Evolução sedimentar holocênica da planície costeira de Icapuí, Nordeste do Brasil

Abstract

This thesis reconstructs the genesis and evolution of the Icapuí Coastal Plain (CE), a Holocene strandplain developed in a semi-arid environment, whose existence challenges the classic model of coastal barriers sustained by significant fluvial input. It proposes that its formation results from the interaction between Holocene regression, a persistent east-to-west longshore drift current, multiple sedimentary sources (cliffs, aeolian deflation, shallow platform), and strong compartmentalization of the accommodation space conditioned by the neotectonic legacy of the Potiguar Basin. The approach integrated photointerpretation of historical aerial photographs (1950- 1980), airborne LiDAR digital terrain models (0.5 m), optically stimulated luminescence (OSL) dating, granulometric and heavy mineral analyses, spatial statistics, remote sensing, and multivariate analysis. The LOE ages (4.53 ± 0.45 kyr to 0.35 ± 0.06 kyr BP) demonstrate that the entire emerged plain is Holocene, refuting previous interpretations of shallow Pleistocene terraces and allowing the establishment of a diachronic evolutionary model divided into five stages. In Stage A (≈ 4.5-1.9 kyr BP), the first set of coastal ridges is formed, preserved only as a dissected tabular paleosurface. A depositional hiatus of ~2.6 ka indicates coastal retrogradation associated with regional aridification and reduced sediment supply. In Stage B (≈ 1.9- 1.2 kyr BP), the resumption of supply and the influence of structural anomalies favor the formation of backbarrier lagoons and the construction of ridges on both flanks of the area. Stage C (≈ 1.2–0.35 kyr BP) is marked by intense sedimentary trapping capacity, continuous progradation, and the development of east-to-west oriented spits and spurs, suggesting inlet migration and reorganization of the lagoon-sea connection. In Stage D (≈ 0.35-0.075 kyr BP), morphological evidence and ages indicate the closure of an old estuary, the establishment of a new external barrier, and the subsequent opening of the current inlet. In Stage E (≈ 75 years BP-present), the welding of barrier islands and internal silting configure the youngest morphology, marked by the interaction between inner and outer tidal flats. Grain size analysis (108 samples) reveals systematic fineness and predominant negative asymmetry, consistent with Case B of McLaren and Bowles, indicating selective and persistent transport by drift. The heavy mineral assemblage (41 samples) documents significant enrichment in hornblende and dilution of ultrastable minerals (RTZ), reflecting hydrodynamic filtration and selection by mineralogical equivalence, not a change in provenance. The Depositional Efficiency Index, developed from Pearson's three moments, operationalizes the principles of GSTA for diachronic surfaces, allowing the mapping of granulometric coherence with transport processes. The coincidence between progradation maxima and structural highs reinforces that neotectonic heritage controls sedimentary anchoring zones and modulates the progradational potential of the strandplain. This demonstrates that voluminous strandplains can develop on semi- arid margins without significant fluvial input, provided there are continuous sedimentary sources, efficient drift, and structural control capable of creating accommodation hotspots.