Oceanic micropaleontology: Progress and prospect

The seventies were marked by explosive development of oceanic micropaleontology and drastic changes in emphasis. The main impetus for expansion came from deep‐sea drilling. Global sampling made possible a global approach to paleoceanography and biostratigraphy. Scanning electron microscopy extended routine study to extremely small particles. The use of computers aided in quantifying paleoenvironmental reconstruction and in refining stratigraphic resolution. Integration of micropaleontologic information with physical and chemical oceanography has helped to make micropaleontology the mainstay of paleoceanographic research. The biogeography of planktonic foraminifera and of the paleontologically important coccoliths is now well documented. This is not yet true for radiolarians and diatoms. Much progress has been made in mapping distributions on the sea floor, in all groups, and in relating such distributions to supply, dissolution, and redeposition. Two major problems have been identified. One is the role of fecal pellets in the transfer of coccoliths and diatoms to the sea floor. The other is the relationship between preburial preservation states of microfossil assemblages and their postburial diagenesis (‘diagenetic potential’ of an assemblage). Important advances in Quaternary research include increased stratigraphic resolution, quantitative temperature determination (accuracy about 2°–3°C), and isotopic evidence for glacial‐interglacial fluctuations. Changes in productivity and preservation patterns remain major questions. Pre‐quaternary paleoceanography has largely been concerned with establishing biogeographic patterns through time and their correlation with changing geography due to plate tectonics. The mechanisms of cause and effect (surface currents, bottom water flow, water mass stratification, etc., versus biogeography and sedimentation patterns) remain speculative on the whole. The question of the origin of diversity and its variations through time continue to attract attention. There appears to be a positive correlation between diversity and isotopic temperature through time. Causes for major extinctions are unknown and are likely to remain so until the fundamental question of which processes control the overall productivity of the ocean is resolved. A model is developed, proposing a control of present microplankton assemblages by successive change of the limiting nutrient (silica‐bionitrogen‐phosphate). It is argued that a low‐fertility ocean should be characterized by high silica and phosphate concentrations and that this should be recognizable in the record. Stratigraphic work has greatly benefited from DSDP results, especially when care was taken to recover long sequences. Zonations, in part preliminary, are now available for all major groups, for Cretaceous and Cenozoic sequences. Attempts to correlate some of these sequences with the less complete standard sections reveal a fundamental weakness in the concept of stratigraphic standard.