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Miocene to Pleistocene sedimentation at ODP Site 133-823
No full textMore than 2000 turbidite, debris-flow, and slump deposits recovered at Site 823 record the history of the Queensland Trough since the middle Miocene and provide new insights about turbidites, debris flow, and slump deposits (herein termed gravity deposits). Changes in the composition and nature of gravity deposits through time can be related to tectonic movements, fluctuations in eustatic sea level, and sedimentological factors. The Queensland Trough is a long, relatively narrow, structural depression that formed as a result of Cretaceous to Tertiary rifting of the northeastern Australia continental margin. Thus, tectonics established the geometry of this marginal basin, and its steep slopes set the stage for repeated slope failures. Seismic data indicate that renewed faulting, subsidence, and associated tectonic tilting occurred during the early late Miocene (continuing into the early Pliocene), resulting in unstable slopes that were prone to slope failures and to generation of gravity deposits. Tectonic subsidence, together with a second-order eustatic highstand, resulted in platform drowning during the late Miocene.
The composition of turbidites reflects their origin and provides insights about the nature of sedimentation on adjacent shelf areas. During relative highstands and times of platform drowning, planktonic foraminifers were reworked from slopes and/or drowned shelves and were redeposited in turbidites. During relative lowstands, quartz and other terrigenous sediment was shed into the basin.
Quartzose turbidites and clay-rich hemipelagic muds also can record increased supply of terrigenous sediment from mainland Australia. Limestone fragments were eroded from carbonate platforms until the drowned platforms were buried under hemipelagic sediments following the late Miocene drowning event. Bioclastic grains and neritic foraminifers were reworked from neritic shelves during relative lowstands. During the late Pliocene (2.6 Ma), the increased abundance of bioclasts and quartz in turbidites signaled the shallowing and rejuvenation of the northeastern Australia continental shelf. However, a one-for-one relationship cannot be recognized between eustatic sea-level fluctuations and any single sedimentologic parameter. Perhaps, tectonism and sedimentological factors along the Queensland Trough played an equally important role in generating gravity deposits.
Turbidites and other gravity deposits (such as those at Site 823) do not necessarily represent submarine fan deposits, particularly if they are composed of hemipelagic sediments reworked from drowned platforms and slopes. When shelves are drowned and terrigenous sediment is not directly supplied by nearby rivers/point sources, muddy terrigenous sediments blanket the entire slope and basin, rather than forming localized fans. Slope failures affect the entire slope, rather than localized submarine canyons. Slopes may become destabilized as a result of tectonic activity, inherent sediment weaknesses, and/or during relative sea-level lowstands. For this reason, sediment deposits in this setting reflect tectonic and eustatic events that caused slope instabilities, rather than migration of different submarine fan facies
Grand parents: raising our children's children
No full textBulletin no. 823 Moscow, Idaho :University of Idaho, College of Agriculture, Cooperative Extension System, 2000-01-01. Author(s): Williams, Doris K
Miocene to Pleistocene dinoflagellate cysts in ODP Sites 133-815 and 133-823
No full textWell-preserved and diverse dinoflagellate cyst assemblages were recovered from Ocean Drilling Program (ODP) Sites 815 and 823. The late middle Miocene is indicated by the presence of Sumatradinium spp. up to Core 133-823C-10R at Site 823 and up to Core 133-815B-47X at Site 815. Melitasphaeridium choanophorum appeared in the late Miocene (Cores 133-823C-19R and 133-815B-45X) and disappeared during the late Pliocene (Cores 133-823C-56X and 133-815 B-4H). Other significant biostratigraphic datums include the disappearances of Hystrichokolpoma rigaudiae (Cores 133-823B-22X and 133-815A-5H) and Dapsilidiniumpasteilsii (Cores 133-823B-23X and 133-815A-5H) at the end of the Pliocene; the first appearance of Blysmatodinium argoi during the late Miocene (Core 133-815B-43X) and subsequent disappearance during the early Pliocene (Cores 133-823B-47X and -815B-27X); and the disappearance of Operculodinium longispinigerum (Sections 133-823A-3H-4 and -815A-1H-3) during the Pleistocene. These results are consistent with the ages determined by nannoplankton and foraminifers at these sites and also with the dinoflagellate biostratigraphy from Leg 123 (McMinn, 1992, doi:10.2973/odp.proc.sr.123.120.1992).
The Neogene assemblages of both sites are characterized by abundant Spinife rites spp., Impagidinium spp., and Operculodinium spp. Both Tuberculodinium vancampoae and Lingulodinium machaerophorum are consistently present and sometimes abundant but most other species occur only sporadically. Peridiniaceae, which is often associated with nutrient enrichment, is rare in all samples. This suggests that the environment has always been oligotrophic. Imp?gidinium spp., taxa typically associated with oceanic environments, are present throughout both cores, but are more abundant in post-Pliocene sediments
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
823. Kyūji
No full textIwao Seiichi, Iyanaga Teizō, Ishii Susumu, Yoshida Shōichirō, Fujimura Jun'ichirō, Fujimura Michio, Yoshikawa Itsuji, Akiyama Terukazu, Iyanaga Shōkichi, Matsubara Hideichi. 823. Kyūji. In: Dictionnaire historique du Japon, volume 13, 1987. Lettre K (3) p. 166
823. Kyūji
No full textIwao Seiichi, Iyanaga Teizō, Ishii Susumu, Yoshida Shōichirō, Fujimura Jun'ichirō, Fujimura Michio, Yoshikawa Itsuji, Akiyama Terukazu, Iyanaga Shōkichi, Matsubara Hideichi. 823. Kyūji. In: Dictionnaire historique du Japon, volume 13, 1987. Lettre K (3) p. 166
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