Sedimentary Geochemistry Group at Virginia Tech Email Benjamin Gill Virginia Tech homepage Geosciences department homepage
Panorama of Tangwangzhai, China
Cliffs of the Chaomidian Formation (Cambrian), Tangwangzhai, China.


Reconstruting past environments and elemental cycles during the evolution of early animal life
Upward perspective image of rock outcrop in Utah
Notch Peak Formation at Lawsons Cove, UT.
Certain time intervals during the Paleozoic Era (542 to 251 million years ago) display major perturbations to the global carbon, sulfur and other elemental cycles, which appear to correspond to episodes of diversification and extinction recorded in the fossil record. The goal of this research is to indentify changes in these elemental cycles and to delineate their precise timing and relation to these biological events. Time intervals that are targets of this work include the Cambrian, Ordovician and Carboniferous. Field sites include locations in South Korea, China, the Great Basin and the Appalachian regions of the USA.

The biogeochemical cycling and feedbacks during the Mesozoic Era
Ocean and cliff view of Yorkshire Coast, UK
Mulgrave Mudstone (Toarcian), Yorkshire Coast, UK.
black shale
Laminated, organic-rich Posidonia shale from southern Germany.
Particular portions of the Mesozoic Era (251 to 65 million years ago) are characterized by widespread deposition of organic-rich sediments under anoxic conditions within the ocean. These time intervals are known as oceanic anoxic events or OAEs. Importantly, the sudden appearance of anoxia in the oceans has been as linked to rapid increases in greenhouse gases in the atmosphere. Not surprisingly, these intervals also contain large perturbations to the global carbon cycle, as well as the sulfur and iron cycles. Like our studies in the Paleozoic, this work involves the construction detailed chemostratigraphic records and the application numerical modeling techniques to simulate elemental cycles. Additionally the iron and trace metal contents of the black shales (the former organic-rich sediments) also contain vital information on the local and global redox state of the oceans. Currently the main subject of study of our group is the Toarcian OAE of the Jurassic Period. Field locations include the United Kingdom, Germany, Western Canada, and the Great Basin and Alaska, USA.

Environmental and chemical controls on the broad-scale evolutionary trajectory of life
soft bodied fossils
Occurrence of marine phosphorite deposits and the phosphorous contents of marine, fine-grain marine sediments and sedimentary rocks through time from Reinhard et al., (2017).
Many of the major changes in the environment — oxygenation of the surface Earth, Snowball Earth Events, etc. — appear to be related to the timing of major evolutionary events in the history of life — the rise of multicellularity, the diversification eukaryotes, proliferation of land plants, etc. The goal our research in this area is to identify the extent of these changes in Earth's environment and biogeochemical cycles and the potential consequences that these changes had on the evolution of life. These studies utilize large databases of geochemical data from the sedimentary record, statistical analysis of these databases, and numerical modeling of biogeochemical cycles based on these data and subsequent analyses.

Serpentinization, elemental cycles, and life
soft bodied fossils
Ophicalcites and calcite-veined serpentinites in a quarry near Levanto in the Northern Apennine, Italy.
Serpentinization of ultramafic rocks is a unique mineralogical reaction that supports microbial activity through formation of hydrogen and/or methane rich, alkaline fluids. These systems play an important role in the cycling of elements between Earth's major reservoirs. Specific to our investigations is the the cycling of sulfur and carbon during the serpentinization process since it potentially has important implications on the global cycles of these elements. Additionally one of the main goals of this work is to identify the environmental controls that support or limit microbial activity (e.g. temperature, redox conditions) during the serpentinization process. Study sites include the ophiolite sequence in the Northern Apennine, Italy and the Santa Elena ophiolite in Costa Rica, as well as submarine sites off the Iberian Margin and the 15°20'N fracture zone along the Mid-Atlantic Ridge.

The geochemistry of exceptional fossil preservation
Close-up shot of fossils with a quarter for scale
Fragmented organic remains of algae from the Wheeler Formation (Cambrian), House Range, UT.
There are many examples in the geologic record of deposits of exquisitely preserved fossil material called Lagerstätten. Famous examples of include the Cambrian Burgess Shale of British Columbia and the Jurassic Solnhofen Limestone of Germany. What is not well understood is the chemical environmental conditions that led to such preservation. The goal of this work is to determine the geochemical and sedimentary conditions that were responsible for promoting exceptional fossil preservation. Subjects of this line of research include the Cambrian Wheeler Shale of Utah, Triassic Cow Branch Formation of Virginia, and the Fernie Formation of Alberta.