New paleomagnetic and rock magnetic cyclostratigraphy for a part of the Calvert Cliffs (Miocene) passive margin deposits

We present a new high-resolution cyclostratigraphic age model assembled from paleomagnetic and rock-magnetic (anhysteretic remanent magnetization, ARM, and magnetic susceptibility, χ) data for 947 cm of section spanning Shattuck bio-lithozones 10-15 of the Calvert Formation exposed at the Calvert Cliffs, Maryland, USA. The model reveals changes in sedimentation rate that we interpret in terms of unsteady margin subsidence, eustasy, and sediment flux. We use thermal demagnetization to show that most of the section has a reversed geomagnetic polarity, with three normal polarity intervals, one near the base of zone 11, and two at the base of zone 13. These data, combined with biostratigraphic constraints at the Calvert Cliffs and elsewhere in the Salisbury Embayment indicate that the normal sections fall in subchrons C5B and C5AD. Time missing in the PP3 unconformity below at the base of zone 14 is constrained to 300 kyr based on a missing normal polarity in subchron C5AC. Overall, the 947 cm of section spans ~1.7 Myr, with ~0.3 Myr missing in the unconformity, resulting in a mean sedimentation rate of ~0.7 cm/1000 yrs. Time series analysis of the ARM and χ time series identifies periodicities that are likely driven by orbitally-forced global climate and eustatic change. We observe cycles with stratigraphic thickness periods of 2.1-2.6 m, 0.22-0.19 m, and 0.15 - 0.1 m. These periodicities represent long eccentricity (405 kyr), obliquity (~40 kyr) and precession (~20 kyr). eCOCO analysis of the χ time series suggests an SAR of ~1.0 cm/kyr below zone 12, a decrease to ~0.5 cm/kyr for zone 12 and the base of zone 13, that increases to rates approaching 2 cm/kyr for the upper part of zone 13, and zones 14 and 15. These results show that the SAR is dominated by the slow margin subsidence at a long-term average of ~7 m/myr, punctuated by long-eccentricity driven eustasy that shifted the locus of siliciclastic deposition on this low-gradient margin, with slow sedimentation associated with deep water condensed section facies, and high sedimentation associated with the neritic inner shelf and coastline.