从岩石学及微区同位素探讨四川盆地灯影组皮壳-葡萄状白云石成因

发布时间：2018-04-15 03:25

本文选题：岩石学 + 微区同位素　；参考：《石油与天然气地质》2017年04期

【摘要】：四川盆地灯影组中的"皮壳、栉壳及葡萄状"白云石是一种非常特殊结构白云石。对四川盆地灯影组葡萄-皮壳状及基岩岩石学、碳氧与锶同位素等研究表明:皮壳-葡萄状白云石早期由内纤状(AC)、外为束状-放射状海底纤柱状(RFC)的文石及犬牙状高镁方解石或粒状方解石构成。不同尺度"球状-哑铃"或菱形的泥微晶白云石沿C轴呈台阶式相向生长,反映了海水潜流带为主的生长模式。微区同位素揭示了环带中的粉细晶白云石要比黑、白相间纤状白云石中的δ~(13)C,δ~(18)O负偏明显;黑色纤状又较白色纤状白云石δ~(13)C,δ~(18)O正偏。环带至少有3种变化情形:(1)δ~(18)O(PDB),δ~(13)C(PDB)负偏,87Sr/86Sr较高,较宽的明、暗阴极条带,指示了周期性弱氧化与弱还原环境的变化海水并叠加了大气淡水作用;(2)有序度变化大,从环带核部至边缘,δ~(13)C(PDB)缓慢下降,δ~(18)O(PDB)缓慢升高,87Sr/86Sr接近同时代的海水平均值,核部中等橙红向外为不发光-暗淡发光,反映了核部弱还原向外变为弱氧化、海水并有持续大气淡水的补给;(3)有序度较低、从环带核部至边缘,δ~(13)C(PDB)缓慢上升,δ~(18)O(PDB)先升后降,边缘稍为偏负,中等橙红色、间隔有相对暗淡阴极发光,推测为停滞浓缩海水为主、后有弱氧化大气淡水补给。据此推断,皮壳-葡萄状白云石是在新元古南华纪冰期的特殊海水背景下,经历了过饱和海水中微生物中细菌参于下成核、准稳态含镁矿物沉淀(AC-RFC)、大气淡水下水岩作用粒状方解石(RFC-PC)和浓缩海水中的准同生云化作用过程。
[Abstract]:The dolomite of the Dengying formation in Sichuan Basin is a very special structure dolomite.The petrology of Grape crust and bedrock of Dengying formation in Sichuan Basin,Carbon-oxygen and strontium isotopic studies show that early crustacean-grape dolomite was composed of internal fibrous actinite and bunchy-radial submarine fibrous columnar RFC) and canine dentate high magnesium calcite or granular calcite.Different scales of "globular dumbbell" or rhombohedral mud-microcrystalline dolomite growth along the C-axis of the pedestal phase, reflecting the sea water subcurrent zone dominated growth pattern.The microregional isotopes reveal that the fine crystalline dolomite in the annular zone is more negative than that in the black, white interphase fibrous dolomite has a negative bias of 13C, 未 ~ (18) O, and the black fiber shape is more positive than that of the white fibrous dolomite 未 ~ (13) ~ (13) C, 未 ~ (18) O.There are at least three variations in the ring zone: 1) 未 ~ (18) O ~ (+) PDBs, 未 ~ (13) C ~ (+) C ~ (DBB)) with a higher negative bias of 87s ~ (86) Sr and a wide strip of bright and dark cathode, indicating the variation of the environment of periodic weak oxidation and weak reduction of seawater and superposing the effect of fresh water in the atmosphere (2) the degree of order varies greatly.From the core of the ring band to the edge, the 未 ~ (13) C ~ (PDBs) decrease slowly, and the 未 ~ (18) O ~ (6 +) increase slowly. The 87s ~ (87) Sr ~ (86) Sr is close to the average value of the sea water of the same time. The medium orange red of the nucleus is non-luminescent and dim, which indicates that the weak reduction of the nuclear region becomes weak oxidation.The order of sea water is low, from the core of the annular zone to the edge, 未 ~ (13) C ~ (C ~ (+)) PDBs rise slowly, and then rise and then decrease, the edge is slightly negative, medium orange red, and the interval is relatively dim and cathodoluminescence, so it is assumed that the concentration of seawater is mainly stagnant and concentrated.Then there is a weak oxidation of fresh water recharge of the atmosphere.It is inferred that the crust-grape dolomite was formed under the background of the special sea water during the Neoproterozoic Southern China glacial period, and the bacteria in the supersaturated seawater were involved in the formation of the bacteria.Quasi-steady precipitation of magnesium-bearing minerals (AC-RFCU), granular calcite (RFC-PC) from freshwater water in the atmosphere and quasi-synchronal clouding processes in concentrated seawater.
【作者单位】：中国石化石油勘探开发研究院无锡石油地质研究所;中国石化石油勘探开发研究院;中国石化西南油气分公司石油勘探开发研究院;中国石化江苏油田分公司采油二厂;
【基金】：国家自然科学基金联合基金项目(U1663209) 国家重点基础研究发展计划(973计划)项目(2012CB214802) 国家科技重大专项(2011ZX05005-0023,2011ZX05008-003-11)
【分类号】：P588.245;P618.13

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