Mid-Wisconsinan stratigraphy and paleoenvironments at the St. Charles site in south-central Iowa

Baker, Richard G.; Schwert, Donald P.; Bettis, E. Arthur; Kemmis, Timothy J.; Horton, Diana G.; Semken, Holmes A.

doi:10.1130/0016-7606(1991)103<0210:mwsapa>2.3.co;2

Cited by 20 publications

(2 citation statements)

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“…No ice bounded the lobe in Iowa to help resist flow (Figure 2), so the reconstructed driving stress of the lobe should provide a good estimate of its average basal shear stress, at least in areas away from the glacier margin. The low basal shear stress indicates that the lobe was not frozen to its bed, an inference consistent with the relatively warm boreal climate during the lobe's advance (Baker, 1996; Bettis et al, 1996; Schwert & Torpen, 1996). The time‐averaged advance rate of the lobe, estimated from radiocarbon dates (Clayton et al, 1985) corrected for variable atmospheric production of C 14 (Stuiver et al, 1998), was ~1700 m year −1 .…”

Section: Introductionmentioning

confidence: 67%

Absent drumlins beneath southern lobes of the Laurentide Ice Sheet: A new hypothesis based on Des Moines Lobe dynamics inferred from landforms

Iverson,

Krueger,

Harding

2023

Earth Surf Processes Landf

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Spatial distributions of drumlin fields encode information about ice sheet dynamics. No drumlins formed beneath the most lobate parts of the Laurentide Ice Sheet's southern margin, in South Dakota, Iowa and Illinois, whereas ice lobes to the northeast generally produced drumlins. This pattern may have resulted from northerly ice overriding permafrost. Here we propose a new hypothesis for this pattern by constructing a LiDAR‐based landform map and applying a model of drumlin formation to account for the absence of drumlins beneath the largest of the ice sheet's southern lobes, the Des Moines Lobe. Broad belts of hummocky topography, ice‐walled lake plains, doughnuts and minor moraines, which together cover 90% of the lobe's upland area in Iowa, attest to widespread ice stagnation, as does the lobe's scarcity of eskers. Most stagnation topography is subtle, with insufficient relief to have obscured drumlins that might have formed before stagnation. Minor moraines are crevasse‐squeeze ridges diagnostic of surging, and their ubiquity indicates that during surging, the lobe's soft bed was weak nearly everywhere. End moraines are generally parallel to a minor moraine setup‐glacier, implying that surge‐driven advances were more numerous than indicated by the three major end moraines of the lobe. In the only physically based model of drumlin formation that includes surging, till deposition occurs during surges when effective pressure is uniformly low, whereas drumlins develop during quiescent flow between surges, when basal slip and low‐pressure R‐channels create the spatial gradients in effective pressure necessary to sculpt drumlins by differential erosion. Landforms of the lobe, however, indicate stagnation and down‐wasting during quiescence, without significant basal slip or hydraulic potential gradients necessary for R‐channels. We hypothesize that for the three southernmost lobes of the Laurentide Ice Sheet, surging followed by widespread down‐wasting of stagnant ice prevented drumlin formation, whereas beneath northern lobes it was permitted by climatically‐forced ice advance.

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Section: Introductionmentioning

confidence: 67%

Absent drumlins beneath southern lobes of the Laurentide Ice Sheet: A new hypothesis based on Des Moines Lobe dynamics inferred from landforms

Iverson,

Krueger,

Harding

2023

Earth Surf Processes Landf

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“…U. dioica ssp. dioica is not officially represented in California; it was, however, introduced to other parts of North America by European settlers in the 1800s and entered into widespread medicinal use by Native Americans after that ( Baker et al, 1991 ; Borchers et al, 2000 ; Preston and Woodland, 2012 ; Santucci and Tweet, 2020 ).…”

Section: Resultsmentioning

confidence: 99%

KCNQ and KCNE Isoform-Dependent Pharmacology Rationalizes Native American Dual Use of Specific Plants as Both Analgesics and Gastrointestinal Therapeutics

et al. 2021

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Indigenous peoples of the Americas are proficient in botanical medicine. KCNQ family voltage-gated potassium (Kv) channels are sensitive to a variety of ligands, including plant metabolites. Here, we screened methanolic extracts prepared from 40 Californian coastal redwood forest plants for effects on Kv current and membrane potential in Xenopus oocytes heterologously expressing KCNQ2/3, which regulates excitability of neurons, including those that sense pain. Extracts from 9 of the 40 plant species increased KCNQ2/3 current at –60 mV by ≥threefold (maximally, 15-fold by Urtica dioica) and/or hyperpolarized membrane potential by ≥-3 mV (maximally, –11 mV by Arctostaphylos glandulosa). All nine plants have traditionally been used as both analgesics and gastrointestinal therapeutics. Of two extracts tested, both acted as KCNQ-dependent analgesics in mice. KCNQ2/3 activation at physiologically relevant, subthreshold membrane potentials by tannic acid, gallic acid and quercetin provided molecular correlates for analgesic action of several of the plants. While tannic acid also activated KCNQ1 and KCNQ1-KCNE1 at hyperpolarized, negative membrane potentials, it inhibited KCNQ1-KCNE3 at both negative and positive membrane potentials, mechanistically rationalizing historical use of tannic acid-containing plants as gastrointestinal therapeutics. KCNE dependence of KCNQ channel modulation by plant metabolites therefore provides a molecular mechanistic basis for Native American use of specific plants as both analgesics and gastrointestinal aids.

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Ice‐wedge casts and relict polygonal patterned ground in North‐East Iowa, USA

Walters

1994

Permafrost & Periglacial

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Sediment‐filled wedges and associated polygonal patterned ground occur in pre‐Illinoian sediments in north‐east Iowa. A total of 183 vertical to near‐vertical wedge‐shaped bodies of sand have been observed at 12 sites in Black Hawk County, Iowa, and 80 of them were examined in detail. The wedges average 105cm in width at their tops and about 190cm in depth. Infilling material is mostly sand, with pockets of silt, silty sand, and gravelly sand. Slump and subsidence features were also noted in some wedges. Loamy sediment about 1 m thick, with a stone line at its base, overlies the sediment‐filled wedges and usually descends slightly into their upper parts.Based on their characteristics, these sediment‐filled wedges are interpreted as ice‐wedge casts. Supportive palaeoenvironmental studies in Iowa and adjacent states indicate that tundra conditions probably existed in places between 21,000 and 16,500 years BP, the coldest part of late Wisconsinan time. Mean annual air temperatures at this time may have been at least 14°C colder than at present. The degradation of permafrost and formation of ice‐wedge casts must have occurred near the end of this episode of cold climate, which also promoted extreme erosion of the landscape in north‐east Iowa. Aeolian and slopewash deposits later buried the erosion surface and the ice‐wedge casts.

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Mid-Wisconsinan stratigraphy and paleoenvironments at the St. Charles site in south-central Iowa

Cited by 20 publications

References 0 publications

Absent drumlins beneath southern lobes of the Laurentide Ice Sheet: A new hypothesis based on Des Moines Lobe dynamics inferred from landforms

Absent drumlins beneath southern lobes of the Laurentide Ice Sheet: A new hypothesis based on Des Moines Lobe dynamics inferred from landforms

KCNQ and KCNE Isoform-Dependent Pharmacology Rationalizes Native American Dual Use of Specific Plants as Both Analgesics and Gastrointestinal Therapeutics

Ice‐wedge casts and relict polygonal patterned ground in North‐East Iowa, USA

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