J. Nannoplankton Res. 32 (1), 2011, pp1-28 © 2011 International Nannoplankton Association
ISSN 1210-8049 Printed by Harcourt Colour Print, Swansea, UK

1Paleogene Calcareous Nannofossils of the South Dover
Bridge core, Southern Maryland (USA)Jean M. Self-Trail

U.S. Geological Survey, 926A National Center, Reston, Virginia, 20192: jstrail@usgs.gov
Manuscript received June 9th, 2010; revised manuscript accepted 22th November, 2010.

Abstract A well-preserved Paleogene calcareous nannofossil assemblage taken from cored material of the subsurface coastal plain of eastern Maryland, USA, is documented and described herein. Taxonomic and biostratigraphic
analyses of 120 m of hemipelagic clays and silts have resulted in the identification of a nearly complete Paleocene/
Eocene section. A lithologic break is identified across the Marlboro Clay/Nanjemoy Formation boundary and thecorresponding upper part of Zone NP10 is missing (from 54.37-53.61 Ma), representing a hiatus of 760,000 years.
Assemblages are compared to other documented hemipelagic sequences worldwide, and biostratratigraphic taxon
ranges are adjusted accordingly. Five new species (Braarudosphaera sequela, Daktylethra basilica, Ellipsolithus aubryae, Hornibrookina weimerae, Pemma bybelliae) and one new combination (Neochiastozygus tenansa) are recorded.
Keywords Paleocene, Eocene, calcareous nannofossils, taxonomy
Division of Mineral Resources as an aid to surficial andgeologic mapping. Analyses of cored material included
calcareous nannofossil biostratigraphy and taxonomyof the Paleogene section (Gibson et al., 1980; Bybell &Gibson, 1991; Bybell & Gibson, 1994; Gibson & Bybell,1994).
Recent drilling of the South Dover Bridge (SDB)
core by the USGS for the Atlantic Watershed Project
has resulted in the recovery of a Paleogene section that
contains exceptionally well-preserved calcareous nannofossils (Figure 1). The corehole reached a total depth of
214.6 m, and bottomed out in the glauconite-rich, quartz
sand of the Aquia Formation (Figure 2). The age of the
Aquia is late Paleocene (calcareous nannofossil Zones
NP 5-NP 9a) but only the uppermost Aquia (Zone NP 9a)
was reached at SDB. The Aquia Formation is conformably overlain by a relatively thick (~15.2 m) section of
the Marlboro Clay, which consists of finely micaceousand faintly, but persistently,
laminated clayey silt to silty
clay. Scattered shell fragments, foraminifera, andostracodes are present inminor amounts. Previous
palynomorph and calcareous nannofossil data (Gibson et al., 1980; Bybell &Gibson, 1991) suggested
that the Marlboro Claywas late Paleocene to early
Eocene in age. This age iscorroborated in the SDB
core, where a nearly complete
Paleocene/Eocene
Thermal Maximum (PETM)
section and carbon isotope excursion (CIE) havebeen identified (Willard etal., 2009; Self-Trail et al.,Figure 1. Map showing the location of the South Dover Bridge core, southeastern Maryland, USA.
2010). The basal Marlboro
1. Introduction
Paleogene sediments of the Maryland Coastal Plain andthe surrounding region have been identified and documented from river bluffs and creek beds for over one hundred years (Clark, 1895). Exposures along the Potomac
River, Aquia Creek, Popes Creek, and the Pamunkey River
allowed for easy access to sediments that were otherwise
unattainable until the advent of modern coring practices.
These bluffs have been variously analyzed for lithologic
content (Clark & Martin, 1901), for stratigraphic purposes(Ward, 1985), for microfossil content (Nogan, 1964;
Bybell & Gibson, 1991), for mapping (Rader & Evans,
1993), and as teaching guides (Gibson & Bybell, 1991).
Starting in the 1980s (as a means of obtaining fresh sediment for analysis and for providing information on subsurface geologic and hydrogeologic frameworks), a seriesof coreholes were drilled by the U.S. Geological Survey(USGS), the Maryland Geologic Survey, and the Virginia

Nearby cities are designated by open circles.

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Jean M. Self-Trail

Figure 2. Stratigraphic column of the Paleocene/Eocene boundary in theSouth Dover Bridge core. The carbon isotope excursion (CIE) marks the
Paleocene/Eocene boundary and an unconformity marks the end of the
Paleocene Eocene Thermal Maximum (PETM). The absence of Rhomboaster contortus and Rhomboaster digitalis suggests that Zone NP10
is truncated and that upper Zone NP 10 is missing at this site. A zone ofpossible drilling mud injection is present at the Marlboro Clay/Nanjemoy Formation contact.

Clay is assigned to calcareous nannofossil Zone NP9a,which includes a 1.8 m thick dissolution zone. The Marlboro Clay is unconformably overlain by the Nanjemoy
Formation, a silty, sandy clay that grades gradually up
into a glauconite-rich clayey sand. The contact between
the Marlboro and the Nanjemoy is intensely burrowed.
Previous dinoflagellate and calcareous nannofossil data
place the Nanjemoy in calcareous nannofossil Zones NP
10 through NP 13 (early Eocene in age) (Gibson & Bybell,
1995; Goodman, 1991). An unnamed unit of alternating
sandy clay and clayey sand, rich in benthic foraminifera,
overlies the Nanjemoy Formation, and is approximately
39 m thick. This unit has previously been identified
from clasts in the Exmore Formation of the Chesapeake
Bay impact structure (Frederiksen et al., 2005), but has
no known surface exposure. It is middle Eocene (upper
Zone NP14 to NP16) in age. The overlying Piney Point
Formation consists of a coarse to fine glauconitic quartz
sand (Figure 3). Ward (1985) placed the Piney Point in the
middle Eocene based on the foraminifera and ostracodedata of Brown et al., (1972), and DiMarzio (1984) placed

the Piney Point of Virginia into calcareous nannofossil Zone NP16, an
age that is corroborated herein.
The calcareous nannofossil
assemblages discussed in this paper
most closely resemble the material
documented by Bown (2005), Bown
& Dunkley Jones (2006) and Bown
& Pearson (2009) from Tanzania,
assemblages documented by Gibbs
et al., (2006) from the Wilson Lakecore, New Jersey, and assemblages
from various New Jersey cores
identified by Bybell & Self-Trail(1995). All are representative ofshelfal depositional environments.
Semi-quantitative analyses serve tohighlight the abundant and diverse
assemblages of calcareous nannofossils that are present in the SDB
core. Post-drilling diagenesis andloss of the calcareous nannofossil assemblages was prevented by
the rapidity of sampling following the coring process. Samples
extracted from outcrop samples andolder cores of the Marlboro Clay
are typically barren of, or containvery sparse, calcareous nannofossils(Bybell & Gibson, 1991; Bybell &Gibson, 1994; Gibson & Bybell, 1994). However, samples obtained from the SDB core immediately after coring contain common to abundant calcareous nannofossil
assemblages throughout the Marlboro Clay.
This paper documents the well-preserved Paleogene
calcareous nannofossil assemblages of the SDB core.
The taxonomy presented herein provides a review ofPaleogene taxa, with special emphasis on documentationof new species identified by Bown (2005) and Bown &Dunkley Jones (2006) from Tanzania, with the intent ofrefining biostratigraphic ranges. Five new taxa are identified and described, and one new combination is recorded.
2. Methods and Materials
The SDB corehole is located in Talbot County, Maryland,at N38.74704 latitude and W76.00697 longitude (Figure 1). Core was recovered in October, 2007, and a total
depth of 214.6 m was attained. The Paleogene section inthis core comprises approximately 120 m of sands, silts,
and clays. The site was cored using a Mobile B-61 drill
rig running a wireline coring system. Cores are archived
at the USGS in Reston, VA.
Sediment to be examined for calcareous nannofossil
content was extracted from the central portion of freshly
broken core in order to avoid contamination. Slides
were prepared at the drillsite within one day of coring,using the double slurry smear slide method of Blair &Watkins (2009) in order to avoid the rapid dissolutionthat is common in organic-rich sediments of the Atlan-

