Recent Projects

Uranium-daughter dating of megafaunal avian eggshells

Work by myself and colleagues has demonstrated eggshells of large flightless birds can be suitable materials to date fossil and archaeological deposits via the radioactive decay of uranium (238U and 234U) to thorium (230Th). Eggshells are made of a stable carbonate mineral called calcite which remains well-preserved in deep time compared to other biominerals (bones, teeth) made of meta-stable, organic-rich phosphate compounds. We have show that uranium-thorium (230Th/U) burial dating of ostrich eggshells provides a new way to date archaeological sites, because they are found frequently as food refuse and artifacts of material culture (see the following section and references).

As part of my postdoctoral research and my new research program at Princeton, we have made developments to date eggshells of other large flightless birds in the archaeological and fossil records. This effort aims to synthesize the applicability of 230Th/U burial dating to other ancient eggshell deposits across other continents. Many large flightless birds are now extinct but left behind robust eggshells in the archaeological and paleontological-sedimentary records. In collaboration with Giff Miller (CU Boulder), we are combining new 230Th/U burial ages with amino acid racemization (AAR) relative ages to develop more robust chronologies for larger datasets with AAR measurements from eggshells. With new dating applications to other eggshell taxa, we are investigating questions such as:

• How did large flightless birds adapt to dynamic ecosystem changes?

• When did humans first arrive to new territories outside of Africa?

• When did megafaunal flightless birds go extinct or become extirpated from continents?

Above: general geographic range of large flightless birds that lived in the Mid-Late Pleistocene, whose eggshells may be datable by 230Th/U dating.  

U-Pb dating of non-avian dinosaur eggshells

Dinosaur eggshells have the potential to provide new information about the age and ecology of megafaunal dinosaurs, as eggshells are a less precious primary fossil material found in deposits with other fossil materials like bones and teeth, and their highly stable carbonate mineralogy remains well-preserved in deep time compared to other biominerals made of meta-stable, organic-rich phosphates. Given the similarities between reptile and avian eggshells, and the likely homologous origin of the hard shell of non-avian and avian eggshells, it is likely that the isotopic composition of well-preserved reptile and dinosaur eggshells may be a similarly useful archive of past environments. Dinosaur eggshells have gone nearly overlooked as a potential paleoenvironmental and chronological archive even though they are found abundantly, and rare studies using carbon and oxygen isotopes indicate dinosaur eggshells can preserve original isotopic information. We are testing the potential of U-Pb dating of fossil dinosaur deposits using eggshells from stratigraphically defined and chronologically constrained deposits to evaluate the efficacy of the application, in addiiton to exploring eggshells from undated deposits to illuminate the age of the eggshells and associated fauna. This work is part of the project of PhD candidate Noe-Heon Kim.

Above: A. fragments of Cretaceous dinosaur eggshells from the North American western interior seaway; B. thin section photomicrographs of eggshells of diverse dinosaur taxa, showing their crystalline structures. Samples courtesy of Prof. Dave Varricchio.

230Th/U burial dating of ostrich eggshells

Established chronometers do not fully meet the needs of researchers investigating Middle Stone Age (MSA, ~300 – 30 ka) sites that co-occur with the first fossils of H. sapiens, provide evidence of accelerated human behavioral innovation, and coincide in time with geographic range expansion of H. sapiens outside Africa. MSA sequences commonly contain ostrich eggshells (OES) which consist of ~2-mm thick, low-Mg calcite with 1-3% organics and are amenable to 14C dating. OES are also geochemically suitable for 230Th/U dating, though previous attempts neglected to account for secondary U uptake from soil pore fluids upon burial. Our novel approach to 230Th/U dating of OES explicitly recognizes U as secondary and has produced U-Th dates concordant with 14C dates on splits of ~10 – 50 ka OES from Lukenya Hill, an East African rock shelter site.  From experiments and blind dating tests with other chronometers at ~10 archaeological sites in Sub-Saharan Africa, we have produced ages which agree with other chronological constraints, preserve stratigraphic principles, and refine the chronologies of localities containing evidence of human biological and cultural evolution up to ~150 ka. Our first paper was recently published on the technique, and we have since produced reliable, reproducible ages for a number of paleoanthropological sites (Niespolo et al., 2021a, Niespolo et al., 2021b, Mackay et al., 2022). We are excited to collaborate with paleoanthropologists in these efforts and to explore sites hosting ostrich eggshells.

This work started during my Ph.D. with Dr. Warren Sharp (Berkeley Geochronology Center). New sites are under study in the Niespolo Lab highlighting under-studied regions in Africa and archaeological sites outside of Africa.

Stable isotopes in ostrich eggshells as paleoenvironmental proxies 

Paleoenvironmental change is commonly invoked as a factor in the development of modern human behaviors and the successful expansion of H. sapiens out of Africa. Paleoenvironmental information from archaeological sequences is central to addressing such questions. Ostrich eggshell (OES) are common in many African archaeological sequences and may be dated by 14C and U-series methods. In eggshells of modern ratites (large flightless birds including the ostrich and emu), the δ13C in eggshell calcite and the δ13C and δ15N in the total organic fraction (TOF) of eggshell have been shown to vary systematically across climate gradients in South Africa and Australia: δ15N varies inversely with mean annual precipitation (MAP) and δ13C co-varies with the C isotopes of vegetation. Thus, if primary C and N isotopic signatures are preserved, assemblages of OES can provide dated records of paleovegetation and paleoprecipitation at archaeological sites. This work began during my Ph.D. and has continued to expand through new applications and methods in light stable isotope analysis of ostrich eggshells.

At Princeton, in collaboration with Daniel Sigman, we are now utilizing two other methods to measure mineral-bound organic δ13C and δ15N values that only requires ~1mg of eggshell material. This work is part of the project of PhD candidate Damon Dai.

