New Tertiary stratigraphy for the Florida Keys and southern peninsula of Florida

Kevin J. Cunningham University of Miami, Rosenstiel School of Marine and Atmospheric Science, Donald F. McNeill Division of Marine Geology and Geophysics, Miami, Florida 33149 Laura A. Guertin } Paul F. Ciesielski University of Florida, Department of Geology, Gainesville, Florida 32611 Thomas M. Scott Florida Geological Survey, 903 West Tennessee Street, Tallahassee, Florida 32304 Laurent de Verteuil Petrotrin, Geological Services Laboratory, Pointe-a-Pierre, Trinidad, West Indies

ABSTRACT Formation prograded toward the southern edge of the Florida Plat- form and downlapped onto the regional unconformity at the top of the Seven lithologic formations, ranging in age from Oligocene to Arcadia. Shallow-marine Pleistocene limestones (Key Largo and Pleistocene, were recently penetrated by core holes in southernmost Miami Limestones), deposited during tropical to subtropical condi- Florida. From bottom to top, they are the early Oligocene Suwannee tions, drape over accretionary successions of the Long Key and Stock Limestone; late-early Oligocene-to-Miocene Arcadia Formation, basal Island Formations. Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly proposed late Miocene-to-Pliocene Long Key INTRODUCTION and Stock Island Formations; and Pleistocene Key Largo and Miami Limestones. The rocks of the Suwannee Limestone form a third-order Quaternary rocks (Pleistocene Key Largo Limestone and Miami Lime- sequence. Although the entire thickness was not penetrated, 96 m of stone) and sediments of the Florida Keys include some of the best studied Suwannee core from one well contains at least 50 vertically stacked, and most well-known carbonate deposits in the world (e.g., Ginsburg, 1956; exposure-capped limestone cycles, presumably related to rapid eustatic Stanley, 1966; Hoffmeister and Multer, 1968; Enos and Perkins, 1977; fluctuations while experiencing tropical to subtropical conditions. The Harrison and Coniglio, 1985; Lidz et al., 1991; Shinn et al., 1989; Ludwig Arcadia Formation is a composite sequence containing four high- et al., 1996). Due to a scarcity of cores, however, the pre-Quaternary geol- frequency sequences composed of multiple vertically stacked carbon- ogy of the Florida Keys has received only sparse scientific inquiry; one con- ate cycles. Most cycles do not show evidence of subaerial exposure and tinuously recovered deep core (290 meters below sea level) on Key Largo were deposited under more temperate conditions, relative to the (Johnson, 1986). In 1993, the University of Miami and Florida Geological Suwannee Limestone. The Arcadia Formation in southernmost Florida Survey (FGS) initiated the South Florida Drilling Project (SFDP). Two prin- is bounded by regional unconformities representing third-order se- cipal goals of the SFDP are to develop (1) a detailed lithostratigraphic, se- quence boundaries. Post-Arcadia transgression produced a major quence stratigraphic, and chronostratigraphic framework for the Oligocene- backstepping of sediment accumulation above the upper sequence to-Pliocene section beneath southernmost Florida; and (2) a high-resolution, boundary of the Arcadia Formation. The Peace River Formation, com- relative sea-level history for this section. The SFDP has collected 15 marine posed of diatomaceous mudstones, has been identified only beneath the seismic profiles seaward of the Florida Keys (Warzeski et al., 1996) and has Florida peninsula and is not present beneath the Florida Keys. Deposi- drilled three deep continuous core holes in the Keys (Stock Island, Long tion occurred during marine transgressive to high-stand conditions Key, and Carysfort Marina Cores; Fig. 1) and one on the southern peninsula and a local phosphatization event (recorded in northeast Florida). The of Florida (Everglades Core; Fig. 1). Early results of the SFDP were dis- transgression is possibly related to a global rise in sea level, which cussed by Warzeski et al. (1996). They integrated seismic profiles and litho- resulted in upwelling of relatively cooler, relatively nutrient-rich water stratigraphic data from the three new core holes in the Keys. Their study masses onto the Florida Platform. produced a preliminary lithostratigraphy and seismic stratigraphy for Neo- It is proposed that the absence of Peace River sediments beneath the gene mixed siliciclastics and carbonates sandwiched between Miocene and Keys is due to sediment bypass of the upper surface of the Arcadia, a Pleistocene carbonates. They also interpreted the depositional environments result of sediment sweeping by an ancestral Florida current. During of the mixed siliciclastics and carbonates, source and transport routes of the late Miocene to Pliocene time in the Florida Keys, siliciclastics of the siliciclastics, and the role of the siliciclastics in creating a foundation for Long Key Formation and fine-grained carbonates of the Stock Island much of the present shelf margin of the Florida Keys. Herein, the focus is on lithostratigraphic results and interpretations from *e-mail: [email protected] the SFDP for Oligocene-to-Pliocene carbonates and siliciclastics under-

Data Repository item 9806 contains additional material related to this article.

GSA Bulletin; February 1998; v. 110; no. 2; p. 231Ð258; 18 figures; 5 tables.

231

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LEE PALM CO. HENDRY BEACH CO. CO.

BROWARD CO. 26° COLLIER CO.

FLORIDA

W-12050 DADE CO. MIAMI TERRACE MIAMI Soldier UM-FGS Key Figure 1. Location of princi- Everglades (W-17273) pal cores used in this study, from the Florida Keys and South Florida peninsula. Inset map Elliott Key shows the location of the type MONROE CO. UM-FGS core (W-12050) for the Arcadia Carysfort Marina Florida (W-17157) and Peace River Formations 25° Big Pine Bay (Fig. 2). Key UM-FGS Key Long Key Largo (W-17156) UM-FGS FKAA, Stock Island OW-1 Indian (W-17086) Key -2020 mm "Buck" Long Key Key Key Vaca

-20 m Key -180 m West Stock POURTALES TERRACE Island

0 km 100 STRAITS OF FLORIDA-180 m-20 m 82° 81° 80°

lying southernmost Florida. These findings comprise a synthesis of a new records will be possible (e.g., Haq et al., 1988; Eberli and Ginsburg, 1989; detailed lithostratigraphy and preliminary sequence stratigraphy and bio- Hodell et al., 1994; Miller et al., 1996; Cunningham et al., 1997). These stratigraphy (palynomorphs, silicoflagellates, diatoms, and planktonic and comparisons will allow for determining the control or controls on relative benthic foraminifers). The pool of new information presented herein creates sea-level changes recorded in the late Neogene stratigraphic record of a bridge to forthcoming results and interpretations of parallel sequence southernmost Florida. stratigraphy, chronostratigraphy, and relative sea-level history. Results of the SFDP have also temporally bracketed a late Miocene Although this study only encompasses the Oligocene-to-Pliocene strati- upwelling event that has the potential to constrain phosphatization events of graphic record, Oligocene and Miocene carbonates have the best potential major economic significance in central Florida (Riggs, 1979; Riggs, 1984). for resolving a high-frequency sea-level record. This is because latest Mapping of latest Miocene-to-Pliocene mixed siliciclastics and carbonates Miocene-to-Pliocene shelf-margin mixed siliciclastics and carbonates con- beneath the Florida Keys and southern peninsular Florida has produced the tain only a low-frequency sea-level record. In contrast, Oligocene-to- first detailed architectural framework for these deposits. Miocene platform and ramp carbonates contain a higher frequency sea-level record. New results indicate a hierarchical vertical stacking of carbonate METHODS depositional sequences and high-frequency cycles within the Oligocene and Miocene stratigraphic record, which are the result of numerous relative sea- Five principal cores (974 m in cumulative length) are used in this study. level fluctuations. The record from southernmost Florida provides a Four were drilled by the FGS and one by the Florida Keys Aqueduct unique opportunity to resolve an Oligocene and Miocene relative sea-level Authority (FKAA). The core holes are located in the Florida Keys on Stock history at a much higher resolution than has been achieved by records from Island, in Marathon on Key Vaca, on Long Key, on Key Largo (Carysfort other margins (e.g., Eberli and Ginsburg, 1989; Miller et al., 1996). This Marina), and on the mainland of southern Florida in the Everglades high-resolution, integrated stratigraphic framework presented here is in the National Park (Fig. 1). The combined distance between these core holes is process of being anchored to a precise chronology by planktonic approximately 200 km, with distances between cores ranging between 33 foraminiferal dating, strontium-isotope chemostratigraphy, and magneto- and 72 km. Each core was described using a binocular microscope to deter- stratigraphy. After tying the local, southernmost Florida record of relative mine the vertical pattern of microfacies, sedimentary structures, and depo- sea level to a precise temporal framework, comparisons to other global sitional sequence boundaries, and to assess the regional-scale variability of

