Faunal Zones Research Articles

Faunal Zones of the Paleocene and Eocene Geologic Section Along Chattahoochee River, Alabama: ABSTRACT

The stratigraphic interval from the top of the Upper Cretaceous Providence Sand to the bottom of the upper Eocene Ocala Limestone, extending 49 miles along the Chattahoochee River, was studied and sampled. The section, more than 600 feet thick, can be correlated with the standard section in central and western Alabama by means of fossil zones. Each of the eight formations studied contains beds with distinctive guide fossils. The Paleocene Series is represented by a limestone facies that contains a more poorly preserved fauna than the equivalent argillaceous facies of western Alabama. The upper Paleocene (Naheola Formation) is absent in eastern Alabama. The lower Eocene Series is lithologically and faunally similar to its equivalent farther west. The middle Eocene Series is more calcareous than in western Alabama. The lower Lisbon (Winona equivalent) and the Gosport Sand are absent. The upper Eocene Series is represented by a limestone facies of the Moodys Branch Formation and Yazoo Clay of western Alabama. Foraminiferal zones established for the geologic section on the Chattahoochee River conform closely to the macrofossil zones. End_of_Article - Last_Page 355------------

Lower carboniferous zones and correlations based on faunas from the Gresford‐Dungog district, New South Wales

Abstract Three Lower Carboniferous marine faunal zones and one faunal assemblage are recognized in the Gresford‐Dungog district, New South Wales following a faunal and stratigraphical study of the region. In ascending order they are the ?Thomasaria voiseyi Assemblage Zone, the Schellwienella cf. burlingtonensis Fauna, the Werriea australis Assemblage Zone and the Delepinea aspinosa Assemblage Zone. They are correlated with the Lower Carboniferous zones of Germany as follows: ?Thomasaria voiseyi Assemblage Zone—Cu IIα, Schellwienella cf. burlingtonensis Fauna—Cu IIα to Cu IIβ; Werriea australis Assemblage Zone—Cu IIδ to Cu IIIα; and Delepinea aspinosa Assemblage Zone— Cu IIIα to Cu IIIβ. The zones are recognized in a belt of country extending from Newcastle to Gunnedah in New South Wales, resulting in correlations being made between formations in the Gresford‐Dungog district and those in the Bulahdelah‐Port Stephens, Clarencetown and Werrie‐Belvue regions. Diagnostic species from the zones occur in the Yar...

Biostratigraphic History of Dead Man Lake, Chuska Mountains, New Mexico

Dead Man Lake (elevation 2,800 m) is one of several hundred shallow lakes on the flat, rolling crest of the Chuska Mountains. The lacustrine sediments consist of 7 to 10 m late—Pleistocene sandy silt or fine sand beneath only 0.1 to 0.3 m Holocene organic mud. Five faunal zones in the Pleistocene sediments contain distinctive assemblages of Cladocera and larval Chironomidae. The Chydoridae were the dominant Cladocera during Wisconsin glaciopluvial time, but only two or three species occurred in any of the zones. Tanytarsini and Procladius (Tanypodinae) were usually the dominant Chironomidae; populations of Orthocladiinae and Chironomini were smaller and chronologically discontinuous. The Pleistocene fauna is an impoverished as in other Pleistocene lake sediments and in modern arctic lakes. Therefore the faunal assemblages support the palynological evidence for alpine conditions on the crest of the Chuska Mountains during Wisconsin glaciopluvial time. The organic mud deposited since the end of the Pleistoc...

