recognition and distinction of normal and forced regression in cyclothemic strata a plio pleistocene case study from eastern north island new zealand

forearc uplift and extension southern hawke s bay new zealand mid pleistocene to present the maraetotara plateau cape kidnappers area in southern hawke s bay new zealand lies in the forearc region of the obliquely convergent hikurangi margin where the pacific plate is presently subducting beneath the leading edge of the australian plate uplift accompanied by extensional faulting has been the dominant style of deformation in this area since mid pleistocene time principal strain directions and strain ratios determined from mesoscale fault arrays associated with major faults document the regional extension in the cape kidnappers area fault arrays record plane strain with northwest horizontal extension and vertical shortening in the maraetotara plateau area fault arrays record triaxial strain with roughly equal magnitudes of horizontal extension in two principal strain directions either east west and north south or northwest and northeast and vertical shortening the morphology seismicity and nature and distribution of active faults of the southern hawke s bay region suggest that the maraetotara plateau cape kidnappers area is the on land expression of an outer arc high which is developed between the accretionary wedge on the east and the forearc basin on the west the cause of uplift and extension in the maraetotara plateau cape kidnappers area may be either upper plate deformation related to structural evolution of the outer arc high and underlying backstop underplating on the hikurangi subduction zone or a combination of these processes the uplift and horizontal extension occurring in the maraetotara plateau cape kidnappers area contrast sharply with active deformation in adjacent parts of the forearc reflecting a distinct partitioning of strain in this part of the obliquely convergent plate boundary

origin and causes of the mammoth steppe a story of cloud cover woolly mammal tooth pits buckles and inside out beringia to account for the vastness of the northern arid steppes during glacial episodes i propose the proximate key variable was simply frequent clear skies this hitherto under emphasized point is the hub which best explains many questions low maritime cloud cover best accounts for today s tundra and in a related way the cloudy polar front accounts for the whole of the taiga even during glacial maxima the proximity of the sea to the bering isthmus created intermittent maritime cloud cover this regional cloud cover produced an ecological interruption or buckle of the arid steppe belt while this beringian mesic buckle did not serve as an intercontinental ecological barrier to most steppe adapted species it does seem to have limited the distributions of woolly rhinos camels american kiangs short faced bears badgers and some others at the beginning of the holocene this narrow refugium seems to have been a source of some mesic adapted species which colonized westward into the now tundra vegetation of northern asia and eastward into northern north america this holocene expansion from a limited and regional pleistocene refugium created our present misconceptions about beringia the mid strait mesic ecological conditions were the exception to the more extensive arid adapted communities of the mammoth steppe 2000 published by elsevier science ltd all rights reserved

multiple water isotope proxy reconstruction of extremely low last glacial temperatures in eastern beringia western arctic abstract precipitation isotopes are commonly used for paleothermometry in high latitude regions here we present multiple water isotope proxies from the same sedimentary context perennially frozen loess deposits in the klondike goldfields in central yukon canada representing parts of marine isotope stages mis 4 3 and 2 allowing us to uniquely corroborate fractionations and temperature conversions during these late pleistocene cold stages we include new and existing proxy data from relict wedge ice a direct archive for snowmelt relict pore ice an archive for bulk soil water integrating year round precipitation and hydrated volcanic glass shards and fossil plant waxes which are also thought to integrate year round precipitation but are subject to large fractionations in some cases our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean new transfer functions calibrated specifically for northern north america d precip 3 1 c 1 t 155 and 18 o precip 0 41 c 1 t 20 2 and novel insights on the apparent net fractionation correction for eastern beringian steppe tundra plant waxes e wax precip 59 10 the snowmelt origin of wedge ice ensures a relatively constrained winter spring seasonality of contributing precipitation as supported by the consistency between water isotope measurements from late holocene wedge ice and modern winter spring precipitation wedge ice dating to the transitional mis 3 2 is isotopically depleted relative to modern spring winter precipitation by an amount that indicates a temperature depression of 14 5 c below modern the soil water origin of pore ice and other proxies integrating year round precipitation from soil water allows for a more variable precipitation seasonality the isotopic composition of modern pore ice is consistent with mean annual precipitation however the isotopic composition of pore ice during mis 3 2 converges on wedge ice values signalling an increase in the ratio of cold to warm season precipitation integrated by pore ice during glacial times possibly due to drier summers as supported by the fossil record and climate model simulations in the study region water isotope proxies integrating year round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality as detected here and thus are best interpreted as upper bound estimates based on these proxies we estimate that annual temperatures during mis 4 3 2 and 2 were depressed below the modern climate to a maximum of 18 c 16 c and 21 c 4 5 c respectively our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate and may be particularly important for studies of the major climate transformations over glacial interglacial timescales

late wisconsin environments of the bering land bridge abstract late wisconsin paleobotanical and fossil insect data from the central and northern sectors of the bering land bridge indicate widespread mesic shrub tundra environments even during the last glacial maximum vegetation before the last glacial maximum was a birch heath graminoid tundra with few or no steppe elements shrubs were not an important element of the vegetation but were present in small numbers during the interval 20 000 14 000 yr bp land bridge vegetation was dominated by birch graminoid tundra with small ponds containing aquatic plants heaths were relatively unimportant insects from this interval were indicative of arctic climate with drier tundra than during the late glacial during the late glacial interval 14 000 11 000 yr bp land bridge vegetation was dominated by birch heath graminoid tundra with small ponds choked with aquatic plants the insect record indicates open ground habitats dominated by mesic tundra by 11 000 yr bp insect data suggest that summer temperatures on the emergent bering shelf were warmer than present day upland regions in western alaska summer temperatures on the chukchi shelf were warmer than the present day north slope of alaska contrary to previous hypotheses we found no evidence of steppe tundra on the land bridge new accelerator mass spectrometer ams 14c dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11 000 yr bp

