Marine and brackish water Cretaceous Ostracoda from wells in central and southern Florida

A small fauna represented by 17 species of ostracods, belonging to 13 genera, has been obtained from white oolitic limestones of probable Washitan (late Albian-early Cenomanian) age in 11 deep wells in Collier, Lee, Monroe, Pinellas, Palm Beach, Hendry, and Highlands Counties, central and southern Florida. Both marine and presumed brackish-water and/or fresh-water species are represented in the fauna. Five of the species are new; Clithrocytheridea? medioreticulata, C.? paucipunctata, C.? holoreticulata, Eocytheropteron highlandsensis and Cytheropteron? pinellensis.


INTRODUCTION
The ostracod fauna discussed in this paper was obtained from the wells listed in Table 1. The locations of the wells are shown in Fig. 1. The ostrilcods are of interest because they appear to be mainly undescribed and include both marine and fresh-water or brackishwater species in an oolitic limestone matrix. Most of the specimens are closed valves filled with opaque matrix and with the shell material corroded or recrystallized, which has made observation of internal shell structures difficult. The specimens that yielded information on internal shell structures were immersed in oil and examined by reflected and transmitted light in oil.

ENVIRONMENTAL ASPECTS OF THE FAUNA
Although most of the ostracods described herein are marine forms, several suggest brackish-water or freshwater conditions. The presumed brackish-water types are: Fossocytheridea sp. and Timiriasevia? sp., and the supposed fresh-water forms are Limnocyihere? sp. 1 and L . ? sp. 2; the latter two may also possibly represent seasonally-variable fresh and brackish-water conditions. All the ostracods collected occur in white, chalky, oolitic limestone. The fresh and brackish-water ostracods may have: (1) lived in the same area of the more definitely marine types, but at seasonally different salinity periods; (2) become adapted to higher salinity or the marine forms may have adapted to lower salinity conditions; or ( 3 ) been washed into the marine environment from inland lakes and ponds or brackish lagoons. It is not possible to decide at present which one or more of these alternatives is correct. It does seem clear that the facies containing the ostracods represent very nearshore conditions. A sabkha environment may be repsesented by the evaporite deposits associated with the oolitic limestone.

STRATIGRAPHY
Rocks of Washitan age occur in the subsurface under the entire state of Florida except for an area in the north central part of the state where they are absent. This area is located on the central part of the Peninsular Arch, a NW-SE trending positive structural feature against which Washitan and older Comanchean rocks pinch out in on-lap relationship. From a featheredge at their updip limit, Washitan strata thicken to the southwest and south. Proximal to the Peninsular Arch and southwestward from it, these strata are composed of nonmarine coarse sands and white to yellow shales. South, on the Florida platform area, they are represented by a carbonate-evaporite facies.
In central and southern Florida, Washitan strata range in thickness from 825 feet in well 10, Pinellas County, to 2169 feet in well 6, Monroe County ( Fig. 1). They overlie microcrystalline tan to grey mottled Fredericksburgian limestone, and are overlain by calcareous grey to black shale, fine-grained sand, and chalky to fine crystalline dolomitic limestone of Woodbinian and Eaglefordian age. The general stratigraphic relationships of these units across south-central Florida are shown in Fig. 2.
No definite assignment of age of the containing deposits can be made on the basis of the Ostracoda alone. The fauna contains several forms suggesting a late Lower Cretaceous age; these include Pontocyprella sp. aff. P . roundyi, Puracypris sp. cf. P . a h , Fossocytheridea sp., and Eocytheropteron sp. aff. E . tumidum.
The best available evidence for Washitan age of the deposits is the presence of the miliolid foraminifer Nummoloculina heimi Bonet, 1956. This form was described from the El Abra Limestone (late Albianearly Cenomanian) of San Luis Potosi, Mexico (Bonet, 1956), and is also recorded from the upper part of the Devils River Limestone of late Albian age, Val Verde County, Texas (Conkin & Conkin, 1956). It is considered a fairly reliable index fossil for middle Albian to Cenomanian calcareous reef facies in the southern United States and Mexico. The occurrence of the ostracod fauna with N . heimi provides a possible future means of age determination of the containing strata on the basis of the ostracods alone. The underlying Lower Cretaceous rocks of peninsular Florida have yielded a different ostracod assemblage (Swain & Miller, 1978). In that assemblage, species of Fabanella Martin  - Brown, 1972), whereas in the present collection from the Washitan, Fossocytheridea sp. and Limnocythere? spp. represent such conditions. As was noted previously (Swain,198l), Fabanella appears not to range above the Aptian or early Albian in the western Atlantic region. A species of Fabanella from the Trinitian (early Albian-late Aptian) of one of the wells studied here is included for comparison with the Washitan deposits. Washitan strata in the area of study consist predominantly of dolomite which commonly shows highly developed vuggy porosity as a result of the dolomite replacing oolitic and foraminifera1 limestone. Tan to white thin-bedded to massive anhydrite, and cream to white oolitic limestone with a chalky matrix are commonly interbedded with the dolomite. These oolitic limestone beds contain the ostracod fauna described herein, along with abundant specimens of the foraminifer N . heimi and occasional small shells of gas#tropods and pelecypods. The Ostracoda occur both as discrete grains in the chalky matrix and as the nucleiii of oolites.
