Sea Level from Meteoric Calcite
Many older fossil corals are too altered for dating because aragonite has recrystallized to calcite. We test a new path: target meteoric calcite cements that filled coral cavities during subaerial exposure. We map fabrics and chemistry with micro-CT and LA-ICP-MS to isolate clean meteoric cements, then obtain U–Th ages (LA-MC-ICP-MS / solution) to provide minimum ages for lowstands and sharpen sea-level histories for older interglacials.
- Key questions: Can meteoric calcite reliably constrain exposure/lowstand timing where skeletal aragonite is lost?
- Approach & methods: Micro-CT to visualize voids/cements; LA-ICP-MS lines to identify meteoric vs neomorphic calcite; select targets with low 232Th; date with LA-MC-ICP-MS and solution U–Th.
- Early results: Meteoric calcite shows no detectable detrital 232Th in screened zones and low but measurable U (≈0.5 ppm avg). U varies along ablation lines with consistent patterns, likely reflecting thin subsurface layers. Sequences include Ribbon Reef 5, IODP 325, One Tree Reef, Windley Key (FL), and Western Australia.
- What’s next: Tighten identification of cement boundaries, prioritize higher-U targets for precision ages, and integrate with coralgal/stratigraphic context to refine MIS-scale sea-level curves.
Notes: meteoric cements commonly have low detrital 232Th and measurable U; we standardize U with Great Canyon Travertine (matrix matched). Lightbox: click any image and swipe/arrow through.
Mid-Holocene Coral Paleoclimate (Heron Reef)
We build two ~60-year, sub-seasonal coral records from ~6.9 ka and ~5.2 ka at Heron Reef (southern GBR) to test how ENSO and the Indo-Australian Summer Monsoon behaved in the mid-Holocene. Using 193-nm LA-ICP-MS, we quantify Li, B, Mg, Sr, Mn, Y, REEs, U, Th along growth bands, evaluate temperature proxies (e.g., Sr/Ca, Li/Mg, B/Ca) and water-quality indicators (Mn/Ca, Y/Ho, Ce/Ce*), and compare seasonal cycles and interannual variance between windows.
- Key questions: Did ENSO amplitude or hydroclimatic forcing differ between ~6.9 and ~5.2 ka, and how did terrigenous influence modulate near-shore water quality?
- Approach & methods: Strict screening for diagenesis; compositional/anomaly metrics; time-series and spectral analysis to isolate seasonal and 2–7-yr variability.
- Work in progress: Extract robust temperature and water-quality signals from low-level trace elements; benchmark spectra and variance across both windows; integrate with regional mid-Holocene frameworks.
Results will clarify the link between ocean–atmosphere dynamics and coastal water quality long before modern observations.