Microbial phylogenetic diversity preserved in facies-specific modern, recent, Holocene and Pleistocene hot-spring travertine deposits of Yellowstone and Turkey

A systematic evaluation has been undertaken of the mechanisms and products of microbial community preservation within modern-to-ancient terrestrial hot-spring calcium carbonate (CaCO3) limestone deposits called travertine. Microbial 16S rRNA gene sequences preserved within Modern travertine deposited within the Proximal Slope Facies (PSF) at Mammoth Hot Springs (MHS), Yellowstone National Park, has been directly compared with analogous Holocene-Late Pleistocene PSF travertine at Gardiner, Montana, and Middle Pleistocene PSF travertine in Denizli, Turkey. Analyses have included: (1) Modern microbial communities inhabiting the PSF of an actively depositing travertine hot-spring system (water, microbial mats, travertine) at MHS (0 YBP Modern travertine, Angel Terrace, Spring AT-1); (2) 9 YBP Modern PSF travertine (Angel Terrace, Spring AT-2; MHS); (2) ~100 YBP Recent travertine (New Highland Terrace, MHS); (3) ~4,000 YBP Holocene travertine (USGS Y-10 Core); (3) ~30,000 YBP Late Pleistocene travertine (Gardiner Quarry); and (4) ~1.1 Ma YBP Middle Pleistocene travertine (all of the Mammoth Hot Springs (YNP) and (Cakmak Quarry, Turkey). Genomic DNA entombed during rapid (up to 5 mm/day) travertine deposition and preserved within CaCO3 fluid inclusions and between crystals, was extracted via bulk rock drilling under sterile clean room conditions. Pooled 16S rRNA gene sequence libraries were constructed via polymerase chain reactions (PCRs), terminal-restriction fragment length polymorphisms (T-RFLP), and MiSeq amplicon sequencing. Blast searches using multiple web-based bioinformatics tools identified over 400 operational taxonomic units (OTUs) affiliated with a total of 19 phyla (16 phyla and 3 candidate phyla) within the Domain Bacteria. Previous analyses of the living microbial communities inhabiting modern active PSF depositional environments at MHS have provided a baseline with which to compare the ancient travertine analyses. Combined results from both MHS and Denizli indicate that only 3 of 19 phyla were detected in PSF travertine samples of all ages. Increasing depositional age of the travertine deposits was associated with increasing extents of post-depositional water-rock geochemical alteration (diagenesis). Microbial community structure shifted across this spatial and temporal transect from being dominated by Cyanobacteria and Proteobacteria in the Modern and Recent, to dominance by Firmicutes in the Holocene and Pleistocene. This is not unexpected, as endospores of Firmicutes are known to be resistant and also persist under harsh environmental conditions and therefore show higher relative abundance in ancient samples in comparison to modern samples. Preliminary blast search results imply that libraries from all PSF travertine samples of all ages contain photoautotrophic, chemoautotrophic and heterotrophic metabolic activities, which is likely the result of both original hot-spring depositional processes and secondary diagenetic alteration

Travertine crystal growth ripples record the hydraulic history of ancient Rome’s Anio Novus aqueduct

Travertine crystal growth ripples are used to reconstruct the early hydraulic history of the Anio Novus aqueduct of ancient Rome. These crystalline morphologies deposited within the aqueduct channel record the hydraulic history of gravity-driven turbulent flow at the time of Roman operation. The wavelength, amplitude, and steepness of these travertine crystal growth ripples indicate that large-scale sustained aqueduct flows scaled directly with the thickness of the aqueous viscous sublayer. Resulting critical shear Reynolds numbers are comparable with those reconstructed from heat/mass transfer crystalline ripples formed in other natural and engineered environments. This includes sediment transport in rivers, lakes, and oceans, chemical precipitation and dissolution in caves, and melting and freezing in ice. Where flow depth and perimeter could be reconstructed from the distribution and stratigraphy of the travertine within the Anio Novus aqueduct, flow velocity and rate have been quantified by deriving roughness-flow relationships that are independent of water temperature. More generally, under conditions of near-constant water temperature and kinematic viscosity within the Anio Novus aqueduct channel, the travertine crystal growth ripple wavelengths increased with decreasing flow velocity, indicating that systematic changes took place in flow rate during travertine deposition. This study establishes that travertine crystal growth ripples such as those preserved in the Anio Novus provide a sensitive record of past hydraulic conditions, which can be similarly reconstructed from travertine deposited in other ancient water conveyance and storage systems around the world

