Continental Red Beds Research Articles

Stratigraphy of the Fungurume Group - evolving foreland basin succession in the Lufilian fold-thrust belt, Neoproterozoic-Lower Palaeozoic, Democratic Republic of Congo

The Lufilian arc (Neoproterozoic-Lower Palaeozoic) is a Pan-African orogen that lies between the Kalahari Craton in the south and the Congo Craton in the north. North vergent thrusting of its Katangan metasedimentary succession formed a fold-thrust belt in the northern sector of the arc. The belt contains prominent bodies of fragmental rocks including thrust sheets and megablocks of older Katangan strata, some of which contain Cu-Co mineralisation. These fragmental rocks were traditionally considered as tectonic friction breccias formed underneath the advancing Katangan nappes. This paper presents the stratigraphic implications of a recent reinterpretation of these breccias as sedimentary conglomerates in the fold-thrust belt of the Lufilian arc. The Katangan succession in Zambia and the Democratic Republic of Congo (DRC) is traditionally subdivided into four main lithostratigraphic units: Roan, Mwashya, Lower Kundelungu and Upper Kundelungu. It has been considered that that the Roan, Mwashya and Lower Kundelungu strata were deposited in a progressively opening rift basin, then folded and thrust northwards during Upper Kundelungu times. No syntectonic sedimentation associated with this orogenesis was previously recognised. Megabreccias within the Kundelungu succession in the northern part of the fold-thrust belt are interpreted here to be sedimentary complexes of synorogenic conglomerates derived from the orogenic front advancing from the south and deposited in a newly recognised foreland basin to the north. The sedimentary origin means that the ‘megabreccias’ should be classified as new lithostratigraphic units of the Katangan succession. The Fungurume Group (new unit), which unconformably overlies older strata, represents foreland basin fill and is subdivided into three formations. The Mutoshi Formation is characterised by continental red beds, previously called RAT. A facies association of hematite-rich, marginal marine, mixed clastic and carbonate rocks constitutes the Dipeta Formation. The Kambove Formation comprises olistostromes deposited by subaqueous sediment-gravity flows. The Mutoshi and Dipeta Formations were previously correlated with the rift-related Roan Group of Zambia. The Cu-Co-bearing Roan-derived strata, traditionally called the Mines Group, occur only as allochthonous blocks embedded in any of the above formations. Therefore, the Mines Group does not form a legitimate lithostratigraphic unit, and it is excluded herein from the revised stratigraphy of the Katanga Supergroup. The undeformed continental molasse of the Plateau Group fills the youngest foreland basin, extending ahead of the fold-thrust belt.

The tectonic and stratigraphic framework of the United Kingdom's oil and gas fields

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.

New dating and interpretation of the sedimentary succession of Fiumara Sant’Angelo (Peloritani Mountains ; southern Italy) : consequences for the Mesozoic palaeogeography of the central Mediterranean

Abstract In the Peloritani Mountains an Alpine nappe stack, involving an Hercynian or older basement, is present. Some nappes involve a Meso-Cenozoic sedimentary cover, which starts with Upper Triassic-Hettangian continental redbeds (Verrucano), followed by Sinemurian neritic limestones and, up to the Oligocene, by marly-calcareous pelagic strata. Locally, Upper Triassic evaporites have been recognised. In the Sant’Angelo di Brolo valley, a peculiar sedimentary succession characterised by about 80 m of graded sandstones overlies the Verrucano redbeds. It has been described by Duée [1969] who ascribed it to the Alì Unit. Later on, Thery et al. [1985] interpreted the sandstones as fluvial deposits, Norian-Rhetian in age on the basis of pollens, and correlated them with the Sardinian « Keuper ». The finding of some ammonites and few nannofloras in the siliciclastic succession allow us to reach quite different conclusions. One ammonite specimen, collected in the uppermost part, shows morphological affinities with Spinammatoceras (M) tenax (Vacek), reported from the Middle Aalenian L. murchisonae Zone. Within the calcareous nannofossils, the presence of Lotharingius umbriensis in the lower part of the succession indicates an age not older than late Pliensbachian. However, the upper part of the same succession is characterised by the occurrence of Hexalithus magharensis, Triscutum tiziense, Watznaueria contracta, whose FO is early Aalenian. The petrographic study evidences that sandstones have two compositional groupings : a quartzose (quartzarenite to sub-litharenite) petrofacies of the continental redbeds (Verrucano), and a quartzo-feldspathic (feldspathic quartz-arenite to sub-arkose) petrofacies of the marine sandstones. The redbeds represent deposition by low gradient rivers and are similar to the composition of the Torrente Duno Fm in the Longobucco Group of the Sila Unit sedimentary cover. Their sources include abundant reworked quartz, felsitic volcanic, and low-grade metamorphic terrains. The overlying Middle Liassic-Aalenian marine sandstones testify an abrupt change in composition, reflecting changing source terrains. Its composition, including oversized feldspar grains, suggests gneissic/plutonic source terrains, added to the quartzose and metamorphic sources of the underlying fluvial sandstone. Identical changing detrital modes is testified in the Liassic formations of the Longobucco Group. These sandstone detrital modes mark the evolving early Jurassic rifted-continental margin of the Neotethys ocean. The studied succession shows characteristics unknown elsewhere in the Peloritanian Units, such as the presence of Mesozoic siliciclastic sediments younger than the « Verrucano » redbeds and the lack of terrains in carbonate platform facies above them. It has been deposited in a basin close to emerged areas, in which a clastic supply persists at least until Aalenian. Therefore, the Jurassic palaeogeography of the Peloritanian domain was more articulated than previously thought: pelagic areas were close to continental regions which supplied with siliciclastic detritus narrow basins, confined in grabens or half-grabens between emerged lands and sea-mounts. In the whole Jurassic of the Calabria-Peloritani Arc, siliciclastic marine terrains are known only in the Sila Unit. Here, Middle Carixian-Lower Domerian marls and sandstones in slope facies and an arenaceous turbiditic succession – late Domerian-early Toarcian in age (Longobucco Group) - have been described [Teale et Young, 1987]. There are close similarities in lithologies, tectono-sedimentary evolution, age and petrographic characters between these two sequences. The studied succession cannot be ascribed either to the Mandanici Unit, or to the Alì Unit. In fact, these units are affected by Alpine metamorphism and their Alpine cover is characterised by Upper Triassic evaporites followed by Jurassic and Cretaceous pelagic limestones and radiolarites. Its original bedrock is probably represented by the phyllites and marbles of the Piraino Unit, recently identified in the same region. In conclusion, the Sant’Angelo di Brolo succession was deposited in a marine environment between Pliensbachian (or Sinemurian) and Aalenian. Thus, both the late Triassic age and the fluviatile environment proposed for these terrains must be abandoned, as well as their correlation with the Sardinian « Keuper ».

VARIATIONS OF SULFUR ISOTOPES, TRACE ELEMENT COMPOSITIONS, ANDCATHODOLUMINESCENCE OF MISSISSIPPI VALLEY-TYPE Pb-Zn ORES FROM THE DRAU RANGE,EASTERN ALPS (SLOVENIA-AUSTRIA): IMPLICATIONS FOR ORE DEPOSITION ON AREGIONAL VERSUS MICROSCALE

The sulfur isotope composition of sulfide ore minerals of the Drau Range varies considerably, down to centimeter-scale variations, both on a regional and a local scale. Broadly scattering δ 34S values, ranging between +2 and –25 per mil with a mean around –17 per mil, are probably related to both local bacteriogenic and thermal reduction of Late Triassic marine sulfate. The 34S is typically more depleted in ore deposited in subtidal carbonate rocks than in the economic Zn and Pb ore, preferably deposited within intratidal carbonate host rock. The 34S/32S ratio increases on the order of FeS2 < PbS < ZnS, which reflects disequilibrium and low-temperature formation. The strong depletion of 34S in botryoidal sphalerite, ranging between –24 and –32 per mil, appears to be correlated with the crystal mode (wurtzite-sphalerite fibers) and the enrichment of the trace elements Fe, As, Tl, and Ge. Sphalerite generations of specific cathodoluminescense, color, and closely related trace element composition are correlated district-wide. A decrease of the trace elements Fe, As, Tl, and Ge in the sphalerite generations is coeval with a minor depletion of 34S in the range of –3 and –12 per mil for δ 34S values in several hand specimens. Variations in δ 34S values and trace element zonation on a regional to local scale indicates mixing of local sulfur sources with a regional metal-rich brine. However, distinct peaks in some ore deposits and more positive δ 34S values of between –5 and –10 per mil are also compatible with derivation of the sulfur from basement rocks. The enrichment of the trace element Cu in orange-luminescing sphalerite negatively correlated with Fe, As, Tl, and Ge and, therefore, strongly suggests leaching of copper from Late Permian to Early Triassic continental red beds. Frequent evaporites in this stratigraphic section might have supplied sulfur of relatively heavy isotopic composition to the brine. Hence, some sulfur may also have been transported with a metal-rich brine.

The 1.1-Ga Midcontinent Rift System, central North America: sedimentology of two deep boreholes, Lake Superior region

