Coastal erosion, including sea-cliff retreat, represents both an important component of some sediment budgets and a significant threat to coastal communities in the face of rising sea level. Despite the importance of predicting future rates of coastal erosion, few prehistoric constraints exist on the relative importance of sediment supplied by coastal erosion versus rivers with respect to past sea-level change. We used detrital zircon U-Pb geochronology as a provenance tracer of river and deep-sea fan deposits from the Southern California Borderland (United States) to estimate relative sediment contributions from rivers and coastal erosion from late Pleistocene to present. Mixture modeling of submarine canyon and fan samples indicates that detrital zircon was dominantly (55%–86%) supplied from coastal erosion during latest Pleistocene (ca. 13 ka) sea-level rise, with lesser contributions from rivers, on the basis of unique U-Pb age modes relative to local Peninsular Ranges bedrock sources. However, sediment that was deposited when sea level was stable at its highest and lowest points since the Last Glacial Maximum was dominantly supplied by rivers, suggesting decreased coastal erosion during periods of sea-level stability. We find that relative sediment supply from coastal erosion is strongly dependent on climate state, corroborating predictions of enhanced coastal erosion during future sea-level rise.A majority of the world's coastlines are net erosive with retreating sea cliffs (Young and Carilli, 2019). Coastal erosion can form an important component of sediment budgets in some sediment-routing systems, contributing to beach nourishment, tourism, and sand resources (Young and Ashford, 2006; Patsch and Griggs, 2007). Rates of coastal erosion are predicted to increase with global sea-level rise in the coming century (Hackney et al., 2013; Limber et al., 2018; Mentaschi et al., 2018), likely exacerbating the consequences of sea-cliff retreat and coastal gullying along heavily populated coastlines, such as in Southern California, where residential and industrial cliff-top developments are widespread (Young and Ashford, 2006). For example, Limber et al. (2018) estimated rates of cliff retreat increasing twofold or greater over the coming century in Southern California.As coastal erosion is episodic, and historical observations are limited to the past few centuries, estimates of long-term erosion rates are relatively sparse and often have high uncertainties (Patsch and Griggs, 2007), making future predictions challenging (Limber et al., 2018). Although estimates of sediment supply from coastal erosion are available over historical (i.e., ≤102 yr) time scales (e.g., Young and Ashford, 2006), relatively few studies (e.g., Rogers et al., 2012; Hurst et al., 2016) have estimated rates of coastal erosion over longer “intermediate” time scales (i.e., 102–106 yr; sensu Romans et al., 2016). Therefore, we used detrital zircon (DZ) as a sediment tracer to track the relative contributions from rivers and coastal erosion to deep-sea fans in the Southern California Borderland over the past 40 k.y.The Oceanside margin consists of a narrow shelf (∼5 km wide) that connects mountainous topography of the northern Peninsular Ranges with deep-marine basins of the Southern California Borderland (Fig. 1A). The northern Peninsular Ranges are underlain by plutonic rocks of a Lower to mid-Cretaceous magmatic arc and associated volcanic rocks (128–91 Ma; Herzig and Kimbrough, 2014; Kimbrough et al., 2014; Premo et al., 2014). Sea cliffs are present along 80% of the coastline, average 25–35 m in height (locally up to 100 m), and are composed of ∼80% siliciclastic sand-sized material (Young et al., 2010). The Oceanside shelf, sea cliffs, and coastal lowlands are composed of Cretaceous–Cenozoic sediments that onlap older, crystalline basement (Fig. 1B; Darigo and Osborne, 1986; Young et al., 2010).Five rivers with headwaters within the northern Peninsular Ranges account for ∼80% of the fluvial drainage area to the Oceanside shelf (Fig. 1). Although dams have reduced sediment supply by rivers to the Oceanside shelf by ∼50% (Patsch and Griggs, 2007), 10Be-derived denudation rates that equate to ∼2 Mt yr−1 mass flux to the Oceanside margin are in broad agreement with estimates of predam mass flux from 20th-century stream gauge data (∼2.2 Mt yr−1; Inman, 2008; Covault et al., 2011). Rates of historical (1930s to 2010) sea-cliff retreat along the Oceanside margin have varied between ∼1 and ∼100 cm yr−1 (Limber et al., 2018), with an average rate of ∼8 cm yr−1 calculated between 1998 and 2004 (Young and Ashford, 2006). Patsch and Griggs (2007) estimated that bluff erosion accounted for ∼34% of the total Oceanside littoral cell budget prior to anthropogenic modification (i.e., river damming and sea-cliff armoring). Young and Ashford (2006) reported higher contributions (∼84%) from sea-cliff erosion and coastal gullying based on data collected from 1998 to 2004.The Oceanside littoral cell is sand-starved at its northern end, and longshore currents transport sediment in a predominantly southeastward direction along the coastline, thus forming a closed system (Patsch and Griggs, 2007). Three major submarine canyons and numerous gullies incise the Oceanside shelf edge (Fig. 1). During sea-level lowstand, rivers cross the exposed Oceanside shelf to deliver their sediment loads directly into submarine canyons at the shelf edge, including the Oceanside and Carlsbad Canyons, which were actively receiving terrigenous sediment prior to latest Pleistocene transgression (Fig. 1; Darigo and Osborne, 1986; Covault et al., 2007). During highstand, sediment is transported by longshore currents southward to the Scripps and La Jolla Canyons, which extend within close proximity of the shoreline. The La Jolla fan is only active during highstand because its feeder canyons lack direct connection with a river (Covault et al., 2007).Sediment sources in the Oceanside margin can be differentiated on the basis of DZ U-Pb ages: (1) The crystalline bedrock of the northern Peninsular Ranges and Upper Cretaceous–Paleocene strata are dominated by Cretaceous U-Pb ages, and (2) Upper Paleocene–Eocene strata are characterized