Sedimentary Member Research Articles

The Torea Breccia and the Papahaua overfold

Abstract The Torea Breccia is an Upper Eocene sedimentary Member of the Kaiata Formation cropping out on the western slopes of the Papahaua Range, near Westport. It was formerly mapped as basement granite and gneiss, or was not differentiated from the marine Kaiata Formation. The type locality and type section are described from Waimangaroa, where the breccia conformably interfingers with the Kaiata Siltstone; here the breccia bands total 110 ft in thickness. The constituent boulders consist of granite, gneiss, pegmatite, schist, hornfels, and quartz. At Granity, where the breccia has a minimum thickness of 700 ft, it rests unconformably on Kaiata Silt- stone. A westerly origin, from a land mass rising along a fault scarp west of Granity is proposed. The recognition of the Torea Breccia renders unnecessary a continuous major fault (Kongahu Fault) mapped by Morgan and Bartrum along the western flank of the Papahaua Range. The structure at Waimangaroa is interpreted as an overfold. To the south-west the ste...

ABSOLUTE AGE OF THE FISSET BROOK FORMATION AND THE DEVONIAN-MISSISSIPPIAN BOUNDARY, CAPE BRETON ISLAND, NOVA SCOTIA

The Fisset Brook formation of sedimentary and volcanic rocks crops out in the Cheticamp area of Cape Breton Island, Nova Scotia. Its stratigraphic age has been determined as earliest Mississippian using spores contained in the sedimentary members. A rubidium–strontium age determination using whole-rock samples of the volcanic members has yielded an age of 349 ± 15 million years. This is in good agreement with age determinations elsewhere for the Devonian–Mississippian boundary. Similar rocks exposed to the east of Lake Ainslie, some thirty miles to the southwest, give an identical age, 348 ± 20 million years. These rocks are clearly correlative with the Fisset Brook formation. Mixed sedimentary and volcanic rocks in the Cape St. Lawrence area, some thirty miles to the northeast of Fisset Brook, appear to be significantly older, 462 ± 25 million years, and should be considered tentatively as Ordovician in age.

Dawson Formation as Expression of Laramide Tectonics: ABSTRACT

The Dawson formation was named the Dawson arkose in 1915 by Richardson, the type locality being at Dawson Butte, 6 miles southwest of Castle Rock. Because much of the stratigraphic section contains more fine clastics and carbonaceous material than arkose, the change in name seems desirable. The writer has differentiated at least six sedimentary members of the Dawson on the southwest flank of the Denver basin in addition to rhyolite flows near and possibly at the top of the formation. On the southeast flank of the basin, eight members have been recognized. Another member develops near the southern end of the southwest flank and spans the trough area of the present basin in its southern part. At the northern end of the present outcrop area, a considerable interval of coarse clastic sediments changes rather abruptly to gray shale with minor amounts of arkose. The Dawson formation on the southwestern flank of the Denver basin is interpreted as a series of alluvial fans and bajada deposits with some intercalated mud flows, all of which were being spread out by streams from the rising Laramide mountains on the west. These fans were formed in varying areas at differing times as uplift was locally intensified or diminished by the shifting of centers of middle Laramide tectonism. Most of the fans coalesce along strike. The section is replete with unconformities. Sediments just east of the fans are mainly fluviatile, becoming lacustrine and paludal in the eastern parts of the basin. The present northwestern limit of the outcrop area contains mainly gray shale of lacustrine origin. Total thickness is in excess of 2,000 feet, but at no one locality on the west flank of the basin are all of the members present because of the oscillatory nature of the fan-forming processes. The formation thins to the north, southeast, and east from the area of its maximum deposition near Sedalia toward the areas of finer-grained sediments. The age of the Dawson was accepted as Eocene by Richardson. He considered it to be the southward and southeastward equivalent of the Arapahoe and Denver formations. Lavington (in 1942) believed there was an unconformity between the Denver and the Dawson, and that the Dawson overlapped the Denver. The present investigation disclosed typical Dawson unconformably overlying the Denver formation. The Dawson unconformably overlies all formations from the Pierre shale to the Denver formation in the Colorado Springs area. Palynological examinations of cuttings from about 750 feet above the base of the Dawson indicate late Late Cretaceous age. Earlier work on fossil leaves from near the top of the formation was reported by Richardson to suggest a Green River Eocene age for the containing strata. The Dawson is in fault contact with the older sediments and with Precambrian rocks along much of the mountain front. In places, the Dawson strata at or near the faults are nearly horizontal while at other localities they are steeply dipping, vertical, or overturned. Folding and faulting are present in the basin to a greater extent than has been heretofore recognized. Some of the folds have dips of as much as 45°. Faults are of both normal and thrust types. Deformation took place before, during, and after the deposition of the Dawson. The Dawson formation is thus a good expression of Laramide tectonics both in its origin and in its present structural expression. End_of_Article - Last_Page 414------------

Contribution to the stratigraphy of the non-marine Tertiary deposits on the south coast of the Nûgssuaq Peninsula, Northwest Greenland

The Tertiary, sedimentary sequence on the south coast of the Nûgssuaq peninsula, North Greenland (The Upper Atanikerdluk Formation) is described. The type area on the south-eastern part of the peninsula (the Atanikerdluk area) shows the Upper Atanikerdluk formation divided into 5 members: Plateau basalts 5. Point 976 member 4. Aussivik member 3. Umiussat member 2. Naujât member 1. Quikavsak member Cretaecous (Atane formation) The Plateau basalts rest upon the Upper Atanikerdluk formation which again rests unconformably upon the Atane formation (Cretaceous). The first occurrence of subaeric lavas is found in Aussivik member. West of the type area (Pautut and more westerly) the basalt volcanism began earlier, and here the number of sedimentary members of the type area substituted by products of the volcanism (basalt breccia and Plateau basalts) is increasing the more westerly one comes. The basal Quikavsak member is only visible locally owing to its origin as an infilling of a river-valley in connection with the Paleocene transgression. This fossil river-valley can be traced from Atanikerdluk (purely fluviatile) by Pautut to Nûk kitdleq, where a marine intercalation has yielded a minor fossil fauna making the Paleocene age probable by its accordance with an occurrence of marine, fixed Lower Paleocene fauna in a delta deposit at Angmârtussut (the Agatdalen valley), whose stratigraphic equivalence to Quikavsak member is proved. With 1) this fixed point in the Agatdalen valley, 2) the faunal agreement between this occurrence and Nûk kitdleq, 3) the agreement between the fossil flora of the fixed occurrence at Angmârtussut and Quikavsak member at Atanikerdluk and the other occurrences of this member at the south coast of the Nûgssuaq peninsula as well as 4) the same position in the geological course of events, all these occurrences of Quikavsak member and the litho-stratigraphically equivalent occurrences at Angmârtussut are linked together as Lower Paleocene deposits. This dating thus applies to the known fossil floras "Upper Atanikerdluk A" and "Upper Atanikerdluk B" of O. Heer. A short survey of the fossil floras from the localities described is given. Finally, Macclintockia Kanei (Hr.) Sew. & Conw. is stated zone fossil of the Lower Paleocene of West Greenland.

La serie dahomeyenne de Takamba dans la boucle du Niger

Abstract Defines and describes a new Precambrian series in the Niger shield area of French West Africa--the Takamba series, composed mainly of quartzites. It is equivalent to the sedimentary member of the Dahomeyan series of other areas of French West Africa, and is overlain unconformably by the Ansongo series.

On Iso-diametric Lines, as means of representing the Distribution of Sedimentary Clay and Sandy Strata, as distinguished from Calcareous Strata, with special reference to the Carboniferous Rocks of Britain

§ 1. — Introduction .—A large and interesting field of inquiry is open to us in comparisons of the relative distribution of the calcareous and the truly sedimentary members of diffcrent geological formations. We have, as it appears to me, been too much in the habit of classing limestones (whether coralline, crinoidal, shelly, or oolitic) as strictly sedimentary; yet it will be found, by such comparisons as those alluded to, that the relation which is borne by sandstones and shales to limestones is one, not of similarity, but of contrast. In other words, that where we have a group of strata, as, for example, the Lower Carboniferous, composed partly of "sedimentary" and partly of calcareous members, it will generally be found that the one series is complemental of the other, and developed from opposite directions. This arises from the differences in the origin of the two classes of stratified rocks, the calcareous being essentially organic, and the "sedimentary " essentially mechanical ; so that where the forces and agencies tending to the accumulation of the latter are in active operation, these very forces and agencies are in direct antagonism to the other, and, as a result, calcareous strata are either not formed or only sparingly*. ( a .) Of these two ever-acting principles we have numerous examples both in recent and in geologic periods. If we take as an illustration the Gulf of Mexico and the West Indian Islands, we find he sediment brought down by the Mississippi forming deposits of sand and clay