Modern Gulf Research Articles

Foraminiferal Biofacies Analysis of the Yakataga Formation, Icy Bay, Alaska: Insights into Pliocene Glaciomarine Paleoenvironments of the Gulf of Alaska

The Upper Miocene to Pleistocene Yakataga Formation of the Gulf of Alaska provides a 5 km thick record of episodic glacially-influenced marine sedimentation. The Pliocene Yakataga Fm. is exposed along western Icy Bay and records the return of glaciomarine deposition in the Gulf of Alaska, after the initiation of glaciation in the Late Miocene, and the onset of major northern hemisphere glaciation by the Late Pliocene. Analysis of foraminifera found in the Yakataga Fm. provides the basis for the interpretation of paleobathymetry and depositional environments from these rocks. Quantitative analysis is used to define eight paleoenvironmentally significant biofacies: (1) Elphidium excavatum clavatum biofacies (inner neritic), (2) Haplophragmoides spp. biofacies (outer neritic--mudline), (3) Cassidulina cf. C. teretis biofacies (outer neritic), (4) Uvigerina juncea biofacies (uppermost bathyal), (5) Elphidiella hannai biofacies (innermost neritic), (6) Epistominella pacifica biofacies (upper bathyal), (7) Cassidulina cf. C. limbata biofacies (outer neritic), (8) Nonionella miocenica biofacies (outer neritic). Paleobathymetric zones defined by these biofacies, which are constrained by modern Gulf of Alaska faunal relationships, indicate bathymetric fluctuations on the order of 100 m in the Icy Bay section. Mixing of biofacies due to downslope transport is common. Analyses of paleobathymetry, benthic formaminiferal biofacies, and sedimentology are usedmore » to interpret depositional environments ranging from innermost neritic to upper bathyal for these rocks.« less

The making of the modern Gulf States: Kuwait, Bahrain, Qatar, the United Arab Emirates, and Oman

The making of the modern Gulf States: Kuwait, Bahrain, Qatar, the United Arab Emirates, and Oman

First and Last Occurrences of Quaternary Benthic Foraminifera in the Gulf of Mexico: Relation to Paleoceanography: ABSTRACT

ABSTRACT The distribution record of benthic foraminifera in late Pleistocene and Recent sediments of the northwestern Gulf of Mexico indicates that occurrences of species are affected by paleoceanography. Two species that are very common in the modern gulf, Bulimina alazanensis and Osangularia culter, were not present in the area during the last glacial stage, due to the absence of Subantarctic Intermediate Water. They reappeared at about 12.5 ka, with the reintroduction of this water mass into the gulf. At the same time, Valvulineria sp. A, common during the last glacial stage, disappeared. This was caused by the cessation of production of the Glacial North Atlantic Intermediate Water during deglaciation. These events, probably isochronous throughout the gulf, do not represent the true first and last occurrences of the species, but may prove useful for the recognition of significant datums. Overall water depth changes or bathymetric shifts of water mass boundaries may lead to the disappearance of certain species in one area, but not in others. This results in a diachronous datum, or stratigraphic climbing. Even planktonic foraminifera can be affected by such processes, because of narrowly stenothermal and stenohaline adaptations of many species, in the context of shoreline shifts and climatic changes.

The making of the modern Gulf states: Kuwait, Bahrain, Qatar, United Arab Emirates, Oman

Journal Article The making of the modern Gulf states: Kuwait, Bahrain, Qatar, United Arab Emirates, Oman Get access The making of the modern Gulf states: Kuwait, Bahrain, Qatar, United Arab Emirates, Oman. By Rosemarie Said Zahlan. London: Unwin Hyman. 1989. 180pp. Index. (The Making of the Middle East.) £22.00; ISBN 0 04 445430 9. Pb.: £8.95; ISBN 0 04 445293 4. F. R. C. Bagley F. R. C. Bagley Search for other works by this author on: Oxford Academic Google Scholar International Affairs, Volume 66, Issue 1, January 1990, Page 202, https://doi.org/10.2307/2622266 Published: 01 January 1990

