Biogeographic and morphological variation in Late Pleistocene to Holocene globorotalid foraminifera

• Main Author: Brown, Kevin Richard
• Other Authors: Wetzel, Andreas, Knappertsbusch, Michael W., Spezzaferri, Silvia
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: Planktonic foraminifera
• Online Access: http://edoc.unibas.ch/diss/DissB_8290; https://edoc.unibas.ch/780/; https://edoc.unibas.ch/780/1/DissB_8290.pdf; https://doi.org/10.5451/unibas-004503399

Planktonic foraminifera are marine, calcite secreting protists. They have a long history of study in both industry and academia. Individual species show distinct biogeographical distributions and ecological tolerances. Traditionally species concepts are based on the gross morphology of the foraminiferal test. The closer the morphology of two species, the closer they are related. This has resulted in a single species being named by several authors from differing global locations and also, in long lived species, differing time intervals. This work investigates morphological variation of Late Pleistocene – Holocene menardiform globorotalids, and links this morphological variation to different ecological and environmental conditions. To achieve this 70 global sample sites are investigated covering a range of differing environmental conditions, but within constrained time limits. Where possible samples dated as Holocene have been used, where absolute dating was unavailable samples from about the Emiliani huxleyi acme zone, giving an upper age is given of 65 – 70 thousand years. Analysis of morphological variation allowed identification ofintergrading morphoclines and a total of six distinct morphotypes (e.g. the menardi-form morphotypes α, β, χ and η and the two tumid form morphotypes ε and φ). The morphotypes are shown to have distinct though overlapping biogeographic distributions. In the bivariate morphospace of spiral height versus axial diameter the equation y = 2.07x –15 separates morphocline(G. menardii morphologies) from morphocline(G. tumida morphologies). Within morphoclinethe line with equation y = 3.2x –160 separates morphotypes α (G. menardii menardii) from morphotype β (G. menardii cultrata). Morphotype β is interpreted as G. menardii cultrata and is seen to dominate environments with mean annual sea surface temperatures over 25°C. Morphotype α is interpreted as G. menardii menardii and becomes more dominant as sea surface temperatures become cooler. In areas where both morphologies are present in a ...