Publication Date:
2023-06-27
Description:
The CRP-3 core, drilled in western McMurdo Sound in October and November 1999, penetrated 823 m of lower Oligocene (to possibly upper Eocene) glacially influenced sediments. The palaeoclimatic record of CRP-3 is examined using major element analyses of bulk core samples of fine grained sediments (mudstones and siltstones) and the Chemical Index of Alteration (CIA) of Nesbitt & Young (1982, doi:10.1038/299715a0). The CIA is calculated from the molar abundances of Al, K, Ca, and Na oxides, and its magnitude increases as the effects of chemical weathering increase. However, changes in sediment provenance can also affect the CIA, so provenance changes have been evaluated by examining the Al2O3/TiO2 ratios and the Sr and Nb contents of the CRP-3 mudstones.
Relatively low Nb contents (〈20 ppm) and relatively high Al2O3/TiO2 ratios (generally 〉15) indicate that little or no McMurdo Volcanic Group detritus was incorporated in these sediments. Instead, these sediments appear to be mixtures of Beacon Supergroup, Ferrar Dolerite, and basement (Granite Harbour Intrusives) components; increased Sr contents suggest that the importance of basement-derived material is greatest above ~200 metres below seafloor (mbsf), whereas Beacon Supergroup and/or Ferrar Dolerite components dominate below that level.
Below ~400 mbsf, the CIA profile is irregular and shows no correlation to the Al2O3/TiO2 record; as a result, the effects of weathering and provenance controls have not yet been interpreted for this part of the CIA profile. Above ~400 mbsf, however, four "cycles" of CIA increase/decrease (each spanning 50-100 m of stratigraphic thickness) are superimposed on a general decrease in CIA values upcore, and Al2O3/TiO2 ratios exhibit a matching pattern of "cycles". This correlation indicates that short-term provenance changes occurred during deposition of the upper half of CRP-3, and affected its CIA record. However, the Al2O3/TiO2 profile does not show any long-term trend above ~400 mbsf, so that the general decrease in CIA values above that level does not appear to be provenance-related. Instead, the general upcore decrease in the importance of chemical weathering above ~400 mbsf may record an episode of climatic deterioration prior to -31 Ma.
Keywords:
Aluminium/Titanium ratio; Aluminium oxide; Arsenic; Barium; Calcium oxide; Calculated; Cape Roberts Project; Chemical index of alteration; Chloride; Chromium; Copper; Core wireline system; CRP; CRP-3; CWS; DEPTH, sediment/rock; Gallium; Iron oxide, Fe2O3; Lead; Loss on ignition; Magnesium oxide; Manganese oxide; Molybdenum; Nickel; Niobium; Phosphorus pentoxide; Potassium oxide; Ross Sea; Rubidium; Sampling/drilling from ice; Silicon dioxide; Sodium oxide; Strontium; Sulfur, total; Thorium; Titanium dioxide; Uranium; Vanadium; X-ray fluorescence (XRF); Yttrium; Zinc; Zirconium
Type:
Dataset
Format:
text/tab-separated-values, 2368 data points
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