Transgressive deposits and morphological patterns in the equatorial Atlantic shallow shelf (Northeast Brazil)

Abstract

The aim of this work is to identify and characterize the Late Quaternary morphological patterns of the west coast of the Ceará shelf, Northeast Brazil, based on Landsat 8, sedimentology, and seismic data. The shallow shelf has three regions: the Acaraú high (AH), unconsolidated floor (UF), and Itapagé 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 Acaraú subbasin 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).