An erosional hiatus over almost the entire area between Pennsylvania and western New Brunswick suggests that the region was mountainous from the Middle Devonian Acadian orogeny through Pennsylvanian time. Of seven basins or deposits of southeast-era New England, the ages of three (Narragansett, Norfolk, and Worcester) are florally determined as Westphalian B (Middle Pennsylvanian) to Stephanian B or C (Late Pennsylvanian); three lack flora but are of inferred Carboniferous age (North Scituate, Woonsocket, and Pin Hill), and one is of possibly Carboniferous age (Sturbridge). The first three are characterized by flora suggesting a tropical or subtropical climate and by alluvial fan facies deposited in an intermontane basin. Four of these basins or deposits lie in the Avalon Terrane, three just west of the Nashoba Terrane, but none has been recognized in the intermediate Nashoba Terrane. These basin deposits can be correlated with similar deposits in Atlantic Canada. Tectonic effects of the Alleghanian orogeny are many and diverse, resulting in important tectonic controls on the formation and evolution of the coal basins. Grabens surrounded by uplands were formed by extension or strike-slip fault-related extension and were filled with Carboniferous sediments during the earliest Alleghanian orogenic episode. These sediments along with the basement complex, were multiply deformed during Permo-Carboniferous Alleghanian orogenic episodes, which involved folding, thrust faulting, plutonism, regional metamorphism, and strike-slip faulting. Metamorphism throughout the outcrop areas ranges from anchizone to K-spar zone in the Narragansett Basin; anchizone to possibly lower greenschist in the Norfolk Basin; and below the almandine zone in the “Worcester Coal Mine” deposit. Important effects of the tectonism are the widespread anthracitization and tectonic thickening of the low-sulfur and high-ash coals.

Utilizing well logging data, outcrop profiles, and previous research, this study analyzes the sedimentary and tectonic evolution of the Yan’an Formation in the Ordos Basin, correlating the resulting sedimentary facies with hydrocarbon reservoirs to establish the necessary connections. The study reveals that: (1) Vertically, the sediment grain size shows a pattern of coarser grains at the bottom and top, with finer grains in the middle. Horizontally, the grain size tends to become finer from the northern, western, and southern parts of the basin toward the central-western region. (2) Tectonic movements during the Yan’an period controlled the sedimentary environment. These tectonic activities, through uplift and subsidence, caused the Yan’an Formation to experience four stages of sedimentary environments: braided river, lake, delta, and meandering river. (3) The Yan’an Formation exhibits four types of reservoir sandbody stacking patterns—continuous superposition, intermittent superposition, interbedded sand-mud, and single sandbody types—with continuous and intermittent stacking being the most common. (4) The hydrocarbons in the Yan’an Formation originated from the Chang 7 Member of the Yanchang Formation and migrated into the Yan’an reservoirs. The oil is characterized by its low density, low viscosity, and low pour point, indicating it is a high-maturity, high-quality crude oil.

Abstract Naturally occurring CO2 often coexists with hydrocarbon accumulations on continental margins around the world, the presence of which may affect hydrocarbon production as a greenhouse gas. In this paper we focus on the natural CO2 in the Surennuoer Oilfield of the Hailar Basin, and investigate CO2 origin, distribution, related tectonic controls and accumulation mechanisms using geochemical, petrophysical and seismic data. Results show that the CO2 is of inorganic origin due to the degassing of magma from the deep crust or mantle, and is mainly stored in structural traps of N1 Member. There are close spatial and temporal relationships among CO2 distribution, major fault distribution and underneath igneous bodies, indicating a genetic link. The magmatic events and major faults are proposed to be the key controlling factors of CO2 distribution, which provided CO2 supply and migration pathways for both magma and degassed CO2. Additionally these faults also play a role in forming structural traps to store CO2. The sandstone reservoirs of low porosity and low permeability may play a limited role due to their poor reservoir quality. Two CO2 accumulation models are outlined in the Surennuoer strike-slip fault zone and the S3 fault zone. The former is characterized by shallower magmatic igneous body and a small amount of CO2 in the shallower N2 Member in addition to N1 Member. The Surennuoer strike-slip faults may have further channelled magma upwards which initially intruded along the basin-controlling fault, while the magma under the S3 fault zone did not migrate further upward along the S3 faults. Generally this study provides a detailed understanding of CO2 distribution, accumulation models and geological controls which may guide future hydrocarbon production in the study area.

The general physiographic and geologic setting, lithostratigraphy, structural geology and regional tectonism, and depositional environments are summarized for six major coal basins in Alaska: the Susitna (Beluga and Yentna), Matanuska, Bering River, Nenana, Chignik Bay-Herendeen Bay, and Northern Alaska basins. Alaska’s Cretaceous and Tertiary subbituminous to bituminous coals are found in most physiographic regions of the state and may underlie as much as 9.0 percent of its land area. Continental Tertiary deposits are widely distributed and contain most of the subbituminous coals. Cretaceous formations contain most of the bituminous coals and usually have been influenced by marine environments during their deposition. Constraints related to paleodepositional environments affecting coal formation and character are expected to play an important role in future mine planning and pre-development site investigations in the Susitna, Nenana, Chignik Bay-Herendeen Bay, and Northern Alaska coal basins. Paleodepositional modeling will probably not greatly assist future mine planning in the Matanuska or Bering River coal basins because of complex geologic structure. Ultimately, other limiting factors such as location with respect to tidewater and potential export markets, coal quality considerations, resource base, permafrost distribution, infrastructure and port development, technological advances, and economics may determine the minability of Alaska’s vast coal resources.