Broad Plain Research Articles

Origin of pore water and salinity in the lacustrine aquitard overlying the regional aquifer of Mexico City

A series of six ancient connected lakes occupied the broad plain of the closed Basin of Mexico. This study pertains to two of these lakes. 18O, 2H and chemical patterns in the pore water of the broad aquitard formed from sediment in these lakes indicate that the origin of this paleo-lake water was local meteoric water, which entered the ancient lakes as runoff, and groundwater from springs. Evaporation of surface water in the former Chalco Lake caused concentration of dissolved salts and enrichment in the heavy isotopes 18O and 2H. During high water periods, the south easternmost ancient Lake Chalco fed partially evaporated water to the closed Lake Texcoco, the lowest of the lakes, where further evaporation occurred causing higher concentration of salts and enrichment of heavy isotopes. These major ions and stable isotopes follow the evaporation trends characteristic of closed or nearly closed evaporatic basins elsewhere in the world. Paleo-lake evaporation lines in Lakes Chalco and Texcoco originated from the same starting water and developed as a consequence of the topographic position of the former lakes and local climatological conditions. A modern evaporation line developed after the drainage of the lakes, reflecting evaporation of modern infiltrating meteoric water. The presence of brackish pore water in most of the Chalco aquitard, which has a maximum thickness of 300 m, indicates that upward vertical groundwater flow has not been capable of displacing the paleo-lake water. This suggests that vertical advection was not significant throughout the hundreds of thousands of years of existence of the aquitard sediments. One-dimensional numerical simulations of the deeper part of the 18O profile representing the thicker part of the aquitard sediments, 140 m, showed that this profile was developed by molecular diffusion with a small upward advective flux, where apparently the Chalco aquitard always had enriched brackish water overlying the fresh water aquifer.

Sandstone-Body and Shale-Body Dimensions in a Braided Fluvial System: Salt Wash Sandstone Member (Morrison Formation), Garfield County, Utah

Excellent three-dimensional exposures of the Upper Jurassic Salt Wash Sandstone Member of the Morrison Formation in the Henry Mountains area of southern Utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics. The Salt Wash Sandstone Member is composed of fluvial channel fill, abandoned channel fill, and overbank/flood-plain strata that were deposited on a broad alluvial plain of low-sinuosity, sandy, braided streams flowing northeast. A hierarchy of sandstone and shale bodies in the Salt Wash Sandstone Member includes, in ascending order, trough cross-bedding, fining-upward units/mudstone intraclast conglomerates, single-story sandstone bodies/basal conglomerate, abandoned channel fill, multistory sandstone bodies, and overbank/flood-plain heterolithic strata. Trough cross-beds have an average width:thickness ratio (W:T) of 8.5:1 in the lower interval of the Salt Wash Sandstone Member and 10.4:1 in the upper interval. Fining-upward units are 0.5-3.0 m thick and 3-11 m wide. Single-story sandstone bodies in the upper interval are wider and thicker than their counterparts in the lower interval, based on average W:T, linear regression analysis, and cumulative relative frequency graphs. Multistory sandstone bodies are composed of two to eight stories, range up to 30 m thick and over 1500 m wide (W:T > 50:1), and are also larger in the upper interval. Heterolithic units between sandstone bodies include abandoned channel fill (W:T = 33:1) and overbank/flood-plain deposits (W:T = 70:1). Understanding W:T ratios from the component parts of an ancient, sandy, braided stream deposit can be applied in several ways to similar strata in other basins; for example, to (1) determine the width of a unit when only the thickness is known, (2) create correlation guidelines and maximum correlation lengths, (3) aid in interpreting the controls on fluvial architecture, and (4) place additional constraints on input variables to stratigraphic and fluid-flow modeling. The usefulness of these types of data demonstrates the need to develop more data sets from other depositional environments.

