Mixed carbonate-siliciclastic deposits provide unique insights into hydrodynamic processes that control sedimentation in tidal systems. This study presents sedimentologic an¬¬d ichnologic data from the upper Miocene¬ to lower Pliocene Bouse Formation, which accumulated during regional transgression at the margin of a tidal strait near the north end of the ancestral Gulf of California. The basal carbonate member of the Bouse Formation records deposition in a tide-influenced, compositionally mixed carbonate-siliciclastic system dominated by salt marsh, tidal flat, and channel environments. The basal carbonate member is an overall deepening up succession of facies associations (FA) comprising: FA1 siliciclastic-rich heterolithic facies, lime mudstone with desiccation cracks, and plant debris rich carbonate silt interpreted as siliciclastic-rich tidal flats; FA2 well-sorted gravels, siliciclastic-rich sandy strata, lime mudstone with desiccation cracks, and sandy microbial micrite interpreted as tidal-channel deposits; FA3 carbonate-rich heterolithic lime mudstone to well sorted, crossbedded bioclastic grainstone interpreted as intertidal to shallow subtidal deposits; and FA4 lime mudstone interpreted as shallow to deep subtidal low-energy deposits that record the end of tidal conditions in the basin. Trace fossils include marine forms Gyrolithes, Teichichnus, Thalassinoides, and non-diagnostic forms Arenicolites, Cochlichnus, Conichnus, Lockeia, Planolites, Skolithos, and Treptichnus (known from marine, brackish, and freshwater environments). The diminutive size of trace fossils reflects brackish conditions created by mixing of freshwater and seawater. This study provides evidence for a late Miocene to early Pliocene humid climate in southwestern North America, in stark contrast to the modern hyperarid climate. Factors that controlled the relative percent of mixed carbonate and siliciclastic sediment include siliciclastic input from local rivers, in situ carbonate production, current energy, degree of tidal mixing, and relative sea level. Pronounced facies variability at bedform, outcrop, and basin scale documented in this study appears to be an important characteristic of mixed carbonate-siliciclastic deposits in tidal depositional systems.

中文翻译：

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加利福尼亚古湾中新世至上新世 Bouse 组碳酸盐-硅质碎屑混合潮汐沉积

混合碳酸盐-硅质碎屑沉积物为控制潮汐系统沉积的流体动力学过程提供了独特的见解。这项研究提供了从中新世上部到上新世下部 Bouse 地层的沉积学和地质学数据，这些数据在区域海侵期间在加利福尼亚湾北端附近的潮汐海峡边缘积累。Bouse 组的基底碳酸盐岩在受潮汐影响、成分混合的碳酸盐-硅质碎屑岩系统中沉积，以盐沼、潮滩和河道环境为主。基底碳酸盐岩是一个整体加深的相组合（FA），包括： FA1 富含硅质碎屑的杂岩相，具有干燥裂缝的灰泥岩，富含植物残骸的碳酸盐淤泥被解释为富含硅质碎屑的潮滩；FA2 分选良好的砾石、富含硅质碎屑的砂质地层、具有干燥裂缝的灰泥岩和被解释为潮汐通道沉积物的砂质微生物泥晶；FA3 富含碳酸盐的杂岩灰泥岩到分选良好的交错生物碎屑颗粒岩，解释为潮间带至浅层潮下带沉积物；和 FA4 石灰泥岩被解释为浅到深的潮下低能量沉积物，记录了盆地潮汐条件的结束。微量化石包括海洋形式的旋石属、Teichichnus、Thalassinoides 和非诊断形式的砗磲、Cochlichnus、Conichnus、Lockeia、Planolites、Skolithos 和Treptichnus（已知来自海洋、半咸水和淡水环境）。微量化石的小尺寸反映了淡水和海水混合产生的微咸条件。这项研究为北美西南部中新世晚期至上新世早期潮湿气候提供了证据，与现代超干旱气候形成鲜明对比。控制混合碳酸盐和硅质碎屑沉积物相对百分比的因素包括来自当地河流的硅质碎屑输入、原位碳酸盐生产、电流能量、潮汐混合程度和相对海平面。本研究中记录的地床、露头和盆地尺度上明显的相变率似乎是潮汐沉积系统中混合碳酸盐硅碎屑沉积物的一个重要特征。与现代的极度干旱气候形成鲜明对比。控制混合碳酸盐和硅质碎屑沉积物相对百分比的因素包括来自当地河流的硅质碎屑输入、原位碳酸盐生产、电流能量、潮汐混合程度和相对海平面。本研究中记录的地床、露头和盆地尺度上明显的相变率似乎是潮汐沉积系统中混合碳酸盐硅碎屑沉积物的一个重要特征。与现代的极度干旱气候形成鲜明对比。控制混合碳酸盐和硅质碎屑沉积物相对百分比的因素包括来自当地河流的硅质碎屑输入、原位碳酸盐生产、电流能量、潮汐混合程度和相对海平面。本研究中记录的地床、露头和盆地尺度上明显的相变率似乎是潮汐沉积系统中混合碳酸盐硅碎屑沉积物的一个重要特征。