lacustrine fan deltaic sedimentation in a proterozoic rift basin the sopa brumadinho tectonosequence southeastern brazil abstract the sopa brumadinho tectonosequence 100 to 200 m thick is the fourth unit in ascending order of the up to 2000 m thick mesoproterozoic espinhaco supergroup representing the depositional products of the third and main phase of the rift stage of the espinhaco basin the sopa brumadinho tectonosequence in the study area consists of diamond bearing lacustrine fan delta deposits bounded by prominent angular and erosional unconformities detailed lithofacies studies were carried out in the central part of the southern serra do espinhatco southeastern brazil to characterize the paleogeography and basin fill architecture of the sopa brumadinho tectonosequence thirteen lithofacies are present massive clast supported conglomerates lithofacies ug cs inversely graded clastsupported conglomerates lithofacies ig cs normally graded clast supported conglomerates lithofacies ng cs massive to crudely stratified clast supported conglomerates lithofacies cs cs sandy matrix supported conglomerates lithofacies s ms muddy matrix supported conglomerates lithofacies m ms talus breccia clast supported conglomerates lithofacies tb cs massive sandstones lithofacies sm horizontal stratified sandstones lithofacies sh trough cross stratified sandstones lithofacies st planar cross stratified sandstones lithofacies sp graded stratified sandstones lithofacies sg and pelites lithofacies p they represent the products of several types of subaerial and subaqueous sediment gravity flows ranging from turbidity currents to cohesive debris flows and ephemeral braided streams the deposits are usually arranged in coarsening to fining upward tectono depositional intervals each tectono depositional interval represents a progradational lobe which starts at the base with lacustrine pelites and evolves with time from distal subaqueous to proximal subaerial characteristics the fining upward part represents the abandonment phase of the depositional lobes the origin characteristics distribution and spatial arrangement of the various lithofacies the interbedding of gravityflow and stream flow deposits the predominance of debris flow conglomerates over aqueous current formed ones the semi radial fan like dispersion pattern of the paleocurrents and the recognition of associated subaerial and subaqueous depositional settings are all indicative of a lacustrine alluvial fan fan delta environment or a fan delta system an interplay between several intrabasinal and extrabasinal controls probably determined the fan evolution the sedimentation of the lacustrine fan delta systems of the sopa brumadinho tectonosequence probably took place in a n s elongated continental rift basin compartmentalized by n s trending normal faults and w e trending transfer faults under a tropical semi arid climate the basin fill architecture was probably determined by episodic subsidence clockwise block tilting and asymmetric graben evolution as well as by inherited characteristics of the source area additionally a new descriptive scheme for classification of conglomerate lithofacies is here proposed

process and discharge estimation in ephemeral channels canadian rocky mountains process determinations and discharge estimates are made for 10 steep alpine channels in the front and main ranges of the southern canadian rocky mountains the catchments which range in size from 0 17 to 1 13 km2 are sufficiently small that their runoff patterns are dominantly ephemeral and are characterized by processes that include water floods debris flows and snow avalanches longitudinal and cross sectional channel profiles demonstrate the importance of bedrock control and the influence of one or more dominant processes debris flow channels have been partially scoured by water floods and avalanche and debris flow sediments are noted in modified alluvial channels the distribution and sorting of sediments support the multiple process origin of specific channels or channel reaches the discrimination of channel processes is essential for estimates of channel discharge slope area and competence methods employed in fluvially dominated reaches of the 10 channels yield maximum instantaneous discharge

isotopic age constraints and metamorphic history of the talladega belt new evidence for timing of arc magmatism and terrane emplacement along the southern laurentian margin abstract u pb and 40ar 39ar dates from the talladega belt southernmost appalachians provide insight into the timing and nature of pre alleghanian tectonism in this region low grade metasedimentary rocks of the talladega belt represent the outermost preserved portions of the southern laurentian margin thus recording the earliest orogenic events that affected the margin in addition to later overprinting events these rocks are structurally overlain by the hillabee greenstone metavolcanic sequence from which metadacite yields an age of 470 4 ma ion microprobe u pb zircon age hillabee geochemistry indicates formation in an arc or back arc setting we suggest correlation of the hillabee greenstone with 460 470 ma arc related rocks in the dahlonega gold belt which extends along strike with the hillabee through georgia and into north carolina and interpret the hillabee as the southernmost volcanic expression of an early middle ordovician arc that formed outboard of laurentia rocks of the talladega be

tectonic evolution of south america during the late proterozoic abstract this paper discusses the evolution and the late proterozoic assembly of the south american continent i e the west gondwana under the light of global tectonics the northern portion of the continent the amazonian craton is a pre brasiliano domain it may be a fragment derived from laurentia this domain behaved as a large continental plate which was accreted to the central and southeastern portions of the continent brasiliano domain the brasiliano domain had a more complex history and composition during the brasiliano cycle middle proterozoic to early paleozoic in the brasiliano domain several late proterozoic continental plates have been identified sao luiz west africa congo kasai sao francisco rio de la plata arequipa antofalla which acted as forelands to the brasiliano orogenic belts that surround and amalgamate these plates smaller fragments of pre brasiliano continental lithosphere are common in the interior of the brasiliano orogenic belts and played diversified roles microplates microcontinents structural highs some of them have acted as true backlands hinterlands flanked by arc magmatism two principal types of brasiliano orogenic belts are recognized between the continental plates a marginal orogenies to the late proterozoic plates with pelitic carbonatic rocks and discrete volcanism which were thrust by collision onto the margin of the plates and which seem to represent final products of previous passive margin sequences b distal orogenics internal belts within the continental masses sometimes a branching system of orogenics that contain varied clastic and minor carbonate sedimentary rocks accompanied by important bimodal volcanism and calc alkaline plutonism for these orogenies a greater variety of basinal scenarios and tectonic settings may be visualized the amalgamation of the continent during the late proterozoic i e the formation of the brasiliano structures indicates the existence of practically synchronous multilateral stresses within lithospheric plates this can be produced by complementary adjustment of the continental plates as a response to major global events elsewhere analogous to modern continental collisions two large and important tectonic zones may be candidates to such a scenario the hijaz mozambique zone site of connection of east and west gondwana and the transbrasiliano lineament which cuts across south america and extends to north africa following the zone of connection between pre brasiliano and brasiliano domains other small ocean openings and closings inside the various brasiliano areas dom feliciano gariep for instance were minor events and complementary to the other two major tectonic zones mentioned above

