Exploring the controls of Early Aptian Tethyan and proto-Atlantic reefal palaeoecology turnover

以前的工作的支持者和同事在实地领域在阿曼，克罗地亚，西班牙和葡萄牙记录特提斯和原大西洋较低的Aptian珊瑚礁生态系统暂时崩溃，取而代之的是有问题的微型encruster社区，如在阿曼平台，分布超过10万平方公里。从珊瑚rudist microencruster相的突然过渡，代表了深刻的古生态周转在这些浅的热带平台设置。重要的特提斯的时间，相，和分类的微encruster事件的差异是公认的。根据高分辨率化学地层学，微结壳间隔（持续时间约为100年）。300 kyr）被认为是OAE 1a、OAE 1a等效间期本身（C4-C6）和OAE 1a后即刻阶段的预兆。在西班牙和葡萄牙的部分，Lithocodium相是强烈钻孔的，并形成了一米大小的碳酸盐体，包裹着珊瑚碎石。在阿曼和克罗地亚，rudist-coral碎片是罕见的缺席和bacinelloid相形式米到公里大小的上层建筑。在现有大量数据的推动下，支持者认为，迄今为止未知的控制触发这些显着的相模式值得足够的重视。出发点是观察特提斯（及以外）的功能，在时间上与白垩纪的主要环境扰动事件（OAE 1a）相吻合。本提案建议探索早期Aptian epeiric-nearitic海水属性，重点是溶解氧水平（沿海缺氧）。在近代世界，全世界已知的缺氧死区水体不少于375个沿海区。近年来海水氧耗竭的机制（高温、营养盐流入增加、微生物消耗溶解氧等）在阿普梯阶早期广阔、温暖、含盐量高的浅海中，这一现象更为强烈（水壶效应）。我们在这里假设，海水属性暂时达到以上的耐受水平的rudist珊瑚群落，并取代了更哈代microencruster相。第一个数据集利用完善的稀土元素和铀同位素（238 U/235 U）的代理敏感的海水氧化还原条件。这两个替代指标都独立地表明所研究地点在OAE 1a期间沿海海水氧气水平较低。 本建议是重要的，原因如下：控制OAE 1a期间沿海生态系统周转的参数，如果得到更好的理解，有很大的潜力来阐明一般的OAE 1a管理过程。这在环境扰动期间的大陆-海洋耦合过程中尤其重要。

Previous work by the proponents and colleagues in field areas in Oman, Croatia, Spain, and Portugal documented that Tethyan and proto-Atlantic lower Aptian reefal ecosystems temporally collapsed and were replaced by problematic micro-encruster communities spreading over more than 100000 km2 such as in the Oman platform. The abrupt transition from coral-rudist to microencruster facies represents a profound palaeo-ecological turnover in these shallow tropical platform settings. Important Tethys-wide differences in the timing, facies, and taxonomy of the micro-encruster events are recognized. Based on high-resolution chemostratigraphy, the microencruster intervals (durations of ca. 300 kyr) have been dated as harbinger of the OAE1a, the OAE1a-equivalent interval itself (C4-C6), and the immediate post-OAE1a phase. In sections in Spain and Portugal, Lithocodium facies is intensely bored and forms meter-sized carbonate bodies encrusting coral rubble. In Oman and Croatia, rudist-coral fragments are scarce to absent and bacinelloid facies forms meter to km-sized superstructures. Motivated by the very substantial data set available, the proponents suggest that the hitherto unknown controls triggering these remarkable facies patterns merit an adequate level of attention. The starting point is the observation of a Tethys-wide (and beyond) feature that coincides in time with a major environmental perturbation event (OAE1a) in the Cretaceous. The present proposal suggests exploring early Aptian epeiric-neritic seawater properties with focus on dissolved oxygen levels (coastal hypoxia). In the Recent world, oxygen-depleted dead zone water bodies are known from not less than 375 coastal zones worldwide. The mechanisms leading to seawater oxygen depletion in the Recent (high temperatures, enhanced nutrient influx, microbial consumption of dissolved seawater oxygen etc.) have arguable been far more intense in the vast, warm and saline shallow epeiric seas of the early Aptian (kettle effect). We here hypothesize that seawater properties temporally reached above-tolerance levels for rudist-coral communities and were replaced by even more hardy microencruster facies. First data sets exploit the well-established REE and uranium isotope (238U/235U) proxies sensitive to seawater redox conditions. Both of these proxies independently point to lower coastal seawater oxygen levels during OAE1a at the sites studied. The present proposal is important for the following reason: The parameters controlling coastal ecosystem turnover during OAE1a have, when better understood, a high potential to shed light on processes governing OAE1a in general. This is particularly significant in the context of coupled continent-ocean processes during time periods of environmental perturbation.