CAJ | 학술논문

为了研究白垩纪中期大洋缺氧事件及其后古海洋环境的变化，对藏南贡扎剖面白垩纪赛诺曼阶/土伦阶和三冬阶/坎潘阶界线附近的浅海相沉积地层开展了详细的岩石磁学对比研究。结果显示，这两个时间段的沉积物中磁性矿物含量和粒度无显著区别，但赛诺曼阶/土伦阶地层中含有高矫顽力磁性矿物，如赤铁矿和针铁矿，而三冬阶/坎潘阶地层中则主要为低矫顽力磁性矿物，如磁铁矿。由于海平面位置在这两个时间段相近，海面变化对沉积物的磁学特征的影响很小。磁性矿物种类的变化可能主要是由于海洋沉积环境的变化所引起的。高矫顽力磁性矿物在赛诺曼阶/土伦阶的出现及其在三冬阶/坎潘阶的缺失，表明赛诺曼阶/土伦阶氧化程度可能比三冬阶/坎潘阶更高。这与深海沉积所记录的赛诺曼阶/土伦阶为缺氧以及三冬阶/坎潘阶为富氧的特征明显不同。这说明以江孜地区为代表的深海—半深海环境和以岗巴定日地区为代表的浅海环境对白垩纪中期气候变化有着不同的响应。深水和浅水环境的演化在这两个时间段的显著差异表明相应时期的大洋环流也可能比以往所认识的更复杂。
위료연구백성기중기대양결양사건급기후고해양배경적변화，대장남공찰부면백성기새낙만계/토륜계화삼동계/감반계계선부근적천해상침적지층개전료상세적암석자학대비연구。결과현시，저량개시간단적침적물중자성광물함량화립도무현저구별，단새낙만계/토륜계지층중함유고교완력자성광물，여적철광화침철광，이삼동계/감반계지층중칙주요위저교완력자성광물，여자철광。유우해평면위치재저량개시간단상근，해면변화대침적물적자학특정적영향흔소。자성광물충류적변화가능주요시유우해양침적배경적변화소인기적。고교완력자성광물재새낙만계/토륜계적출현급기재삼동계/감반계적결실，표명새낙만계/토륜계양화정도가능비삼동계/감반계경고。저여심해침적소기록적새낙만계/토륜계위결양이급삼동계/감반계위부양적특정명현불동。저설명이강자지구위대표적심해—반심해배경화이강파정일지구위대표적천해배경대백성기중기기후변화유착불동적향응。심수화천수배경적연화재저량개시간단적현저차이표명상응시기적대양배류야가능비이왕소인식적경복잡。
In order to study the paleoceangraphic conditions following the mid-Cretaceous oceanic anoxic events (OAEs), we have carried out a rock magnetic study of the Cretaceous shallow marine strata at the Cenomanian/Turonian and Santonian/Campanian boundaries at Gongzha,Southern Tibet, China. The results show that mineral magnetic properties at the two intervals are largely similar including mineral content and particle size, except that the Cenomanian/Turonian boundary statra contain high coercivity magnetic minerals such as hematite and goethite;whereas. Santonian/Campanian boundary strata are dominated by low coercivity minearls such as magnetite. Becaue sea levels at these two intervals are similar, the effects of sea level change on the magnetic characteristics are minimal. The difference in the types of magnetic minerals is probably mainly due to changes in the marine environment. The presence of high coercivity magnetic minerals in the Cenomanian/Turonian boundary strata, but absence in the Santonian/Campanian boundary strata suggest that the shallow marine condition at Gongzha during the Cenomanian/Turonian was more oxic than that during the Santonian/Campanian interval. This observation is different from what is seen in deep ocean where anoxic conditions characterized the Cenomania/Turonian interval and oxygen-rich conditions occurred during the Santonian/Campanian interval. It can be concluded that the deep-bathyal environment represented by Gyantse area and the shallow marine environment represented by Gamba-Tingri area responded differently to climate change in the mid-Cretacrous. And the evolution of the shallow water and deep water were probably different during these time periods and the ocean circulation in these periods may be more complicated than previously thought.