Integrated Reservoir Description and Analysis of the Lance Formation at Jonah Field, Sublette County, Wyoming: ABSTRACT

Log, core, and production data from the 16 wells in Jonah field have been used to characterize sandstone reservoirs in the Lance Formation (Cretaceous) in the northern Green River basin. The Lance Fm. is composed of 2500 feet of heterolithic fluvial strata that were deposited on a broad alluvial plain. Sandstones were deposited in east- flowing channels 10-20 feet deep and 150-4000 feet wide; some amalgamated sandstone intervals are >100 feet thick and over a mile wide. Fluvial architecture varies from isolated meandering river deposits to amalgamated braided river deposits. Sandstones are dominantly composed of detrital chert and quartz grains. The Lance Fm. has been divided into several informal pay intervals that have different reservoir character and performance. Wardell interval sandstones produce gas in eight wells and are poor reservoirs due to fine grain size, high clay and cement content, and greater depth. Yellow Point interval sandstones have shown average performance in five wells. The Jonah interval produces in 10 wells and is the most prolific pay zone with up to 150 net feet of sandstone having core porosity of 8-12% and permeability of .01-0.9 mD. Upper and middle Lance sandstones have better than average performance from five wells. Allmore » pay intervals require greater than 8% porosity and less than 35% water saturation. Pre-frac pressure build-up analysis indicates in situ permeabilities of 3-20 microdarcys and suggests that fractures are a significant contributor to deliverability. Estimated reserves of 0.4-4.0 BCFG/well are based on decline curve analysis. Liquid yields vary from 6-86 BO/MMCFG and increase with depth. Pressure gradients range from .55 to .59 psi/ft. Reservoir overpressure is a result of continuous migration of hydrocarbons into available pore space via microfracture seepage.« less

Response of tide‐dominated mangrove shorelines in Northern Australia to anticipated sea‐level rise

AbstractThe exact response of mangrove shorelines to anticipated sea‐level rise will depend upon the balance between sedimentation and sea‐level change. Within the Top End of the Northern Territory of Australia there are extensive, relatively unmodified, tide‐dominated mangrove forests, where tidal processes redistribute sediment. Harbours, such as Darwin Harbour, and tidal rivers, such as the South Alligator River with its associated coastal and estuarine plains, represent opposite extremes in terms of Holocene sedimentary infill, and will respond differently to sea‐level rise. In Darwin Harbour, mangrove assemblages can be recognized in geomorphologically defined habitats. Similar topography within and between creeks implies morphodynamic equilibrium with tidal processes. Tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level, with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats. In contrast, the plains along the coast and tidal rivers draining into van Diemen Gulf developed during the post‐glacial marine transgression, and since sea level stabilized, around 6000 years ago, coastal plains have prograded. These broad plains are presently not extensively influenced by salt water, but are often at elevations close to, or even below, modern high‐tide levels. They may, therefore, revert to saline conditions particularly rapidly if the sea rises. The pattern of change may not be directly analogous to marine incursion experienced in the early Holocene, because broad plains have been able to prograde during the last 6000 years of relatively stable sea level.

A Continental Clastic Depositional Model for the Permian Unayzah Formation, Hawtah Field, Central Saudi Arabia

The Permian Unayzah Formation lies unconformably on the Silurian Qusaiba Member of the Qalibah Formation. The pre-Unayzah unconformity (PUU) represents a Hercynian tectonic event responsible for uplift and erosion representing 100-150 m.y. worth of missing section along the Hawtah Trend. Overlying the PUU, the Unayzah clastic sequence is comprised of locally sourced sediments from the adjacent paleotopography. Above the thin veneer of locally sourced sediments is a more regionally sourced, confined braided stream sequence, which completely backfills the existing paleotopography. Once the paleotopographic surface had been leveled, the depositional environment changed from a confined braided stream to a broad braided plain. Within this sequence of vertically stacked and laterally migrating braided plain sediments, the bulk of the reservoirs within the Hawtah field are contained. As the transgressive Khuff seas continue to encroach on the Unayzah depositional system, the upper-most sediments of the broad braided plan environment are reworked by transgressive coastal processes. The resulting reworked shoreface and shallow-marine facies are genetically related to the Khuff transgression and lie unconformably on the Unayzah continental clastics.

