Detrital zircon U-Pb studies of mudstone provenance are rare but may preferentially fingerprint distal zircon sources. To examine this issue, Pierre Shale and Trinidad Sandstone deposited in a Late Cretaceous deltaic environment in the Raton Basin, Colorado (USA), were measured for detrital zircon U-Pb age by laser ablation–inductively coupled plasma–mass spectrometry. Two major detrital zircon age peaks at ca. 70 and 1690 Ma are found in both Pierre Shale and Trinidad Sandstone but in inversely varying proportions: 68% and 16%, respectively, for the finest zircon fraction (~15–35 μm) in the shale, and 25% and 32%, respectively, for the coarsest zircon fraction (~60–80 μm) in the sandstone. Proximal sources in the Sangre de Cristo Mountains, directly west of the Raton Basin, contain coarse-grained, ca. 1690 Ma zircon, whereas distal sources in Laramide uplifts and basins in Colorado, New Mexico, and Arizona contain fine-grained, ca. 70 Ma zircon. The results indicate that U-Pb zircon provenance of mudstone reflects availability of volcanic and other fine-grained source rocks rather than simply distal sources. U-Pb zircon provenance studies should routinely include mudstone units because these units may identify fine-grained zircon sources more reliably than sandstones alone.Uranium-lead (U-Pb) detrital zircon geochronology of clastic sedimentary rocks is a critical tool for sedimentary provenance, definition of paleo-drainage routes, and reconstructions of paleogeography through time (Košler et al., 2002). Most studies have focused on sandstones and quartzites, which are typically enriched in sand-sized zircon grains separated routinely from less-dense minerals by heavy-liquid concentration, mounted in epoxy, and dated in moderate to large numbers (n = 100–1000) by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) or secondary ionization mass spectrometry (SIMS).In contrast, mudstone and its metamorphic equivalents, which make up two-thirds of the sedimentary rock record (Schieber et al., 1998), have been dated only rarely by U-Pb detrital geochronology (e.g., Sláma and Pedersen, 2015; Leary et al., 2020). This is because mudstone commonly contains silt-sized detrital zircon grains (Totten and Hanan, 2007) that can be difficult to separate from clay mineral–rich rock matrices using heavy liquids (Hoke et al., 2014). Also, such tiny grains require very small (≤20 μm) laser or ion beam spots for U-Pb analysis by LA-ICP-MS or SIMS and, for LA-ICP-MS, short signal integration times (e.g., 10–15 s of ablation at 5 Hz; Mukherjee et al., 2019) to limit variable sample-to-sample Pb/U downhole fractionation.More fundamentally, the significance and value of U-Pb detrital zircon geochronology of mudstone relative to sandstone from the same deposit is not clear. Sláma and Pedersen (2015) reported that U-Pb ages for fine-grained detrital zircon from metamorphosed siltstone and mudstone