Geosynclinal Facies Research Articles

The anomalous behaviour of properties of seams at the Plessey (M) horizon of the Northumberland and Durham coalfields

The Oligocene coals from the northeastern part of the Assam-Arakan basin show a gradual decrease in the content of moisture, volatile matter and oxygen with corresponding increase in carbon content and calorific value from the Foreland Shelf to the deeper part of the geosyncline, reflecting the coalification trends in this basin. It has been suggested that the oxygen was replaced by organic sulphur, thereby lowering the oxygen content in the coals. The coals are perhydrous in nature with a high sulphur content. The high volatile content, perhydrous nature and high sulphur content in the Oligocene coals, as well as the presence of streaky facies and a very fine clastics unit, indicate that they were probably deposited in a marine-influenced deltaic and lagoonal environment.The plots of carbon versus hydrogen on Seyler's coal band follow a trend which differs from that of Seyler's band of Carboniferous bright coals. The coalification of the Oligocene coals represents the lignitic stage, in the case of the Foreland Shelf, and near subbituminous stage in the deeper geosynclinal part of the basin. A more intense, and probably sudden, dynamic process was involved in bringing about higher coalification in Oligocene coal of the geosynclinal facies than in Foreland Shelf area. This is possibly due to intense mountain-building forces acting from the southeastern direction of the basin.

Palynostratigraphy of the tertiary sediments of Meghalaya, Northeastern India - Present status and gaps

Thick and extensive Tertiary sediments. belonging to both shelf and geosynclinal facies, occupy the southern part of the Meghalaya Plateau. The basal part of these sediments is represented by the Langpar Formation which is followed by Jaintia (Therria. Sylhet Limestone and Kopili formations), Barail (Laisong. Jenam and Renji formations), Surma (Bhuban and Bokabil formations), Tipam (Tipam Sandstone and Girujan Clay formations), Dupitila and Dihing groups. In Garo Hills, these sediments are classified into various other differently named formations. A considerable amount of palynological information has so far been published from these sediments, which provides useful data for biostratigraphic zonation, correlation and age determination and for interpreting palaeoclimate, palaeogeography and environment of deposition. An effort has been made, in the present paper, to synthesize the published palynological work on these sediments in order to understand the present status of the Tertiary palynostratigraphy of Meghalaya. It has been noticed that the various palynozones established in the Tertiary sequence of Meghalaya can be recognized by their peculiar palynofossil assemblages. This is particularly useful in the correlation of homotaxial stratigraphic units in Garo, Khasi and Jaintia Hills and in the interbasinal correlation. In spite of a good deal of palynodata available, there are plenty of gaps in our knowledge regarding Tertiary palynostratigraphy of Meghalaya that deserve attention of palynologists. These gaps have been identified for the future studies.

An overview of chemical properties of marine-influenced Oligocene coal from the northeastern part of the Assam-Arakan basin, India

The Oligocene coals from the northeastern part of the Assam-Arakan basin show a gradual decrease in the content of moisture, volatile matter and oxygen with corresponding increase in carbon content and calorific value from the Foreland Shelf to the deeper part of the geosyncline, reflecting the coalification trends in this basin. It has been suggested that the oxygen was replaced by organic sulphur, thereby lowering the oxygen content in the coals. The coals are perhydrous in nature with a high sulphur content. The high volatile content, perhydrous nature and high sulphur content in the Oligocene coals, as well as the presence of streaky facies and a very fine clastics unit, indicate that they were probably deposited in a marine-influenced deltaic and lagoonal environment. The plots of carbon versus hydrogen on Seyler's coal band follow a trend which differs from that of Seyler's band of Carboniferous bright coals. The coalification of the Oligocene coals represents the lignitic stage, in the case of the Foreland Shelf, and near subbituminous stage in the deeper geosynclinal part of the basin. A more intense, and probably sudden, dynamic process was involved in bringing about higher coalification in Oligocene coal of the geosynclinal facies than in Foreland Shelf area. This is possibly due to intense mountain-building forces acting from the southeastern direction of the basin.