Uplift, subsidence, and volcanism in the southern Neiva Basin, Colombia, Part 1: Influence on fluvial deposition in the Miocene Honda Formation

In the southern Neiva Basin, four large-scale sedimentary sequences are recognized in the deposits of the Miocene Honda Formation on the basis of maximum clast diameter, fluvial channel/overbank deposit ratio, thickness of the overbank and channel sequences, and lithology of the sandstones. These sequences can be related to tectonic activity of the Central Cordillera and the Garzón Massif, to volcanism, and to the rate of basin subsidence. They may be interpreted in terms of different alluvial fan systems and volcanic aprons that prograded onto a broad plain during periods of active uplift or volcanism and braided and meandering river systems that developed during the intervening periods of greater volcanic and tectonic quiescence. The lower two sequences were deposited under relatively quiet tectonic conditions, following the major and final phase of thrust faulting of the Central Cordillera. During deposition of these sequences, sediment loading let to subsidence of the basin. The depositional processes of these sequences, furthermore, were influenced by activity of the Central Cordillera volcanic arc. Radiometric age determinations on two tuff beds located some 300 meters above the base of the formation in the lowermost sequence gave ages of 15.8 ± 0.6 and 14.3 ± 0.5 Ma, respectively. Conglomerates of the third sequence record pronounced uplift of the source area, i.e., the Central Cordillera. Deposition of this sequence very probably coincided with uplift of the Garzón Massif, the southermost extension of the Eastern Cordillera, which took place at about 12 Ma. Uplift of both cordilleras led to rapid subsidence of the basin. The upper sequence was deposited under conditions of waning tectonic activity.

The distribution, formation and engineering properties of Quaternary regional Sediments in China

Abstract In China, there exist various regional sediments of the Quaternary such as loess soils of the Yellow River in northern China, lateritic soils in southern China and expansive soils in the broad plains of the Yangtze River. In the past, these Quaternary Sediments were often treated as special soils and their engineering properties tended to be studied accordingly. However, not much attention was given to relationships that may exist between these regional soils and, so far, the distribution and formation of regional Sediments have not been systematically studied. Only when it was found that regional classifications of soils (their names and their engineering properties) were in disagreement with each other for adjacent areas was the subject of relationship considered. Recently, the author has tested and studied a number of samples of various Quaternary regional Sediments. The relationship of their composition and microstructural features to their engineering properties has first been analysed on the basis of their basic properties. The distribution of regional sediments has then been studied in detail according to geographical environment and climatic conditions. Finally, formation and development processes for the various regional Sediments of the Quaternary in China have been postulated.

Factors Affecting Historical Distribution and Modern Geographic Variation in the South Texas Pocket Gopher Geomys personatus

Geographic distribution and variation were examined in cranial and dental morphology of Geomys personatus in coastal southern Texas and Tamaulipas, Mexico. Unsuitable soils, waterways and a composite of physiographic features were used as criteria for dividing the samples for analysis. Geomys personatus appears to be restricted to fine sands, loamy fine sands, fine sandy loams and sandy loams. The history of coastal processes in the region suggests widespread distribution of G. personatus across a broad sandy plain exposed during lower sea levels of the late Wisconsinan glaciation. Subsequent rise of sea level at the end of this glaciation flooded the river valleys, forming present-day bays and leading to the disjunct distribution seen at present. Patterns of geographic variation, interpreted with reference to the geological history of the area and to modern distribution of soils, generally do not correspond with locations of physiographic features, including waterways that prob- ably now serve as isolating features. Rather, morphological variation corresponds better with soils composition without regard to geographic location.