of the Caledonides in southern Norway were derived from far-traveled (~2000 km) distal sources and thus complement the record of coarser detrital zircon from associated sandstone, which reflects the U-Pb zircon age profile of local sources. However, Leary et al. (2020) found that only some mudstone units in the late Paleozoic Paradox and Eagle Basins, southwestern USA, contained substantial populations of fine-grained zircon derived by long-distance transport from the Grenville and Appalachian orogens.To examine controls on distal and proximal zircon sampling of mudstone and sandstone, we compared the U-Pb detrital zircon geochronology of Pierre Shale and facies-equivalent Trinidad Sandstone in the Raton Basin, south-central Colorado, USA (Fig. 1). A Late Cretaceous fluvial system delivered clastic detritus predominantly from the west, forming the units in a deltaic facies environment (Billingsley, 1977; Cather, 2004). Contribution of Laramide-arc detritus by ash fall is also possible (Bush et al., 2016; Schwartz et al., 2021).The study area is a railroad cut near Trinidad Lake reservoir, 3.7 km southwest of Trinidad, Colorado (37°08′40.1″N, 104°32′21.5″W) (Fig. 1), exposing the upper prodelta facies of Pierre Shale and delta-front facies of Trinidad Sandstone (Flores, 1987). A sample of each of the uppermost Pierre Shale and overlying lowermost Trinidad Sandstone was collected from a 3 m vertical section of interbedded mudstone and sandstone. The top of Pierre Shale in the Trinidad area corresponds with the lower Maastrichtian Baculites clinolobatus ammonite zone (69.59 ± 0.36 Ma) (Berry, 2018).The Trinidad Sandstone sample is a fine-grained subarkosic sandstone composed of very fine sand (63–125 μm) and coarse silt (20–63 μm) grains, whereas the Pierre Shale sample is a silty mudstone made up by coarse silt and finer grains. Three grain mounts were made from heavy-liquid concentrates of coarser (63–125 μm) and finer (20–63 μm) sieve fractions of crushed samples of Trinidad Sandstone, referred to as TSC (C—coarse) and TSF (F—fine), respectively, and the 20–63 μm fraction of Pierre Shale, referred to as PSM (M—grain mount). Also, three polished thin sections (TS) were made from mudstone-rich layers in Pierre Shale, with U-Pb zircon analyses from all three sections pooled to a single sample referred to as PSTS. The pooled thin-section sample was used to date zircons associated with the finest fraction of shale and compare in situ shapes of zircon with those in the grain mounts. Mud-rich layers are not present in Trinidad Sandstone thin sections.Scanning electron microscopy (SEM) with backscattered electron (BSE) imaging guided spot placement within zircon grains for laser ablation (using 20 μm and 12 μm spots in grain mounts and thin sections, respectively) and provided measurements of grain dimensions and definition of grain morphologies. Experimental procedures and metadata