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- Creator:
- Howard, Cecilia M. and Sheldon, Nathan D.
- Description:
- This study uses a compilation of microbialite occurrences in the Archean and Paleoproterozoic from the literature to investigate how depositional environment changed across environmental shifts such as the Great Oxidation Event and the Huronian Glaciations. Key Points: - We compiled microbialite occurrences from the Archean and Paleoproterozoic with broad depositional environment information, which has not previously been incorporated in larger compilations of occurrences. - Tidal and other terrestrially-influenced settings comprise the majority of the early microbialite record, even across major environmental shifts and Abstract: Changes in microbialite abundance during the Archean and Paleoproterozoic have been attributed to a variety of environmental and biological factors. Past work looking at large-scale patterns of microbialite abundance generally assumes shallow marine deposition rather than incorporating specific settings, however, there is significant variance in conditions that might impact microbialite formation and preservation between marine, tidal, and terrestrial environments. We compiled microbialite occurrences from the Archean and Paleoproterozoic with integrated depositional environment information in order to assess how microbialite development and preservation changed across different settings. Microbially induced sedimentary structures formed a significant part of the record, but their identification primarily in conjunction with stromatolites rather than independently suggests that they may be undercounted. Broad trends in abundance were similar to previous compilations, but critically, we found that the majority of microbialites from this period formed in tidal environments. The proportion of terrestrially-influenced (including tidal) microbialites increased during periods of craton development in the Neoarchean and mid-Paleoproterozoic, with increases in marine microbialite abundance trailing. Tidal microbialite abundance also recovered more quickly than marine abundance following the Great Oxidation Event and Huronian Glaciations.
- Keyword:
- Microbialite, Stromatolite, Archean, Paleoproterozoic, Geosciences, and Tidal
- Citation to related publication:
- Howard, C.M. and Sheldon, N.D. (in prep). Chapter 2 Microbialite Niches across the Archean and Paleoproterozoic.
- Discipline:
- Science
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- Creator:
- Howard, Cecilia M., Sheldon, Nathan D., Loveall, Zachary, Keating, Katarina A., Hong, Jungpyo, Smith, Selena Y., and Passey, Benjamin H.
- Description:
- This study uses an array of stratigraphic, morphological, and geochemical tools to investigate lateral and temporal variability in environmental records preserved by microbialites during a global hothouse environment. It also inverts tools for reconstructing environmental conditions to elucidate ancient microbial processes. Key Points: - The Green River Basin, WY, USA preserves lacustrine microbialites deposited during the Early Eocene Climatic Optimum, a period of high CO2 and temperatures - Morphological and geochemical analyses of these microbialites preserve variable local, regional, and global environmental conditions - Measurements of environmental conditions can be inverted to understand ancient microbial processes, which could be used to inform modeling of microbial influences on carbon cycling and Abstract: The Green River Basin, WY, USA, contains extensive lacustrine microbialite beds that formed during the hothouse Early Eocene Climatic Optimum (53–49 Ma). The records of biological, chemical, and physical processes preserved in these microbialites can inform our understanding of terrestrial conditions in this warm climate, but separating the competing signals of local, regional and global changes is difficult. Studies focusing on individual localities may miss spatial drivers of differences in microbialites. In this study, we used stratigraphic, morphological, and geochemical techniques to study microbialites deposited in the Green River Basin across three million years spanning the peak of the EECO, including samples from two beds covering 13–25 km of lateral extent. These samples cover a broad set of lake conditions as well as local differences such as spring deposits. We found that these microbialites preserved a mixture of conditions such as global hothouse temperatures, regional shifts in lake level, and local variability from sediment and water sources. Morphological and elemental variability were driven primarily by local and regional conditions such as stream, spring, and clastic inputs and water depth. Isotopic data preserved these local and regional changes as well as evidence of global hothouse conditions. Comparison of past [CO2] estimates to reconstructions using organic and inorganic carbon isotopes with clumped isotope-derived temperatures provides evidence for low to moderate microbial growth rates in these microbialite building communities, demonstrating that environmental tools can be inverted to better understand ancient microbial processes. A diverse toolkit was necessary to isolate the individual controls on microbialite records, and comparing across both space and time enabled us to identify local drivers that lead to significant differences from the expected regional signal.
- Keyword:
- Geosciences, Paleoclimate, Microbialite, Stromatolite, Eocene, Paleolake, and Green River Basin
- Citation to related publication:
- Howard, C.M., et al. (in prep). Disentangling Morphological and Chemical Records of Climate, Hydrology, and Diagenesis in Microbialites from the Eocene Green River Basin, WY, USA.
- Discipline:
- Science
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- Creator:
- Howard, Cecilia M., Velazquez, Diana, Rico, Kathryn I., and Sheldon, Nathan D.
- Description:
- This study combines a field survey time series with analysis of remotely and locally sensed environmental and climate data. Field survey data consists of sediment chemistry from hand-push cores, and includes %Corg, %N, δ13Corg, Corg:N, collection month and year, and depth in sediment. Climate and environmental data for the region around Middle Island Sinkhole was pulled from publicly available NOAA databases (ERDDAP, National Data Buoy Center, NWS) for as much of the same time period as the sediment data as was available. These data included general weather information from the NDBC and NWS (air temperature, wind speed, wind direction, gust speed, monthly precipitation totals), as well as satellite-derived environmental data from a 0.25° area centered on MIS (ice cover, lake surface temperature, CDOM, DOC, Chlorophyll, suspended minerals). Data were processed to monthly and annual averages as described below in order to compare to sinkhole sediment chemistry. Abstract: Records of recent past climate provide an essential window into understanding how changing climate influences environments and ecosystems such as lakes. Sediment carbon and nitrogen chemistry can offer insight into productivity and biochemistry, and anoxic sediments can often preserve short-term changes in these signals. We found that seasonal and annual changes in local ice season, chlorophyll, and precipitation influenced the amount and isotopic composition of carbon reaching the sediments of Middle Island Sinkhole, an anoxic sinkhole in Lake Huron. Carbon and nitrogen signals reflected the year or season of sample collection in sediments as deep as 12 cm. Our findings demonstrate that declining ice cover in this part of the Great Lakes is leading to increased export of organic carbon into sediments, but that in situ sediment processes may make teasing out short-term changes from sediment cores difficult even in an anoxic setting.
- Keyword:
- Carbon burial, Great Lakes, Ice cover, Sediment carbon, Sediment nitrogen, Anoxia, and Geosciences
- Citation to related publication:
- Howard, C.M., et al. (in prep). Climate-driven changes in sediment carbon and nitrogen of an anoxic Lake Huron sinkhole.
- Discipline:
- Science
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- Creator:
- Mitchell, R.L. and Sheldon, Nathan D.
- Description:
- Samples from a road cut section were analyzed. New paleosols were discovered.
- Keyword:
- Paleosols, Precambrian, Keweenawan, Paleoenvironments, and Midcontinental Rift
- Citation to related publication:
- Mitchell, R.L., Sheldon, N.D., 2009, Weathering and paleosol formation in the 1.1. Ga Keweenawan Rift: Precambrian Research 168, p. 271–283. https://doi.org/10.1016/j.precamres.2008.09.013
- Discipline:
- Science