Siltstone Units Research Articles

Petrology of the Chilhowee Group (Cambrian and Cambrian (?)) in central-eastern and southern Tennessee

The Chilhowee Group is a thick clastic sequence of Early Cambrian (and possibly older) age exposed along the western border of the Blue Ridge province in the southern Appalachians. In central-eastern and southeastern Tennessee, the group is divided into the Cochran Formation, Nichols Shale, Nebo Sandstone, Murray Shale, Hesse Sandstone and Helenmode Formation from bottom to top. The Cochran is the thickest formation and is composed primarily of coarse, moderately sorted subarkose. It is overlain by silty and sandy shale (Nichols and Murray) and medium to fine-grained, well sorted sandstone containing little or no feldspar (Nebo and Hesse). The Helenmode is a thin calcareous unit of shale, siltstone and sandstone. Integration of petrologic and stratigraphic data suggests that the lower Chilhowee detritus accumulated in a basin subsiding rapidly and unevenly along strike. During this time, shallow water nearshore to transitional muddy and sandy environments of low physical energy predominated. In later Chilhowee time, tectonism moderated and the region became more stable. The basin then sank slowly and at an almost equal rate parallel to the shoreline. Shallow marine, higher energy environments in which beach, offshore bar and island, and intertidal sand bodies accumulated characterized this phase of sedimentation. The deposition of argillaceous and calcareous sediments at the end of Chilhowee time completed the cycle of tectonic transition from rapidly subsiding marginal basin to slowly sinking shelf. The primary source area for most of the Chilhowee elastics was an extensive granitic basement complex situated west of the basin. This crystalline landmass was originally of moderate relief and supplied coarse, feldspathic detritus. Intense weathering and low relief in the provenance area subsequently produced fine-grained, primarily quartzose sediments. Patches of metamorphic rocks lying on and folded into the basement complex shed minor amounts of detritus during early Chilhowee deposition. These were apparently stripped off as weathering and erosion lowered source area relief. Pre-existing sediments located also to the west within the craton composed the second major Chilhowee source terrane. The older sediments were the predominant clastic contributors during deposition of the Nebo and Hesse orthoquartzites.

Early Campanian (Cretaceous) Delta-Front Sedimentation, South Flank of Wind River Basin, Wyoming: ABSTRACT

Upper Cretaceous rocks of the Mesaverde Formation, exposed between Hudson and Muskrat Creek on the south flank of the Wind River basin, accumulated in an ascending succession of delta-front, tidal-flat, and delta-plain environments. Rocks of the lower two environments grade east and northeast into strata deposited in an offshore marine environment, whereas rocks of the youngest environment grade east into deposits of a delta-front platform. During early Campanian time, the delta-front facies accumulated across a 14-km-wide belt near Alkali Butte. Repeated fluctuations of strand position produced interbedded units of siltstone and sandstone in the facies, and intermittent development of low-relief bars permitted accumulation of estuarine or swamp sediments across subjacent deposits of the delta front. Sandstone units of the delta-front facies show an upward gradation from siltstone and sandy siltstone End_Page 916------------------------------ beds to silty sandstone and fine sandstone beds characterized by slump and massflow structures. Slumping was triggered by instability of sediments on the delta-front slope and by recurrent tectonic movements along the trend of the ancestral Alkali Butte anticline. Succeeding the slump-dominated sandstone in each unit is well-sorted sandstone, deposited in a variety of littoral marine, beach dune, and estuarine channel environments. Depositional strike of the delta-front sediments, determined from primary sedimentary structures, ranged from N8°W to N30°E, and the slope declined east-southeast. Sandstone units of the delta-front facies are saturated with oil near Alkali Butte. Variations of porosity and permeability of the units along depositional strike in the subsurface, or an association of the units with reversals of dip along faults in the south-central part of the Wind River basin may form traps for petroleum, and make the units worthwhile exploration objectives. End_of_Article - Last_Page 917------------

