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detritalPy: A Python-based Toolset for Visualizing and Analyzing Detrital Geo-Thermochronologic Data
The Depositional Record
Abstract
Detrital geochronology and thermochronology have emerged as primary methods of reconstructing the tectonic and surficial evolution of the Earth over geologic time. Technological improvements in the acquisition of detrital geo‐thermochronologic data have resulted in a rapid increase in the quantity of published data over the past two decades, particularly for the mineral zircon. However, existing tools for visualizing and analyzing detrital geo‐thermochronologic data generally lack flexibility for working with large datasets, hampering efforts to utilize the large quantity of available data.
This paper presents detritalPy, a Python‐based toolset that is designed for flexibility in visualizing and analyzing large detrital geo‐thermochronologic datasets. Any number of samples, or groups of samples, can be selected for plotting and/or analysis. Functionality includes: (1) plotting detrital age distributions using the most commonly employed visualization types, (2) plotting sample locations within an interactive mapping interface, (3) calculating and plotting maximum depositional age, (4) creating multi‐dimensional scaling plots, and (5) calculating inter‐sample similarity and dissimilarity matrices, among other functions. detritalPy is implemented using a Jupyter Notebook, requires no significant coding expertise, and can be modified as needed to meet users’ specific requirements. It is anticipated that detritalPy will provide a platform for analyzing detrital geo‐thermochronologic data within a ‘Big Data’ framework, providing a much needed toolset for efficient utilization of ever‐increasing quantities of data.
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... A complete list of the analytical data and U-Pb method is presented in the Harvard Metaverse repository (Martos et al., 2024). U-Pb ages were plotted in PDP (Probability Density Plot) and KDE (Kernel Density Estimate) to analyze the source area of sediments, using the Isoplot (Ludwig, 1999), IsoplotR (Vermeesch, 2018) and detritalPy (Sharman et al., 2018) software. To determine the maximum depositional age (MDA), we used the youngest single cluster overlapping at 2σ uncertainty and we calculated a weighted mean 206 Pb/ 238 U age (Gehrels, 2014). ...
The early stages of Andean construction have been barely recognized due to a long history of tectonic superposition during the growth of the orogen. In this work, we present a multi‐method approach integrating sedimentological, geochronological, structural, and provenance analyses to reconstruct the architecture of the Late Cretaceous foreland basin at 34°40’S. We identified a new depocenter located in an inner position of the Late Cretaceous foreland basin, a strategic location to understand the sedimentation dynamics near the topographic front of the orogen. Two sandstone samples from the basal and upper sections of the Diamante Formation were collected for detrital zircons dating, which yielded maximum depositional ages between 98 Ma and 91 Ma. The provenance analyses based on U‐Pb zircons ages indicated a main source area located to the west, in the incipient orogenic belt, with a complementary contribution from basement rocks, located to the east. Moreover, growth strata documented in these deposits were compared with structural kinematic models, which suggest that some of these deposits are associated with inherited structures, reactivated during the tectonic inversion of the extensional Jurassic Atuel depocenter. Our paleogeographic model comprises an Andean Cordillera flanked by a hinterland basin to the west and a foreland basin to the east, with a deformational front positioned further east compared to previous models.
... All detrital zircon dates are reported at 1σ (including only analytical uncertainty, but with external uncertainty noted) in Table S2 and in Schwartz (2023). We used detritalPy (Sharman et al., 2018) to visualize our data as kernel density estimates (KDEs), cumulative KDEs (CKDEs), and multidimensional scaling (MDS) plots. ...
Fluvial strata of the Upper Triassic Chinle Formation and Dockum Group, exposed across the Western Interior of North America, have long been interpreted to record a transcontinental river system that connected the ancestral Ouachita orogen of Texas and Oklahoma, USA, to the Auld Lang Syne basin of northwestern Nevada, USA, its inferred marine terminus. Fluvial strata are well-characterized by existing detrital zircon data, but the provenance of the Auld Lang Syne basin is poorly constrained. We present new detrital zircon U-Pb and Hf isotopic data that characterize the provenance of Norian siliciclastic strata that dominate the Auld Lang Syne basin. Mixture modeling of Auld Lang Syne basin data identifies the Alleghany−Ouachita−Marathon belt of eastern Laurentia as a dominant source of sediment, but the presence of Triassic detrital zircon grains in Auld Lang Syne basin strata indicates that at least one peri-Laurentian arc segment had to have also contributed sediment. A comparison of new Hf isotopic data with those characterizing various peri-Laurentian volcanic arcs demonstrates that although multiple arc segments may have simultaneously contributed zircons to the Auld Lang Syne basin, the west Pangean arc of northern Mexico stands out as a unique source of highly evolved Permian to Triassic detrital zircon grains in samples from the Auld Lang Syne basin. Altogether, our data and analyses demonstrate source-to-sink connectivity between the Late Triassic (Norian) Cordilleran margin and remnant late Paleozoic highlands of southern to eastern Laurentia, which ultimately framed a Mississippi River−scale, transcontinental watershed that traversed the topographically subdued Laurentian continental interior.
