Big Brook Preserve, Monmouth County, New Jersey
The drainage basin of Big Brook in Monmouth County exposes formations of the Inner Coastal Plain of New Jersey laid during the Maastrichtian stage of the Cretaceous period. The focus of this article was to explore the sequence stratigraphy and fossil assemblages of the Navesink formation’s strata with regards to determining the depositional environments in which they were formed. The studies involved in the writing of this article were largely centered on summary diagrams of the Navesink formation prepared by Bennington in 2003. The diagrams detail the depositional sequences as organized by being divided into alphabetical facies based on lithology as well its fossil assemblages. The stratigraphic sequences of marine sediments have been determined to be diverse and contain lucina (low sea) and cucullea (deep sea) fauna due to the transgression of the sea level. The Navesink’s invertebrate rich shell beds are concentrated within four major zones: Belemnitella, Exogyra, Agerostera/Choristothyris and Pycnodonte.
This facies is attributed to the under laying Wenonah – Mount Laurel Formation extending upwards approximately 0.3 meters above stream level. This layer consists of fine quartz sand and an abundance of carbonaceous matter (lignite), micaceous mud, siderite and glauconite (average 15% by weight – Fig. 2 [Bennington, 2003]). There is some debate as to the environment in which this facies has been deposited. Some have interpreted it to be sands deposited in an inner shelf environment, while others suggest it strictly represents estuarine valley-fill. Most have settled on the generalization that it was deposited during early transgression being an evolving estuarine/inner shelf transition zone. The sediments of this interval are extensively burrowed, with the distinctive trace fossil of the ichnotaxon, Spongeliomorphia. Spongeliomorpha shares its form with Ophiomorpha which differs with the distinctive absence of unlined burrow walls marked by longitudinal ridges (Bromley, 1996). These burrows are attributed to the callianassid crustacean Protocallianassa mortoni Pilsbury, or indifferently Protocallianassa sp. having been occasionally preserved within the burrows. These muddy sands must have been sufficiently cohesive to permit callianassids to excavate burrows without the need to line the burrow walls with fecal pellets, which would have produced Ophiomorpha traces (Bromley, 1996). Considering the presence of callianassid crustacean, Spongeliomorphia burrowing, coupled with the abundance of lignite and siderite, an iron carbonate mineral formed diagenetically in the pore waters of oxygen depleted sediments in fresh and brackish water environments that are rich in decomposing organic matter, indicates that the deposition occurred under fresh water to marginal marine, estuarine conditions (Berner, 1981). Perhaps, the clinching factor arguing for an estuarine environment comes from sedimentological and heavy mineral analyses which detail the presence of labradorite and clinopyroxene in phases normally destroyed during weathering, particularly in marine environments (Bennington, 2000).
This is the final facies of the under laying Wenonah – Mount Laurel Formation extending upwards approximately 1.7 meters from the contact point of the upper surface of Facies A. This interval shows signs of a gentle transition from estuarine to an inner shelf environment with fining-upward quartz sands, decreasing carbonaceous matter and some glauconite (average 15% by weight – Fig. 2 [Bennington, 2003]). Concentrated nearest the center of the facies, between 0.3 – 0.6 meters, is a diversity of pelecypods (bivalve mollusks). Genera identified include Inoceramus, Trigonia, Crassatellites, Lima, Periplomya, and Linearea (Bennington, 2003). These benthic faunas lived both on and in the substrate being epifaunal and infaunal. The surface of this facies is unconformably overlain by the Navesink Formation. This unconformity is essentially the Campanian-Maastrichian boundary and probably represents several million years of missing time (Miller et al., 1999). This interval is marked by the presence of rounded sand nodules of unknown origin, and a distinct change to a darker colored lithology in Facies C. Sedimentological and heavy mineral analyses data show little silt and clay (18% - Fig. 3) with grains in the fine to very coarse classes with a variety of heavy minerals including chlorapatite, garnet, amphibole, and others including tentatively identified spinel and scapolite (Bennington, 2003). The coarse grains were deposited by migration of the shore face over the estuarine deposits forming a weakly transgressive lag (Bennington, 2000).
