Discussion on ‘Middle Jurassic multi‐scale transgressive–regressive cycles: An example from the Lusitanian Basin’, by Magalhães et al., <i>Depositional Record</i>, 2023, 9(1), 174–202

The paper by Magalhães et al. (2023) concerns the Jurassic coastal outcrop between Consolação and São Bernardino beaches, in the western-central Lusitanian Basin (LB), Portugal (Figure 1). The authors used a sequence stratigraphic approach, defining multi-scale cycles and, based on nannofossils and dinoflagellate cysts (dinocysts) data, they re-assigned the section to the Middle Jurassic ‘Candeeiros Formation’; formerly the section had been established as part of the Upper Jurassic Alcobaça Formation (namely Fürsich et al., 2022; Leinfelder, 1986; Manuppella et al., 1999; Schneider et al., 2009; Werner, 1986). Although the sedimentology and sequence analysis were detailed, we consider their assessment to be incorrect and oversimplified including, for example, the assigned age of the unit and the top of the section. Moreover, the new fossil data are too briefly discussed and based on limited data, and the local/regional geology is barely discussed. The Alcobaça Formation, recently formalised by Fürsich et al. (2022), is an important unit of the Upper Jurassic of the LB (Figure 2). Fürsich et al. (2022) provided an extensive literature overview, in which the formation is thoroughly described, illustrated and correlated within the basin (including the Consolação section); they presented facies analysis, macropalaeontological and micropalaeontological taxonomic and palaeoecological data and palaeogeographical interpretations. However, this seminal work is not mentioned by Magalhães et al. (2023). The Alcobaça Formation is a mixed siliciclastic-carbonate succession; its age is constrained by macrofossil and microfossil data and strontium isotope values, and has been confidently considered to be mainly of Kimmeridgian age, although possible slight age extensions of its base and top have been discussed (Fürsich et al., 2022; Kullberg & Rocha, 2014; Leinfelder, 1986; Manuppella et al., 1999; Schneider et al., 2009; Werner, 1986). … the outcropping succession of the Candeeiros Formation between … Consolação and São Bernardino … This colour pattern contrasts with the … Upper Jurassic continental Lourinhã Formation seen further south. The contact between these units is well exposed at São Bernardino beach (Taylor et al., 2014) and corresponds to the Middle-Upper Jurassic disconformity. Hence, it marks the top of the studied succession. Magalhães et al. (2023) refer to the Candeeiros Formation. The term ‘Candeeiros’ has been used in works on the LB, as an informal name coined by industry for a broad package of mostly shallow-water carbonate deposits from the Middle Jurassic, in parallel with the term ‘Brenha’, used for the more distal marl-limestone facies of the Lower and Middle Jurassic (namely Wilson et al., 1989; Figure 2). It is not a formal Formation (see Azerêdo, 2007 for Middle Jurassic formal lithostratigraphy). In the following sections we use the Candeeiros and Brenha to refer to the two broad concepts. Magalhães et al. (2023) refer to Taylor et al. (2014) to help constrain their section; this warrants discussion. Taylor et al. (2014) described the Lourinhã Formation in this region of the LB and they say at p. 143: “The study area …comprises two … coastal outcrops of the Lourinhã Formation close to … Peniche … These outcrops are approximately 7 km apart. Firstly, a … section between Baleal and Ferrel … The basal part of the Lourinhã Formation in this section is faulted out near Baleal to the west … Secondly, a … section from São Bernardino to Porto Novo displays the Lourinhã Formation … ”. At p. 151: “ … the base of the Lourinhã Formation is only visible in one location (Praia de São Bernardino) … ”; and “The base of the section, which crops out to the east of Baleal is faulted out, with the Lourinhã Formation juxtaposed against the Middle Jurassic carbonates of the Candeeiros Formation”. In the latter sentence, Taylor et al. are clearly referring to the first of their outcrops, the Baleal one (north of Peniche, Figure 1). At Baleal, a Middle Jurassic outer marine carbonate succession (in fact, not Candeeiros but Brenha facies; Azerêdo, 1988, 1993; Ruget-Perrot, 1961) forms a small peninsula and a tombolo links it to the mainland (to the east), where the Upper Jurassic terrigenous Lourinhã Formation is exposed. The contact between the two series is tectonic, as mentioned. The Baleal section is apart from the São Bernardino one; the latter is south of Peniche and Consolação (Figure 1). For São Bernardino, what Taylor et al. (2014) say at p. 151 is: “ … the base of the Lourinhã Formation is only visible in one location (Praia de São Bernardino) … ”; and, describing their São Bernardino Member, the basal member of the Lourinhã Formation: ‘At São Bernardino, the base of the member is marked by the transition from brackish-water embayment facies (Alcobaça Formation) … ’. The contact between these units is well exposed at São Bernardino beach (Taylor et al., 2014). This straight statement that the top of the studied succession at São Bernardino corresponds to the Middle/Upper Jurassic disconformable boundary is objectively incorrect. This means that one of the key tie-points Magalhães et al. (2023) use to constrain the studied interval (the top corresponding to the Middle/Upper Jurassic disconformity) is not valid. Moreover, the Middle/Upper Jurassic basin wide disconformity (late Callovian to early Oxfordian) is a very well constrained and documented event in the LB (namely Azerêdo et al., 2002; Guéry et al., 1986; Kullberg & Rocha, 2014; Leinfelder & Wilson, 1998; Ruget-Perrot, 1961). It is the regional expression of a major discontinuity that exists over the peri-Atlantic basins at the same boundary (Norris & Hallam, 1995, among others), with evidence of specific sedimentary, tectonic, eustatic and climatic processes. In the LB, it records marked environmental changes and it is draped by the freshwater and brackish-lagoonal to marginal-marine Cabaços Formation, which grades into the marine Montejunto Formation (Figure 2). These units are succeeded by varied late Oxfordian/Kimmeridgian deposits relating to the onset of rifting and subsequent evolution of the basin, namely the Abadia (to the south), Alcobaça and Lourinhã formations (Kullberg & Rocha, 2014; Leinfelder & Wilson, 1998; Wilson et al., 1989; Figure 2). A general trend of siliciclastic progradation to the west and to the south is recorded in the Late Jurassic, with the successions becoming increasingly continental in character, like the Lourinhã Formation that is locally erosive (Leinfelder & Wilson, 1998; Manuppella et al., 1999; Mateus et al., 2017). The transition into the Lourinhã Formation at São Bernardino is not related at all with the much earlier phase of the basin's history and the Middle/Upper Jurassic disconformity; it is not just any palaeosurface that may be considered correlative of this disconformity. Magalhães et al. (2023) were apparently unaware of relevant aspects of regional stratigraphy. If the part of the section described by Magalhães et al. (2023) were Middle Jurassic strata, then the local succession would be: the outcrops of Kimmeridgian Alcobaça Formation at the Consolação section, succeeded southwards by the Middle Jurassic (Bathonian/Callovian) ‘Candeeiros Formation’, in turn overlain by the much later Upper Jurassic Lourinhã Formation, the intervening units locally (and implausibly) not present. No considerations of plausible depositional geometries or regional correlations with nearby formations were made to support the drastic sequence changes implied. At Cesareda zone, about 9 km eastwards, and at Baleal Peninsula, about 7 km north-westwards (Figure 1), Middle Jurassic carbonate outcrops occur, dated by ammonites from, respectively, Bajocian to Callovian and Bajocian/Bathonian (Azerêdo, 1988, 1993; Guéry et al., 1986; Ruget-Perrot, 1961). Incidentally, Magalhães et al. (2023) cite Azerêdo (1988) but in the references wrongly assign it to her 1993 thesis; the former work is the original study of the Baleal section. These carbonate successions developed within the framework of a healthy carbonate ramp depositional system that prevailed for the whole of the Middle Jurassic in the LB (Azerêdo, 1988, 1993, 1998, 2007; Azerêdo et al., 2014, 2020). Thus, it is highly implausible that a siliciclastic system occurred simultaneously only in that small local section. Magalhães et al. (2023) do address (p. 22) the idea of a siliciclastic influx from the uplifted Berlengas block to the west into their study area, which would be bounded to the east by a topographic high (diapir related), hence siliciclastic input not influencing the more distant carbonate deposition to the east and north (as at Serra dos Candeeiros—MCE, Figure 1). However, the Middle Jurassic section at Baleal is also to the west of the suggested ‘fence’ and it only exposes marine carbonate. A similar model was presented by Fürsich et al. (2022) for the Alcobaça Formation in the Consolação sub-basin (as those authors call it), but of broader scope and referred to a later, different stage of the LB's history and configuration, in Kimmeridgian times. Magalhães et al. (2023) invoke a very local explanation dubiously in middle Jurassic times. We do not discuss the sequence stratigraphic approach of Magalhães et al. (2023) nor the criteria to define cycles, and we accept that this could be a positive new contribution to understanding the regional stratigraphy if the correct time frame were used. However, the upper top limit of their Sequence J, underlying the Lourinhã Formation, does not represent the Middle/Upper Jurassic (Callovian/Oxfordian) disconformity; and the micropalaeontological evidence for assigning a Bathonian/Callovian age to the section they studied is not robust (discussed in detail below). In addition, they did not compare their sequence scheme with published cycles for the Middle Jurassic interval of the LB (Azerêdo et al., 2014, 2020). Magalhães et al. (2023) address three microfossil groups: ostracods, calcareous nannofossils and palynomorphs. They do not identify the foraminifera and algae taxa in the limestones. Evidence from nannofossils and dinocysts are given to justify revising the dating of the succession. Several aspects warrant further discussion, and we view this dating as highly questionable. Magalhães et al. (2023) report the occurrence of ostracods in only a few samples and they are listed only to generic level and left in open nomenclature; hence no precise information can be deduced from them. Magalhães et al. (2023) do not use the ostracods for biostratigraphy, only palaeoecology, considering those as mostly marine. They note two non-marine genera as probably reworked from the continent to the marine depositional setting, a rare instance in which they consider reworking at all. The calcareous nannofossil assemblages are not diverse and are usually poorly to moderately5preserved. The assemblage composed of Watznaueria barnesiae, W. britannica, W. manivitiae, Cyclagelosphaera margerelii, Lotharingius velatus, L. hauffii, L. contractus and Similiscutum novum is typical of Bathonian–early Callovian age (Bown & Cooper, 1998; Mattioli & Erba, 1999). The criteria for taxonomic identification of calcareous nannofossil species are not mentioned in Magalhães et al. (2023). Moreover, considering the poor to moderate preservation, and the long ranges of some of the species identified, more information and discussion would be needed to determine ages. Several inconsistencies arise, because Magalhães et al. (2023) mix Boreal and Tethyan biostratigraphic schemes. For example, according to Bown and Cooper (1998), at many Boreal locations the last occurrences (LOs) of S. novum and L. hauffii occur at the Bathonian/Callovian boundary, and the first occurrence (FO) of W. manivitiae at the base of the Callovian; however, in Magalhães et al. (2023) work this last event is identified within the lowermost Bajocian. In another example, Mattioli and Erba (1999) recorded the LO of S. novum in the Tethyan Aalenian, very different from the same event for that species in the Boreal scheme of Bown and Cooper (1998), at the Bathonian/Callovian boundary. Moreover, Mattioli and Erba (1999) also identify the LO of L. sigillatus (mentioned in Table S3 and Supplementary Data S2 of Magalhães et al., 2023) in the Aalenian, before the FO of many forms of the genus Watznaueria, whilst Bown and Cooper (1998) located this event within the Oxfordian. Hence, Magalhães et al. (2023) should have considered the palaeogeographical location of the studied area during the appropriate times. In addition, L. hauffii, one of the species Magalhães et al. used to constrain the age to the Middle Jurassic in their figure 9, ranges up to the Callovian/Oxfordian boundary in northern and central Italy and southern France (Mattioli & Erba, 1999) and even the Late Jurassic of the Italian Southern Alps (Casellato, 2010) and north-eastern Spain (Colombié et al., 2014). So, in the Tethyan domain, the species does not disappear during the early Callovian as indicated by Magalhães et al. (2023, figure 9); this is in contrast to the situation shown in their Supplementary Table S3 where a specimen of L. hauffii is indicated in both the uppermost and lowermost studied samples. Hence, this biohorizon is not diagnostic of Middle Jurassic age. In their Supplementary Data S2, Magalhães et al. refer to the Early Jurassic species Parhabdolithus liasicus from one sample, which they considered to be reworked. But for the rest of the assemblage, reworking in the context of detrital influxes is not mentioned. The dinoflagellate assemblage composed of Ctenidodinium cornigerum, Gonyaulacysta jurassica subspecies adecta, Meiourogonyaulax spp., Pareodinia ceratophora, Sentusidinium spp., Systematophora penicillata, and Systematophora spp. spans a stratigraphic range between Bajocian to early Callovian (Riding, 2005; Riding & Thomas, 1992). In our view, this is an oversimplified approach: not all taxa mentioned are diagnostic of a Middle Jurassic age and abundances are also an important aspect. According to their table S3, abundances of dinocysts are consistently very low. The taxa Ctenidodinium cornigerum, Gonyaulacysta jurassica subsp. adecta (Gonyaulacysta adecta in Riding et al., 2022) and Pareodinia ceratophora, are more abundant in the Bathonian and Callovian, but may also occur through the Upper Jurassic, especially in the Oxfordian (Borges et al., 2011; Correia et al., 2019; Feist-Burkhardt & Wille, 1992; Jan du Chêne et al., 1985; Riding & Thomas, 1992; Riding et al., 2022; Smelror, 2021). It is well established that Meiourogonyaulax and Sentusidinium occur from the Bajocian onwards, and various species span the later Mesozoic (Riding & Thomas, 1992; Smelror, 2021; Wood et al., 2016). The presence of these genera without species-level recognition assessment indicates only that the section is no older than Bajocian. Forms of Systematophora occur in the Bathonian/Callovian interval, but confident species assignments are usually possible only in the Upper Jurassic (Borges et al., 2011; Feist-Burkhardt & Wille, 1992; Riding & Thomas, 1992; Smelror, 2021). The holotype of Systematophora penicillata is of late Oxfordian age, so the presence of this species is more indicative of a Late, rather than Middle, Jurassic age. Additionally, table S3 is confusing as it lists dinocyst taxa (e.g. Gonyaulacysta adecta, Systematophora penicillata, Nannoceratopsis sp., Pareodinia sp.) without reference to sample occurrences. We also note an inconsistency in the number of samples with marine palynomorphs between the text (13 samples, p. 190) and S2 (19 samples, line 35). In summary, we consider that the dinocyst assemblage reported by Magalhães et al. (2023) is not unequivocally of Bajocian to early Callovian age. Magalhães et al. (2023) wrote (p. 6): “The main characteristic of the outer ramp carbonate is the presence of calcispheres … , together with skeletal grains of red algae, bivalves, gastropods, ostracods and macroforaminifers. Notably, calcispheres only occur at this location of the studied succession. Moreover, this facies association exhibits the most significant quantity of calcareous nannofossils of the whole succession … ”. In the following, say ‘According to Flügel (2004 … ), abundant pelagic microfossils (planktonic foraminifera, calpionellids, calcispheres and nannofossils) indicate deposition in deep … settings. Therefore, the unique occurrence of calcispheres and the largest amount of calcareous nannofossils of the whole succession suggest this facies association was deposited in an open-marine environment’. Several points need discussion here. The calcispheres are reported to occur only at one level of the succession and, according to their S3, significantly they occur not with planktic foraminifera, but with benthic, especially agglutinated rather than hyaline, forms. From the text, it seems that macroforaminifers may appear together with calcispheres, although this is not clear in their table S3; but benthic agglutinated forms are indicated there. The large benthic foraminifers (the so called macroforaminifers) are a well-defined group, with complex inner structure; they are typical of shallow marine, warm water conditions (namely Bassoullet, 1997, among others) and would not be expected in deeper marine settings. In addition, according to S3, at about 1 m above the level with the calcispheres, green algae are present, as well as the large benthic foraminifera. In our opinion it is much more probable that, as floating structures, the calcispheres have been transported from the outer marine environment by an extraordinary event and redeposited in a shallower inner setting typically inhabited by the benthic forms. The fact that the calcispheres are concentrated at one single horizon within the whole succession supports this idea. Abundant representatives of large benthic foraminifera occur in the Middle and Upper Jurassic of the LB (Azerêdo, 1993; Leinfelder, 1986; Ramalho, 1981, among others). Magalhães et al. (2023) do not identify foraminifera and algae taxa in the limestones. Their figure 5D (a thin-section photograph from higher in the succession relative to the calcispheres) shows sections of a large benthic lituolid foraminifer with complex inner structure. This and other species of the same group are common in the Upper Jurassic of the LB, including the Alcobaça and equivalent formations, as well as over the Tethyan realm during the Late Jurassic (Bassoullet, 1997; Fürsich et al., 2022; Leinfelder, 1986; Ramalho, 1981, among others). Overall, the conclusions of Magalhães et al. (2023) that (i) the Middle/Upper Jurassic disconformity is present in the section they studied; (ii) the studied section is of the Middle Jurassic ‘Candeeiros Formation’; and (iii) the studied succession fills the Middle Jurassic stratigraphic record gap between the Lower Jurassic of Peniche and the Upper Jurassic of São Bernardino, are not convincingly supported. In our view the section belongs to the Upper Jurassic Alcobaça Formation. A. C. Azerêdo acknowledges Fundação para a Ciência e Tecnologia (FCT), I.P./MCTES, National Funds (PIDDAC)—UIDB/50019/2020. The authors are thankful to Dr. Robert Fensome for the helpful comments, which substantially improved the text. This is NRCan contribution number 20230057. The authors are also thankful to the TDR Editor in Chief Peter Swart for his editorial guidance. The authors declare no conflict of interest. Data sharing is not applicable to this commentary article because no new data were created. Data S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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