The soil geomorphic history of the broken plain belt in the northeast corner of the darling basin, eastern Australia

This integrated study of soil patterns, land forms and surficial stratigraphy deals with the multi-stage soil geomorphic history of the development of a belt of low relief, referred to as the ‘broken plain belt’, situated between the higher relief terrain of the Great Dividing Range and the broad flat inland plains of the upper Darling River system. The complex pattern of plains which characterizes this belt is related to three major cyclic planar developments during the Miocene which cut away nearly all of the Early Tertiary deeply weathered lateritized surface. The first planar development sculptured broad valley pediplains or pediment-like slopes depending on the terrain. The second stage was characterized by the cutting of wide shallow valley troughs creating broad plain landscapes up to 15 km or more wide, and the minor valley tributaries formed undulating topographies on the residual land forms of the previous stage. During the third relatively minor stage the floors of the valley troughs were slightly lowered in level and partially refilled with deposits up to 10 km and more wide without any evidence of stream related patterns. Intense soil weathering towards the end of both the second and third stage led to heavy, dense clay formation in weathered rocks and sediments. Alluvial soil landscapes have developed since mid-Pliocene in shallow entrenchments occupying only small proportions of the plain surfaces; there is evidence of two major and three minor cyclic stages. Corresponding colluvial developments, which in general caused only minor modifications occur in different patterns depending on the terrain and are described in terms of soil stratolandscapes. It is concluded from the restricted extent of these alluvial and colluvial developments that the characteristic feature of the broken plain belt is the extensive preservation of Miocene soil landscape features.

Unconformities and Valley-Fill Sequences--Key to Understanding Reservoirs at Lonetree and Poncho Fields, Denver Basin, Colorado: ABSTRACT

Previous interpretations suggested that the Lower Cretaceous ''J'' sandstone in the Denver basin is divisible into three genetic units: a lower delta front (J-3), a middle delta plain (J-2), and an upper destructional marine bar (J-1). The presence of root casts and siderite cement along the upper contact of the J-3 sandstone, however, suggests that J-2 deposits are separated from the J-3 sandstone by a regional unconformity. This contact may mark the same unconformity that separates the Horsetooth and Fort Collins Members in outcrop along the western margin of the basin. J-2 deposits comprise point bar, crevasse splay, and floodplain sequences of a broad alluvial plain. Fluvial deposits at Lonetree and Poncho probably formed in a tributary to a larger order tributary that flowed southwest through the Peoria field area. These tributaries eventually drained into a major trunk stream represented by valley-fill deposits of the Kassler sandstone. Delta-front deposits (J-3) that underlie the unconformity are tightly cemented by siderite and do not produce in either field. J-2 sandstones are productive from north- and west-trending point-bar deposits in both fields and from laterally equivalent crevasse-splay deposits at Lonetree field. Secondary porosity has created a common reservoir in point-bar and crevasse-splay depositsmore » at Lonetree. Laterally equivalent deposits of major trunk streams, such as the Kassler sandstone, generally produce only over structural noses in the southern D-J basin. Overlying J-1 sandstones form northeast-trending marine bars in both field areas. Two echelon bars are present at Poncho but only the western one is productive. The eastern bar at Poncho and the single marine bar at Lonetree are wet.« less

Sedimentary characteristics of cheniers in southern Changjiang Delta and their origin and age determination : Liu, Cangzi, Licheng Wu and Min Cao, 1987. Acta oceanol. sin. (English version), 6(3):405–412. Inst. of Estuarine and Coastal Res., East China Normal Univ., Shanghai, People's Republic of China

According to analyses on the texture and structure of sediment, species component and accumulative way of shells, geometry of sana body and its vertical sequence, this paper points out that the sand ridge located in the west of Shanghai is a kind of ancient chenier, and the entire broad plain of cheniers and the mud flats in between is called chenier plain. The origin of the chenier is related to the shifting of main branch channel in the Changjiang estuary and coastal changes during the historical periods. Based on 14C dating data, the ages of the cheniers from west to east are 6800-6000,5800-5500, 4200-4000 and 3200 years B. P. respectively. These cheniers of different ages illustrate the development processes of the Changjiang Delta during the Middle Holocene.

