AbstractThe 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.

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.

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 lenticular-bedded 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

Robert K. Denton Jr.1 & Paul L. Tashjian2

1Geoconcepts Engineering, Ashburn, VA; 2United States Fish & Wildlife Service

THE ELLISDALE MEMBER OF THE LOWER MARSHALLTOWN FORMATION:EVIDENCE FOR A FRESHWATER TIDAL ESTUARY IN THE LATE CRETACEOUS OF CENTRAL NEW JERSEY

Fully marine, glauconitic mid-shelf.

Very well-sorted marine sands, glauconitic and sideritic at the base with a burrowed zone near the center.

Estuarine, tidal flat sequence, bedded clays with sand channels, rich in lignite, siderite concretions near base with concentrated fossil-bearing pebble layer just above.

Lagoonal/fluviatile sands, with lignitic clay stringers, some cross-bedding. Erosional surface at contact with overlying tidal flat sequence

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Pebble layer with fossils

Site Location Map

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

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.

Englishtown/Marshalltown Outcrop

Stratigraphy along the Strike

WoodstownMt. Holly

Allentown(Ellisdale Site)

Freehold-Marlboro

Sandy Hook

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

Figure 1. Ellisdale Stratigraphic Column

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.

Figure 3A – Well-graded sand stratum (barrier beach)

Figure 3B – Lenticular-bedded clays (estuarine/tidal flat), fossil later at base.

Figure 3C – Englishtown (lagoonal) sands and silty clays.

Figure 3D – Glauconitic sands (marine facies), above the well-graded sand stratum.

Figure 3E – Fossil layer in pedestal. Note lenticular clays in cut behind the pedestal.

Sedimentology

Figure 4. Sedimentological analysis of the Englishtown/Marshalltown contact.

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.

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.

Figure 5 – Cross-section view of the fossil-bearing 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.

PaleontologyRemains 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.

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.

A Freshwater Backbay?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.

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

garsturgeonbowfin

ConclusionsOwens 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.

ReferencesChristopher, 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.

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.

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 short-wave 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.

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.

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a stratigraphic low lying between the Raritan Embayment and the Southern New Jersey stratigraphic high, possibly the estuary of a significant Cretaceous river.