late quaternary mis 3 to mis 1 stratigraphic transitions in a highland beringian landscape along the kuskokwim river alaska stratigraphic records extending to marine oxygen isotope stage mis 3 57 000 29 000 cal yr bp or older in beringia are extremely rare three stratigraphic sections in interior western alaska show near continuous sedimentological and environmental progressions extending from at least mis 3 if not older through mis 1 14 000 cal yr bp present the kolmakof sue creek and vabm vertical angle bench mark kuskokwim sections along the central kuskokwim river once a highland landscape at the fringe of central and eastern beringia contain aeolian deposition and soil sequences dating beyond 50 000 14 c yr bp thick peaty soil shallow lacustrine and tephra deposits represent the mis 3 interstade or older sand sheet and loess deposits wedge cast development and very thin soil development mark the later mis 3 period and the transition into the mis 2 stade 29 000 14 000 cal yr bp loess accumulation with thicker soil development occurred between 16 000 13 500 cal yr bp at the mis 2 and mis 1 transition after 13 500 cal yr bp loess accumulation waned and peat development increased throughout mis 1 these stratigraphic sequences represent transitions between a warm and moist period during mis 3 to a cooler and more arid period during mis 2 then a return to warmer and moister climates in mis 1

cryostratigraphy of the klondike muck deposits west central yukon territory four late quaternary cryostratigraphic units are recognized in the unconsolidated valley bottom deposits of the klondike area yukon territory three of the units in ice rich loessal sediments of pre wisconsinan or wisconsinan age collectively compose the king solomon formation they are overlain by a holocene organic unit the units are distinguished by their cryostratigraphic characteristics and oxygen isotope ratios of included ground ice the basal unit is the last chance creek member a pre late wisconsinan deposit containing preserved ice wedges 18o 28 to 26 d 225 to 209 the overlying quartz creek member a late wisconsinan unit is dominated by organic rich loess massive ice is noticeably absent although the sediments are ice rich the isotopic composition of ice in this unit is characteristic of full glacial conditions 18o 32 to 29 d 234 to 257 an abrupt change to warmer and wetter conditions at the end of glaciation prior to the holocene is recorded by the i

tracking late quaternary extinctions in interior alaska using megaherbivore bone remains and dung fungal spores one major challenge in the study of late quaternary extinctions lqes is providing better estimates of past megafauna abundance to show how megaherbivore population size varied before and after the last extinctions in interior alaska we use both a database of radiocarbon dated bone remains spanning 25 0 ka and spores of the obligate dung fungus sporormiella recovered from radiocarbon dated lake sediment cores spanning 17 0 ka bone fossils show that the last stage of lqes in the region occurred at about 13 ka ago but the number of megaherbivore bones remains high into the holocene sporormiella abundance also remains high into the holocene and does not decrease with major vegetation changes recorded by arboreal pollen percentages at two sites the interpretation of sporormiella was enhanced by additional dung fungal spore types e g sordaria in contrast to many sites where the last stage of lqes is marked by a sharp decline in sporormiella abundance in interior alaska our results indicate the continuance of megaherbivore abundance albeit with a major taxonomic turnover including mammuthus and equus extinction from predominantly grazing to browsing dietary guilds this new and robust evidence implies that regional lqes were not systematically associated with crashes of overall megaherbivore abundance

moraine chronosequence of the donnelly dome region alaska abstract we present 10be exposure ages from moraines in the delta river valley a reference locality for pleistocene glaciation in the northern alaska range the ages are from material deposited during the delta and donnelly glaciations which have been correlated with mis 6 and 2 respectively 10be chronology indicates that at least part of the delta moraine stabilized during mis 4 3 and that the donnelly moraine stabilized 17 ka these ages correlate with other dates from the alaska range and other regions in alaska suggesting synchronicity across beringia during pulses of late pleistocene glaciation several sample types were collected boulders single clasts and gravel samples amalgamated small clasts from around boulders as well as from surfaces devoid of boulders comparing 10be ages of these sample types reveals the influence of pre post depositional processes including boulder erosion boulder exhumation and moraine surface lowering these processes occur continuously but seem to accelerate during and immediately after successive glacial episodes the result is a multi peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly the absence of holocene ages implies relatively minor exhumation and or weathering since 12 ka

tectonic and sea level controls on nontropical neogene limestones in new zealand modern shelf carbonates and neogene on land equivalents have formed upon and adjacent to the new zealand sector of the convergent australia pacific plate boundary they are exclusively skeletal hashes dominated by bryozoans bivalves barnacles and foraminifers typical of nontropical foramol carbonates tectonism has influenced carbonate formation by determining terrigenous sediment supply rates and therefore the dilution factor and has affected the structure of the sea floor by forming imbricate thrust ridges and fault bounded platforms that support the carbonates the neogene limestones are more abundant closer to the plate boundary than their modern counterparts reflecting an increase in tectonism with time in the late pliocene sea level movements combined with uplift of the forearc and transform basins to form widespread limestones only during the glacials

