Kristen Myshrall | University of Connecticut (original) (raw)

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Papers by Kristen Myshrall

Astrobiology Science Conference 2010: Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond, Apr 1, 2010

Relatively little work has been done on modern thrombolites despite being found in all types of a... more Relatively little work has been done on modern thrombolites despite being found in all types of aquatic environments across the world. While we have pieces of the puzzle, we still do not have a clear understanding of thrombolite form and function.

Topics in Geobiology, 2014

ABSTRACT Microbialites dominated the biosphere throughout the Proterozoic, becoming relatively ra... more ABSTRACT Microbialites dominated the biosphere throughout the Proterozoic, becoming relatively rarer into the Phanerozoic. Microbialites are potential analogs of life on the early Earth; therefore, understanding how they form and function can provide a window to the past. Much of what we know about early life and environments derives from investigations of modern microbialites, making studies of these structures critical to interpreting the ancient fossil record. Creating a database of worldwide microbialite specimens, both modern and fossil, to be used for analyzing patterns in modern microbialite distribution, both in space and time, along with environmental characteristics and concurrence with grazing and/or boring organisms, can offer understanding into ancient microbialites, specifically the processes impacting their formation, persistence, and preservation. Additionally, analyzing the composition and structure of modern microbialites may allow for connections to patterns of the past, and also provide a clearer understanding of what is seen (or not seen) in the fossil record. A sample database of microbialites reported from the Phanerozoic was analyzed for characteristics such as distribution in time, space, and across different environments, as well as the alignment of distribution with mass extinctions, global sea level curves, and association with grazing/burrowing organisms. We find microbialite distribution is widespread worldwide and abundance fluctuates over the Phanerozoic with increases often corresponding to mass extinctions. Contrary to previous interpretations, fossil microbialites do not appear to prefer open marine environments, with data showing broad distribution in a variety of environments. Modern microbialites, however, primarily form in restricted environments. Data show that grazers/borers are commonly found in association with microbialites throughout the Phanerozoic, though it is difficult to discern if they did or did not impact microbialite formation.

Relatively little work has been done on modern thrombolites despite being found in all types of a... more Relatively little work has been done on modern thrombolites despite being found in all types of aquatic environments across the world. While we have pieces of the puzzle, we still do not have a clear understanding of thrombolite form and function.

Geobiology, 2009

Calcified cyanobacterial microfossils are common in carbonate environments through most of the Ph... more Calcified cyanobacterial microfossils are common in carbonate environments through most of the Phanerozoic, but are absent from the marine rock record over the past 65 Myr. There has been long-standing debate on the factors controlling the formation and temporal distribution of these fossils, fostered by the lack of a suitable modern analog. We describe calcified cyanobacteria filaments in a modern marine reef setting at Highborne Cay, Bahamas. Our observations and stable isotope data suggest that initial calcification occurs in living cyanobacteria and is photosynthetically induced. A single variety of cyanobacteria, Dichothrix sp., produces calcified filaments. Adjacent cyanobacterial mats form well-laminated stromatolites, rather than calcified filaments, indicating there can be a strong taxonomic control over the mechanism of microbial calcification. Petrographic analyses indicate that the calcified filaments are degraded during early diagenesis and are not present in well-lithified microbialites. The early diagenetic destruction of calcified filaments at Highborne Cay indicates that the absence of calcified cyanobacteria from periods of the Phanerozoic is likely to be caused by low preservation potential as well as inhibited formation.

Geobiology, 2010

Thrombolites are unlaminated carbonate build-ups that are formed via the metabolic activities of ... more Thrombolites are unlaminated carbonate build-ups that are formed via the metabolic activities of complex microbial mat communities. The thrombolitic mats of Highborne Cay, Bahamas develop in close proximity (1–2 m) to accreting laminated stromatolites, providing an ideal opportunity for biogeochemical and molecular comparisons of these two distinctive microbialite ecosystems. In this study, we provide the first comprehensive characterization of the biogeochemical activities and microbial diversity of the Highborne Cay thrombolitic mats. Morphological and molecular analyses reveal two dominant mat types associated with the thrombolite deposits, both of which are dominated by bacteria from the taxa Cyanobacteria and Alphaproteobacteria. Diel cycling of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were measured in all thrombolitic mat types. DO production varied between thrombolitic types and one morphotype, referred to in this study as ‘button mats’, produced the highest levels among all mat types, including the adjacent stromatolites. Characterization of thrombolite bacterial communities revealed a high bacterial diversity, roughly equivalent to that of the nearby stromatolites, and a low eukaryotic diversity. Extensive phylogenetic overlap between thrombolitic and stromatolitic microbial communities was observed, although thrombolite-specific cyanobacterial populations were detected. In particular, the button mats were dominated by a calcified, filamentous cyanobacterium identified via morphology and 16S rRNA gene sequencing as Dichothrix sp. The distinctive microbial communities and chemical cycling patterns within the thrombolitic mats provide novel insight into the biogeochemical processes related to the lithifying mats in this system, and provide data relevant to understanding microbially induced carbonate biomineralization.

Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer produ... more Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer production and microbial communication. Here, we present an overview of field and laboratory observations and emerging models of how these systems may form.

