The Cabullona Basin of northeastern Sonora is a structural depocenter that was formed during Late Cretaceous time. The 2.5 km-thick sedimentary fill of this basin, the Cabullona Group, is composed in ascending order of the Corral de Enmedio formation, Camas Sandstone, Packard Shale, Lomas Coloradas formation, and, laterally equivalent to the last two units, El Cemento conglomerate. Abundant vertebrate and invertebrate as well as pollen identifications from these units indicate the Cabullona Group is of middle Santonian to Maastrichtian age. The Corral de Enmedio formation represents shallow lacustrine deposits. Lithofacies of the Camas and Lomas Coloradas formations indicate they were deposited by braided- and meandering-fluvial systems, whereas the eight members of the Packard Shale represent complex fluvio-deltaic-and-lacustrine systems. The El Cemento conglomerate is a thick clastic wedge of coarse-grained alluvial deposits that was deposited adjacent to the structural margin of the basin. Clast composition and paleocurrent directions of the El Cemento conglomerate indicate it was derived from strata of the nearby uplift of the Sierra Anibacachi-Cerro Cabullona. The low-angle, southwest directed Cabullona thrust fault that separates the uplift from the basin formed the structural margin of the basin. The tectono-sedimentary history of the Cabullona Group, its age and regional tectonic setting support the idea that this basin was formed because of typical Laramide-style deformation and indicates that the Rocky Mountain foreland province of Laramide deformation extended southward to northeastern Sonora.

Fossil bearing continental deposits, the Gila Conglomerate, of the Safford and Duncan Basins, Arizona were correlated with the magnetic polarity time scale by means of magnetostratigraphy and biochronology of mammalian fossils. Within the Safford Basin, the Bear Springs section with a middle Blancan fauna is correlated with the lower or upper Gauss chron; the 111 Ranch section with a middle to late Blancan fauna is correlated with the upper Gauss to early Matuyama chrons; and the San Simon Power Line section with probably a latest Blancan fauna is correlated with the early Matuyama chron. In the Duncan Basin, the Duncan section with a middle Blancan fauna is correlated with the middle Gauss chron; the Pearson Mesa section with a middle Blancan fauna is correlated with the Upper Gauss chron; and the Country Club section with a middle Blancan fauna is correlated with the latest Gilbert to early Gauss chrons or from the middle Gauss to the earliest Matuyama chrons. A late Blancan fauna is not recognized in the Duncan Basin at least within the study area, whereas the Gila Conglomerate in the Safford Basin includes deposits and fauna of the latest Blancan (latest Pliocene) age. A minimum of 37 taxa of small mammals are recognized among the approximately 1,600 specimens from the Gila Conglomerate of the Safford and Duncan Basins. Three new rodent species are described; they are Pappogeomys (Cratogeomys) sansimonensis, new species; Reithrodontomys galushai, new species; and Repomys arizonensis, new species. One new combination of genus and species, Hypolague virginiae, is described. In the Safford Basin, a minimum of 26 small mammal taxa are now recognized in the 111 Ranch fauna, of which three genera (Dipodomys, Peromyscus, and Repomys) are new records to the fauna; a minimum of 6 taxa of small mammals are recognized and described for the first time in the San Simon Power Line fauna. In the Duncan Basin, a minimum of 15 small mammal taxa are recognized and described for the first time.

A stratigraphic radiocarbon study at the Wilicox Playa and vicinity in Cochise County, southeastern Arizona has revealed a sedimentary sequence reflecting the lake level chronology of ancient Lake Cochise. The lower green clay was deposited in a lake at least 30 miles long from before 30,000 years ago until about 13,000 years ago. A marl formation which began depositing about 25,000 years ago and continued until the lake diminishe to about its present state 13,000 years ago, indicates a warm, moist climate at that time. The period from 13,000 B.P. (before present) and 11,000 B.P. was one of alluvial deposition north of the playa and channel cutting east of the playa. An upper green clay, 6 to 8 inches thick, represented the final phase of Lake Cochise, lasting from 11,500 B.P. until 10,500 B.P. A thin marl layer was deposited during this phase, indicating warm moist conditions again. The lake rapidly receded, some playa sediments deflated from the surface, and dunes formed north of the playa. Preliminary studies of two playas near Lordsburg, New Mexico and one at the San Augustin Plains, New Mexico, indicate these fluctuations were responding to a general climate change rather than isolated tectonic disturbances. The climate chronology concluded from this study is consistent with known climatic variations in the world.

Post-Miocene fluvial and lacustrine units coristitute the valley fill of the San Pedro Valley, near Redington, Arizona. These sediments are relatively flat lying units deposited on older, deformed sediments, fault blocks of Tertiary volcanics, and erosion surfaces on Precambrian crystalline rocks. The sedimentary sequence is composed of silts, inudstone, sands, gravels, limestone, gypsum, diatomite, and pyroclastic units. Previous investigations have designated these lithologies one unit, the Gila Conglomerate. A recent study in the Mammoth area (Heindi, 1963) subdivided the Gila Conglomerate into the Quiburis formation, Sacaton formation and Pleistocene to Recent alluvial deposits. In the present study, this nomenclature was utilized, with a proposed subdivision of the Quiburis formation. Detailed mapping of the lithologic units indicate a lateral facies change within the Quiburis formation0 The conglomeritic member of the Quiburis formation interfingers with a central, fine-grained member, and the names Tres Alasnos, and Redington are proposed for these units. The age of the Quiburis formation is based on its stratigraphic position, and vertebrate fossils. The Qulbuns ovenlies tilted sediments containing Miocene fauna, and its upper portions contain fauna which have been assigned a middle to late Pliocene Age. The Sacaton formation was deposited on an erosion surface in the Quiburis in late Pliobene to early Pleistocene time; it was then entrenched and local, middle to late Pleistocene lacustnine units were deposited in the drainage pattern. Fresh water mollusks, horse and mammoth remains are present in the lacusbnine units. The Pleistocene lacustrine units were truncated by late Pleistocene terraces, and degradation proceeded to approximately 80 feet below the present floodplain. Aggradation occurred, to a level above the present floodplain, as attested by prehistoric hearths buried in river sediments, above the present stream gradient. Since 1880 the San Pedro River has begun another period of downcutting. The sedimentary deposits control the movement of ground water in the valley. Two hydrologic systems are present; a shallow water table system in the floodplain and river channel area, and an artesian system at 630- 1,200 feet below the valley floor in the northern portion of the study area. It is believed that deformed, pre- Miocene sedinentary units provide the source of recharge to the artesian system. Detailed mapping of the sedimentary units reveals a meandering central trough of the ancestoral San Pedro River. The contact between the Redington and Tres Alamos members of the Quiburis formation indicate the meander pattern, and its control by bedrock outcrop. Structural activity continued through Pliocene time, and is represented by north trending normal faults. Minor slump structures and small reverse faults are present in the Redington member of the Quiburis formation. A site survey, carried out during the field mapping, resulted in the location of nineteen archaeological sites. The sites range from preceramic Desert Culture to Salado and probably to later cultures such as the Apache. Older sites are peripheral to the valley axis, with more recent sites concentrated along the river. It appears that geologic-hydrologic factors controlling site location are: water sources; agricultural or gathering areas; quarry, or source material sites; and vantage points.

