paleobiogeography of miocene equinae of north america a phylogenetic biogeographic analysis of the relative roles of climate vicariance and dispersal article i nfo the horse subfamily equinae underwent a major radiation during the miocene in north america diversifying from one species parahippus leonensis to 70 species this radiation has been linked to climatic and vegetation changes that occurred in north america during this time however the relationship between climate change and speciation has not previously been studied quantitatively using phylogenetic biogeography distribution and age range data were collected for all north american species within eighteen equine genera through a literature review and use of the paleobiology database fitch parsimony analysis of the taxon area cladogram indicate that speciation by dispersal allopatry model ii was more common in the evolution of the clade than speciation by vicariance allopatry model i distribution data were analyzed using the lieberman modified brooks parsimony analysis lbpa to determine patterns of vicariance and geodispersal using four constrained biogeographic regions within north america in the analysis the great plains the southwest the gulf coast and the southeast resulting general area cladograms are congruent with geological events such as uplift of the rocky mountains and climatic conditions such as the change from a warm and moist to cool and arid climate during the miocene well supported vicariance and geodispersal trees derived from the lbpa analysis are largely congruent with each other indicating that cyclical events in particular climate change during the miocene influenced the radiation of the clade

late cenozoic basalt and gabbro in the subsurface in the phetchabun basin thailand implications for the southeast asian volcanic province abstract fragments of basaltic and gabbroic rocks were obtained in cuttings from 15 exploration wells in the na sanun area of the wichian buri sub basin of the phetchabun basin in central thailand the samples represent flows and sills in lacustrine and fluvial sedimentary rocks of the lower to mid miocene wichian buri group mafic igneous units were identified in the sections based on their typically high amplitude seismic reflections confirmed by the examination of several hundred well cuttings and magnetic susceptibility measurements cross sections of the sub basin were constructed on the basis of previously published subsurface interpretations seismic and well data and petrological observations basaltic flows a b e and f have ages of ca 2 ma 16 ma 24 ma and 18 ma based on inferred stratigraphic position gabbroic sill c and dioritic sill g are inferred to be correlative at ca 11 6 ma and differ petrologically from ca 12 8 ma gabbroic sill d major minerals in both basaltic and gabbroic samples are plagioclase ca an50 anorthoclase and augite with pervasive alteration to na and ca zeolite minerals and analcime leucodioritic sill g also contains amphibole and high ti phlogopite overall the rocks show within plate tholeiitic to alkalic characteristics and show similarities to basaltic surface outcrops of similar ages in the wichian buri lop buri area no evidence was seen in the subsurface for the andesitic to rhyolitic rocks of similar ages that occur at surface but their presence cannot be precluded based on our limited data

fossil horses and carbon isotopes new evidence for cenozoic dietary habitat and ecosystem changes in north america abstract the transformation from low crowned to high crowned horse teeth during the miocene has traditionally been interpreted as an adaptive response to the spread of savanna grasslands during the middle miocene by about 15 m y ago carbon isotope data from 50 north american horse teeth spanning eocene to pleistocene age indicate that savanna grasslands presumably dominated by c 4 grasses as they are today first became widespread much later than do horses with high crowned teeth prior to 7 m y horses had a c 3 based diet and after 7 m y horses started eating c 4 grasses this change in diet occurred when the major drop in the diversity of horses occurs during the late miocene the change in vegetation reflected in horses diet may be related to a significant reduction in atmospheric co 2 level toward the end of the miocene which provided the c 4 grasses with an adaptive advantage and led to their expansion at the expense of c 3 plants

new data on the indosinian orogeny from central thailand the main aspects of the geosynclinal and orogenic evolution of the petchabun foldbelt in central thailand are described this area was previously thought to be deformed by the indosinian triassic orogeny the new data show that the main orogenic event in thailand can be dated post lower permian pre uppermost permian evidence is given that paleotethys closed on thai territory during this orogenic event the known upper triassic deformations in northern thailand are supposed to be strictly intracontinental and therefore of minor importance

