Cambrian Clastics Research Articles

Palaeozoic Formations from Dobrogea and Pre-Dobrogea – An Overview

An overview of lithological, palaeontological and geochronological evidence existing for the Palaeozoic formations from Dobrogea and PrDobrogea has enabled a better understanding of the Palaeozoic history of these areas. The Lower Palaeozoic of Pre-Dobrogea, in places in continuity with the pelitic-silty facies of the underlying Vendian (Ediacaran) deposits, was one of the peri-Tornquist basins of Baltica, suggesting that the Scythian Platform in the Pre-Dobrogea basement represents the rifted margin of the East European Craton. In North Dobrogea two types of Palaeozoic succession have formed in different tectonic settings. Deep marine Ordovician-Devonian deposits, including pelagic cherts and shales, associated with turbidites, and facing Devonian carbonate platform deposits of the East European Craton, form northward-younging tectonic units of an accretionary wedge, tectonically accreted above a south-dipping subduction zone. South of the accretionary prism, the basinal to shallow marine Silurian-Devonian deposits of North Dobrogea, showing a similar lithology to the East Moesian successions, accumulated on top of low-grade Cambrian clastics with Avalonian affinity indicated by detrital zircons. Late Palaeozoic erosion was accompanied by deposition of continental alluvial, fluvial and volcano-sedimentary successions, overlying their basement above an imprecise Carboniferous gap. The low-grade metamorphic Boclugea terrane, showing Avalonian affinity, and the associated Lower Palaeozoic deposits represent East Moesian successions, docked to Baltica by the Lower Devonian and subsequently involved in the Hercynian orogeny, being affected by Late Carboniferous-Early Permian regional metamorphism and granite intrusion. The Late Carboniferous-Early Permian syn-tectonic sedimentation, regional metamorphism of Palaeozoic formations and development of a calc-alkaline volcano-plutonic arc indicate an active plate margin setting and an upper plate position of the Macin-type successions during the Variscan collision, when the Orliga terrane, with Cadomian affinity, was accreted to Laurussia along a north-dipping subduction zone of the Rheic Ocean. The East Moesian Lower Palaeozoic succession, overstepping its Ediacaran basement, represents an Avalonian terrane, docked to the Baltica margin in the Early Palaeozoic. A narrow terrane detached from the Trans-European Suture Zone (TESZ) margin of the Baltica palaeocontinent forms a tectonic wedge within the East Moesian basement. The Palaeozoic sedimentary record of East Moesia shows a quartzitic facies in the Ordovician, graptolite shales in Upper Ordovician-Wenlock, black argillites in the Ludlow-Pridoli and fine-grained clastics in the Lower Devonian. Eifelian continental sandstones are followed by a carbonate platform from Givetian to Tournaisian times and coal-bearing clastics in the Carboniferous, indicating a foredeep basin evolution. By the Eifelian both East Moesia and Pre-Dobrogea were part of Laurussia, sharing the same old red sandstone facies. The Permian is a time of rifting in Dobrogea and Pre-Dobrogea, although evidence for rifting in the East Moesian sedimentary record is very limited. In the eastern basins of Pre-Dobrogea, Permian rifting was accompanied by alkaline bimodal volcanism of the basalt-trachyte association, that affected also the northern margin of North Dobrogea. Late Permian within-plate alkaline magmatic activity emplaced plutonic and hypabyssal complexes along the south-western margin of North Dobrogea. The model proposed for the Palaeozoic history based on existing data for the north-western margin of the Black Sea records early Palaeozoic docking to Baltica of the Avalonian terrane of East Moesia, including the Boclugea terrane of North Dobrogea. Late Carboniferous-Early Permian accretion of the Cadomian Orliga terrane from North Dobrogea, accompanied by Hercynian metamorphism and granite intrusion, correlates with the closure of the Rheic Ocean. Subsequently, Avalonian and Cadomian terranes, together with a narrow terrane detached from the TESZ margin of Baltica palaeocontinent, were displaced southward along the strike-slip fault system of the TESZ.

