On the Geological and Palaeontological Heritage of the Azores Archipelago and the Urgent need to Review the Geosites of the Azores UNESCO Geopark: A Comment on Lima & Meneses (2023), Geoconservation Research, 6: 114-127

Abstract

In a recent review article, Lima & Meneses (2023, Geoconservation Research, 6 (1): 114â127) reported on the Azores Geopark, introducing a new geosite for São Miguel Island. We here express our concerns regarding the data presented in this review article. In our commentary, we focus mainly on the use of older bibliographic sources and inaccurate age estimates for some islands, as well as the absence of important references, which results in a poor revision of the published literature on the geology and paleontology of the Azores Archipelago. Furthermore, and over ten years since the successful application to UNESCO for the implementation of the Azores Geopark, we stress the urgent need to re-evaluate the list of geosites selected by the Azores Geopark team, a task that we suggest could be done involving the collaboration of an expert and multidisciplinary scientific team.

UNESCO Global Geoparks are geographic areas that contain geosites of international relevance and that are managed within a holistic framework that combines conservation with sustainable development, aiming for the protection of the area and a state-of-the-art promotion of its landscapes (including the main geological and palaeontological aspects), while involving local communities. At present, there are 195 UNESCO Global Geoparks distributed in 48 countries (UNESCO Geoparks 2023).

We have read the paper by Lima & Meneses (2023) with great expectations. That work is presented by the authors as a review paper and arrives 12 years after the proposal submitted to UNESCO for the Azores Geopark (Nunes et al. 2011), which was innovative in the way it changed the definition of geoparks from a continuous territory to a discontinuous one, to accommodate archipelagic settings. In our view, this was a good opportunity to present new results from the scientific efforts made by many researchers who have published on the geology and palaeontology of the Azores Archipelago since 2011, and to review the Azores geosite checklist. This need for improvement of the first inventory and characterization of the 121 selected geosites, which are spread over the nine Azorean islands and surrounding seafloor, was already acknowledged by Nunes et al. (2011: 12): €œSeveral researchers of the Region and national and foreigner scientists with assignments about the Azores in several areas have also contributed to this inventory, which has resulted in a sustained and wide approach, although it might be susceptible to improvements.€

Although we acknowledge the effort of Lima & Meneses (2023), in our opinion, this article has several issues that should be clarified:

1. First, and crucial in a review article, is to present a complete bibliography, but there were no papers after 2018. Several important references were omitted (e.g., Gaspar et al. 2003; Luis & Miranda 2008; Hipólito et al. 2013; Larrea et al. 2013; Marques et al. 2013; Meireles et al. 2013; Mendes et al. 2013; Hildenbrand et al. 2014; Larrea 2014; Miranda et al. 2014 2015; Quartau et al. 2014, Ávila et al. 2015a 2015b; Madeira et al. 2015; Pimentel et al. 2015; Genkse et al. 2016; Casas et al. 2018; Melo et al. 2018; Rijsdijk et al. 2020; Andrade et al. 2022; Beier et al. 2022), including key review papers/books (Pacheco et al. 2013; Gaspar et al. 2015; Kueppers & Beier 2018), and books describing internationally relevant geosites (e.g., Ávila et al. 2022).

2. The use of old references such as Laughton & Whitmarsh (1974) affects the quality of description of the complex geotectonic setting of the Azores Archipelago. For instance, Lima & Meneses (2023) write that €œThe Azores UNESCO Global Geopark is located in the North Atlantic Ocean, in a special geotectonic setting, corresponding to the triple junction of the lithospheric plates of Eurasia, Africa and North America (Laughton & Whitmarsh 1974), roughly crossed N€“S by the Mid-Atlantic Ridge and by the GLORIA Fault, that integrates the Azores-Gibraltar Fault, with a general E€“W trend.€ The Azores UNESCO Global Geopark includes nine islands and adjacent islets (Flores and Corvo Islands being located on the North American tectonic plate, west of the Mid-Atlantic Ridge), the channel between Faial and Pico Islands, the Formigas Islets, the Dom João de Castro and Dollabarat submarine banks, and the Mid-Atlantic Ridge and associate hydrothermal fields (Nunes et al 2011), its boundary defined by the 2,000 m bathymetric line. In fact, except for Flores and Corvo, most of those areas integrate the western segment of the Eurasia-Nubia Plate boundary (the €œAzorean sector/segment€; e.g., Dias et al. 2007) which ends in a triple junction, where the North American plate meets the Eurasia and Nubia plates through the Mid-Atlantic Ridge. The Azorean sector noted above corresponds to a diffuse plate boundary where the active Terceira Ridge and some main linear volcanic ridges, such as São Jorge and Pico-Faial Ridges, and the extinct Princesa Alice Rift (Miranda et al. 2018) make up the main volcano-tectonic structures. However, geographically and geologically, the Gloria Fault is outside the Azores region, extending from the eastern tip of the Azores Plateau towards the Madeira-Tore Rise (e.g., Laughton et al. 1972; Batista et al. 2017). Both the Azorean sector of the Eurasian Nubia Plate boundary and the Gloria Fault are part of the Azores-Gibraltar Fracture Zone (e.g., Grimison & Chen 1986; Luis & Miranda 2008; DeMets et al. 2010), the western segment of the Eurasia Nubia Plate boundary, that links the Mid-Atlantic Ridge to the Gibraltar Strait. Hence, most of the Azores UNESCO Global Geopark lies in the western sector of the Azores-Gibraltar Fracture Zone, but it is not crossed by the Gloria Fault (Fernandes et al. 2018; Vogt & Jung 2018).

3. The older references provide outdated age dating for the Azorean islands. For example, although the archipelago's youngest island is Pico Island, its oldest subaerial volcanics did not form about 270 ka ago (Chovelon 1982), but 186 ka (Costa et al. 2015). A more problematic inaccuracy is when Lima & Meneses (2023) report 6€“8 Ma as the age of the oldest Azorean island, Santa Maria, citing Ramalho et al. (2017) as the source; however, these last authors clearly state that the oldest rocks found at Santa Maria (corresponding to the Cabrestantes Formation) yielded an age of 6.01 ± 0.14 Ma (Ramalho et al. 2017).

4. We noted further inaccurate information. For instance, as regards the evolution of the Azores Triple Junction, Lima & Meneses (2023), based on Searle (1980), state that €œThe Azores are oceanic islands of volcanic origin that started to form around 36 million years (My) ago.€ However, Luis & Miranda (2008) concluded that €œthe establishment of the Azores triple junction occurred between chrons C6c (ca. 24 Ma) and C11€“C12 (ca. 30 Ma) following the welding of Iberia to Eurasia, at ~27 Ma ago.€ Moreover, Miranda et al. (2018) state that €œ(€¦) After more than four decades of research, a few questions have been clarified concerning the different phases of development of the Azores triple junction and allowing the design of the following interpretation sketch: ~27 Ma ago there was a major rearrangement of tectonic plates and microplates in the Atlantic amalgamating Iberia to Eurasia and developing a new plate boundary along the Azores-Gibraltar Fracture Zone, here comprising the Gloria Fault and the East Azores Fracture Zone. (€¦)€ Thus, ~27 Ma, not 36 Ma, is the most recent date for the beginning of the history of the Azores Triple Junction, a premise for the magmatic/volcanic formation of the Azores Plateau (Krause & Watkins 1970; Beier et al. 2022), the submarine geomorphological feature defined by a bathymetric swell roughly delimited by the 2,000 m isobath, from which the islands rise. Regarding the formation of the islands, Miranda et al. (2014, 2015, 2018) re-evaluated the magnetic anomaly patterns, by magnetic reconstruction, together with high-resolution bathymetry analyses, in light of present scientific knowledge on the Azorean segment of the Eurasia-Nubia plate boundary, and the authors are consistent in attributing a span of less than 3 Ma for the development of most of the islands (except for Santa Maria Island).

5. Some of the reported geosites are located on the coastline which represents a risk of their destruction by marine erosion. This is, therefore, a piece of important information that should have been reported in this review. A few studies tried to estimate long-term coastal erosion rates in the Azores (Quartau et al. 2010; 2015; 2016; 2018; Zhao et al. 2020) including one important geosite that will likely disappear in the next 100 years (e.g., Capelinhos, Zhao et al. 2019).

6. We also expected to find a much-needed revision of the 121 geosites selected by the Azores Geopark team in their initial proposal (Nunes et al. 2011), as well as a thorough review of their status (international / national / regional interest). However, the review is limited to a description of Ponta da Ajuda, a new geosite for São Miguel Island (Lima & Meneses 2023), whose relevance was not evaluated.

Ponta da Ajuda is a hard rock coastal headland supported by massive basaltic (sensu lato) to intermediate lava flows. This geomorphic feature is developed on the northern flank of the Furnas polygenetic volcano, affecting its older sequences (the Lower Furnas Group; > 95 ka to

The current understanding of columnar joint formation from contractional cooling is coherent in recognizing that the cross-sectional area of basalt columns is inversely proportional to the cooling rate (Toramaru & Matsumoto 2004) and that the length of a polygon-bounding fracture segment is a function of the cooling rate, with slower cooling creating wider columns and faster cooling narrower columns (Het̩nyi et al. 2011). Transitional lava flow morphologies, between purely subaerial to purely subaqueous, have been widely observed in Santa Maria Island (Ramalho et al. 2017), and in the Cabo Verde Archipelago (Ramalho et al. 2010; Ramalho 2011). In Ṣo Miguel Island, the Ponta da Ajuda outcrop is the first to show those distinctive morphological characteristics of columnar jointing, a situation that can be explained by the presence of water at the base of the lava flow, promoting fast cooling. For instance, it is perfectly reasonable to assume this process when lava flows down into stream valleys cutting the volcano۪s flank.

Therefore, it should be emphasized that, in addition to the scientific and touristic (scenic value) interests of Ponta da Ajuda geosite, it has a remarkable pedagogical/ educational interest for the interpretation of distinctive surface and cross-sectional morphologies of basaltic (sensu lato) columnar joints.

Finally, we applied the methodology of Lima (2007), which is fully described in Ávila et al. (2016) and concluded that the Ponta da Ajuda geosite has a Q value of 25.00, meaning it is classified as a geosite of regional relevance.

Figure 1. Ponta da Ajuda geosite seen from the west. A) Detail of the polyhedral jointing. Numbers indicate the units/set of units referred in the text: I €“ simple lava sheet flow (of intermediate composition) with distinctive morphologies of columnar jointing; II €“ sequence of units of volcanic acidic fall and flow deposits; III €“ basaltic (sensu lato) lava flow. Metric scale: lighthouse = 7 m high).

7. Lima & Meneses (2023: 118) state that there are six geosites of international relevance in the Azores: the Mid Atlantic Ridge, the Furnas volcano caldera (São Miguel Island), Pico Mountain (Pico Island), the Graciosa caldera volcano and Furna do Enxofre volcanic cave (Graciosa Island), the Capelinhos and Costado da Nau volcanoes (Faial Island), and Algar do Carvão (Terceira Island). They did not discuss the geology and palaeontology of Santa Maria, based on recent work by over 80 researchers in the last two decades. This easternmost and oldest island of the Azores Archipelago is renowned for the abundant, well-preserved and diversified marine Pliocene and late Pleistocene (Last Interglacial) vertebrate (Estevens & Ávila 2007; Ávila et al. 2012, 2020) and invertebrate fossils (Kroh et al. 2008; Janssen et al. 2008; Winkelmann et al. 2010; Madeira et al. 2011; Ávila et al. 2012, 2015c; Meireles et al. 2012; Santos et al. 2015; Hyzny et al. 2021; Sacchetti et al. 2023), ichnofossils (Uchman et al. 2016, 2017, 2018; Dávid et al. 2021), and fossil algae (Rebelo et al. 2014, 2016, 2021). All this information allowed Ávila et al. (2016) to assess the relevance of the palaeontological locations on Santa Maria Island. Using numerical indices based on the same methodology adapted by Lima (2007), Ávila et al. (2016) concluded that two new palaeosites (the Ponta do Castelo tempestite deposit and the Pedra-que-pica coquina) had international relevance.

An interesting topic is whether Ponta do Castelo and Pedra-que-pica should be considered a single geosite or two independent geosites. Although the ages of these two outcrops are similar (4.78 ± 0.13 to 4.13 ± 0.19 Ma for Pedra-que-pica and 4.13 ± 0.19 to 3.98 ± 0.05 Ma for Ponta do Castelo; cf. Sacchetti et al. 2023), based on stratigraphic criteria, Ponta do Castelo is 104€“106 years younger than Pedra-que-pica (Ávila et al. 2016), from which it is separated by approximately 60 m of volcanic sediments with a lava delta on top of those sediments. Both are fossiliferous outcrops of international relevance, they are about 800 m apart (which is a considerable distance in such a small island as Santa Maria), and their accessibilities are quite different (Pedra-que-pica is best accessed by boat, whereas Ponta do Castelo is easily accessed by a pedestrian trail). Further, their geological histories are very different: Pedra-que-pica is a huge coquina deposited below storm-wave base, over 20,000 m2 in area (Ávila et al. 2015a, 2022), whereas Ponta do Castelo is a much smaller shelf tempestite deposit (less than 300 m2 in area) that resulted from a very large storm whose waves carved the bottom of the ocean at depths of ~55 m, producing a €œwavy€ bottom erosional topography about 4 m in height that was covered by sediments, colonized by marine organisms, and then buried by submarine lavas (Meireles et al. 2013). Thus, from a strict geological history/evolution aspect, we should consider these as two geosites. However, from a geoconservation point of view, the management of these two palaeosites is considerably easier if taken together as a single management unit, i.e., a single geosite. This opinion is also shared by José Brilha (personal communication, October 28th,2023). Therefore, we agree with the former Scientific Coordinator of the Azores UGGp that Ponta do Castelo and Pedra-que-pica are a single geosite for management purposes within the Geopark€™s holistic concept of protection, education and sustainable development. Ávila et al. (2016) also increased the number of relevant geosites indicated by the Azores Geopark team to Santa Maria, from 15 to 26. Thus, it has been known since 2016 that the total number of internationally relevant geosites within the Azores Geopark should be seven (considering Pedra-que-pica and Ponta do Castelo as a single geosite), not six.

Moreover, to the nine geosites indicated by Lima et al. (2014) on Santa Maria Island (five of national relevance and four of regional relevance), Ávila et al. (2016) added 17 palaeosites: two of international relevance (Pedra-que-pica and Ponta do Castelo, which we herein merge into a single geosite), six of national relevance, six of regional relevance and three of local relevance. As the geosites classified as of €œlocal relevance€ were excluded from the list used in 2011 by the Azores Geopark team on the establishment of the 121 Azores UGGp geosites, the total number of geosites currently reported for Santa Maria should be 22: one of international relevance, 11 of national relevance, and 10 of regional relevance.

8. Finally, although rarer and less studied than the marine ones, fossils of terrestrial species have also been reported for the Azores. Bird fossils of extinct taxa were described from sedimentary rocks deposited in volcanic caves on several Azorean islands (Rando et al. 2013; 2017; 2019; Alcover et al. 2015). Some of these fossils were found in recognized Azorean geosites (e.g., Algar do Carvão, Terceira Island), but the majority are not part of any geosite. Further, Holocene Azorean forests have also been redescribed based on plant fossils (Góis-Marques et al. 2015, 2019a, 2020; Góis-Marques 2020) and even reporting on the loss of a palaeobotanical geosite within the Azores UNESCO Global Geopark (Góis-Marques 2019b).

The discussion above illustrates our efforts to add an effective and valuable contribution to updating knowledge of the geoheritage and geosites of the Azores UNESCO Global Geopark. Finally, we would like to stress that, in our opinion, it is very important to re-evaluate the list of the geosites selected in 2011 by the Azores Geopark team, a task that should be carried out.

Acknowledgments

We thank two anonymous reviewers and the guest editor, Dr. João Carlos Nunes, for constructive criticisms. Fieldwork in the Azores was supported by DRCT (Direção Regional da Ciência e Tecnologia) and by the project ACORES-01-0145_FEDER-000078 - VRPROTO: Virtual Reality PROTOtype: the geological history of €œPedra-que-pica€, and by M1.1.A/INFRAEST CIENT/A/001/2021 - Base de Dados da PaleoBiodiversidade da Macaronésia. S.P.A. acknowledges his €œInvestigador FCT€ contract IF/00465/2015, funded by FCT €“ Foundation for Science and Technology; L.B. benefited from a PhD grant SFRH/BD/135918/2018 from FCT. This work also benefited from FEDER funds, through the Operational Program for Competitiveness Factors €“ COMPETE, and from National Funds, through FCT (UIDB/50027/2020, POCI-01-0145-FEDER-006821), as well as through the Regional Government of the Azores (M1.1.a/005/Funcionamento-C-/2016, CIBIO-A; M3.3.B/ORG.R.C./005/2021, M3.3.B/ORG.R.C./008/2022/EDIÇÃO 1, M3.3.G/EXPEDIÇÕES CIENTÍFICAS/005/2022 and M3.3.G/EXPEDIÇÕES CIENTÍFICAS/004/2022 and M3.3.G/EXPEDIÇÕES CIENTÍFICAS/005/2022).

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