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

tectonic implications of the nan suture zone and its relationship to the sukhothai fold belt northern thailand abstract the nan suture and the sukhothai fold belt reflect the processes associated with the collision between the shan thai and indochina terranes in southeast asia the shan thai terrane rifted from gondwana in the early permian as it drifted north a subduction complex developed along its northern margin the nan serpentinitic melange is a thrust slice within the pha som metamorphic complex and in total this unit is a late permian accretionary complex containing offscraped blocks from subducted oceanic crust of carboniferous and permian age the deformational style within the pha som metamorphic complex supports a west dipping subduction zone the late permian to late triassic fore arc basin sediments are preserved in the sukhothai fold belt and include a near continuous sedimentary record at least locally the whole sequence was folded and complexly thrust in the late triassic as a result of the collision late syn to post kinematic granites place an upper limit of 200 ma on the time of collision post orogenic sediments prograded across the suture in the jurassic

geochemistry and geochronology of the chatree epithermal gold silver deposit implications for the tectonic setting of the loei fold belt central thailand abstract the chatree deposit is the largest epithermal au deposit in mainland se asia despite its economic significance the stratigraphy age geochemistry and tectonic setting of the host volcanic sequence is poorly documented in the literature the chatree deposit is located between phichit and phetchabun provinces central thailand and is hosted by late permian to early triassic volcaniclastic and volcanogenic sedimentary rocks detailed field mapping u pb zircon dating geochemistry and stratigraphy suggest that the volcanic sequence can be subdivided into four stratigraphic units and two volcanic suites the late permian suite 1 volcanic units are sourced from a more depleted mantle relative to the overlying early triassic suite 2 volcanic units the late permian suite 1 units probably formed immediately after the beginning of subduction and at the creation of a new island arc the less depleted early triassic suite 2 units were erupted during ongoing subduction once the system had achieved a steady state the chatree au mineralization appears to have occurred during the switch between the two mantle sources and this switch of magma source is marked by a mixed volcano plutonic magmatism at the permo triassic boundary ca 250 ma

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

geodynamic evolution of loei and phetchabun regions does the discovery of detrital chromian spinels from the nam duk formation permian north central thailand provide new constraint abstract the discovery of the chromian spinel detritus in sandstones from the permian nam duk formation phetchabun region confirms that the siliciclastic part of this formation is related to the erosion of a mountain belt caused by compressional deformation the question discussed is whether this detritus is derived from an older orogen exposed today in the region of loei east of the nam duk basin or it is from a mountain belt which evolved during permian times in the west nan uttaradit region in the first case the nam duk formation would represent the passive continental margin sequence of the indochina craton and in the second case it would be part of the sedimentary wedge associated with the compressional deformation and subsequent uplift to the erosional level during middle to upper permian of a rising mountain belt further in the west in this contribution arguments in favour of the second scenario are discussed the region close to the nan uttaradit suture zone shows evidence of compressional deformation and subsequent uplift to an erosional level in the permian when the chromian spinel detritus was deposited in the nam duk formation

correlation of triassic stratigraphy between the simao and lampang phrae basins implications for the tectonopaleogeography of southeast asia abstract based on our extensive fieldwork in southwestern yunnan and northern thailand followed by detailed stratigraphic and paleontological studies we propose that the triassic simao basin in yunnan can be correlated with the triassic lampang phrae basin in thailand strata equivalent to those in the southern lancangjiang sub basin have not been identified in northern thailand we consider that during the triassic the simao and the lampang phrae basins belonged to the same tectonopaleogeographic unit the orogenic belt to the east of this unit includes the nan uttaradit and ailaoshan sutures the shan thai block in northern thailand can be divided from east to west into the sukhothai the inthanon and the shan terranes according to tectonopaleogeographic correlation our results support the idea that the sukhothai terrane including the lampang phrae basin belongs to the cathaysian domain and not to gondwana domain and that the geosuture corresponding to the changning menglian suture in yunnan must lie to the west of the sukhothai terrane in thailand

geochemistry and tectonic setting of the central loei volcanic rocks pak chom area loei northeastern thailand abstract the central loei volcanic rocks as evidenced by those in the pak chom area were formed in the late devonian early carboniferous and can be separated into three magmatic groups transitional tholeiitic basalt tholeiitic microgabbro and calc alkalic basalt andesite on the basis of immobile element contents and ratios of least altered samples all the tholeiitic microgabbro possibly occurred as dikes chemically the transitional tholeittic basalt and tholeiitic microgabbro have higher abundances of tio 2 ni and cr relative to the calc alkalic basalt andesite at similar values for feo mgo they also contain higher ti zr but lower zr nb the transitional tholeiitic basalt has higher concentrations of p 2 o 5 and nb relative to the tholeiitic microgabbro at similar levels of feo mgo and also has higher ratios of nb y and ti v but lower values for ti zr and zr nb in terms of chondrite normalized ree and n morb normalized patterns the transitional tholeiitic basalt tholeiitic basalt and calc alkalic basalt andesite are analogous to those from north atlantic southwest indian ridge and new britain arc on this basis the central loei volcanic rocks are comprised of morbs and oceanic island arc lavas these arc lavas may have erupted on an oceanic basement in the same ocean basin as those in the chiang rai chiang mai volcanic belt

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

the ban houayxai epithermal au ag deposit in the northern lao pdr mineralization related to the early permian arc magmatism of the truong son fold belt abstract the ban houayxai au ag deposit is located in the truong son fold belt in the northern lao pdr mainland se asia the deposit is hosted within an early permian volcano sedimentary unit which is a part of a late carboniferous early permian 310 270 ma volcanic plutonic sequence of the truong son fold belt the main au ag mineralization stages i e stages 2 and 3 at ban houayxai consist of hydrothermal veins breccias associated with a carbonate quartz sulfides pyrite sphalerite galena chalcopyrite sericite chlorite electrum native silver stephanite mineral assemblage geochronological studies from la icp ms zircon u pb and adularia ar ar and k ar dating identified early permian cretaceous and eocene ages the early permian age is related to the emplacement of the mineralized volcanic arc sequence whereas the cretaceous and eocene ages represent resetting probably related to yanshanian and or himalayan orogenies a regional tectonic reconstruction indicates that the au ag epithermal deposit at ban houayxai was formed as a result of southward subduction of an oceanic crust attached to the south china terrane beneath the indochina terrane during the early permian from the metallogenic point of view the recognition of the old epithermal system at ban houayxai implies that the truong son fold belt possesses high potential for the presence of deeper magmatic related deposits such as porphyry and porphyry related skarn deposits

arc like volcanic rocks in nw laos geochronological and geochemical constraints and their tectonic implications abstract the loei fold belt located at the western margin of the indochina block is considered to be tectonically linked to the subduction of the paleotethyan ocean and subsequent collision in northwestern laos the volcanic rocks are traditionally mapped as permian early triassic sequences our la icp ms zircon u pb dating results show that andesitic rhyolitic and tuffaceous samples from the muang feuang region of the loei fold belt have zircon u pb ages of 330 4 2 2 ma 334 9 1 7 ma and 349 6 1 7 ma which are interpreted as their eruption ages respectively these ages are indicative of an early carboniferous origin the basaltic and basaltic andesitic samples from the pak lay region yield zircon u pb ages of 314 6 2 7 ma and 315 4 3 8 ma respectively and have a late carboniferous origin these samples exhibit depletion in hfses e g nb ta ti with high lile hfse ratios and exhibit a geochemical affinity to continental arc volcanic rocks these signatures suggest the presence of an early to late carboniferous active continental margin along the western margin of the indochina block the loei fold belt may extend north into nw laos

investigating equid mobility in miocene florida usa using strontium isotope ratios abstract despite extensive research on the evolutionary history and ecology of horses surprisingly little is known about the daily and seasonal movements i e mobility of extinct species we used strontium isotope ratios 87sr 86sr in tooth enamel to estimate mobility patterns of equids from two miocene fossil sites in northern florida usa thomas farm ca 18 ma and love bone bed ca 9 5 9 ma the species included in our sample have a range of body sizes 45 252 kg and reconstructed diets gomphotheres and tapirs from love bone bed were also included to represent browsers based on modern species behavior we predicted small bodied and browsing taxa living in closed habitats had limited mobility and 87sr 86sr similar to local northern florida limestone we anticipated larger bodied and grazing taxa living in open environments had increased mobility with higher and more variable 87sr 86sr reflecting larger movements across differing geologies contrary to expectations the majority of taxa at both sites have higher 87sr 86sr than expected for local eocene bedrock and instead are similar to contemporary late oligocene to mid miocene seawater the most plausible explanation for these findings is that most individuals foraged close to the paleo coastline where vegetation would have been influenced by marine derived strontium via sea spray or precipitation tapirs have considerably higher and more variable 87sr 86sr than horses or gomphotheres at love bone bed which may reflect foraging on aquatic vegetation in the river channel that is preserved at the site our results suggest that horses were relatively sedentary in florida even during their peak radiation

long term and short term global cenozoic sea level estimates backstripping analysis of three continuously cored well dated boreholes from the new jersey coastal plain ocean drilling program odp leg 150x indicates a long term 10 8 n10 7 yr eustatic fall of 100 m since 55 ma early eocene and suggests short term 0 5n3 m y eustatic falls of less than 70 m eustatic estimates are calculated from residuals between the decompacted unloaded and paleodepth corrected records and tectonic subsidence assuming a cooling lithospheric plate because the residuals are similar among the three sites we interpret them as an approximation of the eustatic signal

