铝土矿是一种重要的工业矿产资源。目前中国大部分的铝土矿依赖进口。因此, 研究铝土矿的沉积模式对我国的资源安全和矿产开发具有重要意义。铝土矿的成矿受多种因素影响, 包括大地构造背景、古气候、侵蚀速率、母岩、时间、古植被和古地形地貌等。要研究这些成矿因素对铝土矿的影响, 并为下一步的找矿勘察工作提供理论支撑, 首先需要准确评估铝土矿的沉积时代。然而, 由于铝土矿的沉积过程涉及复杂的土壤化作用和再沉积过程, 其中保存的植物根系化石或遗迹化石数量很少, 因此很难确定铝土矿的最终沉积时间。目前, 综合分析铝土矿中保存的孢粉化石组合是确定铝土矿沉积时代更有效的方法。在中国, 已经确定的铝土矿沉积时代主要集中在晚古生代。华南产出的晚古生代铝土矿主要以贵州铝土矿为代表, 然而长期以来对贵州铝土矿的形成时代存在较多争议。为了解决这些争议, 本研究在贵州龙里县龙山镇和花溪区高坡苗族乡的两个铝土矿地层剖面上进行了孢粉地层研究。研究结果显示, 贵州龙里县龙山镇SPM095和花溪区高坡苗族乡SPM097剖面的革老河组、汤耙沟组、丰源层铝土岩和祥摆组底部产出的孢粉组合与西欧密西西比亚纪标准Lycospora pussila (Pu)孢粉组合带基本相当, 表明丰源铝土矿的沉积时代不晚于密西西比亚纪维宪早中期, 这是目前已知贵州地区最早的具有明确化石证据的喀斯特型铝土矿。通过与贵州中部清镇至贵州北部遵义等地铝土矿中发现的孢粉组合进行对比, 发现丰源铝土矿中的孢粉组合比上述地区铝土矿中的孢粉组合大致低一个孢粉组合带 (Perotriletes tessellatus—Schulzosopra camplylotera组合带)或一个牙形刺带(Gnathodus bilineatus带), 时代大概相差420万年。这一发现进一步表明晚古生代大冰期(LPIA)引起的频繁海平面变化导致贵州“南海北陆”的古地理格局由南向北逐次被海水淹没, 并接受沉积, 这是导致贵州不同地区铝土矿呈现由南向北时代梯度递减的主要原因。

The study of bauxite depositional patterns is of utmost importance for China’s resource security and mineral explorations, as China relies heavily on imports to meet its demand. Numerous factors, such as tectonic background, paleoclimate, erosion rate, parent rock, age, paleovegetation, and paleotopography, influence the formation of bauxite. Therefore, accurate age estimate is essential in understanding the impacts of these factors on bauxite formation and providing theoretical support for future exploration efforts.
Resolving the depositional age of bauxite deposits presents a formidable challenge due to the intricate processes encompassing pedogenesis and reworking. The scarcity of plant root fossils or trace fossils further complicates the estimate of the ultimate depositional age. Presently, the most successful approach to ascertain the depositional age of bauxite deposits involves a comprehensive examination of preserved palynological assemblages. In China, documented depositional ages of bauxite deposits are predominantly within the late Paleozoic. The bauxite deposit in Guizhou represents such an example in South China. However, the age of the Guizhou bauxite deposit has been controversial.
In order to address the aforementioned controversy, we conducted palynological investigations on two sections containing bauxite in Longshan Town, Longli County, and Gaopo Miaozu Village, Huaxi District, Guizhou. The findings indicate that the palynological assemblages observed in the two sections align with the standard Lycospora pussila (Pu) palynological assemblage zone of the Mississippian in Western Europe. These results suggest that the depositional age of the Fengyuan bauxite deposit is no younger than the early-middle Visean age of the Mississippian. Therefore, the Fengyuan bauxite deposit represents the earliest known karstic bauxite in Guizhou with unequivocal fossil evidence.
The palynological assemblages from the Fengyuan bauxite deposit are generally preserved in lower stratigraphic horizons when compared with those from the bauxite deposits in Qingzhen, central Guizhou, and Zunyi, northern Guizhou. The palynological assemblages of the Fengyuan bauxite deposit is separated from the palynological assemblages in Qingzhen and Zunyi by one palynological assemblage zone (Perotriletes tessellatus-Schulzosopra camplylotera assemblage zone) or one conodont zone (Gnathodus bilineatus zone). This suggests that the depositional age of the Fengyuan bauxite deposit predates those of the bauxite deposits in Qingzhen and Zunyi by 4.2 million years. The frequent sea-level changes caused by the Late Paleozoic Ice Age (LPIA) led to gradual submergence and deposition and likewise, gradual age changes of the bauxite deposits from older in the south to younger in the north of Guizhou.

国家重点研发计划资助(2022YFF0800200)；贵州省地质矿产勘查开发局地质科研项目(黔地矿科合[2022]5 号)联合资助