Carboniferous Horton Group Research Articles

Provenance of the Lower Carboniferous Horton Group, Petit-de-Grat Island, Nova Scotia, as revealed by detrital zircon ages

A quartz sandstone bed in a dominantly conglomeratic section in the central part of the Lower Carboniferous Horton Group on Petit-de-Grat Island, offshore southern Cape Breton Island, Nova Scotia, contains detrital zircon grains with ages ranging from mid-Devonian to Archean. The similarity of the Devonian and Neoproterozoic age spectrum to ages of igneous units in the adjacent Avalonian Mira terrane, in particular the Coastal belt, indicates that it was the main source area. This interpretation is supported by the similarity of the Neoproterozoic and older detrital zircon age spectrum to that of the detrital zircon age spectrum in a Cambrian sandstone unit from the Mira terrane. This interpretation indicates post-depositional dextral fault motion between the Isle Madame area and the Coastal belt.RésuméUne couche de grès quartzeux repérée dans une section principalement conglomératique dans la partie centrale du groupe de Horton du Carbonifère inférieur sur l’île Petit-de-Grat, au sud de l’île du Cap-Breton, en Nouvelle- Écosse, contient des grains de zircon détritique dont l’âge va du Dévonien moyen à l’Archéen. La similitude du spectre d’âge du Dévonien et du Néoprotérozoïque avec celui des unités ignées trouvées dans le terrane Mira d’Avalon adjacent, en particulier la ceinture côtière, indique qu’il s’agit de la région source principale. Cette interprétation est étayée par la similitude du spectre d’âge du zircon détritique du Néoprotérozoïque et de périodes plus anciennes avec celui du zircon détritique trouvé dans une unité de grès du Cambrien provenant du terrane Mira. Cette interprétation indique un mouvement postsédimentaire d’une faille dextre entre la région de l’île Madame et la ceinture côtière.[Traduit par la redaction]

Sediment sources and dispersion as revealed by single-grain 40Ar/39Ar ages of detrital muscovite from Carboniferous and Cretaceous rocks in mainland Nova ScotiaGeological Survey of Canada contribution 20090289.

Single-grain ages of detrital muscovite from 15 sand(stone) samples from the Lower Carboniferous Horton Group and the Lower Cretaceous Chaswood Formation of central Nova Scotia were used to infer the nature of the Early Carboniferous unroofing of the Meguma terrane and the reworking of Carboniferous rocks in the Early Cretaceous. In the western Windsor Basin, a sample from the oldest Horton Group rocks yielded ages principally between ca. 400 and 380 Ma, suggesting that most of the muscovite present came from the metamorphic rocks of the Meguma terrane but was variably reset by the intrusion of the South Mountain Batholith at ca. 380 Ma. Other samples in this part of the basin show partial post-depositional resetting. Younger Horton Group metamorphic rocks in the eastern Windsor Basin contain many grains with ages of ca. 370–360 Ma, suggesting derivation from the central core of the South Mountain Batholith or the Musquodoboit Pluton. Horton Group sandstones from the western part of the St. Marys Basin contain muscovite derived from the Liscomb Complex along with metamorphic muscovite variably reset by the intrusion of this complex. In general, our data suggest predominant northward dispersion of muscovite from the Meguma terrane to the Horton Group and a lack of axial transport along the Horton grabens through central Nova Scotia, a pattern compatible with tectonic models in which the Meguma terrane is ramped over the Avalon terrane. Muscovite ages obtained for the Chaswood Formation compare well with those from the Horton Group rocks in the western St. Marys Basin. These rocks may have been exposed to rapid erosion by reactivation of the Cobequid–Chedabucto fault zone in the Early Cretaceous and the resulting sediments were perhaps transported to depositional sites along northeast-trending faults. Unlike the detrital monazites in these rocks, there is no evidence that any of the detrital muscovites came from distal sources outside the Meguma terrane.

The West Indian Road pit, central Nova Scotia: key to the Early Cretaceous Chaswood Formation

The West Indian Road pit is the only large outcrop in Nova Scotia of the Chaswood Formation, the terrestrial equivalent of the offshore Missisauga and Logan Canyon formations. It provides outcrop information on sedimentology, gravel petrology, and structures for a formation that is otherwise known from a few small overgrown pits and from boreholes. The Chaswood Formation in the pit is > 60 m thick and consists principally of sorted sand and gravel with three thinner clay units. Successions of sedimentary structures indicate deposition from a coarse-bedload river flowing to the east-southeast. Gravel consists principally of vein quartz, quartz arenite, and subarkose, together with minor igneous lithologies that can be matched to sources in the Cobequid Highlands to the north. Quartz arenite and subarkose appear derived from Carboniferous Horton Group. Single-crystal 40Ar/39Ar dates of detrital muscovite are a little older than the muscovite ages for the South Mountain batholith, interpreted to mean that the muscovite is second cycle from the Horton Group, which records the earliest unroofing of the batholith. The Chaswood Formation accumulated during progressive tectonic deformation along NNE-trending strike-slip faults in basement rocks, resulting in syn-sedimentary faulting and local unconformities. Sedimentation kept pace with the creation of accommodation. Unrelated younger deformation folded the Chaswood Formation at the pit into an east–west-trending syncline. The Early Cretaceous paleogeography of the Maritime Provinces is interpreted to have consisted of fault-bound horsts shedding coarse detritus surrounded by an interconnected series of basins that accumulated fluvial sands and gravels and overbank muds with well-developed paleosols.

40Ar/39Ar dating in the Lochaber–Mulgrave area, northern mainland Nova Scotia: implications for timing of regional metamorphism and sediment provenance in the Late Devonian – Early Carboniferous Horton Group

40Ar/39Ar dating of whole-rock samples and muscovite separates using age spectrum analysis, and of single muscovite grains using total fusion analysis, yields new insights into the timing of regional metamorphism and sediment provenance in the Late Devonian – Early Carboniferous Horton Group in the Lochaber–Mulgrave area of Nova Scotia. The time of regional metamorphism is constrained to ca. 340–335 Ma by whole-rock spectra from well-cleaved slate and shale samples from the lowermost Clam Harbour River and overlying Tracadie Road formations of the Horton Group. This ca. 340–335 Ma event may have been the result of burial and deformation of the Horton Group by older volcanic and sedimentary rocks of the Guysborough Group, which were overthrust from the south as the result of development of a positive flower structure at a restraining bend along the Cobequid–Chedabucto fault system, the boundary between the Meguma and Avalon terranes. Detrital muscovite ages of ca. 410–380 and ca. 500 Ma were obtained from single-grain analysis and from spectral analysis of separated grains. Whole-rock spectra for two samples from a mylonitic metasedimentary unit in the Cape Porcupine Complex yielded plateau ages of 364 ± 4 and 367 ± 4 Ma, providing a likely source for ca. 370–360 Ma detrital muscovite, ages that may be reflected in some of the age spectrum data. However, the Meguma terrane to the south is the most likely source for most of the detrital muscovite.

Trace element chemistry of vegetation applied to mineral exploration in eastern Nova Scotia, Canada

