Micrometer-size magnetite crystals with peculiar morphologies, such as spearhead, spindle, needle, and giant bullet, known as giant magnetofossils, were previously identified in marine sediments mainly during the Eocene epoch. The origin of these unusual magnetite crystals remains unclear because no known modern analogues have been found, and data about their spatiotemporal distribution are sparse. Here, using electron microscope observations, we performed a large-scale spatiotemporal search for these mysterious magnetite crystals. We report the occurrence of giant magnetofossils in variable marine sedimentary environments, including the first report in modern South Atlantic and Indian Ocean environments and the oldest occurrence at ca. 93 Ma in the North Atlantic Ocean. Grain-size data for the giant magnetofossils in the Southwest Pacific and North Atlantic Oceans suggest that the dimension of spearheads is sensitive to regional environments during similar warming periods but is insensitive to environmental conditions across the distinct geological periods at the same locality. The grain-size distributions of needles and giant bullets do not show significant changes in diverse environments. These observations greatly expand the known temporal and geographic distribution of giant magnetofossils, shedding new light on their likely biological origin.

中文翻译：

---

巨型磁化石的时空分布为其生物起源提供了线索


微米大小的磁铁矿晶体具有奇特的形态，如矛头状、纺锤状、针状和巨型子弹状，被称为巨型磁化石，主要在始新世时期的海洋沉积物中被发现。这些不寻常的磁铁矿晶体的起源仍不清楚，因为尚未发现已知的现代类似物，并且有关其时空分布的数据也很少。在这里，我们利用电子显微镜观察，对这些神秘的磁铁矿晶体进行了大规模的时空搜索。我们报告了在不同的海洋沉积环境中出现的巨型磁化石，包括在现代南大西洋和印度洋环境中的首次报告以及在大约 1990 年出现的最古老的磁化石。 93Ma，北大西洋。西南太平洋和北大西洋巨型磁化石的粒度数据表明，矛头的尺寸对相似变暖时期的区域环境敏感，但对同一地点不同地质时期的环境条件不敏感。针状和巨型子弹的粒度分布在不同的环境中没有表现出显着的变化。这些观测极大地扩展了巨型磁化石的已知时间和地理分布，为它们可能的生物起源提供了新的线索。