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Adam Maloof - Research

Triple Goose Creek, Andros Island, Bahamas

Carbonate muds deposited in peritidal environments have high preservation potential and are abundant throughout the geologic record. Much of what we know about pre-Mesozoic ocean chemistry, carbon cycling, and global change is derived from isotope and trace element geochemistry of platform carbonates. My group is working on a long-term project to address three fundamental questions in process sedimentology and biostratigraphy on the Great Bahaman Bank. Our aim is to apply the knowledge we attain in the modern carbonate environment to our understanding of ancient carbonate stratigraphic records.


bahamas-mag

1.

Paleomagnetic data from carbonate muds would allow us to place records of paleolatitude, paleogeography, and perturbations to the geomagnetic field in the context and relative chronology of chemostratigraphy. Many workers, however, have questioned the origin of magnetization in carbonates, suggesting that much of the magnetite found in ancient carbonates may have been modified during burial diagenesis or precipitated by migrating pore-fluids millions of years after deposition. So far, we have found that bahamian carbonate muds are magnetic and do record the orientation of Earth's magnetic field. The magnetite is produced near the surface in intertidal and supratidal sediments by magnetotactic bacteria that process the iron dropped on the region by dust storms emanating from the Sahara desert. However, the magnetite is destroyed at depth (unless the carbonate has undergone early cementation) by reducing, sulfur-rich sea water pumped through the pore space by the tides [EPSL].


bahamas-ikonos

2.

In siliciclastic river systems, sediments often accumulate by lateral aggradation of point bar deposits in migrating meandering streams. In this scenario, vertical facies variation may reflect either a stochastic process like stream migration (e.g., the tidal channels in the image on the right), or a periodic process such as astronomical forcing of global sea level, or a combination of the two. Determining the relative importance of these sedimentary processes will influence the way we interpret lithological, isotopic, and paleomagnetic time series from ancient laminated carbonates.  In particular, we want to look at the layering in ancient shallow water carbonate rocks and be able to tell time in a quantitative way. This question has been the subject of two of our GEO 370 class research trips, and will be the focus of a paper we hope to submit this year.

3.

Carbon isotopes (d13C) measured in limestones deposited on ancient carbonate platforms have been in the news a lot lately.  On the one hand, d13C has become increasingly important for correlating unfossiliferous strata from around the world that record events in earth history such as snowball Earth, the radiation of animals, the great oxidation event, and the various mass extinctions in the Phanerozoic.  Furthermore, d13C records frequently tell stories of profound changes to the carbon cycle that are associated with these significant biotic and environmental events. On the other hand, numerous researchers have called into question the fidelity of ancient d13C records, and have suggested that primary d13C signals may be adulterated by internal sedimentary processes, and/or by diagenetic pore fluids.  We are tackling this problem by looking at d13C in the same Holocene carbonate muds, pore waters, pond waters and ocean waters that we study while investigating carbonate magnetization and the migration of tidal channels.  In so doing, we are building a map of d13C variability across an active carbonate platform to determine whether the sedimentary record of d13C is really telling us a simple story about d13C in dissolved inorganic carbon (DIC) in the open ocean.