科研之友
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摘要
Although large-scale transverse drainages (TDs) such as those of the Susquehanna River above Harrisburg, PA, have been recognized since the nineteenth century, only two systematic surveys have been published of TDs (Ver Steeg, 1930; Oberlander, 1965). A topographic and statistical analysis of TDs in the Susquehanna River basin using Google Earth (R) and associated overlays identified 653 TDs in the study area, 95% of which contain streams with discharges of <10 m(3)/s (cms). The TD depths ranged from a 23-m-deep water gap near Blain, PA, to the 539-m-deep gorge of the Juniata River through Jacks Mountain. Although TD depth tends to increase with stream size, significant exceptions were noted. Streams with discharges of <10 cms make up the majority of TDs regardless of the lithology of the breached structure. Overall, TDs through sandstone-capped ridges are deeper than those topped by shales, and TDs in both lithologies display a log-normal depth distribution, which may be indicative of a preferred value. Stream flow direction was primarily perpendicular to local structural strike, with 47% of streams flowing NW and 53% flowing SE. Nineteen percent of the TDs are aligned with at least one other TD, with aligned segment lengths ranging from 0.5 to 14.8 km. The majority of TDs are in rocks of Paleozoic age. The techniques described here allow the frequency and distribution of TDs to be quantified to better integrate them into models of basin evolution.
- 出版日期2013-3-15
