Integrated Sr-isotope and bio-chronology of Oligocene-Miocene sequences, onshore and offshore New Jersey
Abstract
Sr isotopes provide a valuable means for developing chronology in nearshore sediments where biostratigraphic markers are often lacking or suffer environmental exclusion. This approach is most precise when rates of change in seawater Sr-isotopes were high (e.g., Oligocene to early Miocene). Sr-isotope stratigraphy is potentially limited by carbonate diagenesis, reworking, and intervals of low resolution (e.g., later Miocene). Integration of Sr-isotopes and biostratigraphy provide a relatively precise chronology (better than 1 Myr resolution) in onshore and offshore New Jersey strata. We previously developed a chronology for onshore Oligocene-Miocene sequences and correlated them with sequences cored on the continental slope. IODP Expedition 313 cored three sites on the nearshore shallow shelf of New Jersey that link the onshore and offshore studies, focusing on thick lower to lower middle Miocene sections imaged on seismic profiles. At least four Oligocene sequences and one uppermost Eocene-lowermost Oligocene sequence occur at Site M27, where the Oligocene section is unusually thick (>129 m) compared to onshore. From youngest to oldest these are: 1) a sequence dated by bio- and Sr-isotope stratigraphy straddling the Oligocene/Miocene boundary; 2) a well-dated mid-Oligocene sequences with high sedimentation rate (~92 m/m.y.); 3) a poorly dated ca. 30 Ma sequence; 4) one or more lower Oligocene sequences; and 5) a basal Oligocene sequence boundary correlated with isotopic increase Oi1. Several early Miocene sequences are also well constrained: 1) sequence m5.8 is well dated at Site M27; 2) sequence 5.45 is dated at Sites M27 and M28; and 3) sequence m5.2 is well dated at Site M29. A series of relatively thin (<25 m) sequences (m5.3, m5.32, m5.4) span the lower/middle Miocene boundary (16.2 Ma). Preliminary ages for these sequences appear to be younger at Site M27 than at Sites M28 and M29, which we attribute to the early disappearance of taxa at this updip sandy site. Middle Miocene sequences are poorly dated by Sr isotopes due to reworking and low resolution, but diatom and other fossil groups indicate a major hiatus associated with sequence boundary m5 and imply extremely high sedimentation rates (>200 m/Myr) above this. This influx of sediments was associated with the major middle Miocene oxygen isotopic increases.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP13F..03B
- Keywords:
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- 1135 GEOCHRONOLOGY / Correlative geochronology;
- 4999 PALEOCEANOGRAPHY / General or miscellaneous