Precise Regional Correlation Research Articles

High-resolution correlation between contrasting early Tonian carbonate successions in NW Canada highlights pronounced global carbon isotope variations

Carbonate successions older than the 800 Ma Bitter Springs isotope anomaly are sparse and this time is consequently poorly understood. The Shaler and Mackenzie Mountains supergroups of northwestern Canada, however, contain thick ca. 1050–750 Ma carbonate successions recording both deep- and shallow-water depositional environments that are interpreted to have been deposited in two separate, extensive epicratonic basins on the Rodinia supercontinent. When the contrasting sedimentology (benthic- versus pelagic-dominated carbonate production) and basin dynamics of two correlative carbonate successions from these basins are accounted for, a precise regional correlation can be made using sequence stratigraphic and carbon isotope data. This paper presents a regionally correlatable carbon isotope profile, containing substantial excursions between −2 and 7‰vpdb, that can be used to extend the global curve into early Neoproterozoic time prior to the Bitter Springs anomaly.

Revision of the Darriwilian (Middle Ordovician) conodonts documented by Watson (1988) from subsurface Canning Basin, Western Australia

The conodonts documented by Watson form one of the best-known middle Darriwilian faunas from Australia. The present contribution is based on the re-examination of this material. Thirty-one conodont species from the subsurface Goldwyer and Nita formations of the Santalum 1 A drill core section of the Canning Basin, Western Australia are documented and described, including two new species, Belodina watsoni sp. nov. and Scalpellodus percivali sp. nov. The revised fauna is characterized by diagnostic species, namely Histiodella holodentata, Histiodella triangularis, and Eoplacognathus pseudoplanus. It provides compelling evidence to correlate this stratigraphic interval represented by the upper part of the Goldwyer and overlying Nita formations in the Santalum 1 A drill core section to the Histiodella holodentata or Eoplacognathus pseudoplanus biozones of middle Darriwilian age. However, in the Canning Basin, the faunal change signaled by the disappearance of H. holodentata and appearance of E. pseudoplanus reflects shifting of depositional settings from intermediate to outer shelf environments to shallower inner shelf conditions, coinciding with a regional regression event. New taxonomic data also enable more precise regional correlation of middle Darriwilian rocks across the Canning Basin and the Amadeus and Georgina basins in northern-central Australia.Y.Y. Zhen [yong-yi.zhen@planning.nsw.gov.au], Geological Survey of New South Wales, Division of Mining, Exploration and Geoscience, Department of Regional New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry NSW, 2753, Australia.

A marker tephra bed close to the Lower-Middle Pleistocene boundary: Distribution of the Ontake-Byakubi Tephra Bed in central Japan

Tephrochronology is an exceptionally important tool in the precise regional correlation of Early and Middle Pleistocene sedimentary strata in Japan. The present study reveals that the Yukawa tephra 5 (YUT5) derived from the Older Ontake volcano, the Nezumigawa (Nzg) and Mitamitajima (Mtj) tephras of the Ina Bazin, and the Byakubi-E tephra (Byk-E) of the Boso Peninsula are the same tephra on the basis of their lithofacies, bulk grain composition, mafic mineral composition, major element composition of hornblende, and stratigraphic relationships with the dated tephras. We propose to call the series of tephras correlated with Byk-E the Ontake-Byakubi Tephra Bed (On-Byk Tephra) following the naming convention in which the tephra name consists of the names of the source volcano and the type location. The Matuyama-Brunhes Chronozone boundary occurs just above Byk-E in the type section of the Kokumoto Formation in the Kazusa Group, which is a candidate Global Boundary Stratotype Section and Point (GSSP) for the lower boundary of the Middle Pleistocene Subseries. Therefore, On-Byk Tephra becomes a critically important marker tephra bed for the Early-Middle Pleistocene boundary in central Japan. The present study indicates that the major element composition of hornblende can be a useful tool for identification and correlation of strongly weathered tephra layers such as Nzg and Mtj in which all the volcanic glass shards have been altered.

A CONOP9 composite taxon range chart for Ordovician conodonts from Baltoscandia: a framework for biostratigraphic correlation and maximum-likelihood biodiversity analyses

The Middle and Upper Ordovician rocks of Baltoscandia have been divided into spatially distinct, composite litho- and biofacies units called confacies belts. The precise regional correlation of outcrops and boreholes, which is necessary for biodiversity analyses, has always been problematic due to the pronounced biogeographical differentiation of macrofossils and horizontal lithofacies changes. We used a computer-assisted numerical sequencing program (CONOP9) to construct a correlation model and composite range chart from the stratigraphic range data of 159 conodont species in 24 boreholes and outcrops in Baltoscandia. We converted the composite section into a timescale in which to calculate the biodiversity, extinction, origination and fossil sampling probabilities through the Ordovician Period. Rates of extinction and origination were calculated using both simple approaches which do not incorporate estimates of sampling probability, and also more complex maximum-likelihood approaches based on Capture–Mark–Recapture (CMR) models. Our data show that overall biodiversity increases steadily from the base of the Paltodusdeltifer Zone to the uppermost Baltoniodusnorrlandicus Zone and then maintains an uneven diversity plateau until the earliest Sandbian. Diversity then declines dramatically throughout the remainder of the Ordovician. CMR analyses suggest that extinction rates remain constant throughout most of the Ordovician indicating that the dramatic late Middle and Late Ordovician decline in conodont diversity in Baltoscandia is attributable to depressed origination.

High resolution record of environmental changes constrained by volcanic ashes : Western Interior Basin, Cenomanian-Turonian stage boundary (USA)

Abstract Five altered volcanic-ash beds have been correlated near the Cenomanian-Turonian stage boundary through much of the Western Interior Basin. These instantaneous events constitute independent chronostratigraphic marker-beds enabling the synchroneity of lithological, biological or geochemical records to be tested. In this way, the Greenhorn Sea is a unique place where the potentiality of this high-resolution stratigraphic tool is illustrated. The Cenomanian-Turonian interval is the ideal period for this sort of study because major oceanic changes, including the global expansion of the oxygen minimum zone, are recognised across OAE2 event, involving the disappearance of Rotalipora, complex keeled foraminifera which previously occupied deep oceanic waters. Biostratigraphic data coupled with bentonite correlation, in several sections of Colorado, show the diachronism of the occurrences of R. cushmani and H. helvetica. Consequently, the extension of the W. archaeocretacea partial range zone is extremely variable at the regional scale. Thus, this association has a low temporal value. Planktonic foraminiferal analyses also reveal an A. multiloculata event in the M. mosbyense zone. During tens of thousands of years, this species, plentiful in the Western Interior Basin, multiplies and prevails on Rotalipora before a gradual decline. Rotalipora gave rise to Anaticinella by the atrophy of its keel. Thus, Anaticinella may stay in shallower habitats and avoid the expansion of the oxygen minimum zone. However, even if this adaptation allowed a return to the surface water, this selective advantage would not be enough for Anaticinella to survive the ecologically drastic modifications. Extinction of Anaticinella and its ancestor Rotalipora occurred contemporaneously. Carbon stable isotope analyses show that main paleoceanographic events have occurred at Pueblo during the Cenomanian-Turonian stage boundary. The initial rapid increase and first peak of δ13C indicate the first anoxic event (event 1) before a decrease in values and a main manganese enrichment which are the evidence for a well-oxygenated environment (event 2). This assumption is supported by the occurrence of an abundant and diversified benthic community at the same interval. The second increase in δ13C proxies signs the rise of anoxia (event 3). The temporal distribution of these events with the bentonite marker beds and the ammonite biostratigraphy attest to the synchroneity of events 2 and 3 over 600 km between the Pueblo and Lohali Point sections. The absence of event 1 at Lohali Point in the S. gracile zone implies the existence of a hiatus. Thus, thanks to the five bentonite marker beds, extending from the S. gracile to the M. nodosoides ammonite zone over 2 Ma, we have not only achieved precise regional correlation but, dealing with facies variations, our observations also indicate gaps in the sedimentary record. Thus, in detail, some thin levels expressed in Pueblo (reference section) cannot be correlated in any other eastern sections. Furthermore, supposed continuous sections may contain important hiatuses. An example is given at El Vado (New Mexico) where two bentonite marker beds are missing. In spite of the lack of significant planktonic foraminifera, the indications provided by bentonite geometries and by nannofossils reveal the existence of a hiatus of at least 850 kyr. It could be explained by the location of the area along the trend of a tectonic forebulge linked to the Sevier orogeny. This bathymetric high had great consequences on the currents flows in this large interior sea where tethysian and boreal water masses competed.

Chronology and geochemistry of late Holocene eolian deposits in the Brandon Sand Hills, Manitoba, Canada

Abstract Accelerator mass spectrometry and conventional radiocarbon age determinations of organic matter from paleosols indicate that the Brandon Sand Hills area of southern Manitoba has been subjected to recurrent intervals of eolian activity in the past 5000 years. Although precise regional correlations are precluded by dating uncertainties, periods of most notable paleosol development occurred around 2300 to 2000, 1400 to 1000, and 600 to 500 cal yr BP with eolian activity occurring before and after each of these periods. Episodes of eolian activity may correspond to periods of regional drought, whereas paleosols mark periods of increased moisture availability and stabilization by vegetation. The geochemistry of the eolian sands, paleosols and source sediments indicates that partial leaching of carbonates occurs from pedogenesis during humid climatic phases, and that this is probably the primary mechanism of carbonate depletion of eolian sands in this area. Recent trends in sand dune activity from historic aerial photography and early explorers’ accounts indicate that the few active dunes that presently exist have stabilized at a rate of 10–20% per decade, despite several severe droughts in the 20th century. This may be attributed to pre-settlement droughts that were more severe than those in historic times although regional dune stabilization may also be related, in part, to the spread of forest cover in the past few hundred years.

Chalk palaeoenvironments and depositional model, Valhall-Hod fields, southern Norwegian North Sea

Abstract Palaeoenvironmental analysis in the North Sea chalk is hampered by the prevalence of widespread allochthonous units, intervals of massive reworking of microfossils and an often monotonous lithology of massive chalks of uncertain depositional history. Most difficult of all is devising precise regional biostratigraphic correlations in a complex section with large, but very subtly expressed, disconformities and condensed zones. Facies change quickly both laterally and vertically. Without very precise regional correlations, it is impossible to formulate any detailed palaeoenvironmental model. Through a multidisciplinary palaeontological approach, employing graphic correlation methodology and a composite standard database, a highly accurate and detailed regional chronostratigraphy was generated. Biofacies recognized within the section were then scaled in absolute time, allowing for more reliable recognition of facies trends at any one time horizon. Biofacies were formulated based upon recovered benthic foraminifera, planktic foraminifera, calcispheres, siliceous microfossils and macrofossil debris. Biofacies mapping for several higher-order sequences recognized in the Upper Cretaceous chalks has allowed recognition of four major periods of deposition: (1) early Turonian-early Santonian high pelagic productivity and rapid deposition of chalks over a relatively continuous ridge from the Valhall to Hod fields; (2) early Campanian-earliest Maastrichtian deep-water autochthonous chalk deposition off-structure with structural crests mantled by submarine hardgrounds; (3) very heterogeneous autochthonous and allochthonous middle Maastrichtian chalk deposition controlled by local grabens formed from crestal collapse; and (4) widespread sediment flows and redeposition of sediments with crestal shoaling and winnowing in the latest Maastrichtian culminating in crestal erosion of Cretaceous chalks in the early Danian.

A stereotaxic method of anatomical localization by means of H(2)15O positron emission tomography applicable to the brain activation study in cats: registration of images of cerebral blood flow to brain atlas.

In the neuronal activation study of normal animals, precise anatomical correlation, preferentially to a detailed brain atlas, is required for the activation foci co-registration. To obtain precise regional correlation between H(2)15O-PET images and the brain atlas, a method of stereotaxic image reorientation was applied to an activation study with vibrotactile stimulation. Cats anesthetized with halothane underwent repeated measurements of regional cerebral blood flow (rCBF) in the resting condition and during vibration of the right forepaw. The image set was adjusted three-dimensionally to the atlas. The postmortem brain was sectioned according to the atlas planes. The activated areas were determined by the stimulus-minus-resting subtraction images, and the areas were projected to the atlas. The PET images of the cat brain were compatible both to the postmortem brain slices and to the brain atlas. The activation foci obtained from the subtraction images corresponded to the area around the coronal sulcus, which is electrophysiologically known as the primary sensory area as described in the atlas. There were precise regional correlations between the PET image and anatomy in a PET activation study of the cat by means of stereotaxic image reorientation.

A stereotactic method of anatomical localization for positron emission tomography.

Extant methods for anatomical localization within a physiological image are inadequate for precise regional correlations between anatomy and physiology. We have developed a method for determining the location of any region of interest within a positron emission tomographic (PET) image by transformation of the tomographic location coordinates into coordinates within a stereotactic atlas of the human brain. The specific anatomical assumptions of this approach were identified and validated within groups of normal subjects by means of measurements made from lateral skull radiographs and nuclear magnetic resonance proton images. A high degree of accuracy and reproducibility was demonstrated when this technique was applied to groups of normal subjects by determining the anatomical location of two physiologically defined PET areas: the cavernous sinus and visually responsive cortex. This method is simple to implement and highly objective. Generalization of the localization procedure for use with structural tomography is readily accomplished.

Impaired function of salvaged myocardium: two-dimensional echocardiographic quantification of regional wall thickening in the open-chest dog.

This study was designed to examine the functional properties of myocardium subjected to acute coronary occlusion but surviving the ischemic insult. Ten conscious mongrel dogs underwent mild-circumflex coronary occlusion and were treated for 6 hours with prostacyclin, 540 ng/kg/min, and ibuprofen, 110 micrograms/kg/min, or dipyridamole (7-9.7 micrograms/kg/min). At 7 days, each dog was anesthetized, the chest was opened, and cross-sectional two-dimensional echocardiograms were obtained through the middle of the occluded vascular bed. A computer-aided contouring system was used to assess percent systolic thickening in 16 equally spaced segments around the left ventricle. Metal markers sewn to the epicardium permitted precise regional correlation of histology, percent systolic thickening, and flow, as measured by radioactive microspheres. Necrosis was minimal, averaging only 2.2 +/- 0.8% (+/- SEM) of the left ventricular ring corresponding to the echocardiographic cross section. Percent systolic thickening was 28.6 +/- 4.7 in the nonischemic anterior wall, but was reduced to -4.5 +/- 3.1 in the occluded bed (p less than 0.01). In individual echo segments, percent systolic thickening correlated with local flow (r = 0.69, p less than 0.001), but was still depressed even when flow was normal. In six segments within the occluded bed that had normal histology and flow, percent systolic thickening was 52% less than that in the nonischemic region (p less than 0.02). Thus, coronary artery occlusion combined with drug treatment results in myocardium that, although histologically normal and supplied by normal myocardial blood flow, remains functionally abnormal 7 days after occlusion.

Regional Stratigraphy of Limestone Marker Beds in Bridge Creek Member, Greenhorn Limestone (Upper Cretaceous), Western Interior United States: ABSTRACT

Time-parallel limestone beds of the well-known Kansas section have been traced westward in an attempt to determine their total geographic extent, their origin, and their utility in precise regional correlation. The entire sequence of marker beds extends from Canon City, Colorado, to Springer, New Mexico. Certain groups of these markers are traceable southward to White Oaks, New Mexico, northward to the Black Hills, and westward to the northern San Juan basin. The most widespread limestone beds were deposited across areas no smaller than 388,000 sq km (150,000 sq mi). Individual beds are identified positively by position in sequence, relation to adjacent bentonite seams, lithology, and fossils. Each bed is thoroughly bioturbated, and the thickness, fossil content, and fiel characteristics are remarkably uniform for great distances. Dominant mineralogy is calcite; quartz and pyrite are the only consistent accessory minerals. The limestones are micritic to microsparitic wackestones and, uncommonly, packstones. Principal allochems are planktonic forams, inoceramid bivalve fragments and prisms, calcispheres, and oyster fragments. Fecal pellets are scarce west of the Rocky Mountain front but common in Great Plains sections. Limestone bed contacts are mostly gradational with adjacent shaly strata, and evidence for hardgrounds is lacking. Limestone beds of the Bridge Creek Member reflect offshore shelf deposition during the late Cenomanian-early Turonian transgressional maximum of the Western Interior sea. Relative proportions of pelagic versus benthonic allochems confirm that limestone beds represent slow deposition caused by reduced detrital influx. Deposition occurred on a nearly planar surface, with local highs marked by areas of condensed sequences. End_of_Article - Last_Page 464------------