Mancos-Mesaverde (Upper Cretaceous) Intertonguing Relations Southeast Piceance Basin, Colorado

In the southeastern Piceance basin, Delta, Garfield, Mesa, and Pitkin Counties, Colorado, gas has been discovered in sandstones of the Mesaverde Formation (Upper Cretaceous) that interfinger with the Mancos Shale. Electric log correlation from within the basin to the outcrop along the Book Cliffs, Colorado, shows that the producing sands belong to the Corcoran and Cozzette Members of the Mesaverde. These two members and the Rollins Sandstone can be traced in wells across the basin from the outcrop in the type area, near Grand Junction, to the outcrop along the southern Grand Hogback, thus demonstrating their continuity across the basin. By the use of eight measured surface sections, correlations of these members northward along the Grand Hogback has shown that the Corcoran and Cozzette are correlative with the non-marine part of the Iles Formation, near Meeker, and that the Rollins Sandstone is the lithogenetic equivalent of the Trout Creek Sandstone of northwestern Colorado. Fossils from below the Corcoran Member and from above the Cozzette Member date these two units as Campanian and place them stratigraphically between the base of the Baculities scotti faunal zone and the top of the Exiteloceras jenneyi faunal zone. Shoreline trends of the Corcoran and Cozzette Members are generally east-northeast in the southeastern Piceance basin. This east-northeast trend is divergent from a broad north-south trend in the Western Interior as a whole. Shoreline movements during the deposition of these members were transgressive toward the northwest or landward direction and regressive toward the southeast or seaward direction. These northwest-southeast shoreline movements probably did not proceed beyond the limits of the present structural Piceance basin. In the southernmost part of the Piceance basin, where most Corcoran-Cozzette gas discoveries have been made, these sandstones were deposited in an offshore marine environment of low to moderate wave and current action and are therefore silty and have low poros ty and permeability. The total thickness of the Cozzette Member ranges from 0 to 220 feet and isopach trends of the Cozzette conform generally to the east-northeast shoreline trend of this unit. The total Corcoran Member ranges from 0 to about 180 feet in thickness, but it can not everywhere be separated from the upper sandstones of the Sego Member; the combined maximum thickness of the Corcoran and upper Sego reaches 300 feet.

Subsurface Structure and Stratigraphy of Kent Bayou-Turtle Bayou-North Turtle Bayou Complex, Terrebonne Parish, Louisiana

The Kent Bayou-Turtle Bayou-North Turtle Bayou Complex is in northwestern Terrebonne Parish, Louisiana, along a prolific Miocene producing trend. Drilling was initiated in the area in 1936, but the first hydrocarbon reservoir tapped was found by the discovery well at the Turtle Bayou field in 1957. Active exploration is still in progress in Turtle Bayou. The hydrocarbon producing zones lie within a biostratigraphic unit characterized by Bigenerina nodosaria directa, Bigenerina humblei, and Amphistegina B faunal zones. The oldest sediments encountered are characterized by Robulus 43. The basic structural configuration of the Kent Bayou-Turtle Bayou area is that of two anticlinal features with a northeast-southwest-trending axis of elongation. North dip off these two structures is cut by a series of down-to-the-basin faults. Hydrocarbons trapped by closure on the upthrown sides of these faults are produced in the North Turtle Bayou field. Pronounced changes in the character of the sediments from outer shelf to deep-water type deposits, and thickening in the section below the Bigenerina humblei marker across this series of faults, indicate that the area was near the edge of the continental shelf during lower Miocene time. This area is also marked by the apparent updip limit of sediments characterized by the deep-water Harang-like faunal assemblage. The intrusion of a salt mass probably began during lower Miocene time.