The first facies of the Navesink formation extends upwards approximately 1.1 meters from the unconformity of the Mount Laurel / Wenonah Formation. The unconformity is highlighted by iron-stained deposits associated with ground water seepage (fig. 4). Facies C consists of fine quartz sands with some phosphatic grains, very little carbonaceous matter and an increase in glauconite (average 25% by weight – fig. 2 [Bennington, 2003]). Based on the lithology and fauna preserved, the deposits forming Facies C have been determined to be transitional from inner to outer shelf environments. There are massed burrows of Thallassinoides which have extensively bioturbated the sediments. The burrows are relatively large and branch upwards, often intersecting repeatedly. They have only been tentatively identified as being the trace fossils of a burrowing arthropod. These burrows are mostly concentrated to the lower half of the facies, whereas gryphaeid oysters, pectens and belemnites become dominant in the upper half. The gryphaeid species has been identified as Gryphaea arcuata Say (fig. 5) which is present throughout the facies. Gryphaea arcuata Say faired well against predators as they had a thickly enlarged, highly convex and coiled left valve which planted themselves onto the fine grains of the substrate. The umbone of the larger left valve hooks inward earning the folk name Devil’s Toe-nail. There are two main morphotypes related to two general environments. The factors include, but are not limited to temperature and oxygen levels on the sea floor (Nori, 2003). Simply put, if the shell is large and thick then the oyster had lived in cooler more oxygen rich environment which fits the morphology of those which are in Facies C at Big Brook Preserve. If the shells had been small and thin, then the environment would have been hot and humid with lower oxygen levels. The first appearance of belemnites appear in the middle to upper strata of this facies and are noted as being smaller in size than those preserved in Facies D being deposited in more shallow waters.
This is the largest and final facies of the Navesink rising 5.3 meters from the contact point of Facies C. It primarily consists of glauconite sands (average 90% by weight – Fig. 2 [Bennington, 2003]), with little to no detrital quartz grains (Bennington, 2000). Modern sediments composed almost exclusively of glauconite grains are found in current swept, open marine environments of the middle to outer shelf at depths greater than 60 m, with the optimum depth of glauconite formation found to be approximately 200 m near the top of the continental slope (Odin and Fullagar, 1988). At the basal interval the Belemnite, Belemnitella Americana Morton, is common and considerably larger in size than those of Facies C being deposited in a deeper marine environment. Belemnites are squid-like cephlapods related to the modern cuttlefish. Belemnites had an internal skeleton that can be divided into three parts: (i) the robust anterior counterweight – the rostrum or guard; (ii) the buoyancy mechanism – the phragmacone, a chambered conical section with a siphuncle; and (iii) the pro-ostracum – the support for an open body chamber (Fig. 6 [Milsom, 2004]). The internal, bullet shaped shell called the rostum is made up of radially arranged, needle like calcite crystals. The rostum is regularly preserved, whereas the belemnite’s aragonitic phragmacone only occur as casts. At about 1.5 meters from the base of this facies is the largely concentrated Exogyra assemblage. The oyster’s Exogyra costata Say and E. costata var. cancellata Stephenson (Fig. 7) are the most abundant with few other species found. The genus Exogyra is a member of the family Ostreidse of the superfamily Ostracea. It is distinguished from Ostrea and Gryphsea, the other principal genera of the family, chiefly by its spirally curved beaks (Stephenson, 1914). Exogyra costata Say was first described by Thomas Say in 1820, his description is as follows: “Shell inequivalve, inequilateral; cicatrix one, large, deeply impressed, subcentral; inferior valve convex, attached, umbo spiral, spire lateral, prominent, hinge with two parallel, transverse grooves; superior valve discoidal operculiform, umbo not prominent, revolving spirally within the margin, hinge with a single groove on the edge” (Stephenson, 1914). Exogyra costata Say is distinguished from other Exogyra being characterized by having radiating costas on the larger, spiral revolving valve, from the beak to its margin. E. costata var. cancellata Stephenson is very similar to E. costata with the distinct difference that the radiating costae are interrupted by concentric depressions or undulations which give the shell a checkered or cancellated appearance (Stephenson, 1914). In 1914, Lloyd Stephenson remarked that its distinctive ornamentation justifies its recognition as a variety, and even suggested that the form may have developed parallel to rather than from Exogyra costata Say. If so, it should perhaps be classified as its own species, not a varietal rank. The zone of E. costata var. cancellata Stephenson forms the lower part of the Exogyra zone in the Upper Cretaceous and ranges in thickness from about 4 feet in New Jersey to about 200 feet in central Texas. This zone has been traced, with interruptions, through various formations, from the Navesink of New Jersey to Cardenas in the state of San Luis Potosi, Mexico (Stephenson, 1933). The uniformity of this assemblage shows nearly identical environmental conditions from the Northern Atlantic Coastal Plain to the Gulf Region, being traced twenty-five hundred miles. At the time that this assemblage was formed, New Jersey was subtropical and in Texas the occurrence of rudistids suggests a tropical climate. The rudist reefs of the late Cretaceous were limited to the equatorial latitudes and were most abundant in the extra salty and extra warm seaway described as Supertethys (Arthur et al. 1996). Stephenson conservatively estimated that the Exogyra population would be over 4.5 trillion throughout the twenty-five hundred mile expanse.
