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At least 253 records · Page 14Linked to original sources
USGS2023

Poleward amplification, seasonal rainfall and forest heterogeneity in the Miocene of the eastern USA

Paleoclimate reconstructions can provide a window into the environmental conditions in Earth history when atmospheric carbon dioxide concentrations were higher than today. In the eastern USA, paleoclimate reconstructions are sparse, because terrestrial sedimentary deposits are rare. Despite this, the eastern USA has the largest population and population density in North America, and understanding the effects of current and future climate change is of vital importance. Here, we provide terrestrial paleoclimate reconstructions of the eastern USA from Miocene fossil floras. Additionally, we compare proxy paleoclimate reconstructions from the warmest period in the Miocene, the Miocene Climatic Optimum (MCO), to those of an MCO Earth System Model. Reconstructed Miocene temperatures and precipitation north of 35°N are higher than modern. In contrast, south of 35°N, temperatures and precipitation are similar to today, suggesting a poleward amplification effect in eastern North America. Reconstructed Miocene rainfall seasonality was predominantly higher than modern, regardless of latitude, indicating greater variability in intra-annual moisture transport. Reconstructed climates are almost uniformly in the temperate seasonal forest biome, but heterogeneity of specific forest types is evident. Reconstructed Miocene terrestrial temperatures from the eastern USA are lower than modeled temperatures and coeval Atlantic sea surface temperatures. However, reconstructed rainfall is consistent with modeled rainfall. Our results show that during the Miocene, climate was most different from modern in the northeastern states, and may suggest a drastic reduction in the meridional temperature gradient along the North American east coast compared to today.

Global and Planetary Change↗
USGS2008

Late-Holocene fossil rodent middens from the Arica region of northernmost Chile

Identification of >40 taxa of plant macrofossils in 14 rodent (Abrocoma) middens collected from 2800 to 3590 m elevation at the latitude of Arica, Chile (18??S) provide snapshots of vegetation in the northernmost Atacama Desert over the past 3000 years. Midden floras show considerable stability throughout the late Holocene, which may be due in part to the broad elevational ranges of many perennial species and midden insensitivity to changes in plant community structure. The greatest variability is found in annuals in the Prepuna, a climatically sensitive zone. This variability, however might also arise from the brevity of midden depositional episodes. As the first midden record from the Arica-Parinacota Region (Chile's northernmost administrative region), this study demonstrates the potential for future midden research in this area. ?? 2007 Elsevier Ltd. All rights reserved.

Journal of Arid Environments↗
USGS2009

Spatial and temporal patterns across an ecological boundary: Allochthonous effects of a young saltwater lake on a desert ecosystem

We documented changes in the abundance and composition of terrestrial flora and fauna with respect to distance from the sea edge and timing of large allochthonous inputs from the Salton Sea, California. We found significant effects that were most pronounced within 300 m of the shore, but extended 3 km inland via coyote scat deposition. The zone within 300 m of the sea had a higher density of vegetation with a distinctly different plant composition. The denser vegetation supported higher abundances of birds and reptiles. Coyotes exhibited spatial and temporal responses to marine subsidies of fish, while birds were likely subsidized by aquatic aerial insects. Top-down control, as well as dietary and habitat preferences, may have resulted in reduced number of ants, beetles, and small mammals near the sea. Species responses to the habitat edge appeared to be associated with life history, as the near shore habitat favored habitat generalists and shore specialists, while inland desert habitat favored many sand and open desert specialists. Ecosystem responses support current theories of allochthonous spatial subsidies and consumer-resource dynamics but were limited in scope, magnitude, and distance.

Journal of Arid Environments↗
USGS2017

The efficacy of combined educational and site management actions in reducing off-trail hiking in an urban-proximate protected area