Paleogene Calcareous Nannofossils of the South Dover Bridge core3(FO) of D. araneus is oldest, followed in quick
succession by the FO’s of D. anartios, R. spineus, and R. bramlettei, and rarely do all eventsoccur in the same studied section. Therefore,
the NP9a/b boundary is identified in SDB by
the FO of D. araneus.
3. Results
Calcareous nannofossils indicate that Paleogene
sediments between 210 m and 102.2 m in the
SDB core are late Paleocene to middle Eocene
in age. A lithologic change from the sands of the
Nanjemoy Formation below to the silts of theoverlying Calvert Formation reflects a hiatus
spanning the late Eocene to earliest Miocene.
This is corroborated by a change in the calcareous nannofossil assemblages. A minor hiatus(<760,000 yrs) is indicated by the burrowed
contact between the Marlboro Clay and theoverlying Nanjemoy Formation, and this coincides with an increase in calcareous nannofossil
first and last occurrences (LO) at the same interval. The upper part of Zone NP10 is missing
at this contact, as evidenced by the absence ofthe species Rhomboaster contortus and R. digitalis (Figure 2). Calcareous nannofossils are
predominantly common to abundant in both the
Marlboro and Nanjemoy, and show moderate tovery good preservation (Tables 2-4).
Although species richness from the SDB
core is not on par with the diversity recorded
by Bown (2005) and Bown & Pearson (2009)
from Tanzania, averaging only approximately

Figure 3. Stratigraphic column of the early to middle Eocene section of
the South Dover Bridge core. The unnamed middle Eocene unit is ageequivalent to the Shark River Formation of New Jersey.

tic Coastal Plain (Self-Trail & Seefelt, 2005). Cover slips
were affixed to slides using Norland Optical Adhesive 61.
More closely spaced samples were later collected acrossthe PETM in the calcareous nannofossil laboratory in Reston, VA, in order to augment the initial sample set. Samples were analyzed using a Zeiss Axioplan 2 microscopeat x1250 magnification in cross-polarized light (XPL);
phase-contrast (PC) was used as an additional method for
identifying discoasters. Table 1 shows each sample with
its unique number, depth, calcareous nannofossil zone,
and age. Identification of biozones was based primarilyon the Martini (1971) zonation and augmented by the bioevents identified by Okada & Bukry (1980). According
to Aubry (1999) and Aubry et al. (2000), identification of
the NP9a/b boundary is based on the simultaneous lowest
occurrences of Rhomboaster calcitrapa, R. spineus, Discoaster anartios, and D. araneus. However, analysis ofmultiple Atlantic Coastal Plain sections (Bybell and SelfTrail, unpub. data, 2010) suggests that the first occurrence

Table 1. Sample depth, number and age for illustrated calcareous nannofossil specimens from the South Dover Bridge core, Maryland. Calcareous nannofossil zones from Martini (1971).

4
Table 2. Calcareous nannofossil
occurrences in the South Dover
Bridge core, Maryland, for the
Paleocene and early Eocene. Species abundance: A, abundant or 1
per every field of view (FOV); C,
common or 2 per 1-10 FOV’s; F,
frequent or 1 per 11-100 FOV’s; R,
rare or 1 per >100 FOV’s. Slideabundance: A, abundant or >10
specimens per FOV; C, commonor 1-10 specimens per FOV; F,
frequent or 1 specimen per 1-10
FOV’s; R, rare or 1 specimen per
11-100 FOV’s; B, barren of calcareous nannofossils. Preservation:
VG, very good; G, good; M, moderate; P, poor. Other symbols: rw,
reworked specimen; ct, contamination from higher in the core; ?,questionable occurrence. Shaded
area indicates dissolution interval
at the base of the Eocene.

Jean M. Self-Trail

Paleogene Calcareous Nannofossils of the South Dover Bridge core

5

Table 2 (continued). Calcareous
nannofossil occurrences in theSouth Dover Bridge core, Maryland, for the Paleocene and early
Eocene. Species abundance: A,abundant or 1 per every field ofview (FOV); C, common or 2 per
1-10 FOV’s; F, frequent or 1 per
11-100 FOV’s; R, rare or 1 per>100 FOV’s. Slide abundance:
A, abundant or >10 specimens
per FOV; C, common or 1-10
specimens per FOV; F, frequentor 1 specimen per 1-10 FOV’s;
R, rare or 1 specimen per 11-100
FOV’s; B, barren of calcareous
nannofossils. Preservation: VG,
very good; G, good; M, moderate; P, poor. Other symbols: rw,
reworked specimen; ct, contamination from higher in the core; ?,questionable occurrence. Shaded
area indicates dissolution interval
at the base of the Eocene.

6Jean M. Self-Trail

Table 3. Calcareous nannofossil occurrences in the South
Dover Bridge core, Maryland,
for the early Eocene. Species abundance: A, abundantor 1 per every field of view(FOV); C, common or 2 per
1-10 FOV’s; F, frequent or 1
per 11-100 FOV’s; R, rare or 1
per >100 FOV’s. Slide abundance: A, abundant or >10
specimens per FOV; C, common or 1-10 specimens per
FOV. Preservation: G, good;M, moderate. Other symbols:
rw, reworked specimen; ?,questionable occurrence.

Paleogene Calcareous Nannofossils of the South Dover Bridge core

7

Table 4. Calcareous nannofossil occurrences in theSouth Dover Bridge core,
Maryland, for the middle
Eocene. Species abundance:
A, abundant or 1 per field ofview (FOV); C, commonor 1 per 1-10 FOV’s; F,
frequent or 1 per 11-100
FOV’s; R, rare or 1 per >100
FOV’s. Slide abundance: A,abundant or >10 specimens
per FOV; C, common or
1-10 specimens per FOV.
Preservation: VG, very
good; G, good; M, moderate.
Other symbols: ?, questionable occurrence.

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Jean M. Self-Trail

35 species per sample, abundances of individual specimens in the SDB core are much higher than in the Tanzania material, and many species occur as frequent to common (one specimen per 11-100 fields of view (FOV) to
1 specimen per 2-10 FOV, respectively) throughout theirrange.
3.1.1. The Paleocene/Eocene Boundary
Calcareous nannofossil biostratigraphy, coupled with a
gradual, rather than sharp, lithologic change at the Aquia/
Marlboro Clay contact and a well-defined CIE, shows that
the Paleocene/Eocene boundary in the SDB core is complete. The PETM hyperthermal event is documented in the
SDB core by the presence of calcareous nannofossil excursion taxa (D. anartios, D. araneus, Rhomboaster spp., andC. bownii), an increase in the abundance of the dinoflagellate species Apectodineum augustum, a fern spike, and adissolution interval (Willard et al., 2009; Self-Trail et al.,2010). This event and the identification of restricted taxa
are documented from numerous Paleocene/Eocene boundary sites in both shallow and deep-sea settings (Kahn &Aubry, 2004; Lourens et al., 2005; Raffi et al., 2005; Gibbs
et al., 2006; Jiang & Wise, 2006; Sluijs & Brinkhuis, 2009).
Missing section at the Marlboro Clay/Nanjemoy Formation contact has removed the top of the PETM interval,
as well as evidence for additional hyperthermals such as
the Eocene Thermal Maximum 2 (ETM2) at approximately 53.7 Ma and the H2 event (at approximately 53.3
Ma; Stap et al., 2010). These transient events ushered
in a period of extreme global warmth, the Early Eocene
Climatic Optimum (EECO), which lasted from approximately 51-53 million years ago (Zachos et al., 2008).
Evidence for the EECO should be present in the Nanjemoy Formation of the SDB core and therefore this sectionof the core requires additional work.
3.1.2. Braarudosphaeraceae
Analyses of fossil and modern pentalith assemblages suggest that Braarudosphaera and some Micrantholithus
species thrive in nearshore hyposaline conditions influenced by increased nutrients (Bukry, 1974; Street and
Bown, 2000), although some evidence suggests that they
could also flourish in areas of upwelling of cold, nutrient-rich, low salinity water (Peleo-Alampay et al., 1999;
Bartol et al., 2008). During the early to middle Eocene,
rapid diversification and speciation of Pemma, Micrantholithus, and Braarudosphaeara occurred, and Eocene
representatives of this family are present in hemipelagicand shelfal settings worldwide (Bybell, 1975).
Although the paleoceanographic and paleobiogeographic conditions at SDB seem favorable for pentalith
production and preservation, including location in a shelfenvironment, high terrigenous input, and probable hyposaline conditions, the diversity of pentaliths in SDB is relatively low (two species of Pemma, three species of Micrantholithus, and two species of Braarudosphaera). For
comparison, Bown (2005) recorded 18 species of pentaliths
from Tanzania. The difference in pentalith diversity may
reflect different sedimentary conditions. The majority ofpreviously described sections, whether dominated by terrigenous sediments (e.g. Svabenicka, 1999), clays andmarls (Bybell, 1975; Bartol et al., 2008), mudstones (Bown,
2005) or deep-ocean chalks (Peleo-Alamay et al., 1999), arepredominantly fine-grained. However, sediments from theSDB core are somewhat coarser grained, containing quartzrich to glauconite-rich sand or sandy silt, especially in the
Aquia Formation. Pentaliths are more abundant in the SDB
core in the fine-grained Marlboro Clay and in the basal
Nanjemoy Formation, which is also clay rich. The coarser
grained sediments of the Aquia Formation are correlativewith low planktic/benthic (P/B) ratios (Willard et al., 2009),
indicating inner to middle neritic water depths, and suggestthat water depth played a role in pentalith diversity.
3.1.3. Coccolithaceae
Previous work has suggested that the genus Chiasmolithus was typically restricted to cooler or more temperate
regimes (Bukry, 1973; Wei & Wise, 1992; Persico & Villa,2004), and analysis of sediments from the Atlantic Coastal
Plain supports this interpretation. In general, Chiasmolithus marker species are sporadic or absent from sediments
south of Cape Hatteras (Self-Trail, unpubl. data, 2010;
Bybell, unpubl. data, 2010), but become more abundantand consistent north of Cape Hatteras, NC (Table 2-4).
Nine Chiasmolithus species are consistently present from
SDB and are rare to abundant in occurrence. Diversity ofchiasmoliths in SDB is lowest during the Paleocene, but
rapidly increases into the middle Eocene.
3.1.4. Discoasteraceae
Discoasters were typically at their most abundant in oligotrophic open-ocean, warm-water environments (Bukry,
1973; Aubry, 1992). The middle- to outer nertic setting of
the SDB core was not conducive to discoaster propagation, and thus their diversity and abundance in the SDB
core are relatively low when compared to open-ocean
sites. Twenty-seven species were identified, with diversity being lowest in the late Paleocene and increasing to
its greatest amounts in the early Eocene, during the CIE(Self-Trail et al., 2010). Discoaster diversity remained
fairly stable throughout the early and middle Eocene.
3.1.5. Prinsiaceae
Specimens of the genus Toweius dominate the calcareous
nannofossil assemblage from the late Paleocene throughthe early Eocene, becoming less diverse and less abundantin lower middle Eocene sediments.
3.1.6. Rhabdospheraceae
Abundant and diverse rhabdoliths are recorded from thesediments of the SDB core. Although Perch-Nielsen(1985) suggested a shelfal habitat for fossil rhabdoliths,
Bown (2005) pointed out that extant species are found inboth oceanic and shallow-marine conditions and suggested
that their paucity in many fossil assemblages may be a
result of their low preservation potential. Previous work by
Bybell & Gibson (1994) and Gibson & Bybell (1994) fromcores in Virginia and Maryland documented only minor
assemblages of rhabdoliths from these regions.

Paleogene Calcareous Nannofossils of the South Dover Bridge core

A total of seventeen species of rhabdoliths are documented from SDB, including seven that have only beenpreviously reported from Tanzania. Diversity increases
from nine species in the early Eocene to twelve in the
middle Eocene, with representatives of the informal
Blackites perlongus group being the most common. Only
two species (B. herculesii and B. truncatus) are common
in the early Eocene.
Although Bown & Pearson (2009) record the presenceof rhabdoliths from upper Paleocene (Zone NP 9a) sediments in Tanzania, none were found in this interval in the
SDB core. The absence of rhabdoliths from cored material of Paleocene age across the Atlantic Coastal Plain,including sediments from Georgia, South Carolina, North
Carolina, Virginia, Maryland and New Jersey (Self-Trail,
unpubl. data, 2010; Bybell, unpubl. data, 2010), suggeststhat fossil rhabdoliths were responding to as yet unidentified environmental controls.
4. Systematic Paleontology
A comprehensive taxonomic review of calcareous nannofossils identified from the SDB core follows below. All illustrated taxa are included, along with short descriptions of thosespecies only recently identified or rarely illustrated. Descriptions are also included for new taxa, problematic taxa, andthose taxa requiring clarification. The classification systemsof Young et al. (2003) and Young & Bown (1997) are usedherein. All images are at the same magnification (x2000).
Type material and digital images are stored in the calcareous
nannofossil laboratory at the USGS National Center, Reston,
VA. Calcareous nannofossil occurrence data from the SDB
core are recorded in Tables 2-4 and comparison of occurrence data with other published sections is noted in the text.
4.1. Placolith coccoliths
Order ISOCHRYSIDALES Pascher, 1910
Family PRINSIACEAE Hay & Mohler, 1967 emend.
Young & Bown, 1997
Girgisia gammation(Bramlette & Sullivan, 1961) Varol, 1989cPl. 1, fig 8.
A circular form placed in the genus Girgisia, G. gammation is characterized by an indistinct proximal shield covered by a distal shield of almost the same diameter witha closed central area. The central area is characterized
by a strongly birefringent extinction cross in the shapeof a swastika. Perch-Nielsen (1985) recorded this species from NP 11-NP 16. Girgisia gammation is rare tofrequent in lower to upper Eocene sediments of SDB.
Occurrence: NP 11-upper NP 14.
Hornibrookina arca Bybell & Self-Trail, 1995
Pl. 1, figs 16-18.
A convexly arched species of Hornibrookina with a wide
central area filled with transverse laths and a longitudinalbar. It has only been described from shelfal sequences(Bybell & Self-Trail, 1995; Bown, 2005; Gibbs et al.,2006). It occurs in common to abundant amounts in SDB

9(Table 2), and up to common amounts in the Wilson Lakecore, NJ (Gibbs et al., 2006), just prior to the onset of theCIE. Occurrence: NP 9a-NP 10.
Hornibrookina weimerae sp. nov.
Pl. 1, figs 19-21.
Derivation of name: After the late Lisa Weimer, a graduate student in micropaleontology and physical science
technician for the USGS. Diagnosis: Small species ofHornibrookina with somewhat rounded ends and a narrow central area filled by a central longitudinal bar. Individual transverse laths are impossible to discern withthe light microscope. The proximal shield is relatively
bright in XPL. Differentiation: Hornibrookina weimerae
most closely resembles H. teuriensis in being elongate
oval with a relatively bright distal shield. However, it ismuch smaller in lengthand diameter, with a narrower central area (Table
5). Dimensions: L =2.0-2.6 µm; W = 1.2-1.7µm. Holotype: Pl. 1, fig.
21. Paratype: Pl. 1, fig.
20.Type locality: SDB
core, Talbot County,
MD (USA). Type level:
Upper Paleocene, Sample
Table 5. Length and width mea- N12496, 207.6m (ZonesurementsforHornibrookina NP 9a). Occurrence:
weimerae specimens.
NP 9a.
Toweius callosus Perch-Nielsen, 1971
Pl. 1, figs 1-2.
Toweius eminens (Bramlette & Sullivan, 1961)
Gartner, 1971 var. eminens Bybell & Self-Trail, 1995
Pl. 1, figs 3-4.
The taxonomy of Bybell & Self-Trail (1995) for Toweius
eminens var. eminens is followed herein; the two varietiesof T. eminens are distinguished based on the number ofpores in the central area. The last occurrence of T. eminens var. eminens in SDB is at the top of Zone NP 10.
Occurrence: NP 9a-NP 10.
Toweius eminens (Bramlette & Sullivan, 1961)
Gartner, 1971 var. tovae Perch-Nielsen, 1971
Pl. 1, figs 5-7.
The taxonomy of Bybell & Self-Trail (1995) for Toweius
eminens var. tovae is followed herein. Occurrence: NP
9a-NP 10.
Toweius? magnicrassus (Bukry, 1971) Romein, 1979
Pl. 1, figs 9-11.
Large, robust, elliptical species of Toweius with a brightcentral area in XPL. The proximal shield may have as
many as three rows of elements around the central area
(Plate 1, fig. 11). This species is identified based on its
large size and very bright birefringence in XPL. Bukry(1971) identified this species from the Discoaster lodoen-

