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Quarternary and Tertiary |
Institute of Oceanographic Sciences, Brook Road, Wormley, Godalming, Surrey GU8 5UB, UK
The highest resolution stratigraphy of marine sequences can be obtained in the Quaternary. Oxygen isotope stratigraphy can be used to divide the Quaternary (0–1.66 Ma) into 63 isotope stages representing alternating glacials and interglacials. These climate changes are controlled by astronomical forcing involving eccentricity of the earth’s orbit (100 000 year periodicity); obliquity of the earth’s axis (41 000 year periodicity); and precession of the equinoxes (23 000 year periodicity). These factors can be combined to produce a time scale which has been used to tune the isotope records, providing ages for all the isotope stage boundaries. The percentage of calcium carbonate also varies in many marine sediments with similar frequencies to the isotope record and has been used in similar ways. Both these methods are unreliable in areas with reworking or sediment disturbances. They work best in combination with independent stratigraphic zonations such as those derived from calcareous nannofossils. Planktonic foraminifera provide palaeoclimate data but they are less well suited to detailed biostratigraphy in the Quaternary. Other microfossil groups including diatoms and radiolaria provide useful biostratigraphic information in some areas but they are often poorly preserved due to dissolution and when present they have rarely been used to provide high resolution stratigraphy.