Park and protected area managers are tasked with protecting natural environments, a particularly daunting challenge in heavily visited urban-proximate areas where flora and fauna are already stressed by external threats. In this study, an adaptive management approach was taken to reduce extensive off-trail hiking along a popular trail through an ecologically diverse and significant area in the Chesapeake and Ohio National Historical Park near Washington DC. Substantial amounts of off-trail hiking there had created an extensive 16.1 km network of informal (visitor-created) trails on a 39 ha island in the Potomac Gorge. A research design with additive treatments integrating educational and site management actions was applied and evaluated using self-reported behavior from an on-site visitor survey and unobtrusive observations of off-trail hiking behavior at two locations along the trail. Study treatments included: 1) trailhead educational signs developed using attribution theory and injunctive-proscriptive wording, 2) symbolic “no hiking” prompter signs attached to logs placed across all informal trails, 3) placement of concealing leaf litter and small branches along initial sections of informal trails, 4) restoration work on selected trails with low fencing, and 5) contact with a trail steward to personally communicate the trailhead sign information. The final, most comprehensive treatment reduced visitor-reported intentional off-trail hiking from 70.3% to 43.0%. Direct observations documented reduction in off-trail hiking from 25.9% to 2.0%. The educational message and site management actions both contributed to the decline in off-trail travel and the two evaluation methods enhanced our ability to describe the efficacy of the different treatments in reducing off-trail travel.

Bear Island↗
USGS2025

Ecovoltaic solar energy development effects to microclimate, temperature, and soil moisture in panel array interspaces in a warm desert

Solar energy development is increasing in warm deserts of the southwestern United States, and ecovoltaics has emerged as an approach to maintain ecosystem function within solar facilities while meeting increasing regional energy demands. The Solar Gemini Project, located in the northeastern Mojave Desert, USA, is one of largest photovoltaic facilities incorporating an ecovoltaics approach, including novel installation practices to reduce disturbance to soil and vegetation and solar tracking bifacial photovoltaic panels to maximize energy generation. To further understand the influence of the facility on environmental conditions, we compared microclimate, temperature, and soil moisture in bare soil interspaces between panel arrays inside the facility to undisturbed desert in nearby areas outside the facility from June 2023–February 2025. Our comparisons included different seasons (summer versus winter), soil depth (shallow versus deep), and facility operation (inactive versus active panels with solar-tracking). We found lower solar radiation, wind speed, and evaporative demand inside the facility compared to outside the facility, with greater differences when panels were actively tracking. When panels were active, air temperature inside and outside the facility was similar on average, but was higher inside the facility during the day and lower at night. Soil surface temperature was lower inside the facility due to panel shading in the morning and evening, whereas soil temperature (0–15 cm) was consistently higher inside the facility. Soil moisture was higher inside the facility and did not drop to the low levels observed outside the facility. In total, we found lower evaporative demand, less heat loading, and higher soil moisture inside the Gemini facility, potentially benefitting flora and fauna in the harsh desert landscape. Yet, we also found daytime increases in air and soil surface temperature inside the facility, and persistent increases to soil temperature. These findings highlight the potentially positive and negative environmental changes associated with ecovoltaics solar energy development in warm deserts and provide evidence that can inform the optimization of solar photovoltaics design and management.

Nevada↗
USGS2022

Invasive plant hitchhikers: Appalachian Trail thru-hiker knowledge and attitudes of invasive plants and Leave No Trace practices

Hiking and backpacking on American National Scenic Trails has increased in popularity in recent years. To encourage responsible and sustainable outdoor recreation on these much-loved trails, direct and indirect management strategies must be employed by managerial agencies. The Leave No Trace (LNT) education program aims to protect natural resources by promoting minimum-impact behaviours that lessen environmental impacts. The accidental introduction and dispersal of non-native invasive flora by hikers is little studied but can have a detrimental environmental impact on protected areas. The purpose of our study was to understand whether Appalachian Trail thru-hikers are: 1) aware of this problem, 2) adhering to LNT principles to reduce this problem, and 3) willing to learn and adopt minimum-impact behaviours to address this problem. We found that thru-hiker knowledge of invasive plants was limited and that very few thru-hikers adopted low-impact practices to minimise plant introduction and spread. Promisingly, we found that most thru-hikers, once aware of the problems, were willing to learn and apply low-impact practices to minimise plant introduction and spread. We discuss the barriers to their adoption of these behaviours and present a comprehensive list of suggested LNT practices to limit invasive plant introduction and spread. We conclude that, whilst challenging, protected area managers can help deter the spread of invasive plants along trails by improving educational messaging, signage, personal communication, and providing supporting infrastructure that encourages visitors to adopt specific practices to minimise invasive plant introduction and spread within protected areas.

