Figure F27. Summary log, Hole U1356A. Chemical index of alteration is [Al2O3/(Al2O3 + CaO* + K2O + Na2O)] × 100 (Nesbitt and Young, 1982). CaO* represents the CaO fixed in silicate minerals; values between 50 and 70 can be observed in the upper interval. Values are intermediate between fresh feldspar (33–50) and chemically weathered detritus (70–75) and are typical for environments affected by physical weathering (e.g., Passchier and Krissek, 2008). Higher values in the lower interval (>80) strongly indicate intense chemical weathering and manifest different environmental conditions in the source area of the sediments.
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