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

许多沉积盆地边缘的碎屑沉积物通常形成在均匀加深的斜坡上前阶和后阶的三角洲序列，而不是更常见的陆架-斜坡-盆地底测深模式。序列边界的性质、序列元素（“系统域”）的几何形状和堆叠在这种斜坡环境中是非常有争议的，很少有公开的例子得到很好的约束。这个项目是坡道设置序列几何的综合研究。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进行严格的现场测试：新墨西哥州圣胡安盆地的上白垩纪边缘海相沉积。该项目的主要目标是：(1)识别、评估和绘制符合层序边界客观标准的地层表面，如较老海相地层的上覆和水下暴露向下移动；(2)检验层序边界的瞬时形成和历时形成的概念；(3)记录层序不同元素（体系域）间沉积物的堆积模式和体积分配；(4)正演模拟不同构造沉降速率、海平面变化速率和幅度以及沉积物供应对层序几何变化的响应。二维、弯曲回剥将被用于重建沉积表面的几何形状。建模将基于两种数值方法的结合。一种是运动学模型，利用预设的沉积坡度和泥沙供应来产生对海平面和构造波动的地层响应。第二种是模拟“前陆”盆地环境下泥沙运移的扩散模型。该项目的总体目标是提高预测斜坡边缘盆地中岩性单元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精确信息。

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.