GEOCHRONOLOGY, GEOCHEMISTRY, AND TECTONIC CHARACTERIZATION OF QUATERNARY LARGE-VOLUME TRAVERTINE DEPOSITS IN THE SOUTHWESTERN UNITED STATES AND THEIR IMPLICATIONS FOR CO2 SEQUESTRATION

Travertines are freshwater carbonates that precipitate from carbonic groundwater due to the degassing of CO2. Travertine deposits are often situated along faults that serve as conduits for CO2-charged groundwater and their geochemistry often records mixing of deeply-derived fluids and volatiles with shallow meteoric water. Travertines are surface expressions of dynamic mantle processes related to the tectonic setting. This dissertation includes four chapters that focus on different aspects of travertine formation and their scientific value. They are excellent, although underestimated, diagnostic tools for climatology, hydrology, tectonics, geochemistry, geomicrobiology, and they can inform carbon sequestration models. Quaternary Large-volume travertine deposits in New Mexico and Arizona occur in an extensional tectonic stress regime on the southeastern Colorado Plateau and along the Rio Grande rift. They accumulated above fault systems during episodes of high hydraulic head in confined aquifers, increased regional volcanic activity, and high input of mantle-derived volatiles such as CO2 and He. Stable isotope and trace element geochemistry of travertines is controlled by groundwater geochemistry as well as the degassing of CO2. The geochemical composition allows for distinguishing different travertine facies and evaluating past groundwater flow. The travertine deposits in New Mexico are interpreted to be extinct CO2 fields due to the large volumes that accumulated and in analogy to the travertine deposits in Arizona that are associated with an active CO2-gas field. Travertines are natural analogues for CO2 leakage along fault systems that bypassed regional cap rocks and they provide important insight into the migration of CO2 from a reservoir to the surface. The volume of travertine can be used to infer the integrated CO2 leakage along a fault system over geologic time. This leakage is estimated as: (1) CO2 that becomes fixed in CaCO3/travertine (tons of carbon converted into tons of carbonate), (2) the amount of CO2 that degassed into the atmosphere (twice the amount of (1), based on reaction stoichiometry), (3) dissolved CO2 that is carried away with the water discharging from a spring (based on modern spring discharge and dissolved carbon content), and (4) CO2 that escapes through the soil (based on modern soil flux measurements). Better understanding of integrated CO2 leakage and fault-related seal bypass is needed to design CO2 sequestration sites to effectively store anthropogenic CO2 in the subsurface

MICROBIAL ECOLOGY AND ENDOLITH COLONIZATION: SUCCESSION AT A GEOTHERMAL SPRING IN THE HIGH ARCTIC

A critical question in microbial ecology concerns how environmental conditions affect community makeup. Arctic thermal springs enable study of this question due to steep environmental gradients that impose strong selective pressures. I use microscopic and molecular methods to quantify community makeup at Troll Springs on Svalbard in the high arctic. Troll has two ecosystems, aquatic and terrestrial, in proximity, shaped by different environmental factors. Microorganisms exist in warm water as periphyton, in moist granular materials, and in cold, dry rock as endoliths. Environmental conditions modulate community composition. The strongest relationships of environmental parameters to composition are pH and temperature in aquatic samples, and water content in terrestrial samples. Periphyton becomes trapped by calcite precipitation, and is a precursor for endolithic communities. Microbial succession takes place at Troll in response to incremental environmental disturbances. Photosynthetic organisms are dominantly eukaryotic algae in the wet, high-illumination environments, and Cyanobacteria in the drier, lower-illumination endolithic environments. Periphyton communities vary strongly from pool to pool, with a few dominant taxa. Endolithic communities are more even, with bacterial taxa and cyanobacterial diversity similar to alpine and other Arctic endoliths. Richness and evenness increase with successional age, except in the most mature endolith where they diminish because of sharply reduced resource and niche availability. Evenness is limited in calcite-poor environments by competition with photosynthetic eukaryotes, and in the driest endolith by competition for water. Richness is influenced by availability of physical niches, increasing as calcite grain surfaces become available for colonization, and then decreasing as pore volume decreases. In most endoliths, rock predates microbial colonization; the reverse is true at Troll. The harsh Arctic environment likely imposes a lifestyle in which microbes survive best in embedded formats, and to preserve live inocula for regrowth. ARISA is commonly used to assess variations in microbial community structure. Applying a uniform threshold across a sample set, as is normally done, treats samples non-optimally and unequally. I present an algorithm for optimal threshold selection that maximizes similarity between replicate pairs, improving results