Oolitic limestone occurs predominantly in the upper third of the Washitan unit, and is also found near its base, 50 to 200 feet above Fredericksburgian rocks. At both levels, it is interbedded with vuggy dolomite. Anhydrite and dolomite comprise the lower two-thirds of the Washitan unit. A thin green "pencil" shale which carries Fossocytheridea sp. marks the top of Washitan strata in many wells, particularly those in Palm Beach County. The following ostracods arc present in the collection: Pontocyprella sp. aff. P. roundyi (Alexander, 1929) Paracypris cf. P . ultu Alexander, 1929 Clithrocytheridea? medioreticulata, sp. nov .  (Alexander, 1929) (PI. 1, figs. 1-3)

Material. Four carapaces.
Remarks. This form is similar to the typc species P . harrisiana (Jones, 1849) (Howe & Laurencich, 1958) in general shape and relationships, but is more convex clorsally than is characteristic of that species, and less concave ventrally. It is similar top.? roundyi (Alexander) from the Kiamichi and Duck Creek Formations of Tcxas, but is less pointed posteriorly than that species (Alexander, 1929). Variation in relative elongation of shells may rcpresent sexual dimorphism.
Genu\ Parncypris Sars, 1866 Puracypris sp. cf. P. alta Alexander, 1929 (PI. 1 , fig. 4 (Alexander, 1929;Lozo, 1951 Description. Shell subovate in lateral view in presumed male, more elongate and subelliptical in presumed female; highest about three-fifths of length from anterior end; dorsal margin strongly convex with median to posteromedian slope straightened; ventral margin of left valve slightly convex, that of right valve sinuous; anterior margin broadly rounded, most extended slightly ventral of midheight, subtruncate above; posterior margin narrowly rounded in presumed male, less narrowly rounded in presumed female. Left valve larger than right, overlapping and extending beyond edge of right valve strongly in midventral twothirds, less strongly elsewhere. Valves strongly convex, greatest convexity submedian. Median to posteromedian half of shell reticulate; the reticulating ridges are broad and low with rounded crests and are irregular in pattern and distribution; remainder of shell surface smooth or weakly pitted. Hinge not clearly observed but appears to be antimerodont; infolds (inner lamellae) narrow; vestibules present terminally; radial canals few? and widely spaced; normal pores widely spaced and in part are accompanied by sieve plates (PI. I , fig. 7B). Adductor muscle scars consist of an anteromedian vertical row of four spots, with two frontal scars. Remarks. The medially reticulate surface of this species distinguishes it from other species of Clithrocytheridea?
All specimens are of Washitan (Albian-Cenomanian) age, housed in the Paleontological Collections of the University of Minnesota. Numbers in parentheses refer to length, height and width of specimens in mm. shcll are nested, Fla-PB-OT-3 well, 7,37 I-7,372 feet.
in the present collection. The shape and overlap relationships of this and the following forms tentatively asigned to the genus appear to resemble Clithrocytheridea Stephenson more than other described genera.
The species is abundant in beds of Washitan age in the following wells in Florida: Fla-Col- depths 8,803 and 8,909  Distribution. The species occurs in beds of Washitan age in the following wells in southern Florida: Fla-Pin-OT-2 wcll, depth 7,s 15-7,520 feet, Pinellas County; Fla-Lee-OT-2 well, depth 9,470-9,480 feet, Lee County; Fla-Col-OT-6 well, depth 8,590-8,600 feet, Fla-Col-OT-5 well, depth 8,802-8,803 feet, Collier County; and Fla-PB-OT-1 well, depth 7,690-7,700 feet, Palm Beach County. Description. Shell subovate in lateral view, highest about three-eighths from anterior end, dorsal margin strongly convex; ventral margin slightly convex; anterior margin broadly rounded, slightly extended below; posterior margin more narrowly rounded, extended below. Valves strongly convex, greatest convexity slightly postcromedian. Left valve larger than right, overlapping and extending beyond edge of right valve around entire periphery; greatest overlap mid-ventrally. Surfaces of valves covered by a coarse pattern of low reticulating ridges having irregular distribution rather than occurring in distinct alignment; widths of ridges equal to or less than pits between ridges. Internal features obscured by recrystallization of shell. Remarks. The species is more completely reticulate o n the shell surface than are others of the genus in the present fauna. The figured shell is believed to be a male specimen but females have not yet been found. Distribution. Rare in beds of Washitan age (late Albian-early Cenomanian), occurring only in the Fla-Hen-OT-5 well, depth 8,620-8,650 feet, Hendry County, Florida. Material. 25+ specimens. Distribution. In the present collection the species was found in beds of Washitan age, Fla-Col-OT-5 well, depth 8,802-8,803 feet, Collier County, Florida. It was described from beds of Trinitian to Washitan age from the subsurface of North Carolina (Swain & Brown, 1972).
