Outcrop to subsurface cycle correlation in the Milankovitch frequency band: Middle Cretaceous, central Italy |
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| Authors: | David H Melnyk David G Smith |
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| Institution: | BP Research Centre, Sunbury-on-Thames, Surrey TW16 7LN |
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| Abstract: | Time series analysis of the Cenomanian through Aptian interval, in well logs from offshore Adriatic boreholes, facilitates a cycle-by-cycle correlation with measured sections of equivalent age in Umbria, central Italy. The cycle-by-cycle match can be demonstrated between filtered spontaneous potential logs and filtered bed thickness data, but is unequivocal only at wavelengths of greater than 10 metres, which are believed to represent a 2 Myr eccentricity signal; at shorter wavelengths tool resolution becomes a limiting factor. As a result of low sedimentation rates the 100, 41, and 21 kyr Milankovitch signals all appear to be aliased to longer wavelengths in the sonic and gamma ray log records and tend to blend with the 400 kyr signal; this is especially true in the Aptian-Albian interval. Attempts to filter and correlate on the bases of these shorter wavelengths were therefore unsuccessful.
Accepting a 2 Myr duration for each cycle permits an estimation of less than 7 Myr to be made for the duration of the Cenomanian Stage. |
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