- Email: [email protected]
Comments on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia ice sheet” by Thorndycraft et al. [Quat. Sci. Rev. 203 (2019), 102–127]
Quaternary Science Reviews 213 (2019) 167e170
Contents lists available at ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Comment
Comments on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia ice sheet” by Thorndycraft et al. [Quat. Sci. Rev. 203 (2019), 102e127] Jacques Bourgois a, *, Maria Eugenia Cisternas b, Jose Frutos c Sorbonne Universit e, CNRS-INSU, Institut des Sciences de la Terre Paris, ISTeP UMR 7193, 4 place Jussieu, 75252, Paris Cedex 05, France Instituto de Geologia Economica Aplicada, Universidad de Concepcion, Casilla, Concepcion, Chile c San Juan de Luz, 4060, Providencia, Santiago, Chile a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 January 2019 Accepted 29 March 2019 Available online 15 April 2019
Underlying the scientific method developed by Thorndycraft et al. (2019, T19 hereafter) for the morphological analysis is the idea that producing a large enough landform dataset treated statistically would facilitate quantification of regional isostatic rebound together with the reconstruction of the Lago Chalenko paleolake history. Also, they associate the landform dataset to a Bayesian modeling of ages. This Comment adresses 5 key points questionning the proposed assumptions. © 2019 Published by Elsevier Ltd.
Keywords: South America North Patagonia Icefield Last glacial maximum General Carrera lake (Chile) Buenos Aires lake (Argentina) Atlantic-Pacific drainage reversal Facinal cold events 8.2 ka cold event
1. Introduction Thorndycraft et al. (2019, T19 hereafter) present a comprehensive review on paleolake evolution models (Rio Baker catchment, Andean Patagonia, 46 -48 S) for the General Carrera-Buenos Aires (GCBA) and the adjacent Cochrane-Pueyrredon (CP) glacial lakes. Since the Last Glacial Maximum (LGM) at ~19-29 ka (Fleming et al., 1998; Singer et al., 2004; Kaplan et al., 2004, 2011; Douglass et al., 2006; Hein et al., 2009; Boex et al., 2013) the GCBA and CP lakes have been connected as a Large Unified Lake (Turner et al., 2005; Hein et al., 2010; Bourgois et al., 2016a; Glasser et al., 2016). T19 have renamed this ephemeral Unified Lake the Lago Chalenko. Here after we focus on 5 key points questioning the proposed assumptions. 2. Dated samples missing The Bayesian modeling for age refining used by T19 to reconstruct the age sequence at T19-figure 13 is an important technique in statistics. As any other statistical procedure, the Bayesian method
DOI of original article: https://doi.org/10.1016/j.quascirev.2019.04.005. * Corresponding author. E-mail address: [email protected] (J. Bourgois). https://doi.org/10.1016/j.quascirev.2019.03.036 0277-3791/© 2019 Published by Elsevier Ltd.
requires taking into account all the experiments and must not eliminate any data. Since the main objective is reconstructing the Lago Chalenko evolution it is paradoxical for T19 to use no GCBA age data from dropstones on terraces that are direct records of lake level. The C14, OSL, and cosmogenic missing ages in T19 are: (1) 15.2 ± 0.5 cal ka, C14 age at Rio Fenix Chico (Douglass et al., 2006); (2) 9.7 ± 0.7 ka, OSL age at Rio Tranquilo-Rio Bayo divide (Glasser et al., 2006); (3) 10.9 ± 1.3 ka and 7.9 ± 1.1 ka, 10Be ages from moraines at Facinal (Douglass et al., 2005; Bourgois et al., 2016a,b); (4) 18.5 ± 3.7 (sample 57), 9.9 ± 2.5 (sample 73), 18.8 ± 4.0 (sample 71), 15.2 ± 3.7 (sample 61), 13.9 ± 2.7 (sample 13), 16.5 ± 4.1 ka (sample 31), 10Be ages from dropstones on terraces with elevations from 451 to 528 m (Bourgois et al., 2016a; samples located at Fig. SM1); (5) 15.0 ± 1.8 ka (sample 59), 10Be age from dropstone on terrace with elevation from 443 to 452 m (Bourgois et al., 2016a; sample located at Fig. SM1); (6) 8.6 ± 2.0 (sample 53) and 14.4 ± 3.0 ka (sample 39), 10Be ages from dropstones on terraces with elevation from 305 to 349 m (Bourgois et al., 2016a; samples located at Fig. SM1). The Fig. 1 shows the missing ages on the T19-figure 11 used as a background. 3. Ho tethra age The end of the Phase 1 (Bayesian age sequence, T19-figure 13)
168
J. Bourgois et al. / Quaternary Science Reviews 213 (2019) 167e170
OAPF: oldest age possible for; YAPF: youngest age possible for
Facinal
Inner moraine Youngerr Dryas
CND(71DS) CND(57DS)
Massive flooding event
8.2 8. 8 .2 . ka a co cold de event e
Outer moraine