Lithostratigraphy of the Tertiary sediments exposed along Jowai-Badarpur Road in Jaintia hills (Meghalaya) and Cachar (Assam)

The paper includes the field observations on the sediments along Jowai-Badarpur Road section in Jaintia Hills and Cachar, depicting their lithostratigraphy. Starting from Jowai towards Badarpur various Tertiary sediments were observed. In ascending order, these are Therria, Sylhet Limestone, Kopili, Laisong, Jenam, Renji, Bhuban, Bokabil, Tipam Sandstone and Recent alluvia. The lithology, nature and location of contacts and fossil contents of each of these formations are discussed.
 At Sonapur, 76 km from Jowai, the section is crossed by the Dauki Tear Fault, which separates the Palaeocene-Eocene rocks of the shelf facies to the north from the Oligocene-Miocene rocks of the geosynclinal facies to the south.

Geology and Geochronology of the Wollaston Lake Fold Belt in Northwestern Manitoba

Recent studies in the northeastern extension of the Wollaston fold belt in Manitoba suggest that Aphebian metasedimentary rocks of the southern Churchill province comprise a geosynclinal facies that is conformably overlain by a platform facies. A possible period of emergence and embryonic Hudsonian tectonism separates this lower sequence from a blanket of continental deposits, which is probably of large regional extent and includes part of the Hurwitz Group in the District of Keewatin.Rubidium–strontium total-rock isochron ages have been obtained for five rock units in the Kasmere Lake area of Manitoba. The ages reveal that the metasedimentary rocks of the Wollaston fold belt are bounded to the east by an Archean complex comprising a differentiated hypersthene-bearing rock series having a minimum age of 2745 ± 124 Ma (87Rb = 1.39 × 10−11 yr−1) and a quartz monzonite unit having a minimum age of 2636 ± 163 Ma.Hudsonian igneous rocks are mostly syn- to post-kinematic. The age of 1855 ± 62 Ma for a quartz monzonite of batholithic dimension coincides with the ages of similar syntectonic Hudsonian intrusions in the Northwest Territories. The age of 1800 ± 60 Ma obtained from a pelitic gneiss unit is a minimum age for the Hudsonian metamorphism and dates the end of the Hudsonian orogeny in this part of the Churchill province. An age of 1941 ± 25 Ma for a granitic gneiss along the western margin of the Wollaston fold belt indicates early or pre-Hudsonian magmatic activity.

Tectonomagmatic History of the Precambrians in Bellary District, Mysore State

Abstract A chronostratigraphic classification of the Precambrians in Bellary district, Mysore State, based on tectonomagmatic cycles in the evolution of geosynclinal facies is presented for the first time by the author. The older metamorphics are grouped under 'Archaeans' (2500 m.y. and above) and the Dharwars, under Proterozoic (2500-900 m.y.), Structurally four kinds of folds are described. The first cycle of folding, F1, consists of the earlier formed anticlines and synclines plunging northerly or NNW. The second cycle, F2, comprises asymmetric cross-folding of the earlier structures, plunge being parallel to the direction of plunge of the earlier folds. The third, F3, and the fourth, F4, cycles of folding consist of antiforms and Synforms on bedding and en echelon drag folds. the structural pattern in the district reveals that all the different tension and stress expressions are together consistent with orle general stress field, a horizontal compression.

Sedimentology and Dolomitization of Muschelkalk Carbonates (Triassic), Iberian Range, Spain

Triassic rocks of the Iberian Range consist of a succession of continental sandstones (Buntsandstein), peritidal carbonates and shales (Muschelkalk), and continental claystones and evaporites (Keuper). This Germanic platform facies closely resembles equivalent rocks in the Balearic Islands; consequently, any hinge line separating platform from geosynclinal facies must lie an undetermined distance southeast of the Balearics. Dolostone, which comprises 75 percent of Muschelkalk carbonates, bears no relation to sedimentary facies; to the contrary, it is demonstrably joint controlled. This fact, together with the near absence of dedolomite, indicates a late and sustained magnesium/calcium ratio in excess of that expected from an evaporite-bearing assemblage. Water samples from Keuper salinas (salt-producing evaporating pans) show that meteoric water descending through the Keuper evolves into a brine with Mg:Ca ratios locally 4:1, in spite of the abundant gypsum and anhydrite. X-ray analysis suggests chlorite as a source of the magnesium, the solubility of which probably reflects diagenetic fixing in the Keuper evaporite basin. The composition of Keuper water, aided prior to unloading by geothermal gradient, is thought to be responsible for Muschelkalk dolomitization.

Basement Rock facies—Northern North Island

Abstract Geographic names are proposed for three geosynclinal facies of the northern North Island in preference to those in current use. Rocks of the Oparau Facies (synonyms—Hokonui; Shelf; Western; and Marginal, in part) are fossiliferous and tuffaceous, are simple structurally, and show increasing low-grade metamorphism with age. They form part of the zeolite mineral facies. Rocks of the Morrinsville Facies (synonyms—Alpine, in part; Marginal, in part; and Eastern) are thick monotonous sparsely fossiliferous greywackes, chipwackes, and siltwackes that include neither tuff beds nor lavas. They lie in the quartz-prehnite zone of the prehnite-pumpellyite metagreywacke facies. Rocks of the Hunua Facies (synonyms—Alpine, in part; Axial, in part; and Marginal, in part) are very thick, commonly sheared, siltwackes and greywackes, with intercalated spilitic lavas, cherts, and limestone. They lie in the quartz-prehnite zone of the prehnite-pumpellyite metagreywacke facies, probably somewhat higher grade than roc...

Possible Future Petroleum Provinces of United States Western Gulf Basin--Pre-Jurassic: ABSTRACT

In the western Gulf basin, the pre-Jurassic section can be subdivided into (1) foreland Paleozoic strata (Black Warrior basin), (2) orogenic geosynclinal facies (Ouachita tectonic belt), (3) late-orogenic, late Paleozoic rocks, and (4) post-orogenic, Late Triassic strata. A good potential for future petroleum provinces of economic interest can be recognized in the Black Warrior basin, and on the Gulf of Mexico side of the Ouachita tectonic belt, in late-orogenic, late Paleozoic strata. A remote possibility is recognized for the presence of commercial accumulations of hydrocarbon in sub-thrust lower Paleozoic foreland carbonates beneath the interior part of the Ouachita fold belt. The hydrocarbon potential of geosynclinal sediments of the Ouachita tectonic belt, and of the post-orogenic Triassic section, is considered to be negligible. The Black Warrior basin of Mississippi and Alabama contains a thick section of Paleozoic foreland rock. Although production dates back to 1909 and hydrocarbon shows have been numerous, the proved reserves are insignificant. The deep structural configuration has been difficult to map, and this has deterred deep drilling. The basin tectonics should be comparable to those of other foreland basins, in which large, buried, normal faults are characteristic. Improved seismic techniques should reveal similar anomalies in the Black Warrior basin. Large hydrocarbon accumulations may ultimately be found in deep fault traps in lower Paleozoic carbonates, and such prospects are sparsely tested. There is no production from pre-Jurassic rocks gulfward from the Ouachita front. However, exploration of this section has been quite limited, mainly because of the absence of attractive objectives. Most wells drilled below the Jurassic have found either tight, highly deformed, geosynclinal facies of the Paleozoic Ouachita system, or redbeds and igneous rocks of the Late Triassic Eagle Mills Formation. Since 1960 a few highly significant, but unpublicized, wildcats have penetrated relatively undeformed, very fossiliferous, shallow-water shelf carbonates and clastics of Pennsylvanian age beneath the coastal plain. These strata, identified from fusulinids as Desmoinesian, are present on the Gulf of Mexico side of the Ouachita fold belt in wells drilled in northeast Texas and southwest Arkansas. Commercial porosities have been found in both sandstones and carbonates. Only fragmentary data are available, but the mere presence of these strata suggests that a potentially large, virtually unexplored, petroleum province may be present in late Paleozoic rocks of the Gulf coastal plain. End_Page 1792------------------------------ A recent 20,000-ft test in Texas penetrated thick lower Paleozoic shelf carbonates on a large seismic anomaly beneath the interior zone of the Ouachita system. Although the objective carbonates were metamorphosed there, the possibility of finding favorable reservoir rock elsewhere in this trend is not necessarily eliminated. End_of_Article - Last_Page 1793------------

The Mesozoic of New Zealand: Chapters in the history of the Circum-Pacific Mobile Belt