Farming Systems in the Niger Inland Delta, Mali

The Inland Delta of Mali has a concentration of diverse ethnic groups, a relatively dense population, and various farming systems that are adapted to local conditions. More than 20,000 square kilometers of the delta are flooded annually by the Niger River. Most cultivation depends on some type of irrigation. Pastoralism is also practiced. Recent droughts and increased human and livestock populations are factors in environmental degradation and disruption of traditional productive systems. T HE purpose of this article is to examine the traditional farming systems of the Inland Delta of the Niger River in Mali and to summarize controls instituted to protect agriculture from flooding. The Inland Delta of the Niger River is a broad plain of almost 50,000 square kilometers, extending from the Bani River on the south to Lake Faguibine on the north (Fig. 1). The name of this delta derives from the fact that the Niger River overflows and annually inundates more than 20,000 square kilometers. The region is characterized by a diversity of ethnic groups, a relatively dense population, and various productive systems that have adapted in different ways to the annual flooding. Located in a zone where yearly rainfall ranges between 200 and 600 millimeters, the area has marginal potential for rainfed cultivation. However, the annual flooding provides a resource for the development of water-managed farming systems and creates a node for dry-season grazing by livestock of pastoralists. HYDROLOGY OF THE DELTA The Inland Delta, located at the confluence of the Niger and Bani rivers in Mali, comprises three physiographic regions (Fig. 2). To the south, the active delta, or delta vif, extends from the Bani River to lakes Debo and Korientze. The active delta is subject to annual flooding. Northward is the lacustrine zone, characterized by lakes, pools, and elongated dunes. The relatively higher local relief precludes complete inundation by the floodwaters, which flow along established channels to fill the pools and lakes. The inactive delta, or delta mort, has dunes, sandy plains, bush pasturelands, and areas of sparse vegetation and is located on the peripheries of the other * This article is a result of Mr. Thom's participation in the Mali Land Use Project, which was funded by USAID. He and Mr. Wells acknowledge the cooperation and suggestions of team members of that project, especially Charlotte Bingham, Seydou Bouare, Geoffrey King, and Joel Thomas. Paul Rainaldi, Utah State University, drafted the illustrations. * DR. THOM is a professor of geography at Utah State University, Logan, Utah 843220710. MR. WELLS, who received a M.S. in agricultural engineering from Cornell University in January 1987, is currently studying at the Institut de Mecanique de Grenoble, St. Martin d'Heres, France. This content downloaded from 157.55.39.223 on Wed, 24 Aug 2016 05:36:12 UTC All use subject to http://about.jstor.org/terms INLAND DELTA, MALI 329

Archeological Exploration of the Lu City at Qufu

The city of Lu is located in the Qufu district of Shandong at the edge of the southwestern foothills of the Taiyi mountain chain, between the Si and Xiaoyi rivers. The Si River winds around the north and west of the city, and the Xiaoyi River flows to its south. On the city's western side is a broad plain. In 1961 the State Council declared the city of Lu a major national cultural site. From 1971 to 1978 the Shandong Archeological Department under the direction of the National Cultural Bureau carried out a systematic survey of the northern part of the Lu city from the east to the west, along with major excavations involving the ancient city wall and the remains of residences, workshops, and the palace. The first task was to ascertain the dating, form, and basic ground plan of the city. This is a general introduction to the results of those explorations.

