The trace fossil Rosselia with its dominant species Rosselia socialis is found with various densities in both open-marine and delta systems of the Lower Ordovician Lashkerak Formation (Alborz, Iran). The trace fossil shows two types of occurrence in these two depositional systems: solitary Rosselia and crowded Rosselia ichnofabric (CRI). On a proximal-to-distal transect, solitary Rosselia occurs during long-term stable conditions with enriched bottom currents in areas above storm-wave base together with a fair-weather community of dwellers and followed equilibrium strategies (K-selected). In shallower parts, in substrates around and below fair-weather wave base with high amount of deposition and erosion, dense populations of Rosselia (CRI) occur together with subordinate trace-fossil suites (such as Diplocraterion, Skolithos and Arenicolites) produced by deep-tier, suspension-feeding animals due to short-term stable conditions with low food flux. Solitary Rosselia, with lifelong activity due to sophisticated feeding strategies, are well developed in storm deposits, and are part of shallow tiers. Forms with concentric muddy laminae indicate long-term occupation and belong to the Cruziana ichnofacies. In contrast, the behavioural style of the studied CRI, which occurs in unstable, high stress, physically controlled substrates, is comparable to the Skolithos ichnofacies in the occurrence of equilibration traces with stacked segments. In terms of sequence stratigraphy, the transgressive system tract (TST) with lower amounts of organic detritus and low accumulation rates favours the development of solitary Rosselia. In this system tract, CRI is developed during times of ravinement when winnowing and erosion led to the early development of unstable substrates. However, most occurrences of CRI are observed within the progradational packages of the highstand system tract (HST). This study suggests that CRI in event beds can be a good signature of low accommodation space and prograding clinoforms.

在下奥陶统 Lashkerak 组（Alborz，伊朗）的开放海洋和三角洲系统中发现了具有不同密度的痕迹化石Rosselia及其优势种Rosselia socialis。痕迹化石显示在这两个沉积系统中出现两种类型：单独的Rosselia和拥挤的Rosselia ichnofabric (CRI)。在近端到远端的横断面上，孤立的Rosselia发生在长期稳定的条件下，在风暴波基地以上的地区有丰富的底流，以及天气晴朗的居民社区，并遵循平衡策略（K 选择）。在较浅的部分，在具有大量沉积和侵蚀的晴天波基周围和下方的基底中，密集的Rosselia (CRI)种群与由深部产生的次级微量化石套件（如Diplocraterion、Skolithos和Arenicolites）一起出现由于短期稳定条件和低食物流量，层级悬浮喂养动物。孤独的罗塞利亚，由于复杂的饲养策略而终生活动，在风暴沉积物中发育良好，并且是浅层的一部分。具有同心泥质纹层的形式表明长期占据并属于Cruziana地层相。相比之下，所研究的 CRI 的行为风格，发生在不稳定、高应力、物理控制的基底中，与Skolithos ichnfacies 在出现具有堆叠段的平衡痕迹方面相媲美。在层序地层学上，有机碎屑含量低、堆积率低的海侵系统域（TST）有利于孤生罗塞利亚的发育. 在这个系统域中，CRI 是在沟壑时期发展起来的，当时风选​​和侵蚀导致不稳定基质的早期发展。然而，大多数 CRI 发生在高位系统域 (HST) 的前积包中。这项研究表明，活动床中的 CRI 可能是低住宿空间和前倾斜面的良好标志。