... Red and yellow bars mark the inflection points in the CDF. Plots made using DetritalPy (Sharman et al. 2018). Weighted mean dates for zircon from the b Sierra Chicharra quartz diorite (sample 161-2), c Sierra Atacama diorite (sample 161-9), and d hornblende grano-diorite dike (sample 191-N116). ...
The Punta del Cobre district near Copiapó is a center of iron oxide-copper–gold (IOCG) mineralization spatially and temporally associated with regional sodic-calcic hydrothermal alteration, the Atacama fault system (AFS), and two phases of Early Cretaceous magmatism. Here, we investigate the spatiotemporal and geochemical relationships between magmatism, ductile deformation, and hydrothermal alteration along the ~ 200 to 300-m-thick steeply NW-dipping Sierra Chicharra shear zone, interpreted to be the major strand of the AFS. Mylonitic fabrics and oblique sinistral-reverse kinematic indicators together record coaxial flattening in a transpressional regime. Deformation on the AFS took place before, during, and after intrusion of the synkinematic Sierra Chicharra quartz diorite of the Coastal Cordillera arc at ~ 122 Ma and terminated before intrusion of the unstrained ~ 114 Ma Sierra Atacama diorite of the Copiapó batholith. Geochemical data show that the Copiapó batholith was more mafic and more K-rich than the calc-alkaline Coastal Cordillera arc. This time period thus overlaps IOCG mineralization in the Punta del Cobre district (~ 120 to 110 Ma). Multiple phases of sodic-calcic alteration in and around the AFS shear zone are recognized. Textures of altered rock in the shear zone show both synkinematic assemblages and post-kinematic hydrothermal oligoclase. A ~ 775-m-long andradite vein that cuts the shear zone formed broadly at the end of magmatism in the district (~ 95 Ma). Oxygen isotope ratios from the vein indicate that hydrothermal fluids were likely magmatically derived. Together, this work shows the AFS-related shear zone and nearby IOCG mineralization developed in a regional transpressional regime produced by SE-directed oblique convergence across a NE-striking shear zone. IOCG-related magmatic-hydrothermal fluids exploited this transcrustal shear zone to produce multiple episodes of regional sodic-calcic alteration formed from fluids exsolved from magmas or driven by the heat of the Coastal Cordillera arc and Copiapó batholith.
The Mesozoic in the Bohai Bay Basin lacks unified stratigraphic framework. Based on logging data, sporopollen assemblage and age analysis of clastic and volcanic rocks, the stratigraphic subdivision and correlation of the Mesozoic were studied. The Mesozoic strata can be divided into eight stratigraphic units. The Triassic continental red strata develops the Aratrisporites－Triassisporis－Chordasporites assemblage, and the maximum depositional ages range from (241.4±6.8) Ma to (248.2±1.9) Ma. The Cyathidites－Osmundacidites－Cycadopites－Classopollis assemblage forms in the Jurassic coal-bearing strata, and the maximum depositional ages of the strata are from (173.4±1.1) Ma to (187.2±4.8) Ma. For the Jurassic gray sandstone strata, the maximum depositional ages range from (155.3±1.3) Ma to (164.4±3.8) Ma and the Cyathidites－Osmundacidites－Deltoidospora－Cycadopites assemblage are developed. The Jurassic red sandstone and gravel strata develop the Classopollis－Abietineaepollenites assemblage. In early stage of early Cretaceous, the red clastic strata with basic volcanic rock and the Cicatricosisporites－Lygodiumsporites－Classopollis assemblage formed. The volcanic rocks ages are from 140 to 132 Ma. For the gray clastic strata with intermediate-basic volcanic rock in the middle part of the lower Cretaceous, the Lygodiumsporites－Cicatricosisporites－Osmundacidites－Cycadopites assemblage and the volcanic rocks of the ages from 130 to 116 Ma are developed. The clastic strata with intermediate-basic volcanic rock in the upper part of the lower Cretaceous develop the assemblage of Cicatricosisporites－Schizaeoisporites－classopollis－Piceites, and the volcanic rocks ages range from 119 to 103 Ma. The Schizaeoisporites－Ephedripites－Classopollis assemblage forms in the Upper Cretaceous red clastic strata with acidic volcanic rock ranging from 76 to 69 Ma in age.
Sedimentary basins adjacent to subduction-related continental arcs provide important archives for deciphering the intricate history of convergent plate margins. The east-west trending Gangdese magmatic arc was one of the most predominant topographic features located at the southern margin of Tibet before the arrival of the Indian plate. However, the detailed Cretaceous growth and evolution across the arc system remains ambiguous. Stratigraphy of the adjacent Xigaze forearc basin provides a well-preserved and well-exposed record of the tectonic and magmatic evolution of the arc throughout the Cretaceous period. We report new stratigraphic, sedimentological, geochronological, and provenance analyses of the Quarry Ridge sandstone in the Xigaze forearc basin along with compiled zircon U-Pb ages (n = 9674) and Lu-Hf isotopic signatures (n = 3389) from the Gangdese arc, the Xigaze forearc basin, and the Linzhou retroarc foreland basin to reconstruct the Early to middle Cretaceous magmatism and uplift of the Gangdese arc and concurrent sedimentary responses within both basins. Exhumation of the arc initiates at around 113 Ma suggested by arc detritus first arriving in both basins. Another episode of inferred uplift occurs at around 108 Ma, which resulted in coarse-grained sedimentation in adjacent basins, preventing Central Lhasa detritus from reaching the Xigaze forearc basin further south and a facies and provenance change within the Linzhou basin. Finally, a third episode at around 101 Ma is reflected by deposition of the progradational Quarry Ridge clastic succession and marks the initiation of a substantial coarse-grained depositional stage in the Xigaze forearc basin. Our study emphasizes the connection between coarse-grained deposition in the forearc basin and arc magmatism and uplift. This study also provides an orogen-scale assessment of the history of arc magmatism, uplift, and sedimentation across the Gangdese magmatic arc system, which supports interpretations that Tibet was already characterized by complex and substantial topographic relief during the Cretaceous before the collision between the Indian and Eurasian plates.
Present day submarine canyons are active conduits for large volumes of sediment, carbon, and pollutants from continents to oceans. However, the evolution of submarine canyons over geological timescales remains poorly understood due to their erosional nature and low preservation potential. The Late Cretaceous Punta Baja Formation represents a well-preserved submarine canyon-fill on a tectonically-active ocean-facing margin. Outcrops provide km-scale continuous strike and dip sections of the 120 m thick and 1.2 km wide feature. An inherited tectonic fabric influenced the location and orientation of canyon incision into fluvial bedrock. The stratigraphic evolution of the Punta Baja submarine canyon is reconstructed from incision to fill, and shows that it remained an active sediment conduit throughout the time period represented by the preserved fill. The depositional architecture of the north-south oriented erosionally confined canyon-fill is asymmetric, with sub-vertically stacked channel-fills to the west, and an overbank confined by the canyon margin in the east. Sedimentary process interactions led to depositional patterns that we consider distinct to submarine canyon fills. Dynamic topography created by mass wasting processes captured sediment and drove knickpoint development, an autogenic mechanism that modifies sediment delivery to the ocean floor. We interpret widespread upstream dipping surfaces in channel-fills as the stratigraphic expression of migrating supercritical-flow bedforms, playing an important role in sediment storage and transport in the canyon. The proximal location of canyons and unique confinement configuration impact transverse and lateral gravity flow filtering, causing depositional patterns in the intra-canyon overbank areas that are less well organised than in published examples of external levees and which were previously poorly characterised for submarine canyons. This study provides insight into how processes that are observed in modern canyons are selectively preserved through the lifetime of the canyon and construct or destroy stratigraphy on geological timescales.