for SEM imaging and LA-ICP-MS U-Pb zircon ages are given in Table S1 of the Supplemental Material1.LA-ICP-MS U-Pb age results for sample and reference zircons are listed in Tables S2–S7 and plotted on concordia diagrams in Figures S2–S4 in the Supplemental Material. Typical precision on individual 206Pb/238U dates for both 20 μm and 12 μm spots for Paleozoic zircons (Plešovice and Temora-2) is ~2%. U-Pb detrital zircon age histogram–kernel density estimation plots for Pierre Shale (PSTS, PSM) and Trinidad Sandstone (TSF, TSC) samples are shown in Figure 2A. Two major age peaks at ca. 70 Ma and 1690 Ma are found in all four samples but in inversely varying proportions (Fig. 2B). The ca. 70 Ma peak decreases progressively in abundance from 68% and 43% for Pierre Shale samples PSTS and PSM, respectively, to 37% and 25% for Trinidad Sandstone samples TSF and TSC, respectively. In contrast, the ca. 1690 Ma peak increases progressively in abundance from 16% and 25% for PSTS and PSM, respectively, to 25% and 32% for TSF and TSC, respectively. An older ca. 1740 Ma peak is present in Trinidad Sandstone (16% for TSF and 14% for TSC) but absent from Pierre Shale (Fig. 2B). Two other significant but subordinate peaks are found in all four samples but without systematic differences between Pierre and Trinidad varieties: ca. 160 Ma peak (6%–14%) and ca. 1410 Ma peak (2%–8%).Four types of zircon grain morphologies (Fig. 3) are present in Pierre Shale and Trinidad Sandstone samples: complete, euhedral grain sections with discrete oscillatory zoning (type 1); complete or nearly complete, subhedral grain sections, commonly fractured, with diffuse oscillatory to patchy zoning (type 2); grain sections with irregular, embayed crystal faces (type 3); and crystal fragments (type 4). Additional BSE images of various types of zircons in the two dominant ca. 70 Ma and 1690 Ma age populations are given in Figure S1.Type 2 and 4 zircons are dominant in all samples. At least for the Pierre Shale thin sections, fracturing in type 2 and grain breakage in type 4 zircons are not the result of laboratory crushing. Textures and zoning of type 1, 2, and 3 grains indicate derivation from magmatic source rocks. Euhedral shapes of type 1 grains imply early crystallization free from competing mineral growth (e.g., in rapidly quenched ash-fall tuffs). Embayed textures of type 3 grains suggest late crystallization interstitial to adjacent minerals. Type 1 and 3 grains are absent from the ca. 1690 Ma zircon age population.The Th/U ratios of 71 ± 3 Ma zircon tend to be greater in Pierre Shale compared to Trinidad Sandstone. Mean ratios for PSTS and PSM are 1.01 ± 0.08 (n = 21) and 0.95 ± 0.13 (n = 13), respectively, with 12/34 or 35% with Th/U ≥1.2. In contrast, mean values for TSF and TSC are 0.66 ± 0.10 (n = 14) and 0.71 ± 0.08 (n = 12), respectively, with only 1/26 or 4% with Th/U ≥1.2 (Fig. 4A). Zircon with Th/U ≥1 is