232 Geological Society of America Bulletin, February 1998

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the Arcadia Formation and overlying Pliocene siliciclastics and carbonates. (1986) mapped the Suwannee Limestone throughout the southern peninsula Geophysical logs or cuttings or both from approximately 200 additional of Florida and the Florida Keys. The lithologic and sequence stratigraphic wells were used to determine local lateral and vertical variations in litho- aspects of the Suwannee Limestone in the Long Key Core (Fig. 1) correlate facies, formation thicknesses, and structural setting. Distance between wells best with descriptions reported by Hammes (1992) for the Suwannee Lime- varies from 0.4 to 38 km. stone in southwest Florida. More than 250 thin sections were examined using standard transmitted- Scott (1988) formally proposed the name Arcadia for a carbonate unit of light petrography (100 thin sectionsÐ500 counts/slide) or visual estimation the lower Hawthorn Group that overlies the Suwannee Limestone (Fig. 2) (150 thin sections). Rock colors where recorded by comparison to the Geo- in much of southern Florida. He reported that evidence from stratigraphic logical Society of America (1991) rock-color chart with Munsell color correlations and mollusks suggests the Arcadia Formation ranges in age chips. Mineral concentrations (low- and high-magnesium calcite, aragonite, from late early Miocene and early early Miocene. Alternatively, Brewster- dolomite, and quartz) were calculated for 1131 bulk specimens from peak- Wingard et al. (1997) used lithostratigraphy, biostratigraphy, and chrono- area ratios produced by a Scintag XDS-2000 X-ray diffractometer (XRD). stratigraphy to show that Arcadia deposition in southern Florida began dur- XRD analysis was completed on selected samples for determining presence ing middle early Oligocene to at least early Miocene. The Arcadia of phosphorite. Formation contains limestones previously assigned to the Tampa Formation Approximately 900 reliable measurements of permeability were taken or Limestone (Scott, 1988). The type section of the Arcadia Formation using a probe permeameter with a 12.7 mm outer diameter and 6.35 mm (Scott, 1988) occurs in Core W-12050, Hogan #1, DeSoto County, Florida inner diameter, flat, neoprene, washer-tip seal. The instrument produces a (Fig. 1). Scott (1988) produced regional maps of the upper surface and constant nitrogen injection flow rate of 200 ml/min. The permeameter is thickness of the Arcadia Formation, which extends beneath the southern capable of excellent reproducibility (typically ± relative error) over a range peninsula of Florida and upper Keys. of 0.2 to 2000 md. The reproducibility for samples with >3000 md had Scott (1988) formally proposed the Peace River Formation for the com- greater error, with 3000 ± 1000 md and 5000 ± 2000 md typical. bined upper Hawthorn siliciclastic strata and Bone Valley Formation of Eight reconnaissance samples from each core from Stock Island, Long Florida. He reported a possible range in age from latest early or early middle Key, Key Largo, and Everglades National Park (Fig. 1) were examined for Miocene to early Pliocene. The type section for the Peace River Formation palynomorphs. Samples are more or less evenly distributed throughout inter- (Scott, 1988) is in Core W-12050, Hogan #1, DeSoto County, Florida vals of interest. Sample maceration (selectively) followed the procedure in (Fig. 1). Both regional structural contour and isopach maps of the Peace Barss and Williams (1973), and residues were sieved at 15 µm using nylon River, completed by Scott (1988), show the Peace River underlying the screens. Following de Verteuil and Norris (1996), the qualitative terms rare southern peninsula of Florida and upper Keys. (specimens are seldom encountered when scanning a slide), common (typi- A succession of siliciclastic rocks, as thick as 145 m, are between platform cally a few specimens are encountered in two short-axis traverses of a slide), carbonates of the Arcadia Formation and the Key Largo or Miami Lime- and abundant (typically at least one specimen is encountered in most fields of stones and extends south of Miami for 160 km along the arcuate strike of the view) are used for slides scanned with a 25× magnification. Four separate Florida Keys (Figs. 3Ð5). Mapping of the siliciclastics shows that they later- reconnaissance samples of diatomaceous mudstone from the Everglades ally grade into fine-grained limestones west of Key Vaca (Figs. 3 and 4). Core (Fig. 1) were analyzed for diatoms, radiolarians, and silicoflagellates. Hovey (1896) first described the fine-grained limestone unit based on Ages are reported in accordance to the integrated magnetobiochronologic well cuttings from a well on Key West (Fig. 6). Vaughan (1910) first pub- Cenozoic time scale of Berggren et al. (1995 = BKSA95) for which bio- lished a description of the siliciclastic unit (Long Key Fm.) by combining stratigraphic events are correlated to a recently revised geomagnetic polar- the records of two wells, one drilled on Key Vaca and another on “Buck” ity time scale (Cande and Kent, 1995 = CK95). Key (Figs. 1 and 6). He concluded that the quartz sands encountered in these wells are Miocene to Pliocene, based on paleontologic data, and noted the OLIGOCENE-PLEISTOCENE STRATIGRAPHY OF THE vast geographic distribution of Miocene-to-Pliocene siliciclastics beneath FLORIDA KEYS AND SOUTHERN PENINSULA the southern end of the Florida peninsula. Matson and Sanford (1913), Goodell and Yon (1960), and Jordan et al. (1964) discussed or showed the Development of the Stratigraphic Nomenclature for the Oligocene-to- transition between siliciclastic and limestone units between the middle and Pleistocene Rocks of the Florida Keys and Southern Peninsula lower Florida Keys (Fig. 3). Scott (1988) assigned these rocks to the Peace River Formation of the Hawthorn Group. The type section for the Peace Cooke and Mansfield (1936) proposed the name Suwannee Limestone River Formation is, however, located in DeSoto County, some 220 km north (Fig. 2) for yellowish limestone exposed along the Suwannee River in of the Florida Keys (Fig. 1). Warzeski et al. (1996) questioned Scott’s northern Florida, where they described it as unconformably overlying lime- (1988) correlation of the siliciclastics beneath the Florida Keys with the stone containing Vicksburg (Oligocene) fossils and unconformably under- Peace River Formation and suggested the need for a formal change in the lying the Miocene Hawthorn “formation.” Cooke and Mansfield (1936) nomenclature of the siliciclastics because of distinct lithologic differences. assigned the Suwannee Limestone to the North American Vicksburgian We propose, herein, that the siliciclastics be assigned the formational name stage; however, more recently it has been assigned to the chronostrati- of Long Key Formation (Fig. 2) and the fine-grained limestones be assigned graphic Rupelian (early Oligocene) stage (COSUNA, 1988; Brewster- the formational name of Stock Island Formation (Fig. 2). Wingard et al., 1997). In a stratigraphic cross section, Parker and Cooke In the Long Key Core (Fig. 1), siliciclastics of the Long Key Formation (1944) showed that the Suwannee Limestone occurs beneath the southern are overlain by wackestones and packstones of the basal Pleistocene Key peninsula of Florida. Applin and Applin (1944) reported Suwannee lime- Largo Formation (Fig. 2) of Hoffmeister and Multer (1964) or Perkin’s stone beneath the south end of the Florida peninsula and Florida Keys. They (1977) Q1 and Q2 units (Fig. 2). Perkin’s Q units are now included in reported 137.2 m of Suwannee Limestone in cuttings from a well (FGS Scott’s (1992) informal Okeechobee formation (Fig. 2). The upper contact No. W-265) on Key West (Fig. 1). Puri and Winston (1974) also showed the of the Stock Island Formation is gradational in the Stock Island Core Suwannee Limestone in a stratigraphic cross section, which included the (Fig. 1). Here, lime grainstones and well-washed packstones of the Stock southern peninsula of Florida and the upper Keys. More recently, Miller Island Formation change gradually into overlying molluscan and bioclastic

Geological Society of America Bulletin, February 1998 233

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Late C1n Middle r 1 n 1 Pt1 C1r Q5 Miami 2r PLEIST. Calabrian Early coralline 2 C2n facies Lms. 1 Pl6 C2r Q4 2r Gelasian

1 Pl4-5 3 Late 2 C2An Pl3 Q3 Key Piacenzian 3n 4 C2Ar Pl2 Largo 1 calcarenite & PLIOCENE Q2 2

C3n formation

Early calcilutite facies

Zanclean 3 Pl1 Lms. 5 4n Pleistocene

Okeechobee Q1 C3r M14 6 1 C3An 2n

Messinian C3Ar 7 C3Bn 2r/n C3Br M13b 1n/r C4n Stock 2n 8 1n/r 2r C4r upper Island C4An Pliocene

9 Late Long Key 1 MIOCENE 2 C4Ar Tortonian M13a Fm. 1 Formation 10 C5n (Florida 2n (Florida Peninsula Keys) 11 1 and Keys) 2 M12

C5r lower M11 3r

12 1 Pliocene 2n C5An M11-8 1 C5Ar 3r 13 C5AAn ? C5AAr C5ABn

Serravallian C5ABr M7 14 Middle C5ACn C5ADn C5ADr 15 1 C5Bn M6 Peace C5Br M5 16

Langhian River 1 C5Cn 2 Hiatus 3n M4 17 C5Cr Fm.

C5Dn Miocene ? (Florida AGE (Ma) AGE C5Dr upper.-upper 18 M3 Peninsula) C5En 19 C5Er Burdigalian C6n 20 MIOCENE M2 C6r Early

1 C6An 21 2n C6Ar

22 1 C6AAr 2 lower-

Aquitanian M1 1 C6Bn 23 2n C6Br Arcadia 1 C6Cn 2 24 upper Miocene?? C6Cr Formation 25 2n C7n C7r P22 Hawthorn Group 26 C8n Late Chattian C8r 27 upper- C9n 28

C9r - Oligo. lower P21 C10n

29 OLIGOCENE C10r

C11n 30 P20 C11r C12n Suwannee 31 P19 Early

32 Rupelian C12r lower Limestone P18

33 Oligocene C13n

Figure 2. Proposed stratigraphic nomenclature for southern Florida and its correlation to the chronology of a portion of the Cenozoic Era. Chronology is from Berggren et al. (1995), and stratigraphic nomenclature is modified from Perkins (1977), Scott (1992), and Brewster-Wingard et al. (1997). The Okeechobee formation is an informal unit introduced by Scott (1992).

234 Geological Society of America Bulletin, February 1998

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-20 m 26° ? ? LEGEND Core Continuous Core ? Partial Core ? MIAMI TERRACE Cuttings Figure 3. Distribution of late Miocene-to-Pliocene siliciclastics Top Arcadia penetrated UM-FGS Everglades of the Long Key Formation and Top Arcadia not penetrated UM-FGS Carysfort Pliocene carbonates of the Stock Marina Island Formation and location of ? Long Key Fm. Siliciclastics ? UM-FGS 25° Long wells used in this study. The litho- Stock Island Fm. Carbonates Key Key logic boundaries seaward of the Key ? Largo Florida Keys were extrapolated Big Pine Vaca Key using well data on the Keys and Key West -20 m ? marine seismic data (Warzeski ? et al., 1996). Marquesas Keys FKAA, UM-FGS OW-1 Stock -20 m TERRACE ? Island FLORIDA -180 m POURTALES OF 0 km 100 -180 m STRAITS -20 m 82° 81° 80° 24°

lime floatstones. These floatstones are probably the basal Pleistocene Key tains minor zones composed of both low-magnesium calcite and aragonite Largo Formation of Hoffmeister and Multer (1964) or the Q1 and Q2 units (Fig. 7). Except for minor dolomite near the top of the Suwannee (Fig. 7), of Perkins (1977). dolomite and phosphorite grains are not present. Silt- to fine sand-sized An early description of rocks from the present Key Largo Formation by quartz grains occur uncommonly. Skeletal fragments, mollusks, miliolids, Charles Howe was reported by Hunt (1862). Hunt (1862) interpreted Howe’s peloids, Halimeda, corals, and peneroplids are the principal carbonate description as a 40-m-thick unit of coralline limestone, recovered from the grains. These indicate a chlorozoan association as defined by Lees and shallow section of an artesian well drilled on Indian Key between the years Buller (1972), which is consistent with subtropical to tropical conditions 1839 and 1840 (Figs. 1 and 6). Hovey (1896) described samples derived during deposition. from an artesian well drilled on Key West (Fig. 1) in 1895, which he inter- The Suwannee Limestone is a low-order (third-order) depositional preted as oolite from the surface to 7.6 m below the surface. Sanford (1909) sequence, which is composed of two high-frequency sequences and at least first used the names Miami Oolite on the southern tip of Florida and Key 50 vertically stacked, exposure-capped, subtidal, and, less commonly, peri- West Oolite between Key West and Big Pine Key (Figs. 1 and 6). Sanford tidal sedimentary cycles (Fig. 8). Brecciated calcretes occur at the tops of (1909) first described and named the Key Largo Limestone. Cooke and four exposure-capped cycles (Fig. 8). These four calcretes contain re- Mossum (1929) described the Miami Oolite in more detail and applied the cemented angular clasts of the host rock and are up to 1.5 m thick. Upper- name Miami Oolite to include the oolites of the Keys (Fig. 6). Hoffmeister most zones of both the low-order and two high-order depositional sequences et al. (1967) divided the Miami Limestone into an upper unit, an oolitic (Fig. 8) are composed of brecciated karst and have root molds suggesting rel- facies, and a lower unit, a bryozoan facies, for the southern mainland of atively long-lived subaerial exposure (cf. Grammer et al., 1996). Near the top southeastern Florida (Fig. 6). Hoffmeister and Multer (1964; 1968) and of the Suwannee Limestone, a 3-m-thick zone (low-order sequence bound- Stanley (1966) further refined descriptions and environmental interpretations ary) of subaerial erosion contains mottled coloration, root molds, glaebules of the Key Largo Limestone. and breccia-filled, semivertical, solution cavities (cf. Esteban and Klappa, 1983). The upper contact of the Suwannee (Fig. 9A) is replaced by a black, CHARACTERIZATION OF THE SUWANNEE LIMESTONE IN laminated phosphorite (up to 2 mm thick). The replacement by phosphorite THE FLORIDA KEYS is interpreted to be associated with transgression of the upper sequence boundary of the Suwannee Limestone (cf. Mallinson et al., 1994). Lithostratigraphy and Sequence Stratigraphy of the Suwannee Each of the 50 cycles is overlain by a landward shift in sedimentary facies Limestone (marine flooding). Most commonly the cycles are capped by moderate yellowish brown (10YR 5/4) or pale yellowish brown (10YR 6/2) laminar The lithostratigraphy of the Suwannee Limestone is principally based on calcrete (Fig. 9B). The surfaces beneath the laminar calcretes are slightly examination and analysis of the Long Key Core (Fig. 1). The mineralogy of undulatory to irregular with up to 5 cm of relief and overhanging micro- the Suwannee Limestone is prominently low-magnesium calcite, but it con- topography. The calcretes range in thickness from 1 mm to 3.8 cm. Root

Geological Society of America Bulletin, February 1998 235

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A Miami Lms. Key Largo Lms. A' Carysfort Stock Island FKAA Long Key Marina W-3174 W-17086 W-972 W-5152 OW-1 W-12799 W-17156 W-12554 W-17157 W-3011 0 ? 0 Key Largo Lms. Long 100 Stock Key Fm. 100 Island 0

Fm. 30 60 90 200 Gamma Ray 200 (c.p.s.) Arcadia Fm. 300 300 0

200 400 Suwannee Lms.

400 0 400 Gamma Ray and 40 80 Depth (meters below sea level) sea below (meters Depth (c.p.s.) Gamma Ray

pre-Suwannee 0

30 60 (c.p.s.) 500 500 0 Gamma Ray 10 20 0 (c.p.s.) Gamma Ray 50 100 (c.p.s.) Gamma Ray (c.p.s.)

88 km 38 km 2 km 25 km 0.5 km 28 km 56 km 8 km 2 km

Lithology DAD DADE E MIAMI

CO. TERRACE CO. Oolitic limestone

Sinclair Oil A' (W-3011) Coralline framestone MONROE CO. Big Pine Florida UM-FGS, 25° Key Bay Carysfort Marina Shallow-marine carbonate UM-FGS, (W-17157) CALCO Long Key (W-5152) (W-17156) Largo Brand UM-FGS, FKAA, (W-12554) Stock Island OW-1 Sandy shallow-marine carbonate (W-17086) FKAA 2020 mm (W-12799)

Gulf Oil-CALCO Key Fine-grained limestone (W-3174) Vaca 20 m 180 m A POURTALES TERRACE Quartz sands

0 km 100 Gulf Oil (W-972) STRAITS OF FLORIDA180 m 20 m Marine carbonates 82° 81° 80° Location of cross-section (A-A') in Florida Keys.

Figure 4. Southwest-to-northeast stratigraphic cross section along the arcuate strike of the Florida Keys from the Dry Tortugas (A) to northern Key Largo (A′ ).

molds, Microcodium, glaebules, and alveolar septal structures (cf. Esteban Photomicrographs of six of the facies are displayed in Figure 10, and their and Klappa, 1983) occur beneath some of the high-frequency, exposure- vertical distribution is shown in Figure 8. Results of permeability measure- capped cycles (Fig. 9, C and D). Peritidal deposits are capped by thin ments of the Suwannee Limestone are shown in Table 1 and Figure 11. deposits of lime mudstones containing fenestral fabric, which is composed of pores commonly elongate in a horizontal direction. CHARACTERIZATION OF THE ARCADIA FORMATION IN THE FLORIDA KEYS AND SOUTHERN PENINSULA Suwannee Lithofacies in the Long Key Core Lithostratigraphy and Sequence Stratigraphy of the Arcadia Seven lithofacies have been identified in the Suwannee Limestone of the Formation Long Key Core on the basis of floral and faunal composition and deposi- tional texture: (1) skeletal floatstone and rudstone facies; (2) coral frame- The lithostratigraphy of the Arcadia Formation is based mainly on exami- stone and floatstone facies; (3) molluscan rudstone and floatstone facies; nation and analysis of the Stock Island, Long Key, and Everglades Cores (4) peloid grainstone and packstone facies; (5) benthic foraminifer grain- (Fig. 1). The mineralogy of the Arcadia Formation is principally low- stone facies; (6) Halimeda rudstone and floatstone facies; and (7) peneroplid magnesium calcite with subordinate amounts of dolomite and aragonite packstone facies. Characterization of these facies is shown in Table 1. (Fig. 7). Aragonite is most abundant in the Stock Island Core (Fig. 7).

236 Geological Society of America Bulletin, February 1998

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Fort Miami Lms. Thompson Fm. Miami Lms. Key Largo Lms. B B' Gulf Park Gulf Everglades NP-100 FP&L FP&L Sinclair Carysfort-Marina W-3510 W-2404 W-1115 W-17232 W-7363 PTW GB-2/2a W-3011 W-17157 0 0 ? ? Key Largo Lms. Lms.(?) Long Key Fm. Key Largo Long Key Fm. ? 100 ? ? 100 Depth (meters below sea level) Peace River Fm. Peace River Fm. Channel ? ? Fill(?)

200 200 0

50 Arcadia Fm. 100 Gamma Ray (c.p.s.) ? Arcadia Fm. 300 300 Depth (meters below sea level) sea below (meters Depth Suwannee Lms. ? Avon Park Fm. 400 Arcadia & Ocala Gp.(?) 400 0

Fm. 50 ? ? Avon Park Fm. 100 Gamma Ray (c.p.s.) 500 ? 500

18 km 10 km 20 km 10 km 10 km 7 km 15 km 4 km

Lithology

Oolitic limestone Marine carbonates

Coralline framestone Quartz sands

Shallow-marine carbonate Siliciclastic conglomerate

Sandy shallow-marine carbonate Diatomaceous mudstone

Mudstone Formation contact

MONROE CO. DADE CO.

25.5° FP&L UM-FGS, GB-2/2a Everglades NP-100 (W-17273) (W-7363)

FP&L Sinclair Oil Figure 5. West-to-east stratigraphic cross section from Florida PTW (W-3011) Gulf Oil Bay (B) to northern Key Largo (B′ ). (W-1115) B' Everglades Park (W-2404) UM-FGS, Florida Carysfort Marina Bay (W-17157) ° Gulf Oil km 25 B (W-3510) 0 30 81° 80.5°

Location of cross-section (B-B') in southern Florida.

Quartz grains are very minor components of cores from the Keys but assemblage indicates a foramol association as defined by Lees and Buller increase northeastward in the upper Arcadia of the Everglades Core, where (1972). The assemblage is consistent with deposition during temperate con- they may constitute as much as 20% of the rock (Fig. 7). The Stock Island ditions and possibly episodic upwelling across the Florida Platform. Core contains as much as about 3% black phosphorite grains in the Arcadia. The Arcadia Formation is a composite sequence composed of four high- Phosphorite grains also increase in a northeastward direction with as much frequency sequences that consist of multiple high-frequency cycles (Fig. 12; as 10% black phosphorite grains contained in thin beds of the Long Key and cf. Kerans, 1995). Correlation of gamma-ray signatures between the Stock Everglades Cores. Principal grains of the Arcadia Formation are skeletal Island core hole and Long Key core hole suggests that exposure surfaces that fragments, mollusks, benthic foraminifers, red algae, and echinoids. This cap high-frequency sequences HFS1 and HFS2 in the Stock Island Core are

Geological Society of America Bulletin, February 1998 237

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Cooke & Hoffmeister Mossum et al. Hoffmeister Sanford (1929); (1967); & Multer Hunt Hovey* (1909); Vaughan** Perkins Perkins (1964, 1968); Perkins (1862) (1896) Perkins (1977) (1910) (1977) (1977) Perkins (1977) (1977) This Study This Study

Q5 oolite coral facies beds Miami Lms. coralline Miami oolite Miami Lms. Q4

facies limestone Key West West oolite Key bryozoan Indian limestone mixed oolite Key West Key to with quartz Q3 Key Largo Big Pine grains at depth Key West to Lms.

Key Pleistocene

Pleistocene SE Florida

Key Largo Lms. Key Key Largo calcarenite Q2 Lms. Key Largo limestone Key and calcilutite Q1

quartzose Big Pine calcareous sand ? Key to limestone with Soldier Florida Keys and trace of quartz Key South Florida sand Big Pine Key Stock Island Long Key to Soldier Key Fm. Fm. Pliocene Pliocene

quartz sand

Arcadia Fm. Miocene Miocene Arcadia Fm.

Stock Island limestone with Vicksburg minor quartz sand quartz sand Suwannee Lms. Oligocene Oligocene

Long Key Key Vaca & "Buck" Key sand Eocene *Hovey (1896) placed his Vicksburg limestones in the Eocene, but Eocene **Vaughan (1910) assigned an Oligocene age to his Vicksburg sands. with trace quartzwith trace Vicksburg limestone Vicksburg

Key West

Figure 6. Correlation of previous stratigraphic terminology used in the Florida Keys with stratigraphic designations at Stock Island and Long Key of this study. Hovey (1896) placed his Vicksburg limestones in the Eocene, and Vaughan (1910) assigned an Oligocene age to his Vicksburg sands. For geographic locations see Figure 1.

correlative to hardgrounds at the tops of HFS1 and HFS2 in the Long Key formably overlain by a deep-water carbonate facies of the Stock Island Core (Fig. 12). The top of HFS3 is an exposure surface in the Stock Island Formation (Fig. 13A). Typically the uppermost Arcadia is replaced by a thin Core; however, correlation of gamma-ray signatures suggest that this sur- layer of black phosphorite (Fig. 13A). In the Everglades Core the upper face is truncated by erosion in the Long Key Core (Fig. 12). The upper sur- 0.46 m of the Arcadia contains black (N2 to N3), phosphorite clasts up to face of HFS4 is an erosion surface in the Stock Island, Long Key, and Ever- small-cobble size, in a matrix of very finely crystalline, moldic, fossil- glades Cores. In the Long Key Core subaerial exposure is suggested; fragment dolomite. Here, two irregular erosion surfaces within the upper however, lithologic evidence suggests erosion during subaerial exposure or 4.1 m of the Arcadia may indicate an amalgamated upper sequence boundary flooding or both for the Stock Island and Everglades Cores (Fig. 12). High- defining the top of the Arcadia Formation. frequency cycles most commonly coarsen upward, but some fine upward In southernmost Florida, the Suwannee-Arcadia contact can be identified (Fig. 12). High-frequency cycles capped by laminated crusts or auto- in well cuttings by the last down-hole occurrence of phosphorite grains and brecciated calcretes are only found in the Stock Island Core (Fig. 12). High- the first down-hole occurrence of light brown (5YR 6/4) to dark yellowish frequency cycles capped by hardgrounds are common in both the Stock orange (10YR 6/6) calcretes. Also, floral and faunal assemblages change Island and Long Key Cores (Fig. 12). The top of the Arcadia is bounded by down-hole from a foramol assemblage in the Arcadia to a chlorozoan a regional unconformity. In the Stock Island Core, a relatively shallow- assemblage in the Suwannee. This is the most important distinction between marine carbonate facies of the uppermost Arcadia Formation is uncon- the Arcadia Formation and the Suwannee Limestone. In the past, many

238 Geological Society of America Bulletin, February 1998

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LMC LMC Aragonite Key Largo Lms. Largo Key 50 50 50 50 LMC

Key Largo Lms. Largo Key Quartz Dolomite Long Key Fm. Long Key

100 100 100 100 Quartz

Quartz Peace River Fm. No Data Long Key Fm. Long Key 0

150 20 40 60 80

150 100 Quartz

Stock Island Fm. Stock Mineralogy Quartz (weight %) ARAG LMC Dolomite Arcadia Fm. Arcadia Depth (mbsl) 0 0 40 60 80 20 40 60 80 200 200 20 100 100 Gamma Ray Mineralogy (c.p.s.) (weight %) LMC

Dolomite 250 250

Explanation ARAG Mineralogy Arcadia Fm. Arcadia Aragonite

LMC Fm. Arcadia 300 300 Dolomite LMC

HMC 0 0 20 40 60 80 100 200 300 400 100 Dolomite Gamma Ray Mineralogy (c.p.s.) (weight %) 350 Quartz

Aragonite LMC=Low-Mg Calcite

HMC=High-Mg Calcite

ARAG=Aragonite

400 Suwannee Lms. LMC 0 0 20 40 60 80 20 40 60 100

Gamma Ray Mineralogy (c.p.s.) (weight %)

Figure 7. Mineralogy, gamma-ray response, and lithostratigraphic units for UM-FGS Stock Island, Long Key, Carysfort Marina, and Everglades Cores. Depth is in meters below sea level (mbsl).

Geological Society of America Bulletin, February 1998 239

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/110/2/231/3382991/i0016-7606-110-2-231.pdf by guest on 26 September 2021 Figure 8. Distribution of lithofacies throughout the Suwannee Formation in the Florida Geological Survey, Long Key Core (W-17156). Shown are numerous shallowing-upward parasequences that are capped by exposure surfaces. All depths are reported in meters below ground level (mbgl).

