Lower Paleozoic strata of the Roberts Mountains allochthon were derived both directly and indirectly from Precambrian basement rocks. The Upper Cambrian(?) Harmony Formation was derived directly from erosion of Proterozoic crystalline rocks along the western margin of North America. Zircon data from feldspar-bearing strata of the Vinini Formation (Lower Ordovician) suggest a provenance link with the Harmony Formation. Compositionally mature, Middle Ordovician eugeoclinal (Palmetto Formation) and miogeoclinal (Eureka Quartzite) quartzites exhibit similar isotopic signatures except that the miogeoclinal quartzite unequivocally contains an Archean component. Volcaniclastic sediment within the Slaven Chert (Middle Devonian) contains Precambrian zircon but no evidence of neovolcanic zircon. New U-Pb isotopic data for detrital zircon from the allochthon are most consistent with models of Antler orogenesis that do not require significant interaction (collision) of a fringing volcanic arc with the continental margin.

Abstract Paleozoic and Mesozoic rocks in the Osgood Mountains region can be grouped into five terranes based on distinct lithologic, age, and structural characteristics. These terranes are: the Lower Paleozoic Osgood block, the Lower Paleozoic Roberts terrane, the Cambrian and Devonian Dutch Flat terrane, the Mississippian to Permian Golconda terrane, and the Triassic to Jurassic Jungo terrane. Each of these terranes is structurally bounded by moderately to steeply dipping fault zones or melange belts and has a distinct internal structural fabric. Geologic evidence exposed in the Osgood Mountains provides support for a revised model for the Paleozoic tectonic history of the region. Paleozoic tectonic events in Nevada can be reinterpreted in a new framework that portrays the traditional Antler and Sonoma orogenies as complex, transpressive episodes of tectonism along the Paleo-Pacific North American plate margin. Recognizing the accreted Paleozoic terranes of Nevada as tectonic blocks that have experienced significant translational displacement and deformation relative to each other and to the continental margin explains many of the geologic observations that have not been accounted for in other models of the tectonic history of Nevada. Several world-class gold deposits in Nevada, notably the Carlin area deposits, the Getchell region, and Pipeline, among others, are located close to inferred high-angle fault boundaries that can be related to these accreted and dislocated terranes. It is proposed that these terrane boundaries are a first-order control for subsequent gold mineralization in these regions. During younger (Tertiary) mineralizing events, these boundaries served as the preexisting deep crust/upper mantle deep-sourcing conduits, circulating large quantities of auriferous fluids through prospective host rocks.

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.

Previous structural interpretations of the Sonoma Range in north-central Nevada have concluded that the Tobin thrust fault—regarded as the equivalent of the Golconda thrust fault—is younger than other thrust faults of post-Triassic age in the range. However, thrust emplacement of the distinctive oceanic upper Paleozoic rocks of the Golconda allochthon over a large region in western and north-central Nevada, and perhaps even beyond, seems to have taken place prior to deposition of Triassic strata in the region. Hence, the structural relationships in the Sonoma Range that bear on the age of the Golconda thrust fault have been questioned. Restudy of the critical part of the Sonoma Range in the vicinity of Clear Creek shows that the oldest faults in the area that bound rocks of the Golconda allochthon and therefore may represent the Golconda thrust fault are, in fact, segments of a single fault that has been displaced by several successive slices of the Clear Creek thrust fault, the north end of which cuts Triassic rocks exposed in the northwestern Sonoma Range. Furthermore, the geometry of rocks displaced since Triassic time on the Clear Creek system of thrust faults suggests that the faults regarded as parts of the Golconda thrust fault in the Sonoma Range are offset segments of the type Golconda thrust fault as exposed about 15 km to the northeast. Consequently, the Golconda thrust fault in its type locality, as well as in the Sonoma Range, is evidently older than faults that cut Triassic rocks, and its age relationships do not conflict with the generally accepted Late Permian or Early Triassic time of emplacement of the Golconda allochthon. Integrated into this structural reinterpretation of the Sonoma Range are several other conclusions and findings of more than local significance, including the following: (1) Prior to emplacement of the Golconda allochthon, lower Paleozoic rocks in the Sonoma Range area, such as the Harmony and Valmy Formations and perhaps the Preble Formation, were intricately deformed and faulted together, presumably during the middle Paleozoic Antler orogeny. (2) Coarse clastic detritus derived from the Harmony and Valmy Formations occurs in the Golconda allochthon of the Sonoma Range, which suggests that it was originally deposited along the North American continental margin. (3) Radiometric ages of plutonic rocks in the Sonoma Range suggest that post-Triassic displacement, perhaps as gravity slides, of parts of the Golconda allochthon on the Clear Creek system of thrust faults took place between about 170 and 100 m.y. ago.

Abstract The classic Cambrian succession of SW Wales comprises a succession of clastic rocks some 1250 m thick that make up part of the Dyfed Supergroup. The existing lithostratigraphical framework owes much to the Nineteenth Century researchers, with relatively little detailed work having been published since. We here present a detailed, rationalized and revised lithostratigraphy for the Cambrian part of the Dyfed Supergroup of the area. Where possible and appropriate, we have retained original and well-known names for formations and other units in harmony with current usage. However, the recognition of four lithostratigraphical groups is overly complex and sometimes unworkable, and a two-fold subdivision is proposed instead. The Caerfai and much of the Lower and Middle Solva groups of earlier usage comprise conglomerates, pebbly sandstones and brightly coloured fine- to coarse-grained sandstones: all are here combined into a revised Caerfai Group. By excluding the silt-dominated Upper Solva division, the Caerfai Group is readily divided into lower and upper parts comprising conglomerates and/or pebbly sandstones, with sandstones and siltstones dominant in between. These rocks comprise the Ogof Golchfa (new), St Non's, Caerfai Bay, Caer Bwdy Bay, Newgale (new) and Porth Clais (new) formations. The following members (all new) are recognized within the Newgale Formation: the Trwyncynddeiriog, Pen-y-Cyfrwy and Cwm Mawr members. Ichnofossils from the upper part of the Ogof Golchfa Formation suggest that Cambrian deposition in the area began in Unnamed Cambrian Series 2 (C2) times. Body fossils and radiometric dating show that the Caerfai Bay to Porth Clais formations span the interval from Cambrian Series 2, Unnamed Cambrian Stage 3 (such stages are denoted by CS3, CS4 etc. below), probably to the Ptychagnostus gibbus Biozone (CS5). The former Upper Solva Group, Menevian Group and Lingula Flags comprise the newly erected Porth-y-rhaw Group, a 687 m-thick unit of fine sandstones, siltstones and mudstones, within which a further five formations are recognized. These are the Whitesands Bay, Menevia, Aber Llong (all new), Ogof Velvet (revised) and Treffgarne Bridge formations. The Porth-y-rhaw Group spans the Tomagnostus fissus Biozone (C3, Drumian) to the Olenus cataractes Biosubzone (Furongian, Paibian). The overall two-fold subdivision of the Cambrian part of the Dyfed Supergroup in the area accords broadly with the first lithostratigraphical scheme proposed for the area, and is comparable with the separation of the Harlech Grits and Mawddach groups in northern and central Wales. The oldest part of the Caerfai Group formed in a tectonically active context and records a transition from alluvial fan deposits, through braided stream environments, into transgressive nearshore marine sandstones. These sediments were derived from the west, and as well as locally-sourced material, include lithic clasts and grains derived from a presumed southwestwards extension of the Monian Composite Terrane. Above lie sedimentary deposits formed under a wide range of conditions, ranging from tidally-influenced to turbidites. Further evidence of active tectonism is found in the easterly-derived fan-delta sedimentary deposits of the higher part of the Caerfai Group and lower part of the Porth-y-rhaw Group. Deposition of the latter began with fine-grained turbidites deposited in a mid–outer shelf setting. These pass up first into hemipelagites, then into sedimentary rocks deposited on a storm-dominated shelf, and finally a very extensive shallow subaqueous delta platform formed in a passive margin setting.