Tectonic and stratigraphic evolution of the Cambrian basin of northern Northwest Territories

Abstract The Cambrian basin of the mainland Northwest Territories has been of considerable economic interest since gas was first discovered in Mount Clark Formation sandstones in 1974. A recently completed assessment by the Geological Survey of Canada has estimated that the Cambrian Clastics play contains almost a billion barrels of oil and 10.7 TCF of gas. The play’s reservoirs, seals and source rocks are all of Cambrian age, making the understanding of the basin’s evolution and contents critical to any exploration effort. The basin is a semi-enclosed, epicontinental marine basin, bordered by positive elements and open to a subsiding continental shelf and margin, and represents the eastern portion of a much larger deposystem that developed after the breakup of Laurentia. A multi-disciplinary study of a large regional reflection seismic grid, supported by borehole and potential field data, shows the basin to have evolved in three stages: 1) Early Cambrian pre-rift regional subsidence of the area lying inland of the Mahony and Bulmer arches, and a newly identified high that pre-dated the Mackenzie Trough. It was during this period that the Mount Clark Formation was deposited; 2) A middle Cambrian rift phase during which a graben system, about 50 km wide and over 400 km long, developed in the basin’s core. The grabens are deepest in south Mackenzie Trough where rifting began, and are progressively shallower and younger to the north and northeast. Mount Cap was deposited during this phase and it is expected that the grabens received finer-grained clastics than did the shallower areas on their flanks; 3) A post-rift subsidence phase that began with deposition of the Saline River Formation during the Late Cambrian and continued, with interruptions, until the middle of the Devonian. Throughout Cambrian time, sediment onlapped the basin’s flanks and its internal arches, each layer advancing further than its predecessor. It was not until the latest Cambrian that the internal arches were completely covered by beds of the lower Franklin Mountain Formation. A previously undocumented Cambrian age graben (herein named McConnell Graben) lies in the hanging wall of the unnamed Laramide thrust fault that emerges from the east flank of the McConnell Range. The fault began as a Cambrian normal fault that separated the Bulmer and Mahony arches on the east from McConnell Graben on the west. The present day ‘St. Charles’ range developed in a similar manner. A preliminary exploration risk analysis, based on the predicted distribution of reservoir, seal and source rocks, reveals two attractive areas for exploration. The larger one, centred on Lac des Bois, is about 150 km wide and extends on a NW-SE trend for about 300 km across the Aubry and Good Hope depocentres. The smaller area (less than 50 × 100 km in extent) lies within Mackenzie Plain depocentre.

A probable late Neoproterozoic age for the Kennedy Channel and Ella Bay formations, northeastern Ellesmere Island and its implications for passive margin history of the Canadian Arctic

The Kennedy Channel and Ella Bay formations are the two oldest stratigraphic units exposed in the Franklinian margin sedimentary sequence in the Canadian Arctic Islands. An Early Cambrian age had previously been accepted by the occurrence of trilobites and small shelly fossils in the type section of the Kennedy Channel Formation. Reinvestigation of the area around the type section shows that several large strike-slip faults cut the succession and that the olenelloid trilobites are from an infaulted slice of a younger unit, the Lower Cambrian Kane Basin Formation. Thus, there is no unambiguous paleontological evidence for the age of either the Kennedy Channel or Ella Bay formations. However, the abundance of stromatolites, absence of trace fossils, and separation from overlying Lower Cambrian clastics by a regional angular unconformity indicate a probable late Neoproterozoic age for these two formations. The Ella Bay Formation likely correlates with the Portfjeld Formation in North Greenland, the Spiral Creek Formation in East Greenland, and the Risky Formation of the Mackenzie Mountains in northwestern Canada. The passive margin that existed in northern Laurentia during the early Paleozoic was, therefore, established in the late Neoproterozoic, and the onset of rifting must have preceded this, rather than occurring in the Early Cambrian as some authors have suggested.

Paleomagnetic results from the Cambrian and Ordovician sediments of Bornholm (Denmark) and Southern Sweden and paleogeographical implications for Baltica