240 Geological Society of America Bulletin, February 1998

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/110/2/231/3382991/i0016-7606-110-2-231.pdf by guest on 26 September 2021 Figure 9. Representative exposure features from Suwannee Formation. (A) Slabbed core of depositional sequence boundary separating the Arcadia and Suwannee Formations. The upper surface of the Suwannee Formation shows up to 2.5 cm of microrelief with overhanging micro- topography. The upper surface of the Suwannee Formation is composed of a 1- to 2-mm-thick, black phosphorite (arrow). Sequence boundary is at a core depth of 331.4 m. Increments on scale to the left-hand side of photo are 1 cm long. (B) Slabbed core of a laminated crust from the Suwannee Formation. A 1.3-cm-thick laminated calcrete is overlain by pebble-sized rounded intraclasts. The pebble lag above the exposure surface is a transgressive palimpsest deposit. Top of laminated crust is at a core depth of 366.5 m. Increments on scale to the left-hand side of photo are one centimeter long. (C) Thin-section photomicrograph of root mold filled with alveolar septal structure from Suwannee Formation. Porosity calculated from point counting is 8%. Long Key Core (END-14; 394.3 m core depth). (D) Thin-section photomicrograph of Microcodium (cf. Esteban and Klappa, 1983) showing radially elongate calcite crystals filling a root mold. Cut of thin section is perpendicular to long axis of root mold. Porosity calculated from point counting is 15%. Long Key Core (END-23; 422.1 m core depth).

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workers discerned the Arcadia-Suwannee contact as the first down-hole TABLE 1. LITHOFACIES CHARACTERISTICS OF THE SUWANNEE LIMESTONE IN THE LONG KEY CORE occurrence of Oligocene-Miocene and Eocene-Miocene benthic Skeletal floatstone and rudstone facies* (Figs. 8 and 10A) foraminifers, such as Miogypsina spp. and Lepidocyclina spp.; respectively. Depositional textures Skeletal floatstones with a packstone matrix and skeletal These foraminifers were at one time considered to be Oligocene, at rudstones with a packstone or grainstone matrix youngest (e.g., Cole, 1938; 1944). More recently, it has been demonstrated Color Very pale orange (10YR 8/2), pale yellowish (10YR 6/2) or uncommon light gray (N7) that the first down-hole occurrence of Miogypsina spp. and Lepidocyclina Grains Skeletal fragments, benthic foraminifers (including miliolids, spp. occurs in the lower Arcadia of southern Florida (Peacock, 1983; peneroplids, and Sorites), mollusks, echinoids, peloids, gastropods, ostracods, Halimeda and intraclasts Cunningham and Rupert, 1996a, 1996b). Consequently, the first down-hole Grain size Grains range from silt to medium pebble size occurrence of Miogypsina spp. and Lepidocyclina spp. cannot be used as Accessory minerals Quartz grains occur variably and range from silt to fine sand criteria for recognition of the Arcadia-Suwannee boundary (Peacock, 1983; size Porosity Principally moldic; ranges from 4% to 20%, average 12% Cunningham and Rupert, 1996a, 1996b). In southwest Florida, Brewster- Coral framestone and floatstone facies* Wingard et al. (1997) have shown that Arcadia deposition began during the Depositional textures Coral framestones and floatstones; floatstones have a late-early Oligocene. Various authors have mistakenly placed the Arcadia- packstone matrix Color Very pale orange (10YR 8/2) Suwannee boundary within the Arcadia (Meyer, 1971; Puri and Winston, Grains Coral heads, stick-shaped Porites, miliolids, echinoids, 1974; Miller, 1986; Meyer, 1989; Reese, 1994), thus complicating the mollusks, gastropods and benthic foraminifers Grain size Grains range from silt to cobble size stratigraphy of southern Florida. Accessory minerals None Porosity Mainly moldic and intraparticle; ranges from 20% to 30%, Arcadia Lithofacies average 25% Molluscan rudstone and floatstone facies (Figs. 8 and 10B) Depositional textures Molluscan rudstones with a grainstone matrix and Seven lithofacies have been identified in the Arcadia Formation based on floatstones with a packstone matrix floral and faunal composition, depositional texture, and lithology: (1) wacke- Color Very pale orange (10YR 8/2) Grains Mollusks, skeletal fragments, benthic foraminifers (including stone, packstone (intergranular space, mainly lime mud), skeletal well- miliolids and peneroplids), echinoids, peloids, gastropods, washed packstone (intergranular space mainly cement and pores but contains ostracods and intraclasts Grain size Grains range from silt to medium pebble size lime mud), and grainstone facies; (2) molluscan floatstone and rudstone Accessory minerals Quartz grains which range from silt to fine sand size; ≤1% facies; (3) benthic foraminifer grainstone and rudstone facies; (4) red algal Porosity Mainly moldic and interparticle; ranges from 12% to 21%, rudstone, grainstone, packstone, and wackestone facies; (5) dolomite facies; average 15% Permeability 402 md (6) bryozoan rudstone and floatstone facies; and (7) coral framestone facies. Peloid grainstone and packstone facies (Figs. 8 and 10C) These facies are characterized in Table 2, examples shown in Figure 13 and Depositional textures Peloid grainstones and packstones their distribution shown in Figure 12. Results of permeability measurements Color Very pale orange (10YR 8/2) and uncommon light gray (N7) Grains Peloids, benthic foraminifers (including Dictyoconus cookei in the Arcadia are shown in Table 2 and Figure 11. between 422 and 426 m core depth), skeletal fragments, mollusks, echinoids and gastropods Grain size Grains range from silt to coarse sand size Palynomorphs and Benthic Foraminifers from the Arcadia Formation Accessory minerals Quartz grains range from silt to very fine sand size; trace amount Three samples for a pilot study of palynomorphs of the upper Arcadia Porosity Principally moldic and interparticle; ranges from 11% to 37%, average 21% Formation were taken from the Stock Island (210.3 m), Long Key Permeability 168Ð754 md, mean = 400 md (196.9 m), and Everglades (159.9 m) Cores (Fig. 12). They ranged from Benthic foraminifer grainstone facies (Figs. 8 and 10D) 3.2 m to 12.1 m below the top of the Arcadia. Palynofacies principally com- Depositional textures Benthic foraminifer grainstones and packstones Color Very pale orange (10YR 8/2) and pale yellowish brown prise microforaminiferal test linings, noncellular membranes, and mem- (10YR 6/2) branous sheaths of uncertain affinity. Pollen is absent or rare. Dinocysts are Grains Benthic foraminifers (including miliolids), skeletal fragments, mollusks, echinoids, peloids, gastropods and intraclasts common and the assemblage is consistent with deposition in a middle to Grain size Grains range from silt to fine sand size; ≤1% outer neritic environment, far enough from land to result in almost total Porosity Mostly moldic and interparticle; ranges from 7% to 32%, exclusion of pollen. Two reconnaissance samples from the upper Arcadia of average 8% Permeability 572 md the Everglades (159.9 m core depth) and Stock Island (210.3 m core depth) Halimeda rudstone and floatstone facies (Figs. 8 and 10E) Cores produced Sumatradinium soucouyantiae without Systematophora Depositional textures Halimeda floatstones and rudstones with a packstone matrix placacantha, suggesting a middle middle or early late Miocene age Color Very pale orange (10YR 8/2) and pale yellow brown (10YR 6/2) (cf. de Verteuil et al., 1996). This age is somewhat younger than an earliest Grains Halimeda, skeletal fragments, benthic foraminifers (including middle Miocene age for the uppermost Arcadia as suggested by Wingard miliolids), mollusks, peloids, encrusting red algae, ostracods, echinoids and gastropods et al. (1994), based on results from dinocyst and molluscan assemblages for Grain size Grains range from silt to large pebble size a core in southwestern Florida, a late early Miocene age (16.7 Ma) reported Accessory minerals Quartz grains uncommon by Sugarman et al. (1994) for the upper Arcadia of Florida, and at least the Porosity Mainly moldic; ranges from 13% to 18%, average 16% Permeability 89Ð278 md, mean = 184 early Miocene as proposed by Brewster-Wingard et al. (1997) for the south- Peneroplid packstone facies (Figs. 8 and 10F) ern peninsula of Florida. Our age, based on palynomorphs, for the upper Depositional textures Peneroplid packstones Arcadia suggests that either deposition of the Arcadia continued longer in Color Very pale orange (10YR 8/2) Grains Peneroplids, other benthic foraminifers, (including miliolids southernmost Florida or that the upper Arcadia north of southernmost and Sorites), Halimeda, skeletal fragments, echinoids and Florida has been removed by erosion. mollusks Grain size Grains range from silt to very coarse sand size We tentatively assign an age near the Oligocene-Miocene boundary to the Accessory minerals Quartz grains ≤trace lower Arcadia in the Florida Keys based on the occurrence of the benthic Porosity Principally moldic; ranges from 11% to 40%, average 26% foraminifers Miogypsina spp. and Lepidocyclina cf. undosa and preliminary Permeability 275 md results of strontium-isotope chemostratigraphy. Miogypsina spp. also occurs *No permeability measurements recorded. in cuttings of the lower Arcadia from a well on the southern mainland of

242 Geological Society of America Bulletin, February 1998

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/110/2/231/3382991/i0016-7606-110-2-231.pdf by guest on 26 September 2021 Figure 10. Representative lithofacies from the Suwannee Formation. (A) Skeletal floatstone and rudstone facies: Thin-section photomicrograph of well developed moldic porosity with a micritic matrix. Porosity calculated from point counting is 20%. Long Key Core (END-8; 377.9 m core depth). (B) Molluscan rudstone and floatstone facies: Thin-section photomicrograph of a partially leached molluscan rudstone with a broken molluscan grainstone matrix. Both interparticle and moldic porosity are well developed. Calculated porosity from point counting is 13%. Long Key Core (END-10; 382.5 m core depth). (C) Peloid grainstone and packstone facies: Thin-section microphotograph of peloid lime grainstone with well-developed interparticle porosity. Porosity calculated from point counting is 37%. Long Key Core (END-20; 416.4 m core depth). (D) Benthic foraminifer grainstone facies: Thin-section microphotograph of abundant miliolid foraminifers and other undifferentiated benthic foraminifers with well-developed intraparticle porosity. Porosity calculated from point counting is 16%. Long Key Core (END-17; 405.8 m core depth). (E) Halimeda rudstone and floatstone facies: Thin-section photomicrograph of abundant broken Halimeda fragments comprising a Halimeda rudstone. Well-developed moldic porosity associated with Halimeda grains. Porosity calculated from point counting is 18%. Long Key Core (END-2; 349.5 m core depth). (F) Peneroplid packstone facies: Thin-section microphotograph of peneroplid lime packstone, most of the interparticle porosity is occluded by sparry calcite. Porosity calculated from point counted is 11%. Long Key Core (END-13; 393.3 m core depth).

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50

100 Fm. Long Key

Peace River Fm. Long Key Fm. Long Key 1 10 0.1 150 100 1,000 10,000 Permeability 100,000 (millidarcies) Stock Island Fm. Stock Arcadia Fm. Arcadia 200 1 10 0.1 100 1,000 10,000 Permeability 100,000

Depth (mbgl) (millidarcies)

250 Legend for Permeability

15-50 md (medium)

300 Fm. Arcadia 50-250 md (good)

1 250-1,000 md (v. good) 10 0.1 100 1,000 10,000 350 Permeability (millidarcies) > 1,000 md (excellent)

Figure 11. Results of perme- 400 ability measurements from probe permeameter for Stock Island,

Suwannee Lms. Long Key, Carysfort, and Ever- glades Cores (Fig. 1). 1 10 100 1,000 10,000 Permeability 10,0000 (millidarcies)

244 Geological Society of America Bulletin, February 1998

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/110/2/231/3382991/i0016-7606-110-2-231.pdf by guest on 26 September 2021 Figure 12. Distribution of lithofacies and surfaces that bound parasequences throughout the Arcadia Formation in the Stock Island Core (W-17086); Long Key Core (W-17156), and the Everglades Core (W-17273).