The Effect of Mississippi River Delta Lobe Development on the Habitat Composition and Diversity of Louisiana Coastal Wetlands

The patterns of habitat changes that occur during the growth and decay of Mississippi River deltaic lobes were examined by comparing different-aged lobes using habitat maps constructed from aerial photographs. Mudflats and fresh marshes dominated young delta lobes (10-1000 years old). Intermediate-aged lobes (1000-2000 years old) contained higher proportions of brackish and salt marshes. Old lobes (2000-4000 years old) contained large areas of salt and brackish marshes and open water. The number of habitat types (N) and Shannon-Wiener index of habitat diversity (H') were lowest in the youngest lobe (N = 14, H' = 0.68), highest in a medium-aged lobe (N = 56, H'= 1.77), and intermediate in the oldest lobe (N = 44, H' = 1.38). A new cycle of vegetation change is initiated approximately every 1000 years when upstream river diversion reintroduces fresh water and sediment into an old lobe. INTRODUCTION This study examines the effect of the large-scale disturbance caused by major shifts in the course of the Mississippi River on the distribution of plant communities in the Mississippi River deltaic plain region of Louisiana. Land in the Mississippi River delta region was formed during the last 6000 years by sediment deposited in major deltaic lobes by the Mississippi River (Fig. 1). Together the delta lobes built a broad plain of approximately 3 million ha. The nature and timing of these deltaic deposits control the long-term dynamics and persistence of the habitats found in this predominantly wetland coastal region. The five delta lobes that today make up the Mississippi River deltaic plain range in age from 10-4000 years. New delta lobes begin to form approximately once every 1000 years in response to a major change in the course of the river (Fig. 1). Each delta lobe undergoes a cycle of geological development (Kolb and van Lopik, 1966; Frazier, 1967; Gagliano and van Beek, 1975) and each of the existing five lobes lobes represents a different stage of development (Fig. 2). The initial phase includes below-water (subaqueous) deposition and limited above-water (subaerial) development. This is followed by a second phase of sustained land building. Land building continues until the river's hydraulic gradient becomes too flat to efficiently transport water and sediment to the Gulf of Mexico. This sets the stage for an upstream diversion to a new stream course with a steeper gradient (Morgan, 1967). A third phase of prolonged subsidence, land erosion and lobe decay follows diversion of the river course. During this stage of delta abandonment, progressively less water and sediment are transported by the dying distributary. The reduced quantity of sediment at its mouth cannot compensate for subsidence and wave attack, and erosion becomes the dominant process acting on a delta lobe (Morgan, 1967). Salinity decreases as a delta lobe develops, is lowest during time of greatest land building because of large riverine freshwater input, and increases again as freshwater input declines (Fig. 2). Land deposition and erosion and changes in salinity during this geologic cycle pro'Present address: Department of Forestry and Wildlife Management, University of Massachusetts, Amherest, 01003

Norphlet Formation (Upper Jurassic) of Southwestern and Offshore Alabama: Environments of Deposition and Petroleum Geology

Upper Jurassic Norphlet sediments in southwestern and offshore Alabama accumulated under arid climatic conditions. The Appalachian Mountains of the eastern United States extended into southwestern Alabama to provide a barrier for air and water circulation during the deposition of the Norphlet Formation. These mountains produced topographic conditions that contributed to the arid climate, and they affected sedimentation. Norphlet paleogeography in southwestern Alabama was dominated by a broad desert plain, rimmed to the north and east by the Appalachians and to the south by a developing shallow sea. The desert plain extended westward into eastern and central Mississippi. Norphlet sedimentation initiated as a result of basin subsidence accompanied by erosion of the southern Appalachians. Norphlet conglomerates were deposited in coalescing alluvial fans in proximity to an Appalachian source. The conglomeratic sandstones grade downdip into red beds that accumulated in distal portions of alluvial fan and wadi systems. Quartz-rich sandstones were deposited as dune and interdune sediments on a broad desert plain. The principal source of the sand was updip alluvial fan and plain and wadi deposits. Wadi and playa lake sediments also accumulated in the interdune areas. A marine transgression was initiated during the late phase of deposition of the Norphlet Formation, resulting in the reworking of previously deposited Norphlet sediments. Norphlet hydrocarbon potential in southwestern and offshore Alabama is excellent; six oil and gas fields already have been established. Petroleum traps discovered to date are primarily structural traps involving salt anticlines, faulted salt anticlines, and extensional fault traps associated with salt movement. Reservoir rocks consist primarily of quartz-rich sandstones that are eolian, wadi, and marine in origin. Porosity is principally secondary (dissolution) with some intergranular porosity. Smackover algal carbonate mudstones were probably the source for the Norphlet hydrocarbons. Jurassic oil generation and migration probably were initiated in the Early Cretaceous.