Middle Devonian Stratigraphy of Northeastern Spanish Sahara

In support of petroleum exploration, four stratigraphic sections were measured and described in the Middle Devonian outcrop area of northeastern Spanish Sahara. These sediments are exposed in an east-west belt along the south flank of the Tindouf basin. Near the Mauritanian border the Middle Devonian is 106 meters thick, and about 140 kilometers farther west (10° 12^primeW. Long.) it is 356 meters thick, the increased thickness being due to a progressively greater amount of clastics entering the sequence from the west. It is postulated that Caledonian movements affected the West African Paleozoic geosyncline and that emergent areas existed in late Silurian and early Devonian time, located at the western end of the cratonic Tindouf basin. These uplifted areas furnished more Middle Devonian clastics than did the Reguibat arch, which was probably a low, peneplaned area forming the southern boundary of the Tindouf basin. Five major lithologic units are recognized. Unit 1: At the base of the sequence, which rests with slight angular unconformity on Lower Devonian beds, is a uniform shale unit, lower Eifelian in age. Unit 2: Shale with many thin beds of blocky, calcareous siltstone. Includes the only sandstone found in the Middle Devonian and a faunal zone characterized by Uncinulus lodanensis Lower Eifelian. Unit 3: Has characteristics of deposition in an environment of restricted circulation. The beds include two well developed phosphatic limestones, some shales with dwarfed and phosphatized fossils, and a coquinal limestone yielding phosphatic nodules. It is believed to be upper Eifelian in age. Unit 4: Fossiliferous limestone, including patch reefs, interbedded with yellowish gray, calcareous to marly, fossiliferous shale. The circular or elliptical reefs appear to have developed on topographic highs, with bottom sediment type not an important factor. The largest is 24 meters high and 500 meters in basal diameter. Two faunal zones are described from this unit. It is characterized by the presence of Calceola sandalina and is lower Givetian in age. Unit 5: Alternating shale or siltstone and biostromal limestone, characterized by the presence of Phillipsastraea. Upper Givetian. The contact with the Upper Devonian is conformable, but chemical and biological changes are believed to indicate a colder climate following the warm conditions of the Givetian.

Late Tertiary and Quaternary Events as Interpreted from Radiolaria in Antarctic Sediments: ABSTRACT

A study of the radiolaria from the tops of more than 80 cores spaced around the Antarctic continent between 35° and 77°S. has revealed two distinct faunas, the boundary between them corresponding closely with the position of the South Polar Front (Antarctic Convergence). End_Page 530------------------------------ An examination of samples taken at 40-cm. intervals down cores from both north and south of the Polar Front shows that several cores located north of the Polar Front contain alternating layers of the two faunas, whereas cores located at the south show no such faunal fluctuations. If the alternating faunal zones observed in the northern cores are caused by a shift in the position of the Polar Front, then the data collected so far suggest that the Polar Front today may be as far south as it has been during the time period represented by the cores sampled. Other changes are exhibited by 10 cores from the area. In these cores there is an abrupt change from a fauna composed predominantly of recent species, the majority of which are not found living in Antarctic waters today. This change in the radiolarian assemblage is accompanied in 80 cores by a large decrease in other siliceous or calcareous organisms. In two cores the carbonate content drops from 40-60 per cent to zero. In one core the older assemblage is associated with abundant discoasters and on this basis is tentatively assigned a Late Tertiary age. The cause of the change in planktonic assemblages from Late Tertiary to Quaternary is not known, but it is suggested that it may be due to a change from a relatively stable stratification of the Antarctic Ocean during Late Tertiary to a stronger degree of vertical convection in the Quaternary associated with the cooling of this part of the world during the growth of the Antarctic ice cap. End_of_Article - Last_Page 531------------

Paleontologic Investigations at Big Bone Lick State Park, Kentucky: A Preliminary Report

The Big Bone Lick area in Kentucky, the first widely known collecting locality for vertebrate fossils in North America, is being investigated for further faunal and geologic evidence. Mammal bones, ranging in age from Wisconsin (Tazewell?) to Recent, were recovered in 1962 from four different faunal zones in two terrace fills.

Transgressive Marginal Lithotopes in Niagaran (Silurian) of Northern Michigan Basin