The Mesozoic includes the later history of the New Zealand Geosyncline, the Rangitata Orogeny that ended the geosynclinal phase, superposing a new structural system, and the beginning of the transgression that followed. The main elements of the geosyncline, from west to east, are: (1) a foreland, metamorphosed and intruded by granite in a relatively high temperature/low pressure environment; (2) a geosynclinal margin or hinge-line, the median tectonic line of Landis and Coombs; (3) a western or marginal belt of geosynclinal sediments (Hokonui Facies) relatively fossiliferous, apparently deposited over the Pacific edge of the sial and now forming a western marginal syncline; (4) an abrupt facies junction marked by ultramafic intrusions and Permian volcanics, perhaps the early Mesozoic oceanic boundary of sialic crust; and (5) an eastern belt of relatively unfossiliferous deformed sediments of the greywacke suite (Torlesse Facies), metamorphosed in a high pressure environment, their lower parts to schist. The western or Hokonui zone records rapid and almost continuous marine sedimentation during the Triassic and Jurassic, with some brief local interruption during the Middle Jurassic. The eastern or Torlesse zone of thick quartzo–feldspathic greywackes and argillites, with some spilitic lavas, occupying a Pacificmargin trench, has proved difficult to interpret owing to structural complexity, lithological monotony and scarcity of fossils. The metamorphic boundaries vary in age in different places, and the known fossils show a nonrandom distribution in age and space, as if basins of rapid sedimentation migrated up and down its axis throughout Permian to Tithonian time, reacting to variable thermal gradients. The Rangitata Orogeny began with precursor movements in the Middle Jurassic but climaxed in the Lower Cretaceous. The orogeny led to the main metamorphism and folding of the geosyncline, long the East phases of granite intrusion in the foreland, and the torsion and rupture of the geosyncline along the transcurrent Alpine Fault. In the Aptian, basins within the New Zealand geosyncline received sediment still of geosynclinal facies, so that it remains uncertain whether deposition was locally continuous or whether the Cretaceous is everywhere unconformable on underlying rocks. Synorogenic breccias (pre-Campanian) locally overlie schist and foreland granites that have been dated isotopically as mid-Cretaceous, and thus point to rapid uplift and erosion. By the Macstrichtian, freshwater and marine sediments indicate peneplanation and dominantly chemical weathering. The Tasman Sea is first evident in the Cretaceous, and the Cretaceous transgression, continuing in the Tertiary, reduced the land to a changing archipelago. Early Mesozoic structures are consistent with a simple continent–ocean boundary and trench trending north-west, parallel to the Mesozoic Darwin Rise. The Cretaceous orogeny superposed north-east trending structures that have dominated later history; their northern parts face the Pacific and parallel a section of the East Pacific Rise, but their southern parts face the Tasman Sea in a kind of scissors or ‘anceps’ structure. The change from a single Pacific margin to the present anceps structure facing both the Pacific and Tasman is consistent with post-Jurassic development of the Tasman and other marginal ocean basins during the Cretaceous orogeny, which entailed considerable horizontal movements of the crust. New Zealand geology can be extrapolated onto the surrounding shallow sea-floors, underlain by subcontinental crust, using evidence from outlying islands, submarine geology, and geophysics. The speculative process of rationalizing Lower Mesozoic palaeogeography is made easier if it is assumed that the early Mesozoic arc, now sinuous, was originally straighter, and that the marginal ocean basins now interrupting its course developed during the Cretaceous deformation that led to its curvature.

Tectonic and Sedimentary History of Raton Basin and Notes on San Luis Basin: ABSTRACT

