ABSTRACT Southeastern New England is largely composed of Ediacaran granitoid and related volcanic rocks formed during the main phase of arc-related magmatism recorded in West Avalonian lithotectonic assemblages extending through Atlantic Canada to eastern Newfoundland. In situ Lu-Hf analyses presented here for zircons from the Dedham, Milford, and Esmond Granites and from the Lynn-Mattapan volcanic complex show a restricted range of εHf values (+2 to +5) and associated Hf- T DM model ages of 1.3–0.9 Ga, assuming felsic crustal sources. The most evolved granites within this suite lie in a belt north and west of the Boston Basin, whereas upfaulted granites on the south, as well as the slightly younger volcanic units, show more juvenile Hf isotopic compositions. Similar inferences have been drawn from previously published Sm-Nd isotopic signatures for several of the same plutons. Collectively, the isotopic compositions and high-precision U-Pb geochronological constraints now available for southeastern New England differ in important respects from patterns in the Mira terrane of Cape Breton Island or the Newfoundland Avalon zone, but they closely resemble those documented in the Cobequid and Antigonish Highlands of mainland Nova Scotia and New Brunswick’s Caledonia terrane. Particularly significant features are similarities between the younger than 912 Ma Westboro Formation in New England and the younger than 945 Ma Gamble Brook Formation in the Cobequid Highlands, both of which yield detrital zircon age spectra consistent with sources on the Timanide margin of Baltica. This relationship provides the starting point for a recent model in which episodic West Avalonian arc magmatism began along the Tonian margin of Baltica and terminated during diachronous late Ediacaran arc-arc collision with the Ganderian margin of Gondwana.

Terminal Neoproterozoic (Ediacaran) granitoid rocks underlie most of the Southeastern New England Avalon Zone. Major- and trace-element analyses on representative samples from Massachusetts and Rhode Island corroborate earlier interpretations that these rocks were formed in a subduction-related setting. New crystallization ages from the same suite are 609.5 ± 1.1 Ma, 609.1 ± 1.1 Ma, and 608.9 ± 1.2 Ma for units of the Dedham Granite; 606.3 ± 1.2 Ma for the Milford Granite; 604.4 ± 1.2 Ma for the Fall River Granite; and 599 ± 2 Ma for the Esmond Granite (2σ errors, including internal and external uncertainties). The Avalonian magmatic interval defined by these and other reliable dates is ca. 610–590 Ma, which is considerably shorter and younger than previously thought. These dates provisionally link the southeastern New England Avalon zone with the Antigonish and Cobequid Highlands in northern mainland Nova Scotia as distinctive blocks in the Northern Appalachian Avalonian collage.

