18 research outputs found

    Eogenetic Karst Hydrology: Insights From the 2004 Hurricanes, Peninsular Florida

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    Eogenetic karst lies geographically and temporally close to the depositional environment of limestone in warm marine water at low latitude, in areas marked by midafternoon thunderstorms during a summer rainy season. Spring hydrographs from such an environment in north-central Florida are characterized by smooth, months-long, seasonal maxima. The passage of Hurricanes Frances and Jeanne in September 2004 over three field locations shows how the eogenetic karst of the Upper Floridan Aquifer responds to unequivocal recharge events. Hydrographs at wells in the High Springs area, Rainbow Springs, and at Morris, Briar, and Bat Caves all responded promptly with a similar drawn-out rise to a maximum that extended long into the winter dry season. The timing indicates that the typical hydrograph of eogenetic karst is not the short-term fluctuations of springs in epigenic, telogenetic karst, or the smoothed response to all the summer thunderstorms, but rather the protracted response of the system to rainfall that exceeds a threshold. The similarity of cave and noncave hydrographs indicates distributed autogenic recharge and a free communication between secondary porosity and permeable matrix—both of which differ from the hydrology of epigenic, telogenetic karst. At Briar Cave, drip rates lagged behind the water table rise, suggesting that recharge was delivered by fractures, which control the cave’s morphology. At High Springs, hydrographs at the Santa Fe River and a submerged conduit apparently connected to it show sharp maxima after the storms, unlike the other cave hydrographs. Our interpretation is that the caves, in general, are discontinuous

    Paleo-Yardangs -- Wind-Scoured Desert Landforms at the Permo-Triassic Unconformity

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    In Canyonlands National Park, south-east Utah, at least 29 partly exhumed, aligned sandstone ridges trending generally N20-degrees-W occur at the upper unconformable surface of the Lower Permian (Leonardian) White Rim Sandstone. The ridges are at least 1.5 km long, 250 m wide and have up to 14 m of vertical relief (mean of 9 m). A thin lag of coarse sandstone that contains wind-ripple laminae and granule ripples directly overlies the ridges. Angular blocks of sandstone within the lag and sand-filled fissures immediately below the lag, within the ridges, attest to early cementation of the ridge-forming material. SE-dipping aeolian cross-strata within the White Rim Sandstone and within the lag closely parallel the ridge trend. The ridges are interpreted as wind-sculpted desert landforms (yardangs) that developed on the lithified upper surface of the White Rim Sandstone during an extended period of hyperaridity towards the end of the Permian
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