Nanjemoy Formation Research Articles

New bird remains from the early Eocene Nanjemoy Formation of Virginia (USA), including the first records of the Messelasturidae, Psittacopedidae, and Zygodactylidae from the Fisher/Sullivan site

ABSTRACT We report new avian remains from the early Eocene Nanjemoy Formation of the Fisher/Sullivan site in Virginia, USA. The fossil material includes the first records of the Messelasturidae, Psittacopedidae, and Zygodactylidae from the Nanjemoy Formation, with these taxa being widespread and fairly common in coeval North American and European sites. Psittacopedidae and Zygodactylidae are stem group representatives of the Passeriformes, and a tibiotarsus assigned to the Psittacopedidae is unusual in that it lacks a supratendinal bridge (this bridge is, however, also absent in the psittacopedid taxon Pumiliornis). We further report more material of the Charadriiformes and corroborate a previous tentative referral of a tarsometatarsus to the Parvicuculidae. It is noted that this latter bone is likewise very similar to the tarsometatarsus of the Fluvioviridavidae, which indicates close affinities between the two higher-level clades. Because of the comparatively small extent of the new avian material, it is remarkable that it includes a comparatively high number of fossils that represent previously unknown taxa. This supports the hypothesis that early Eocene avifaunas featured a high taxonomic diversity, but that higher-level clades showed low species richness. We hypothesise that this may indicate low rates of cladogenetic diversification in a rather homogenous paleoenvironment.

Early Eocene omomyid from the Nanjemoy Formation of Virginia: first fossil primate from the Atlantic Coastal Plain

ABSTRACT The first known primate fossil from the Atlantic Coastal Plain, a mandibular fragment representing the family Omomyidae, is described from the early Eocene Fisher/Sullivan Site in northeastern Virginia. The jaw, containing m1–m2, was found near the base of the Potapaco Member, Bed B, of the Nanjemoy Formation, indicating an early Ypresian age, ca. 54.5 Ma. As the specimen lacks diagnostic antemolar dentition, its precise identity cannot be confidently determined. However, its diminutive size and plesiomorphic molar morphology suggest that it represents a primitive omomyid. Comparison with a diversity of omomyids finds that nearly all omomyid genera are larger and/or derived in various features compared to the Nanjemoy specimen. Closest resemblances are to the primitive omomyids Steinius, Anemorhysis, Loveina, Melaneremia, and especially Teilhardina.

An Exceptionally Preserved Specimen From the Green River Formation Elucidates Complex Phenotypic Evolution in Gruiformes and Charadriiformes

The stem lineage relationships and early phenotypic evolution of Charadriiformes (shorebirds) and Gruiformes (rails, cranes, and allies) remain unresolved. It is still debated whether these clades are sister-taxa. New phylogenetic analyses incorporating Paleogene fossils have the potential to reveal the evolutionary connections of these two speciose and evolutionarily critical neoavian subclades. Although Gruiformes have a rich Paleogene fossil record, most of these fossils have not been robustly placed. The Paleogene fossil record of Charadriiformes is scarce and largely consists of fragmentary single elements. Only one proposed Eocene charadriiform-like taxon,Scandiavis mikkelseniof Denmark, is represented by a partial skeleton. Here, we describe a new species from the early Eocene Green River Formation of North America comprising a partial skeleton and feather remains. Because the skeleton lacks the pectoral girdle and forelimbs as inS. mikkelseni, only features of the skull, axial skeleton, and hind limb are available to resolve the phylogenetic placement of this taxon. These anatomical subregions initially showed features seen in Charadriiformes and Gruiformes. To assess placement of this taxon, we use a matrix consisting of 693 morphological characters and 60 taxa, includingS. mikkelseniand the oldest known charadriiform taxa represented by single elements. These more fragmentary records comprise two distal humeri from the earliest Eocene Naranbulag Formation of Mongolia and the early Eocene Nanjemoy Formation of Virginia. Our phylogenetic analyses recover the new taxon andS. mikkelsenialternatively as a charadriiform or as a stem-gruiform; placement is contingent upon enforced relationships for major neoavian subclades recovered by recent molecular-based phylogenies. Specifically, when constraint trees based on results that do not recover Charadriiformes and Gruiformes as sister-taxa are used, the new taxon andS. mikkelseniare recovered within stem Gruiformes. Both Paleogene fossil humeri are consistently recovered within crown Charadriiformes. If placement of these humeri or the new taxon as charadriiforms are correct, this may indicate that recent divergence time analyses have underestimated the crown age of another major crown avian subclade; however, more complete sampling of these taxa is necessary, especially of more complete specimens with pectoral elements.

Coprolites from shallow marine deposits of the Nanjemoy Formation, Lower Eocene of Virginia, USA

Coprolites from shallow marine deposits of the Nanjemoy Formation, Lower Eocene of Virginia, USA

Bony-Tongue Fishes (Teleostei: Osteoglossomorpha) from the Eocene Nanjemoy Formation, Virginia

Bony-tongue fishes, Osteoglossomorpha, are distributed in North and South America, Africa, Asia, and Australia and are found on all continents except Antarctica in the fossil record. The group includes fishes such as the mooneyes (Hiodontidae), freshwater knifefishes (Notopteridae), elephantfishes (Mormyridae), and the arowanas and pirarucu (Osteoglossidae). Remains identified as belonging to the family Osteoglossidae are known from the Nanjemoy Formation of Maryland and northern Virginia and comprise isolated teeth and fragmentary jaw bones assigned to the now extinct ???Brychaetus muelleri. The second author discovered a partial toothed parasphenoid among other isolated and fragmentary vertebrate microfossils from the Fisher???Sullivan Site of the Nanjemoy Formation in northern Virginia. This element resembles the base of the parasphenoid of the extant osteoglossid taxa Osteoglossum and Scleropages. Although this fossil is fragmentary and not sufficient to differentially diagnose taxonomically, it provides further evidence of the substantial diversity of Osteoglossidae during the Eocene.

The world’s smallest owl, the earliest unambiguous charadriiform bird, and other avian remains from the early Eocene Nanjemoy Formation of Virginia (USA)

New avian remains from the early Eocene Nanjemoy Formation in Virginia (USA) are described. The material stems from the Fisher/Sullivan site and consists of isolated bones. These belong to at least 13 species, most of which have not yet been reported from the Nanjemoy Formation. The fossil material includes the oldest unambiguous record of a charadriiform bird and a new species of protostrigid owl, which represents the smallest known owl species. Other specimens are tentatively assigned to the Procellariiformes, the suliform Fregatidae, the gruiform Messelornithidae, and the apodiform Eocypselidae. A complete and well-preserved tarsometatarsus of the psittacopasserine Halcyornithidae provides new data on the osteology of these enigmatic birds, and a distal tibiotarsus is tentatively assigned to the Trogoniformes. The identification of a number of fossils is uncertain, with the bones showing similarities to Threskiornithidae and extinct taxa from the early Eocene of Europe (Microena, Morsoravis). All bird fossils from the Nanjemoy Formation are three-dimensionally preserved and, therefore, allow a detailed assessment of osteological features, which complements studies of compression fossils from lagerstatten-type fossil sites.

Paleogene chelonians from Maryland and Virginia

Author(s): Weems, Robert E. | Abstract: Fossil remains of 22 kinds of Paleogene turtles have been recovered in Maryland and Virginia from the early Paleocene Brightseat Formation (four taxa), late Paleocene Aquia Formation (nine taxa), early Eocene Nanjemoy Formation (five taxa), middle Eocene Piney Point Formation (one taxon), and mid-Oligocene Old Church Formation (three taxa). Twelve taxa are clearly marine forms, of which ten are pancheloniids (Ashleychelys palmeri, Carolinochelys wilsoni, Catapleura coatesi, Catapleura sp., Euclastes roundsi, E. wielandi, ?Lophochelys sp., Procolpochelys charlestonensis, Puppigerus camperi, and Tasbacka ruhoffi), and two are dermochelyids (Eosphargis insularis and cf. Eosphargis gigas). Eight taxa represent fluvial or terrestrial forms (Adocus sp., Judithemys kranzi n. sp., Planetochelys savoiei, cf. “Trionyx” halophilus, “Trionyx” pennatus, “Kinosternoid B,” Bothremydinae gen. et sp. indet., and Bothremydidae gen. et sp. indet.), and two taxa (Aspideretoides virginianus and Allaeochelys sp.) are trionychian turtles that probably frequented estuarine and nearshore marine environments. In Maryland and Virginia, turtle diversity superficially appears to decline throughout the Paleogene, but this probably is due to an upward bias in the local stratigraphic column toward more open marine environments that have preserved very few remains of riverine or terrestrial turtles.

New marsupial from the early Eocene of Virginia

A new species of the marsupial Peradectes is described from the early Eocene Nanjemoy Formation of Virginia. It is the first Tertiary marsupial known from the Atlantic Coastal Plain north of Florida. The smallest species of Peradectes, it is more closely related to species known from the Western Interior of North America than to contemporaneous European species.

Rediscovery of figured Paleogene echinoid specimens from Clark and Martin (1901)

Clark and Martin (1901), in their study of the Paleogene deposits of Maryland, figured drawings of a fragment of a spatangoid echinoid from the Lower Eocene Nanjemoy Formation and a broken echinoid spine from the Upper Paleocene Aquia Formation. Echinoids are an important element of Paleogene faunas in the eastern United States, but these are the only reported occurrences of this age from either Maryland or Virginia and are therefore significant to the understanding of the evolution and paleogeography of echinoids in this region. The figured specimens were attributed to collections at Johns Hopkins University, but without catalog numbers. During study of the paleobiology collections of the National Museum of Natural History (NMNH), Smithsonian Institution, two vials were discovered with small, handwritten labels referencing the figure numbers in Clark and Martin (1901). The contained specimens were recognized as those figured in the report. They have been cataloged in the NMNH collections as follows:

Foraminiferal Paleoenvironments and Biostratigraphy of Eocene Nanjemoy Formation, Virginia and Maryland: ABSTRACT

Foraminiferal and sedimentologic data from 80 spot samples collected in Virginia and Maryland were used to investigate the paleoenvironments and biostratigraphy of the lower Eocene Nanjemoy Formation. The predominant lithology of the Nanjemoy Formation is variably glauconitic fossiliferous muddy sands, with foraminiferal abundance decreasing up section. The sediments of the lower Potapaco member are typically fine to medium-grained muddy sands containing abundant lignite and sparse glauconite. The upper Woodstock member is characterized by fine to coarse-grained sands with a decreased mud content and increased glauconite abundance. Distributions of individual foraminiferal taxa, planktonic-benthic ratios, foraminiferal suborder ratios, and species diversity patterns were used to determine variations in the Nanjemoy paleoenvironment throughout the lower Eocene Salisbury embayment. Planktonic foraminifera place the samples sections within established biostratigraphic schemes. Supplemental evidence of paleoenvironmental variations was obtained from grain size and composition data of all samples collected. Cluster and canonical variate analyses were used to investigate further similarities and differences in the foraminiferal content between samples, locations, and members. End_of_Article - Last_Page 314------------

Comparison of Cubitostrea (Mollusca, Bivalvia) Assemblages from Atlantic and Gulf Coastal Plains: ABSTRACT

Specimens of the oyster genus Cubitostrea from lower and middle Eocene beds in Maryland and Virginia were compared with collections of that taxon from correlative units in North Carolina, South Carolina, Alabama, and Mississippi. Material from these collections indicates some differences with Stenzel's model of successional speciation. Stenzel proposed a single lineage of Cubitostrea including (from oldest to youngest) C. perplicata (Dall)--1.m. Eocene, C. lisbonensis (Harris)--m.m. Eocene, C. smithvillensis (Harris)--m.m. Eocene, and C. sellaeformis (Conrad)--m.m. Eocene. Stenzel's model suggested a change from a primitive trigonal form to one with well-developed auricles and finally to one with a profound fold in the valves. The development of auricles and folds in the enus Cubitostrea appears to depend on the maturity of the individuals, however, and is not an evolutionary progression, because the oldest known representative, Cubitostrea sp. from the lower Eocene Nanjemoy Formation, exhibits both of these tendencies. We believe that there are two distinct oyster lineages, both belonging to the genus Cubitostrea. The first lineage consists of C. perplicata and C. lisbonensis; the second consists of C. sp. and C. sellaeformis. C. smithvillensis appears to be an ecophenotypic variant of C. sellaeformis as are C. divaricata (Lea) and C. vermilla (de Gregorio). Specimens of Cubitostrea that have been identified as C. lisbonensis from South Carolina (Santee Limestone) and North Carolina (Castle Hayne formation) are immature and resemble the young of C. sellaeformis from Virginia and Alabama. End_of_Article - Last_Page 1443------------

Reexamination of Middle Eocene Genus Cubitostrea Based on Collections from Central Virginia Coastal Plain: ABSTRACT

Three species of oysters from the middle Eocene Cubitostrea lineage are used for local and regional correlation and zonation of sediments in the Gulf coastal plain. However, oysters from the middle Eocene Piney Point Formation in Virginia also include the co-occurrence of specimens that exhibit the morphologic characteristics of these 3 Gulf Coast species. Examination of approximately 150 specimens from 8 bulk samples collected in a vertical sequence along the Pamunkey River revealed that, in addition to co-occurring, a continium exists from one form to the next. The general shape of the forms is related to size, with juvenile oysters characterized by a triangular shape and prominent ribs, whereas the adults are oval with large auricles and a saddle-shaped form. Results indicate that the morphologic variation of oysters in the middle Eocene sediments of Virginia does not represent an evolutionary lineage with each form a species, as proposed for the Gulf coastal plain. Rather, the forms are related to the growth stages of the species C. sellaeformis. Therefore, the Gulf model is not applicable to the middle Eocene sediments of Virginia and possibly not to other depositional areas. Oysters from the underlying Nanjemoy Formation (lower Eocene) previously included within the species C. sellaeformis should not be so designated. This distinction is based on the coarser and fewer number of ribs on the Nanjemoy oyster as compared to C. sellaeformis from the Piney Point Formation. End_of_Article - Last_Page 290------------

RbSr glauconite ages, Sabinian, Claibornian and Jacksonian units, southeastern Atlantic Coastal Plain, U.S.A

Hand-picked, disordered to ordered authigenic glauconite from the Nanjemoy Formation (Virginia), the Santee Limestone (restricted) and Cross Formation (South Carolina), and the Castle Hayne Limestone (North Carolina) yield RbSr isochron ages ( λ 87Rb = 1.42 × 10 −11 yr −1) for Eocene units in the southeastern Atlantic Coastal Plain. The units, zonal assignment of their contained nannofossil floras and radiometric age, are: 3 Unit Nannofossil zone Age (m.y.) Castle Hayne Limestone NP 19–20 34.9 ± 1.1 Cross Formation NP 18, NP 19, NP 20 34.1 ± 1.5 Santee Limestone (upper part) NP 16–17 36.7 ± 0.6 Nanjemoy Formation NP 13 46.7 ± 3.0 These ages, and their nannofossil assemblages, provide means of correlating southeastern Atlantic Coastal Plain units with Gulf Coastal Plain and European stratoypes. Correlation to Gulf Coast stratotypes, based on nannofossil zones, indicates that the Nanjemoy Formation (in part) is equivalent to the Hatchetigbee Formation; the upper part of the Santee Limestone (restricted) is equivalent to the upper Lisbon Formation, the Gosport Sand, and the Moodys Branch Formation (upper Claibornian-lower Jacksonian); and the Cross Formation and the Castle Hayne Limestone are equivalent to the Yazoo Group (Jacksonian). Previously reported KAr glauconite ages for the Gulf Coast units are different from the RbSr ages determined in this study. As the RbSr age determinations show internal consistency when compared to their contained nannofossil zones, whereas the KAr ages do not, it is suggested that the previously reported KAr ages for the Gulf Coast Claibornian and Jacksonian are in error. Correlation of the southeastern Atlantic Coastal Plain units to European stratoypes based on nannofossil zones indicates that the Nanjemoy Formation (in part) is equivalent to the type Lutetian; the upper part of the Santee Limestone (restricted) is equivalent to the Upper Bracklesham and Barton Beds; and the Cross Formation and Castle Hayne Limestone are equivalent to the Lower and Middle Headon Beds. Previously determined KAr and RbSr radiometric ages for the type Lutetian, the Bracklesham and Barton Beds are identical to the ages determined in this study. As a result, it is suggested that Rb-Sr glauconite isochron ages can be used for regional and inter-regional correlation and that the Eocene/Oligocene boundary is younger than 34 m.y.

Paleocene-Eocene Boundary in Eastern Gulf Coast: ABSTRACT

The Paleocene-Eocene boundary in Alabama has been placed at various levels within the Tuscahoma Formation and the overlying Bashi Formation. The location of this boundary is important because both lignite- and petroleum-bearing deposits occur within this sequence in the Gulf Coast, and the region appears to be a good locality to test the local coastal-onlap models. The middle beds of the Tuscahoma Formation are upper Paleocene (calcareous nannofossil Zone NP9 and Morozovella End_Page 1429------------------------------ velascoensis Internal zone). The entire overlying Bashi Formation is lower Eocene (Zone NP10 and lower part of the Morozovella subbotinae Interval zone). No calcareous fossils are known from the upper part of the Tuscahoma. Therefore, the boundary problem was investigated, using abundant sporomorphs in cores of the Tuscahoma and the Bashi at Ozark, Alabama, and other cores and outcrops in Alabama and western Georgia. The sporomorph assemblages of the Tuscahoma and the Bashi differ considerably, but the assemblages within each formation are generally quite uniform from base to top. According to sporomorph data, a small hiatus appears to exist between the Tuscahoma and the Bashi. In the Oak Grove core hole in Virginia, the shallow-marine Aquia Formation contains Tuscahoma-like sporomorphs in beds within Zone NP9. The overlying lagoonal Marlboro Clay is either entirely upper Paleocene or may span the Paleocene-Eocene boundary. Above the Marlboro is the marine-transgressive Nanjemoy Formation (Zone NP10), containing Bashi-like sporomorphs. Thus, sporomorphs from the top of the Tuscahoma in Alabama are most probably of late Paleocene age, as are the similar sporomorphs from the upper Paleocene middle part of the Tuscahoma and upper Paleocene Aquia Formations. The uppermost beds of the Tuscahoma in eastern Alabama and western Georgia are marginal-marine to nonmarine deposits. The overlying Bashi Formation is of inner neritic origin. Therefore, in the Atlantic and Gulf coastal plains, a regression marked the end of the Paleocene, and a fairly rapid, sea-level rise occurred at or just after the beginning of the Eocene; this agrees with published global sea-level curves. End_of_Article - Last_Page 1430------------

Dinoflagellate “communities”; from the lower Eocene Nanjemoy formation of Maryland, U.S.A.

Abstract Six distinctive stratigraphically sequential dinoflagellate cyst communities in the Lower Eocene Nanjemoy Formation (Woodstock Member) of Maryland, possibly relate to fluctuations in local environmental conditions. Individual species most commonly are not stratigraphically restricted to a single community; however, their relative abundances (in particular, of the dominant species), as illustrated by rank abundance analysis, are unique to each of the six communities. Major changes in species composition and relative abundances are, for the most part, correlative with pronounced changes in the number of species per sample for the sections. Cluster analyses of the ten most abundant species in each sample, which comprise from 76 to 100 percent of all the dinoflagellates in each sample, also tend to demonstrate the existence of the same six diagnostic cyst communities.

Petrology of the Paleocene-eocene Aquia Formation of Virginia, Maryland, and Delaware

ABSTRACT The Paleocene-Eocene Aquia Formation crops out in the coastal plain of Maryland, Delaware, and Virginia. A field and laboratory study of the exposed Aquia north of Fredericksburg, Virginia, was conducted to determine the petrologic features and the environment of deposition of the sediments, as well as the relationships of this formation with the underlying Brightseat unit. Sieve and hydrometer analyses of 116 samples show that the Aquia is a well-sorted, very fine to medium-grained sand or silty sand. Median diameter increases and sorting improves both vertically upward through the section and northward along strike. Sediments from the type locality of the Brightseat unit are texturally equivalent to parts of the Aquia at the Aquia type locality. Glauconite content of the sand grades of the Aquia samples ranges from approximately 20 percent to 70 percent. Lateral and vertical changes in glauconite content are frequent. Both authigenic and detrital glauconite grains are present. The heavy mineral suite of the Aquia is a full suite with the exception of hornblende. Clay minerals include illite, glauconite, montmorillonite, and kaolinate. Mineral composition of the Brightseat unit is essentially the same as that of the Aquia, and falls within the range of extremes of Aquia composition. The Aquia was probably deposited in inner neritic marine waters where generally slow rates of deposition varied from time to time. A change in deposition rate could account for the previously proposed unconformable break between the Brightseat and the Aquia without any withdrawal of the sea. Irregularities in the coastline and changing patterns of current activity resulted in deposition of sediments with varying texture and mineralogy. Source rocks for the Aquia material included crystalline rocks, sedimentary rocks, and possibly, unconsolidated sediments. The source area was probably to the west in the Appalachian Piedmont, Blue Ridge, and Valley and Ridge provinces. Unconsolidated Cretaceous coastal plain sediments were a minor source of Aquia material. Relief of the source area was low. Areal variations of lithofacies within the Aquia show that the center of clastic sedimentation shifted somewhat during Paleocene and Early Eocene times. Continuous shoaling of the sea during Aquia deposition culminated in deposition of the pink Marlboro Clay Member of the overlying Nanjemoy Formation in brackish water.

STRUCTURAL RELATIONS OF CRETACEOUS AND TERTIARY FORMATIONS IN PART OF MARYLAND AND VIRGINIA

This paper presents results of study of the structural and overlap relations of several formations of Tertiary age in the region east of Washington, Baltimore, and Fredericksburg. Attention is also given to the relations of various formations of Cretaceous age (Upper and Lower). The altitude of the base of the Calvert formation (Miocene) was determined at many places, and from these data structure contours were constructed as shown in Plate 1. These show that in a wide area the base of the Calvert has a fairly regular easterly slope of about 10 feet to the mile, with a somewhat steeper rate in the outliers west of Washington. In the Baltimore region this southeasterly slope averages nearly 15 feet to the mile, also with some steepening on the west. In the Fredericksburg region the slope is less than 10 feet to the mile, and farther south this rate carries the plane of Calvert overlap west onto the crystalline rocks. The Econe succession which I named the Pamunkey formation in 1891 was later divided by W. B. Clark into a lower formation, Aquia, and an upper one, Nanjemoy, the latter having a basal member of clay, named Marlboro. Near Washington this clay member thins out to the west under the Miocene, the edge of which also extends considerably farhter west than the edge of the overlying greensand of the Nanjemoy. The last named gradually thickens to the east and south. South of Fredericksburg the Aquia formation overlaps the edge of the Potomac group slightly, onto the old crystalline rocks, and the Potomac in turn is overlapped by the Calvert formation (Miocene), the Nanjemoy formation with its Marlboro clay member having thinned out or been eroded.