the stratigraphic architecture of late pliocene 2 8 2 4 ma asymmetrical shelf sequences western wanganui basin new zealand abstract the western wanganui basin in the vicinity of parikino contains a 410 m thick succession of thirteen sequences that accumulated between 2 8 and 2 4 ma traditional facies analysis of the succession indicates accumulation of the sequences in shoreface to mid shelf depositional palaeoenvironments the late pliocene sequences have been correlated with oxygen isotope stages g10 to g92 and each of 41 ka glacial interglacial stage couplets is represented by an individual depositional sequence comprising transgressive tst highstand hst and regressive rst systems tracts most sequence boundaries are unconformable and coincide with transgressive surfaces of erosion tse ravinement surface with ophiomorpha burrows extending down into underlying sandstone one sequence boundary at the base of the wilkies shellbed is a correlative conformity two types of shellbed occur within tsts and are associated with key sequence stratigraphic surfaces onlap and backlap shellbed onlap shellbeds onlap the tse and sequence boundary backlap shellbeds result from stratigraphic condensation at the top of the tst and are overlain by the downlap surface dls in most of the sequences the onlap and backlap shellbeds are superposed forming compound shellbeds rarely a downlap shellbed overlies the dls within the base of hsts hsts are composed typically of massive aggradational mid shelf siltstone that grades up into sandstone which forms thick progradational inner shelf to shoreface lithofacies attributed to regressive systems tracts rst lensoidal toplap shellbeds comprised of reworked nearshore storm emplaced fauna occur within the upper part of rsts all of the parikino sequences have asymmetrical architectures with thin tsts this arises because of the very low rates of non tropical carbonate accumulation during the transgressions that is about half of the 41 ka period of each cycle amounting to a few metres at most of shellbed followed by very high rates of terrigenous sediment accumulation during the latter half of cycles an implication of this work is that marked 40 60 m eustatic sea level changes occurred repeatedly during the interval 2 8 to 2 4 ma this implies substantial and successive continental glaciations from at least 2 8 ma probably in the northern hemisphere

full glacial paleosols in perennially frozen loess sequences klondike goldfields yukon territory canada perennially frozen loess deposits in the klondike goldfields include paleosols formed in full glacial environments correlated by alaskan distal tephra with marine isotope stages mis 2 and 4 patterns of organic and inorganic carbon and clay distribution microstructures and profile morphologies indicate that soil formation occurred in a base rich environment in which organic matter accreted predominantly as root detritus at sites approximately 20 km apart the expression of cryoturbation and ice wedge development decreases in strength upward in loess paleosol sequences correlated with mis 4 suggesting increasing aridity configurations of cryoturbation features and ice wedge thaw unconformities the presence of numerous ground squirrel burrows and an absence of peat accumulation suggest that these substrates were predominantly welldrained with active layers of equal or greater thickness than in modern soils on similar sites in the west central yukon some characteristics of these paleosols are similar to those of modern steppe and tundra soils consistent with plant macrofossil evidence for local ecological diversity during full glacial conditions in eastern beringia

application of bryozoan zoarial growth form studies in facies analysis of non tropical carbonate deposits in new zealand abstract the fragmental remains of bryozoan colonies are the dominant skeletal contributor in many modern and ancient occurrences of non tropical shelf carbonate deposits the taxonomic complexity of the bryozoa the difficulties of systematic classification except by specialists the wide range of particle sizes and of preservation state in the carbonate deposits and the often well cemented nature of host limestones all limit the sedimentological interpretation of the commonly diverse bryozoan component however following the pioneer work of stach in the 1930 s the potential exists for sedimentologists to obtain useful paleo environmental information about the deposits by recording simply the nature and relative abundances of the various growth shapes of the bryozoan material known as their zoarial colonial growth forms here we propose a simple descriptive terminology covering both cheilostome and cyclostome bryozoans that involves four main growth forms encrusting erect rigid erect flexible and free living and a selection of subcategories based on shape identification of these habitat related growth form types is aided by reference to line drawings specimen photographs and photomicrographs of thin section slices the scheme is illustrated by examining briefly some possible environmental controls on the spatial and or time variations in the nature and distribution of colonial growth forms in several examples of modern and tertiary bryozoan dominated carbonate deposits in new zealand we anticipate that the routine description and quantification of bryozoan colonial growth types in non tropical carbonates generally will facilitate the recognition and interpretation of contrasting sub facies within the global foramol bryomol group of carbonate deposits

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

pre glacial and interglacial pollen records over the last 3 ma from northwest canada why do holocene forests differ from those of previous interglaciations we synthesize pollen spectra from eleven dated stratigraphic sections from central and northern yukon palaeomagnetic and tephra dating indicates the earliest assemblages representing closed canopy pinus and picea forest are middle late pliocene age more open forest conditions indicated by increased poaceae and with evidence of permafrost are dated at ca 3 ma while pinus pollen is abundant at 3 ma it is reduced in records after 2 6 ma and subsequent pleistocene interglacial forest records are repeatedly dominated by picea along with alnus and small but significant amounts of abies surface sample comparisons indicate that abies was more widespread and abundant in past interglaciations than at present and that middle pleistocene piceaeabies forest grew in the northern yukon porcupine basin 500 km beyond modern abies limits in contrast pinus which occurs today in southern and central yukon was not a significant component of these pleistocene interglacial forests late holocene pollen assemblages with rare abies and high pinus are the most distinct in the past 2 6 ma possible factors driving holocene difference are paleoclimate paludification changes in megafaunal herbivory and an unusual fire regime anthropogenic burning is a factor unique to the holocene and if it is shown to be important in this case it would challenge our notion of what constitutes boreal wilderness

barnacle dominated limestone with giant cross beds in a non tropical tide swept pliocene forearc seaway hawke s bay new zealand abstract pliocene non tropical widespread and locally thick up to 100 m limestones occur in hawke s bay eastern north island where they are intimately associated with very thick 5 km terrigenous dominated neogene sequences that formed in a tectonically active convergent margin setting the non tropical character of the limestones is shown unequivocally by 1 the complete dominance of skeletal calcarenites and calcirudites 2 the occurrence of oyster banks as the only in situ organic structures 3 the dominance of barnacles epifaunal molluscs bryozoans echinoderms foraminifers brachiopods and calcareous red algae as skeletal components and 4 the preponderance of calcite over aragonite in the mineralogy of the skeletal grains and cements the abundance of barnacle fragments in the limestones and the related exclusive occurrence of only one major organic association a barnacle epifaunal bivalve bryozoan assemblage is striking and unusual given the extent of the limestones pecten and oyster valves acted as substrates for barnacle attachment and their growth was promoted by strong tidal paleocurrents that swept the depositional setting a long 450 km narrow 30 50 km forearc basin seaway which formed between an actively deforming subduction complex to the east and an uplifting structural ridge to the west synsedimentary deformation promoted limestone formation on the margins of the seaway by creating current swept clastic free submarine ridges that acted as the sites of carbonate production tidal flows dispersed the carbonate constituents and organised them into a wide spectrum of tide influenced cross bedded and horizontal structures most spectacular are occurrences of giant tabular cross beds with sets 10 40 m thick and foreset dips of 7 36 some interpreted as the deposits of major sand bars on carbonate deltas marginal to the mouths of saddles traversing the rising antiforms and others analogous to modern linear sand ridges the small to large scale planar and trough cross beds and the horizontal and lenticular beds that are invariably associated with the giant cross beds and dominate most sections represent mainly the deposits of sand waves and sand sheets at inner to mid shelf depths in the seaway

arctic ground squirrels of the mammoth steppe paleoecology of late pleistocene middens 24000 29450 14c yr bp yukon territory canada abstract this paper presents paleoecological analyses of 48 fossil arctic ground squirrel spermophilus parryii middens nests and caches recovered from ice rich loess sediments in the klondike region of west central yukon territory ams radiocarbon dates and stratigraphic association of middens with dawson tephra 25 300 14 c yr bp indicate these paleoecological data reflect the onset of glacial conditions of early marine isotope stage mis 2 and terminal mis 3 24 000 29 450 14 c yr bp plant macrofossils include at least 60 plant taxa including diverse graminoids poa elymus trachycaulus kobresia myosuroides steppe forbs penstemon gormanii anemone patens var multifida plantago cf canescens tundra forbs draba spp bistorta vivipara dwarf shrubs salix cf arctica s cf polaris sage artemisia frigida and rare trees picea mariana many of these taxa identified in the middens represent the first recorded fossils for these plants in eastern beringia and add to our knowledge of the floristic composition of pleistocene vegetation and biogeography in this region fossil beetles include typical members of the eastern beringian steppe tundra fauna lepidophorus lineaticollis and connatichela artemisiae and others suggesting predominantly dry open habitats cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens bistorta vivipara kobresia myosuroides ranunculus spp potentilla erysimum cf cheiranthoides poa carex and draba factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the klondike in which they are rare or absent at present this fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well adapted to the open steppe tundra vegetation loessal soils and glacial climates of the mammoth steppe biome

microstratigraphy of calcite cements in pliocene cool water limestones new zealand relationship to sea level burial and exhumation events

a late quaternary record of eolian silt deposition in a maar lake st michael island western alaska abstract recent stratigraphic studies in central alaska have yielded the unexpected finding that there is little evidence for full glacial late wisconsin loess deposition because the loess record of western alaska is poorly exposed and not well known we analyzed a core from zagoskin lake a maar lake on st michael island to determine if a full glacial eolian record could be found in that region particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian silt deposition took place from at least the latter part of the mid wisconsin interstadial period through the holocene based on radiocarbon dating based on the locations of likely loess sources eolian silt in western alaska was probably deflated by northeasterly winds from glaciofluvial sediments if last glacial winds that deposited loess were indeed from the northeast this reconstruction is in conflict with a model derived reconstruction of paleowinds in alaska mass accumulation rates in zagoskin lake were higher during the pleistocene than during the holocene in addition more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape the thinner loess record on land may be due to the sparse herb tundra vegetation that dominated the landscape in full glacial time herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height the lack of abundant full glacial eolian silt deposition in the loess stratigraphic record of central alaska may be due therefore to a mimimal ability of the landscape to trap loess rather than a lack of available eolian sediment

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

a review of the milankovitch climatic beat template for plio pleistocene sea level changes and sequence stratigraphy the milankovitch theory of climate change predicts that global ice volume and hence sea level changes were controlled by long term quasi periodic variations in the earth s orbital parameters obliquity precession and eccentricity d 18 o records from deep sea cores are a proxy for sea level changes and have an orbitally tuned chronology covering the last 5 ma the sea level signal in d 18 o data from east equatorial pacific core v19 30 is well calibrated with sea level data from coral terraces on huon peninsula new guinea over the last 140 ka and with less certainty back to 340 ka over the last 140 ka the sea level contribution to benthic glacial interglacial isotopic variation is about 1 2 1 3 or 0 011 m 1 and for core v19 30 the glacial age temperature contribution from deep ocean cooling of 1 7oc is 0 4 independent constraints on late pliocene sea level changes interpreted from shallow marine continental margin records indicate that the sea level d 18 o calibration may not have been the same over the last 2 6 ma and the temperature correction is unlikely to have been the same in all glacial periods and all ocean settings nevertheless the astronomically tuned isotopic records from deep sea cores provide an accurate chronology and approximate the magnitudes of sea level changes over the last 2 6 ma against which the facies architecture of stratigraphic sequences can be analysed and the concepts of sequence stratigraphy properly evaluated 1998 elsevier science b v all rights reserved

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

sequence stratigraphic context of syndepositional diagenesis in cool water shelf carbonates pliocene limestones new zealand abstract pliocene limestones in eastern north island new zealand are cool water deposits composed of barnacle epifaunal bivalve bryozoan dominated calcitic biota formed in shoal areas about the margins of a tectonically active forearc basin seaway vertical changes in the thickness and depositional facies of the limestones and fundamentally the position and nature of internal bounding discontinuities within them have enabled identification of high order likely 41 ka transgressive deepening upwards and transgressive regressive deepening then shallowing upwards sequences within the formations syndepositional or sea floor or pre compaction diagenesis in the limestones involves a spectrum of destructive to constructive features including skeletal abrasion bioerosion encrustation dissolution and cementation upward changes in the type and extent of these pre compaction diagenetic features within the discontinuity bounded sequences relate closely to the stacking patterns of depositional facies and their associated skeletal and mineralogical composition consequently it has been possible to develop a series of predictive diagenetic models for cool water shelf carbonates deposited upon and about upthrust antiforms in the forearc that integrate their patterns of syndepositional diagenesis into a sequence stratigraphy based framework driven ultimately by relative sea level changes marine constructive diagenesis characterized by bioencrustation turbid cements and interstratified internal sediments occurs most commonly in those facies close to the sequence bounding discontinuities within the lower levels of transgressive systems tracts tsts and the uppermost levels of regressive systems tracts rsts these sediments equate to the highest energy facies upon antiform tops close to the wave abrasion base where sedimentation rates were low in contrast destructive diagenetic processes typically dominate over constructive ones often exclusively so in the upper part of tsts in highstand systems tracts hsts and in the lower portion of rst carbonates where the sediments were not so influenced by active fluid circulation or strong reworking for prolonged periods but were more rapidly buried within accommodation traps below wave abrasion base about the antiforms the link between the facies motifs and synsedimentary diagenesis in these cool water pliocene limestones helps unlock their otherwise often cryptic high order sedimentary architecture such an interpretive opportunity is not afforded by the subsequent post compaction diagenetic features in the limestones because these are no longer closely related to the sedimentation realm

plio pleistocene cliff bound wedge shaped warm temperate carbonate deposits from rhodes greece sedimentology and facies abstract the pliocene to pleistocene temperate carbonates of rhodes were deposited in a tectonically active region strongly influenced by a complicated and rapidly changing topography provided by the highly tectonised late cretaceous lindos limestone as basement rock deposition on this basement took place in accommodation loci restricted to micrograbens and their downslope extension to the foot of steep submarine cliffs to basement neptunian dykes and depressions in the basement rock consequently the sediments comprise a high degree of facies variability and are typically thin and laterally discontinuous the integration of several outcrops is necessary for the reconstruction of the stratigraphy and the relative sea level changes the sediments were deposited during a large scale tectonically driven transgressive regressive cycle in water depths changing from zero to several hundreds of metres at the studied lindos pefkos road cutting the kolymbia limestone bound to the foot of lindos limestone cliffs marks the onset of the marine deposition in the late pliocene its fabric is a rudstone consisting of unsorted angular lindos limestone clasts up to boulder size with a matrix dominated by molluscs and coralline algae the overlying plio pleistocene st paul s bay limestone consists of deep water float and rudstones containing the white coral community dominated by the coral lophelia pertusa its matrix shows a complex fabric of up to five sediment zones separated by differing states of lithification in this maximum flooding phase mineralised hardgrounds indicate depositional hiati the subsequent shallowing phase is represented by the cape arkhangelos calcarenite a series of distinctive facies of very patchy distribution they are characterised by the bryozoan brachiopod facies overlain by a facies heavily dominated by the bivalve mytilaster sp mytilaster facies conspicuous for the mytilaster facies is the inverse concave up stacking pattern of shelly material this facies is followed by a serpulid framestone and associated serpulid rudstone neptunian dykes cut through the first two facies and are filled with an intraformational breccia grading into a breccia with abundant mytilaster facies clasts neptunian dyke facies the sedimentology and interpretation of each facies include a description of the ichnology in particular the bioerosion peculiar to each facies the separation of different gravity transport processes in steep submarine environments is rarely described and most of the literature concentrates on siliciclastic dominated coarse grained sandy or gravely sand delta environments for a classification of the transport processes of the examined deposits the following criteria were evaluated sediment body symmetry inclination of the palaeorelief sediment constituents fabric complexity sedimentary structures and availability of fine matrix sedimentary structures and grading can be camouflaged in carbonates due to density differences of bioclasts however bioclast orientations such as bivalve stacking patterns can give information about the sedimentary process we suggest the inverse concave up stacking pattern of bivalve shells to be a texture potentially indicative for debris falls because of the above mentioned criteria we classified the kolymbia limestone as rock fall deposits and the st paul s bay limestone as well as the mytilaster facies of the cape arkhangelos calcarenite as debris fall deposits the bryozoan brachiopod facies could not be classified with certainty because of the lack of sedimentary structures and bioclast orientation however a grain flow or most likely a debris fall transport process seems probable