The Klamath Mountains Province of Northern California and southern Oregon, USA, consists of generally east-dipping terranes assembled via Paleozoic to Mesozoic subduction along the western margin of North America. The Klamath Mountains Province more than doubled in mass from Middle Jurassic to Early Cretaceous time, due to alternating episodes of extension (e.g., rifting and formation of the Josephine ophiolite) and shortening (e.g., Siskiyou and Nevadan events). However, the tectonic mechanisms driving this profound Mesozoic growth of the Klamath Mountains Province are poorly understood. In this paper, we show that formation of the Condrey Mountain schist (CMS) of the central Klamath Mountains Province spanned this critical time period and use the archive contained within the CMS as a key to deciphering the Mesozoic tectonics of the Klamath Mountains Province. Igneous samples from the outer CMS subunit yield U-Pb zircon ages of ca. 175–170 Ma, which reflect volcanic protolith eruptive timing. One detrital sample from the same subunit contains abundant (~54% of zircon grains analyzed) Middle Jurassic ages with Paleozoic and Proterozoic grains comprising the remainder and yields a maximum depositional age (MDA) of ca. 170 Ma. These ages, in the context of lithologic and thermochronologic relations, suggest that outer CMS protoliths accumulated in an outboard rift basin and subsequently underthrust the Klamath Mountains Province during the Late Jurassic Nevadan orogeny. Five samples of the chiefly metasedimentary inner CMS yield MDAs ranging from 160 Ma to 130 Ma, with younger ages corresponding to deeper structural levels. Such inverted age zonation is common in subduction complexes and, considering existing K-Ar ages, suggests that the inner CMS was assembled by progressive underplating over a >10 m.y. timespan. Despite this age zonation, age spectra derived from structurally shallow and deep portions of the inner CMS closely overlap those derived from the oldest section of the Franciscan subduction complex (South Fork Mountain schist). These relations suggest that the inner CMS is a composite of South Fork Mountain schist slices that were sequentially underplated beneath the Klamath Mountains Province. The age, inboard position, and structural position (i.e., the CMS resides directly beneath Jurassic arc assemblages with no intervening mantle) of the CMS suggest that these rocks were emplaced during one or more previously unrecognized episodes of shallow-angle subduction restricted to the Klamath Mountains Province. Furthermore, emplacement of the deepest portions of the CMS corresponds with the ca. 136 Ma termination of magmatism in the Klamath Mountains Province, which we relate to the disruption of asthenospheric flow during slab shallowing. The timing of shallow-angle subduction shortly precedes that of the westward translation of the Klamath Mountains Province relative to correlative rocks in the northern Sierra Nevada Range, which suggests that subduction dynamics were responsible for relocating the Klamath Mountains Province from the arc to the forearc. In aggregate, the above relations require at least three distinct phases of extension and/or rifting, each followed by an episode of shallow-angle underthrusting. The dynamic upper-plate deformation envisioned here is best interpreted in the context of tectonic switching, whereby slab steepening and trench retreat alternate with slab shallowing due to recurrent subduction of buoyant oceanic features.
Plain Language Summary
The Tethyan slab subduction and following collision of India and Asia produced two magmatic belts in the Lhasa‐Tengchong terrane. How did the magmatic flare‐ups or high‐flux episodes and sources spatiotemporally vary? We combine the new U‐Pb and Lu‐Hf isotopic data of captured zircons (xenocrystic zircons caught by volcanics from country rocks) and a comprehensive data set to show that the peak ages of early Cretaceous flare‐up of the northern magmatic belt are ca.10 Ma younger in central and northern Lhasa than in eastern Tengchong, possibly related to the diachronous closure of the Meso‐Tethys and flat subduction of the Neo‐Tethys. The southern magmatic belt in Tengchong and western southern Lhasa exhibit 75–45 Ma flare‐ups featured by the reworking of ancient crust, different from the eastern southern Lhasa with the flare‐ups at 100–85 Ma and 65–45 Ma which are dominated by the juvenile crustal growth. Such flare‐up variations may be related to changes of the Neo‐Tethyan slab dip.
