Secular Changes in the Major-Ion Chemistry and Salinity of Seawater

We are testing the hypothesis that ancient seawater has undergone changes in chemical composition from chemical analyses of samples of seawater brines preserved as fluid inclusions in marine halites. The Environmental SEM-X-ray-EDS technique, developed at Binghamton, shows, from chemical analyses of individual inclusions in halite, that global seawater has undergone significant oscillations in major element chemistry over the Phanerozoic. The fluid inclusion data indicate that seawater had high Mg²⁺/Ca²⁺ ratios (>2) and relatively elevated Mg²⁺, Na⁺, and SO₄^2- during the Late Precambrian, Permian, and over the last 40 Ma.  In contrast, during the Cambrian, Silurian, Devonian and Cretaceous, seawater had relatively low Mg²⁺/Ca²⁺ ratios (<2.3) and low Na⁺, Mg²⁺, and SO₄^2-.

Current research, funded by an ACS-PRF Grant from 2003-2006, is allowing continued ESEM X-Ray EDS analyses of frozen inclusions in marine halite of different ages.  The research is also evaluating the hypothesis that CaCl₂ brines, commonly found as sedimentary basin formation waters and as fluid inclusions in diagenetic minerals, originated as seawater when the world’s oceans were enriched in Ca²⁺. These basinal brines are chemically distinct from seawater and other common surface and near-surface waters (Na-Cl-SO₄, Ca-HCO₃, or Na-CO₃ types) in their high concentrations of Ca²⁺ which exceed the combined concentrations of SO₄^2-, HCO₃^-, and CO₃^2- ions, specifically m_Ca²⁺>∑ (m_SO4^2- + ½ m_HCO3^- + m_CO3^2-). Three sedimentary basins containing evaporites and CaCl₂ basinal brines are being studied (Silurian, Michigan-Illinois basins; Devonian, Western Canada Sedimentary basin; and Jurassic, U.S. Gulf Coast).  ESEM-X-ray-EDS analyses of fluid inclusions in marine halites enable calculation of Silurian, Devonian, and Jurassic seawater chemistry, which can be compared to the chemical composition of formation brines from the basins under investigation. Mass balance calculations identify which major ions may have been added to or subtracted from the evaporated seawater to produce the basinal brines. Sediment-brine interactions, when necessary, complete the mass balance (i.e., dolomitization, precipitation of CaSO₄, K-aluminosilicates, albitization of plagioclase). Genetic connections between Na-Ca-Cl-rich fluid inclusions in diagenetic and Mississippi Valley type (MVT) minerals, ancient evaporated seawater, and basinal brines are being investigated.  Progressive changes in the chemistries of these waters, from CaCl₂“parent” seawater to inclusion brine to the “post-reaction” basinal brine, will be used to quantify mineral-brine interactions in the burial diagenetic environment.

A new area of investigation of our paleoseawater research is the study of changes in the SALINITY of ancient seawater.  Little is known quantitatively about processes that control the salinity of seawater over long periods of time and whether the salinity of paleoseawater has varied.  The paleosalinity of ancient seawater may be obtained from simple measurements of the freezing point depression of aqueous inclusions in marine calcites. Theoretically, seawater paleosalinity determinations can be made from measurement of the freezing point depression of ice in fluid inclusions that contain trapped seawater.  Our research will continue the investigation of the paleosalinity of the ancient oceans begun by others on Cambrian and Devonian calcites [Johnson and Goldstein (1993), Ward et al. (1993), Kwong (1995), and Cicero (1997].

Long-Term Survival of Microorganisms in Fluid Inclusions

We are studying the survival of microorganisms trapped inside ancient halite crystals. Preservation of ancient microorganisms and their DNA has profound implications for long-term survival on Earth and for astrobiology.  Our research has developed new methods and media to isolate, quantify and analyze ancient microbes trapped in halite crystals and has improved understanding of life and the paleoenvironment at the time the crystals formed.

There is little information about the number of microorganisms trapped inside geological materials and the survival of those organisms for periods of 10¹ to 10⁶ years.  We have begun research on Quaternary age salt cores from three basins (Death Valley, California, Salar de Atacama, Chile, and Salar de Uyuni, Bolivia) which provide a rich archive for study of the distribution of microorganisms in fluid inclusions in saline minerals (NSF funding Biogeosciences program, 2004-2007). The goal of the research is to obtain data on the distribution, survival, and diversity of microorganisms that have been in the subsurface for periods of several hundred thousand years. The presence or absence of microorganisms and DNA in fluid inclusions in halite crystals will be interpreted in the context of the original surface environments (saline lakes, saline pans, saline groundwaters) and physico-chemical conditions (temperatures, major ion chemistries) in which the salts precipitated. 

Samples of halite for microbiological work are surface sterilized and dissolved in sterile distilled water. DNA extracted from halite crystals is analyzed by PCR (polymerase chain reaction) assays targeting portions of 16S rRNA genes, followed by denaturing gradient gel electrophoresis (DGGE) to characterize the diversity of microorganisms.  Cloning and sequencing of PCR products and individual bands excised from DGGE gels will be done to establish the phylogenetic affinities of the microorganisms. Culturing methods attempt to isolate microbes from fluid inclusions in halite crystals. 

Antiquity of Life in Salt Deposits? A Rb-Sr Age-Dating Study

We are attempting to verify geological evidence that microorganisms can survive inside the brine-filled inclusions of halite crystals for periods of 10⁸ years (funding from NSF Geology and Paleontology Program). Our goal is to obtain absolute radiometric ages of brine inclusions from two ancient halites from which microorganisms have been cultured: cement crystals from the Permian Salado Formation, New Mexico and “chevrons” from the Cretaceous Muribeca evaporites of Brazil.  Such dating will remove doubts about the ages of the fluid inclusions from which the purported Permian and Cretaceous microorganisms were extracted. Obtaining absolute ages of brine inclusions in halite has profound implications for long-term survival on Earth, and may influence future exploration for life on Mars and other parts of the solar system. Our research is a collaboration between Binghamton University and Juske Horita and Lee Riciputi from Oak Ridge National Lab.

The purported world’s oldest living organism, the spore-forming bacterium Virgibacillus sp. Permian strain 2-9-3, was cultured from a brine inclusion in halite cement of the 250 Ma Permian Salado Formation (Vreeland et al. 2000).  Rb-Sr dating of individual brine inclusions from these samples will establish unequivocally whether Virgibacillus sp. 2-9-3 was trapped in a fluid inclusion at the time of deposition of the Salado salts.  Archaeal strains have been cultured from brine inclusions from primary chevron halite of the Cretaceous Muribeca Formation. Dating brine inclusions in these Cretaceous halites by Rb-Sr methods will ascertain with certainty whether the brine inclusions that yielded the newly discovered halophilic Archaea are >100 Ma in age.

National Science Foundation Grant for Binghamton Geoscience Microscopy Laboratory:

The Binghamton Geoscience microscopy laboratory has received funding in 2005 for the following equipment for microscopy:

Linkam fluid inclusion system, to complement the two Fluid Inc. adapted USGS Gas-flow heating-freezing stages presently in our lab.  In addition, we will obtain a 100X long working distance objective for improved observation of minute inclusions in calcite and a new stereomicroscope for improved low magnification petrography of carbonate cements.

Zeiss Axioskop optical microscope system; filter cube sets will allow testing of whether microparticles (microbes?) trapped in fluid inclusions fluoresce under ultraviolet light.  Digital camera, computer work station, and image processing software will allow manipulation of images of 3000 X 4000, and permit live motion capture of microorganism movement in brine inclusions.