Marginal Seas as Source of an Oceanic Oxygen Minimum and Origin of Organic Carbon-Rich Deposits: ABSTRACT

Cretaceous marginal seas extending across America, Asia, Africa, and Australia connected oceanic areas in different climate zones. Water masses in such regions may have had the same density but very different salinities and temperatures, as is the case with the modern Gulf of Mexico and eastern Arctic Ocean. Cretaceous seaways permitted such different water masses to mix, resulting in a third water mass of greater density. Preliminary calculations indicate that this mechanism may have caused the Western Interior seaway of North America to become a source of intermediate water with a strength equal to the modern Weddell Sea, the source of Antarctic bottom water. Intermediate water production would be maximized at times of maximum transgression. The surface waters of the world ocean would be drawn into both ends of such a seaway and the plankton killed at the front, where mixing occurred, as environmental conditions changed drastically. This introduced large amounts of organic matter into the intermediate water, causing development of an intense oxygen minimum and deposition of large quantities of organic carbon in seas of intermediate depth to form extensive hydrocarbon source beds.

Late Quaternary evolution of Lake Carpentaria on the Australia‐New Guinea continental shelf

During the Late Pleistocene, the large and shallow Lake Carpentaria occupied part of the continental shelf linking northern Australia and New Guinea. The former lake lay within the modern Gulf of Carpentaria, between the —53 m isobath and the deepest part of the embayment at — 67 m, and may have been as much as 500 km long, 250 km wide and 15 m deep. The basinal feature is separated from the outer margin of the continental shelf in the northwest by an area of shallower sea floor with a maximum water depth of about — 53 m and referred to as the Arafura Sill. We have investigated the sedimentary record of the shallow substrate, both within and beyond the basin perimeter, by using surficial sediment samples, piston cores, and continuous seismic reflection profiling. Sediments interpreted to be of lacustrine origin occur only within the enclosed basin, and have been covered by a blanketing marine sandy mud deposit approximately 1 m thick. Beneath the lacustrine mud and sandy mud is a cohesive clay and sandy c...

Sea-level history, 45,000 to 30,000 yr B.P., inferred from Benthic foraminifera, Gulf St. Vincent, South Australia

Surficial sediments of Gulf St. Vincent, South Australia, are predominantly bioclastic, cool-temperate carbonates. Benthic foraminifera are abundant and distribution of species is closely related to water depth. For example, Massilina milletti is most common at depths ca. 40 m, while Discorbis dimidiatus is characteristics of shallow, subtidal environments. Elphidium crispum, a shallow-water species, and E. macelliforme, favoring deeper water, provide a useful numerical ratio. Their logarithmic relative abundance, in the sediment size fraction 0.50–0.25 mm, correlates strongly with water depth. Vibrocores SV 4 and SV 5 recovered undisturbed sections of Quaternary strata from the deepest part (ca. 40 m) of Gulf St. Vincent. Amino acid racemization and radiocarbon age determinations show that late Pleistocene sections of the cores were deposited over the time ca. 45,000 to 30,000 yr B.P. Species of fossil foraminifera, recovered from these sections, are mostly extant in modern Gulf St. Vincent, thus allowing paleoecological inferences of late Pleistocene sea levels. These inferred sea-level maxima can be correlated with those determined from study of Huon Peninsula coral reef terraces. Initial estimates of tectonically corrected sea levels for transgressions in Gulf St. Vincent at 40,000 and 31,000 yr B.P. are −22.5 m and −22 m, respectively. The intervening regression lowered sea level to −28 m.