Abstract The Midcontinent Rift System (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction rift developed over a mantle plume. As much as 20 km of subaerial lava flows, mainly flood basalts, are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds. This rock sequence, known as the Keweenawan Supergroup, has been penetrated by a few deep boreholes in the search for petroleum. In this paper, two deep boreholes in the Upper Peninsula of Michigan are described in detail for the first time. Both the Amoco Production #1-29R test, herein referred to as the St. Amour well, and the nearby Hickey Creek well drilled by Cleveland Cliffs Mining Services, were 100% cored. The former is 7238 ft (2410 m) deep and the latter is 5345 ft (1780 m) deep. The entirety of the stratigraphic succession of the Hickey Creek core correlates very well with the upper portion of the St. Amour core, as determined by core description and point-counting of 43 thin sections selected out of 100 studied thin sections. Two Lower Paleozoic units and two Keweenawan red bed units—the Jacobsville Sandstone and the underlying Freda Sandstone—are described. The Jacobsville is largely a feldspatholithic sandstone and the Freda is largely a lithofeldspathic sandstone. Below the Freda, the remaining footage of the St. Amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate, sandstone, siltstone, and shale; black shale; individual basalt flows; and a basal ignimbritic rhyolite. This lower portion of the St. Amour core presents an enigma, as it correlates very poorly with other key boreholes located to the west and southwest. While a black shale sequence is similar to the petroleum-bearing Nonesuch Formation farther west, there is no conglomerate unit to correlate with the Copper Harbor Conglomerate. Other key boreholes are distributed over a 1300-km distance along the better known southwest arm of the triple-junction MRS, and can be correlated rather well with the units that are exposed in the Lake Superior region. However, a definitive explanation of the anomalous, deeper St. Amour stratigraphy is elusive and any explanation is tenuous. A possible explanation for this anomalous stratigraphy may be the geographic proximity of the St. Amour borehole to the Keweenawan Hot Spot (mantle plume), the suggested thermal force behind the development of the MRS. Similarly, a drastic change in structural architecture may be explained by this geographic relationship. Thus, within the locale of this rifting center, complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the rift arm.

Introduction to the geology of SW Bulgaria

The geologic structure of Southwest Bulgaria is characterized by a complex Mid Cretaceous pile of thrust sheets, a complex system of horsts and grabens of Palaeogene age, and a neotectonic (Neogene - Quaternary) pattern dominated by the Strouma rift system and the Serbo-Macedonian neotectonic swell. Amphibolite-facies metamorphic rocks belong to the Ograzhdenian (Prerhodopian) and Rhodopian Supergroup and the Osogovo “Formation”. The last intensive metamorphic event is proven to be of Cadomian age, and later superimposed metamorphic and deformation events have had a local occurrence. The greenschist-facies Frolosh Formation (Vendian - Lower Cambrian) has a diabasephyllitoid composition and is typical for the Strouma tectonic superunit. The basement of the latter Ograzhdenian Supergroup, Osogovo “Formation”, Frolosh Formation) is covered with a major depositional unconformable contact by sedimentary complexes of Ordovician (only in the Bosilegrad District in Yugoslavia) and Permian and Triassic age. Palaeozoic formations of Ordovician to Devonian age are present only in the thrust sheets of the Morava superunit, and in parts of the southern edge of the Srednogorie zone. Permian formations (mostly continental red beds) have a restricted occurrence. The Triassic (only in the Strouma superunit and parts of the Srednogorie) consists of the Petrohan Terrigenous Group (continental red beds), the Iskur Carbonate Group (marine) and the Moesian Group (marine red beds). After folding, uplift and erosion, the transgressive Jurassic formations have been formed in several different environments, in latest Jurassic - earliest Cretaceous times represented by the carbonate platform to the North, and the Nish-Troyan flysch trough. The principal orogenesis occurred in Mid Cretaceous times, and Upper Cretaceous sedimentary formations are present only in parts of the Srednogorie zone. Late Cretaceous intrusive rocks are known from the Srednogorie (of mantle origin) and in Pirin (crustal granitoids). The Late Cretaceous orogenesis formed the Srednogorie superunit (to the North) and the Morava-Rhodope superunit (to the South). Thus, the Alpine structure consists of the following principal tectonic units: Late Cretaceous Srednogorie superunit (with fragments from the Mid-Cretaceous Lyubash, Golo-burdo, Melovete, Radomir and Verila units) and Morava-Rhodope superunit with the Mid-Cretaceous Morava superunit and Ograzhden unit (allochthonous), Strouma superunit (Louzhnitsa-Trun and Osogovo-Vlahina unit), Rhodope and Pirin-Pangaion superunit. The Palaeogene and Neogene formations have the character of a neoautochthone that is controlled by the Late Alpine and neotectonic block movements.

Stratigraphic assessment of the Arcelia–Teloloapan area, southern Mexico: implications for southern Mexico's post-Neocomian tectonic evolution

Stratigraphic assessment of the “Tierra Caliente Metamorphic Complex” (TCMC) between Arcelia and Teloloapan in southern Mexico, based on photo interpretation of Landsat Thematic Mapper images and field mapping at the 1:100,000 scale, tests different tectonic evolution scenarios that bear directly on the evolution of the southern North American plate margin. The regional geology, emphasizing the stratigraphy of a portion of the TCMC within the area between Arcelia and Teloloapan is presented. Stratigraphic relationships with units in adjacent areas are also described. The base of the stratigraphic section is a chlorite grade metamorphic sequence that includes the Taxco Schist, the Roca Verde Taxco Viejo Formation, and the Almoloya Phyllite Formation. These metamorphic units, as thick as 2.7 km, are covered disconformably by a sedimentary sequence, 2.9 km thick, composed of the Cretaceous marine Pochote, Morelos, and Mexcala Formations, as well as undifferentiated Tertiary continental red beds and volcanic rocks. The geology may be explained as the evolution of Mesozoic volcanic and sedimentary environments developed upon attenuated continental crust. Our results do not support accretion of the Guerrero terrane during Laramide (Late Cretaceous–Paleogene) time.

