D. L. Gautier 1987 <div id="abstracts" class="Abstracts u-font-serif text-s"><div id="ab1" class="abstract author" lang="en"><div id="aep-abstract-sec-id3"><p>The S isotope composition of pyrite in Cretaceous shales from the Western Interior of North America is related to organic C abundance, kerogen type and Fe availability. Both calcareous and noncalcareous rocks show a correlation between S and C, but noncalcareous rocks are relatively enriched in S with a higher S/C ratio. This higher ratio probably shows that pyrite formation was Fe limited in the calcareous rocks. Organic-carbon-rich noncalcareous shales accumulated slowly beneath anoxic bottom waters. The anoxic bottom waters allowed hydrogen-rich organic matter to be preserved. Such shales have a narrow range of<span>&nbsp;</span>³⁴S-depleted sulfide and have Fe/S ratios like stoichiometric pyrite, suggesting that pyrite formation in organic-rich shales was also limited by Fe availability. Conversely, organic-poor shales commonly accumulated at comparatively high rates, contain hydrogen-poor and refractory organic matter, and have a wide range of pyrite-S isotopic compositions. These organic-poor shales contain post-sulfidic authigenic minerals such as siderite and have excess reactive Fe rather than pyrite stoichiometry. Evidently Fe played a large role in early diagenesis and determined the course of post-sulfidic diagenesis. Fe availability was, however, mainly controlled by provenance, by the rates of sediment accumulation, and by the oxygen content of the depositional environment.</p></div></div></div> application/pdf 10.1016/0168-9622(87)90009-1 en Elsevier Isotopic composition of pyrite: Relationship to organic matter type and iron availability in some North American cretaceous shales article