TY - JOUR
T1 - Eocene-Oligocene proto-Cascades topography revealed by clumped (Δ47) and oxygen isotope (δ18O) geochemistry (Chumstick Basin, WA, USA)
AU - Methner, Katharina
AU - Fiebig, Jens
AU - Wacker, Ulrike
AU - Umhoefer, Paul
AU - Chamberlain, C. Page
AU - Mulch, Andreas
N1 - Funding Information:
Data supporting Figures 5, 6, and 10 areavailable in the supporting information Tables S2 and S9, and data supporting Figure 8 are available in the supporting information Tables S6-S8. A.M. and K.M. acknowledge support through the LOEWE funding program (Landes-Offensive zur Entwicklung wissenschaftlich-konomischer Exzellenz) of Hesse's Ministry of Higher Education, Research, and the Arts. J.F. acknowledges support through DFG FI-948/4-1. Funding was also provided by the National Science Foundation (USA) grant EAR-1019648 (C.P.C.) and EAR-1119063 (P.U.). We further thank P. Larson and an anonymous reviewer for clarifying many aspects of this paper, S. Hofmann (Goethe University, Frankfurt) and T. Emmel (Senckenberg, Frankfurt) for technical assistance, and W. Torres (Stanford) for field assistance. K.M. further thanks R. Miller, S. Bowring, and J. Tepper for introduction to Cascade geology
Publisher Copyright:
©2016. American Geophysical Union. All Rights Reserved.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - The topography of the present-day Washington Cascades impacts atmospheric circulation and precipitation patterns in the Pacific Northwest, introducing a pronounced orographic rain shadow in the lee of the mountain range. The temporal development of Cascade topography, however, remains largely unconstrained for the early Cenozoic. Based on coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18O) measurements we reconstruct δ18O values of Eocene groundwater (δ18Owater) in the Chumstick basin (central Washington), today located in the Cascade rain shadow. Δ47 (paleo)thermometry indicates a systematic change in basin burial temperatures from 110°C to 70°C depending on burial depth in the basin. These data are in good agreement with low-T thermochronological and vitrinite reflectance data, and further constrain the basin burial and exhumation history. In concert with field observations, microstructural analysis, and δ18O values of the analyzed carbonates, we suggest that the Δ47 temperatures and δ18O values reflect open-system carbonate cement recrystallization in meteoric-derived groundwaters during early burial diagenesis. Assuming open-system behavior, reconstructed mean δ18Owater values of ~ -7‰ (middle Eocene) to -9‰ (late Eocene/early Oligocene) are consistent with a low-elevation origin of the corresponding meteoric waters that permeated the sandstone/conglomerate members of the Eocene sedimentary units. In light of the paleogeographic setting of the Chumstick basin, the reconstructed δ18Owater values agree well with Pacific-derived moisture that did not experience strong rainout. The absence of a rain shadow effect therefore permits only moderate Eocene/Oligocene elevations at least for the southern part of the Washington proto-Cascades.
AB - The topography of the present-day Washington Cascades impacts atmospheric circulation and precipitation patterns in the Pacific Northwest, introducing a pronounced orographic rain shadow in the lee of the mountain range. The temporal development of Cascade topography, however, remains largely unconstrained for the early Cenozoic. Based on coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18O) measurements we reconstruct δ18O values of Eocene groundwater (δ18Owater) in the Chumstick basin (central Washington), today located in the Cascade rain shadow. Δ47 (paleo)thermometry indicates a systematic change in basin burial temperatures from 110°C to 70°C depending on burial depth in the basin. These data are in good agreement with low-T thermochronological and vitrinite reflectance data, and further constrain the basin burial and exhumation history. In concert with field observations, microstructural analysis, and δ18O values of the analyzed carbonates, we suggest that the Δ47 temperatures and δ18O values reflect open-system carbonate cement recrystallization in meteoric-derived groundwaters during early burial diagenesis. Assuming open-system behavior, reconstructed mean δ18Owater values of ~ -7‰ (middle Eocene) to -9‰ (late Eocene/early Oligocene) are consistent with a low-elevation origin of the corresponding meteoric waters that permeated the sandstone/conglomerate members of the Eocene sedimentary units. In light of the paleogeographic setting of the Chumstick basin, the reconstructed δ18Owater values agree well with Pacific-derived moisture that did not experience strong rainout. The absence of a rain shadow effect therefore permits only moderate Eocene/Oligocene elevations at least for the southern part of the Washington proto-Cascades.
KW - Washington Cascades
KW - clumped isotope thermometry
KW - early Cenozoic
KW - paleoelevation
KW - stable isotopes
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U2 - 10.1002/2015TC003984
DO - 10.1002/2015TC003984
M3 - Article
AN - SCOPUS:84963938607
SN - 0278-7407
VL - 35
SP - 546
EP - 564
JO - Tectonics
JF - Tectonics
IS - 3
ER -