苏皖辽地区新元古代微亮晶构造碳酸盐岩的沉积岩相与环境约束

Microspar Structure Carbonate and Constrain of Sedimentary Facies and Environments in Jiangsu, Anhui and Liaoning Provinces of the Northern China

国内外元古代碳酸盐岩中常见席状、透镜状、脉状和块状等形态的微亮晶碳酸盐岩。微亮晶体宏观、微观边界清晰,内部充填均一等粒结构的方解石微亮晶。宿主岩相以含泥质或粉砂质的细砂屑、粉泥屑灰岩为主,经常与风暴岩共生。微亮晶构造碳酸盐岩发育在缓坡型台地,沉积层序中常见潮汐流、风暴流侵蚀—充填和浪成交错层理与递变层理。微亮晶构造碳酸盐岩发育严格受沉积环境和岩相约束,形成于 (内缓坡深部—中缓坡浅部 )潮下带和环潮坪,风暴浪基面是其发育的最大深度。垂向序列由高频潮下带和环潮坪微层序加积而成,单个微层序顶部通常为环潮坪为纹层状含铁质有机质泥屑碳酸盐岩披盖层,是一个向上沉积动力减弱、沉积物变细和水体变浅的沉积旋回。

Microspar structuresrepresented by complex ptygmatically folded, dotted lags,blobs or vertical and horizontal ribbonsand veinsare common in Proterozoic carbonates worldwide.Microspar structures being filled by fine, equant sparry calcite (or dolomite) crystalsdisplay sharpen lateralboundaries with hosting rocks composed dominantly of lime mud or fine-grained carbonates with quartz silt &clay occasionally and tempestites-carbonaceous tubidite rhythmiteswith microspar veinsand microspar-intraclast lagsin themiddle and upper. Microspar structure limestones are mainly deposited on a remarkably rampcarbonate platform,and common with tidal and storm current plane and gradedbeddings, rhythmites with scalloped erosional surfacesand depositional filled structures in microspar-bearing carbonates. Occurence of microspar structure are identically constrained within shallow subtidal and peritidal(in term of ramp, i.e., deep inner ramp to shallow mid-ramp), andstorm-base in the ramp is the distalsea-floor limit of microspar formation. Vertical successions of microspar-bearing carbonate are stacked by high-frequency shallow subtidal and peritidal cyclic depositional micro-sequences, which showing a cycle of thinning, shallowing and depositional dynamic decreasing-upward, and with a peritidalcap of red iron and organic carbonaceous laminiteattrited to sabuha-like microfacies on the top of individual cycles.