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Abstract The aim of this work is to identify and characterize the Late Quaternary morphological patterns of the west coast of the Ceara shelf, Northeast Brazil, based on Landsat 8, sedimentology, and seismic data. The shallow shelf has three regions: the Acarau high (AH), unconsolidated floor (UF), and Itapage bank (IB). The AH occurs in the inner shelf (0–5 m water depth) and shows various bedforms and in part a rocky bottom. The UF (>5 m) has many subaqueous dunes with bioclastics, structures for catching lobsters, and an escarpment. The IB is an extensive feature (delimited by the 20-m isobath) with large dunes and a shipwreck. Three seismic boundaries were identified as follows: transgressive surface (TS), subaerial exposure (SE), and miscellaneous surface (MS = TS + SE). Four seismic units were defined as follows: U1 — transparent facies with low amplitude, underlying the SE; U2 — chaotic to parallel facies with moderate to high amplitude, overlying the SE and underlying the TS; U3 — chaotic facies above the SE or TS and below the TS or sea floor, with the largest spatial extension; U4 — periodically occurring chaotic facies above the TS and below the seafloor. U1 is probably related to the falling stage systems tract or previous highstand systems tract. U2 and U3 belong to the transgressive systems tracts and U4 is associated with bedforms of the highstand systems tract. Ancient topography favored the development of transgressive deposits and modern bedforms. The AH, escarpment, and IB are morphostructures influenced by Acarau sub-basin faults. The inner shelf is characterized by shallow geomorphology strongly influenced by structural inheritance (Precambrian and post-breakup of Pangea), bedrock control, and the Holocene transgressive systems tract (the largest thickness occurs with subaqueous dunes).

This paper presents gravimetric and morphologic analyses based on the satellite-derived data set of EGM2008 and TOPEX for the area of the oceanic mantle massif of the Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean. The free-air anomaly indicates that the present plate boundary is not situated along the longitudinal graben which cuts peridotite ridge, but about 20 km to the north of it. The high Bouguer anomaly of the peridotite ridge suggests that it is constituted mainly by unserpentinised ultramafic rocks. The absence of isostatic compensation and low-degree serpentinisation of the ultramafic rocks indicate that the peridotite ridge is sustained mainly by active tectonic uplift. The unparallel relation between the transform fault and the relative plate motion generates near north-south compression and the consequent tectonic uplift. In this sense, the peridotite massif is a pressure ridge due to the strike-slip displacement of the Saint Paul Transform Fault. Este trabalho apresenta análises gravimétricas e morfológicas com base nos dados de satélites de EGM2008 e TOPEX para a área do maciço do manto oceânico da cadeia peridotítica de São Pedro e São Paulo, Oceano Atlântico Equatorial. A anomalia ar-livre indica que o contato atual das placas não se situa ao longo da graben longitudinal que se cruza com a cadeia peridotítica, mas em cerca de 20 km ao norte dessa. A alta anomalia Bouguer da cadeia peridotítica sugere que o maciço é constituído principalmente por rochas ultramáficas não serpentinizadas. A ausência de compensação isostática e o baixo grau de serpentinização das rochas ultramáficas indicam que a cadeia peridotítica é sustentada principalmente pelo soerguimento tectônico ativo. A relação não paralela entre a falha transformante e o movimento relativo das placas gera a compressão quase norte-sul e o consequente soerguimento tectônico. Neste sentido, o maciço peridotítico é uma cadeia de pressão devido ao deslocamento lateral da Falha Transformante de São Paulo.