Paleoenvironments and Hydrocarbon Potential of Upper Jurassic Norphlet Formation of Southwestern Alabama and Adjacent Coastal Water Area: ABSTRACT

Upper Jurassic Norphlet sediments in southwestern Alabama and the adjacent coastal water area accumulated under arid climatic conditions. The Appalachian Mountains of the eastern United States extended into southwestern Alabama, providing a barrier for air and water circulation during Norphlet deposition. These mountains not only contributed to the arid climate but also affected sedimentation. Norphlet paleogeography was dominated by a broad desert plain rimmed to the north and east by the Appalachians and to the south by a developing shallow sea. The desert plain extended westward into eastern and central Mississippi. Initiation of Norphlet sedimentation was a result of erosion of the southern Appalachians. Norphlet conglomerates were deposited in coalescing alluvial fans in proximity to an Appalachian source. The conglomeratic sandstones grade downdip into red-bed lithofacies that accumulated in distal portions of alluvial fan and wadi systems. Quartzose sandstones (Denkman Member) were deposited as dune and interdune sediments on a broad desert plain. The source of the sand was the updip and adjacent alluvial fan, plain, and wadi deposits. Wadi and playa lake sediments probably also accumulated in the interdune areas. A marine transgression was initiated late in Denkman deposition, resulting in the reworking of previously deposited Norphlet sediments. Norphlet hydrocarbon potential in southwestern and offshore Alabama is excellent with four oil and gas fields already established. Petroleum traps discovered to date are primarily structural traps involving salt anticlines, faulted salt anticlines, and extensional fault traps associated with salt movement. Reservoir rocks consist of quartzose sandstones, which are principally eolian in origin. Porosity types include both intergranular and secondary dissolution. Smackover algal carbonate mudstones were probably the source for the Norphlet hydrocarbons. End_of_Article - Last_Page 1215------------

Stratigraphy, Depositional Rates, and Other DSDP Leg 96 Conclusions: Mississippi Fan: ABSTRACT

The Quaternary Mississippi fan consists of at least seven seismically mappable fan lobes. Eight sites were drilled into the youngest fan lobe during DSDP Leg 96. The Holocene (Ericson Zone Z) is capped by a marly foraminiferal ooze. Assuming an age of 12,000 yr for the Holocene/Pleistocene boundary, a minimum accumulation rate of 3-30 cm/1,000 yr (1-12 in./1,000 yr) is computed for the Holocene. The youngest fan lobe was deposited during the upper part of Ericson Zone Y (late Wisconsin glacial, 12,000-85,000 y.B.P.). Deposition rates for the Y Zone are extremely high for the middle fan sites, averaging 12 m/1,000 yr (39 ft/1,000 yr). Lower fan accumulation rates are 7 m/1,000 yr (23 ft/1,000 yr) for the channel sites and 6 m/1,000 yr (20 ft/1,000 yr) for the channel-mouth depositional lobes. These rates are not corrected for compaction. Foraminifera are scarce; the occurrence of shallow-water benthic species indicates a displaced inner and middle neritic origin for the sediments. Drilling on the youngest fan lobe shows that most of the silts and sands were transported through the upper and middle fan channel onto the lower fan, producing a 6 to 10-km (4 to 6-mi) wide, 135-m (443-ft) thick aggradational channel deposit. Much of the fine-grained sediment spilled out of the channel onto the adjacent overbank areas, constructing a broad marginal plain. The channels on the lower fan are smaller and shift position frequently. Channel-mouth depositional lobes are constructed at the end of the active channels and are composed of more than 50% net sand. End_of_Article - Last_Page 463------------