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Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/110/2/231/3382991/i0016-7606-110-2-231.pdf by guest on 26 September 2021 Figure 13. Representative lithofacies from Arcadia Formation. (A) Arcadia FormationÐStock Island Formation contact in slabbed core. Arrow points to sequence boundary between the Arcadia and Stock Island Formations (206.7 m core depth). Smallest increments on scale are 1 mm long. (B) Skeletal wackestone, packstone, well-washed packstone, and grainstone facies: Thin-section microphotograph of skeletal floatstone with a grainstone matrix. Porosity calculated from point counting is 5%. Long Key Core (DPP-17; 241.9 m core depth). (C) Molluscan floatstone and rudstone facies: Thin-section microphotograph of molluscan lime rudstone with wackestone and packstone matrix. Porosity calculated from point counting is 16%. Long Key Core (DPP-14; 238.3 m core depth). (D) Benthic foraminifer grainstone facies: Thin-section microphotograph of benthic foraminifer rudstone with a grainstone matrix. Porosity calculated from point counting is 17%. Long Key Core (DPP-22; 251.3 m core depth). (E) Red algal rudstone, grainstone, packstone, and wackestone facies: Thin-section microphotograph of red algal grainstone. Porosity calculated from point counting is 11%. Long Key Core (DQQ-13; 271.9 m core depth). (F) Dolostone facies: Euhedral dolomite. Thin-section microphotograph of porosity calculated from point counting is 18%. Long Key Core (DQQ-33; 294 m core depth).

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TABLE 2. LITHOFACIES CHARACTERISTICS OF THE ARCADIA FORMATION Skeletal wackestone, packstone, well-washed packstone and grainstone Red algal rudstone, grainstone, packstone and wackestone facies (Figs. 12 facies (Figs. 12 and 13B) and 13E) Depositional textures Skeletal well-washed packstones, packstones, grainstones, Depositional textures Red algal rudstone with packstone and grainstone matrix, and wackestones and red algal grainstones, packstones and wackestones Color Very pale orange (10YR 8/2) to grayish orange (10YR 7/4), Color Very pale orange (10YR 8/2) to pale yellowish brown yellowish gray (5Y 8/1 to 5Y 7/2) or uncommonly white (10YR 6/2), yellowish gray (5Y 8/1 to 5Y 7/2) or (N9) uncommonly white (N9) Grains Skeletal fragments, benthic foraminifers, mollusks, Grains Branching and encrusting red algae, benthic foraminifers echinoids, planktonic foraminifers, red algae, bryozoans and bryozoans (including Cyclostomata and Cheilostomes (including Cyclostomata in Long Key and Everglades in the Long Key core) Cores), peloids, ostracods, gastropods and Halimeda Grain size Grains range from silt to medium pebble size Grain size Grains range from silt to pebble size Accessory minerals Presence of quartz grains is variable; ≤trace. Phosphorite Accessory minerals Quartz grains occur variably (0%Ð2% in cores from the Keys grains comprise ≤1% of rock and 0%Ð20% in the Everglades Core) and range from silt Porosity Mostly moldic, vuggy, interparticle and intercrystalline; to medium sand size. Phosphorite grains comprise <1% of ranges from 8% to 23%, averages 16% rock, but are locally up to 10% Permeability 61Ð307 md, mean = 172 md Porosity Principally moldic, interparticle and intraparticle; ranges from Dolomite facies (Figs. 12 and 13F) 5% to 16%, average 11% Depositional textures Euhedral sucrosic and anhedral mosaic dolomites Permeability 66Ð615 md, mean = 175 md Color Very pale orange (10YR 8/2) to pale yellowish brown Molluscan floatstone and rudstone facies (Figs. 12 and 13C) (10YR 6/2), yellowish gray (5Y 8/1) to olive gray (5Y 3/2) Depositional textures Molluskan floatstones with a wackestone or packstone or dusky yellow (5Y 6/4) matrix and molluscan rudstones with a wackestone, Grains Skeletal fragments, mollusks, red algae and benthic packstone or grainstone matrix foraminifers Color Very pale orange (10YR 8/2), yellowish gray (5Y 8/1 to Grain size Grains range from silt to large pebble size. Euhedral 5Y 7/2) or uncommonly white (N9) dolomite crystals range in diameter from 0.75Ð0.125 mm Grains Mollusks, benthic foraminifers, (including Sorites), skeletal and anhedral dolomite crystals 0.75Ð0.30 mm fragments, echinoids, red algae, bryozoans (including Accessory minerals Silt- to very fine-sand sized quartz grains occur uncommonly. Cyclostomata in the Long Key core), peloids, planktonic Phosphorite grains comprise <1% of the rock foraminifers, gastropods, miliolids, ostracods and Porosity Mainly intercrystalline, vuggy and moldic; ranges from intraclasts 18%Ð34%, average 26% Grain size Grains range from silt to large pebble size Permeability 1027Ð5056 md, mean = 3125 md Accessory minerals Quartz grains range from silt to fine sand size. Where Bryozoan rudstone and floatstone facies* (Fig. 12) present are only a trace in Keys cores and up to 20% in Depositional textures Bryozoan rudstones with a wackestone or packstone matrix Everglades core. Phosphorite grains comprise <1% of in Long Key Core. Bryozoan floatstone with a grainstone rock, locally up to 10% matrix in the Stock Island Core Porosity Mainly moldic; ranges from 7% to 32%, average 16% Color Rudstone is yellowish gray (5Y 7/1) or very pale orange Permeability 30Ð275 md, mean = 205 md (10YR 8/2), and floatstone is pale yellowish brown Benthic foraminifer grainstone and rudstone facies (Figs. 12 and 13D) (10YR 6/2) or very pale orange (10YR 8/2) Depositional textures Benthic foraminifer grainstones, rudstones with a grainstone Grains The rudstones contain bryozoans (including Cyclostomata matrix and uncommon floatstones with a well-washed and Cheilostomes), benthic foraminifers, skeletal packstone or packstone matrix fragments, red algae and echinoids. The floatstones Color Very pale orange (10YR 8/2) or yellow gray (5Y 8/1 to contain bryozoans, skeletal fragments and benthic 5Y 7/2) foraminifers (including Miogypsina spp. in the lower Grains Benthic foraminifers (including Sorites and miliolids), skeletal Arcadia) fragments, red algae, echinoids, planktonic foraminifers, Grain size Grains range from silt to medium pebble size bryozoans (including Cyclostomata in the Long Key Core), Accessory minerals Quartz grains not observed. Phosporite grains ≤1%, but mollusks, peloids, intraclasts, ostracods and in the lower locally up to 8% Arcadia of the Stock Island Core the benthic foraminifers Porosity Principally intercrystalline and moldic with values up to 26% Sphaerogypsina globulus, Miogypsina spp., Sorites Coral framestone facies* (Fig. 12) marginalis, Lepidocyclina cf. parvula, Amphistegina Depositional textures Coral framestones with a matrix of wackestones, packstones chipolensis, Quinqueoculina seminula, Q. fulgida, and grainstones in Stock Island Core Q. lamarckiana, Q. crassa, Triloculina oblonga, Color Very pale orange (10YR 8/2) T. tricarinata, Archaias angulatus, Eponides Grains At least two massive varieties of hermatypic corals, skeletal vicksburgensis and E. byramensis fragments and benthic foraminifers (including Miogypsina Grain size Grains range from silt to medium pebble size spp. in the lower Arcadia) Accessory minerals Quartz grains range from silt to very fine sand size; ≤2%. Grain size Grains range from silt to cobble size Phosphorite grains comprise ≤1% of rock, locally up to 4% Accessory minerals Quartz and phosphorite grains were not observed Porosity Mainly interparticle, intraparticle and moldic; ranges from Porosity Mainly intraparticle porosity, up to 27% 16% to 27%, average 21% Permeability 223Ð2760 md, mean = 790 md *No permeability measurements recorded.

Florida (USGS, NP-100; FGS No. W-7363), 15 km east of the Everglades CHARACTERIZATION OF THE PEACE RIVER FORMATION Core (Fig. 1). In Florida, Miogypsina spp. has generally been regarded as late OF THE SOUTHERN PENINSULA Oligocene (Cole, 1938), but Cunningham and Rupert (1996a) reported that Miogypsina spp. range from late Oligocene to early Miocene in Florida. In Lithostratigraphy and Sequence Stratigraphy of the Peace River Florida, the uppermost range of Lepidocyclina spp. are thought to be Formation restricted to the Oligocene (Cole, 1944). A late Oligocene age for the lower Arcadia has been reported for areas in peninsular Florida by Missimer et al. In the cores examined for this study, the Peace River Formation only (1994), Sugarman et al. (1994), and Wingard et al. (1994) and an early late occurs in the Everglades Core (Figs. 1 and 5), where it is composed of two Oligocene age by Brewster-Wingard et al. (1997). Alternatively, preliminary distinct lithologic units: a lower diatomaceous mudstone unit and an upper results from strontium-isotope chemostratigraphy of the Arcadia suggest the unit composed of mud-rich, very fine to fine quartz sandstone. McNeill possibility of an early Miocene age in the Florida Keys. et al. (1996) proposed that the upper formation contact of the Peace River is

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at 98.8 m (core depth) in the Everglades Core. This contact is best shown by TABLE 3. LITHOFACIES CHARACTERISTICS OF THE PEACE RIVER FORMATION IN THE EVERGLADES CORE changes in gamma-ray activity and interval transit time derived from sonic Clay-rich quartz sandstone facies* logs (McNeill et al., 1996). The base of the Peace River overlies a major Lithology Clay-rich sandstone regional unconformity or sequence boundary which separates it from the Thickness Thickness is 71 m Color Pale olive (10Y 6/2) and yellowish gray (5Y 7/2) Arcadia Formation. Correlation of the lower diatomaceous mudstone and Grains Quartz grains, range from mainly very fine to fine sand size with upper quartz sandstone in the Everglades Core to the Peace River Formation minor silt and medium to coarse sand size, moderate to well is based on the presence of (1) a swelling clay (probably montmorillonite); sorted, angular to subrounded. Phosphorite grains, black, very fine to fine sand size, comprise up to 5% of rock (2) 2%Ð5% phosphorite grains; and (3) micropaleontologic age dating. Porosity Mainly interparticle The clays of the Peace River are most likely expanding clays (possibly Permeability 791Ð2547 md, mean = 1556 md † montmorillonite), as implied by an approximate doubling in length of the Clay-rich quartz sandstone facies* Lithology Clay-rich sandstone core by expansion throughout the diatomaceous mudstone. Scott (1988) Thickness Basal 0.46 m of Peace River Formation observed the common occurrence of clay beds in the Peace River, and Color Pale olive (10Y 6/2) to grayish olive (10Y 4/2) Grains Quartz grains, range from very fine to fine sand size, moderate to Reynolds (1962) determined that the clays are smectite (montmorillonite), well sorted, angular to subrounded. Phosphorite grains, black, palygorskite, and sepiolite. Pirkle et al. (1985) reported that the clay miner- very fine sand to medium pebble size, comprise 2% of rock. Up als within the Peace River are mainly montmorillonite and palygorskite. to pebble size reworked clasts of Arcadia limestone. Slightly calcareous They also found that the dominant clay mineral of the Pliocene Citronelle Porosity Principally interparticle Formation (possible Long Key Formation equivalent) in peninsular Florida Clay-rich, diatom- and radiolarian-bearing quartz sandstone facies*† is kaolinite, a nonswelling clay. Lithology Clay-rich, radiolarian- and diatom-bearing quartz sandstone Thickness Thickness is 4 m, suprajacent to clay-rich quartz sandstone facies Color Pale olive (10Y 6/2) to grayish olive (10Y 4/2) Peace River Lithofacies Grains Quartz grains, range from very fine to coarse sand size. Phosphorite grains, black, very fine sand to fine sand size, <2%. Fossils include up to 10% diatoms and radiolarians Three lithofacies have been identified in the lower lithologic unit of Porosity Mainly interparticle the Peace River Formation, distinguished by conformable vertical Diatomaceous mudstone facies* Lithology Diatomaceous mudstone changes in lithology and fossil content. From bottom to top they are: Color Yellowish gray (5Y 7/2) to pale olive (10Y 6/2) (1) a clay-rich quartz sandstone facies (0.5 m thick); (2) a clay-rich, Thickness Thickness is 23 m, suprajacent to clay-rich, radiolarian- and diatom- and radiolarian-bearing quartz sandstone facies (4 m thick); and diatom-bearing quartz sandstone facies Laminations Convolute and horizontal laminations common (3) a diatomaceous mudstone facies (23 m thick). These three lithofacies Grains Clay mud principle constituent, silt to fine sand quartz grains are of the lower Peace River and the sandstones of the upper Peace River are minor components. Black phosphorite grains, silt to very fine sand size, up to 5%. Fossils include diatoms, radiolarians, characterized in Table 3. Results of permeability measurements in the sponge spicules, silicoflagellates and broken fossil fragments. Peace River are shown in Table 3 and Figure 11. Trace mica Porosity Mainly intraparticle Permeability 7Ð30 md, mean = 18 md Silicoflagellates, Diatoms, and Palynomorphs of the Peace River *Porosity not calculated. Formation †No permeability measurements recorded.

