Zachos Louis G, Platt Brian F
Institut für Evolutionsbiologie und Ökologie, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn, Germany.
Department of Geology & Geological Engineering, University of Mississippi, University, MS, USA.
PeerJ. 2019 May 21;7:e6975. doi: 10.7717/peerj.6975. eCollection 2019.
Trace fossil zonation in the Hartselle Sandstone of Mississippian age (Chesterian: Visean-Serpukhovian) exposed on Fielder Ridge, Alabama is compared with modern macro-tidal flat ichnocoenoses on the Bay of Fundy at Lubec, Maine, and demonstrated to be analogous by sedimentologic and ichnotaxonomic criteria. The modern flat has minimal influence from either waves or freshwater influx, and can be divided into five distinct ichnocoenoses, characterized by surface traces (epichnia) and four sedimentologic facies defined by gross grain texture or hydrodynamic characteristics, but lacking significant surface traces. Several characteristics of tidal flat deposits in a fetch-limited, marine (i.e., non-estuarine), meso- to macro-tidal regime can be used to recognize similar environments as old as the late Paleozoic. These criteria include (1) limited influence of wind and waves on the depositional environment, (2) lack of significant freshwater influence and therefore any persistent brackish environments, (3) a distinct spatial distribution of microenvironments defined by substrate and exposure period, (4) high diversity of epichnial traces directly associated with microenvironments across the tidal flat, (5) generally low degree of reworking of traces by bioturbation but high degree of reworking by tidal currents, and (6) preservation of traces of predation and scavenging behavior on an exposed surface. These features, together with the regional depositional pattern of the Hartselle Sandstone interpreted as tide-influenced bars and shoals, support a meso- to macro-tidal interpretation of the depositional environment.
对阿拉巴马州菲尔德山脊出露的密西西比纪（切斯特阶：维宪阶-谢尔普霍夫阶）哈茨维尔砂岩中的遗迹化石分带，与缅因州卢贝克芬迪湾的现代大潮坪遗迹群落进行了比较，并根据沉积学和遗迹分类学标准证明它们具有相似性。现代潮坪受波浪或淡水注入的影响极小，可分为五个不同的遗迹群落，其特征为表面痕迹（表生迹）以及由总体粒度纹理或水动力特征定义的四种沉积相，但缺乏明显的表面痕迹。在一个受风浪影响有限的海洋（即非河口）、中潮至大潮环境中，潮坪沉积物的几个特征可用于识别与晚古生代一样古老的类似环境。这些标准包括：（1）风和浪对沉积环境的影响有限；（2）缺乏明显的淡水影响，因此不存在任何持久的咸淡水环境；（3）由基质和暴露时间定义的微环境具有明显的空间分布；（4）与整个潮坪微环境直接相关的表生迹高度多样；（5）生物扰动对痕迹的改造程度一般较低，但潮流对痕迹的改造程度较高；（6）在暴露表面保存有捕食和清道夫行为的痕迹。这些特征，连同哈茨维尔砂岩被解释为受潮汐影响的沙坝和浅滩的区域沉积模式，支持了沉积环境为中潮至大潮的解释。