Cyclicity of Triassic to Lower Jurassic continental red beds of the Argana Valley, Morocco: implications for palaeoclimate and basin evolution

Cyclical playa deposits form a prominent part of the continental clastic succession of the Argana Valley, Western High Atlas of Morocco. The red beds formed in Triassic to Lower Jurassic times during rifting of the North American and African plates. Detailed stratigraphic work revealed asymmetrical, metre-scale cycles in mudstone-dominated successions that constitute the intermediate and upper portion of the basin fill. Sedimentary cycles commonly comprise ephemeral lake shales at the base, playa mudflat mudstones in the intermediate part, and both fluvial and aeolian sandstones at the top. Cycles of the Aglegal Member (T4) are mainly characterized by analcime-rich playa mudflat deposits displaying features indicative of palaeo-Vertisols. Cycles of the Sidi Mansour (T7) and Hasseine (T8) Members are represented by ephemeral lake or dry playa mudflat deposits grading into saline mudflat mudstones that are overlain by sheet flow and minor aeolian sandstones. Sedimentary cycles of the Imerhrane Member (T9) comprise sheet delta sandstones at the base overlain by ephemeral lake and dry playa mudflat mudstones. Upper cycle portions consist of aeolian dune and sand sheet sandstones. Cyclicity is attributed to palaeoclimatic and associated palaeohydrological fluctuations, probably within the Milankovitch frequency band. Sedimentary facies of each cycle provide evidence for a gradual climatic drying with time. The asymmetrical drying-upward cycles possibly record the precession cycle, since they are modulated by symmetrical (i.e., oscillating drying/wetting) cycles of a lower frequency indicative of eccentricity. A long-term change in palaeoclimate ranging from semi-arid conditions with seasonal precipitation (T4) towards an arid, non-seasonal climate (T8) is preserved within the cyclical units spanning a time interval of several million years. Individual cycles can be traced laterally for tens of kilometres. Correlative sections are almost identical in thickness, suggesting a phase of tectonic quiescence during their deposition. Sediment accumulation was not restricted to small-scale grabens, but took place continuously throughout the exposed area of the Argana Valley, implying that accommodation space has not been controlled by syndepositional tectonism.

Palaeomagnetic constraints on the age of the Red Arch Formation and associated sandstone dykes (Northern Ireland)

The Red Arch Formation is a continental red bed succession of uncertain age exposed on the northeast coast of Ireland. There are lithological similarities with the Old Red Sandstone of the Highland Border region, although unconformities within the succession, the presence of reworked aeolian sand grains and variations in the induration of the rocks have prompted earlier workers to suggest that the upper part of the succession may be Triassic in age. This paper reports palaeomagnetic results from the Red Arch Formation. The characteristic magnetizations (ChRMs) are exclusively of reversed polarity and the palaeomagnetic pole position for the sequence bears close comparison with other results from the Old Red Sandstone in Scotland and southern Britain. These poles are regarded as magnetic overprints formed during the Kiaman Superchron because they fall in the Permo‐Carboniferous segment of the apparent polar wander path. Sandstone dykes that cut the Red Arch Formation on a NNE–SSW and NNW–SSE trend have also been studied palaeomagnetically. The dykes show more steeply inclined ChRMs predominantly of normal polarity. The dykes are therefore interpreted to be post‐Kiaman in age, a conclusion consistent with our structural observations. The age of the dykes cannot be determined precisely because they have also been, at least partially, remagnetized. Lithological and regional geological considerations suggest the dykes are Triassic in age and formed in an extensional stress regime prior to the opening of the North Atlantic. They were remagnetized in Tertiary times, possibly associated with uplift and emplacement of the British Tertiary Igneous Province.

Scottish Silurian shorelines

ABSTRACTThe Silurian inliers of the Midland Valley of Scotland all exhibit a regressive sequence, and despite evident facies differences between inliers, marine successions invariably pass upwards into redbeds of continental origin. Contrasting types of shoreline facies can be seen in different inliers; here the beds in the North Esk Inlier (NEI) are compared with those previously described from Knockgardner. At Knockgardner a high energy coastal environment prevailed, but in the NEI very different conditions can be identified in near-contemporaneous deposits. In the NEI thin sandstones and siltstones of the Reservoir and Deerhope formations are succeeded by the sandstones and conglomeratic beds of the Cock Rig Formation. These are overlain by the marine mudstones of the Wether Law Linn Formation and, at the top of the sequence, the continental redbeds of the Henshaw Formation.The Wether Law Linn Formation is interpreted, on various lines of evidence, as a lagoonal system. Conditions therein were initially fully marine, though within the photic zone, but subsequently the faunas were increasingly influenced by fluctuating salinity, prior to deposition of the redbeds. Such a lagoon would have required an offshore bar impounding it, which is represented by the Cock Rig Formation. These sedimentary rocks, previously interpreted as deposits of a laterally unconfined submarine channel, are now considered to be of shallow water origin. The succession closely conforms to classic models in which shoreface sands, consisting of small cross-bedded packets, are succeeded by tabular sandstone sheets representing foreshore beach deposits. Coarser and thicker beds, with herringbone cross-sets, linguoid ripples and trains of rounded pebbles, are interpreted as the deposits of tidal channels within the barrier complex. The barrier-lagoon system persisted throughout the whole of Cock Rig time and most or all of the time during which the Wether Law Linn Formation was deposited, and was either static or prograded seawards until the lagoon dried up during a final marine regression. The sedimentary and faunal evidence is consistent with this interpretation, and the contrast between the shoreline environments of the NEI and Knockgardner is striking. Brief reference is made to other inliers in the Midland Valley.

Pseudomorphous transformation of goethite needles into hematite in sediments of the Triassic Skagerrak Formation, Denmark

Van Houten (1973), Walker (1976) and Turner (1980) have documented the authigenic origin of red coatings in continental red beds. Pigmentary hematite, ferrihydrite, goethite and clay-associated Fe-oxide crystallites have been suggested as the principal colouring agents of continental red beds (Walker, 1968, 1976; Walker &amp; Honea, 1969; Larson &amp; Walker, 1975; Turner, 1980; Fine, 1986, Besly et al., 1993). The red pigment in most Mesozoic red beds consists of hematite, whereas ferrihydrite and goethite are more common in younger sediments (van Houten, 1973). This has led several authors to the assumption that poorly crystalline Fe-oxides/hydroxides age into hematite (Walker, 1968, 1976; Walker &amp; Honea, 1969; Larson &amp; Walker, 1975; Turner, 1980).

The interplay of lithospheric flexure and thrust accomodation in forming stratigraphic sequences in the southern Apennines foreland basin system, Italy

Most of the regional shortening in the type area of the southern Italy orogenic belt, Calabria and southern Apennines, was accomodated by displacement on the Calabrian Terrane (Oligocene to middle Miocene), the Liguride and Sicilide Complex (lower to middle Miocene), the Alburni-Cervati-Pollino-Monti della Maddalena units (inner carbonate platform and slope; middle to upper Miocene), Lagonegro units (upper Miocene), the Monte Alpi unit (lower Pliocene) thrust systems. Inception of each thrust system generated synorogenic sediment associated with frontal thrust-tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland. The Neogene kinematic and sedimentary evolution of the southern Italy is related by shortening of the Apennines and Calabria and stretching of the Tyrrhenian Basin. The southern Italy orogenic belt consists of tectonic assemblages of Paleozoic crystalline rocks (various metamorphic rocks and plutonics), Triassic through upper Miocene platform to deep-marine carbonatic and siliceous rocks, Jurassic to Cretaceous ophiolites and related oceanic sedimentary strata, Paleogene to lower Miocene Subduction Complex assemblage, and lower Miocene through Pleistocene foreland clastic strata. Triassic through Quaternary clastic sediments are accumulated in tectonically diverse sedimentary basins, recording the key geodynamic events affected the Mediterranean region after the Late Paleozoic-Early Mesozoic breakup of Pangea. These sediments are generated following the onset of the sequential rift development and continental separation (Triassic to Early Jurassic), the Tethyan proto-oceanic rifting and open-ocean phases (Early-Middle Jurassic to Early Cretaceous), the Tethyan subduction and onset of Alpine orogenesis (Middle-Late Cretaceous to Paleogene), the Adria (or Apennines) orogenesis (early Miocene to present), and the Tyrrhenian backarc rifting (or Tyrrhenian phase; 15 Ma to present). The oldest (early-middle Triassic) siliciclastic sediments of southern Italy are on the Apulia plate (the buried base of the Apulia platform), the Monte Facito Formation of the Lagonegro Basin, and redbeds of Sardinia (Iberian plate). During Upper Triassic to Middle Jurassic, continental redbeds (rift-valley phase), and shelf-slope-basin sediments (proto-oceanic rift phase) having quartzose composition were accumulated directly on the crustal basement of the Iberia plate margin, in Calabria-Peloritani domain, but siliciclastics are absent on the southern Apulia plate. These sediments record the initial phases of the Tethyan rifting processes. Siliciclastic accumulations in southern Italy assemblages during the main alpine phases (Cretaceous to Paleogene) are scarse or absent. The Cretaceous to early Miocene alpine tectonic phases in southern Italy include remnants of the Alpine orogen (Calabrian Block) and quartzofeldspathic siliciclastic deposits of the Oligocene to early Miocene Paludi, Stilo-Capo d’Orlando and Frazzano formations, and volcanolithic, quartzolithic and quartzofeldspathic sands of the Calabro-Lucanian Flysch Unit. The siliciclastic deposits are directly related to new subduction plane of the Adriatic-Ionian oceanic lithosphere beneath the Iberia plate, generating an oceanic subduction complex (Liguride Complex of southern Italy), and a calcalkaline volcanic arc (Sardinia). From late Paleogene to the present, the siliciclastic sedimentary sequences of southern Italy filled basins that are directly related to this convergent setting, causing consumption of the oceanic lithosphere, and subsequent accretion of the Calabrian allochthonous terranes over the Adria-Africa plate, generating post-Oligocene foreland basin systems. The composition as well as stratigraphic and structural relations of clastic sediments derived from erosion of the Calabrian microplate provide constraints for paleogeographic and tectonic models of southern Italy. Clastic detritus in the following sedimentary assemblages were derived mainly from provenance terranes within the strongly deformed Calabrian Arc allochthon: (A) the Paleogene «Calabro-Lucanian Flysch Unit» accretionary wedge, deposited in a remnant ocean basin that lay east of the Calabrian Arc and west of the Adria margin; (B) Burdigalian to lower Messinian foreland basin successions, widely developed in the southern Apennines, representing progressively shifted foredeep basins and related wedgetop basins; (C) Upper Tortonian to Messinian nonmarine to shallow-marine and deep-marine successions, cropping out on the western and eastern Calabrian Arc, representing synrift clastic wedges related to backarc rifting in the peri-Tyrrhenian area (western sequences), or foreland clastic wedges in the peri-Ionian area (eastern sequences); (D) Pliocene and Quaternary of the northern Calabrian Arc, represented by foredeep and related wedge-top basins on the eastern side (Gulf of Taranto and Corigliano Basin), and a slope basin on the western side, the eastern Tyrrhenian margin (Paola Basin). These receive detritus primarily from deep erosion of northern Calabria. The modern deep-marine basins of offshore northern Calabria have many similarities to the middle to upper Miocene clastic sequences in both foreland and backarc regions of the southern Italy. The type of sedimentary provenance of the southern Italy foreland basin system, providing an example of the changing nature of the orogenic belt through time, may contribute to general understanding and application of other major orogens.