Four lithostratigraphic alluvial formations and eight chronostratigraphic "accumulation phases" occur along the middle Duck River Valley. Each accumulation consists of about 2 m of sandy and gravelly bottom stratum facies overlain by 2.5-4 m of clayey and silty top stratum facies. An additional 1-2 m of clayey and silty terrace veneers blanket all but the youngest accumulation. Based on numerous excavations into this fill, and 14 radiocarbon dates, a history of floodplain sedimentation can be traced: 1) Yellowish brown clay loam was deposited during the late Pleistocene, above a bedrock thalweg 5 in higher than the present level. Severe bedrock and floodplain erosion then occurred. 2) During the early Holocene, aggradation of dark yellowish brown clay loam occurred, over a bedrock valley floor already as deep as that at present. Scattered within this unit are early Archaic (ca. 9000 yr B.P.) chert artifacts. 3) Following a brief interval of stability, brown silty clay loam accreted, but by 7200 ¹⁴C yr B.P. the floodplain surface was again stable and soil formation dominated over deposition. Abundant mid-Archaic chert artifacts as young as 6400 ¹⁴C yr B.P. in age were left behind by their makers on this fossil floodplain surface, and pollen analytical studies document an effectively drier climate in the region during this time. 4) By 6400 ¹⁴C yr B.P., renewed overbank accretion was underway and pollen analyses indicate an increasingly humid climate. Aggradation continued up to 4200¹⁴C yr B.P., by which time the older surface, artifacts, and soil were buried by veneers of dark brown silty clay loam, itself containing late Archaic artifacts. 5) Two periods of floodplain stability and soil formation, separated by aggradation, occurred during the past 4000 years. The last period of stability ended in the early 1800's; the introduction of row crop agriculture into the basin at this time probably caused the historic episode of renewed accretion which is still underway. In response to altered hydrologic regimes, the Duck River forms new floodplains by suspended load deposition on older floodplain surfaces, on vegetated channel banks, and on the higher portions of vegetated in-channel bars. In contrast, lateral accretion of point bar sands and gravels is not an important floodplain forming process along this river.

The late Holocene flood history and associated channel changes were reconstructed for the Escalante River in south-central Utah. Analyses of flood deposits at 8 sites in the bedrock canyon indicate that the frequency of large floods was at a maximum 1100 to 900 yrs BP and in historic times in a 2000 year record. The largest flood occurred approximately 900 to 1000 yrs BP and was 7 times the largest flood recorded at a gaging station. The paleoflood discharges were close to the "maximum expected flood" derived from a regional flood envelope curve, and the 100-yr flood was increased 220% to 800 cubic meters per second (cms) with the addition of four historic flood discharges. Possible nonstationarity in the distribution due to channel changes and climatic shifts reduced the reliability of statistical flood-frequency analyses. The additional parameters of the "largest recorded flood" in 2000 years of paleoflood record -- 720 ems -- and the "maximum expected flood" -- 1180 cms -- were added to the flood-frequency summary. Channel changes in the upstream alluvial channel were related to flood-frequency changes. Valley-margin stratigraphy representing 1600 years of deposition indicated that after 1100 yrs BP, a time of increased frequency of large floods, a marshy floodplain was converted to a dry, fire-swept meadow and an arroyo 24-m wide and 2.5-m deep formed. This arroyo quickly filled with sediments between 500 and 400 yrs BP and a smaller channel then formed and persisted until settlement of the basin. Floods between 1909 and 1940 transformed the small channel into an arroyo up to 100-m wide and 17-m deep. The cause for flood-frequency and consequent channel changes on the Escalante River is complicated. Land-use practices caused pronounced changes in watershed and floodplain conditions. A subtle shift in climate increased the amount of summer precipitation and intensity of storms. The inability to test either the land-use practices or climatic shift hypotheses independently precludes the determination of a regional cause for arroyos.

The North Alpine Foreland Basin (NAFB) comprises sediments of late Eocene to middle Miocene age. The earliest deposits are the North Helvetic Flysch which are exposed in the regions of Glarus and Graubunden, eastern Switzerland. The Taveyannaz sandstones are the first thrust wedge (southerly) derived sediments of the North Helvetic Flysch. The Taveyannaz basin was divided into two sub-basins by a thrust ramp palaeohigh running ENE/WSW (parallel to the thrust front). Palaeocurrent directions were trench parallel towards the ENE. Sedimentation in the Inner basin (140m thick) is characterised by very thick bedded turbidite sands generated by thrust induced seismic events confined within the thrust-top basin. The Outer basin (240m min. thickness) comprises 10-15 sand packages (5-100m thick) formed by turbidite sands which are commonly amalgamated. Sedimentation in the Outer basin is considered to have been controlled by thrust-induced relative sea-level variations. The Inner basin underwent intense deformation at the sediment/water interface prior to the emplacement of a mud sheet over the basin whilst the sediments were partially lithified. Later tectonic deformation involved fold and thrust structures detaching in the underlying Globigerina marls. The stratigraphy of the NAFB can be considered as two shallowing upward megasequences separated by the base Burdigalian unconformity. This stratigraphy can be simulated by computer by simplifying the foreland basin/thrust wedge system into 4 parameters: 1) the effective elastic thickness of the foreland plate, 2) a transport coefficient to describe the erosion, transport and deposition of sediment, 3) the surface slope angle of the thrust wedge, 4) the thrust wedge advance rate. The Alpine thrust wedge underwent thickening during the underplating of the External Massifs at about 24-18Ma. This event is simulated numerically by slowing the thrust wedge advance rate, and increasing the slope angle and keeping all other parameters constant. This event causes rejuvenation of the forebulge, and erosion of the underlying stratigraphy, so simulating the base Burdigalian unconformity without recourse to eustasy or anelastic rheologies to the foreland plate.

No description available.

No description available.

A detailed stratigraphic analysis of the Lower Lias of southern Britain using the technique of gamma-ray spectrometry is presented. Gamma-ray data were collected, at the maximum stratigraphic resolution possible, from the Rhaetian to Pliensbachian successions exposed in southern Britain in the Bristol Channel Basin, Wessex Basin and East Midland Shelf. The data, in the form of measured gamma-ray signatures and hence geochemical profiles, is placed within a biostratigraphic framework. The outcrop gamma-ray logs collected from the Somerset coast (Rhaetian - Lower Sinemurian) can be subdivided, on the basis of both total gamma-ray signature and elemental log-signature into 9 gamma-ray units. These units are at a higher level of resolution than the single LL 1 gamma-ray unit defined by Whittaker et al (1985) for the Blue Lias in the subsurface. Outcrop gamma-ray correlation is possible between Somerset and Glamorgan, in some cases at a resolution greater than that offered by ammonite subzonal biostratigraphy. This resolution of correlation suggests the presence of a stratigraphic gap in Somerset within the johnstoni Subzone of the planorbis Zone. The outcrop gamma-ray logs collected from the Dorset coast (Rhaetian - Pliensbachian) can be divided into 10 gamma-ray units. These gamma-ray units can be correlated with the subsurface succession in the Winterborne Kingston and the Burton Row boreholes. The ability to correlate across numerous fault blocks and between different basins suggests that the controls upon gamma-ray signature were probably regional. A model is presented in which the degree of detrital influence within a fine grained mud and pelagic carbonate depositional system can be qualitatively assessed. Proximal and distal mudrock facies can be identified from the Th concentration log with proximal facies characterised by a Th concentration 10 ppm and above and distal facies characterised by a Th concentration of 8 ppm and below. The Th concentration log can also be used to determine intervals of mudrock progradation (increasing Th concentration) and retrogradation (decreasing Th concentration). These signatures can be interpreted within a sequence stratigraphic framework, of which the genetic stratigraphic model of Galloway (1989) is most applicable to the Lower Lias of southern Britain. The succession can be divided into eight genetic stratigraphic sequences. Maximum flooding surfaces are inferred at condensed limestone horizons of low Th concentration. The distal expression of the sequence boundary (the correlative conformity) is inferred at horizons of highest Th concentration. The development of anoxia within the epeiric sea can only partly be explained in terms of sequence stratigraphy with anoxia developing during periods of relative sea-level fall and rise or not at all.