Classical stratigraphic studies of the Niagaran of the Michigan basin have all been made in the zone of outcrop, which nearly encircles the southern peninsula of Michigan at the periphery of the basin. Here there is little difficulty establishing equivalency of units, for distinctive faunal and lithologic zones can be traced from Manitoulin Island, Ontario, through the northern peninsula of Michigan and southward into eastern Wisconsin. This has led to the generally accepted stratigraphic interpretation of a succession of Niagaran seas, each with a distinctive environment and the deposits of each separated from those of the preceding and succeeding seas by significant unconformities. With recent drilling information, however, it has become increasingly apparent that the characteristic outcrop zones quickly disappear in the subsurface of Michigan. A detailed examination has been made by the writer of the field relationships of these units on Manitoulin Island which has excellent exposures and which is used as the reference area of this paper. This study has failed to confirm any widespread unconformities above the base of the Niagaran. It is here proposed that the entire Niagaran sequence of the northern rim of the Michigan basin belongs to one large transgressing littoral-lagoon-barrier reef association. Evidence for this hypothesis is seen in the results of insoluble residue analyses made from samples collected at typical Manitoulin Island sections. An unconformity is indicated at the base of the Dyer Bay carbonate unit, which is interpreted as a littoral accumulation of fine carbonate sand deposited at the shoreward edge of the advancing lagoon. The overlying Wingfield and St. Edmund siltstones and calcisiltites reflect the calm, shallow bottom conditions of the lagoon proper, while the Fossil Hill calcarenites and calcirudites were deposited in the higher energy environment of the back-reef detrital zone. The Am bel comprises several facies of the reef core. Overlying the Amabel are detrital beds, formerly mapped as Fossil Hill or its correlatives, which are interpreted as fore-reef detritus, Detritus also occurs in passes through the Amabel reef-core facies.

New Mississippian Formations and Faunal Zones in Chesterfield Range, Portneuf Quadrangle, Southeast Idaho

Mississippian rocks in the Chesterfield Range, southeast Idaho, consist of the Lodgepole Limestone overlain by a 1,900-foot limestone-sandstone sequence here designated the Chesterfield Range Group. The lower terrigenous part, about 965 feet thick, is the Little Flat Formation; it has a basal siltstone member, a middle sandstone member, and an upper sandy limestone member. The upper carbonate part of the Chesterfield Range Group, here named the Monroe Canyon Limestone, is about 925 feet thick and contains a lower massive member, a medial medium-bedded member, and an upper cherty member. The Chesterfield Range Group is of Late Mississippian age. Three coral zones and four brachiopod zones are recognized. The coral sequence is composed of a lower Eksvasophyllum Zone succeeded by the Faberophyllum Zone and, at the top, the Caninia Zone. The lowest brachiopod zone of Quadratia hirsutiformis is succeeded by the Echinoconchus cf. E. alternatus Zone, the Striatifera brazeriana Zone, and the Spirifer brazerianus Zone. Correlations with Mississippian sequences elsewhere in the northern Rocky Mountains emphasize relationships with the Dry Lake and Old Laketown Canyon sections in northern Utah and with the Deep Creek Mountains section in southeastern Idaho. Relationships with the faunal zones recently established for the Mississippian in western Canada are indicated.

Foraminiferal Facts, Fallacies and Frontiers: ABSTRACT

Erroneous statistics applied to foraminiferal studies have resulted in misleading statements. The notorious volume of publications is a figment of thorough bibliographic documentation. The degree of classification and number of foraminiferal taxa are relatively conservative as compared to other invertebrate groups. Unjustified interpretations have resulted from misapplication of concepts originally developed for metazoan invertebrates or vertebrates. Geographic subspecies can not be differentiated on size variation, as this results from environmentally controlled delay or acceleration of the reproductive cycle. Prolonged vegetative growth, with delayed cycle, results in robust specimens, thus to be expected with depauperate invertebrate faunas. Abundant material lessens the necessity of statistical methods of determining population characteristics from a few specimens. Evidence of floating bottles used in ocean current studies, even with the present relatively emergent continents, shows the migration time for planktonic species to be negligible. Effective rate of evolutionary changes in forami ifera is relatively rapid, due to short life span, abundant progeny, and rapid production of new generations. Many detailed faunal and biostratigraphic studies are needed, as are studies of interrelationships of benthonic faunal facies and planktonic faunal zones. For many genera and families, little is known of gross external and internal test morphology and wall microstructure or morphology, physiology, genetics, life cycle, and ecology of the living animal. End_of_Article - Last_Page 1773------------