If apparent polar wander paths (APWP) cross, the question arises how to prove the older magnetization to be primary and not just a younger overprint. This problem is typically met in areas affected by percolating mineralizing fluids and/or heating due to a younger regional igneous activity. The Permian magnetic overprint is the classical example. Earlier paleomagnetic studies over the Lowermost Cambrian Nekso Sandstone Fm (NSF) of Bornholm (Denmark) yielded a characteristic remanent magnetization (ChRM) similar to the Permian directions for Baltica. Since a possible reason could be a chemical overprint, we checked whether this phenomenon did take place on a regional scale. Some samples therefore were collected from other Lower Cambrian clastics of Bornholm and Southern Scandinavia. In result we show that the well‐grouped and stable ChRM of the NSF contrasts with fairly chaotic, soft, and badly preserved magnetizations of the Balka, Hardeberga, Mickwitzia, and Lingulid sandstones of Bornholm and Southern Sweden, thus not indicating widespread paleomagnetic overprint. We demonstrate that the ChRM of the NSF is most probably of syndepositional/early diagenetic origin and its similarity to the Permian direction for Baltica is only casual. We propose a normal polarity and a near‐equatorial position on the Southern Hemisphere for Baltica in the early Cambrian time, as well as a more complicated trend of the APWP for this paleocontinent than envisaged by other authors. Paleomagnetic results from the Arenigian limestones of the Laesaa Formation (Bornholm) that yield excellently defined but most probably only secondary components are also presented.

Tectonically induced fluid flow in Devonian carbonate aquifers of the Western Canada Sedimentary Basin

This study investigates paleofluid flow through the Devonian carbonate aquifers in the deep part of the Alberta Basin, Canada, using the distribution and geochemical composition of deep burial, late diagenetic, sparry calcite and dolomite cements, as well as that of the Precambrian metasediments that make up the underlying basement and much of the adjacent Rocky Mountain Main Ranges. The objective of this study is to characterize regional, tectonically induced (squeegee-type) fluid flow in these Devonian aquifers. The data indicate sublateral injection of fluids from a basin-external, probably metamorphic source during deep burial diagenesis in some gas pools close to the deformed belt and/or injection of such fluids via subvertical faults from the metasedimentary basement, or sublaterally via the intervening Cambrian clastics. The fluxes and possible geothermal anomalies during injection of basin-external fluids appear to have been low. Also, tectonically induced fluid flow appears to have been rather limited laterally, extending perhaps only 100–200km into the foreland basins.

Devonian Matrix Dolomites and Deep Burial Carbonate Cements: A Comparison Between the Rimbey-Meadowbrook Reef Trend and the Deep Basin of West-Central Alberta

The Upper Devonian Rimbey-Meadowbrook reef trend is an extensive subsurface carbonate aquifer system in the southern part of the Western Canada Sedimentary Basin and is compared with Swan Hills, Leduc and Wabamun carbonates of west-central Alberta. These Devonian levels are part of a structural homocline that crops out near its northeastern end and stretches for several hundred kilometers southwestward into the deepest part of the basin. Most Devonian carbonates are pervasively dolomitized into grey matrix dolomite, which commonly comprises about 85-90 vol % of the rocks. Despite its large regional extent and subsurface depths (0 to 6500 m), the Rimbey-Meadowbrook reef trend displays little if any systematic variations in petrography or geochemistry. Stratigraphic, petrographic and geochemical evidence suggest that the grey matrix dolomite formed at depths of about 500-1500 m from marine pore waters with relatively minor modification by water-rock interaction. Volumetrically minor amounts of calcite and dolomite cements, replacive and cement anhydrite, and elemental sulfur and hydrocarbons fill some of the remaining porosity. The volumetrically minor intermediate burial (>600-1500 m) dolomite cements and deep burial saddle dolomite and calcite cements occur as coarse-crystalline spars in secondary porosity. Intermediate burial dolomite cements display a slight decrease down the reef trend in delta 18 O values (-4 to -7 per mil PDB) with increasing depth that correspond to slightly elevated 87 Sr/ 86 Sr ratios. Fluid inclusions of these dolomite cements are highly saline and have relatively uniform homogenization temperatures (122 to 131 degrees C), suggesting that they formed from relatively hot fluids before significant basin tilting. Deep burial (>2000-3000 m) saddle dolomites are rare in the Rimbey-Meadowbrook reef trend and the available fluid inclusion homogenization temperatures increase with burial, suggesting that they precipitated under normal geothermal gradients after significant tectonic tilting. The calcites fall into two groups, a relatively early and a relatively late group. The relatively early calcites follow a 30 degrees C/km geothermal gradient when corrected for pressure, whereas the later calcites that formed as a by-product of thermochemical sulfate reduction follow a 20 to 25 degrees C/km gradient and may reflect cooler post-Laramide conditions. The deep basin of west-central Alberta includes the Obed, Kaybob South, Fox Creek, Pine Creek and Simonette fields from the Swan Hills, Leduc and Wabamun stratigraphic levels. Replacement matrix dolomites in all three stratigraphic levels are similar in terms of textures, trace elements and C, O and Sr isotopes, and to those of the Rimbey-Meadowbrook reef trend. In addition, fault-controlled, late-stage burial dolomitization is evident in the Swan Hills, Kaybob South and Simonette buildups, and in the Wabamun Pine Creek Field. Homogenization temperatures from fluid inclusions in saddle dolomites range from about 127 to 167 degrees C and late calcites have similar T h ranges from 124 to 164 degrees C. Temperatures for anhydrite are cooler, ranging from 104 to 116 degrees C, and suggest secondary alteration of inclusions at present reservoir temperatures and/or that some anhydrite was remobilized at somewhat cooler conditions after maximum burial. Downdip to the southwest in the Obed buildup, deep burial calcite cements in fractures and vugs have highly radiogenic 87 Sr/ 86 Sr ratios (0.7252) and highly depleted delta 13 C values (minimum -27.1 per mil PDB), indicating incorporation of oxidized carbon from Thermochemical Sulphate Reduction (TSR). In other buildups, delta 13 C values of late calcite cements are not as depleted in their carbon isotopic values (0.9 to -10 per mil PDB). Radiogenic Sr occurs updip to the northeast in saddle dolomite and calcite cements (Swan Hills, Kaybob South 0.7221, 0.7310; Simonette 0.7370, 0.7369; Leduc Pine Creek 0.7140, 0.7195; Wabamun Pine Creek 0.7150, 0.7188). The radiogenic 87 Sr/ 86 Sr signal appears to be derived from fluids that had interacted with the crystalline basement and/or overlying Proterozoic/Lower Cambrian clastics. It is possible that at least some radiogenic Sr was injected into the Devonian section by tectonic loading during the Laramide Orogeny. The Rimbey-Meadowbrook reef trend and the Devonian carbonates in the west-central Alberta deep basin are similar in terms of overall diagenetic phases and their characteristics. The late-stage cements exhibit somewhat higher temperatures in the deep basin of west-central Alberta. The regions differ mainly in radiogenic Sr with all west-central Alberta late-stage dolomite and calcite cements being more radiogenic, especially along established or inferred faults as in Kaybob South, Swan Hills Simonette and Wabamun Pine Creek fields. The west-central Alberta calcites also contain lighter delta 13 C (-3.5 to -10.0 per mil PDB) and even lower (0 to -27 per mil) in some high sour gas fields like Obed.

