Closing an early Miocene astronomical gap with Southern Ocean δ18O and δ13C records: Implications for sea level change. (17th June 2017) - Miller, Kenneth G.
Abstract: We present orbital‐scale resolution (~10 kyr) benthic foraminiferal δ 18 O and δ 13 C records from the Kerguelen Plateau (Ocean Drilling Program Sites 751 and 747) from 14.5 to 20.0 Ma spanning the Miocene climate optimum (15–17 Ma). Our records fill a critical gap from ~17 to 18 Ma, a time when many other deep‐sea records are affected by dissolution. We tested the fidelity of published magnetobiostratigraphic age models for these sites by astronomically tuning to the 405 kyr eccentricity cycle. A comparison of spectral estimates between the untuned and tuned records, as well as coherency with Laskar's (2004) eccentricity solution, revealed quasi‐100 kyr cyclicity in δ 18 O and δ 13 C. There is only a weak signal associated with the 41 kyr obliquity cycle, likely due to the 10 kyr sampling limiting resolution. The δ 18 O variations point to persistent 405 and quasi‐100 kyr modulations of temperature and sea level changes through the early to middle Miocene as predicted by astronomical solutions, with changing dominance of the 100 and 41 kyr beat. Comparison of δ 18 O records with early to middle Miocene sequences from the New Jersey shelf, northeast Australian margin, Bahamas, and Maldives suggests that the dominant sea level period preserved is the 1.2 Myr obliquity cycle, with sequence boundaries associated with δ 18 O increases or maxima. On the New Jersey margin, higher‐order sequences reflect the quasi‐100 kyr eccentricity cycles as modulated by 405 kyr cycles. We suggest that "nesting" of stratigraphic cycles is a function of the following: (1) pervasive (though changing) Milankovitch forcing of global mean sea level change and (2) preservation that depends on sufficient sediment supply and accommodation. Key Points: We provide new astronomically tuned benthic foraminiferal δ 18 O and δ 13 C data to fill a critical gap from ~17 to 18 Ma We delineate 100 and 41 kyr cyclicity to understand the significance of Mi events during the early to middle Miocene and the Miocene climate optimum On the New Jersey margin, higher‐order sequences reflect the quasi‐100 kyr eccentricity cycles as modulated by 405 kyr cycles Plain Language Summary: We present orbital‐scale resolution benthic foraminiferal δ 18 O and δ 13 C records from 14.5 to 20.0 Ma spanning the Miocene climate optimum (15–17 Ma). Our records fill a critical gap (~17–18 Ma) during a time period when other deep‐sea records are affected by dissolution. A comparison between the untuned and tuned records, as well as coherency with Laskar's (2004) eccentricity solution, revealed a roughly 100 kyr cyclicity in both δ 18 O and δ 13 C. The δ 18 O variations point to persistent 405 and quasi‐100 kyr modulations of temperature and sea level changes through the early to middle Miocene, with changing dominance of the 100 and 41 kyr beat. Comparison of δ 18 O records with early to middle Miocene sequences on the New Jersey shelf, northeast Australia, Bahamas, and Maldives suggests that the dominant period preserved in the sediment record is the 1.2 Myr obliquity cycle. On the New Jersey margin, higher‐order sequences reflect the quasi‐100 kyr eccentricity cycles. We suggest that such "nesting" of stratigraphic cycles is a function of both: (1) pervasive Milankovitch forcing of global average sea level change and (2) preservation that is largely a function of sufficient sediment supply and accommodation.