Stratigraphy and Paleoecology of the Richmond Group in Southeastern Indiana

The Richmond Group (Upper Ordovician) in southeastern Indiana is subdivided into rock-stratigraphic units (formations and members) and biostratigraphic units (assemblage zones). The formations and members established by earlier workers on the basis of faunal zones are either redefined as mappable rock units or discarded. A newly proposed formation replaces the lower three “formations,” Arnheim, Waynesville, and Liberty, which are based on paleontologic criteria and are lithologically indistinguishable. The new unit consists of thin layers of fossiliferous and barren limestone alternating with layers of calcareous shale. Two barren shale beds in conjunction with silicified fossil and pyritic limestone horizons are used to subdivide the new unit for a quantitative study of its lithologic variation. The Whitewater Formation above is redefined and subdivided into five rock units on the basis of lithology: (1) a lower unnamed member of massive earthy limestone, (2) a black carbonaceous shale bed, (3) the lower Saluda Member, which is a northward thinning wedge of mud-cracked slabby limestone with layers of massive dolomitic limestone at the base and top, (4) the upper Saluda Member, lithologically similar to the lower wedge but separated from it by a layer of massive dolomitic limestone, and (5) an upper unnamed member of massive earthy limestone. Four faunal assemblage zones are recognized in the newly proposed unit: (1) Resserella meeki, (2) Leptaena richmondensis, (3) Sowerbyella rugosus, and (4) Strophomena planumbona. The assemblage zones become thin and pinch out to the south, and their boundaries cross lithologic marker horizons within the newly proposed rock unit. The Homotrypa wortheni and Tetradium minus assemblage zones within the Whitewater Formation are split into upper and lower parts by the barren Saluda Member. The numbers of individuals in each species are counted in small unit areas and are statistically analyzed to determine the distribution of species within the assemblage zones and the geographic extent of the zones. The following interpretation of depositional environments is based on the distribution of the rock types and faunal assemblage zones. The lower unit of the Richmond Group was deposited in a shallow, inner sub-littoral, marine environment. The Whitewater Formation was formed during the regression and transgression of a shoal area with the lower and upper unnamed members representing the submerged mud flats, and the Saluda Member, the exposed mud flats.

Mississippian Rocks of Sun River Canyon Area, Sawtooth Range, Montana

The Madison Group (Mississippian) of the Sun River Canyon area, northwestern Montana, is subdivided into two newly named and defined formations--the Allan Mountain Limestone and Castle Reef Dolomite. The Allan Mountain Limestone is composed of three unnamed members: the lower member, middle member, and upper member. The Castle Reef Dolomite consists of an unnamed lower member and the redefined Sun River Member. The recognition of four faunal zones in the Madison permits tentative correlation of these rocks with rocks of Mississippian age in central and southwestern Montana and in Alberta, Canada. Formational boundaries and lithologic types recognized in southern Montana can not be consistently followed in the Sawtooth Range. The faunas indicate that the Allan Mountain Limestone is approximately the same age as the Lodgepole Limestone of southwestern Montana and that the Castle Reef is approximately the same age as the Mission Canyon Limestone. The top of the middle member of the Allan Mountain Limestone is approximately equivalent to the boundary between the Banff and Rundle Formations of Alberta. The Ca/Mg molar ratio substantiates field determinations of the lithologic composition and boundary between the two formations. Local correlation of certain units are indicated by the molar ratio.

