Synrift to syntransform deformation along the Côte d’Ivoire–Ghana transform margin: evidence from deep-sea dives

Fourteen deep dives were conducted along the southern slope of the Côte d’Ivoire–Ghana marginal ridge. Detrital rock samples reveal Early Cretaceous synrift sediments. In situ observations and microtectonic analysis identify the nature and the timing of three successive episodes of deformation. Clay layers are affected by early diagenetic deformational structures such as slump microfolds and normal microfaults. Most of the clastic deposits display a second deformational episode. These structures result from a layer-parallel extension and are related to extensional synrift tectonics. The last stage of deformation is identified by right lateral wrench folds associated with brittle joints and slaty cleavage. It is attributed to the syntransform evolution of the Côte d’Ivoire–Ghana marginal ridge.     

The distribution of solar flares and probable relations to biological effects

We have compared the monthly distribution of the total number of flares to the monthly mortality from cardiovascular and myocardial infarctions for the time period 1974–1983, and computed correlation coefficients. Periodicities of 3 and 5 months (150 days) have been found in both distributions.     

Crustal structure and ocean–continent transition at marginal ridge: the Côte d’Ivoire–Ghana marginal ridge

 Crustal structure of the Co^te d’Ivoire–Ghana marginal ridge and its transition with oceanic lithosphere are deduced from multichannel seismic reflection, wide-angle seismic, and gravity data. The CIGMR is cut into rotated blocks and displays a crustal structure quite similar to that of the nearby northern Ivorian extensional basin. These results strongly support that the CIGMR represents an uplifted fragment of continental crust. Transition with the oceanic crust appears sharp; continental crustal thinning occurs over less than 5 km. We did not find evidence for underplating and/or contamination as anticipated from such a sharp contact between continental and oceanic crust. Received: 12 March 1995/Revision received: 2 July 1996     

Sedimentary and structural record of the Albian growth of the Bakio salt diapir (the Basque Country,northern Spain)

However salt has a viscous rheology, overburden rocks adjacent to salt diapirs have a brittle rheology. Evidence of deformation within the overburden has been described from diapirs worldwide. Gravity‐driven deposits are also present along the flanks of several diapirs. The well‐known example from the La Popa Basin in northern Mexico shows that such deposits may be organized into halokinetic sequences. This leads to several questions: (i) How does diapir growth contribute to overburden deformation? (ii) Are halokinetic sequence models valid for other areas beyond the La Popa Basin. The Bakio diapir and its well‐exposed overburden in Basque Country, Spain provides key elements to address these questions. The Bakio diapir consists of Triassic red clays and gypsum and is flanked by synkinematic middle to upper Albian units that thin towards the diapir. The elongate diapir parallels the Gaztelugatxe normal fault to the NE: both strike NE–SW and probably formed together during the middle Albian, as synkinematic units onlap the fault scarp. The diapir is interpreted as a reactive diapir in response to middle Albian motion on the Gaztelugatxe fault. The rate of salt rise is estimated to be about 500 m Myr^?1 during this passive stage. During Late Albian, the diapir evolved passively as the Gaztelugatxe fault became inactive. Synkinematic units thinning towards the diapir, major unconformities, slumps and other gravity‐driven deposits demonstrate that most deformation related to diapir growth occurred at the sea floor. Halokinetic sequences composed of alternating breccias and fine‐grained turbidites recorded cyclic episodes of diapir flank destabilization. This work provides insights into drape fold and halokinetic sequence models and offers a new simple method for estimating rates of diapir growth. This method may be useful for outcrop studies where biostratigraphical data are available and for other passive diapirs worldwide.     

Life strategy traits of the liana Sericostachys scandens spreading in the montane forests in the Kahuzi-Biega national park (DR Congo)

Sericostachys scandens is a monocarpic and heliophilous liana, native in tropical African forests. In the montane forests of the Kahuzi-Biega National Park (KBNP) (East of DR Congo), it has been expanding very strongly for a decade, and is currently considered as having negative impacts on biodiversity conservation. In this paper, we test if S. scandens differs from three co-occurring, native, non spreading lianas (Gouania longispicata, Tacazzea apiculata and Adenia bequaertii) for functional traits which might influence plant expansion. For leaf traits (SLA, dry matter content, nitrogen concentration), S. scandens did not show extreme values compared to those of the three other lianas. In contrast, S. scandens had much higher biomass allocation to sexual reproduction. It also differs from the three other lianas for its reproductive strategy that combines both vegetative propagation and sexual reproduction, and propagule dispersal by wind. Moreover, S. scandens has larger leaves and a greater number of lateral branches per unit stem length. It is argued that the particular combination of functional traits exhibited by S.scandens may in part explain its propensity to behave as an opportunistic weed in the disturbed areas in the montane forests of Kahuzi-Biega.     

Early Cretaceous deltaic sedimentary environment of the Côte d’Ivoire–Ghana transform margin as deduced from deep dive data

During the Equanaute cruise (June 1992), 14 submersible deep dives were conducted along the steep southern slope of the Côte d’Ivoire–Ghana marginal ridge. In situ diving observations and sample analysis were done to specify the clastic lithology of a sedimentary sequence about 2200?m thick. Most of the rocks collected consist of dark shales, greenish lenticular- to wavy-bedded siltstones and large-scale trough cross-bedded sandstones. Lithofacies analysis favors a deltaic origin for this sedimentary synrift succession, which is probably of Early Cretaceous age.     

TrackDip: A multi-scale processing of dipmeter data – Method,tests, and field example for 3-D description of gravity-driven deformations in the Eocene foreland basin of Ainsa,Spain

This paper presents TrackDip, a new method for dipmeter data processing. This method selects, localizes and measures significant tilts from the comparison at various scales of the changes of orientation of sedimentary beddings. We tested this method on simple cases (unconformity, gradual tilt, successive tilts, without and with additional random noise) and on a field example, along three sections in the Eocene Sobrarbe delta, Ainsa foreland basin, northern Spain. For synthetic data sets, the method clearly identifies and measures the introduced tilts.On the field, sedimentary and tectonic structures, especially three main syn-sedimentary sliding surfaces (S1–S3), were successfully identified from processed dipmeter data. The tilt axis are mainly trending N–S in sandstones, associated to Westward transport of sediments. The sliding surfaces S1 and S3 correspond to E–W-trending tilt axis, tentatively correlated either to the flexural subsidence of the basin, or to anticline growth during sedimentation South of the studied area. Combination of these sedimentary and tectonic directions results in a NE–SW striking submarine slope, which locally controls the gravity-driven deformations, especially on the S2 sliding surface. Finally, NNW–SSE-trending tilts above the uppermost S3 sliding surface are interpreted as the result of infilling on the side of the scar produced by sliding.