【作者】 邢智峰；

【导师】 齐永安；

【作者基本信息】 河南理工大学 ， 矿产普查与勘探， 2010， 博士

【摘要】 豫西地区中元古界云梦山组隶属于汝阳群,在构造古地理上属于华北地台南缘,主要为一套陆源碎屑岩沉积。微生物成因沉积构造(MISS)主要产于本组中段和上段的紫红色或黄白色砂岩层面,多发育在与泥岩的接触面上,常与波痕伴生,类型多样。云梦山组的微生物成因沉积构造可分为微生物席生长相关构造、微生物席代谢相关构造、微生物席破坏相关构造和微生物席腐烂相关构造四大类,其中捆绑波痕、强烈皱饰和不规则网状凹坑为云梦山组发现的新类型。微生物成因沉积构造发育在无障壁海岸环境的上临滨、前滨以及潮坪环境的潮下带到潮上带的广大地区,在豫西云梦山组具有较显著的分布和演化特征:(1)类型分布的差异。无障壁海岸环境发育的微生物成因沉积构造以大型多边形网状脱水裂痕为主,含少量的微生物席砂片,类型单调;而碎屑岩潮坪环境发育的微生物成因沉积构造类型更加多样化,包含从生长构造到腐烂构造四大类型,以微生物席破坏相关构造最为常见。微生物成因沉积构造多样化的特点可作为潮坪环境的指示标志。(2)相比较而言,云二段潮坪环境中发育的微生物成因沉积构造比云四段密集,可能是云一段的火山活动给海水带来了丰富的矿物成分,有利于微生物的生长。(3)云梦山组微生物成因沉积构造的发育与海进、海退的旋回有密切联系,微生物成因沉积构造往往发育在海泛面上。(4)用微生物席干裂多边形的大小对微生物席厚度进行估测,无障壁海岸环境比潮坪发育了更厚的微生物席,这说明当时的微生物席能繁盛在水动力较强的区域。从云梦山组底部到顶部,古代微生物席的厚度总体上在减薄。云梦山组微生物成因沉积构造的时空分布和演化特征对古环境具有重要的指示作用。微生物成因沉积构造样品的纵切观察可见典型的微生物席纹层,代表着微生物席在沉积表面的多次生长和埋藏。深色层包含有泥质物和细砂-粉砂颗粒,被认为是先前微生物席的残留区;浅色层则是较纯净的石英颗粒,由物理沉积作用形成。显微观察发现五种明显的微生物成因沉积构造的微结构类型,分别是:波曲层、网状结构、定向颗粒层、细小颗粒层和重矿物层,可作为当时微生物席存在的证据。云梦山组微生物成因沉积构造的大量发育表明了当时微生物席的繁盛,代表了远古微生物席在沉积物表面殖居、生长、代谢以及与沉积物相互作用的一些特征,同时也指示了当时的水动力状况和古环境特征。对微生物成因沉积构造中微生物化石的探索性研究发现在薄层粉砂质泥岩层存在一些丝状菌化石、球状菌化石、硅化的EPS和未知的生物化石。化石的生物类型以蓝细菌为主,并可见分层分布。这些发现为认识古代微生物席群落的结构和功能提供了依据。通过现代微生物席与古代微生物席的比较研究,对云梦山组微生物席发育的环境特征、微生物群落的结构以及微生物成因沉积构造的成因进行了讨论,对气隆构造、不规则网状凹坑和网状生长脊的成因有了直观认识。更多还原

【Abstract】 TheYunmengshan Formation, belonging to Mesoproterozoic Ruyang Group, lies in the south margin of the North China platform and consists mainly of siliciclastic sedimentary successions. Microbially Induced Sedimentary Structures(MISS) occur in purple or yellow sandstone interbedded with mudstone or siltstone, especially in junction surface between sandstone and mud lamination. They displayed a plenty of morphologies and preserved in acompanying with ripple markers as usual. The well-preserved structures include mat growth features, mat metabolism features, mat destruction features and mat decay features with three new types founded in this paper: binding ripples, intense ornamentations and reticulate irregular pits.MISS were well preserved in beach environment from the shoreface to the foreshore and especially in peritidal siliciclastic environments from the subtidal to the supratidal zones. They display some features in Yunmengshan Formation as follows: (1) Some big polygonal desiccation cracks with microbial sand chips are common in beach environments, and middle-small polygonal desiccation cracks with kinds of other MISS mainly occur in tidal flat environments displaying the MISS diversity; (2) The ancient microbial mat became thinner from the bottom to the top of Yunmengshan Formation and the thicker ancient mat colonized in beach facies to fit for higher hydrodynamic condition; (3) MISS are much more abundant in the Second Member of Yunmengshan Formation than that of other Members; and (4) MISS from Yunmengshan Formation correlate with turning points of regression and transgression and especially well developed and preserved in deposits that mark marine flooding surfaces.In vertical section, the typical stacked mm-level siliciclastic biolaminites consisting of alternations of dark silty mudstones and light quartz sandstone represent repeated growth and burial of mats during repeated depositional events. The dark layers are considered to represent the remains of microbial mats, whereas the light layers consist of physical process induced quartz grains. In the further investigation of thin-sections, five types of microstructures have been found: wavy crinkled laminae, network fabrics, mat layer bound small grains, mat layer bound heavy minerals and oriented grains. These structures can reflect the unique characters of mat growth, mat metabolism, interactions with sediments and can be used to trace the thriving microbial mat colonized in this area and reveal the sedimentary dynamics and paleoenvironmental features in this area.Filament fossils, coccoid fossils, silicified EPS and unknown fossils have been found in dark silty mudstones of MISS. Most of the microbial taxa were cyanobacteria which mainly display the horizontal distribution. These Proterozoic microfossils are valuable for the research of microbial communities and their functions. Comparison the ancient mat with modern microbial mat can help us to well understand the colonized palaeoenvironments, microbial community structures and origins of MISS. From this study, we have built the origin model of gas domes, reticulate irregular pits , reticulate growth ridge etc.更多还原