Asciocythere? sp. (PI. 1, Material. Three specimens. Remarks. This form is more triangular than either ,4. rotunda (Vanderpool, 1928) or A . macropunctata Swain, 1952, from the Lower Cretaceous 'of Arkansas, Louisiana, Texas, and the southwestern states. It is less convex than the species here assigned to Clithrocytheridea ? Distribution. This form is rare in beds of Washitan age, Fla-PB-OT-3 well, depth 7,371-7,372 feet, Palm Beach County; and Fla-Pin-OT-2 well, depth 7,250-7,260 feet, Pinellas County, Florida.
Remarks. This species was first described from beds of Trinity? and pre-Trinity? age, undifferentiated, in wells in North Carolina (Swain, 1952) andl has further been recorded from beds of Trinitian (late Aptian-early Albian), Nuevo Leonian (late Neocomian-early and middle Aptian) and Durangoan (early and middle Neocomian) ages (Swain & Brown, 1972 Material. Five specimens. Description. Shell subquadrate (presumed female) to elongate-subelliptical (presumed male) in side view, highest one-fourth to one-fifth from anterior end, dorsal margin slightly convex to nearly straight, with poorly defined, broadly obtuse cardinal angles, the anterior larger than the posterior; ventral margin sinuous to slightly concave; anterior margin broadly curved, generally incompletely preserved in present specimens, slightly extended below, subtruncate above; posterior margin narrower, extended medially to ventro-medially, but poorly preserved in present specimens. Anteromedian and posteromedian surface of each valve swollen, posterior more elevated than anterior swelling; in presumed male the swollen areas are not connected ventrally and are separated by a narrow anteromedian sulcus that reaches four-fifths of distance All specimens are of Washitan (Albian-Cenomanian) age, unless otherwise stated, housed in the Paleontological Collections of the University of Minnesota. Numbers in parentheses refer to length, height and width of specimens in mm.  Fabanelfa tumidosa (Swain). d c a r . L side, UMPC 13248, x 26, Fla-Col-OT-5 well, 11,916-11,917 feet. Beds of early Trinitian (Neocomian?) age.
t o ventral margin, and broadens toward dorsum; in presumed female, sulcus reaches very slightly ventrally of midheight and swollen areas are connected ventrally; ventral part of posteromedian swelling forms a low subalate expansion; valve surfaces in terminal areas o f shell compressed. Internal shell structure not seen. Remarks. The tentative assignment of this species to Limnocythere is based o n the shape, general surface ornamentation and dimorphism shown by the shells. N o described species appears to be similar to these forms.
Forms referred to Eucytherura ansata Weingeist, 1Y49, and E . strumom Weingeist from the Weno and Grayson formations of Texas are similar to the Limnocythere sp. of the present paper in general outline and surface ornamentation, but differ in details of shell features. The present writer does not believe that the Texas species belong in Eucytherura. Distribution. This species is rare in beds of Washitan age, occurring in the Fla-Hen-OT-2 well, depth 8,620-8,630 feet, Hendry County, Florida, and Fla-Pin-OT-2 well, depth 7,570-7,575 feet, Pinellas County, Florida.