Astrobiology Science Conference 2010: Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond, Apr 1, 2010

Relatively little work has been done on modern thrombolites despite being found in all types of a... more Relatively little work has been done on modern thrombolites despite being found in all types of aquatic environments across the world. While we have pieces of the puzzle, we still do not have a clear understanding of thrombolite form and function.

Topics in Geobiology, 2014

ABSTRACT Microbialites dominated the biosphere throughout the Proterozoic, becoming relatively ra... more ABSTRACT Microbialites dominated the biosphere throughout the Proterozoic, becoming relatively rarer into the Phanerozoic. Microbialites are potential analogs of life on the early Earth; therefore, understanding how they form and function can provide a window to the past. Much of what we know about early life and environments derives from investigations of modern microbialites, making studies of these structures critical to interpreting the ancient fossil record. Creating a database of worldwide microbialite specimens, both modern and fossil, to be used for analyzing patterns in modern microbialite distribution, both in space and time, along with environmental characteristics and concurrence with grazing and/or boring organisms, can offer understanding into ancient microbialites, specifically the processes impacting their formation, persistence, and preservation. Additionally, analyzing the composition and structure of modern microbialites may allow for connections to patterns of the past, and also provide a clearer understanding of what is seen (or not seen) in the fossil record. A sample database of microbialites reported from the Phanerozoic was analyzed for characteristics such as distribution in time, space, and across different environments, as well as the alignment of distribution with mass extinctions, global sea level curves, and association with grazing/burrowing organisms. We find microbialite distribution is widespread worldwide and abundance fluctuates over the Phanerozoic with increases often corresponding to mass extinctions. Contrary to previous interpretations, fossil microbialites do not appear to prefer open marine environments, with data showing broad distribution in a variety of environments. Modern microbialites, however, primarily form in restricted environments. Data show that grazers/borers are commonly found in association with microbialites throughout the Phanerozoic, though it is difficult to discern if they did or did not impact microbialite formation.

Relatively little work has been done on modern thrombolites despite being found in all types of a... more Relatively little work has been done on modern thrombolites despite being found in all types of aquatic environments across the world. While we have pieces of the puzzle, we still do not have a clear understanding of thrombolite form and function.

Geobiology, 2009

Calcified cyanobacterial microfossils are common in carbonate environments through most of the Ph... more Calcified cyanobacterial microfossils are common in carbonate environments through most of the Phanerozoic, but are absent from the marine rock record over the past 65 Myr. There has been long-standing debate on the factors controlling the formation and temporal distribution of these fossils, fostered by the lack of a suitable modern analog. We describe calcified cyanobacteria filaments in a modern marine reef setting at Highborne Cay, Bahamas. Our observations and stable isotope data suggest that initial calcification occurs in living cyanobacteria and is photosynthetically induced. A single variety of cyanobacteria, Dichothrix sp., produces calcified filaments. Adjacent cyanobacterial mats form well-laminated stromatolites, rather than calcified filaments, indicating there can be a strong taxonomic control over the mechanism of microbial calcification. Petrographic analyses indicate that the calcified filaments are degraded during early diagenesis and are not present in well-lithified microbialites. The early diagenetic destruction of calcified filaments at Highborne Cay indicates that the absence of calcified cyanobacteria from periods of the Phanerozoic is likely to be caused by low preservation potential as well as inhibited formation.

Geobiology, 2010

Thrombolites are unlaminated carbonate build-ups that are formed via the metabolic activities of ... more Thrombolites are unlaminated carbonate build-ups that are formed via the metabolic activities of complex microbial mat communities. The thrombolitic mats of Highborne Cay, Bahamas develop in close proximity (1–2 m) to accreting laminated stromatolites, providing an ideal opportunity for biogeochemical and molecular comparisons of these two distinctive microbialite ecosystems. In this study, we provide the first comprehensive characterization of the biogeochemical activities and microbial diversity of the Highborne Cay thrombolitic mats. Morphological and molecular analyses reveal two dominant mat types associated with the thrombolite deposits, both of which are dominated by bacteria from the taxa Cyanobacteria and Alphaproteobacteria. Diel cycling of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were measured in all thrombolitic mat types. DO production varied between thrombolitic types and one morphotype, referred to in this study as ‘button mats’, produced the highest levels among all mat types, including the adjacent stromatolites. Characterization of thrombolite bacterial communities revealed a high bacterial diversity, roughly equivalent to that of the nearby stromatolites, and a low eukaryotic diversity. Extensive phylogenetic overlap between thrombolitic and stromatolitic microbial communities was observed, although thrombolite-specific cyanobacterial populations were detected. In particular, the button mats were dominated by a calcified, filamentous cyanobacterium identified via morphology and 16S rRNA gene sequencing as Dichothrix sp. The distinctive microbial communities and chemical cycling patterns within the thrombolitic mats provide novel insight into the biogeochemical processes related to the lithifying mats in this system, and provide data relevant to understanding microbially induced carbonate biomineralization.

Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer produ... more Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer production and microbial communication. Here, we present an overview of field and laboratory observations and emerging models of how these systems may form.