22. PLIOCENE–PLEISTOCENE MAGNETOSTRATIGRAPHY OF SEDIMENTARY SEQUENCES FROM THE IRMINGER BASIN1Koji Fukuma2 |
ABSTRACTMagnetostratigraphic data are presented for Pliocene–Pleistocene sedimentary sequences recovered at Sites 918 and 919 in the Irminger Basin. Results taken from archive halves of core sections with the shipboard pass-through magnetometer were examined by applying progressive alternating field demagnetization to 88 discrete samples on shore. Some possible polarity chrons, identified from the shipboard results, were recognized as artifacts caused by spurious secondary remanences. Based on downhole inclination variations, clear magnetic reversal patterns, correlative to the geomagnetic polarity time scale, could be defined for both sites, and it provides a firm chronostratigraphic framework for the Pliocene–Pleistocene sequences. At Site 918, a dramatic change in the sedimentation rate is bounded by a hiatus lasting for about 340 k.y. from about 1.4 to 1.7 Ma. In the Irminger Basin, sedimentation rates may have fluctuated significantly in response to the growth and decay of glaciers in Greenland and changes in the depositional setting. |
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