The nature of the δ13C of periplatform sediments: Implications for stratigraphy and the global carbon cycle

✍ Scribed by Peter K. Swart; Gregor Eberli

• Book ID: 104092308
• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 728 KB
• Volume: 175
• Category: Article
• ISSN: 0037-0738
• DOI: 10.1016/j.sedgeo.2004.12.029

✦ Synopsis

The carbon-isotopic composition (y 13 C) of bulk carbonates, obtained from a transect of sites drilled through platform and periplatform sediments of Holocene to Early Miocene age, has been compared to ascertain whether changes in the y 13 C can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the y 13 C of the dissolved inorganic carbon in the oceans over this time period. Five of the sites were drilled during Leg 166 of the Ocean Drilling Project (1003-1007) in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of Holocene to Oligocene age that are contained in 17 depositional sequences (A-Q). Two shallow-water sites, Clino and Unda were situated on a extension of the same transect on Great Bahama Bank in a water depth of 10-15 m. With the exception of Unda and Clino, the y 13 C of the carbonates ranges from +5x in the younger sequences to +1x in the Early Miocene. In each of the sites, the y 13 C is strongly positively correlated with the percentage of aragonite. As a consequence, the y 13 C of sequences A through F is strongly correlated, reflecting the decreasing amount of aragonite with increasing depth. In the two platform sites, the y 13 C is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the Pleistocene. Although the y 13 C of the individual sequences can be correlated in most instances between the ODP holes, the changes are not related to global changes in the y 13 C of the oceans which in contrast to the y 13 C of the platform sediments become isotopically lower towards the present day. Instead variations in the y 13 C appear to be related to varying mixtures of y 13 C-rich banktop sediments and pelagic material.