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lithographic limestone
Lithographic limestone is hard limestone that is sufficiently fine-grained, homogeneous and defect free to be used for lithography. Geologists use the term ''lithographic texture'' to refer to a grain size under 1/250 mm.〔Lithographic limestone, Lithographic Texture, (Glossary of Geology and Related Sciences ), 2nd ed, The American Geological Institute, 1960; pages 170-171.〕 The term ''sublithographic'' is sometimes used for homogeneous fine-grained limestone with a somewhat coarser texture.〔Ronald K. DeFord, Grain Size in Carbonate Rock, (Geological Notes ) , Vol. 30, No. 11, 1946; pages 1921-1928; see particularly pages 1922-1923.〕
==Origin==
The generally accepted theory for the origin of lithographic and sublithographic limestones is that they were formed in shallow stagnant hypersaline and anoxic lagoons. The combination of mild hypersalinity and low oxygen content is believed to have inhibited the formation of microbial mats and prevented the invasion of bottom dwelling organisms. Microbial mats and bottom dwelling organisms would have left fossils, and bottom dwelling organisms would have churned the accumulating sediment, producing a less homogeneous rock. Stagnancy was required to avoid churning or sculpting of the sediment by currents or wave action.〔Brian J. Witzke and Bill J. Bunker, Sedimentation and stratigraphic architecture of a Middle Devonian (late Givetian) transgressive-regressive carbonate-evaporite cycle, Coralville Formation, Iowa area, (Paleozoic Sequence Stratigraphy, Biostratigraphy, and Biogeography ) Geological Society of America Special Paper 321, 1997; pages 67-88.〕〔Walter Etter, Solnhofen: Plattenkalk Preservation with Archaeopteryx, Chapter 18 of (Exceptional Fossil Preservation: A Unique View of the Evolution of Marine Life ); Columbia University Press, 2002; pages 327-350.〕
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