Ordovician Snatigraphy of the Florentine Synclinorium, south-west Tasmania

The Florentine Synclinorium consti tutes the type area of the Ordovician Junee Group in Tasmania, and the group is herein re-defined according to the formations present in this area. The base on the western side is formed by the Reeds Conglomerate, a unit of siliceous fanglomerate up to l,560 m thick lying conformably above a thick Upper Cambrian sequence on the Denison Range. The laterally-equivalent sandstone unit on the southeastern side is also given formation status (Tim Shea Sandstone). The overlying sequence of marine sandstone and siltstone is designated the Florentine Valley Formation, and is of Late Tremadocian-Arenigian age. A sub-unit of siltstone and limestone occurs in the middle part of the formation in some areas, but is not given formal status pending further mapping. The subdivided into three formations, becomes the Gordon Limestone Sub-Group. The basal Karmberg Limestone, of Upper Canadian -? Chazyan age, includes a mappable chert-rich unit which forms chert- covered ridges and is designated Wherretts Chert Member. The Cashions Creek Limestone, corresponding to the “Maclurites-Girvanella zone of earlier reports, succeeds the Karmberg Limestone. Above this, and forming the bulk of the sequence, is the Benjamin Limestone, consisting of three members, viz. Lower Limestone Member, Lords Siltstone Member, Upper Limestone Member. A characteristic coral fauna with Favosites and cateniporines occurs near the top of the latter member, and includes conodonts which suggest an age not younger than Maysvillian. Above the limestone sequence and transitional with the overlying Eldon Group sandstone is a unit of siltstone and fine sandstone designated Westfield Beds. These contain a fauna correlated with the Richmondian, and the fauna in the overlying sandstone also appears to be Late Ordovician.

Interpretation of Miocene Shallow Marine Depositional Environments Using Sedimentary Structures: ABSTRACT

Comparison of sedimentary structures in certain sedimentary rocks with those that form in the modern environment can provide a powerful interpretive tool. An example can be drawn from a well-exposed middle Miocene marine-nonmarine transition in the southeastern Caliente Range, California. Within this transition, shallow-marine sandstone (part of Branch Canyon Sandstone) intertongues on the northwest with marine siltstone (Saltos Shale Member of the Monterey Formation), and intertongues on the southeast with nonmarine redbeds (part of the Caliente Formation). Flow structure in extrusive basalts in the upper part of the transition and paleocurrent features in overlying Miocene alluvial deposits indicate that the shoreline at the time of deposition trended north-northwest. > The marine-nonmarine transition consists of a succession of individual progradational sequences that extend westward (seaward) into marine strata. The sequences exhibit a fairly consistent internal stratigraphic arrangement. A typical complete sequence has a basal unit of unbedded siltstone (Saltos Shale) lying on an erosion surface. A thin zone of conglomerate commonly occurs within the siltstone directly above the lower contact. The siltstone grades up into bedded or unbedded fine-grained sandstone (Branch Canyon Sandstone). This fine sediment is sharply overlain by a coarse, pebbly, crossbedded facies of the Branch Canyon, which grades upward into finer and predominantly planar-bedded sandstone. The planar-bedded sandstone grades up into muddy structureless sandstone that in turn g ades up into red or green mudstone (Caliente Formation), which caps the sequence. The progradational nature of the sequences implies that the fine-grained sandstone near the base was deposited in the marine environment somewhat shoreward from the gradationally underlying siltstone, which locally contains marine invertebrates. Bedding, where present in the fine sandstone, is defined by concentrations of biotite; the bedding is either planar or shows medium- and small-scale cross-stratification. Bioturbational disruption abounds. Crossbedded lenses of well-sorted granular sand are interbedded with the fine sand in its upper part. Foresets in these lenses dip predominantly toward the southeast. Similar structures form in response to the passage of waves in modern high-energy environments. The foreset orientation thus suggests that during the time of deposition the wav s approached from the northwest. The coarse, pebbly sandstone that sharply overlies the fine-grained sandstone is the thickest and best exposed unit of most sequences. Bedding is generally well developed, and bioturbational structures are rare. Pebbles tend either to occur as lag deposits scattered along extensive erosion surfaces within the sandstone or to be concentrated within conglomeratic beds. Crossbedding is abundant and dips predominantly west-southwest (offshore); a small secondary mode dips south-southeast. This secondary mode may reflect the influence of longshore currents resulting from the oblique approach of the waves with respect to the shoreline. A few large-scale crossbedding units dip east and southeast and suggest the presence of offshore bars trending oblique to the coast, parallel with the prevai ing wave crests. The dominantly offshore-dipping crossbeds are best explained as the result of rip currents. The erosional contact at the base of the coarse sandstone resembles the contact formed at the base of rip channels in the modern environment. The planar-bedded sandstone in the upper part of the sequence is well sorted and contains planar concentrations of magnetite that resemble those formed on the upper foreshore of modern beaches. Many planar laminations are inversely graded like those that form at present in the upper swash zone. Where attitudes were measured, most of the planar beds dip gently seaward (west), which also supports a beach origin. End_Page 431------------------------------ The overlying structureless muddy sandstone may represent deposition in a vegetated back-beach environment. The redbeds of the Caliente Formation probably formed in coastal swamps, lagoons, or alluvial plains. End_of_Article - Last_Page 432------------

The Camsell River–Conjuror Bay Area, Great Bear Lake, N.W.T.