Middle Hettangian (Lower Jurassic) ammonites from Isle of Raasay, Inner Hebrides, and correlation of the Hettangian-lowermost Sinemurian Breakish Formation in the Skye area, NW Scotland

Synopsis Liasicus Zone (middle Hettangian) ammonites, allocated to a new species, Franziceras sorleyi, are described from Hallaig, Isle of Raasay and indicate that the Breakish Formation (formerly lower Broadford Beds) there is older than previously thought. The new finds have been integrated with the limited available biostratigraphic information from the rare record s of Hettangian and basal Sinemurian ammonites, and with local lithostratigraphy based on marker beds, to develop a new interpretation of correlations within the Skye–Raasay–Applecross area. This concludes that there was a diachronous early Jurassic transgression and facies change from the continental red beds of the Stornoway Formation into the marginal marine carbonate-dominated sediments of the Breakish Formation.

Mud-Filled Ophiomorpha from Upper Cretaceous Continental Redbeds of Southern Mongolia: An Ichnologic Clue to the Origin of Detrital, Grain-Coating Clays

At Flaming Cliffs-a famous vertebrate locality in southern Mongolia - sand grains in red sandstones of fluvial and eolian origin within the Upper Cretaceous Djadokhta Formation are coated with detrital clay. The nearest correlative marine deposits are thousands of kilometers distant. Structureless sandstones with stringers and lenses of reworked caliche pebbles lie laterally adjacent to sets of eolian cross-strata up to 20 m thick. These pebbly sandstones, interpreted as the deposits of intermittent streams that occupied interdune positions, contain abundant Ophiomorpha. Burrows are 1 to 3 cm in diameter, with a knobby exterior. The traces occur not only as simple tubes, but also as Teichichnus-like spreiten, produced by the systematic upward and lateral migration of a spiral burrow. Spreiten can reach vertical extents greater than 3 m and widths of 30 cm. Although they commonly appear in stratal sequences that contain no mudstone beds, many of the burrows are filled by mud. The best modern analog is provided by freshwater crustaceans that excavate deep burrows to the water table in order to escape desiccation during drought. Mud was emplaced during fluvial flood events when the open, near-vertical shafts acted as storm sewers through the vadose zone. Spreiten probably were generated by systematic offsets from the original burrow axis during repeated re-excavations. One mechanism for emplacing detrital clays in sandstones calls upon infiltration of muddy water through the vadose zone during flood events. The burrow fills within the fluvial facies of the Djadokhta Formation provide corroborative, independent evidence for the passage of muddy water through the strata. Like the Callianassa burrows that fill with coarse, shelly debris during the passage of Caribbean hurricanes (tubular tempestites), burrows in continental settings also can provide unique testimony to important depositional events and early diagenetic processes.

