Cambrian Ordovician Sedimentary Rocks Research Articles

Northern Svalbard Composite Tectono-Sedimentary Element

Abstract The Northern Svalbard Composite Tectono-Sedimentary Element (CTSE) comprises Proterozoic, Early Paleozoic and Devonian sedimentary rocks preserved in northern Svalbard and on the adjacent shelf margin between complexes of metamorphic and crystalline basement rocks. The Northern Svalbard CTSE covers four main tectono-sedimentary elements: Tonian synrift, Neoproterozoic–Cambrian post-rift, Ordovician passive margin and late Silurian?/Devonian synextensional basins. The oldest documented sedimentary strata are greywacke and shale deposited after the Greenvillian Orogeny and assumed to be younger than 980–960 Ma. The present CTSE further includes Cambrian–Ordovician sedimentary rocks in Ny-Friesland and Nordaustlandet, while the dominant part of the CTSE are continental Old Red Sandstone sediments of the late Silurian?/Early Devonian Red Bay and Siktefjellet groups and the Early–Late Devonian Andreé Land Group onshore northern Spitsbergen. Locally, the Cambrian–Ordovician formations contain petroleum source rocks with moderate total organic carbon contents and relatively high hydrogen index values, suggesting a good potential for oil generation. There are possible reservoirs, seals and traps in some of the basins but the CTSE generally holds a very limited potential as a petroleum province, particularly as the region is under strict environmental protection.

Neoproterozoic to early Paleozoic crustal growth, recycling, and the changing geodynamics of North Gondwana

Understanding crustal growth, reworking, and geodynamics of the northern continental margin of Gondwana during Ediacaran to Silurian times plays an important role in Gondwana's paleogeographic reconstruction. This study uses a combination of bulk-rock geochemistry, magmatic and detrital zircon geochronology, zircon trace element, and O-Hf isotope data to evaluate the Ediacaran-early Paleozoic magmatic history of northern Gondwana. Our detrital zircon data from Ediacaran to Ordovician sedimentary successions of central Iran show that the 620–500 Ma detrital zircon likely originates from the erosion of the Cadomian arcs in Iran and Anatolia. This zircon shows variable εHf(t) and δ18O values and Nb/Yb, U/Yb, and U/Nb, resembling arc rocks. The Cryogenian (1000–620 Ma) detrital zircon with juvenile εHf(t) and mantle-like δ18O values could have been supplied from erosion of the juvenile crust of the ANS. The youngest age peaks of 488–450 Mafor detrital zircon, in upper Cambrian-Ordovician sedimentary rocks, are considered to show the rifting of Gondwana and Paleotethys opening. Abundant unrounded 2.5 Ga detrital zircon from Ediacaran sandstones probably shows uplift and exhumation of a local source, i.e., the Archean crust of Iran. The Neoproterozoic igneous rocks formed firstly during the subduction of oceanic lithosphere (Mozambique Ocean) beneath northern Gondwana around 880 Ma to form the ANS juvenile crust. Later, the magmatism moved from the ANS toward the northern territories of Gondwana, with peak magmatism at 570–525 Ma. In Cambrian to Ordovician, the Cadomian magmatic arc was uplifted and eroded, and the geodynamic setting switched into juvenile magmatism following rifting of northern Gondwana.

Structure of the Assynt window, Moine Thrust Zone and relationship of thrusts to alkaline igneous complexes, Caledonian orogeny, NW Scotland

AbstractThe Moine Thrust Zone forms the Caledonian orogenic thrust front where the Moine Supergroup metamorphic rocks have been thrust westward across the Laurentia plate stable foreland, comprising Archean-Proterozoic granulite and amphibolite facies rocks (Lewisian gneisses), with unconformably overlying Mesoproterozoic and Neoproterozoic Torridonian clastic sediments and Cambrian-Ordovician passive margin sedimentary rocks. Four major thrusts beneath the Moine thrust in the Assynt window include the (i) Ben More Thrust, which places the Loch Ailsh syenite intruded into Lewisian basement and Cambrian-Ordovician sedimentary rocks over the Sole thrust sheet, (ii) Glencoul thrust, which places Lewisian basement and folded cover rocks over Cambrian-Ordovician sedimentary rocks, (iii) Borralan thrust, which carries a large alkaline syenite intrusion beneath the Ben More roof thrust and (iv) the Sole thrust sheet, which carries imbricated Cambrian-Ordovician sedimentary rocks and lamprophyre sills over the stable foreland. Three further thrust sheets within the Lewisian basement gneisses are now recognised through restoration of balanced cross-sections, which were responsible for doming of the Assynt window. Although the Moine thrust is mapped as a single line on the map it encompasses, (a) deep ductile shear zone formed of mylonites derived from hangingwall Moine schists, footwall Cambrian quartzites and Ordovician limestones, and basement Lewisian gneisses, (b) roof thrust of the Glencoul and Ben More Thrust sheets and (c) brittle out-of-sequence motion where the Moine schists have been thrust over mylonites, which directly overlie the stable foreland (Knockan Crag).