With the recognition of the Hope Valley shear zone (HVSZ) as a terrane boundary, the Esmond-Dedham terrane (EDT) was subdivided, and the western division was named the Hope Valley terrane (HVT). The oldest rocks of the HVT consist of schist, gneiss and quartzite (Plainfield Formation), and metavolcanic and metaplutonic gneisses and amphibolites (Waterford Group), some of the latter yielding a radiometric age of 620 Ma. Members of the Sterling Plutonic Suite, consisting of granite gneiss and alaskite gneiss, intrude these older units. An exact radiometric age could not be determined for the alkaline pluton, Joshua Rock Granite Gneiss, but is assigned to the broad age range from c. 380 to 280 Ma. The Narragansett Plutonic Suite yields a radiometric age of c. 273 Ma, is a terrane-linking plutonic sequence cutting through the HVSZ, and links the HVT to the EDT. The EDT has a stratigraphic sequence that in many respects is similar to that of HVT, but has pronounced differences that mainly consist of a wider range of rock units and ages represented. Additionally, the rocks of HVT, and especially those near coastal Connecticut, have been elevated more generally to higher metamorphic grades than the EDT. The Harmony Complex and the Blackstone Group predominantly consist of plutonic and volcanic rocks, and schist, quartzite, and basaltic volcanics, respectively, into which have been intruded members of the Esmond Plutonic Suite or rocks correlated with them. The Price Neck Formation, of the Newport Basin, contrasts notably with the Harmony and Blackstone, but is intruded by the Cliff Walk Granite, similar in age and composition to the Esmond, and consists predominantly of fine-grained graded sedimentary rocks with volcanogenic beds. Fossiliferous limestone, phyllite, and siltstone make up Lower and Middle Cambrian rocks of the Pirate Cave Formation and the Conanicut Group of the Newport Basin, rocks unknown in HVT. A large part of the EDT is underlain by alkaline plutonic and volcanic rocks of the Scituate Plutonic Supersuite, whose radiometrically determined age is c. 373 Ma. Fluvial coal-bearing sedimentary rocks (Rhode Island Group) of the Narragansett and related basins contain a rich floral assemblage, which permits accurate dating to Westphalian and Stephanian stages of the Carboniferous. These rocks are unrepresented in the HVT. On the basis of structural and metamorphic data for the above stratigraphic units, a pre-Mesozoic evolutionary history has been outlined from late Proterozoic through Permian events. Compressional tectonic events within the Avalon superterrane and the composite Avalon terrane include the late Proterozoic Avalonian orogeny and the Alleghanian orogeny; mid-Paleozoic rifting events are interpreted for the alkaline plutonic rocks. Collisions involving the Avalon composite terrane with terranes farther to the west were responsible for Acadian and possibly late-stage Taconian orogenic events elsewhere in southern New England.

The New Bedford area is among the least studied in eastern New England, yet an understanding of its tectonic history is essential to the development of a viable paradigm for the assemblage of Avalonian terranes in New England. We review previous work and present the preliminary results of an ongoing program whose goal is to systematically study the structural, petrographic, and geochemical relations in the New Bedford area of southeastern Massachusetts. The region can be divided into two suites of rocks. Group I includes variably deformed granitoids that bear close resemblance to the Proterozoic- to Devonian-aged granitic basement of the Esmond-Dedham terrane. Of particular interest is a newly recognized unit of slightly deformed ~600-Ma, alkalic granite plus diorite, in which contact relations imply comingling of magmas of contrasting composition. In contrast, Group II consists of alaskitic and banded gneisses and schist that are reminiscent of gneissic rocks in western Rhode Island and adjacent Connecticut. Trace-element analyses for both groups are presented, and form the basis for discussion of their possible correlation with other granitoids in southeastern New England. The dominant structural feature in the New Bedford area is a steeply dipping to vertical, east-west–trending foliation that becomes more pervasively developed to the south. This tectonic fabric is strongly oblique to the northeast-trending schistosity of the southern Narragansett Basin, and geometrically more comparable to the east-northeast–trending folds found in the Carboniferous rocks of the northern Narragansett Basin. At present, the geometric and temporal relations among structural features in the New Bedford area and the adjoining Carboniferous rocks remain unclear. Although several interpretations of the regional setting of the lithologies of the New Bedford area are possible, currently the most plausible considers the lithologies of Group I to be a continuation of the Esmond-Dedham terranes, while Group II may be correlative with either the Hope Valley terrane or the Bass River Complex.