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

comment on environmental setting micro morphologies and stable c o isotope composition of cold climate carbonate precipitates a review and evaluation of their potential as paleoclimatic proxies by denis lacelle quaternary science reviews 26 1670 1689

late cretaceous heterozoan carbonates palaeoenvironmental setting relationships with rudist carbonates provence south east france abstract during late cretaceous coniacian early santonian times heterozoan rich bioclastic carbonates prevailed in the provence platform area they substituted for rudist rich carbonates which flourished during the late turonian in the same area this article presents a detailed sedimentological study of these heterozoan rich carbonates carried out in the mejean syncline west of marseille at this locality the thickness of the bioclastic series exceeds 500 m the heterozoan carbonates are referred mainly to packstones and grainstones organized in meter thick cross bedded sedimentary strata microfacies analysis has shown that bryozoans red algae and echinoderms are the main skeletal constituents mixed with reworked fragments of rudists and benthic foraminifera detritic elements are mainly represented by quartz and glauconite grains in the study area heterozoan carbonates underwent a complex diagenetic evolution iron precipitation occurred early in environments with high carbonate productivity and a high hydrodynamic level early marine cements developed mainly in the upper portions of shallowing upward parasequences during intervals with decreasing sedimentation rates late burial cements occurred sequentially as syntaxial rim cements dentate calcite crystals and blocky calcite during the mesogenetic burial history microstylolitisation developed in the packstones deposition of the heterozoan carbonates began during the transgressive coniacian cycle following a relative sea level fall recorded in the late turonian bioclastic sedimentation rates during the coniacian vary between 74 and 88 m myr a value similar to that recorded in the holocene australian and new zealand shelves coniacian santonian heterozoan carbonates had a widespread palaeogeographic distribution in south east france and sardinia the availability of hard substrates due to a high hydrodynamic level during the coniacian transgression was a major cause for the development of the heterozoan association as a whole likewise iron rich terrigenous supply and upwelling patterns probably enhanced nutrients on the shelf and favoured in turn the development of suspension feeders and mesotrophic organisms possible open marine relatively deep cool water conditions were responsible for the deposition of the heterozoan association versus the photozoan rudist association during the coniacian this latter association progressively recovered and thrived when shallow marine warm water conditions re established during the santonian comparisons are made with modern analogue environments in which heterozoan dominated cool water carbonate sedimentation occur

paleoecology of beringian packrat middens from central yukon territory canada rodent middens from ice rich loess deposits are important new paleoenvironmental archives for eastern beringia plant macrofossils recovered from three middens associated with dawson tephra ca 24 000 14 c yr b p at two sites in yukon territory include diverse graminoids forbs and mosses these data suggest substantial local scale floristic and habitat diversity in valley settings including steppetundra on well drained soils moist streamside meadows and hydric habitats fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during pleistocene glacial periods than at present on north facing slopes d 2004 university of washington all rights reserved

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

age and significance of the late pleistocene dawson tephra in eastern beringia abstract dawson tephra recently recognized in the klondike area of yukon territory records one of the largest quaternary volcanic eruptions in beringia its composition is similar to that of old crow tephra indicating a source in the aleutian arc alaska peninsula region of southwestern alaska its primary thickness in central yukon is nearly twice that of old crow tephra which has an estimated eruption volume of 50 km 3 the distribution of dawson tephra is still poorly known but based on its source area and occurrence in central yukon it should be widespread across southern alaska yukon and the gulf of alaska new radiocarbon ages indicate the eruption occurred at about 24 000 14 c yr bp ca 27 000 cal yr bp the dawson tephra is a valuable marker bed for correlating late pleistocene records across large areas of eastern beringia and adjacent marine records

on the nature and origin of muck deposits in the klondike area yukon territory organic rich muck deposits which blanket auriferous gravels in the klondike area yukon territory comprise two principal stratigraphic units i a silty late pleistocene deposit and ii holocene organics lying unconformably on the silt the deposits are found predominantly in valley bottoms and if undisturbed are normally perennially frozen field and laboratory investigations of particle size mineralogy and morphology as well as organic matter and sedimentary structures indicate that the silt is both primary massive and redeposited bedded loess by weight 87 medium and coarse silt and fine sand radiocarbon dates indicate that the loess was deposited during late wisconsinan mcconnell glaciation beginning after 27 000 14c years bp the loess was likely derived from the floodplain of the yukon river during periods of low flow turf in growth position and organic matter in the silt similar to that of loessal grasslands near kluane lake suggest a grassland environment for the area during

seasonality of the late pleistocene dawson tephra and exceptional preservation of a buried riparian surface in central yukon territory canada abstract the late pleistocene dawson tephra was deposited by one of the largest quaternary eruptions in northwestern north america its distribution is known sparsely from sites near the source area in southwestern alaska and central yukon territory where more than 20 occurrences are documented in the klondike region dawson tephra erupted about 25 300 14 c yr bp near the onset of the last glaciation and provides a stratigraphic marker across eastern beringia we report radiocarbon ages paleobotanical data and cryostratigraphic observations from a new dawson tephra locale at goldbottom creek in the klondike region of yukon territory which collectively indicate that the eruption occurred in the late winter or early spring multiple fining upward tephra rich ice beds are interpreted as remnants of surface icings which presently are common in the region during spring a buried in situ riparian meadow preserved below the icing and tephra consists of abundant tufted hair grass deschampsia caespitosa with interspersed horsetails equisetum cf palustre and mosses detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits consistent with a late season surface when the icing was active the extraordinary thickness of dawson tephra in central yukon likely reflects reworking of a winter deposited tephra by snow melt in the spring following the eruption indicating that the primary thickness may be overestimated at valley bottom sites winter deposition of the tephra may have in part minimized the terrestrial ecological impacts of the eruption on zonal steppe tundra vegetation through the retransportation of tephra from hillslopes to the riparian areas where the tephra became incorporated into local fluvial systems

dune stabilization in central and southern yukon in relation to early holocene environmental change northwestern north america abstract eolian deposits of central and southern yukon northwestern canada consist of loess mantles small areas of active dunes and larger stabilized dune fields dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation infrared stimulation luminescence irsl dating in central and southern yukon reveals that these dune fields stabilized as late as 9 8 5 ka well after the retreat of cordilleran glaciers these findings are comparable to other valley setting dune fields and loess from central alaska which record activity during the period from the lateglacial to the holocene thermal maximum htm and reduced or altered activity after 9 8 ka post glacial dune activity was most likely related to warm dry conditions during the htm under predominantly shrub tundra vegetation early holocene stabilization of these dunes probably occurred in response to cooler moister conditions and replacement of predominantly tundra by boreal forest cover dominated by spruce stabilization of dune fields in southern yukon and alaska most likely represented an extension of the time transgressive stabilization of dune fields that occurred across northwestern north america with the post glacial expansion of the boreal forest

post glacial sea level control and sequence stratigraphy of carbonate terrigenous sediments wanganui shelf new zealand abstract shallow marine mixed carbonate terrigenous sediments have been accumulating in water depths of 20 110 m on wanganui shelf central western new zealand during the latest quaternary post glacial sea level rise since about 18 000 years bp cores show an upward change from coarse mostly terrigenous dominated sands and gravels to shell rich sediments and then to terrigenous dominated muddy very fine sands and sandy muds these post glacial carbonate terrigenous sediments are a modern analogue for similar episodes of cyclothemic shelf deposition that characterise onland plio pleistocene sections in central western new zealand like their ancient counterparts the latest quaternary sediments can be interpreted in a sequence stratigraphic context a transgressive systems tract 4 15 m thick overlies a transgressive erosion surface evident on seismic reflection records and is represented by slightly shelly coarse sands and gravels at the base of several cores and as palimpsest surficial deposits on the modern shallow shelf out to a depth of about 50 m the overlying shelly deposits both shell rich and matrix rich are equivalent to mid cycle or backlap shellbeds described elsewhere they comprise a diverse in situ or locally transported bivalve molluscan and bryozoan biota typical of temperate latitude cool water carbonate shelf facies these condensed section shellbeds are up to at least 1 5 m thick gradationally overlie the transgressive sediments in cores and occur as modern surficial shelf facies between about 25 and 100 m water depth cores are locally capped by up to a few metres of terrigenous sands or muds that represent highstand systems tract deposits fed onto the shelf from opposing onshore and offshore directions in the nearshore region north island derived felsic fine sands are beginning to prograde seawards westwards across the shellbeds while in the offshore zone south island derived micaceous very fine sands and muds are encroaching upon and covering the shellbeds from the west and south

palaeobotanical evidence for warm summers in the east siberian arctic during the last cold stage plant macrofossils from the mamontovy khayata permafrost sequence 71 60 n 129 25 e on the bykovsky peninsula reflect climate and plant biodiversity in west beringia during the last cold stage 70 ams and 20 conventional 14c dates suggest sediment accumulation between about 60 000 and 7500 14c yr b p the plant remains prove that during the last cold stage arctic species minuartia arctica draba spp kobresia myosuroides coexisted with aquatic potamogeton vaginatus callitriche hermaphroditica littoral ranunculus reptans rumex maritimus meadow hordeum brevisubulatum puccinellia tenuiflora and steppe taxa alyssum obovatum silene repens koeleria cristata linum perenne the reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast yakutian relict steppe areas thus productive meadow and steppe communities played an important role in the siberian arctic vegetation during the late pleistocene and could have served as food resource for large populations of herbivores the floristic composition reflects an extremely continental arid climate with winters colder and summers distinctly warmer than at present holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression increased oceanic influence and atmospheric humidity although some steppe taxa were still present in the early holocene they disappeared completely before 2900 14c yr b p

late pleistocene climates of beringia based on analysis of fossil beetles thirty one fossil beetle assemblages from central and eastern beringia alaska the yukon territory and the now submerged bering land bridge have yielded seasonal temperature estimates for the interval 43 550 9250 14c yr before present yr b p estimates of the mean temperature of the warmest tmax and coldest tmin months were derived by the mutual climatic range method assemblages from northern and western sites show a mid wisconsin interstadial tmax warming from 35 000 30 000 yr b p this warming is less pronounced in assemblages for interior regions there is little or no beetle evidence for the spread of coniferous forest in eastern beringia during this interstade except for in parts of the yukon territory during the last glacial maximum tmax values were depressed by about 2 2 5 c in arctic regions of beringia and by about 4 c in the interior tmin values were about 8 c colder in both regions tmax and tmin values rose rapidly at northern sites after 12 000 yr b p seasonal temperatures peaked at 11 000 yr b p just as the bering land bridge was inundated this was followed by a sharp climatic cooling between 11 000 and 10 000 yr b p the equivalent of a younger dryas cooling in eastern beringia

early wisconsinan mis 4 arctic ground squirrel middens and a squirrel eye view of the mammoth steppe abstract fossil arctic ground squirrel spermophilus parryii middens were recovered from ice rich loess sediments in association with sheep creek klondike and dominion creek tephras ca 80 ka exposed in west central yukon these middens provide plant and insect macrofossil evidence for a steppe tundra ecosystem during the early wisconsinan mis 4 glacial interval midden plant and insect macrofossil data are compared with those previously published for late wisconsinan middens dating to 25 2914c ka bp mis 3 2 from the region although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils the co occurrence of steppe tundra plants and insects e g elymus trachycaulus kobresia myosuroides artemisia frigida phlox hoodii connatichela artemisiae provides evidence for successive reestablishment of the zonal steppe tundra habitats during cold stages of the late pleistocene arctic ground squirrels were well adapted to the cold arid climates steppe tundra vegetation and well drained loessal soils that characterize cold stages of late pleistocene beringia these glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of alaska and yukon including the klondike where they are absent today arctic ground squirrels have endured numerous quaternary climate oscillations by retracting populations to disjunct interglacial refugia during warm interglacial periods e g south facing steppe slopes well drained arctic and alpine tundra areas and expanding their distribution across the mammoth steppe biome during cold arid glacial intervals

composite sedimentary record of falling stages of pleistocene glacio eustatic cycles in a shelf setting crotone basin south italy abstract a thick pleistocene shelf and nearshore cyclical succession was deposited in the s mauro sub basin of the crotone basin southern italy the regressive units of the cycles are mostly represented by coastal siliciclastic and bioclastic prograding wedges showing a clinoform geometry these are separated by blanket like deposits of high lateral persistence recording major transgressive episodes the aim of this paper is 1 to describe facies patterns and depositional setting of two prograding wedges particularly focussing on their polycyclic internal architecture 2 to analyze these units within a sequence stratigraphic framework and 3 to speculate on the possible origin of the small scale cyclicity the two wedges analyzed in this paper consist of a number of shingles individual shingles consist of two physically connected units 1 a relatively thin package of sigmoid clinoforms grading into 2 a volumetrically dominant package of oblique tangential clinoforms with toplap terminations the shingles are bounded by seaward dipping surfaces with sigmoid clinoform geometry which are ravinement surfaces updip passing into conformable flooding surfaces downdip the wedges are thus organized into high frequency small scale sequences each comprising transgressive highstand and falling stage systems tracts as a whole individual prograding wedges are interpreted as forced regressive units as the shoreline was subject to an overall shift basinwards and downwards along a low angle trajectory in spite of the repeated minor relative sea level rises tectonic subsidence and particularly the syndepositional growth of gentle synclines are thought to have been the key factors allowing the preservation of these forced regressive units progradation of the wedges took place in a high energy wave climate characterized by high frequency of storms and very efficient alongshore redistribution of sediments recurrent storm driven offshore currents led to intense reworking of sediments on the topset platform and gravity spreading on the foreset slope of the prograding wedges well oxygenated conditions over the shelf due to intensified storm activity during glacial periods may have enhanced the rate of production of skeletal foramol type carbonates it can reasonably be assumed that progradation took place from a line source and that the sand bodies are to be regarded as coastal prograding bodies in spite of active syndepositional tectonics the cycles can be correlated to pleistocene high amplitude sea level oscillations the older of the two wedges can be correlated through bio magnetostratigraphy to the major climatic transition which occurred from the marine oxygen isotope stage 25 to 24 22 rio et al 1996 the younger probably developed during the sea level fall that ended with substage 18 2 as suggested by sequence and bio stratigraphic data the prograding wedges are thus interpreted to record long lived sea level falls of fourth order cycles due to the particular depositional setting we are inclined to exclude authigenic mechanisms in the origin of small scale cyclicity although the concomitance and interaction of different controlling factors may be taken into account it is tempting to ascribe this cyclicity to minor eustatic changes punctuating long lived erratic falling stages possibly accompanied by climate driven fluctuations of sediment supply shelf perched and shelf edge prograding units consisting of foramol type carbonates are apparently a common falling stage to lowstand depositional feature in the mediterranean area during the late pliocene and pleistocene

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

global cyclostratigraphy a model of carbonate growth patterns abstract cyclostratigraphy is the study of cyclic depositional patterns produced by climatic and tectonic processes a global scale quantitative cyclostratigraphic model is described which simulates carbonate growth patterns controlled by tectonic and climatic processes the model uses seven factors simulating the effects of physical and chemical environments on the deposition rates of carbonate accumulations these factors are sea level change the rate of basement subsidence food supply influence of nutrients available sunlight temperature salinity and dissolved oxygen the factors are considered as functions of climatic and tectonic processes the model also integrates milankovitch induced short term climatic changes with the long term tectonic evolution of basins to examine the potential carbonate accumulation patterns the two dimensional computer model results provided here show that 1 carbonate growth patterns in different climates and under different tectonic processes can be modelled quantitatively 2 carbonate production increases towards the equator decreasing latitude as the temperature and nutrition supply increase in tropical belts and production changes because of expansion or contraction of the tropical belt in different climatic periods 3 when matched with the turbidity the model describes different carbonate accumulation patterns in different climatic patterns 4 at either abnormally high or low salinity carbonate accumulation rates decline sharply and the salinity becomes normal away from the strand line and 5 cyclic sea level changes cause a cyclic change of carbonate accumulation a case study is presented from the upper pennsylvanian of texas the simulation results indicate that carbonate growth patterns observed from field well or seismic data are accurately modelled by the quantitative procedure given here

last interglacial western camel camelops hesternus from eastern beringia abstract western camel c hesternus fossils are rare from eastern beringia thus there is little available information on their chronology paleoecology and biogeography in this region in august of 2010 a partial proximal phalanx of a western camel was recovered from a sedimentary exposure along the white river in the formerly glaciated terrain of southwest yukon northwest canada the fossil specimen was recovered in situ from sediments that are correlated by stratigraphic tephra and radiocarbon data to the marine isotope stage mis 5 interglacial period sangamonian associated paleoenvironmental data indicates that this western camel inhabited a shrub tundra ecosystem that did not include spruce trees or boreal forest during a relatively cold interval between mis 5e and 5a this is the oldest reliably dated western camel fossil from eastern beringia and supports the model of range expansion for this species to the high latitudes of northwest north america during the last interglacial sensu lato

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr