哈尔滨居仁砂砾石剖面沉积特征及其环境意义

Sedimentary Characteristics and Environmental Significance of the Juren Sandy Gravel Profile in Harbin

前人将黑龙江宾县居仁镇的砂砾石层(居仁剖面)视为罗家窝棚组,成因类型为早更新世早期的冰碛物堆积。然而,居仁剖面和罗家窝棚组的研究极为薄弱,极大限制了该地层所记录的区域构造—地貌—气候—水系演化信息。选择居仁剖面为研究对象,对其沉积学、矿物学和元素地球化学特征进行研究。结果表明,居仁剖面砾石风化程度较低、分选差、磨圆较好、无定向性,砾石成分以陆源碎屑岩(43%)、花岗岩(28%)和石英质(26%)为主,凝灰岩和流纹岩少量出现。重矿物组成以绿帘石(42%)和锐钛矿(9.9%)占绝对优势,其次为白钛石(8.7%),重晶石(15.2%)、黄铁矿(14.5%)和萤石(11.3%)在个别样品中大量出现,其他重矿物含量较少。元素地球化学揭示了居仁剖面沉积物弱—中等的化学风化程度,大部分沉积物经历了首次循环以及其长英质的母岩属性。与罗家窝棚组标准地层的沉积学特征对比,沉积物的颜色、固结程度、沉积物结构、地层结构、沉积物成因类型以及地貌特征等都存在显著差异。因此,居仁剖面不是罗家窝棚组,成因类型为湖滨或河流入湖三角洲沉积。上述研究对于哈尔滨地区第四纪地层的划分和早更新世区域环境的重建有重要意义。

The gravel layer(Juren profile)in Juren town,Bin county,Heilongjiang province has previously been re⁃garded as part of the Luojiawopeng Formation,and its genesis was thought to be Early Pleistocene glacial moraine de⁃posits.Very little research has been done on the Juren profile and the Luojiawopeng Formation,however,which has greatly restricted reconstruction of the regional tectonic-landform-climate-drainage evolution from the information re⁃corded in the strata.To throw more light on this topic,the Juren profile was selected to study its sedimentology,min⁃eralogy and elemental geochemistry.It was found that the gravel has a low degree of weathering,poor sorting,good rounding,and is non-directional.It is dominated by terrigenous clastic rocks(43%),granite(28%)and quartz(26%),and contains small amounts of tuff and rhyolite.The composition of heavy minerals is dominated by epidote(42%)and anatase(9.9%),followed by leucoxene(8.7%),barite(15.2%),pyrite(14.5%)and fluorite(11.3%).They occur in large amounts in individual samples,with a lower content of other heavy minerals.Elemental geochemical tests revealed a weak-to-medium degree of chemical weathering,most of which has undergone the first cycle and retains its felsic source-rock properties.Sediment color,degree of consolidation,sediment structure,strati⁃graphic structure,sediment genetic type and geomorphological characteristics are all significantly different from those in the Luojiawopeng Formation,from which it is inferred that the two are not related.The genetic type is lakeside or river inflow delta deposit.These findings are of great importance for the division of Quaternary strata in the Harbin area and for the reconstruction of the regional environment in the Early Pleistocene.