CND(73DS) C CND(7 (
CND(61DS) ND(61DS D(61D ( S)) S CND(31DS)
Deseado level
CND( CND(13DS) C CN ND((13 13DS 3DS S
CND(59DS)
CND(39DS) Bayo level
SL(b) OSL( O OS S L(b) L( L (b b)) OSL(b) CND(5 CND(53DS) CN C ND ND(5
C14(a)
YAPF cold event 2
OAPF cold event 2
YAPF cold event 1
OAPF cold event 1
YAPF Deseado and Bayo terraces
OAPF Deseado and Bayo terraces
O SL(c) OSL(c) OS SL( L(c) c)
Fig. 1. Age versus sample elevation for the “dated samples missing” (thick black line) listed at section 1 shown on the T19-figure 11 used as background. (a): C14 age constrains the oldest age possible for the Menucos moraine at 15.7 ka (Douglass et al., 2006). (b): OSL age documents ice at the Rio Bayo/Rio Tranquilo divide area at 9.7 ± 0.7 ka (Glasser et al., 2006; Fig. SM2 for location). (c): OSL age documents the age of Bayo terrace (333 m) at Facinal at 11 ± 0.7 ka (Glasser et al., 2016). This age together with the ages of the Outer (10.9 ± 1.3 ka) and Inner (7.9 ± 1.1 ka) moraines at Facinal (Douglass et al., 2005; Bourgois et al., 2016a and b) constrain ice readvance at 9.1 to 11.7 ka and 6.8 to 9 ka. CND: 73DS sample records age and elevation of the massive flooding event (Bourgois et al., 2016a). CNDeCosmogenic nuclide dating. Number in bracket following CND refers to samples located at Fig. SM1. DSeDropstone.
event for the paleolake evolution is the end date (16.94 ± 0.12 ka BP) documented from the “High-resolution varve chronology” (Bendle et al., 2017). This ~1000 years varve chronology exhibits only one “visible tephra layer”, the Ho tephra. No absolute age for this tephra layer exists. Bendle et al. (2017) claim that the Ho tephra has originated from the Ho oldest eruption of the Hudson volcano (between 17,300 and 17,440 cal years BP). The detailed 50- and 10- cm isopach mapping for the Ho eruption (Weller et al., 2014, 2015) shows that no tephra has been ejected to the area studied by Bendle et al. (2017). The 10-cm isopach for the Ho eruption from the Hudson volcano is located 140 km to the north (tephra airfall toward the NE). No confident age for the tephra anchoring the “High-resolution varve chronology” exists. 4. Deseado and Bayo levels T19 define the main lake levels from a paleoshoreline histogram analysis (T19-figure 10a). They document two major shoreline frequency peaks along the GCBA Lake, the Deseado and Bayo levels at 405 and 299 m, respectively. Using altimeter, the Deseado and Bayo levels have been previously identified (Turner et al., 2005; Bell, 2008). Subsequently, GPS measurements (Bourgois et al., 2016a) have documented the Deseado and Bayo terrace
elevations ranging from 432 to 468 m and 302e347 m, respectively. These level/terrace elevations obtained through different methods portraying the same paleolake levels reveal discrepancies. At T19-figure 10b the “shoreline elevation” plotted against “distance along direction of maximum uplift” (across trend of the Andes) shows a high concentration of datum points between ~10 and ~45 km, a long segment with sparsely or no data between ~45 and ~110 km, and a concentration between ~110 and ~140 km. This distribution reflects the first order morphotectonic signatures controlled by the Andean tectonic front located at ~45 km along the GCBA Lake profile. (1) To the east is the low foreland area of the Andes exhibiting the wide-open Buenos Aires Lake (Argentina) with low glacial rebound signature (Ivins and James, 1999, 2004). (2) As the GCBA Lake crosses the Andes front, the glacial valley exhibits steep walls becoming narrow and deep. Between ~45 and ~110 km the General Carrera Lake (Chile) exhibits little records of paleolake levels. (3) From ~110 to ~140 km, the low region of the western GCBA basin (Chile) is suitable for preserving terraces and strandlines in a wider open area with high glacial rebound signature (Dietrich et al., 2010; Bourgois et al., 2016a). Mixing the ~10e45 km and the ~110e140 km datum points from areas with contrasting glacial rebound induces a bias producing not only a shift of the histogram peaks towards lower elevations, but also questions the reconstruction of the "isostatic shorelines" for
J. Bourgois et al. / Quaternary Science Reviews 213 (2019) 167e170
the Deseado and Bayo levels (T19-figures 10 and 12). Also the C14 and OSL ages (a and c Fig. 1, and section 1) are constraining the oldest and youngest ages possible for the Deseado and Bayo terraces at 15.7 and 10.3 ka, instead of 15.5 and 7.0 ka, respectively.
