Datum Planes Research Articles

Toward an improved Silurian conodont biostratigraphy

Silurian conodonts have been widely reported and many species have worldwide distribution. However, present zonations utilizing them have many limitations and no single scheme provides a suitable standard. A good standard zonation for Silurian conodonts is desirable, but impossible at our present state of knowledge. Environmental differentiation, the rapid evolution of several unrelated conodont lineages and the lack of distributional data are the principal factors producing this situation. Existing Silurian conodont zonations are evaluated, and zonal schemes based on well documented phylogenetic lineages are advocated. Eight datum planes are proposed as an additional biostratigraphic framework in the system. These are the Distomodus staurognathoides Datum, Pterospathodus amorphognathoides Datum, Pterospathodus Extinction Datum, Kockelella walliseri Datum, Kockelella variabilis Datum, Ancoradella ploeckensis Datum, Kockelella Extinction Datum and Ozarkodina crispa Datum. Six of these datum planes are based on the evolutionary appearance of the datum-defining species. Extinction datum planes correspond to a significant level of extinction amongst the conodont-bearing animals.

Changes in size and test porosity of Orbulina universa d'Orbigny in the Pleistocene record of Cape Bojador (DSDP Site 397, eastern North Atlantic)

Measurements of the diameter of O. universa carried out on 30 specimens from 39 samples covering a sediment thickness of 78 m and going back in time to approximately 750 000 y resulted in the construction of a curve of the mean diameter and a curve of the maximum diameter. Both curves, as well as those calculated with the running-averages technique, display cyclic fluctuations with durations of the order of 100 000 y and downwards decreasing amplitudes. These curves are compared with a carbonate curve (on bulk sediment) and an isotopic curve (on benthic foraminifers) obtained from the same set of samples. Correlations are fair to good, but a time-lag is noticed between the isotopic curve and the faunal ( O. universa mean diameter) curve, with the isotopic signal coming first, in the middle part of the Brunhes Epoch. Biostratigraphic calibration to the paleomagnetic record is provided by four datum planes (two based on calcareous nannofossils, two on diatoms) identified in the succession. Changes recorded in test porosity seem to be less meaningful than changes in test size.

Tephrochronological study on the middle Pleistocene deposits in the Kanto and Kinki districts, Japan

The middle Pleistocene time range is defined here the period before the last interglacial in the Brunhes epoch. In Japan, the Shimosa-Kazusa Groups around the Tokyo Bay in Kanto and the upper part of the Osaka Group in Kinki both represent the standard middle Pleistocene sequences and have been studied in detail. These groups are characterized by the cyclic sedimentation caused by transgression and regression corresponding to climatic changes.The purpose of this paper is to attempt the correlation of the Kazusa Group and the Osaka Group by identification of widespread marker-tephras. Accurate determinations of the refractive indices of volcanic glass, orthopyroxene and hornblende, together with other determinations, have enabled successful characterization for correlation to be made for several tephra layers in southern Kanto and Kinki. The following marker-tephras are found over two districts, resulting in the establishment of several important datum planes in the middle Pleistocene sequences.The vitric tephra called Ks 11, which is sandwiched in the Kasamori Formation and its correlatives in southern Kanto, can be identified as a marker tephra of the Osaka Group called Sakura ash, in the vicinity of Osaka and Kyoto. The estimated age of this tephra, about 450, 000 years, is based on its stratigraphic relationship with the underlying dated tephra, Kinukawa ash (460, 000-470, 000 years). Stratigraphically, it is included in the deposits immediately below the transgressive horizon (Tama-f and Ma 7) and also occurrs in the biozone of Stegodon orientalis in both districts. The vitric tephra called Ku 1, sandwiched in the Kokumoto Formation, is identified and correlated with a tephra called Imakuma I ash. It is included in the deposits immediately above the Brunhes-Matuyama boundary. The very important dated tephra, Azuki ash (870, 000 years), in the Osaka Group, can be correlated with Ku 6C tephra in the lower part of the Kokumoto Formation by their peculiar petrographic properties. Both are sandwiched in the deposits below the Brunhes-Matuyama boundary.From the relationship between the identified tephras and marine sequences, it is concluded that during the period from 700, 000 years to 450, 000 years at least three interglacial-glacial cycles are recorded, and that after 450, 000 years the following major interglacial episodes are indicated; 450, 000YBP, 370, 000YBP, 300, 000YBP, 230, 000YBP, and 130, 000YBP.

Late Quaternary Foraminiferal Record in Eastern Caribbean Cores--Paleo-Oceanographic Implications: ABSTRACT

Oxygen-isotope variations in planktonic Foraminifera (Orbulina universa, Globorotalia menardii, and Globigerinoides sacculifer) indicate that, in two Grenada Basin cores, paleontologic datum planes do not coincide with isotope boundaries. The time lag is greater when the boundaries are transitional from glacial to interglacial phases. Recurrent-groups analysis of benthic foram assemblages led to the recognition of five groups. Only one of these, containing Osangularia culter, Bulimina buchiana, and Chilostomella oolina, appears to have any stratigraphic significance. The group shows its best development during interglacial times. In accordance with Weyl's paleo-oceanographic model, this group is associated with colder bottom waters and can be used to draw inferences about the influx of such waters. Periods of cold-water influx ranged from before 367,000 to 210,000 years B.P., from 139,000 to 81,000 years B.P., and from 22,000 to 8,600 years B.P. Cessation of influx 8,600 years B.P. is further substantiated by heat-flow calculations. End_of_Article - Last_Page 538------------

Paleoenvironments of Mowry Shale (Lower Cretaceous), Western and Central Wyoming: GEOLOGIC NOTES

The Lower Cretaceous Mowry Shale of western and central Wyoming contains three distinct facies, each of which is characterized by a unique suite of physical and biogenic sedimentary structures: (1) laminated mudstone, (2) bioturbated mudstone, and (3) bioturbated sandstone. We interpret the facies to represent the following marine biotopes (Schafer's terminology): (1) lethal isostrate--quiet, anaerobic, >150 m deep; (2) vital isostrate--quiet, marginally aerobic, 15 to 150 m deep; and (3) vital heterostrate--agitated, fully aerobic, <15 m deep. Bentonite datum planes show that the boundaries between facies are time transgressive, and indicate a west-to-east progradation of the shoreline and lateral filling of the Mowry sea. An east-dipping paleoslope inclined at 0 76;13^prime has been estimated. The depositional topography of the Mowry basin as reconstructed from the facies pattern shows that the thickest accumulation of sediment occurred along the western margin where water was shallowest, whereas in the deeper water basin center a much thinner section was deposited. Thus, isopach patterns of the Mowry in no way reflect the original depositional topography. The significance of this study for petroleum geology is threefold: (1) a facies sequence is used to reconstruct the depositional basin configuration of a known source rock; (2) the facies correlate with previously published regional variations in organic carbon concentration in the Mowry; and (3) the facies also correspond approximately to facies based on electrical resistivity.

Late Pliocene-quaternary biostratigraphy and climatic change in DSDP 208, Lord Howe rise

Site 208 from Leg 21 of the Deep Sea Drilling Project contains a well preserved and almost complete sequence of Pliocene and Pleistocene planktic foraminifera and calcareous nannoplankton. The upper 42.5 m of sediment has been analysed at 50 cm intervals. Several major cold episodes are recognised. The strongest occur at 39 m, 27 m and about 11 m. The first of these may represent the onset of major continental glaciation in the Late Pliocene, about 3.0 m.y. ago. Oceanic palaeo-temperatures were found to vary by at least 8 °C, implying a latitudinal water mass movement of about 10°. The biostratigraphy has strong affinities with Tropical zonations, except that two species whose extinctions are used elsewhere as datum planes were found to occur here much higher in the sequence. They were Globorotalia rnulticamerata and Globigerinoides fistulosus. Four coiling reversals were found in Pulleniatina obliquiloculata in the Pleistocene and were apparently unrelated to climate. Dates for these reversals agree closely with those found elsewhere. They may be useful datum points for Early Pleistocene correlation.

Phonolitic lava domes and other features of the Dunedin Volcano, East Otago

Abstract Outward dips of flows on the periphery of the Dunedin Miocene volcanic massif indicate the flanks of a complex, eroded shield volcano. Pillow-form lavas low in the section on the southeast flank suggest that the volcano continued to impinge on the sea for some time during its growth. Mapping of flow planes and contact relations show that the more felsic lavas, notably benmoreites, nepheline benmo:eites, and phonolites, were erupted as steep-sided lava domes of internal growth, as short coulees, and as wider-ranging flows extending in some cases at least 7 km from their vents. Strongly developed flow “schistosity” sometimes linea ted by microcorrugations, may indicate the site of lava spines forced upwards through viscous lava domes. Units such as the Logan Point and Waitati Phonolite as mapped by Benson were each erupted from several quite separate vents and cannot validly be used as datum planes for the study of post-effusive crustal deformation, nor can they be used with confidence as stratigra...

Magnetic Polarity Stratigraphy of Pliocene-Pleistocene Terrestrial Deposits and Vertebrate Faunas, San Pedro Valley, Arizona

Horizontally stratified magnetic zones are observed throughout the Pliocene-Pleistocene valley fill of the upper San Pedro Valley, Arizona. Within one detailed 150-m stratigraphic section (Curtis Ranch), twelve superposed magnetic polarity zones are identified spanning the time from the upper Gilbert Epoch through the Brunhes Epoch. These magnetic polarity zones extend over a 64-km stretch of the valley and serve as convenient chronostratigraphic units. Based on the position of mammalian fossils within the chronostratigraphic zones, we have defined four mammal datum planes for the upper San Pedro Valley, including the first appearance of Lepus sp. at 1.9 m.y. Lepus sp. marks the first occurrence of a definitive Irvingtonian land mammal in the San Pedro Valley and thus places the local boundary of the Irvingtonian Land Mammal Age shortly below the Olduvai event. This position equates approximately with the Pliocene-Pleistocene boundary of the pelagic marine record.

Globorotalia truncatulinoides Datum Plane: Evidence for a Gauss (Pliocene) Age in Subantarctic Cores

IN the past, the first appearance of the planktonic foraminifer Globorotalia truncatulinoides (d'Orbigny) was one of the most reliable Neogene foraminiferal datum planes. It was widely accepted as marking the onset of the Pleistocene at about 1.8 m.y. BP during the Matuyama Magnetic Epoch1, but this datum must now be restricted in the southern hemisphere to areas north of about 36° S. A concurrent analysis of radiolarians and planktonic foraminifers in 18 deep-sea cores (12 of which were dated palaeomagnetically) from south of Australia and the Tasman Basin (Table 1; ref. 2) demonstrates that, in that area, G. truncatulinoides appeared during the Gauss Epoch. This predates its appearance in lower latitudes by 1–1.5 m.y.

Pennsylvanian and Early Permian Depositional History, Southeastern Arizona

In southeastern Arizona the Black Prince Limestone, Horquilla Limestone, Earp Formation, Colina Limestone, and Supai Formation are Pennsylvanian and Lower Permian strata with complex transgressive and regressive relations. Subdivision of these formations into easily recognizable lithologic members is possible only above the basal unconformities of the Black Prince and Horquilla Limestones where red clastic sediments intertongue with the predominantly limestone sequence. Lithologic facies changes in the upper part of the Horquilla Limestone pass laterally and vertically into the Earp Formation which intertongues upward with the overlying Colina Limestone and on the north with the lower part of the Supai Formation. Regional unconformities are common and 15 are recognized an traced as stratigraphic datum planes subdividing Pennsylvanian and Lower Permian strata into depositional units. These depositional units, dated by fusulinaceans, include Morrowan to early late Wolfcampian deposits. Only two regional hiatuses of long duration occur: one within the Derryan Series and the other at the base of the Missourian Series. Longer hiatuses occur locally where parts of the succession are missing because of lack of deposition or because of erosion associated with local structural adjustments. Four main tectonic features influenced sedimentary environments in the region: the Papago inner shelf in the southwest received shallow marine sediments; the San Pedro outer shelf in the central part of the region received slightly deeper water sediments; the Mogollon inner shelf on the north and northeast was frequently emergent and received principally clastic deltaic sediments; and the Pedregosa basin in the southeast was rimmed with carbonate banks and shoals and its center, particularly during Late Pennsylvanian and Early Permian time, was the site of thick clastic sedimentation. Contemporaneous faulting locally accompanied major changes in lithofacies on the Mogollon shelf. A complicated set of faulted blocks separated the San Pedro outer shelf from the Pedregosa basin and diffe ences in times of deposition and erosion, thicknesses, and lithologies suggest that each fault block had an independent history of structural adjustment and sedimentary conditions.

Time-Transgressive Aspects of Some Critical Planktonic Species: ABSTRACT

The origin of Globigerina bulloides in temperate areas occurs in the middle Miocene in Neogene zones 9 or 10, whereas in tropical sections it appears in the upper Miocene in Neogene zones 16 or 17, a cool-water cycle. In both cases it could be represented as being derived from Globigerina praebulloides. The origin of the temperate Globorotalia (Turborotalia) pachyderma, dextrally coiled, occurs in Neogene zone 13 or just below in temperate areas, whereas it invaded subtropical areas only during the principal cold cycles subsequent to deposition of zone 13. Forms of Neogloboquadrina lacking umbilical toothlike structures such as N. dutertrei subcretacea appeared in tropical and warm temperate areas in the late Miocene. Neogloboquadrina dutertrei dutertrei with umbilical toothlike structures appeared near the end of Pliocene or at the beginning of Pleistocene time in Neogene zone 22 in tropical areas, whereas the primitive forms continued into the Holocene in temperate areas. Thus, there is an apparent extinction datum plane of the primitive form near the end of Neogene zone 21 deposition in tropical areas but not in temperate areas. Coiling characteristics and form ratios distinguish this group from Globorotalia (Turborotalia) pachyderma. Praeorbulina spp. appear initially in the lower Miocene Neogene zone 8 in tropical areas; isomorphs of this genus appear initially in temperate areas in Neogene zones 11 or 12. The earlier forms originated from species of Globigerinoides whereas those in temperate areas appear to have originated from Globigerina. Ecologic-evolutionary relations are responsible for these and many other kinds of time-transgressive aspects of planktonic datum planes. End_of_Article - Last_Page 330------------

Planktonic foraminiferal datum planes in the Pacific and Trinidad Tertiary

Abstract In the circum-Pacific region 29 homotaxial datum planes have been chosen from the ranges of the Tertiary planktonic Foraminifera. Correlation of the datum planes is mainly dependent on the original geographic distribution of the species, the preservation of the fossils, and the accuracy of published information.

Quaternary Glaciation in the Coast Range, Northern British Columbia and Alaska

On the higher mountains in the Coast Range of British Columbia and Alaska the action of ice and snow is so severe and the surface is changing so rapidly that little record of old suface features remains and an estimate of the amount of erosion by ice is difficult to make. In the valleys likewise, ice erosion has been active and the surface has changed rapidly; but here reference to certain datum planes, such as sea-level and the levels of certain rivers, suggests that glacial scour has deepened some of the major valleys 2,000 feet or more. In the period between 9,000 and 4,500 years ago conditions of intense alpine glacia-tion prevailed. Between 5,500 and 4,500 years ago the climate was moderating; the ice retreated rapidly and disappeared from Stikine and Taku fiords. From 4,500 until about 1,500 years ago the climate was warmer than at present. Subsequently the ice advanced in places for 20-25 miles beyond present glacier termini. It then retreated to its present stage.

Canada's Datum Level

THE use of different datum planes in Canadian surveys has in the past led to some confusion. The first precise levels run in 1883 were linked to the United States Coast and Geodetic Survey datum level, but since then others have been used. All precise levelling is now under control of the Geodetic Survey of the Department of the Interior, and an order in council dated March 11, 1935, is quoted in the Canadian Surveyor of January. This order decrees that mean sea-level as determined at coastal points by the Canadian Hydrographic Service shall be the official datum line for elevation in Canada, and shall be known as the Canadian Geodetic Datum.

Conroe Oil Field, Montgomery County, Texas

The Conroe oil field, located in Montgomery County, Texas, was discovered in 1931. It is a broad ovate structure crossed by several normal faults which form a central graben area. The maximum vertical displacements of these faults range from 130 to 165 feet. Production is obtained at an average depth of 5,050 feet from the Cockfield formation of Upper Claiborne (Eocene) age, which has been uplifted more than 800 feet above its normal position. The average thickness of the Conroe producing sand throughout the field is 60 feet. The recoverable reserves have been estimated to be about 600 million barrels. Currently the field is producing daily 47,700 barrels of oil from 829 wells, of which 53 wells are producing salt water in varying amounts. There is free communication and equalization of fluid across the fault planes so that there exists a unit reservoir wherein the fluids segregate themselves at uniform levels throughout the field. The interval within which sand may contain oil is 130 feet, or between the -4,860-foot and -4,990-foot datum planes. A large gas cap overlies the oil and occupies an interval of 170 feet, or between the datum planes of -4,690 and -4,860 feet. Conroe has a proved area of 17,200 acres and has produced a little more than 40 million barrels of oil up to January 1, 1935. Reservoir pressures became stabilized after the field has produced about 29 million barrels of oil and the pressure decline since then has been less than one pound per million barrels of oil produced.

Earth-Movements in California determined from apparent variation in tidal datum planes*

Other| January 01, 1934 Earth-Movements in California determined from apparent variation in tidal datum planes* Harry Leypoldt Harry Leypoldt Search for other works by this author on: GSW Google Scholar Author and Article Information Harry Leypoldt Publisher: Seismological Society of America First Online: 03 Mar 2017 Online Issn: 1943-3573 Print Issn: 0037-1106 Copyright © 1934, by the Seismological Society of America Bulletin of the Seismological Society of America (1934) 24 (1): 63–68. https://doi.org/10.1785/BSSA0240010063 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Harry Leypoldt; Earth-Movements in California determined from apparent variation in tidal datum planes. Bulletin of the Seismological Society of America 1934;; 24 (1): 63–68. doi: https://doi.org/10.1785/BSSA0240010063 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.