Roof pendants of a late Aphebian (~1800 m.y.) volcano–sedimentary complex, within Hudsonian granites, outcrop on the eastern shore of Great Bear Lake. The volcano–sedimentary complex is similar to, and may be correlated with, the Echo Bay Group which outcrops farther to the north.The volcanic rocks are interbedded with immature volcanoclastic sedimentary rocks and with thinner units of calcargillite and dolomite. A unit of conglomerate, tuff, and siltstone, previously correlated with the Cameron Bay Group, is assigned to the 'Balachey Unit', until its relationships with other groups in the area are more clearly understood.Hudsonian granitic stocks and batholiths (~ 1750 m.y.) intruded the complex. Sharp contacts and narrow aureoles characterize these as high level intrusions. Zones of sulfide replacement are common in the aureoles. Porphyry dikes and stocks of similar age to the granites and rare, pegmatitic magnetite–apatite–actinolite bodies, also intrude the volcano–sedimentary complex.Three sets of diabase intrusions are identified, and related to three distinct fault directions. Giant quartz veins and mineralization of the U–Ag–Ni, Co arsenide – Bi type are found in zones of northeast-striking dextral faults.The volcano–sedimentary complex is interpreted as the molasse phase of the rising orogen of the Coronation Geosyncline, and is related to earlier deposits (the Snare and Epworth Groups) closer to the craton in the eastern part of the geosyncline.

THE GROWTH OF CAMBRIAN AND LIASSIC CONCRETIONS

ABSTRACTConcretions from Upper Cambrian sediments in South Wales can be divided into two groups of different ages. An early group (type) are characterised by the association of septarian structures and deformed laminae; whilst later (type Ha) concretions developed both cone‐in‐cone structures and parallel laminae.Determinations of the cement content of individual concretions revealed centrifugal variations related to the porosity changes within the sediment during concretionary growth. Growth of type‐I concretions began in sediment of approx. 70% porosity and continued until compaction had reduced the porosity to less than 40%. Later, type‐IIa concretions began growth in sediment of approx. 30–40% porosity and experienced only slight compaction over their growth spans.Liassic concretions from a prolific concretionary horizon in Dorset developed parallel laminae, but grew early in the absence of compaction (type IIIb) concretions at this horizon grew within the sediment during a pause in deposition.Evidence is described for distinguishing between concretions formed in systems open or closed to seawater. It is concluded that Cambrian concretions grew in closed systems, but the early Liassic concretions may have developed in a partially open system.A model is offered to explain the closed system growth of prolific concretionary horizons. The Cambrian concretions often proliferated along 2–3 cm thick siltstone units, which it is suggested were more permeable than the surrounding mudstones and therefore became pore‐water migration paths. Along these migration paths concretionary growth may have relieved the supersaturation of mobile pore waters.

Liverpool and Strangways Craters, Northern Territory: Two structures of probable impact origin

Two circular structures in the Northern Territory, Australia, are identified as being of probable impact origin. At Liverpool Crater, 1.6 km in diameter, a ring of sandstone breccia with tangentially striking sandstone at the base is exposed. Quartz grains in the breccia exhibit planar features, mosaic structure, and cleavage, indicating moderate shock deformation. At Strangways crater, tangentially striking sandstone and siltstone units define a circular pattern about 16 km in diameter. In the interior are large outcrops of melt breccia with highly shocked inclusions and an outcrop of basement rock, which may mark a central uplift.

Stratigraphy, Age, and Interregional Correlation of the Exshaw Formation, Alberta Rocky Mountains

ABSTRACT The Exshaw Formation of the Alberta Rocky Mountains and foothills consists of a lower, black shale unit and an upper, siltstone unit, which are separated by a gradational contact. At the type section on Jura Creek, near Exshaw, Alberta, the upper contact of the Exshaw is redefined so that the formation includes all, rather than merely the lower part, of an unbroken sequence of dark-yellowish orange-weathering calcareous siltstone. At the type section, the black shale unit is 33 ft thick and the siltstone unit 127 ft. X-ray diffraction data from the type section indicate that the shale is composed mostly of quartz and contains only minor amounts of illite, feldspar, and carbonates. The siltstone has considerably more calcite and dolomite than most of the shale. Throughout its area of outcrop, the Exshaw unconformably overlies limestones of the Devonian Palliser Formation, and is sharply (disconformably?) overlain by shales at the base of the Mississippian Banff Formation. The silts and clays, and some of the carbonaceous material in the black shale unit, were probably derived from soils and deposited in shallow-marine, euxinic lagoons. The siltstone unit was deposited in a regressive, marginal-marine environment of widespread, well-oxygenated tidal flats. Physical continuity is demonstrated between the Exshaw Formation and a) the lower two members of the Bakken Formation in the subsurface of southeastern Alberta and Saskatchewan, b) the Sappington Member of the Three Forks Formation in Montana. Conodont evidence from the Exshaw Formation and circumstantial conodont and spore evidence from the Sappington Member and Bakken Formation show the age of the Exshaw to be Devonian and Mississippian. The systemic boundary is probably positioned near the middle of the black shale unit. Evidence previously cited for the age of the Exshaw at Crowsnest Pass is shown to be more pertinent to the age of the overlying Banff Formation. End_Page 32-------------------------

Stratigraphy and Paleoenvironments of Cretaceous Rocks, Mitchell Quadrangle, Oregon

Cretaceous marine and continental sedimentary rocks, of Albian and possibly Cenomanian ages, crop out in the south half of the Mitchell quadrangle in central Oregon. More than 70 sq mi of Cretaceous rocks is exposed along a northeast-trending, doubly plunging anticline. The sequence, 9,023 ft thick as described along three principal reference sections, lies with angular unconformity on Permian metasedimentary rocks, and is overlain unconformably by Tertiary lava flows and volcanic sedimentary rocks. In part, the rocks have been faulted complexly and there are numerous fault-controlled and randomly oriented intrusions of Tertiary age. These rocks are divided into two intertonguing formations. One, a widespread and thick sequence of marine mudstone with subordinate siltstone and sandstone, is defined herein as the Intertonguing intricately with the marine rocks are conglomerate and sandstone; these, predominantly of fluvial and deltaic origin, are defined herein as the Creek The total sequence consists of the Basal of the Hudspeth Formation, a thin sandstone and conglomerate unit lying unconformably on the Permian basement rock; a thick mudstone and siltstone unit referred to as the Main Mudstone member of the Hudspeth Formation; and 11 numbered conglomerate and sandstone members of the Gable Creek Formation intertonguing with a like number of mudstone and siltstone members of the Hudspeth Formation. Seven tongues of the Gable Creek Formation wedge out southward into the marine facies of the Hudspeth Formation; the four other tongues thin southward. Three Hudspeth Formation marine tongues wedge out northward into the Gable Creek Formation; the six other tongues thin northward. Shapes of tongues, textural and thickness variations, primary sedimentary structures, and current-flow directions indicate that during middle Cretaceous time there was a rising landmass on the north. Very large volumes of coarse sediment were delivered by a major river to a shallow-marine embayment, and extensive alluvial piedmont and delta plains projected into the sea. Swinging distributaries, episodic uplift of the source area, and intermittent subsidence of the basin caused the shoreline to fluctuate and produce a complex intertonguing of fluvial-deltaic sediments with marine sediments.

Stratigraphy and Sedimentology of the Middle Precambrian Rove Formation in Northeastern Minnesota

ABSTRACT The Middle Precambrian Rove Formation as exposed in northeastern Minnesota is approximately 3200 feet thick, and consists of dark gray to black argillite overlain by interbedded argillaceous siltstone and sandstone. The sandstones appear to have been deposited by turbidity currents, for numerous laterally continuous sandstone beds are intercalated with argillite, and persistent sequences of structures occur within the sandstone beds indicating that each bed was deposited by a current of continually decreasing velocity. The orientation of directional structures, chiefly flutes and grooves, indicates that the currents flowed in a southeasterly direction perpendicular to the inferred shoreline. Three lithologic units are recognized: (1) a lower argillite unit, 400 feet thick, (2) a transition unit of intercalated graywacke and silty argillite, 70 to 100 feet thick, and (3) a unit of graywacke and argillaceous siltstone, 2700 feet thick, having thin quartzitic beds in the upper 700 feet. Transition of rocks in the lower argillite to those in the thin-bedded graywacke records an increase in frequency of contribution of coarse detritus to the depositional basin. The mineralogy of the rocks indicates that the source area was composed largely of granitic plutonic rocks and high grade metamorphic rocks, and to a lesser extent of low grade metamorphic rocks. The heavy minerals in the Rove Formation are similar in composition and relative proportion to those in the Lower Precambrian igneous rocks now exposed to the north of the Rove outcrop belt.

