Sand ridges, a common feature of modern open shelves, reflect persistent currents and sediment availability under recent transgressive conditions. They represent the largest bedforms in the oceans and, as such, can yield information on long-term oceanographic processes. However, there is a limited number of tidal sand ridges documented from the rock record, examples of regressive tidal sand ridges are scarce and studies describing ridges in straits are even more rare. This study analyses a Gelasian succession within a structurally controlled, tide-dominated strait in the Siderno Basin, southern Italy. The strait connected two wider basins, and accumulated sediments reworked by amplified tidal (bi-directional) currents. A series of tidal sand ridges with superimposed dunes developed close to the south-eastern end of the strait, where bathymetry was deeper and flow expansion occurred. One of the best-exposed tidal sand ridges, 65 m thick, crops out along a ca 2 km long cliff. Large-scale, ESE-prograding, seaward-offlapping shingles contain sets of bioclastic–siliciclastic, coarse-grained, cross-stratified sandstones, erosionally overlying upper Pliocene shelf marls and fine-grained sandstones. Cross-strata show angular, tangential and sigmoidal foresets with compound architectures and a SSE migration, i.e. oblique to the main growth direction. Fossil content indicates open-marine conditions. The succession changes abruptly across an erosion surface to non-tidal, highly burrowed mixed siliciclastic–bioclastic fine-grained sandstones, less than 15 m thick. Documented features reflect stages of nucleation, active accretion and abandonment of an individual sand ridge, during a complete cycle of relative sea-level change. The ridge formed during a phase of normal regression, with accretion occurring during an initial highstand and the ensuing falling stage. During the lowstand the ridge was split into several minor bodies by enhanced tidal currents. The ensuing transgression draped the moribund ridge with tabular strata, whereas final highstand shelf sedimentation reworked the top of the underlying sand body with weak currents.

中文翻译：

---

混合生物碎屑 - 硅质碎屑回归潮汐沙脊的解剖：来自意大利南部更新世西德诺海峡的基于相的案例研究

沙脊是现代开放式陆架的一个共同特征，反映了近期海侵条件下持续的水流和沉积物的可用性。它们代表了海洋中最大的海底形态，因此可以产生关于长期海洋过程的信息。然而，岩石记录中记载的潮汐沙脊数量有限，退行潮汐沙脊的例子很少，描述海峡中潮汐脊的研究更是罕见。本研究分析了意大利南部 Siderno 盆地结构控制、潮汐主导的海峡内的 Gelasian 序列。海峡连接了两个更宽的盆地，积累的沉积物被放大的潮汐（双向）流重新加工。在海峡东南端附近形成了一系列带有叠加沙丘的潮汐沙脊，在那里测深更深并且发生了流量膨胀。最暴露的潮汐沙脊之一，65 m 厚，沿着一条钙2公里长的悬崖。大规模的、ESE 进积、向海上翻的带状疱疹包含成组的生物碎屑-硅质碎屑、粗粒、交叉层状砂岩，侵蚀覆盖在上新世陆架泥灰岩和细粒砂岩上。跨地层显示具有复合结构和 SSE 迁移的角、切线和 S 形预测，即与主要增长方向倾斜。化石含量表明开放的海洋条件。整个侵蚀面的序列突然变化为非潮汐的、高度挖掘的混合硅质碎屑-生物碎屑细粒砂岩，厚度小于 15 m。记录的特征反映了在相对海平面变化的完整周期中单个沙脊的成核、主动增生和废弃阶段。在正常回归阶段形成的脊，吸积发生在最初的高位和随后的下降阶段。在低位期间，海脊被增强的潮汐流分裂成几个小天体。随之而来的海侵使垂死的海脊覆盖了板状地层，而最终的高位陆架沉积使下伏砂体顶部的水流微弱。