Provenance variation of the Cambrian-Ordovician sedimentary rocks across South China and implication for its paleogeography in East Gondwana

The tectonic nature of the Early Paleozoic Kwangsian event in the South China Block (SCB) and the paleogeographic position of the SCB in East Gondwana remain enigmatic. Clastic rocks contain significant clues for their detritus provenances, paleogeographic reconstruction and tectonic setting. This study presents detailed detrital zircon UPb geochronology and Hf isotope analyses for the Cambrian sandstones in the SCB, as well as summarizing previously-published data of other Cambrian-Ordovician sedimentary rocks. All the Cambrian-Ordovician sedimentary samples can be subdivided into three groups: the ZD-CL (between Zhenghe-Dapu and Chenzhou-Linwu faults), CL-AL (between Chenzhou-Linwu and Anhua-Luocheng faults) and AL-West (west of Anhua-Luocheng Fault) zones. These three subgroup samples have similar detrital zircon age spectra, cumulative proportion curves and εHf(t) values. Their detrital zircon age spectra are characterized by one prominent age-peak at ∼953 Ma and three subordinate age-peaks at ∼2500 Ma, ∼788 Ma and ∼ 529 Ma. Such signatures argue against provenance variation throughout the SCB during the Early Paleozoic, suggesting an intra-continental affinity for the Kwangsian event in the SCB. The Cambrian-Ordovician sedimentary samples in the SCB have similar detrital zircon age spectra and cumulative proportion curves to those in Australia, Qiangtang and Himalaya. The detrital zircons of ∼953 Ma and ∼ 529 Ma age-clusters in the SCB have similar εHf(t) values to those in Australia and Qiangtang. These features imply that the SCB was located at the nexus between Australia and India during the Cambrian-Ordovician, receiving sediment detritus both from India and Australia.

Diagenetic evolution of a sedimentary system (Michigan Basin): Insights from petrography and S-isotope micro-analysis of pyrite

The study presents a detailed investigation of S-isotope systematics of pyrite from Cambrian-Ordovician sedimentary rocks along the eastern flank of the Michigan Basin, Ontario, Canada. Whole-rock and secondary-ion mass spectrometry (SIMS) pyrite analyses of 34S/32S were undertaken in association with a detailed petrographic investigation of the different crystal morphologies to better constrain the diagenetic history of the sedimentary rocks by informing about the processes of pyrite formation. The broad range of SIMS isotopic data (i.e., −37.1‰ < δ34S < +80.3‰) reveals that three different stratigraphic units experienced different diagenetic pathways of pyrite formation: (1) the Ordovician shales containing primarily biogenic framboidal pyrite formed during two different crystal growth phases (i.e., early diagenesis with δ34S from ~−20 to +5.0‰ and late diagenesis with δ34S from ~+20.0 to +80‰); (2) the Cobourg formation containing relatively 34S-depleted tabular pyrite (i.e., δ34S ~ −25‰) which likely reflects a late replacement phase after sulphate mineral dissolution; and (3) the Cambrian and the Ordovician Black River Group carbonates that share a genetic link in pyrite formation and a complex history of hydrothermal fluid movement. In general, the pyrite in the studied stratigraphic sequence seems to have retained S-isotope signatures indicative of a closed system at the scale of pyrite formation. This study demonstrates the importance of investigating the isotopic systematics of S-species at the microscale level to help understand the evolution of sedimentary basins over geological time scales.

