Stratigraphic Groups Research Articles

The trace element composition of the lavas and dikes from a 3‐km vertical section through the lava pile of eastern Iceland

The Tertiary lava succession of eastern Iceland dips at shallow angles towards and beneath the axial Quaternary volcanic zone. A 3‐km vertical section through part of this Tertiary pile, studied during the Iceland Research Drilling Project, contains flows ranging in composition from basalt to icelandite. This succession can be divided into three distinct stratigraphic groups: upper and lower groups, 1.7 and 0.6 km thick with Zr/Y ratios of about 4.5, and a 0.7‐km‐thick middle group with a Zr/Y ratio of about 6.5. The middle group also has a significantly higher Ce/Yb ratio and higher elemental Sr abundances. The data on within‐group variation are equally compatible with high‐level fractionation of a plagioclase‐olivine‐clinopyroxene assemblage with accessory apatite and opaque minerals or with open system fractionation models. Dikes occur throughout the 3‐km section and are comparable in trace element composition to the lavas of the upper group. The dikes are part of a N‐S trending swarm originating from the Breiddalur volcanic center some 15 km to the south. These dikes were injected laterally, northward into the Reydarfjordur lava pile at the time of the eruption of the upper group lavas. The lower two major lava groups may be related to similar, but unidentified, discrete volcanic centers perhaps buried downdip. The new data on this deeper section corroborate earlier studies which indicated that on a gross scale, the eastern Iceland lava pile becomes less mafic with depth. This vertical change occurs because each major volcanic center erupted more silicic lavas close to the center and more magnesium‐rich compositions toward the periphery. The formation of the lava pile occurred by tilting toward the spreading center and overlapping repetition of such major units which resulted in the more mafic edges of the lava groups forming the topographically higher parts of the crustal section.

Paleomagnetic results from the Narosura and Magadi volcanics of Kenya

Results of a paleomagnetic study carried out on the exposed volcanic rocks on the western side of the South Kenya Rift Valley are presented. Nine stratigraphic groups ranging in age from Miocene to Pleistocene were sampled. The rocks consist of basalts, trachytes, nephelinites, melanephelinites, olivine melanephelinites and ignimbrites. Paleomagnetic poles obtained for different age ranges are as follows: Period I (0.64–0.72 Ma), 116°E, 85°N ( A 95 = 6°); Period II (1.6–6.9 Ma), 297°E, 84°N ( A 95 = 4°); Period III (12.0–15.0 Ma), 34°E, 80°N ( A 95 = 9°). The results for Period II show large secular variations which are in disagreement with the model predictions for near-equatorial sites.

Shallow-Submarine Seismic Stratigraphy, Mississippi River Delta Front: ABSTRACT

High-resolution seismic, and engineering borehole data were integrated to interpret the shallow seismic stratigraphy of the Mississippi River delta front. Three seismic stratigraphic units have revealed the transgressive-regressive depositional sequences associated with late Pleistocene glacio-eustatic changes in sea level. Each of the stratigraphic groups was found to consist of a lower clayey unit and an upper fine-sand and shell unit. Paleotopographic maps of the stratigraphic units reveal the morphology of the former continental shelves. Structural features observed within the delta front area include shelf-edge growth faults, a salt diapir, and an extensive erosional unconformity which is believed to be the result of a large slide mass of early Holocene age. The modern, prodeltaic sedimentary wedge includes up to 100 m of soft, underconsolidated, gas-bearing silty clays, deposited during the past 500 years. The thickness of this unit within the delta-front area has been mapped. End_of_Article - Last_Page 542------------

Some new Namurian bivalve faunas and their significance in the origin of carbonicola and in the colonization of carboniferous deltaic environments

