Biostratigraphic and Paleoecologic Potential of Calcareous Nannofossils in Nearshore Environments: IODP Expedition 313 New Jersey Shallow Shelf
Abstract
Calcareous nannofossils are one of the primary microfossil groups used for biostratigraphic applications due to their abundance in marine sediments and cosmopolitan nature, particularly in open ocean conditions. On the nearshore continental shelf, their biostratigraphic utility may be somewhat limited due to reduced abundances or environmental exclusion; however, nannofossils have been successfully used for biostratigraphy in these settings by the petroleum industry, although this work is largely unpublished. Integrated Ocean Drilling Program (IODP) Expedition 313, drilled on the New Jersey shallow shelf, offers an opportunity to illustrate the utility of the standard global calcareous nannofossil zonations when applied in a nearshore setting. In addition, there have been few studies examining the relationship between the calcareous nannofossil assemblage and the proximity to the shoreline. This is a particularly interesting avenue of research, as recent studies support that adaptation to the coastal realm represents a refuge for stressed taxa that appear to go extinct within the oceanic realm. Three holes spanning the Pleistocene to Eocene/Oligocene transition were drilled on the New Jersey shallow shelf during IODP Exp. 313. These sites link sites previously drilled onshore and on the continental slope as part of a larger study to examine the relationship between sequence stratigraphy and changes in eustatic sea level. Preliminary chronologies for the Exp. 313 sites were developed by combining microfossil biostratigraphies (calcareous nannofossils, planktonic foraminfers, dinoflagellate cysts, and diatoms) with Sr-isotope stratigraphy. In general, calcareous nannofossil abundances increase offshore, with lower abundances and more barren intervals that are typically associated with clinoform tops in the most proximal site (Hole M27A). Although sphenoliths are rare in the New Jersey sediments, most standard calcareous nannofossil markers for the Oligocene through middle Miocene are present at all three sites, and correlate well with the other microfossil groups and Sr-isotope stratigraphy. This indicates that the standard calcareous nannofossil zonation schemes can be applied to nearshore sediments, albeit with some caveats. For instance, at Hole M27A, the ranges of some species (e.g., Helicosphaera ampliaperta, Sphenolithus heteromorphus) appear to be truncated, either through dilution or environmental exclusion. Reworking of Paleogene nanofossils occurs at all three sites, and is typically associated with toe-of-clinoform deposits; however, the consistent presence of specimens resembling Cruciplacolithus and Cyclagelosphaera in the Oligocene and Miocene sediments may represent refugia taxa rather than reworking.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP11E1465K
- Keywords:
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- 1125 GEOCHRONOLOGY / Chemical and biological geochronology;
- 1641 GLOBAL CHANGE / Sea level change;
- 4944 PALEOCEANOGRAPHY / Micropaleontology;
- 4950 PALEOCEANOGRAPHY / Paleoecology