The Raton basin of northeastern New Mexico and southeastern Colorado is a Laramide structural basin bounded on the west by the Sangre de Cristo uplift, on the north by the Wet Mountains uplift and Apishapa arch and on the east by the Sierra Grande and Las Animas arches. The basin is strongly asymmetrical and the northerly-trending axis is near the Sangre de Cristo uplift. The intrabasinal Cimarron arch separates the structurally deeper northern part of the Raton basin from the shallower, southern, Las Vegas subbasin. During most of Paleozoic time the Raton basin and its bounding uplifts were part of the relatively stable Continental backbone. The oldest known sedimentary rocks in the basin are Devonian (?). In Early Pennsylvanian the Rowe-Mora basin was formed in the area of the present Sangre de Cristo uplift and the western half of the present Raton basin. The Rowe-Mora basin was bounded on the west by the intermittently rising San Luis uplift and on the east and north by the ancestral Sierra Grande Apishapa and Wet Mountains uplifts. An unstable-shelf facies of the Magdalena Group of Pennsylvanian age in the southern part of the Rowe-Mora basin is 1,500-2,500 feet thick. These rocks grade abruptly northward into a geosynclinal facies which is as much as 6,000 feet thick in the Las Vegas subba in. The Magdalena Group is absent from the Cimarron arch, but it probably is present in the western half of the northern part of the Raton basin where it may be 4,000 feet thick. Orogenic debris of the Sangre de Cristo Formation of Pennsylvanian and Early Permian age was derived mainly from the San Luis uplift, filled the Rowe-Mora basin, and lapped into Precambrian rocks of the other bounding uplifts. The Sangre de Cristo Formation is 700-3,500 feet thick at the south, and 6,000-10,000 feet thick at the north. Higher Permian rocks and Upper Triassic and Upper Jurassic rocks have average aggregate thicknesses ranging from 2,300 feet at the south to 1,100 feet at the north. These deposits blanketed the entire region and buried most of the late Paleozoic uplifts. Cretaceous shales interbedded with some sandstones also blanketed the region. These rocks are about 4,500 feet thick at the north, and remnants in the Las Vegas subbasin are 900-1,000 feet thick. The latest Cretaceous and early Tertiary rocks, which are about 12,000 feet in aggregate maximum thickness in the northern part of the Raton basin, were derived mainly from the rejuvenated San Luis uplift. During early and middle Tertiary the western part of the Paleozoic Rowe-Mora basin was elevated to form the Sangre de Cristo uplift, and the present Wet Mountains uplift and the Apishapa, Las Animas, and Sierra Grande arches were formed. In late Tertiary the San Luis uplift was tilted eastward and its eastern part foundered to form the northern part of the complex Rio Grande trough. The San Luis basin in southcentral Colorado is the northeastern part of this tilted and faulted block. The western part of the basin merges into the eastern flank of the San Juan dome. The eastern and northern boundaries are a complex fault zone along the western margin of the Sangre de Cristo uplift which merges, around the northern end of the basin, with the Sawatch and Gunnison uplifts. Much of the San Luis basin is filled with upper Tertiary and Quaternary sediments and interbedded andesites and basalts that are at least 2,000 feet thick locally. This basin fill rests on lower and middle Tertiary volcanics that are related to the volcanics of the San Juan Mountains. Because the region of the San Luis basin was a part of the Paleozoic and Laramide San Luis uplift, it is doubtful that extensive areas of Paleozoic and Mesozoic rocks are preserved beneath the volcanics. End_of_Article - Last_Page 1875------------

Distribution and Facies of Pennsylvanian Rocks of Sangre de Cristo Mountains and Raton Basin, New Mexico: ABSTRACT

