Quaternary High-Resolution Stratigraphy and its Application in Studies of the Canary Basin
WEAVER, P. P. E., Institute of Oceanographic Sciences Deacon Laboratory, Godalming, Surrey, United Kingdom
The Quaternary nannofossil stratigraphy has three zones based on the last appearance datum of Pseudoemillania lacunosa and the first appearance datum of Emiliania huxleyi. Other first and last occurrences can be added to this to give a conventional stratigraphy with zones a few hundred thousand years long. The calcareous nannofossil flora however is frequently dominated by a single species which allows acme zones to be identified giving a resolution of a few tens of thousands of years (individual oxygen isotope stages). The acmes are not controlled by climate since they span both cold and warm stages through a range of latitude.
This high-resolution stratigraphy has been used in two ways to study sedimentation in the Canary basin off West Africa. First, it has been combined with the lithostratigraphy to identify particular oxygen isotope stages in sediments from the Madeira Abyssal Plain. Turbidite input can be shown by this method to be modulated by climatic change with single turbidites being deposited both during periods of rising and falling sea levels. Second, it has been used to identify the age range of material included in each turbidite by comparing coccolith mixtures in each turbidite with calculated synthetic mixtures based on the proportions of particular species in each oxygen isotope stage. The results show that each turbidite contains a mixture of sediment representing a few hundred thousand ye rs.
Since we know the volume of each turbidite and the rate of sediment accumulation in the source areas, we can calculate the depth and area of erosion of each flow. The calculated values tie in with our knowledge of recent erosion in the area off West Africa and suggest that areas of the margin have periodically failed removing 50-100 m thick units. The focus of this erosion has varied with time.
AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)