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1 November 2007 Lithofaciology and Palaeoenvironmental Analysis of Holocene Beachrocks in Northeastern Brazil
Marcela Marques Vieira, Luiz Fernando De Ros, Francisco Hilário Rego Bezerra
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Abstract

Five lithofacies were identified in beachrock ledges distributed along the eastern and northern coasts of the state of Rio Grande do Norte, northeastern Brazil: (1) massive to weakly stratified conglomerate, (2) low-angle cross-stratified conglomerate and sandstone, (3) medium-scale tabular-planar and trough cross-stratified sandstone, (4) Skolithos-bioturbated conglomeratic sandstone, and (5) massive sandstones. Most of the described beachrocks (53% relative to total thickness) were deposited on the upper shoreface zone, represented by lithofacies 3 and 4. Lithofacies 2, which was deposited on the foreshore zone, represents 31% of the sections described. The remaining 16% are attributed to collapse of overlying material as a result of sea cliff undercutting (massive conglomerate, lithofacies 1), transport as a traction carpet deposit (weakly stratified conglomerate, lithofacies 1), and a high degree of alteration (lithofacies 5). The distribution of 14C-dated beachrock samples in a sea level envelope curve shows that, along the northern coast, framework constituents were predominantly deposited between approximately 4140 and 2190 cal. yr. BP, when sea level dropped, and during low sea level stillstand. On the northern coast, the upper shoreface sedimentation zone is preferentially distributed during sea level drop and low sea level stillstand phases, whereas the foreshore sedimentation zone can be found along the whole sea level curve. Conversely, the beach deposits distributed along the eastern coast were preferentially formed between approximately 7460 and 4240 cal. yr. BP during rapid sea level rise and high sea level stillstand. In the case of the eastern coast, both zones are equally concentrated in the first stages of rapid sea level rise and high sea level stillstand.

Marcela Marques Vieira, Luiz Fernando De Ros, and Francisco Hilário Rego Bezerra "Lithofaciology and Palaeoenvironmental Analysis of Holocene Beachrocks in Northeastern Brazil," Journal of Coastal Research 2007(236), 1535-1548, (1 November 2007). https://doi.org/10.2112/05-0562.1
Received: 22 July 2005; Accepted: 1 August 2006; Published: 1 November 2007
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