169
Acknowledgements We thank the Institut National des Sciences de l’ Univers (INSU) for financial program “ Syster” and the Sorbonne-Universite supports.
5. Rio Bayo spillway
Appendix A. Supplementary data
As argued by T19, the Deseado spillway (~400 m in elevation) towards the Atlantic has been working from 16.0 to 15.0 ka during stages 3 and 4 (T19-figure 15c, d). At 15.0 ka, the Deseado spillway becomes inactive the GCBA Lake flowing towards the Pacific through the Rio Bayo spillway (Fig. SM2) during stages 5 and 6 (T19-figures 15e, f) from 15.0 to 12.6 ka. Glasser et al. (2006) have documented that icefield withdrew the divide area (the T19 Bayo spillway) between the Pacific and the GCBA Lake after 12.7 ± 0.9 ka (mean age of samples LTE1 and LTE2, T19-Table SM1) remaining at site until 9.7 ± 0.7 ka (OSL age (b) Fig. 1, see section 1). Conflicting to what is proposed by T19, the available data document that the Rio Bayo glacial valley has been ice-dammed during the Stages 5 and 6 as previously proposed by Turner et al. (2005), and Bourgois et al. (2016a,b). Available data allow inferring that the Bayo valley was icedammed not only at the beginning of the Bayo level but also during stages 5 and 6 (T19-figure 15e and f) preventing out-flowing towards the Pacific.
Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2019.03.036.
6. Facinal cold events At T19-Table 2, T19 claim: « there is no evidence for … a glacier readvance at 10.9 ± 1.3 ka and 7.9 ± 1.1 ka (Bourgois et al., 2016a,b) …because morpho-stratigraphic data from Fenix Chico (Bendle et al., 2017) indicates the maximum lake level of Lago General Carrera/Buenos Aires was at the Deseado level (~400e440 m asl, T19-Fig. 10) ». Two main points weaken the T19 statement: First, at section 2 we have contemplated that no confident assumption can be constructed from the varve chronology (Bendle et al., 2017). Second, the glacier readvances have been robustly documented. At Facinal (Fig. SM3) Douglass et al. (2005) have described two parallel moraine belts overlying a Bayo level terrace. Recalculated ages for these moraines are 10.9 ± 1.3 and 7.9 ± 1.1 ka (Bourgois et al., 2016b) for the Outer and Inner moraine belts, respectively. Also, the underlying Bayo level terrace (elevation ranging from 293 to 314 m) was dated at 11.0 ± 0.7 ka by OSL (Glasser et al., 2016). These age data substantiate the youngest possible age for the Bayo terrace accumulation at 9.6 ka, which is 2.6 ka older than the 7 ka proposed by T19.
7. Conclusions The T19 assumptions for the Lago Chalenko evolution and Atlantic-Pacific drainage reversal exhibit the following weaknesses. First, disregarding 13 ages over 37 available along the GCBA Lake allow T19 rebutting the ice damming of the Rio Bayo until 9.7 ± 0.7 ka together with the two major ice readvances at 10.9 ± 1.3 and 7.9 ± 1.1 ka. Second, in mixing datum points from disconnected areas having different geomorphic signatures with contrasted glacial rebound induces an analytical bias. Third, the “High-resolution varve chronology” from Bendle et al. (2017) induces major age uncertainties into the Phase 1 for the T19 proposed Bayesian age sequence model. This together with the disregarded age data and the geomorphic analytical bias propagates inconsistencies throughout the T19 paleolake evolution model.
