The Cenomanian-Turonian strata of the Second White Specks (2WS) Formation on the cratonic margin of the Western Interior Seaway (WIS) are comprised of organic-rich, carbonate-siliciclastic successions. This study focuses on a carbonate-siliciclastic succession of the 2WS in two cored wells located on the eastern margin of the Cretaceous Interior Seaway. Based on sedimentary facies and organic/inorganic geochemistry representing distal and proximal sections of the 2WS, it was possible to interpret factors, including productivity, preservation, and dilution of the Organic Matter (OM). The results revealed eight subfacies and three main facies associations, including deep shelf calcareous mudstones and marlstones, and shallow shelf bioclastic limestones. The carbonaceous mudstones have high type II immature kerogen content and the bioclastic limestones have low organic content dominated by type III and degraded type II kerogen. The 2WS mineralogy primarily consists of calcite, clay minerals, and quartz, and is characterized by a low degree of physical and chemical diagenesis. Based on mineralogical analysis, carbonate is the dominant component, and its proportion is inversely associated with terrigenous silica content. There is a general increase in carbonates and a decrease in siliciclastics from the distal to the proximal sections within the study area. Lateral changes in physical and chemical properties of similar facies associations are mainly controlled by changes in water depth. The 2WS was deposited during a long-lived transgression comprised of higher order parasequences. Core logging data from multiple drillholes show that these parasequences have a general coarsening upward trend with an upward shift from pelagic (i.e., planktonic foraminifera and coccoliths) to benthic (i.e., ) carbonate productivity. During deposition of the mudstone/marlstone facies association, a clear and oxygenated water column allowed for a high photosynthetic activity to occur within the photic zone, which is reflected in OM enrichment and higher micronutrient content, such as Zn and Ni, predominance of fecal aggregates, and planktonic foraminifera. In the mudstone/marlstone facies, oxygen deficient pore water conditions, which are reflected in the high redox-sensitive trace element concentrations such as V, contributed to the high degree of OM preservation. The 2WS along the eastern margin of the WIS was deposited on a low gradient carbonate ramp environment. The oxygenated broad ramp accommodated the bioclastic limestones, which are characterized by high benthic carbonate dilution rate that resulted in lower OM preservation potential. The shallow shelf setting was characterized by restricted wave energy and minimal fluvial input from the adjacent craton under temperate climatic conditions. This study contributes to our understanding about paleo-oceanography and hydrocarbon exploration in analogous epeiric seas and mixed siliciclastic‑carbonate marine settings around the world.

中文翻译：

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加拿大西部内海道东缘白垩纪第二白斑地层的相分析和古环境重建的多学科方法


位于西部内海道 (WIS) 克拉通边缘的第二白斑 (2WS) 地层的塞诺曼阶-土伦阶地层由富含有机质的碳酸盐-硅质碎屑层序组成。本研究重点研究位于白垩纪内海道东缘的两口取心井中 2WS 的碳酸盐-硅质碎屑层序。根据代表 2WS 远端和近端部分的沉积相和有机/无机地球化学，可以解释因素，包括有机质 (OM) 的生产力、保存和稀释。结果揭示了8个亚相和3个主要相组合，包括深陆棚钙质泥岩和泥灰岩，以及浅陆棚生物碎屑灰岩。碳质泥岩具有较高的II型未成熟干酪根含量，而生物碎屑灰岩有机质含量较低，以III型和退化II型干酪根为主。 2WS矿物主要由方解石、粘土矿物和石英组成，具有物理和化学成岩程度低的特点。根据矿物学分析，碳酸盐是主要成分，其比例与陆源二氧化硅含量成反比。研究区内从远端到近端碳酸盐岩普遍增加，硅质碎屑岩减少。相似相组合物理化学性质的横向变化主要受水深变化控制。 2WS 是在由高阶准层序组成的长期海侵期间沉积的。来自多个钻孔的岩心测井数据表明，这些准层序总体上具有粗化上升趋势，并且从远洋向上移动（即、浮游有孔虫和颗石藻）到底栖（即）碳酸盐生产力。在泥岩/泥灰岩相组合的沉积过程中，清澈的含氧水柱使得透光区内发生高光合作用活动，这反映在 OM 富集和较高的微量营养素含量（例如 Zn 和 Ni）、粪便聚集体的优势中。和浮游有孔虫。在泥岩/泥灰岩相中，缺氧的孔隙水条件（反映在V等氧化还原敏感微量元素浓度高）有助于OM的高度保存。沿 WIS 东缘的 2WS 沉积在低梯度​​碳酸盐缓坡环境中。含氧宽坡道容纳了生物碎屑石灰岩，其特点是底栖碳酸盐稀释率高，导致有机质保存潜力较低。浅陆架设置的特点是波能有限，并且在温带气候条件下来自邻近克拉通的河流输入最少。这项研究有助于我们了解世界各地类似的浅海和混合硅质碎屑-碳酸盐海洋环境中的古海洋学和碳氢化合物勘探。