re evaluation of the middle miocene eagle mountain formation and its significance as a piercing point for the interpretation of extreme extension across the death valley region california u s a abstract the death valley area of eastern california and southern nevada has been highly influential in the development of ideas about extreme crustal extension one of the tightest constraints on death valley extension is apparently provided by clasts in inferred alluvial fan deposits of the eagle mountain formation 15 11 ma and their source in the hunter mountain batholith now located 100 km from some of the deposits because alluvial fans are usually less than 10 20 km in radius the remaining separation has been interpreted as tectonic new research reported here suggests that the eagle mountain formation at its type location was deposited in a fluvial lacustrine setting and provides no constraint on either the magnitude or the direction of tectonic transport and or crustal extension confidence in palinspastic reconstruction thus depends on resolving ambiguities in the correlation of pre extensional markers or on the recognition of demonstrably proximal facies tectonically distributed across the region the succession at eagle mountain comprises 1 diffusely stratified monolithologic carbonate breccia and sandstone 140 m onlapping cambrian carbonate rocks at an unconformity with 110 140 m of relief fluvial or fluvially influenced 2 10 m of tabular bedded siltstone diamictite and sandstone lacustrine 3 cross stratified and channelized sandstone and polymict conglomerate bearing hunter mountain clasts with minor siltstone and carbonate 110 m mostly fluvial and 4 tabular bedded sandstone siltstone and minor carbonate 140 m mostly lacustrine eight prominent stratigraphic discontinuities mapped within the third interval are characterized by up to 15 m of local erosional relief and by abrupt upward coarsening from siltstone or carbonate to conglomerate or sandstone a fluvial interpretation for the same critical part of the succession is based upon the existence of the mapped surfaces the ubiquitous development of channels trough cross stratification and upward fining trends particularly between the mapped surfaces and the abundance of well rounded clasts in conglomerate paleocurrents are generally directed between southward and eastward although with considerable dispersion and they shift from approximately southward or southeastward in the mostly fluvial deposits to approximately eastward in the upper lacustrine interval an unusual feature of the eagle mountain formation at eagle mountain is the presence of five crosscutting conglomerate bodies interpreted as vertically infilled fissures of tectonic origin numerous normal reversed normal and oblique slip faults with up to 34 m of stratigraphic separation are thought to postdate sedimentation and tilting of the eagle mountain formation after 11 ma

facies relationships alluvial architecture and paleohydrology of a paleogene humid tropical alluvial fan system chumstick formation washington state u s a the middle to late eocene chumstick formation represents a thick sequence of fluvial and lacustrine rocks that filled a tectonically active basin under humid tropical paleoclimatic conditions four facies associations are recognized in the chumstick formation gravel bedload sand bedload and mixed load stream deposits and lacustrine deposits the depositional system is interpreted as a humid tropical alluvial fan system five sets of basinal characteristics are believed to result from the combination of humid tropical paleoclimate active basin margin faulting and high 0 2 to 1 2 m k y basin subsidence rates 1 fluvial architecture was strongly affected by basin margin faulting proximal regions of the fan consist of broadly lenticular laterally stacked i e offlapping ribbons gravel bedload stream deposits representing fanhead channels distal regions of the fan consist of gravel and sand bedload stream deposits with a sheet like geometry the basin fill is dominated by multistory vertically stacked sand bedload and mixed load stream deposits and lacustrine deposits 2 rapid subsidence has resulted in the preservation of compositionally immature sediments sublithic feldspathic arenites with thin shallow paleosols 3 paleohydraulic reconstructions indicate that streams carried coarse grained bedload through channel reaches with paleoslopes 5 m km 4 rapid vegetation growth resulted in the bank stabilization of sandy sediments development of paleosols leaf litter layers on emergent bar tops and the introduction of woody debris into channels even coarse grained proximal fluvial deposits have a significant overbank component and show evidence for bank stability cutbanks and cohesive bank failures 5 debris flow deposits are relatively minor except for local talus cone deposits the rarity of debris flows throughout the basin may be due to hillslope stability imparted by vegetation

unravelling the formation histories of placer gold and platinum group mineral particles from corrego bom successo brazil a window into noble metal cycling abstract gold and platinum group metals pgm are cycled through earth s environments by interwoven geological physical chemical and biological processes leading to the trans neoformation of metallic particles in placers the placer deposit at corrego bom successo cbs brazil is one of the few localities worldwide containing secondary gold and pgm particles placer gold consists of detrital particles from nearby hydrothermal deposits that were transformed in the surface environment processes that have affected these particles include short distance transport chemical de alloying of the primary gold silver and bio geochemical dissolution re precipitation of gold leading to the formation of pure secondary gold and the dispersion of gold nanoparticles the latter processes are likely mediated by non living organic matter om and bacterial biofilms residing on the particles the biofilms are largely composed of metallophillic and proteobacteria abundant mobile gold and platinum nanoparticles were detected in surface waters suggesting similar mobilities of these metals earlier hydrothermal processes have led to the formation of coarsely crystalline arborescent dendritic potarite pdhg on potarite surfaces biogeochemical processes have then led to the formation of platinum and palladium rich micro crystalline layers which make up the botryoidal platinum palladium aggregates subsequently potarite was dissolved from the core of many aggregates leaving voids now often filled by secondary anatase tio2 containing biophilic elements the presence of fungal structures associated with the anatase suggests that fungi may have contributed to its formation for the first time a primary magmatic pgm particle comprising a mono crystalline platinum palladium alloy with platinum iridium osmium inclusions was described from this locality finally defining a possible primary source for the pgm mineralisation in conclusion the formation of modern day placer gold and pgm particles at cbs began 100s of millions of years ago by magmatic and hydrothermal processes these provided the metal sources for more recent biogeochemical cycling of pges and gold that led to the trans neoformation of gold and pgm particles

