Magma accumulation rates and thermal histories of plutons of the Sierra Nevada batholith,CA

Zircon U–Pb geochronology results indicate that the John Muir Intrusive Suite of the central Sierra Nevada batholith, California, was assembled over a period of at least 12 Ma between 96 and 84 Ma. Bulk mineral thermochronology (U–Pb zircon and titanite, ⁴⁰Ar/³⁹Ar hornblende and biotite) of rocks from multiple plutons comprising the Muir suite indicates rapid cooling through titanite and hornblende closure following intrusion and subsequent slow cooling through biotite closure. Assembly of intrusive suites in the Sierra Nevada and elsewhere over millions of years favors growth by incremental intrusion. Estimated long-term pluton assembly rates for the John Muir Intrusive Suite are on the order of 0.001 km³ a⁻¹ which is inconsistent with the rapid magma fluxes that are necessary to form large-volume magma chambers capable of producing caldera-forming eruptions. If large shallow crustal magma chambers do not typically develop during assembly of large zoned intrusive suites, it is doubtful that the intrusive suites represent cumulates left behind following caldera-forming eruptions.     

Middle to late Holocene chironomid-inferred July temperatures for the central Northwest Territories,Canada

We analyzed subfossil chironomids, sediment organic matter and sediment particle size data from a 1.11-m-long freeze core collected from Carleton Lake (unofficial name), located approximately 120 km north of the modern treeline. This well-dated core spans the last ca. 6,500 years. Two chironomid transfer functions were applied to infer mean July air temperatures. Our results indicated that the chironomid-inferred temperatures from this lake sediment record did not pass a significance test, suggesting that other factors in addition to temperature may have been important in structuring the chironomid community through time. Although not statistically significant, the chironomid-inferred temperatures from this site do follow a familiar pattern, with highest inferred temperatures occurring during the Holocene Thermal Maximum (~6–4 cal kyr BP), followed by a long-term cooling trend, which is reversed during the last 600 years. The largest change in the chironomid assemblage, which occurred between ca. 4,600 and 3,900 cal yr BP is possibly related to the well-documented northward advance and subsequent retreat of treeline in this region.     

Access to reeds and mat making in the lower Volta basin of Ghana

This paper explores the origins of pressures on reeds and sedges used for mat making in the lower Volta basin of Ghana, and their impact on the socially embedded system which dictates access to reed fields. Data for the study were collected through field work employing participatory rural appraisal methods in 18 communities, involving 152 mat weavers. The findings showed that the mat‐weaving industry has contributed immensely in providing poor women a means of livelihood but reed marshes in the basin have reduced in recent years due to hydrological changes in the area caused by the damming of the Volta upstream. The decline in the availability of reed is exerting immense pressure on this once freely available resource, thus inducing landlords to impose a price on the rights of entry into marshlands by reed collectors. The imposition of these charges affected the very people that the mat‐weaving industry is targeted to help. The study recommends the local and central government to play a more active role and civil society groups to broaden the livelihood base of women living in this region.     

Reduction of lithologic-log data to numbers for use in the digital computer

The development of a standardized system for conveniently coding lithologic-log data for use in the digital computer has long been needed. The technique suggested involves a reduction of the original written alphanumeric log to a numeric log by use of computer programs. This numeric log can then be retrieved as a written log, interrogated for pertinent information, or analyzed statistically.publication authorized by Director, U.S. Geological Survey.     

Compound paleovalley fills in the Lower Pennsylvanian New River Formation, West Virginia, USA

Ancient paleovalley fills are typically interpreted in the rock record using over-generalized models without carefully considering modern analogs, especially in light of recent discoveries. It is now known that many Quaternary paleovalleys are compound in origin, exhibit considerable stratigraphic complexity, contain multiple incisions, and can be orders of magnitude larger than their putative ancient counterparts. Compound paleovalley fills in the Lower Pennsylvanian New River Formation (NRF) are directly comparable to these Quaternary analogs, stimulating a paradigm shift in the interpretation of ancient paleovalleys. In the NRF, multiple laterally- and vertically-juxtaposed fill successions, separated by incision surfaces, record high-frequency fluvial responses to external controls within lower-order sequences. Lowstand incision and sediment bypass, as predicted in sequence stratigraphy, is largely discounted by the available evidence and the definition of regional sequence boundaries is not straightforward. The identification of genetic sequences may be the most effective approach to understanding the NRF and, by inference, many other ancient paleovalleys. Results from this study of the NRF promote a revised model for ancient paleovalleys that incorporates: 1) the pre-eminence of compound architecture, 2) periodic episodes of incision and subaerial exposure occurring in response to high-frequency changes in climate or relative sea level, 3) fluvial downcutting as the primary cause of paleovalley incision, although some sediments are still preserved in a net-erosional regime, and 4) composite, time-transgressive sequence boundaries that may be difficult or impossible to correlate regionally.     

Long-term environmental change and shifts in the aquatic plant community of Jones Creek,Thousand Islands National Park,Ontario, Canada based on plant macrofossil analysis

Plant macrofossils and pollen were analyzed from sediment cores to identify long-term changes in the aquatic plant community of Jones Creek, Thousand Islands National Park, Ontario, Canada. Six sediment cores were recovered from Jones Creek in February 2014. One complete core and five top/bottom samples were analyzed for plant macrofossil abundance and diversity. Sediment analysis and ²¹⁰Pb dating confirmed a productive wetland throughout the core, dating back beyond 1883 AD. Jones Creek is currently dominated by thick stands of cattails, particularly the hybrid white cattail (Typha x glauca Godr). The relative abundance of Typha pollen began to increase in the late nineteenth and early twentieth century, reaching a relative abundance of nearly 40% in the modern day surface sediment. Common macrofossils recovered from the sediment record included seeds of Carex, Schoenoplectus, Najas, and Eleocharis. There is evidence that community composition, as recorded by the macrofossil record, has shifted in Jones Creek in response to human activities. In particular there has been a reduction in sedge species between historical and present day conditions as the wetland shifted from a sedge dominated wet-meadow wetland to a cattail dominated system. The results of our study indicate that future restoration efforts should be directed towards reintroducing native sedge species that were present prior to major changes in land-use that occurred in the St. Lawrence region throughout the nineteenth and twentieth centuries.     

Some genetic implications of silica and aluminosilicates in peat and coal

The inorganic content of Okefenokee peat, in the absence of a significant detrital contribution, is a function of sponge spicule, phytolith, and diatom abundance in addition to the degree of organic matter decomposition and the frequency of fires. The detrital component (quartz) dominates ash composition where it is present.No clear correlation has been observed between the inorganic content of coals examined in this study and their maceral composition. Vitrinite-rich coals have a wide range of ash yield. These observations suggest that the minerals have been introduced detritally rather than accumulated as a result of peat degradation. Quartz in the coals appears to be detrital, and the presence of 2m₁ mica indicates that there is also a detrital contribution to the clay minerals present.