• journal_title：Geology
• Contributor：Clinton A. Cowan ; David L. Fox ; Anthony C. Runkel ; Matthew R. Saltzman
• Publisher：Geological Society of America
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.1130/G21434AR.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：33
• issue：8
• firstpage：661

Carbon isotope compositions (δ¹³C) of inarticulate brachiopod shells from Upper Cambrian sandstone in the cratonic interior of Laurentia record a 5‰ positive excursion that correlates biostratigraphically with the global Steptoean positive isotopic carbon excursion. A consistent 6‰ negative displacement in brachiopod δ¹³C relative to carbonate values is interpreted to represent an onshore-offshore gradient in the isotopic composition of dissolved inorganic carbon in Cambrian seawater. Thus, these ∼500-m.y.-old chitinophosphatic brachiopod shells preserve evidence for carbon cycle coupling between the ancient atmospheric, oceanic, and terrestrial reservoirs in the time before embryophytic land plants.