Reply to the discussion and comments of Azerêdo et al. (2023) and Schneider et al. (2023) on the paper by Magalhães et al. ‘Middle Jurassic multi-scale transgressive–regressive cycles: An example from the Lusitanian Basin’, The Depositional Record, 9, 174–202

Abstract

We want to acknowledge the comments about our recently published paper. The exchange of ideas, data and interpretation improves our knowledge and is the right way to discuss science's advances.

This reply considers the points raised by Azerêdo et al. (2023) and Schneider et al. (2023). In both manuscripts, these authors raised many issues about sedimentological and stratigraphic aspects that can be separated into two groups: (a) those related to the age of the studied succession; and (b) those assigning the studied succession to the Candeeiros Formation.

There is a long tradition of using macropalaeontology in the Lusitanian Basin, and many authors have used macrofossils as palaeoenvironmental indicators and to date sedimentary deposits. However, except for ammonoids, micropalaeontology data are much more accurate than those from corals or bivalves, for example. This is particularly important in the Consolação–São Bernardino succession because of the lack of micropalaeontological and biostratigraphical studies.

It is noteworthy that Magalhães et al. (2023) presented a hitherto unpublished micropalaeontological and biostratigraphical analysis of the Consolação–São Bernardino succession. The association of two fossil groups (calcareous nannofossil and dinoflagellates) support our biostratigraphic data, in which we performed taxonomic and biostratigraphic analyses with care and due importance. Hence, our analysis assures the age of the studied succession, which confirms the Bathonian–early Callovian age. Azerêdo et al. (2023) and Schneider et al. (2023) questioned our age assignments, but failed to present their micropalaeontological and biostratigraphical analysis for the same Consolação–São Bernardino succession. Moreover, our findings were integrated with facies analysis, ichnofacies, petrography and macrofossil content to support the proposed age. Azerêdo et al. (2023) and Schneider et al. (2023) have no doubts about the taxonomy presented, and their issues about our dating are based on reinterpretations of our data. They assumed that the literature had already defined the age of the studied succession, which we consider is beyond debate as a result of the new data. That paper acknowledged the previous studies in the Consolação-São Bernardino section. Still, the arguments by Azerêdo et al. (2023) and Schneider et al. (2023) are not based on micropalaeontological data collected in the Consolação-São Bernadino section, but rather on correlations with supposed chronoequivalent units that do not consider our new age. Their comments failed to include irrefutable evidence of the Upper Jurassic age based on micropalaeontological data from the Consolação–São Bernardino succession to contrast with dates presented by Magalhães et al. (2023).

New data bring new interpretations. Even though all issues raised by Azerêdo et al. (2023) and Schneider et al. (2023) are welcome, they need to be supported by comparable data collected from the Consolação–São Bernardino succession. Those authors offered correlations with other sections and dating from previous studies but failed to present new micropalaeontological and biostratigraphic dating evidence from the Consolação–Sâo Bernardino succession. Therefore, it is not acceptable to state that the paper by Magalhães et al. (2023) needs to provide a better interpretation based on the correlation of data from supposed chrono-equivalent lithological units. We affirm they are not. For instance, Azerêdo et al. (2023) and Schneider et al. (2023) argued that reworking might explain our microfossil data. However, there is no sedimentological evidence for the proposed reworking. At the base of the section, calcispheres occur associated with the highest concentration of calcareous nannofossils in the outer ramp facies association. Facies analysis and microfossil content indicate this facies association was deposited in an environment of relatively deep and calm waters incompatible with the energy level required to rework, transport and deposit older Middle Jurassic sediments. This conclusion is supported by evidence and discussion presented in section 4 ‘Results’ and section 5 ‘Discussion’ of our paper. Again, it is not true as contended by Azerêdo et al. (2023) and Schneider et al. (2023) that the paper by Magalhães et al. (2023) lacks data supporting interpretation.

Once the Bathonian–early Callovian age was established, the assignment to the Candeeiros Formation was evident since it is the lithological unit tied to that age. Again, assuming the Candeeiros consists only of carbonate avoids any possibility of enhancing the understanding of this lithological unit. The local variation from carbonate to mainly siliciclastic lithology in the study area is explained by the terrigenous input from the basin's border. This input is evident in nearby Early Jurassic units (Cabo Carvoeiro Formation, Peniche section), indicating the proximity of a western border. The same palaeogeography could explain the Middle Jurassic input of siliciclastics to the studied area, which would become predominant in Late Jurassic times.

The detailed facies analysis, incorporating ichnofacies and fossil content, and the multicyclic stratal stacking pattern improved the depositional model. Depositional facies were described at a 1:40 scale to capture slight changes and enough evidence to propose the depositional model. For instance, recognising Skolithos, Cruziana and Glossifungites Ichnofacies helped envisage a more appropriate palaeoecological evolution through time. This is the first time hummocky cross-stratified sandstone and sharp-based shoreface strata deposited during forced regression were recognised in the Consolação-São Bernardino section. How could they be formed in shallow, protected water settings? Therefore, the previous interpretation of deposition in shallow, protected waters is inappropriate following the evidence presented in Magalhães et al. (2023).

The Upper Jurassic age, lithological characteristics and depositional systems associated with the Lourinhã Formation are widely accepted (Taylor et al., 2014 and references herein). For instance, the fluvial strata and reddish palaeosol interval at the bottom of the Lourinhã Formation attests to continental origin. The contact between the Lourinhã and Candeeiros formations is seen in São Bernardino. In this location, the contrast between the characteristics of these units is evident, with continental strata from the Lourinhã Formation truncating offshore siltstone and shoreface sandstone from the Candeeiros Formation. Therefore, recognising the Middle–Upper Jurassic disconformity at the contact between the Candeeiros and Lourinhã formations is straightforward. Besides erosive, this surface encompasses a significant hiatus, as demonstrated by the sequence stratigraphic framework.

The local diapir-related uplift explains the absence of the lower units of the Upper Jurassic (Cabaços and Montejunto formations) in the studied area. This uplift is responsible for the significant regional thickness changes in the Upper Jurassic units, as seen, for example, to the east and west of the Lourinhã fault. In this western basin area, close to the Bolhos and Caldas da Rainha diapirs, the Oxfordian to Kimmeridgian units probably were thinner and eroded or absent. Therefore, the basinwide Middle–Upper Jurassic disconformity has a different signature in the studied section.

The Magalhães et al. (2023) paper presents an innovative methodology to integrate and interpret the variety of data gathered in their research. Such an approach, based on micropalaeontological, ichnofacies and facies analysis supporting a new depositional model and a novel sequence stratigraphic framework, assures a much more robust interpretation than the more traditional approach founded on separated methods presented by previous authors.

New studies in the Consolação-São Bernardino section are welcome to complement the knowledge about the Lusitanian Basin, such as our work seeks. The discussion remains open and is welcome. Meanwhile, we are waiting for evidence of an irrefutable Upper Jurassic age and depositional systems characterisation from the Consolação–São Bernardino succession that explain the observed data and disagree with the findings of Magalhães et al. (2023).

Our attempts at calibrating the age for these deposits using dinoflagellates and calcareous nannofossils contribute to the comprehension of this basin's depositional evolution and biochronostratigraphy. Moreover, our review covered all data we gathered in this research, which confirmed the interpretation of the depositional facies, the depositional system, the sequence stratigraphic framework and the assignment of the Consolação–São Bernardino succession to the Candeeiros Formation.

The authors declare no conflict of interest.