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R. Vahdati, Ali,Weissmann, John David,Timmermann, Axel,Ponce de Leó,n, Marcia S.,Zollikofer, Christoph P.E. Pergamon Press 2019 Quaternary science reviews Vol.221 No.-
<P><B>Abstract</B></P> <P>Understanding Late Pleistocene human dispersals from Africa requires understanding a multifaceted problem with factors varying in space and time, such as climate, ecology, human behavior, and population dynamics. To understand how these factors interact to affect human survival and dispersal, we have developed a realistic agent-based model that includes geographic features, climate change, and time-varying vegetation and food resources. To enhance computational efficiency, we further apply machine learning algorithms. Our approach is new in that it is designed to systematically evaluate a large-scale agent-based model, and identify its key parameters and sensitivities. Results show that parameter interactions are the major source in generating variability in human dispersal and survival/extinction scenarios. In realistic scenarios with geographical features and time-evolving climatic conditions, random fluctuations become a major source of variability in arrival times and success. Furthermore, parameter settings as different as 92% of maximum possible difference, and occupying more than 30% of parameter space can result in similar dispersal scenarios. This suggests that historical contingency (similar causes – different effects) and equifinality (different causes – similar effects) are primary constituents of human dispersal scenarios. While paleoanthropology, archaeology and paleogenetics now provide insights into patterns of human dispersals at an unprecedented level of detail, elucidating the causes underlying these patterns remains a major challenge.</P>
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>