Spatial Discrimination of Complex, Low-Relief Quaternary Siliciclastic Strata Using Airborne Lidar and Near-Surface Geophysics:An Example from the Texas Coastal Plain, USA

Jeffrey G.Paine; Edward W.Collins; Lucie Costard

摘要

Depositional units preserved on coastal plains worldwide control lithologic distribution in the shallow subsurface that is critical to infrastructure design and construction,and are also an important repository of information about the large-scale climate change that has occurred during many Quaternary glacialinterglacial cycles.The lateral and vertical lithologic and stratigraphic complexity of these depositional units and their response to climatic and sea-level change are poorly understood,making it difficult to predict lithologic distribution and to place historical and future climate and sea-level change within a natural geologic context.Mapping Quaternary siliciclastic depositional units on low-relief coastal plains traditionally has been based on their expression in aerial photographs and low-resolution topographic maps.Accuracy and detail have been hindered by low relief and lack of exposure.High-resolution airborne lidar surveys,along with surface and borehole geophysical measurements,are being used to identify subtle lateral and vertical boundaries of lithologic units on the Texas Coastal Plain within Quaternary strata.Ground and borehole conductivity measurements discriminate sandy barrier island and fluvial and deltaic channel deposits from muddy floodplain,delta-plain,and estuarine deposits.Borehole conductivity and natural gamma logs similarly distinguish distinct lithologic units in the subsurface and identify erosional unconformities that likely separate units deposited during different glacial-interglacial stages.High-resolution digital elevation models obtained from airborne lidar surveys reveal previously unrecognized topographic detail that aids identification of surface features such as sandy channels,clay-rich interchannel deposits,and accretionary features on Pleistocene barrier islands.An optimal approach to identify lithologic and stratigraphic distribution in low-relief coastal-plain environments employs ① an initial lidar survey to produce a detailed elevation model;② selective surface sampling and geophysical measurements based on preliminary mapping derived from lidar data and aerial imagery;and ③ borehole sampling,logging,and analysis at key sites selected after lidar and surface measurements are complete.

机译：全球沿海沿海平原上保存的沉积单元控制着浅层地下的岩性分布，这对基础设施的设计和建设至关重要，也是许多第四纪冰川间冰期循环中发生的大规模气候变化信息的重要信息库。这些沉积单元的垂直岩性和地层复杂性及其对气候和海平面变化的响应知之甚少，这使得难以预测岩性分布以及难以将历史和未来的气候和海平面变化置于自然地质背景下。低起伏沿海平原上的硅质碎屑沉积单元传统上是基于它们在航空照片和低分辨率地形图中的表达而来的，其准确性和细节受到低起伏和缺乏暴露的阻碍。高分辨率的空中激光雷达测量以及表面和钻孔地球物理测量地层和井眼的电导率测量可以区分泥质洪泛区，三角洲平原和河口沉积物的沙质屏障岛以及河流和三角洲河道沉积物钻孔电导率和天然伽马测井同样可以区分地下不同的岩性单元并识别出侵蚀不整合面，这些不整合面可能会将在不同的冰川间期沉积的沉积单元分开。从机载激光雷达勘测获得的高分辨率数字高程模型揭示了先前无法识别的地形细节，有助于识别地层特征，如砂质河道，富粘土的河道间沉积物和更新世屏障岛上的增生特征。识别低起伏沿海平原环境中岩性和地层分布的最佳方法是：①初步进行激光雷达勘探以产生一个详细的高程模型;②基于从激光雷达数据和航拍图像得出的初步映射进行的选择性地表采样和地球物理测量;以及③激光雷达和地表测量完成后在选定的关键地点进行了井眼采样，测井和分析。

Spatial Discrimination of Complex, Low-Relief Quaternary Siliciclastic Strata Using Airborne Lidar and Near-Surface Geophysics:An Example from the Texas Coastal Plain, USA

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