coastal landscape evolution as a function of eustasy and surface uplift rate cascadia margin southern oregon we explore the relative importance of eustatic versus tectonic factors in sculpting preserving and modifying coastal landforms the study area is a 30 km coastal reach in southern oregon using degree of soil development as a means of correlating wave cut platforms along the coast we document that surface uplift rate is variable in a shore parallel sense variability being a function of differential vertical displacement of crustal blocks along faults and flexures in the upper plate of the cascadia subduction zone a consequence of this variability is that in areas of moderate uplift rate 0 7 0 9 m k y flights of up to seven emergent wave cut platforms are preserved along the interfluves of coastal drainages whereas in areas of low uplift rate 0 05 0 2 m k y only one wave cut platform commonly exists within a few meters of present sea level preservation of shore platforms in both areas is the result of the inter action of tectonic uplift and eustatic sea level changes operating on a high energy coast subject to platform planation platform reoccupation can be a consequence of late pleistocene eustatic sea level changes operating on low up lift rate coasts particularly in the cases of the 200 ka and 125 ka high sea stands reoccupation by the later highstand is probable when coastal uplift rates are about 0 2 m k y the same eustatic history operating on a higher uplift rate section of the coast results in multiple emergent platforms and no instances of reoccupation coastal drainage basins in the size range of 5 10 km2 have different hypsometries reflecting whether platforms in coastal basins are preserved over a range of altitudes or only near sea level the hypsometric differences are thus a product of differences in uplift rate the dominant mechanism of base level fall varies between the two areas coastal retreat during sea level highstands drives baselevel fall in lower uplift rate basins whereas tectonic uplift mainly drives base level fall in moderate uplift rate basins even though the magnitude of coastal retreat may be about the same in the two areas where coastal retreat largely provides the mechanism for base level fall steep coastal drainages discharge their debris onto coastal piedmonts benches and the resultant alluvial fans prograde over marine deposits in southern oregon the alluvial fan building episode was relatively short about 2 20 k y in duration fan aggradation ceased as a consequence of fan entrenchment most likely brought on by buildup and steepening of the fan over time

on late miocene abyssal hydrography abstract this contribution is a summary of our studies on late miocene isotope stratigraphy we interpret the results using simple models and present additional evidence that the 13 c shift at 6 2 ma was a time stratigraphic event the average deep water metabolic co 2 and nutrient content remained unchanged across the 13 c shift but the net flow of deep waters towards the north pacific was intensified the late miocene deep ocean density structure was similar to that of today s oceans and bottom water temperatures were 1 c warmer if constant ice volume is assumed

neogene stratigraphy foraminifera diatoms and depositional history of maria madre island mexico evidence of early neogene marine conditions in the southern gulf of california abstract foraminifera and diatoms have been analyzed from an upper miocene through pleistocene sequence of marine sediments exposed on maria madre island largest of the tres marias islands off the pacific coast of mexico the neogene stratigraphic sequence exposed on maria madre island includes a mid miocene non marine and or shallow marine sandstone unconformably overlain by a lower upper miocene to uppermost miocene upper to middle bathyal laminated and massive diatomite mudstone and siltstone unit this unit is unconformably overlain by lower pliocene middle to lower bathyal sandstones and siltstones which in turn are unconformably overlain by upper pliocene through pleistocene upper bathyal to upper middle bathyal foraminiferal limestones and siltstones these beds are unconformably capped by pleistocene terrace deposits basement rocks on the island include cretaceous granite and granodiorite and tertiary andesites and rhyolites the upper miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of bolivina indicating low oxygen conditions in the proto gulf maria madre basin the diatomaceous unit grades into a mudstone that contains a latest miocene upper to middle bathyal biofacies characterized by baggina californica and uvigerina hootsi along with displaced neritic taxa an angular unconformity separates the upper miocene middle bathyal sediments from overlying lower pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including neogloboquadrina acostaensis and pulleniatina primalis indicating an early pliocene age significantly this pliocene unit contains common occurrences of benthic species restricted to miocene sediments in california including bulimina uvigerinaformis pliocene to pleistocene foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the tres marias island area and include abundant planktonic foraminifera such as pulleniatina obliquiloculata and neogloboquadrina duterteri common benthic foraminifera in this unit are indicative of upper bathyal water depths the neogene depositional history recorded on maria madre island involves an early late miocene subsidence event marking formation of the tres marias basin with relatively undiluted diatomaceous sediment deposited in a low oxygen setting subsidence and deepening of the basin continued into the early pliocene along with rapid deposition of terrigenous clastics uplift of the basinal sequence began in late pliocene time accompanied by deposition of upper pliocene pleistocene foraminiferal limestones on a rising submarine bank continued episodic uplift of the neogene deposits brought the island above sea level by late pleistocene time

response of deep sea benthic foraminifera to miocene paleoclimatic events dsdp site 289 abstract changes in the miocene deep sea benthic foraminifera at dsdp site 289 closely correlate to the climatically induced variations in deep and bottom waters in the pacific ocean in early miocene time oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated benthic foraminiferal assemblages are characterized by various species inherited from the oligocene expansion of the antarctic icecap in the early middle miocene 14 16 m y ago increased oxygen isotope values produced cold more oxygenated bottom waters and lead to a turnover in the benthic foraminifera an oligocene early miocene assemblage was replaced by a cibicidoid dominated assemblage some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean in mid miocene time epistominella exigua and e umbonifera indicative of young oxygenated bottom waters are relatively common at dsdp site 289 further glacial expansion 5 9 m y ago lowered sealevel increased oceanic upwelling and associated biological productivity and intensified the oxygen minima abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as e umbonifera becomes common to abundant below 2500 m by late miocene time benthic faunas similar in species composition and proportion to modern faunas on the ontong java plateau had become established

deep water circulation in the northeast atlantic and climatic changes during the late neogene dsdp site 141 abstract oxygen and carbon stable isotope data of pyrgo murrhina and flux rates of calcium carbonate in the bio and magnetostratigraphically dated sediment sequence at dsdp site 141 were used for a reconstruction of the deep water circulation in the northeast atlantic during late miocene and pliocene times a distinct change towards reduced advection of deep water recorded near 5 4 ma is contemporaneous with the cessation of the outflow of the saline mediterranean water into the atlantic during the pliocene between 4 5 and 2 75 ma and between 2 1 and 1 8 ma north atlantic deep water nadw circulation was sluggish and site 141 possibly influenced by antarctic bottom water aabw near 2 75 ma the advection of well oxidized nadw was strongly intensified this change is related to an onset of major arctic ice growth and or a major cooling of nadw

late miocene paleoclimatology subantarctic water mass southwest pacific abstract the late miocene early pliocene paleoclimatic history has been evaluated for a deep drilled sediment sequence at deep sea drilling project site 281 and a shallow water marine sediment sequence at blind river new ealand both of which lay within the subantarctic water mass during the late miocene a major faunally determined cooling event within the latest miocene at site 281 and blind river coincides with oxygen isotopic changes in benthonic foraminiferal composition at dsdp site 284 considered by shackleton and kennett 1975 to indicate a significant increase in antarctic ice sheet volume however at site 281 benthonic foraminiferal oxygen isotopic changes do not record such a large increase in antarctic ice volume it is possible that the critical interval is within an unsampled section no recovery in the latest miocene two benthonic oxygen isotopic events in the late miocene 0 5 and 1 in the light direction may be useful as time stratigraphic markers a permanent negative carbon isotopic shift at both site 281 and blind river allows precise correlations to be made between the two sections and to other sites in the pacific region close interval sampling below the carbon shift at site 281 revealed dramatic fluctuations in surface water temperatures prior to a latest miocene interval of refrigeration kapitean and a strong pulse of dissolution between 6 6 and 6 2 0 1 m y which may be related to a fundamental geochemical change in the oceans at the time of the carbon shift 6 3 6 2 m y no similar close interval sampling at blind river was possible because of a lack of outcrop over the critical interval paleoclimatic histories from the two sections are very similar surface water temperatures and antarctic ice cap volume appear to have been relatively stable during the late middle early late miocene early late tongaporutuan by 6 4 m y cooler conditions prevailed at site 281 between 6 3 and 6 2 0 1 m y the carbon isotopic shift occurred followed within 100 000 yr by a distinct shallowing of water depths at blind river the earliest pliocene opoitian is marked by increasing surface water temperatures

miocene biochronology and paleoceanography of the north pacific abstract biostratigraphic correlation based on microfossil datum levels directly or indirectly tied to the paleomagnetic time scale provides a high resolution time control for the miocene in the equatorial and middle latitude north pacific faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen pacific faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers reveal the paleoclimatic and paleoceanographic history the planktic foraminiferal assemblage change in the early miocene extinction of oligocene fauna and rise of a highly diverse neogene fauna appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum antarctic circulation an increase in the siliceous productivity in the eastern equatorial pacific region between 20 and 18 ma suggests that the vertical and horizontal circulation was intensified at that time climates cooled rapidly during the middle miocene between 14 and 13 ma suggesting the growth of a major east antarctic ice sheet paleoclimatic conditions remained generally cool although oscillating during the late miocene in the late early to middle miocene faunal provincialism developed between low and middle latitudes and by late miocene time a distinct provincialism similar to the present was established

atlantic mediterranean water exchange during the late neocene the nature of water exchange between the mediterranean and the atlantic is examined for three time periods during the late neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans the large volume of carbonates and evaporites deposited in the mediterranean during the messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate resulting in increased dissolution of deep sea carbonates during the latest miocene during the earliest pliocene an estuarine type of flow existed between the atlantic and mediterranean waters entered the mediterranean at depth and flowed out at the surface benthic foraminiferal stable isotopic evidence from the north atlantic indicates that north atlantic deep water nadw was produced throughout the early pliocene and that the absence of saline mediterranean outflow did not have a significant effect on bottom water production eustatic lowering of sea level during the last glacial maximum 18 000 years b p reduced water exchange between the atlantic and the mediterranean as a result salinities in the mediterranean increased substantially but it seems unlikely that diminished nadw production during the last glacial episode can be attributed to a reduction in mediterranean outflow

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

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

stable isotopes in benthic foraminifera from ontong java plateau box cores erdc 112 and 123 abstract detailed oxygen and carbon isotope stratigraphies for two species of benthic foraminifera planulina wuellerstorfi oridorsalis umbonatus are compared between two box cores spanning the period of deglaciation and holocene within core stratigraphies are quite well correlated between core signals less so vertical mixing and possibly horizontal redeposition processes disturb the signals nevertheless there is a strong suggestion of fluctuations in the ambient bottom water conditions fo the entire time span considered

late neogene paleoceanography and paleoclimatology of the gulf of aden region based on calcareous nannofossils quantitative study of climatically sensitive nannofossils in the sediments of the gulf of aden has provided a climatic and oceanographic scenario for the northwestern indian ocean during the late neogene the surface water temperature was relatively cold during the latest middle miocene to late miocene 10 7 to 6 32 ma with a probable warm interval in the early late miocene 9 82 to 8 49 ma this cooling is attributed to increased upwelling in the northwestern indian ocean the surface water was relatively warm from the latest late miocene to the middle of the late pliocene 6 32 to 2 59 ma the most intense cooling took place during the late pliocene to early pleistocene 2 59 to 1 69 ma intense upwelling during this interval coincides with worldwide climatic deterioration a probable short warm interval 1 69 to 1 59 ma followed this cold interval in the pleistocene the surface water was cold from 1 59 to 1 00 ma and from 0 61 to 0 24 ma and warm from 1 00 to 0 61 ma and after 0 24 ma

miocene benthic foraminiferal isotope records a synthesis abstract 18 o 16 o and 13 c 12 c ratios of miocene benthic foraminifera from a number of atlantic pacific and indian ocean dsdp sites 71 77b 206 208 238 279 289 296 329 357 and 366a have been compiled these provide a rather detailed history of miocene deep water especially in the pacific ocean bottom water temperatures rose during the early miocene and then declined rapidly during the middle miocene this decline was accompanied by an increase in antarctic glaciation late miocene bottom temperatures and antarctic ice volumes are inferred to be similar to today s but exhibited some fluctuation the early miocene ocean was less thermally stratified at intermediate and abyssal depths while the late miocene deep ocean had a thermal structure generally similar to the modern ocean foraminiferal carbon isotope ratios at most of the sites varied quasi sympathetically throughout the miocene these variations must reflect comparable variations in the mean 13 c 12 c of marine hco 3 however the causes of such variations are not yet clear

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

pacific miocene carbon isotope stratigraphy using benthic foraminifera abstract seven miocene pacific ocean deep sea drilling project sites from four different water masses planktonic foraminiferal biogeographic regions have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal 13c records in dsdp site 289 the correlations are based on the assumption that there are global or at least pacific wide controls on the 13c of deep water hco3 each of the individual 13c records is correlated to site 289 based on the shape of the curves in a manner analogous to that used to correlate sea floor magnetic anomaly patterns the results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to 100 000 years correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than 200 000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized globally applicable correlation tool with an interregional precision of 100 000 years or better as more continuous and undisturbed deep sea sections become available as a result of the hydraulic piston coring program

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval

major neogene events of the southeastern pacific the chilean and peruvian record abstract according to the biochronostratigraphic model proposed the neogene marine deposits in chile and peru represent two independent transgressive sequences alloformations separated by a major regional hiatus the earlier sequence nseps i would stretch from the top of the early miocene up to the base of the late miocene ca 19 10 m y b p the upper sequence nseps ii would correspond in turn to the late pliocene ca 3 5 1 6 m y b p the regional hiatus separating both sequences would encompass the late miocene and the early pliocene ca 10 3 5 m y b p the planktonic foraminiferal events described suggest an age of terminal early miocene middle miocene and late pliocene respectively the paleoclimatic events recorded are three a warming event lasting from the terminal early miocene to the end of the middle miocene mmwe 18 11 5 m y b p a cooling event of the middle late pliocene lpce 2 5 0 2 m y b p and warming event spanning most of the late pliocene lpwe 3 5 2 2 m y b p restricted to the surface and intermediate sea waters of the middle and low latitudes the last paleoclimatic event not recorded as such so far is both synchronous and mutually exclusive in latitudinal terms with the second one three tectonic regional events are analyzed the quechuan 1 phase 19 1 5 m y b p the quechuan 2 phase 10 1 m y b p and the geographic rhodanian phase 3 5 0 5 m y b p in the studied area there is no late miocene marine sedimentary record to confirm the terminal tortonian or quechuan 3 tectonic phase ca 7 m y b p admitted to occur in the volcanoclastic continental sequences of northern chile and southern peru