Comparative Ichnological Studies of Tertiary Depositional Sequences, Alabama Coastal Plain

阿拉巴马州第三系的层序地层学研究已经划定了大约20个沉积层序，这些层序被解释为反映了不同量级的明显的海平面升降旋回。PI最近完成了对其中两个序列的详细研究。在组成体系域内部和之间观察到生物扰动程度、一般遗迹组构和离散遗迹化石的显著差异，反映了与相关的海平面旋回的阶段和大小相一致的基质浓度、物理环境能量、沉积速率和底水和/或孔隙水化学的变化。这些结果证明了在层序地层学的背景下扩展遗迹化石研究的潜力。为了更全面地评估这一潜力，建议对阿拉巴马州第三系划定的所有20个沉积层序所代表的地层进行详细研究。这些分析的目的是：1)进一步评估遗迹化石组合对预测的海平面介导性古环境变化的响应；2)评估体系域之间和体系域内存在的生物变异性，作为沉积环境、岩相以及相关的海平面旋回的阶段和大小的差异的函数。这项研究将1)提供层序地层学概念和解释的海平面历史的独立测试，2)建立一套改进的遗迹标准，可以纳入到有助于识别海平面信号的模型中，3)提高我们对遗迹化石作为古环境指标的整体理解。

Sequence stratigraphic studies of the Alabama Tertiary have resulted in the delineation of approximately twenty depositional sequences, which are interpreted to reflect distinct eustatic sea-level cycles of varying magnitude. The PI recently completed detailed studies of two of these sequences. Significant variations in degree of bioturbation, general ichnofabrics, and discrete trace fossils are observed within and between component systems tracts, and reflect changes in substrate consistency, physical environmental energy, sedimentation rate, and bottom- and/or pore-water chemistry that are consistent with both the phase and magnitude of the associated eustatic cycles. These results demonstrate the potential of extended trace fossil studies in the context of sequence stratigraphy. In order to more fully assess this potential, detailed studies of strata representative of all of the twenty depositional sequences delineated in the Alabama Tertiary are proposed. The objectives of these analyses are: 1) to further assess the response of trace-fossil assemblages to predicted sea- level-mediated paleoenvironmental changes; and 2) to evaluate the ichnological variability that exists between and within systems tracts as a function of differences in depositional environment, lithofacies, and phase and magnitude of associated eustatic cycles. This research will 1) provide an independent test of sequence stratigraphic concepts and interpreted sea-level histories, 2) establish an improved set of ichnological criteria that can be incorporated into models useful for recognizing the eustacy signal, and 3) improve our overall understanding of trace fossils as paleoenvironmental indicators.