10Jean M. Self-Trailsis zone (NP 12); it is identified in SDB from Zone NP
11 to mid-NP 12, where it is common. Its occurrence inthe uppermost two NP 10 samples is most likely due toburrowing across the unconformity between the Marlboro
Clay and the overlying Nanjemoy Formation. Occurrence: NP 11-NP 12.
Toweius occultatus (Locker, 1967) Perch-Nielsen, 1971
Pl. 1, fig 12.
Toweius pertusus (Sullivan, 1965) Romein, 1979
Pl. 1, fig 13.
Toweius serotinus Bybell & Self-Trail, 1995
Pl. 1, figs 14-15.
Family NOELAERHABDACEAE Jerkovic, 1979
emend. Young & Bown, 1997
Reticulofenestra dictyoda (Deflandre in Deflandre &Fert, 1954) Stradner in Stradner & Edwards, 1968
Pl. 1, fig 22.
Reticulofenestra umbilicus (Levin, 1965)
Martini & Ritzkowski, 1968
Pl. 1, fig 23.
Order COCCOSPHAERALES Haeckel, 1894 emend.
Young & Bown, 1997
Family COCCOLITHACEAE Poche, 1913 emend.
Young & Bown, 1997
Coccolithus mutatus (Perch-Nielsen, 1971) Bown, 2005
Pl. 1, fig 24.
Coccolithus pelagicus (Wallich, 1877) Schiller, 1930
Pl. 1, fig 25.
Coccolithus bownii Jiang & Wise, 2007
Pl. 1, figs 26-27. A subcircular placolith with a wide central
area which occupies almost half the diameter of the nannofossil. Jiang and Wise (2007) documented this species
from Zone NP 10 of the Demerara Rise, stating that it has
an acme event within the PETM interval. A similar acme
event is documented in Tanzania (Bown & Pearson, 2009)
and from SDB (Table 2). Occurrence: NP 9a-NP 10.
Ericsonia subpertusa Hay & Mohler, 1967
Pl. 1, figs 28. This species is distinguished from Coccolithus pelagicus by its more subcircular outline and by theraised, rather than recessed, outer edge of the inner collar.
Identification of heavily overgrown specimens of this species can be difficult. Bybell and Self-Trail (1995) document the presence of E. subpertusa into the early Eocene.
Occurrence: NP 9a-NP 16.
Camplyosphaera dela (Bramlette & Sullivan, 1961)
Hay & Mohler, 1967
Pl. 1, figs 29-30.

Camplyosphaera differta Bown, 2010
Pl. 1, fig 31.
A medium-sized nannofossil with a narrow central area
filled by two broad axial bars. This species of Camplyosphaera is longer and somewhat thin, and lacks the open
central area, of C. dela. It is documented from NP 9b-NP
10 by Bown (2005, 2010). Occurrence: NP 10.
Cruciplacolithus frequens(Perch-Nielsen, 1977) Romein, 1979
Pl. 1, figs 32-33.
Chiasmolithus bidens(Bramlette & Sullivan, 1961) Hay & Mohler, 1967
Pl. 1, figs 34-35.
Chiasmolithus grandis(Bramlette & Riedel, 1954) Hay, Mohler & Wade, 1966
Pl. 2, fig 1.
Chiasmolithus nitidus Perch-Nielsen, 1971
Pl. 2, fig 8.
A relatively small chiasmolith having a split cross that
almost entirely fills up the central area. This species issimilar to C. frequens, but can be distinguished based on
its smaller size, the split cross, and the lack of discernable
feet. Occurrence: NP 13-NP 16.
Clausicoccus fenestratus(Deflandre & Fert, 1954) Prins, 1979
Pl. 2, figs 9-10.
?Family CALCIDISCACEAE Young & Bown, 1997
Coronocyclus bramlettei(Hay & Towe, 1962) Bown, 2005
Pl. 2, figs 11-12.
Circular placolith having a narrow, bright inner cycle with
non-axial extinction lines and a dark, narrow outer cycle.
This species is similar to C. nitescens, but is smaller andnarrower in overall width of the cycles and lacks the serrated appearance of the distal rim in XPL. Occurrence:
NP 9a-NP 14.
Calcidiscus? bicircus Bown, 2005
Pl. 2, fig 13.
Circular to subcircular medium-sized placolith with abicyclic central rim and non-birefringent distal shield.
The central area is partially filled by a narrow, brighttube-cycle and can have a small, central opening. Similar
to Calcidiscus? parvicrucis, but lacking the central axial
cross. Bown (2005) recorded this species from NP 15a17. It is recorded at SDB in lower to mid-Eocene sediments. Late Eocene sediments are missing from this site.
Occurrence: NP 13-NP 16.
Calcidiscus? pacificanus (Bukry, 1971) Varol, 1989
Pl. 2, fig 16.

Paleogene Calcareous Nannofossils of the South Dover Bridge core

Calcidiscus? parvicrucis Bown, 2005
Pl. 2, figs 14-15.
Circular to semi-circular placoliths with a non-birefringent distal shield, and a small birefringent tube-cycle.
A small axial cross fills the central area and distinguishes this species from Calcidiscus? bicircus. Bown
(2005) recorded this species from lower Eocene sediments (Zones NP 10-11). It is recognized in Maryland
from upper Paleocene through mid-Eocene sediments,
although its sporadic occurrence in middle Eocene sediments may be due to reworking. This species is commonly frequent in abundance where it occurs, but gaps inits occurrence suggest that it may have been sensitive tochanging paleoenvironmental parameters. Occurrence:
NP 9a-NP 14, possibly NP 16.
4.1.1. Placolith coccoliths incertae sedis
Ellipsolithus anadoluensis Varol, 1989
Pl. 2, figs 17-20.
Inconspicuous Ellipsolithus species with a very brightinner tube cycle and a dark distal plate. A thin, non-birefringent central area structure can occasionally be distinguished, and faint scalloping on the inner rim in somespecimens is suggestive of a possible net. In his originaldescription, Varol (1989) states that the central structure
is similar to E. bollii, although this is not visible from thephotomicrographs. Bown (2005) reported the first occurrence of this species in Zone NP 9b in Tanzania, and Varol(1989) recorded its presence in NP 12. This biostratigraphic range is corroborated at SDB, where Ellipsolithus
anadoluensis is first recorded from Zone NP9a (Table 2)
and occurs sporadically throughout its range. Occurrence: NP 9a-NP 12.
Ellipsolithus distichus(Bramlette & Sullivan, 1961) Sullivan, 1964
Pl. 2, fig 5.
Ellipsolithus macellus(Bramlette & Sullivan, 1961) Sullivan, 1964
Pl. 2, figs 2, 6.
Ellipsolithus aubryae sp. nov.
Pl. 2, figs 3-4, 7.
Derivation of Name: Named in honour of Marie-Pierre
Aubry, who first recognized this species in sediments fromthe NJ Coastal Plain. Diagnosis: Large Ellipsolithus consisting of closely appressed proximal and distal shields anda wide central area that is 2x wider than the sum of the twoouter rims. The central area is covered by a net of variably
sized small to medium round pores that are somewhat randomly distributed in two loose rings. A thin longitudinal bar
bisects the central area. This species can be distinguishedfrom E. bollii by its larger pores and wider central areaand from E. distichus by the random placement of poresin the two rings in the central area. Remarks: Ellipsolithus aubryae was illustrated by Bybell & Self-Trail (1997,
Pl. 4, figs. 3-5) from DSDP Site 605 in the Atlantic Ocean

