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Research Article| March 01, 2000 Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal T. P. Ojha; T. P. Ojha 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar R. F. Butler; R. F. Butler 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar J. Quade; J. Quade 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar P. G. DeCelles; P. G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar D. Richards; D. Richards 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar B. N. Upreti B. N. Upreti 2Department of Geology, Tri-chandra Campus, Ghantaghar, Kathmandu, Nepal Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (3): 424–434. https://doi.org/10.1130/0016-7606(2000)112<424:MPSOTN>2.0.CO;2 Article history received: 13 Aug 1998 rev-recd: 18 Mar 1999 accepted: 26 Mar 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. P. Ojha, R. F. Butler, J. Quade, P. G. DeCelles, D. Richards, B. N. Upreti; Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal. GSA Bulletin 2000;; 112 (3): 424–434. doi: https://doi.org/10.1130/0016-7606(2000)112<424:MPSOTN>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The middle Miocene–Pliocene Siwalik Group was deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold-thrust belt. Results of thermal demagnetization experiments on samples from the Siwalik Group in central and western Nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies. Sandstones and paleosols of the Siwalik Group, however, generally display highly erratic paleomagnetic behavior during thermal demagnetization. On the basis of these observations, siltstones from a well-exposed, 2423-m-thick section of the Siwalik Group in Khutia Khola, far western Nepal, were sampled for magnetic polarity stratigraphy. The Siwalik Group is composed of informal lower, middle, and upper members. Correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13.30 to 7.65 Ma. The lower-middle Siwalik boundary occurs at 11.05 Ma, near the beginning of chron C5n. The rate of sediment accumulation increases upsection, similar to rate changes previously observed in the Pakistan Siwalik Group, and probably in response to increasing proximity of the Himalayan thrust belt. In the Khutia Khola section, a discordant declination indicates that this region has rotated about a vertical axis 16.6° counterclockwise with respect to the Indian subcontinent. Measurements of δ13C in paleosol carbonate indicate the predominance of C3 plants until 7.65 Ma, and the clear presence of C4 plants higher in the undated portion of the section. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Carbonate is abundant in many Neolithic tells and is a potentially useful archive for dating and climate reconstruction. In this paper, we focus on the mineralogy, radiocarbon dating, and stable isotope systematics of carbonate in hackberry endocarps. Hackberry fruits and seeds are edible in fresh and stored forms, and they were consumed in large quantities in many Neolithic sites in the Near East, including the site of our study, Aşıkli Höyük in central Anatolia, an Aceramic Neolithic tell occupied from about 9.4 to > 10.3 BP (7.4 to > 8.3 BCE). Detailed 14 C age control provided by archaeological charcoal permits a test of the fidelity in 14 C dating of hackberry endocarps. Modern endocarps and leaves yield fraction modern 14 C values of 1.050–1.066, consistent with levels present in the atmosphere when sampled in 2009. On the other hand, archaeological endocarps yield consistently younger ages than associated charcoal by ca. 130 14 C years (ca. 220 calendar years) for samples about 10,000 years old. We speculate this is caused by the slight addition of calcite or recrystallization to calcite in the endocarp, as detected by scanning electron microscopy. Subtle addition or replacement of calcite by primary aragonite is not widely recognized in the 14 C community, even though similar effects are reported from other natural carbonates such as shell carbonate. This small (but consistent) level of contamination supports the usefulness of endocarps in dating where other materials like charcoal are lacking. Before dating, however, hackberries should be carefully screened for mineralogical preservation and context. We examined the carbon and oxygen isotopic systematics of the fossil endocarps to try to establish potential source areas for harvesting. Most of the hackberries are enriched in 18 O compared to local water sources, indicating that they were drawing on highly evaporated soil water, rather than the local (perched and regional) water table sampled in our study. Isotopic evidence therefore suggests that most but not all of the hackberries were harvested from nearby mesas well above the local streams and seeps fed by the water table.
Significance This article provides original results on the formative conditions of sheep domestication in the Near East. To our knowledge, none of the results has been published before, and the results are expected to be of wide interest to archaeologists, biologists, and other professionals interested in evolutionary and cultural processes of animal domestication.
Both aquatic and land snails are common in the geologic record, but their utility in dating is greatly restricted by their well-documented tendency to yield 14 C dates inconsistent with true 14 C ages. In this study, we examine the use of 14 C ages from (1) small, previously unstudied, terrestrial snails to date hosting spring deposits and from (2) cooccuring aquatic snails to constrain groundwater travel times during the last glacial period. Our study area in the southern Great Basin encompasses Yucca Mountain, site of the proposed high-level nuclear waste repository, where information on the age and extent of past high water tables and on groundwater flow times is crucial to several licensing issues. Our results show that shells of small terrestrial snails belonging to Vallonia sp. yield 14 C dates consistent with 14 C ages of associated carbonized wood. These results imply that these taxa can provide reliable 14 C age control on the broadly distributed deposits in which they have been described. In contrast, cooccurring aquatic snails from fossil spring deposits yield 14 C ages generally greater than the control age. This is because the aquatic shells often formed in spring waters that had an initial 14 C deficiency. However, the magnitude of the deficiency is much less than that observed in nearby modern springs, arguing for much higher average 14 C contents in late Pleistocene groundwaters in these basins. If representative, this implies shorter groundwater travel times through aquifers in southern Nevada during late-glacial time.
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