THE ELLISDALE MEMBER OF THE LOWER MARSHALLTOWN FORMATION:
EVIDENCE FOR A FRESHWATER TIDAL ESTUARY IN THE LATE CRETACEOUS OF CENTRAL NEW JERSEY
Robert K. Denton
Abstract
The vertebrate fauna and geology of the Ellisdale Fossil Site in Monmouth
County, New Jersey has been the subject of intensive studies since its discovery in
1980. The site occurs within the basal portion of the Marshalltown Formation, of
the Late Cretaceous Matawan Group of New Jersey. Vertebrate fossils are
concentrated with rip-up clasts near the base of a lenticular-bedded clay sequence
in a lag deposit consisting of siderite pebbles, poorly graded sand, and lignite.
Remains of animals from at least four paleo-environments are represented at the
Ellisdale Site: marine, lagoonal/backbay, estuarine/freshwater, and terrestrial,
suggesting an allogenic model where pre-burial transport, mixing and
concentration of the fossils took place prior to their deposition in the pebble layer.
1Geoconcepts
Engineering, Ashburn, VA;
Stratigraphy along the Strike
The Ellisdale section is different from previously described Englishtown and Marshalltown Formation sections in
that it contains a 2.5 meter thick sequence of bedded clays and a 1.5 meter thick unit of well-sorted sands. These
strata are not recognized in modern descriptions of these formations (Owens and Minard, 1966; Petters, 1976).
No descriptions of either formation mentions the Ellisdale
pattern of tidal flat clays, overlain by well-sorted marine
sands overlain by glauconitic sands. The overall sequence
suggests that the Ellisdale deposits were laid down within
a stratigraphic low lying between the
Raritan Embayment and the Southern New
Jersey stratigraphic high, possibly the
estuary of a significant Cretaceous river.
Englishtown/Marshalltown Outcrop
A recent palynological study has determined that the silty, lenticular bedded clays
found above and below the pebble layer span the entire Middle Campanian (76.4 –
79.6 ma), and that the sediments were laid down in a fresh water environment of
deposition. The presence of well-preserved amphibian remains also supports the
idea that the environment was fresh water as amphibians are salt-intolerant. Study
of the larger clasts has shown chaotic orientation, indicative of a tidal depositional
regime.
MAPPED AS MARSHALLTOWN
(Owens & Minard, 1966)
The importance of the Ellisdale Site was recognized soon after its
discovery in 1980 and prompted a detailed study of its paleontology and
geology under a grant from the National Geographic Society in 1987 –
88. Although the fossil layer was considered to be located in the
uppermost stratum of the Englishtown Formation, a review of the
descriptions of the Englishtown/Marshalltown contact did not support
this conclusion. The contact between the two formations was
traditionally placed at the base of the glauconitic marine sands lying
above an unconformity in the uppermost Englishtown (Owens & Minard,
1966), yet at Ellisdale there was a 3-meter
& Paul L.
2United
Mt. Holly
Woodstown
States Fish & Wildlife Service
Sedimentology
The strata at Ellisdale were analyzed for mean grain size, sorting, clay mineral content and marine heavy mineral
content. Low percentages of marine clays and heavy minerals suggest the “Englishtown” facies was not deposited
in a fully marine environment nor continental facies. They generally have the characteristics of a lagoonal
environment of deposition.
Both the field data and mineralogical data suggest that the “tidal-flat” facies were deposited in a salt marsh/tidal
flat environment. The sands of this facies fine upwards and the clay minerals trend from less marine (26%
montmorillonite) to more marine (45% montmorillonite). These patterns coincide with a transgressive sequence.
Likewise the heavy minerals are increasingly marine upwards through the section.
The sand facies above the tidal flat sediments are well-sorted, and interpreted as marine sands (barrier beach and
bar). Above them lie the glauconitic (marine) sands of the ‘classic” Marshalltown Formation.
Allentown
(Ellisdale Site)
FreeholdMarlboro
Figure 4. Sedimentological analysis of the Englishtown/Marshalltown contact.
The “Pebble Layer” – The fossil bearing “pebble layer” at Ellisdale is an intra-formational conglomerate that
has been interpreted as a storm deposit. It is poorly sorted (2.8) and has large mean grain size (-2 phi). The
Ellisdale fossil concentration appears to be the result of a high energy event that ripped-up and rediposited the
fossils along with mud clasts and siderite nodules. These structures are analogous to storm deposits (Jones and
Dixon, 1976) and overbank flood deposits (Wood, et al., 1988). At Ellisdale, the high fossil concentration in the
pebble layer has been attributed to a period of preconcentration associated with shallow marine transgressive
deposition (Tashjian, 1990). The reduced minerals and fossils seem to occur just above a transgressive surface,
and this basal “lag” deposit would seem to mark the transition from the fining downward (regressive)
Englishtown facies, and the fining upward (transgressive) Marshalltown facies.
Fluorescent Minerals - One of the more unexpected finds
within the pebble layer was the discovery of relatively
abundant grains of zircon which fluoresced orange under shortwave UV light. Orange fluorescing zircon is only known from
the zinc deposits of Franklin Township, Sussex County, NJ,
approximately 70 miles north of Ellisdale (Metzger, 1990).