Devonian-Mississippian Stratigraphy of Western Mid-Continent Area: ABSTRACT

Stratigraphic relationships of Devonian and Mississippian rocks in the western Mid-Continent region provide overwhelming evidence that mid-Paleozoic seas were transgressive and widespread throughout the area. The present distribution of these marine strata is largely the result of erosion along the Transcontinental arch and adjacent uplifts. Strata of Early Devonian age are known only in areas that were included in the Cordilleran, Ouachita, and Arbuckle geosynclines and the Tobosa, Illinois, and North Kansas basins. These rocks were deposited on a highly eroded terrane. In medial Devonian time the seas transgressed southward from Alberta, Canada, into the North Dakota part of the Williston basin; westward and southward from Iowa into the Kansas-Nebraska part of the North Kansas basin; and eastward from the Cordilleran geosyncline into western Colorado. Middle Devonian strata are absent from Oklahoma and the Transcontinental arch, but are present farther south in the Tobosa basin and the Ouachita geosyncline. If Middle Devonian strata were deposited in Oklahoma and South Dakota, they have been completely removed by pre-La e Devonian erosion which was widespread throughout the eastern half of the western Mid-Continent. Late Devonian rocks indicate a resumption of transgression, and they may have covered the entire region although present distribution of these rocks is the result of Early Mississippian and later periods of emergence along the Transcontinental and associated arches. Mississippian rocks are conveniently divided into Lower Mississippian Series (Waverlyan) which comprises the Kinderhookian Stage and the Osagian Stage, and the Upper Mississippian Series (Tennesseean) which is made up of the Meramecian and Chesteran strata. The dark-shale units of western Montana and northwestern Wyoming, the shale and siltstone units of the Williston basin, and the black shale units which surround the Ozark uplift seemingly contain the Devonian-Mississippian systemic boundary. Elsewhere, basal Mississippian clastic and carbonate rocks are found unconformably not only on Devonian but also on Silurian, Ordovician, Cambrian, and Precambrian rocks. Local facies changes of Mississippian rocks in the area of the Ozark uplift indicate that this region was emergent during th early part of Mississippian time. Mississippian rocks of the western Mid-Continent are dominantly marine, shallow-water deposits. Seaways must have been very extensive in Mississippian time and the Kinderhookian transgressing sea probably came from both the north and south and was deposited on a peneplain-like surface. In western Kansas, late Kinderhookian rocks overlie Early and medial Ordovician rocks and are overlain by late Osagian rocks. Conodonts recovered from cores of western Kansas indicate that Upper Devonian rocks once were present west of the Central Kansas uplift. Mississippian rocks probably covered the entire Mid-Continent and Rocky Mountain regions but were most thin over the Transcontinental arch and the incipient Ancestral Rockies. Locally in south-central Kansas, rocks of Osagian age rest directly on pre-Mississippian rocks and show either (a) that the sea covered territory not inundated by the first transgression, or (b) that rocks of the Kinderhookian Stage were entirely eroded before deposition of Osagian rocks. Some workers believe that a major unconformity is present between Lower and Upper Mississippian rocks on the basis of megafossil studies recovered from outcrops peripheral to the Ozark uplift. However, study of microfossils from these rocks fails to support this hypothesis. Late Meramecian carbonate rocks in western Kansas End_Page 1901------------------------------ contain abundant quartzose clastics thought to be derived from the Central Kansas uplift and Las Animas arch. In the Williston basin, Mississippian rocks are dominantly carbonates but in Late Mississippian time thick evaporites were deposited. Late Mississippian or Chesteran deposits are not common in the Rocky Mountain region and may have been removed by pre-Pennsylvanian erosion. Chesteran time was characterized by advance and retreat of the shallow seas in the Mid-Continent area and strata reflect rhythmic displacement of the strandlines into basinal areas. The Chesteran seas were less widespread than Meramecian seas. Present distribution of Mississippian rocks outlines Late Mississippian-Early Pennsylvanian tectonic features, but the dominant tectonic feature throughout Devonian-Mississippian time was the Transcontinental arch. End_of_Article - Last_Page 1902------------

Stratigraphy and Petrology of Crow Mountain Sandstone Member (Triassic), Chugwater Formation, Northwestern Wyoming

In northwestern Wyoming the Crow Mountain Sandstone Member (Triassic) of the Chugwater Formation is underlain by either the Alcova Limestone Member or the sandy facies of the Red Peak Member. An unnamed redbed unit is locally disconformable on the Crow Mountain. The boundaries of the Crow Mountain are redefined and the member is divided into a basal sandstone unit and an upper sandstone and siltstone unit. The basal sandstone unit is characterized by red and drab, massive, very fine-grained sandstone with medium-scale cross-stratification. The sandstone of the upper sandstone and siltstone unit is red and drab, flaggy to slabby, and very fine-grained. Well-sorted to poorly sorted siltstone beds contain abundant ripple marks and small-scale cross-stratification. Oil staini g is common in the sandstone. Based on 22 modal analyses, the sandstone and siltstone are arkose and subarkose. Of 356 paleocurrent directions that were measured, 32 per cent are between 31° and 90°, and 31 per cent are between 181° and 270°. The two dominant directions were apparently at right angles to the shorelines. The Crow Mountain is interpreted to have been deposited during a westward regression of the sea. The principal environments of deposition were: (1) shallow marine, with moderate to strong currents during deposition of the basal sandstone unit; (2) tidal flat, with weak currents during deposition of most of the upper sandstone and siltstone unit; and (3) beach, during deposition of the uppermost part of the upper sandstone and siltstone unit. Deposits of associated tracts, such as dunes, marshes, and a few alluvial plains, probably occur.

