Stratal stacking patterns and factors influencing peat accumulation in coastal and continental settings represent a significant problem in studying coal-bearing sequences. To address this issue, this work focused on the Cretaceous-Paleogene Guaduas Formation on the Checua-Lenguazaque Syncline (CLS) coalfield in the Eastern Cordillera Basin (Colombian Andes). This study relies on geological survey, facies analysis, sequence stratigraphy, organic geochemistry, and coal petrography. Through these methods, depositional systems and sequences were characterized, and their relationship with coal composition was established. Sedimentary facies were categorized into four Facies Associations (FAs): lagoon, tidal flat, delta plain, and mixed fluvial system. Five T-R sequences (S1 to S5, in ascending order) were identified. S1 consists of lagoon and tidal sandstone, mudstone, and coal. S2-S4 comprise tidal, deltaic, and fluvial deposits. S5 is composed mainly of deltaic and fluvial facies. Thick coal seams (> 0.7 m) were concentrated in the regressive system tracts of S1 and S3, while the transgressive coals were deposited in S2-S3 and are associated with tidal environments. The organic petrography showed enrichment in vitrinite (30.00–85.20 %), while liptinite (0.00–16.60 %) and inertinite (4.60–34.40 %) varied according to depth and paleoenvironments. CLS coalfield displays an environmental evolution from shallow marine and lagoon deposits to deltaic and fluvial environments. Minor sea-level fluctuations, changes in accommodation, siliciclastic influx, and plant community distinguish this sedimentary succession. The deposition of the Guaduas Formation is characterized by a prograding pattern with dominant shallowing-upward cycles in a high accommodation setting. The organic matter accumulated under limno-telmatic to telmatic conditions in mesotrophic to ombrotrophic environments with nutrients derived mainly from rainfall. The paleoclimate for the Guaduas Formation indicates wet and hot conditions for flora expansion. This investigation determined paleoenvironments of the Maastrichtian-Paleocene coastal to fluvial successions within the tropical latitudes, indicating a strong relationship between depositional systems, sequence stratigraphy, paleoclimate, and coal composition.

中文翻译：

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哥伦比亚安第斯山脉东部科迪勒拉盆地白垩纪-古近纪过渡时期煤沉积的古环境重建


沿海和大陆环境中影响泥炭堆积的地层堆叠模式和因素是研究含煤序列的一个重大问题。为了解决这个问题，这项工作集中在东科迪勒拉盆地（哥伦比亚安第斯山脉）的 Checua-Lenguazaque Syncline （CLS） 煤田的白垩纪-古近纪 Guaduas 组。本研究依赖于地质调查、相分析、层序地层学、有机地球化学和煤岩相学。通过这些方法，表征了沉积体系和序列，并建立了它们与煤成分的关系。沉积相分为四个相组合 （FA）：泻湖、潮滩、三角洲平原和混合河流系统。确定了 5 个 T-R 序列 （S1 到 S5，按升序排列）。S1 由泻湖和潮汐砂岩、泥岩和煤组成。S2-S4 包括潮汐、三角洲和河流沉积物。S5 主要由三角洲相和河流相组成。厚煤层（> 0.7 m）集中在S1和S3的回归系统区，而海侵煤沉积在S2-S3，与潮汐环境有关。有机岩相学显示镜质体富集 （30.00-85.20 %），而脂质石 （0.00-16.60 %） 和惰性石 （4.60-34.40 %） 根据深度和古环境而变化。CLS 煤田展示了从浅层海洋和泻湖矿床到三角洲和河流环境的环境演变。微小的海平面波动、住宿变化、硅碎屑流入和植物群落区分了这种沉积演替。Guaduas 组的沉积特征是呈前移模式，在高容纳环境中具有主导的浅层-向上循环。 在中营养到营养环境中，在 limno-telmatic 到 telmatic 条件下积累的有机物，营养物质主要来自降雨。Guaduas 组的古气候表明植物群扩张的潮湿和炎热条件。这项调查确定了马斯特里希-古新世沿海的古环境到热带纬度内的河流演替，表明沉积系统、层序地层学、古气候和煤炭成分之间存在密切关系。