In Pennsylvanian and early Permian time north-central New Mexico and the adjacent part of Colorado were the site of the Rowe-Mora geosyncline--a narrow, north-trending depositional basin bounded on the west by the ancestral San Luis-Uncompahgre highland and on the east by the ancestral Sierra Grande uplift. The southern part of the geosyncline was divided by the Pedernal uplift, the main trough being at the west, and the Las Vegas sub-basin at the east. Sediments of the Magdalena group of Pennsylvanian age were deposited as a predominantly marine suite during formation of the geosyncline, and sediments of the overlying Sangre de Cristo formation of Pennsylvanian and Permian age were deposited as a predominantly non-marine suite which finally filled the geosyncline. During Laramide orogeny the troughal part of the geosyncline was elevated to form the Sangre de Cristo uplift and the shallower eastern part was downfolded to form the Raton basin. Rocks of the Magdalena group exhibit two facies. Thick limestone and sandstone and interbedded shale were deposited on a shelf in the southern part of the geosyncline. These rocks are as much as 2,500 feet thick. The shelf facies thickens northward and grades rapidly into a geosynclinal facies. The gradation occurs along a belt trending northeastward across the mountains and into the subsurface of the southern part of the Raton basin. The geosynclinal facies is dominantly black shale containing thick beds of sandstone and thin beds of limestone. This facies originally was more than 10,000 feet thick in the deeper part of the trough and is more than 5,000 feet thick in the subsurface of the western part of the Raton basin in Mora County. In the southern part of the geosyncline on the Pedernal uplift, the shelf facies of the Magdalena group is truncated locally by the Sangre de Cristo formation. At the east side of the Las Vegas sub-basin the shelf facies is truncated by the Sangre de Cristo formation, which rests on Precambrian rocks of the ancestral Sierra Grande uplift. At the north in Colfax County, on much of the eastern limb of the Raton basin, the Sangre de Cristo formation or Triassic rocks rest on Precambrian rocks of the ancestral Sierra Grande uplift. A thick sequence of the geosynclinal facies of the Magdalena group is present in the mountains at the west. These rocks wedge out beneath the Sangre de Cristo formation in the subsurface of the western part of the Raton basin. Thick black shales of the geosynclinal facies might be sources of petroleum; however, the interbedded sandstones and limestones are tight. Sandstones of the shelf facies generally are more porous and permeable. Limestones of the shelf facies could be the best reservoirs, and shows of oil and End_Page 1093------------------------------ gas have been reported from these rocks in the Las Vegas sub-basin and near the southern end of the mountains. Small bioherms and associated calcareous clastic rocks occur at places in the shelf facies, particularly near the western margin of the Pedernal uplift, and may be present also in the subsurface along the eastern margin of the uplift and along the northeast-trending belt of transition from shelf to geosynclinal facies. Combination stratigraphic and structural traps may occur along the belts of wedge-out of the Magdalena on the Pedernal uplift and the west flank of the ancestral Sierra Grande uplift. Whether suitable reservoir rocks are present in these areas of wedge-out is not known. A thin but widespread sequence of Devonian(?) and Mississippian age contains cavernous limestone and breccia, but these rocks lie beneath possible source beds and rest on Precambrian crystalline rocks. End_of_Article - Last_Page 1094------------

Revision of Lower Cretaceous Stratigraphy of Venezuela

The understanding of the Cretaceous stratigraphy in Venezuela is hampered by some vaguely defined or unsuitable type localities. A revision of the formation of Western Venezuela is proposed as fresh exposures at the type locality on the Rio revealed that the contact with the La Luna is a fault zone, and that a large part of the succession is repeated by a thrust. The name Cogollo is retained for a unit (group) between the underlying Rio Negro formation and the overlying La Luna formation, as defined by Hedberg and Sass (1937). Three distinct rock units, namely, from top to bottom, the Maraca, Lisure, and Apon formations, are recognized in the group. The Apon formation was introduced by Sutton in 1946 for the lower part of the group. By a very conspicuous and widespread interval of black laminated limestones containing limestone concretions (La Luna lithotope), the Apon formation is again subdivided into three units: the lower, middle, and upper Apon members. The lithologic character, combined with a rich ammonite fauna, makes the middle Apon an outstanding key formation. The Apon formation of Sutton is unchanged but his overlying Aguardiente is just a small part of the new Lisure formation. The upper part of Sutton's Capacho is an equivalent of the Maraca formation. For a long time it was felt that the El Cantil formation (Liddle, 1928) of northeastern Venezuela needed a revision. It comprises the interval between the Barranquin formation below and the Guayuta group above. As type locality of a unit of such magnitude the section of El Cantil on Rio Punceres is so poor that it should be discarded. Hedberg and Pyre (1944) made the first step to correct the erroneous conception of the El Cantil when they recognized the Chimana formation. It is proposed to subdivide the interval between the Barranquin and Guayuta group into three formations: the Borracha, Chimana, and Boqueron formations which, in turn, are subdivided into members (lower Borracha, middle Borracha or Garcia, upper Borracha members; lower Chimana (Placeta), middle Chimana (Guacharo), and upper Chimana (Corral Viejo) members. The biostromal limestone facies of the shaly Boqueron formation is called the Majagual formation. All the unmetamorphosed Cretaceous sediments observed in Western Venezuela, the Andes of Merida, and northeastern Venezuela are shelf deposits. Beds transitional toward a geosynclinal facies (geosyncline used here in the restricted sense of Krumbein and Sloss) are exposed only in the Barquisimeto area or now form part of the metamorphics in the Caribbean Coast Ranges. End_Page 193------------------------------ New ammonite faunas, determined by Ralph W. Imlay and L. F. Spath, and some foraminiferal key species identified by the writer (W.M.) serve as a basis for a time-stratigraphic correlation of the Cretaceous sequence of Venezuela. A tentative biostratigraphic comparison with the Lower Cretaceous of Texas is presented. Certain foraminiferal species have a rather restricted stratigraphic range and thus lend themselves for correlative purposes. In Venezuela, Choffatella decipiens Schlumberger is confined to strata of Aptian age; Haplostiche texana (Conrad) and some species of Lituola occur in Albian beds; Dictyoconus walnutensis (Carsey) is indicative of the Middle Albian Guacharo limestone; and Globotruncana (Rotalipora) appenninica Renz is a key species of the Cenomanian Boqueron formation. In Venezuela, several genera and species appear earlier in the Cretaceous time scale than in the Texas column, which suggests a migration of these faunal elements from the Caribbean Province into the Gulf Coastal Plain of the United States.