Virginia, West Virginia↗
USGS2013

Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica

The late Pliocene, ~ 3.3–3.0 Ma, is the most recent interval of sustained global warmth in the geologic past. This window is the focus of climate reconstruction efforts by the U.S. Geological Survey's Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) Data/Model Cooperative, and may provide a useful climate analog for the coming century. Reconstructions of past surface ocean conditions proximal to the Antarctic continent are essential to understanding the sensitivity of the cryosphere to this key interval in Earth's climate evolution. An exceptional marine sediment core collected from the southwestern Ross Sea (78° S), Antarctica, during ANDRILL's McMurdo Ice Shelf Project preserves evidence of dramatic fluctuations between grounded ice and productive, open ocean conditions during the late Pliocene, reflecting orbitally-paced glacial/interglacial cycling. In this near-shore record, diatom-rich sediments are recovered from interglacial intervals; two of these diatomites, from ~ 3.2 Ma and 3.03 Ma, are within the PRISM chronologic window. The diatom assemblages identified in PRISM-age late Pliocene diatom-rich sediments are distinct from those in mid-Pliocene and later Pliocene/Pleistocene intervals recovered from AND-1B, and comprise both extant taxa with well-constrained ecological preferences and a diverse extinct flora, some members of which are previously undescribed from Antarctic sediments. Both units are dominated by Chaetoceros resting spores, an indicator of high productivity and stratification that is present at much lower abundance in materials both older and younger than the PRISM-age sediments. Newly described species of the genus Fragilariopsis , which first appear in the AND-1B record at 3.2 Ma, are the most abundant extinct members of the PRISM-age assemblages. Other extant species with established environmental affinities, such as Fragilariopsis sublinearis , F . curta , Stellarima microtrias , and Thalassiothrix antarctica , are present at lower abundances. Environmental inferences drawn from extant diatom assemblages are in good agreement with those from Chaetoceros resting spores and the Fragilariopsis radiation. All three lines of evidence indicate the onset of late Pliocene cooling in the Ross Sea near-shore environment at 3.2 Ma, with intensification and possible regional persistence of summer sea ice by 3.03 Ma. An important implication of this research is the indication that the Ross Ice Shelf fluctuated dramatically on orbital timescales at a time when nearshore Antarctic conditions were only modestly warmer than present.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2017

Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California

The pollen assemblage of a deep-sea core (15G) collected at lower bathyal depths (3491 m) on a levee of Monterey Canyon off central California was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record. Thirty-two samples were obtained down the length of the core, 19 from hemipelagic and mixed mud deposits considered to be the background record, and 13 others from displaced flow deposits. The pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19,000 cal yrs BP. A Q-mode cluster analysis defined three pollen zones: a Glacial Pollen Zone (ca. 20,000–17,000 cal yr BP), an overlying Transitional Pollen Zone (ca. 17,000–11,500 cal yr BP), and an Interglacial Pollen Zone (ca. 11,500 cal yr BP to present). Another Q-mode cluster analysis, of both the background mud and flow deposits, also defined these three pollen zones, but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position. This was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched (∼10–35% in some cases) in hydraulically-efficient Pinus pollen. A selective bias in the pollen assemblage, such as demonstrated here, may result in incorrect interpretations (e.g., climatic shifts or environmental perturbations) based on the floral record, indicating turbiditic deposits should be avoided in marine palynological studies. Particularly in the case of fine-grained flow deposits that may not be visually distinct, granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits. Determining the relative abundance and source of displaced shallow-water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so.

California↗
USGS2017

Reconstructing the response of C3 and C4 plants to decadal-scale climate change during the late Pleistocene in southern Illinois using isotopic analyses of calcified rootlets

The ??13C and ??18O values of well-preserved carbonate rhizoliths (CRs) provide detailed insights into changes in the abundance of C3 and C4 plants in response to approximately decadal-scale changes in growing-season climate. We performed stable isotope analyses on 35-40 CRs sampled at 1-cm intervals from an 18-cm-thick paleosol formed in southern Illinois during Wisconsin interstadial 2. Minimum ??13C values show little variation with depth, whereas maximum values vary dramatically, and average values show noticeable variability; maximum ??18O values vary less than the minimum ??18O values. These findings indicate that a diverse and stable C3 flora with a limited number of C4 grass species prevailed during this interval, and suggest that the maximum growing-season temperatures were relatively stable, but minimum growing-season temperatures varied considerably. Two general patterns characterize the relationships between the ??13C and ??18O values obtained from the 1-cm samples. In some cases, low ??13C values correspond to low ??18O values and high ??13C values correspond to high ??18O values, suggesting that cooler growing-season temperatures favored C3 and warmer growing-season temperatures favored C4 plants. In other cases, low ??13C values correspond to high ??18O values, likely suggesting that wetter growing-season conditions were favorable to C3 plants. The high density of well-preserved CRs in this paleosol provides a unique opportunity to study detailed ecological responses to high-resolution variability in growing-season climate. ?? 2006 University of Washington.