A reconnaissance analysis (four samples) was made of diatomaceous mudstones, between core depths of 114.9 and 145.6 m of the Everglades Core. These samples were all found to contain a similar assemblage of com- Tortonian to lower Messinian, based upon the stage boundary as defined by mon silicoflagellates and abundant diatoms and radiolarians. Marine depo- Krijgsman et al. (1994). Furthermore, the age of the Everglades Core is con- sition on a deep continental shelf is indicated by (1) the presence of exclu- current with a late Miocene “carbon shift” (Haq et al., 1980). sively marine silicoflagellates and radiolarians; (2) the common occurrence Radiolarians do not constrain the age of the Everglades Core as closely of cosmopolitan pelagic species not normally present in the neritic zone; as the silicoflagellate taxa; however, a number of cosmopolitan taxa are (3) the abundance of very well preserved biogenic opal; (4) high species present with well-known ranges within the Tortonian-Messinian. Among diversity; and (5) the scarcity of benthic diatoms. those radiolarian taxa present are: Didymocyrtis penultima, Stichocorys A quantitative study of the silicoflagellate assemblage indicated an peregrina, Spongaster berminghami, and Didymocyrtis avitus. unusually high percentage of the silicoflagellate genus Distephanus (91.7% The occurrence of the diatomaceous mudstones in the Peace River of the to 98.4%). Tropical to temperate waters are usually dominated by the warm Everglades Core is consistent with transgressive to early highstand condi- water genus Dictyocha, rather than Distephanus, which predominates in tions and upwelling onto the Florida Platform during the late Miocene. The polar to subpolar waters (Ciesielski and Case, 1989). The abundance of age of these diatomites suggests correlation to a phosphogenic event Distephanus, in conjunction with tropical to temperate radiolarians and recorded in the Hawthorn Group of northeast Florida by Mallinson et al. abundant biogenic opal, instead is inferred to be a consequence of upwelling. (1994) between 6 and 8 Ma (BKFV85) or 6.56Ð7.43 Ma (BKSA95). The Two cosmopolitan silicoflagellate species, Distephanus “pseudofibula latest Tortonian-earliest Messinian age for the Peace River of the Ever- plexus” (McCartney and Wise, 1990) and Bachmannocena triodon, are glades Core is consistent with deposition during the TB3.2 eustatic cycle used to constrain the age. Both taxa range concurrently in the upper of Haq et al. (1988). Miocene, between the older first occurrence of the former species and the Two samples were analyzed for palynomorphs from the Peace River younger last occurrence of the later species. Herein, we determined the age Formation in the Everglades Core, one from the clay-rich, diatom- and of the first occurrence of the Distephanus “pseudofibula plexus” at 7.44 Ma radiolarian-bearing quartz sandstone facies at 145.6 m and another from the (Chron C4n.1n;BKSA95) and the last occurrence of Bachmannocena diatomaceous mudstones facies at 132.2 m (Table 3). Organic matter triodon at 6.83 Ma (lower Chron C3Ar;BKSA95) from ODP Hole 704B, (>15µm) from the lowest sample is composed of greater than 90% peloidal which has a paleomagnetic and a carbon and oxygen isotopic record. The amorphous organic matter (AOM). All pollen is extremely rare and dinocysts 7.44Ð6.83 Ma age range for the Everglades Core places it in the uppermost are rare. Spiniferites spp., Operculodinium spp., and Brigantedinium spp. are

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the most common taxa. The latter group belongs to the heterotrophic proto- contact of quartz sands of the Long Key Formation and overlying sandy peridinioid dinoflagellates. Heterotrophic dinoflagellates derive most of their wackestones and packstones. The relationship between the Stock Island nutrition through ingestion of organic compounds (Gaines and Elbrächter, Formation and the Long Key Formation appears to be a gradual lateral 1987). The absence of Polysphaeridum zoharyi from the assemblage is note- change in facies. Further core borings will be required to confirm this rela- worthy and may be a response to the upwelling of relatively cooler, relatively tionship. The boundary between the two formations is placed at the lateral nutrient-rich water masses onto the platform. Such upwelling best explains transition between Stock Island planktonic foraminiferal lime grainstones the overwhelming occurrence of peloidal AOM (de Verteuil et al., 1996) that or packstones, which contain <50% siliciclastic sand grains, and silici- is produced by the action of zooplankton and the abundance of diatoms. clastic sandstones of the Long Key Formation, which contain <50% plank- These data suggest that the lowest siliciclastic unit of the Peace River was tonic foraminiferal lime grainstones or packstones. In the Florida Keys, the deposited as a basal lowstand wedge or by reworking of relict siliciclastics Long Key Formation has been identified as far west as the Gulf Oil, State during transgression. Lease No. 373, No. 1 well (FGS No. W-972) on Big Pine Key (Fig. 1). In the sample taken from within the middle of the diatomaceous mudstone Analysis of planktonic foraminifers indicate that the siliciclastics of the facies (132.2 m), peloidal AOM constitutes only about 5%Ð10% of the parti- Long Key Formation have a maximum age of Messinian and a minimum cles greater than 15 microns. Foraminiferal linings and zoomembranes make age of Gelasian. The Long Key Formation may be correlative to the up 50%Ð60% and abundant dinocysts plus rare bisaccate pollen account for Cypresshead Formation, principally a quartz sand, which is reported to be the remainder. Spiniferites spp. are by far the most common dinocyst, with Pliocene in northern Florida (Scott, 1988) and middle-to-late Pliocene in lesser numbers of Operculodinium spp., protoperidinioids, Hystricholpoma southeastern Georgia (Huddlestun, 1988; 1993). The Long Key Formation rigaudiae, and Lingulodinium machaerophorum. Only rare specimens of may be, at least in part, equivalent to the Tamiami and, possibly, the P. zoharyi are present, indicating that an atypical nutrient-thermal regime, Caloosahatchee Formations (cf. Scott and Wingard, 1995). Partial correla- probably shallow upwelling, was still in effect, although perhaps less so than tion to the upper Peace River Formation in central peninsular Florida is sug- lower in the formation (i.e., sample at 145.6 m). gested by age results from Wingard et al. (1994) and Weedman et al. (1995). The response of the sonic log through the Long Key Formation in the CHARACTERIZATION OF THE LONG KEY FORMATION OF type core hole indicates a slower interval transit time (Fig. 14) relative to THE FLORIDA KEYS AND SOUTHERN PENINSULA suprajacent and subjacent carbonate rocks. The sonic log also suggests higher porosity for the Long Key sandstones relative to the overlying and underlying carbonates. The density log shows that the density of the Long Definition of the Long Key Formation Key sandstones is lower relative to limestones of the Arcadia Formation, but no significant density change is indicated at the contact of the Long Key The Long Key Formation is a new formational name proposed for a suc- sandstones and the overlying Key Largo Limestone (Fig. 14). There is a cession of subsurface siliciclastics up to 145 m thick underlying southern- slight increase in gamma-ray activity above the contact between the Long most Florida (Fig. 3), suprajacent to the Arcadia or Peace River Formations, Key Formation and the overlying shallow-marine limestones (Fig. 14). subjacent to the Key Largo and Miami Limestones (Figs. 4 and 5), and Gamma-ray activity increases slightly below the contact of the Long Key laterally equivalent to the Stock Island Formation (Fig. 4). Beneath the Formation and the Arcadia Formation (Fig. 14). In many wells there is a dis- Florida Keys, at least as far north as Carysfort Marina (Fig. 1), the Peace tinct increase in gamma ray activity at the Long Key-Arcadia contact. This River Formation is absent, probably due to nondeposition, and the Long Key is in response to a high-concentration phosphorite crust, which forms the Formation directly overlies the Arcadia Formation. However, on the Florida upper surface of the Arcadia (Fig. 14). No resistivity measurements were peninsula the Long Key Formation commonly overlies the Peace River recorded across the Long Key Formation in the Long Key core hole. Formation but may locally occur suprajacent to the Arcadia where erosion has completely removed the Peace River Formation. A distinct regional Long Key Formation Lithofacies unconformity and subaerial exposure surface at the top of the Arcadia Formation separates the Long Key and Arcadia Formations (Warzeski et al., One principal lithofacies, called the quartz sand or sandstone facies, 1996). The regional unconformity separates the formations with a major constitutes the Long Key Formation and is distinguished by identification temporal hiatus, at the millions of years scale (Guertin et al., 1995, 1996). of lithology and fossils (see Table 4). Examples are shown in Figure 15, and Warzeski et al. (1996) showed that marine seismic data just south of the the type core for the Long Key Formation is shown in Figure 14. Results of Florida Keys suggest beds of the Long Key Formation prograded southward permeability measurements for the Long Key Formation are shown in to eastward over the unconformity at the top of the Arcadia Formation and Table 4 and Figure 11. downlap onto the unconformity at the top of the Arcadia Formation. The type section for the Long Key Formation is designated as Core Palynomorphs of the Long Key Formation W-17156, FGS-Long Key No. 1 (Fig. 14), located just northeast of the island of Long Key (Fig. 1), Monroe County, Florida (lat. 24¡ 50′ 08′′ long. The distribution of palynomorph assemblages and their paleoenvironmen- 80¡ 47′40′′)1. The thickness of the Long Key Formation at the type locality tal significance are consistent with the interpretation by Warzeski et al. (1996) is 143.7 m and occurs between core depths of 48.2 and 191.9 m. The upper that the Long Key Formation represents a shallowing-upward succession. contact of the Long Key Formation is gradational or abrupt with overlying quartz-sand rich, bioclastic wackestones and packstones. In the Long Key CHARACTERIZATION OF THE STOCK ISLAND FORMATION Core, the upper contact of the Long Key Formation is placed at the upper OF THE FLORIDA KEYS

Definition of the Stock Island Formation 1GSA Data Repository item 9806, detailed stratigraphic descriptions of the Long Key Formation in the type core (W-17156) and the Stock Island Formation in the type core (W-17086), is available on request from Documents Secretary, GSA, P.O. Box The Stock Island Formation is proposed as a new formational name for 9140, Boulder, CO 80301. E-mail: [email protected]. subsurface fine-grained limestones that are suprajacent to the Arcadia

Geological Society of America Bulletin, February 1998 249

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Quat. 0

HMC Aragonite

LMC Platform Carbonates Key Largo Lms. Key

Explanation Mineralogy 100 Aragonite Quartz LMC Marine Sands HMC

Long Key Formation Long Key Dolomite

Quartz

Lithology

200 Limestone

Dolomite

LMC Dolomitic Limestone

Dolomitic Sandstone Sonic Sand Depth (mbsl) Density

Carbonate Ramp Texture Arcadia Formation Boundstone 300 Dolomite Wacke-Packstone

Grainstone

Sand

LMC=Low-Mg Calcite

HMC=High-Mg Calcite Aragonite

400 Carbonate Platform Suwannee Limestone Suwannee LMC 0 0 20 40 20 60 40 50 60 80 cobble pebble 100 150 100 200 boulder mud-silt v. fine-fine v.

Gamma Ray Sonic XRD very coarse (c.p.s.) (micro-sec./ft.) (%) Averagemedium-coarse Lithology

Grain Size Depositional & Texture Environmets Figure 14. Type core for the Long Key Formation. Florida Geological Survey, Long Key Core (W-17156), Monroe County. See GSA Data Repository item 9806, a detailed stratigraphic description of the Long Key Formation in the type core (W-17156) (see footnote 1 in text).