References Bell, C.M., 2008. Punctuated drainage of an ice-dammed Quaternary lake in southern South America. Geogr. Ann. 90, 1e17. Bendle, J.M., Palmer, A.P., Thorndycraft, V.R., Matthews, I.P., 2017. High-resolution chronology for deglaciation of the Patagonian ice sheet at Lago Buenos Aires (46.5 S) revealed through varve chronology and Bayesian age modelling. Quat. Sc. Rev. 177, 314e338. Boex, J., Fogwill, C., Harrison, S., Glasser, N.F., Hein, A., Schnabel, C., Xu, S., 2013. Rapid thinning of the late Pleistocene Patagonian ice sheet followed migration of the southern Westerlies. Nat. Sci. Rep. 3, 2118. https://doi.org/10.1038/ srep02118. Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016a. Geomorphic records along the General Carrera (Chile)-Buenos Aires (Argentina) glacial lake (46 -48 S), climate inferences, and glacial rebound for the past 7-9 ka. J. Geol. 124, 27e53. Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016b. Geomorphic records along the general Carrera (Chile)eBuenos Aires (Argentina) glacial lake (467e487S), climate inferences, and glacial rebound for the past 7e9 ka: a reply. J. Geol. 124, 637e642. Dietrich, R., Ivins, E.R., Casassa, G., Lange, H., Wendt, J., Fritsche, M., 2010. Rapid crustal uplift in Patagonia due to enhanced ice loss. Earth Planet. Sci. Lett. 289, 22e29. Douglass, D.C., Singer, B.S., Kaplan, M.R., Ackert, R.P., Mickelson, D.M., Caffee, M.W., 2005. Evidence of early Holocene glacial advances in southern South America from cosmogenic surface-exposure dating. Geology 33, 237e240. Douglass, D.C., Singer, B.S., Kaplan, M.R., Mickelson, D.M., Caffee, M.W., 2006. Cosmogenic nuclide surface exposure dating of boulders on last-glacial and late-glacial moraines, lago Buenos Aires, Argentina: interpretative strategies and paleoclimate implications. Quat. Geochronol. 1, 43e58. Fleming, K., Johnston, P., Zwartz, D., Yokoyama, Y., Lambeck, K., Chappell, J., 1998. Refining the eustatic sea-level curve since the last glacial maximum using farand intermediate-field sites. Earth Planet. Sci. Lett. 163, 327e342. Glasser, N.F., Harrison, S., Ivy-Ochs, S., Duller, G.A.T., Kubik, P.W., 2006. Evidence from the Rio Bayo valley on the extent of the north Patagonian icefield during the late Pleistocene-holocene transition. Quat. Res. 65, 70e77. Glasser, N.F., Jansson, K.N., Duller, G.A., Singarayer, J., Holloway, M., Harrison, S., 2016. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Sci. Rep. 6, 21064. Hein, A.S., Hulton, N.R.J., Dunai, T.J., Schnabel, C., Kaplan, M.R., Naylor, M., Xu, S., 2009. Middle Pleistocene glaciation in Patagonia dated by cosmogenic nuclide measurements on outwash gravels. Earth Planet. Sci. Lett. 286, 184e197. https:// doi.org/10.1016/j.epsl.2009 .06.026. Hein, A.S., Hulton, N.R.J., Dunai, T.J., Sugden, D.E., Kaplan, M.R., Xu, S., 2010. The chronology of the last glacial maximum and deglacial events in central Argentine Patagonia. Quat. Sci. Rev. 29, 1212e1227. Ivins, E.R., James, T.S., 1999. Simple models for late Holocene and present-day Patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response. Geophys. J. Int. 138, 601e624. Ivins, E.R., James, T.S., 2004. Bedrock response to Llanquihue Holocene and presentday glaciation in southernmost South America. Geophys. Res. Lett. 31, L24613. https://doi.org/10.1029/2004GL021500. Kaplan, M.R., Ackert, R.P., Singer, B.S., Douglass, D.C., Kurz, M.D., 2004. Cosmogenic nuclide chronology of millennial-scale glacial advances during O-isotope stage 2 in Patagonia. Geol. Soc. Am. Bull. 116, 308e321. https://doi.org/10.1130/ B25178.1. Kaplan, M.R., Strelin, J.A., Schaefer, J.M., Denton, G.H., Finkel, R.C., Schwartz, R., Putnam, A.E., Vandergoes, M.J., Goehring, B.M., Travis, S.G., 2011. In situ cosmogenic 10Be production rate at Lago Argentino, Patagonia: implications for late-glacial climate chronology. Earth Planet. Sci. Lett. 309, 21e32. Singer, B.S., Ackert, R.P., Guillou, H., 2004. 40Ar/39Ar and K-Ar chronology of Pleistocene glaciations in Patagonia. Geol. Soc. Am. Bull. 116, 434e450. https:// doi.org/10.1130/B25177.1. Thorndycraft, V.R., Bendle, J.M., Benito, G., Davies, B.J., Sancho, C., Palmer, A.P., Fabel, D., Medialdea, A., Martin, J.R.V., 2019. Glacial lake evolution and AtlanticPacific drainage reversals during deglaciation of the Patagonia Ice Sheet. Quat. Sc. Rev. 203, 102e127. Turner, K.J., Fogwill, C.J., Mcculloch, R.D., Sugden, D.E., 2005. Deglaciation of the eastern flank of the north Patagonian icefield and associated continental-scale lake diversions. Geogr. Ann. Ser. A Phys. Geogr. 87 (2), 363e374. https://doi.org/
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10.1111/j.0435-3676.2005.00263.x. Weller, D., Miranda, C.G., Moreno, P.I., Villa-Martínez, R., Stern, C.R., 2014. The large late-glacial Ho eruption of the Hudson volcano, southern Chile. Bull. Volcanol. 76, 831e849.
Weller, D.J., Miranda, C.G., Moreno, P.I., Villa-Martínez, R., Stern, C.R., 2015. Tephrochronology of the southernmost Andean southern volcanic zone, Chile. Bull. Volcanol. 77, 107e131.
Contents lists available at ScienceDirect
Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev
Comment
Comments on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia ice sheet” by Thorndycraft et al. [Quat. Sci. Rev. 203 (2019), 102e127] Jacques Bourgois a, *, Maria Eugenia Cisternas b, Jose Frutos c Sorbonne Universit e, CNRS-INSU, Institut des Sciences de la Terre Paris, ISTeP UMR 7193, 4 place Jussieu, 75252, Paris Cedex 05, France Instituto de Geologia Economica Aplicada, Universidad de Concepcion, Casilla, Concepcion, Chile c San Juan de Luz, 4060, Providencia, Santiago, Chile a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 January 2019 Accepted 29 March 2019 Available online 15 April 2019
Underlying the scientific method developed by Thorndycraft et al. (2019, T19 hereafter) for the morphological analysis is the idea that producing a large enough landform dataset treated statistically would facilitate quantification of regional isostatic rebound together with the reconstruction of the Lago Chalenko paleolake history. Also, they associate the landform dataset to a Bayesian modeling of ages. This Comment adresses 5 key points questionning the proposed assumptions. © 2019 Published by Elsevier Ltd.
Keywords: South America North Patagonia Icefield Last glacial maximum General Carrera lake (Chile) Buenos Aires lake (Argentina) Atlantic-Pacific drainage reversal Facinal cold events 8.2 ka cold event
1. Introduction Thorndycraft et al. (2019, T19 hereafter) present a comprehensive review on paleolake evolution models (Rio Baker catchment, Andean Patagonia, 46 -48 S) for the General Carrera-Buenos Aires (GCBA) and the adjacent Cochrane-Pueyrredon (CP) glacial lakes. Since the Last Glacial Maximum (LGM) at ~19-29 ka (Fleming et al., 1998; Singer et al., 2004; Kaplan et al., 2004, 2011; Douglass et al., 2006; Hein et al., 2009; Boex et al., 2013) the GCBA and CP lakes have been connected as a Large Unified Lake (Turner et al., 2005; Hein et al., 2010; Bourgois et al., 2016a; Glasser et al., 2016). T19 have renamed this ephemeral Unified Lake the Lago Chalenko. Here after we focus on 5 key points questioning the proposed assumptions. 2. Dated samples missing The Bayesian modeling for age refining used by T19 to reconstruct the age sequence at T19-figure 13 is an important technique in statistics. As any other statistical procedure, the Bayesian method
DOI of original article: https://doi.org/10.1016/j.quascirev.2019.04.005. * Corresponding author. E-mail address: [email protected] (J. Bourgois). https://doi.org/10.1016/j.quascirev.2019.03.036 0277-3791/© 2019 Published by Elsevier Ltd.
requires taking into account all the experiments and must not eliminate any data. Since the main objective is reconstructing the Lago Chalenko evolution it is paradoxical for T19 to use no GCBA age data from dropstones on terraces that are direct records of lake level. The C14, OSL, and cosmogenic missing ages in T19 are: (1) 15.2 ± 0.5 cal ka, C14 age at Rio Fenix Chico (Douglass et al., 2006); (2) 9.7 ± 0.7 ka, OSL age at Rio Tranquilo-Rio Bayo divide (Glasser et al., 2006); (3) 10.9 ± 1.3 ka and 7.9 ± 1.1 ka, 10Be ages from moraines at Facinal (Douglass et al., 2005; Bourgois et al., 2016a,b); (4) 18.5 ± 3.7 (sample 57), 9.9 ± 2.5 (sample 73), 18.8 ± 4.0 (sample 71), 15.2 ± 3.7 (sample 61), 13.9 ± 2.7 (sample 13), 16.5 ± 4.1 ka (sample 31), 10Be ages from dropstones on terraces with elevations from 451 to 528 m (Bourgois et al., 2016a; samples located at Fig. SM1); (5) 15.0 ± 1.8 ka (sample 59), 10Be age from dropstone on terrace with elevation from 443 to 452 m (Bourgois et al., 2016a; sample located at Fig. SM1); (6) 8.6 ± 2.0 (sample 53) and 14.4 ± 3.0 ka (sample 39), 10Be ages from dropstones on terraces with elevation from 305 to 349 m (Bourgois et al., 2016a; samples located at Fig. SM1). The Fig. 1 shows the missing ages on the T19-figure 11 used as a background. 3. Ho tethra age The end of the Phase 1 (Bayesian age sequence, T19-figure 13)
168
J. Bourgois et al. / Quaternary Science Reviews 213 (2019) 167e170
OAPF: oldest age possible for; YAPF: youngest age possible for
Facinal
Inner moraine Youngerr Dryas
CND(71DS) CND(57DS)
Massive flooding event
8.2 8. 8 .2 . ka a co cold de event e
Outer moraine
CND(73DS) C CND(7 (
CND(61DS) ND(61DS D(61D ( S)) S CND(31DS)
Deseado level
CND( CND(13DS) C CN ND((13 13DS 3DS S
CND(59DS)
CND(39DS) Bayo level
SL(b) OSL( O OS S L(b) L( L (b b)) OSL(b) CND(5 CND(53DS) CN C ND ND(5
C14(a)
YAPF cold event 2
OAPF cold event 2
YAPF cold event 1
OAPF cold event 1
YAPF Deseado and Bayo terraces
OAPF Deseado and Bayo terraces
O SL(c) OSL(c) OS SL( L(c) c)
Fig. 1. Age versus sample elevation for the “dated samples missing” (thick black line) listed at section 1 shown on the T19-figure 11 used as background. (a): C14 age constrains the oldest age possible for the Menucos moraine at 15.7 ka (Douglass et al., 2006). (b): OSL age documents ice at the Rio Bayo/Rio Tranquilo divide area at 9.7 ± 0.7 ka (Glasser et al., 2006; Fig. SM2 for location). (c): OSL age documents the age of Bayo terrace (333 m) at Facinal at 11 ± 0.7 ka (Glasser et al., 2016). This age together with the ages of the Outer (10.9 ± 1.3 ka) and Inner (7.9 ± 1.1 ka) moraines at Facinal (Douglass et al., 2005; Bourgois et al., 2016a and b) constrain ice readvance at 9.1 to 11.7 ka and 6.8 to 9 ka. CND: 73DS sample records age and elevation of the massive flooding event (Bourgois et al., 2016a). CNDeCosmogenic nuclide dating. Number in bracket following CND refers to samples located at Fig. SM1. DSeDropstone.
event for the paleolake evolution is the end date (16.94 ± 0.12 ka BP) documented from the “High-resolution varve chronology” (Bendle et al., 2017). This ~1000 years varve chronology exhibits only one “visible tephra layer”, the Ho tephra. No absolute age for this tephra layer exists. Bendle et al. (2017) claim that the Ho tephra has originated from the Ho oldest eruption of the Hudson volcano (between 17,300 and 17,440 cal years BP). The detailed 50- and 10- cm isopach mapping for the Ho eruption (Weller et al., 2014, 2015) shows that no tephra has been ejected to the area studied by Bendle et al. (2017). The 10-cm isopach for the Ho eruption from the Hudson volcano is located 140 km to the north (tephra airfall toward the NE). No confident age for the tephra anchoring the “High-resolution varve chronology” exists. 4. Deseado and Bayo levels T19 define the main lake levels from a paleoshoreline histogram analysis (T19-figure 10a). They document two major shoreline frequency peaks along the GCBA Lake, the Deseado and Bayo levels at 405 and 299 m, respectively. Using altimeter, the Deseado and Bayo levels have been previously identified (Turner et al., 2005; Bell, 2008). Subsequently, GPS measurements (Bourgois et al., 2016a) have documented the Deseado and Bayo terrace
elevations ranging from 432 to 468 m and 302e347 m, respectively. These level/terrace elevations obtained through different methods portraying the same paleolake levels reveal discrepancies. At T19-figure 10b the “shoreline elevation” plotted against “distance along direction of maximum uplift” (across trend of the Andes) shows a high concentration of datum points between ~10 and ~45 km, a long segment with sparsely or no data between ~45 and ~110 km, and a concentration between ~110 and ~140 km. This distribution reflects the first order morphotectonic signatures controlled by the Andean tectonic front located at ~45 km along the GCBA Lake profile. (1) To the east is the low foreland area of the Andes exhibiting the wide-open Buenos Aires Lake (Argentina) with low glacial rebound signature (Ivins and James, 1999, 2004). (2) As the GCBA Lake crosses the Andes front, the glacial valley exhibits steep walls becoming narrow and deep. Between ~45 and ~110 km the General Carrera Lake (Chile) exhibits little records of paleolake levels. (3) From ~110 to ~140 km, the low region of the western GCBA basin (Chile) is suitable for preserving terraces and strandlines in a wider open area with high glacial rebound signature (Dietrich et al., 2010; Bourgois et al., 2016a). Mixing the ~10e45 km and the ~110e140 km datum points from areas with contrasting glacial rebound induces a bias producing not only a shift of the histogram peaks towards lower elevations, but also questions the reconstruction of the "isostatic shorelines" for
J. Bourgois et al. / Quaternary Science Reviews 213 (2019) 167e170
the Deseado and Bayo levels (T19-figures 10 and 12). Also the C14 and OSL ages (a and c Fig. 1, and section 1) are constraining the oldest and youngest ages possible for the Deseado and Bayo terraces at 15.7 and 10.3 ka, instead of 15.5 and 7.0 ka, respectively.
