COLLABORATIVE RESEARCH: Controls on Sequence Geometry and Bounding Surfaces in Ramp Settings

输送到许多沉积盆地边缘的碎屑沉积物通常形成三角洲序列，在均匀加深的斜坡上前进和后退，而不是更常见的陆架-斜坡-盆地底部测深。层序界面的性质，以及在这种斜坡环境中的层序元素(“体系域”)的几何和堆积是非常有争议的，很少有公开发表的例子受到很好的约束。该项目是对斜坡环境中的层序几何学的综合研究。该项目将包括概念和数值模拟，并在世界上暴露最好的碎屑斜坡序列之一：新墨西哥州圣胡安盆地的上白垩统边缘海相沉积中进行严格的野外测试。该项目的主要目标是(1)识别、评价和绘制符合层序界面客观标准的地层面，如较老海相地层的超覆下移和地面暴露；(2)检验层序界面的瞬时形成与历时形成的概念，(3)记录层序不同元素(体系域)之间的沉积堆积模式和体积分配；(4)层序几何结构随不同构造沉降率、海平面变化速率和幅度以及沉积物供应的正演模型变化。二维弯曲反剥离将被应用于重建随时间推移的沉积表面的几何形状。建模将基于两种数值方法的组合。一种是运动学模型，利用预设的沉积坡度和沉积物供应来产生对海平面和构造波动的地层响应。第二种是扩散模型，它模拟了“前陆”盆地环境中的泥沙运移。该项目的总体目标是提高预测斜坡边缘盆地中岩性单元的时空分布的模型的精度，并能够从地层记录中提取有关过去海平面波动的更准确的信息。

Clastic sediments delivered to the margins of many sedimentary basins commonly form deltaic successions which forestep and backstep on evenly deepening ramps, rather than the more commonly modeled shelf-slope-basin floor bathymetry. The properties of sequence boundaries, and the geometry and stacking of sequence elements ("systems tracts") in such ramp settings are highly controversial and very few published examples are well constrained. This project is an integrated study of sequence geometry in ramp settings. The project will consist of conceptual and numerical modeling accompanied by rigorous field testing in one of the best exposed successions of clastic ramp sequences in the world: the Upper Cretaceous marginal marine deposits of the San Juan basin, New Mexico. The primary objectives of this project are to (1) identify, evaluate and map stratigraphic surfaces, which meet such objective criteria for a sequence boundary as downward shift in onlap and subaerial exposure of older marine strata, (2) test the concepts of instantaneous versus diachronous formation of sequence boundaries, (3) document stacking patterns and volumetric partitioning of sediment between different elements (systems tracts) of the sequences, (4) forward model variations in sequence geometry in response to different rates of tectonic subsidence, rates and amplitudes of sea level change, and sediment supply. Two-dimensional, flexural backstripping will be applied to reconstruct the geometry of the depositional surfaces through time. The modeling will be based on a combination of two numerical methods. One is a kinematic model using preset depositional slopes and sediment supply to generate the stratigraphic response to sea level and tectonic fluctuations. The second is a diffusion model that simulates sediment transport in a "foreland" basin setting. The overall goal of the project is to provide improved precision in models predicting the spatial and temporal distribution of lithologic units in basins with ramp margins, and to enable the extraction of more precise information about past sea level fluctuations from the stratigraphic record.