Reply to 'Ar-40/Ar-39 dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion' by A.K. Baksi

Knight, K. B. and Renne, P. R. and Baker, J. and Waight, T. and White, N. J. (2005) Reply to 'Ar-40/Ar-39 dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion' by A.K. Baksi. Earth and Planetary Science Letters, 239 (3-4). pp. 374-382. DOI 10.1016/j.epsl.2005.08.013

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Abstract

We appreciate this opportunity for further discussion of flow and field relations within the Rajahmundry Traps, and their timing relative to Deccan Trap volcanism. Knight et al., 2003a relied on simplified stratigraphic designation and nomenclature for Rajahmundry Trap flows, labeling dUpperT or dLowerT flows relative to the presence of a primary sedimentary interlayer [1]. This designation and its implication of related lava packages may not be strictly valid, as suggested by Baski (this volume), and we present further insight below. Several points of the comment [2] are based on the assumption that a single flow is present for each of the Upper and Lower Rajahmundry Trap units. Both drill hole and field observation, however, suggest otherwise. Multiple flows (as many as 8) of Rajahmundry Trap lavas assigned to both Upper and Lower units are well documented [e.g., 3–5], often occurring sandwiched between multiple sedimentary horizons above and below the thick (and thus designated as the dmainT) sedimentary interlayer. The assumption of a single flow may hold for the surface exposures of the Upper unit used in the study of [1], where flow boundaries (if present) were not possible to discern. Within Lower unit exposures, however, at least two distinct lava flows were observed and sampled in the field (Fig. 1), and have been reported by multiple authors from [6], to the present. Further geochemical evaluation (discussed here) supports the presence of at least three lava groups. The discussion [2] also presents a re-evaluation of our age data resulting in conclusions identical to those of [1].We stand by our published acceptance and rejection criteria for our data, as well as our quoted errors. Additional graphics relating unpublished geochemical and chronological data [2] are interesting, but cannot be properly evaluated in the absence of the inclusion of the raw data.

Item Type: Article
Uncontrolled Keywords: 2005 AREP 2005 P IA49
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 239
Page Range: pp. 374-382
Identification Number: 10.1016/j.epsl.2005.08.013
Depositing User: Sarah Humbert
Date Deposited: 04 Mar 2011 15:45
Last Modified: 23 Jul 2013 09:59
URI: http://eprints.esc.cam.ac.uk/id/eprint/1713

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