DOI: 10.25921/6p0y-gr60
title: NOAA/WDS Paleoclimatology - Dare County, North Carolina Quaternary Subsurface Aminostratigraphy

description: Amino acid enantiomeric ratio data are presented for Pleistocene mollusks obtained from a suite of split-spoon and vibracore samples at sites in Dare County, northeastern North Carolina. The region lies within the Albemarle Embayment, a thick sequence of Quaternary and pre-Quaternary strata in the mid-Atlantic coastal plain, eastern United States. Land surface elevations range from 0 to +2 m. Sample depths range from ~ 4 meters to ~ 35 m below mean sea level. Specimens of the bivalve mollusk Mulinia and Mercenaria have been analyzed by ion-exchange and gas chromatography. Aminozones representing clusters of D/L values are used to correlate depositional sequences in the study area and to estimate times of deposition based on kinetic modeling of amino acid racemization. Deepest units are estimated to be older than 1 million years, while the shallowest Pleistocene units are estimated to be last interglacial (~80,000 - 125,000 yrs) in age, based on both racemization and uranium-thorium age estimates.
description: Extent of Racemization (D/L) data for mollusks from Pleistocene 
coastal units, subsurface sections of the Atlantic Coastal Plain, 
Dare County, North Carolina. 

Samples collected by L.L. York, S.R. Riggs, W. Miller III, 
and T.M. Cronin. Samples collected in 1970's and 1980's 
by vibracoring, excavation (Stetson Pit), and split-spoon 
drilling (Stetson Pit). 


Samples prepared and analyzed at the University of Delaware, 
Newark DE. [UDEL].  Lab PI John F. Wehmiller. 


Pretreatment: Fragments cut from shell valves; surface cleaning 
with dental tools; dilute HCl and distilled water wash; air dry 
AA fraction="amino fraction" 
THAA = total hydrolyzable amino acids; 
FAA = free amino acids (zero hydrolysis time) 
Hydrolysis procedure: 6N HCl 22 hours 105 deg C (for THAA only) 
Bleach: No 
Instrumental programming: GC temperature program; HPLC buffer gradient 
Blank corrections: no 
Response factors: no 

Lab Code UDEL= University of Delaware 

Sample ID = identity of specific shell analyzed 
Analytical method: GC = gas chromatography, used for multiple amino acids; 
Ion-exchange High Pressure Liquid Chromatography used for determination 
of A/I values  (HPLC) 
Subsample ID =  usually the same as sample ID; repeat fragments of same 
shell will have unique identification 
Ratio type =  (peak area or peak height ratios) 


D/L values are reported as the means of multiple chromatograms, 
usually at least 2. For GC results, in most cases sample derivatives 
were analyzed using more than one GC column. 

Samples selected for analysis were chosen because they appeared 
to be the most robust specimens among those available.  In most cases, 
samples were not whole valves.  Abraded, rounded, or chalky fragments 
were avoided where possible, and multiple shells from each collection 
were analyzed in almost all cases.  No data screening procedures have 
been applied. No interlab sample comparisons were made during 
the period of these analyses. 

Information on sample quality (fragment, whole shell, abraded, chalky, etc. 
will be compiled for a future version of this datafile. 

Abbreviations: 

A/I     D-alloisoleucine/L-isoleucine 
Ala     Alanine 
Asx     Aspartic acid and asparagine 
Glx     Glutamic acid and glutamine 
Leu     Leucine 
Phe     Phenylalanine 
Pro     Proline 
Val     Valine 

9999 = no data available for this amino acid in this sample 


UDAMS LOCALITY DESIGNATIONS  (UDAMS = UDAMinoStratigraphy) 

07002	Excavation in 1981-1982 (W. Miller to T. M. Cronin to J. Wehmiler)  Surface elevation ~ 2m 
07004	Excavation in 1981-1982 (W. Miller to T. M. Cronin to J. Wehmiler)  Surface elevation ~ 2m 
07005	Core taken in 1982 (Miller, 1982). Top of core at ~ 0 m elevation 
07077	Core taken in 1982 (Miller, 1982). Top of core at ~ 0 m elevation 
07127	Core taken in 1982 (Miller, 1982). Top of core at ~ 0 m elevation 
07128	Samples from original excavation in early 1980's.