四川盆地下三叠统飞仙关组层序—岩相古地理特征

Sequence-based Lithofacies and Paleogeography of Lower Triassic Feixianguan Formation in Sichuan Basin

四川盆地下三叠统飞仙关组发育碳酸盐台地相沉积体系,可划分为开阔台地、局限台地、蒸发台地、台地边缘、台地前缘斜坡和海槽盆地等六种相类型。以单井、野外剖面层序划分和连井层序地层对比为基础,将四川盆地下三叠统飞仙关组划分为两个三级层序(SQ1、SQ2)以及四个高位和海侵体系域,编制了全盆地下三叠统飞仙关组各体系域的层序—岩相古地理平面展布图。研究表明,四川盆地下三叠统飞仙关组自西南向东北的相带分异明显。在SQ1层序时期,四川盆地以开阔台地相和局限台地相沉积为主,在中部和东北部一带发育鲕滩和浅滩微相沉积;在SQ2层序时期,四川盆地的中部和东北部广泛发育局限台地潮坪亚相沉积。指出SQ1层序的高位体系域和SQ2层序的海侵体系域为飞仙关组中的鲕滩最为发育的层位,具有较好的油气勘探潜力。

The Lower Triassic Feixianguan sedimentary system of carbonate platform that develops in Sichuan basin consists of six sedimentary facies, including restricted platform facies, open platform facies, evaporite platform facies, platform margin facies, platform foreslope facies and trough basin facies.According to the single-well and outcrop se-quence division and the well-to-well sequence correlation, the Lower Triassic Feixianguan Formation can be divided into a SQ1 and a SQ2 third-order sequences and corresponding HST and TST system tracts. Feixianguan sequence-based lithofacies and paleogeographic maps at each system tract in the whole basin are compiled. It is shown that Feixianguan sedimentary facies presents obvious differentiation from the southwest to the northeast of the basin. During the SQ1 peri-od, the open platform facies and the restricted platform facies commonly developed in the basin but the intraplatform oolitic beach microfacies and the platform-margin shoal microfacies developed in the central and the east of the basin, and during the SQ2 period, the restricted platform tidal flat subfacies widely developed in the central and northeast of the basin. It is concluded that the oolitic beach microfacies deposited in the HST (SQ1) and the TST (SQ2) may be the good reservoirs for exploration potential.