This would suggest that at least some of the heavy mineral
component of the clastic load being deposited in the Ellisdale
estuary was originating in the north, providing an important
clue as to the possible course of the ancient river which
transported the sediment to its final destination.
Fully marine, glauconitic mid-shelf.
Figure 3A – Well-graded sand stratum (barrier beach)
MAPPED AS ENGLISHTOWN
(Owens & Minard, 1966)
Very well-sorted marine sands,
glauconitic and sideritic at the base
with a burrowed zone near the
center.
Figure 5 – Cross-section view of the fossilbearing pebble layer at Ellisdale. Note the sandy,
sideritic layer below the imbricated pebbles. This
is the assumed parent layer for the siderite
pebbles in the main fossil-bearing stratum.
Estuarine, tidal flat sequence,
bedded clays with sand channels,
rich in lignite, siderite concretions
near base with concentrated fossilbearing pebble layer just above.
Figure 3D – Glauconitic sands (marine
facies), above the well-graded sand stratum.
Figure 3B – Lenticular-bedded clays (estuarine/tidal
flat), fossil later at base.
We suggest that the Ellisdale Site may preserve the sediments and fossils present in a freshwater tidal backbay or estuarine
environment. A similar environment is found today in the backbays of the northern Outer Banks of North Carolina, in
particular the Currituck and Albemarle Sounds. Many of the taxa present at Ellisdale as fossils are still found in these
environments today. However even though the waters of these sounds are technically non-saline, they are separated from the
ocean only by the thin strip of barrier spits. Strong storms periodically breach the barrier spits of the modern Outer Banks, and
a similar storm event may account for the mixed fauna found at the Ellisdale Site.
aquatic amphibians
terrestrial amphibians
Remains of animals from at least four paleo-environments are represented at the Ellisdale Site: marine,
lagoonal/backbay, estuarine/freshwater, and terrestrial. Mixed faunal assemblages of this type are typically
associated with transgressive lag deposits, and result from the slow accumulation of transported skeletal remains in
tidal channels, back bays, and lagoons. Wave action and storms relocated the bones of marine animals to shallow
water, while river currents and flooding events transported and deposited the remains of freshwater and upland
terrestrial animals such as crocodilians and dinosaurs. Due to the fact that many of the larger bones have flaked
surfaces (indicative of cyclic wetting and drying) and show no consistent orientation, it is assumed that they were
exposed within the intertidal zone (Grandstaff, et al, 1989) before being transported to the pebble layer stratum.
Figure 3C – Englishtown (lagoonal) sands and silty
clays.
Figure 3E – Fossil layer in pedestal.
Note lenticular clays in cut behind
the pedestal.
Figure 6 – The
present-day
freshwater tidal
Currituck and
Albemarle sounds, and
the adjacent sand spits
and interfluve
peninsulas, are home
to many taxa similar
closely related to those
found at the Ellisdale
site. At least three
types of fish found at
Ellisdale (bowfins, gar,
and sturgeon) still
occur in this
environment today.
Owens and Minard (1966) mapped the contact between the Englishtown and Marshalltown Formations at the base of the
glauconitic marine sands, placing the tidal flat and marine sands facies within the Englishtown Formation. The tidal flat and
marine sand facies are not genetically or lithologically connected to the Englishtown Formation, and should be considered as
part of the Marshalltown Formation. We propose that these strata be renamed the Ellisdale Member of the Marshalltown
Formation. A member classification is warranted due to their genetic connection yet lithological differences from the
previously described Marshalltown Formation. It is of particular interest to distinguish these strata, in order to emphasize the
paleontological importance of this section, and place the fossil concentration found at Ellisdale into a depositional context.
The following sequence of events is proposed for the depositional origin of the Ellisdale local fauna and its enclosing strata:
1. Deposition of Englishtown strata in a near-shore/lagoonal environment.
2. Regression and associated erosion of the Englishtown strata.
3. Transgression causing rapidly changing environments (fluviatile, prograding delta, freshwater backbay), formation of
siderite and concentrations of fauna from different environments.
4. A high energy event (i.e. storm/tsunami) that mixes the faunal remains that had been preconcentrated in different
environments and includes “proximal” fauna possibly killed by mechanisms during the event (flooding, intrusion of
saline water, etc.)
5. The continuation of the transgression, and preservation of the bone bed.
References
Christopher, Ray, 2011. Palynological analysis of two samples from the Ellisdale Fossil Site near Allentown, Monmouth County, New Jersey.
USGS (unpublished study).
Denton, R. K., R. C. O’Neill., 1998. Parrisia neocesariensis, a new batrachosauroidid salamander and other amphibians from the Campanian
of New Jersey. Jour. Vert. Paleo. 18(3): 484-494.
Grandstaff, B., Parris, D. C., and Denton, R. K. Jr., 1989. Preliminary Report of National Geographic Grant: 4109-89.
