Objective:Abundant soft-sediment deformation structures (SSDS) were found in the Lower Cretaceous Lingshandao Formation on the Lingshan Island.The study aims to discuss the triggers of different SSDS and related environmental meanings.Methods:Field work was conducted for three sections:Chuangchang,Dengta and Qiancengya.Lithology and sedimentary structures were logged.Photos were taken for various SSDS.Thickness was also measured for both deformed and undeformed intervals.Results:Based on field survey of Chuanchang,Dengta and Qiancengya sections,two basic subdivisions were recognized as deformation intervals and undeformation intervals respectively,in both of which SSDS are developed.Folds,deformation laminations and load structures are observed in the deformation intervals,and flame structures,syn-sedimentary boudinage structures and syn-sedimentary micro-faults are seen in the undeformation intervals.SSDS show large scale (up to ＞ 10m thick and up to a few hundred meters long) and good lateral continuity in the deformation intervals,but small scale (only few cm) and poor lateral continuity in the undeformation intervals.Statistical relationship of thickness about undeformation and deformation intervals displays no direct relationship between SSDS of deformation intervals and sandstone thickness.However,SSDS of undeformation intervals occur at the base of graded sandstone or closely with sandstone beds with increased thickness in a thickening-upward cycle.Sedimentary environment analysis indicates a low-angle deep-water slope for the accumulation of Lingshandao Formation containing undeformation and deformation intervals.The slope topography,in a way,controls the morphology and quantity of SSDS.Based on sedimentary environment and sedimentary structures,the trigger is considered to be seismicity for the SSDS of the deformation intervals and over-loading for that of undeformation intervals.Dated age using zircon evidences approximated deposited time between the Lingshandao Formation and overlying rhyolite bed.As a result,the seismicity of the triggers may be related to volcanic activities or early magma intrusion.Besides,catastrophic events(e.g.Early Cretaceous Anoxic Events) are inferred in the Early Cretaceous based on time—consistence of Lingshandao Formation,cooling event,dinosaur activity,sea-level fluctuation and carbon isotope excursion.Conclusions:The SSDS observed are considered to be caused by two kinds of triggers:seismicity and sediment load.Besides,the triggers imply contemporary volcanic activity.With other evidence,a catastrophic event like Early Cretaceous Anoxic Events is inferred.%灵山岛早白垩灵山岛组发育丰富的软沉积物变形构造.野外踏勘船厂、灯塔和千层崖三个剖面,根据沉积外观可分为变形层段和非变形层段两个部分.软沉积物变形构造在变形层段和非变形层段均有发育.其中,变形层段中可见褶皱变形、变形层理及大型负载构造.非变形层段可见火焰构造、同沉积布丁构造和同沉积微断层.研究发现,变形层段软沉积物变形构造尺度大(厚度可至十多米,长度可至数百米),侧向连续性好;非变形层段软沉积物变形构造尺度小(厚度仅几个厘米),侧向连续性差.且变形层段和未变形层段厚度统计数据表明,变形层段软沉积物变形构造与砂岩厚度无必然联系,而非变形层段软沉积物变形构造多出现在粒序砂岩层底部或旋回砂岩层变厚过程中.沉积环境表明,非变形层段和变形层段为一深水低角度斜坡沉积产物.软沉积物变形构造发育形态和数量受到斜坡地形的控制.结合沉积环境及沉积特征分析,认为变形层段软沉积物变形构造触发机制为地震,而非变形层段软沉积物变形构造触发机制为负载作用.锆石测年数据表明灵山岛组与上覆流纹岩沉积时间相近,因此地震活动可能与岩浆侵入或早期火山喷发活动相关.此外,汇总早白垩世重要事件,发现灵山岛组沉积、变冷事件、恐龙迁移、海平面变化和同位素偏移具有时间一致性,因此推断这些事件可能共同对应了早白垩世一次与火山活动相关的短期灾难性事件(如早白垩世缺氧事件).
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