gives rise to the most complicated barrier system in the world. Mean annual wave height is about 25cm and mean tidal range is less than one meter. Hurricanes are important but infrequent occurrences on this coast.

Sediment samples were collected with streamer traps at different elevations in the water column and across the surf zone. Beach profiles and breaking waves were measured together with the sediment sampling. The experiments were conducted on beaches with various sediment composition ranging from well-sorted fine sand to poorly sorted gravel and shell debris. The cross-shore variation of sediment mean grain size ranged from less than 1 phi to significant variation of up to 3.5 phi . The resultant database contains 99 vertical grain-size profiles, composed of 99 bottom samples and 552 trap samples taken throughout the water column and at 29 different locations along the southeast coast of the United States and the Gulf coast of Florida. A homogeneous vertical profile of mean grain size and grain-size distribution pattern was found on most of the beaches with a wide range of sediment sizes. The homogeneous vertical profile, representing 92% of the measurements, was found on all morphological features: swash zone, breaker line, mid-surf zone, trough, and bar. A homogeneous distribution indicates that the vertical mixing mechanism in the water column of the surf zone is independent of sediment size ranging from fine sand to fine pebbles. Bottom sediment, represented by an 8-cm core sample, was generally coarser than the sediment trapped in the water column.

Successful nesting of loggerhead turtles is an important aspect of beach management along the Gulf Coast of Florida. A detailed time series of beach monitoring has provided a wealth of data on turtle nesting and resistance to penetration in order to assess the effect of beach nourishment on turtle nesting. Three adjacent, nourished beaches, and nearby unnourished beaches provided the locations for systematic measurement of conditions. Two years of data are provided, 1994 and 1995, with the latter including tilling of the nourished beach on one of the projects. Nesting density increased from 1994 to 1995. Although cone penetrometer measurements routinely exceeded guidelines for turtle nesting, the turtles paid no attention to compaction. The nature of the sediment with large quantities of bivalve fragments is such that although vertical penetration is very difficult, the style of digging by turtles experiences little resistance. Data provided in this study indicate that the current guidelines based on cone penetrometer data for nesting in highly compacted beaches are incorrect. Nourished beaches on the Gulf Coast of Florida do not inhibit turtle nesting, they encourage it by providing a wide, dry beach.

Detailed beach-profile monitoring was conducted at the three phases of Sand Key beach nourishment on the Gulf Coast of Florida. The nourishment at Indian Rocks Beach, Indian Shores, and Redington Beach was monitored during six years, four years, and eight years respectively after nourishment. Quarterly or more frequent beach and nearshore profile surveys were conducted in order to determine short-term (1 year) and long-term (4 to 8 years) rates of shoreline and beach-nearshore volume changes. The overall performance of the Sand Key beach nourishment is excellent. Redington Beach project has already exceeded the design lifetime of 7 years, and Indian Rocks Beach and Indian Shore projects are likely to exceed the design lifetime. The measured beach-nearshore volume loss is small: 31% at Indian Rocks Beach over six years, 30% at Indian Shores over four years, and only 10% at Redington Beach during eight years. Performance of beach nourishment is influenced by many factors. Those that are directly related to the three nourishment projects include: (1) relative location in the regional longshore sediment transport regime, (2) magnitude of wave energy, (3) sediment characteristics of the borrow material, (4) local reversal and/or gradient in longshore transport, (5) presence of hard structures, (6) adjacent beach nourishment, (7) variation of shoreline orientation, and (8) sand transfer and beach-fill construction technique. The shoreline and beach-nearshore volume change patterns at the three nourishment projects were different due to the different degrees of influence from the above factors, however, construction style is deemed to be an important contributor. The much less costly dragline and conveyorbelt transfer technique used in the construction of Indian Shores project does not prove to be most cost effective for long-term performance.

