Written in Stone: A Geological History of the Northeastern United States.

1991 ◽  
Vol 118 (2) ◽  
pp. 216
Author(s):  
Steward T. A. Pickett ◽  
Chet Raymo ◽  
Maureen E. Raymo

Author(s):  
Marta F. Nammack ◽  
J. A. Musick ◽  
J. A. Colvocoresses


1995 ◽  
Vol 32 (8) ◽  
pp. 1180-1193 ◽  
Author(s):  
H. Elizabeth Anderson ◽  
Donald W. Davis

The Mesoproterozoic Purcell Supergroup (and its equivalent in the United States, the Belt Supergroup) is a thick sedimentary sequence formed in an extensional basin of uncertain age and tectonic setting. The voluminous tholeiitic Moyie sills intrude turbidites of the lower and middle Aldridge Formation, the lowest division of the Purcell Supergroup. Many of the sills were intruded into soft sediment and one intrudes the Sullivan sedimentary exhalative (SEDEX) orebody, so their age approximates that of the sediments and the Sullivan deposit. New U–Pb dates of zircon from four sills are older than previously published U–Pb zircon ages. One sill contained concordant zircons with an age of 1468 ± 2 Ma. Near concordant zircons from the other samples have similar 207Pb/206Pb ages, indicating that all of the sills crystallized at the same time. U–Pb dates of titanites from two of these sills yielded concordant dates ranging from 1090 to 1030 Ma, indicating that they have undergone a previously unrecognized Grenville-age metamorphism. The U–Pb systematics of abraded zircons from one sill indicate that they have also been affected by this event. The recognition of Grenville-age metamorphism in the Purcell (Belt) basin suggests that the prevalent 1.0–1.1 Ga Rb–Sr and K–Ar mineral and whole-rock dates from a wide variety of Purcell (Belt) igneous and sedimentary rocks are also metamorphic, and are not ages of sedimentation or "hybrid" dates reflecting partial resetting by the ca. 760 Ma Goat River orogeny. On this basis, all sedimentation in the Purcell (Belt) basin is constrained to be older than 1.1 Ga and is probably older than 1.25 Ga.



2013 ◽  
Vol 27 (2) ◽  
pp. 578-591 ◽  
Author(s):  
Rebecca L. Hale ◽  
Joseph H. Hoover ◽  
Wilfred M. Wollheim ◽  
Charles J. Vörösmarty




2020 ◽  
Vol 118 (2) ◽  
pp. 124-138
Author(s):  
David I Maass ◽  
Lloyd C Irland ◽  
James L Anderson ◽  
Kenneth M Laustsen ◽  
Michael S Greenwood ◽  
...  

Abstract Abstract Field measurements of operational plantations and research plots demonstrate that growth rates of exotic larches in unmanaged stands can exceed 12 m3 per hectare per year in Maine and elsewhere. This paper briefly reviews the recent history of exotic larch (Larix decidua, L. kaempferi, and L. × marschlinsii) in northeastern United States and Canada. Stands can be commercially thinned as early as 15 years; further thinnings add to significant volume accumulation, based on stand table projections. Genetic development of the hybrid (L. × marschlinsii) could yield additional volume. Even at current low stumpage values, exotic larch plantations offer positive returns at realistic discount rates. In map form, we report a current inventory of known trials and operational plantings across the Northern United States, including adjacent Canada.



2020 ◽  
Vol 39 (1) ◽  
pp. 99-119
Author(s):  
ROBERT T. MCMASTER

From 1830 to 1833, Edward Hitchcock (1793–1864) of Amherst College conducted a geological survey of the state of Massachusetts, the first comprehensive government-sponsored survey in the United States. It was an ambitious undertaking that resulted in a 700-page report published in 1833. The main goal of the survey was to assess the state's mineral resources, the better to promote their extraction and utilization. Increasing the understanding of the geological history of the state was a secondary goal. Some of Hitchcock's projections of potential economic benefit such as from coal, bog iron, and peat, proved to be illusory. But many of the geological insights gained from the survey were formative for Hitchcock and important in the development of geological thought in America. Perhaps the greatest legacy of the survey was its influence on other states, encouraging governors and legislators to emulate the high standard set by Hitchcock. In this paper I examine the major findings of the survey, the effects of those findings on Hitchcock's geological thinking, and the influence of the survey on American geology in the mid-nineteenth century.



2016 ◽  
Author(s):  
Jennifer R. Marlon ◽  
Neil Pederson ◽  
Connor Nolan ◽  
Simon Goring ◽  
Bryan Shuman ◽  
...  


Sign in / Sign up

Export Citation Format

Share Document