Below: Recent analyses of OES from Ysterfontein 1 rockshelter (South Africa) utilized these proxies to interpert local paleoenvironmental changes during shelter occupation ~120-113 ka (Niespolo et al., 2021a, PNAS).

Hydrogeology and the search for potable water in drought-prone environments of Kenya

Expanding speleothem records, the gold standard for terrestrial paleoclimate

Revealing paleoclimate from coral reefs

Projects from my graduate research

Refining chronologies of Polynesian colonization and settlement with U-Th dating of coral artifacts

Polynesian archaeology has relied primarily on 14C dating to establish the timing of human colonization of the eastern Pacific and the tempo of ensuing cultural development and human-environmental interactions. Despite advancements in 14C dating including accelerator mass spectrometry, selection of short-lived plant remains to avoid in-built age, and the use of Bayesian models to refine 14C-based chronologies, large uncertainties introduced during calibration to calendar ages can severely limit the resolution of 14C dates in this context. 230Th dating of coral abraders, which are common to many Polynesian archaeological sequences, can potentially provide much more precise dates.  The first suite of results are presented in this paper from Tangatatau rock shelter, on Mangaia Island (below, red star) - stay tuned for additional records coming from sites shown in the blue stars below.

Intercalibration of the Alder Creek sanidine standard for 40Ar/39Ar geochronology

The Alder Creek Sanidine (ACs) has yielded published ages spanning a range of ~2%, creating a challenge to determining precise and accurate ages of Quaternary unknown samples. In our recent paper in Quaternary Geochronology, we outline an intercalibration study with astronomically tuned tephra to calibrate both directly and as a stepwise intercalibration to Fish Canyon sanidine (FCs), which has an astronomically tuned age of 28.201 ± 0.023 Ma (σ). Since samples were co-irradiated, we utilize the intercalibration factor R to deal directly with 40Ar*/39ArK ratios (called F values in the paper) to yield an R matrix (seen below). This concept is useful not only to relate two samples measured under the same conditions, but it also aides conversion of ages from other published work whose data was calibrated to other standard (fluence monitor) ages. Combining these results with similarly treated data from other laboratories yields interlaboratory R values and an interlaboratory Astronomical age of ACs. Using the interlaboratory R value relating ACs to FCs, we also provide an optimization age for ACs. Work is ongoing to understand the difference in these two calibrations.

Above, Left: Intercalibration factors (R values) for two commonly used standards in 40Ar*/39ArK geochronology, ACs and FCs, and for two astronomically-dated tephra, Messâdit 4 (Mellila Basin, Morocco; Kuiper et al., 2008), and A1 (Faneromeni, Crete; Rivera et al., 2011). Above, Right: Interlaboratory ages of ACs. Figure content from Niespolo et al., 2017.

Geochronology of hominid evolution and archaeology in the Middle Awash, Ethiopia 

The Middle Awash project has provided crucial insights in the field of human evolution and has expanded our understanding of the emergence of hominids in eastern Africa. The ages of type specimens have been determined with 40Ar/39Ar ages of intercalated tephra. I am currently working on dating tephra to constrain ages of previously undescribed hominid and archaeological deposits in the Middle Awash. 

Above: Left, map of the the northern sector of the Middle Awash study area, Ethiopia; Right: Stratigraphic sections hosting dated horizons, fossils, and archaeology ranging in age from >158 ka to ~21 ka in the localities labeled on the map. Localities and river catchments labeled in the maps are discussed in Niespolo et al 2021b, PNAS.

The Fucino Basin Drilling Program, Italy

This Fucino Basin drilling project is an international collaboration aiming to develop a continuous paleoclimate record from the ancient Fucino Lake that may date as far back as 5 Ma. The preliminary results were published in Scientific Drilling (Giaccio et al., 2015) and since then a number of paleoclimate and tephrostratigraphic records are showing that the Fucino Basin has incredible potential as a central Mediterranean paleoclimate archive perhaps as old as the Pliocene. Figures below are from the 2015 publication, found here.

Above, Left: Map of location of Fucino lake relative to other lacustrine records in Europe of similar or overlapping ages; in center are the calculated and modeled 40Ar/39Ar ages for tephra intercalated in cores (After Manella et al., 2019, QSR)

Geochemistry of Guatemalan Jadeitites and Provenance of Maya Jade Artifacts

Thesis title: Mineralogy, Geochemistry, and Stable Isotopes of Guatemalan Jadeitites: a New Method to Determine the Provenance of Mesoamerican Jade Artifacts (Link to Abstract Here)

In my Master of Science thesis (Niespolo, 2014), I examined geochemical heterogeneities of jadeitites from the Motagua Valley, Guatemala, to infer metasomatic alteration in a subduction zone setting. Using a suite of geochemical analyses, including mineral phase composition and trace-element analysis of jadeite, coupled with stable isotope values of major minerals in jadeitites, I concluded that there may be an alternative protolith of jadeitite than that previously proposed in the literature. In addition, goechemical results showed that pairing oxygen stable isotope composition of jadeite with trace-element abundances of a specific group of elements may distinguish between geological source areas within the Motagua Valley. This discrimination is useful for identifying the provenance of jade artifacts recovered far from their geologic sources in Maya and other Mesoamerican archaeological sites. 

Above, Left: Oxygen and Hydrogen isotope calculations for the fliud interacting with the protolith to form jadeitites: these values were calculated using stable isotope compositions of jadeite, albite, and white micas in jadeitite rocks from the Motagua Valley, Guatemala. Data from this project (Niespolo, 2014) and a previous study (Johnson & Harlow, 1999) conclude a similar fluid origin. Right: A cartoon model of jadeite formation in the subduction zone (For more information, see the AGU 2014 Poster)