Susquehanna Shale Hills CZO hosts Dorothy Merritts for All Hands 2015

The annual SSHCZO All Hands meeting featured Dr. Dorothy Merritts, Harry W. and Mary B. Huffnagle Professor of Geosciences and Chair of the Department of Earth and Environment at Franklin and Marshall College, as invited guest.  In addition to visiting the CZO catenas in Shale Hills and Garner Run, Merritts presented the opening seminar “Lidar and Field Analysis of Periglacial Landforms and their Paleoclimatic Significance, Unglaciated Pennsylvania.”

(Top): Gelifluction lobes and sheets along the slopes of the Tien Shan Mountains, Kyrgyzstan. Note that lobes widen downslope, becoming sheets, and in the valley bottom become much broader sheets with thermokarst features. Photographer and copyright: Marli Miller, University of Oregon (http://marlimillerphoto.com/). (Bottom) Lidar-derived (LAS files) slopeshade on color-shaded DEM showing solifluction lobes and sheets along the north- and south-facing slopes of Nittany Mountain, approximately 40 km south of the LGM maximum ice limit, near Madisonburg, central Pennsylvania. Lobes are better developed on the south-facing slope, and become longer and wider downslope. On the south-facing slope, lobes become sheets that trend become oriented obliquely with respect to slope. At this location, Nittany Mountain is the northern limb of a syncline. Sandstone dipping south along the ridge crest is the Silurian Tuscarora Formation; mid-slopes and valley bottom are Silurian Clinton Group (sandstone and shale). Lobes along mid-slope contain Tuscarora sandstone from the ridge crest area.

Abstract:  The advent of high-resolution orthoimages, topographic datasets acquired with lidar, and GPS surveying offers opportunities to map relatively fine-scale landforms, even where forested, over broad areas. Using all three technologies, we are compiling a statewide GIS database of periglacial landforms south of Pleistocene full glacial ice margins in Pennsylvania. Results from our fieldwork, which includes backhoe trenching and vibra-coring, are combined with this GIS database and previous research to evaluate the use of periglacial landforms as paleoclimatic indicators. In particular, we search for periglacial landforms that are diagnostic of the former existence and degradation of permafrost, which is ground that remains at or below the freezing point of water (0° C) for two or more consecutive years and which has an uppermost seasonally thawed active layer (typically ≤0.5 m thick). Continuous permafrost exists today in regions with mean annual air temperatures (MAAT) less than approximately -6° to -8° C, and discontinuous permafrost occurs in regions with MAAT less than approximately -0.5° C to -2° C. The boundaries of continuous and discontinuous permafrost have shifted south and north with multiple cold glacial to warm interglacial climate cycles during the Quaternary Period (~2.6 million years to present), and the last glacial maximum (LGM) extended from 26.5 to 19-20 ka.
We have identified the following evidence of permafrost throughout Pennsylvania, at all altitudes: 1) extensive networks of thermal contraction polygons on shale hills and side slopes; 2) thick, ubiquitous gelifluction sheets and lobes on quartzite, sandstone, and diabase ridges and side slopes (continuing downslope over shale benches at many locations); and 3) several pingos in valley bottoms. In addition to these landforms, we document two others—retrogressive thaw slumps and thermokarst gullies--that are common in regions of permafrost thaw today. Our radiocarbon dating, combined with paleoseed analysis, indicates that valley bottom wetlands became established on periglacial rubble (including extensive, low-gradient colluvial debris aprons and tributary fans) and thermokarst features after permafrost thaw during the late Pleistocene, and that in many locations these wetlands persisted throughout the Holocene until European settlement. Wetland (hydric) soils are still preserved at numerous locations where buried beneath historic sediment that was shed from hillslopes and trapped in valley bottoms as a result of land clearing, farming, and mill damming that began in the 1700s.

Chen Bao, PhD Candidate Petroleum and Natural Gas Engineering, discusses the finer points of RT-Flux-PIHM model.

Chen Bao, PhD Candidate Petroleum and Natural Gas Engineering, discusses the finer points of RT-Flux-PIHM model.

(Top): Gelifluction lobes and sheets along the slopes of the Tien Shan Mountains, Kyrgyzstan. Note that lobes widen downslope, becoming sheets, and in the valley bottom become much broader sheets with thermokarst features. Photographer and copyright: Marli Miller, University of Oregon (http://marlimillerphoto.com/). (Bottom) Lidar-derived (LAS files) slopeshade on color-shaded DEM showing solifluction lobes and sheets along the north- and south-facing slopes of Nittany Mountain, approximately 40 km south of the LGM maximum ice limit, near Madisonburg, central Pennsylvania. Lobes are better developed on the south-facing slope, and become longer and wider downslope. On the south-facing slope, lobes become sheets that trend become oriented obliquely with respect to slope. At this location, Nittany Mountain is the northern limb of a syncline. Sandstone dipping south along the ridge crest is the Silurian Tuscarora Formation; mid-slopes and valley bottom are Silurian Clinton Group (sandstone and shale). Lobes along mid-slope contain Tuscarora sandstone from the ridge crest area.


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