volcanic arc emplacement onto the southernmost appalachian laurentian shelf characteristics and constraints in the southernmost appalachians the hillabee greenstone an ordovician volcanic arc fragment lies directly atop the outermost laurentian devonian earliest mississip pian shelf sequence at the structural top of the greenschist facies talladega belt the frontal metamorphic allochthon along this orogenic segment the hillabee greenstone was emplaced between latest devonian and middle mississippian time it and the upper most laurentian section were later repeated together within a series of map scale imbri cate slices of a postmetamorphic dextral transpressional alleghanian thrust duplex system that placed the high grade eastern blue ridge allochthon atop the talladega belt geochemical and geochronologic u pb zircon studies indicate that the hillabee greenstone s interstratifi ed tholeiitic meta basalt and calc alkaline metadacite rhyolite formed within an extensional setting on con tinental crust ca 460 470 ma palinspastic reconstructions of the southern appalachian ordovician margin place the hillabee green stone outboard of the present position of the pine mountain terrane and suggest links to ordovician plutonism in the overlying east ern blue ridge and possibly to widespread k bentonite deposits within ordovician plat form units the tectonic evolution of the hil labee greenstone exhibits many unusual and intriguing features including 1 premeta morphic emplacement along a basal cryptic thrust which is remarkably concordant to both hanging wall and footwall sequences across its entire extent 230 km 2 forma tion transport and emplacement of the arc fragment accompanied by minimal deforma tion of the hillabee greenstone and under lying outer margin shelf rocks 3 emplace ment temporally coincident with the adjacent collision of the younger tectonically indepen dent ouachita volcanic arc with southeastern laurentia these features highlight strong contrasts in the ordovician taconian evolu tion of the southern and northern parts of the appalachian orogen

millennial scale variability in the asian monsoon evidence from oxygen isotope records from stalagmites in southeastern china abstract two stalagmites from xiangshui x3 and yaoba don yb1 caves in southeastern china provide high resolution 18o time series that exhibit prominent millennial scale fluctuations in the intensity and character of the asian monsoon for the period from 20 000 to 50 000 yr b p timing of these fluctuations established by u series disequilibrium 230th 234u correlates with dansgaard oeschger events 2 13 and heinrich events h2 h5 recorded in the gisp2 ice core indicating a climatic link between asian monsoon circulation and air temperatures over the north atlantic for much of the last glaciation although the exact mechanisms linking climatic fluctuations in the north atlantic to those in eastern china have yet to be identified climatic signals associated with changes in global ice volume and air temperatures over greenland may be transferred to asia by atmospheric mechanisms that affect the strength of the siberian high pressure cell and the amount of snow cover on the tibetan plateau which force the intensity of the asian monsoon another mechanism linking climate of the north atlantic to the asian monsoon relates to variation in oceanic circulation millennial scale fluctuations in thermohaline circulation in the north atlantic may have affected ocean currents in the tropical western pacific ocean which is the moisture source for the east asian monsoon despite the similarity of these paleoclimatic records and the implication of global teleconnections the magnitude and timing of millennial scale events at different locations in china reveal regional variations in climatic conditions comparisons of the 18o curves from xiangshui and yaoba don cave stalagmites with those from qixin cave and hulu cave show general concordance between millennial scale events albeit with some notable differences among all the records the well studied hulu cave records show 18o values that are lower than those of xiangshui and yaoba don caves reflecting geographical differences hulu cave is located near the eastern coast at a relatively low elevation dominated by the east asian monsoon by comparison xiangshui cave and yaoba don cave are further inland on the eastern slope of the yunnan guizhou plateau which receives precipitation from both the east asian monsoon and quasi stationary frontal systems rainfall contributed by the east asian summer monsoon is relatively diminished in this region by these geographic and atmospheric circulation conditions resulting in higher 18o values

glacial interglacial variation in catchment weathering and erosion paces the indian summer monsoon during the pleistocene abstract silicate weathering via co2 consumption is considered to regulate the long term climate change discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate however owing to the paucity of well dated and continuous records of weathering and erosion the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial interglacial climate remain elusive geochemical analysis of a 666 m core from the heqing basin a paleolake situated at the southeastern margin of the tibetan plateau demonstrates silicate versus carbonate weathering and erosion changes under indian summer monsoon ism conditions spanning the entire pleistocene via respective tracing between rb sr and al na ratios the rb sr record is interpreted as reflecting a competition between clayey silicate origin rb versus carbonate origin sr fluxes whereas al na ratio is a balance between weathering and erosion of silicate minerals both pacing the glacial interglacial cycles of the ism during interglacials strong silicate weathering intensity reflected by low al na values is mainly controlled by warmer temperatures with the reduced variability during 1 82 0 92 ma recalling the pacing of the arabian sea surface temperature amplitudes within glacials the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval in conclusion the heqing rb sr and al na records reveal the sensitivity of catchment weathering and erosion to ism changes over glacial interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

geomorphology mountains and monsoons the influence of climate on mountain building has long been debated a reconstruction for the past 25 million years suggests coincidence of himalayan erosion and monsoon intensification hinting at a causal relationship

sedimentology of proterozoic cratonic sheet sandstones of the eastern canadian shield sims formation labrador canada abstract the upper lower proterozoic to middle proterozoic sims formation rests unconformably on lower proterozoic strata of the knob lake group of the labrador trough sequence the 700 m thick sims formation consists of basal fluvial arkoses and conglomerates about 100 m and an upper sheet like sand body about 600 m thick composed of quartz arenites and minor quartz clast conglomerates this upper unit is interpreted as beach shoreface tidal and shallow shelf deposits the lowest 70 m of the quartz arenite unit appear to be of fluvial origin but probably were formed by reworking of quartzose sands produced in coastal environments during a period of elevated sea level the lower sims formation probably represents molasse shed from either the hudson or labrador orogens rivers flowed northwest away from these upland areas the upper part of the sims formation records deposition during a period of slow steady sea level rise in an ocean that deepened to the west the sims formation outliers are remarkably similar to outliers of the sakami formation of northern quebec a unit that has a poorly constrained early to middle proterozoic age if these units are correlative a hypothesis supported mainly by identical facies and facies sequences then the transgressive quartz arenites would originally have covered an area of at least 200 000 km2

laramide tectonics and humid alluvial fan sedimentation ne uinta uplift utah and wyoming abstract laramide uplift and erosion of the uinta mountains are recorded in a 10 km long outcrop of the lower eocene wasatch formation on the utah wyoming border this 750 m thick package of interbedded sandstones and conglomerates is dominated by a coarsening then fining upward megasequence 650 m thick that records the growth and abandonment of a humid alluvial fun system during a major cycle of uplift and unroofing of the thrust bounded northern flank of the uinta mountains grain size thickness and lateral extent of channel complex deposits increase upward in the lower 400 m of the sequence reflecting construction and northward progradation of the fan grain size and channel complex thickness decrease upward in the upper 250 m of the sequence reflecting gradual reduction of both sedime t yield and sediment caliber during postorogenic lowering of source area relief within the megasequence coarsening up sequences 10 100 m thick built mainly of channel complex deposits reflect progradation of fan lobes punctuated by periodic fan head avulsions these medium scale sequences in turn comprise small scale fining up cycles 1 10 m thick that reflect such fluvial processes on the fan as bar building discrete flood events and the filling and lateral migration of braided stream channels both the medium scale and small scale sequences are commonly underlain by paleosols evidence of debris flows or other mass movement processes is conspicuously lacking above the main megasequence a second thinner megasequence containing lacustrine mudstones and wave reworked conglomerates indicates that the fan persisted as a locus of coarse clastic deposition during the first of a series of lacustrine transgressions that began as ratios of sediment flux to subsidence rate decreased toward the end of the early eocene partial inundation of the fan during this transgression transformed it into a fan delta

tectono sedimentary evolution of sedimentary basins from late paleoproterozoic to late neoproterozoic in the sao francisco craton and aracuai fold belt eastern brazil abstract two first order regional unconformities separate proterozoic supracrustal rocks of the sao francisco craton and the aracuai fold belt eastern brazil into three genetic units these constitute three superimposed first order basin fill cycles the espinhaco macaubas salinas and bambui megasequences the paleo mesoproterozoic espinhaco megasequence ca 1730 1500 ma was deposited in an intracratonic rift sag basin in four stages pre rift rift transitional and flexural each of these stages is bounded by regional second order unconformities basin evolution was controlled primarily by tectonics although sea level variations were also important in the transitional and flexural stages after a hiatus of several hundred million years subsidence renewed during extension related to the early neoproterozoic breakup of the supercontinent rodinia with rift to passive margin sedimentation in the macaubas salinas basin ca 950 700 ma initial glaciogenic sedimentation possibly induced by uplift related to a mantle plume occurred in a rift setting subsequent a shelf slope deep sea passive margin deposits represent opening of a northern branch of the adamastor ocean tectonic magmatic climatic and eustatic processes all combined to control basin evolution the bambui megasequence ca 800 650 ma was deposited in a foreland basin during convergent and collisional tectonics related to closure of the brazilide ocean and generation of the brasilia fold belt west of the sao francisco paleocontinental region the evolution of the bambui basin whose fill is characterized by three transgressive progradational shallowing upward sequences was mainly controlled by tectonic processes

boron isotopic constraints on the petrogenesis of hematitic phyllite in the southern serra do espinhaco minas gerais brazil abstract metasiliciclastic rocks predominate in the lower units of the palaeo mesoproterozoic espinhaco supergroup in the southern serra do espinhaco minas gerais brazil the lower units also comprise rocks with locally preserved igneous fabrics but which have very unusual chemistries these rocks collectively known as hematitic phyllite are characterised by abundant fine grained muscovite i e sericite and variable amounts of titaniferous hematite rutile and tourmaline currently the hematitic phyllite has been interpreted as a metamorphosed palaeosol after basaltic rocks and as such has been used as a palaeoclimatic indicator however the lateritic nature of the hematitic phyllite cannot unambiguously be determined because of the k metasomatism hematitisation and tourmalinisation recorded in the hematitic phyllite and in the arenaceous country rocks here we report the b isotopic and chemical compositions of tourmaline from the hematitic phyllite our 11b data are in the range between 15 and 4 the tourmaline compositions fall along the povondraite oxy dravite join which defines a meta evaporitic tourmaline trend a meta evaporitic b source is constrained by the b isotopic data as non marine our model for the hematitic phyllite suggests that b and k rich brines were derived from the metamorphic dewatering of non marine evaporites such brines extensively altered volcanic rocks of basaltic and rhyolitic compositions leading to tourmaline bearing hematite sericite assemblages of the hematitic phyllite

fan delta sequence in the archean fig tree group barberton greenstone belt south africa abstract the fig tree group of the barberton greenstone belt in south africa records the onset of tectonism and significant terrigenous and volcaniclastic sedimentation following a period of predominantly effusive volcanism in the southern part of the greenstone belt the lower fig tree conformably overlies the onverwacht group and can be grouped into either 1 volcaniclastic deposits consisting of pyroclastic and reworked volcanic detritus or 2 non volcanogenic terrigenous deposits of sandstone and conglomerate these petrologic groups are further divided into six lithofacies the lithofacies within the lower fig tree formation can be grouped into two facies associations 1 a subaqueous delta front association made up of fine grained airfall pyroclastic and slightly reworked pyroclastic debris along with resedimented land derived sandstone and conglomerate and 2 a subaerial association that is interpreted as forming from deposition of sandstone and conglomerate by flashy ephemeral stream processes on an alluvial fan surface the stratigraphic sequence coarsens upward from predominantly siltstone and fine grained sandstone at the base to pebble and cobble conglomerate at the top this sequence is interpreted as forming from the progradation of a fan delta into a body of relatively shallow quiet water composition of clasts in the conglomerates indicates that immediately underlying greenstone belt rocks or coeval volcanic rocks were the source for these coarse sedimentary accumulations erosion of uplifted greenstone belt terrain was apparently only to shallow levels both tectonic and volcanic activity played a role in producing several cycles of fan delta progradation

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

subaerial debris flow deposition in the upper paleozoic cutler formation western colorado abstract outcrops of the lower part of the cutler formation near gateway colorado contain proximal alluvial fan deposits of two principal lithofacies the diamictite lithofacies d consists of a variety of sharply bounded massive muddy beds which are interpreted as deposits of subaerial debris flows the gravelly sandstone lithofacies s consists of amalgamated beds of laminated and cross bedded conglomeratic sandstones which are interpreted as water deposited sediments clasts in s are rarely larger than 0 5 m in maximum diameter but clasts in d are commonly much larger up to 8 m both normal and inverse grading are visible in d but grading is generally not well developed in either lithofacies imbrication of clasts although more pronounced and more consistent in s is fairly commo in both lithofacies four subfacies of diamictite are distinguishable on the basis of clast packing and grading massive matrix supported dram graded matrix supported dmg inversely graded clast supported dci and massive clast supported dcm given the hydrodynamic and rheologic properties of debris flows as reported by previous workers four debris flow regimes are postulated on the basis of varying water content and clast interaction subfacies dram and drag typify deposits of flows having viscous clast interactions subfacies dci represents deposits of flows having inertial or colliding clast interactions subfacies dram comprises deposits of flows with demonstrably high yield strengths subfacies dcm represents deposits of flows in which yield strength was insufficient to support most clasts this classification specifically recognizes turbulence selective deposition and bedload transport of clasts as essential characteristics of certain dilute debris flows it also accommodates as debris flow deposits some beds which have features usually associated with aqueous deposition including clast frameworks channelization imbrication and normal grading

lithofacies and fluvial lacustrine environments of the palaeogene sevkhuul and ergil members ergiliin zoo formation south gobi mongolia the clastic sequence of the ergiliin zoo formation stretches along the mongolian chinese border in the southern gobi desert mongolia its members sevkhuul ergil exposed in the erdene sum region are well known for their vertebrate remains of late eocene and oligocene age based upon field work the continental red beds were subdivided into four units described as i prodelta mud sand flat ii delta front iii delta plain and iv calcretes all sub environments are in a fluvial lacustrine setting electronmicroprobe analysis in addition to conventional thin section examination was applied to shed some light on the complex mineral association made up of light minerals quartz plagioclase ternary feldspar orthoclase smectite illite rare palygorskite heavy minerals almandine pyrope solid solution series zoisite epidote s s s and abundant goethite and carbonate minerals calcite dolomite igneous rocks being exposed in the source area have contributed to the formation of carbonate minerals and mg bearing sheet silicates during diagenesis higher up on the delta plain transitional between distal alluvial and deltaic deposits fluids emerged from the distal alluvial fluvial deposits and formed calcareous duricrusts drawing conclusions from the rock colour the mineral assemblage and the palaeoecological data the climatic conditions may be described as alternating wet and dry seasons closely resembling those conditions of a modern savannah

lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins an example from the early cretaceous jiuquan basin northwestern china development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins however these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development this paper documents fan delta deposition alongside an intrabasinal structural high within the early cretaceous xiagou formation of the jiuquan basin china using subsurface geological and geophysical data deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts suggesting that deposition alongside the structural high is sensitive to lake level changes the temporal and spatial distribution of the fan deltas display retrogradational stacking patterns where fan deltas exhibit a decreasing lateral extent up sequence until fan delta deposition terminated and was replaced by deposition of fine grained lacustrine deposits the retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the xiagou formation subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation likely resulting from border fault movements these data suggest that non uniform stacking patterns in the lower parts of the xiagou formation reflect basin scale tectonic movements as the dominant control on synrift deposition patterns however later stages of xiagou formation deposition were characterized by uniform subsidence across the basin and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault these observations suggest that basin scale tectonic movements played a relatively limited role in controlling sediment deposition and imply a potential change to regional scale processes affecting fan delta deposition during later synrift stages climate change is favored here as the region scale control on the uniform retrogradational fan delta stacking patterns this assertion is supported by pollen assemblages isotope signatures and organic geochemical analyses which collectively suggest a change from a humid to semi arid environment during later synrift stages we suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin and regional scale processes that control rift basin deposition

normal faulting and alluvial fan deposition basal windermere tectonic assemblage yukon canada in the ogilvie mountains west central yukon the upper proterozoic lower mount harper group informal name is stratigraphically equivalent to basal windermere supergroup rocks that occur in other areas of the north american cordillera a preserved synsedimentary normal fault system forms the southern margin of an east trending half graben basin the basin fill was derived from the south the fill consists of fault proximal talus breccia and as much as 1 100 m of debris flow conglomerate deposited in coalescing alluvial fans intermediate and distal alluvial fan facies include mid to lower fan conglomerate and sandstone deposited by sheetfloods distal debris flows and braided channel streamflows a thick coarsening upward megasequence in the eastern part of the study area records the change from waterlaid lacustrine red beds to lower alluvial fan sandstones and conglomerates clastic deposition ended soon after volcanism was initiated resulting in the overlying mount harper volcanic complex ca 750 ma the half graben basin was formed by the southern margin faulting comparison with strike slip basin depositional patterns indicates significant differences suggesting that faulting was predominantly dip slip synsedimentary fault movements and minor back stepping of the fault system controlled development of the megasequences volcanism postdates sedimentation in this half graben but north derived coarse clastic rocks which intertongue with the volcanic rocks were deposited to the northwest and are not directly related to lower mount harper group deposition a model is proposed in which diachronous opposed symmetry half grabens formed with volcanism concentrated in the accommodation zone between half grabens basins in the western arm of the east africa rift system provide geometric and evolutionary analogues

tectonics and sedimentation in a paleo mesoproterozoic rift sag basin espinhaco basin southeastern brazil abstract sedimentologic paleogeographic stratigraphic structural and tectonic studies in a paleo mesoproterozoic metasedimentary succession espinhaco megasequence southeastern brazil indicates deposition in a rift sag basin four basin evolution stages are recognized prerift rift transitional and flexural the four stages can be represented by six unconformity bounded tectonosequences the unconformities are recognized in the field and mappable even on a regional scale the prerift and rift stages of the espinhaco basin were filled by products of continental depositional systems the prerift stage probably represents the first product of the rifting process before the development of the half grabens that characterize the rift stage during the rift stage mechanical subsidence due to lithospheric stretching was predominant and led to episodic rising of the depositional base level as a result the basin fill is characterized by coarsening upward intervals paleocurrent patterns indicate that block tilting and half graben subsidence uplift controlled sediment dispersion the first marine incursion within the espinhaco basin marks the change in the subsidence regime of the basin the evolution of the transitional and flexural stages was probably controlled by thermal subsidence due to thermal contraction of the lithosphere during cooling the transitional stage was characterized by relatively low subsidence rates higher subsidence rates and a consequent sea level rise characterize the flexural stage of the espinhaco basin in which three second order transgressive progradational sequences can be recognized

alluvial lithofacies recognition in a humid tropical setting abstract cobble gravel deposits in the antigua formation accumulated on a large alluvial fan or braid plain west of the cordillera occidental in southwest colombia this formation was probably deposited during the pleistocene in a very wet tropical climate 500 cm yr rainfall fining upwards sequences of clast supported imbricated boulders and cobbles dominate with maximum clast sizes between 30 and 300 cm the sand matrix in the antigua gravels and the minor 10 sand facies are weathered to clay at depths of up to 20 m the sand facies contains abundant drift logs and leaf mats except for the absence of debris flows and the very coarse nature of the gravel the antigua gravels have lithofacies similar to the glacial outwash braid plain in the proximal area of the scott type model gravels and sands of the younger panambi formation were deposited by a braided stream that was smaller confined by valley walls and flowing at a lower gradient than the river that deposited the antigua gravels we recognize no sedimentologic characteristics of these deposits as diagnostic of a humid tropical environment except for textural and compositional changes in matrix sediments caused by deep and rapid chemical weathering

correlation of himalayan exhumation rates and asian monsoon intensity although most data suggest that the india eurasia continental collision began 45 55 myr ago the architecture of the himalayan tibetan orogen is dominated by deformational structures developed in the neogene period 23 myr ago the stratigraphic record and thermochronometric data indicate that erosion of the himalaya intensified as this constructional phase began and reached a peak around 15 myr ago it remained high until 10 5 myr ago and subsequently slowed gradually to 3 5 myr ago but then began to increase once again in the late pliocene and pleistocene epochs here we present weathering records from the south china sea bay of bengal and arabian sea that permit asian monsoon climate to be reconstructed back to the earliest neogene these indicate a correlation between the rate of himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 myr we interpret this correlation as indicating dynamic coupling between neogene climate and both erosion and deformation in the himalaya although the india eurasia collision initiated 50 myr ago major deformation and exhumation of the himalaya did not begin until the early neogene 23 myr ago this coincides with the increased intensity of the asian monsoons as indicated by weathering records from the south china sea bay of bengal and arabian sea and hints at a dynamic coupling between climate and both erosion and deformation in the himalaya

braidplain sedimentation in a proterozoic rift basin the sao joao da chapada formation southeastern brazil abstract the sao joao da chapada formation 100 200 m thick is the basal unit of the middle proterozoic espinhaco supergroup this up to 3000 m thick and slightly metamorphosed sedimentary succession is exposed in the central part of the southern serra do espinhaco southeastern brazil detailed lithofacies studies were carried out to characterize the sedimentation and paleogeography of the sao joao da chapada formation six lithofacies are present horizontal to low angle cross stratified sandstones lithofacies sh sl trough cross stratified sandstones lithofacies st planar cross stratified sandstones lithofacies sp ripple cross laminated sandstones lithofacies sr massive to horizontally stratified conglomerates lithofacies gm and fine grained rocks lithofacies f these are usually arranged in fining and thinning upward successions characterizing waning flood cycles which are always bounded by erosional surfaces no complete cycles have been found however and the cycles are normally composed only of lithofacies sh sl and st the other lithofacies are rare the observed sedimentary structures and their arrangement the geometry of the bodies mainly sheet like to slightly lenticular the low relief morphology of the erosion surfaces bounding the waning flood cycles the coarse and poorly sorted texture of the sediments and the measured paleocurrent pattern unidirectional with little dispersion throughout the study area point to deposition on a wide ephemeral braidplain characterized throughout by relative uniformity of facies and paleocurrent directions water depths on this subsiding braidplain were maintained by high discharge streams debouching onto it from the upland catchment areas as these rivers spread onto the depositional plain the changes in gradient and substratum transformed them into channels of remarkable width and very large width depth ratios these rivers ran in braided tracts and floods were temporarily confined within banks in these tracts channel switching events associated with tilting and subsidence of the basin floor resulted in the accumulation of extensive sandstone sheets interfingering laterally with one another and succeeding one another vertically which built up a braidplain succession extending up to 35 km transverse to the paleoslope the sao joao da chapada braidplain flanked the west margin of a n s elongated rift basin

late proterozoic glaciation in central eastern brazil synthesis and model abstract in the surroundings of the middle proterozoic sao francisco craton of central eastern brazil numerous traces of an ancient glaciation can be found almost all criterua necessary to prove an ancient glaciation occur including scratched and facetted pebbles a striated surface quarrying outwash plains eskers varvites dropstones decollement structures etc poorly sorted tillites with varying pebble composition are widely distributed continental tillites and glaciomarine sequences interfinger in the east and southeast of the craton traces of ice movement suggest flow directions of the ice towards the east and the southeast of the craton at the coast the wet base glaciers passed over to floating shelf ice in the northeast glaciers also came from the serrinha craton in northeastern bahia the glaciation covered an area of at least 1300 700 km the sequences containing traces of glaciation discordantly overlie archean to middle proterozoic rocks they in turn are overlain by late proterozoic calcareous and psammopelitic sediments of the bambui group present data indicate that glaciation took place around 1000 ma ago

climatic and tectonic influences on fan deltas and wave to tide controlled shoreface deposits evidence from the archaean keskarrah formation slave province canada the 2 6 ga keskarrah formation located in the central slave province northwest territories canada is a late orogenic tectonically controlled sedimentary sequence that developed under unusual climatic and depositional conditions the formation is adjacent to the crustal scale north trending beniah lake fault and overlies the 3 15 ga augustus granite the 2 69 2 7 ga mafic volcanic peltier formation and the turbiditic contwoyto formation unconformably principal lithofacies in the keskarrah formation include conglomerate sandstone and siltstone sandstone the conglomerate lithofacies represents coalescing gravelly streamflow dominated fan deltas adjacent to topographic highs up section quartz rich arenites and quartz arenites of the sandstone lithofacies are interpreted to be shallow water shoreface deposits influenced by wave action and tides the overlying feldspathic litharenites of the siltstone sandstone lithofacies are consistent with a lower shoreface to proximal offshore environment dominated by wave and tide interaction tidal influence in both sandstone dominated lithofacies is inferred from the presence of mudstone laminae between bedforms and on foresets of cross beds as well as from abundant reactivation surfaces with local mudstone drapes intense chemical weathering during the archaean resulting from elevated atmospheric co2 levels higher temperatures and moist climatic conditions played an important role in the development of quartz rich arenites that appear to be first cycle deposits few lithic fragments and feldspar grains are preserved due to in situ host rock weathering chemical weathering during transport and wave and tide action hydraulic sorting and abrasion in the shoreface environment contributed to the continued breakdown and transport of labile minerals increased proportions of lithic fragments in sandstone beds of the conglomerate lithofacies are the result of shorter transport distances from source areas to the depositional environment abundant conglomerate with up to 4 m large granitic boulders derived from the adjacent augustus granite and mafic clasts from the peltier formation indicate high relief and fault related uplift and subsidence the intimate association of fan deltas and wave and tide influenced shallow marine deposits in association with quartz rich sandstones forming in a high relief area make the keskarrah formation remarkable in the rock record

provenance and paleogeographic reconstruction of a mesoproterozoic intracratonic sag basin upper espinhaco basin brazil we would like to thank the capes cnpq grant no 304045 2010 1 and petrobras for their financial support for the field work and analysis

tectonic and hydrologic controls on cyclic alluvial fan fluvial and lacustrine rift basin sedimentation jurassic lowermost cretaceous todos santos formation chiapas mexico abstract the nonmarine upper jurassic lowermost cretaceous todos santos formation of central chiapas mexico was deposited in half graben basins formed during the early rifting stage of the southern gulf of mexico basin this formation consists of alluvial fan fluvial and lacustrine sequences that were deposited under arid climatic conditions alluvial fans were built outwardly from the elongate basin margins by runoff that flowed transverse to the basin axis whereas fluvial units were deposited by rivers that flowed parallel to the basin axis lacustrine deposition took place in a topographic depression adjacent to the basin margin the presence of alluvial fan and fluvial or lacustrine deposits in vertically stacked cyclic megasequences hundreds of meters thick indicates that the basin opography changed through time this cyclicity denotes that periodically fluvial or lacustrine environments occupied the basin margin position and at other times alluvial fan sedimentation occurred there cyclicity was caused by periodic changes from high to low rates of basin subsidene the response of these three depositional environments to basin subsidence differed due to the unique hydrologic controls on sediment transport and deposition in each environment lakes were maintained by springs that emanated from the fractured fault margin and by fluvial discharge fluvial discharge and deposition resulted from precipitation or annual snowmelt anywhere in the river s expansive drainage basin whereas alluvial fan sedimentation occurred only when there was infrequent significant precipi ation in the small drainage basin from which fan sediment was derived as a result of these hydrologic controls the lacustrine or fluvial environments responded more quickly to periods of active tectonic subsidence and migrated over the fans to occupy the basin margin depression aided by a decrease in basin subsidence alluvial fans eventually prograded and displaced the fluvial or lacustrine environments away from the basin margin

