OLD CURRITUCK INLET, VA/NC: INLET HISTORY DOCUMENTED BY FORAMINIFERAL EVIDENCE (PART II)

摘要

Six vibracores were collected from the relict flood tidal delta at Old Currituck rnInlet, Virginia/North Carolina, to provide geologic evidence of a once active tidal inlet and rna comparison of the present environment to pre-inlet and active inlet conditions. Three rncores were examined to determine sedimentology, and the foraminiferal assemblages were rnanalyzed for environmental settings. The cores are characterized by four distinct rnsedimentological facies, from bottom to top: S1) dark gray, laminated silty clay; S2) light rngray to tan, laminated quartz sand; S3) light gray to tan, massive to highly bioturbated rnquartz sand; and S4) a dark brown, bioturbated, rooted, muddy, organic-rich layer. Four rndistinct foraminiferal facies are also present. F1 contains few foraminifera with the rnexception of Elphidium excavatum that occurs only in occasional thin sand layers within rnthe mud. F2 is dominated by Elphidium but also contains other calcareous genera rn(Hanzawaia, Planulina and Quinqueloculina) that typically inhabit regions of normal rnocean salinity. Foraminifera are absent in most of the samples from F3. Samples from F4 rncontain only agglutinated species (Jadammina macrescens, Trochammina inflata and rnMiliammina fusca) that occur today in brackish and salt marshes. The sedimentological rnand foraminiferal patterns suggest the following sequence of depositional environments, rnfrom bottom to top: 1) a muddy, semi-enclosed freshwater to brackish bay (<6ppt) rnsusceptible to washover during hurricanes and northeasters; 2) a sandy active flood tidal rndelta (~34ppt); 3) an abandoned flood tidal delta/washover fan (5-25ppt); and 4) a capping rnbrackish marsh (1-7ppt).