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ORIGIN OF CARBONATE CONCRETIONS IN SHALES, MAGDALENA VALLEY, COLOMBIA

1957; Geological Society of America; Volume: 68; Issue: 1 Linguagem: Inglês

10.1130/0016-7606(1957)68[95

1943-2674

Lewis G. Weeks,

Geological and Tectonic Studies in Latin America

Research Article| January 01, 1957 ORIGIN OF CARBONATE CONCRETIONS IN SHALES, MAGDALENA VALLEY, COLOMBIA L. G WEEKS L. G WEEKS 30 ROCKEFELLER PLAZA, NEW YORK 20, N. Y. Search for other works by this author on: GSW Google Scholar GSA Bulletin (1957) 68 (1): 95–102. https://doi.org/10.1130/0016-7606(1957)68[95:OOCCIS]2.0.CO;2 Article history received: 21 Sep 1953 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation L. G WEEKS; ORIGIN OF CARBONATE CONCRETIONS IN SHALES, MAGDALENA VALLEY, COLOMBIA. GSA Bulletin 1957;; 68 (1): 95–102. doi: https://doi.org/10.1130/0016-7606(1957)68[95:OOCCIS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Carbonate concretions that include marine organisms such as ammonites or even the full body of a fish are abundant in Cretaceous shales of the Magdalena Valley of Colombia, South America. The occurrence of carbonate concretions in central basin shale facies is common not only throughout the Cretaceous of the lengthy Andean geo-syncline but also in similar facies throughout the world. The concretions are of syngenetic or early diagenetic origin. They formed soon after deposition, when the now compact muds were plastic enough to flow in around them. The fish and other organisms calcified rapidly, and the enveloping concretions developed sufficiently early to arrest extreme decomposition and to withstand compression from the many thousands of pounds of subsequent overburden.The central-basin environments in which most carbonate concretion-bearing shales were deposited were not favorable to carbonate deposition. Such environments are stagnant and so are charged with carbon dioxide while the pH is too low for calcium carbonate deposition. However, an alkalinity adequate for such deposition in calcium-ion-rich waters may be locally created by the ammonia that evolves rapidly with decomposition of proteinaceous (nitrogen-bearing) organic matter.Similarly, limited decomposition, mainly anaerobic, of organic matter that impregnates deeper basinal muds may create enough alkalinity to free calcium carbonate from the lime-bearing solutions permeating the muds. This may account for calcareous shales in basins where pure limestones are restricted to the aerated shallow flank, shelf, or lesser bottom-high areas. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.