Abstract The Toirano karst system is located in the Ligurian Alps (north Italy), around 4.5 km inland from the coastline and carved in Middle Triassic dolostone. It comprises five cave levels over a 154 m altitudinal range, specifically Ulivo (340 m a.s.l.), Colombo (247 m a.s.l), Upper Santa Lucia (215 m a.s.l.), Lower Santa Lucia (201 m a.s.l.) and Basura (186 m a.s.l.) caves. The system is active at lower altitudes, as testified by the thermal spring currently located at 70 m a.s.l. along the Varatella valley. Speleogenesis was attributed to the action of epigenic processes by other authors. However, the extraordinary geodiversity of the underground morphologies and deposits are at odds with this interpretation. Accordingly, this work investigates the genesis of the Toirano karst system, in relation to the landscape evolution of the surrounding area. A detailed morphological and mineralogical investigation of cave geoforms and deposits, together with the presence of an active low thermal sulphide spring on the Varatella valley and only ~100 m below the Basura Cave, sustain the hypothesis of a hypogene origin of the caves. This work shows that most of the caves formed close to the former water table (base) level, in turn determined by the mean sea level. Geochronological analyses, including U/Th (n = 13) and cosmogenic burial (n = 1) dating, together with an estimated incision rate of the Varatella valley of around 0.1 mm y-1, have allowed to assess the age of the highest cave (Ulivo) at around 2.7 Ma, Colombo at ~1.8 Ma, Upper Santa Lucia at ~1.5 Ma, Lower Santa Lucia ~1.3 Ma and Basura at ~1.2 Ma. Estimated palaeotemperature attained through isotope analyses and fluid inclusions on speleothems suggest that the temperature of rising waters was lower than 50 °C and possibly ranging between ~12 and ~20°C, indicating that hydrothermal fluids were not the main driver of speleogenesis, at least in the late speleogenic phases. Additionally, sulphuric acid speleogenesis by-products were not identified. Accordingly, hypogenic speleogenesis occurred because of the action of low temperature CO2-rich rising fluids. A late stage of epigenic speleogenesis has been detected because of the clear evidences of condensation-corrosion morphologies, occurred since ~150 ka (possibly earlier) when caves were finally connected to the surface because of valley enlargement. Besides uncovering the genesis of the Toirano karst system, this study demonstrates that the combination of local geology, surface vs underground geomorphological observations, climate change vs landscape evolution evaluation and geochemical data is of key importance for interpreting subsurface land-shaping processes.

中文翻译：

---

与景观演化相关的复杂洞穴系统中的低生洞穴生成、后期表观叠印和冷凝腐蚀（意大利利古里亚托伊拉诺）

摘要 托伊拉诺岩溶系统位于利古里亚阿尔卑斯山（意大利北部），距海岸线内陆约4.5公里，由中三叠统白云岩雕刻而成。它包括海拔 154 m 的五个洞穴层，特别是 Ulivo (340 m asl)、Colombo (247 m asl)、Upper Santa Lucia (215 m asl)、Lower Santa Lucia (201 m asl) 和 Basura (186 m asl) ) 洞穴。该系统在低海拔地区是活跃的，目前位于瓦拉泰拉山谷沿线海拔 70 m 处的温泉证明了这一点。洞穴生成归因于其他作者的表观过程的作用。然而，地下形态和沉积物的非凡地质多样性与这种解释不一致。因此，这项工作调查了 Toirano 岩溶系统的起源，与周边地区的景观演变有关。对洞穴地质构造和沉积物的详细形态学和矿物学调查，以及 Varatela 山谷和 Basura 洞穴下方仅约 100 m 的活跃低热硫化物泉的存在，支持了洞穴起源的假设。这项工作表明，大多数洞穴形成于前地下水位（基准）水平附近，反过来又由平均海平面决定。地质年代学分析，包括 U/Th (n = 13) 和宇宙成因埋藏 (n = 1) 年代测定，以及 Varatela 山谷约 0.1 毫米 y-1 的估计切口率，已允许评估最高洞穴的年龄(Ulivo) 约 2.7 Ma，科伦坡约 1.8 Ma，上圣卢西亚约 1.5 Ma，下圣卢西亚约 1.3 Ma 和巴苏拉约 1.2 Ma。通过同位素分析和洞穴岩石上的流体包裹体获得的估计古温度表明，上升水域的温度低于 50 °C，可能介于 ~12 至 ~20°C 之间，表明热液流体不是洞穴生成的主要驱动力，至少在晚期成穴阶段。此外，未鉴定出硫酸成穴副产物。因此，由于低温富含 CO2 的上升流体的作用，发生了低成因洞穴发生。由于冷凝腐蚀形态的明显证据，已检测到表生洞穴发生的晚期阶段，发生于约 150 ka（可能更早），当时由于山谷扩大，洞穴最终连接到地表。除了揭示托伊拉诺喀斯特系统的起源，