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Map of early Eocene fluvial networks (white), gravel deposits (yellow), and mean kaolinite δ 18 O values (circles, ‰) from the ancestral Yuba and American Rivers used in this study (Table 1). Transect A-A′ denotes the profile used in Figure 2. Shaded region is greenstone, interpreted as Paleogene ridge in Figure 3C. SLD-Saint Louis, FC-French Corral, NC-North Columbia, UB-You Bet, GR-Gold Run, IH-Iowa Hills, YJYankee Jim's Mine.
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Despite broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California’s Sierra Nevada remains actively debated. Prior stable isotope–based studies of the Sierra Nevada have relied primarily on hydrogen isotopes in kaolinite, hydrated volcanic glass, and leaf n-alkanes. Here, we reconstruct the...
Citations
... Surface uplift in the Sierra Nevada, Basin and Range, or Cascades in the early Miocene would intercept storms coming from the Pacific before they reach the SJVF (Molnar, 2010), leading to precipitation that would have lower 18 O-16 O ratios relative to older precipitation and potential rain-shadows (Takeuchi et al., 2010). However, paleoaltimetric studies have identified high surface elevations in the Basin and Range extending from the Eocene into the late Oligocene (Cassel et al., 2014) and in the Eocene Sierra Nevada as well (Mix et al., 2016), although the effects of evaporation can complicate such interpretations (Smith et al., 2017). In addition, the downstream isotopic consequences of higher upstream elevations are complex in the western US because of significant atmospheric deflection associated with high topography (Wheeler et al., 2016) leading to the possibility the surface uplift of the Sierra Nevada might have, counter-intuitively, led to a subdued upstream isotopic "altitude" effect on precipitation in the SJVF. ...
Plain Language Summary
Past surface elevations are commonly reconstructed from the stable isotope ratios of oxygen and hydrogen in paleo‐precipitation. These ratios change systematically as air lifts up and over mountains and other topographic barriers. Direct samples of ancient precipitation do not exist so we rely on proxies instead. The most common proxies used are individual minerals, such as calcium carbonate, or fossils, such as leaves. We present a new approach, where we instead use the isotopic “footprint” of large hydrothermal cells associated with ancient volcanoes as a record of precipitation isotope ratios. By processing these large patterns with an inverse model to “undo” the alteration, we find that there was a large change in oxygen isotope values in precipitation between 20 and 12 million years ago in the San Juan Volcanic Field, Colorado, USA. This is consistent with surface uplift of 2–3 km over this timeframe. Unlike other isotopic proxies for paleo‐precipitation our technique captures an isotopic signal integrated over the space‐ and timescales of hydrothermal alteration, which approach those of the tectonic processes that make and break mountains.
... The climate and topography of mountainous western North America during the hothouse of the early Eocene remain enigmatic because contemporaneous changes in surface temperature, elevation, and hydrologic processes are entangled in the geologic record (Hren et al., 2010;Mix et al., 2016;Ibarra et al., 2021). The δ 18 O of authigenic carbonates is widely used as a proxy for δ 18 O of meteoric waters in reconstructing paleoclimates and paleo-elevation histories. ...
... The range in temperatures likely reflects seasonal variation; Δ 47 measurements were from bands that likely each record <1 yr of shell growth (i.e., Surge et al., 2001). These Δ 47 temperatures are among the coldest temperatures reported for the latest Paleocene-early Eocene amongst nearsea-level terrestrial records from western North America, marine records, and climate model predictions (e.g., Yapp, 2008;Mix et al., 2016;Hollis et al., 2019;Zhu et al., 2019). While most modern mollusks preferentially grow during the warm season, hot Eocene summers could have limited oyster productivity at that time (Surge et al., 2001), leading to an overall cool bias in the measured TΔ 47 . ...
... While most modern mollusks preferentially grow during the warm season, hot Eocene summers could have limited oyster productivity at that time (Surge et al., 2001), leading to an overall cool bias in the measured TΔ 47 . We also might expect estuarine waters to be colder than zonal means as a result of embayment depth and upwelling (Macarewich et al., 2021), coastal fog (Mix et al., 2016), or contributions of high-elevation runoff. Water temperatures can be as low as ∼5 °C in free-flowing rivers once they reach sea level in modern California (e.g., the Mad River; see the Supplemental Material). ...
