The Dolomite Problem

 

The question of how the mineral dolomite, occurring in sedimentary rocks throughout the Earth, was created in large quantities has concerned the geology for over 200 years now – with only moderate success in explaining it. Dolomite was identified in 1791 by the French mineralogist Déodat de Dolomieu (1750-1801). Its best-known occurrence in Europe are the Dolomites in the Italian Alps, so named after the mineralogist.

CaMg[CO3]2 (dolomite) is part of the mineral class of anhydrous carbonates. It differs from limestone in that the calcium is replaced in half the layers by magnesium. Today (or during Holocene) dolomite occurs only in very limited scale in selected salt lakes and lagoons. Under what conditions it arose in the past in such huge quantities is still an unsolved mystery.

According to geologists dolomite occurs under the influence of seawater containing magnesium during the sedimentation (early diagenetic dolomitization) or much later in the already solidified sediment (late diagenetic dolomitization), with areas that cut through the existing layers. A direct sedimentation of dolomite plays no significant role according to the prevailing theory [Vinx, 329]. The Dolomites for example consisted originally of calcium carbonate, dead coral and shells from the ocean floor. Only later (late diagenetic) the calcium carbonate in the dolomite has been converted. This is accompanied by a reduction in volume, and the rock becomes porous. Dolomite deposits in the United States, however, contain no or very few fossils over large areas [example Cressman or Dennis].

These assumptions of geologists are also questioned within the standard theory. The dolomite problem is well recognized as such. Dolomite has been found in soil, coal, rivers, lakes, pearls and even kidney stones of Dalmatian dogs. A diagenetic dolomitization in these examples is not possible. Also chemical experiments show [Wright], that the supposed geological formation mechanism of limestone under current static seawater conditions (salinity, temperature) does not work. The carbonate precipitation is prevented by several simple kinetic limitations in salt water. In particular, it is just the required magnesium in the form of sulfates which hinders the typical carbonate precipitation. To demonstrate dolomite growth in reactors under appropriate pressure, temperatures between 100° and 200°C [Arvidson/Mackenzie] had to be applied, as well as larger amounts of CO2 dissolved in water. On the other hand, other chemists were apparently able to synthesize dolomite at normal temperature [Liebermann, Deelman] in a dynamic, complex, multi-stepped process. The secret here seems to be a higher salt content, an ideal sequence of temperature changes and urine (for pH adjustment), and again CO2 in large quantities. The described process seems to rule out a late diagenetic dolomitization. In addition: The origin of carbonate sediments (limestone), from which in turn the dolomite is supposed to have originated, is also not free of contradictions. Regardless of whether the calcite is precipitated directly from seawater or incurred by way of marine organisms – the source is always the seawater. A simple calculation [Kervran, 31] shows that the amount of calcium carbonate, which may arise in the sum of the calcite dissolved in seawater, is by far not sufficient to either explain the existing limestone layers nor diagenetic dolomite created out of it. There is not just a particular dolomite problem, there is even a full-blown carbonate problem.

Mainly in sulfate-rich, oxygen-free environments today, dolomite growth is observed to a lesser extent [Preiser]. This is attributed to bacteria, which get their oxygen from the sulfates, and thereby excrete the components of dolomite. It appears questionable whether the existing massive dolomite deposits may have originated in this way. C.L. Kervran’s approach of biological transmutation [Kervran] of calcite and dolomite by bacteria at least provides a starting point, but it is highly controversial within research, or even completely rejected.

Undeniably, main aspects of the dolomite problem (its uneven development over time and the unlikelihood of its diagenetic origin) are still awaiting a solution. Why does the dolomite occur in such large quantities? How is it made? Why was it created only temporarily?

Michael Steinbacher [2011] suggests another possible answer to this (at least for the deposits in the U.S.). NASA discovered that up to 7% of the dust of some comets consisted of Mg-carbonates (dolomite), which may still be set too low because the detectors were not suitable for very fine particles [Flynn]. It is entirely possible that the dolomite in the world could be in part of extraterrestrial origin: It may have “rained down” during one or more close encounters with a great comet. Is direct sedimentation of dolomite back on the playing field? In such an encounter, in addition to the extreme atmospheric wind effects, not only dolomite dust but also other cometary material in large quantities would penetrate the atmosphere. Strong winds and abundant particles in the atmosphere – these are the ingredients for the formation of large dunes.

Next: Duning

Literature

Arvidson, Rolf S. / Mackenzie, Fred T. (1999): The Dolomite Problem: Control of Precipitation Kinetics by Temperature and Saturation State; in American Journal of Science, Vol. 299, 257-288

Cressman, Earle R. / Peterson, Warren L. (2001): Ordovician System; http://pubs.usgs.gov/pp/p1151h/ordo.html

Deelman, J. C. (1999): Low-temperature nucleation of magnesite and dolomite; Neues Jahrbuch für Mineralogie, 289–302

Dennis, Bob (2006): An integrated Petroleum Evaluation of Northeastern Nevada; http://westerncordillera.com/sevy_dolomite.htm

Flynn, G. J. (2008): Carbonate in Comets: A comparison of Comets1P/Halley, 9P/Temple 1, and 81P/Wild 2; http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080012481_2008010014.pdf

Liebermann, Otto (1967): Synthesis of Dolomite; Nature, 21. January 241-245

Kervran, C. L. (1972): Biological Transmutation; Bristol

Preiser, Rachel (1996): The Dolomite Problem; http://discovermagazine.com/1996/feb/thedolomiteprobl700

Steinbacher, Michael (2011): A new Approach to Mountain Formation; in Proceedings of the Natural Philosophy Alliance. 18th Annual Conference of the NPA, 6 – 9 July 2011 at the University of Maryland, College Park, USA; Mt. Airy, 584-590

Wright, Dave (2008): Sedimentary dolomite – a reality check on the Dolomite Problem; http://www.scitopics.com/Sedimentary_dolomite_a_reality_check_on_the_Dolomite_Problem.html

Vinx, Roland (32011): Gesteinsbestimmung im Gelände, Berlin / Heidelberg

Other related information

http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=NVCAc;0

http://historyofgeology.fieldofscience.com/2010/08/dolomite-mountains-and-dolomite-problem.html

http://www.nasa.gov/mission_pages/deepimpact/media/spitzer-di-090705.html

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