Deciphering depositional age from deposits that accumulate in deep-water slope settings can enhance understanding of shelf-margin evolutionary timing, as well as controlling mechanisms in ancient systems worldwide. Basin analysis has long employed biostratigraphy and/or tephrochronology to temporally constrain ancient environments. However, due to poor preservation of index fossils and volcanic ash beds in many deep-water systems, deducing the timing of slope evolution has proven challenging. Here, we present >6600 new U-Pb zircon ages with stratigraphic information from an ∼100-km-long by ∼2.5-km-thick outcrop belt to elucidate evolutionary timing for a Campanian−Maastrichtian slope succession in the Magallanes Basin, Chile. Results show that the succession consists of four stratigraphic intervals, which characterize four evolutionary phases of the slope system. Overall, the succession records 9.9 ± 1.4 m.y. (80.5 ± 0.3 Ma to 70.6 ± 1.5 Ma) of graded clinoform development punctuated by out-of-grade periods distinguished by enhanced coarse-grained sediment bypass downslope. Synthesis of our results with geochronologic, structural, and stratigraphic data from the basin suggests that slope evolution was largely controlled by an overall decline in basin subsidence from 82 to 74 Ma. In addition to providing insight into slope evolution, our results show that the reliability of zircon-derived depositional duration estimates for ancient sedimentary systems is controlled by: (1) the proportion of syndepositionally formed zircon in a stratigraphic interval; (2) the magnitude of the uncertainty on interval-bounding depositional ages relative to the length of time evaluated; and (3) the geologic time (i.e., period/era) over which the system was active.
Previous research demonstrates that large basins on the periphery of the northern edge of the Tibetan Plateau were partitioned during development of intra-basin mountain ranges. These topographic barriers segregated basins with respect to surface flow and atmospheric circulation, ponded sediments, and formed rain shadows. However, complex mixing between airmasses and non-systematic isotope-elevation lapse rates have hampered application of quantitative paleoaltimetry to determine the timing of development of critical topographic barriers. We address the timing and drivers for changes in surface connectivity and atmospheric circulation in the Linxia and Xunhua basins using a multidisciplinary approach incorporating detrital zircon geochronology, Monte Carlo inverse flexural modeling, and published stable isotope data.
Despite recent advances in quantitative methods of detrital provenance analysis, there is currently no widely accepted method of unmixing detrital geochronology data. We developed a mixing model that determines mixing proportions for source samples through inverse Monte Carlo modeling, wherein mixed samples are compared to randomly generated combinations of source distributions, and a range of best mixing proportions are retained. Results may then be used to constrain a forward optimization routine to find a single best-fit mixture. Quantitative comparison is based on the Kolmogorov-Smirnov (KS) test D statistic and Kuiper test V statistic for cumulative distribution functions, and the Cross-correlation coefficient for finite mixture distributions (probability density plots or kernel density estimates). We demonstrate the capacity of this model through a series of tests on synthetic data sets and a published empirical data set from North America mixed in known proportions; this proof-of-concept testing shows the model is capable of accurately unmixing highly complex distributions. We apply the model to two published empirical data sets mixed in unknown proportions from Colombia and central China. Neither data set yields perfect model fits, which provides a cautionary note of potentially inadequate characterization of source and/or mixed samples, and highlights the importance of such characterization for accurate interpretation of sediment provenance. Data set size appears to be a major control on mixture model results; small (n < 100) detrital data sets may lead to misinterpretation of sediment provenance. The model is available as a MATLAB-based stand-alone executable (.exe file) graphical user interface.
South central Pyrenean foreland basin fill preserves the eroded remnants of the early stages of fold-thrust belt evolution and topographic growth. Specifically, the Eocene Hecho Group in the Ainsa Basin contains a succession of turbiditic channels and levees deposited in the transition zone between the fluvial-deltaic and deep marine depozones. Detailed isotopic provenance analyses allow for the reconstruction of sediment sources of the ancient sediment routing systems. This study presents 2332 new detrital zircon (DZ) U-Pb ages and 246 new DZ double dated (U-Th)/(He-Pb) ages from 19 turbiditic and fluvio-deltatic sandstones in the Ainsa Basin. These data indicate a progressive provenance shift from Cadomian/Caledonian plutonic and metamorphic rocks of the eastern Pyrenees to Variscan plutonic rocks in the central Pyrenees. Minor sediment contributions from sources located to the S and SE of the basin are seen throughout the section. New DZ (U-Th)/He results identify four main cooling events: Pyrenean orogenesis (~56 Ma), initial basin inversion (~80 Ma), Cretaceous rifting (~100 Ma), and pre-Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that high frequency fluctuations in sediment delivery processes and sediment routing introduces superimposed noise upon the basin scale long term provenance evolution during orogenesis.
The method of obtaining zircon samples affects estimation of the global U-Pb age distribution. Researchers typically collect zircons via convenience sampling and cluster sampling. When using these techniques, weight adjustments proportional to the areas of the sampled regions improve upon unweighted estimates. Here, grid-area and modern sediment methods are used to weight the samples from a new database of 418,967 U-Pb ages. Preliminary tests involve two age models. Model-1 uses the most precise U-Pb ages as the best ages. Model-2 uses the 206Pb/238U age as the best age if it is less than a 1000 Ma cutoff, otherwise it uses the 207Pb/206Pb age as the best age. A correlation analysis between the Model-1 and Model-2 ages indicates nearly identical distributions for both models. However, after applying acceptance criteria to include only the most precise analyses with minimal discordance, a histogram of the rejected samples shows excessive rejection of the Model-2 analyses around the 1000 Ma cutoff point. Because of the excessive rejection rate for Model-2, we select Model-1 as the preferred model. After eliminating all rejected samples, the remaining analyses use only Model-1 ages for five rock-type subsets of the database: igneous, meta-igneous, sedimentary, meta-sedimentary, and modern sediments. Next, time-series plots, cross-correlation analyses, and spectral analyses determine the degree of alignment among the time-series and their periodicity. For all rock types, the U-Pb age distributions are similar for ages older than 500 Ma, but align poorly for ages younger than 500 Ma. The similarities (>500 Ma) and differences (
Resolving the role of longitudinal versus transverse sediment dispersal in ancient sedimentary basins is paramount for understanding filling history and the timing of source area exhumation. The southern Patagonian Andes provide a unique opportunity for constraining these relationships because Upper Cretaceous shallow- and deep-marine strata that record the longitudinal filling history of the Magallanes-Austral foreland basin are exposed along a 500+ km outcrop belt. New stratigraphic, sedimentologic, and facies analyses of the Cenomanian-aged Lago Viedma Formation indicate a protracted phase of a dominantly shoreface and foreshore depositional setting at the northern end of the basin (Austral basin sector), whereas 200 km to the south, age-equivalent strata of the Punta Barrosa Formation are characterized by southward-flowing deep-water fan systems. New sandstone compositional data from both formations are rich in intermediate volcanic grains and suggest an un-dissected to transitional volcanic arc source. However, detrital zircon populations from the shallow-marine Lago Viedma Formation are dominated by arc sources (126-75 Ma), whereas deep-water strata of the Punta Barrosa Formation contain much greater abundances of Jurassic (199-161 Ma) and pre Jurassic (>200 Ma) ages. This indicates that deep-water fan systems were not linked to a shelfal sediment dispersal system by a simple northward point-source model, despite consistent southward-directed paleocurrents in deep-water strata. Time-transgressive provenance variations continue southward (along strike), where lithostratigraphic equivalents in the Ultima Esperanza and Fuegian sectors of the basin contain a mix of arc and pre Jurassic metamorphic basement sources and a paucity of Jurassic ages. We interpret these along-strike provenance variations to be the result of significant local sediment contributions from transverse sources. The influence of transverse tributaries during the early history of the Magallanes-Austral foreland basin suggests that the diachronous onset of coarse clastic deposition in the basin was likely due to the progressive delivery (and initiation) of more locally derived coarse clastic sediment. We attribute this to southward-progressing thrust-belt development associated with progressive north to south collision (or suturing) of the parautochthonous Patagonian arc with attenuated continental crust of South America.