Limnocythere? sp. 2 (Pl. 2, fig. 14) Material. O n e carapace. Description. Lateral outline subquadrate, highest about one-fourth from posterior end, dorsum straight, venter sinuate with anteromedian concavity; anterior margin rounded, slightly extended below, truncate above; posterior margin more broadly rounded, extended above, subtruncatc below (some of the outline features may be due to imperfect preservation or distortion). Left valve slightly larger than right valve. Surfaces of valves with an anteromedian ventral narrow sulcus and nodelike and tidgelike elevations; two low nodes lie anterior to sulcus; the node posterior t o sulcus is the highest elevation, the ridge midventrally forms a low ala; terminal fifth of valves compressed. Internal shell structures not observed. Remarks. This form differs from the preceding one in features of surface ornamentation; it has more strongly elevated nodes and a better defined midventral alaform ridge than L . sp. 1. Distribution. The species is very rare in beds of Washitan age; Fla-PB- OT-1 well, depth 7,691-7,696 feet, Palm Beach County, Florida. Subfamily Timiriaseviinae Mandelstam, 1960 Genus Timiriaseviu Mandelstam, 1947 Timirimevia? sp. cf. T . polymorphu Mandelstam, 1955(PI. 2, fig. 8) 1955 Timiriasevia polymorpha M a n d e l s t a m in Galeeva, 1955: 61, pl. 15, figs. 4a-b;Lyubimova, 1956, p. 121, pl. 23, figs. 7, 8.  Adductor muscle scars a submedian vertical row of four longitudinally elongate spots, with one frontal spot anterior of middle of adductor group. Normal pores widely spaced, surrounded by subcircular sieve plates which, in most cases, bear elevated rims. Hinge margin not clearly observed, but appears to be feebly a n timerodon t . Remarks. This form is less caudate posteriorly than the following species, but ha5 a similar pattern of surface ridges and minute pits; the two forms may be dimorphs or variants. As compared to E . acaudalurn (Swain, 1952) from the subsurface Washitan beds of North Carolina the present species is less turned inward kentrally and has lesser overhang of the ventral margin by the ventral surface. Distribution. This form occurs frequently in beds of Washitan age; Fla-Hi-OT-1 well, depth 8,0 10-8,020 fcet, Highlands County, Florida; and Fla-Mon-OT-5 well, depth 8,300-8,310 feet, Monroe County, Florida.
Remarks. This form is more strongly caudate and lacks the anterodorsal sulcus and eye? node of the preceding form. Whether or not those differences are iritraspecific variations cannot be determined, but they aippcar to be sufficient for recognition of the two forms. The species resembles E. turnidurn (Alexander)  Description. Shell subelliptical to subovate in lateral view, highest posteromedially; dorsal margin nearly straight to gently convex, ventral margin gently convex to sinuous depending on degree to which alae are developed and extend beyond ventral margin; anterior margin in male shells broadly and nearly uniformly rounded, in females broadly rounded and somewhat extended below; posterior margin in males somewhat less broadly rounded than anterior margin; in females posterior margin bears pointed caudate extension dorsomedially. Left valve slightly larger than right valve. Valves strongly convex in male, greatest convexity posteromedian, strongly inflated in female, greatest convexity also posteromedian; in dorsal view female is more tapered and less blunt at posterior end than male. Surfaces of valves variably ornamented with narrow reticulating ridges; many shells incompletely reticulate, due to abrasion or recrystallization of shell surface; widths of interspaces are two to three times widths of ridges; ventral surface has four or five longitudinal ridges on each valve; anterodorsal oblique broad sulcus defines a low rounded eye tubercle o n each valve; posteroventrally blunt alae rise from surface; these are more elevated in female than in male; terminal borders compressed, and anterior margin bears a narrow rim.
Adductor muscle scars an anteromedian vertical row of four longitudinally elongate spots; with two frontal spots anterior of top and bottom of adductor group. Hinge, as viewed by reflected light in oil, appears to be weakly merodont. .80 .42 .45 Remarks. The quadrate outline, sulcation, ventral alae, and reticulate surface of this species provide a relationship to Cytheropteron Sars. C.? ahundens Donze, 1964 from the Berriasian of southern France, is closely similar to the present species in shape and dimorphic characteristics, but is more weakly reticulated, and is also less elongated than C. ? pinellensis. Eocytheropteron acaudaturn (Swain, 1952) from Washitan? beds of North Carolina, lacks the posteroventral alate expansions of the present species, has different surface ornamentation, and is not known to be dimorphic. Distribution. The species is common in beds of Washitan age; Fla-Pin-OT-2 well, depth 7,570-7,575 feet, Pinellas County, Florida; Fla-Col-OT-5 well, depth 8,802-8,803 feet, Collier County, Florida; Fla-Hi-OT-1 well, depth 8,010-8,020 feet, Highlands County, Florida; and Fla-Lee-OT-2 well, depth 9,470-9,480 feet, Lee County, Florida.
Family Uncertain Genus Taxodiella Kuznetsova, 1957 Taxodiella? sp. (PI. 2, fig. 10) Material. One carapace. Remarks. The shape and longitudinal ventral ridge of this form are similar to features of Taxodiella. It is more elongate the T. sp. from the Neocomian of North Carolina (Swain & Brown, 1972) and lacks the reticulate surface ornamentation of that form. It is very much like the illustrated male specimens of Klieuna data Martin, 1940(Neale, 1978 from the Lower Purbeck beds, Late Jurassic, of England, but lacks the partially reticulated surface of that species. The adductor muscle scar in this form consists of an antero-submedian vertical row of four elongate spots; one rounded frontal spot lies opposite the middle of the main group. Hinge not seen. Distribution. This species is very rare in beds of Washitan age in the Fla-Lee-OT-2 well, depth 8,950-8,960 feet, Lee County, Florida.