ABSTRACT The Avalon terrane of southeastern New England is a composite terrane in which various crustal blocks may have different origins and/or tectonic histories. The northern part (west and north of Boston, Massachusetts) correlates well with Avalonian terranes in Newfoundland, Nova Scotia, and New Brunswick, Canada, based on rock types and ages, U-Pb detrital zircon signatures of metasedimentary rocks, and Sm-Nd isotope geochemistry data. In the south, fewer data exist, in part because of poorer rock exposure, and the origins and histories of the rocks are less well constrained. We conducted U-Pb laser ablation–inductively coupled plasma–mass spectrometry analysis on zircon from seven metasedimentary rock samples from multiple previously interpreted subterranes in order to constrain their origins. Two samples of Neoproterozoic Plainfield Formation quartzite from the previously interpreted Hope Valley subterrane in the southwestern part of the southeastern New England Avalon terrane and two from the Neoproterozoic Blackstone Group quartzite from the adjacent Esmond-Dedham subterrane to the east have Tonian youngest detrital zircon age populations. One sample of Cambrian North Attleboro Formation quartzite of the Esmond-Dedham subterrane yielded an Ediacaran youngest detrital zircon age population. Detrital zircon populations of all five samples include abundant Mesoproterozoic zircon and smaller Paleoproterozoic and Archean populations, and are similar to those of the northern part of the southeastern New England Avalon terrane and the Avalonian terranes in Canada. These are interpreted as having a Baltican/Amazonian affinity based primarily on published U-Pb and Lu-Hf detrital zircon data. Based on U-Pb detrital zircon data, there is no significant difference between the Hope Valley and Esmond-Dedham subterranes. Detrital zircon of two samples of the Price Neck and Newport Neck formations of the Neoproterozoic Newport Group in southern Rhode Island is characterized by large ca. 647–643 and ca. 745–733 Ma age populations and minor zircon up to ca. 3.1 Ga. This signature is most consistent with a northwest African affinity. The Newport Group may thus represent a subterrane, terrane, or other crustal block with a different origin and history than the southeastern New England Avalon terrane to the northwest. The boundary of this Newport Block may be restricted to the boundaries of the Newport Group, or it may extend as far north as Weymouth, Massachusetts, as far northwest as (but not including) the North Attleboro Formation quartzite and associated rocks in North Attleboro, Massachusetts, and as far west as Warwick, Rhode Island, where eastern exposures of the Blackstone Group quartzite exist. The Newport Block may have amalgamated with the Amazonian/Baltican part of the Avalon terrane prior to mid-Paleozoic amalgamation with Laurentia, or it may have arrived as a separate terrane after accretion of the Avalon terrane. Alternatively, it may have arrived during the formation of Pangea and been stranded after the breakup of Pangea, as has been proposed previously for rocks of the Georges Bank in offshore Massachusetts. If the latter is correct, then the boundary between the Newport Block and the southeastern New England Avalon terrane is the Pangean suture zone.

ABSTRACT West Avalonia is a composite terrane that rifted from the supercontinent Gondwana in the Ordovician and accreted to Laurentia during the latest Silurian to Devonian Acadian orogeny. The nature and extent of West Avalonia are well constrained in Nova Scotia, New Brunswick, and Newfoundland, Canada, by U-Pb detrital zircon data and/or isotope geochemistry of (meta)sedimentary and igneous rocks. The southeastern New England Avalon terrane in eastern Massachusetts, Connecticut, and Rhode Island has generally been interpreted as an along-strike continuance of West Avalonia in Canada, but the ages and origins of metasedimentary units along the western boundary of the Avalon terrane in Massachusetts and Connecticut remain poorly constrained. In this study, new detrital zircon U-Pb and Lu-Hf laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) data from three samples of metasedimentary units along the western boundary of the southeastern New England Avalon terrane in Connecticut and Massachusetts were compared with existing data to test whether these metasedimentary units can be correlated along strike. The data were also compared with existing detrital zircon U-Pb and εHf data in New England and Canada in order to constrain the extent and provenance of West Avalonia. The maximum depositional age of two of the three detrital zircon samples analyzed in this study, based on the youngest single grain in each sample (600 ± 28 Ma, n = 1; 617 ± 28 Ma, n = 1) and consistency with existing analyses elsewhere in the southeastern New England Avalon terrane, is Ediacaran, while that of the third sample is Tonian (959 ± 40 Ma, n = 4). Detrital zircon analyses of all three samples from this study showed similar substantial Mesoproterozoic and lesser Paleoproterozoic and Archean populations. Other existing detrital zircon U-Pb data from quartzites in the southeastern New England Avalon terrane show similar Tonian populations with or without Ediacaran grains or populations. Most published detrital zircon U-Pb data from (meta)sedimentary rocks in West Avalonia in Canada yielded Ediacaran youngest detrital zircon age populations, except for a quartzite unit within the Gamble Brook Formation in the Cobequid Highlands of Nova Scotia, which showed a Tonian maximum depositional age, and otherwise a nearly identical detrital zircon signature with rocks from the southeastern New England Avalon terrane. All samples compiled from the southeastern New England Avalon terrane and West Avalonia in Canada show main age populations between ca. 2.0 Ga and ca. 1.0 Ga, with major peaks at ca. 1.95, ca. 1.50, ca. 1.20, and ca. 1.00 Ga, and minor ca. 3.1–3.0 Ga and ca. 2.8–2.6 Ga populations. The εHf ( t ) values from the three samples yielded similar results to those from West Avalonia in Canada, suggesting that both regions were derived from the same cratonic sources. The εHf ( t ) values of all West Avalonian samples overlap with both Amazonia and Baltica, suggesting that there is a mixed signature between cratonic sources, possibly as a result of previous collision and transfer of basement fragments between these cratons during the formation of supercontinent Rodinia, or during subsequent arc collisions.

