Pleistocene Distribution Research Articles

Sources and Distribution of Upper Pleistocene Sand, Eastern United States Atlantic Shelf: ABSTRACT

A 2-yr study of the sources and distribution of upper Pleistocene and Holocene sand on the eastern United States shelf between the Bay of Fundy and Cape Hatteras reveals that 3 sand types are found on this shelf: (1) glacially transported, very angular sands, (2) fluvially transported, well-rounded sands derived from unlithified coastal plain deposits, and (3) fluvially transported, moderately angular sands derived from lithified sedimentary and crystalline rocks of the Appalachian and New England areas. For the most part, the distribution of these sand types reflects the late Pleistocene paleogeography of this shelf. Glacial sands are found in the areas of upper Pleistocene till, moraine, and outwash-plain deposits east and northeast of the Hudson Canyon; the 2 fluvial s nds are found in coast-normal stripes that correspond to the ancestral paths of the many rivers that traversed this shelf during the late Pleistocene. The preservation of relict paleogeographic patterns of these sorts are an indication of diffusive transport of sand through most of this shelf. The exceptions to this are found in the shallow waters of Nantucket Shoals and Georges Bank, where glacial sands are presently being advected to the southwest by the strong tidal currents that prevail. End_of_Article - Last_Page 278------------

CONNATICHELA ARTEMISIAE, A NEW GENUS AND SPECIES OF WEEVIL FROM THE YUKON TERRITORY (COLEOPTERA: CURCULIONIDAE: LEPTOPIINAE): TAXONOMY, PALEONTOLOGY, AND BIOGEOGRAPHY

AbstractConnatichela artemisiae, a new genus and species of leptopiine weevil endemic to the Yukon Territory, Canada, is described and illustrated. The genus is placed in the group of leptopiine genera characterized by the absence of metepisternal suture, lack of scales on antennal funiculus, and presence of broad scales on antennal scape. Connatichela members are readily distinguished from related leptopiine genera by the presence of connate tarsal claws and the structure of male and female genitalia. Phylogenetic and zoogeographic relationships of the genus are unresolved at present. Adult specimens were found in association with plants of a small species of Artemisia.Fossil material of mid-Wisconsin age assignable to C. artemisiae from the Yukon Territory, extreme western Northwest Territories, and Alaska suggests a slightly more widespread Pleistocene distribution, with recent restriction to the Yukon Territory. This restriction may have resulted from a decrease, during the post Wisconsin, in availability of dry steppe-tundra habitats throughout most of Beringia.

Sources, Distribution, and Mixing of Late Pleistocene and Holocene Sands on the South Texas Continental Shelf

ABSTRACT Gross grain shape and mineralogical analyses were used to determine the source, distribution, and mixing of late Pleistocene and Holocene sands on the South Texas continental shelf. Two major gross grain-shape types are found to be present in varying proportions in the sands of this shelf. The first sand type is associated with sands which are relatively enriched in plutonic-metamorphic quartz, volcanic quartz, feldspar and igneous and metamorphic rock fragments, and thus is considered to represent first-cycle sands derived from the Llano Uplift and the silicic volcanic rocks of the Southwest U.S. The second sand type is associated with more quartzose sands rich in sedimentary quartz and sedimentary rock fragments, and is considered to represent multicyclic sands eroded from the Texas Coastal Plain and High Plains. Variations in the relative proportions of these sand types in the sands of the nearshore/inner shelf region reflect both the changing sources of the sand and their transport, mixing, and convergence by modern nearshore processes. Three distinct sedimentary petrologic provinces, corresponding to three provinces previously defined by heavy mineral analysis (Van Andel and Poole 1960), are defined herein on the basis of their relative content of first- and multicyclic sand. Modern sands of the first of these provinces, the Rio Grande, are derived from the drainage basin of the Rio Grande and characteristically contain high proportions of first-cycle sand; such sands are presently found in the nearshore/inner shelf region between the mouth of the Rio Grande and the 27°N latitude to the north of the mouth of the river. Modern sands of the second province, the Texas Coast, are derived largely from the drainage basins of the South Texas coastal plain rivers and characteristically contain high proportions of multicyclic sand; such sands are presently transported southwestward by longshore currents to the 27°N latitude, where they converge with the northward-transported sands of the Rio Grande Province. Modern sands of the third province, the Western Gulf, are derived from the drainage basins of the Colorado and Brazos rivers and characteristically contain high proportions of first-cycle sands', such sands are also transported by longshore currents towards the southwest, where they are gradually diluted by Texas Coast Province sands. Sands of these three provinces are also found in the relict late Pleistocene fluvial and deltaic sediments on the outer part of the South Texas shelf. Previous studies had considered the fluvial and deltaic sediments on the northern part of the shelf to be entirely derived from the Western Gulf Province; however, this study shows that the relict fluvial deposits of certain South Texas coastal plain rivers which occur on the northern part of the shelf should be assigned to the Texas Coast Province. In all, multicyclic sands constitute approximately 48% of the late Pleistocene and Holocene sand of the South Texas continental shelf.

Provenance and Areal Distribution of Late Pleistocene and Holocene Quartz Sand on the Southern New England Continental Shelf

ABSTRACT Sand from the southern New England shelf is a mixture of three sand types, each characterized by quartz grains with distinctive morphologies. The first sand type consists of well-rounded and equant grains derived from Tertiary and Cretaceous coastal plain strata which have been smoothed and rounded by chemical and mechanical processes; sands of this type are found in significant quantifies in both the relict fluvial sediment of the middle and outer shelf and in the Recent sediment of Rhode Island Sound, but not in the glacial sediment of the inner and middle shelf. The second sand type consists of highly angular and elongate grains which were transported to the area by glaciers and subsequently reworked in subaqueous environments; this sand type is found in abundance in the relict gla ial moraine and outwash plain sediment of the inner shelf and in the palimpsest sediment of the middle shelf to the west of the relict glacial deposits, but is not generally found in appreciable quantities in the relict fluvial sediment of the middle and outer shelf except in the westernmost part of the study area. A third sand type, heretofore unrecognized in these strata, consists of grains derived from sedimentary rocks exposed in late Paleozoic and Mesozoic basins of southern New England. This sand type is found in appreciable quantities in both relict and Recent fluvial sediment on the entire shelf and in the relict glacial sediment of the inner shelf, indicating that the glacial sediment also was derived from the southern New England area. The patterns of distribution of these thre sand types reflect the paleogeography of the shelf during the late Pleistocene; the resolution of well-defined paleogeographic features by a morphological study of surficial sediment indicates that throughout most of the study area, modern sediment transport processes acting on the shelf have not yet destroyed the provenance record imprinted upon the shelf during the late Pleistocene.

Paléosols d'âge Pléistocène supérieur dans les loess des Matmata (Sud Tunisien) / Upper Pleistocene palaeosoils in the lœss of Matmata (Southern Tunisia)

Significant variations in the amount of carbonate and gypsum and also in the thickness of preserved aeolian deposits are shown by the distribution of Upper Pleistocene lœss on the plateau of Matmata and its borders. There are four or five palaeosoils present when the sections are most complete ; in such cases, a reddish horizon is present above a variably developed Bca horizon. However, in each section, the granulometric decay of clayey particles is not always noticeable between these reddish horizons and the less altered lœss. Inherited typical aeolian textures and post-depositional alteration surface features are shown by the SEM study of quartz grains. In particular, staining of quartz results from superficial amorphization which in turn allows clay minerals and iron particles to attach to the surface of the altered grains and in superficial cavities. Free-iron and total iron slightly increase at each palaeosoil level. In contrast there is a carbonate migration associated with significant decarbonatization of the reddish horizons. The silty fraction is explained by contribution from aeolian deposition. Pedological nodules are irregularly distributed along each section. Generally, the clay mineralogy of the sections is very homogeneous. Palygorskite occurs as small fibres scattered in the palaeosoils or as coarser «heaps » in the less altered lœss. ТЕМ study suggests that the palygorskite is originally derived from aeolian processes but altered in the pedological horizons.

Glacial Lithofacies of Neogene Yakataga Formation, Gulf of Alaska: ABSTRACT

Lithofacies, biofacies, and chronostratigraphic analyses indicate three relatively warm and three relatively cool paleoclimatic intervals within the 5,000-m thick strata of the lower Miocene through Holocene Yakataga Formation of the Robinson Mountains, eastern Gulf of Alaska. Glacial periods, recognized by the predominance of glacial lithofacies associated with populations of Neoglobigerina pachyderma s.l., are interpreted for the cool intervals. In the sections studied, the interglacial intervals have little or no glacial deposits. Yakataga Formation strata of glacial origin can be classified as having formed in either ice-contact or glacial-aqueous depositional environments. Ice-contact deposits consist of stratified or chaotic sedimentary materials, but erratics are rare in the Yakataga Formation. Glacial-aqueous deposits are of three principal types: glaciolacustrine, glaciofluvial, and glaciomarine. Glaciolacustrine deposits have not been identified in the Yakataga Formation. Glaciofluvial deposits, characterized by interbedded poorly sorted lenticular sand and gravel, occur in geographically limited and stratigraphically restricted intervals of the Yakataga Formation. Glaciomarine silts and clays, containing floating pebbles and cobbles and in-situ marine fossils, are the dominant glacial aqueous deposits i the Yakataga Formation. Detailed lithofacies associations and geometries define open-shelf and fjord glaciomarine subenvironments. Lithofacies sequences within these subenvironments suggest deposition by advancing and retreating ice masses. Mapping of the relative percentages of lithofacies types within the late Pliocene-Pleistocene glacial sequence defines the late Neogene paleogeography of the Yakataga district. This mapping suggests that the late Pliocene and Pleistocene distribution of alpine glaciers, coastal-outwash and alluvial flood plains, and fjords, and the associated rates of sedimentation, are analogous to the depositional pattern during the Holocene. End_of_Article - Last_Page 891------------

Distribution and thickness of quaternary sediments in the lake constance basin

Distribution and thickness of Pleistocene and Holocene sediments are derived from a continuous seismic reflection survey of the Lake Constance Basin. The sediment distribution within the lake confirms the concept that the Lake Constance Basin has been formed by glacial erosion rather than by structural deformation.