more typical of crystallization in basic to intermediate than acidic magmatic rocks (Wang et al., 2011; Kirkland et al., 2015). Th/U ratios of 1690 ± 15 Ma zircon tend to be low for both Pierre and Trinidad samples: 0.65 ± 0.12 (n = 14) for PSTS; 0.63 ± 0.08 (n = 22) for PSM; 0.52 ± 0.06 (n = 23) for TSF; and 0.70 ± 0.05 (n = 26) for TSC (Fig. S5).Proximal sources of ca. 1740, 1690, 1410, and 160 Ma detrital zircons of the Pierre-Trinidad sedimentary system are exposed presently in the Sangre de Cristo Mountains along the western margin of the Raton Basin but in the Late Cretaceous may have been exposed farther west in the San Luis Uplift, a broad Laramide highland, exposed today as a valley (Cather, 2004) (Fig. 1). Jones and Connelly (2006) reported U-Pb zircon ages for 1695–1682 Ma post-orogenic plutons, ca. 1700 Ma quartzite, a suite of 1750–1730 Ma calc-alkaline intrusions, and 1434–1407 Ma granites in Sangre de Cristo crystalline basement (Fig. 2C). Siliciclastic cover units in the Sangre de Cristo Mountains could also be proximal zircon sources for Pierre Shale and Trinidad Sandstone. Bush et al. (2016) found that the Pennsylvanian–Permian Sangre de Cristo Formation has major detrital zircon U-Pb ages peaks at ca. 1720 and 1680 Ma, whereas the Cretaceous Dakota Formation has a major detrital zircon peak at ca. 160 Ma (Fig. 2C).Sources of ca. 70 Ma detrital zircons of Pierre Shale–Trinidad Sandstone are found only in more distal terranes (Fig. 1) with Cretaceous volcanic rocks, hypabyssal intrusions, and sedimentary units exposed in basement-cored uplifts and basins related to Laramide arc magmatism (Seedorff et al., 2019). In southwestern New Mexico, felsic ash-fall tuffs with U-Pb zircon ages of 75–70 Ma are present in Love Ranch Basin (Amato et al., 2017) and Ringbone Basin (Clinkscales and Lawton, 2015) (Fig. 2D). A dacite sill and monzonite porphyry in the Burro Mountains have U-Pb zircon ages of ca. 75 Ma (Amato et al., 2017). Cretaceous Ringbone Formation contains a major U-Pb detrital zircon age peak at 73 Ma (Clinkscales and Lawton, 2015) (Fig. 2D). Volcanic and hypabyssal rocks with 75–70 Ma U-Pb zircon ages are present farther west in Arizona (Mizer, 2018; Seedorff et al., 2019) (Fig. 1).In the Colorado Mineral Belt (Fig. 1), U-Pb zircon ages are 73 Ma for the diorite of Sleeping Ute Mountain, 70 Ma for the diorite of La Plata Mountains, 68 Ma for the granodiorite-diorite porphyry of Hermosa Peak, and 69–65 Ma for the granite-diorite porphyry of Coal Bank Pass (Gonzales, 2015) (Fig. 2D). In the San Juan Basin, the upper Campanian Kirtland Formation, a fluvial sandstone, and the overlying basal McDermott Formation, a trachyandesite debris flow (Wegert and Parker, 2011), have major U-Pb detrital zircon age peaks of 75 and 70 Ma, respectively (Pecha et al., 2018) (Fig. 2D).Zircon from the trachyandesite of the McDermott Formation have unusually high Th/U ratios (as high as 3) compared to those of zircons measured in other Laramide sources of ca. 70 Ma detrital zircons such as the Kirtland Formation sandstone, Ringbone Formation, and felsic ash-fall tuffs of southwestern New Mexico, which are mostly <1 (Fig. 4B). Elevated Th/U ratios in ca. 70 Ma detrital zircon population of Pierre Shale are consistent with sampling a significant component of basic to intermediate sources of zircon like those in the McDermott Formation.The ca. 1740, 1690, 1410, and 160 Ma zircon age peaks of the Pierre-Trinidad sedimentary system are also found in distal Proterozoic crystalline basement rocks and Cretaceous magmatic and sedimentary units in Laramide uplifts and basins (Fig. 2D) as well as in proximal sources described above. In the Burro Mountains of southwestern New Mexico, amphibolite and rapakivi granite have U-Pb zircon ages of 1684 Ma (Amato et al., 2011) and 1461 Ma (Rämö et al., 2003), respectively. Inherited grains in ash-fall tuff in the Little Hatchet Mountains of southwestern New Mexico have a mean U-Pb zircon age of 163 Ma (n = 6) (Clinkscales and Lawton, 2015). In the Needle Mountains of southwestern Colorado, U-Pb zircon ages are 1772–1754 Ma for the Twilight Gneiss and 1698–1695 Ma for the Bakers Bridge Granite (Gonzales and Van Schmus, 2007). Among Cretaceous sedimentary units, the Ringbone Formation contains U-Pb detrital zircon age peaks of 1700 and 165 Ma (Clinkscales and Lawton, 2015), Kirtland Formation has peaks of 1700, 1430, and 170 Ma, and basal McDermott Formation has peaks of 1690, 1410, and 165 Ma (Pecha et al., 2018). Thus, it is probable that both proximal and distal sources contributed to ca. 1740, 1690, 1410, and 160 Ma zircon age peaks of the Pierre-Trinidad delta.Late Cretaceous (ca. 70 Ma) distal magmatic activity associated with the Laramide arc in southwestern New Mexico and Arizona and with the Colorado Mineral Belt was a major source of detrital zircon for both Pierre Shale and Trinidad Sandstone of the Raton Basin but relatively more so for the shale. The presence of substantial basic to intermediate rocks, which tend to be zircon poor relative to felsic sources (Keller et al., 2017), in the Laramide source region are more clearly identified by the elevated Th/U ratios of the Late Cretaceous detrital zircon population of Pierre Shale than Trinidad Sandstone samples.Fluvial transport of distal, fine-grained detritus derived from Laramide volcanic and hypabyssal intrusive rocks, possibly in concert with Laramide ash-fall volcanism, enhanced eastward delivery of zircon silt to the Raton Basin and incorporation in Pierre Shale. Zircon grain size may have been reduced further by crystal breakage (morphology type 4; Fig. 3) during Laramide faulting of the source rocks. Grain fragmentation is more likely caused by deformational events at the weathering site prior to transport, which simply tends to abrade and chip grains