Dataset: The sedimentological signature of impact spherules and its relation to ejecta transport mechanisms during the Chicxulub asteroid impact (Cretaceous/Paleogene boundary)

The Chicxulub impact is the most likely cause of the Cretaceous/Paleogene boundary (KPB) mass extinction and the only impact event in Earth’s history with a globally traceable ejecta bed. Although the impact spherules are thought to represent molten or vaporized material, precise genesis and transport mechanisms remain underconstrained. Here, we show that the morphology, size, internal structure, and distribution of the spherules within the KPB deposits are related to origin and transport processes. The study of thousands of spherules from KPB deposits in Colombia, the USA, and Spain has revealed the presence of three fractions related to three different distribution processes, each with a distinctive sedimentological signature. The coarser fraction ("aspergo deposit," from the Latin aspergo, meaning splash) comprises rotational and agglutinated/irregular forms (size >2 mm) abundant vesicles, unmelted inclusions, and schlieren, implying an origin from molten materials and transport following ballistic trajectories. The intermediate fraction ("pyrocloud deposit" from the Greek pyr, meaning fire) represents a mixture of molten and condensed droplets, including spheres, rotational, and agglutinated/irregular forms (size 0.3–2 mm), transported by the rapid expansion of a fast-moving, high-temperature turbulent cloud. The globally distributed finer fraction ("fireball layer") is composed exclusively of spheres (size <0.3 mm) condensed from a vapor plume after the Chicxulub impact. These observations provide valuable insights into ejecta distributions during massive asteroid impacts and enhance our understanding of the Chicxulub impact and its aftermath.希克苏鲁伯（Chicxulub）撞击事件被认为是白垩纪-古近纪界线（Cretaceous/Paleogene boundary，简称KPB）生物大灭绝的最可能诱因，也是地球历史上唯一可在全球范围内追溯到喷出物层的撞击事件。尽管学界普遍认为撞击球粒（spherules）代表熔融或汽化的物质，但其确切成因与运移机制仍未得到充分约束。 本研究对哥伦比亚、美国及西班牙境内白垩纪-古近纪界线沉积层中的数千颗撞击球粒展开分析，结果表明，球粒的形态、粒径、内部结构及其在沉积层中的分布特征，与其成因及运移过程密切相关。研究揭示了三类与不同运移过程相关的组分，每一类均具备独特的沉积学标识。 较粗粒组分（源自拉丁语aspergo，意为“溅落”，命名为“溅积层”）包含旋转状、粘结状及不规则形态的颗粒（粒径＞2 mm），内部富含气孔、未熔融包裹体及条痕构造，指示其起源于熔融物质，并通过弹道轨迹完成运移。中等粒径组分（源自希腊语pyr，意为“火”，命名为“火积云沉积层”）由熔融液滴与冷凝液滴混合而成，包含球状、旋转状及粘结状/不规则形态颗粒（粒径0.3~2 mm），由高速运动的高温湍流云团快速膨胀作用完成运移。全球分布的细粒组分（命名为“火球层”）仅由粒径＜0.3 mm的球状颗粒组成，全部源自希克苏鲁伯撞击后蒸汽羽流的冷凝产物。 上述观测结果为大型小行星撞击过程中的喷出物分布研究提供了关键视角，也进一步深化了我们对希克苏鲁伯撞击事件及其后续效应的认知。