Bathyal Conditions Research Articles

Oligocene through Pliocene Foraminifera from the Yakataga Reef Section, Gulf of Alaska Tertiary Province, Alaska

Oligocene through Pliocene foraminifera in the Yakataga Reef section, Gulf of Alaska Tertiary Province, help reconstruct the depositional history of the upper Poul Creek and lower Yakataga formations. Biofacies patterns reflect middle bathyal conditions during the Oligocene and Early Miocene, a Middle Miocene hiatus and upper bathyal to shelfedge depths during the Late Miocene and Early Pliocene. A regressive episode in the lowermost Yakataga Formation may represent a terminal Miocene event. Surface water temperatures during the Late Miocene-Early Pliocene change upsection from cold subarctic to cool temperate. The foraminifera also indicate that the Poul Creek-Yakataga Formation contact is Late Miocene. Oligocene through Pliocene foraminifera from the Yakataga Reef section, Gulf of Alaska Tertiary Province, Alaska INTRODUCTION Objectives The Gulf of Alaska Tertiary Province contains an impressive accumulation of Middle and Late Cenozoic marine rocks (7500 m, 25,000 ft; Miller, 1957). In the Yakataga District this accumulation is represented by two major marine units-the Poul Creek and the Yakataga formations. Study of these rocks can provide important insights into the geologic, climatic, and tectonic history of the northeast Pacific margin. The Yakataga Reef section (text-fig. 1) is a useful reference for studying the Middle Cenozoic rocks of the Yakataga District. This tidewater section exposes a relatively unweathered and accessible sequence of rocks across the contact of the Poul Creek and Yakataga formations. The objectives of this study are to: 1) document the major foraminiferal trends in the Yakataga Reef section; 2) briefly describe the major lithologic units in the Yakataga Reef section; 3) infer the paleoenvironments in which the rocks were deposited; 4) determine provisional biostratigraphic units for use in a general study of the Miocene of the Yakataga District (Lagoe, in preparation); 5) determine the age of the Poul Creek/Yakataga contact at Yakataga Reef.

Sedimentation and tectonic controls in the Early Jurassic Central High Atlas trough, Morocco

Stratigraphical and sedimentological studies of Lower Jurassic deposits at the western end of the Central High Atlas Mountains, Morocco, has led to a reappraisal of the tectonic significance of this linear feature during the critical period of the opening of the Atlantic Ocean. Lower Jurassic deposits south and east of Marrakech represent an extremely shallow water and supratidal marine carbonate accumulation that formed in fault-controlled basins at the western end of the trough. The basins were aligned east-northeast and the character and distribution of the deposits strongly suggests that no connection with the basins of the Western High Atlas existed. To the east, sediments indicate more open conditions, but no evidence of bathyal or abyssal conditions was seen. Sedimentation was probably structurally controlled by vertical tensional and compressional movements as the result of reorientation of stress between major strike-slip faults. Volcanic flows and shallow intrusions, which occur at the base of the Jurassic sequence, and associated carbonate and clastic sediments show no evidence of being part of ophiolite sequences; they more closely resemble extrusive basalt sequences associated with rifting as seen in the Triassic of the Eastern United States and the Tertiary of Northwest Europe. Evidence from this area suggests that the High Atlas seaway represented only an arm of the Tethyan Ocean, which extended along a long-standing zone of crustal weakness.

Subsurface Study of Foraminiferal Fauna of Vaqueros Sandstone, Rincon Shale, and Lower Monterey Formation, from Elwood Oil Field, Santa Barbara County, California: ABSTRACT

Core samples taken from Texaco's Bishop A-1 well in the Elwood oil field in Santa Barbara County, California, penetrated 4,350 ft of section consisting of sediments of the lower Monterey Formation, the Rincon Shale, and the Vaqueros Sandstone. The two uppermost samples recorded at 558 and 561 ft contained Foraminifera indicating a Luisian age. The Relizian was represented by a thickness of about 700 ft. Approximately 1,500 ft of Saucesian age sediments were present. The upper Zemorrian was represented by 190 ft of section. The bottom 900 ft of preponderantly sandstones proved to be barren of Foraminifera. A foraminiferal faunule of late Zemorrian age, 138 ft below the Vaqueros/Rincon contact indicated an upper bathyal depth in this particular area, as opposed to much shal ower conditions, indicated elsewhere at the time of deposition of the Vaqueros Sandstone. Bathyal conditions persisted throughout the subsequent deposition of the Rincon Shale and lower Monterey Formation. End_of_Article - Last_Page 436------------

Outline of Geologic Occurrence of Oil in Tertiary Basins of West Indonesia

The regional tectonic setting and Tertiary stratigraphy of west Indonesian basins suggest that they are similar in stratigraphic successions, sedimentation history, and structural development. Each basin underwent a megacycle of sedimentation, beginning with a transgression, followed immediately by bathyal conditions, and terminating with a regression at the end of basin evolution. There are, however, differences in the time sequence between basins. In the basins, with one exception, oil is in the upper regressive facies. In south and central Sumatra and in southeast Borneo (Kalimantan), oil also is present in the lower transgressive facies. A study of reservoir rocks suggests that the oil is confined largely to coarse clastic beds of the transgressive and regressive facies. Possibilities are excellent for petroleum discovery in the transgressive facies of all basins, and this sequence potentially has greater reserves than the regressive facies. A heavy paraffinic oil is to be expected in the transgressive strata in contrast to the light paraffinic or asphaltic oil in the regressive facies.

Escarpments, Reef Trends, and Diapiric Structures, Eastern Gulf of Mexico

Dredging, coring, and arcer profiling of the Florida escarpment southward from 28°1.5^primeN, 86°24^primeW, to the Florida Strait, of Jordan Knoll (23°20^primeN, 83°45^primeW) in the Florida Strait, and of the Campeche escarpment northeast of Yucatan (23°39^prime-23°45^primeN, 85°22^prime-85°26^primeW) have revealed the presence in all three areas of late Aptian-Albian reef and forereef facies which lithologically and paleontologically are nearly identical to the Glen Rose-Stuart City reefs of the U.S. Gulf Coast and the El Abra-Golden Lane reefs of eastern Mexico. The late Aptian-Albian reefs--or banks--apparently were not continuous from the Florida escarpment to the Campeche escarpment, but were separated by a deep-sea channel wh ch crossed Pinar del Rio Province, western Cuba. Jordan Knoll may have been an Early Cretaceous atoll, isolated from the reefs of the Florida escarpment and similar to the Golden Lane atoll of eastern Mexico. A core from Jordan Knoll penetrated a late Pliocene carbonate mud containing abundant angular limestone clasts up to 2.1 cm in diameter. The clasts range in age from late Aptian-Albian through middle Miocene to early Pliocene. The source of the clasts is unknown but regional geologic data eliminate a southern source; the clasts most probably were derived from Jordan Knoll itself. The lithology and paleontology of the clasts show that the Jordan Knoll region was a shallow-water bank until latest Albian or early Cenomanian time; that the present Florida Strait area deepened steadily from Cenomanian through Santonian times; and that, from Santonian time until the present, bathyal conditions generally prevailed. The knoll may have been uplifted during middle Eocene time as a result of the Laramide deformation of Cuba. The eastern Gulf of Mexico has had a complex geologic history since Early Cretaceous time or before; the geologic data from Cuba, Yucatan, Florida, and our samples reveal some of this complexity, and suggest that the site of the Florida Strait has shifted through time. Much of the complexity is related to middle Cretaceous and Laramide tectonic events in Cuba. An understanding of the tectonic and stratigraphic history of South Florida, the Florida Strait, and the Campeche (Yucatan) platform ultimately may lead to the discovery of substantial petroleum accumulations in this region.

Base of Pleistocene in Los Angeles Basin, California: ABSTRACT

Populations of Globigerina pachyderma (Ehrenberg) are consistently left-coiling, cool-water types in sections of the lower Pleistocene of the Los Angeles basin, California; right-coiling, warm-water populatons are predominant in the upper Pliocene. The base of the Pleistocene, defined in this way, indicates a major change in water masses of the southern California area at that time. Recent radiometric dates by Obradovich place this boundary about 3 m.y. ago. Populations of Globigerina pachyderma reflect bathyal conditions generally; modern populations in End_Page 604------------------------------ typical form live suspended deeper than about 50-100 m. Basing the beginning of the Pleistocene on planktonic foraminiferal criteria, benthic Foraminifera indicate that outer-shelf conditions prevailed at the beginning of the Pleistocene in some areas, upper-bathyal depths existed in other places, middle-bathyal depths in some areas, and lower-bathyal depths at still other locations. Thus, a boundary based on upper limits of benthic species (Epistominella pacifica and Uvigerina peregrina), and defined by comparing sections from different parts of the Los Angeles basin, differs hundreds of meters in stratigraphic position. End_of_Article - Last_Page 605------------

Middle Tertiary Foraminiferal Paleoecology, San Joaquin Valley, California: ABSTRACT

A detailed study was made of the foraminiferal paleoecology of the Middle Tertiary of the San Joaquin Valley, California. General trends of use in paleoecology include: (1) increase of authigenes away from shorelines, (2) progressive diversification of foraminiferal species and increase in foraminiferal abundance away from shore, and (3) concentration of planktonic species in the upper bathyal and outer shelf zones of marine basins. Bathymetry of modern homeomorphs of Tertiary species serves as the basis for establishing seven major biofacies for the California Tertiary, representing depths ranging from estuarine to deep bathyal conditions. From Zemorrian to Luisian time, water depths in the San Joaquin marine basin were about 6,000 feet; in later Miocene time there was gradual shoaling, resulting in widespread shallow marine and paralic conditions in the Pliocene. Displaced faunas were most abundant near the base of steeper slopes of the reconstructed marine environments of the Middle Tertiary. Abyssal and shoal faunas appear to have longer geologic ranges, generally, than biofacies representing intermediate depths. Paleotectonism was assessed in terms of vertical changes; changes amounted to many thousands of feet for each stage, especially in perimeter areas of the marine basin. Volumetric analyses suggest that about 900 cubic miles of subsidence occurred in the Zemorrian, with a progressive decrease to a minimum value of about 300 cubic miles in the Relizian, and increasing values for the remainder of the Miocene. More than 5,000 cubic miles of rock represent the marine sediment deposited in the San Joaquin basin during the middle Tertiary stages; more than 4,000 cubic miles of this were deposited in bathyal marine conditions, and most of the oil produced has come from these sediments. Oil fields occur in areas that have been active tectonically, near steeper bottom slopes of the reconstructed environment, and where there are rapid changes in biofacies. End_of_Article - Last_Page 516------------