Paper No. 90
Presentation Time: 9:00 AM-6:00 PM
PLANKTONIC FORAMINIFERA BIOSTRATIGRAPHY OF HOLOCENE- LATE PLEISTOCENE CORE MD02-2535, TUNICA MOUND, GULF OF MEXICO
An age model was developed for Calypso Core MD02-2535, Tunica Mound, Gulf of Mexico, using planktonic foraminifera biostratigraphy. Twenty-two bulk samples were dried, weighed, and sieved at 150µm. The greater than 150µm fraction was split to ~300 specimens and identified to species level to characterize the assemblage. Biostratigraphic zones were assigned based on zonation schemes and species frequency patterns defined by Kennett and Huddlestun. Abundances of warm water (Globorotalia menardii, Globorotalia tumida and Pulleniatina obliquiloculata) and cool water (Globorotalia inflata, Globigerina falconensis and Globigerina bulloides) forms covary throughout much of the core as glacial and interglacial periods alternated in the Pleistocene. The Holocene is marked by the dominance of warm water forms. The upper 0.19m of core belong to the Z1 planktonic foraminifera subzone. The Z1/ Z2 subzone boundary lies at 0.24mbsf and is assigned an age of 6ky. Sedimentation rates for the Z zone are higher than those found in the Y zone, likely due to increased warm water productivity and runoff in the Holocene. The Z/Y boundary is located at 0.94mbsf, correlating to the beginning of the Holocene at 9.8ky. The Y1 subzone correlates with the Younger Dryas and the warming trend that preceded it. The Y1/Y2 boundary lies at approximately 1.8m, and is assigned an age of 16ky. The base of the Y2 subzone is assigned an age of 24ky, correlating with much of the Last Glacial Maximum, due to the high abundance of Globorotalia inflata and other cold water forms. Sedimentation rates in the Y1 and Y2 subzones are 0.13m/ky, likely due to deglaciation events preceding the LGM and Younger Dryas. Sedimentation rates are lower than those found in the Pigmy and Orca basins, where they range from 0.21m/ky to 2m/ky in the Z zone and 0.5m/ky to 2.2m/ky in the Y1 subzone. The Y3, Y4, and Y5 subzones could not be distinguished based solely on planktonic foraminifera assemblages. We suspect the age of core section VII does not exceed the Y6 subzone at 68ky because the first ash layer correlating with MIS 4 was not detected, nor was Globorotalia flexuosa, a species whose last occurrence is 68ky. Planned oxygen and carbon stable isotope analyses will help constrain the remaining Y subzones and will be used to evaluate the effect of gas hydrates on foraminifera tests.