The δ18O of carbonate minerals that formed at Earth’s surface is widely used to investigate paleoclimates and paleo-elevations. However, a multitude of hydrologic processes can affect δ18O values, including mixing, evaporation, distillation of parent waters, and carbonate growth temperatures. We combined traditional carbon and oxygen isotope analyses with clumped (Δ47) and triple oxygen isotopes (Δ′17O) analyses in oyster shells (Acutostrea idriaensis) of the Goler Formation in southern California (USA) to obtain insights into surface temperatures and δ18O values of meteoric waters during the early Eocene hothouse climate. The Δ47-derived temperatures ranged from 9 °C to 20 °C. We found a correlation between the δ18O of growth water (δ18Ogw) (calculated using Δ47 temperatures and δ18O of carbonate) and the δ13C values of shells. The Δ′17O values of shell growth waters (0.006‰–0.013‰ relative to Vienna standard mean ocean water–standard light Antarctic precipitation [VSMOW-SLAP]) calculated from Δ′17O of carbonate (–0.087‰ to –0.078‰ VSMOW-SLAP) were lower than typical meteoric waters. These isotopic compositions are consistent with oyster habitation in an estuary. We present a new triple oxygen isotope mixing model to estimate the δ18O value of freshwater supplying the estuary (δ18Ofw). The reconstructed δ18Ofw of –11.3‰ to –14.7‰ (VSMOW) is significantly lower than the δ18Ogw of –4.4‰ to –9.9‰ that would have been calculated using “only” Δ47 and δ18O values of carbonate. This δ18Ofw estimate supports paleogeographic reconstructions of a Paleogene river fed by high-elevation catchments of the paleo–southern Sierra Nevada. Our study highlights the potential for paired Δ47 and Δ′17O analyses to improve reconstructions of meteoric water δ18O, with implications for understanding ancient climates and elevations.
... Rock samples were obtained from the bottom of soil pits, or from a nearby road cut in the case of deeply weathered profiles. Underlying bedrock consists of andesitic lahar material from late Miocene to Pliocene age from the Mehrten formation, basalt flows from the mid to late Pleistocene, and the granite batholith of the Sierra Nevada thought to be Eocene in age (Piper et al., 1939;Mix et al., 2016). Regolith residence times calculated from cosmogenic nucleotides for the granite sites are thought to be <100,000 years (Riebe and Granger, 2013). ...
The fate of phosphorus (P) during pedogenesis has been historically conceptualized (Walker-Syers model) with time as the primary controlling state factor. Herein, we demonstrate that both climate and lithology exert a strong and interacting influence on the fate of P by examining coupled bioclimatic and parent material effects on soil P fractions. Three transects were investigated spanning a 2150-m elevation gradient (MAT = 17 → 3 °C/MAP = 330 → 1400 mm) across three separate bedrock lithologies (lithosequence: granite, andesite and basalt) within the Sierra Nevada and southern Cascades of California. The elevation gradient entails four bioclimatic zones (bioclimosequence: blue oak, ponderosa pine, white fir and red fir). Soil P fractions were determined by sequential fractionation and interpreted in the context of associated soil characterization data. The bioclimatic sequences demonstrate a weathering gradient with maximum intensity at mid-elevation sites, and corresponding changes in Fe/Al-(hydr)oxide content and aluminosilicate crystallinity. Phosphorus content of parent material varied by an order of magnitude (mean; mg P kg⁻¹): andesite (1500) > basalt (1000) > granite (131). Differences in P content of parent material influenced Pt in soils. However, amounts and proportions of P in fractions were influenced by subtle to significant interactions between climate and lithology, owing to differences in chemical weathering and the abundance and crystallinity of Fe/Al-(hydr)oxides and aluminosilicates. This interactive effect of pedogenesis on clay mineralogy led to differences in P fractions dependent upon lithology and bioclimatic zone. Labile inorganic P (Pi) was uniformly higher in soils derived from granite, despite granite having significantly lower P content, a result of lower Fe/Al-(hydr)oxide generation in granitic soils. With descending elevation and increased weathering intensity, HCl-Pi (primary mineral bound P-apatite) declined in basalt and andesite but remained unchanged in granite owing to its greater resistance to chemical weathering. As weathering intensity increased, occluded P increased in basalt, decreased in andesite and was unchanged in granite, contradicting the paradigm of progressive P occlusion with increased weathering. This incongruity for andesite results from a dominance of poorly crystalline materials (e.g., ferrihydrite, allophane/imogolite) at less weathered sites versus more crystalline minerals at more weathered sites. This study highlights several caveats to the paradigm that time (i.e., degree of weathering) is universally the dominant pedogenic control of P fractionation. We identify the importance of interactions between lithology and climate in regulating the amount and types of weathering products that in turn control P fractionation and ecosystem P availability.