169
Acknowledgements We thank the Institut National des Sciences de l’ Univers (INSU) for financial program “ Syster” and the Sorbonne-Universite supports.
5. Rio Bayo spillway
Appendix A. Supplementary data
As argued by T19, the Deseado spillway (~400 m in elevation) towards the Atlantic has been working from 16.0 to 15.0 ka during stages 3 and 4 (T19-figure 15c, d). At 15.0 ka, the Deseado spillway becomes inactive the GCBA Lake flowing towards the Pacific through the Rio Bayo spillway (Fig. SM2) during stages 5 and 6 (T19-figures 15e, f) from 15.0 to 12.6 ka. Glasser et al. (2006) have documented that icefield withdrew the divide area (the T19 Bayo spillway) between the Pacific and the GCBA Lake after 12.7 ± 0.9 ka (mean age of samples LTE1 and LTE2, T19-Table SM1) remaining at site until 9.7 ± 0.7 ka (OSL age (b) Fig. 1, see section 1). Conflicting to what is proposed by T19, the available data document that the Rio Bayo glacial valley has been ice-dammed during the Stages 5 and 6 as previously proposed by Turner et al. (2005), and Bourgois et al. (2016a,b). Available data allow inferring that the Bayo valley was icedammed not only at the beginning of the Bayo level but also during stages 5 and 6 (T19-figure 15e and f) preventing out-flowing towards the Pacific.
Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2019.03.036.
6. Facinal cold events At T19-Table 2, T19 claim: « there is no evidence for … a glacier readvance at 10.9 ± 1.3 ka and 7.9 ± 1.1 ka (Bourgois et al., 2016a,b) …because morpho-stratigraphic data from Fenix Chico (Bendle et al., 2017) indicates the maximum lake level of Lago General Carrera/Buenos Aires was at the Deseado level (~400e440 m asl, T19-Fig. 10) ». Two main points weaken the T19 statement: First, at section 2 we have contemplated that no confident assumption can be constructed from the varve chronology (Bendle et al., 2017). Second, the glacier readvances have been robustly documented. At Facinal (Fig. SM3) Douglass et al. (2005) have described two parallel moraine belts overlying a Bayo level terrace. Recalculated ages for these moraines are 10.9 ± 1.3 and 7.9 ± 1.1 ka (Bourgois et al., 2016b) for the Outer and Inner moraine belts, respectively. Also, the underlying Bayo level terrace (elevation ranging from 293 to 314 m) was dated at 11.0 ± 0.7 ka by OSL (Glasser et al., 2016). These age data substantiate the youngest possible age for the Bayo terrace accumulation at 9.6 ka, which is 2.6 ka older than the 7 ka proposed by T19.
7. Conclusions The T19 assumptions for the Lago Chalenko evolution and Atlantic-Pacific drainage reversal exhibit the following weaknesses. First, disregarding 13 ages over 37 available along the GCBA Lake allow T19 rebutting the ice damming of the Rio Bayo until 9.7 ± 0.7 ka together with the two major ice readvances at 10.9 ± 1.3 and 7.9 ± 1.1 ka. Second, in mixing datum points from disconnected areas having different geomorphic signatures with contrasted glacial rebound induces an analytical bias. Third, the “High-resolution varve chronology” from Bendle et al. (2017) induces major age uncertainties into the Phase 1 for the T19 proposed Bayesian age sequence model. This together with the disregarded age data and the geomorphic analytical bias propagates inconsistencies throughout the T19 paleolake evolution model.
