Rodolfo José Angulo

The Brazilian sea-level curves: a critical review with emphasis on the curves from the Paranaguáand Cananéia regions

Abstract Relative sea-level curves for the mid- to late-Holocene have been proposed for eight different sectors along the Brazilian coast. This paper aims to review the data used to construct the curves proposed for two sectors, the Paranaguaand Cananeia regions in southeast Brazil. More specifically, we analyze the palaeo-sea-level indicators (vermetid tubes, shells, wood fragments and shell-midden deposits) related to (1) the sea-level maximum of the mid-Holocene and (2) the two secondary oscillations that would have occurred between 4100-3800 years B.P. and 3000-2700 years B.P. The sedimentary deposits of the coastal plain as well as vermetid datings suggest a mid-Holocene sea-level maximum between + 3.5 and + 4 m. The great majority of the indicators used to infer the secondary oscillations in previous studies were derived from shell middens. Besides being unreliable palaeo-sea-level indicators, these data also showed inconsistencies that undermine the existence of such oscillations. The plot of all the data derived from vermetid samples found along the Brazilian coast also indicate a rather smoother sea-level fall in the last 5100 years.

Relative sea-level changes in the last 5500 years in southern Brazil (Laguna–Imbituba region, Santa Catarina State) based on vermetid 14C ages

Abstract Twenty-six new radiocarbon dates from vermetid shells collected in the southernmost sector of the Brazilian rocky coast presented dates ranging from 5410±80 to 190±65 years B.P., with associated paleosea levels varying from +2.10 m to +0.20 m above present sea level. The overall suggested trend of the relative sea level (RSL), declining until at least 190 years B.P., is somewhat contradictory to a proposed RSL rise in the last 1000 years in southern Brazil. The data also seem to undermine a more widely accepted RSL trend that suggests that at least two negative RSL oscillations occurred between 4100 and 3800 years B.P. and between 3000 and 2700 years B.P. The maximum elevation of the RSL in the Holocene in southern Brazil was possibly lower than that observed in most of the Brazilian eastern coast. Discrepancies between ancient sea levels of similar ages are attributed to coincidental methodological problems, to imprecisions in determining past relative sea levels and to possible changes in the geomorphology and wave climate close to shore during the last 5000 years. A general trend of increasing δ 18 O with a reduction in age in the studied samples may suggest a gradual reduction of water temperature in the region during the same period.

RESERVOIR EFFECT OF THE SOUTHERN AND SOUTHEASTERN BRAZILIAN COAST

A regional marine reservoir correction ( Δ R) of 33 24 14C yr for southern Brazil was obtained from 6 marine shell samples collected in the states of Santa Catarina and Paran. This work also presents a Δ R estimation of 8 17 14C yr for the southern and southeastern Brazilian coast from the states of Rio de Janeiro to Santa Catarina, obtained by including 7 ages published in previous works. The high variability of R in modern and Holocene samples from the Brazilian coast is also discussed.

Re-evaluation of the Holocene sea-level maxima for the State of Paraná, Brazil

Abstract The best defined relative sea-level curves for the Brazilian coast, such as the Salvador (State of Bahia) curve, exhibit three Holocene maxima with progressively decreasing heights dated at about 5100, 3600 and 2500 years B.P. Although the maximum reached a height of 3 to 5 m in different sectors of the Brazilian coast, previous workers (Martin et al., 1988) postulated that for the coast of ParanaState (Southern Brazil) it would have been less than 2.5 m and that the other maxima would likewise also have been lower than in other sectors. Re-evaluation of available evidence, including new data on Vermetidae, indicated an ancient sea level of 2.9 ± 0.5 m above the present at 3500 ± 60 years B.P., approximately coincidental with the second Holocene maximum in Parana. If the relative differences in height between the maxima that are observed elsewhere along the Brazilian coast hold for the Paranacoast as well, then it is possible that the first maximum may have been 4 m above the present sea-level in this state. Consequently, great changes must be made in the distinction between the Pleistocene and Holocene coastal palaeogeography of Parana. Moreover, if the difference in height of the first maximum along the Brazilian coast must now be reduced from 2.5 m to less than 1 m, the prevailing hypothesis attributing the larger value to a migrating geoidal depression during the past 5000 years must be modified or even called into question.

A TENTATIVE DETERMINATION OF UPWELLING INFLUENCE ON THE PALEO- SURFICIAL MARINE WATER RESERVOIR EFFECT IN SOUTHEASTERN BRAZIL

Previous work has suggested that seasonal and interannual upwelling of deep, cold, radiocarbon-depleted waters from the South Atlantic has caused variations in the reservoir effect (R) through time along the southern coast of Bra- zil. This work aims to examine the possible upwelling influence on the paleoreservoir age of Brazilian surficial coastal waters based on paired terrestrial/marine samples obtained from archaeological remains. On the Brazilian coast, there are hundreds of shell middens built up by an ancient culture that lived between 6500 to 1500 yr ago, but there are few shell middens located on open-coast sites with a known upwelling influence. Three archaeological sites located in a large headland in Arraial do Cabo and Ilha de Cabo Frio on the southeastern coast of Brazil, with open-ocean conditions and a well-known strong and large upwelling of the Malvinas/Falkland current, were chosen for this study. The 14C age differences between carbonized seed and marine samples varied from 281 ± 44 to 1083 ± 51 14C yr. There are also significant age differences between car- bonized seed samples (977 14C yr) and marine samples (200 and 228 14C yr) from the same archaeological layer that cannot be explained by a reservoir effect or an old-wood effect for charcoal. Therefore, the present data from the southeastern Bra- zilian coast are inconclusive for identifying an upwelling effect on R. To do so, it would be necessary to more precisely define the present-pre-bomb R in upwelling regions, and to analyze paired marine/terrestrial samples that are contemporaneous beyond doubt.