... Oxygen isotopic composition was determined using a laser fluorination line and measured on a Thermo Finnigan MAT 252 mass spectrometer in a dual inlet configuration (e.g., Sharp, 1990;Sjostrom et al., 2006;Mix et al., 2016). Prior to laser fluorination samples were exposed to three BrF 5 prefluourinations at 30 millitorr and then fluorinated using a New Wave Research MIR 10-25 infrared CO 2 laser in a 130 millitor BrF 5 atmosphere. ...
The shift from denser forests to open, grass‐dominated vegetation in west‐central North America between 26 and 15 million years ago is a major ecological transition with no clear driving force. This open habitat transition (OHT) is considered by some to be evidence for drier summers, more seasonal precipitation, or a cooler climate, but others have proposed that wetter conditions and/or warming initiated the OHT. Here, we use published (n = 2,065) and new (n = 173) oxygen isotope measurements (δ¹⁸O) in authigenic clays and soil carbonates to test the hypothesis that the OHT is linked to increasing wintertime aridity. Oxygen isotope ratios in meteoric water (δ¹⁸Op) vary seasonally, and clays and carbonates often form at different times of the year. Therefore, a change in precipitation seasonality can be recorded differently in each mineral. We find that oxygen isotope ratios of clay minerals increase across the OHT while carbonate oxygen isotope ratios show no change or decrease. This result cannot be explained solely by changes in global temperature or a shift to drier summers. Instead, it is consistent with a decrease in winter precipitation that increases annual mean δ¹⁸Op (and clay δ¹⁸O) but has a smaller or negligible effect on soil carbonates that primarily form in warmer months. We suggest that forest communities in west‐central North America were adapted to a wet‐winter precipitation regime for most of the Cenozoic, and they subsequently struggled to meet water demands when winters became drier, resulting in the observed open habitat expansion.
... Variations in (U-Th)/He cooling ages along constant elevation profiles suggests relief of 1-2 km in the early Cenozoic southern Sierra, which by comparison to modern ranges of similar relief permit an estimated paleoelevation in excess of 4 km (House et al., 2001(House et al., , 1998. Similarly, stable isotope paleoaltimetry (Cassel et al., 2009b(Cassel et al., , 2012a(Cassel et al., , 2014Crowley et al., 2008;Mix et al., 2016;Mulch et al., 2006Mulch et al., , 2008 and paleobotany (Hren et al., 2010) data sets have been used to argue that the elevation of the western slope of the Sierra has remained largely unchanged from the Eocene through modern time. Both stable isotope paleoaltimetry and the paleobotanical work by Hren et al. (2010) rely on the assumption that atmospheric flows pass over high topography, but modern atmospheric flows in the Sierra have been shown to largely flow around instead of over portions of the range with elevations in excess of 2.5 km (Lechler and of the air mass and the amount of moisture in the atmosphere, which are sensitive to the prevailing paleoclimate in terms of temperature and seasonality of precipitation (dominantly summer versus dominantly winter). ...
... A significant body of literature based on stable isotope paleoaltimetry and paleobotany suggests that the Sierra was a topographic feature as high or higher as that of today throughout the Cenozoic (Cassel et al., 2014(Cassel et al., , 2012a(Cassel et al., , 2009bCrowley et al., 2008;Hren et al., 2010;Mix et al., 2019Mix et al., , 2016Mulch et al., 2008Mulch et al., , 2006Poage and Chamberlain, 2002;Wolfe et al., 1997). The lower half of our estimates of surface uplift are within that permitted by these geochemical data and as discussed in the introduction, these studies are based on methods and assumptions that have associated large uncertainties (Molnar, 2010). ...
The timing, rates, and spatial patterns of elevation change in the Sierra Nevada, California, USA, have long been the subject of vigorous debate owing to their importance in constraining the tectonic history of western North America and models of orogenesis. Here we present a systematic analysis of multiple measures of fluvial geomorphology along the entire length of the range and interpret these observations using 1-D and 2-D landscape evolution modeling based on the stream power fluvial erosion rule with the rate parameter calibrated from a large data set of millennial-scale erosion rates. We demonstrate that westward-draining rivers in the Sierra Nevada are in a disequilibrium state and that this state is consistent with the transient fluvial response expected from significant down-to-the-west tilting in the last 11 m.y. Assuming rigid-block tilting and using multiple independent measures of tilt magnitude, we find that the magnitude of surface uplift from late Cenozoic tilting appears to have been similar along strike and likely resulted in ∼500–1300 m of surface up- lift at the crest (0.3–0.8° tilt) from the Yuba through the Stanislaus rivers (∼39.2–38.2°N) and 1000–1400 m of surface uplift at the crest (0.6–0.9° tilt) from the Tuolumne River south through the Kings River (∼38.2–36.4°N). We show that the transient fluvial response to tilting in the northern Sierra is heavily modulated by heterogeneous lithology and drainage area exchange in a manner that reconciles the high spatial variability in basement incision observed in numerous prior studies. However, we find that heterogeneous lithology alone cannot explain both the transient state and observed patterns in channel steepness, which seem to require late Cenozoic changes in tectonic forcing. Beyond the regional implications of a short-lived rapid pulse of late Cenozoic surface uplift along the entire length of the range, our results demonstrate that a range-wide approach in which river networks are analyzed both in planform and profile can elucidate tectonic histories despite heterogeneous lithology and ongoing changes in network topology.
... This implies that the Sierra Nevada has maintained its elevation, or decreased in mean elevation, since Oligocene time or earlier, in turn implying that the observed channel gradients of any Cenozoic paleostreams are the original gradients. The reality of late Cenozoic uplift has been contested on a variety of evidence, including evidence for crustal thinning (leading to subsidence) in the late Cenozoic (Wernicke et al., 1996); comparison of early Cenozoic stable-isotope profiles and other paleoenvironmental indicators with elevation against modern profiles (little difference) (Cassel et al., 2009;Hren et al., 2010;Mix et al., 2016); lack of evidence for deflection of atmospheric circulation by an uplifting orographic barrier (Chamberlain et al., 2012;Mix et al., 2019); and weakness of the geomorphic evidence for uplift (Gabet, 2014). We note that most of this evidence comes from the northern Sierra Nevada, which is currently ∼2 km lower in average elevation at the crest than the central/southern Sierra Nevada. ...
Tectonic interpretation of the central Sierra Nevada—whether the crest of the Sierra Nevada (California, USA) was uplifted in the late Cenozoic or whether the range has undergone continuous down-wearing since the Late Cretaceous—is controversial, since there is no obvious tectonic explanation for renewed uplift. The strongest direct evidence for late Cenozoic uplift of the central Sierra Nevada comes from study of the Trachyandesite of Kennedy Table, which followed the course of the Miocene San Joaquin River but has a steeper gradient than the modern river. Early workers attributed this steeper gradient to tilting of the Sierra Nevada block since the late Miocene, resulting in 2 km of range-crest uplift. However, this interpretation has been contested on grounds that the Miocene river gradient had to be assumed and that the Sierran Batholith could have warped during tilting, thus failing to uplift the range crest. The objective of this study was to obtain quantitative data that test these criticisms.
The Trachyandesite of Kennedy Table is a chain of 33 remnants of a single lava flow as thick as 65 m, preserved for 21 km from Squaw Leap to Little Dry Creek, close to the modern San Joaquin River in the foothills of the Sierra Nevada. Several remnants lie on fluvial gravel of the late Miocene San Joaquin River. Early workers speculated that the lava concealed its own (unrecognized) vent, but in 2011, we identified the vent on the Middle Fork of the San Joaquin River, 13.5 km south of Deadman Pass and 70 km northeast of Kennedy Table. The vent complex intrudes Cretaceous granite, has 285 m relief, and is an intricately jointed intrusion that grades up into a glassy lava flow. Composition (58% SiO2) and 40Ar/39Ar age (9.3 Ma) are identical at the vent and downstream. Basal elevations of remnants were recorded, and the present-day basal gradients of several were adjusted for apparent dip and projected along a vertical plane at 220° (the estimated tilt azimuth). The basal gradients are far steeper than that of the modern river, but they differ slightly from reach to reach and are thus inconsistent measures of the post-Miocene tilt. Likewise, relief eroded atop most remnants renders modeling of upper surfaces suspect. At Little Dry Creek, however, a chain of nine remnants rests on fluvial floodplain sand and gravel; this chain trends 230°, and its smooth basal contact now dips 1.36° (adjusted at 220°). Projection of this dip 89 km from the 207 m base of the most distal remnant at Little Dry Creek to the vent intrusion falls far below the 2760 m intrusion-to-lava-flow transition near the Sierran crest, showing that the Sierran block has not undergone pronounced convex warping. Using elevation data on paleoriver meanders preserved by the lava flow, we show that the paleogradient has a cosine dependence on meander-section azimuth, indicating tilting. Subtraction of 1.07° of dip restores the data to an azimuth-independent configuration, indicating total tilting since 9.3 Ma of 1.07° and an original large-scale gradient of 0.46°, similar to the published value of 0.33° at Squaw Leap, but larger than the previously obtained value of 0.057° at Little Dry Creek. Subtraction of those Miocene estimates from the observable 1.643° tilt along the section from Little Dry Creek to the vent yields vent uplift of 2464 m (for 0.057°), 1835 m (for 0.46°), and 2040 m (for 0.33°). Confirmation of earlier assumptions regarding Miocene river gradient and block rigidity greatly strengthens the case for ∼2 km of late Cenozoic uplift of the central Sierra Nevada crest.
... Lund Snee et al. (2016) inferred that the Cretaceous to Eocene deposits in the Elko Basin represents a lake basin covered with volcanic rocks situated in relatively subdued topography, with regional rugged Basin and Range style topography only forming in the Miocene. However, upstream rainout could be due to either Eocene topography and associated rainout through the Sierra Nevada further west inferred by hydrogen and oxygen paleoaltimetry (Mulch et al., 2006;Cassel et al., 2009;Hren et al., 2010;Mix et al., 2016), or a drainage divide just west of the Elko Basin inferred from ash-flow tuffs (Henry, 2008), which are both likely and thus this possibility cannot be ruled out. ...
... Assuming a coastal Eocene precipitation δ 18 O value of −7.1 equivalent to previous studies (e.g., Mulch et al., 2006;Cassel et al., 2009;Hren et al., 2010;Mix et al., 2016), we calculate paleoelevation using the thermodynamic model of Rowley et al. (2001). The δ 18 O for scenario 1 is −7.0 , which for Eocene model results for the western United States give a mean elevation of 2.75 +0.55/−0.42 ...
... In Figures 2A,B we show a box and whisker plot (yellow) of all glass δD data from the Late Eocene sediments in and near the Elko Basin previously reported and converted to δ 18 O using the fractionation factor of Friedman et al. (1993) to convert to environmental water values and the assumption that waters fall along the global meteoric water line. This approach is similar to assumptions relating δD and δ 18 O data in clays (e.g., Poage and Chamberlain, 2002;Sjostrom et al., 2006;Mix and Chamberlain, 2014;Mix et al., 2016). The average δ 18 O of the unevaporatively enriched samples reported by volcanic glass δD studies (Cassel et al., 2014(Cassel et al., , 2018Smith et al., 2017), converted to δ 18 O, is −18.4 ± 1.0 . ...
Triple oxygen isotope measurements are an emerging tool in paleoclimate reconstructions. In this contribution we develop the application of triple oxygen isotope measurements to lacustrine sediments to reconstruct past elevations. We focus on a well-constrained sample set from the Eocene North American Cordillera (Cherty Limestone Formation, Elko Basin, NV, United States, 42–43.5 Ma) on the east side of the elevated Nevadaplano. We present triple oxygen isotope measurements on freshwater lacustrine chert samples from the Cherty Limestone Formation. Across an evaporation trend spanning 6.5‰ in δ¹⁸O values we observe a negative correlation with Δ′¹⁷O ranging from −0.066 to −0.111‰ (λRL = 0.528), with an empirical slope (λchert, δ′¹⁷O vs. δ′¹⁸O) of 0.5236. Additionally, we present new carbonate clumped isotope (Δ47) temperature results on the overlying fluvial-lacustrine Elko Formation, which indicate an error-weighted mean temperature of 32.5 ± 3.8°C (1σ), and evaporatively enriched lake water spanning δ¹⁸O values of −3.7 to +3.5‰ (VSMOW). Paired chert and carbonate δ¹⁸O values demonstrate that co-equilbrium among the carbonate and chert phases is unlikely. Thus, as also previously suggested, it is most likely that Elko Basin chert formed during early diagenesis in equilbirium with pore waters that reflect evaporatively ¹⁸O-enriched lake water. Using this scenario we apply a model for back-calculating unevaporated water composition to derive a source water of δ′¹⁸O = −16.1‰ (VSMOW), similar to modern local meteoric waters but lower than previous work on paired δ¹⁸O- δD measurements from the same chert samples. Further, this back-calculated unevaporated source water is higher than those derived using δD measurements of Late Eocene hydrated volcanic glass from the Elko Basin (average δ′¹⁸O equivalent of approximately −18.4‰, VSMOW). This suggests, assuming Eocene meteoric water Δ′¹⁷O values similar to today (∼0.032‰), either that: (1) the hypsometric mean elevation recorded by the lacustrine Cherty Limestone was lower than that derived from the average of the volcanic glass δD measurements alone; or (2) there was hydrogen exchange in volcanic glass with later low δD meteoric fluids. Nonetheless, our new findings support a relatively high (∼2.5–3 km) plateau recorded in the Elko Basin during the mid-Eocene.
... In this study we present spatial and temporal oxygen isotope data from authigenic clay minerals, a proxy for past precipitation δ 18 O, to constrain the spatial expression of Blue Mountains topography and its effect on regional precipitation patterns. Isotopes of authigenic clays have been widely applied to studying tectonic and climatic change in Cenozoic western North America (Takeuchi and Larson, 2005;Mulch et al., 2006;Sjostrom et al., 2006;Mix et al., 2011, Mix et al., 2016, Mix et al., 2019Chamberlain et al., 2012;Mix and Chamberlain, 2014) and they are particularly useful in places like John Day where soil carbonates-a more commonly used paleo-δ 18 O proxy-are not continuously present through the sedimentary record (Bestland et al., 2002). Here, we document a ∼3‰ offset in authigenic clay δ 18 O between the western and eastern facies, with lower values in the east. ...
... Any remaining vapor and any sorbed water in smectite minerals was removed through 2-4 pre-flourinations where samples were exposed to bromine pentaflouride (BrF 5 ) for ∼90 s. Afterward, samples were laser ablated with a New Wave Research MIR10-25 infrared laser ablation system in the presence of BrF 5 to liberate O 2 gas (Sharp, 1990;Sjostrom et al., 2006;Mix and Chamberlain, 2014;Mix et al., 2016). Oxygen isotope analyses on O 2 gas were performed in dual-inlet mode at the Stanford University Stable Isotope Biogeochemistry Laboratory on a Thermo Finnigan MAT 252 or 253+, depending on the date of acquisition (Abruzzese et al., 2005;Hren et al., 2009;Mix et al., 2016;Chamberlain et al., 2020). ...
... Afterward, samples were laser ablated with a New Wave Research MIR10-25 infrared laser ablation system in the presence of BrF 5 to liberate O 2 gas (Sharp, 1990;Sjostrom et al., 2006;Mix and Chamberlain, 2014;Mix et al., 2016). Oxygen isotope analyses on O 2 gas were performed in dual-inlet mode at the Stanford University Stable Isotope Biogeochemistry Laboratory on a Thermo Finnigan MAT 252 or 253+, depending on the date of acquisition (Abruzzese et al., 2005;Hren et al., 2009;Mix et al., 2016;Chamberlain et al., 2020). We purified O 2 gas from samples run on the MAT 252 with two liquid nitrogen cold traps and one potassium bromide (KBr) trap before freezing O 2 on a liquid nitrogen-temperature zeolite and subsequently equilibrating it with the mass spectrometer sample bellows. ...
The John Day region of central Oregon, United States contains ∼50 million years of near-continuous, fossiliferous sedimentation, representing one of the world’s richest archives of Cenozoic terrestrial ecosystems and climate. Stable isotope proxy data from this region are commonly used to infer the elevation history of the Cascades, which intercept westerly moisture in transit to the John Day region. However, the Blue Mountains, which accreted in the Mesozoic, create a region of local high topography that can confound signals of Cascades uplift. John Day deposits, including the John Day Formation, are divided into an eastern facies located within the Blue Mountains and a western facies in the adjacent plains. As a result, the Blue Mountains may have supported gradients in climate and ecology between the eastern and western facies, and constraining these gradients is necessary for reconstructing past topography and ecosystem change. In order to define the Cenozoic extent and magnitude of Blue Mountains topography we use oxygen isotopes in authigenic clay minerals to construct a spatially resolved map of local elevation. We find that the oxygen isotope composition of clay minerals within the Blue Mountains is ∼3‰ lower than in the adjacent high plains, and this offset is mostly constant throughout our record (spanning ∼50 – 5 Ma). We attribute this offset to Blue Mountains topography, either directly from upslope rainout or indirectly through the effect of elevation on local variations in precipitation seasonality. Our results highlight the importance of local topographic features in regional paleotopography reconstructions and provide important biogeographical context for the rich paleo-floral and -faunal records preserved in John Day sediments.
... Samples were then rinsed by deionized water and dried in oven at 60 • C for 40 h. Oxygen isotopic composition was determined using a laser fluorination line coupled to a Thermo Finnigan MAT 252 mass spectrometer in a dual inlet configuration (e.g., Mix and Chamberlain, 2014;Mix, Ibarra, Mulch, Graham, and Chamberlain, 2016). δD values of clay separates samples were measured by continuous flow mass spectrometry using a thermal combustion elemental analyzer (TC/EA) coupled to a Thermo Finnigan DeltaPlus XL at Stanford University following previously established protocols (e.g., Mix and Chamberlain, 2014). ...
... Stable oxygen and hydrogen isotopes of pedogenic clay minerals (δ 18 O clay and δD clay ) are useful proxies for reconstructing paleoclimate, as they reflect the isotopic composition of soil water, which in turn is affected by temperature, humidity, evaporation, and post-condensation processes (Stern, Page Chamberlain, Reynolds, and Johnson, 1997;Mix and Chamberlain, 2014;Mix et al., 2016). Here, we report new δ 18 O clay and δD clay measurements of <0.2 μm clay separates from 16 paleosol layer samples with dominant clay composition of smectite and randomly-mixed layer illite-smectite identified by Gao et al. (2013Gao et al. ( , 2015b. ...
... Paired δ 18 O clay and δD clay measurements serve as a single-mineral thermometer and constrain the soil water δ 18 O (δ 18 O water ) from which the minerals would have formed (e.g., Savin and Epstein, 1970b;Capuano, 1992;Mix and Chamberlain, 2014;Mix et al., 2016). While the separates are dominantly smectite, we apply both the smectite-water and illite-water oxygen isotope fractionation factors from Sheppard and Gilg (1996), and the smectite-water hydrogen isotope fractionation factor from Capuano (1992), to calculate temperatures. ...
From the latest Cretaceous (late Campanian to Maastrichtian, ~75–66 Ma) to the earliest Paleogene, fluctuations in greenhouse climate, inferred primarily from marine sediments, have been linked to volcanism, the Chicxulub asteroid impact, and the Cretaceous-Paleogene (K-Pg) mass extinction. In this paper, we summarize terrestrial climate records in mid-latitude East Asia during the latest Cretaceous and across the K-Pg boundary, based on a multi-proxy approach from the geochronologically well-constrained Sifangtai and Mingshui formations (SMF), accessed by scientific drilling of the Songliao Basin in northeastern China. Evolution of sedimentary environments is characterized by five depositional units of fluvial-deltaic-lacustrine facies. Development of four types of paleosols, including Inceptisols, Aridisols, Vertisols and Alfisols, is interpreted to primarily reflect climatic changes. Correlations among sedimentary facies, paleosol features, illite chemistry index, chemical index of alteration, as well as stable and clumped isotopes of pedogenic carbonates and clay minerals of the SMF validate their reliability for paleoclimate reconstruction, and indicate significant fluctuations in terrestrial climate and sedimentary environment. During global warming intervals possibly triggered by volcanism (e.g. ~69.5–68.5 Ma), the Songliao Basin experienced a warmer and wetter climate with stronger terrestrial chemical weathering and more monsoon-derived moisture sourced from the Pacific. In contrast, during global cooling intervals (e.g. ~70.5–69.5 Ma and ~ 68.5–66.5 Ma), the SMF record a cooler and drier climate with less intensive chemical weathering and more westerlies-derived moisture. Across the K-Pg boundary, dramatic changes in land temperatures and hydroclimate correspond to the latest Maastrichtian warming episode (~66.4–66.1 Ma), the transient cooling preceding the K-Pg boundary (~66.1–66.0 Ma), and the earliest Paleogene warming interval (~66.0–65.7 Ma). Temporal correlation of weathering index changes with the Deccan Traps volcanism suggests that volcanism and subsequent intensified weathering played a major role for climatic changes across the K-Pg boundary. The integrated records of sedimentological and geochemical datasets from the Songliao Basin robustly demonstrate that the terrestrial climate of mid-latitude East Asia responded strongly to greenhouse climate changes and to the catastrophic geological events from the latest Cretaceous to the earliest Paleogene.
... To the southwest, contrasting models for the evolution of the Sierra Nevada mountains propose that elevations were attained either recently or in the early Cenozoic. Revised geomorphological observations have, however, shown that the Sierra Nevada has been at high elevations at least since the Eocene in agreement with stable isotope data (Gabet, 2014;Mix et al., 2016;Mulch et al., 2006). The high elevation in the Nevadoplano and Sierra Nevada contrast with elevations in the Colorado Plateau where stable isotopes are compatible with paleoelevations of around 1000 m (Cather et al., 2012;Licht et al., 2017). ...
Paleogeographic maps are essential tools for understanding Earth system dynamics. They provide boundary conditions for climate and geodynamic modelling, for analysing surface processes and biotic interactions. However, the temporal and spatial distribution of key features such as seaways and mountain belts that govern climate changes and biotic interchange differ between various paleogeographies that require regular updates with new data and models. We developed a reproducible and systematic approach to paleogeographic reconstruction and provide a set of worldwide Cenozoic paleogeographic maps at 60, 40 and 20 Ma. We followed a six-stage methodology that integrates an extensive review of geological data into a coherent plate tectonic model using the open source software GPlates. (1) We generated a global plate kinematic model, and reconstructed intensely-deformed plate boundaries using a review of structural, paleomagnetic and other geologic data in six key regions: the Andes, the North American Cordillera, the Scotia Arc, Africa, the Mediterranean region and the Tibetan-Himalayan collision zone. (2) We modified previously published paleobathymetry in several regions where continental and oceanic crust overlap due to differences in the plate models. (3) We then defined paleoshorelines using updated fossil and geologic databases to locate the terrestrial to marine transition. (4) We applied isostatic compensation in polar regions and global eustatic sea level adjustments. (5) Paleoelevations were estimated using a broad range of data including thermochronology and stable isotopes, combined with paleobotanical (mostly pollen and leaf physiognomy), structural and geomorphological data. We address ongoing controversies on the mechanisms and chronology of India-Asia collision by providing alternate reconstructions for each time slice. We finally discuss the implications of our reconstructions on the Cenozoic evolution of continental weatherability and review methodological limitations and potential improvements. Future addition of new data, tools and reconstructions can be accommodated through a dedicated interactive website tool (https://map.paleoenvironment.eu/) that enables users to interactively upload and download data and compare with other models, and generate their own plots. Our aim is to regularly update the models presented here with new data as they become available.