by an abundance of latest Cretaceous, Permian–Triassic, and Proterozoic zircon that lacks a local source in the northern Peninsular Ranges (Fig. 2; Jacobson et al., 2011; Premo et al., 2014; Sharman et al., 2015). The distinct signatures produced by Cretaceous versus Upper Paleocene–Eocene strata reflect an early Cenozoic shift from local to nonlocal sediment sources that extended as far as Arizona (USA) and Sonora (Mexico) (Fig. 2; Kies and Abbott, 1983; Sharman et al., 2015).To characterize the DZ signature of river sediment supply and submarine canyon-fan deposits, we sampled (1) each of the five major rivers of the Oceanside margin, and (2) five offshore samples from core and the shallow subsurface (Figs. 1 and 2; Table S1 in the Supplemental Material1). The three core samples were collected from sections with calibrated 14C ages from the Oceanside fan (sample 503-P1; ca. 15.8–7.2 ka), Carlsbad fan (H5-P1; ca. 20.3 ka), and La Jolla fan (EM3–4, ca. 40 ka) (Covault et al., 2007; Normark et al., 2009). Although the age of the Oceanside fan sample is constrained to be between ca. 15.8 and 7.2 ka based on calibrated 14C ages (Normark et al., 2009), we interpret that the sample is likely older than ca. 13 ka based on the timing when the Oceanside Canyon was drowned and the Oceanside fan became inactive (Covault and Romans, 2009). Two additional samples were collected from the shallow subsurface (0.3–0.8 m depth) within the La Jolla Canyon (sample L2–79-SC g68) and La Jolla fan (sample L2–79-SC 98) (Fig. 1). Samples were processed using standard mineral separation and U-Pb analytical procedures (see the Supplemental Material text for details and Tables S2 and S3 for analytical results).We used the forward mixture modeling approach of Malkowski et al. (2019) to estimate the relative contributions of DZ from rivers and coastal erosion. The five sampled rivers were combined into two parents (P1 and P2) based on similarity in DZ U-Pb age distributions between San Juan and San Mateo Creeks (P1) and between Santa Margarita, San Luis Rey, and San Dieguito Rivers (P2) (Fig. 2). A compilation of eight Upper Paleocene–Eocene samples (523 grain analyses) from sea cliffs and coastal outcrops was used as a proxy for sediment input from coastal erosion (P3; Fig. 2; Table S4). Best-fit mixing proportions and 95% confidence intervals were determined using 5000 iterations of a bootstrapping sampling-with-replacement routine, with Vmax used as a goodness-of-fit metric (Fig. S1, Table S6; Malkowski et al., 2019).DZ U-Pb ages from rivers were all dominated by Cretaceous zircon, with a progression from multimodal to unimodal age peaks from northwest to southeast (Fig. 2). San Juan and San Mateo Creeks displayed more latest Cretaceous (90–66 Ma) zircon (16%–20% of the total number) relative to rivers to the southeast (Fig. 1). Four of the submarine canyon and fan samples (Carlsbad and La Jolla) displayed broadly similar U-Pb age distributions to the rivers. Early to mid-Cretaceous age peaks (114–97 Ma) were dominant in these samples, with modest abundances of latest Cretaceous (6%–13%) or Proterozoic (2%–9%) zircon. The Oceanside fan sample, however, displayed abundant Late Cretaceous zircon (33%) with an age peak of 82 Ma and had an elevated proportion (26%) of Proterozoic zircon. The Oceanside fan sample also displayed a minor Late Jurassic peak (ca. 149 Ma) that was not present in the other marine or river samples (Fig. 2).Mixture modeling indicated elevated contributions of zircon derived from recycling of Cenozoic coastal outcrops (P3) in the Oceanside fan sample (55%–86% inner 95th percentile range; Table S6). The four other deep-sea fan samples yielded markedly lower estimates for zircon supply from coastal outcrops (inner 95th percentile ranges between 0% and 37%; Table S6).DZ ages from the four submarine fan samples deposited during stable lowstand and highstand sea levels (Carlsbad and La Jolla canyon-fans) are consistent with primary derivation from rivers (Fig. 3). For instance, samples show general overlap with the integrated river U-Pb age distribution that was computed by normalizing to the expected sediment load of each river based on catchment area and 10Be-derived millennial erosion rates (Fig. 2; Covault et al., 2011). Mixing calculations confirmed that these four samples were dominated by river input (average of 76%–89%; Fig. 3; Table S6). Although the DZ ages from the La Jolla canyon-fan system indicate river input, the river sediment is delivered to the littoral zone, where longshore currents deliver it to canyon heads (Fig. 3).In contrast, the ca. 13 ka Oceanside fan sample, deposited during sea-level rise, contained abundant latest Cretaceous (90–66 Ma) and Proterozoic DZ grains, which lack a local source in the northern Peninsular Ranges (Fig. 2; Premo et al., 2014). Instead, these grains were likely recycled from Upper Paleocene–Eocene, and possibly younger, strata that compose the majority of the Oceanside shelf and coastal inland exposures (Fig. 1B). Correspondingly, mixture modeling results indicated that the ca. 13 ka Oceanside fan sample was dominantly supplied via coastal erosion (i.e., 55%–86%; Fig. 3).We considered two explanations for the anomalous result from the single Oceanside fan sample (Fig. 2): (1) local derivation from submarine erosion (e.g., mass wasting) of the proximal Oceanside shelf and/or canyon, or (2) sediment supplied from coastal erosion (Fig. 3). Although the first explanation is challenging to rule out, several considerations suggest that the Oceanside fan sample resulted from enhanced coastal erosion during latest Pleistocene and early Holocene sea-level rise. On the basis of sand mineralogy on the Oceanside shelf, Darigo and Osborne (1986) interpreted a Peninsular Ranges batholith source for lowstand Pleistocene deposits and a local, Eocene sea-cliff source for transgressive Holocene deposits that blanketed the shelf north of La Jolla during sea-level rise. Similarly, Covault et al. (2011) noted that deep-sea sediment budgets indicated an imbalance between fluvial input (∼2 Mt yr−1) and deep-sea sediment deposition (∼3 Mt yr−1) during Holocene sea-level rise; sediment supply from coastal erosion could make up the