Abstract Depositional processes operating in deltaic shorelines create a variety of physico-chemical stressful conditions that impact directly on benthic fauna. The ichnological signatures of deltaic successions reflect these physico-chemical stresses, such as rapid sediment influx, elevated water turbidity, periodically reduced oxygenation, salinity fluctuations, and wave- and tidal-energy. In the Campanian La Anita Formation of the Austral-Magallanes Basin, two examples of deltaic successions, each showing different relative dominance of wave and fluvial processes, are described in detail, allowing the recognition of contrasting stresses that acted differentially in a wave-dominated, fluvial-influenced delta and a fluvial-dominated delta. Variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico-chemical stresses. In the wave-dominated, fluvial-influenced deltaic deposits, the alternation between fair-weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front, displaying facies-crossing and horizontal elements attributable to the Skolithos and Cruziana Ichnofacies, such as Arenicolites isp., Chondrites isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp. , Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. and Skolithos isp. Water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role. The proximal delta front, and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate Skolithos Ichnofacies with few Diplocraterion isp., Gordia isp., Lockeia isp., Macaronichnus isp., Ophiomorpha isp., Schaubcylindrichnus coronus and Siphonichnus isp., showing stress conditions associated with rapid sediment influx, high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors. Periodically, fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles. The fluvial-dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river-sediment influx with no clear influence of wave or tidal action. The facies of the distal delta front were controlled by episodic sedimentation, elevated water turbidity, periodically reduced oxygenation and salinity fluctuations, the associated trace fossil suite consists of a monospecific assemblage of Ophiomorpha isp. and sparse Palaeophycus isp. The proximal delta front and the distributary channel deposits are mostly unburrowed, locally displaying a few Arenicolites isp., Lockeia isp., Ophiomorpha isp., Psilonichnus isp. and Teredolites isp. The development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges, elevated water turbidity due to heightened suspended load and buoyant plumes, periodic fluctuations in salinity conditions caused by river discharges and channel avulsion. Interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment. Fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers. Wave processes tend to buffer the stresses produced by river discharge. The effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave-dominated deltaic deposits of the La Anita Formation delta show in relation to the fluvial-dominated ones.

中文翻译：

---

来自波浪和河流主导的三角洲的地质特征：LA Anita 地层，上白垩纪，南麦哲伦盆地，巴塔哥尼亚

摘要 三角洲海岸线的沉积过程会产生各种物理化学压力条件，直接影响底栖动物群。三角洲序列的地质特征反映了这些物理化学应力，例如沉积物快速流入、水浊度升高、氧合周期性降低、盐度波动以及波浪能和潮汐能。在 Austral-Magallanes 盆地的 Campanian La Anita 地层中，详细描述了两个三角洲序列的例子，每个例子都显示出波浪和河流过程的不同相对优势，从而可以识别在波浪主导下作用不同的对比应力，受河流影响的三角洲和受河流影响的三角洲。挖洞强度和鱼类多样性的变化使我们能够区分不同的物理化学应力。在以波浪为主导、受河流影响的三角洲沉积物中，前三角洲和远三角洲前缘相中，晴天海浪与风暴事件的交替是主控底栖动物群落的主控因素，表现出相交和水平要素到 Skolithos 和 Cruziana Ichnofacies，例如 Arenicolites isp., 球粒陨石 isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp. , Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. 和 Skolithos isp。水浊度和周期性降低的底水氧化条件也起到了重要但次要的作用。近端三角洲前缘，和分流和末端分流河道沉积物显示出低挖洞强度和鱼类多样性，其结构可归因于枯竭的 Skolithos Ichnofacies，很少有 Diplocraterion isp.、Gordia isp.、Lockeia isp.、Macaronichnus isp.、Ophiomorpha isp.、Schaubcylinussnus.isp.显示与快速沉积物流入、高能量和与河流排放相关的盐度降低条件相关的压力条件是最重要的控制因素。周期性地，由于河流排放和河道撕脱导致的盐度条件波动也可能发挥了重要作用。河流主导的三角洲沉积表明控制因素与河流流量和河流泥沙流入有关，没有明显的波浪或潮汐作用。远端三角洲前缘的相受偶发沉积、水浊度升高、氧合周期性降低和盐度波动的控制，相关的痕量化石套件由 Ophiomorpha isp 的单种组合组成。和稀疏的Palaeophycus isp。近端三角洲前缘和分流河道沉积物多为未挖洞，局部有少量砗磲、Lockeia、Ophiomorpha、Psilonichnus isp。和 Teredolites isp。这些套房的发展主要受高河流排放引起的沉积率增加、悬浮载荷和浮力升高引起的水浊度升高、河流排放和通道撕脱引起的盐度条件的周期性波动的控制。流域间区域的特征是相保留证据，表明氧合减少是该亚环境中最重要的控制因素。河流过程为示踪剂的底栖殖民产生了最极端的压力条件。波浪过程倾向于缓冲河流排放产生的压力。波浪对河流应力的影响反映在较高的生物扰动强度和海洋多样性上，La Anita 组三角洲的波浪主导的三角洲沉积物与河流主导的三角洲沉积物相比表现出更高的生物扰动强度和多样性。