Strontium geochemistry of Miocene primary gypsum; Messinian of southeastern Spain and Sicily and Badenian of Poland
Strontium geochemistry of Miocene primary gypsum; Messinian of southeastern Spain and Sicily and Badenian of Poland
复制标题
中新世原生石膏的锶地球化学；
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
T. Peryt
中科院分区：
文献类型：
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作者：
L. Rosell;F. Ortí;A. Kasprzyk;E. Playà;T. Peryt
摘要对西班牙东南部和西西里岛的梅西尼期(上中新统)盆地和波兰巴登期(中中新世)喀尔巴西亚前陆盆地的原生海相石膏相进行了锶含量研究。所获得的结果是根据关于地中海西海岸现代萨利纳斯石膏相的报告结果而解释的。从索尔巴斯盆地(西班牙东南部)石膏矿床下部获得的锶剖面具有均一的锶含量，反映了水文稳定和相对深水条件下的沉积，但根据其他沉积学标准，上部的锶含量变化较大，与盆地变浅有关。这与西班牙东南部其他梅西尼亚盆地(San Miguel de Salinas和Palma de Mallorca)报告的数据一致。在Caltanissetta盆地(西西里)，Eraclea Minoa(上蒸发岩)研究的剖面由6-8个石膏旋回组成，每个旋回的相演化从每个旋回底部的细粒层状石膏到顶部的Selenite，并伴随着锶含量的增加。这种演化归因于盐度条件的增加，并与文献中报道的地球化学数据一致。在巴丹扬盆地，所研究的6个石膏剖面来自不同的次盆地。石膏矿床由两个成员组成。下段以富硒为主，在下段向上段的过渡过程中，可区分出两个部分，并记录到明显的锶增加(归因于盐度的上升)。在上段，主要是碎屑石膏，锶的普遍减少表明盐度的下降与地台的加深或淡化有关。在巴登亚铁质层中，锶的含量存在横向变化：边缘带的锶含量较高和较不均匀，表明盐度条件不同，而在更深的地区，石膏层显示出更均匀的锶含量，预计来自更稳定和更低浓度的卤水。这一分布与西班牙东南部圣米格尔·德·萨利纳斯的梅西尼亚盆地报告的数据一致。梅西期和巴登期富硒样品中的锶含量均低于现代萨利纳期富硒结壳中的锶含量。这些较低的含量可能是由于在富硒层序沉淀过程中稳定状态的母卤水的盐度低于现代盐湖的高浓缩(无回流)卤水所致。我们的发现强调了研究海相原始石膏相中锶含量作为解释蒸发环境的古地理和古盐度以及对比旋回亚硒建造的工具的意义。这种方法在与其他地球化学指标(即同位素和(或)流体包裹体成分)相结合时可能特别有用。
ABSTRACT The strontium contents of primary marine gypsum facies were studied in Messinian (Upper Miocene) basins of SE Spain and Sicily, and in the Badenian (Middle Miocene) Carpathian foreland basin of Poland. The results obtained were interpreted on the basis of the findings reported for the gypsum facies of recent salinas in the western Mediterranean coast. The strontium profile obtained from the lower part of the gypsum deposit of the Sorbas basin (SE Spain) has homogeneous strontium contents, reflecting deposition under conditions of hydrological stability and relatively deep waters, but the upper part has a more variable strontium content related, in accordance with other sedimentological criteria, to a shallowing of the basin. This is consistent with data reported from other Messinian basins of SE Spain (San Miguel de Salinas and Palma de Mallorca). In the Caltanissetta basin (Sicily), the section studied in Eraclea Minoa (Upper Evaporite) is made up of 6-8 gypsum cycles that have a facies evolution from fine-grained laminar gypsum at the base of each cycle to selenites at the top, accompanied by increasing strontium values. This evolution is attributed to increasing salinity conditions and is consistent with geochemical data reported in the literature. In the Badenian basin the six gypsum sections studied are from different subbasins. The gypsum deposits comprise two members. In the lower member, which is mainly selenitic, two parts can be differentiated and a significant strontium increase (attributed to a rise in salinity) was recorded in the transition from the lower to the upper part. In the upper member, which is mainly clastic gypsum, a general strontium decrease indicates a fall in salinity linked to a deepening or freshening of the platform. In the Badenian selenitic layers a lateral variation in the strontium contents exists: higher and less homogeneous strontium contents were recorded in the marginal zones, suggesting variable salinity conditions, whereas in the deeper areas the gypsum layers show more homogeneous strontium values, expected from more stable and less concentrated brines. This distribution is in agreement with data reported from the Messinian basin of San Miguel de Salinas (SE Spain). The strontium contents in both the Messinian and Badenian selenitic samples are lower than those in the selenitic crusts of the recent salinas. These lower contents may be a result of a lower salinity of the mother brines at the steady state achieved during the precipitation of the thick selenitic sequences, with respect to the highly concentrated (with no reflux) brines of the recent salinas. Our findings highlight the relevance of studying strontium contents in primary gypsum facies of marine formations as a tool for interpreting the paleogeography and the paleosalinity of the evaporitic enviroents and for correlating cyclic selenite formations. This method could be especially helpful when combined with other geochemical indicators (i.e., isotopic and/or fluid inclusions composition).