to rounded shapes (Novák-Szabó et al., 2018). The zircon silt, mostly <45 μm, was capable of substantial long-distance transport in the suspended loads of fluvial (Milliman and Meade, 1983) and aerial volcanic systems (Stevenson et al., 2015). In contrast, older, mostly Proterozoic zircon sources for Pierre Shale–Trinidad Sandstone were typically deeper-level intrusions and gneisses (or sedimentary units derived from them) that crystallized a large fraction of coarser grains in both distal and proximal rocks and preferentially formed the detritus supply of the Trinidad Sandstone.The broader significance and implications of our results are that U-Pb zircon provenance of mudstone reflects availability of volcanic and other fine-grained source rocks rather than simply distal sources. Mudstones will not record distal sources dominated by coarse-grained source rocks, as shown by the results of Leary et al. (2020). U-Pb zircon provenance studies should routinely include mudstone because it may identify zircon derived from fine-grained source rocks more clearly than associated sandstones. This extends earlier studies that reported biases in detrital zircon populations in sandstones as a function of grain size (e.g., Ibañez-Mejia et al., 2018) and facies (e.g., Anders et al., 2021). Future studies should explore controls on zircon populations in mudstone-sandstone pairs of depositional settings beyond the fluvially influenced delta studied here.We thank Geology editor Marc Norman, reviewers David Chew and Jaime Toro, an anonymous journal reviewer, and U.S. Geological Survey reviewer Marieke Dechesne for helpful comments. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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U-Pb碎屑锆石年代学对泥岩物源的意义

泥岩物源的碎屑锆石 U-Pb 研究很少见，但可能优先识别远端锆石来源。为了研究这个问题，美国科罗拉多州拉顿盆地晚白垩世三角洲环境中沉积的 Pierre 页岩和特立尼达砂岩通过激光烧蚀电感耦合等离子体质谱法测量了碎屑锆石 U-Pb 年龄。两个主要的碎屑锆石年龄峰值在 ca。在 Pierre 页岩和特立尼达砂岩中都发现了 70 Ma 和 1690 Ma，但比例相反：分别为 68% 和 16%，页岩中最细的锆石部分（~15-35 μm），25% 和 32%，分别为砂岩中最粗的锆石部分（~60-80 μm）。位于拉顿盆地以西的 Sangre de Cristo 山脉的近源含粗粒，约 1690马锆石，而科罗拉多、新墨西哥和亚利桑那州拉拉米隆隆起和盆地的远端源含有细粒，约 70 Ma 锆石。结果表明，泥岩的 U-Pb 锆石物源反映了火山岩和其他细粒烃源岩的可用性，而不仅仅是远端烃源岩。U-Pb 锆石物源研究通常应包括泥岩单元，因为这些单元比单独砂岩更可靠地识别细粒锆石来源。碎屑沉积岩的铀铅 (U-Pb) 碎屑锆石年代学是沉积物源的关键工具，古排水路线的定义和古地理的重建（Košler et al., 2002）。大多数研究都集中在砂岩和石英岩上，它们通常富含沙粒大小的锆石颗粒，通常通过重液浓缩从密度较低的矿物中分离出来，安装在环氧树脂中，并通过激光烧蚀 - 电感耦合等离子体 - 质量测定中到大量（n = 100-1000）质谱法 (LA-ICP-MS) 或二次电离质谱法 (SIMS)。相比之下，占沉积岩记录三分之二的泥岩及其变质等效物 (Schieber et al., 1998) 只有很少通过 U-Pb 碎屑地质年代学（例如，Sláma 和 Pedersen，2015 年；Leary 等人，2020 年）。这是因为泥岩通常含有粉砂大小的锆石碎屑颗粒（Totten 和 Hanan，2007 年），使用重液很难从富含粘土矿物的岩石基质中分离出来（Hoke 等人，2014 年）。还，对于 LA-ICP-MS 或 SIMS 的 U-Pb 分析，如此微小的晶粒需要非常小的 (≤20 μm) 激光或离子束点，对于 LA-ICP-MS，信号积分时间短（例如，10-15 s 5 Hz 的烧蚀；Mukherjee et al., 2019) 以限制可变的样品间 Pb/U 井下分馏。更根本的是，泥岩相对于同一矿床砂岩的 U-Pb 碎屑锆石地质年代学意义和价值是不清楚。Sláma 和 Pedersen（2015 年）报告说，来自挪威南部 Caledonides 变质粉砂岩和泥岩的细粒碎屑锆石的 U-Pb 年龄来自远距离（约 2000 公里）的远端来源，因此补充了粗碎屑的记录来自伴生砂岩的锆石，它反映了当地来源的 U-Pb 锆石年龄分布。