A paleomagnetic study of about 95 samples from 16 sites sampled in the Early Cretaceous in Luanping basin in Hebei Province was reported. Stepwise thermal demagnetization was used to isolate magnetic components. Most samples have a characteristic direction with a high temperature component above 500°C. The tectonic-corrected data areD = 347.8°,I = 50.4°, α95 = 7.l°, and the corresponding pole position is at 76.1°N, 346.3°E,with dp =6.4°,dm = 3.8°, paleolatitude λ = 31.1°N. This result indicates a counterclockwise post-Cretaceous rotation of 30.7° ±9.8° with respect to the stable Ordos basin in the west of North China Block, and a non-significant northward motion. This rotation could be related to local fault action or structural detachment, or regional NNW-NWWward motion and collision of Kula-Pacific plate with eastern China since the Early Cretaceous.
The Oligocene ostracod fauna of IISDP Site 292 of the western Philippine Sea was marked by high density, diversity and origination,
probably reflecting a favorable period for deep-sea Ostraroda; while the sharp decrease in dtmsity and diversity as well as
the repeatedly occurring vxtinctions in thc. Neogene may indicate the deterioration in bottom-water environmcnts at that tlme.
Five rriajor faunal changes have been recognized in terms of density, diversity and evolutionary artivity (origination and
extinction), occurring in the earliest Oligocene (PI8), mid-Oligocene (P21), earliest Miocene (N4), early Middle Miocene (N8)
and late Pliocene (N21). respectively. These changes in ostracod faunas are suggested to represent short-term events related
to global paleoceanographical changes and to record the Cainozoic cooling history of the West Pacific Ocean and Philippine
Sea deep-water.
Project supported by the National Natural Science Foundation of China (Grant No. 49676287). 相似文献
A paleomagnetic study of about 95 samples from 16 sites sampled in the Early Cretaceous in Luanping basin in Hebei Province was reported. Stepwise thermal demagnetization was used to isolate magnetic components. Most samples have a characteristic direction with a high temperature component above 500°C. The tectonic-corrected data areD = 347.8°,I = 50.4°, α95 = 7.l°, and the corresponding pole position is at 76.1°N, 346.3°E,with dp =6.4°,dm = 3.8°, paleolatitude λ = 31.1°N. This result indicates a counterclockwise post-Cretaceous rotation of 30.7° ±9.8° with respect to the stable Ordos basin in the west of North China Block, and a non-significant northward motion. This rotation could be related to local fault action or structural detachment, or regional NNW-NWWward motion and collision of Kula-Pacific plate with eastern China since the Early Cretaceous. 相似文献