Magnetostratigraphy of the Miocene Corque Basin, Bolivia: Implications for the geodynamic evolution of the Altiplano during the Late Tertiary

A magnetostratigraphic study of a thick Miocene continental red bed sequence (Totora Formation) located in the north central Altiplano (the Corque syncline) yielded quantitative determinations of the sedimentation rate and better constraints of the timing of the deformation within the Altiplano. Paleomagnetic results obtained in 653 samples from a composite 4.5 km thick red bed sequence across the Corque syncline indicate that most of the Totora sequence was deposited in the middle Miocene from 14 to 9 Ma with high sedimentation rates up to 970 m/Myr from 12 to 9 Ma. The high rate of infill of the Corque basin demonstrates active subsidence of the northern Altiplano during the middle Miocene. Deformation ceased in the northern Altiplano domain only at the end of the Miocene. Two major tuff beds within the sequence have been previously dated by 39Ar/40Ar of sanidine minerals [Marshall et al, 1992]. The excellent agreement between the magnetostratigraphic dating of the tuffs and the radiometric dating independently supports the age calibration of the geomagnetic reference timescale proposed by Cande and Kent [1995]. The numerous paleomagnetic results obtained in middle Miocene sediments within the Corque syncline, a structure which can be traced for more than 100 km along its axis, demonstrate that the Corque syncline rotated counterclockwise by 10.8°±2.9° since 9 Ma as a consequence of the internal deformation of the Altiplano. Inclination flattening of 17° is recorded in these red bed sediments. This result provides additional evidence that detrital magnetizations, especially in red beds, should be taken with caution when estimating paleolatitudes or long‐term variations of the geomagnetic field.

Paleomagnetism of Peninsular Malaysia

Paleomagnetic results from Upper Jurassic to Paleocene rocks in Peninsular Malaysia show counter clockwise (CCW) rotations, while clockwise rotations (CW) are predominantly found in older rocks. Continental redbeds of the Upper Jurassic to Lower Cretaceous Tembeling Group have a post folding remagnetization, giving a VGP at N54°E29°, corresponding to approximately 40° of CCW rotation relative to Eurasia and 60° CCW relative to the Indochina block (Khorat Plateau). Samples from Cretaceous to Paleocene mafic volcanics of the Kuantan dike swarm and the Segamat basalts give VGPs at N59°E47° and N34°E36°, respectively. These Malayasian data are indistinguishable from the Late Eocene and Oligocene VGPs reported for Borneo and the Celebes Sea and are similar to the Eocene VGPs reported for southwest Sulawesi and southwest Palawan. The occurrence of CCW deflected data over this large region suggests that much of Malaysia, Borneo, Sulawesi, and the Celebes Sea rotated approximately 30° to 40° CCW relative to the Geocentric Axial Dipole (GAD) between the Late Eocene and the Late Miocene, although not necessarily synchronously, nor as a single rigid plate. These regional CCW rotations are not consistent with simple extrusion based tectonic models. CW declinations have been measured in Late Triassic granites, Permian to Triassic volcanics, and remagnetized Paleozoic carbonates. The age of this magnetization is poorly understood and may be as old as Late Triassic, or as young as Middle or Late Cretaceous. The plate, or block rotations, giving rise to these directions are correspondingly weakly constrained.

Paleogene Extension in the Southern Basin and Range Province of Mexico: Syndepositional Tilting of Eocene Red Beds and Oligocene Volcanic Rocks in the Guanajuato Mining District

The Guanajuato region, located in the southern part of the Basin and Range tectonic province, is characterized by a rhombohedral fault pattern. Extensional faulting-as well as related uplift, erosion, and deposition of continental clastic deposits-was in progress at 49 Ma, as indicated by K-Ar dating of intercalated mafic volcanic lavas. Earliest extension is registered in the lower member of the Guanajuato conglomerate and produced NW-trend-ing, down to the southwest, normal faults and northeast tilting of the hanging-wall clastic sequence. Beds in the upper member of the Guanajuato conglomerate display lateral thickness variations, changes in size and composition of the clasts, and ENE and SE inclination, all of which suggest activity along a second set of NE-trending younger faults. Extension continued also after emplacement of the overlying Bufa ignimbrite (∼37 Ma, K-Ar). Dip differences between the conglomerate and the Calderones Formation (<37 but >30 Ma), which is part of the volcanic sequence that conformably overlies the Guanajuato conglomerate, indicate at least 13° and probably more than 20° of rotation prior to 37 Ma. Consistent northeast tilting in the Calderones Formation indicates that subsequent extension preferentially reactivated the NW-trending faults. This sequence of deformational events produced the rhombohedral fault pattern observed in the region. Later pulses of extension (late Oligocene and younger) produced simultaneous movement on both sets of faults, as suggested by others. In addition to this strong evidence for Paleogene extension in the Guanajuato region, indication of Paleogene extension also may be present at scattered localities throughout central and southern Mexico, where continental red beds occur stratigraphically between pre-Cenozoic rocks and Tertiary volcanic rocks (Eocene-Oligocene). Detailed structural and stratigraphic data are lacking for these localities, but they may provide an important record of a regional Paleogene extension episode that has been largely overshadowed by the obvious evidence for extension during the Neogene.

