Solleiro-Rebolledo ElizabethGolyeva Alexandra A.Barceinas-Cruz HermenegildoAbrosimov Konstantin N....
19页
查看更多>>摘要：Abstract Paleosols interbedded with pyroclastic deposits have been proven to be an important paleoenvironmental proxy for the late Quaternary in Central Mexico. We studied a key upland section and several profiles on the slopes and lowlands of the Tlaxcala Block, assuming that the topographic variability of the soil-sedimentary mantle contains the complete record of the landscape history. The upland section included three paleosols separated by tepetates (compact volcanic pedosediments) and reflected a general trend of environmental evolution during the last 40 ka. Particle-size distribution, bulk chemical composition, magnetic characteristics, computed tomography, and micromorphological observations demonstrated a strong seasonality of paleoclimate at the end of MIS3, followed by cool wet conditions during the last glacial maximum, subsequent warming at the beginning of the Holocene, and drying during the last 3 ka. It was shown that tepetates had well-developed pedogenetic features that contribute to the paleosol record. The studied slope and lowland profiles reflected the main phases of geomorphic activity in the terminal Pleistocene and the early Holocene. These phases are linked to paleoclimate fluctuations in Central Mexico at the end of the last glaciation.
Lockley Martin G.Helm Charles W.Cawthra Hayley C.De Vynck Jan C....
15页
查看更多>>摘要：Abstract A trackway and burrows of a small rodent-sized bounding mammal (attributed to the Cape gerbil, Gerbilliscus afra) and a traceway of a large arachnid (spider) from the Pleistocene Waenhuiskrans Formation represent two biological groups not previously reported from this track-rich dune facies, which is widely distributed along the Cape south coast of South Africa. This may be due to biases against the preservation of small tracks. Trackways of hopping or bounding rodent-sized mammals are rare in the fossil record, occurring at only two known Mesozoic sites and three Cenozoic sites. Where these occur in dune facies, they are commonly associated with arachnid and other arthropod surface trails. The arachnid trace fossils commonly include the spider traceway Octopodichnus, known from the Permian to Recent, which is also the temporal range of the eponymous Octopodichnus ichnofacies. The abundance of small-mammal tracks associated with dune ichnofaunas led to the naming of the late Palaeozoic and Mesozoic Chelichnus ichnofacies, which is largely co-extensive with the Octopodichnus ichnofacies at this time. However, the recognition of similar mammal–arthropod dune facies assemblages in the Cenozoic requires adjusting our understanding of their distribution in space and time, and extends the known distribution of dune ichnofacies.
NSTL
Cambridge Univ Press