Depositional architecture, facies character and geochemical signature of the Tivoli travertines (pleistocene, acque albule basin, central Italy)

Facies character, diagenesis, geochemical signature, porosity, permeability, and geometry of the upper Pleistocene Tivoli travertines were investigated integrating information from six borehole cores, drilled along a 3 km N-S transect, and quarry faces, in order to propose a revised depositional model. Travertines overlie lacustrine and alluvial plain marls, siltstones, sandstones and pyroclastic deposits from the Roman volcanic districts. In the northern proximal area, with respect to the inferred hydrothermal vents, travertines accumulated in gently-dipping, decametre-scale shallow pools of low-angle terraced slopes. The intermediate depositional zone, 2 km southward, consisted of smooth and terraced slopes dipping S and E. In the southernmost distal zone, travertine marshes dominated by coated vegetation and Charophytes interfingered with lacustrine siltstones and fluvial sandstones and conglomerates. Travertine carbon and oxygen stable isotope data confirm the geothermal origin of the precipitating spring water. The travertine succession is marked by numerous intraclastic/extraclastic wackestone to rudstone beds indicative of non-deposition and erosion during subaerial exposure, due to temporary interruption of the vent activity or deviation of the thermal water flow. These unconformities identify nine superimposed travertine units characterized by aggradation in the proximal zone and southward progradation in the intermediate to distal zones. The wedge geometry of the travertine system reflects the vertical and lateral superimposition of individual fan-shaped units in response to changes in the vent location, shifting through time to lower elevations southward. The complexity of the travertine architecture results from the intermittent activity of the vents, their locations, the topographic gradient, thermal water flow paths and the rates and modes of carbonate precipitation

U-series dating, geochemistry, and geomorphic studies of travertines and springs of the Springerville area, east-central Arizona, and tectonic implications.