Stratigraphic Traps in a Valley Fill, Western Nebraska

Oil is trapped in a trend of valley-fill sandstone bodies in the Cretaceous J interval in Cheyenne and Morrill Counties, Nebraska. The valley fill is composed chiefly of porous and permeable sandstone; it trends north-south and is about 1,500 ft. wide and 50 ft. thick. Oil has accumulated in the valley fill where it crosses the axes of northwest-plunging anticlines. Updip (eastward) escape of oil is prevented by the enclosing marine sediments of the J interval, in which sandstone beds with low oil-entry pressures are discontinuous and separated by sandstone or shale beds with higher oil-entry pressures. The traps therefore involve a combination of stratigraphic and structural conditions. The J in this area is a sandstone and siltstone unit, 38-77 ft. thick, deposited in predominantly marine environments. The J is overlain and underlain by dark gray marine shale. The interval can be divided into two marine members, an upper and a lower, each relatively thin and with distinctive mineralogy, sedimentary structures, fossil content, and electric-log character. These members can be traced over hundreds of square miles in western Nebraska. After deposition of the upper member, the area emerged and a stream cut a narrow valley which was filled mainly with sandstone of distinctive character. The stream in the valley cut through most or all of the two previously deposited marine members. The trend of the valley fill is nearly straight, suggesting that erosion and deposition were the work of a meandering stream whose width was much less than that of the valley. Seven fields have been discovered along the valley-fill trend within the study area. One well of every 1.9 wells drilled into the valley fill has been completed successfully. These wells are rated as good producers and have long productive lives by Denver basin standards. Some production also has been developed in marine sandstone beds of the J near the area of the valley fill, but only one well of approximately every 10.9 drilled is completed successfully; moreover, productivity commonly is low and total reserves are small. Therefore, stratigraphic study leading to an improved understanding of the genesis and form of the sandstone reservoirs is of considerable economic value.

THE STRATIGRAPHY OF THE PERMIAN OF THE NORTHERN PERTH BASIN, WESTERN AUSTRALIA

The Perth Basin is a narrow, deep graben flanking the lower 400 miles of the west coast of Western Australia. It attains a maximum width of 60 miles and may contain more than 40,000 feet of sediments.Permian rocks crop out around the northern margin of the basin, between the Greenough Precambrian Inlier on the west and the Darling Fault on the east. Bores near the northern margin of the basin and down the west coast for some 120 miles south of Geraldton have encountered Permian rocks. Because of the limited nature of the outcrop, most of our information concerning variations of stratigraphy within the Permian comes from these bores.As in other basins in Australia, the Permian sedimentation in the Perth Basin started with a cycle of intense glaciation. Two units were deposited: the lower one is a submarine tillite consisting of boulders set in a sandstone and siltstone matrix; the upper unit is a fossiliferous marine shale. The thickest development of these units is adjacent to the eastern boundary fault of the basin. They thin rapidly to the west by sedimentary onlap on to the Beagle Ridge.The glacial cycle is followed by a continual cycle in which coal measures predominate. This unit shows a remarkable constancy of thickness, indicating very stable tectonic conditions during its deposition.The coal measures are followed by a monotonous marine siltstone unit which completes the Lower Permian (Artinskian) sequence in this basin.After a hiatus in which both tectonism (faulting and tilting) and erosion occurred, a series of estuarine lakes developed in uppermost Permian times, and the Wagina Sandstone was deposited. These rather restricted lakes were then followed by the more widespread Lower Triassic transgression in which the Kockatea Shale blankets most of the Permian.Significant signs of oil are seen in several of the Permian units-oil in the Coal Measures, oil and gas in the overlying marine strafes, and oil and gas associated with the Wagina Sandstone. Thus the Permian ranks as one of the best potential source and reservoir sequences for hydrocarbons in the Perth Basin.

POLYGONAL SANDSTONE FEATURES IN BOUNDARY BUTTE ANTICLINE AREA, SAN JUAN COUNTY, UTAH

Research Article| September 01, 1965 POLYGONAL SANDSTONE FEATURES IN BOUNDARY BUTTE ANTICLINE AREA, SAN JUAN COUNTY, UTAH I. Q TOMKINS I. Q TOMKINS 1425 EAST 9TH SOUTH, SALT LAKE CITY 5, UTAH Search for other works by this author on: GSW Google Scholar Author and Article Information I. Q TOMKINS 1425 EAST 9TH SOUTH, SALT LAKE CITY 5, UTAH Publisher: Geological Society of America Received: 04 May 1964 Revision Received: 26 Mar 1965 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 Copyright © 1965, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1965) 76 (9): 1075–1080. https://doi.org/10.1130/0016-7606(1965)76[1075:PSFIBB]2.0.CO;2 Article history Received: 04 May 1964 Revision Received: 26 Mar 1965 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 I. Q TOMKINS; POLYGONAL SANDSTONE FEATURES IN BOUNDARY BUTTE ANTICLINE AREA, SAN JUAN COUNTY, UTAH. GSA Bulletin 1965;; 76 (9): 1075–1080. doi: https://doi.org/10.1130/0016-7606(1965)76[1075:PSFIBB]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 Large sandstone polygons interbedded with siltstone units of the Carmel Formation of Jurassic age were formed by eolian infilling of mud cracks with sand, followed by lithification and partial removal of the easily eroded siltstone “mold.” Experimental and field evidence indicates that the thickness of a homogeneous mud deposit controls the dimensions of mud-crack development. 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.

Eddy viscosity as a possible acoustic absorbtion mechanism in the ocean : Schulkin M., 1963. J. Acoust. Soc. Amer., 35 (2): 253–254

Foraminifera and diatoms have been analyzed from an upper Miocene through Pleistocene(?) sequence of marine sediments exposed on Maria Madre Island, largest of the Trés Marias Islands off the Pacific coast of Mexico. The Neogene stratigraphic sequence exposed on Maria Madre Island includes a mid-Miocene(?) non-marine and/or shallow marine sandstone unconformably overlain by a lower upper Miocene to uppermost Miocene upper to middle bathyal laminated and massive diatomite, mudstone, and siltstone unit. This unit is unconformably overlain by lower Pliocene middle to lower bathyal sandstones and siltstones which, in turn, are unconformably overlain by upper Pliocene through Pleistocene(?) upper bathyal to upper middle bathyal foraminiferal limestones and siltstones. These beds are unconformably capped by Pleistocene terrace deposits. Basement rocks on the island include Cretaceous granite and granodiorite, and Tertiary(?) andesites and rhyolites. The upper Miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of Bolivina indicating low oxygen conditions in the proto-Gulf Maria Madre basin. The diatomaceous unit grades into a mudstone that contains a latest Miocene upper to middle bathyal biofacies characterized by Baggina californica and Uvigerina hootsi along with displaced neritic taxa. An angular unconformity separates the upper Miocene middle bathyal sediments from overlying lower Pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including Neogloboquadrina acostaensis and Pulleniatina primalis indicating an early Pliocene age. Significantly, this Pliocene unit contains common occurrences of benthic species restricted to Miocene sediments in California including Bulimina uvigerinaformis. Pliocene to Pleistocene(?) foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the Trés Marias Island area, and include abundant planktonic foraminifera such as Pulleniatina obliquiloculata and Neogloboquadrina duterteri. Common benthic foraminifera in this unit are indicative of upper bathyal water depths. The Neogene depositional history recorded on Maria Madre Island involves an early late Miocene subsidence event marking formation of the Trés Marias Basin with relatively undiluted diatomaceous sediment deposited in a low oxygen setting. Subsidence and deepening of the basin continued into the early Pliocene along with rapid deposition of terrigenous clastics. Uplift of the basinal sequence began in late Pliocene time accompanied by deposition of upper Pliocene-Pleistocene foraminiferal limestones on a rising submarine bank. Continued episodic uplift of the Neogene deposits brought the island above sea level by late Pleistocene time.

The stratigraphy and sedimentary features of the Old Red Sandstone, portishead coastal section, north-east Somerset

Detailed examination of the Old Red Sandstone succession, which is unconformably overlain by Triassic Dolomitic Conglomerate, has permitted subdivision into twelve formations. The Lower Old Red Sandstone comprises cross-bedded sandstones but the younger rocks are more diversified and may be separated into conglomerate, sandstone and siltstone units. The Lower and Upper Old Red Sandstone contact is a conspicuous disconformity. The beds above and below the disconformable surface display layers of well-developed cornstone, which are interpreted as ancient caliche deposits. Cross-bedding studies show that the Old Red Sandstone sediments were mainly derived from the north-west.

On the 'Snake Hill Shale'

Restudy of the terrain mapped as Hill Shale in eastern New York reveals that at least 3 lithic units are present in it. One of these underlies the other 2, which are lateral equivalents of each other. At Snake Hill, the type locality of the Hill Shale, the upper part of the Normanskill Formation is the only unit present and the Austin Glen Graywacke member forms the crest of the hill. A lithic unit composed of pebbles, cobbles, and boulders of graywacke, mudstone, and argillite as well as other lithologies in a matrix of highly contorted black shale overlies the Normanskill Formation E. of Snake Hill and a unit composed mostly of siltstone overlies it W. of Snake Hill. The siltstone unit apparently grades laterally into the Canajoharie Shale. The upper part of the Normanskill Formation and the 2 overlying units are early Trenton in age. The name Hill Shale should be abandoned.

Paleozoic Sequence in Eastern Brooks Range, Alaska

The sequence described lies in the eastern Brooks Range in northeastern Alaska. Rocks of late Paleozoic age predominate but rocks as young as Jurassic are present. Rocks of Devonian and possibly older age occur in two east-trending belts. In the southern belt the Skajit Limestone, 500-2,600(?) feet thick, formerly believed to be of Silurian age, is now determined to be of Middle(?) and Late Devonian age. An unnamed unit of limestone and siltstone (Upper Devonian), 0-2,500(?) feet thick, rests on the Skajit. The limestone-siltstone unit intertongues with and is overlain by an unnamed unit of slate and sandstone (Upper Devonian) 2,000-4,500 feet thick, which locally rests disconformably on the Skajit. The Kanayut Conglomerate (Upper Devonian), 0-5,000 feet thick, conformably overlies the slate-sandstone unit and probably grades into it laterally. Rocks in the northern belt comprise the four members of the Neruokpuk Formation of Late(?) Devonian or older age; a quartzite-schist member more than 4,000 feet thick, a limestone member 1,000± feet thick, a limestone-phyllite member 1,000± feet thick, and a phyllite-chert member, as much as 3,300 feet thick, which overlies the other members, locally with strong angular unconformity. The Kekiktuk Conglomerate, a new formation of Devonian or Mississippian age, 0-400 feet thick, unconformably overlies the Neruokpuk Formation. The formations of Mississippian age occur in both belts. The Kayak Shale (Lower Mississippian) and Kayak(?) Shale (Lower(?) and Upper Mississippian), 400-1,200 feet thick, rest on the Kanayut and Kekiktuk Conglomerates and, locally, on the Neruokpuk Formation. The Lisburne Group comprises three formations. The Wachsmuth Limestone (Lower Mississippian), 0-950 feet thick, disconformably overlies the Kayak Shale in the western part of the area. The Alapah Limestone (Upper Mississippian), 600-1,950 feet thick, rests disconformably on the Wachsmuth Limestone. Where the Wachsmuth is absent, the Alapah rests conformably on the Kayak(?) Shale. The Wahoo Limestone (a new formation of Pennsylvanian(?) and Permian age), 0-1,400 feet thick, overlies the Alapah with probable disconformity. The Siksikpuk Formation (Lower(?) Permian), is more than 600 feet thick and consists mostly of shale. It rests unconformably on the Wahoo Limestone at Galbraith Lake and on the Alapah Limestone west of Galbraith Lake. East of Galbraith Lake the Sadlerochit Formation (Permian and Triassic) overlies the Wahoo limestone. The Sadlerochit is more than 1,000 feet thick, and consists of sandstone, siltstone, and shale. Unconformities suggest uplift during early Late Devonian time and folding during Late Devonian to Early Mississippian time. The regional unconformity between Mississippian and Permian rocks diminishes eastward and deposition may have been continuous through Pennsylvanian time in part of the eastern Brooks Range.

Formational Divisions of Difunta Group, Parras Basin, Coahuila and Nuevo Leon, Mexico

The Difunta Group of the Parras Basin, southern Coahuila and western Nuevo Leon, Mexico, consists of two major intertonguing lithic facies with a composite thickness of approximately 4,000 meters. Three gray, brown, red, and green, partly variegated, fine- to coarse-grained calcareous sandstone, siltstone, and mudstone units are thickest on the south in the Saltillo-General Cepeda area; they wedge out north and east in the vicinity of the Saltillo-Paredon-Hipolito railroad. Four units of interbedded, black, gray, brown, and green calcareous shales and siltstones and gray to brown sandstones and shales occur between the red units. East of the Saltillo-Paredon-Hipolito railroad they compose an as yet undifferentiated sequence. The various red and gray-brown units have been mapped westward and northward from the vicinity of Saltillo for distances of approximately 100 and 50 miles, respectively, in a region of relatively complex structure. They are, therefore, mappable lithic units and are thus defined as formations in this paper, being named in descending order: Rancho Nuevo, Las Encinas (redbeds), Cerro Grande, Las lmagenes (redbeds), Canon del Tule, Cerro Huerta (redbeds), and Cerro del Pueblo Formations. Type localities for the various formations are located along or adjacent to major roads leading south-southwest and north-northwest from Saltillo.