Appendix A contains a tabulation by field of approximately 900 published references and other publicly accessible sources covering around 500 UK fields, both developed and undeveloped, onshore and offshore. Where possible, hyperlinks to the source document are provided. Fields in production are current to the July 2020 OGA listing of consented fields. References listed include all relevant Geological Society (GS) publications including the Petroleum Geology Conference series 1–8 (only 4–8 published by GS), and PESGB DEVEX presentations up to and including DEVEX 2019, with content from multiple additional sources. Papers published by the Society of Petroleum Engineers are not routinely listed below but can be readily searched online via www.onepetro.org .

Abstract The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history. The past, present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals, ranging from the Lower Carboniferous to Cenozoic. In the period between 2007 and 2017, a total of 95 new hydrocarbon fields were discovered, particularly in Upper Carboniferous, Rotliegend and Triassic reservoirs. Nineteen geothermal systems were discovered in the Netherlands onshore, mainly targeting aquifers in the Rotliegend and Upper Jurassic/Lower Cretaceous formations. Although the Southern North Sea Basin area is mature in terms of hydrocarbon exploration, it is shown that with existing and new geological insights, additional energy resources are still being proven in new plays such as the basal Upper Rotliegend (Ruby discovery) for natural gas and a new Chalk play for oil. It is predicted that hydrocarbon exploration in the Southern North Sea Basin area will probably experience a slight growth in the coming decade before slowing down, as the energy transition further matures. Geothermal exploration is expected to continue growing in the Netherlands onshore as well as gain more momentum in the UK.

Abstract Onshore exploration success during the first half of the 20th century led to petroleum production from many, relatively small oil and gas accumulations in areas like the East Midlands, North Yorkshire and Midland Valley of Scotland. Despite this, the notion that exploration of the United Kingdom’s continental shelf (UKCS) might lead to the country having self-sufficiency in oil and gas production would have been viewed as extremely fanciful as recently as the late 1950s. Yet as we pass into the new century, only thirty-five years on from the drilling of the first offshore well, that is exactly the position Britain finds itself in. By 2001, around three million barrels of oil equivalent were being produced each day from 239 fields. The producing fields have a wide geographical distribution, occur in a number of discrete sedimentary basins and contain a wide spectrum of reservoirs that were originally deposited in diverse sedimentary and stratigraphic units ranging from Devonian to Eocene in age. Although carbonates are represented, the main producing horizons have primarily proved to be siliciclastic in nature and were deposited in environments ranging from aeolian and fluviatile continental red beds, coastal plain, nearshore beach and shelfal settings all the way through to deep-marine, submarine fan sediments. This chapter attempts to place each of the main producing fields into their proper stratigraphic, tectonic and sedimentological context in order to demonstrate how a wide variety of factors have successfully combined to produce each of the prospective petroleum play fairways and hence, make the UKCS such a prolific and important petroleum province.