SILICEOUS SEDIMENTS OF OUACHITA FACIES IN OKLAHOMA

Certain sedimentary rocks cropping out in the Ouachita Mountains of southeastern Oklahoma and western Arkansas are unusual in that they contain large amounts of silica disseminated through a relatively thick series of beds which are laterally continuous over large areas. They range in age from Ordovician to Pennsylvanian and may be divided into (1) sedimentary rocks of the main anticlinorium of the Ouachita Mountains in southeastern Oklahoma and southwestern Arkansas, and (2) sedimentary rocks exposed in the fault blocks lying between the central Ouachita Mountains and the Arbuckle Mountains and McAlester Basin. The former group consists largely of chert and siliceous shale of typical geosynclinal facies; the latter group consists largely of chert and siliceous limestone intermediate in lithology and fabric between rocks of geosynclinal facies and those of foreland facies exposed near by in the Arbuckle Mountains. The siliceous sedimentary rocks of typical geosynclinal facies comprise the Bigfork chert (Ordovician); the Arkansas novaculite (Devonian-Mississippian); the siliceous shales of the Stanley (Mississippian), Jackfork (Pennsylvanian), and Atoka (Pennsylvanian) formations; and the Hatton tuff lentil (Mississippian). Siliceous sedimentary rocks of atypical geosynclinal facies exposed in the fault blocks are the Pine-top chert (Devonian), the Woodford chert (Devonian ?), and the Chickachoc chert (Pennsylvanian). Although there are conspicuous lithologic differences between these siliceous sedimentary rocks of Ouachita facies, it is considered that most of the silica was supplied by extrusive vulcanism and submarine weathering of volcanic ash. Furthermore, all the siliceous sediments apparently were deposited when relatively little clastic material was being supplied to the “Ouachita geosyncline”. Subsequent to their deposition, the siliceous sediments have been modified by epigenetic redistribution of part of their silica, resulting partly from metamorphism accompanying the Ouachita orogeny and partly from surface exposure.

Pre-Carboniferous Stratigraphy of Marathon Uplift, West Texas

Beneath the Carboniferous strata in the Marathon uplift are rocks of Cambrian, Ordovician, and probably Devonian ages, whose total exposed thickness is 2,500 feet. Of these, the most completely represented is the Ordovician, which includes representatives of the Beekmantown, Black River (?), Trenton, and Cincinnatian of the standard sections, with a possible partial representation of the Chazy. The system is divided into five formations, four of which are new. The Cambrian is represented by sandy strata of which only the highest beds are exposed, and the Devonian is probably represented by cherts and novaculites. The pre-Carboniferous rocks of the district are of geosynclinal facies, with terrigenous clastic members. They have little in common, in either lithology or faun s, with the sections near by, at Van Horn, Big Lake, or the Llano-Burnet uplift. They have many resemblances to the section in the farther removed Ouachita Mountains, where the strata are also prevailingly clastic, with many siliceous beds, and with graptolites as the chief element in their faunas. This is thought to be the result of the influence of the old land mass of Llanoris.