Quaternary Research↗
USGS2017

Vegetation history along the eastern, desert escarpment of the Sierra San Pedro Mártir, Baja California, Mexico

Plant macrofossils from 38 packrat middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Mártir, northern Baja California. The middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum , Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C 4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.

Baja California, Sierra San Pedro Mártir↗
USGS1998

Speciation and isotopic composition of sedimentary sulfur in the Everglades, Florida, USA

We have studied the sulfur speciation and isotopic composition of two peat cores from Water Conservation Area 2A (WCA 2A) in the Florida Everglades. Core site E1 is affected by agricultural runoff from the Hillsboro Canal which drains the Everglades Agricultural Area; Core site U3 is distant from the canal and relatively unaffected by agricultural runoff. Depth profiles of the total sulfur content of both cores show fairly constant levels (??0.7 wt.%) below about 25-30 cm depth in Core E1 and below 40-45 cm in Core U3. Above these depths, total sulfur increases to as much as 1.52 wt.% in Core E1 and 1.74 wt.% in Core U3, suggesting that more sulfur has entered the sediments and/or that more sulfur is being retained in recent times at both sampling sites. These changes in total sulfur content with depth in Core E1 correlate with changes in total phosphorus that have been observed in other studies at core sites near the Hillsboro Canal. This correlation of total sulfur with phosphorus with depth is not seen in Core U3 located away from the canal, possibly because phosphorus is more effectively retained than sulfur in the organic sediment near the canal. Organic-sulfur (OS) concentrations are at least twice as high as the dusulfide-sulfur (DS) concentrations in the upper parts of both cores suggesting that iron is presently limiting the amount of dusulfide minerals formed in these sediments. The degree of pyritization (DOP) in the upper parts of the cores suggest that sulfide mineralization is limited by the availability of highly reactive iron during the earliest stages of diagenesis. Positive ??34S values for reduced sulfur forms in both cores indicate a relatively restricted sulfate reservoir, consistent with nearly complete reduction of the sulfate available in the sediment at any given time. Differences between the two core appear in the ??34S values for the near-surface sediments. The DS ??34S values in the upper 10.0 cm of sediment are more posotive at site E1, with a mean ??34S value of +12.9???, than at site U3, with a mean ??34S value of +2.9???. These reuslts may indicate that increased rates of organic deposition due to nutrient loading near the canal have increased the rate of sulfate reduction at the E1 site in recent times. Acid-volatile-sulfide (AVS) concentrations are lower than DS and OS concentrations by at least a factor of 10. Increasing ??34S values for AVS with increasing depth in both cores suggests ongoing reduction of a limited porewater sulfate reservoir after deposition. The disulfide and organic-sulfur ??34S values diverge from the ??34S values for AVS with depth, suggesting that most of the transformation of AVS into disulfide minerals or incorporation of sulfur into orgnaic matter occurs in the near-surface sediments. A comparison of organic-sulfur ??34S values in the dominant flora at the U3 site (sawgrass leaves and periphyton) with organic-sulfur ??34S values at the top of the U3 core indicates that there was early incorporation of an isotopically light sulfide species into the orgnaic matter.

Chemical Geology↗
USGS2003

A vegetation history from the arid prepuna of northern Chile (22-23°S) over the last 13,500 years

The Quaternary paleoclimate of the central Andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region. The exact timing, duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another, and there have been few opportunities to compare climatic records from the same proxy along environmental gradients. Vegetation histories from fossil rodent middens provide one such opportunity on the Pacific slope of the Andes. We previously reported a vegetation history from the upper margin (2400–3000 m) of the absolute desert in the central Atacama Desert of northern Chile. That record identified a distinct wet phase that peaked between 11.8 and 10.5 ka, when steppe grasses and other upland elements expanded as much as 1000 m downslope, and a secondary wet period during the middle to late Holocene (7.1–3.5 ka). The latter wet phase remains controversial and is not as readily apparent in our low-elevation midden record. We thus sought to replicate both phases in a midden record from the mid-elevations (3100–3300 m) of the arid prepuna, where slight precipitation increases would be amplified. Midden records from these elevations identify conditions wetter than today at 13.5–9.6, 7.6–6.3, 4.4–3.2 and possibly 1.8–1.2 ka. Dry phases occurred at 9.4–8.4 ka and possibly at ca. 5.1 ka. Present floras and modern hyperarid conditions were established after 3.2 ka. The records from the two elevational bands generally match with some important differences. These differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2000