Provenance investigation for the Cambrian–Ordovician strata from the northern margin of the western Yangtze Block: implications for locating the South China Block in Gondwana

AbstractWe report new U–Pb isotopic data for detrital zircons from Cambrian–Ordovician strata on the northern margin of the western Yangtze Block, which together with published U–Pb isotopic data for coeval strata in the South China Block, provide critical constraints on the provenance of these sediments and further shed light on the early Palaeozoic position of the South China Block in the context of Gondwana. Detrital zircons in this study yield four major age peaks in the early Palaeoproterozoic, early Neoproterozoic, middle Neoproterozoic and late Neoproterozoic – early Palaeozoic. The dominant age population of 900–700 Ma matches well with magmatic ages from the nearby Panxi–Hannan Belt, which indicates that Cambrian–Ordovician sedimentary rocks in the western Yangtze Block were mainly of local derivation. However, compilations of detrital zircon ages for the Cambrian–Ordovician strata from the Cathaysia Block and the eastern Yangtze Block show that both blocks are dominated by late Mesoproterozoic- and early Neoproterozoic-aged detrital zircons, which suggests a remarkable exotic input with typical Gondwana signatures. According to the integrated detrital zircon age spectra of the Cambrian–Ordovician sedimentary rocks from the entire South China Block and palaeocurrent data, the South China Block should have been linked with North India and Western Australia within East Gondwana. Specifically, the Cathaysia Block was located adjacent to Western Australia, while the Yangtze Block was connected with North India.

Structure of the Northern Moine thrust zone, Loch Eriboll, Scottish Caledonides

This paper reviews the geology of the Late Ordovician - Silurian Caledonian Moine Thrust zone in the Loch Eriboll region, NW Scotland. We present new detailed mapping and balanced/restored cross-sections to examine its structural evolution. This thrust zone comprises four major thrust slices, carried by the Moine, Lochan Riabhach, Arnaboll and Sole thrusts. Ductile mylonites were derived from lithologies in both the hangingwall (Moine schists) and the footwall (Lewisian basement gneisses, Cambrian quartzites, Ordovician dolomites) of the Moine Thrust. The mylonites are bounded by the Lochan Riabhach thrust below and the Moine thrust above. The Arnaboll thrust sheet comprises Lewisian basement gneisses and Cambrian-Ordovician sedimentary rocks over the Sole Thrust sheet, which exposes a spectacular imbricate sequence of Cambrian-Ordovician sedimentary rocks. Although thrusts sequentially propagated in-sequence from higher (Moine) to lower (Sole) thrusts with time, there is evidence for minor out-of-sequence thrusting and breakback thrusting. Thrusts evolve from deep ductile shears where strain is concentrated along mylonite zones up into the brittle field where they become discrete planar thrust faults. The Early Silurian Scandian metamorphism (~435–415 Ma) is related to a Himalayan style structure with SSE-directed subduction and WNW directed extrusion of a migmatitic core, which we liken to channel flow. We suggest that two major crustal-scale thrusts that extend down into the upper mantle imaged on seismic profiles across the foreland, the Outer Isles and Flannan thrusts, are unrelated spatially or temporally to the Moine thrust sequence.

U–Pb ages and Hf isotopes of detrital zircons from pre-Devonian sequences along the southeast Yangtze: a link to the final assembly of East Gondwana

AbstractThe Early Palaeozoic geology of the South China Craton (SCC) is characterized by an Early Palaeozoic intracontinental orogen with folded pre-Devonian strata and migmatites, MP/MT metamorphic rocks and Silurian post-orogenic peraluminous magmatic rocks in both the Yangtze and the Cathaysia blocks. In this contribution, we present new zircon U–Pb ages and Hf isotope data for detrital zircons from the Neoproterozoic to Silurian sedimentary sequences in the southeastern Yangtze Block. Samples from Neoproterozoic rocks generally display a major peak at 900–560 Ma, whereas samples from Lower Palaeozoic rocks are characterized by several broader peaks within the age ranges 600–410 Ma, 1100–780 Ma, 1.6–1.2 Ga and 2.8–2.5 Ga. Provenance analysis indicates that the 900–630 Ma detritus in Cryogenian to Ediacaran samples was derived from the Late Neoproterozoic igneous rocks in South China that acted as an internal source. The occurrence of 620–560 Ma detritus indicates the SE Yangtze was associated with Late Neoproterozoic arc volcanism along the north margin of East Gondwana. The change of provenance resulted in the deposition of 550–520 Ma and 1.1–0.9 Ga detrital zircons in the Cambrian–Ordovician sedimentary rocks. The εHf(t) values of these detrital zircons are similar to those of zircons from NW Australia–Antarctica and South India. This change of provenance in the Cambrian can be attributed to the intracontinental subduction between South China and South Qiangtang, and the convergence of India and Australia when East Gondwana finally amalgamated.

Combining high resolution vertical gradients and sequence stratigraphy to delineate hydrogeologic units for a contaminated sedimentary rock aquifer system

Summary Hydrogeologic units (HGUs), representing subsurface contrasts in hydraulic conductivity, form the basis for all conceptual and numerical models of groundwater flow. However, conventionally, delineation of these units relies heavily on data sets indirect with respect to hydraulic properties. Here, we use the spatial and temporal characteristics of the vertical component of hydraulic gradient (i.e., vertical gradient) as the primary line of evidence for delineating HGUs for Cambrian–Ordovician sedimentary rocks at a site in Dane County, Wisconsin. The site includes a 16 km2 area encompassing a 3 km long mixed organic contaminants plume. The vertical gradients are derived from hydraulic head profiles obtained using high resolution Westbay multilevel systems installed at 7 locations along two, orthogonal 4 km long cross-sections and monitoring to depths between 90 and 146 m with an average of 3–4 monitoring zones per 10 m. These vertical gradient cross-sections reveal 11 laterally extensive HGUs with contrasting vertical hydraulic conductivity (Kv). The position and thickness of the Kv contrasts are consistently associated with sequence stratigraphic features (maximum flooding intervals and sequence boundaries) distinguished at the site using cores and borehole geophysical logs. The same sequence stratigraphic features are also traceable across much of the Cambrian–Ordovician aquifer system of the Midwest US. The vertical gradients and sequence stratigraphy were arrived at independently and when combined provide a hydraulically calibrated sequence stratigraphic framework for the site. This framework provides increased confidence in the precise delineation and description of the nature of HGU contacts in each borehole, reduced uncertainty in interpolation of the HGUs between boreholes, and some capability to predict HGU boundaries and thickness in offsite areas where high resolution hydraulic data sets are not available. Consequently, this HGU conceptual model will serve as a better basis for numerical simulations of groundwater flow and contaminant transport needed for continued risk assessment and to evaluate potential remedial technologies for the site. More broadly, the association between Kv contrasts and sequence stratigraphy demonstrated at this site provides valuable insight into the relationship between geology and hydraulic contrasts that can be transferred to other areas of the upper Midwest US and perhaps elsewhere to strata deposited in similar settings.

Precambrian sources of Early Paleozoic SE Gondwana sediments as deduced from combined Lu–Hf and U–Pb systematics of detrital zircons, Takaka and Buller terrane, South Island, New Zealand

Combined U–Pb–Lu–Hf isotope investigations on small detrital zircons (30–120 μm) using solution ID-MC-ICPMS and ID-TIMS were carried out on Cambrian–Ordovician sedimentary rocks from the Buller and Takaka terranes of the northeastern South Island of New Zealand. The sediments in these two terranes are considered correlatives of voluminous sedimentary belts in the Lachlan and Adelaidian fold belts of southeastern Australia and in the Wilson and Bowers terranes of Antarctica (SE Gondwana). In order to constrain the sources of these sediments, we use combined U–Pb and Lu–Hf data from detrital zircons, enabling the calculation of Lu–Hf model ages that date the crustal residence time of the zircon protoliths. The Lu–Hf age information is combined with Nd model ages for the bulk sediments. U–Pb systematics of the detrital zircons show age maxima at 0.5–0.6 Ga, 0.8 Ga, and 1.0–1.2 Ga, with initial εHf values for the New Zealand detrital zircons ranging from + 14.9 to − 27.6. These zircon age populations broadly agree with age patterns for sediments found elsewhere in SE Gondwana, confirming a link between the Paleozoic belts of New Zealand and Australia–Antarctica. Lu–Hf model ages obtained from the detrital zircon populations range from 0.9 to 3.7 Ga with an age maximum at ~ 1.5 Ga. A comparison with average crustal residence ages of potential source regions indicates that the Ross-Delamerian orogen of present day Eastern Australia and Antarctica, and crustal provinces in Western Australia are likely sources. The presence of sources as distant as Western Australia suggests long transport pathways for the zircons, possibly via large river systems. A comparison of model age distributions for sediments from Australia, Antarctica, and New Zealand indicate that the Australian sediments have been fed by an additional Archean source (~ 2.8–3.1 Ga), in contrast to sedimentary rocks from New Zealand and Antarctica that lack an Archean model age peak.

Sm-Nd isotopic compositions of Cambrian-Ordovician strata at the Jinggangshan area in Jiangxi Province: Tectonic implications

Whole-rock Sm-Nd isotopes were investigated for Cambrian-Ordovician strata from the Jinggangshan area between the Yangtze Block and Cathysia Block in South China. These strata were deposited as a greatly thick unit of muddy-sandy laminas with intercalated carbonate and organic carbon-bearing layers. They have low ɛNd(t) values of −13.9 to −7.9 and old Nd model ages of 1842 to 2375 Ma. In tDM-tStr diagram, they are far away from the concordant line but fall within the evolution zone of the Proterozoic crust of South China. This indicates that the Cambrian-Ordovician strata are mainly composed of matters eroded from ancient Paleoproterozoic crust that may mainly consist of continental-derived detrital sediments with high maturity in the Cathysia Block. However, the Ordovician Jueshangou Formation and Dui’ershi Formation have ɛNd(t) values of −10.5 and −7.9 at the higher end of the above range and Nd model ages of 1842 to 2059 Ma at the lower end of the above range. This suggests involvement of more detritus that were eroded from the relatively juvenile crust from Late Paleoproterozoic to the Early Neoproterozoic. All the Nd model ages for the Cambrian-Ordovician sedimentary rocks in the Cathysia Block and the southeastern margin of the Yangtze Block are older than 1800 Ma, suggesting that no material from the Early Paleozoic depleted mantle-derived magmas was involved in these regions.

Taconic deformation and metasomatism in Proterozoic rocks of the easternmost Adirondacks

Proterozoic gneiss exposed in readcuts between Fort Ann and Whitehall, New York, is close to the Precambrian/Paleozoic unconformity. It exhibits several features not previously described in Adirondack rocks. These (features include (1) extensive slickensides (azimuth 120°–150°, plunge 0°–30°, southeast-over-northwest sense of movement) on preexisting foliation surfaces; (2) coexistence of calcite marbles that contain granulite facies mineral assemblages with dolomite marbles that contain dolomite, quartz, microcline, and serpentine in unreacted mutual contact; (3) ferroan dolomite that fills veins, faults, and fractures and occurs in thin, foliation-parallel lamellae in gneiss; and (4) minerals of probable low-temperature origin (adularia, celadonite, and cherty silica) that fill veins and interstitial spaces in gneiss and marbles. We suggest that these features can best be explained by minor rotational shear deformation during the Taconic orogeny, accompanied by local metasomatism caused by Mg-rich connate brines expelled from Cambrian–Ordovician sedimentary rocks by overriding Taconic thrust slices.

Tectonic cycles and sedimentary sequences in the Brazilian intracratonic basins

The geometry and petrology of sedimentary rocks preserved in the three intracratonic basins of the Brazilian craton (Parana, Parnaiba, and Amazon) indicate the history and character of vertical movements of the cratonic area. Cyclic successions of erosional and depositional events are synchronous on the Brazilian craton and are correlated with cratons of other continents. The principal evolutionary stages of the Brazilian craton are interpreted as tectonic-sedimentary cycles, each represented by a stratigraphic record identified as a sequence , and each distinguished by its own special characteristics. Cambrian-Ordovician sedimentary rocks, representing deposition in paraplatform basins during a transitional stage at the close of the Brazilian orogenic cycle, are assigned to the Alpha sequence. The Beta (Ordovician and Silurian), Gamma (Devonian–early Carboniferous), and Delta (late Carboniferous–Late Permian sequences) and the Delta-A subsequence (Middle Triassic–Jurassic), corresponding to geotectonic cycles of the cratonic stabilization stage, indicate accumulation in large subsiding basins. The succession of facies in each of these sequences documents cyclical changes in the ratio of sediment supply to subsidence. Marine transgression and basin subsidence increased progressively through the Devonian phase of the Gamma sequence and declined thereafter, in a pattern similar to that of the North American craton and the Russian platform. The frequency of stratigraphic discordances in the three lower sequences suggests a higher degree of cratonic upwarping, progressively diminishing to a stage of maximum stabilization during Delta-A deposition, perhaps related to conditions immediately prior to rupture of the Gondwana plate. Breakup of the Gondwana plate, accompanied by volcanism and remobilization of cratonic areas, initiated the reactivation stage during which two geotectonic cycles are recognized. The first, represented by the Epsilon sequence (Cretaceous), began with local subsidence in isolated basins, followed by widespread continental sedimentation under platform conditions. The second reactivation cycle was responsible for accumulation of the Zeta sequence (Cenozoic), which was characterized by thin residual deposits on an extensive Tertiary peneplain and by accumulations in Quaternary basins, the latter of minor importance except where adjacent to the uplifted eastern continental margin.