Upper Miocene to Recent magnetic stratigraphy in deep-sea sediments

Two of the longest piston cores of deep-sea sediment ever recovered were taken in the equatorial Pacific on the twelfth cruise of the research vessel Robert D. Conrad. The two cores, 26 and 28 meters in length, penetrate calcareous and siliceous ooze to sediments of Miocene age. Paleomagnetic measurements were made on samples partially demagnetized in a 60-Hz alternating field of 50 oe. The sampling interval was every 10 cm between reversals and continuously across reversal boundaries. Similar paleomagnetic measurements were made at 10-cm intervals on a siliceous ooze core 15 meters in length and on a red lutite core 8 meters in length. All four cores show a magnetic stratigraphy extending below the Gilbert polarity series/epoch 5 boundary. One of the long cores has an apparently continuous magnetic record back to an epoch we correlate with the sea-floor-spreading anomaly 5 at nine million years or older. For ease in correlation, this magnetic record has been subdivided into seven new magnetic epochs numbered from epoch 5 to epoch 11. The magnetic stratigraphy observed is in substantial agreement with the pattern of magnetic polarity epochs predicted by sea-floor spreading.