deficit and close the sediment budget. Terraces on the Oceanside shelf, correlated to latest Pleistocene to early Holocene (ca. 15–10 ka) sea-level oscillations and stillstands, provide additional evidence for shelfal and coastal erosion during sea-level rise (Darigo and Osborne, 1986). Although relative DZ supply cannot be unequivocally related to relative sediment supply from rivers and coastal erosion, given the lack of constraint on zircon concentration (Amidon et al., 2005; Malkowski et al., 2019), our estimate of relative DZ yield from coastal erosion during highstand and lowstand (average of 15%, range of 0%–37%) is within the uncertainty of the Patsch and Griggs (2007) estimate of 33% sediment supply from sea-cliff erosion prior to river damming and cliff armoring.The DZ results presented herein and sedimentological observations from previous work are consistent with historical observations and predictions of accelerated sea-cliff retreat during periods of sea-level rise (Hackney et al., 2013; Limber et al., 2018; Mentaschi et al., 2018). For example, 4–87 m of sea-cliff retreat has been estimated for 2 m of sea-level rise over the coming century in the vicinity of the city of Oceanside, California (Young et al., 2014; Limber et al., 2018). Changes in wave power, the frequency and intensity of storms, and anthropogenic activity may also promote coastal erosion (Mentaschi et al., 2018; Reguero et al., 2019). Terrestrial paleoclimate proxies from Lake Elsinore (north of Oceanside) suggest decreased precipitation and storm intensity from early to late Holocene time (Kirby et al., 2007). Thus, although river sediment supply may have been high during the relatively wet early Holocene (Wells and Berger, 1967; Kirby et al., 2005, 2007), deep-sea sediments suggest that any increases in fluvial sediment supply were overwhelmed by even larger increases in coastal erosion, perhaps driven by increased frequency and magnitude of storms in conjunction with sea-level rise.We used DZ as a sediment tracer to reveal that rivers supplied the bulk of sediment to deep-sea fans in the Southern California Borderland during periods of stable sea level (lowstand and highstand). However, we interpret one sample deposited during latest Pleistocene sea-level rise (ca. 13 ka) to be dominantly supplied by sediment from coastal erosion. These findings suggest that the role of sediment supplied from coastal erosion versus rivers is dependent on sea level and climate state, supporting predictions of enhanced coastal erosion as a consequence of future sea-level rise. Furthermore, we demonstrated the utility of DZ as a sediment tracer of different components of coastal sediment budgets. The sand-sized fraction of deep-sea depositional systems is thus a valuable archive of the effects of environmental changes (such as sea-level rise in response to climate change) on coastal erosion and sediment supply.Financial support was provided by the industrial affiliate members of the Quantitative Clastics Laboratory and the UTChron Laboratory, University of Texas at Austin. We thank Alexandra Hangsterfer at Scripps Institute of Oceanography (La Jolla, California) for assistance with sampling the Mohole core. Lisa Stockli provided assistance with data collection. Mary McGann provided updated calibrations of 14C ages. We thank three anonymous reviewers and Nora Nieminski for constructive feedback. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