Correlation of gravity with the Maquereau Group, southern Gaspe Peninsula, Quebec

Gravity observations at 150 locations in the Port-Daniel and Chandler area, southeastern Gaspé, Quebec, delineate an E-W to ENE-WSW trending elliptical positive Bouguer gravity anomaly with an amplitude of 19 mGal and a residual gravity anomaly of circa 22 mGal. This anomaly correlates closely with the Lower Cambrian and/or Hadrynian Maquereau Group, the steep gradients defining it coinciding with the contact between the group and the surrounding Ordovician and Siluro-Devonian sedimentary rocks. On the basis of its similar geological setting, this gravity anomaly may be compared with the positive Bouguer anomalies observed over the Fleur de, Lys zone to the east of the Baie Verte lineament in Newfoundland. Tridimensional modelling of the gravity data is inconsistent with a serpentinite dome as originally proposed and it suggests that the Maquereau Group represents an upthrusted slice of deep-seated volcanosedimentary sequences. These were originally located on the lower segment of the continental slope; they constituted a topographic high during the final process of the mountain building at the Taconic phase (Middle to Upper Ordovician time). The most probable way of emplacement of the Maquereau block is through a tear-fault running E-W to ESE-WNW in the southern Gulf of St. Lawrence west of Cape Breton and resulting from Early Paleozoic continental collision between a Eurafrican continent and a North American continent which had a salient located beneath the site of the modern Gulf. The Maquereau may then have been reactivated with a left-lateral motion accompanied of a rotation about a sub-horizontal axis. The presumed Baie Verte-Brompton line ought to be displaced to the north and the Humber zone is narrowed.

Benthic Foraminiferal Morphology: New Approach to Paleodepth Interpretations in Northern Gulf of Mexico: ABSTRACT

Variation in benthic foraminiferal morphology is a potentially powerful tool in paleoenvironmental and paleobathymetric interpretations. Recognition of distribution patterns of particular characters in modern Gulf of Mexico taxa will enable these distributions to be applied to bathymetric interpretations of Tertiary core samples. The morphology of the 295 most commonly recorded benthic foraminiferal species in the northern Gulf of Mexico was scored into 68 categories describing test shape, chamber shape, chamber arrangement, apertural characteristics, and surface sculpture. Cluster analyses of these data at 300 localities resulted in maps showing the distribution of particular sets of features. Many of these morphologic biofacies are depth relatable. Canonical variate analysis was used to determine which variables were most important in distinguishing the various biofacies. This approach to paleobathymetric interpretations should be applicable throughout the Cenozoic and perhaps into the Mesozoic, as morphology can be considered as an adaptive response to environmental factors. Even though different taxa are involved throughout the Cenozoic, similar characters can indicate adaptations to similar environments. Hence, this modern data set can be applied to determine paleobathymetry in older samples. End_of_Article - Last_Page 247------------

Stratigraphy and sedimentology of the Late Proterozoic Rock Harbour Group, Flat Islands, Placentia Bay, Newfoundland Avalon Zone

The Late Proterozoic Rock Harbour Group, as exposed on the Flat Islands, Placentia Bay, consists of a 700 m thick fining-upward sequence of deep-water conglomerates, pebbly sandstones, and thinly-bedded siltstones, capped by a chaotic olistostrome. This sequence rests unconformably on sediments and pillowed tholeiitic basalts of the Burin Group, which were deformed, eroded, and then exposed on the sea floor before Rock Harbour deposition. The conglomerates, sandstones, and siltstones of the Rock Harbour Group may have been deposited within a deep slope canyon cut into the Burin Group, or in a perched slope basin at the margin of the rift system, which was initiated immediately before extrusion of the oceanic tholeiites that characterize the Burin Group. Remarkably good analogues for these two depositional settings can be found in the modern Gulf of California.Although the precise age of the Rock Harbour Group is uncertain, it may be a deep-water equivalent of mixtites found within the Conception Group in the eastern Avalon Zone. However, lithologically similar deep-water sandstones and conglomerates spanning the entire period of development of the Burin Rift Zone may be present in the vicinity of Placentia Bay. If so, then it is reasonable to expect a considerable range in the ages of these units from place to place.