The ability to quantify the (dis)similarity between detrital age distributions is an essential aspect of sedimentary provenance studies. This paper reviews three different ways to do this. A first class of dissimilarity measures is based on parametric hypothesis tests such as the t- or chi-square test. These are designed to objectively decide whether two samples were derived from a common population. Appealing though such tests may appear in theory, in practice they offer limited value to sedimentary geologists because their outcome depends on sample size. In contrast, the effect size of said tests is independent of sample size and can be used as an objective point of comparison between detrital age distributions. The main limitation of this approach is that it requires binning or averaging, which discards valuable information. A second class of dissimilarity measures is based on non-parametric hypothesis tests such as the Kolmogorov-Smirnov test. These do not require pre-treatment of the data and are able to capture more subtle differences between age distributions. Unfortunately, non-parametric tests do not have well defined sample effect sizes and so it is not possible to use them as an absolute point of comparison that is independent of sample size. Nevertheless, non-parametric dissimilarity measures can be used to quantify the relative differences between samples. A third class of dissimilarity measures aims to account for the analytical uncertainties of the age determinations. The likeness and cross-correlation coefficients are ad-hoc dissimilarity measures that are based on Probability Density Plots (PDPs). These apply a narrow smoothing kernel to precise data, and a wide smoothing kernel to imprecise data. In contrast, the Sircombe-Hazelton L2-norm uses Kernel Functional Estimates (KFEs), which use exactly the opposite strategy as PDPs. They apply a wide smoothing kernel to precise data, and a narrow smoothing kernel to imprecise data. This paper shows that the KFE-based approach produces sensible results, whereas the likeness and cross-correlation methods do not. The added complexity of the KFE approach is only worth the effort in studies that combine data acquired on equipment with hugely variable analytical precision. In most cases, there is no need to account for the analytical uncertainty of detrital age distributions. The sample effect size, non-parametric statistics, or L2-norm can be used to graphically compare samples by Multidimensional Scaling (MDS). In contrast with previous claims, there is no need for these measures to be independent of sample size for this purpose.
Sediment mixing within sediment routing systems can exert a strong influence on the preservation of provenance signals that yield insight into the effect of environmental forcing (e.g., tectonism, climate) on the Earth's surface. Here, we discuss two approaches to unmixing detrital geochronologic data in an effort to characterize complex changes in the sedimentary record. First, we summarize ‘top-down’ mixing, which has been successfully employed in the past to characterize the different fractions of prescribed source distributions (‘parents’) that characterize a derived sample or set of samples (‘daughters’). Second, we propose the use of ‘bottom-up’ methods, previously used primarily for grain size distributions, to model parent distributions and the abundances of these parents within a set of daughters. We demonstrate the utility of both top-down and bottom-up approaches to unmixing detrital geochronologic data within a well-constrained sediment routing system in central California. Use of a variety of goodness-of-fit metrics in top-down modeling reveals the importance of considering the range of allowable that is well mixed over any single best-fit mixture calculation. Bottom-up modeling of 12 daughter samples from beaches and submarine canyons yields modeled parent distributions that are remarkably similar to those expected from the geologic context of the sediment-routing system. In general, mixture modeling has the potential to supplement more widely applied approaches in comparing detrital geochronologic data by casting differences between samples as differing proportions of geologically meaningful end-member provenance categories.
Continental-scale drainages host the world's largest rivers and offshore sediment accumulations, many of which contain significant petroleum reserves. Rate of sediment supply in these settings may be a signal of external controls (e.g., tectonics) on landscape evolution, yet deciphering these controls remains a major challenge in interpreting the ancient stratigraphic record. Integration of new and published detrital zircon U-Pb ages from the United States Rocky Mountain region and Gulf of Mexico (GOM) sedimentary basin demonstrates profound changes in the U.S. continental drainage divide that controlled the rate of sediment delivery to the northern GOM during Paleocene-Eocene time. Sedimentation rate increased dramatically during deposition of the lower Wilcox Group, reaching approximately three times the Cenozoic average, accompanied by pronounced shoreline regression and delivery of a large volume of sand to the basin floor. We hypothesize that this increase in sediment delivery to the GOM resulted from drainage capture of a significant portion of the Sevier-Laramide structural province (~900,000 km2) that included the headwaters of the California and Idaho Rivers. Capture of the California River drainage may have occurred in the vicinity of the Hanna Basin of eastern Wyoming that previously emptied northward into a shallow seaway, but was subsequently diverted southward to the Rockdale delta, which accumulated within the Houston embayment during the time of deposition of the lower Wilcox Group. Detrital zircon U-Pb ages from Wilcox samples within the Rockdale delta show a remarkable similarity with contemporaneous Laramide synorogenic units, including enrichment in detritus derived from the Cordilleran arc and basement terranes of western North America relative to older and younger units in the Houston embayment. A subsequent order of magnitude decline in sedimentation rate to the GOM can be partly attributed to well-documented drainage closure (~800,000 km2) that accompanied lake formation in interior Laramide basins (ca. 53-51.8 Ma). Our results demonstrate that tectonically induced drainage migration in the high-relief segments of continental-scale drainages can have a pronounced effect on the rate of sediment transfer to continental margins.