Foraminifer test preservation and diagenesis: comparison of high latitude Eocene sites

Abstract

Abstract Foraminifer tests are prone to diagenetic recrystallization on a micron scale that can affect their geochemical composition, hence it is important to identify fossil material that is well-preserved. Here we illustrate the textures of tests from several high-latitude Eocene sites using a combination of Reflected Light Microscopy and high-resolution Scanning Electron Microscopy. The sites are Ocean Drilling Program (ODP) Site 647 in the Labrador Sea (53°N), ODP Site 689 at Maud Rise in the Weddell Sea (64°S), ODP Site 1135 (Kerguelen Plateau c . 59°S) and outcrop samples from Hampden Beach, New Zealand (palaeolatitude c . 55°S). The foraminifera studied from Site 647 and Hampden Beach have glassy, transparent tests that show only minor signs of diagenetic alteration, whereas the foraminifera from Sites 690 and 1135 are opaque and recrystallized. We associate the better state of foraminifer preservation at the former sites with the high clay content of the sediments. Our observations suggest that Site 647 and Hampden Beach may be useful for the establishment of high-latitude sea-surface temperatures and hence global temperature gradients in the Eocene.