AN ANALYSIS OF SEISMIC STRATIGRAPHY THROUGH GROUND-TRUTHING OF SEDIMENT CORES FROM TEA POND, EUSTIS, ME

Tea Pond, Eustis, ME has the potential to contain a high resolution Holocene sedimentary record due to its high depth to surface area ratio. The purpose of this study is to define seismic stratigraphic units preserved in the Holocene sedimentary package to assist with ongoing lithostratigraphic analyses of sediment cores. Geophysical data were collected using a 200 kHz Humminbird depth sounder and a 10 kHz StrataBox sub-bottom profiler during the summers of 2009-10. The bathymetric survey revealed three basins, the deepest of which is 32.3 m. Sub-bottom data reveal a maximum of 6.7 m of sediment above “basement,” which is likely Pleistocene glacial sediment. Five seismic reflectors (A, B, C, D, and E) are observed above acoustic basement at depths of 1.2 mblf, 2.0 mblf, 3.4 mblf, 4.0 mblf, 5.2 mblf, respectively.

In order to ground-truth the observed seismic facies, a composite sediment record was constructed from sediment cores taken from the deepest basin of Tea Pond. A multi-proxy approach is being conducted on the cores, including visual core logging, image analysis, loss on ignition, magnetic susceptibility, dry and wet bulk density, OC/N ratios, δ¹⁵N, and δ¹³C. Preliminary data suggest common sub-bottom depths between seismic reflectors and changes in lithology and dry bulk density. A change in lithology occurs at 1.22 mblf from a massive brown gyttja to a brown and black laminated gyttja. At the depth in the cores, an increase in dry bulk density is observed from 0.10 g/cm³ to 0.13 g/cm³. The observed lithofacies change is correlative with seismic reflector A (1.2 mblf). Seismic reflectors B, C, and D occur within the same black laminated gyttja lithofacies, and dry bulk density anomalies occur at these depths. A strong reflector (E) occurs at 5.2 mblf in the sub-bottom data. A change in lithofacies from dark black laminated gyttja to a gray clay unit, as well as an increase in dry bulk density from 0.19 g/cm³ to 0.75 g/cm³, at a depth of 5.4 mblf appears to correspond with this reflector. Additionally, core refusal occurred at 6.68 mblf, which is consistent with the depth to “basement”. Data to date suggest that Tea Pond contains a high resolution record of sedimentation during the Holocene Epoch. Ongoing multiproxy analyses are being utilized to reconstruct environmental change in the region throughout the Holocene.