World‐class sediment‐hosted stratiform copper deposits: Characteristics, genetic concepts and metallotects

Detailed studies of the host lithologies, mineral textures, metal zoning and configurations of numerous sediment‐hosted stratiform copper deposits have established a post‐sedimentary (diagenetic) timing and overprint concept for the genesis of this important mineral deposit type. Metals were probably deposited from low‐temperature oxidised saline brines which circulated across the colour‐distinctive redoxcline between host greybeds (commonly sulfidic ‘black shales’ or marginal‐marine microbial mats) and immature footwall redbeds filling continental rift basins. Adequate sources of ore metals (principally copper ± silver or cobalt) and associated metals (e.g. lead, zinc, cadmium) can be found in the redbeds (or deeper rocks), and the circulation of saline pore fluids to and across the redoxcline may have been induced and focused by normal features of rift geology, such as marginal basin faults, contrasting stratigraphic permeabilities, overpressured pore fluids and anomalous thermal gradients. Besides the identification of major greybed/redbed contacts and the longstanding recognition that stratiform copper deposits are commonly associated with extensive continental redbed and evaporitic units, exploration may be guided by the observation that stratiform copper deposits are restricted in geologic time to continental rift zones, to low palaeolatitudes where evaporites tend to form, and to sediments younger than the apparent oxidation of the Earth's atmosphere at about 2.3 Ga (essentially post‐Archaean time). Thus, successful exploration for stratiform copper deposits will probably depend more and more commonly on the detection and refined reconstruction of redbed/greybed sedimentary environments in zones of crustal extension at low palaeolatitudes post‐dating Archaean time and especially on hypothesised patterns of ore brine circulation in the redbed/greybed package following sedimentation.

Initiation of ∼2.45-2.1 Ga intracratonic basin sedimentation of the Hurwitz Group, Keewatin Hinterland, Northwest territories, Canada

Continental to shallow-marine rocks of the Hurwitz Group, exposed as outliers across the Hearne Province in northern Canada, were deposited between ∼2.45 and 2.11 Ga on a 3.3-2.6 Ga granite-greenstone basement. Initiation of the Hurwitz Basin was characterized by low relief and rates of subsidence that never progressed beyond the intensity of regional sagging. During stage 1, polymictic conglomerate (lower Noomut Formation) was deposited in palaeovalleys cut into Archaean basement, and subarkose to quartz arenite ± quartz pebble conglomerate (upper Noomut Formation) was deposited on a low-relief sand plain. Abundant first-cycle quartz-rich sandstones are attributed to intense humid climate weathering in low-relief source areas and at sites of temporary storage, as well as to repeated fluvial and eolian reworking. Interbedding of pyritic palaeoplacers and continental redbeds denotes fluctuating levels of atmospheric oxygen; disappearance of pyritic palaeoplacers upsection signifies ultimate changeover to an atmosphere with sustained free oxygen. Stage 2 (Padlei Formation) was marked by a climatic shift toward cold (glacial?) conditions as indicated by dropstones, greywacke (till?) pellets and possible ikaite pseudomorphs in lacustrine rhythmites. Stage 3 (Kinga Formation) represents a return to wet/warm conditions with fluvial (± eolian) deposition of subarkose and quartz arenite on a low-relief sand plain (Maguse Member) and deposition of supermature quartz arenite in a vast (100,000 km 2 minimum), shallow-water lake or series of lakes (Whiterock Member). Local chert beds at the top of the Kinga Formation (Hawk Hill Member) formed by spring discharge due to regional, gravity-driven, convective groundwater flow. An intracratonic setting is implied by: (1) a symmetric, basin-centred fill; (2) absence of features indicating a shelf-slope break; (3) absence of rift rocks; (4) a prolonged slow-subsidence history; (5) likely correlation with other continental to shallow-marine deposits scattered across the Keewatin Hinterland; and (6) positioning 1000–2000 km away from closest coeval passive margin sequences. We speculate that Hurwitz Basin formed due to lithospheric stretching related to a large-scale mantle upwelling during the protracted breakup of an earliest Palaeoproterozoic supercontinent (‘Kenorland’).

The Late Carboniferous to Late Triassic segment of the apparent polar wander path of Iberia

A palaeomagnetic study has been carried out at 16 well-dated sites from four areas in central Spain (southeastern Iberian Massif and western Iberian Ranges) in order to constrain the Late Carboniferous to Late Triassic segment of the apparent polar wander path (APWP) of Iberia. 322 samples (218 with useful results) were collected from andesitic rocks at Atienza (287 ± 12 Ma) and from Triassic continental red beds at Molina de Aragon (Anisian-Ladinian), Alcaraz (Ladinian-Carnian), Alcazar de San Juan (Ladinian-Carnian) and Cuevas de Ayllon (Carnian-Norian). Comparison of the palaeomagnetic results from the western Iberian Ranges and from the Iberian Massif indicates that the investigated area of the Iberian Ranges forms part of Stable Iberia. The palaeomagnetic poles obtained in this study and a revision of previous palaeomagnetic data, discarding poles obtained from areas of doubtful stability, show together a gradual and consistent change in latitude and longitude resulting in a coherent segment of the APWP for the Late Carboniferous to Late Triassic time span.