Trace element analysis of conifer tissues demonstrates the application of biogeochemistry to mineral exploration for gold and other metals hosted by lower Paleozoic metasediments in eastern Nova Scotia. At the regional scale, enrichment of up to 170 ppb Au and 72 ppm As in the ash of twigs from balsam fir (Abies balsamea) coincides with known gold districts and major shear zones. These concentrations are approximately 30 times background level. The twig trace element chemistry indicates previously unsuspected Au potential in Carboniferous Horton Group sedimentary rocks, and around the contact aureoles of Devonian granitoids where the twigs are also enriched in Cs (×30), Sb (×3), Rb (×3) and W (×10). Along the Minas Fault, separating the Avalon and Meguma terranes, anomalous groupings of Ba and Cr in twigs suggest exploration potential for base metal (Cu-Pb-Zn) and mafic or ultramafic (Co-Ni-Pt group element) associations. Detailed biogeochemical studies at five till- and/or bog-covered localities near the Beaver Dam gold deposit outline mineralization buried beneath up to 25 m of surficial sediment. An association of Au, As and Cs in the vegetation provides consistent patterns equal to or better than the more erratic geochemical response in soil and till surveys over the same areas. Concentrations of up to 170 ppb Au in the ash of twigs indicate locations suitable for further exploration. The low shrubs Labrador tea (Ledum groenlandicum), leather leaf (Chamaedaphne calyculata) and bog laurel (Kalmia polifolia) were collected from two small boggy areas suspected to overlie gold-bearing bedrock. Typically, these species contain <10 ppb Au in ash. At one site they contained 22 to 36 ppb Au, and at the other they yielded 55 to 85 ppb Au, in association with Cs and weak Co enrichment. In the glaciated terrain of eastern Nova Scotia, biogeochemical exploration is an effective method for delineating metalliferous zones. Multi-site anomalous concentrations of Au and related pathfinder elements occur where subcropping mineralization is covered by till. Regional and prospect-level biogeochemistry can assist exploration by providing valuable data to aid in the discovery of buried or blind mineralization.

Thermal maturity of the lower carboniferous Horton group, Nova Scotia

The Thermal Alteration Index (TAI) obtained from spore colouration is a useful maturity indicator that may be obtained from palynological preparations. Thermal maturity is an important parameter in determining the hydrocarbon potential of the Lower Carboniferous lacustrine and fluviatile sediments of the Horton Group, and coeval rocks, of Nova Scotia. Samples studied from fifty-two separate localities indicate a wide range in thermal maturity from low (TAI 2 to 3) to high (TAI 4 to 5?). Variation in depth of burial was probably the main factor responsible for the regional differences in thermal maturity. The thickness of Horton sedimentation varied considerably in a series of half grabens, as did the overburden of post-Tournaisian Lower Carboniferous, Upper Carboniferous, Permian and possibly Triassic rocks. The organic matter in most samples is composed of exinous (Type II) and woody and coaly material (Types III and IV). Locally in a few localities amorphous algal material (Type I) consisting of Botryococcus sp. is common. The composition of the organic matter and the thermal maturity data suggest that in most of the study area rocks of the Horton Group are in the dry gas generation zone, although in some areas oil generation may have taken place; in a few localities where the thermal maturity is high the organic matter has been altered beyond the dry gas preservation limit.

Tectono‐sedimentary analysis of alternate‐polarity half‐graben basin‐fill successions: Late Devonian‐Early Carboniferous Horton Group, Cape Breton Island, Nova Scotia