blancan hemphillian land mammal ages and late cenozoic mammal dispersal events vertebrate fossils have produced a reliable and useful framework for interpreting geologic history during the cenozoic era and for unraveling the complex evolution of mammals this framework was formalized for north america in 1941 as the north american provincial land mammal ages wood et ai 1941 during the last 40 years that framework has been revised extended and calibrated so that land mammal ages are now the prime chronologie standard for terrestrial deposits of the cenozoic land mammal ages have been calibrated and resolved because of numerous studies relating mammal fossils and fossil sites to modern systematic analyses detailed biostratigraphic analyses new radiometric dating

an alternative plate tectonic model for the palaeozoic early mesozoic palaeotethyan evolution of southeast asia northern thailand burma abstract an alternative model for the geodynamic evolution of southeast asia is proposed and inserted in a modern plate tectonic model the reconstruction methodology is based on dynamic plate boundaries constrained by data such as spreading rates and subduction velocities in this way it differs from classical continental drift models proposed so far the different interpretations about the location of the palaeotethys suture in thailand are revised the tertiary mae yuam fault is seen as the emplacement of the suture east of the suture we identify an indochina derived terrane for which we keep the name shan thai formerly used to identify the cimmerian block present in southeast asia now called sibumasu this nomenclatural choice was made on the basis of the geographic location of the terrane eastern shan states in burma and central thailand and in order not to introduce new confusing terminology the closure of the eastern palaeotethys is related to a southward subduction of the ocean that triggered the eastern neotethys to open as a back arc due to the presence of late carboniferous early permian arc magmatism in mergui burma and in the lhasa block south tibet and to the absence of arc magmatism of the same age east of the suture in order to explain the presence of carboniferous early permian and permo triassic volcanic arcs in cambodia upper triassic magmatism in eastern vietnam and lower permian middle permian arc volcanites in western sumatra we introduce the orang laut terranes concept these terranes were detached from indochina and south china during back arc opening of the poko song ma system due to the westward subduction of the palaeopacific this also explains the location of the cathaysian west sumatra block to the west of the cimmerian sibumasu block

evolution of the se asian continent from u pb and hf isotopes in single grains of zircon and baddeleyite from large rivers to better understand the evolution of the se asian continent 235 single zircon and baddeleyite grains from large rivers were dated by the u pb chronometer and 148 of these grains were simultaneously analyzed for hf isotopes this combination of methods is applied to sand samples from the mekong irrawaddy salween and red rivers which sample the continent on the plate scale u pb dates and hf isotopic signatures of these grains resolve the age spectra of crust and they elucidate source characteristics of magmas involved in continental growth and recycling for sufficient statistical coverage more than 80 of zircons and baddeleyites from each river sample were analyzed representing an erosion area of about 1 6 106 km2 our analyses reveal five different proterozoic crustal growth events occurring at about 2 5 ga 2 3 ga 1 9 ga 1 1 ga and 0 8 ga however none of these basement terrains is exposed in se asia being entirely covered by phanerozoic sediments the data also substantiate granitoid magmatism during the caledonian indosinian and himalayan orogenies initial hf isotope signatures ehfi obtained for grains lying less than 15 discordant in the concordia diagram range between 13 3 and 16 7 plotting in both the domains of strongly lile depleted and enriched reservoirs relative to a chondritic evolution of the mantle approximately half of the grains crystallized in magmas derived from significantly depleted mantle sources and about 18 formed in magmas showing nearly chondritic signatures ehfi 1 37 to 1 59 27 grains the remaining grains yield strongly negative ehfi documenting the incorporation of important amounts of melts generated from crust formed during the paleoproterozoic events at 2 3 and 1 9 ga which seem to have produced the dominant mass of the se asian continent all younger orogenic cycles are characterized by substantial melting of continental material which probably dominate over juvenile crust addition an exception are the irrawaddy terrains where substantial mantle input characterizes post collisional magmatism since 50 ma