Structure, Stratigraphy, and Geologic History of Florida-Hatteras Shelf and Inner Blake Plateau

This study of the structure and stratigraphy of the Florida-Hatteras Shelf and inner Blake Plateau is based on 4,780 km of single-channel air-gun seismic reflection profiles and correlation with data from offshore wells and dredge hauls. Regional unconformities at the tops of the Albian, Santonian, Maestrichtian, Paleocene, and Oligocene units as well as one between Turonian and the Santonian have been mapped. Two styles of sedimentary accumulation have been active: (1) platform upbuilding and (2) platform outbuilding or progradation of the shelf. In post-Albian time, the area became a marine province, and sediment accumulated on a level platform. During the Santonian-Coniacian a shelf prograded seaward across this platform, but during the Campanian, Maestrichtian, and Paleocene, deposition on a level plateau resumed. There is no evidence to indicate that a feature similar to the present Florida-Hatteras Slope existed prior to the Eocene. Paleocene strata are deeply eroded in the subsurface, and this erosion may mark the initial appearance of the Gulf Stream in this region. During the Eocene and Oligocene, another wedge of shelf sediments prograded across the plateau but was interrupted at he end of the Oligocene by erosion. A progradational wedge of Miocene to Holocene age covers the unconformity at the base of the Miocene. The accumulation of post-Paleocene sediment at the foot of the Florida-Hatteras Slope and seaward on the Blake Plateau has been very slow, owing in part to a reduction in sediment supply as well as to erosion by the modern Gulf Stream. Tertiary isopach maps suggest that there is a triangular depocenter under the Florida-Georgia Shelf. The margins of the depocenter coincide with magnetic anomalies, and we suggest that the basin is related to differential subsidence across older crustal structures during the Tertiary.

Lower Cretaceous Shelf Storm Deposits, North Texas: ABSTRACT

Many of the important features of shelf storm deposits are displayed in the Lower Cretaceous Washita Group in Grayson County, Texas. Proximal shelf sands are up to 2 m thick. They show channeled tops and abrupt lateral thickness variation and are stacked vertically or separated by thin, sparsely fossiliferous marine muds. Each sand unit has a scoured base and comprises a structureless lower interval that grades upward into hummocky cross-stratification. These features in turn are overlain by subhorizontal lamination, with an uppermost interval consisting of small-scale wave ripples containing abundant horizontal burrows and feeding trails. Distal shelf sands are thin (10 to 40 cm) compared to the intervening muds, and are comparable to modern storm deposits of the Texas s elf. A basal shelly lag, with a scoured base of upward-convex, disarticulated bivalves or current-aligned high-spired gastropods merges upward into subdued hummocky cross-stratification and subhorizontal lamination. Powerful bottom return currents, that in the modern Gulf of Mexico are generated by wind immediately prior to storm landfall, were probably the dominant mechanism of offshore sand transport. Storm waves operated contemporaneously and probably contributed toward sediment entrainment, as evidenced by hummocky cross-stratification. However, the disposition of fossils suggests that initially, at least, unidirectional currents were the dominant transport mechanism. Relatively shallow-water depths (50 m or less) are indicated by associated regressive deltaic sequences. End_of_Article - Last_Page 723------------

Quantitative evaluation of the depth of the western Mediterranean before, during and after the Late Miocene salinity crisis

ABSTRACTQuantitative geophysical calculations which take into consideration the isostatic loading of sediment overburden, the overlying water cover, and the thermal cooling history of the continental edge, and its adjacent oceanic lithosphere, demonstrate the foundering of the margins of the western Mediterranean had already commenced in the Aquitanian stage of the early Miocene. The calculations are based on magnitudes and rates of sediment accumulation observed along a profile of three commercial boreholes into the subsurface of the continental shelf of southern France. By the time of the late Miocene (Messinian) salinity crisis, the depth of the seafloor within the Balearic basin exceeded 2.5 km.Sea‐level fluctuations induced by evaporitic draw‐down permitted the exposure of large tracts of the former submerged continental margins to subaerial processes. The measured magnitude of sediment removal by erosion and channel incision near the outer shelf of the modern Gulf of Lion surpasses 1 km.The subsidence history of this shelf platform south of France provides new evidence that the continental lithosphere behaves as if it is rigidly coupled to its oceanic counterpart commencing with the initial phase of the pull‐apart. No major vertical fault displacements have subsequently offset their overlying crustal layers.The sedimentary shaping and construction of the margin seaward of the Rhône delta resulted in a pronounced shelf edge migration and slope progradation during the pre‐salinity crisis Miocene. It has taken 5 million years of predominant upbuilding to establish a new equilibrium profile similar in cross‐section to the precrisis depositional surfaces created by outbuilding.

