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Madhavaraju, J.,Lee, Yong Il,Scott, R.W.,Gonzá,lez-Leó,n, C.M.,Jenkyns, H.C.,Saucedo-Samaniego, J.C.,Ramasamy, S. Elsevier 2018 Journal of South American earth sciences Vol.82 No.-
<P><B>Abstract</B></P> <P>The 420-m thick stratigraphic section of the Mural Formation that is exposed in the Cerro Pimas area of northern Sonora, Mexico, is composed of limestone lithofacies ranging from bioclastic wackestone to boundstone, whose biota is characterized by low diversity. Prominent age-diagnostic fossils are benthic foraminifera and long-ranging calcareous algae that indicate the Aptian/Albian boundary is close to the base of the Los Coyotes Member. The carbonates of this formation have negative to positive δ<SUP>13</SUP>C values (−4.63 to +2.6‰) and highly depleted δ<SUP>18</SUP>O values that range from −12.74 to −8.34‰. The absence of correlation between δ<SUP>13</SUP>C and δ<SUP>18</SUP>O values supports a primary marine origin for the δ<SUP>13</SUP>C values of these limestones.</P> <P>The carbon-isotopic curve of the Cerro Pimas stratigraphic section has well-defined δ<SUP>13</SUP>C segments (C8 – C15) that compare with published curves of similar age. In the lower part of the early Albian Los Coyotes Member, the presence of OAE 1b is indicated by an increase followed by a decrease in δ<SUP>13</SUP>C values, suggesting correlation with the Kilian Event. The middle part of the Los Coyotes Member has a significant negative carbon-isotope excursion correlated with the globally recognizable early Albian Paquier event. Moreover, another significant negative carbon-isotope shift is observed in the upper part of the Los Coyotes Member, which can be correlated with the Leenhardt Event. The occurrence of the Kilian, Paquier and Leenhardt Events (OAE 1b cluster) in the Cerro Pimas stratigraphy confirms the global nature of these early Albian disturbances of the carbon cycle.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Benthic foraminifera and calcareous algae that indicate the Aptian/Albian boundary. </LI> <LI> The Aptian–Albian boundary is placed at the base of the Los Coyotes Member. </LI> <LI> High-resolution carbon-isotope curves of the Cerro Pimas are divided into seven well-defined δ<SUP>13</SUP>C segments. </LI> <LI> The upper Aptian-lower Albian Cerro Pimas section of the Mural Formation records the impact of OAE 1b. </LI> <LI> The occurrences of Kilian, Paquier and Leenhardt Events (OAE 1b clusters) are documented in the Cerro Pimas section. </LI> </UL> </P>
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