We determined concentrations of trace elements in the carbonate fraction by atomic absorption analysis following the procedure described by Renard and Blanc (1971, 1972). The age of the samples studied range from Barremian to middle Eocene (Holes 390, 390A), Tithonian to Aptian (Hole 391C), and late Campanian to Barremian (Hole 392A). Mineralogically, they all contain low magnesian calcite. The results of the analysis are given in Tables 1 to 4. HOLE 391C Relationship With Insoluble Residues In some samples, we obtained sufficient insoluble residues, following treatment with acetic acid, to relate certain element concentrations to percentage of insoluble residue (Figure 1). We noted a distinct, positive correlation between concentrations of potassium, sodium, and magnesium and the percentage of insoluble residue. (Some of these elements may have been flushed into the insoluble fraction in spite of the precautions taken.) We found a positive, but less pronounced, relationship between zinc and strontium concentrations and insoluble residue, whereas we detected no correlation between manganese concentrations and insoluble residue. Because of this relationship we consider the results obtained for potassium, sodium, and magnesium, and those obtained for strontium, and zinc, when the samples contain more than 10 per cent insoluble, to be unreliable. Strontium The concentration curve of strontium contents is very characteristic for samples containing more than 90 per cent carbonates (Figure 2). The amount of strontium decreases continuously from the Aptian to the Tithonian sediments; a rapid decrease occurs in the lower Valanginian-upper Barremian sediments. We attribute this to increased diagenesis with greater depth which reflects the degree of diagenesis as a function of age. This is consistent with earlier claims of Sheeiman and Shirmohammadi (1969), Kinsman (1969), and Renard (1972) that strontium is a reliable measure of carbonate diagenesis. The similarity of the strontium concentrations and the sediment accumulation curves illustrates that the highest rate of sedimentation (2.8 cm/10 3 years) corresponds to the greatest loss of strontium. A rough correlation between the gradient of the strontium concentration curve and the sedimentation rate is given in Figure 3.
This paper presents data on trace elements (Sr, Mg, Na, K, Mn, Fe, Ni, Cr) and isotopes ( 13 C, 18 O) on the carbonate fraction of bulk sediments from the Coniacian to Paleocene samples of Hole 516F. Relationships of trace elements to mineralogy and stratigraphic position are discussed at length, with special emphasis on 1) the differences between Hole 516F and other oceanic sites, and 2) the transitions observed at the Cretaceous/Tertiary boundary. Isotope data are compared to those obtained in other localities of the same age. The sections show the same major 13 C variations at the Cretaceous/Tertiary boundary, indicating that this event is a planetary phenomenon.
Trace element contents (Sr, Mg, Mn, and Fe) and the composition of oxygen and carbon isotopes show that late burial diagenesis did not play an important role in pelagic carbonate chemistry in the bulk carbonates recovered from Holes 638B, 638C, and 641C (except for anoxic pore-water diagenesis in Valanginian sediments). The evolution of these different geochemical markers documents the importance and global extent of the Barremian ocean chemistry crisis. A reconstruction of paleoceanographic and climatic conditions during the Early Cretaceous is proposed. Sea level rose eustatically from the early Hauterivian to early Albian, but a rapid down and up fluctuation occurred during the Barremian. Soluble supply from the continent decreased during the Valanginian-early Hauterivian while oceanic hydrothermal supply increased. The climate cooled slightly during the Hauterivian, rapidly warmed during the Barremian, and cooled again during the Aptian.
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