A new dinoflagellage cyst sequence biostratigraphic framework for the Miocene of the Baltimore Canyon Trough and adjacent Salisbury Embayment

Abstract

Over the past two decades, extensive seismic mapping of the Baltimore Canyon Trough off New Jersey, Delaware and Virginia, has documented a succession of progradational Miocene stratigraphic sequences. Understanding the depositional timing of these sequences is critical in evaluating the role of eustasy in their development, but has until now been hampered by the lack of suitably high resolution biostratigraphic data. Attempts to produce an integrated Neogene basin history have previously been frustrated by an inability to directly correlate individual shelf-based seismic sequences, with regionally mapped onshore, unconformity-bound, stratigraphic units. This study addresses both problems using data comprising the stratigraphic distribution of dinoflagellate cysts in two composited outcrop and ten subsurface sections from the Salisbury Embayment and adjacent Baltimore Canyon Trough. The result is a detailed age model for the entire Miocene depositional history of the area. Onshore samples are from the type sections of the Chesapeake Group in Maryland and Virginia. Offshore COST B-2 & B-3, Exxon 684 & 902 and Mobil 500 wells are directly tied to the regional seismic grid.According to our model, the magnitude and timing of mapped sequences in the Baltimore Canyon Trough compare well with Miocene third order cycles of the Exxon Cycle Chart. With the exception of the 22 Ma sequence (Cycle 1.5 of Haq et al., 1988), all of the other postulated eustatically controlled sequences are potentially present in the study area. In addition, on the basis of seismic mapping and integrated biostratigraphy, our model predicts one additional lower Serravalian sequence between 15.5 Ma and 13.8 Ma, and two additional lower Tortonian sequences between 10.5 Ma and 8.2 Ma. The onshore expression of these sequences are, respectively, the Calvert Beach Member of the Calvert Formation and parts of the Little Cove Point Beds of the Saint Marys Formation. An important implication of the age model is that the entire Fairhaven Member and “beds 4-9” of the Plum Point Marl Member, of the Calvert Formation, are lower Miocene strata.These dinocyst data were not available when the Exxon model of Miocene eustatic cycles was developed and therefore represent a critical independent test of that model. This is particularly so because the tectonically quiescent, mature, divergent-margin setting of the basin limits the role of causative variables other than eustasy, in the development and architecture of third order depositional sequences. Our model should be further tested by detailed sedimentological and taphonomic field studies of the Chesapeake Group.

Taphonomic expressions of sedimentary hiatuses: field observations on bioclastic concentrations and sequence anatomy in low, moderate and high subsidence settings

“…Sequence-bounding unconformities appear as Thalassinoides-burrowed firmgrounds in profile and bevel older strata regionally, and all of the third-order sequences known from the same Miocene interval in thick offshore records (e.g. Greenlee and Moore, 1988) are present in these very thin coastal plain records [TB2.2-TB3.2 cycles of Haq et al (1987); see biostratigraphic data of Verteuil and Norris (1992) to update Kidwell (1984;]. Incised valleys are rare and are filled exclusively with estuarine and intertidal facies, so that transgressive surfaces coincide with lower sequence boundaries across a broad (30-50 kin) outcrop belt.…”

Palynological delineation and regional correlation of lower through upper Miocene sequences in the Cape May and Atlantic City boreholes, New Jersey Coastal Plain

“…Residues were subjected to 30 to 45 seconds in an ultrasonic bath (Blackman HT1.9 tank, at 23 kHz) and then sieved at 15 µm using Nitex (nylon) screen. Residues were stained and mounted as described in de Verteuil and Norris (1996a).…”

“…Dinocyst events are recorded as lowest occurrences (LOs) or highest occurrences (HOs). Age relationships for each borehole were determined using the dinocyst zonation of de Verteuil and Norris (1996a) as calibrated to the BKSA95 time scale, augmented by Sr-isotopic age estimates (Sugarman et al,Chapter 12,this volume). Dinocyst taxonomy follows de Verteuil and Norris (1996a.…”

“…De Verteuil and Norris (1996a) used the HO of Distatodinium biffii to define the base of the Chiropteridium galea Zone (DN1) which spans the Oligocene/Miocene boundary. The upper boundary of Zone DN1 is defined by the HO of Chiropteridium galea.…”

“…Dinoflagellate cysts (dinocysts) provide the primary Neogene biostratigraphic control at transect sites. De Verteuil and Norris (1996a) calibrated dinocyst events in the Baltimore Canyon Trough and Salisbury Embayment to the Cenozoic time scale of Berggren et al (1995; hereafter BKSA95) by integrating dinocyst stratigraphy, calcareous biostratigraphy, strontium isotopic (Sr) stratigraphy, magnetostratigraphy and well log and seismic stratigraphy from the Salisbury Embayment and Ocean Drilling Program (ODP) Leg 150 sites (see Mountain, Miller, Blum, Poag, and Twichell, 1996). Consistent dinocyst stratigraphies and excellent core-to-seismic ties permit confident site-to-site sequence correlations and allowed de Verteuil and Norris (unpubl.…”