Taphonomy of Marsh Foraminiferal Assemblages: Implications for Rates and Mechanisms of Holocene Sea-Level Rise

沼泽有孔虫组合的埋藏学：对全新世海平面上升速率和机制的影响

• 批准号: 9614155
• 负责人: Ronald Martin
• 金额: $ 15万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-01-15 至 2000-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9614155&HistoricalAwards=false
• 关键词: Taphonomy; Marsh; Foraminiferal; Assemblages; Implications

9614155 Martin/Pizzuto Over the last decade, the applied Earth Sciences have moved from an emphasis on resource exploitation to one of resource conservation and management. In order for paleontology to fully participate in this "paradigm shift", the science of taphonomy, which has largely stressed information loss and stratigraphic disorder, must instead accentuate what can be regained from the fossil record. Data must be used to reconstruct stratigraphic signals in order to evaluate natural versus anthropogenic disturbances. Precise understanding of taphonomic filters bears strongly on the future application of paleontology and other traditional fields of the Earth sciences to environmental problems. Marshes provide a fertile proving ground for applied taphonomy. Marsh environments are extremely susceptible to natural and anthropogenic disturbance, so they are ideal for distinguishing between natural and anthropogenic change using historical (pre-anthropogenic) records. Marshes also display exceptional temporal resolution (low signal attenuation) that approaches or surpasses that of deep-sea cores, and which makes them ideal for taphonomic modeling. Nevertheless, differential preservation of marsh foraminiferal assemblages, which have been used to analyze natural and anthropogenic causes of sea-level rise, has been largely ignored. By itself, though, differential preservation can mimic sea-level change when none has actually occurred. We propose to construct taphonomic-age-environment models that describe shell input, preservation, and temporal resolution of foraminiferal assemblages in easily accessible intertidal Holocene marsh facies of the Delaware coast. We will then test our forward models (taphonomic filters) by using them to reconstruct the same inputs used to produce the filters. We will further test our models by using them to reconstruct paleoenvironments of the last ~2 ka preserved in vibracores taken from nearby sites, and assess the implications for distinguishin g natural versus anthropogenic sea-level rise. We will use multiple techniques to constrain sedimentary parameters and the reconstructions based on them. Inputs and decay rates of tests ("half-lives"), which affect the abundance, preservation, probability of reworking, and temporal resolution of foraminiferal assemblages, will be determined by seasonal sampling of selected marsh sites. Mixed layer thickness (m), sedimentation rate (v), and the bioturbation coefficient (D) will be estimated using x-rays and radiotracers (7Be, 137Cs, 210Pb, 14C). Field experiments involving artificial conservative (non-decaying) "impulse" layers of glass beads (analogous to microtektite and volcanic ash layers of similar deep-sea studies) will assess sedimentary parameters independently of radiotracers. Temporal resolution will be examined by applying several quantitative approaches, including graphic correlation, to dispersion (attenuation or smearing) of bead layers and other datums. Pollens profiles will control for possible anthropogenic changes (eutrophication due to deforestation and runoff) in test production and sedimentation. Besides the implications for the role of paleontology and stratigraphy in the environmental sciences, our investigation also bears on a number of critical (paleo) environmental issues, such as: 1) Calculation of the magnitude and rates of Holocene sea-level rise, their correlation with rates and mechanisms of proposed causal climatic phenomena, and distinguishing between natural and anthropogenic sea-level change; 2) Paleoenvironmental resolution in the Holocene below that of available climate proxies such as the marine oxygen isotope curve; 3) The natural evolution of wetlands and their management in light of the Holocene transgression; 4) Precise understanding of taphonomic filters an the integrity, time-averaging, and temporal resolution of stratigraphic sections, all of which ultimately bear on such profound paleobiological questions as patterns of extinction and the record of biodiversity dynamics in the fossil record. Answers to these questions are crucial to understanding, for example, past (and therefore current) biodiversity crises, but they are dependent upon very high temporal resolution. Other modeling efforts have concentrated on deep-sea assemblages and stable isotopes, but because of the intrinsically high temporal resolution of march assemblages, our study serves as an excellent starting point for applying quantitative taphonomic models to more stratigraphically-complex shelf and slope settings where much of the fossil record has formed.

9614155马丁/皮祖托 在过去的十年中，应用地球科学已经从强调资源开发转向资源保护和管理。 为了让古生物学充分参与这一“范式转变”，在很大程度上强调信息丢失和地层混乱的埋藏学必须转而强调可以从化石记录中恢复的东西。 数据必须用于重建地层信号，以评估自然与人为干扰。 对埋藏过滤器的准确理解对古生物学和地球科学的其他传统领域在环境问题中的未来应用有很大的影响。 沼泽为应用埋藏学提供了肥沃的试验场。 沼泽环境极易受到自然和人为干扰的影响，因此它们是利用历史（人类活动前）记录区分自然和人为变化的理想环境。 沼泽还显示出特殊的时间分辨率（低信号衰减），接近或超过深海岩心，这使得它们成为埋藏学建模的理想选择。 然而，差异保存沼泽有孔虫组合，这已被用来分析海平面上升的自然和人为原因，在很大程度上被忽视。 然而，差异保存本身可以模拟实际上没有发生的海平面变化。 我们建议构建埋藏年龄环境模型，描述壳输入，保存和时间分辨率的有孔虫组合在容易访问的潮间带全新世沼泽相的特拉华州海岸。 然后，我们将测试我们的前向模型（埋藏滤波器），使用它们来重建用于产生滤波器的相同输入。 我们将进一步测试我们的模型，用它们来重建保存在附近场地的振动岩芯中的最后~ 2ka的古环境，并评估自然与人为海平面上升的影响。 我们将使用多种技术来约束沉积参数和基于它们的重建。 测试的输入和衰减率（“半衰期”）影响有孔虫组合的丰度、保存、改造的可能性和时间分辨率，将通过对选定的沼泽地进行季节性取样来确定。 将使用X射线和放射性示踪剂（7 Be、137 Cs、210 Pb、14 C）估算混合层厚度（m）、沉积速率（v）和生物扰动系数（D）。 涉及人工保存（非衰变）玻璃珠“脉冲”层（类似于类似深海研究中的微玻璃陨石和火山灰层）的实地实验将评估不依赖放射性示踪剂的沉积参数。 时间分辨率将通过应用几种定量方法（包括图形相关性）来检查珠层和其他基准的分散（衰减或涂抹）。 花粉分布图将控制测试生产和沉积过程中可能的人为变化（由于砍伐森林和径流造成的富营养化）。 除了古生物学和地层学在环境科学中的作用外，我们的研究还涉及到一些关键的（古）环境问题，如：1）计算全新世海平面上升的幅度和速率，它们与可能的气候现象的速率和机制的关系，以及区分自然海平面变化和人为海平面变化; 2）全新世的古环境分辨率低于海洋氧同位素等气候指标，3）全新世海侵过程中湿地的自然演化及其管理; 4）准确理解埋藏滤波器和地层剖面的完整性、时间平均和时间分辨率，所有这些最终都与诸如灭绝模式和化石记录中生物多样性动态记录等深刻的古生物学问题有关。 这些问题的答案对于理解过去（因此也是当前）的生物多样性危机至关重要，但它们依赖于非常高的时间分辨率。 其他建模工作集中在深海组合和稳定同位素，但由于本质上的高时间分辨率的三月组合，我们的研究作为一个很好的起点，应用定量埋藏模型更地层复杂的大陆架和斜坡设置，其中大部分的化石记录已经形成。