RUI: Salinity, source rocks, and cyclothems: Using paleosalinity proxies to track marine influence in the Maritimes Basin

The Maritimes Basin contains thousands of feet of Devonian-Permian (about 419–251 million year-old) sedimentary rocks of global significance. These strata comprise two UNESCO World Heritage Sites; have supported more than 200 years of resource-based economic activity; and have yielded important insights into Earth's organisms, ecosystems, and evolutionary patterns. Despite the importance of these rocks, fundamental questions about water chemistry during their deposition remain unanswered. This research will identify intervals that were influenced by marine waters and provide new information about the conditions that shaped the evolution of plant and animal life on land and the nature and distribution of economic resources in the basin. The project will also provide hands-on research experience for undergraduate students as well as teaching and research experience for future K-12 Earth science teachers. Information about the chemistry of ancient water bodies in the Maritimes Basin from recently developed whole-rock elemental paleosalinity proxies (boron/gallium, excess boron, and strontium/gallium ratios) will be combined with the well-established oxygen isotope proxy data to reconstruct changes in marine influence throughout the Late Paleozoic era. These elemental proxies can be used to estimate paleosalinity in mudrocks (and in some cases limestones) because (1) boron and strontium have high concentrations in seawater, (2) the bulk composition of fine-grained sediments reflects the chemistry of the overlying waters, and (3) there is a well-established relationship between the elemental ratios and salinity in modern sediments and ancient mudrocks. The geochemical datasets generated by this project will be interpreted within their sedimentological and paleontological context to test hypotheses about the timing and geographic variability of marine influence in the basin and about how marine waters affected the accumulation and properties of organic-rich deposits, including coal and oil shale. These results will provide new insights into the environments in which key evolutionary transitions occurred that allowed life to become fully established on land. Finally, the paleosalinity record generated by this project will provide new constraints on the drivers of cyclic sedimentation in the Late Paleozoic paleotropics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.