The southwestern High Plateaus of Utah and an adjacent portion of the Great Basin were the site of extensive and prolonged volcanism during much of the Cenozoic Era. The volcanic pile that is centered near Marysvale, Utah, consists mostly of intermediate lava flows and volcanic breccia and dominates the vast accumulation of eruptive deposits that blankets this region; this study includes the southern half of the Marysvale pile. Regional emplacement of ash-flow tuff sheets, probably erupted from sources in the Great Basin, along with local intrusive activity and deposition of continental sediments, was contemporaneous with Marysvale volcanism. The Cenozoic stratigraphy of the area is complex, but the regional ash-flow tuff sheets serve as time-stratigraphic marker units throughout most of the area. The Cenozoic rocks of the southwestern High Plateaus are subdivided into three stratigraphic sequences: lower Tertiary, middle Tertiary, and upper Tertiary and Quaternary. The lower Tertiary (Eocene and Oligocene) sequence is regional in extent and consists of continental sedimentary strata of the Claron Formation and ash-flow tuff of the Needles Range Formation. These formations covered almost the entire area of the southwestern High Plateaus and nearby Great Basin, indicating that there was at that time neither marked structural differentiation nor significant buildup of the Marysvale pile. The middle Tertiary (uppermost Oligocene-lower Miocene) sequence includes most Cenozoic deposits in the area. It is made up of two intertonguing rock assemblages that were deposited contemporaneously but derived from different sources. The western assemblage, best exposed in the southwestern Black Mountains but representative of much of the southeastern Great Basin, consists almost entirely of regional ash-flow tuff derived from Great Basin sources. In ascending order, it includes the Isom Formation and the Quichapa Group, the latter comprising the Leach Canyon Formation, Condor Canyon Formation, and Harmony Hills Tuff. East of these rocks lies the contemporaneous Marysvale pile of volcanic and sedimentary strata, most of which were derived and distributed locally. This eastern assemblage is exposed in the northern Black Mountains, southern Tushar Mountains, northern Markagunt Plateau, and southern Sevier Plateau. The lower rocks consist of lava flows, volcanic breccia, and ash-flow tuff of the Mount Dutton Formation and its lateral correlatives, which are, in ascending order, volcanic breccia and ash-flow tuff(?) of the Buckskin Breccia, sandstone of the Bear Valley Formation, and ash-flow tuff of the Osiris Tuff. All are overlain by rhyodacitic lava flows of the Dry Hollow Formation, basalt of the older basalt flows, intermediate lava flows and volcanic breccia of the Horse Valley Formation, rhyolite flows of the Mount Belknap Rhyolite, and ash-flow tuff of the Joe Lott Tuff. The Mount Dutton Formation, which makes up most of the Marysvale pile, is divided into a vent facies, composed largely of andesitic and basaltic(?) lava flows and flow breccia near the eruptive center of the pile, and an alluvial facies, composed largely of volcanic mudflow breccia derived from the vent facies. Most of the vent facies is restricted to the southern Tushar Mountains, whereas the alluvial facies occurs radially outward in the northern Black Mountains, northern Markagunt Plateau, and southern Sevier Plateau. The upper Tertiary (upper Miocene-Pliocene) and Quaternary sequence is made up of the Sevier River Formation, which consists mostly of detritus shed from upfaulted structures of the High Plateaus, and younger basalt flows, which represent the latest volcanism in the area. New radiometric age determinations demonstrate that most of the Tertiary volcanism occurred during a 5-m.y. time span, in latest Oligocene and early Miocene time (about 25 to 20 m.y. B.P.). The younger basalt flows and, by inference, the closely associated Sevier River Formation may be older (latest Miocene) in part than was believed heretofore. Deposition of the Sevier River Formation and extrusion of the younger basalt flows probably were synchronous with the faulting that led to the structural formation of the High Plateaus; therefore, it appears that this faulting began at least as early as latest Miocene time and has continued intermittently.

ABSTRACT The Santa Ynez Unit of Offshore California consists of three main structures known to contain hydrocarbons; Pescado, Hondo, and Sacate Fields. Hondo Field is currently being produced from two platforms, Harmony and Hondo. The Pescado Field is being developed from the Heritage Platform. These fields are east-west trending anticlines related to extensional and compressional events dating back to the Oligocene. The productive stratigraphic section includes clastic rocks from the Eocene to the Miocene. The sandstone reservoirs account for only a small percentage of the hydrocarbon reserves in the Santa Ynez Unit. These clastic rocks are overlain by deep-water, fine-grained rocks of the Rincon, Tranquillon, and Monterey Formation. The Monterey Formation is the major reservoir unit. These pelagic and hemipelagic rocks contain a high proportion of silica, and are extensively fractured. The fractures are the critical element to production from the Monterey. The fractures provide not only the necessary permeability for fluid flow in the subsurface, but also a significant amount of hydrocarbon storage capacity. Geochemtcal analysis has revealed that two different hydrocarbon systems exist in the unit. The Monterey Formation contains oil generated from within the Monterey Formation. This oil is generalty high in sulfur, with API gravity ranging from less than 10 to 24 degrees. The sandstone reservoirs below the Monterey Formation contain hydrocarbons derived from a more “standard” clastic-rich source rock and are characterized by API gravity of 30 degrees and greater.