alluvial playa sedimentation in the lower keweenawan sibley group thunder bay district ontario the middle proterozoic sibley group is a mixed clastic carbonate red bed sequence located in the thunder bay nipigon area on the north shore of lake superior the lowest unit the pass lake forma

nature and regional significance of unconformities associated with the middle ordovician hagan k bentonite complex in the north american midcontinent stratal patterns of the middle ordovician hagan k bentonite complex and associated rocks show that the black river trenton unconformity in the north american midcontinent formed through the complex interplay of eustasy sediment accumulation rates siliciclastic influx bathymetry seawater chemistry and perhaps local tectonic uplift the unconformity is diachronous and is an amalgamated surface that resulted from local late turinian lowstand exposure followed by regional early chatfieldian transgressive drowning and sediment starvation the duration of the unconformity is greatest in southern wisconsin northern illinois and northern indiana where the deicke and millbrig k bentonite beds converge at the unconformity on the basis of published isotopic ages for the deicke and millbrig beds it is possible that in these regions erosion and nondeposition spanned a period of as much as 3 2 m y two broad coeval depositional settings are recognized within the north american midcontinent during early chatfieldian time 1 an inner shelf subtidal facies of fossiliferous shale spechts ferry shale member and ion shale member of the decorah formation and argillaceous lime mudstone and skeletal wackestone guttenberg and kings lake limestone members extended from the canadian shield and transcontinental arch southeastward through minnesota wisconsin iowa and missouri 2 a seaward relatively deep subtidal sediment starved middle shelf extended eastward from the mississippi valley region to the taconian foreland basins in the central and southern appalachians and southward through the pericratonic arkoma and black warrior basins in the inner shelf region the black river trenton unconformity is a composite of at least two prominent hardground omission surfaces one at the top of the castlewood and carimona limestone members and the other at the top of the guttenberg and kings lake limestone members both merging to a single surface in the middle shelf region the inner and middle shelves redeveloped later in approximately the same regions during devonian and mississippian time

facies related diagenetic alteration in lacustrine deltaic red beds of the paleogene ergeliin zoo formation erdene sum area s gobi mongolia the late eocene ergeliin zoo formation mongolia was subdivided into four facies associations stratigraphic units which are characterized by various carbonate minerals 1 mud sand flat low fe dolomite high mg calcite 11 delta front high mn dolomite low mg calcite 111 delta plain high mn calcite low mg and moderate fe calcite iv calcretes high mg calcite besides carbonate minerals prevailing among the cement minerals some sheet silicates ca smectite palygorskite illite apatite and fe oxide hydroxides occur in the siliciclastics of these lacustrine deltaic red beds the prodelta mud sand flat deposits unit 1 were dolomitized and cemented by high mg calcite during evaporative pumping at times of low lake stand under redox conditions greater than 0 and intrastratal solutions of strong alkalinity manganoan dolomite is fairly widespread in the delta front sediments unit 11 the mn content of which is likely to have been derived from decomposition of vertebrate remains the mn fe ratio in the carbonate minerals was controlled by the redox conditions and the shallow burial depth in the porous delta front sediments eh values around zero and ph values slightly above 7 occurred as a result of basinward fluid movements high mn dolomite high fe dolomite low mg calcite fluid movement was locally impeded by finer grained delta plain deposits unit iii intertonguing with arenaceous aquifers low mg moderate fe calcite high mn calcite higher up on the delta plain with deposits laid down in an environment transitional between distal alluvial and deltaic unit iv closed lake basin conditions reappeared as fluids emerged from the distal alluvial fluvial deposits or were driven by capillary force to ascend and form calcretes abundant in mg bearing calcite the climatic conditions in the erdene sum area mongolia are likely to have been semi and transitional into arid c 2005 elsevier b v all rights reserved

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

messinian climate change and erosional destruction of the central european alps at the end of the miocene the european alps ceased outward expansion and tectonic uplift and exhumation shifted into the orogen interior this shift is consistent with a change from orogenic construction to orogenic destruction reflecting an increase in the ratio of erosional flux to accretionary flux the coincidence of this change with an increase in sediment yield from the alps suggests a climate driven increase in erosional flux the timing of deformation and sediment release from the southern alps indicates that the tectonic change occurred synchronous with the last phase of the messinian salinity crisis we attribute the increase in erosional flux to a climatic shift to wetter conditions throughout europe likely augmented by the base level fall that occurred during the mediterranean dessication this climate change is represented in the stratigraphic record by the lago mare deposits of the mediterranean salinity crisis

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

anatase nanoparticles on supergene platinum palladium aggregates from brazil titanium mobility in natural waters abstract supergene aggregates of platinum palladium pt pd intermetallic compounds from the corrego bom sucesso alluvial deposit minas gerais brazil are coated with abundant poorly crystalline nanoparticles of anatase tio 2 the anatase coating is widespread suggesting that the surface of the pt pd grains catalytically destabilised ti which was likely dissolved by organic ligands in the ground waters association of tio 2 nanocrystallites with organic matter further suggests that biogenic processes could have mediated their formation these anatase coated pt pd grains demonstrate an unexpected ti mobility in supergene environments