The Tecopa basin in eastern California was a terminal basin that episodically held lakes during most of the Quaternary until the basin and its modern stream, the Amargosa River, became tributary to Death Valley. Although long studied for its sedimentology, diagenesis, and paleomagnetism, the basin’s lacustrine and paleoclimate history has not been well understood, and conflicting interpretations exist concerning the relations of Tecopa basin to the Amargosa River and to pluvial Lake Manly in Death Valley. Previous studies also did not recognize basinwide tectonic effects on lake-level history. In this study, we focused on: (1) establishing a chronology of shoreline deposits, as the primary indicator of lake-level history, utilizing well-known ash beds and new uranium-series and luminescence dating; (2) using ostracodes as indicators of water chemistry and water source(s); and (3) correlating lake transgressions to well-preserved fluvial-deltaic sequences. During the early Pleistocene, the Tecopa basin hosted small shallow lakes primarily fed by low-alkalinity water sourced mainly from runoff and (or) a groundwater source chemically unlike the modern springs. The first lake that filled the basin occurred just prior and up to the eruption of the 765 ka Bishop ash during marine isotope stage (MIS) 19; this lake heralded the arrival of the Amargosa River, delivering high-alkalinity water. Two subsequent lake cycles, coeval with MIS 16 (leading up to eruption of 631 ka Lava Creek B ash) and MIS 14 and (or) MIS 12, are marked by prominent accumulations of nearshore and beach deposits. The timing of the youngest of these three lakes, the High lake, is constrained by a uranium-series age of ca. 580 ± 120 ka on tufa-cemented beach gravel and by estimates from sedimentation rates. Highstand deposits of the Lava Creek and High lakes at the north end of the basin are stratigraphically tied to distinct sequences of fluvial-deltaic deposits fed by alkaline waters of the Amargosa River. The High lake reached the highest level achieved in the Tecopa basin, and it may have briefly discharged southward but did not significantly erode its threshold. The High lake was followed by a long hiatus of as much as 300 k.y., during which there is evidence for alluvial, eolian, and groundwater-discharge deposition, but no lakes. We attribute this hiatus, as have others, to blockage of the Amargosa River by an alluvial fan upstream near Eagle Mountain. A final lake, the Terminal lake, formed when the river once again flowed south into Tecopa basin, but it was likely short-lived due to rapid incision of the former threshold south of Tecopa. Deposits of the Terminal lake are inset below, and are locally unconformable on, deposits of the High lake and the nonlacustrine deposits of the hiatus. The Terminal lake reached its highstand at ca. 185 ± 21 ka, as dated by infrared-stimulated luminescence on feldspar in beach sand, a time coincident with perennial lake mud and alkaline-tolerant ostracodes in the Badwater core of Lake Manly during MIS 6. A period of stillstand occurred as the Terminal lake drained when the incising river encountered resistant Stirling Quartzite near the head of present-day Amargosa Canyon. Our studies significantly revise the lacustrine and drainage history of the Tecopa basin, show that the MIS 6 highstand was not the largest lake in the basin as previously published (with implications for potential nuclear waste storage at Yucca Mountain, Nevada), and provide evidence from shoreline elevations for ∼20 m of tectonic uplift in the northern part of the basin across an ENE-trending monoclinal flexure.

中文翻译：

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加利福尼亚州特科帕盆地的更新世湖泊和古水文环境：Amargosa河排水一体化的约束

加利福尼亚东部的特科帕（Tecopa）盆地是一个终端盆地，在第四纪的大部分时间里，它一直被湖泊封住，直到该盆地及其现代河流Amargosa河成为死亡谷的支流。尽管对其沉积学，成岩作用和古磁性作用进行了长期研究，但该盆地的湖相和古气候历史尚未得到很好的理解，关于Tecopa盆地与Amargosa河和死亡谷的Manly湖之间的关系存在矛盾的解释。以前的研究也没有认识到整个盆地对湖平面历史的构造作用。在这项研究中，我们着重于：（1）利用著名的灰床，新的铀系列和发光测年法建立海岸线沉积物的年代学，作为湖平面历史的主要指标；（2）使用Ostracodes作为水化学和水源的指标；（3）将湖泊的海侵与保存完好的河流三角洲序列相关联。在更新世早期，特科帕盆地拥有小型浅湖，主要由低盐度水喂养，这些水主要来自径流和（或）化学上不同于现代泉水的地下水。充满盆地的第一个湖泊发生在海洋同位素阶段（MIS）19之前，直到765 ka Bishop火山灰喷发为止。这个湖预示着Amargosa河的到来，并输送了高碱性的水。随后的两个湖泊周期与MIS 16（导致631 ka Lava Creek B火山灰爆发）和MIS 14和（或）MIS 12并存，其标志是近岸和海滩沉积物的大量堆积。这三个湖中最年轻的时间，High湖，受约铀系列年龄的限制。由石灰胶结的海滩砾石上的580±120 ka，根据沉积速率估算。盆地北端的熔岩河和高湖的高位沉积物在地层上与由Amargosa河的碱性水供给的河流-三角洲沉积物的不同序列相关。High湖达到了Tecopa盆地的最高水平，它可能曾向南短暂排放过，但并未显着侵蚀其阈值。高湖之后是长达300 ky的长裂隙，在此期间有冲积，风积和地下水排放的证据，但没有湖泊。与其他情况一样，我们将此中断归因于鹰山上游的冲积扇堵塞了阿马戈萨河。最后一个湖，即终端湖 当河流再次向南流入特科帕盆地时形成，但由于对特科帕南部的前门迅速切开，它可能是短暂的。Terminal湖的沉积物位于High湖的沉积物和裂隙的非湖相沉积物的下方，并且在局部不整合。码头湖达到了高潮。185±21 ka，由红外激发在沙滩沙子中的长石上测得，这与MIS 6期间曼利湖恶水核心的多年生湖泊泥浆和耐碱雌激素同时发生的时间相同。当切入的河流在现今的阿马戈萨峡谷（Amargosa Canyon）头附近遇到抗性斯特林石英岩时，水被排干。我们的研究极大地改变了特科帕盆地的湖泊和排水史，