Low-temperature thermochronological evolution of the Menderes and Alanya massifs (Turkey)

The application of two low-temperature thermochronometers [fission-track analysis and (U-Th)/He analyses, both on apatite] to various tectonostratigraphic units of the Menderes and Alanya Massifs of Turkey has provided significant new constraints to the understanding of their structural evolution. The Menderes Massif of western Anatolia is one of the largest metamorphic core complexes on Earth. The integration of the geochronometric dataset presented in this dissertation with preexisting ones from the literature delineates three groups of samples within the Menderes Massif. In the northern and southern region the massif experienced a Late Oligocene-Early Miocene tectonic denudation and surface uplift; whereas data from the central region are younger, with most ages ranging between the Middle-Late Miocene. The results of this study are consistent with the interpretation for a symmetric exhumation of the Menderes Massif. The Alanya Massif of SW Anatolia presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. Petrological and geochronological data clearly indicate that the tectonometamorphic evolution Alanya started from Late Cretaceous with the northward subduction of an ‘Alanya ocean’ under the Tauride plate. As an effect of the closure of the İzmir–Ankara–Erzincan ocean, northward backthrusting during the Paleocene-Early Eocene created the present stacking order. Apatite fission-track ages from this study range from 31.8 to 26.8 Ma (Late Rupelian-Early Chattian) and point to a previously unrecognized mid-Oligocene cooling/exhumation episode. (U-Th)/He analysis on zircon crystals obtained from the island of Cyprus evidentiate that the Late Cretaceous trondhjemites of the Troodos Massif not recorded a significant cooling event. Instead results for the Late Triassic turbiditic sandstones of the Vlambouros Formation show that the Mamonia mélange was never buried enough to reach the closure temperature of the ZHe radiometric system (ca. 200°C), thus retaining the Paleozoic signature of a previous sedimentary cycle.

Description of an ancient social bee trapped in amber using diagnostic radioentomology

The application of non-invasive imaging technologies using X-radiation (diagnostic radioentomology, ‘DR’) is demonstrated for the study of amber-entombed social bees. Here, we examine the external and internal morphology of an Early Miocene (Burdigalian) stingless bee (Apinae: Meliponini) from the Dominican Republic using non-destructive X-ray microtomography analysis. The study permits the accurate reconstruction of features otherwise obscured or impossible to visualize without destroying the sample and allows diagnosis of the specimen as a new species, Proplebeia adbita Greco and Engel.

Age of the Peach Springs Tuff, Southeastern California and Western Arizona

Sanidine separates from pumice of the early Miocene Peach Springs Tuff are concordantly dated at 18.5 ± 0.2 Ma by two isotopic techniques. The Peach Springs Tuff is the only known unit that can be correlated between isolated outcrops of Miocene strata from the central Mojave Desert of southeastern California to the western Colorado Plateau in Arizona, across five structural provinces, a distance of 350 km. Thus the age of the Peach Springs Tuff is important to structural and paleogeographic reconstructions of a large region. Biotite and sanidine separates from bulk samples of the Peach Springs Tuff from zones of welding and vapor-phase alteration have not produced consistent ages by the K-Ar method. Published ages of mineral separates from 17 localities ranged from 16.2 to 20.5 Ma. Discordant 40Ar/39Ar incremental release spectra were obtained for one biotite and two of the sanidine separates. Ages that correspond to the last gas increments are as old as 27 Ma. The 40Ar/39Ar incremental release determinations on sanidine separated from blocks of Peach Springs Tuff pumice yield ages of 18.3 ± 0.3 and 18.6 ± 0.4 Ma. Laser fusion measurements yield a mean age of 18.51 ± 0.10. The results suggest that sanidine and biotite K-Ar ages older than about 18.5 Ma are due to inherited Ar from pre-Tertiary contaminants, which likely were incorporated into the tuff during deposition. Sanidine K-Ar ages younger than 18 Ma probably indicate incomplete extraction of radiogenic 40Ar, whereas laser fusion dates of biotite and hornblende younger than 18 Ma likely are due to postdepositional alteration. Laser fusion ages as high as 19.01 Ma on biotite grains from pumice suggest that minerals from pre-Tertiary country rocks also were incorporated in the magma chamber.

Age determination with strontium isotopes on sediment core CRP-1 from the Ross Sea, Antarctica

Strontium isotope stratigraphy was used to date five discrete horizons within CRP-1. Early and late Quaternary (0.87-1.3 Ma and 0-0.67 Ma respectively) age sediments overlie a major sequence boundary at 43.15 meters below sea floor (mbsf). This hiatus is estimated to account for ~16 m.y. of missing section. Early Miocene (16.6-~20.8-25 Ma) age deposits below this boundary are in turn cut by multiple erosion surface representing hiatus is of between 0.2 and 1.2 m.y. Estimated minimum sedimentation rates range between 0.9 and 2.8 cm/k.y. in the Quaternary, and 1.5 and 6.4 cm/ky in the lower Miocene.

Chronostratigraphy on sediment core CRP-2 from the Ross Sea, Antarctica

Strontium isotope stratigraphy was used to date 16 discrete horizons within the CRP-2/2A drillhole. Reworked Quaternary (<1.7 Ma) and possible Pliocene (<2.4 Ma) sediments overlie a major sequence boundary at 25.92 meters below sea floor (mbsf). This hiatus is estimated to account for c. 16 Myr of missing section. Early Miocene to ?earliest Oligocene (c. 18.6 to >31 Ma) deposits below this boundary were cut by multiple erosion surfaces of uncertain duration. Strontium isotope ages are combined with 40Ar/39Ar dates, diatom and calcareous nannofossil datum and a palaeomagnetic polarity zonation, to produce an age model for the core.

Grain size analysis on CRP sediment cores from the Ross Sea, Antarctica

The upper 1200 m of pre-Pliocene sediment recovered by Cape Roberts Project (CRP) drilling off the Victoria Land coast of Antarctica between 1997-1999 has been subdivided into 54 unconformity-bound stratigraphic sequences, spanning the period c. 32 to 17 Ma. The sequences are recognised on the basis of the cyclical vertical stacking of their constituent lithofacies, which are enclosed by erosion surfaces produced during the grounding of the advancing ice margin onto the sea floor. Each sequence represents deposition in a range of offshore shelf to coastal glacimarine sedimentary environments during oscillations in the ice margin across the Western Ross Sea shelf, and coeval fluctuations in water depth. This paper applies spectral analysis techniques to depth- and time-series of sediment grain size (500 samples) for intervals of the core with adequate chronological data. Time series analysis of 0.5-l.0m-spaced grainsize data spanning sequences 9-11 (CRP-2/2A) and sequences 1-7 (CRP-3) suggests that the length of individual sequences correspond to Milankovitch frequencies, probably 41 k.y., but possibly as low as 100 k.y. Higher frequency periodic components at 23 k.y. (orbital precession) and 15-10 k.y. (sub-orbital) are recognised at the intrasequence-scale, and may represent climatic cycles akin to the ice rafting episodes described in the North Atlantic Ocean during the Quaternary. The cyclicity recorded by glacimarine sequences in CRP core provides direct evidence from the periphery of Antarctica for orbital oscillations in the size of the Oligocene-Early Miocene East Antarctic Ice Sheet.

Grain size analysis of sediment coring site CRP-2 from the Ross Sea, Antarctica

The purpose of this note is to present results of grain size analyses from 118 samples of the CRP-2/2A core using sieve and Sedigraph techniques. The samples were selected to represent the range of facies encountered, and tend to become more widely spaced with depth. Fifteen came from the upper 27 m of Quaternary and Pliocene sediments, 62 from the early Miocene-late Oligocene strata (27 to 307 mbsf), and 41 from the early Oligocene strata beneath (307 to 624 mbsf). The results are intended to provide reference data for lithological descriptions in the core logs (Cape Roberts Science Team, 1999), and to help with facies interpretation. The analytical technique used for determining size frequency of the sand fraction in our samples (sieving) is simple, physical and widely practised for over a century. Thus it provides a useful reference point for analyses produced by other faster and more sophisticated techniques, such as the Malvern laser particle size analysis system (Woolfe et al., 2000), and estimates derived from measurements taken with down-hole logging tools (Bücker, pers. com., 1999).

(Table 1) Maceral composition and organic carbon chemistry of ODP Leg 104 samples

The Cenozoic sediments sampled in ODP Leg 104 on the Vøring Plateau show a distinct variability of the total organic carbon content (TOC) and the accumulation rates of TOC. Based on the geochemical and organic-petrographic characterization of the sedimentary organic matter (OM), the allochthonous and autochthonous proportion of the OM could be quantified. The results clearly demonstrate that high TOC percentages and TOC accumulation rates in Cenozoic sediment sections display a generally high input of allochthonous organic matter. Oxidized and partly well-rounded organic particles built up the main portion of OM within the Miocene, TOC-rich sediments. The most probable source of this oxidized OM are reworked sediments from the Scandinavian shelf. Changes in the input of these organic particles are to some degree correlative with sea-level changes. The Cenozoic accumulation of autochthonous OM is low and does not reveal a clear variation during the Miocene and early Pliocene. In spite of a high accumulation rate of biogenic opal during the Early Miocene, the accumulation rate of autochthonous TOC is low. The autochthonous particle assemblage is dominated by relatively inert OM, like dinoflagellate cysts. This points to an intensive biological and/or early diagenetic degradation of the marine OM under well oxidized bottom water conditions during the last 23 Myr. Nevertheless, a continuation of marine OM degradation during later stages of diagenesis cannot be excluded. A prominent dominance of allochthonous OM over autochthonous is documented with the beginning of the Pliocene. At 2.45 Ma the episodic occurrence of ice-rafted, thermally mature OM reflects the onset of the glacial erosion of Mesozoic, coal and black shale bearing sediments on the Scandinavian and Barents Sea shelves. The first occurrence of these, in view of the actual burial depth, thermally overmature OM particles is, therefore, a marker for the beginning of the strong Scandinavian glaciation and the advance of the glacial front toward the shelves.

(Table 2) Radiolaria species in nodule samples from the Clarion-Clipperton province, Pacific Ocean

Radiolaria were studied in 19 manganese nodules raised from the bottom. The nodules occurred mainly on the surface of thin Quaternary sediments covering Tertiary deposits of various ages (Middle Eocene to Early Miocene). Radiolaria in nodule cores and in inner and surface layers were studied. We found 85 radiolaria species and groups of species. Usually 1-4 to 6-19 radiolaria species were detected in each of the samples. Species belonging to Middle Eocene, Late Miocene to Early Oligocene, and Oligocene to Early Miocene were found. Rare Neogene species were revealed only in fractured surface layers. Age of the nodules is mainly Oligocene. Seismic waves cause sediment vibration, loosening disintegration, and removal of suspension by bottom currents. The vibration effect causes ancient nodules to float up to the surface of Quaternary sediment. This hypothesis suggests the reason for characteristics of the Clarion-Clipperton zone: regional stratigraphic hiatus, accumulation of residual fields of nodules, and the ''floating up'' of nodules to the surface of the Quaternary sediments.

Sedimentology of ODP Leg 119 samples

Cretaceous to Quaternary sediments recovered at Leg 119 Sites 738 and 744 on the southern tip of the Kerguelen Plateau were studied in order to determine the depositional environment and the paleoceanography of the southern Indian Ocean and especially the long-term glacial history of East Antarctica. Emphasis is given to bulk-sediment composition, grain-size data, and clay mineralogy. The sediment sequence at the two sites is generally of a highly pelagic character, with nannofossil oozes, chalks, and limestones dominant from the Turanian to upper Miocene and diatom oozes dominant within the uppermost Miocene to Holocene interval. The first indication of glaciation at sea level is the occurrence of isolated gravel and terrigenous sand grains, which indicate ice rafting in the middle Eocene interval of 45.0-42.3 Ma. A major intensification of glaciation, probably the onset of continental East Antarctic glaciation, is recorded in sediments of early Oligocene age (36.0 Ma). All major sediment parameters document this event. The clay mineralogy changes from smectite-dominated assemblages, typical of moderately warm and humid climatic conditions in which chemical weathering processes are prevalent, to illite- and chlorite-dominated assemblages, indicative of cooler climates and physical weathering. Ice-rafted debris of both gravel and sand size occurs in large quantities in that interval and coincides with a change in the mode of carbonate deposition. Carbonate contents are relatively high and uniform (90%-95%) in strata younger than early Oligocene; in Oligocene to upper Miocene strata they fluctuate between 65% and 95%. Oligocene and Neogene hiatuses reflect an intensification of oceanic circulation and the increased erosional force of Circumpolar Deep Water. The long-term Cenozoic cooling trend was interrupted by a phase of early Miocene warming indicated by maximum Neogene smectite concentrations. Although ice-rafted debris is present only in minor amounts and mainly in the silt fraction of early Oligocene to late Miocene age, it shows that glaciers advanced to the East Antarctic shoreline throughout that time. Ice-rafting activity drastically increased in latest Miocene time, when carbonate deposition decreased and diatom ooze sedimentation started. This suggests a pronounced intensification of Antarctic glaciation combined with a northward migration of the Polar Front.

(Table 1) Paleomagnetic of ODP Leg 126 sites

A paleomagnetic study was made on the deep-marine sediments and volcanic rocks drilled by Ocean Drilling Program Leg 126 in the Izu-Bonin forearc region (Sites 787, 792, and 793). This study evaluates the sense and amount of the tectonic drift and rotation associated with the evolution of the Philippine Sea Plate and the Izu-Bonin Arc. Alternating-field and thermal demagnetization experiments show that most of the samples have stable remanence and are suitable for paleomagnetic studies. Paleomagnetic declinations were recovered by two methods of core orientation, one of which uses a secondary viscous magnetization vector of each specimen as an orientation standard, and the other of which is based on the data of downhole microresistivity measurement obtained by using a formation microscanner. Oligocene to early Miocene samples show 10° to 14° shallower paleolatitudes than those of the present. Middle Miocene to early Oligocene samples show progressive clockwise deflections (up to ~80°) in declination with time. These results suggest large northward drift and clockwise rotation of the Izu-Bonin forearc region since early Oligocene time. Considering previous paleomagnetic results from the other regions in the Philippine Sea, this motion may reflect large clockwise rotation of the whole Philippine Sea Plate over the past 40 m.y.

Preliminary results and documentation of sediment core CRP-1 from the Ross Sea off Cape Roberts, Antarctica

The first hole of the Cape Roberts Project, CRP-1, was drilled in October, 1997, to a depth of 148 metres below the sea floor (mbsf) before being terminated unexpectedly the loss of fast sea-ice seaward of the rig following a severe storm. The site lies in 150 m of water at 77.008°S and 163.755°E, 16 km off Cape Roberts. This part of the report outlines the geologic setting, a gently tilted sequence near the margin of the Victoria Land Basin, and describes the history of the growth of sea ice, which provided the drilling platform, as well as the history of the drilling itself. Core recovery was around 77% in soft and brittle strata to 100 m and 98% below that. The sequence was found to comprise a Quaternary glacigenic interval down to 43.55 mbsf and below this an early Miocene interval that was also glacigenic. Core properties that were studied include fracture patterns, porosity, sonic velocity and magnetic susceptibility. Velocity in particular was useful in relating the cored sequence to the regional seismic stratigraphy. A preliminary assessment suggests that the bottom of the hole is 15 m short of the boundary between seismic sequences V3 and V4. Analytical facilities new to the Antarctic and used for processing samples for the project are described here and include a bench top palynological processing system and a palaeomagnetic laboratory. The core management and sampling system, which recorded over 2000 samples, is also outlined.

Geochemistry at DSDP Legs 36 and 71 Holes

For Middle Jurassic to Pleistocene times, clay mineralogical and geochemical data provide information on the evolution of continental and marine paleoenvironments. They are a source of information on marginal instability, on the continental and shallow marine environments related to the development of the Southern Ocean during the Middle and Late Jurassic, and on tectonic relaxation of the continental margins at the end of the Late Jurassic. They also provide evidence for the influences of the South Atlantic opening and the movement of the Falkland Plateau in a reduced marine environment until Aptian-Albian times, and the transition to an open marine environment during Albian time; the influences of the Albian-Turonian and Coniacian-Santonian Andean deformations in an open marine environment; the limited tectonic effects and strong influence of marine currents at the Cretaceous/Tertiary boundary; the influences of the global climatic cooling and inferred bottom water circulation during the late Eocene and Oligocene; the widening of the South Atlantic Ocean during Oligocene time, which was accompanied by an increased influence of the biogenic components on sedimentation; increased carbonate dissolution from late Oligocene to early Miocene, related to the deepening of the ocean; limited mineralogical and important geochemical modifications when the Drake Passage opened in the early Miocene; the influence of the late Miocene development of the Antarctic ice-sheet; the major Antarctic cooling and Patagonian glaciation during Pliocene time; and the change in the Antarctic Bottom Water circulation at the Pliocene/Pleistocene boundary.

Insoluble residues of the fine-grained sediments from DSDP Leg 67 Holes

Insoluble residues of Late Cretaceous to Quaternary deep-sea samples from slope, trench, and oceanic plate sites south of Guatemala were examined, specifically for the distribution of clay minerals in the <2-µm fraction and of silt grains in the 20-63-µm fraction. Widespread "oceanic" particles (biogenic opal, rhyolitic glass) and their diagenetic products (smectite, clinoptilolite, heulandite) were distinguished from terrigenous material - illite, kaolinite, chlorite, plagioclase, quartz, and heavy minerals. The main results of this investigation are: (1) At Site 494 on the slope immediately adjacent to the trench, terrigenous supplies testify to a slope position of the whole sequence back to the Late Cretaceous. (2) At Site 495 on the Pacific Cocos Plate, "oceanic" and terrigenous sedimentation are clearly separated. Whereas the pelagic sedimentation prevailed in the early Miocene, terrigenous minerals appeared in the middle Miocene in the clay fraction, and in the early Pliocene in the coarse silt fraction. These terrigenous supplies are interpreted as having been transported by suspension clouds crossing the slope and even the trench. The alternative, however, an eolian transport, cannot be excluded.