Jones, B. and Dixon, O., 1976. Storm deposits in the Read Bay Formation (Upper Silurian), Somerset Island, Arctic Canada (An application
of Markov Chain Analysis). Journal of Sedimentary Petrology, 46 (2): 393-401.
Metzger, Robert, 1990. Personal Communication.
Paleontology
Figure 1. Ellisdale Stratigraphic Column
thick stratum of lenticular-bedded, non-micaceous silty clays overlain by 2-meters of well sorted
marine sands, neither of which conformed to the previously published descriptions of the Englishtown
Formation. As a result of these observations, a detailed sedimentological study was undertaken as part
of the National Geographic Society grant research to better understand the nature of the environment
of deposition at the Ellisdale Site, and determine the possible origin of this seemingly unique stratum
in the uppermost Englishtown Formation.
Most of the Ellisdale fossils reflect a fauna that inhabited either an estuarine or lagoonal environment. It is thought that the
well-preserved microvertebrate (proximal) fauna may have lived within a freshwater deltaic estuary that was affected by a
coastal storm surge or a possible tsunami. A recent palynological study (Christopher, 2011) of specimens obtained from the
silty clays above and below the pebble layer demonstrated the presence of large quantities of well-preserved fossil pollen
equivalent to Wolfe’s biozones CA-3B (upper part) through CA-5A (lower part). The interval incorporates the uppermost
Woodbury, Englishtown and Marshalltown Formations and is Middle Campanian in age (79 – 76.5 Ma). It is of note that
marine algae were extremely rare in the samples, and due to the preponderance of terrestrial components a nonmarine and
possible freshwater environment of deposition has been proposed.
Conclusions
Sandy Hook
Site Location Map
Lagoonal/fluviatile sands, with
lignitic clay stringers, some crossbedding. Erosional surface at
contact with overlying tidal flat
sequence
A Freshwater Backbay?
gar
sturgeon
bowfin
Figure 2. Stratigraphy of the Englishtown/Marshalltown Contact along the strike, based on
published descriptions of the Englishtown/Marshalltown contact present in the respective
geological quadrangles shown below the columns. See Fig. 1 for key to colors and symbols.
Pebble layer with fossils
2
Tashjian
Proposed Ellisdale Member
Throughout most of its outcrop zone, the Englishtown/Marshalltown contact is
present as an unconformity at the top of the Englishtown Fm., with a basal
transgressive lag above the unconformity transitioning immediately into the
glauconitic marine sand facies of the Marshalltown Formation. The lenticularbedded clays and sands observed at Ellisdale were previously considered part of
the Englishtown Formation, the climax of the marine regression of the Matawan
Group. However, sedimentological analysis has demonstrated that this stratum is
trangressive and is more appropriately placed in the Marshalltown. Thus, we
propose the recognition of an Ellisdale Member of the Marshalltown Formation
present in the central portion of the NJ strike zone. Structural models suggest the
Ellisdale Member may represent the estuary of a significant Late Cretaceous river
that lay between the northern flank of the Southern New Jersey structural high and
the southern edge of the Raritan Embayment in a low spot.
Introduction and Background
1
Jr.
The microvertebrate fauna of the site probably represents a "proximal" assemblage that lived at or near the final
point of deposition, while the heavily worn bones represent a "distal" fauna (Denton and O’Neill, 1998). The
disarticulated bones which accumulated in the lagoonal back bays by river transport, and in the shallow marine
environment offshore, would have been mixed with the skeletal remains of the animals that lived within the delta as
the storm surge swept over the estuary. Return flooding from the overfilled lagoons and estuarine channels after the
storm's passage would have subsequently filled with debris, resulting in the mixed assemblage of animal and plant
remains that are found at the site today.
Minard, J. P., 1965. Geologic Map of the Woodstown Quadrangle, Gloucester and Salem Counties, New Jersey. USGS Geologic Quadrangle
Map GQ-404.
Minard, J. P. 1969. Geology of the Sandy Hook Quadrangle in Monmouth County, New Jersey. USGS Geological Survey Bulletin 1276.
Minard, J. P., Owens, J. P., and T. C. Nichols, 1964. Pre-quaternary geology of the Mount Holly Quadrangle, New Jersey. USGS Geological
Quadrangle Map GQ-272.
Owens, J.P. and Minard, J. P., 1966. Pre-Quaternary Geology of the Allentown Quadrangle, New Jersey. USGS Geological Quadrangle Map
GQ-566.
Sugarman, J. P. and Owens, J. P. 1996. Bedrock geologic map of the Freehold and Marlboro Quadrangles, Middlesex and Monmouth
Counties, New Jersey. NJGS Geologic Map Series GMS 96-1.
Tashjian, P., 1990. The sedimentology and stratigraphy of a fossiliferous layer in the Upper Cretaceous (Campanian),
Englishtown/Marshalltown Formations near Ellisdale, New Jersey. Temple University, unpublished thesis.
Wood, J. M., Thomas, R. G. and Visser, J., 1988, Fluvial processes and vertebrate taphonomy: The Upper Cretaceous Judith River Formation,
South-Central Dinosaur Provincial park, Alberta, Canada. Paleogeography, Paleoclimatology, Paleoecology, 66: 127-143.