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Research on Whitings (Floating Patches of Calcium Carbonate Mud) Leads to Possible Explanation of Immense Middle East Oil Deposits
"Whitings"mysterious patches of milky water that drift around on the Great Bahama Bank and on other shallow carbonate bankshave long been a topic of scientific curiosity and controversy. What makes the seawater look milky are suspended, mud-size particles of aragonite, a form of calcium carbonate. The question is, does the aragonite in whitings precipitate spontaneously from seawater, or is the cloudiness simply aragonitic mud resuspended from the bottom by schools of fish?
A recent outgrowth of research into this question demonstrates how curiosity-driven science can lead to important information that, in this case, is particularly relevant to the "oil crisis" controversy of today. In a poster presented at the April 2007 American Association of Petroleum Geologists (AAPG) Annual Convention in Long Beach, California, scientists Christopher Kendall (retired and Emeritus Professor at the University of South Carolina), Gene Shinn (retired, U.S. Geological Survey [USGS], and currently a Courtesy Professor at the University of South Florida), and Xavier Janson (Research Associate at the University of Texas, Austin) proposed "that whitings of the modern Arabian Gulf are the key to the origin of the vast petroleum reserves of this region."
The poster, entitled "Holocene Cyanobacterial Mats and Lime Muds: Links to Middle East Carbonate Source Rock Potential," won the 2007 Excellence of Poster Presentation award, which was presented to the authors in April 2008 at the Society for Sedimentary Geology (SEPM) Annual Meeting in San Antonio, Texas. This is the story of the research leading to that award.
For years, the origin of aragonite in whitingswhether as seawater precipitate or derived from aragonitic mud stirred into the water by fishwas considered an academic question. Investigations produced anything but consensus. In the 1950s, Preston Cloud, the first USGS geologist to study whitings, concluded that they form by instantaneous precipitation. Wally Broecker and Taro Takahashi (Lamont Geological Observatory of Columbia University) observed in the mid-1960s that the pH and other major chemical characteristics of seawater were the same inside and outside Bahamian whitings and thus concluded that the whitings could not be precipitating from seawater. John Morse (Texas A&M University) supported these findings in a paper published in 1984. In the 1950s, Heinz Lowenstam (California Institute of Technology) pointed out the similarities between aragonite needles made by algae and those found in whitings.
In the early 1960s, geologist Gene Shinn, who would go on to a highly productive 31-year career at the USGS (see article in Sound Waves, February 2006, "Retirement of Gene Shinn, Pioneer in Carbonate Sedimentology and Coral-Reef Ecosystems"), was working for Bob Ginsburg at the Shell Development Field Station in Coral Gables, Florida. At that time, Shinn concurred with the "fish mud" theory for the origin of whitings. He participated in a study with Ginsburg and Ken Stockman, also a Shell Development Co. geologist, in which they monitored the growth rate of Penicillus (an alga that produces aragonite crystals) in the Florida Keys and concluded that Penicillus species were capable of making about a third of the mud that had accumulated in Florida Bay. Two Royal Dutch Shell geologists, Leslie Illing and Allen Wells, examined whitings in the Persian Gulf and decided that they were seawater precipitates. Others in Shell said, "Impossible!" and insisted that seawater chemistry would not allow precipitation.
While Shinn was working for Shell in the Persian Gulf city of Doha, Qatar, in the 1960s, not far away in Abu Dhabi Chris Kendall was working under the guidance of Douglas Shearman (Imperial College, London) on a dissertation on algal mats that form on Abu Dhabi’s huge coastal sabkha, or salt flat. Kendall and Shinn each knew the other was there, but the ruler of Abu Dhabi would not allow anyone from Shell to visit his sheikhdom. It would be another 10 years before the two would meetin Houston, Texas, where Shinn was working for Shell and Kendall for Exxon Production Research. Similar interests and a strong affection for their respective experiences in the Middle East caused them to quickly become friends as well as scientific colleagues.
Shinn joined the USGS in the 1970s and, in 1974, established the USGS Fisher Island Field Station in Miami Beach, Florida. In 1982, Randy Steinen (University of Connecticut, Storrs) and Shinn, Bob Halley, and Barbara Lidz from the Fisher Island Field Station returned to the Bahama Bank for a better look at whitings. Eric Sundquist, a USGS geologist studying atmospheric CO2 and the global carbon cycle, contributed some of his project funds to the cause. No fish were found in the whitings.