Low-flux, tectonically-induced squeegee fluid flow (“hot flash”) into the Rocky Mountain Foreland Basin

This study investigates paleofluid flow through the Devonian carbonate aquifers in the deep part of the western Alberta Basin, using the distribution and geochemical composition of deep burial, late diagenetic, sparry calcite and dolomite cements, as well as the Precambrian metasediments that make up the underlying basement and much of the adjacent Rocky Mountain Main Ranges. The objective of this study is to characterize regional, tectonically-induced (squeegee-type) fluid flow in these Devonian aquifers, the fluxes and thermal anomalies, their timing and duration, as well as their possible influence on hydrocarbon migration and trapping. New data from the Southesk-Cairn complex and the surrounding shales show intriguing patterns. Firstly, the data define the regional (background) value of the MAximum Sr Isotope Ratio of BAsinal Shale (MASIRBAS) at 0.7120. Comparison with literature data shows that MASIRBAS is valid for the entire stratigraphic section from the Pleistocene glacial till down to at least the Middle Devonian, probably also to the base of the Cambrian. Consequently, any carbonate (or sulphate) cement with a 87 Sr/ 86 Sr-ratio of >0.7120 is likely to have formed from formation waters with a basin-external (extra-basinal), metamorphic component that is derived from Precambrian rocks. Many carbonates close to the deformed belt host sour gas pools that are hydrologically relatively isolated at present. However, highly elevated 87 Sr/ 86 Sr-ratios (up to 0.7370) indicate sublateral injection of fluids from a basin-external, probably metamorphic source during deep burial diagenesis in some pools close to the deformed belt, such as at Obed. At other locations, such as Simonette or Kaybob-South, basin-external fluids appear to have been injected via subvertical faults from below, with highly radiogenic Sr derived from the metasedimentary basement or sublaterally via the intervening Cambrian clastics. The fluxes and possible geothermal anomalies during injection of these external fluids appear to have been low, as estimated from the volumes of late calcites with elevated 87 Sr/ 86 Sr-ratios and from their fluid inclusion homogenization temperatures. Reasons for the low fluxes include low volumes of expelled fluids and a relatively poor hydraulic connection between the source of these fluids and the Devonian aquifers, reminiscent of an ill-fitting garden hose connection. Tectonically-induced fluid flow appears to have been laterally rather limited, extending perhaps only 100 to 200 km into the foreland basins, where the radiogenic Sr signal disappears. Another important finding is that late diagenetic carbonate cements from outcrops in thrust sheets of the Rocky Mountain Main Ranges do not exhibit the highly elevated 87 Sr/ 86 Sr-ratios found in the subsurface. These findings have several important implications. Firstly, large-scale hydrothermal dolomitization, which requires large fluxes and has been advocated recently for the deep part of the Alberta Basin and similar geologic settings elsewhere, is not possible by squeegee-type flow, unless the fluids are focused into and funnelled through relatively narrow confined aquifers. Secondly, the pervasive Laramide-aged remagnetization of much of the sedimentary sequence close to the limit of the disturbed belt in Alberta is not possible by this type of flow. Lastly, the recognition that metamorphic Sr, albeit present in the deep basin, is absent from at least some of the thrust sheets in the Main Ranges, indicates a different type of hydrologic regime during their formation.