Facies Relations and Paleontology in Eocene-Oligocene, Santa Ynez Mountains, California: ABSTRACT

End_Page 809------------------------------Facies relations between deep and shallow-marine to continental deposits in the Eocene-Oligocene sequence of the Santa Ynez Mountains, California, have been studied in detail. The rocks studied include the Anita, Sierra Blanca, Juncal (with Camino Cielo Member), Matilija, Cozy Dell, and Coldwater formations. The topmost unit of the Eocene-Oligocene sequence, the nonmarine Sespe Formation, was not included in this study. In landward sequence, the facies recognized include turbidites and marine lutites, proximal turbidites, shallow-marine, coastal, and continental facies. These are present in 2 major regressive sequences. In the first, the Juncal-Matilija sequence, thin-bedded turbidites and marine lutites are overlain by, and are laterally equivalent to, very thick proximal turbidites which pass upward into shallow-marine and coastal sands. The major sand accumulations are in the basin-margin shallow-marine, coastal, and proximal-turbidite facies. The second regression, the Cozy Dell-Sespe sequence, lacks significant proximal-turbidite deposits, but has extensive shallow-marine and coastal deposits. Facies distribution and stratigraphic sequence are explained as responses to the interplay of depositio al and structural processes. Detailed stratigraphic mapping has clarified correlation in the Eocene sequence of the Santa Ynez Mountains. Micropaleontology is used in support of correlations and bathymetric interpretations. Stratigraphic and paleontologic data resolve a biofacies problem in the lower to upper Narizian interval and clarify definition of the Eocene-Cretaceous boundary. Bathymetric interpretations based on comparison of fossil assemblages with modern Gulf of Mexico fauna are in better agreement with depths of deposition interpreted from lithologic data than interpretations based on comparison with modern assemblages in the Pacific Ocean off California. End_of_Article - Last_Page 810------------

Tectonic and Stratigraphic Evidence for Miocene Gulf of California: ABSTRACT

The correlation of clasts in Eocene river gravels in Baja California with the sources for the clasts in Sonora has indicated the necessity for the dilation of the northern Gulf of California depression prior to, or concurrent with, the 23-18 m.y. opening of the Basin Range province in Sonora. The appearance of an extensive, basin-filling seaway in Baja California and Sonora during the Miocene is consistent with a regional subsidence resulting from crustal extension. The presence of shelf-type lower Miocene marine sediments on both coasts of Baja California Sur, between Loreto and La Paz, suggests that the marine waters entered the early Gulf across a shallow, nontectonic seaway which opened to the Pacific Ocean. The recognition of the early Miocene seaway extending into the northern Gulf, coupled with a later (4-10 m.y.) opening of the modern Gulf, supports the idea of a Gulf formed in at least 2 tectonic stages. End_of_Article - Last_Page 795------------

Fossil Box Turtles (Terrapene) from Central North America, and Box Turtles of Eastern Mexico

Aftonian of the Pleistocene in Kansas. Only two fossil specimens of Terrapene ornata ornata were examined. Both were from New Mexico, one from a Wisconsin and one from a post-Wisconsin deposit. Most of the fossil box turtles from the central United States are referred to Terrapene carolina. The oldest specimens are from pre-Sangamon deposits of Texas and Kansas and are identified as T. carolina putnami. A number of the fossils are of Sangamon and early Wisconsin age and are identified as Terrapene carolina putnami x triunguis. The majority of the fossils are of late Wisconsin age and are identified as T. carolina triunguis, which occupies most of the central U. S. today. It is suggested that at times during the Pliocene and Pleistocene conditions comparable to those of the modern Gulf Coastal Plain extended as far inland as Kansas, New Mexico, and eastern Mexico, and that this broad coastal plain area was occupied by a single subspecies, T. carolina putnami. Climatic fluctuations and associated environmental changes during the Pleistocene ultimately led to the differentiation of putnami into T. carolina major in the southeast and T. carolina triunguis in the west. In Mexico, T. carolina putnami, or forms intermediate between putnami and triunguis, gave rise to T. carolina mexicana (formerly T. m. mexicana), T. carolina yucatana (formerly T. m. yucatana), and T. coahuila. T. carolina mexicana has a restricted distribution in southeastern Mexico and it is morphologically close to T. carolina triunguis. Texas fossils of late Wisconsin times indicate that the isolation of mexicana and triunguis is a relatively recent occurrence. T. carolina yucatana is restricted in distribution to the Yucatan Peninsula and it is morphologically close to T. carolina major. It is suggested that yucatana reached the Yucatan Peninsula during a glacial state of the Pleistocene when sea levels were low and a coastal plain was exposed between the present gulf coast and the mountains. The isolation of yucatana occurred prior to that of mexicana, and yucatana is somewhat closer to the older putnami stock than is mexicana. T. coahuila is restricted in distribution to a bolson in central Coahuila where it maintains an aquatic existence. Its distinct morphology may be attributed either to isolation from putnami at a time earlier than the other turtles were isolated or to a higher evolutionary rate as a result of rigorous selective pressure.

THE SURF “BREAK”: KEY TO PALEOGEOGRAPHY?

SUMMARYAncient geosynclinal coastal deposits, preserved and exposed for present‐day examination, probably represent interior—and hence protected—shores, and were therefore characterized by low‐to‐moderate breaker energy levels, as is the modern Gulf of Mexico. Modern low‐energy beach sand size distributions are distinguished by an inflection, here called the surf “break”, formed by a winnowing or statistical filtering process, by the breakers, in the finer sizes. The result is a two‐segment curve having an intersection in many cases not far from 1.5 phi. If the energy level is very low, a tail of fines may be added, producing a three‐segment curve having two inflection points. Along high energy beaches, the surf “break” occurs at such large grain sizes that it cannot be preserved in sand; whether or not it can be recognized in gravel is not known.Ancient sandstones which represent the breaker zone, along a low‐to‐moderate energy coast, should also exhibit the surf “break”. The Lyons Sandstone, a known Permian beach deposit, provides an example. Other examples are cited.Any useful indicator of the shoreline position, in lithified rocks, should have three characteristics: ease of recognition, high reliability, and strong probability of preservation. The surf “break” scores reasonably well on all three points. Hence it may be an important key to paleogeography. Nevertheless, there still remains a question inasmuch as certain river sands have similar inflections. Whether these kinks were inherited from near‐by, but older, beach deposits, or were formed by stream action, is not known. The reliability of the surf “break” is estimated at 80% or better, except for the case where near‐shore sands, of whatever age, are reworked briefly by running water.

Arae Philaenorum and Automalax

From antiquity down to the present century the shores of the Greater Syrtis (the modern Gulf of Sidra) have had the ill fame of constituting the most desolate and inhospitable part of the Mediterranean seaboard. Absence of landmarks, scarcity of water, and abundance of venomous serpents are all attested by the ancient writers, who spared no pains to paint as terrifying a picture as possible of this unhappy region. The child-devouring Lamia did well to select as her residence a cave in this very area, somewhere not far west of Automalax.Yet where horror is greatest there will heroism shine the most brightly, and we may recall that the Syrtic Gulf was the scene not only of the epic marches of Ophellas and of the younger Cato, but also of the supreme sacrifice of the Philaeni brothers, who gave their lives to secure for Carthage a favourable eastern frontier against the rival claims of Cyrene, and whose tombs later served to mark the political and cultural boundary between the eastern and western halves of the Roman Empire.