High CO2 springs and related travertine deposits of the Springerville area of east-central Arizona provide an exceptional field laboratory for understanding travertine-depositing spring systems. U-series dating of travertines provides an opportunity to unravel paleohydrologic and neotectonic histories near the southeastern edge of the Colorado Plateau. This interdisciplinary study combines water and gas chemistry data, travertine morphology and geochronology, analysis of geologic structures, basalt geochronology, and river incision studies to formulate an integrative model for both travertine formation and for landscape evolution of this region. More than 70 individual travertine mounds and large platforms, formed from the coalesced deposits of multiple spring vents, cover a surface area of \u3e33 km2 near Springerville, Arizona. This area is at the intersection of the southeastern edge of the Colorado Plateau with the Jemez lineament, a northeast-trending zone of volcanic activity over the last 4.5 Ma. Travertine deposits occur in clusters near the Little Colorado River (LCR) and along fault lineaments overlying the Springerville-St. Johns Dome, a faulted asymmetric anticline trapping a large natural CO2 reservoir. This travertine and CO2 system is bounded on the west by the Plio-Pleistocene Springerville volcanic field (SPV) which was active until 308 ka and on the east by the late Mio-Pleistocene Red Hill-Quemado volcanic field where volcanic activity continued until as recently as 71 ka. Modern springs adjacent to the CO2 field are actively degassing CO2, have Cexternal values of 50%, concentrations of TDS up to 2538 mg/l, and are currently depositing minor volumes of travertine. 3He/4He ratios from wells in the CO2 field and adjoining springs range up to 0.58 RA, indicating the presence of asthenospheric mantle-derived gases in modern spring waters (up to about 7% of the total helium). To explain the diversity of water chemistry in this small region, we hypothesize that deeply sourced fluids rise along NE- and NW-trending basement-penetrating faults that intersect at the SE end of the dome. These endogenic waters then mix with groundwater producing a complete mixing trend between meteoric and bicarbonate rich, high TDS end members. Precise new U/Th dates indicate that travertine deposition began \u3e350 ka, overlapping with waning volcanic activity in the Springerville and Red Hill-Quemado volcanic fields, and is still ongoing. Major times of accumulation at 350-300, 280-200, and 100-36 ka are interpreted to represent wetter paleohdrologic intervals. Synchronous outflow occurred from springs at different elevations above the LCR (from near river level up to 400 m above the river at ca. 200 ka) reflecting an unresolved combination of fluctuations in hydraulic head, gas pressure in the CO2 reservoir, paleoseismicity, and partitioning dynamics of traps within the stacked CO2 reservoir system. The life of one major travertine mound system near the LCR that accumulated \u3e20 m of layered travertine has been bracketed between 73 and 48 ka (25 ka). This mound formed from the sustained outflow of CO2-charged spring waters from a central vent with a deposition rate of 0.94 m/ka. Hiatuses of ~25-60 ka in the travertine rock record correlate with obliquity-forced warm interglacial peaks in the Devils Hole calcite δ18O paleotemperature and global paleoclimate records. Periods of deposition also correlate with the five most recent volcanic episodes in the SPV and Red Hill-Quemado fields. Thus, the apparent ~70 ka cyclicity of travertine deposition appears to be due to a combination of increased climatically-modulated groundwater recharge during wet/glacial times and over-pressuring of the CO2/groundwater system due to the periodic influx of magmatically sourced fluids. Dated travertines and basalts associated with elevated LCR gravel terraces in the region provide constraints on river incision and landscape denudation. Using the base of flows, basalt incision points indicate a long-term rate of 40-50 m/Ma. U-series dates on travertine that cements gravels directly above bedrock straths indicate incision rates of 100-150 m/Ma near Lyman Lake from 350-100 ka, increasing to 320 m/Ma in the last 100 ka

Bacterial and archaeal community structure across a gradient of saline lakes in Kiritimati, Republic of Kiribati

Microbial mats, multilayered sheets of microorganisms often found in extreme environments, are increasingly gaining attention for their utility and influence on the global carbon cycle. However, our understanding of the organisms that define microbial mats and how they vary across environmental gradients remains limited, given the sparse sampling of these systems worldwide. Here we investigate a series of distinct microbial communities across a gradient of natural saline lakes on Kiritimati to define how mat communities in hypersaline lakes, where microbial mats have been previously assessed, differ from microbial communities in fresher lakes. Preliminary terminal restriction fragment length polymorphism analysis indicated that samples from the least saline lakes were statistically distinct from the most saline lake microbial communities. Results from Illumina sequencing of 16S rRNA gene amplicons support this finding and also pointed to both salinity and pH as major drivers of community variability. Alpha diversity measurements show no apparent link between salinity and microbial diversity. Extremely saline samples had both higher and lower Shannon index values, whereas lower salinity groups showed a range of Shannon index values. Our findings suggest pH may interact with salinity to influence microbial community structure and that diversity at high salinities may be controlled by both environmental and temporal factors. Greater insight into the drivers of community structure and diversity requires a deeper understanding of functional groups within brackish and brine lakes

U-Th dating of travertines on the Colorado Plateau: implications for the leakage of geologically stored CO2

