Discharge variability-based facies models are key to understanding depositional dynamics and controlling mechanisms of fluvial accumulation. The well-exposed Silurian-Devonian Jaicós Formation, lower Parnaíba Basin, NE Brazil, allows for detailed fluvial architectural analyses in terms of variations in discharge patterns. This field-based study comprises a collection of high-resolution sedimentological, stratigraphic and paleocurrent data from 120 m of integrated logs. Eight architectural elements were recognized and fit into two distinct fluvial styles, termed fluvial units 1 and 2. Fluvial unit 1 is dominated by deposits of straight- and sinuous-crested bedforms, as constituents of downstream accretionary bars and subcritical, aggradational dunes. These elements indicate deposition in a low discharge variability perennial system, where water flow was perennial but bedforms migrated during peak-discharge events, related to a humid climate. Fluvial unit 2 abruptly overlies unit 1 and is dominated by small- to large-scale humpback dunes and antidunes deposited by unstable, transcritical and supercritical flows during non-periodic, peak-flood events. These deposits characterize an ephemeral system, in a high discharge variability regime linked to a semi-arid climate. The Jaicós fluvial system was deposited in a low subsidence basin, in low accommodation settings. Minimally affected by tectonic activity and latitudinal displacements, the Jaicós Formation displays a climate-controlled change in fluvial architecture that reflects shifts in discharge regime. These climate changes were probably triggered by global oscillations in the carbon cycle that were common during the Silurian, but most evidence is from low paleolatitude marine deposits. Thus, the abrupt fluvial architecture change in the Jaicós Formation comprises an example of climate-induced change in a hinterland fluvial system situated at moderate to high paleolatitudes in western Gondwana.

基于排放变异性的相模型是理解沉积动力学和控制河流堆积机制的关键。巴西东北部下帕纳伊巴盆地下部的志留系-泥盆系Jaicós地层暴露良好，可以根据排放模式的变化进行详细的河流建筑分析。这项基于野外的研究包括来自120 m集成测井的高分辨率沉积学，地层学和古流数据的收集。八个建筑元素被确认并适合两种截然不同的河流样式，分别称为河流单元1和2。河流单元1主要由平直和弯曲的床形沉积物组成，它们是下游增生条和亚临界，聚集沙丘的组成部分。这些元素表明多年生低排量变化系统中的沉积，该地区常年有水流，但在与潮湿气候有关的洪峰排放事件中床形迁移。河流单元2突然位于单元1之上，并且在非周期性，高峰洪水事件中，不稳定，跨临界和超临界流沉积的小到大型驼背沙丘和反沙丘占主导地位。这些沉积物以短暂的系统为特征，处于与半干旱气候相关的高排放可变性制度中。Jaicós河床系统沉积在低沉降盆地的低适应环境中。Jaicós组受构造活动和纬向位移的影响最小，在河流构造中显示出受气候控制的变化，反映了出水方式的变化。这些气候变化可能是由志留纪时期普遍存在的碳循环全球振荡引发的，但大多数证据来自古纬度低的海洋沉积物。因此，Jaicós组中突然的河流结构变化包括一个气候变化的例子，该气候变化是冈瓦纳西部中度至高古纬度腹地河流系统中的变化。