Ostracode Biostratigraphy of the Yorktown Formation (upper Miocene and lower Pliocene) of Virginia and North Carolina

GEOLOGICAL SURVEY PROFESSIONAL PAPER 704

Ostracode Biostratigraphy of the Yorktown Formation (upper Miocene and lower Pliocene) of Virginia and North Carolina

By JOSEPH E. HAZEL

GEOLOGICAL SURVEY PROFESSIONAL PAPER 704

Three ostracode assemblage zones are proposed for deposits assigned to the Yorktown Formation. The older two zones are considered to be late Miocene in age and the youngest early Pliocene

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY William T. Pecora, Director

Library of Congress catalog-card No. 76-610127

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 30 cents (paper cover) CONTENTS

Page Abstract.______1 Age of the Yorktown Formation.______-----_-___ 8 Introduction ______1 Paleogeography.___-_____-______-__----__---___---___ 8 Acknowledgments.- - ____---_-__-______-_-______-_ 2 Localities. ______10 Previous work______2 References.______-______---___----__-___ 10 Ostracode biostratigraphy______2

ILLUSTRATIONS

FIGURE 1. Map showing location of collections-______---______-_-____---_-___-__----_------_--_----__------_--__ 1 2. Q-mode dendrogram and trellis diagram based on calculation of Dice similarity coefficients.______3 3. Chart showing suggested biostratigraphic position of Yorktown samples used in Q-mode analysis.__.-____--_.____ 4 4. R-mode dendrogram for 80 ostracode species that occur in five or more samples. -______--__-__--___-_-.-______5 5. Map showing location of samples containing brackish-water elements______-_-___----____--______----__---_ 9 6. Diagram showing general trend through time of the Yorktown transgression and regression______10

TABLE

TABLE 1. Occurrence of 84 Yorktown species that occur in four or more samples.______6 in

OSTRACODE BIOSTRATIGRAPHY OF THE YORKTOWN FORMATION (UPPER MIOCENE AND LOWER PLIOCENE) OF VIRGINIA AND NORTH CAROLINA

By JOSEPH E. HAZEL

ABSTRACT 78 The Yorktown Formation of Virginia and North Carolina is divided into three ostracode assemblage zones based on the occur­ rence of 230 species in 43 samples. The samples were compared in Q-mode using the Dice binary similarity coefficient and cluster analysis. From oldest to youngest, the three zones are the Pterygo- cythereis inexpectata, Orionina vaughani, and Puriana mesacostalis Zones. The first two are late Miocene in age and the last, which is poorly represented in Virginia, is considered to be early Pliocene in age. The level of association (R-mode study using the Dice coeffi­ cient) between 80 of the more commonly occurring species is shown by means of a dendrogram; values for the biostratigraphic fidelity and constancy of each of these species for each of the zones are given. A general trend through time from late Miocene to early Pliocene for the Yorktown transgression and regression is suggested, based on the occurrence of brackish-water ostracodes and bivalves, particularly Cyprideis and Corbicula. It is suggested that rapid transgression of the sea occurred during early Yorktown time to a maximum during the time represented by the middle Orionina vaughani Zone. A more or less steady regression of the sea followed during the remainder of Yorktown time. INTRODUCTION The Yorktown Formation (upper Tertiary) of North Carolina and Virginia is a very fossiliferous, lithologi- cally heterogeneous unit with an exposed thickness (natural exposures or open-pit mines) of about 70-120 feet. The sandy clays and clayey sands assigned to the Yorktown crop out discontinuously in a 16,800-square- mile area between the Rappahannock River in Virginia and the Neuse River in North Carolina (fig. 1). South of the Neuse River, deposits of the same general age as the Yorktown are usually mapped as Duplin Marl. No microfossil zonation exists for the Yorktown. This report presents the results of a reconnaissance col­ lecting program in conjunction with examination of ex­ isting museum collections, the object being to provide a regional ostracode zonation. Localities (fig. 1; p. 10) were chosen on the basis of geographic and strati- graphic spread. More detailed collecting will be done in 0 25 50 75 100 KILOMETERS locally complex areas such as the York-James peninsula i i i i 11 i I I where the distribution of numerous lithofacies within FIGURE 1. Location of collections; numbers correspond to those the Yorktown is being studied (Johnson, 1969; Coch, in locality list (p. 10). Dashed line encloses area in which 1968; Bick and Coch, 1969). Yorktown Formation crops out in natural exposures. 1 OSTRACODES, YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

ACKNOWLEDGMENTS large ostracode assemblage of 230 species. In 43 of the I am grateful to T. R. Waller, P. C. Valentine, and samples the species diversity was sufficiently high to Druid Wilson for critically reading the manuscript and allow sample comparison using binary similarity co­ making suggestions for its improvement. Warren Blow, efficients and cluster analysis. A discussion of the appli­ T. R. Waller, Druid Wilson, L. W. Ward, and T. G. cation of these techniques to biostratigraphy is in Gibson made collections available for this study. The Hazel (1970). Texas Gulf Sulphur Co. allowed me access to exposures Figure 2 is a Q-mode (samples compared on the basis in their Lee Creek, N. C., mine. Mr. Blow also provided of their species content) dendrogram (unweighted pair- valuable technical assistance. group method) and trellis diagram for 43 samples re­ The calculations used in this paper were made on sulting from the calculation of Dice similarity coeffi­ the U. S. Geological Survey IBM system 360/65. The cients 2C/Ni + AT2, where C = number of species in program used is coded A243. I thank Paul Zabel and common between two samples, and Ni and AT2 are the Nancy J. Cotner for their technical help and advice number of species in the two samples; the similarity during this phase of the study. values are multiplied by 100 to remove the decimal point. There are three major clusters in the dendrogram, PREVIOUS WORK labeled A, B, and C. One of the samples, 31, clusters The only extant formal zonation for the Yorktown late; it will be discussed later. The three major clusters deposits is that of W. C. Mansfield (in Gardner, 1943) of faunally similar samples are interpreted as repre­ which is based on mollusks collected in the 1920's and senting three ostracode assemblage zones here named 1930's. Mansfield divided the Yorktown of Virginia into from lowest to uppermost, the Pterygocythereis inex- two zones. He placed the lower beds of the formation in pectata Zone (cluster A), Orionina vaughani Zone (clus­ the Pecten clintonius Zone (or Zone 1) which he said ter B), and Puriana mesacostalis Zone (cluster C). did not exceed 25 feet in thickness. He referred the re­ Correlation of certain samples within major clusters mainder of the Yorktown of Virginia to the Turritella is not obvious from inspection of the dendrogram in alticostata Zone (or Zone 2), which he divided into figure 2. This is a result of environmental "noise" and "beds" or "groups" of beds. As Mansfield defined and species provinciality, because the samples within the used them, these are neither lithic nor biostratigraphic clusters are spread over a wide area and may represent units (see discussions by McLean, 1956; Johnson, 1969), different environments. The trellis diagram of figure 2 and the correlations he proposed for some of the units gives the similarities, in 20-point classes, among all the of Zone 2 are of doubtful validity. Despite this and samples. Analysis of the trellis diagram (as well as the poor locality data for many of the species listed as indi­ computer printout of the matrix of calculated coeffi­ cators of either of the zones, Mansfield's two-zone cients of which the trellis diagram is a summary) and scheme has been a workable macrofossil zonation for of the stratigraphic position of the samples results in the Yorktown of Virginia. the correlations suggested in figure 3. Although the foraminifers of the Yorktown have Figure 4 is an R-mode (species compared to each been studied (see McLean, 1956, 1966, and references other on the basis of the samples in which they occur) therein), no zonation based on them has been proposed. dendrogram for 80 of the more commonly occurring Ulrich and Bassler (1904), Malkin (1953), Swain (1951), Yorktown species. The clusters represent groups of Brown (1958), and McLean (1957, 1966) have studied closely associated species. Opposite the endpoints in the ostracodes, and only about 50 species occurring in the dendrogram are numbers indicating the biostrati­ the Yorktown have been reported by these authors. graphic fidelity (BF) and constancy (C) of that species Malkin (1953) suggested a zonation for the Yorktown for each of the proposed zonal units. Constancy is sim­ based on 30 species identified from 12 samples from ply the percentage, expressed in tens, of samples from three localities in the York-James peninsula area. She a zonal unit in which a species occurs. Biostratigraphic proposed two zones, a lower Hemicythere schmidtae fidelity is calculated by Zone and an upper Hemicythere conradi Zone. Unfortu­ nately, Malkin's zones are virtually impossible to de­ BF,-.t. = -^- X 10, lineate, partly because of taxonomic advances, but principally because she identified too few species from too few samples and localities. where j is the species (j = a, b, c . . . ri); and Pi is the OSTRACODE BIOSTRATIGRAPHY percentage of occurrences in a biostratigraphic unit i Ostracodes were identified from 46 samples and 16 (i = 1, 2, 3 ... p). The BF of a species for a particular localities (fig. 1). The Yorktown Formation contains a biostratigraphic unit is therefore calculated by dividing OSTRACODE BIOSTRATIGRAPHY

DICE SIMILARITY COEFFICIENT X 100

DICE COEFFICIENT 100 90

FIGURE 2. Q-mode (samples compared on the basis of the species content) dendrogram and trellis diagram based on calculation of Dice similarity coefficients for 43 Yorktown samples containing 230 ostracode species. The unweighted pair-group method was used in clustering for the dendrogram. Values in the trellis diagram are given in 20-point classes. the percentage of occurrences of a species in a biostrati- species are deposited in the collections of the U.S. graphic unit by the sum of the percentage of occurrences National Museum under Nos. 167376 through 167456. of that species in all other biostratigraphic units within The specimens may be borrowed from the Museum for the limits of the problem. (See Hazel, 1970, for further study. discussion.) Biostratigraphic fidelity and constancy are The assemblage of the Pterygocythereis inexpectata expressed in tens to indicate the level of precision of the Zone is smaller than those of the two upper zones; 52 method and to remove the decimal point. Biostrati­ species have been identified, but relatively few of these graphic fidelity can be considered a quantification of the guide-fossil concept, and the values listed in figure characterize the assemblage. The forms with the highest 4 can be used as guides for monothetic biostratigraphic BF and C values for this zone appear in figure 4 in the placement of samples. The values for C and BF may 61-71 cluster. Species of the 22-31 cluster of figure 4 change as more data accumulate. also occur commonly in the Pterygocythereis inexpectata A list of the species used in the R-mode analysis is Zone, but have equal or higher values of BF for the Ori- given in table 1. Representative specimens of the 80 onina vaughani Zone. OSTRACODES, YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

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Biostratigraphic fidelity and zonal constancy / 2C \ DICE SIMILARITY COEFFICIENT Pterygocythereis X 100 Orionina Puriana \N,+N2 / inexpectata vaughani mesacostalis Zone Zone Zone 100 90 80 70 60 50 40 30 20 10 BF C BF C BF C

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FIGURE 4. R-mode (species compared with each other on the basis of the samples in which they occur) dendrogram (Dice coefficient; unweighted pair-group method) for the 80 Yorktown ostracode species that occur in five or more samples. The constancy, C, and biostratigraphic fidelity, BF, of each species for each zone are indicated on the left (see text for discussion). The BF and C values are based on the occurrences within the 43 samples used in Q-mode analysis (fig. 2); sample 31 was not used because it contains specimens reworked from the underlying bed (see text p. 7). The names and occurrences of the 80 species are shown in table 1.

415-720 O - 71 - 2 OSTRACODES, YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

TABLE 1. Occurrence of 84 Yorktown ostracode species that occur in four or more samples

[The species are listed in the order they appear in the It-mode dendrogram (fig. 4). The last four species were not used in the R-mode study]

Samples Species 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 4445

X X X X X X X X X X X X ------X X -- X X -- X ------X X X X X X X X X X X X 5 Cwhmanidea&p.I--. __ ... _ .. .. __ _ _ X X X X X X X X X X X X X X X X X X X X X X 9 Radimella ftoridana (Benson and Coleman, 1963) __ ------X X -- X X X X X X X X X X X X X X X X 13 Cytherurasp. N ______...... X X X 14 "Haplocytheridea" bradyi (Stephenson, 1938). __ . ------X X -- X X X -- -- X X X X X X X X X X X X X X X X X X -- X - X X X X X X X X X X X X X X X X X X X X X xll X X X -- X ------X X X X X X X X X X X X X X X X X X 21 MueUerina sp. F ______X X X X X X X X X X X 22 Radimetta eonradi (Howe and McGuirt, 1935) ...... -- -- X -- X ------X X X X X X X y X X X X X X X X X X " X X X X X X X X X X X -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 27 Hulingsina ashermani (Ulrich and Bassler, 1904). -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X __ X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X -- -- X X X X X X X X -- -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X -- -- X X X X X X X -- X X X X X X X X X X X X X X X X X X X X X -- -' -- X X '- X X X X -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 37 Orionina vaughani (Ulrich and Bassler, 1904) ___ . ------X X - X X X X -- -- X ------X X ------X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X ------X - X X ------X X X X X X X X X X X X- X X X X X X X X X X X X X - X 41 Puriana rugipunctata (Ulrich and Bassler, 1904). ... -- -- X - X X -- X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X - X X X X X X X X X X X X X X X X X 44 Bensonocythere sp. B... ______... -- X -- X X X X X X X X X X X X X X X X X X X X -- -- X X X X- X X X X X X X X X X X X X X X X X X X X X X X X X X X X 47 Bensonocythere sp. K. ______. __ ...... -- -- X -- X ------X X X X -- -- X X X X X X X X X X X X X X X X X -- X - X 49 Thaerocythere schmidtae (MaJkin, 1953).. __ . _ X X X X X X X X ;; X X -- X X X X X -- X X X X X X X X X X X X X X X X X X 52 Cytherurasp. L ______...... ------X X -- X -- X -- X X X X X -- -- X 53 Cythervra howei (Puri, 1954)...... X X -- -- X -- X -- -- X -- X X -- X X -- X xll y X X y X X X 55 Eucythere gibba Edwards, 1944 ------X X -- -- X ------X -- X X ------X X -- X X ------X X X X X X X X X X X -- X -- -- X X X X X X X X X X X X X X X X " X X 61 Mudlerina aft. M. canadensis (Brady, 1870) ...... X -- X X X ------X X ------X X X X X X X -- X X ------X X -- X 62 Adinocythereis cf. A. marylandica (Howe and Hough, 1935) _ _ X X X X X X X X X X X- X X X X X X X X X X X X X X X X X X X X -- -- X ------X X -- - X X ---- X X X X X X X X X X X X 66 Echinocythereis planibasalis (Ulrich and Bassler, 1904)...... X X X ------X X ------X X X -- - -- X X X X X X X X X X 68 Loxoconcha sp. M ______X X X ------X -- X -- X X X X X 69 Bensonocythere sp. D._ ...... _....._...... -- X -- X X -- X X X -- X X -- X -- X X X X X X X 71 Munayina barclayi McLean, 1957...... -- X -- X -- X -- X X -- -- X X -- - X X- X X X X X X X -- X X X X -- X X X - -- -- X X X X X X X - X X X X X

X X X X X X X X X X X X X X X- X V OSTRACODE BIOSTRATIGRAPHY

Deposits considered to be in the Pterygocythereis in- River at Mount Gould Landing (loc. 4) and at Colerain expectata Zone include (fig. 3) the lower 10 feet of York- Landing (loc. 3), at least the upper 12 feet of the York- town at the Lee Creek open-pit mine on the Pamlico town at the Lee Creek open-pit mine (fig. 3), and sample River, N. C. (loc. 1, p. 10) (also see Gibson, 1967); the 31. Sample 31 was collected in a borrow pit near Yadkin, fossiliferous beds overlying the granite at Halifax, N. C. Va. (loc. 8), from an unconsolidated to indurated 3- (loc. 5); at least the lowermost bed of the Yorktown on foot-thick unit of dark-red iron-stained clayey sand the Roanoke River near Palmyra Landing, N. C. (loc. containing sparse unstained clayey sand beds. The iron- 2); and the lower beds of the Yorktown on the James stained unit occurs stratigraphically below the marine River near Mount Pleasant, Va. (loc. 13). The Ptery­ Norfolk Formation (Pleistocene) (as used by Oaks and gocythereis inexpectata Zone is approximately equivalent Coch, 1963; Oaks, 1964) and contains hematite nodules, to the Pecten clintonius Zone of Mansfield (in Gardner, indurated mudballs, much comminuted shell, whole 1943). However, some of the beds along the York and specimens of the bivalve Corbicula densata (Conrad, James Rivers assigned by Mansfield to the upper part 1843), and 37 species of Ostracoda. Underlying this of his Pecten clintonius Zone contain ostracode assem­ unit are exposed at least 10 feet of blue clayey sand blages referable to the lower part of the Orionina packed with broken and whole mollusks (sample 30, vaughani Zone, for example, the beds assigned by Mal- placed in the Orionina vaughani Zone). Spencer and kin (1953) to her Hemicythere schmidtae Zone. Rogers (1969) place the iron-stained bed in the basal Ostracodes are abundant and diverse in the Orionina Pleistocene and the blue fossiliferous clayey sand in vaughani Zone; 160 species have been identified from the the Yorktown. 21 samples assigned to this zone. The large cluster in The comminuted shell in the iron-stained bed is figure 4 from species 16 through 60 contains forms probably reworked from the underlying blue fossilif­ which have high BF and C values for this zone. erous sand. Several of the ostracode specimens also In North Carolina the Orionina vaughani Zone assem­ appear to be reworked. The assemblage is a mixture of blage occurs in the Lee Creek mine from about 13 feet species that occur in both the Orionina vaughani and to at least 33 feet above the base of the Yorktown Puriana mesacostalis Zones with species otherwise re­ (material from the interval between 33 and 53 ft above stricted to either the Orionina vaughani or Puriana the base of the Yorktown could not be collected when mesacostalis Zones. This is reflected in the late clustering the mine was visited in June 1969). All the samples of sample 31 in figure 2. studied from the Yorktown of Virginia except 31 and 41 Five species occur in sample 31 that are known only are assigned to the Orionina vaughani Zone. Malkin's from the Orionina vaughani Zone. Two of these occur (1953) samples from the area of the type Yorktown commonly in that zone and in the blue fossiliferous beds can be assigned to the Orionina vaughani Zone on the below the iron-stained bed (sample 30); one of these basis of the BF values for the species she lists. species is represented in sample 31 by a single specimen In Virginia the Orionina vaughani Zone approximates and the other by three specimens. The presence of these the Turritetta alticostata Zone of Mansfield with some species in sample 31 probably represents reworking from important differences. Mansfield (in Gardner, 1943) in­ the beds below. The other three species occur rarely in dicated that Yorktown beds at Suffolk and near Frank­ the Orionina vaughani Zone in assemblages judged to lin (his Bigg's Farm locality) were the youngest York- represent environments similar to that of sample 31 town in Virginia. He correlated these beds with the (samples 38 and 45, for example) and therefore may Yorktown in the Colerain and Mount Gould areas on very well be part of the natural assemblage of the sam­ the Chowan River in North Carolina. In the present ple. study the subaerially out-cropping beds at Colerain Also present in sample 31 are species such as Puriana Landing as well as those at Mount Gould Landing are mesacostalis (Edwards, 1944) (species 4), Bensonocythere considered younger than any of the Yorktown of Vir­ sp. M (species 3), and Radimetta confragosa (Edwards, ginia, except for that represented by sample 31. Mac- 1944) (species 12) which are common in and restricted Neil (1938) on the basis of the distribution of certain to the Puriana mesacostalis Zone and younger levels. Noetinae (bivalves) also concluded that the Chowan The samples with which sample 31 has the highest simi­ River, N. C., beds are younger than any of the York- larity values are those from the Puriana mesacostalis town of Virginia. Zone on the Chowan River (samples 16, 17). The iron- The 1-15 cluster in figure 4 contains species with high stained bed is considered part of the Puriana mesacos­ BF and C values for the Puriana mesacostalis Zone. In talis Zone and not of Pleistocene age (so placed by Spen­ addition, the 16-60 cluster contains many species with cer and Rogers, 1969). This interpretation is corrobora­ high C values for this zone. In the Puriana mesacostalis ted by the presence of Corbicula densata which is not Zone are placed the beds in the bluffs on the Chowan known to occur in deposits as young as Pleistocene 8 OSTRACODES, YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

(Gardner, 1943). The bed is the youngest Yorktown matrix from inside a bivalved specimen of Dosinia ace- yet found in Virginia. tabulum (Conrad, 1832) collected from the type locality The nature of the contact between the iron-stained of the Ecphora Zone at Alum Bluff on the Apalachicola Corbicula-bearing bed and the blue bioclastic beds sug­ River (the specimen is from bed 4 of Puri and Vernon, gests a disconformity. If the biostratigraphic placement 1964, p. 204; USGS 2210) has yielded the following of samples 30 and 31 (fig. 3) is correct, the contact rep­ planktonic foraminifers (identified by Ruth Todd, U.S. resents the upper part of the Orionina vaughani Zone Geological Survey): and lower part of the Puriana mesacostalis Zone, sug­ Globigerina bulloides apertura Cushman, 1918 gesting erosion occurred during this time. G. dutertrei d'Orbigny, 1839 As mentioned above, it is this contact that Spencer Globigerinoides quadrilobatus sacculifer (Brady, 1879) and Rogers (1969) selected as the Yorktown-Pleisto- G. quadrilobatus trilobus (Reuss, 1850) cene contact and presumably mapped in the subsurface G. ruber (d'Orbigny, 1839) of Norfolk County, Va. The northwest-southeast trend­ Globorotalia acostaensis pseudopima Blow, 1967 ing flexure which they consider the cause of the thinning G. miocenica Palmer, 1945 of the "Pleistocene" in the Yadkin area may be the Sphaeroidinellopsis subdehiscens (Blow, 1959) structural control for the disconformity within the Turborotalita quinqueloba (Natland, 1938) Yorktown. See also the discussion of structural features by Oaks (1964, p. 70-80). This assemblage suggests that the Ecphora Zone should be assigned to Blow's (1969) planktonic zones AGE OF THE YORKTOWN FORMATION N18 or N19. The lower part of N18 is considered by The Yorktown Formation has traditionally been con­ Blow to be upper Miocene (Messinian); upper N18 and sidered the youngest Miocene unit in the Middle Atlan­ N19 are lower Pliocene (Zanclian). Thus, it may be tic Coastal Plain (Cooke and others, 1943). However, that the upper Miocene-lower Pliocene boundary in virtually no benthonic species which allow correlation the Atlantic and Gulf Coastal Plain eventually will be with the late Miocene (Tortonian-Messinian) of the revised further downward to include in the Pliocene type areas in Italy occur in the Yorktown. Diagnostic more of the deposits that have been traditionally as­ planktonic foraminifers are rare in the Yorktown be­ signed to the upper Miocene. cause most of the beds represent shallow water deposi­ tion under temperate conditions. However, Gibson PALEOGEOGRAPHY (1967) reports a late Miocene planktonic foraminiferal The ostracode genera Cyprideis and Perissocytheridea assemblage from beds here assigned to the Pterygocy- are primarily inhabitants of brackish water (see Sand- thereis inexpectata Zone at the Lee Creek mine in North berg, 1964a, b, Morkhoven, 1963). Also a brackish water Carolina. Diagnostic foraminifers from other parts of inhabitant is the late Miocene-Holocene species Cythero- the Yorktown are not known. morpha curta Edwards, 1944. (See Darby, 1965). Mod­ As pointed out above, Mansfield (in Gardner, 1943) ern species of the bivalve Corbicula live in fresh to brack­ correlated the upper part of his Turritella alticostata ish habitats (Zhadin, 1952,1965). In upper Miocene and Zone of Virginia (this zone is approximately equivalent Pliocene deposits of the Atlantic Coastal Plain, this to the Orionina vaughani Zone) with the Yorktown ex­ genus is represented by Corbicula densata (Conrad, posed on the Chowan River near Colerain and Mount 1843). Thus, in fossil assemblages the presence of the Gould, N. C. However, because the ostracode assem­ bivalve Corbicula or of the ostracodes listed above, par­ blages indicate that the latter deposits are clearly ticularly Cyprideis, indicates reduced salinity or at least younger than those of the Yorktown of Virginia, except proximity to a brackish water environment from which for that represented by sample 31, they are placed in specimens could be transported into shallow marine the Puriana mesacostalis Zone, habitats. Therefore, the presence of such forms as Cypri­ The Puriana mesacostalis Zone is therefore younger deis and Corbicula in fossil assemblages indicates near­ than Yorktown deposits traditionally considered late ness to shore. Miocene in age; it is here tentatively considered to be of Specimens of Cyprideis, Perissocytheridea, and Cy- early Pliocene age. Even this heterodox view of the age theromorpha curta occur in seven of the Yorktown sam­ of the Yorktown and its correlatives may be conserva­ ples studied. Corbicula densata occurs with these forms tive. The occurrences of certain mollusks and ostracodes at four of the localities and has been reported from near indicate that the Jackson Bluff Formation of Puri and the fifth locality. Vernon (1964), containing the Ecphora and Cancellaria The oldest Yorktown sample containing Cyprideis is Zones, of western Florida is correlative with the upper No. 23 from Halifax, N. C. (loc. 5). Here the Yorktown Yorktown of Virginia (Orionina vaughani Zone). The overlies granitic basement, and sample 23 was collected PALEOGEOGRAPHY about 4 feet above the base of the Yorktown. There is about 40 feet of Yorktown exposed at locality 5, but only in the lower few feet are microfossils preserved. Two species of Cyprideis occur in sample 38 from Lieutenant Run at Petersburg, Va. (loc. 12). Corbicula densata was originally described from Petersburg by Conrad (1843), but the exact locality is unknown. Cyprideis, Perissocytheridea, Cytheromorpha curta, and Corbicula densata occur in sample 44 at Williamsburg (loc. 15). Cyprideis, Cytheromorpha curta, and Corbicula densata occur together in the iron-stained bed in the borrow pit near Yadkin, Va. (sample 31 at loc. 8). Sample 19 at locality 4 on the Chowan River contains Cyprideis; Corbicula densata was found in the same bed. Cyprideis is present in sample 10 from the uppermost fossiliferous beds of the Yorktown at the Lee Creek mine; Corbicula densata occurs here also. The geographic positions of the Cyprideis-Corbicula- bearing samples are shown in figure 5. Their biostrati- graphic positions are indicated in figure 3. These Cyprideis-Corbicula points are interpreted to represent approximate positions of the shoreline of the Yorktown sea. Figure 6 shows the postulated general regional trend of the Yorktown transgression and regression. The Cyprideis-Corbicula points are plotted against the bio- stratigraphy (fig. 3) and the distance normal to the inferred depositional strike of about N. 20°-25° E., based on the azimuth of the inner edge of the outcrop 34° belt. Positions of samples from Yorktown beds that 0 25 50 75 100 MILES i i _J I immediately overlie older formations are also plotted; 0 25 50 75 100 KILOMETERS these are useful in delineating the pattern of trans­ gression. The plane of figure 6 is normal to the inferred depositional strike. FIGURE 5. Location of samples containing brackish-water ele­ The basal 1 foot of the Yorktown at the Lee Creek ments, particularly Cyprideis (all samples indicated) and Corbi­ mine (loc. 1) contains quartz pebbles and cobbles, phos­ cula (samples 10, 19, 31, 44). It is inferred that the shoreline of phate blocks, and cetacean bones. As Gibson (1967) the Yorktown sea was very near these localities when the de­ points out, this bed represents a basal transgressive con­ posits represented by these samples were laid down. glomerate. Placopecten clintonius and Pterygocythereis time characterized by the Pterygocythereis inexpectata inexpectata are found in this bed of the Yorktown. This Zone. is the farthest downdip that the base of the Yorktown At Petersburg, Va., beds of the middle Orionina can be seen in outcrop; the contact with the underlying vaughani Zone overlie St. Marys Formation and con­ Pungo River Formation (middle Miocene) is about 100 tain species of Cyprideis. The shoreline was no doubt feet below present sea level. nearby to the west. The maximum Yorktown trans­ A Yorktown bed of middle Pterygocythereis inexpectata gression was during the time of the middle Orionina Zone age overlies the Cretaceous near Palmyra Landing, vaughani Zone, probably at about the time represented N. C. (loc. 2), at about 20 feet above sea level. At Hali­ by the middle part of the Yorktown exposure at Peters­ fax, N. C. (loc. 5), 50 feet above sea level, a bed consid­ burg. The Yorktown beds at Petersburg are about 100 ered the same age as that near Palmyra Landing over­ feet above sea level. lies Paleozoic (?) granite. Cyprideis occurs in sample 23 The Yorktown at the Trego Quarry (loc. 6) overlies about 4.0 feet above the granite. The shoreline was granite at about 100 feet above sea level. The only sam­ probably never very far west of this area during the ple yet processed from this locality may also be from the

415-720 O - 71 - 3 10 OSTRACODES. YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

DISTANCE, IN MILES, NORMAL TO DEPOSITIONAL STRIKE Thickness Unit and description (feet) 0 10 20 30 40 50 60 70 80 Pleistocene: 10 (-30) 10. Buff crossbedded sand.______10.0 19 (+10) Cy,Co Yorktown Formation: Cy.Co . 9. Blue clayey sand, weathered; no macrofossils; microfossil sample barren______2.0 .31 (-5) 8. Blue clayey sand; macrofossils very common; Cy,Cc,Co Corbicula densata present in upper part; sample 8 (TJSGS 24886) in lower 1.0 ft, sample 9 (TJSGS 24887) taken 7.0 ft above base, sample 10 (TJSGS 24888) in upper 0.5 ft of unit. ______11.0 7. Covered or otherwise inaccessible______23.0 Cy,Cc,P,Co 6. Bluish-gray clayey sand; Turritella molds and casts in lower 6 ft; sample 7 (TJSGS 24885) col­ 38 ( + 100) lected 10.0 ft above base; barren microfossil * Cy,?Co samples collected 1.0 ft and 5.5 ft above base.__ 13.0 5. Blue clayey sand, indurated; many Turritella___ 3.0 4. Blue clayey sand; Pecten and Turritella; contact with underlying unit irregular; sample 6 (TJSGS 24884)______l.O 23,(+54) Cy 41 (+30) 3. Blue clayey sand; phosphate and quartz pebbles 11 (+20) in lower part; macrofossils present; burrows in 21 (+50)" upper 1.0-2.0 ft; sample 5 (TJSGS 24883) in upper 0.5 ft between burrows; sample 4 (TJSGS 24882) collected 12.0 ft above base; sample 3 1 (-100) (TJSGS 24881) 7.0 ft above base; sample 2 (TJSGS 24880) in lower 10 ft__-______14.0 FIGURE 6. General trend through time of the Yorktown trans­ 2. Blue clayey sand; phosphate pebbles and quartz gression and regression. The plane of the figure is normal to the cobbles and pebbles; bone; macrofossils, includ­ inferred general depositional strike of N. 20°-25° E. Samples ing Placopecten clintonius and Mercenaria; sam­ (10,19, 31, 44, 38, 23) containing brackish Water ostracodes and ple 1 (TJSGS 24879)._..______.___..___.__. 2.0 Corbicula are plotted against the distance between the samples Pungo River Formation: normal to the depositional strike and their biostratigraphic posi­ 1. Phosphatic sands and diatomaceous clay______43.0 tion (fig. 3). Also plotted are samples (1, 11, 21, 41) from York- town beds that immediately overlie older formations. The num­ Total exposed______122.0 bers within the parentheses indicate feet above or below present sea level. The abbreviations Cy, Co, P, and Cc stand for Cypri- Locality 2. Bluff on right bank of Roanoke River about 1.25 deis, Corbicula, Perissocytheridea, and Cytheromorpha curia miles below the landing 1.0 mile east of Palmyra, Halifax (Edwards, 1944), respectively. County, N. C. Sample 11 (TJSGS 24889) from blue clayey sand with Pecten in basal 1.0 foot of the Yorktown Formation where middle Orionina vaughani Zone. However, it clusters it overlies a 3-foot indurated sand containing fossil logs in the upper part. Collected by T. G. Gibson and Charles Budden- late (see fig. 2), and its exact position within the zone is hagen, November 1965. equivocal. Cyprideis-Corbicula-bearmg beds marking the regres­ Locality 8. Landing at Colerain, Bertie County, N. C. About 16 feet of Yorktown is exposed in bluffs 100-200 yards south of sion of the Yorktown sea are present at Williamsburg, Colerain Beach Club, right (west) bank of Chowan River. In Va. (loc. 15), Yadkin, Va. (loc. 8), Mount Gould Land­ addition, in June 1969 a spoil pile of fossiliferous sediment (unit ing, N. C. (loc. 4), and the Lee Creek mine (loc. 1). 1 below) was present at a Mr. White's cabin. This material was The Williamsburg sample represents the Orionina vaugh­ collected by Mr. White from the river bottom some distance off­ ani Zone; the last three samples represent the Puriana shore at low spring tide after several days of offshore winds; it is not knowta how far stratigraphically this is below the base of mesacostalis Zone. the subaerial outcrop. The disconformity within the Yorktown at Yadkin, Thickness Va., (see p. 8) indicates that at least locally the sea Unit and description (feet) readvanced over an eroded middle Yorktown surface Pleistocene: 7. Sand, crossbedded-______25.0 during early Pliocene time. Yorktown Formation: 6. Clayey sand; weathered buff; macrofossils present; LOCALITIES Corbicula densata and Mercenaria present- _____ 6.0 Locality 1. Open-pit phosphate mine of the Texas Gulf Sulphur 5. Clayey sand; weathered buff in upper part, mottled Co. on south shore Pamlico River at mouth of Lee Creek near in lower part; Pecten and Mercenaria present; Aurora, Beaufort County, N. C. (see Gibson, 1967). The follow­ sample 15 (TJSGS 24892) taken 4 ft above base_ _ 6.0 ing section was collected in the southwestern part of the pit in 4. Greenish blue clayey sand; macrofossils present; June 1968. sample 14 (TJSGS 24891)______.___._ 1.5 LOCALITIES 11

Thickness Unit and description (feet) Locality 6. Trego Stone Corporation quarry, 2.0 miles west of Skippers, Greenville County, Va. Sample 27 (USGS 24830) from 3. Greenish-blue clayey sand; macrofossils very com­ upper 1.0 foot of 7.0-foot-thick outcrop of clayey sand with mon; Glycymeris and Pecten common; bed is at macrofossils, west side of road into quarry. Sample collected by water level; sample 13 (USGS 24890) ______1.0 Druid Wilson and Warren Blow. 2. Normally below water level______? 1. Greenish-blue clayey sand; macrofossils very com­ Locality 7. Bluff on right (south) bank of Nansemond River, mon; spoil collected from river bottom (see 0.5 mile downstream from Virginia Routes 10 and 32 bridge, above); sample 12 (USGS 24911)______._ ? about 500 feet northwest of cemetery, city of Suffolk, Va.; about 13 feet of Yorktown exposed near south end of outcrop. Sample Total exposed______39.5 28 (USGS 24811) from greenish-blue clayey sand in lower 0.5 foot of exposure; sample 29 (USGS 24814) from buff clayey sand Locality 1*. One-half mile below landing at Mount Gould, about 11.5 feet above beach. Samples collected by Richard H. Bertie County, N. C.; bluffs on right (west) bank of Chowan Bailey and Warren Blow. River. Thickness Locality 8. Borrow pits 0.5 mile southwest of Yadkin, Virginia, Unit and description (feet) and 0.3 mile south of Norfolk and Western Railroad near inter­ Pleistocene: section of Portsmouth Ditch and powerlines; U.S. Geological 4. Sand, crossbedded-__.___-______-__--_.___ 15.0 Survey Norfolk South 7 ^-minute quadrangle map, 1965; Yorktown Formation: lat. 36°45'30" N., long. 76°22'00" W. Section measured in cut 3. Gray to buff clayey sand; shell fragments.______1.0 between north and south pits and in north pit. 2. Buff, clayey sand, slightly weathered; macrofossils Thickness Unit and description very common; Pecten, Glycymeris, Corbicula (feet) densata, corals; sample 20 (USGS 24897) (from (?) Sand Bridge Formation (of Oaks and Coch, 1963; Oaks, 1964): upper 1.0 ft; sample 19 (USGS 24896) 3.0 ft 4. Sand, crossbedded; clay and peat interbeds__--_- 4.0 above base; sample 18 (USGS 24895) 1.5 ft Norfolk Formation (of Oaks and Coch, 1963; Oaks, 1964): above base_-_-__-____--___-_--__-__-______4.5 3. Gray clayey sand; macrofossils present; iron- 1. Green to buff mottled clayey sand; scattered shell cemented concretions and cobbles in lower part; fragments; sample 17 (USGS 24894) in upper bed with many Ensis in upper part-______7.5 1.0 ft; sample 16 (USGS 24893) in lower 1.0 ft_. 4.0 Yorktown Formation: 2. Red clayey sand; variably iron cemented; hematite Total exposed______24.5 nodules and indurated mudballs present; many worn broken shells; well-preserved bivalved Locality 5. Banks of a northward flowing tributary to Quankey specimens of Corbicula densata; contact with Creek, north side of North Carolina route 561 0.5 mile west of underlying unit irregular; sample 31 (USGS railroad crossing over route 561 in Halifax, Halifax County, 24905)-..-. ___-_ -__ .--. . _ 3.5 N. C. 1. Blue clayey sand; macrofossils very common, unit Thickness Unit and description (feet) packed with broken and whole mollusk shells; Pleistocene: sample 30 (USGS 24904) in upper 4.0 ft---___- 10.0 13. Sand _._ - __ - 6.0 Yorktown Formation: Total exposed,---_-----_-_.____-_-----___ 25.0 12. Gray, clayey sand, unfossiliferous______7.0 Locality 9. Lone Star Cement Co. open-pit mine, 0.5 mile north 11. Greenish-gray clayey sand; casts and molds of of Chuckatuck, Nansemond County, Va. Sample 32 (USGS aragonitic mollusks; scattered oysters and 24622) collected from very fossiliferous clayey sand 12.0 feet pectenids; elongated concretions in lower 2.0 ft; below present land surface and 2.5 feet below Pleistocene, west microsamples barren.______7.5 wall, 150 yards from northwest corner (in December 1967) 10. Clayey sand; indurated; macrofossils present; of pit. Collected by Warren Blow. forms waterfall------1.0 9. Greenish-gray clayey sand; scattered macrofos­ Locality 10. Vertical 9.0 to 10.0 foot exposure of Yorktown sils; sample 26 (USGS 24903) 5.0 ft above base. 11.0 Formation overlain by Pleistocene on south bank of ravine ap­ 8. Blue clayey sand; macrofossils very common; proximately 0.45 mile northwest of Tormentor Creek; 150 feet sample 25 (USGS 24902)_-.__.__.. . _.__ 2.0 east of smaller of two abandoned Lone Star Cement Co. pits and 7. Covered------2.0 0.2 mile south of Virginia Route 673, Isle of Wight County, Va.; 6. Blue clayey sand; macrofossils very common; U.S. Geological Survey Mulberry Island 7^-minute quadrangle sample 24 (USGS 24901)._._-_._._.__ - 2.0 map, 1965. Sample 33 (USGS 24823) collected 0.5 feet below 5. Covered______--_-_____--____-__-_--_-_--- 1.5 top of Yorktown in brown sandy shell hash. Section measured 4. Blue clayey sand; macrofossils very common; and collected by Brian Dyer and Warren Blow. sample 23 (USGS 24900)-_--_-___--____---- 2.0 Locality 11. Pit belonging to Mr. William Rice, just north of 3. Covered _ -__ . - 2.0 intersection of Fox Hill and Harris Creek Roads, Hampton City, 2. Buff clayey sand; macrofossils very common; Va.; U.S. Geological Survey Hampton 7^-minute quadrangle sample 22 (USGS 24899) in upper 1.0 ft and map, 1965. Section measured and collected by Warren Blow, sample 21 (USGS 24898) in basal 0.5 ft_ - _ _ - _ 2.0 Brian Dyer, and T. R. Waller. Thickness Paleozoic (?): Unit and description (feet) 1. Buff granite-.-.-.------_..._._._.__.__ 2.0 Pleistocene: Total exposed-__...____..___-._____. 48.0 Sand and gravel. 6.0 12 OSTRACODES, YORKTOWN FORMATION, VIRGINIA AND NORTH CAROLINA

Thickness Unit and description (feet) in 15.0-foot-deep gully about 50.0 feet north of road which is normal to and directly behind center of west wall of Gary Yorktown Formation: Stadium. Sample 45 (USGS 24819) from upper 1.0 foot of York- Buff to gray clayey sand; becoming more clayey and town in buff to orange fossiliferous coarse sand below contact less fossiliferous toward bottom of pit; concentration with Pleistocene (?) sand with pebbles and cobbles; sample 44 of Ensis 1.5-2.5 ft below top; sample 37 (USGS 24805) (USGS 24820) of same lithology from 2.0-3.0 feet below top of from matrix inside delphinapterid whale skull col­ Yorktown. Corbicula densata and Rangia are present in the inter­ lected just below Ensis bed; sample 36 (USGS 24907) val from which samples 45 and 44 were collected. Sample 43 about 7.0 ft below top; sample 35 (USGS 24906) about (USGS 24821) collected 4.5 feet below sample 44 in fossiliferous 15.0 ft below top; sample 34 (USGS 24810) from brownish-gray clayey sand. Collections made by Richard H. matrix inside Echinocardium about 30.0 ft below top Bailey and Warren Blow. and 4.5 ft above bottom of pit-_----__-__-___---_- 34.0 Locality 16. Left (north) bank of Piankatank River 0.25 mile Total exposed--_--_---___------____------40.0 above mouth of Cores Creek, Middlesex County, Va. U.S. Geological Survey Wilton and Deltaville 7>£-minute quadrangle Locality 12. Banks of Lieutenant Run, a northeast-to north- maps, 1964. Section measured and collected by L. W. Ward. flowing tributary to the Appomattox River, in southern Peters­ Thickness burg, Va.; fossiliferous beds are east of the railroad crossing over Unit and description (feet) Lieutenant Run and east and north of West Clara Drive, im­ Pleistocene: mediately behind (north) of houses on Marshall Court and 3. Sand, mostly covered.------______--______10.0 Field Court. Yorktown Formation Thickness Unit and description (feet) 2. Sandy coquina, partly indurated; shells broken; sample 46 (USGS 24801)______.______2.0 Yorktown Formation: 1. Sand; macrofossils very common______3.0 4. Blue clay; casts and molds of mollusks, including Yoldia; microfossil sample barren ______3.0 Total exposed_-__-______15.0 3. Blue clayey sand with scattered blebs of clay (possibly cross sections of burrows)______.5 REFERENCES 2. Gray clayey sand; macrofossils very common; Bick, K. F., and Coch, N. K., 1969, Geology of the Williamsburg, more clay toward top; Panopea in living posi­ Hog Island, and Bacons Castle quadrangles, Virginia: Virginia tion; sample 40 (USGS 24910) in very clayey Div. Mineral Resources Rept. Inv. 18, 28 p. sand in upper 1.0 ft of unit; sample 39 (USGS Blow, W. H., 1969, Late middle Eocene to Recent planktonic 24909) collected 6.0 ft above base; sample 38 foraminiferal biostratigraphy, in Internat. Planktonic Conf. (USGS 24908) collected 1.5 ft above base; con­ Microfossils, 1st, Geneva, 1967, Proceedings: Leiden, E. J. tact with underlying unit irregular, with sedi­ Brill and Co., v. 1, p. 199-422. ment of this unit filling burrows of underlying Brown, P. M., 1958, Well logs from the Coastal Plain of North unit______10.0 Carolina: North Carolina Div. Mineral Resources Bull. 72, St. Marys Formation: 68 p. 1. Greenish-gray clayey sand grading downward to Coch, N. K., 1968, Geology of the Benns Church, Smithfield, greenish-gray sandy clay; scattered macrofossils Windsor, and Chuckatuck quadrangles, Virginia: Virginia in upper 6.0 ft______+6.0 Div. Mineral Resources Rept. Inv. 17, 40 p. Conrad, T. A., 1843, Descriptions of nineteen species of Tertiary Total exposed______+19.5 fossils of Virginia and North Carolina: Acad. Nat. Sci. Locality IS. Right (south) bank of James River, first cliff ex­ Philadelphia Proc., vol. 1, p. 323-329 [1844]. posure east of first low-lying point of land 1800 feet west of the Cooke, C. W., Gardner, Julia, and Woodring, W. P., 1943, Correla­ colonial home on the Mount Pleasant Estate; 2.7 miles west of tion of the Cenozoic formations of the Atlantic and Gulf Jamestown, Va., lat. 37°12'20" N., long., 76049'50" W. U.S. Coastal Plain and the Caribbean region [chart no. 12]: Geol. Geological Survey Surry 7J^-minute quadrangle map, 1965; Soc. America Bull., v. 54, no. 11, p. 1713-1723. sample 41 (USGS 24717) from buff clayey sand about 26 feet Darby, D. G., 1965, Ecology and taxonomy of Ostracoda in the above beach in lower Yorktown just above bed of Isognomen in vicinity of Sapelo Island, Georgia, Rept. 2 in Kesling, R. V., St. Marys Formation. Sample collected by Warren Blow. and others, Four reports of ostracod investigations: Ann Arbor, Mich., Univ. Michigan Press, p. 57-136. Locality 14.. Left (north) bank of James River at Camp Gardner, Julia, 1943, Mollusca from the Miocene and lower Plio­ Wallace Military Reservation, James City County, Va.; see U.S. cene of Virginia and North Carolina: U.S. Geol. Survey Prof. Geological Survey Hog Island 7j^-minute quadrangle map, Paper 199-A, 178 p. 1965. The sample (42, USGS 24912) from this locality was from Gibson, T. G., 1967, Stratigraphy and paleoenvironment of the a slightly glauconitic gray clayey sand matrix adhering to mol­ phosphatic Miocene strata of North Carolina: Geol. Soc. lusks in the S. F. Blake collection of the U.S. National Museum. America Bull., v. 78, no. 5, p. 631-650. The exact stratigraphic and geographic location are unknown; Hazel, J. E., 1970, Binary coefficients and clustering in biostra­ the lithology is similar to that of the lower beds of the York- tigraphy: Geol. Soc. America Bull., v. 81, no. 11, p. 3237-3252. town at nearby Carters Grove described by Malkin (1953, Johnson, G. H., 1969, Guidebook to the geology of the York- p. 763). James Peninsula and south bank of the James River: College of William and Mary Dept. Geology Guidebook no. 1, pre­ Locality 15. Campus of the College of William and Mary, pared for Tenth Annual Field Conference of the Atlantic Williamsburg, Va.; outcrop is at southeastern face of small knoll Coastal Plain Geol. Assoc., 33 p. REFERENCES 13

MacNeil, F. S., 1938, Species and genera of Tertiary Noetinae: eastern Virginia: Science, v. 140, no. 3570, p. 979-983. U.S. Geol. Survey Prof. Paper 189-A, 50 p. Puri, H. S., 1953, Contribution to the study of the Miocene of the McLean, J. D., 1956, The Foraminifera of the Yorktown formation Florida panhandle; Part 3, Ostracoda; Florida Geol. Survey in the York-James Peninsula of Virginia, with notes on the Bull. 36, p. 217-345 [1954]. associated mollusks: Bull. Am. Paleontology, v. 36, no. 160, Puri, H. S. and Vernon, R. O., 1964, Summary of the geology of p. 255-394. Florida and a guidebook to the classic exposures: Florida 1957, The Ostracoda of the Yorktown formation in the Geol. Survey Spec. Pub. No. 5 (revised), 312 p. York-James Peninsula of Virginia: Bull. Am. Paleontology, Sandberg, Philip, 1964a, The ostracod genus Cyprideis in the v. 38, no. 167, p. 57-103. Americas: Stockholm Contr. Geology, v. 12, 178 p. -1966, Miocene and Pleistocene Foraminifera and Ostracoda 1964b, Notes on some Tertiary and Recent brackish-water of southeastern Virginia Pt. 1, Text; Pt. 2, Taxonomy and Ostracoda: Sta. Zool. Napoli, Pub. v. 33, Supp., p. 496-514. fossil plates: Virginia Div. Mineral Resources Rept. Inv. 9; Pt. Spencer, R. S., and Rogers, W. S., 1969, The Miocene-Pleistocene 1, 79 p.; Pt. 2, 123 p. unconformity in Norfolk County, Virginia: Virginia Jour. Malkin, D. S., 1953, Biostratigraphic study of Miocene Ostracoda Sci., v. 20, no. 1, p. 19-21. of New Jersey, Maryland, and Virginia: Jour. Paleontology, Swain, F. M., 1951, Ostracoda from wells in North Carolina; pt. 1, v. 27, no. 6, p. 761-799. Cenozoic Ostracoda: U.S. Geol. Survey Prof. Paper 234-A, Morkhoven, F. P. C., 1963, Post-Paleozoic Ostracoda, their mor­ 58 p. phology, taxonomy, and economic use: Amsterdam, Elsevier, Ulrich, E. O., and Bassler, R. S., 1904, Systematic paleontology, v. 2 (general descriptions), 478 p. Miocene Arthropoda: Maryland Geol. Survey, Miocene [vol­ Oaks, R. Q., 1964, Post-Miocene stratigraphy and morphology, ume], p. 98-130. Outer Coastal Plain, southeastern Virginia: U.S. Office of Zhadin, V. I., 1952, Mollyuski presnykh i solonovatykh vod SSSR: Moskva-Leningrad, Izdatl'stvo Akademii Nauk SSSR, 376 p. Naval Research, Geography Branch, Tech. rept. 5, Task 1965, Mollusks of fresh and brackish waters of the U.S.S.R.: Order NR 388-064, 240 p. (available from Clearinghouse for Israel Program for Scientific Translations, 368 p. (available Federal Scientific and Technical Information, U.S. Dept. through the Clearinghouse for Federal Scientific and Tech­ Commerce, Springfield, Va. 22151). nical Information, U.S. Dept. Commerce, Springfield, Va. Oaks, R. Q., and Coch, N. K., 1963, Pleistocene sea levels, south­ 22151.)

U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 415-720