In order to avoid the damaging climatic consequences of rising atmospheric CO2, and reduce current atmospheric CO2 concentrations to pre-industrial levels, anthropogenic CO2 emissions must be mitigated by capturing CO2 at power plants and storing it for thousands of years. Underground storage within deep geological formations, such as depleted gas and oil fields or deep saline aquifers, is the best understood solution for storage of CO2. In order for this method to gain more public and political acceptance it is important to characterise the potential causes, quantities and rates of CO2 release that could result if leakage were to occur from anthropogenic storage projects. This study examines two sites in the Colorado Plateau where faulted and actively leaking CO2 reservoirs provide natural analogues for failed anthropogenic storage sites. The two sites in question, the Little Grand Wash and northern Salt Wash graben faults are situated at the northern end of the Paradox Basin in Utah and represent classic three way traps due to juxtaposition of the shallow, north plunging Green River anticline against a set of east-west trending normal faults. In addition to active leakage sites in each area there are numerous fossilised travertine deposits. Along the Little Grand Wash fault the ancient mounds are restricted to the fault trace whereas ancient travertine mounds associated with the northern fault of the Salt Wash graben are far more numerous and occur up to ~530 m into the footwall of the fault. This more diffuse pattern of flow is due to the outcropping of unconfined aquifer units at the surface. A total of 45 U-Th dates from the majority of these travertine mounds provides a unique data set. The oldest deposits from the Little Grand Wash and northern Salt Wash graben faults produced ages of 113,912 ± 604 and 413,474 ± 15,127 years respectively. Repeat ages show reasonable reproducibility and analytical errors on results are of the order of 1% of the ages. The coupling of travertine elevation measurements with their radiometric ages gives an incision rate for each site. A rate of 0.342 m/ka for the Little Grand Wash fault relates directly to Green River incision and agrees with previous work on the Colorado Plateau, providing a further data point for characterisation of uplift of the province. For the northern fault of the Salt Wash graben a rate of 0.168 m/ka for the tributaries running through the area gives a robust method with which to estimate ages for un-dated mounds. The results of radiometric dating and incision rate age estimation of travertine mounds shows that leakage can last for timescales of 100,000’s of years, while high resolution U-Th dating of an individual mound demonstrated that leakage from a single point can last for a minimum of ~11,000 years. A range of travertine ages show that leakage to the surface has constantly switched location through time, while the presence of three mounds of distinct age at one location demonstrate that pathways can become repeatedly re-used over periods of ~45,000 years. There is no evidence of temporal periodicity in travertine deposition but there is a distinct spatial pattern of leakage as shown by localised similarities in the initial uranium chemistries of travertine mounds. Initial leakage is proximally located to the axial trace of the Green River anticline and subsequent leakage spreads from this central point along the fault plane in both east and west directions. The switching of fluid flow pathways to the surface can be explained by three main mechanisms: mineralisation, 3-phase interference of CO2 related fluid flow and seismically triggered alteration in dynamic strain acting upon the hydrology of the faults. These mechanisms have differing influences in each area - demonstrating that the behaviour of fluid flow switching in a system confined to damage zone fractures (Little Grand Wash fault) is different to a system leaking through an unconfined aquifer (northern fault of the Salt Wash graben). Coupling of travertine ages with estimates of their volumes provided a total worse case scenario for quantity of CO2 leakage of 6.2 x 10^6 ± 1.7 x 10^6 tonnes for the Little Grand Wash fault and 7.4 x 10^6 ± 2 x 10^6 tonnes for the northern fault of the Salt Wash graben. From these totals time averaged leakage rates of 55 ± 15 and 47 ± 13 tonnes/year were estimated for each fault. The leakage rate for the actively precipitating Crystal Geyser travertine (which is the result of anthropogenic exploration drilling) is estimated to be 3,153 ± 851 tonnes/year. These total and modern rates provide analogues for leakage via caprock failure and catastrophic wellbore failure. Applying them to large scale storage sites such as Weyburn and Gorgon revealed that for caprock failure complete leakage of these reservoirs will take place over timescales of 10^5-10^6 years, while for catastrophic failure of a single well complete leakage of these reservoirs could occur over as little as 10^3 – 10^4 years. This finding has important implications for the successful monitoring of anthropogenic storage sites