Twelve washover deposits were cored on the west-central Gulf Coast of Florida to provide data to permit development of a model to help identify washover facies in the stratigraphic record. Typical modern washover stratigraphy displays landward-dipping plane beds comprised of well-sorted sand with distinct laminae of shells and heavy minerals. Five subfacies are delineated which show variations in composition, texture, and bioturbation throughout the washover facies. These subfacies represent differences in flow conditions during overwash, position relative to sea level, and variable degrees of reworking after deposition. Three shell assemblages aid in identification of washover deposits. Backbarrier sediments composed of shoreface/open water species or mixed shoreface/backbarrier species may potentially be washover in origin. Sediments with purely backbarrier/quiet water shell species are likely to have been deposited independently of washover activity. Examination of washover deposits of differing ages reveals that preservation of washover stratigraphy is not exclusively a function of time. Reworking of small-scale stratification can occur in as short as a decade; however, this same stratification was found to be preserved in deposits several hundred years old. Destruction of original washover signatures is related to the position of the deposits relative to sea level, and the rate and depth of burial. Even after the destruction of small-scale stratigraphic features, washover deposits may still be identified as such due to their texture, composition, and shell assemblages. Key features in recognizing the facies after bioturbation and reworking are: (1) the presence of clean sand in otherwise muddy backbarrier sediments, (2) the landward thinning of the facies, and (3) the presence of shoreface shells or mixed shoreface/backbarrier shells on landward portions of the barrier island system. If reworking is severe and/or there are limited subsurface data, distinguishing washovers from genetically similar deposits (e.g. flood tidal deltas and spillover deposits) in the stratigraphic record is difficult and when considered out of stratigraphic context may not be recognizable.

Seaward-dipping strata of carbonate-cemented shell debris located along the coast of Siesta Key on the Gulf Coast of the Florida peninsula have long been interpreted to be beachrock equivalent in age to the Pleistocene Anastasia Formation (Stage 5e) of the east coast of Florida. Detailed examination of thin sections along with radiometric dating and isotopic analyses demonstrates clearly that this is a Holocene deposit that is not beachrock but was lithified in a meteoric environment. Whole rock dates, dates from shells only, and from cement only demonstrate that these beach deposits were in place by at least 1800 yr BP and might have been there as long ago as 4300 yr BP. This means that some type of barrier island was in place at that time. Previous investigations have depicted Siesta Key as having a maximum age of 3000 yr with these deposits being located about 2 km landward of the beach deposits. This suggests that the beach deposits might have been the site of the original position of Siesta Key. These data also indicate that sea level must have been near its present position at the time that these foreshore beach deposits were deposited; sometime between 1800 and 4300 yr ago. This scenario indicates that sea level along this coastal reach probably reached its present level at least about 2000 yr ago.

This paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west-central Florida. This is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large-scale control on coastal geomorphology, the availability of sediments, and the level of wave energy. In order to understand the Holocene geologic history of this depositional system, a regional study defined by natural boundaries (north end of a barrier island to the apex of a headland) was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques. It is the purpose of this introductory paper to define the character of this coastal/inner shelf system, provide a historical geologic perspective and background of environmental information, define the overall database, present the collective objectives of this regional study, and very briefly present the main aspects of each contribution. Specific conclusions are presented at the end of each paper composing this volume.

The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.

Extensive vibracoring of both flood- and ebb-tidal deltas along the central Gulf Coast of the Florida peninsula reveals a strong overall similarity with subtle distinctions between flood and ebb varieties. Although the coast in question is microtidal, the inlets range from tide-dominated to distinctly wave-dominated. Both types of tidal deltas overlie a muddy sand interpreted to have been deposited in a back-barrier environment. The sharp contact at the base of the tidal delta sequence is typically overlain by a thin shell gravel layer. The ebb-tidal delta sequence is characterized by fine quartz sand with shell gravel in various concentrations; coarse and massive at the margins of the main ebb channel, and finer and imbricated at the marginal flood channels. The flood-tidal deltas are characterized by the same facies but with a small amount of mud. Shelly facies on the channels on flood deltas are not as well developed as on the ebb deltas. The combination of the stratigraphic sequence and the lithofacies make tidal deltas readily identifiable in the ancient record. The differences between flood and ebb varieties are subtle but consistent.

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems.