Ruth A. J. Robinson

Integrating Sandstone Petrology and Nonmarine Sequence Stratigraphy: Application to the Late Cretaceous Fluvial Systems of Southwestern Utah, U.S.A.

ABSTRACT Petrographic and dispersal data are essential to correct interpretation of mechanisms that create continental sequence-stratigraphic architecture. A case study from southern Utah demonstrates that Upper Cretaceous (upper Santonian-Campanian) alluvial successions in the southernmost part of the Cordilleran foreland basin were deposited by fluvial systems of contrasting drainage directions and provenance, and suggests that different mechanisms governed their sequence architecture. Most of the rivers flowed northeast, subparallel to the basin foredeep. Less common fluvial systems flowed to the east-southeast. The fluvial sandstones fall naturally into four petrofacies: (1) quartzofeldspatholithic (mean Qt61F19L20); (2) feldspatholithic (Qt29F19L52); (3) quartzolithic (Qt75F6L20); and (4) quartzose (Qt99F1L1). Petrofacies 1 and 2 were derived from mixed supracrustal and basement sources to the southwest and south, respectively, whereas petrofacies 3 and 4 were derived from uplifted thrust sheets of the Sevier orogenic belt to the southwest and west, respectively. Only the east-southeast-flowing rivers transported the quartzose petrofacies. The fluvial strata, which include the uppermost Straight Cliffs, Wahweap, and Kaiparowits formations, form two large-scale stratigraphic successions typically interpreted as continental stratigraphic sequences hundreds of meters thick. Each succession begins with an amalgamated braided-fluvial deposit, grades to mudstone-rich strata with low sandstone-body connectivity, and culminates in highly connected sandstone bodies with multistory stacking. The basal amalgamated deposits of each succession are architecturally similar, but their compositional and dispersal characteristics are different. Quartzofeldspatholithic, quartzolithic, and quartzose sandstones above the lower base-level shift are variable, but generally similar in compositional and dispersal characteristics to both underlying and overlying strata, a phenomenon termed here congruence. In contrast, quartzose amalgamated fluvial sandstone above the upper base-level shift differs sharply in composition and dispersal direction from underlying and overlying lithic-rich strata. The foredeep axis controlled the progradation direction of the congruent shift, which was likely driven by climatically induced sediment influx, a eustatic fall, or both. In the case of the incongruent shift, increased sediment supply permitted the rivers to cross the foredeep. Temporal association of the upper amalgamated deposit with active structures in the thrust belt and foreland basin indicates that syntectonic thrust uplift, not isostatic uplift or climate, caused the influx of quartz.

The Irrawaddy River Sediment Flux to the Indian Ocean: The Original Nineteenth-Century Data Revisited

The Irrawaddy (Ayeyarwady) River of Myanmar is ranked as having the fifth‐largest suspended load and the fourth‐highest total dissolved load of the world’s rivers, and the combined Irrawaddy and Salween (Thanlwin) system is regarded as contributing 20% of the total flux of material from the Himalayan‐Tibetan orogen. The estimates for the Irrawaddy are taken from published quotations of a nineteenth‐century data set, and there are no available published data for the Myanmar reaches of the Salween. Apart from our own field studies in 2005 and 2006, no recent research documenting the sediment load of these important large rivers has been conducted, although their contribution to biogeochemical cycles and ocean geochemistry is clearly significant. We present a reanalysis of the Irrawaddy data from the original 550‐page report of Gordon covering 10 yr of discharge (1869–1879) and 1 yr of sediment concentration measurements (1877–1878). We describe Gordon’s methodologies, evaluate his measurements and calculations and the adjustments he made to his data set, and present our revised interpretation of nineteenth‐century discharge and sediment load with an estimate of uncertainty. The 10‐yr average of annual suspended sediment load currently cited in the literature is assessed as being underestimated by 27% on the basis of our sediment rating curve of the nineteenth‐century data. On the basis of our sampling of suspended load, the nineteenth‐century concentrations are interpreted to be missing about 18% of their total mass, which is the proportion of sediment recovered by a 0.45‐μm filter. The new annual Irrawaddy suspended sediment load is \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Luminescence dating of alluvial fans in intramontane basins of NW Argentina

364\pm 60

REAPPRAISAL OF THE MISSISSIPPIAN PALYNOSTRATIGRAPHY OF THE EAST FIFE COAST, SCOTLAND, UNITED KINGDOM

\end{document} MT. Our revised estimate of the annual sediment load from the Irrawaddy‐Salween system for the nineteenth century (600 MT) represents more than half the present‐day Ganges‐Brahmaputra flux to the Indian Ocean. Since major Chinese rivers have reduced their load due to damming, the Irrawaddy is likely the third‐largest contributor of sediment load in the world.

Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity

A seismic stratigraphic analysis of Miocene deposits in the Baltimore Canyon region (offshore New Jersey) reveals tremendous threedimensional complexity and challenges traditional approaches to sequence stratigraphic interpretation. Individual sequences vary dramatically in along-strike thickness, revealing the locations of the sediment sources. Within sequences, the lowstand wedge thins dramatically along strike (tens to hundreds of meters) and is interpreted to record variable paleobathymetry along strike. As indicated by sequence thickness distributions, shelf break positions, lithologic composition, and stratigraphic relationships, sequences record sediment migration and progradation across the basin through time. As a result of these depositional complexities, relative sea-level curves, interpreted from parallel dip lines, vary in magnitude and amplitude across the basin. Development of Neogene stratal patterns within the Baltimore Canyon region has been closely linked to glacioeustatic change. Our reconstructions of delta switching and progradation emphasize that Miocene stratal patterns were greatly influenced by autocyclic depositional processes.

Holocene slip rate along the Gyaring Co Fault, central Tibet

Abstract Alluvial fans are sensitive recorders of both climatic change and tectonic activity. The ability to constrain the age of alluvial-fan sequences, individual sedimentary events and the rates of sediment accumulation are key for constraining which mechanisms most control their formation. Recent advances in optically stimulated luminescence (OSL) measurement and analysis have resulted in vast improvements in the dating technique and reliability of age determinations, particularly for OSL dating of quartz grains, and routine application to a wide variety of depositional environments is now possible. Here we apply OSL methods to date a variety of deposits within Late Pleistocene conglomeratic alluvial sequences in NW Argentina. The ages obtained range from 39 to 83 ka and were determined from debris-flow- and fluvial-dominated deposits and lacustrine sequences in intramontane basins bounded by tectonically active mountain ranges with as much as 2 km of relief. With careful choice of facies and sample collection, OSL techniques can be used to date Late Pleistocene, predominately matrix-supported, cobble-conglomerate alluvial deposits.

Fluvio-deltaic avulsions during relative sea-level fall

The Carboniferous Pottsville Formation of eastern Pennsylvania in the central Appalachian foreland basin is considered a classic orogenic molasse, typical of other Acadian-Alleghanian clastic wedges along the eastern margin of Laurentia. Although the Pottsville conglomerates are thought to be derived entirely from early Alleghanian highlands, we have documented an unrecognized dramatic change in the sediment-dispersal pattern within the formation; northwest-directed paleocurrent indicators in older units (implying an orogenic provenance) are superseded abruptly by southwestward-directed paleocurrent indicators (implying a cratonal provenance). This alteration in the sediment-dispersal pattern is attributed to basin reorganization during Early Pennsylvanian time as tectonic loads migrated southward during orogenesis. The paleocurrent data warrant a revision of Early Pennsylvanian paleogeography and demonstrate that molasse facies can record a complex interplay between sediment dispersal systems along both active and cratonal margins of a foreland basin.

Squeezing river catchments through tectonics: Shortening and erosion across the Indus Valley, NW Himalaya

Abstract Palynomorph assemblages from an extended succession of Mississippian (Viséan) sediments ranging in age from probable late Arundian to the latest Brigantian exposed on the East Fife coast of Scotland, United Kingdom have been investigated. The stratigraphical distribution of miospores closely reflects that established elsewhere in central and southern Scotland. The occurrence of certain stratigraphically significant miospore taxa permits the assignment of chronostratigraphic ages to locally defined lithostratigraphic units. The latest Asbian to Brigantian (VF miospore Biozone) age of the upper part of the Sandy Craig, Pathhead and Lower Limestone formations is confirmed. The Pittenweem Formation and remainder of the Sandy Craig Formation are both assigned to the NM miospore Biozone of Asbian age and the Anstruther Formation is assigned a late Arundian or Holkerian (TC miospore Biozone) age. The Fife Ness Formation, originally assigned to the early Asbian and considered older than the Anstruther Formation, yielded evidence of both the uppermost part of the TC and lower NM miospore biozones and is suggested to be a member of the Pittenweem Formation.