中文翻译：

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美国南加州冰川-海平面上升期间海岸侵蚀和河流沉积物供应的碎屑信号

海岸侵蚀，包括海崖后退，既是一些沉积物预算的重要组成部分，也是面对海平面上升对沿海社区的重大威胁。尽管预测未来海岸侵蚀的速度很重要，但关于海岸侵蚀提供的沉积物与河流相对于过去海平面变化的相对重要性，几乎没有史前限制。我们使用碎屑锆石 U-Pb 年代学作为南加州边境（美国）河流和深海扇沉积物的来源示踪剂，以估计从晚更新世到现在的河流和海岸侵蚀的相对沉积物贡献。海底峡谷和扇形样品的混合模型表明碎屑锆石主要（55%–86%）来自最新更新世（约 13 ka) 海平面上升，河流贡献较小，基于相对于当地半岛山脉基岩源的独特 U-Pb 年龄模式。然而，自末次盛冰期以来，当海平面稳定在最高点和最低点时沉积的沉积物主要由河流提供，这表明在海平面稳定期间海岸侵蚀减少。我们发现海岸侵蚀的相对沉积物供应强烈依赖于气候状态，这证实了未来海平面上升期间海岸侵蚀加剧的预测。世界上大部分海岸线都随着海崖的退缩而受到净侵蚀（Young 和 Carilli，2019）。海岸侵蚀可以成为一些沉积物路线系统中沉积物收支的重要组成部分，有助于海滩营养、旅游业、和砂资源（Young 和 Ashford，2006 年；Patsch 和 Griggs，2007 年）。预计未来一个世纪，随着全球海平面上升，海岸侵蚀率将增加（Hackney 等人，2013 年；Limber 等人，2018 年；Mentaschi 等人，2018 年），这可能会加剧海崖后退的后果和沿人口稠密的海岸线形成的沿海沟壑，例如在南加州，住宅和工业悬崖顶的开发项目非常普遍（Young 和 Ashford，2006 年）。例如，Limber 等人。(2018) 估计未来一个世纪南加州的悬崖撤退率将增加两倍或更多。由于海岸侵蚀是偶发性的，而且历史观察仅限于过去几个世纪，长期侵蚀率的估计相对较少，并且通常有高不确定性（Patsch 和 Griggs，2007 年），使未来的预测具有挑战性（Limber 等人，2018 年）。尽管在历史（即≤ 102 年）时间尺度（例如，Young 和 Ashford，2006 年）中可获得海岸侵蚀沉积物供应的估计值，但研究相对较少（例如，Rogers 等人，2012 年；Hurst 等人，2016 年） ) 估计了较长“中间”时间尺度上的海岸侵蚀率（即 102-106 年；sensu Romans 等，2016）。因此，我们使用碎屑锆石 (DZ) 作为沉积物示踪剂来跟踪过去 40 ky 南加州边境地区河流和海岸侵蚀对深海扇的相对贡献。 ）将半岛山脉北部的山区地形与南加州边境的深海盆地连接起来（图 1A）。北部半岛山脉的下方是下白垩世至中白垩世岩浆弧的深成岩和相关火山岩（128-91 Ma；Herzig 和 Kimbrough，2014；Kimbrough 等，2014；Premo 等，2014）。80% 的海岸线都存在海崖，平均高度为 25-35 m（局部高达 100 m），由约 80% 的硅质碎屑砂大小的材料组成（Young 等，2010）。Oceanside 陆架、海崖和沿海低地由白垩纪-新生代沉积物组成，这些沉积物覆盖在较旧的结晶基底上（图 1B；Darigo 和 Osborne，1986 年；Young 等人，2010 年）。五条河流源头位于半岛北部山脉占到欧申赛德大陆架的河流流域面积的约 80%（图 1）。尽管大坝已将河流向欧申赛德大陆架的沉积物供应减少了约 50%（Patsch 和 Griggs，2007），10Be 衍生的剥蚀率相当于到 Oceanside 边缘的 ∼2 Mt yr−1 质量通量与来自 20 世纪河流测量仪数据（∼2.2 Mt yr−1；Inman，2008；Covault等人，2011 年）。沿欧申赛德边缘的历史（1930 年代至 2010 年）海崖后退率在约 1 至 100 cm yr-1 之间变化（Limber 等人，2018），计算出的平均速率为约 8 cm yr-1 1998 年和 2004 年（Young 和 Ashford，2006 年）。Patsch 和 Griggs (2007) 估计，在人为改造（即河流筑坝和海崖装甲）之前，断崖侵蚀占欧申赛德沿岸细胞总预算的约 34%。Young 和 Ashford（2006 年）根据 1998 年至 2004 年收集的数据报告了海崖侵蚀和沿海沟壑的更高贡献（~84%）。欧申赛德沿岸单元的北端缺沙，沿岸洋流沿海岸线主要向东南方向输送沉积物，从而形成一个封闭系统（Patsch 和 Griggs，2007）。三个主要的海底峡谷和众多的沟壑切割了欧申赛德大陆架边缘（图 1）。在海平面低位期间，河流穿过裸露的欧申赛德陆架，将其沉积物直接输送到陆架边缘的海底峡谷，包括欧申赛德和卡尔斯巴德峡谷，这些峡谷在最近更新世海侵之前积极接收陆源沉积物（图 1；Darigo和 Osborne，1986 年；Covault 等人，2007 年）。在高位期间，沉积物由沿岸流向南输送到斯克里普斯峡谷和拉霍亚峡谷，这些峡谷在海岸线附近延伸。La Jolla扇仅在高位活动，因为它的馈线峡谷与河流缺乏直接联系（Covault等，2007）。Oceanside边缘的沉积物来源可以根据DZ U-Pb年龄进行区分：（1）半岛山脉北部和上白垩统-古新世地层结晶基岩以白垩纪 U-Pb 年龄为主，(2) 上古新世-始新世地层以晚白垩世、二叠纪-三叠纪和元古代锆石丰度为特征，缺乏半岛山脉北部的一个本地源（图 2；Jacobson 等人，2011 年；Premo 等人，2014 年；Sharman 等人，2015 年）。白垩纪与上古新世-始新世地层产生的不同特征反映了早期新生代从局部向非局部沉积物来源的转变，其延伸至亚利桑那（美国）和索诺拉（墨西哥）（图 2；凯斯和雅培，1983 年；Sharman 等人，2015 年。为了表征河流沉积物供应和海底峡谷扇沉积的 DZ 特征，我们对 (1) 欧申赛德边缘的 5 条主要河流中的每一条进行了采样，以及 (2) 来自岩心和浅层地下（图 1 和 2；补充材料 1 中的表 S1）。三个岩心样本是从 Oceanside 扇（样本 503-P1；大约 15.8–7.2 ka）、Carlsbad 扇（H5-P1；大约 20.3 ka）和 La Jolla 扇（EM3– 4, 约 40 ka)（Covault 等人，2007 年；Normark 等人，2009 年）。