250 Geological Society of America Bulletin, February 1998

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Figure 15. Representative lithofacies from the Long Key and Stock Island Formations. (A) Thin-section microphotograph fine-grained quartz sand from the Long Key Formation. Porosity calculated from point counting is 42%. Long Key Core (ECW-2; 48.5 m core depth). (B) Thin- section microphotograph coarse quartz sand with medium pebble-sized quartz grains from the Long Key Formation. Porosity calculated from point counting is 38%. Long Key Core (ECW-42; 191.4 m core depth). (C) Thin-section microphotograph planktonic foraminifer-rich, quartz sandstone from the Long Key Formation. Porosity calculated from point counting is 32%. Carysfort Core (EDM-7; 130.8 m core depth). (D) Thin- section microphotograph fine-grained fossil fragment, planktonic foraminifer lime grainstone from the Stock Island Formation. Porosity calculated from point counting is 36%. Stock Island Core (DFN-2; 171.1 m core depth).

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Formation, has been found nowhere above or transitional to the Peace River (W-12799) on Key Vaca and the Gulf Oil-CALCO well (W-3174) west of Formation, is subjacent to the Key Largo Limestone, and is laterally equiv- the Marquesas Keys (Fig. 4). alent to the Long Key Formation (Fig. 4). The Stock Island Formation extends westward of the Long Key Formation between the middle and Palynomorphs of the Stock Island Formation lower Keys (Figs. 3 and 4). A well-developed subaerial exposure surface at the top of the Arcadia Formation forms a regional unconformity that sepa- Seven samples from the Stock Island Formation of the Stock Island Core rates the Stock Island and Arcadia Formations (Warzeski et al., 1996). The all contain abundant P. zoharyi, ranging from about 50% to 75% of organic unconformity represents a major temporal hiatus, at the millions of years grains greater than 15 µm. Other major components of palynofacies are scale (Guertin et al., 1996). Marine seismic data available at the University zoomembranes and microforaminiferal test linings. Degraded structureless of Miami suggest that beneath the Florida Keys, beds of the Stock Island organic matter and bisaccate pollen are variably present as subordinate con- Formation prograde southward and downlap onto the regional uncon- stituents of palynofacies. Regardless of the absolute age of the limestones formity at the top of the Arcadia Formation. of the Stock Island Formation, the general composition of the dinocyst The type section for the Stock Island Formation is designated as Core assemblage provides circumstantial evidence for its temporal correlation W-17086, FGS-Stock Island, No. 1 (Fig. 16), located on Stock Island, with the siliciclastics of the Long Key Formation in the Long Key, Carysfort Monroe County, Florida (lat. 24¡ 33′ 40′′ long. 81¡ 44′ 08′′) (see footnote 1). Marina, and Everglades Cores (de Verteuil, 1996). The thickness of the Stock Island Formation at the type locality is 121.3 m and occurs between core depths of 85.5 and 206.8 m. The upper contact of DISTRIBUTION OF LONG KEY FORMATION AND STOCK the Stock Island Formation is gradational with overlying floatstones, which ISLAND FORMATION are likely equivalent to the Pleistocene Key Largo Formation of Hoffmeis- ter and Multer (1964). The contact between the Stock Island Formation Examination of five new cores (Fig. 1), well cuttings, and logs constrain limestones and the Long Key Formation sandstones has already been de- the lateral and vertical distribution of the Long Key and Stock Island Forma- scribed. Results from planktonic foraminiferal analyses by L. A. Guertin in- tions beneath the Florida Keys and southernmost Florida (Figs. 3, 4, and 5). dicate that the limestones of the Stock Island Formation have a maximum Beneath Key Vaca a tongue of fine-grained limestones of the Stock Island age of Zanclean and a minimum age of Piacenzian(?). Formation occurs between overlying and underlying sandstones of the Long The response of the sonic log through the Stock Island carbonates at the Key Formation (Fig. 4). The next control point eastward (Long Key Core) type section recorded a slower interval transit time (Fig. 16) relative to car- indicates that the transition of the Stock Island tongue of limestones termi- bonate rocks above and below. The density log indicates that the density of nates between Key Vaca and the Long Key Core (Fig. 4). Two wells at Big the Stock Island Formation is lower relative to the Arcadia Formation and Pine Key indicate that a tongue of sandstones of the Long Key Formation the Key Largo Limestone (Fig. 16). The resistivity log shows a marked re- occurs between the top of fine-grained limestones of the Stock Island duction in resistivity throughout the Stock Island carbonates relative to the Formation and the base of the Key Largo Limestone. This tongue of sand- overlying Key Largo Limestone and underlying Arcadia. The decrease in stones terminates between Big Pine Key and the Stock Island Core (Fig. 4). resistivity in the Stock Island Formation is related to high moldic and inter- The western and northern limits of the Stock Island Formation are un- particle porosity throughout the Stock Island Formation and saline water known due to lack of well control (Fig. 3). The southern extent has been filling pore voids. Sonic, density, and resistivity logs indicate higher poros- inferred from marine seismic profiles reported in Warzeski et al. (1996). The ity for the Stock Island Formation relative to overlying and underlying car- southern and eastern extent of the Long Key Formation has been inferred bonates. There is a marked increase in gamma-ray activity above the con- from marine seismic profiles reported in Warzeski et al. (1996). The north- tact between the Stock Island Formation and the overlying Key Largo ern extent of the Long Key Formation is also unknown due to lack of cores Limestone (Fig. 16). Gamma-ray activity also increases significantly at the and a complex stratigraphy on the southern Florida peninsula (Fig. 3). Both contact of the Stock Island Formation and the Arcadia Formation (Fig. 16). the Long Key and Stock Island Formations accumulated after deposition of Increased gamma-ray activity at the contact of the Stock Island and Arcadia the Peace River Formation (Fig. 2). The northern limits of the Long Key Formations is observed on many logs from wells in southern Florida, a re- Formation are being addressed by additional onshore coring in southern sponse to a high concentration of phosphorite crusts at the upper surface of Florida by a consortium that includes the University of Miami, South the Arcadia Formation (Fig. 13A). Florida Water Management District, and FGS.

Stock Island Formation Lithofacies DISCUSSION

One principal lithofacies constitutes the Stock Island Formation; it is dis- Major Sequence Boundaries tinguished by identification of floral and faunal composition and deposi- tional textures. It is called the moldic skeletal and planktonic foraminifer Arcadia FormationÐSuwannee Limestone Contact. We consider the lime grainstone and well-washed packstone facies and is characterized in Arcadia-Suwannee contact to be a third-order (1.0Ð10.0 m.y. duration) depo- Table 5; examples are shown in Figure 15, and the type core for the Stock sitional sequence boundary. This interpretation is based on (1) the thickness Island Formation is shown in Figure 16. of the exposure zone underlying the top of the Suwannee (3 m) relative to On Key Vaca in the FKAA, OW-1 Core (Fig. 1), siliciclastic grain size other exposure surfaces (1 mm to 5 cm) within the Suwannee Limestone; ranges from silt to granule size and is mainly very fine- to medium-sand (2) a landward shift in sedimentary facies above the upper sequence bound- sized in the moldic skeletal and planktonic foraminifer lime grainstone ary; (3) a distinct change in lithofacies associations within the Arcadia and well-washed packstone facies. Quartz grains are moderate to well Formation and Suwannee Limestone; and (4) a significant hiatus separating sorted and angular to rounded, primarily angular to subangular. Percent- the Suwannee Limestone and Arcadia Formation in the Long Key Core. This age of quartz grains range from a trace to 50%. Visually estimated poros- interpretation is consistent with an early Oligocene age (36Ð31 Ma + 1.2 m.y.; ity ranges from 15% to 30%. The known eastern and western extent of the ages tied to COSUNA chart, 1988) of the Suwannee reported by Hammes Stock Island Formation is constrained by the FKAA-Marathon well (1992) and an early Oligocene age for a core from southwestern Florida

252 Geological Society of America Bulletin, February 1998

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0 Quat.

16" Aragonite 64"

LMC Explanation Mineralogy Carbonate Platform

Aragonite Key Largo Limestone Key

LMC

Dolomite Caliper 100 Quartz Density Lithology

Limestone Gamma Ray Dolomite Sonic Dolomitic Limestone Carbonate Slope Depth (mbgl) Dolomitic Quartz Sandstone

Stock Island Formation Stock Sand

LMC Texture 200 Boundstone

Wacke-Packstone

Grainstone

LMC=Low-Mg Calcite Dolomite 64" 16" Carbonate Ramp Arcadia Formation

300 Aragonite 0 0 2 4 6 8 0 20 40 60 80 cobble 100 200 300 400 200 100 100 pebble boulder mud-silt

Gamma Ray Sonic Normal Resistivity XRD fine-fine v. very coarse (c.p.s.) (micro-sec./ft.) (ohm-meters) (%) medium-coarse Lithology

Average Depositional Grain Size Environments & Texture Figure 16. Type core for the Stock Island Formation. Florida Geological Survey, Stock Island Core (W-17086), Monroe County. See GSA Data Repository item 9806, a detailed stratigraphic description of the Stock Island Formation in the type core (W-17086) (see footnote 1 in text).

