Distributional signatures of depositional system of Pinghu Formation, Pinghu slope, Xihu Sag, East China Sea Shelf Basin
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摘要: 东海陆架盆地西湖凹陷平湖斜坡带始新统平湖组是目前已证实的主力油气富集层系,对其沉积体系已开展过多轮研究,但是仍然存在很大争议。在前人研究的基础上,基于新处理的三维地震、岩心和多种地球化学测试等资料,对平湖斜坡带平湖组沉积环境和沉积体系重新展开了系统分析。平湖斜坡带主要发育三种沉积体系类型:河控三角洲、潮汐改造为主的三角洲和潮坪沉积体系。这三种沉积类型在平面上具有明显的分区性,平北地区以河控三角洲沉积为主,平中地区发育受潮汐改造的三角洲沉积,平南地区处于半封闭海湾湾口,以潮坪体系为主,洋流控制着砂体的空间展布形态和规模。整体而言,平湖斜坡带平湖组沉积格局从北向南表现出受海水影响逐渐加强的变化规律。Abstract: The Eocene Pinghu Formation on the Pinghu slope of Xihu Sag of East China Sea Shelf Basin is a main confirmed strata for hydrocarbon enrichment. At present, many studies have been carried out on its sedimentary system, but certain controversies are still existed. On the basis of previous studies and newly processed 3D seismic, core and geochemical data, it was re-analyzed in this paper for the sedimentary system of Pinghu Formation. Results show that there are three types of sedimentary system on the slope belt: river-controlled delta, tidal-transformed delta and tidal flat depositional system. These three types of sedimentary modes have obvious zoning characteristics in plane. The northern area is dominated by river-controlled delta deposits. The middle area is dominated by tidal-transformed delta deposits. The southern area is in the mouth of a semi-closed bay, dominated by tidal flat system, and ocean currents control the spatial distribution shape and scale of sand bodies. It is concluded that the influence of seawater on the sedimentary pattern of the Pinghu Formation in the slope belt is strengthening from north to south.
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Key words:
- sedimentary distribution law /
- sedimentary system /
- Pinghu Formation /
- Eocene /
- Xihu Sag /
- East China Sea Shelf Basin
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图 3 东海西湖凹陷平湖组典型岩心照片
a-e为8井,4 104.86~4 114.21 m:a.灰白色含砾中砂岩,最大粒径0.8 cm;b.板状交错层理,底见冲刷面;c.灰白色砂砾岩,低角度交错层理;d.灰白色中砂岩,冲刷面,正粒序;e.灰白色中砂岩,楔状交错层理。f-h为7井,4 465.89~4 474.79 m:f.灰白色中细砂岩,板状交错层理;g.灰白色中细砂岩,小型交错层理;h.灰色粉砂岩,脉状层理。i.5井,4 015.2 m,灰色细—粉砂岩,羽状交错层理;j.5井,4 341.8 m,粉砂岩,透镜状层理;k.4井,4 203.17 m,灰白色细沙岩,暗色矿物定向,含泥砾;l.4井,4 211.67 m, 灰白色细沙岩,倒粒序。m-o为1井,3 235.5~3 240.7 m:m.浅灰色泥质粉砂岩,岩性截变面;n.底砾岩及碳质泥岩;o.浅灰色泥质粉砂岩,撕裂状泥砾、脉状层理
Figure 3. Typical core pictures of Pinghu Formation in Xihu Sag, East China Sea Shelf Basin
图 6 东海西湖凹陷平湖斜坡带碎屑锆石年龄多维尺度分析
a-l为样品编号,位置见图 1;实线表示亲缘关系最近的样品,虚线表示亲缘关系次之的样品
Figure 6. Multidimensional scale analysis of detrital zircon ages, Pinghu slope belt, Xihu Sag, East China Sea Shelf Basin
表 1 东海西湖凹陷平湖斜坡带平湖组沉积体系类型划分
Table 1. Classification of sedimentary system types of Pinghu Formation in Pinghu slope belt, Xihu Sag, East China Sea Shelf Basin
沉积相 亚相 微相 河控三角洲 三角洲平原 水上分流河道、分流河道间 三角洲前缘 水下分流河道、分流间湾、河口砂坝 前三角洲 前三角洲泥 潮汐改造为主的三角洲 三角洲平原 水上分流河道、分流河道间、沼泽 三角洲前缘 水下分流河道、河口砂坝、潮汐砂坝、砂脊、席状砂 前三角洲 前三角洲泥 潮坪 潮上带 沼泽、泥坪 潮间带 泥坪、混合坪、砂坪、潮汐砂脊、潮砂丘 潮下带 潮汐水道、潮砂席、水下沙坝 注:表中内容据刘晓晨(2018)[19]修改。 -
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