复合海平面变化控制下的碳酸盐向上变浅层序──以贵阳地区三叠系大冶组灰岩为例

SIIALLOWING-UPWARD CARBONATE SEQUENCESCONTROLLED BY COMPOSITE EUSTASY:AN-EXAMPLEFROM THE LIMESTONES IN THE TRIASSICDAYE FORMATION IN GUIYANG

碳酸盐向上变浅层序形成的主因乃因在被动大陆边缘至克拉通盆地中，构造沉降速率一般要小于碳酸盐生产速率，而碳酸盐生产速率又要小于海平面变化相对上升速率。由此就形成了台地淹没事件形成的“淹没不整合”界面之上发育的碳酸盐向上变浅层序。这种低频率海平面变化快速上升超过碳酸盐生产速率形成的向上变浅层序，可由许多种类型的米级旋回层序有规律的垂直叠加所构成。在低频率海平面变化的上升阶段则以淹没节拍为主的米级旋回层序为特征，而在停滞至下降阶段则以暴露节拍的米级旋回层序为特征。而且组成向上变浅层序的下部单元──淹没事件形成的凝缩面具有从靠近盆地区到靠近台地区变薄的趋势。贵阳地区三叠系大冶组灰岩由两个向上变浅层序组成，每一层序包括若干个不同类型的米级旋四层序。

The genetic nlechallism of the shallowinguupward carbonate sequences is that the carbonate prodtlctloll rates are greater than the tectonic subsidence rates, hut smaller than therelative risillg rates of sea- level changes. So the shallowing upward carbonate sequencesare developed On the "drowning unconformity surface,’ resulted from the platform drowning evellts. These carbonate sequences are con1Posed of the vertica stacking patterns ofvarlotls nletrc scale cyclic sequences. In the rising stages of low-frequency sea-levelchanges, the metre scale cyclic sequences are characterized by the ’drowning band", whileby the "exIJosillg band,’ in the stalldstill and fall stages. The condensed sections consistingof the lower units of the shal lowing-upward sequences become progresslvely t hinner frombasinwards to plat formwards. The limestones in t he Triassic Daye Formation in theGuiyang area comprise two shallowing t]Pward carbonate sequences, each of which, Inturn,consits of various metreuscale cyclic sequences.