然而，Leary 等人。（2020）发现，在美国西南部的晚古生代悖论盆地和鹰盆地中，只有一些泥岩单元含有大量细粒锆石，这些锆石是从格伦维尔和阿巴拉契亚造山带的长距离运输中产生的。检查对远端和近端锆石的控制通过泥岩和砂岩取样，我们比较了美国科罗拉多州中南部拉顿盆地的皮埃尔页岩和相等效的特立尼达砂岩的 U-Pb 碎屑锆石年代学（图 1）。晚白垩世河流系统主要从西部输送碎屑碎屑，形成三角洲相环境中的单元（Billingsley，1977；Cather，2004）。灰烬落下对拉拉胺弧碎屑的贡献也是可能的（Bush 等人，2016 年；Schwartz 等人，2021 年）。研究区域是特立尼达湖水库附近的铁路切口，3。科罗拉多州特立尼达西南 7 公里处（37°08′40.1″N，104°32′21.5″W）（图 1），出露 Pierre 页岩的上前三角洲相和特立尼达砂岩的三角洲前缘相（弗洛雷斯，1987 ）。最上层 Pierre 页岩和上层最下层特立尼达砂岩的样品是从 3 m 的互层泥岩和砂岩垂直剖面中采集的。特立尼达地区皮埃尔页岩顶部对应于下马斯特里赫特 Baculites clinolobatus 菊石带 (69.59 ± 0.36 Ma) (Berry, 2018)。特立尼达砂岩样品是由极细砂 (63-125 μm) 和粗粉砂 (20–63 μm) 颗粒，而 Pierre 页岩样品是由粗粉砂和细颗粒组成的粉质泥岩。三种颗粒样品由特立尼达砂岩粉碎样品的较粗（63-125 μm）和较细（20-63 μm）筛分的重液浓缩物制成，称为 TSC（C-粗）和 TSF（F-细） )，以及 20-63 μm 的 Pierre 页岩部分，称为 PSM (M-grain mount)。此外，三个抛光薄片 (TS) 由 Pierre 页岩中富含泥岩的层制成，将所有三个切片的 U-Pb 锆石分析汇总到一个称为 PSTS 的样品中。汇集的薄片样品用于对与最细部分页岩相关的锆石进行测年，并将锆石的原位形状与晶粒支架中的锆石形状进行比较。特立尼达砂岩薄片中不存在富泥层。扫描电子显微镜 (SEM) 和背散射电子 (BSE) 成像引导在锆石晶粒内放置激光烧蚀光斑（分别在晶粒底座和薄片中使用 20 μm 和 12 μm 光斑），并提供晶粒尺寸测量和晶粒形态定义. SEM 成像和 LA-ICP-MS U-Pb 锆石年龄的实验程序和元数据在补充材料 1 的表 S1 中给出。样品和参考锆石的 LA-ICP-MS U-Pb 年龄结果在表 S2-S7 中列出并绘制在补充材料中图 S2-S4 的协和图上。古生代锆石（Plešovice 和 Temora-2）的 20 μm 和 12 μm 点的单个 206Pb/238U 测年的典型精度约为 2%。Pierre 页岩 (PSTS, PSM) 和特立尼达砂岩 (TSF, TSC) 样品如图 2A 所示。两个主要的年龄高峰在 ca。在所有四个样品中都发现了 70 Ma 和 1690 Ma，但比例相反（图 2B）。约。70 Ma 峰的丰度从 Pierre 页岩样品 PSTS 和 PSM 的分别为 68% 和 43% 逐渐减少到特立尼达砂岩样品 TSF 和 TSC 的分别为 37% 和 25%。相比之下，约。1690 Ma 峰的丰度从 PSTS 和 PSM 分别为 16% 和 25% 逐渐增加到 TSF 和 TSC 分别为 25% 和 32%。年龄较大的约。特立尼达砂岩中存在 1740 Ma 峰（TSF 为 16%，TSC 为 14%），但 Pierre 页岩中不存在（图 2B）。在所有四个样品中都发现了另外两个重要但次要的峰，但皮埃尔和特立尼达品种之间没有系统差异：约。160 Ma 峰值 (6%–14%) 和 ca。1410 Ma 峰（2%~8%）。 Pierre 页岩和特立尼达砂岩样品中存在 4 种类型的锆石颗粒形态（图 3）：完整的、具有离散振荡分带的自形颗粒截面（1 型）；完整或接近完整的半自形颗粒截面，通常断裂，具有弥散的振荡到斑片状分区（类型 2）；具有不规则凹凸晶面的晶粒截面（3 型）；和晶体碎片（4型）。两个主要的 ca 中各种类型的锆石的附加 BSE 图像。图 S1 给出了 70 Ma 和 1690 Ma 年龄种群。2 型和 4 型锆石在所有样品中占主导地位。至少对于 Pierre 页岩薄片而言，2 型压裂和 4 型锆石的晶粒破碎并不是实验室破碎的结果。类型 1、2 的纹理和分区，3 粒表示来源于岩浆烃源岩。1 型晶粒的自面体形状意味着早期结晶没有相互竞争的矿物生长（例如，在快速淬火的落灰凝灰岩中）。3 型晶粒的浮雕纹理表明晚期结晶间隙与相邻矿物。ca 中没有 1 型和 3 型谷物。1690 Ma 锆石年龄人口。与特立尼达砂岩相比，Pierre 页岩中 71 ± 3 Ma 锆石的 Th/U 比往往更大。PSTS 和 PSM 的平均比率分别为 1.01 ± 0.08 (n = 21) 和 0.95 ± 0.13 (n = 13)，Th/U ≥1.2 时为 12/34 或 35%。相比之下，TSF 和 TSC 的平均值分别为 0.66 ± 0.10 (n = 14) 和 0.71 ± 0.08 (n = 12)，Th/U ≥1.2 时只有 1/26 或 4%（图 4A）。与酸性岩浆岩相比，Th/U≥1 的锆石在基性至中性岩浆岩中更典型地结晶（Wang et al., 2011; Kirkland et al., 2015）。对于 Pierre 和 Trinidad 样品，1690 ± 15 Ma 锆石的 Th/U 比率往往较低：PSTS 为 0.65 ± 0.12 (n = 14)；PSM 为 0.63 ± 0.08 (n = 22)；TSF 为 0.52 ± 0.06 (n = 23)；TSC 为 0.70 ± 0.05（n = 26）（图 S5）。Pierre-Trinidad 沉积系统的 1740、1690、1410 和 160 Ma 碎屑锆石目前在拉顿盆地西缘的 Sangre de Cristo 山脉中出露，但在晚白垩世，可能在更西端的 San Luis 出露隆起，一个广阔的拉拉米高地，今天暴露为一个山谷（Cather，2004）（图1）。Jones 和 Connelly (2006) 报道了 1695-1682 Ma 造山后岩体的 U-Pb 锆石年龄，大约 Sangre de Cristo 结晶基底中的 1700 Ma 石英岩、一套 1750-1730 Ma 钙碱性侵入体和 1434-1407 Ma 花岗岩（图 2C）。Sangre de Cristo 山脉的硅质碎屑覆盖单元也可能是 Pierre 页岩和特立尼达砂岩的近端锆石来源。布什等人。(2016) 发现宾夕法尼亚-二叠纪 Sangre de Cristo 组的主要碎屑锆石 U-Pb 年龄峰值在 ca。1720 年和 1680 年 Ma，而白垩纪 Dakota 组有一个主要的碎屑锆石峰在 ca。160 Ma（图 2C）。皮埃尔页岩-特立尼达砂岩的 70 Ma 碎屑锆石仅在更远的地体中发现（图 1），白垩纪火山岩、浅海侵入体和沉积单元暴露在与拉拉米弧岩浆作用相关的基底取心隆起和盆地中（Seedorff 等人., 2019)。在新墨西哥州西南部，Love Ranch 盆地（Amato 等，2017）和 Ringbone 盆地（Clinkscales 和 Lawton，2015）（图 2D）中存在 U-Pb 锆石年龄为 75-70 Ma 的长英质灰凝灰岩。 . Burro 山脉的英安岩基台和二长斑岩的 U-Pb 锆石年龄约为 75 Ma（Amato 等人，2017 年）。白垩纪环骨组在 73 Ma 处有一个主要的 U-Pb 碎屑锆石年龄峰（Clinkscales 和 Lawton，2015）（图 2D）。在亚利桑那州西部更远的地方存在具有 75-70 Ma U-Pb 锆石年龄的火山岩和浅海底岩（Mizer，2018；Seedorff 等，2019）（图 1）。在科罗拉多矿带（图 1）中，U -Pb 锆石年龄为 Sleeping Ute Mountain 闪长岩 73 Ma，La Plata Mountains 闪长岩 70 Ma，Hermosa Peak 花岗闪长-闪长斑岩 68 Ma，和 69-65 Ma 为 Coal Bank Pass 的花岗闪长斑岩（Gonzales，2015）（图 2D）。在圣胡安盆地，Campanian Kirtland 组上层是河流砂岩，上覆的基底 McDermott 组是粗安岩泥石流（Wegert 和 Parker，2011 年），U-Pb 碎屑锆石年龄峰值分别为 75 和 70 Ma，分别（Pecha 等人，2018 年）（图 2D）。与在 ca 的其他 Laramide 来源中测量的锆石相比，来自 McDermott 组粗面安山岩的锆石具有异常高的 Th/U 比（高达 3）。70 Ma碎屑锆石，如新墨西哥州西南部的Kirtland组砂岩、Ringbone组和长英质灰凝灰岩，大多<1（图4B）。ca 升高的 Th/U 比率。皮埃尔页岩的 70 Ma 碎屑锆石群与对像 McDermott 组中的锆石基本到中间源的重要组成部分进行采样是一致的。Pierre-Trinidad 沉积系统的 1740、1690、1410 和 160 Ma 锆石年龄峰也在拉拉米隆隆起和盆地的远古宙结晶基底岩和白垩纪岩浆和沉积单元中发现（图 2D）以及近源如上所述。在新墨西哥州西南部的 Burro 山脉，角闪岩和 rapakivi 花岗岩的 U-Pb 锆石年龄分别为 1684 Ma (Amato et al., 2011) 和 1461 Ma (Rämö et al., 2003)。新墨西哥州西南部小哈切特山脉的灰落凝灰岩中的继承颗粒具有 163 Ma 的平均 U-Pb 锆石年龄（n = 6）（Clinkscales 和 Lawton，2015 年）。在科罗拉多州西南部的针状山脉，暮光片麻岩的 U-Pb 锆石年龄为 1772-1754 Ma，贝克斯桥花岗岩的年龄为 1698-1695 Ma（Gonzales 和 Van Schmus，2007）。白垩纪沉积单元中，Ringbone 组的 U-Pb 碎屑锆石年龄峰值分别为 1700 和 165 Ma（Clinkscales 和 Lawton，2015），Kirtland 组的峰值分别为 1700、1430 和 170 Ma，基底 McDermott 组的峰值年龄分别为 1690 Ma 、1410 和 165 Ma（Pecha 等人，2018 年）。因此，很可能近端和远端来源都促成了约。皮埃尔-特立尼达三角洲的 1740、1690、1410 和 160 Ma 锆石年龄峰。70 Ma) 与新墨西哥州西南部和亚利桑那州的拉拉米德弧以及科罗拉多矿带相关的远端岩浆活动是拉顿盆地的皮埃尔页岩和特立尼达砂岩的主要碎屑锆石来源，但页岩相对较多。晚白垩世碎屑锆石的高 Th/U 比更清楚地表明，Laramide 源区存在大量基性至中间岩，相对于长英质源，锆石往往贫乏（Keller 等，2017）皮埃尔页岩的数量比特立尼达砂岩样品的数量。来自拉拉米火山和浅海侵入岩的远端细粒碎屑的河流运输，可能与拉拉米火山灰火山作用一致，加强锆石粉砂向东输送到 Raton 盆地并并入 Pierre 页岩。在烃源岩的拉拉米德断层过程中，锆石粒度可能因晶体破裂（形态类型 4；图 3）而进一步减小。晶粒破碎更可能是由运输前风化现场的变形事件引起的，这只会将晶粒磨损和碎裂成圆形（Novák-Szabó 等人，2018 年）。锆石粉砂大多 < 45 μm，能够在河流（Milliman 和 Meade，1983 年）和空中火山系统（Stevenson 等，2015 年）的悬浮载荷中进行大量长距离运输。相比之下，年纪大了，Pierre Shale-Trinidad 砂岩的主要元古代锆石来源通常是更深层次的侵入体和片麻岩（或由它们衍生的沉积单元），它们使远端和近端岩石中的大部分较粗颗粒结晶，并优先形成特立尼达砂岩的碎屑供应. 我们的结果更广泛的意义和影响是，泥岩的 U-Pb 锆石物源反映了火山和其他细粒烃源岩的可用性，而不仅仅是远端源。正如 Leary 等人的结果所示，泥岩不会记录以粗粒烃源岩为主的远端源。（2020 年）。U-Pb 锆石物源研究通常应包括泥岩，因为它可以比伴生砂岩更清楚地识别源自细粒烃源岩的锆石。这扩展了早期的研究，这些研究报告了砂岩中碎屑锆石种群的偏差作为粒度（例如，Ibañez-Mejia 等人，2018 年）和相（例如，Anders 等人，2021 年）的函数。未来的研究应探索在此处研究的受河流影响的三角洲之外的泥岩-砂岩对沉积环境中锆石数量的控制。我们感谢地质编辑 Marc Norman、审稿人 David Chew 和匿名期刊审稿人 Jaime Toro 以及美国地质调查局审稿人 Marieke Dechesne有用的意见。对贸易、产品或公司名称的任何使用仅用于描述目的，并不意味着得到美国政府的认可。未来的研究应探索在此处研究的受河流影响的三角洲之外的泥岩-砂岩对沉积环境中锆石数量的控制。我们感谢地质编辑 Marc Norman、审稿人 David Chew 和匿名期刊审稿人 Jaime Toro 以及美国地质调查局审稿人 Marieke Dechesne有用的意见。对贸易、产品或公司名称的任何使用仅用于描述目的，并不意味着得到美国政府的认可。未来的研究应探索在此处研究的受河流影响的三角洲之外的泥岩-砂岩对沉积环境中锆石数量的控制。我们感谢地质编辑 Marc Norman、审稿人 David Chew 和匿名期刊审稿人 Jaime Toro 以及美国地质调查局审稿人 Marieke Dechesne有用的意见。对贸易、产品或公司名称的任何使用仅用于描述目的，并不意味着得到美国政府的认可。