11

and has been observed
by Bybell (unpubl. data,2010) and Aubry (pers.
comm.,
2009)
fromCoastal Plain sediments of
Alabama, Virginia, Maryland, and New Jersey. It
is restricted to sedimentsof early Eocene age (NP10-NP 11). Dimensions: L= 10.4-13.6µm; W = 6.4Table 6. Length and width mea- 9.6µm (Table 6). Holosurements for Ellipsolithus aubryae
type: Pl. 2, fig. 4. Paraspecimens.
type: Pl. 2, fig. 7. Type
Locality: SDB core, Easton, MD (USA). Type level:
Early Eocene, Sample N12672, 187.1 m, (Zone NP 11).
Occurrence: NP 11.
Markalius apertus Perch-Nielsen, 1979
Pl. 5, figs 2-4.
Markalius inversus (Deflandre in Deflandre & Fert,
1954) Bramlette & Martini, 1964
Pl. 5, figs 5, 10.
4.2. Murolith coccoliths
Order EIFFELLITHALES Rood et al., 1971
Family CHIASTOZYGACEAE Rood et al., 1973
Placozygus sigmoides(Bramlette & Sullivan, 1961) Romein, 1979
Pl. 2, fig 21.
Order ZYGODISCALES Young & Bown, 1997
Family HELICOSPHAERACEAE Black, 1971
Helicosphaera bramlettei(Muller, 1970) Jafar & Martini, 1975
Pl. 2, figs 22-23.
An elliptical form with a wide central area, an opticallydistinct, slightly oblique central bridge and a terminal
flange folded relatively close to the body with a small
notch. The bridge in H. bramlettei is more oblique than
the transverse bridge seen in H. seminulum. This species
is rare in SDB (Table 4). Occurrence: NP 16.
Helicosphaera lophota(Bramlette & Sullivan, 1961) Locker, 1973
Pl. 2, figs 24-25.
A large, elliptical form with an oblique, optically distinct
bridge that spans the relatively wide central area at greaterthan 45°. The terminal flange is folded close to the body ofthe helicosphaere and has no terminal notch. This species
is relatively rare and sporadic in SDB, and is present onlyin middle Eocene sediments. Occurrence: NP 14-NP 15b.
Helicosphaera seminulum Bramlette & Sullivan, 1961
Pl. 2, figs 26-27.

12Jean M. Self-Trail

A large, elliptical to ovoid helicosphaere with an optically distinct, nearly vertical central bridge. The terminal
flange is folded close to the body and lacks a distinctivenotch. This species can be difficult to separate from H.
bramlettei, which overlaps in range in the middle Eocene(Perch-Nielsen, 1985). Occurrence: NP 12-NP 16.
Family PONTOSPHAERACEAE Lemmermann, 1908
Pontosphaera is used herein to describe species withmany small perforations in the basal plate or species withno discernable perforations in the basal plate. Transversopontis is distinguished from Pontosphaera by the presence of two large perforations in the basal plate. These
perforations can vary in size and it can sometimes be difficult to distinguish between the two genera. Specimens
having two large perforations along with smaller perforations in the central area are placed in the genus Pontosphaera.
Pontosphaera cf. P. clinosulcata Bown, 2005
Pl. 2, fig 30.
Medium-sized, elliptical coccolith with one row of perforations near the outer rim and an indistinct series of perforations in the central area. Two central, longitudinal slits
are inclined to near horizonal. This species differs from P.
clinosulcata in that it lacks the inclined furrows and elongate pores present in that species. Occurrence: NP 16.
Pontosphaera distincta(Bramlette & Sullivan, 1961) Roth & Thierstein, 1972
Pl. 2, fig 31.
Pontosphaera multipora(Kamptner, 1948 ex Deflandre, 1959) Roth, 1970
Pl. 2, figs 28-29.
Transversopontis ocellata(Bramlette & Sullivan, 1961) Locker, 1971
Pl. 2, fig 32.
Transversopontis cf. T. ocellata(Bramlette & Sullivan, 1961) Locker, 1971
Pl. 2, fig 33.
Medium to large-sized, elliptical coccolith with faint perforations in the basal plate and two large central, inclined
pores. This species differs from T. ocellata in the size andslight inclination of the central pores. Occurrence: NP
16.
Pontosphaera plana(Bramlette & Sullivan, 1961) Haq, 1971
Pl. 3, figs 1-2.
Simple, plain plate with little or no rim visible in XPL andtwo thin, indistinct slits oriented parallel to the long axis.
This species is present in sporadic occurrences from thelate Paleocene and into the middle Eocene. Occurrence:
NP 9a-NP 16.

Transversopontis pulcher (Deflandre in Deflandre &Fert, 1954) Perch-Neilsen, 1967
Pl. 3, figs 3-7.
Elliptical discoliths with a transverse bar aligned with theshort axis of the ellipse. The bar has a distinctive breakaligned with the long axis of the ellipse. Rim perforations
can sometimes be present, but are often lacking, possibly
due to dissolution. The species concept of Bybell & SelfTrail (1995) is followed herein and T. pulcher as figuredin this paper most likely combines Pontosphaera pulchra
and Pontosphaera exilis as illustrated by Bown (2005).
The FO of T. pulcher occurs just before the onset of the
CIE in the upper Aquia Formation of Maryland and is a
useful secondary marker for the PETM. Occurrence: NP
9a-NP 16.
Transversopontis pulcheroides(Sullivan, 1964) Baldi-Beke, 1971
Pl. 3, figs 9-10.
Medium sized discolith having a pronounced oblique,transverse bar and an outer rim pierced by faint tostrongly visible furrows and elongate pores. Occurrence:
NP 12-NP 16.
Transversopontis pulchriporus(Reinhardt, 1967) Sherwood, 1974
Pl. 3, figs 8, 11.
Small to medium sized discolith having an oblique, transverse bar and an outer rim pierced by circular pores. Similar to T. pulcheroides, but lacking the furrows that line
the outer rim. Occurrence: NP 16.
Pontosphaera punctosa(Bramlette & Sullivan, 1961) Perch-Nielsen, 1984
Pl. 3, figs 12-13.
Discolith having a thin rim with furrows and a wide central area covered by a perforate plate. Occurrence: NP
15-NP 16.
Transversopontis zigzag Roth & Hay in Hay et al., 1967
Pl. 3, figs 14-16.
Small discolith with a narrow rim and a transverse bar witha distinct kink, centrally located. Small pores can be present on the basal plate, and faint scalloping of the rim ispresent in some specimens. Occurrence: NP 14-NP 16.
Family ZYGODISCACEAE Hay & Mohler, 1967
Lophodolithus nascens Bramlette & Sullivan, 1961
Pl. 3, figs 17-18.
Zygodiscus herlyni Sullivan, 1964
Pl. 3, fig 19.
Zygodiscus sheldoniae Bown 2005
Pl. 3, figs. 20-21.
Medium-sized murolith with distinctive disjunct bar.
Occurs sporadically in the Aquia Formation, but never ingreat abundance. Bown (2005) reported the presence ofPaleogene Calcareous Nannofossils of the South Dover Bridge core

this species in late Paleocene Zone NP 9b from Tanzania. Its biostratigraphic range is extended herein. Occurrence: NP 9a.
Neochiastozygus junctus(Bramlette & Sullivan, 1961) Perch-Nielsen, 1971
Pl. 3, figs 22-23
Neochiastozygus tenansa(Deflandre in Deflandre & Fert, 1954) comb. nov.
Pl. 3, figs 24-29.
Basionym: Zygolithus tenansa Deflandre in Deflandre &Fert, 1954, p. 19, pl. 11, fig. 18-19; Annales de Paleontologie, 40: 115-176. Remarks: Elliptical coccolith with
two thin vertical walls and a central cross that is slightly
oblique to the major and minor axes. Previous illustrations
show only one strut along the long axis of the coccolith(Deflandre & Fert, 1954), giving this species a superficial
resemblance to species from Pontosphaera or Transversopontis. However, a slender, delicate strut along theminor axis is clearly visible in some specimens from theSDB core (Pl. 3, fig. 26, 27), although it is almost always
missing (Pl. 3, fig. 24, 25, 28, 29). The outer cycle is typically not visible in XPL.
Although this species was
originally described fromthe Oligocene, its small
size makes it easy to overlook in the microscopeand its delicate structure
probably makes it prone
to dissolution. Dimensions: L = 2.0-3.2 µm;
W = 1.2-2.4µm (Table 7).
Occurrence: NP 9a-NP
Table 7. Length and width measurements for Neochiastozygus ten- 11; SDB core. Oligocene
ansa specimens.
(Deflandre & Fert, 1954).
Neococcolithes protenus(Bramlette & Sullivan, 1961) Black, 1967
Pl. 4, figs 2-5.
This species has its FO in the Paleocene, and has an
X-shaped central cross with bars of slightly unequal lengthand a rounded elliptical outline. Occurrence: NP 9a-NP 14.
Neococcolithes minutus(Perch-Nielsen, 1967) Perch-Nielsen, 1971
Pl. 4, figs 8-10.
This species is present from the early Eocene, and is distinguished from N. protenus by its H-shaped central crossand by its more long elliptical outline and slightly pointed
ends. Occurrence: NP 10-NP 16.
Order SYRACOSPHAERALES Hay, 1977 emend.
Young et al., 2003
Family CALCIOSOLENIACEAE Kamptner, 1927
The taxonomy of Bown (2005) for the genus Calciosolenia is followed herein.