Evolution of Cambrian-Ordovician Carbonate Shelf, United States Appalachians: ABSTRACT

Cross sections and isopach maps (palinspastic) of the Cambrian-Ordovician continental shelf, United States Appalachians, show that thickness and facies trends are controlled by the Adirondack, New Jersey, and Virginia highs and depocenters in Tennessee, Pennsylvania, and by the Rome trough. Carbonate sedimentation was initiated with drowning of Early Cambrian clastics, deposition of carbonate ramp and rimmed shelf facies followed by drowning, then regional regression and deposition of Early to Middle Cambrian red beds and platform margin rimmed shelf facies. During subsequent regional transgression, the Conasauga intrashelf shale basin formed, bounded toward the shelf edge and along depositional strike by Middle to Upper Cambrian oolitic ramp facies and cyclic peritidal c rbonates. Intrashelf basin filling and regional regression caused progradation of Late Cambrian cyclic carbonates and clastics across the shelf. By this time, the margin had a relief of 2.5 km. During the Early Ordovician, incipient drowning of the shelf formed subtidal carbonates and bioherms that passed up into cyclic carbonate as sea level oscillations decreased in magnitude. Numerous unconformities interrupt this sequence in the northern Appalachians. The earlier high relief rimmed shelf was converted into a ramp, owing to uplift in the basin, heralding approaching collision. Subsidence rates on the margin were low (4 cm/1,000 yr) and typical of a mature passive margin. Shelf sedimentation in the southern Appalachians ceased with arc-continent collision and development of the Knox un onformity, which dies out into the Pennsylvania depocenter. Major exploration targets are in the Late Cambrian-Early Ordovician Knox Group. End_of_Article - Last_Page 299------------

Introduction to Stratigraphy, Structure, and Geologic Problems in Big Horn Basin, Wyoming and Montana: ABSTRACT

End_Page 1342------------------------------As the cumulative production of oil from the Big Horn basin approaches the 2 billion bbl mark, it is appropriate that we look at the geology once again. The Big Horn basin, located in northwestern Wyoming and south-central Montana, is bordered on the east by the Big Horn Mountains; on the south by the Owl Creek Mountains; on the west by the Absaroka and Beartooth Mountains; and on the north by the Nye-Bowler lineament. The combination of a great reservoir-source duet in the Paleozoic rocks and the creation of large anticlines during the Laramide orogeny has been the key to the Big Horn basin's success as an oil producer. Stratigraphy of the Big Horn basin can be divided generally into (1) the Middle Cambrian clastics, (2) the Paleozoic shelf carbonates, (3) the Mesozoic clastics, (4) the Late Cretaceous to Tertiary synorogenic clastics, and (5) the Tertiary post-orogenic clastics and volcanics. By far the most economically important formations have been the Permian Phosphoria and Pennsylvanian Tensleep Formations. This dynamic duo consists of porous eolian and shallow marine, quartz sandstones of the Tensleep overlain by shallow marine, oil-rich carbonates of the Phosphoria. The two have combined to produce over 1.5 billion bbl of oil in the Big Horn basin alone. The draping of the Tensleep and Phosphoria over large Laramide structures (closures of over 5,000+ ft, 1,500 m, and areal extents up to 15 mi2, 40 km2) was the final key. An upcoming afternoon session of papers will explore the proposed anatomies and mechanisms of folding in the Cordilleran foreland. There is a controversy over the morphology of the folds in the foreland. Put simply, there is some disagreement over how much the horizontal or thrusting component contributes to these folds. Stearns, who described the fold at Rattlesnake Mountain in the 1971 Wyoming Geological Association guidebook, favors drape folding over near-vertical faults in the Precambrian. Berg in the 1962 AAPG Bulletin and Gries in the 1983 AAPG Bulletin favor a more thrusted model with reverse fault planes dipping 60° to 30°. Sales in the 1968 AAPG Bulletin agrees with the morphology of Berg and Gries, but feels that the folds in the foreland were generated by faults with strong lateral components. Concerning other problems, Stone in the October 1967 AAPG Bulletin pointed out that the Paleozoic reservoirs often have a common oil-water contact (OWC) within individual structures. He attributed the common OWC to fractures joining the reservoirs. The OWC is commonly tilted; this he attributed to hydrodynamic flow. An understanding of fractures and tilted oil-water contacts is imperative for successful exploration and production programs in the Big Horn basin. End_of_Article - Last_Page 1343------------

