Proc. IODP, 320/321, Data report: late Miocene to early Pliocene coccolithophore and foraminiferal preservation at Site U1338 from scanning electron microscopy

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Chapter contents Abstract Introduction Methods and materials Sediment processing Scanning electron microscopy Results Foraminifer SEM Fine fraction SEM Calcite preservation—implications for the robustness of geochemical proxies Summary Acknowledgments References Figures F1. Location map. F2. SEM images of Cibicidoides mundulus. F3. SEM images of Globigerinoides sacculifer. F4. More detailed SEM images of Globigerinoides sacculifer. F5. BSE SEM images, Samples c1 and c2. F6. EDS on Sample c2. Table T1. Samples investigated. PDF file			Previous \| Next doi:10.2204/iodp.proc.320321.218.2014 Summary The BSE-TOPO SEM images of various benthic and planktonic foraminifer specimens from Site U1338 show that both sets of foraminifers have undergone some alteration. The benthic foraminifers are generally only slightly affected by minor calcite overgrowth. There is also only very minor evidence for dissolution in a couple of the specimens. A quarter of the specimens investigated show a reasonable amount of overgrowth. As diagenetic alteration is not thought to greatly alter the original isotopic composition of the benthic foraminiferal calcite, the state of benthic foraminifer preservation is unlikely to be an issue for geochemistry. The BSE-TOPO SEM images of the planktonic foraminifer specimens show signs of definite alteration. The preservation state ranges from specimens with some overgrowth and internal recrystallization, but which retain original features such as pores, spine pits and internal test-wall growth structure, to specimens where recrystallization and overgrowth disguise many of the original features. Preservation state is also highly variable, with specimens that are <1 m apart showing considerably different levels of alteration. Because of the preservation issues, geochemistry on these archives should be interpreted cautiously. SE and BSE-TOPO SEM images show that coccolith calcite preservation is moderate or moderate to poor. Dissolution has removed all evidence of holococcoliths, and slight to moderate etching has removed the central features of the heterococcolith preservation of the coccolith calcite. A small amount of secondary overgrowth is also visible on many heterococcoliths. EDS analyses show that the main sedimentary components of the fine fraction sediment is biogenic CaCO₃ and SiO₂. Marine barite was also found. Top of page \| Previous \| Next

Summary