Petroleum Geology of Coastal Peru and Ecuador: ABSTRACT

Oil fields of coastal Peru and Ecuador lie within the only significant coastal plain along the western margin of South America. This plain is underlain by chiefly marine lower Tertiary and variably marine to continental upper Tertiary sediments, and is capped by a spectacular, but locally heavily dissected, elevated Quaternary marine terrace, or Tablazo. Although evidence is meager, the marine lower Tertiary sediments are considered not to have been deposited as in a basin, but more likely as in a half-basin or marine bank on a narrow continental shelf, facing the open ocean on the west. The principal producing areas in this belt, from north to south are (Ecuador) Ancon, and (Peru) El Alto, Lobitos, Talara-Negritos, and Portachuelo. Estimated ultimate recovery from established reserves are: Ecuador, possibly in excess of 125 million barrels of 37° gravity oil; and Peru, possibly up to 1 billion barrels of 37° gravity oil. Production comes chiefly from Eocene sandstones and conglomerates, with fracturing commonly playing a major part in reservoir permeability. The Tertiary coastal belt is one of both common stratigraphic complications and a rather unique structural arrangement. Much of the marine Tertiary sedimentary sequence demonstrates rapid facies change and evidence of large-scale submarine landslides, resulting in common turbidity deposits and recurrent faunal zones. The structural situation is dominated by a myriad of normal faults having no regular pattern, but predominantly following a rule of faulting which favors downward movement of the updip block (in a regional sense), which is interpreted as dislocation resulting from a westerly spreading or creep of the sediments of this ancient marine bank during periodic recurrent elevations of the ancestral Amotape mountains on the east, with no massive basement buttress on the west to co tain this semi-plastic mass. Because of both the restricted remaining undeveloped area and vertical sedimentary column in the onshore, particularly in Peru, development of additional major reserves may be expected to come chiefly from the submerged continental margin adjacent to existing production. End_of_Article - Last_Page 279------------

Atlantic Deep-Sea Sediment Cores

Studies of lithology, particle-size distributions, and micropaleontology and chemical analyses of 221 Atlantic and Caribbean deep-sea cores lead to new conceptions of processes of sedimentation, rates of sediment accumulation, Pleistocene chronology, and pre-Pleistocene history of the Atlantic Basin. Anomalous layers of sand, silt, and lutite occur widely in the deep basins of the Atlantic. Evidence for deposition of these layers by turbidity currents is as follows: (1) the layers occur in submarine canyons, in deltalike features at the terminal ends of canyons, in basins and depressions, never on isolated rises; (2) they are interbedded with late Pleistocene sediments of abyssal facies; (3) they are well-sorted and commonly graded; and (4) they commonly contain organic remains of shallow-water origin. Late Pleistocene slumping of compacted Neogene sediments along the banks of the Hudson Submarine Canyon at depths exceeding 3000 m indicates deepening of the canyon by erosion by turbidity currents. Variations in the planktonic Foraminifera in 108 of the cores and extrapolation of rates of sediment accumulation determined by 37 radiocarbon dates in 10 cores show that the last period of climate comparable with the present ended about 60,000 years ago. A faunal change indicating climatic amelioration, probably corresponding to the beginning of postglacial time, occurred about 11,000 years ago. Cross-correlations by micropaleontological methods establish the continuity of the climatic record deduced from the planktonic Foraminifera. Study of variation in the Planktonic Foraminifera leads to a different Pleistocene chronology from that proposed by Emiliani (1955). Cross-correlations of faunal zones and radio-carbon dates show that rates of continuous sediment accumulation, as opposed to turbidity-current deposition, range from 0.5 cm to 274.4 cm in 1000 years, depending upon bottom configuration. Cross-correlations by means of changes in coiling direction of planktonic Foraminifera give relative rates of sediment accumulation beyond the range of the radiocarbon method of dating. Forty one of the cores contain pre-Pleistocene sediments. The oldest sediment is Upper Cretaceous. Foraminifera and discoasters indicate the ages. Absence of sediment older than Late Cretaceous and thickness, 800–1000 m, of sediment in the Atlantic Basin as determined by seismic methods suggest that a large-scale reorganization of the Atlantic Basin took place in the Mesozoic.

Stratigraphie du Senonien dans les Dinarides yougoslaves d'apres les rudistes

Abstract Outlines the paleogeography and describes the stratigraphy of Senonian (Cretaceous) deposits in both the inner and outer zones of the Dinaric Alps of Yugoslavia. The stratigraphic scheme is based largely on rudistid faunal zones which have been established in eastern Serbia (southern Carpathians). Some horizons are very extensive, particularly certain Pironea-bearing zones. Three new varieties of Pironea polystyla (dalmatinica, bacevicensis, and dinarica) are represented in the Dinaric faunas described.

Chenier Plain and Its Stratigraphy, Southwestern Louisiana: ABSTRACT

The Chenier Plain of southwestern Louisiana is a low coastal marshland characterized by numerous relict beach ridges, or cheniers, which parallel the shore and rise generally 5-10 feet above the marsh level. From analyses of cores along a north-south line of section through Creole, Louisiana, it has been possible to identify four faunal zones and seven distinct sedimentary facies in the post-Pleistocene deposits which underlie the plain. The faunal zones, named after the dominant foraminifers, are: the Streblus, Streblus-Elphidium, Quinqueloculina, and Trochammina zones. The sedimentary facies consist of varying proportions of sand, silt, and clay which, together with their contained fauna, clearly reflect the environments of deposition, including marsh, bay, mudflat, ope gulf, and beach. The relict beaches or cheniers are lenticular sand and shell bodies similar to certain shoestring sands of older rocks which commonly serve as oil reservoirs; thus, they hold special interest for the petroleum geologist. They are biconvex in section, average less than 1,000 feet across, and extend as uninterrupted coastwise ridges up to 30 miles in length. They average about 10 feet in thickness and are characterized by a smooth, generally arcuate seaward front and irregular landward margin. These deposits rest on shallow gulf-bottom mud and are overlapped by organic marsh clay. Should the ridges eventually be buried by such deposits, they will form potential stratigraphic traps. The characteristic shape, trend, and dimensions of the chenier sands, together with their distinctive sedi entary and faunal properties should aid materially in identifying similar potential reservoirs in the subsurface. End_of_Article - Last_Page 2520------------

Frio Formation of Upper Texas Gulf Coast: ABSTRACT

A study group of the Houston Geological Society has concerned itself with the Tertiary Frio formation as it exists in the subsurface in the area from Jackson County, Texas, to Louisiana. To facilitate study, the formation was divided into upper and lower units and each was traced over the area of interest by means of electrical log characteristics. An electrical log correlation point in the Marginulina zone of the overlying Anahuac formation was used as a practical expedient for the of the Frio. A horizon near the Nodosaria blanpiedi faunal zone in the middle of the Frio served as the top of the lower Frio unit. No specific electrical log datum was used for the base of the Frio. The number of feet of porous and permeable sand within each unit was counted from the electrical End_Page 2513------------------------------ logs. From these data, sand percentage and net sand maps were constructed for the upper and lower Frio units. Lower Frio sand values range from 2 feet to 1,600 feet. Maps tend to indicate that the center of deposition of the lower Frio unit is in Matagorda and Brazoria counties. Thick sequences of sand and shale occur in this area, particularly in the Textularia seligi (mississippiensis) and Anomalina bilateralis faunal zones. Wells here indicate as much as 1,600 feet of sand in a total interval of more than 2,600 feet. The center of deposition of the upper Frio unit appears to be in Jefferson and Orange counties. This is accentuated by the occurrence of thick sands in the Hackberry zone, which results in more than 1,200 feet of sand in an interval exceeding 3,600 feet. Sand values range from 16 feet to 1,289 feet and sand percentages from 3% to 62%. Efforts were made to minimize the effects of local structure and local lithologic variations. Nevertheless, such large subregional features as the western Jefferson County graben; the Red Fish Reef-South Mayes complex of Chambers County; the Chocolate Bayou complex, Danbury dome, and the Chenango complex of Brazoria County; and the Old Ocean complex of Matagorda County exhibit lithologic anomalies coincident with the area of their structural influence. These anomalies indicate that structural movement was taking place during deposition. End_of_Article - Last_Page 2514------------

Stratigraphy and Conditions Governing Petroleum Occurrence in Lower Cretaceous Rocks, Rocky Mountain Region: ABSTRACT

Lower Cretaceous stratigraphy of the Rocky Mountain region is complicated by problems of nomenclature, lateral extent, correlation, and age variation of the Dakota group. Lower members of the Dakota group have three different relationships to the underlying Morrison formation: (1) in some areas the basal units were deposited in channels and are unconformable on the Morrison; (2) in many areas the basal units have an intertonguing facies relationship with the upper Morrison, and, (3) a regional unconformity at the base of the Dakota group is developed only in the Great Plains region. Regional time lines are necessary for an understanding of facies relations. Marine Jurassic formations define an approximate time line at the base of the Morrison in the northern part of the Rocky Mountain region. The Todilto limestone forms an approximate time line in the San Juan basin, but it can not be related precisely to the marine formations farther north. In the northern part of the region the boundary between the Upper Cretaceous and the Lower Cretaceous is placed at the top of the Mowry shale which is marked by the Clay Spur bentonite bed, an excellent time horizon. The marker bentonite of the Denver basin (X bentonite), 100-300 feet above the Mowry shale, can be traced throughout the Powder River basin of Wyoming where it marks the base of the Greenhorn faunal zone (Upper Cretaceous). The X bentonite bed, and in its absence, the base of the Greenhorn limestone form an excellent time line. Sediments of the Dakota group were deposited in a sea that advanced from the north and thus these basal sediments become younger in easterly, southerly, and westerly directions. Marine shales of the Thermopolis and overlying Mowry and Graneros formations of Wyoming and Montana were deposited contemporaneously with sandstones of the Dakota group farther south. The lower part of the Dakota group of Wyoming and Montana was deposited contemporaneously with upper Morrison sediments on the south. Over most of the Rocky Mountain region the Dakota group is Lower Cretaceous, but in deposits just south of the San Juan basin the upper part is as young as the Greenhorn limestone, a relation similar to that found in eastern Nebraska, at the type locality, where the Dakota sandstone is largely, if ot entirely, Upper Cretaceous. In Wyoming and Montana, sandstones of the lower Dakota group (Lakota, Fall River, Dakota, Cloverly, Cat Creek, and upper Morrison) produce oil in areas where distinctive, linear, thick sandstones are developed and are notably unproductive in areas of patchy, heterogeneous sand development. In eastern Colorado, the lower part of the Dakota group (Dakota, Lytle, M, O, R, and T sandstones) is essentially non-productive. Significant oil production in the Dakota sandstone of western Colorado and the San Juan basin is found in areas characterized by linear sandstone development. D and J sandstones of the Denver basin produce petroleum from stratigraphic traps and the southeast limit of significant production coincides with the zero isopach of the Mowry shale. Oil production in the Muddy and Newcastle sandstones of Wyoming (equivalents of lower J) is stratigraphically trapped in or near linear sandstone trends. Structural entrapments are present where linear trends cross structural highs. End_of_Article - Last_Page 1098------------

The zoogeographical distribution of the deep-water bottom fauna in the abyssal zone of the ocean

Analysis of the geographical distribution of certain groups of benthic invertebrates (1031 species) in depths greater than 2000 m showed that 84 per cent of the species are confined to a single ocean and only 4 per cent occur in the Pacific, Atlantic and Indian Oceans. Each ocean has its own characteristics fauna. In the Pacific and Atlantic Oceans, 75 per cent of the deep-sea species are endemic. In the Indian Ocean, the percentage is somewhat lower. However, the genera and families of deep-sea animals are generally widely distributed. The specificity (endemism) of the fauna increases with increasing depth of habitat. Three zoogeographical regions can be distinguised in the abyssal zone of the ocean : the Pacific-North Indian, the Atlantic and the Antarctic. These may be divided into sub-regions and provinces. One of the chief factors affecting the distribution of deep-sea bottom fauna seems to be the configuration of the ocean floor, especially the macrorelief. Consequently, the boundaries between zoogeographical regions follow underwater ridges and other elevations. The species of deep-sea bottom invertebrates with a wide vertical range generally have an extensive horizontal range as well. Almost all cosmopolitan deep-sea forms are eurybathic. The stenobathic species, on the contrary, occur only in a restricted area.