PALEOCEANOGRAPHIC EVENTS AND OLIGOCENE/MIOCENE STRATIGRAPHY OF THE ATLANTIC CONTINENTAL MARGIN: RESOLVING PARADOXES IN THE MIOCENE PALEOCEANOGRAPHIC RECORD

A comparison of isotopic, lithologic and sequence stratigraphic data from the New Jersey, North Carolina, and Florida continental margins reveals correlations that provide insight into global paleoceanographic processes operating during the Oligocene and Miocene. Strontium isotope stratigraphy allows the correlation of continental margin sequences to the paleoceanographic record of sea-level change, carbon budget changes, and climate transitions. Depositional sequences corresponding to negative d¹⁸O shifts in the marine isotope record (sea-level rise and highstands) can be correlated along the U.S. east coast. Periods of maximum phosphogenesis within the depositional sequences on the southeast U.S. (SEUS) margin, and elsewhere globally, correspond to the early to mid-Miocene episode of Himalayan-Tibetan Plateau (HTP) uplift and denudation (21 to 16 Ma). Estimates of total reactive P flux resulting from HTP weathering between 21 and 16 Ma are similar to the episodic P burial rates during this time in sediments of the SEUS margin. Modeling the response of the P inventory to 0.4 My sea-level cycles and changing P sinks and sources reveals significant oscillations. It appears probable that decreasing P inventories occurred during highstands and periods of high P export to shelf sediments, and increasing P inventories occurred during lowstands. Oscillating P inventories directly affected total oceanic biomass such that d¹³C shifts were negative during highstands, and positive during lowstands, consistent with the paleoceanographic record (CM events). The long-term (>1 My duration) increase in P influx may have increased total biomass and organic carbon burial during the early- to mid-Miocene, thereby causing the long-term positive carbon isotope shift generally referred to as the Monterey Event. Links between HTP uplift and erosion, sea-level change, phosphogenesis, and changing oceanic biomass and carbon export are called upon to resolve paradoxes in the Miocene paleoceanographic record.