Abstract The chemostratigraphic record of the Toarcian Oceanic Anoxic Event (T-OAE) is generally well documented in epicontinental basins; however, the duration of anoxia and recovery remains poorly constrained in the Tethys Ocean owing to limited stratigraphic resolution of oceanic sections with hiatuses. In this paper, we describe a relatively continuous hemipelagic record in the Central Western Carpathians of Slovakia (Skladana Skala section), which contains the Pliensbachian/Toarcian boundary, the T-OAE, and the subsequent recovery phase. In our section, the Pliensbachian Spinatum Zone is represented by a ~ 7 m thick alternation of spotted, spiculitic marly limestones and limestones of the Allgau Formation that contain moderately diverse trace fossils including abundant Zoophycos, Lamellaeichnus and Teichichnus. In the uppermost part of the Spinatum Zone, a ~ 0.8‰ decline in δ13Ccarb values marks the carbon isotope excursion (CIE) at the Pliensbachian/Toarcian boundary. This isotope anomaly is overlain by a ~ 3 m-thick interval of spotted marly limestones and marls, which contains a positive CIE that represents the base of the T-OAE. The T-OAE interval comprises a 60 cm-thick pyritic black shale interval that lacks bioturbation and shows a negative CIE (δ13Corg values drop by 4–5‰), coincident with an increase in TOC values (from 0.3% to 2–3%), and a drop in CaCO3 values (from 50 to 80% to 3–7%). The black shale is overlain by ~8 m thick marls with rare intercalations of marly limestones, which show ammonites of the Exaratum Subzone in the lowermost part (~1 m) succeeded by Serpentinum Zone beds. This unit exhibits a second positive CIE (δ13Corg increases by 2.5‰ and δ13Ccarb increases by 1.5‰), significantly more negative δ18O values relative to the pre-T-OAE interval, and a low diversity of trace fossils dominated by Chondrites and extremely thin Zoophycos. Sponge spicules re-appear in the uppermost 6.5 m-thick interval of the section formed by the alternation of spotted marls and limestones, with ammonites of the Falciferum Subzone in the lower part and of the Bifrons Zone in the uppermost parts; however, diversity of trace fossils remains low. Based on these findings, we argue that the 60 cm-thick pyritic black shale that represents the T-OAE is a strongly condensed succession because it includes the onset of the negative CIE and the subsequent rebound, and thereby encompasses the full duration of the anoxic event. Anoxia in basins open to the oceanic Tethys thus coincided not only with reduced carbonate production but also with reduced siliciclastic supply, generating very thin black shale deposits. In contrast to current-swept swells where black shales associated with hardgrounds are thin or missing owing to winnowing, carbonate starvation was induced by a calcification crisis coincident with the T-OAE and siliciclastic starvation was probably induced by rapid sea-level rise. Although bottom waters were not anoxic in the aftermath of T-OAE, bioturbation remained restricted during the Falciferum Subzone in basinal settings, indicating that environmental stress induced by limited ventilation and/or high bottom-water temperatures were persistent. The reduced diversity of trace fossils and the re-appearance of sponge spicules close to the lower/middle Toarcian boundary indicate that the ecological recovery in basins open to the oceanic Tethys was delayed, a pattern similar to the epicontinental seas that experienced anoxia.

中文翻译：

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评估 Toarcian 海洋缺氧事件（西喀尔巴阡山脉）期间半远洋特提斯盆地的缺氧、恢复和碳酸盐生产挫折

摘要 Toarcian 大洋缺氧事件 (T-OAE) 的化学地层记录通常在陆上盆地中得到很好的记录；然而，由于具有间断的海洋剖面的地层分辨率有限，特提斯洋的缺氧和恢复的持续时间仍然受到很大限制。在本文中，我们描述了斯洛伐克中西部喀尔巴阡山脉（Skladana Skala 部分）的一个相对连续的半远洋记录，其中包含 Pliensbachian/Toarcian 边界、T-OAE 和随后的恢复阶段。在我们的剖面中，Pliensbachian Spinatum 带由约 7 m 厚的斑点、针状泥灰岩和 Allgau 组石灰岩交替代表，其中包含适度多样的痕迹化石，包括丰富的 Zoophycos、Lamellaeichnus 和 Teichichnus。在 Spinatum 带的最上部，δ13Ccarb 值下降约 0.8‰标志着 Pliensbachian/Toarcian 边界处的碳同位素偏移 (CIE)。该同位素异常被约 3 m 厚的斑点泥灰岩和泥灰岩层覆盖，其中包含代表 T-OAE 底部的正 CIE。T-OAE 层段包括一个 60 cm 厚的黄铁矿黑色页岩层段，该层段缺乏生物扰动并显示负 CIE（δ13Corg 值下降 4–5‰），同时 TOC 值增加（从 0.3% 到 2–3%） )，以及 CaCO3 值下降（从 50% 到 80% 到 3–7%）。黑色页岩被约 8 m 厚的泥灰岩覆盖，其中夹杂着罕见的泥灰岩，显示最下部（约 1 m）的 Exaratum 亚带的菊石被 Serpentinum 带层接替。该单元表现出第二个正 CIE（δ13Corg 增加 2.5‰，δ13Ccarb 增加 1.5‰），相对于前 T-OAE 间隔明显更多的负 δ18O 值，以及以球粒陨石和极薄的动物藻为主的痕量化石的低多样性. 海绵状针状体在斑纹泥灰岩和石灰岩交替形成的断面最上层6.5 m 厚间隔内重新出现，下部为镰刀菌亚带的菊石，最上部为Bifrons 带的菊石；然而，痕迹化石的多样性仍然很低。基于这些发现，我们认为代表 T-OAE 的 60 cm 厚的黄铁矿黑色页岩是一个强烈凝聚的序列，因为它包括负 CIE 的开始和随后的反弹，从而涵盖了缺氧的整个持续时间事件。因此，通向大洋特提斯的盆地缺氧不仅与碳酸盐产量减少而且与硅质碎屑供应减少相吻合，从而产生了非常薄的黑色页岩沉积物。与硬地相关的黑色页岩因风选而变薄或缺失的洋流涌浪相反，碳酸盐饥饿是由与 T-OAE 一致的钙化危机引起的，而硅质碎屑饥饿可能是由海平面快速上升引起的。尽管在 T-OAE 之后底层水没有缺氧，但在盆地环境中的镰刀菌亚带期间生物扰动仍然受到限制，这表明由有限的通风和/或高底层水温度引起的环境压力是持续存在的。