Regional Stratigraphy and Sedimentology of Phosphatic Event Beds and Associated Strata in the San Gregorio Formation (Upper Oligocene-Lower Miocene), Baja California Sur, Mexico

PI将整合地层学、沉积学和 岩石学方法在富磷酸盐矿床研究中的应用 圣格雷戈里奥组（上渐新世-下中新世），a 下加利福尼亚分布广泛且经济上重要的单位 墨西哥苏尔 与墨西哥调查人员合作， 我们的目标是澄清古地理和事件的作用 磷块岩及伴生地层的沉积作用。 初步实地观察表明，圣格雷戈里奥 形成是事件分层的。 我们的发现表明 许多磷酸盐沉积物的运输是遗传的- 与爆发性火山事件有关;此外， 磷酸盐事件层仅与短- 底栖生物扰动的持续时间间隔。 磷酸盐颗粒 类型差异很大，但在内部始终是单峰的 个人的床;我们希望了解系统的 磷酸盐颗粒类型地层和区域变异性 并解读这些变异对进化的意义 是外来磷块岩的源区。 岩石学 磷酸盐颗粒的研究，包括使用 在抛光薄切片上的反向散射SEM将允许 在磷酸盐颗粒类型中观察到的趋势与 圣格雷戈里奥区域沉积古地理 形成，并将进一步记录微生物的协会 和其他生物群中的磷酸盐颗粒的起源。

PI's will integrate stratigraphic, sedimentologic and petrologic approaches in an investigation of the phosphate-rich San Gregorio Formation (Upper Oligocene- Lower Miocene), a widespread and economically-important unit in Baja California Sur, Mexico. Working collaboratively with Mexican investigators, we aim to clarify the roles of paleogeography and event deposition in the origin of phosphorites and associated strata. Initial field observations indicate that the San Gregorio Formation is event stratified. Our findings suggest that transportation of many phosphatic sediments was genetically- linked to explosive volcanic episodes; furthermore, deposition of phosphatic event strata was exclusively associated with short- duration intervals of infaunal bioturbation. Phosphatic grain types vary widely, but are consistently unimodal within individual beds; we wish to understand the systematic stratigraphic and regional variability in phosphatic grain type and to decipher what these variations signify about the evolution of source areas for allochthonous phosphorites. Petrologic studies of phosphatic grains, including the employment of backscatter SEM on polished thin sections, will permit correlations between observed trends in phosphatic grain type and regional sedimentary paleogeography within the San Gregorio Formation and will further document the association of microbes and other biota in the origin of phosphatic grains.