Charbeckia macrophylla gen. et sp. nov. from the Lower Mississippian Price (Pocono) Formation of southeastern West Virginia

A fossil plant discovery from the Price (Pocono) Formation of southeastern West Virginia provides new information on the poorly known compression floras of the Lower Mississippian of North America. The new plant described herein consists of long tapering bipinnate fronds with imbricate basal pinnae, planate apical pinnae, and unlobed, elliptical to obovate pinnules with open dichotomous venation. Veins concentrated in the medial region of the pinnule curve toward the lateral margin, suggestive of an early stage in the evolution of a midrib. Pinnules exhibit a distinctly revolute or otherwise reinforced margin. The exceptional length of some fronds (over 1 m) and pinnule size (some over 3 cm by 2 cm) strongly contrast with the generally diffusely branched fronds and small or highly dissected pinnule morphology that typify Early Mississippian leaf taxa. A new generic assignment, Charbeckia macrophylla , is thereby justified. The rigid appearance of the tapering rachis, the imbricate pinnae that appear to have resisted compression, and the reinforced pinnule margins imply thick evergreen leaves, perhaps adapted for drought tolerance. A possible Calamopityalean affinity is indicated by the size of the fronds and the stout petioles, which fall within the expected size range of the Kalymma -type petiole bases described from the nearby New Albany Shale of Tournaisian age.

Review of Palaeobotany and Palynology↗
USGS1976

Textural variation within Great Salt Lake algal mounds

This chapter discusses textural variation within the Great Salt Lake algal mounds. Great Salt Lake algal mounds contain: (1) a framework of non-skeletal, algally induced aragonite precipitates; (2) internal sediment; and (3) inorganic cement. These three elements create a variety of laminated, poorly laminated, and unlaminated internal textures. Interior framework precipitates bear little resemblance to the present living film of the mound surface. Internal texture of the mounds is believed to be largely relict and to have resulted from precipitation by algae different than those presently living at the surface. The most probable cause of local extinction of the algal flora is change in brine salinity. Precipitated blue-green algal structures in ancient rocks may indicate other than normal marine salinity and near shore sedimentation. Extreme variation of internal texture reflects extreme environmental variability typical of closed basin lakes. Recognition of mounds similar to those in the Great Salt Lake can be a first step toward recognition of ancient hyper-saline lake deposits, if such an interpretation is substantiated by consideration of the entire depositional milieu of precipitated algal mounds.

Utah↗
USGS2001

The geology and palynology of lower and Middle Pennsylvanian strata in the Western Kentucky Coal Field

The Western Kentucky Coal Field is the southern tip of the Eastern Interior, or Illinois Basin. Pennsylvanian rocks in this area, which include conglomerate, sandstone, shale, limestone and coal, were deposited primarily in coastal-deltaic settings at a time when western Kentucky was located close to the equator. This paper discusses temporal changes in regional sedimentation patterns and coal-forming floras of Lower and Middle Pennsylvanian strata in the Western Kentucky Coal Field. Lower Pennsylvanian strata of the Caseyville Formation are characterized by paleovalley-filling sedimentation patterns and extabasinal quartz pebbles. Caseyville Formation coals are characterized thin and discontinuous and were strongly influenced by subsidence within underlying paleovalleys, and the dissected lower Pennsylvanian paleotopography. Caseyville coals are commonly dominated by Lycospora, but can also have variable palynofloras, which probably reflects variable edaphic conditions and edge effects within small, patchy paleomires. Tradewater Formation strata show increased marine influences and tidal-estuarine sedimentation, especially in the middle and upper parts. Coal beds in the lower part of the Tradewater typically are thin and discontinuous, although some economically important beds are present. Coals become thicker, more abundant and more laterally persistent towards the top of the formation. Palynologically, lower and middle Tradewater Formation coals are dominated by Lycospora, but begin to show increased amounts of tree fern spores. Middle and upper Tradewater coals are thicker and more continuous, and contain high percentages of tree fern spores. In addition, cordaite pollen is locally abundant in this interval. Carbondale and Shelburn (Desmoinesian) strata are much more laterally continuous, and occur within classic cyclothems that can be traced across the coal field. Cyclothems have long been interpreted as being eustatically driven, and glacio-eustacy controlled not only sedimentation but also the formation of Desmoinesian paleomires. Palynologically, Carbondale and Shelburn coals are either dominated by Lycospora or have heterogeneous palynofloras. Palynologic and coal-quality data suggest that hydrologic base level may have been the primary control on Desmoinesian paleomires, rather than paleoclimate, as the coals display rheotrophic, rather than ombrotrophic characteristics. ?? 2001 Elsevier Science B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2000