Lithologic and Faunal Aspects of the Lower Paleozoic at Royal Creek, Yukon Territory [Abstract

ABSTRACT In stratigraphically ascending order, the Early Paleozoic sequence consists of Lower Cambrian clastics with minor carbonates, recessive Upper Cambrian mudstones, and resistant Lower Ordovician cherty dolomites, and Upper Ordovician carbonates. The latter are well dated in all sections by the Arctic Coral The former sequences are very poorly fossiliferous and dating is based on sparse collections of Olenellus, Dresbachian brachiopods, and trilobites of the Leiostegium-Kainella Zone. Major facies variations are absent within this basal sedimentary package. A gradual carbonate-shale transition occurs within the Lower, as well as Upper, Silurian Series. The former displays a lateral change from mainly restricted carbonates with a sparse ostracod-brachiopod fauna to open marine limestones and shales with a rich and varied trilobite-brachiopod-graptolite assemblage. Upper Silurian sediments range from restricted ostracod-bearing carbonates to open marine limestones and shales with the Atrypella scheii fauna. Apparently, most of the Middle Silurian is absent. An abrupt carbonate-shale transition is assigned to the earliest Devonian. Extensive faunal collections, from closely-spaced measured outcrop sections straddling these transitions, indicate conformable relations from Late Middle Silurian into Early Devonian and contribute to the definition of the Siluro-Devonian boundary. Intercalations of shelly and graptolitic sequences render the area particularly interesting. The various carbonate facies indicate a progression from restricted shelf to normal marine basinal deposits. End_of_Record - Last_Page 601-------

Chronology of Appalachian Folding

A generalized summary of orogenic events starts with an epoch of mountain building that occurred before the Cambrian period began and produced an eastern highland from which most Cambrian clastics were derived. From the middle of the early Cambrian to at least the beginning of the Mid-Ordovician, there are no evidences of any contemporaneous mountain building. The eastern highlands were essentially destroyed by erosion before the middle of the Cambrian, and Cambro-Ordovician carbonate rocks testify to a continental-shelf site of deposit instead of a geosynclinal site as is commonly assumed. Commencing in the Mid-Ordovician with the uplift of low positive axes and heralded by volcanic activity that produced widespread beds of bentonite, a great and vigorous earth movement affected the country and the eastern border of what is now the North American continent. From the onset of the Silurian to the end of the Paleozoic, there was probably no time when this wide area was completely free from the effects of contemporaneous orogeny or vulcanism. The chief pre-Silurian effort, known as the Taconic disturbance, must have been the most profound of all orogenies--much more vigorous, more extensive, and more intense than any mountain building to follow in eastern North America. Most Devonian phases of deformation are associated with the Acadian disturbance of which the major effort, known as the Schickshockian disturbance, came during the middle and late Devonian for most areas of its influence. The terminal Paleozoic or so-called Appalachian orogeny, here renamed the Alleghany revolution, variously affected parts of the province from Mississippian time to the close of the era and may have continued into the early and early middle Triassic before it came to a final close. The discussion briefly covers the sedimentary, structural, igneous, and metamorphic records of folding.