At about 3.3 meters from the base of this facies is the largely concentrated Pycnodonte – Agerostrea assemblage. The oysters Pycnodonte mutabilis Morton and Agerostrea mesenterica Morton are most prevalent with an accessory fauna of Choristothyrisbrachiopods and small pectens (Bennington, 2003). Pycnodonte mutabilis Morton (Fig. 8), formally called Gryphaea convexa Morton, is inequilateral, whereas the left valve is rounded or convex and the right valve is flattened or concaved. The orthogyrous umbone is inflated and evenly rounded on the anterior of the left valve. The umbone of the larger left valve hooks inward similar to Gryphaea arcuata Say. Both the left and right valves are regularly sculptured with crowded corrugation growth layers that form the thick and solid shell. Agerostrea mesenterica Morton is the most abundant oyster species of the Navesink formation at Big Brook Preserve (Fig. 9 [Bennington, 2003]). These oysters are easily distinguished from any other oyster species having distinctive “U” shaped valves with zig-zag plications. The valves are relatively symmetrical being equal in size (on average about 3 cm in length) and shape. Adult Agerostreain the Navesink Formation frequently are found cemented to other individuals. Choristothyris, a punduculate brachiopod that also requires a hard substrate for attachment, was the only species seen to covary with Agerostrea, suggesting that its abundance also may be related to the density of shells in the substrate (Bennington, 2003). The brachiopod Choristothyris plicata Say(Fig. 10 [Clarkson, 1993])is subcircular or subovate in outline and is marked by 8 to 12 angular plications which extend to the beak. The larger pedicle or ventral valve is strongly convex and the dorsal valve is slightly concaved. Choristothyris plicata Sayis relatively small measuring on average about 1.25 cm (Richards, 1958).
The vast majority of oysters collected from the Navesink Formation at Big Brook Preserve, are biocorroded. The most prevalent is shown at both the anterior and interior of the shells valves having been bored into by clionids and lithophagid bivalves. Cliona retiformis Stephenson and C. cretacica Fenton and Fenton are the main culprit sponge borers which would attach themselves and slowly replace the shell (Fig. 11). The boring or drilling pelecypods leave behind bored holes but do not replace the shell as is the case with Cliona retiformis Stephenson (Case, 1982). Another form of biocorrosion is that of serpulid annelids. The serpulid annelids can be found wrapped in matrix occurring as casts (Fig. 11).
The Navesink formation is unconformably overlain by the Red Bank Formation which makes up Facies E extending upwards 1.4 meters from the contact point of Facies D (Bennington, 2003). The upper intervals of Facies D and lower intervals of Facies E show at least two series of regression and transgression. As interpreted from figure 1, at 4.6 meters from the contact point of Facies C, there is an abrupt change in lithology going from silty, glauconitic sand to a leeched silt, fine quartz sand which rises about 0.3 meters. Then there is a short interval of glauconite sand rising about 0.5 meters, followed by a 0.3 meter interval of leeched silt, fine quartz sand. Then there is another small interval of glauconite sand rising 0.3 meters that is followed by the final 1.2 meter interval of leeched silt, fine quartz sands. Groundwater flowing through the sand has leached away most fossil remains, and has altered the glauconite to limonite which has resulted in its red coloring (USGS, 2003). Strontium-isotope age estimates for the Red Bank average 65.8 Ma (Sugarman and others, 1995).
The environment in which the formations of Big Brook Preserve were formed, from stream level to the surface, show transgressive intervals from estuarine to deep marine followed by a regression back to an inner shelf to near shore environment. Facies A and B, attributed to the Wenonah – Mount Laurel Formation, extends upwards 2.0 meters from stream level. This formation consists of fine quartz sands with an abundance of lignite, siderite, and containing 15% glauconite by weight. The additional presence of labradorite and clinopyroxene, coupled with the spongeiomorpha burrows suggest the conditions of an estuarine environment. At the upper portion, transgression is shown through the quartz sands becoming finer and the amount of carbonaceous matter decreasing. At this interval Pelecypods emerge as benthic faunas, both epifaunal and infaunal, fill the substrate. Facies C and D, attributed to the Navesink Formation. extends upwards 6.4 meters from the unconformity of the Mount Laurel / Wenonah Formation, A transgression is represented from an inner shelf to an open marine environment as fine quartz sands decrease to low trace percentages and glauconite increases to a dominant 90% by weight. The fossil assemblages of the inner to outer shelf lithology consist of Exogyra oysters, pectens and small belemnites. As the sea level rises belemnites increase in size, and the shell bed assemblages of Pycnodonte and Agerostea oysters, as well as brachiopods flourish in the deep marine environment where sediment deposition is low. This is supported by the high rate of biocorrosion by clionids and lithophagid bivalves. Facies E attributed to the Redbank Formation, extending upwards 1.4 meters from the contact point of the Navesink Formation represents the regression from a deep marine to a near shore environment as quartz sands increase and glauconite decreases.
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