Robert B. Kidd

Abyssal sediment wave fields on Feni Ridge, Rockall Trough: Long-range sonar studies

Abstract Large-scale plan views of the surface of a major abyssal sediment drift, the Feni Ridge, have been obtained using the GLORIA Mk II dual, long-range side-scan sonar system. Sixty kilometre wide sonographs show a complex array of sediment wave fields that decorate the surface of the Feni Ridge. Individual wave fields have trends either subparallel or markedly transverse to the regional contours. The subparallel trend is dominant along the eastern flank of the drift. Individual waves are typically 25–50 m in height and 1–4 km in wavelength and can be followed on the sonographs for up to 26 km. In the north of the survey area, the wave fields are disrupted by a major sediment slump thought to have been emplaced in Late Pleistocene time. Over the past 100,000 years the net migration of the waves has in almost all cases been up towards the ridge crest and downcurrent, in the direction of the prevailing currents. Upslope, upcurrent migration has been documented on other abyssal sediment drifts. The sense of net migration may have been unchanged since Oligocene—Miocene time. Growth of the Feni Ridge itself appears to have resulted from this migration. It is not known at the present time whether the wave fields are actively or episodically migrating. Quantitative oceanographic and geological observations are required to solve this problem.

Sonar acoustic facies and sediment distribution on an area of the deep ocean floor

Abstract Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope.

Indian Ocean sediment distribution since the Late Jurassic

Abstract Cores obtained by deep sea drilling in the Indian Ocean provide a sedimentary record from which are deduced changing patterns of sedimentation through the Late Mesozoic and Cenozoic. Comparisons between: (1) empirical subsidence curves and sediment sequences at individual sites; and (2) paleobathymetric reconstruction maps and past sediment distributions, convincingly demonstrate the interrelationship of sedimentary and tectonic development within this the most recently formed of the major oceans.

Turbidity-current and debris-flow pathways to the Cape Verde Basin: status of long-range side-scan sonar (GLORIA) surveys

Summary A regional GLORIA survey in the southern Cape Verde Basin identified highly variable patterns of backscattering intensity that were interpreted as resulting from seabed roughness and small-scale slope changes. It was inferred that their origin was linked to turbidity-current pathways across the continental rise. Farther north, a survey of the Saharan Continental Rise SE of Madeira identified even more spectacular changes in backscattering. Follow-up 3.5 kHz echo-sounder surveys together with core-sampling and bottom-camera studies allowed an assignment of acoustic facies to sediment type. In this area turbidity-current channels and deposits have been overrun by long-range debris flows resulting from the late-Quaternary Saharan sediment slide. Preliminary results of a further GLORIA survey that links the previously studied areas with a single swath along the continental rise are reported in this paper. The resulting sonographs show details of submarine-slide-debris-flow complexes on this margin that had previously been mapped from 3.5 kHz records. They extend across the lower continental rise to the plain areas. Others do not extend as far as the lower rise. Debris flows can no longer be thought of as unequivocal indicators of proximality in the geological record.

Sedimentary and structural patterns on the Iberian continental margin: an alternative view of continental margin sedimentation

Abstract A long-range side-scan sonar (GLORIA) survey of the entire West Iberian slope and rise has provided the first overview of the interrelationship between structure and sedimentation patterns on a continental margin. The results emphasize the importance of slope-following contour currents as a depositional mechanism in fashioning this continental rise. Terrigenous sediments transported down-canyon by-pass the rise which does not consist of a series of coalescing fans. The sedimentation patterns identified on the sonographs can be interpreted in terms of facies models and caution must be exercised against over-emphasis of downslope processes in models for the construction of lower slopes and rises.

High resolution stratigraphy in modern and ancient marine sequences: ocean sediment cores to Palaeozoic outcrop

The Deep Sea Drilling Project (DSDP), over its initial ten years of operations, relied almost entirely on a developing biostratigraphy based on microfossil groups for its stratigraphic control. During that same period, high resolution stratigraphic methods were developed for Quaternary marine cores through combination of microfossil biostratigraphy and paleomagnetic reversal sequences. The introduction of the hydraulic piston corer in 1982 provided the means to extend the surface core studies to depth and a major impulse to paleoceanographic studies. By the end of the DSDP programme in 1984, an integrated high resolution stratigraphy for the North Atlantic had emerged, based on microbiostratigraphy, magnetostratigraphy and isotope stratigraphy which had extended the identification of Milankovitch cycles to the Pliocene. Through the Ocean Drilling Program’s operations since 1986, integrated Cenozoic stratigraphies have been extended to all the major oceans and emphasis is now placed on extending these to land sections. Resolution in pre-Cenozoic marine sequences has begun to benefit from the same integrated approach along with emerging techniques such as strontium isotope stratigraphy and ‘cyclostratigraphy’. The deciphering of geological events from the sedimentary record requires increasingly precise stratigraphic resolution if we are to advance our understanding of the Earth’s system and its processes. An important development of the 1980s was the recognition that the record of orbitally-modulated late Cenozoic and Quaternary climatic fluctuations might provide a key to improving resolution further back in the stratigraphic record (e.g. Imbrie 1985). It is important to improve stratigraphic resolution on these longer in order to explore the

Indian Ocean Sediment Distribution since the Late Jurassic

Abstract Cores obtained by deep sea drilling in the Indian Ocean provide a sedimentary record from which are deduced changing patterns of sedimentation through the Late Mesozoic and Cenozoic. Comparisons between: (1) empirical subsidence curves and sediment sequences at individual sites; and (2) paleobathymetric reconstruction maps and past sediment distributions, convincingly demonstrate the interrelationship of sedimentary and tectonic development within this the most recently formed of the major oceans.