Palynomorphs of Permian Gondwana coal from borehole GDH-38, Barapukuria Coal Basin, Bangladesh

Thirty-two core samples of Permian Gondwana coal from three coal beds of borehole GDH-38, Barapukuria Coal Basin, Dinajpur, the north-northwestern part of Bangladesh, have been collected for palynological analysis. All samples except one yielded palynomorphs and some samples contain well-preserved and abundant palynomorphs of the gymnospermal and cryptogamic groups that are considered to be useful for future correlation studies. The lower coal bed (331.6–372.5 m) can easily be differentiated from the upper two coal beds by the presence of Alisporites, Cordaitina, Corisaccites, Hamiapollenites, Leuckisporites, Nuskoisporites, Tumoripollenites, Vestgisporites and Vittatina . It is difficult to palynologically differentiate the middle (198.1–208 m) and upper (162.3–172.9 m) coal beds as they contain a very limited number of specimens by which they can be identified. The middle bed is distinguished by the presence of Microbaculispora and Weylandites and the upper bed by the presence of a single taxon Acanthotriletes . Some of the vesiculate or saccate taxa extracted from these coal beds are typical of those occurring in Permian strata of Gondwana in India, South Africa, South America, Russia, Australia and Antarctica. They are thought to be derived from Glossopteris flora, which is characterised by an abundance of Pteridospermic plants of the gymnosperm group.

Dinajpur↗
USGS2003

Quaternary vegetation and climate change in the western United States: Developments, perspectives, and prospects

This chapter explores the strengths and shortcomings of the major sources of data on Quaternary vegetation and climate change and discusses the use of models as a means to explore past and potential future environmental changes. The flora and major vegetation types of the western United States are present for several million years. Ongoing changes in atmospheric chemistry , climate, and human activities may lead to major vegetation changes over the coming decades to centuries. The combination of observations from the paleoenvironmental record, modern ecological studies, and modeling now permit assessments of the magnitude of potential future changes in the context of natural variability. They also provide opportunities for hypothesis testing and identification of the processes driving past changes in vegetation and climate. Understanding the dynamics of paleoenvironmental change can contribute to current conservation and natural resource management efforts and will help conservation and natural resource managers anticipate the potential rate, magnitude, and complexity of future vegetation change.

western United States↗
USGS1998

Peat characteristics and groundwater geochemistry of calcareous fens in the Minnesota River Basin, U.S.A

Calcareous fens in Minnesota are spring-seepage peatlands with adistinctive flora of rare calciphilic species. Peat characteristics andgroundwater geochemistry were determined for six calcareous fens in theMinnesota River Basin to better understand the physical structure andchemical processes associated with stands of rare vegetation. Onset of peataccumulation in three of the fens ranged from about 4,700 to 11,000 14 C yrs BP and probably resulted from acombination of climate change and local hydrogeologic conditions. Most peatcores had a carbonate-bearing surface zone with greater than 10%carbonates (average 27%, dry wt basis), an underlyingcarbonate-depleted zone with 10% or less carbonates (average4%), and a carbonate-bearing lower zone again with greater than10% carbonates (average 42%). This carbonate zonation washypothesized to result from the effect of water-table level on carbonateequilibria: carbonate precipitation occurs when the water table is above acritical level, and carbonate dissolution occurs when the water table islower. Other processes that changed the major ion concentrations inupwelling groundwater include dilution by rain water, sulfate reduction orsulfide oxidation, and ion adsorption or exchange. Geochemical modelingindicated that average shallow water in the calcareous fens during the studyperiod was groundwater mixed with about 6 to 13% rain water.Carbonate precipitation in the surface zone of calcareous fens could bedecreased by a number of human activities, especially those that lower thewater table. Such changes in shallow water geochemistry could alter thegrowing conditions that apparently sustain rare fen vegetation.

Minnesota↗