Mud in the surf: Nature at work in a Brazilian bay

Massive discharge of mud from coastal rivers is a well-documented phenomenon. However, in areas with limited historical and instrumental records it is often difficult to assess the nature and history of the process. This article looks at Tijucas Bay, in southern Brazil (Figure 1a) (an area that was the landfall region in March 2004 for South Americas first recorded hurricane [Bossack, 2004]), to examine the time frame for extensive deposition of fluid muds in the nearshore (Figure 1b). The new geological data suggest that whereas recent human activities (e.g., massive sand mining) along the Tijucas River may be important in increasing the suspended sediment discharge, the shift to a mud-dominated regime was part of the natural evolution of this coastal plain.

The State of Paraná Beaches

Parana beaches are composed primarily of mature polycyclic fine quartz sand and are characterized by wave-dominated beaches along the open coast and tidal-modified beaches inside the estuaries. At the estuary mouths large ebb-tidal-deltas influence beach sand transport and budget and cause shifts in the shoreline of hundreds of meters during periods of a few (<10) years. In contrast, the open ocean coast, away from the influence of ebb-tidal deltas, has remained stable (<10 m shift) over the last 5–6 decades. Erosion problems on the Parana coast are related to natural coastline shift induced by ebb-tidal delta dynamics as well as human destruction of foredune ridges and constructions over the beach and the beach dynamic fringe. At present time, several erosion problems remain without correct environmental and long- term solutions.

Holocene paleo-sea level changes along the coast of Rio de Janeiro, southern Brazil: Comment on Castro et al. (2014).

The present work discusses and reinterprets paleo-sea level indicators used to build Holocene sea-level curve for the coast of Rio de Janeiro at former works. We conclude that: (a) the paleo-sea levels inferred by vermetid remains show that sea-level has fallen over the past 4400 years, at least; (b) the paleo-sea level inferred by the beachrock facies and dated shells of Jaconé shows that sea-level was near the present elevation between 8198 and 5786 years before present; and (c) several shells from other beachrocks were deposited probably thousands of years after the specimens died and consequently do not allow precise reconstructions of paleo-sea levels. These conclusions differ from the conclusions of the original paper.

Reply to Castro et al. 2018 on “Holocene paleo-sea level changes along the coast of Rio de Janeiro, southern Brazil”.

Discussions are useful to the advance of science, and we appreciate the opportunity to discuss the paper by Castro et al. (2014) for the second time. Here we maintain the interpretations presented in our discussion paper (Angulo et al. 2016). In the discussion paper we emphasized that the vertical position of a paleo-sea level indicator is not the position of the paleo-sea level. We pointed out that: (1) to reconstruct paleo-sea levels it is crucial to determine the vertical distance between the indicators to their present homologous one; (2) margin of errors can only be established if considering the indicators intrinsic characteristics and (3) the interpretation of a sea level 3.0 to 4.5 m below the present one at 11.9 to-11.1 ka BP is in strong contradiction with worldwide established data and would require a detailed discussion. We consider that Castro et al. (2018) do not properly address or answer the comments we made in the discussion paper. More work and discussions are necessary to elucidate several questions that still remain about the sea level behavior in the Holocene.

Modelo gravimétrico-magnético do gráben de Paranaguá-PR, Brasil

We study the Paranagua Graben, which is part of the Cenozoic Rift System of southeastern Brazil. Specifically, it is considered a gravimetric-magnetic model of the top of the Precambrian basement under the Cenozoic sediments of the Parana state coastal plain. We aim to identify the main structures of the Paranagua Graben. We also evaluate the thickness of the sedimentary section and the Mesozoic basic intrusions in the basement. We use a regional geophysical survey that extends for more than 55 km of gravimetric profiles with 500 m of spacing between the stations and about 45 km of magnetic profiles with spacing of 25 m. The geophysical profiles were located between Paranagua Bay and the Sai-guacu river outlet, both in the context of the central region of the Ponta Grossa Arch (PGA). Data were collected along NE-SW acquisition lines, perpendicularly to the principal trend of the PGA. We present a 2-D geologic model using on gravity and magnetic data. We incorporate prior knowledge about the basement depth provided by boreholes. The identification of gravity high was related to a basement uplifting (Canoas structural high). Contiguous gravity lows had been interpreted as structural lows and called Albatroz and Shangri-la, whose maximum thickness of the sediments is 130 m. The magnetic model allowed to estimate the thicknesses of the basic dykes and to calculate an average crustal extension of 27% related to 45 km of the magnetic profiles.