Delineation of Delta Types: Norias Delta System, Frio Formation, South Texas: ABSTRACT

The Norias delta system was the major depositional component of the Frio Formation, South Texas. The Norias was an expansive, predominantly sandy, progradational complex fed by the updip Gueydan fluvial system. This progradational complex effectively filled the Rio Grande embayment of South Texas by the end of Frio deposition. Initiation of Norias deltaic progradation was probably associated with the early rise in sea level following a lowstand. As sea level rose following the lowstand, topographic expression of the preexisting Vicksburg progradational wedge caused a northward deflection of the Gueydan fluvial system within the Rio Grande embayment. Subsequently, the Norias delta complex was established as a stable progradational system in a position lateral to the north lanking margin of the main Vicksburg deltaic platform. The Norias delta system was flanked laterally with time-equivalent depositional systems, including a northerly strand-plain/barrier-bar system and to the south there are indications of a possible deltaic complex in northern Mexico. Entrenchment of the Vicksburg shelf during sea level lowstand probably led to development of a submarine canyon adjacent to the south flank of the Norias delta system. Incorporated within the complex body of the progradational sequence a well-defined evolution of Norias delta styles can be documented through the time of Frio deposition. Early Frio high-constructive, fluvially dominated, lobate geometries were characterized by meandering distributary systems as well as thick delta-front and delta-margin san s. Middle Norias deltaic deposits continued to be generally high-constructive lobate in style, but evidence for significant reworking of deltaic sediments can be inferred based on the strand-plain/barrier system developed to the north. Late Norias deltas were high-destructive wave dominated in nature. Essentially the Norias depositional complex had become a broad alluvial plain feeding a strand-plain/barrier-bar system with little physiographic expression of a delta lobe. End_of_Article - Last_Page 1463------------

Late Paleolithic and Mesolithic Coastlines of Greece and the Aegean

AbstractReconstructions of the late Quaternary paleogeography of Greece and the Aegean show that at 18,000 years B.P. the northern Aegean and northern Adriatic formed large coastal plains traversed by many rivers. Broad plains also existed off the coast of Elis and the present Gulf of Korinth, and along the Anatolian coast. Many islands, such as Kerkira, Euboea, and the northern Sporadhes, were connected with the mainland, and most of the Cycladic islands were joined together in a Cycladic semi-peninsula. The post-glacial rise of sea level beginning ca. 15,000 B.P. restored around 9,000 B.P. the coastal geography to approximately its present configuration. The late Quaternary paleogeography and its subsequent changes have many archeological implications that are worth serious consideration. The well-watered northern coastal plains may have furnished subsistence for a plains population quite independent of the resources of the northern mountain regions, and they constituted easy access to the Greek peninsu...

The Turnip Wagon: A Boschian Motif Transformed

The theme of the Haywain, Hieronymus Bosch's great allegory of avarice (Fig. I), seems to have enjoyed a certain vogue in Brabant during the third quarter of the sixteenth century. Two manifestations of its influence were published and extensively analyzed some years ago by Lebeer, Grauls and Keyser. One of these is an etching by Frans Hogenberg, issued in 1559 by the Antwerp print publisher Bartholomeus de Mompere (Fig. 2). It depicts a broad plain crowded with figures whose acts of folly are epitomized by the large hay cart dominating the middle distance. The cart unmistakably shows Hogenberg's debt to Bosch, although he replaced the music-making lovers seated on Bosch's wagon with a devil triumphantly displaying two tufts of hay.