Shells which have been attributed to the genus Carbonicola are known from certain Viséan and early Namurian (E 1 ) beds of Scotland, and were recorded from a single local Viséan horizon in the north of England. Re-examination of well preserved material from both these stratigraphic groups indicates that Viséan-early Namurian shells differ in internal features, as well as in external shape, from late Namurian (R 2 -G 1b ) and Westphalian Carbonicola , to which they do not appear to have been directly related. The former have been assigned to the new genus Paracarbonicola , with Pleurophorus elegans Kirkby 1880 as type species. Paracarbonicola is present in the Flora Beds of Poland, considered to be of E 1 age, and in Czechoslovakia, where it ranges upward into beds of E 2 age. In Britain and northern Europe no Carbonicola -like shells have been reported in measures lying unquestionably between the top of Stage E 2 and the bottom of R 2 . In beds of late R 1c age two newly found correlated assemblages of shells, the first in County Limerick, southwest Ireland, and the second near Glitheroe, northern England, are herein referred to cf. Sanguinolites Hind non M’Goy. These faunas existed in shallow-water marginally marine conditions, as evidenced by the associated Mollusca. Their shells were highly variable in both lateral outline and surface features. In the English Pennines, upward gradation of these faunas with unquestionable Carbonicola of R 2 and higher horizons may be demonstrated in terms of internal and external features of the shell. It therefore appears that British late Namurian Carbonicola faunas were probably derived from marine ancestors in late R 1 time. Limited evidence suggests a similar sequence of events in Belgium and the Netherlands. Both in lithological facies and in ranges of variation of shape of shell, the Irish and north Pennine faunas of cf. Sanguinolites Hind non M’Coy compare respectively with established and invading faunas of later Carbonicola . Moreover, the comparison is made more close by the fact that bivalve burrows, referred to Pelecypodichnus Seilacher, have not been seen on horizons lower than those of late R 1c , but recur above this horizon, tending to become more nearly vertical, more numerous and longer, as Pelecypodichnus escape shafts, on higher horizons. These trends culminate in the well known, extremely abundant burrows of the Haslingden Flags, mid-Pennines, of G 1 age. It is concluded that during the time when Carbonicola was probably evolving from cf. Sanguinolites Hind non M’Goy, which has been found without burrows in the Shale Grit (middle R 1c ) of Derbyshire, steep burrowing of bivalves was common, the long axes of the shell being near the vertical; that from this position rising movements of the shells took place, enabling the bivalves to escape burial from rapidly advancing delta lobes; furthermore, that in the process of rising the more elongate shells, having shorter anterior ends and relatively low measures of obesity, such as Carbonicola bellula (Bolton), held selective advantage over other shapes of shell. In these particular circumstances therefore the delta invaded the bivalves, rather than vice versa. During the deposition of bands of established faunas of Carbonicola , when rates of deposition were evidently lower than in the case of invading ones, shallow burrowing appears to have taken place obliquely, the long axis of the shell making characteristically a small angle with the plane of the substratum. From work on Recent analogous bivalve species, functional advantage in shallow downward burrowing may be assumed to have lain with the more oval and more obese varieties. Established faunas with the latter trends characterized lower-energy muddy environments of the delta, including those which immediately followed coal-forming conditions. These environments tended mainly to succeed the phases of rapid deltaic growth, of sands and silts in Namurian time, and are reflected in the prevalence of established faunas of Carbonicola in Westphalian time.

1: The Dalradian rocks of Rosneath and south-east Cowal

Introduction This excursion guide deals with the Upper Dalradian rocks which are exposed northwest of the Highland Boundary Fault in the South-west Highlands of Scotland. The exposures to be described are formed by the shores of Loch Long, and by the coast of the Firth of Clyde. The excursion based on Rosneath is largely independent of the state of the tide since the exposures are mostly above the high-water mark on raised beaches. However, the excursion based on Dunoon should be undertaken when the tide is low at localities 16 and 17. General Geology The Dalradian rocks exposed to the north-west of the Highland Boundary Fault form four stratigraphic groups in the South-west Highlands. The first group is exposed in the north-west of the area under consideration as a thick series of schistose grits, quartzose mica-schists and pelitic schists. These rocks are known as the Beinn Bheula Schists. They are succeeded to the south-east by a varied series of rocks forming the Dunoon Phyllites. This group include schistose pebbly grits, schistose grits and greywackes, schistose semi-pelites and pelites, together with purple or black phyllites and dark fine-grained limestones. The last two rock-types are characteristic of the Dunoon Phyllites. These rocks are followed to the south-east by the Bullrock Greywacke which consists mainly of massive schistose grit. Finally, the Innellan Group of schistose pebbly grits and phyllites is found to the south-east of the Bullrock Greywacke in south-east Cowal. The rock-types in this group are similar to those forming the Dunoon . . .

Geotechnical Implications of Pleistocene Deposits in Southern Saskatchewan

Significant advances in understanding Pleistocene stratigraphy have provided a new framework for geotechnical investigations in southern Saskatchewan. In Saskatchewan, three formal stratigraphic groups have been recognized in the Pleistocene based on the concept of multiple glaciation. The engineering significance of this stratigraphic framework has now been established.Some of the geotechnical problems in Saskatchewan, related to Pleistocene deposits include slope instability, problems associated with groundwater, location of gravel aggregates, and excavating and handling embankment materials. It can now be demonstrated that these problems are fundamentally related to Pleistocene stratigraphy. Examples are included to illustrate this approach.The analysis of these deposits requires special criteria to establish the true stratigraphic column in terms of reference sections. It has been shown that the reference sections can be extended over very large areas of the region. The principal investigation technique involves the use of rotary drilling and geophysical logging which has proven to be extremely effective when properly interpreted. The criteria used for establishing the stratigraphy are described and examples included. The possibility exists that this approach to investigating geotechnical problems in Pleistocene deposits may extend to other parts of Canada.

Structural evidence of the age of folded rocks on the south coast of New South Wales

Abstract The pre‐Devonian sedimentary and volcanic sequence exposed along the south coast of New South Wales has previously been divided into three stratigraphic groups: (1) Upper Ordovician graptolite‐bearing slate which is conformable with (2) interlayered thinly‐bedded greywacke and pelite of undifferentiated Ordovician age and (3) Cambrian successions of interlayered chert, pelite and volcanic rock at Bate‐mans Bay and Narooma. The main bases for this subdivision are a change in rock types between (1) and (2), and the unconformity between (2) and (3) formerly proposed on the basis of changes in rock type and fold style across the boundary. New structural data are presented which refute the presence of the unconformity, and conformity of (2) and (3) with the fossiliferous slates is established.

Sequence and geochronology of the Kenya rift volcanics

The Upper Cenozoic volcanic formations associated with the Kenya rift valley are divided into seven main stratigraphic groups representing widespread ‘plateau’ formations, and a number of central volcano groups of more localised occurrence. 75 K/Ar isotopic age determinations including 30 unpublished dates are listed and the age-range of most of the volcanic groups is given. A tabulation of the sequence of volcanic groups is provided and their distribution is illustrated. The Kenya rift volcanics were erupted nearly continuously from Early Miocene to Holocene times. Miocene volcanism was mostly of nephelinites, alkali basalts and phonolites. Pliocene activity was trachytic, phonolitic and nephelinitic in central and southern parts of the rift valley, while contemporaneous basaltic volcanism took place along its whole length. The only extensive rhyolitic activity occurred in northwest Kenya in Pliocene times. Late Pliocene and Quaternary volcanism was mainly trachytic in the rift valley floor and basaltic to the east.

Additional Information on Clays in Pleistocene Deposits of Northeastern Kansas

In a previous study (Tien, 1968), relative intensities of first reflections of mixed-layer mineral, illite and kaolinite, and the diffraction intensity (D.I.) ratio of illite to kaolinite were used to differentiate stratigraphic units of till and nontill deposits. At least two Kansan tills could be distinguished. Associated nontill deposits could not be subdivided into meaningful stratigraphic groups. On the basis of 74 samples from southeastern Doniphan County, it was concluded that claymineral assemblages are diagnostic features of Pleistocene deposits, and that further sampling would not alter the results. A new road cut, 0.4 mile north of SWc sec. 33, T.8 S., R.19 E., along US Highway 59, 6 miles north of Oskaloosa, Jefferson County, Kansas (Fig. 1) offers not only an opportunity for additional information on clays of Pleistocene deposits, but also for testing the conclusions made from the previous study. The purpose of this note is (1) to present the results of X-ray diffraction studies on samples from this new road cut, and (2) to discuss the significance of these results to correlate Pleistocene deposits by use of clay minerals in northeastern Kansas. Twelve samples (noting relative stratigraphic position and lithology) were collected from the road cut. The samples were analyzed in the same manner as those used in the previous study (Tien, 1968, p. 99-100). Results of X-ray diffraction analyses of the less than 2 micron fraction and stratigraphic position of samples are listed in Table 1. Each of the 12 samples was plotted on the ternary diagram in terms of the relative intensities of the first basal reflections of the three principal clay minerals. Those samples studied previously were plotted also for comparison (Fig. 2). It was found that the clay-mineral assemblages in the samples from this new road cut were identical to those in samples previously studied. All three till samples had a low D.I. ratio (less than 0.50) of illite to kaolinite. Relative intensities of the first basal reflections of kaolinite, mixed-layer mineral, and illite ranged from 15 to 17, 75 to 79, and 6 to 8 respectively. The nontill samples had a D.I. ratio of illite to kaolinite ranging from 1.11 to 1.82, and the intensities of the first basal

Magnetization of Basalt of Bed I, Olduvai Gorge, Tanganyika

PALAEOMAGNETIC data which bear on the time-scale of geomagnetic polarity epochs are here reported for a radiometrically dated Pleistocene basalt flow in East Africa, The occurrences in various places of stratigraphic groups of rocks which are magnetized either with the sense of the present geomagnetic field (normal polarity) or with the opposite sense (reversed polarity) have been interpreted to mean that the geomagnetic field has reversed itself at various times in the geological past1,2. The accumulated evidence for the reality of such fteld reversals has recently been reviewed3,4, and palaeomagnetic investigations of radiometrically dated volcanic rocks have permitted a preliminary attempt by Cox et al. to bracket the ages of the most recent reversals5.

Petrology of Some Pennsylvanian Sedimentary Rocks

ABSTRACT The middle Allegheny Kittanning Formation near Brookville, Pennsylvania is composed mainly of detrital rocks--sandstone, siltstone, and claystone, with minor volumes of coal, limestone, and ironstone. Detrital constituents are quartz (approximately 25%), micaceous metamorphic and sedimentary rock fragments, coarse micas and clays (about 70%), and miscellaneous silicates totalling about 5%. The average grain size is medium silt. Sandstones and coarse siltstones can be classified into four descriptive-genetic groups based on quartz content and color relative to grain size and on primary structure and fossil content. Alluvial channel sandstone and coarse siltstone are characterized by relatively low quartz content, intermediate relative color, well-developed tabular-lenticular stratification, and a large stem flora. In contrast, beach sandstone and siltstone are relatively quartz rich and, excepting for possible worm burrows, are without distinctive fossils. Coarse grained lacustrine deposits have properties intermediate between those of channels and beaches. Lagoonal sandstone and siltstone are distinctive because of their relatively dark color and low quartz content. They also la k stratification and contain a marine fauna. Varieties of finer grained sediments are distinguished by relative color and by structure and fossil content. Fine grained alluvial sediments are relatively light colored, generally contain roots or upright stems and often lack stratification. Offshore lacustrine, brackish, and marine deposits are differentiated mainly by fossil content. Both fine and coarse grained sediments of similar genetic type occur in stratigraphic groups of considerable areal extent and reflect two times of marine transgression interrupted by an episode of fluvial-lacustrine deposition.

THE STRATIGRAPHY AND STRUCTURE OF THE ORDOVICIAN ROCKS OF THE RHINNS OF GALLOWAY

Re-examination of the stratigraphy and structure of Ordovician rocks in the northern part of the Rhinns of Galloway has led to amplification and some reinterpretation of the concepts of succession and structure advocated by Poach and Horne (1899). A stratigraphical succession within the greywackes has been erected on the basis of palaeontological and lithological evidence, and with the aid of “way-up” criteria. Stratigraphical groups have been subdivided on petrological grounds. The intercalation of at least two bands of Glenkiln (black) shale in a relatively thin greywacke sequence has been detected as far north as Broadsea Bay, and it can be demonstrated that a few miles farther north these black shales are represented by at least ten bands of fissile siltstone with black graptolite-bearing films, separated by some 6000 feet of greywackes. Relatively rapid cross-strike variations in thickness and lithological character have been found in several formations, amounting in the Glenkiln rocks to a general southward attenuation and concomitant increase in the proportion of shale and siltstone in the sequence. Palaeontological evidence shows that all the greywackes are of Glenkiln age, with the exception of the uppermost beds, the Portpatrick Group, which is probably Hartfell. Structurally the area is believed to comprise four main units, namely, three major complex monoclinal structures of Caledonoid trend with vertical northern limb and tightly folded and otherwise complicated southern limb, and one complex synclinal structure. The units are separated by major faults, mainly thrusts but including the Southern Uplands (= Glen App) fault, which is here normal, throwing south. Minor faults, especially wrench-faults, are of considerable importance.

Preliminary Subsurface Study of Southeastern Appalachian Interior Plateau

Recent deep drilling in eastern Kentucky is adding much new subsurface information, making possible a reinterpretation of this portion of the Interior Plateau region. The present study is a preliminary report on the subsurface stratigraphy and structure of that region, including six newly made geologic cross sections and eight isopachous maps of various stratigraphic groups or series. Three matters in particular are reported. 1. There is a newly discovered Lower Cambrian coastal declivity which may be a fault scarp or a steep coastwise cliff that is responsible for an abrupt thickening of Early Cambrian deposits on its south-east side. Apparently it does not affect sediments of Dresbachian age. 2. As they appear to have quite different thickness-distribution patterns, rocks commonly called Mt. Simon-Eau Claire, or Lamotte-Bonneterre (the group known as Dresbachian) should be separated from overlying sediments and not regarded as Upper Cambrian. In this paper they are placed in the late Middle Cambrian. 3. There is a broad low concealed arch extending from north-central Ohio southward into eastern Kentucky, on top of which all Beekmantown strata have been removed by pre-Chazy erosion that also cut deeply into the Upper Cambrian below the Beekmantown. This arch, here named the Waverly Arch, lies about 60 miles east of the Cincinnati anticline which was apparently absent in pre-Trenton time. Many paleogeographic and structural relations hitherto assigned to the Cincinnati arch during pre-Trenton epochs are attributed now to the Waverly arch. If these and other preliminary observations are substantiated as is confidently expected, considerable revision is required of various subsurface interpretations previously held for this region.

The Wenlock Strata of South Mayo

AbstractSouth of Clew Bay, Co. Mayo, Wenlock strata, cut off to the north by a belt of serpentine marking the Highland Boundary, are divisible into three stratigraphical groups. The succession is repeated by a syncline overturned towards the south, which is modified by north-west cross-folds. The Wenlock strata have undergone low-grade “regional” metamorphism, in spite of which fossils have been preserved at a few localities.

THE GEOLOGY OF THE WOOLHOPE INLIER (HEREFORDSHIRE)

The Silurian rocks of the Woolhope inlier (Herefordshire) present a typical calcareous and shelly development of the shelf facies. Upper Llandovery and Wenlock deposits resemble those of neighbouring Silurian areas. The Ludlow Series (215 to 1300 feet) is subdivided into eight stratigraphical groups based essentially upon variation in lithology and faunal assemblage. The succession is continuous except for minor breaks at the base of the Dayia Beds and immediately below the base of the Upper Ludlow, and the absence of deposits equivalent to the Ayrnestry Limestone in the extreme south of the inlier. A distinctive fauna, with abundant Shaleria ornatella, can be recognized in the thin division which succeeds the Dayia Beds. Upper Ludlow deposits yield many thin condensed beds, biotite-bearing bands and bone-beds. The Ludlow Bone-bed separates the Ludlovian Series from overlying sandstones and siltstones of the Downtonian. The succession compares closely with those of both May Hill and Usk, and a tentative correlation with the successions of the Ludlow district and Builth area is offered. Structurally the Woolhope inlier is a much-faulted, asymmetric pericline, its axis trending N W —SE. The northern part of this upfold has been subjected to rotation with the formation of two domes. The Shucknall inlier, a sub-parallel anticlinal structure, is separated from the Woolhope pericline by a topographic depression, believed to mark the site of a deep-seated fracture which is probably a continuation of the Neath disturbance. The main structural elements of the two inliers are attributable to an E —W . compression and a later N.—S. compression, both believed to be phases of a complex Armorican orogeny.

THE GEOLOGY OF THE USK INLIER (MONMOUTHSHIRE)

Calcareous and shelly Upper Silurian beds, about 2000 feet in thickness, outcropping over approximately 28 square miles in the Usk inlier (Monmouthshire) have been investigated. The lithological and faunal succession has been established and found to be constant, with minor exceptions, throughout the inlier. The Wenlock Shale is represented by at least 800 feet of mainly argillaceous beds which become sandy and micaceous in their transition upwards into a thin (40 feet) development of Wenlock Limestone. The Ludlow Series is between 1050 and 1300 feet thick and has been subdivided, mainly on the basis of total fossil assemblages, into seven stratigraphical groups. With the possible exception of a thin conglomerate band in the south of the inlier, there is no sign of any important break in the succession. This contradicts the claim by Gardiner (1917 and 1927) that the Lower Ludlow and Aymestry beds are missing. The presence of the Ludlow Bone-bed has been established and the succeeding Speckled Grit Beds are considered to be Downtonian in age. Structurally, the Usk inlier is a complex pericline whose major axis trends NNE.-SSW. A “Sudetic” phase of embryonic arching, and a possible “Malvernian” phase, preceded the main movements of Armorican age.

KNOXVILLE SERIES IN THE CALIFORNIA MESOZOIC

Research Article| October 01, 1945 KNOXVILLE SERIES IN THE CALIFORNIA MESOZOIC F. M ANDERSON F. M ANDERSON * Deceased September 24, 1945. Dr. Hermann Sommer kindly read and corrected galley proof. 58 HILLCREST ROAD, BERKELEY, CALIF. Search for other works by this author on: GSW Google Scholar GSA Bulletin (1945) 56 (10): 909–1014. https://doi.org/10.1130/0016-7606(1945)56[909:KSITCM]2.0.CO;2 Article history received: 14 Nov 1944 first online: 02 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 F. M ANDERSON; KNOXVILLE SERIES IN THE CALIFORNIA MESOZOIC. GSA Bulletin 1945;; 56 (10): 909–1014. doi: https://doi.org/10.1130/0016-7606(1945)56[909:KSITCM]2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract The Knoxville series, the latest West Coast Jurassic, is best developed and best preserved and exposed in its type area on the west border of the Sacramento Valley, in Tehama County. It consists of deltaic deposits having a maximum thickness of 16,300 feet and an average thickness of 11,600 feet. It forms three major stratigraphic groups, each characterized lithologically and stocked with appropriate faunas of marine invertebrates, which occupy a chronological span from early-middle Portlandian to latest Tithonian time of the European scale. In part the series crops out at intervals on the west border of the Great Valley for nearly 300 miles. Outside this valley it is traceable southward to the Santa Ynez Range and northward to partly correlative deposits in western Oregon, Washington, British Columbia, and southern Alaska. The Knoxville series contrasts strongly in composition, structures, faunistic features, and geologic history with the next older, the Franciscan and Mariposa groups, both of which occupy distinct geographical areas.Historically the Knoxville epoch is a distinct chronological unit between the Nevadan orogeny at the close of the Mariposa-Mount Jura epoch and the earliest Cretaceous epoch, the deposits of which occupy distinct areas on the West Coast. It includes the earliest marine deposits laid down in the Great Valley trough and in other troughs developed farther north by the Nevadan orogeny. Correlative deposits occur in many parts of the world—Cutch, southwest India; the Lower Volga basin, Russia; in western Germany; at Speeton, England; and in Japan. 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.

Faunal differentiation in the Upper Devonian

FOREWORD This is a preliminary compilation and analysis of Upper Devonian faunas, recognizedly incomplete. The compiler seeks the aid of others to ameliorate its errors and omissions so that a more perfect list may eventuate. Nevertheless, as it stands, it will serve to rectify widespread correlations of the American Upper Devonian strata, by reference to the distinctive faunas herein differentiated in the standard section of New York and the adjoining portions of Pennsylvania and Ohio, for there are four or five faunas known as “Chemung,” surely two that have been lumped as “Portage,” while the fishes, called “Catskill,” belong to seven faunas at least. Stratigraphic work in the area, as it affects the broader correlations herein employed, is practically finished. The difficulties that now arise in sorting out the published faunas into their correct stratigraphic groups are chiefly those due to inaccurate or vague records of localities for the described . . .

The Ranikot Beds at Thal (North-West Frontier Provinces of India)

According to the late E. Vredenburg (28 a ), ‘the Ranikot Series is of very limited occurrence, and is entirely unknown outside of a relatively small area in Western Sind.’ It apparently crops out in Sind in three disconnected patches: one being in the Laki Range, another in the Band Vera plain north-west of Kotri, and the third in the neighbourhood of Jhirak. Only the second and third of these outcrops show the Upper (and fossiliferous) Ranikot Beds. In his map of the area (28 b ) Vredenburg shows these three blocks of Ranikot Beds as lying between longitudes 67° 40′–68° 20′ east, and latitudes 24° 40′–26° 20′ north (25° 50′ north, in the case of the Upper Ranikot Beds). Later on (28 c ), he repeats that ‘beds of lower eocene age are not known anywhere else in India outside the limited area briefly described above.’ ‘In all instances,’ he goes on to say, ‘where certain stratigraphical groups have been assimilated with the Ranikot, closer investigation has shown that they should be regarded as middle eocene.’ This was written in 1909; and Vredenburg seems to have held to these opinions to the end of his life, as regards India, although he admitted as ‘most important,’ in 1923, the discovery by Bankim Behari Gupta of three species of Ranikot gastropods in the lower beds of the Laungshe Shales in Burma, at a spot a mile and a half south of Yeshin, 94° 8′ long, east, 21° 52′ lat. north (30). This being the

Types of sedimentary overlap

Research Article| January 01, 1906 Types of sedimentary overlap* AMADEUS W. GRABAU AMADEUS W. GRABAU Search for other works by this author on: GSW Google Scholar GSA Bulletin (1906) 17 (1): 567–636. https://doi.org/10.1130/GSAB-17-567 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation AMADEUS W. GRABAU; Types of sedimentary overlap. GSA Bulletin 1906;; 17 (1): 567–636. doi: https://doi.org/10.1130/GSAB-17-567 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract IntroductionThe sedimentary formations of the earth’s crust fall readily into two great stratigraphic groups, the marine and the non-marine, which in their essential characteristics are strongly contrasted and which in the analysis of sedimentary series must be carefully differentiated. In spite of the practice to the contrary, stratigraphers will admit that only marine deposits are suited to furnish the record for a complete time scale, and that consequently the standard column of any region should be based on marine deposits only. Where, as is often the case, the column selected as a standard contains non-marine members, the column is imperfect as long as these are retained. Thus the standard Cretacic column of North America is impaired by the retention in it of the non-marine Dakota and Laramie formations, and until recently the standard Triassic section of Germany was practically useless, as it contained only one marine member. The substitution . . . This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.