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L.M. Parson

Publications and source records attributed to L.M. Parson.

5 recordsLinked to original sources
USGS2022

Dipping reflectors in the Norwegian Sea—ODP Leg 104 drilling results: LEG 104 SCIENTIFIC PARTY

Ocean Drilling Program (ODP) Leg 104 successfully completed a number of deep drill holes on the Outer V0ring Plateau and the Vering Basin during July and August 1985 (Fig. 1; Eldholm, Thiede, Taylor et al. 1986). One of the principal objectives of the leg was to drill and sample a thick oceanward-dipping wedge of seismic reflectors, known to characterize much of the multichannel seismic (MCS) profile data recorded across ocean-continent transitions in the NE Atlantic north of 55°N. Elsewhere, these reflectors have previously been the target of deep drilling during Legs 48 and 81 of the International Phase of Ocean Drilling IPOD (Montadert, Roberts et al. 1979; Roberts, Schnitker et al. 1984). These efforts met with some success, sampling only the uppermost part of the sequence and identifying a series of tholeiitic lava flows. Over the Outer V~ring Plateau, a number of MCS profiles reveal a distinct change in seismic character at the base of the well-stratified dipping reflector sequence, where an irregular surface characterized by a band of low-frequency, high-amplitude reflectors occurs. This surface is referred to as K. Prior to Leg 104, therefore, relatively little was known regarding the variation in petrographic character of the flows at depth, their evolution and origin, and particularly the character of the material below the reflector sequence. A single deep drillhole (642E) successfully recovered a section through the

Journal of the Geological Society↗
USGS1992

Accretionary margin of north-western Hispaniola: morphology, structure and development of part of the northern Caribbean plate boundary

Broad-range side-scan sonar (GLORIA) images and single- and multi-channel seismic reflection profiles demonstrate that the margin of north-western Hispaniola has experienced compression as a consequence of oblique North American-Caribbean plate convergence. Two principal morphological or structural types of accretionary wedges are observed along this margin. The first type is characterized by a gently sloping (≈4°) sea floor and generally margin-parallel linear sets of sea-floor ridges that gradually deepen towards the flat Hispaniola Basin floor to the north. The ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath Hispaniola. Anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope. In contrast, the second type of accretionary wedge exhibits a steeper (≈6–16°) sea-floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin. The internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults. We suggest that changes in sea-floor declivity and internal structure may result from variations in the dip or frictional resistance of the décollement, or possibly from changes in the cohesive strength of the wedge sediments. The observed pattern of thickening of Hispaniola Basin turbidites towards the insular margin suggests differential southwards tilting of the Hispaniola Basin strata, probably in response to North America-Caribbean plate interactions since the Early Tertiary. Based upon indirect age control from adjacent parts of the northern caribbean plate boundary, we infer a Late Eocene to Early Miocene episode of transcurrent motion (i.e. little or no tilting), an Early Miocene to Late Pliocene period of oblique convergence (i.e. increased tilt) during which the accretionary wedge began to be constructed, and a Late Pliocene to Recent episode of increased convergence (i.e. twice the Miocene to Pliocene tilt), which has led to rapid uplift and erosion of sediment sources on the margin and on Hispaniola, generating a submarine fan at the base of the insular slope.

Marine and Petroleum Geology↗
USGS1991

Terraces on the Florida escarpment: Implications for erosional processes

SeaBeam bathymetric data and GLORIA (Geologic LOng-Range Inclined Asdic) sidescan sonar images of a 175-km-long section of the Florida escarpment in the eastern Guff of Mexico show that this carbonate escarpment has been eroded since its initial formation, but its morphology suggests that erosional processes have not acted uniformly on the escarpment. Parts of the escarpment are notched by box canyons that have extremely steep headwalls and may be sites off active ground-water sapping. The intercanyon areas commonly have previously unrecognized terraces below 2600 m. Above 2600 m, the escarpment is steeper and has no terraces. The terraces may reflect differences in platform strata exposed at the escarpment that are responding differently to erosional processes.

Gulf of Mexico↗
USGS1990

Variations in the styles of erosion along the Florida Escarpment, eastern Gulf of Mexico

GLORIA sidescan sonographs and Seabeam bathymetric data show morphological differences along the Florida Escarpment which reflect that different erosional styles have been active along different parts of this carbonate platform edge. The northern half of the escarpment is cut by numerous small ravines spaced 1-5 km apart. Its southern half is deeply incised by large box canyons that have flat floors and steep headwalls. The northern half of the escarpment is covered by Cenozoic-aged sediments, and erosion appears to be limited to this Cenozoic cover. An apron of this eroded material is accumulating along the base of this half of the escarpment, extending as much as 30 km from its base. South of 27??N, active erosion of older strata of the escarpment is shown by talus deposits of Lower Cretaceous limestone that occur at the heads of box canyons. The box canyons are not evenly distributed, but instead are most abundant where two basins that underlie the Florida Platform intersect the escarpment. Pleistocene-aged sediments eroded from the slope above the escarpment are funnelled through small valleys into the heads of the box canyons. The smooth headwalls of the box canyons suggest that downslope transport of the material from the slope above the escarpment does little to erode the escarpment. Instead, erosion triggered by dissolution of the carbonate rocks by acidic brines that seep out of the escarpment is the proposed mechanism of escarpment retreat. The concentration of the erosion at the heads of the box canyons may indicate sites where the platform rocks are more intensely fractured, thus enhancing permeability and flow of brines. The concentration of box canyons in the escarpment sections adjacent to sedimentary basins beneath the platform may reflect regional differences in the geology and hydrology of the platform. ?? 1990.

Florida Escarpment, Gulf of Mexico↗