Detrital zircon U-Pb provenance of the Colorado River: A 5 m.y. record of incision into cover strata overlying the Colorado Plateau and adjacent regions

Abstract

New detrital zircon U-Pb age distributions from 49 late Cenozoic sandstones and Holocene sands (49 samples, n = 3922) record the arrival of extraregional early Pliocene Colorado River sediment at Grand Wash (western USA) and downstream locations ca. 5.3 Ma and the subsequent evolution of the river's provenance signature. We define reference age distributions for the early Pliocene Colorado River (n = 559) and Holocene Colorado River (n = 601). The early Pliocene river is distinguished from the Holocene river by (1) a higher proportion of Yavapai-Mazatzal zircon derived from Rocky Mountain basement uplifts relative to Grenville zircon from Mesozoic supracrustal rocks, and (2) distinctive (~6%) late Eocene-Oligocene (40-23 Ma) zircon reworked from Cenozoic basins and volcanic fields in the southern Rocky Mountains and/or the eastern Green River catchment. Geologic relationships and interpretation of 135 published detrital zircon age distributions throughout the Colorado River catchment provide the interpretative basis for modeling evolution of the provenance signature. Mixture modeling based upon a modified formulation of the Kolmogorov-Smirnov statistic indi cate a subtle yet robust change in Colorado River provenance signature over the past 5 m.y. During this interval the contribution from Cenozoic strata decreased from ~75% to 50% while pre-Cretaceous strata increased from ~25% to 50%. We interpret this change to reflect progressive erosional incision into plateau cover strata. Our finding is consistent with geologic and thermochronologic studies that indicate that maximum post-10 Ma erosion of the Colorado River catchment was concentrated across the eastern Utahwestern Colorado region.

Importance of groundwater in propagating downward integration of the 6–5 Ma Colorado River system: Geochemistry of springs, travertines, and lacustrine carbonates of the Grand Canyon region over the past 12 Ma

“…This Temple-Gregg curve generally resembles those in the Rainbow Garden and Thumb Members and the northern Grand Wash Trough, as well as Pliocene-Holocene Colorado River sands ( Fig. 9; Kimbrough et al, 2011Kimbrough et al, , 2015, except that the Hualapai Limestone in Gregg and Temple basins lacks age peaks younger than 235 Ma (middle Triassic). Additional analyses are needed to preclude this being a sampling bias, but data so far suggest that no strata younger than Moenkopi Formation were present in the provenance.…”

“…K09-Hual 21 was collected near the junction of the South Cove and Pearce Ferry roads in red siltstone that underlies a thin Hualapai Limestone section. An additional sample (32606-1) was collected in approximately the same location as K09-Hual 21 (Kimbrough et al, 2015;Supplemental K09-13 has a well-constrained age (13 Ma), and all of these lower Grand Wash Trough samples (320 grains; number 6 of Fig. 9) represent deposition of red siltstones and fanglomerates in the Grand Wash Trough from 13 to ca.…”

“…9; Kimbrough et al, 2015). The lowest sample (K09-Hual-13) was collected from a sandstone bed that immediately underlies the 13.11 ± 0.08 Ma ash near Pierce Ferry (Fig.…”

detritalPy: A Python‐based toolset for visualizing and analysing detrital geo‐thermochronologic data

“…Yet development of an efficient means of visualizing and analysing large datasets remains a critical need in the detrital geo‐thermochronologic community (Gehrels, ). For example, the ability to easily create sample groups within detritalPy will facilitate construction of reference curves (Gehrels, Dickinson, Ross, Stewart, & Howell, ; Kimbrough et al., ) that can be compared with the magmatic and/or metamorphic history of known basement terranes (Dickinson & Gehrels, ) or with other detrital samples (Sharman, Covault, Stockli, Wroblewski, & Bush, ). The ability to quickly visualize and analyse related detrital geochronological and geochemical data also have relevance for characterization of source terranes, such as the magmatic flux of volcanic arc terranes (Ducea, ; Malkowski, Schwartz, Sharman, Sickmann, & Graham, ; Sharman et al., ).…”

Does Pebble Abrasion Influence Detrital Age Population Statistics? A Numerical Investigation of Natural Data Sets

“…At the same time, numerical models have increasingly been applied as a tool to unravel the source of zircons in modern rivers (Sundell & Saylor, ). Several of these models apply a forward mixing approach, whereby empirical observations such as exposure area and zircon fertility (i.e., the concentration of the mineral of interest in the source area) are used to generate an artificial grain age probability density function (PDF) that is compared to the best fit of the measured grain age distribution (e.g., Kimbrough et al, ; Licht et al, ; Saylor et al, ; Sharman & Johnstone, ). There is often a mismatch between the model‐predicted and best fit age distributions that is typically explained by a variety of natural factors such as differences in erosion rates (e.g., Amidon et al, ), mineral fertility over the study area (e.g., Dickinson, ; Moecher & Samson, ), and fractionation by transport processes (e.g., hydraulic sorting) (Lawrence et al, ; Malusà et al, ).…”