In the late 1980s, Lisa Robbins, a USGS postdoctoral researcher who would later become Center Chief of what is now the USGS Florida Integrated Science Center in St. Petersburg, demonstrated with amino-acid analysis that the aragonite in whitings is not the same as that made by algae. She also found spherical cyanobacteria associated with whiting formation. In the meantime, the USGS Fisher Island scientists published their first paper on whitings in the Journal of Sedimentary Petrology (Shinn, E.A., Steinen, R.P., Lidz, B.H., and Swart, P.K., 1988, Whitings, a sedimentological dilemma: v. 59, no. 1, p. 147-161). The data showed that fish were not the cause of the Bahamian whitings. The Electric Power Research Institute (EPRI) became interested. If whitings were precipitates, then they might scrub CO2 from the atmosphere, which had been the thought of Eric Sundquist when he helped fund whitings research in 1982.
The USGS could not accept research funds from EPRI, but Robbins, who had taken a job as an Associate Professor at the University of South Florida (USF) in Tampa, could. Over the next several years, she obtained about $1 million in funding from EPRI. In a 1992 paper published in Geology (Biochemical and ultra-structural evidence for the origin of whitings: A biologically induced calcium carbonate precipitation mechanism: v. 20, no. 5, p. 464-468), Robbins and Patricia Blackwelder (Rosenstiel School of Marine and Atmospheric Science of the University of Miami) became the first researchers to document the association between organic matter and calcium carbonate in Bahamian whitings; the paper included scanning and transmission electron micrographs of aragonite crystals attached to the cell walls of cyanobacteria. In her dissertation, Kim Yates, Robbins' first graduate student, reported on her studies of whitings and the organic chemistry associated with their formation. That research showed that the metabolism of cyanobacteria creates local conditions that cause calcium carbonate to precipitate on the cell walls.
From the late 1990s through mid-2000 during vacations in the Bahamas, Shinn lived aboard a boat and spent time chasing and studying whitings when he wasn't fishing. About that time, Chuck Holmes, then a USGS geochemist (now retired), suggested using short-lived isotopes that occur in water to shed light on the origin of whitings. Beryllium-7, which is produced in the atmosphere and is present in water, has a half-life of only 53 days. Holmes reasoned that if fish, or anything else, stirred up bottom mud, the mud would likely be more than 53 days old and would therefore produce very little gamma radiation. On the other hand, if whitings were precipitating from seawater, and if the samples were run within a few days of collection, the water samples should be "hot." They were. Although some geochemists remain skeptical, Shinn, once a proponent of the fish-mud theory, now embraced the theory that aragonite in Bahamian whitings precipitates from seawater. In a 1996 paper in the Bahamas Journal of Science (Whitings on the Great Bahama Bank: A microscopic solution to a macroscopic mystery: v. 4, no.1, p. 2-6), Robbins, Yates, Shinn, and Blackwelder proposed that blooms of cyanobacteria initiate aragonite precipitation to create whitings.
Cyanobacteria are also a topic of interest to Kendall. While investigating the geochemistry of oil during a sabbatical in 2007 at the Jackson School of Geosciences (University of Texas, Austin), Kendall became convinced that the un-oxidized stable remains of cyanobacteria, matching those generated within algal mats and whitings in shallow-marine settings, might be converted to oil more effectively than other potential sources of petroleum that include marine algae and zooplankton. Putting together the oil-producing potential of cyanobacteria and the close association between cyanobacteria and whitings led to the award-winning poster, which consisted of three parts: Bahama whitings (Shinn), Persian Gulf whitings (Janson), and tidal-flat algal mats and the subsurface geology of the Persian Gulf region (Kendall). This winding road of research that investigated how whitings form now shed startling new light on the potential source of the immense oil deposits of the Middle East. The poster hypothesized that the dispersed un-oxidized biological membranes of cyanobacteria associated with Permian and Mesozoic algal mats and whitings likely collected in the arid rain shadow of Gondwanaland on the southern margin of the Tethys as they do today in the shadow of Arabia and Africa. Though low in total organic carbon, this material was preserved in sufficient quantities to ensure that the large volumes of oil we find today could be generated over a short time. It's a wonderful story on how curiosity-driven science can have large applications.
To read the poster abstract, visit URL http://aapg.confex.com/aapg/2007am/preliminaryprogram/abstract_110223.htm.
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