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Abstract

Centime ter-scale stratigraphic anaJysis of facies deposited around the Cenomanian-Turonian (C-T) boundary in Colombia reveals that the interval is a condensed section caused by a series of transgressive pulses near the Cretaceous peak transgression with subsequent sediment trapping nearshore, omission and sediment starvation rn basinal facies. The condensed section thickens basinward and has a diachronous base and top: the base becomes younger landward whereas the top becomes younger basinward.

Facies across the C-T boundary in Colombia were interpreted as being deposited in a high-upwelling regime as evidenced by phosphate-rich shales, scattered chert beds with abundant nidiolarians, foraminifers filled with silica, changes in pianktic foraminifer populations, high values of total organic carbon (TOC up to 16%) and anoxic to dysoxic bottoms. Dysoxia was widespread, and affected the sediment-water interface and the water column.

For this paper, we used biostratigTaphic data to define and recognize the Cenomanian-Turonian bouadary in northern South America. Paleobiology, geochemistry, petrography, stratal geometries, and the modification of the paleogeography were used to characterize the uppermost Cenomanian-lowest Turonian stratigraphic interval (CTI) and to substantiate sea-level interpretations and other events occurring during this time. The CTT is here correlated to the proposed stratotype section in Pueblo, Colorado.

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