2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 279-2
Presentation Time: 8:30 AM


HAWKES, Andrea D.1, PETH, Joanna2, LANE, Chad3, DONNELLY, Jeffrey P.4, PRATOLONGO, Paula5 and GOMEZ, Eduardo5, (1)Geography and Geology, University of North Carolina Wilmington, 5600 Marvin K. Moss Lane, Wilmington, NC 28409, (2)Geography and Geology, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403, (3)Geography and Geology, University of North Carolina Wilmington, 601 S. College Rd, Wilmington, NC 28403, (4)Geology & Geophysics Department, Woods Hole Oceanographic Institution, MS #22, 266 Woods Hole Rd, Woods Hole, MA 02543, (5)Instituto Argentina de Oceanografia, Florida 8000, Bahia Blanca, Buenos Aires Province, CC 804, Argentina, hawkesa@uncw.edu

The utility of sediment and foraminiferal isotopic proxies are tested for developing relative sea-level (RSL) records in coastal central Argentina. Single and multi- proxy reconstructions were investigated based on foraminiferal δ13C and δ18O signatures and bulk sedimentary δ13C compositions with respect to modern marsh elevations. An absence of agglutinated foraminifera commonly used for RSL reconstructions necessitated alternative proxy development. Ammonia parkinsoniana δ13C and δ18O values produced the strongest linear correlations with modern marsh elevation compared to other species or sediment isotopic composition. There was positive covariance between the δ13C and δ18O signatures defining the parameters of four marsh zones with elevation (tidal flat, low marsh, mid-marsh, and high marsh). However, initial tests show that the isotopic range of each of the four zones varies by site making the proxy site specific. This site specificity is likely due to changes in vital effects (respiration), microhabitat effects related to pore water composition (pH, OM degradation), or a combination of both.

When applied to sediment cores, the proxy reconstruction approaches (δ13C, δ18O, and multi) record a sea-level regression <3m over the last 4,000 years, agreeing with and refining previously published RSL records in the region. An abrupt marsh elevation increase in the last ~40 years is hypothesized to be a result of increased human activities in the Bahía Blanca estuary, such as dredging, maritime and urban development, and river divergence. The exposure of eroded or barren mudflats facilitated the expansion of S. alterniflora marshes and produced an apparent relative sea-level drop in the recent sedimentary record contrary to tide gauge data.