Reworking Of Older Sediments Research Articles

Sea-level, monsoonal, and anthropogenic impacts on the millennial-scale variability of siliciclastic sediment input into the western Philippine sea since 27 ka

Multiproxy records from Core MD06-3054 in the western Philippine Sea and published results from the nearby Core MD06-3052, which are both located at the northern margin of the Western Pacific Warm Pool (WPWP), provide precise reconstructions and evidence for the potential controls on continental erosion and weathering intensities in Luzon. These data also constrain sediment source-to-sink processes in the sea since 27 ka at the millennial scale. We demonstrate that the siliciclastic fraction is derived from Luzon volcanic rocks and eolian dust from mainland Asia. Stronger physical erosion and chemical weathering generally occurred during the last glaciation, Heinrich Event 1, the Younger Dryas, and the period from 10.3 to 11.3 ka. In contrast, the Bølling-Allerød was characterized by weaker physical erosion and chemical weathering. During the last glaciation, Heinrich Event 1, and the Younger Dryas, the lower sea level led to enhanced erosion and weathering of the exposed shelf sediments. In contrast, the weaker physical erosion and chemical weathering that occurred during the Bølling-Allerød and the Holocene, except after 2.1 ka, are closely correlated with the higher sea level. The stronger physical erosion and chemical weathering at 10.3–11.3 ka may be derived from the reworking of older sediments during the time of a strengthening summer monsoon. Furthermore, enhanced human activity since 2.1 ka has become the dominant control on erosion in Luzon. Rapid weathering changes in the WPWP during the last deglaciation highlight the high variability in local controls at low latitudes during these periods and the potential influence of controls at high latitudes.

Signatures of Holocene Hydrological Processes from Sedimentary Archives in Southwestern India: Case Studies from Wetlands of Kerala Coast

The subsurface sediments of the Kerala coast provided signatures of hydrological processes that have influenced in the modifications and conversion of larger part of the lowland and the forest cover into a major wetland system during the Holocene which in turn has transformed into one of the best carbon sinks in the Indian subcontinent. The most significant and well recognized signature is the paleoflood event during the Early to Middle Holocene coinciding with the Holocene Climate Optimum (HCO). The excessive rainfall seems to have flooded the entire forest area in the coastal plains and the forests that flourished in the abandoned river channels and other low-lying areas in the midland. Formation of peat and peat land development in the inland region, but not far away from the coast, towards the Middle Holocene has been another important imprint of the hydrological process. Occurrence of peat sequence of 1–3 m at shallower depths stands testimony to such episodes. The other recognized imprints include the erosion and reworking of older sediments that contain the Neogene pollen elements and development of bay head deltas and other alluvial deposits in the mouth of the rivers. The mangrove dynamics too provided sufficient evidence of their prevalence, stability and decreasing tendency depending up on the hydrological regimes during the Holocene. Though episodes related to mud bank formation, as of now, are restricted to recent times, sediment archives, dated as Late Holocene, revealed scope for decoding the signatures of hydrological and geological processes associated with the monsoon vicissitudes.

AGE DETERMINATION AND PALAEOGEOGRAPHIC RECONSTRUCTION OF PINDOS FORELAND BASIN BASED ON CALCAREOUS NANNOFOSSILS

The study area is part of the Pindos foreland (Underhill, 1985). Pindos foreland is a tertiary turbiditic foreland basin fill trending parallel to the external Hellenides and occupies Gavrovo and Ionian isopic zones (Aubouin, 1959). The age of Pindos foreland sediments is still a matter of discussion. B.P. (1971) proposed an early Miocene to middle Miocene age, explaining the presence of Oligocene fauna as a product of large scale erosion and reworking of older sediments during Miocene. IGSR&IFP(1966) suggested a late Eocene to early Miocene age for the basin fill while Fleury (1980), Leigh (1991), Wilpshaar (1995), Bellas (1997) assigned an Oligocene age. Avramidis et al (1999) proposes a middle Eocene to early Miocene age assessment, using nannofosil zones from three studied cross sections in the Klematia-Paramythia basin (middle Ionian zone). The determination of the sediment ages was based on the study of calcareous nannofossils, which came from almost 120 samples covering 11 geological cross sections. The nannofosil marker species that were found in the samples were classified using the biozones proposed by Martini in 1971. According to the age assessments arose from the studied samples, clastic sedimentation in the study area began in the Middle Eocene, with small differences among the basin. The end of clastic sedimentation seems to be at different times in different parts of the basin.

Malian Paenungulata (Mammalia: Placentalia): new African afrotheres from the early Eocene

ABSTRACT Fossils from early Tertiary phosphate deposits of northern Mali include a new diminutive proboscidean taxon intermediate in size between Daouitherium rebouli and Phosphatherium escuilliei. Although a fragmentary specimen, it has two dentary characters previously demonstrated to be diagnostic for basal proboscideans: a labially expanded mandibular corpus in the region of m2 and m3 and a mesiolabially positioned mandibular ramus. The locality that produced the fossils, Tamaguèlelt, has historically been hard to date even though it has produced many vertebrates. A section is presented that includes the locality and relates it to surrounding sediments. The locality is Eocene, lies very close to the Paleocene-Eocene boundary, and is most likely early Eocene (Ypresian). The depositional environment suggests substantial reworking of older sediments, and the fossils within them, including the proboscideans, may be even older than early Eocene. The Mali proboscidean is one of the oldest members of Afrotheria that has been found in Africa and this locality is the southernmost African early Eocene locality for mammals.

Scanning electron microscopy of quartz grains in supraglacial debris, Adishy Glacier, Caucasus Mountains, USSR

The surface microtopography of quartz grains in glacial depostis has often been attributed to mechanical release from source rocks during weathering and prior to entrainment by glaciers. Fractures on quartz particles, including subparallel and conchoidal features, often attributed to cryostatic pressure in ice and stick‐slip processes at the base of glaciers, have been considered, in part, to result from mechanical weathering of source rocks. To test this hypothesis we studied 15 samples of supraglacial debris from the Adishy Glacier in the central Caucasus Mountains, USSR. Clasts in transport on the surface of the glacier originate primarily from the cirque headwall by weathering and mass wasting processes; a minor amount is presumed to have been derived from aeolian influx following reworking of older sediments down valley. The results show unequivocally that mechanical weathering is only likely to produce grains with pronounced fracture faces that lack subparallel and conchoidal fracture features. No fresh glacial‐crushing type features were observed on these samples. Grains that had been glacially crushed, weathered and retransported, presumably by aeolian processes, were observed in four samples of the data set.

Coarse-grained volcanic detritus in deep-sea sediments of the northeastern Equatorial Pacific

Coarse-grained volcanic detritus in near-surface sediments of the northeastern equatorial Pacific consists mainly of feldspar (plagioclase with An 35–70Or 0–4) and magnetite, with minor parts of pyroxene (augite, Wo 25–32En 53-32) and volcanic quartz. Except for plagioclase (0.005–0.5% of total sediment) all concentrations range between 0 and 30 grains m −1 of piston-core, where differences exist within the stratigraphic sequence and also from mineral to mineral. The following relationships have been found: • —Plagioclase > magnetite >volcanic quartz >pyroxene. • — Contents are low in Plio-Quaternary sediments and in Lower Miocene pure radiolarian ooze. They increase within the Late Eocene to Early Oligocene sediments and near the Early Oligocene hiatus. The morphology, distribution and alteration of the minerals are described and singlegrain analyses for plagioclase and pyroxene are given. The origin of plagioclase, pyroxene and magnetite is related to the formation of new oceanic crust at the East Pacific Ridge. Transport and distribution by slumping, high-density currents and reworking of older sediments are assumed. The origin of volcanic quartz from potential source areas in northern Central America and Western Mexico and transport and accumulation in deepsea sediments are discussed.

Mineralogy and Petrology of the Rocks Near the Quadrant-phosphoria Boundary in Southwest Montana

ABSTRACT A petrographic study was made of the rocks near the boundary of the lower Pennsylvanian Quadrant and the Permian Phosphoria formations. The mineralogy is described in detail and some of the detrital minerals, quartz, chert, tourmaline, and zircon, are subdivided into a variety of species. The chemical minerals described in detail are chert, calcite, dolomite, collophane, kaolinite, and illite. The Quadrant in this area is composed largely of fine-grained siltstones (dolomitic, illitic, and kaolinitic) and carbonate rocks. There is little significant difference in the detrital minerals of the two formations. However, the Phosphoria contains a much larger percentage of chemical rocks than the Quadrant. The detritus of the two formations was primarily derived by the reworking of older sediments. The minerals of the two formations, in this basin-edge area, comprise a quartzite-limestone series and are typical of a period of near peneplaination in the source area and belong in the shallow water marine facies of sedimentation. It is indicative of epeirogenic tectonic control both in the source area and in the locus of deposition. The rocks in the Phosphoria are modified by the deposition of an abundance of authigenic minerals and a decrease in detrital minerals. This modification was likely caused by an abundance of volcanic material in the source area.