Comparative Ichnological Studies of Tertiary Depositional Sequences, Alabama Coastal Plain

对阿拉巴马第三纪的层序地层学研究已经圈定了大约20个沉积层序，这些层序被解释为反映了不同幅度的明显的海平面上升旋回。PI最近完成了对其中两个序列的详细研究。在组成系统域内部和之间观察到生物扰动程度、一般技术结构和离散痕迹化石的显著变化，反映了基质一致性、物理环境能量、沉积速率以及底部和/或孔隙水化学的变化，这些变化与相关的上升旋回的阶段和幅度一致。这些结果显示了在层序地层学背景下扩展痕量化石研究的潜力。为了更充分地评估这一潜力，建议对阿拉巴马第三系所圈定的所有20个沉积层序的代表性地层进行详细研究。这些分析的目的是：1)进一步评估痕迹化石组合对预测海平面介导的古环境变化的响应；2)评价系统域之间和系统域内存在的技术变异性，作为沉积环境、岩相以及相关的上升旋回的相位和幅度差异的函数。本研究将为层序地层学概念和解释海平面历史提供一个独立的测试；2)建立一套改进的技术标准，可用于识别海平面信号的模型；3)提高我们对痕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.