13

Calciosolenia alternans Bown & Dunkley Jones, 2006
Not figured. This species is documented only sporadicallyfrom middle Eocene sediments of the SDB core and its
range is concurrent with the findings of Bown and Dunkley
Jones (2006) from Tanzania. Occurrence: NP 16.
Calciosolenia aperta (Hay & Mohler, 1967) Bown, 2005
Pl. 3, figs 30-31.
The last occurrence datum of C. aperta is useful as a proxy
for the Paleocene/Eocene Boundary and for the beginning of
the CIE. Bybell & Self-Trail (1995) noted the concurrenceof the LO of C. aperta with the Vincentown/Manasquanformational boundary, now considered to be synonomouswith the PETM and the Aquia/Marlboro contact in the SDB
core (Kopp et al., 2009). Occurrence: NP 9a.
Calciosolenia fossilis (Deflandre in Deflandre & Fert,
1954) Bown in Kennedy et al., 2000
Pl. 3, fig 32.
Family RHABDOSPHAERACEAE Haeckel, 1894
Blackites cf. B. bullatus Bown, 2005
Pl. 3, fig 33.
A species of Blackites with a hollow, doubly inflated spine
and a relatively broad rim. Superficially resembles B. bullatus of Bown (2005; see his Pl. 22, fig. 8), but is characterized by a spine that has two bulges instead of one.
Occurrence: NP 14.
Blackites cf. clavus Bown, 2005
Pl. 3, figs 34-35.
A species of Blackites with a relatively short, tapering
spine and a broad rim cycle. The general morphology
is reminiscent of a traffic cone. Similar to B. clavus from
Zone NP10 in Tanzania. This species is identified fromonly one sample in the SDB core (N12412, 169.2 m) andis middle Eocene in age. Occurrence: NP 14.
Blackites creber (Deflandre in Deflandre & Fert, 1954)
Stradner & Edwards, 1968
Pl. 4, fig 26-27
Blackites dupuisii (Steurbaut, 1990) Bown, 2005
Pl. 4, fig 6.
Rhabdolith with a tapering, hollow stem and a distinct
collar that appears to consist of two or more cycles. This
species was originally described from Zone NP 11 (Steurbaut, 1990), but its range was extended by Bown (2005)
to include Zones NP 9b-NP15. Occurrence: NP 16.
Blackites fustis Bown, 2005
Pl. 4, fig 7.
A small, hollow-stemmed rhabdolith whose spine is parallel-sided near the base and flaring towards the top. A
small papilla is present on the distal end of the spine. This
species, as figured by Bown (2005), shows a great deal ofvariation in the shape of the spine. Blackites fustis is rarein SDB and was identified from only one early Eocene
sample. Occurrence: NP 12.

14Jean M. Self-Trail

Blackites gamai Bown, 2005
Pl. 4, fig 11.
A distinctive species of Blackites with a bullet-shaped,
broadly tapering spine and narrow, but distinct, collar. Occurs sparsely and sporadically in lower to middle
Eocene sediments of the SDB core. Its geologic range is
extended herein. Occurrence: NP 11-NP 16.
Blackites gladius (Locker, 1967) Varol, 1989
Pl. 4, figs 12-14
Blackites globosus Bown, 2005
Pl. 4, fig 15.
A species of Blackites having an inflated, hollow spinewith a narrow collar attached to a small basal cycle. It
is distinguished from B. morionum by its exaggerated,roundly inflated spine and its narrower collar. This species is very rare in the SDB core. Occurrence: NP 16.
Blackites herculesii(Stradner, 1969) Bybell & Self-Trail, 1997
Pl. 4, figs 16-19.
Rhabdoliths with a claviform spine that widens towards
the distal end. Spine displays outer serrated surface.
Bybell & Self-Trail (1997) recorded its presence in New
Jersey in Zone NP10 and Bown (2005) recorded its presence in Tanzania in NP9b/10-11 (early Eocene). Blackites
herculesii is present in SDB in lower Eocene sediments.
Occurrence: NP 10-NP 12.
Blackites inflatus(Bramlette & Sullivan, 1961) Kapellos & Schaub, 1973
Pl. 4, figs 21-23
Blackites morionum(Deflandre in Deflandre & Fert, 1954) Varol, 1989
Pl. 4, figs 20, 25.
Blackites rotundus Bown, 2005
Pl. 5, fig 1.
Rhabdolith with an inflated, hollow spine that is narrowat the base and quickly inflates to a rounded globe at its
distal end. Basal coccolith has a prominent collar. Bown
(2005) recorded B. rotundus from middle Eocene sediments of Tanzania (NP 15b-c), and the biostratigraphic
range of this species is extended slightly in this study.
Occurrence: NP 16.
Blackites spinosus(Deflandre & Fert, 1954) Hay & Towe, 1962
Pl. 4, figs 1, 24, 29.
This species is somewhat morphologically difficult to separate from B. tenuis using the light microscope (LM). In
well-preserved specimens, the attachment of the spine tothe base in B. tenuis is very abrupt and presents an angularappearance (Pl. 4, fig. 28), whereas the attachment of thespine to the base in B. spinosus is gradual (Pl. 4, fig. 29).
Occurrence: NP 12-NP 16.

Blackites? stilus Bown 2005
Pl. 4, fig 30.
A tapering rhabdolith having a central canal of variablewidth. This species is placed questionably in Blackites due to the lack of a clear basal plate. Observed andfigured specimens do not appear to be broken and it isassumed that the small or absent plate is real. Bown
(2005) recorded this species from the middle Eocene (NP14b/15a-15c) of Tanzania. Blackites? stilus is present
only sporadically from SDB in lower Eocene sediments
and its basal range is extended slightly in this study.
Occurrence: NP 13-NP 14.
Blackites tenuis(Bramlette & Sullivan, 1961)
Pl. 4, fig 28
Blackites truncatus(Bramlette & Sullivan, 1961) Varol, 1989
Pl. 5, figs 6-7
4.3. Holococcoliths
Family CALYPTROSPHAERACEAE
Boudreaux & Hay, 1967
Holodiscolithus geisenii Bown, 2005
Pl. 5, fig 9.
Small, elliptical coccolith with diagnostic gently curving
axial sutures along patches of higher birefringence. Overall birefringence is low, and the outer rim is dark in XPL.
Bown (2005) described this species from the lower Oligocene of Tanzania and recorded its range from the lower tomid-Eocene (NP 11-23). Self-Trail et al. (2009; supplemental material) reported the sporadic occurrence of H.
geisenii from the mid-Eocene Exmore Formation of the
Chesapeake Bay impact crater. It is present sporadicallyin SDB in rare abundances from middle to upper Eocene
sediments. Occurrence: NP 13-NP 16.
Holodiscolithus serus Bown, 2005
Not figured.
This small holococcolith is very rare in sediments from theSDB core and is recorded from only one sample (199.2m).
Its occurrence in lower Eocene sediments concurs with thefindings of Bown (2005). Occurrence: NP 10
Semihololithus biskayae Perch-Nielsen, 1971
Pl. 5, figs 8, 13-14.
Holococcoliths are comprised of a compact, solid, anddomed distal plate on a thick proximal plate. They are
most often seen in side view. Distal views show that thedome contains a central plug (Pl. 5, fig. 8). This species ispresent in SDB in the upper Paleocene Aquia Formationin frequent abundances and is very limited in its range.
Bown and Pearson (2009) recorded its presence in Tanzania from Zone NP 9a. Occurrence: NP 9a.
Semihololithus aff. S. biscayae Perch-Nielsen, 1971
Pl. 5, figs 11-12.

Paleogene Calcareous Nannofossils of the South Dover Bridge core

Similar in size and shape to S. biscayae, but basal plate is
crystallographically continuous with the dome and a small
central plug is visible in side view. Occurrence: NP 9a.
Semihololithus dimidius Bown, 2005
Not figured.
This small holococcolith is distinctive in side view, having a central cavity sectioned in half by a thin wall. It
is present in sediments from SDB in only two samples(190.0 m and 205.7 m) of late Paleocene and early Eocene
age. Bown (2005) recorded its presence from Zone NP
9b. Occurrence: NP 9a-NP 10.
Daktylethra basilica sp. nov.
Pl. 5, figs 15-20.
Derivation of name: From the Latin for a “colonnaded
house”, a reference to its resemblance to St. Peter’s Basilica
in Rome, Italy. Diagnosis: A cavate holococcolith, seen inside view, with a thick basal plate extending up to one-third
the height of the specimen and forming slight protruding
wings to the side, and a domed distal cover showing perforations. The basal plate and dome are crystallographicallycontinuous and bright at 45° in XPL (Pl. 5, fig. 16), darkening slightly when rotated to 0° (Pl. 5, fig. 17). The central
cavate area forms an almost perfect “O” (Pl. 5, fig. 15).
Differentiation: Daktylethra basilica differs from D. unitatus (Bown and Dunkley Jones 2006, also from Zone NP16) in having a thicker basal plate that extends away fromthe central dome and in having an almost perfectly circular
central cavity. Daktylethra unitatus has a subcircular central cavity that is somewhat flattened at its base and lacks
prominent basal colonnades. It differs from D. punctulata
in having prominent wings
and a well-defined cavate
central area. Dimensions:
H = 2.4-3.2µm; W = 2.84.4µm (Table 8). Holotype: Pl. 5, fig. 15. Paratype: Pl. 5, fig. 16 (figs.
17-18 same specimen).
Type locality: SDB core,
Easton, MD (USA). Typelevel: Middle Eocene,
Sample N12402, 139.0 m
Table 8. Height and width measurements for Daktylethra basilica (Zone NP 16). Occurrence: NP 16.
specimens.
Zygrhablithus bijugatus bijugatus(Deflandre in Deflandre & Fert, 1954) Deflandre, 1959
Pl. 5, figs 21-24
Zygrhablithus bijugatus (Deflandre in Deflandre & Fert,
1954) Deflandre, 1959 cornutus Bown, 2005
Pl. 5, figs 25-28.
Medium-sized holococcolith with a tall central spine anda basal process. Central spire has a narrow axial canaland tapers towards the distal end, which is decorated by
two small horns. Bown (2005) recorded this species fromlower Oligocene sediments of Tanzania (NP 23). Bybell

15(1975, Pl. 24, figs. 2, 3) figured Z. bijugatus cornutus frommiddle Eocene sediments of Little Stave Creek, AL, andGartner and Smith (1967; Pl. 8, figs. 1, 5a) figured specimens from the late Eocene of Louisiana. Zygrhablithus
bijugatus cornutus is documented from middle Eocene
sediments of the SDB core, thus extending its biostratigraphic range. Occurrence: NP 16.
Zygrhablithus bijugatus (Deflandre in Deflandre & Fert,
1954) Deflandre, 1959 nolfii Steurbaut, 1990
Pl. 5, figs 29-30.
Medium-sized holococcolith with shortened central spire,a wide axial canal, and a pronounced notch above thebasal plate. Occurs sporadically in the SDB core throughout its range. Occurrence: NP 10-NP 12.
4.4. Nannoliths
Family BRAARUDOSPHAERACEAE
Deflandre, 1947
Braarudosphaera bigelowii(Gran & Braarud, 1935) Deflandre, 1947
Pl. 5, figs 31-33
Braarudosphaera sequela sp. nov.
Pl. 5, figs 34-35
Derivation of name: From the Latin sequela, meaning“that which follows”, referring to its higher stratigraphic
position and younger age than Braarudosphaera hockwoldensis, which it resembles. Diagnosis: Large Braarudosphaera with protruding, diamond-shaped pentalithsegments. Similar to B. hockwoldensis, which was firstdescribed in the Lower Cretaceous Gault Clay (Black,1973). Bown (2005) tentatively used the name Br. cf. B.
hockwoldensis for specimens recorded from the Eocene/
Oligocene of Tanzania. However, the large stratigraphic gap
between B. hockwoldensis and B. sequela argues in favor of
iterative evolution and that they are two separate species.
Dimensions: H = 10.414.4µm; W = 9.6-12.0µm(Table 9). Holotype: Pl.
5, fig. 34. Paratype: Pl.
5, fig. 35. Type locality: SDB core, Easton,
MD (USA). Type level:
Table 9. Height and width mea- Lower Eocene, Sample
surements for Braarudosphaera N12488, 198.7 m (Zone
sequela specimens.
NP 10). Occurrence: NP
10-NP 11.
Micrantholithus astrum Bown, 2005
Pl. 6, figs 1-3.
A large nannolith with deeply indented sides and pointed
ray terminations. It is difficult to distinguish from M.
attenuatus, which is more angular and has thinner rays,and differs from M. vesper in having a more acute inner
ray angle and blunter ray terminations. This species israre in SDB. Occurrence: NP 12-NP 16.

16

Jean M. Self-Trail

Micrantholithus attenuatus Bramlette & Sullivan, 1961
Pl. 6, fig 4.
Occasional zones of abundant M. attenuatus pieces are
documented from the middle Eocene of SDB and a nearby
core in Cambridge, MD. Whole specimens are rarely documented. Occurrence: Upper NP 14-NP 15b.
Micrantholithus excelsus Bown, 2005
Not figured.
This nannolith is present in rare abundances in sedimentsof early Eocene age from only one sample (195.7 m) of
the SDB core. Bown (2005) documented this species fromthe early Eocene (NP 11) through early Oligocene (NP23). Its biostratigraphic range is extended herein. Occurrence: NP 10.
Pemma basquense basquense(Martini, 1959) Bybell & Gartner, 1972
Pl. 6, figs 5-6.
Pemma bybelliae sp. nov.
Pl. 6, figs 7-10.
Deriviation of name: Named in honor of Laurel M.
Bybell, a Cenozoic nannofossil paleontologist, in recognition of her early work on taxonomy and morphology of
the Pemma genus. Diagnosis: Large, circular Pemma thatexhibits a diagnostic thin base with peripheral crenulatededges. Central area consists of a layer of basal thickenings
superimposed on the base, resulting in a hazy appearanceof the outer edge of the nannolith and a central area more
highly birefringent than the edges. This species is similarin shape to P. rotundum, which lacks the thin base exhibitedby P. bybelliae. Pemma balium is the
only other described member of thisgenus to exhibit a thin base, and it iseasily distinguished from P. bybelliae
by its subcircular outline. Dimensions:
D = 7.5-13.5µm (Table 10). Holotype:
Pl. 6, fig. 7. Paratype: Pl. 6, fig. 9.
Type locality: SDB core, Easton, MD
Table 10. Diameter (USA). Type level: Middle Eocene,measurements
for Sample N12402, 139.0 m (Zone NP
Pemma
bybelliae
16). Occurrence: NP 16.
specimens.
Family DISCOASTERACEAE Tan, 1927
Discoaster anartios Bybell & Self-Trail, 1995
Pl. 6, figs 11-16.
A stellate, multi-rayed discoaster, exhibiting variable raylengths and angles between the rays, that is frequent tocommon in sediments of the PETM interval in the SDB
core. This species is commonly rare or absent in sedimentsof pelagic origin (i.e., Jiang & Wise, 2006; Mutterlose etal., 2007) and more abundant in sediments deposited in ashelf setting (i.e., Gibbs et al., 2006; Angori et al., 2007).
Typically, it is abundant if D. araneus is rare and vice versa.
In the SDB core, D. anartios has its FO at 200.5 m, at thesame interval that the first rare specimens of Rhomboasterspp. appear (Table 2). It is consistently present throughout

the lower PETM, but disappears from the section at 193.9m, coinciding with a change in bulk carbon isotope values
that is interpreted to represent the beginning of the PETM
recovery (Self-Trail et al., in prep). Occurrence: NP 10.
Discoaster araneus Bukry, 1971
Pl. 6, fig 17.
Stellate, 7-9 rayed discoaster having variable angles
between individual rays and often having variable raylengths. Distinguished from Discoaster anartios byfewer rays and by having 1/2 to 2/3 free ray length. Discoaster araneus is extremely rare in SDB sediments andis quite often overgrown. It was identified by Kahn &Aubry (2004) as being restricted to the PETM. In the
SDB core, this species is restricted to the basal PETM. Its
FO is at 201.9 m, slightly below the FO of D. anartios andRhomboaster spp. and its LO is at 194.8 m, just below the
LO of D. anartios. Occurrence: NP 9b-NP 10.
Discoaster barbadiensis Tan Sin Hok, 1927
Pl. 6, figs 18-20.
Discoaster deflandrei Bramlette & Riedel, 1954
Pl. 7, figs 15-16.
Discoaster distinctus Martini, 1958
Pl. 6, figs 21-24.
Distinctive stellate, six-rayed discoaster with nodes oneither side of the ray tip bifurcations. It is present for only
a short interval during the early to mid-Eocene of SDB.
Occurrence: NP 13-NP 14.
Discoaster falcatus Bramlette & Sullivan, 1961
Pl. 7, fig 1.
Discoaster gemmifer Stradner, 1961
Pl. 7, fig 17.
A discoaster with 8 bifurcating rays that displays no prominent central knob. The rays form an overlapping patternthat spirals dextrally and is distinctive of this species. D.
gemmifer is present in only one sample from SDB (166.1m). Occurrence: Upper NP 14.
Discoaster kuepperi Stradner, 1959
Pl. 7, figs 2-4, 8.
Discoaster lenticularis Bramlette & Sullivan, 1961
Pl. 7, figs 5-6, 9-10.
Discoaster lodoensis Bramlette & Riedel, 1954
Pl. 7, figs 7, 11-12.
Discoaster mediosus Bramlette & Sullivan, 1961
Pl. 7, figs 13-14.
Discoaster multiradiatus Bramlette & Riedel, 1954
Pl. 7, figs 21-24.
Discoaster salisburgensis Stradner, 1961
Pl. 7, fig 18.
Discoaster splendidus Martini, 1960
Pl. 7, figs 19-20.

Paleogene Calcareous Nannofossils of the South Dover Bridge core17

A multi-rayed discoaster having 9-12 rays with raisedouter ridges and depressed central areas. A broad, flatstem occupies 2/3 of the central area. Discoaster splendidus is present in the CIE interval in SDB in frequent torare amounts, and first occurs at the top of the dissolution
zone. Bybell & Self-Trail (1995) recorded its presencefrom Zones NP 8 to NP 9 in the New Jersey Coastal Plain.
Occurrence: NP 9a-NP 10.

Lithostromation simplex (Klumpp, 1953) Bybell, 1975
Pl. 8, figs 18-19.
A stellate nannofossil with numerous circular depressions,raised ridges, and short rays. This species is most often
prevalent in middle Eocene sediments, and can occur incommon abundances locally. It is consistently present in
the sediments of the unnamed unit in SDB. Occurrence:
NP 14-NP 16.

Discoaster sublodoensis Bramlette & Sullivan, 1961
Pl. 8, figs 1-2.
A medium-sized discoaster with 5 pointed rays withstraight sides. Smaller than D. lodoensis and lacking thedistinctive curving rays. Occurrence: NP14-NP15b.

Family RHOMBOASTERACEAE Bown, 2005

Family FASCICULITHACEAE Hay & Mohler, 1967
Fasciculithus involutus Bramlette & Sullivan, 1961
Pl. 8, figs 5-7.
Fasciculithus richardii Perch-Nielsen, 1971
Pl. 8, figs 8-10.
A robust, large fasciculith with a somewhat cubic outline,
columnar depressions, and a moderately tall cone. This
species is restricted to the late Paleocene Aquia Formationand the dissolution zone of SDB. Perch-Nielsen (1985)
recorded this species from Zone NP 9. Occurrence: NP 9a.

According to Bown (2005), the Rhomboasteraceae comprise two nannolith genera of differing, yet related, morphologies; rhombic (Rhomboaster) through triradiate (Tribrachiatus). Bybell & Self-Trail (1995) placed the genus
Tribrachiatus into synonomy with Rhomboaster, citing
similarity of construction as the reason and thus making
Tribrachiatus a junior synonym of Rhomboaster. Overa decade of research by this author has led to the conclusion that Tribrachiatus, as defined by Shamrai (1963) andwith T. orthostylus as the type species, is a valid genus,
although the author continues to place R. contortus intosynonomy with Rhomboaster, based on basic construction of the nannolith. The taxonomy of Bybell & SelfTrail (1995) is followed herein with regards to the Rhomboaster bramlettei/cuspis plexus.

Fasciculithus schaubii Hay & Mohler, 1967
Pl. 8, figs 11-12.

Rhomboaster bramlettei (Bronnimann & Stradner, 1960)
Bybell & Self-Trail, 1995
Pl. 8, figs 20-21.

Fasciculithus thomasii Perch-Nielsen, 1981
Pl. 8, figs 13-14.

Tribrachiatus orthostylus Shamrai, 1963
Pl. 8, figs 3-4.

Family HELIOLITHACEAE Hay & Mohler, 1967

Family SPHENOLITHACEAE Deflandre, 1952

Bomolithus supremus Bown & Dunkley-Jones, 2006
Pl. 8, figs 15-16.
Circular nannolith consisting of three distinct cycles. The
inner cycle shows high-order birefringence in XPL andhas a small central opening. The outermost cycle is darkin XPL, and consists of approximately 30 sinistrally curving elements. Bown & Dunkley-Jones (2006) recorded
its presence in Tanzania from upper Paleocene Zone NP
9. Bomolithus supremus is restricted to the PETM lower
Eocene Marlboro Clay in the SDB core. Occurrence:
NP 9a-lower NP10.

Sphenolithus anarrhopus Bukry & Bramlette, 1969
Pl. 8, figs 22-23, 26-7.

Family LITHOSTROMATIONACEAE
Deflandre, 1959
Lithostromation operosum(Deflandre in Deflandre & Fert, 1954) Bybell, 1975
Pl. 8, fig 17.
A nannofossil with numerous circular depressions andraised projections. This species appears to be restricted
to the middle Eocene. Lithostromation operosum occurs
only sporadically in the SDB core. Occurrence: NP 15bNP 16.

Sphenolithus furcatolithoides Locker, 1967
Pl. 8, figs 24, 28-29.
Small sphenolith having two long apical spines thatdiverge distally and are often overgrown. Specimens arebright in XPL at 0° and are dark and inconspicuous at
45°. Sphenolithus furcatolithoides is typically present in
middle Eocene sediments. Occurrence: NP 16.
Sphenolithus spiniger Bukry, 1971
Pl. 8, figs 25, 30-32.
A relatively small sphenolith with a modest apical spine
and a proximal shield approximately one-half to two-thirds
the height of the specimen. Occurrence: NP 14-NP 16.
4.5. Incertae sedis nannoliths
Leesella? sp.
Pl. 8, figs 33-34.
Leesella was first described by Bown & Dunkley Jones(2006) to document small nannoliths with a proximal

18Jean M. Self-Trail

basal disc and a tall trumpet shaped cone with an axial
canal. The specimen figured from SDB is smaller than L.
procera, with a wider axial canal and a less pronounced
trumpet shape. The basal disc is small, but prominent.
Bown & Dunkley Jones (2006) recorded L. procera fromthe middle Eocene (NP 16). Occurrence: NP 9a-NP 9b.
Acknowledgements
The author wishes to thank Laurel Bybell and Ellen Seefelt
for reviewing an early version of this manuscript. Taxonomic discussions with Paul Bown, Osman Varol, andLaurel Bybell greatly improved this paper. Photographic
assistance was provided by Colleen Durand and Gregory
Wandless provided the carbon isotope data. The thoughtful reviews of Paul Bown and Liam Gallagher greatly
improved the manuscript. Funding for this research wasprovided by the National Cooperative Geologic Mapping
Program (USGS).
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Paleogene Calcareous Nannofossils of the South Dover Bridge core

Plate 1
Placolith coccoliths

21

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Jean M. Self-Trail

Plate 2
Murolith coccolithus

Paleogene Calcareous Nannofossils of the South Dover Bridge core

Plate 3
Pontosphaeraceae; Zygodiscaceae; Calciosoleniaceae; Rhabdosphaeraceae

23

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Jean M. Self-Trail

Plate 4
Rhabdosphaeraceae; Zygodiscaceae

Paleogene Calcareous Nannofossils of the South Dover Bridge core

Plate 5
Rhabdosphaeraceae; Holococcoliths; Nannoliths

25

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Jean M. Self-Trail

Plate 6
Nannoliths: Braarudosphaeraceae, Discoasteraceae

Paleogene Calcareous Nannofossils of the South Dover Bridge core

Plate 7
Nannoliths: Discoasteraceae

27

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Jean M. Self-Trail

Plate 8Nannoliths