T222 Applied Reef Coral Paleoecology

Wednesday, 25 October 2006
1:30 PM - 5:30 PM

HIGH RESOLUTION DATING AND TAPHONOMY OF AN ACROPORA CERVICORNIS REEF REVEAL MID-HOLOCENE REEF ARCHITECTURE

Paper number: T222-6
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Abstract

The Enriquillo Valley, Dominican Republic, is distinguished for the pristine preservation of a Holocene fringing coral reef complex. For over 3,500 years during the mid-Holocene extensive (~11m in height), virtually monospecific Acropora cervicornis reefs accumulated at multiple sites. The examination of taphonomic state in conjunction with high resolution dating and stable isotope analyses of individual A. cervicornis specimens allows a three-dimensional reconstruction of reef morphology. Data show that A. cervicornis was able to thrive at shallow and intermediate depths on a steep gradient and that the seawater it lived in was relatively well mixed to intermediate depths. The data have potential to reveal the rate at which this coral grew at both depths and how variable growth rate affected preservation of the species.

A. cervicornis corals were collected from three sites at Arroyo Las Clavallinas in the Enriquillo Valley. The reef accumulated from ~9.45 to ~5.85 ka. with a potential break in deposition some time between ~6.06 and 5.85 ka. High-resolution 14C data show that A. cervicornis grew consistently and remained in stratigraphic continuity with few interruptions for at least the first 2000 years of accumulation. 234U/230Th data are in remarkable agreement, with only minimal potential carbon reservoir effect for the oldest sample.

Coral taphonomy values of 1-5 (pristine to degraded) were assigned for 5779 individual A. cervicornis specimens at the Las Clavallinas site and a comparison site elsewhere in the valley. An increase in taphonomic values up section and at contemporaneous up-slope sections of the outcrop may indicate spatial and temporal shallowing.

Stable isotope data show that mean δ18O decreased from -0.9 to -2.2o/oo while mean δ13C increased from -4.5 to -1.4o/oo from ~9.45 to ~6.06 ka with continued enrichment in δ13C and depletion in δ18O after that time. If the decrease in δ18O were attributed to temperature alone, the shift would imply a 6oC increase in mean annual temperature within this period, which is unlikely. A decrease in salinity due to an increase in precipitation associated with the mid-Holocene thermal maximum is a likely contributor to the shift in isotopic values.