the chanthaburi terrane of southeastern thailand stratigraphic confirmation as a disrupted segment of the sukhothai arc a permo triassic volcanic arc system the sukhothai arc is recognised between the indochina and sibumasu continental blocks the chanthaburi terrane is here interpreted as a fault detached highly disrupted southern segment of the sukhothai arc occupying part of southeastern thailand and extending into cambodia the klaeng tectonic line is defined as the boundary between the chanthaburi terrane and sibumasu block the stratigraphy of the chanthaburi terrane is compared with that of the sukhothai terrane in northern thailand the late palaeozoic mesozoic sequences of these two volcanic arc terranes in the sukhothai zone share important similarities but show marked contrasts to those of the sibumasu and indochina blocks where the late permian triassic is largely absent due to the indosinian i unconformity western indochina or is dominantly carbonates with little terrigenous clastic input sibumasu there is no clear evidence of pre carboniferous sedimentary rocks for either the sukhothai or chanthaburi terranes late permian lyttoniid brachiopod shale near klaeng in the chanthaburi terrane was revisited the brachiopod previously reported as leptodus is re identified to oldhamina the genus previously known elsewhere in southeast asia only in the huai tak formation of the sukhothai terrane oldhamina in thailand is confined to the sukhothai arc the marine stratigraphy of the sukhothai arc is represented by a permian triassic lithological succession of mixed carbonates and siliciclastics with common volcanic material the late permian and triassic litho and biostratigraphy of the chanthaburi terrane are comparable with the upper ngao and lampang groups of the sukhothai terrane in particular they share similar successions from oldhamina brachiopod bearing shale to palaeofusulina colaniella foraminifer bearing limestone in the latest permian marine depositional conditions were terminated on the sukhothai arc by end triassic times later than on the indochina block late permian but earlier than on the sibumasu block jurassic cretaceous

paleobiogeographic patterns in the middle and late devonian emphasizing laurentia abstract the relative importance of tectonism and sea level change in driving middle to late devonian biogeographic patterns in marine invertebrates is investigated using phylogenetic biogeography taxa considered include two clades of brachiopods one bivalve clade and a suborder of phyllocarid crustaceans these organisms colonized different depositional environments and played different roles in the devonian ecosystem which allows biogeographic patterns to be considered in a cross faunal analysis vicariance patterns are well resolved and may reflect biogeographic relationships developed in the early to early middle devonian due to the uplift of intracratonic arches uplift of tectonic arches is inferred to occur during times of tectonic quiescence during the second and third and possibly also the first tectophase after ettensohn f r 1985 the catskill delta complex and the acadian orogeny a model in woodrow d l sevon w d eds the catskill delta geological society of america boulder co special paper 201 pp 39 49 of the acadian orogeny geo dispersal patterns are not as well resolved but may indicate dispersal across tectonic arches during downwarping associated with increased compressional tectonism during ettensohn s 1985 ettensohn f r 1985 the catskill delta complex and the acadian orogeny a model in woodrow d l sevon w d eds the catskill delta geological society of america boulder co special paper 201 pp 39 49 tectophases ii and iii geo dispersal across relatively low arches may also be coincident with transgressive events iia and iic of johnson et al 1985 johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 the overall lack of congruence between the vicariance and geo dispersal patterns suggests that singular tectonic events exerted more profound influence on devonian biogeography than cyclical changes in sea level furthermore the offset in perceived timing between vicariance and geo dispersal patterns may indicate a fundamental change in the style of biogeographic patterns during the middle devonian and may have played a major factor in regulating biodiversity dynamics during the late devonian biodiversity crisis

petrology and shock metamorphism of the olivine phyric shergottite yamato 980459 evidence for a two stage cooling and a single stage ejection history abstract the basaltic martian meteorite yamato 980459 consists of large olivine phenocrysts and often prismatic pyroxenes set into a fine grained groundmass of smaller more fe rich olivine chromite and an interstitial residual material displaying quenching textures of dendritic olivine chain like augite and sulfide droplets in a glassy matrix yamato 980459 is thus the only martian meteorite without plagioclase maskelynite olivine is compositionally zoned from a mg rich core to a fe rich rim with the outer few micrometers being especially rich in iron with fo84 the cores are the most magnesian olivines found in martian meteorites so far pyroxenes are also mostly composite crystals of large orthopyroxene cores and thin ca rich overgrowths separate pigeonite and augites are rare on basis of the mineral compositions the cooling rates determined from crystal morphologies and crystal grain size distributions it is deduced that the parent magma of yamato 980459 initially cooled under near equilibrium conditions e g in a magma chamber allowing chromite and the mg rich silicates to form as cumulus phases fractional crystallization at higher cooling rates and a low degree of undercooling let to the formation of the ca al and fe rich overgrowths on olivine and orthopyroxene while the magma was ascending towards the martian surface finally and before plagioclase and also phosphates could precipitate the magma was very quickly erupted quenching the remaining melt to glass dendritic silicates and sulfide droplets the shape preferred orientation of olivine and pyroxene suggests a quick thin outflow of lava according to the shock effects found in the minerals of yamato 980459 the meteorite experienced an equilibration shock pressure of about 20 25 gpa its near surface position allowed the ejection from the planet s surface already by a single impact event and at relatively low shock pressures

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented