摘要
文章对泸定海子坪昔格达组重新进行了详细的古地磁测试，结果显示昔格达组发育时代为4．2-2．6MaB．P．，地质时代属上新世中、晚期，与前人的研究结果一致。泸定海子坪剖面是目前所知的记录昔格达古湖沉积起始年代最早的剖面。泸定海子坪剖面记录了5个大的从粗→细的沉积旋回，15个沉积阶段。沉积物中值粒径的巾值直接指示了各旋回的沉积阶段，巾值小，水动力较强，为动荡的沉积环境；φ值大，水动力较弱，为稳定的沉积环境。另外，沉积记录显示在约2．8MaB．P．青藏高原的强烈隆升就已开始，昔格达古湖为过水湖；至2．6MaB．P．，昔格达古湖完全消失，与黄土高原风尘沉积环境由红粘土堆积转变为黄土堆积的显著的改变相一致。海子坪剖面TOC高值段，沉积物的φ值也较大，沉积物为粘土、粉砂质粘土沉积；TOC低值段，沉积物的书值也较小，沉积物为中、粗砂沉积，表明昔格达古湖沉积物有机质含量主要受岩性控制。
A detailed re-study of the paleomagnetic polarity stratigraphy of Xigeda Formation with an approximate thickness of 400m in Haiziping, Luding, Sichuan suggests that the upper and lower parts separated at a depth of 360m from the surface belong to the Gauss normal polarity chron and the Gilbert reverse polarity chron respectively. According to the Cande＇s polarity time scale, the age of the Xigeda Formation ranges from 4.2MaB. P. to 2.6MaB. P. , assigned to the Middle and the Late Pliocene, which is consistent with our previous result. This series is known to be the earliest in the Xigeda lacustrine deposition. Based on the φ value of the median size, the sedimentation in Haiziping displays five cycles from coarse to fine including fifteen sedimentary stages. Furthermore, the low φ value indicating strong hydropower infers a queasy sedimentary environment ; while the high φ value infers a stale sedimentary environment. The sediments records indicates that the strongest rising of the Tibetan Plateau begins at about 2.8MaB. P. , and ends at 2.6MaB. P. , consisting with the result from the obvious change of the eolian sedimentary environment in the Loess Plateau. The high TOC value corresponds to the high φ value and the low TOC value the low φ value, showing that the content of the organic matter in lacustrine sediments of the Xigeda Formation is mainly controlled by the lithology.
出处
《第四纪研究》
CAS
CSCD
北大核心
2006年第2期257-264,共8页
Quaternary Sciences
基金
中国地质调查局地质调查项目(批准号:200312300034)
国家自然科学基金重点项目(批准号:90211019)共同资助
关键词
昔格达组
磁性地层学
沉积旋回
中值粒径φ值
TOC
海子坪
泸定
Xigeda Formation, magnetostratigraphy, cycle of sedimentation, the φ value of the median size, TOC, Haiziping, Luding