References Bell, C.M., 2008. Punctuated drainage of an ice-dammed Quaternary lake in southern South America. Geogr. Ann. 90, 1e17. Bendle, J.M., Palmer, A.P., Thorndycraft, V.R., Matthews, I.P., 2017. High-resolution chronology for deglaciation of the Patagonian ice sheet at Lago Buenos Aires (46.5 S) revealed through varve chronology and Bayesian age modelling. Quat. Sc. Rev. 177, 314e338. Boex, J., Fogwill, C., Harrison, S., Glasser, N.F., Hein, A., Schnabel, C., Xu, S., 2013. Rapid thinning of the late Pleistocene Patagonian ice sheet followed migration of the southern Westerlies. Nat. Sci. Rep. 3, 2118. https://doi.org/10.1038/ srep02118. Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016a. Geomorphic records along the General Carrera (Chile)-Buenos Aires (Argentina) glacial lake (46 -48 S), climate inferences, and glacial rebound for the past 7-9 ka. J. Geol. 124, 27e53. Bourgois, J., Cisternas, M.E., Braucher, R., Bourles, D., Frutos, J., 2016b. Geomorphic records along the general Carrera (Chile)eBuenos Aires (Argentina) glacial lake (467e487S), climate inferences, and glacial rebound for the past 7e9 ka: a reply. J. Geol. 124, 637e642. Dietrich, R., Ivins, E.R., Casassa, G., Lange, H., Wendt, J., Fritsche, M., 2010. Rapid crustal uplift in Patagonia due to enhanced ice loss. Earth Planet. Sci. Lett. 289, 22e29. Douglass, D.C., Singer, B.S., Kaplan, M.R., Ackert, R.P., Mickelson, D.M., Caffee, M.W., 2005. Evidence of early Holocene glacial advances in southern South America from cosmogenic surface-exposure dating. Geology 33, 237e240. Douglass, D.C., Singer, B.S., Kaplan, M.R., Mickelson, D.M., Caffee, M.W., 2006. Cosmogenic nuclide surface exposure dating of boulders on last-glacial and late-glacial moraines, lago Buenos Aires, Argentina: interpretative strategies and paleoclimate implications. Quat. Geochronol. 1, 43e58. Fleming, K., Johnston, P., Zwartz, D., Yokoyama, Y., Lambeck, K., Chappell, J., 1998. Refining the eustatic sea-level curve since the last glacial maximum using farand intermediate-field sites. Earth Planet. Sci. Lett. 163, 327e342. Glasser, N.F., Harrison, S., Ivy-Ochs, S., Duller, G.A.T., Kubik, P.W., 2006. Evidence from the Rio Bayo valley on the extent of the north Patagonian icefield during the late Pleistocene-holocene transition. Quat. Res. 65, 70e77. Glasser, N.F., Jansson, K.N., Duller, G.A., Singarayer, J., Holloway, M., Harrison, S., 2016. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Sci. Rep. 6, 21064. Hein, A.S., Hulton, N.R.J., Dunai, T.J., Schnabel, C., Kaplan, M.R., Naylor, M., Xu, S., 2009. Middle Pleistocene glaciation in Patagonia dated by cosmogenic nuclide measurements on outwash gravels. Earth Planet. Sci. Lett. 286, 184e197. https:// doi.org/10.1016/j.epsl.2009 .06.026. Hein, A.S., Hulton, N.R.J., Dunai, T.J., Sugden, D.E., Kaplan, M.R., Xu, S., 2010. The chronology of the last glacial maximum and deglacial events in central Argentine Patagonia. Quat. Sci. Rev. 29, 1212e1227. Ivins, E.R., James, T.S., 1999. Simple models for late Holocene and present-day Patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response. Geophys. J. Int. 138, 601e624. Ivins, E.R., James, T.S., 2004. Bedrock response to Llanquihue Holocene and presentday glaciation in southernmost South America. Geophys. Res. Lett. 31, L24613. https://doi.org/10.1029/2004GL021500. Kaplan, M.R., Ackert, R.P., Singer, B.S., Douglass, D.C., Kurz, M.D., 2004. Cosmogenic nuclide chronology of millennial-scale glacial advances during O-isotope stage 2 in Patagonia. Geol. Soc. Am. Bull. 116, 308e321. https://doi.org/10.1130/ B25178.1. Kaplan, M.R., Strelin, J.A., Schaefer, J.M., Denton, G.H., Finkel, R.C., Schwartz, R., Putnam, A.E., Vandergoes, M.J., Goehring, B.M., Travis, S.G., 2011. In situ cosmogenic 10Be production rate at Lago Argentino, Patagonia: implications for late-glacial climate chronology. Earth Planet. Sci. Lett. 309, 21e32. Singer, B.S., Ackert, R.P., Guillou, H., 2004. 40Ar/39Ar and K-Ar chronology of Pleistocene glaciations in Patagonia. Geol. Soc. Am. Bull. 116, 434e450. https:// doi.org/10.1130/B25177.1. Thorndycraft, V.R., Bendle, J.M., Benito, G., Davies, B.J., Sancho, C., Palmer, A.P., Fabel, D., Medialdea, A., Martin, J.R.V., 2019. Glacial lake evolution and AtlanticPacific drainage reversals during deglaciation of the Patagonia Ice Sheet. Quat. Sc. Rev. 203, 102e127. Turner, K.J., Fogwill, C.J., Mcculloch, R.D., Sugden, D.E., 2005. Deglaciation of the eastern flank of the north Patagonian icefield and associated continental-scale lake diversions. Geogr. Ann. Ser. A Phys. Geogr. 87 (2), 363e374. https://doi.org/
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10.1111/j.0435-3676.2005.00263.x. Weller, D., Miranda, C.G., Moreno, P.I., Villa-Martínez, R., Stern, C.R., 2014. The large late-glacial Ho eruption of the Hudson volcano, southern Chile. Bull. Volcanol. 76, 831e849.
Weller, D.J., Miranda, C.G., Moreno, P.I., Villa-Martínez, R., Stern, C.R., 2015. Tephrochronology of the southernmost Andean southern volcanic zone, Chile. Bull. Volcanol. 77, 107e131.