Abstract The Devono‐Carboniferous Horton Group of Cape Breton Island was mostly deposited in two fault‐bounded asymmetric sub‐basins which were part of a large intracontinental rift system. This system lay at a palaeolatitude of about 10–15o S–a warm, semi‐arid climate. The half‐graben sub‐basins had opposed polarity, were approximately 100 times 50 km in size and were separated by a narrow zone of elevated Acadian basement. These features are common to the adjacent structural segments of known rifts, and are unlike those of transtensive pull‐apart systems. Sedimentation occurred in four successive depositional systems which reflect a tectonic evolution of increased and then decreased extensional subsidence through the 8–12 Myr interval represented. Post‐Acadian sedimentation began with System 1 bimodal volcanics and grey distal braided fluvial sediments deposited in a slowly subsiding broad linear sag basin. System 2 consists of reddened braidplain sediments near fault‐bounded margins and mudflat/playa sediments in sub‐basin centres, deposited in two discrete asymmetric sub‐basins with a general upward‐fining trend. Gradual expansion of the mudflat setting and confinement of coarse marginal fades is interpreted as a response to increasingly rapid and deep fault‐bounded subsidence. Depositional System 3, is a complex of grey lacustrine offshore, shoreline and fan delta facies deposited in two adjacent half‐graben segments with opposed polarity of asymmetry. An increased rate of tectonic subsidence allowed a large standing body of water to accumulate lacustrine sediments along the axis of each sub‐basin during this phase of maximum subsidence. System 4 consists of reddened proximal alluvial fan, medial fluvial and distal grey meandering fluvial/floodplain sediments which accumulated in sub‐basins with fault‐bounded margins and asymmetry identical to those of earlier systems, indicating a continuation of tectonic style. However, an overall coarsening‐upward trend indicates waning of active fault‐related subsidence and consequent progradation of marginal coarse wedges to fill the sub‐basins. Rapid marine transgression and deposition of Windsor Group carbonates, evaporites and elastics continued within a more extensive rift basin during renewed fault‐bounded subsidence.

Lithostratigraphy of the Late Devonian-Early Carboniferous Horton Group of the Moncton Subbasin, southern New Brunswick

The threefold subdivision of the Late Devonian - Early Carboniferous Horton Group in the Moncton Sub-basin of southern New Brunswick conforms to the original description and subsequent adoption of the group elsewhere in the Maritimes Basin. The Horton Group consists of the Memramcook, Albert and Moncton formations, the Moncton Formation having previously been regarded as a group. The Memramcook Formation rests unconformably on pre-Carboniferous basement and is conformably overlain by and in part the lateral facies equivalent of the Albert Formation. The Albert Formation contains five variably developed members (both spatially and, in part, temporally): the Dawson Settlement, Frederick Brook, Hiram Brook, Round Hill and Gautreau members. Of these, the Round Hill and Gautreau members have previously been the subject of much stratigraphic debate but are herein proposed simply as members of the Albert Formation. The formally proposed Moncton Formation is subdivided into a lower Weldon Member and an upper Hillsborough Member; where the contact can actually be defined it is un— conformable. The Albert Formation - Weldon Member contact is conformable and transitional. The Hillsborough Member - Windsor Group contact is marked by an abrupt facies change where Windsor Group strata are marine as distinct from non-marine in origin.&#x0D; &#x0D; RÉSUMÉ&#x0D; Le groupe Horton (Dévonien supéirieur - Carbonifère inférieur) que l'on retrouve dans le sous-bassin de Moncton au sud du Nouveau-Brunswick est divisé en trois formations, conformément à la description originale telle qu'adoptée ailleurs dans le bassin sédimentaire des Maritimes. Le groupe Horton comprend les formations de Memramcook, Albert et Moncton (la formation de Moncton était autrefois considérée comme un groupe). La formation de Memramcook repose en discordance sur un socle pré-Carbonifère et est recouverte de façon concordante par la formation d'Albert. La formation de Memramcook est également en partie un faciès latéral de la formation d'Albert. La formation d'Albert compte cinq membres dont l'emplacement à varié dans l'éspace, et em partie, dans le temps: les membres Dawson Settlement, Frederick Brook, Hiram Brook, Round Hill et Gautreau. Les membres Round Hill et Gautreau, qui par le passe ont soulevé maints débats stratigraphiques, sont ici présentés comme membres de la formation d'Albert. La formation de Moncton, présentée de façon officielle, est divisée en un membre inférieur, Weldon, et un membre supérieur, Hillsborough; la où il peut être indenting, le contact est discordant. Le contact concordant entre la formation d'Albert et le membre Weldon en est Ggalement un de transition. Le contact entre le membre Hillsborough et le groupe Windsor n'est marqué par un brusque changement de faciès que la où les strates du groupe Windsor sont distinctement d'origine marine, plutôt que non-marine.&#x0D; &#x0D; [Traduit par le journal]