a new 122 mm electromechanical drill for deep ice sheet coring disc 4 drill cable the deep ice sheet coring disc drill developed by ice coring and drilling services icds under contract with the us national science foundation requires a drill cable capable of transmitting high amounts of electrical power as well as high rates of data the disc cable was designed and manufactured by the rochester corporation to core ice to depths of 4000 m in addition to the steel strength members to support the drill the cable has copper wires for conducting electrical power for the drill sonde cutter pump motors and the sonde electronics and an optical fiber core for data transmission the outer steel layers are filled with a special compound to minimize fluid penetration of the cable

cretaceous paleogeography of southern south america abstract during berriasian hauterivian times the andean regions north of 38 s and south of 42 s were occupied by two magmatic island arcs and two back arc marine basins the andean and austral basins at the same time the chubut basin of central patagonia was being filled with continental sediments in northern argentina and bolivia the aimara basin began to develop with deposition of continental sediments intercalated with basaltic rocks in northeastern argentina paraguay uruguay and southern brazil a series of basins formed in precambrian paleozoic basement were the site of continental sedimentation and eruption of basic flows in barremian cenomanian times the uplift of the cordillera principal of argentina and chile began and a general regression occurred in the andean and austral basins continental sedimentation prevailed in the chubut basin of central patagonia as well as in all other basins of central northern and eastern argentina and southern brazil in bolivia a shallow marine transgression occurred during cenomanian time and in the santos basin of southern brazil a proto oceanic stage is represented by aptian evaporites in turonian coniacian santonian campanian times most of the andean area was uplifted and thick volcanic and volcanoclastic sequences were accumulated in a series of restricted continental basins along the andes of central and northern chile in the easternmost areas south of 33 s red continental sediments were deposited in the austral basin marine sedimentation was restricted to the southern part most of the parana basin was emergent although in the northern areas continental sedimentation continued in northern argentina and bolivia continental sediments with interbedded basalts and shallow marine deposits were accumulated the atlantic basins of southern brazil were characterized by marine sedimentation and the salado basin was the site of continental deposition in maastrichtian time sedimentation was discontinued in the continental basins of west central argentina and central and northern chile although volcanism was still active the marine area of the austral basin became more restricted a large region of northern patagonia northeastern argentina and bolivia were covered by a shallow sea and some restricted marine basins were developed on the coast of central chile marine sedimentation was also continuous in the atlantic basins of southern brazil and central argentina continental deposition was restricted to central patagonia and the intracratonic parana basin of southern brazil there was a correlation between diastrophism magmatic activity and global cycles of sea level changes contemporary regression existed in areas such as the andean basin where tectonic vertical movements were greater than eustatic changes of sea level the cretaceous flora is mostly known from patagonia lower cretaceous invertebrates are mostly known from west central argentina whereas upper cretaceous invertebrates are almost exclusively known from southern patagonia vertebrates are better known from continental upper cretaceous strata of central northern patagonia and southern brazil the cretaceous climate north of 43 s was characterized by warm and extremely arid conditions south of this arid belt was an area with temperate and humid climate

disc drill and replicate coring system a new era in deep ice drilling engineering the deep ice sheet coring disc drill and replicate coring system rcs were designed and manufactured by ice coring and drilling services ice drilling design and operations group of the university of wisconsin madison the disc rcs is an electromechanical system designed to take 122 mm diameter ice cores from the main borehole and 108 mm diameter replicate ice cores to depths of 4000 m detailed design of the disc drill began in 2003 and the completed drill was tested in greenland in 2006 during five consecutive field seasons at west antarctic ice sheet wais divide 3405 m of ice core were drilled setting the us deep ice drilling record the rcs based on the disc drill was developed and built in 2010 11 tested in antarctica during the 2011 12 wais divide field season and tested further in madison wi during summer fall 2012 during the 2012 13 antarctic field season the system produced five azimuth and depth controlled deviations at four target depth levels a total of 285 m of replicate ice core was recovered in the first coring of its kind the entire main replicate ice core including ductile brittle and warm ice had excellent quality and satisfied the needs of the ice science community

andean tectonics as a consequence of sea floor spreading abstract the evolution of sea floor spreading directions and rates in the southeast pacific shows a close relationship with the andean structural directions and the plutonic episodicity as well as the succession of short compressive orogenic phases alternating with relatively longer periods of extension the orogenic periods coincided with the beginning of periods of relatively higher rates of plate convergence immediately after periods of relative quiescence with the following periodicity 110 85 76 70 63 60 49 45 35 33 16 13 7 m y the presence of oceanic structures as aseismic ridges or fracture zones produces weak benioff zones shallow and poorly defined without a corresponding active volcanism on the other hand ancient continental structures such as the precambrian paleozoic orogenic belts have active volcanism and neat deep and well developed benioff zones

new isotopic ages and the timing of orogenic events in the cordillera darwin southernmost chilean andes abstract the cordillera darwin a structural culmination in the andes of tierra del fuego exposes an orogenic core zone that has undergone polyphase deformation and metamorphism some of the classic problems of orogenic zones have remained unanswered in the cordillera darwin the age of deformed plutonic rocks the distinction of structurally reactivated basement and metamorphosed cover rocks and the timing of orogenic events this study addresses and partially answers these questions a well constrained rb sr isochron age of157 8m y and an initial 87 sr 86 sr ratio of 0 7087 obtained from a pre tectonic granitic suite suggest a genetic relation between this suite and upper jurassic silicic volcanic rocks in the cover sequence tobifera formation and also suggest involvement of continental crust in formation of these magmas a poorly constrained rb sr isochron age of240 40m y obtained from supposed basement schists is consistent with field relations in the area which suggest a late paleozoic early mesozoic metamorphism for these pre late jurassic rocks however because of scatter in the data and the uncertainties involved in dating metasedimentary rocks the significance of the isotopic age is dubious compilation of previously published ages in the area 9 with new mineral ages reported here indicate that early andean orogenic events occurred between 100 and 84 m y ago and that subduction related magmatism has contributed probably discontinuously to the crustal evolution of the region throughout the mesozoic

a new 122 mm electromechanical drill for deep ice sheet coring disc 3 control electrical and electronics design the deep ice sheet coring disc drill developed by ice coring and drilling services under contract to the us national science foundation is an electromechanical drill designed to take 122 mm ice cores to depths of 4000 m electronic electrical and control systems are major aspects of the disc drill the drill sonde the down hole portion of the drill system requires approximately 5 kw of d c power for the cutter and drill motors and instrumentation power is transmitted via a drill cable from a modified commercially available surface d c power supply operating at 1000v to power modules in the sonde instrumentation section these modules regulate the power to the motors to 300 v d c and to lower voltages for the instrumentation and control electronics cutter and pump motors are controlled by electronics that include motor controllers there are 20 distinct sensors in the drill sonde which measure conditions such as hole fluid temperature motor fluid temperature drill orientation etc on board electronics facilitate communication of control commands and data between the surface and the drill sonde electronics also play an integral part in the operation of surface equipment such as the winch in raising and lowering the sonde in the borehole overall control of the disc drill system is provided by a pc based supervisory control system that allows the drill operators to monitor and control all aspects of the drilling operation

paleobiogeographic relationships of andean angiosperms of cretaceous to pliocene age abstract a review of the geological data suggests that mountains existed in western south america since the late cretaceous these data combined with a review of the earliest occurrences of angiosperm fossils indicate that the floral elements centered in the south andes lived there during the late cretaceous while elements centered in the north andes existed there by the mid tertiary examinations of reports elsewhere in south america and in surrounding continents show that each andean fossil flora is mostly composed of andean or amazonian centered taxa in addition the south andean fossil flora also shares many taxa with the antarctica australia paleoflora while the fossils from the north andes are also found in meso and north america in combination these geological and fossil data suggest that the mountain centered floras have had a long history

a new 122 mm electromechanical drill for deep ice sheet coring disc 1 design concepts the deep ice sheet coring disc drill developed by ice coring and drilling services icds under contract with the us national science foundation is an electromechanical drill designed to take 122 mm diameter ice cores to depths of 4000 m the conceptual design of the disc drill was developed in 2002 03 based on science requirements written by k taylor and the united states ice coring community and on engineering performance objectives detailed design of the drill began in june 2003 special attention was paid to building safety into the design and operation of the drill system the drill was designed and manufactured by a team of engineers and technicians from the university of wisconsin madison and various subcontractors with assistance from the science community the european ice drilling community and polar logistical support organizations icds successfully tested the drill in greenland in 2006 and will continue its development to meet the science objectives of the west antarctic ice sheet divide ice core project

the mid cretaceous super plume carbon dioxide and global warming carbon dioxide releases associated with a mid cretaceous super plume and the emplacement of the ontong java plateau have been suggested as a principal cause of the mid cretaceous global warming the authors developed a carbonate silicate cycle model to quantify the possible climatic effects of these co sub 2 releases utilizing four different formulations for the rate of silicate rock weathering as a function of atmospheric co sub 2 they find that co sub 2 emissions resulting from super plume tectonics could have produced atmospheric co sub 2 levels from 3 7 to 14 7 times the modern pre industrial value of 285 ppm based on the temperature sensitivity to co sub 2 increases used in the weathering rate formulations this would cause a global warming of from 2 8 to 7 7c over today s global mean temperature altered continental positions and higher sea level may have been contributed about 4 8c to mid cretaceous warming thus the combined effects of paleogeographic changes and super plume related co sub 2 emissions could be in the range of 7 6 to 12 5c within the 6 to 14c range previously estimated for mid cretaceous warming co sub 2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20 of the mid cretaceous increase in atmospheric co sub 2

a new 122 mm electromechanical drill for deep ice sheet coring disc 2 mechanical design the deep ice sheet coring disc drill consists of four major mechanical drilling subsystems and four subsystems supporting on surface activities the mechanical drilling subsystems are a drill sonde a drill cable a tower and a winch the drill sonde is the down hole portion of the drill system and consists of six distinct sections 1 the cutter head 2 the core barrel 3 the screen section 4 the motor pump section 5 the instrument section and 6 the upper sonde which includes anti torques and drill cable terminations the drill cable not only provides the means of supporting the drill sonde in the borehole but also provides conduits for electrical power and data transmission the tower tilts to allow the drill sonde to be serviced in the horizontal position without removing it from the tower the winch provides a means of quickly raising the sonde from the borehole and providing the fine control necessary for coring operations

a thermal balancing act heat is constantly transported from earth9s core through the mantle to the crust where it results for example in volcanic eruptions the heat transport depends on the thermal conductivity of the different materials in the core and the mantle but for many years the numbers did not add up and the power could not be balanced between the core and the mantle anderson now shows that a reevaluation of the thermal conductivity of the mantle by hofmeister may balance the power

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

melange formation by subduction erosion the case of the osa melange in southern costa rica the convergent plate margin off the osa peninsula in southern costa rica is characterized by the indentation of the cocos ridge at 4 5 ma the indentation causes the uplift of the osa melange which we interpret to represent an exhumed major channel for the transport of tectonically eroded material down into the subduction zone we present evidence that similar to the nicoya segment of the costa rica convergent margin subduction erosion rather than accretion has been the dominant process along the plate boundary the composition of the osa melange is dominated by tectonized material of the upper plate nicoya ophiolite complex basalt radiolarite limestone strong deformation is concentrated in numerous discrete shear zones and produced the layered fabric of large rock volumes which partly experienced temperatures 200 c we thus interpret the osa melange to be a product of subduction erosion at the base of the outer arc wedge structure

the impossible galapagos connection geometric constraints for a near american origin of the caribbean plate geometric constraints derived from the present plate configuration and from plate motion vectors of the caribbean as well as the north and south american plates within a hotspot reference frame indicate that the thickened caribbean oceanic crust was formed in a near american position rather than at the galapagos hotspot a lateral displacement of more than 1000 km between the caribbean plate and the north and south american plates is related to differences in plate motion velocities during the cenozoic era the differential motion between the caribbean and the american plates results from trench parallel mantle flow as a response to the westward motion of the american plates

a new 122 mm electromechanical drill for deep ice sheet coring disc 5 experience during greenland field testing the deep ice sheet coring disc drill developed by ice coring and drilling services under contract with the us national science foundation is an electromechanical ice drill system designed to take 122 mm ice cores to depths of 4000 m the new drill system was field tested near summit camp in central greenland during the spring summer of 2006 testing was conducted to verify the performance of the disc drill system and its individual components and to determine the modifications required prior to the system s planned deployment for coring at the wais divide site in antarctica in the following year the experiments results and the drill crew s experiences with the disc drill during testing are described and discussed

long lived early cretaceous seamount volcanism in the mariana trench western pacific ocean abstract an alkaline volcanic rock sample peralkaline rhyolite pillow lava in addition to some radiolarian bearing pelagic sedimentary rocks were collected by the japanese submersible shinkai 6500 from quesada seamount on the oceanward slope of the mariana trench 40ar 39ar dating resulted in a plateau age of 129 3 2 6 ma which is approximately 10 myr younger than the radiolarian age of the oldest intercalated tuffaceous radiolarian claystone of early berriasian age approximately 140 ma fragments of volcanic glass that are of alkali basalt hawaiite composition may indicate that this tuffaceous claystone was formed during the shield building volcanic stage because the peralkaline rhyolite is a very differentiated volcanic rock and commonly erupts in the post shield stage we interpret that the activity lasted for a long period approximately 10 myr this long lived shield building stage may be due to the slow moving rate of the pacific plate during the early cretaceous

magmatic intervals transgression regression cycles and oceanic events in the cretaceous and tertiary of southern south america abstract the southern part of south america provides an excellent test area to analyse relationships between transgression regression cycles along a passive continental margin with magmatic activity and tectonic movements of the andean orogen most of the tectono eustatic sea level changes recognized are related to magmatic activity whether calc alkaline or alkaline the magmatic activity depends on whether tectonic convergence or extension forces are dominant

la presence de fossiles marins dans le cretace terminal des andes centrales et ses consequences paleogeographiques abstract the maastrichtian deposits late campanian to early danian of the central andes comprise three transgressive regressive sequences in bolivia el molino formation they have yielded diverse terrestrial brackish water or marine fossils which make it possible to define the depositional environments at their exact stratigraphic position marine influenced transgressive facies are by far the best developed in the first sequence among the vertebrates five groups of fishes are restricted with some rare exceptions to marine environmentsl some other fish families genera or species are known to occur both in freshwater brackish and marine environments and therefore provide no precise environmental indications among the invertebrates echinoids serpulids foraminifera and some pelecypods and gastropods attest to a marine influenced environment which may however have experienced periodic salinity variations the other pelecypods and gastropods generally indicate freshwater environments the ostracods often ubiquitous only provide paleoecologic indications when they constitute oligospecific shell beds suggesting abnormally low salinity values calcispheres and dinoflagellates indicate a stronger marine influence charophytes especially when abundant suggest a lacustrine environment because of their stratigraphic and paleogeographic positions stromatolites may indicate intertidal to supratidal environments the fossils most likely of marine generally occur in the transgressive lower parts of the three sequences where marine oolites and glauconite are also observed the often endemic nature of the marine assemblages the common occurrence of dwarfism and the lack of true nektonic forms suggest that most part of the basin was permanently rather shallow and subjected to important frequent and or local salinity variations the freshwater fishes appear to be reworked and dissociated in the marine levels but are better preserved in the mainly continental upper parts of the sequences marine fossils are rare in the upper sequence these data contradict with interpretations which suggest that the central andean senonian deposits are exclusively terrestrial given other paleogeographic constraints we propose that maastrichtian sedimentation took place in a wide elongated subsident basin forming the eastern foreland of the paleo andes and showing a cul de sac shape in the south this restricted basin was periodically connected with the open sea through present day venezuela the salinity of its southern part situated far from the basin mouth was shallow and affected by fresh water from inflowing rivers

biogeography and diversity of south atlantic cretaceous echinoids implications for circulation patterns abstract this survey of echinoid species living on the african and south american margins of the south atlantic ocean in cretaceous times is based on a review of published species and abundant unpublished material the synthetic approach is used to ascertain how the south atlantic was colonised by echinoids from the time it first opened in the early cretaceous until communications were established with the north atlantic and mediterranean tethys in the late cretaceous the survey focuses on the biogeographical origin of immigrant species and their relations with indo madagascan north atlantic and mediterranean tethyan faunas qualitative variations in species diversity are also studied where available fossil material permits together with the in situ evolution of certain lineages and their endemism finally echinoid colonisation of the south atlantic during the cretaceous is viewed against palaeocurrent patterns the survey shows within the limits of material available that no echinoid fauna attests to the existence of the narrow marine trough separating south america and africa in the barremian in the aptian west african echinoids display a mediterranean tethyan influence indicating a probable link between south east and west of africa via the strait opened between africa and madagascar echinoid fauna on the brazilian margin includes species found in what is now continental north america and on the pacific seaboard of south america during the albian south america separated completely from africa and normal marine communications were established with the western tethys to the north and the southern ocean domain to the south the echinoid fauna of the south atlantic during the albian and early cenomanian was particularly rich and diversified with the earliest ubiquitous species on both margins of the ocean in the late cenomanian early turonian a tethys south atlantic ocean link probably formed in west africa through the sahara and nigeria favouring the influx of mediterranean tethyan species to the south atlantic during the mid turonian coniacian the trans saharan channel closed slowing down colonisation of the south atlantic by mediterranean tethyan echinoids as the only connection was via the central atlantic this period was marked by the stability of a number of lineages that survived without major morphological changes in areas colonised during cenomanian times in the late senonian the south atlantic was largely open to the neighbouring ocean domains and a new trans saharan channel linked the mediterranean tethys and south atlantic directly this allowed substantial faunal exchanges and most senonian echinoids found on the south atlantic rim are common to both its eastern and western margins