Birth and evolution of the Rio Grande fluvial system in the last 8 Ma:Progressive downward integration and interplay between tectonics, volcanism, climate, and river evolution

The Rio Grande-Rio Chama (RG-RC) fluvial system has evolved dramatically over the last 8 Ma, undergoing channel migrations, drainage capture and integration events, volcanic damming, and carving and refilling of paleocanyons. Volcanism concurrent with the development of the river system provides a unique opportunity to apply multiple geochronometers to the study of its incision and drainage evolution. This paper reports 19 new 40Ar/39Ar basalt ages and 19 detrital mineral samples (zircon and sanidine) collected from RG-RC alluvium overlain by dated basalt flows in the context of a compilation of published 40Ar/39Ar basalt ages. The “run-out” geometry of 4.8 Ma basalts at Black Mesa suggests that the course of the northern Rio Grande connecting the San Luis to Española basins was established by then. Detrital zircon age spectra for ancestral Rio Grande alluvium underlying these basalt flows contain 10-12% of 37-27 Ma grains suggesting that the ~5 Ma Rio Grande had its headwaters in the San Juan Mountains. The 5-3 Ma accumulation of basalt flows on the Taos Plateau was accompanied by inset relationships downstream (near Black Mesa) documenting the v existence of a developing 5-2.5 Ma Rio Grande valley that provided downstream discharge. Coincident timing and pre-volcanic knickpoints suggest that surface uplift associated with the construction of the Taos Plateau volcanic field drove downward integration to the Palomas basin by 4.5 Ma. Changes in ancestral Rio Grande sediment provenance from 2.6 Ma to 1.6 Ma document a northward shift of the RG-RC confluence and indicate that surface uplift of the Jemez Mountains (Valles Caldera) likely drove further downstream integration. The Taos Plateau volcanic field reduced through-flowing surface drainage from the San Juan Mountains relative to the Sangre de Cristo Mountains until the ~0.69-0.44 Ma spillover of Lake Alamosa, but we view this event as a re integration, not initial integration, of upper Rio Grande drainage. Progressive downward integration of rift-aligned basins from 8 to 1 Ma was likely facilitated by waning rift extension that allowed aggradation to exceed subsidence. Downward integration events crudely mimic climate change “events” at 6 Ma (onset of the southwestern monsoon) and 2.5 Ma (global change toward glacial-interglacial climate). Magmatic influences include the 6-2.5 Ma building of the Taos Plateau volcanic field, Jemez Mountain caldera eruptions at 1.6 and 1.25 Ma, along with continued magmatism that developed constructional topography and Jemez lineament volcanism that may have been associated with mantle-driven epeirogenic uplift across northern New Mexico. Integration of the RG-RC system to the Gulf of Mexico by 0.8 Ma was facilitated by headwater uplift as well as increased frequency of ~100 ka high-amplitude glacial-interglacial cycles that contributed to higher discharge and bedrock incision rates during the Pleistocene. We conclude that magmatic and tectonic drivers dominated over the last ~8 Ma, but were amplified by climate change events to determine the fluvial evolution of the RG-RC system

Fluvial organic carbon composition regulated by seasonal variability in lowland river migration and water discharge

Identifying drivers of seasonal variations in fluvial particulate organic carbon (POC) composition can aid sediment provenance and biogeochemical cycling studies. We evaluate seasonal changes in POC composition in the Río Bermejo, Argentina, a lowland river running ∼1,270 km without tributaries. Weekly POC concentration and isotopic composition from 2016 to 2018 show that during the wet season, increased lateral channel migration generates an influx of 13C-enriched and 14C-enriched floodplain-sourced material, overprinting the 13C-depleted and 14C-depleted headwater signature that is observed during the dry season. These findings demonstrate how channel morphodynamics can drive variability of POC composition in lowland rivers, and may modulate the composition of POC preserved in sedimentary archives

Data publication: The fate of fluvially-deposited organic carbon during transient floodplain storage

The data set contains all relevant luminescence measurement data used in the corresponding article: Scheingross et al. 2021. The fate of fluvially-deposited organic carbon during transient floodplain storage. EPSL 561, 116822, doi: 10.1016/j.epsl.2021.116822

Bulk organic carbon and n-alkane composition data for leaf litter, soil, and floodplain sediment from the Rio Bermejo (Argentina) collected in 2015 - 2018

Endmember samples were collected and analyzed to determine the sources of organic material in the river suspended sediment. Endmembers include soil, leaf litter, and floodplain sediment. Soil and leaf litter samples were collected using an ethanol-cleaned hand trowel. Floodplain sediment samples were collected using an Edelman-type hand auger drilled down to a maximum of ~5 m. Samples were stored in paper bags, and then oven-dried at 40°C. n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Bulk organic carbon and n-alkane composition data for time-series samples from the Rio Bermejo (Argentina) at river km 865 collected in 2017 - 2018

Additionally, we employed a local resident to collect surface water suspended sediment samples at river km 865 throughout the 2017-2018 water year. These samples were collected in a bucket, the sediment was allowed to settle, and then the water was decanted off the top. Recovered sediment was stored in sterile Whirlpak bags, and then dried in an oven at 40°C. We homogenized and disaggregated the dry sediment using a mortar and pestle, and removed coarse plant material >1 mm. For each sample, we weighed an aliquot of sediment and loaded the material into aluminum cells for lipid extraction. Total lipid extracts (TLE) were recovered using an accelerated solvent extraction system (Dionex ASE) with 9:1 v/v dichloromethane: methanol. We added exactly 10 µg of internal standard (5-a-Androstane) to the TLE for unknown compound quantification. We then separated the TLE into three fractions using silica gel column chromatography with hexane (alkanes), 1:1 v/v hexane: dichloromethane (ketones), and 1:1 v/v dichloromethane: methanol (alcohols + acids) (Rach et al., 2020; doi:10.1016/j.orggeochem.2020.103995). Unsaturated compounds were removed from the alkane fraction using AgNO3-silica gel column chromatography with n-hexane (saturated n-alkanes) and DCM (unsaturated n-alkanes). n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Dissolved concentrations of major elements and water isotopes for water samples from the Rio Bermejo mainstem, tributaries, spring-fed channels, and groundwater wells

Water samples were filtered to 0.2 micron prior to measurement. Samples for cation analysis were acidified in the field to pH < 2 using 6N HNO3. Cation concentrations were measured with a Varian 720 inductively coupled plasma optical emission spectrometer (ICP-OES) at the GFZ Helmholtz Laboratory for the Geochemistry of the Earth Surface (HELGES), using SLRS-5 (Saint-Laurent River Surface, National Research Council - Conseil National de Recherches Canada) and USGS M212 and USGS T187 as external standards. We corrected for instrument drift by measuring an internal standard (GFZ-RW1) every 10 samples and we determined measurement uncertainty using calibration curve uncertainty. Anion concentrations were measured with a Dionex ICS1100 Ion Chromatograph, using USGS standards M206 and M212 as external standards for quality control, with uncertainty determined from triplicate analysis. We corrected cation concentrations for cyclic salt inputs following Bickle et al. (2005, doi:10.1016/j.gca.2004.11.019)

Bulk organic carbon and n-alkane composition data for river sediment depth profile samples from the Rio Bermejo (Argentina) collected in March 2017

We extracted and analyzed n-alkane compounds from river suspended sediment collected from the Rio Bermejo in Argentina. We collected 24 river depth profile samples collected during March 2017. We collected suspended particulate matter from water depth profiles at four locations along the mainstem Rio Bermejo (river km 135, 420, 865, 1220), one location on the Rio San Francisco (RSF) (river km -15), and one location on the Rio Bermejo upstream from the RSF confluence (river km -10) (Fig. 1a). We homogenized and disaggregated the dry sediment using a mortar and pestle, and removed coarse plant material >1 mm. For each sample, we weighed an aliquot of sediment and loaded the material into aluminum cells for lipid extraction. Total lipid extracts (TLE) were recovered using an accelerated solvent extraction system (Dionex ASE) with 9:1 v/v dichloromethane: methanol. We added exactly 10 µg of internal standard (5-a-Androstane) to the TLE for unknown compound quantification. We then separated the TLE into three fractions using silica gel column chromatography with hexane (alkanes), 1:1 v/v hexane: dichloromethane (ketones), and 1:1 v/v dichloromethane: methanol (alcohols + acids) (Rach et al., 2020; doi:10.1016/j.orggeochem.2020.103995). Unsaturated compounds were removed from the alkane fraction using AgNO3-silica gel column chromatography with n-hexane (saturated n-alkanes) and DCM (unsaturated n-alkanes). n-alkanes were identified and quantified using an Agilent gas chromatograph (GC 7890-A) with flame ionization detection (FID) coupled to a single quadrupole mass spectrometer (MS 5975-C). We quantified n-alkane concentrations relative to the peak response of the internal standard, and then normalized the abundance to the sediment mass. We measured n-alkane d13C via GC-C-IRMS (gas chromatography/combustion/isotope-ratio mass spectrometry) with helium as a carrier gas (Agilent 7890N, ThermoFisher Delta V Plus). All compounds were measured in triplicate with a standard deviation of =0.5‰. Measurement quality was checked regularly by measuring n-alkane standards (nC15, nC20, nC25) with known isotopic composition (provided by Campro Scientific, Germany). d13C values were normalized to the Vienna Pee Dee Belemnite (VPDB) standard. We measured n-alkane d2H via GC-IRMS using a ThermoFisher Scientific Trace GC 1310 coupled to a Delta-V isotope ratio mass spectrometer. All d2H measurements were made in duplicate, and measurement quality was checked with d2H values were normalized to the Vienna Standard Mean Ocean Water (VSMOW) standard using an n-alkane standard mix with known d2H values (nC16 - nC30, from A. Schimmelman/Indiana University)

Relative elevation of the Rio Bermejo with respect to its floodplain

Relative elevation data was extracted from the map of residual topography over 25-40 km swaths extending from the Rio Bermejo channel centerline. We quantified the superelevation and incision of the Rio Bermejo relative to the surrounding topography by making a residual elevation map (sensu Cohen et al. (2015, doi:10.1130/2015.1212(16); McGlue et al. (2016, doi:10.2110/jsr.2016.82)). We created a series of 1 km wide swaths set perpendicular to the Rio Bermejo flow direction and extracted the minimum elevation of the active Rio Bermejo channel within each swath using the TanDEM-X DEM. Variability in DEM values for water surfaces created ~2-4 m noise in elevation values of the active channel which we smoothed by fitting a 4th order polynomial to the extracted active channel elevations to estimate the downstream change in elevation. We subtracted the polynomial fit from the DEM to yield a DEM that was de-trended from the Rio Bermejo channel slope, with values representing the local relief between the active channel and the surrounding terrain

Time series of water samples and stable water isotope measurements collected at Puente Lavalle

This dataset contain stable isotope values for water samples collected ~weekly from the Rio Bermejo at the Lavalle bridge (-25.6513, -60.1277) from March 2016 to February 2018. Water samples were filtered to 0.2 micron using a custom filtration device. We measured d2H and d18O on a Picarro L-2140i Cavity Ring-Down Spectrometer at the GFZ Potsdam. Measurements were made in duplicate, normalized to the Vienna Standard Mean Ocean Water (VSMOW), and analytical uncertainty is reported as one standard deviation from the mean. River discharge was measured at the El Colorado gauging station, which is ~100 km down slope from the sampling location

River water chemistry, channel morphometrics, and river incision data for the Rio Bermejo, Argentina

This dataset was generated to study the effects of lithospheric flexure on river geomorphology and river water chemistry of the Rio Bermejo fluvial system in the east Andean foreland basin of northern Argentina. Tectonics exerts a strong control over the morphology of Earth's surface that is apparent in active mountain belts. In lowland areas, subtle processes like lithospheric flexure and isostatic rebound can impact Earth surface dynamics, hydrologic connectivity, and topography, suggesting that geomorphic and hydrologic analyses can shed light on underlying lithospheric properties. The Rio Bermejo is an outstanding field laboratory to study these feedbacks because it has a long reach that traverses the foreland basin without any tributaries. To examine the hydrologic effects, we sampled river water from the Rio Bermejo at several stations along the lowland flow path and measured dissolved solute concentrations (major cations and anions) and stable isotope composition (d2H and d18O). Additionally, we collected a timeseries of water samples for stable isotope measurements, where water samples were collected every week from March 2016 to February 2018 at the Lavalle bridge on the lower Rio Bermejo (Time series of water samples and stable water isotope measurements collected at Puente Lavalle (-25.6513, -60.1277)