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TABLE 5. LITHOFACIES CHARACTERISTICS Ginsburg, 1974); alternatively, the origin is driven by eustasy. Because OF THE STOCK ISLAND FORMATION recovery of core was only 55% of the total thickness of the Suwannee Moldic skeletal and planktonic foraminifer lime grainstone and well-washed packstone facies* (Fig. 15D) drilled, more cycles likely exist through the cored interval. Depositional Textures Moldic skeletal and planktonic foraminifer grainstones and Hammes (1992) bracketed the age of the Suwannee Limestone in well-washed packstones Color Yellowish gray (5Y 8/1 to 5Y 7/2) southwestern Florida by strontium-isotope chemostratigraphy, indicating Grains Moldic and non-moldic skeletal fragments, planktonic and an age between 36 and 31 Ma (+1.2 m.y.). Assuming a similar range in benthic foraminifers, echinoid spines and plates, age for the Suwannee Limestone in the Long Key Core, it is possible that ostracods, peloids, mollusks, and red algae. Percentage of planktonic foraminifers in the Stock Island Core de- the maximum amount of time represented by the Suwannee is 7.4 m.y. creases upward and a minimum of 2.6 m.y. Further, assuming that the 44 cycles inter- Grain size Carbonate grains are principally fine sand size preted as resulting from eustatic sea-level changes occurred within either Accessory minerals Abundance of quartz grains and their size increases from west to east, with the most abundant and largest grains 7.4 m.y. or 2.6 m.y, it is possible that the changes in sea level occurred at encountered in the FKAA OW-1 Core on Key Vaca (Fig. a maximum of every 170 k.y. or a minimum of 59 k.y. This suggests that 1). West of Key Vaca, quartz grains range from silt to medium sand size and are mainly very fine to fine sand the high-frequency cycles are climatically driven sea-level cycles (Read et size. Quartz grains are well sorted, angular to sub- al., 1995). This is consistent with documentation of an Eocene-to- rounded, angular to subangular. In the Stock Island Core, Oligocene global climatic change from “greenhouse” conditions during black phosphorite grains are ≤6% Porosity Principally moldic and interparticle; ranges from 16% to the Eocene to “cryospheric” conditions of the Oligocene-Neogene, which 36%, average 28% resulted in glacial eustatic sea-level changes (Miller et al., 1987; Zachos Permeability Measured at about 0.3 m intervals and have consistently et al., 1994; Pekar and Miller, 1996). A eustatic origin for the high- high permeabilities (1000 to 6000 md; Fig. 11) frequency cycles of the Suwannee Formation is also consistent with the conclusion of Zachos et al. (1996) that early Oligocene eustatic oscilla- (Wingard et al., 1994). Preliminary strontium-isotope chemostratigraphy for tions fluctuated with high frequency (41 k.y.) due to high-latitude ice- the Arcadia in the Long Key Core indicates an oldest age of early Miocene. volume events of ice growth and decay. Peace River, Long Key, and Stock Island FormationsÐArcadia Limited accommodation space, frequency of exposure of subtidal Formation Contact. This sequence boundary is interpreted to be a third- facies, and lithofacies (chlorozoan) suggests that Suwannee deposition order boundary (1.0Ð10.0 m.y. duration). This interpretation is based on occurred on a shallow carbonate platform influenced by subtropical-to- (1) a landward shift in sedimentary facies above the upper sequence bound- tropical conditions. ary; (2) a distinct change in lithofacies associations between the Stock Sequences and Cycles of the Arcadia Formation. Figure 12 shows the IslandÐLong Key Formations and underlying Arcadia Formation; and Arcadia is composed of a three-tiered hierarchy of vertically stacked (3) a hiatus separating the Peace RiverÐStock IslandÐLong Key Formations sequences and cycles (cf. Snyder et al., 1990; Kerans, 1995). The compos- and the Arcadia Formation (Missimer et al., 1994; Scott et al., 1994; Sugar- ite sequence, 120 m thick at Long Key, is bounded at top and bottom by man et al., 1994; Guertin et al., 1995; Guertin, 1996; Guertin et al., 1996; regional subaerial unconformities, which are third-order sequence bound- Missimer, 1997). aries. Tens of meter-scale sequences comprise the low-frequency sequences. Multiple meter- to tens of meter-scale cycles make up the higher-frequency Cyclic Deposition sequences. The cycles are composed of fining upward or coarsening upward successions. HFS4 is absent in the Long Key Core, probably due to erosion Depositional Sequences and Cycles of the Suwannee Limestone. Fig- during the hiatus between last deposition of the Arcadia Formation and the ure 8 shows the hierarchical vertical stacking of a low-frequency sequence, beginning of deposition of the Stock Island Formation (Fig. 12). The higher- two potential higher-frequency sequences, and multiple high-frequency cy- order sequences can be correlated by gamma-ray logs some 200 km to the cles (50 cycles). The low-frequency sequence corresponds to the entire north of the Keys, indicating their bounding unconformities or equivalent Suwannee Limestone penetrated in the Long Key Core. It is bounded at the conformities reflect regional events. top by a regional unconformity (cf. Hammes, 1992), which in the Long Key Subsurface data from the Arcadia Formation show that it contains wide- Core is a thick zone (3 m) displaying features indicative of subaerial expo- spread facies (foramol) patterns and no striking changes in paleoslope, sug- sure. The exposure zone (top HFS2) is capped by a thin phosphatic crust gesting deposition occurred on a carbonate ramp influenced by temperate (<2 mm), which formed during transgression of the unconformity (cf. conditions (cf. Wilson, 1975). Deposition on a ramp in southernmost Mallinson et al., 1994). The upper surface of the higher-frequency sequence Florida is consistent with work by Mullins et al. (1987, 1988a, 1988b) for a HFS1 is also a thick exposure zone (Fig. 8). The upper surface of HFS1 is a Neogene carbonate-ramp in west Florida. The Arcadia ramp dipped to the brecciated calcrete, which is at least 1.5 m thick (Fig. 8). This zone is inter- northeast and thus paleotopographic position on the ramp controlled preted to indicate the upper bounding surface of a higher-frequency se- whether sequences or cycles were exposed during relative falls in sea level. quence based on the m-scale thickness of the exposure zone relative to the Nine exposure surfaces have been identified in the Stock Island Core but mm- and cm-scale thickness of the laminar crusts that cap the high- none in the Long Key and Everglades Cores (Fig. 12). The lower Keys are frequency cycles (Fig. 8). The increase in the scale of the thickness of the considered to represent an inner ramp, which contained a patchy distribu- brecciated calcrete may indicate an increase in the duration of exposure, as tion of coral reefs (cf. Burchette and Wright, 1992). The middle and upper in the case of the exposure zone at the top of HFS2 (Fig. 8). Keys, and southern peninsular Florida are considered to represent the Most high-frequency cycles (44) contain subtidal facies that are truncated middle ramp, where more temperate and deeper-water facies were depos- by erosion and capped by a thin laminated calcrete or brecciated calcrete. ited (cf. Burchette and Wright, 1992). Six of the high-frequency cycles are capped by peritidal sedimentary facies. The subaerial exposure of 44 subtidal facies is probably due to an allocyclic Transport of Siliciclastics to the Florida Keys process, that is, eustatic changes in sea level. A tectonic control is unlikely because of the frequency of the cycles, 44 identified within a 96 m vertical A net thickness map of coarse-grained siliciclastics shows that maxi- section. The peritidal capped cycles may have an autocyclic origin (cf. mum current strength for transport of the siliciclastics occurred along a

254 Geological Society of America Bulletin, February 1998

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AB

27° 27° LAKE LAKE OKEECHOBEE OKEECHOBEE

-90 -70

-90 -190 Captiva Captiva

Island Island -70 -90

-130 -130 • • • • -170

-150 -90 -110 -110 -110

-110 ° ° 26 -130 26

-130 Marco Island Marco Island MIAMI LEGEND LEGEND Contour Interval = 30 m Contour Interval = 20 m -130 -150 -130 -150 -110 Core Core Core & logs Core & Logs Cuttings Cuttings Cutings & logs Cutings & Logs

Coarse-sand channel -170 U Fault(?) U D 25° Fault(?) 25° D -230 -210 -190 -170 -190 -2020 mm -20 m -230 -210 -250 -270 -2020 mm Florida -290 -20 m Florida -180 m -180180 m m -310 Straits of Straits of -180 m 0 km 100 0 km 100 -180 m -20 m -20 m 82° 81° 80° 24° 82° 81° 80° 24°

0 to 30 m 60 to 90 m 120 to 150 m

30 to 60 m 90 to 120 m 150 to 180 m

Figure 17. (A) Net thickness of coarse-grained (>1 mm) Miocene-to-Pliocene siliciclastic sands. Subsurface data from examination of cores, cuttings and published sources (Causarus, 1985, 1987; Knapp et al., 1986a, 1986b; Smith and Adams, 1988a, 1988b; McNeill et al., 1996; Warzeski et al., 1996). (B) Structure contour map of the top of the Arcadia Formation. Bold stippled line shows the location of a structural “channel” that is coincident with the maximum net thickness of coarse-grained Miocene-to-Pliocene sands. Subsurface data from examination of cores, cuttings, geophysical logs, and published sources (Peacock, 1983; Knapp et al., 1986a, 1986b; Smith and Adams, 1988a, 1988b; Warzeski et al., 1996).

corridor from west of Lake Okeechobee to the Florida Keys (Fig. 17A). Warzeski et al., 1996). Deposition of the mixed siliciclastic-carbonate This corridor of maximum current strength corresponds to a low mapped foundation postdates the late Miocene (carbon shift equivalent; Haq et al., on a structural contour map on the top of the Arcadia Formation (Fig. 17B). 1980) deposition of the Peace River Formation in the Florida Everglades This suggests that an accumulation of the coarse-grained siliciclastics was Core. Earliest seaward extension of the foundation most likely occurred focused within a tectonically produced low or erosional paleotopography during the Messinian lowstand. at the top of the Arcadia. Testing this hypothesis is an objective of the SFDP. The SFDP will map the thickness of the Arcadia Formation in CONCLUSIONS southern Florida and core the top of the Arcadia to establish whether the top of the Arcadia Formation has been eroded or the Arcadia has been 1. Glacial eustatic changes probably had a profound effect on high- structurally lowered. frequency stacking patterns, lithostratigraphy, and petrophysical char- acteristics of the Suwannee Limestone during transition from the Earliest Development of the Siliciclastic-Carbonate Foundation of the “greenhouse” conditions of the Eocene to “cryospheric” conditions of Florida Shelf Margin the Oligocene-Neogene. 2. Major erosional depositional sequence boundaries bounding the upper On the basis of an inferred seaward extension of late Miocene-to- surfaces of the Suwannee Limestone and Arcadia Formation are likely due Pliocene siliciclastics and carbonates of the Long Key and Stock Island to third-order, eustatic lowstands. Formations seaward of the Florida Keys, this mixed siliciclastic-carbonate 3. A post-Oligocene shift in depositional conditions produced a distinct deposit formed the foundation for the Pleistocene-to-Holocene southern sedimentary facies shift in biological components (from a chlorozoan to a Florida carbonate shelf margin and its discontinuous reefs (Fig. 18; foramol assemblage) in the Suwannee Limestone and Arcadia Formation.

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UM-FGS Everglades N Core Hole

Florida Key Largo Florida Mainland Limestone UM-FGS Bay UM-FGS Long Key Carysfort Marina Core Hole Core Hole Key Largo Peace River Formation Long Key Formation Shelf-Margin Reefs 100 m

Arcadia Formation

? Avon Park Formation

Suwannee Limestone and Ocala Group(?)

Suwannee 10 km Limestone

Figure 18. Block diagram showing the geometries of the stratigraphic framework of south Florida.

This suggests a shift in oceanographic conditions from tropical to sub- Pleistocene-to-Holocene southern Florida carbonate shelf margin and its tropical during the early Oligocene to temperate conditions following the discontinuous reefs. Earliest initial development of the foundation for the late Oligocene (cf. Read et al., 1995). southern Florida carbonate shelf margin most likely occurred during the late 4. A major upwelling event occurred during latest Tortonian to early Miocene lowstand of the Messinian, following deposition of the Peace Messinian (6.83Ð7.44 Ma; lower Chron C3Ar-C4n.1; BKSA95) and corre- River Formation in the Everglades Core. lates to a phosphogenic event recorded in the Hawthorn Group of northeast Florida by Mallinson et al. (1994), suggesting that the upwelling is associ- ACKNOWLEDGMENTS ated with a global rise in sea level. 5. Two new formational names are proposed for late Miocene to Pliocene Financial support for the analyses of cores was provided by the Donors siliciclastics and fine-grained limestones occurring suprajacent to the of the Petroleum Research Fund, administered by the American Chemical Arcadia Formation beneath the Florida Keys and the Peace River Formation Society. The Industrial Associates of the Comparative Sedimentology Lab- under the southern peninsula of Florida and subjacent to the Key Largo and oratory are gratefully acknowledged for financial support. The Southeast- Miami Limestones of southern Florida. The succession of siliciclastics is ern Section of the Geological Society of America and Sigma Xi provided named the Long Key Formation and the fine-grained limestones are named support to L. A. Guertin. the Stock Island Formation. Maximum age of the Long Key Formation is Four core holes drilled by the Florida Geological Survey (F.G.S.) made Messinian to a minimum of Gelasian based on planktonic foraminifers. The this study possible. CH2M Hill, Inc. supplied a core from Key Vaca. The Stock Island Formation has a maximum age of Zanclean and a minimum South Florida Water Management District generously ran geophysical logs age of Piacenzian(?) based on planktonic foraminifers. in three core holes. The Florida Keys Aqueduct Authority, John Pennecamp 6. On the basis of an inferred extension of the deposits of the Long Key State Park, and Everglades National Park provided access to the F.G.S. core- and Stock Island Formations seaward of the Florida Keys (Fig. 18), this hole locations. Much insight into the project was provoked from discussions mixed siliciclastic-carbonate deposit formed the foundation for the with R. N. Ginsburg, E. R. Warzeski, G. O. Winston, and T. M. Missimer.

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R. S. Caughey (FGS) is thanked for providing logs and well cuttings. R. S. Enos, P., and Perkins, R. D., 1977, Quaternary sedimentation of South Florida: Geological Soci- ety of America Memoir 147, 198 p. Reese (U.S. Geological Survey) generously supplied geophysical logs and Esteban, M., and Klappa, C. F., 1983, Subaerial exposure environment, in Scholle, P.A., Bebout, lithologic descriptions from numerous southern Florida wells. F. R. Rupert D. G., and Moore, C. H., eds., Carbonate depositional environments: American Association (F.G.S.) assisted in identification of benthic foraminifers, and Alex Amigo of Petroleum Geologists Memoir 33, p. 1Ð63. Gaines, G., and Elbrächter, M., 1987, Heterotrophic nutrition, in Taylor, F. J. R., ed., The biology identified silicoflagellates. Exxon Production Research Company and J. L. of dinoflagellates: London, Blackwell Scientific, p. 224Ð268. Foreman are thanked for use of their probe permeameter. L. A. Melim, F.A. 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