尽管欧申赛德扇样本的年龄被限制在大约 15.8 和 7.2 ka 基于校准的 14C 年龄（Normark 等人，2009 年），我们解释样本可能比大约更旧。13 ka 基于欧申赛德峡谷被淹和欧申赛德风扇停止活动的时间（Covault 和 Romans，2009）。从拉霍亚峡谷（样品 L2-79-SC g68）和拉霍亚扇（样品 L2-79-SC 98）内的浅层地下（0.3-0.8 m 深）收集了另外两个样品（图 1）。使用标准矿物分离和 U-Pb 分析程序处理样品（详细信息见补充材料文本，分析结果见表 S2 和 S3）。我们使用了 Malkowski 等人的正向混合建模方法。(2019) 估计 DZ 对河流和海岸侵蚀的相对贡献。根据 San Juan 和 San Mateo Creeks (P1) 以及 Santa Margarita、San Luis Rey、和 San Dieguito Rivers (P2)（图 2）。来自海崖和海岸露头的八个上古新世-始新世样品（523 个谷物分析）的汇编被用作海岸侵蚀沉积物输入的代理（P3；图 2；表 S4）。最佳拟合混合比例和 95% 置信区间是使用自举抽样替换例程的 5000 次迭代确定的，其中 Vmax 用作拟合优度指标（图 S1，表 S6；Malkowski 等人，2019 年） ）。河流DZ U-Pb年龄均以白垩纪锆石为主，从西北向东南呈多峰向单峰变迁（图2）。相对于东南部的河流，San Juan 和 San Mateo Creeks 显示了更多最新的白垩纪（90-66 Ma）锆石（占总数的 16%-20%）（图 1）。四个海底峡谷和扇形样本（卡尔斯巴德和拉霍亚）显示出与河流大致相似的 U-Pb 年龄分布。在这些样品中，早到中白垩纪时代的峰值（114-97 Ma）占主导地位，晚白垩世（6%-13%）或元古代（2%-9%）锆石丰度适中。然而，Oceanside 扇样品显示出丰富的晚白垩世锆石 (33%)，年龄峰值为 82 Ma，元古代锆石的比例升高 (26%)。欧申赛德扇样本还显示了一个较小的晚侏罗世峰（约 149 Ma），这在其他海洋或河流样本中不存在（图 2）。混合模型表明来自新生代沿海露头再循环的锆石的贡献增加（P3 ) 在 Oceanside 扇样本中（55%–86% 内 95% 的百分位数范围；表 S6）。其他四个深海扇样本对来自沿海露头的锆石供应的估计明显较低（内部 95% 的范围介于 0% 和 37% 之间；表 S6）。来自在稳定的低位和高位海平面期间沉积的四个海底扇样本的 DZ 年龄（Carlsbad 和 La Jolla canyon-fans）与来自河流的原始推导一致（图 3）。例如，样本显示出与综合河流 U-Pb 年龄分布的总体重叠，该分布是通过基于集水区和 10Be 衍生的千年侵蚀率对每条河流的预期泥沙负荷进行归一化计算得出的（图 2；Covault 等人， 2011）。混合计算证实这四个样本以河流输入为主（平均为 76%–89%；图 3；表 S6）。尽管拉霍亚峡谷扇系统的 DZ 年龄表明河流输入，河流沉积物被输送到沿岸带，在那里沿岸水流将其输送到峡谷头（图 3）。相比之下，约。在海平面上升期间沉积的 13 ka Oceanside 扇样本包含丰富的最新白垩纪 (90-66 Ma) 和元古代 DZ 颗粒，在半岛北部缺乏本地来源（图 2；Premo 等，2014） . 相反，这些谷物很可能是从上古新世-始新世中回收的，也可能是更年轻的地层，这些地层构成了欧申赛德大陆架和沿海内陆暴露的大部分（图 1B）。相应地，混合建模结果表明大约 13 ka Oceanside 扇样本主要通过海岸侵蚀提供（即，55%–86%；图 3）。我们考虑了对来自单个 Oceanside 扇样本的异常结果的两种解释（图 2）：(1) 近端欧申赛德大陆架和/或峡谷的海底侵蚀（例如，大规模浪费）的局部衍生，或 (2) 海岸侵蚀提供的沉积物（图 3）。尽管排除第一种解释具有挑战性，但一些考虑表明，欧申赛德扇样本是由于最新更新世和全新世早期海平面上升期间海岸侵蚀加剧造成的。Darigo 和 Osborne (1986) 根据 Oceanside 陆架上的砂矿物学解释了低位更新世沉积物的半岛山脉基岩源和海侵期间覆盖拉霍亚大陆架以北的全新世沉积物的本地始新世海崖源-水平上升。同样，Covault 等人。(2011) 指出，深海沉积物收支表明在全新世海平面上升期间河流输入（~2 Mt yr-1）和深海沉积物沉积（~3 Mt yr-1）之间存在不平衡；海岸侵蚀造成的沉积物供应可以弥补赤字并关闭沉积物收支。与最新更新世至早全新世（约 15-10 ka）海平面振荡和静止状态相关的海滨大陆架上的梯田，为海平面上升期间的陆架和海岸侵蚀提供了额外的证据（Darigo 和 Osborne，1986 年）。虽然相对 DZ 供应不能明确地与河流和海岸侵蚀的相对沉积物供应相关，但鉴于缺乏对锆石浓度的限制（Amidon 等人，2005 年；Malkowski 等人，2019），我们对沿海 DZ 产量的估计高位和低位期间的侵蚀（平均 15%，0%–37% 的范围内）在 Patsch 和 Griggs (2007) 估计的 33% 沉积物供应的不确定性以内与海平面上升期间海崖加速退缩的历史观察和预测一致（Hackney 等人，2013 年；Limber 等人，2018 年；Mentaschi 等人，2018 年）。例如，据估计，未来一个世纪，加利福尼亚州欧申赛德市附近海平面上升 2 米，海崖撤退 4-87 米（Young 等人，2014 年；Limber 等人， 2018）。波浪功率的变化、风暴的频率和强度以及人为活动也可能促进海岸侵蚀（Mentaschi 等，2018；Reguero 等，2019）。来自埃尔西诺湖（欧申赛德以北）的陆地古气候代表表明，从全新世早期到晚期，降水和风暴强度减少（Kirby 等，2007）。因此，尽管在相对潮湿的全新世早期河流沉积物供应可能很高（Wells 和 Berger，1967 年；Kirby 等人，2005 年，2007 年），但深海沉积物表明，河流沉积物供应的任何增加都被更大的海岸侵蚀的增加，可能是由于风暴频率和强度的增加以及海平面上升导致的。我们使用 DZ 作为沉积物示踪剂来揭示河流在一定时期内为南加州边境的深海扇提供了大部分沉积物稳定的海平面（低位和高位）。然而，我们解释了最近更新世海平面上升期间沉积的一个样本（约 13 ka) 主要由海岸侵蚀的沉积物提供。这些发现表明，海岸侵蚀与河流提供的沉积物的作用取决于海平面和气候状态，支持对未来海平面上升导致海岸侵蚀加剧的预测。此外，我们证明了 DZ 作为沿海沉积物收支不同组成部分的沉积物示踪剂的效用。因此，深海沉积系统中沙粒大小的部分是环境变化（如气候变化引起的海平面上升）对海岸侵蚀和沉积物供应影响的宝贵档案。工业附属公司提供了资金支持德克萨斯大学奥斯汀分校定量碎屑实验室和 UTChron 实验室的成员。我们感谢斯克里普斯海洋学研究所（加利福尼亚州拉霍亚）的 Alexandra Hangsterfer 协助对 Mohole 岩心进行采样。Lisa Stockli 协助收集数据。Mary McGann 提供了 14C 年龄的更新校准。我们感谢三位匿名审稿人和 Nora Nieminski 的建设性反馈。任何对贸易、公司或产品名称的使用仅用于描述目的，并不意味着得到美国政府的认可。