Middle Jurassic multi-scale transgressive–regressive cycles: An example from the Lusitanian Basin

Abstract

Multi-scale transgressive–regressive cycles from the mid-Jurassic were recognised in the Central Lusitanian Basin, Portugal. These cycles allow the depositional evolution of the basin to be better understood and aid in the construction of stratigraphic sequences composed of three hierarchies. The stacking pattern of high-frequency transgressive–regressive sequences forms larger clusters that define medium-frequency transgressive–regressive sequences. Likewise, the stacking pattern of medium-frequency transgressive–regressive sequences generates two Bathonian–early Callovian low-frequency transgressive–regressive sequences. Integration of several methods supported the interpretation of facies associations representing clastic deposition in offshore to shoreface environments and carbonate sediments in outer to inner ramp settings. New data from calcareous nannofossils and dinoflagellate assemblages constrained the interval's Bathonian–early Callovian age, thus unveiling the Middle–Upper Jurassic disconformity and filling the Middle Jurassic stratigraphic record gap in the Central Lusitanian Basin. This study may be helpful for similar successions in Tethyan domains and comparable depositional settings elsewhere.

INTRODUCTION

Multiple parameters influence the dynamics of the generation and preservation of sedimentary rocks, challenging their recognition in the stratigraphic record. In continental to marine depositional systems, the type and volume of sediment that may be preserved over geologic time is mainly controlled by the interplay of regional tectonics, eustatic fluctuations, climate, sedimentary supply, ecological boundary conditions, and the intrinsic energy of the environment (Catuneanu, 2006; Fragoso et al., 2022; Holbrook & Miall, 2020; Matenco & Haq, 2020; Miall, 2016; Miall et al., 2021; Strasser et al., 1999, 2006). These parameters act at various temporal and spatial scales and amplitudes, radically altering the physiography of a sedimentary basin across time and leaving their imprints on the stratigraphic record through cycles at multiple scales (Fragoso et al., 2021).

Recent developments in sequence stratigraphy have focussed on standardising a methodology and nomenclature (Catuneanu et al., 2009, 2010, 2011) applicable to describe the cyclic observable record at different scales, organising them within a chronostratigraphic hierarchical structure (Fragoso et al., 2021; Magalhães et al., 2020, 2021). Sequence stratigraphy is particularly useful at constraining shoreline regression and transgression trends by identifying stacking patterns limited by stratigraphic surfaces. In this way, the definition of transgressive–regressive (T–R) cycles circumscribed by the maximum flooding surface (end of transgression) or by the maximum regressive surface (end of regression) is a primary descriptive requirement for stratigraphic sequence analysis (Embry, 1993, 1995, 2009). Realistic representations, interpretable from the standpoint of processes operating over geological time, can be found in conceptual models developed under a hierarchical stratigraphic framework of sequences that integrate the recognition of depositional trends. This knowledge is potentially valuable for quantitative methods such as studies that employ numerical simulation of sedimentary processes (Faria et al., 2017; Huang et al., 2015) or investigate orbital cycles to calibrate stratigraphic time scales (Hilgen et al., 2015; Hinnov, 2018). In the oil industry, for instance, it is used to estimate the vertical recurrence of stratigraphic units (Magalhães et al., 2020; Melo et al., 2020, 2021).

The great exposure of the outcrops in the Lusitanian Basin provides unique opportunities to investigate the sedimentation and stratigraphic evolution during the Jurassic. The outcrop section along the west coast of Portugal, between the villages of Consolação and São Bernardino, was analysed using modern sequence stratigraphy concepts to evaluate the Middle Jurassic cyclic deposits. To maximise the outcrop description, data were collected using numerous methods, including facies analysis, conventional petrography, macrofossil identification, ichnological and microfossil analysis (ostracods, calcareous nannofossil and palynomorphs), as well as virtual outcrop models (VOMs). The integration of several methods applied in this study is an original, state-of-the-art approach to this location. Results indicate a Bathonian–early Callovian age, thus filling the Middle Jurassic stratigraphic record gap in the Central Lusitanian Basin. Such integration strengthened the proposed high-frequency, medium-frequency and low-frequency sequence stratigraphic framework and improved the general knowledge about the stratigraphic organisation of this succession.

Although only a little piece of the complex geological puzzle is revealed here, it completes part of the story related to the basins developed during the breakup of Pangea and the subsequent opening of the North Atlantic between the Grand Banks of Newfoundland and the Iberian margin. In addition, new information from facies analysis and stratigraphic organisation shed light on the processes that acted in the depositional environments of marginal basins during the Middle Jurassic. Therefore, the aims of this paper are:

• To integrate several methods to re-examine the depositional systems, stacking patterns and sequence stratigraphic surfaces.
• To determine the age of this succession and unveil the Middle Jurassic disconformity in the studied area.
• To reconstruct the stratigraphic evolution and offer a robust hierarchical system for the observed multi-scale cyclicity.

GEOLOGICAL SETTING Geodynamic evolution

The Lusitanian Basin is located in Portugal, at the western margin of the Iberian micro-plate and was formed during the breakup of Pangea and the subsequent opening of the North Atlantic (Manspeizer, 2015; Wilson et al., 1989). The dominant structural controls on its development follow the NNE and NW trends of the Caledonian–Variscan orogenic basement formed at the end of the Palaeozoic (Pastor-Galán et al., 2015; Wilson et al., 1989). The Lusitanian Basin palaeogeographical position, close to the triple junction formed by the African, Iberian and North American plates (Fernandéz, 2019), conditioned its tectono-sedimentary evolution in two main rift phases between Newfoundland Grand Banks and the Iberia margin: the Late Triassic–Middle Jurassic rift 1 and the Late Jurassic–Early Cretaceous rift 2 (Figure 1; Tucholke et al., 2007). The influence of Tethys Ocean waters remained active during both rift phases. It controlled the distribution of organisms since there was no physical barrier preventing the free circulation of Tethys waters in the Lusitanian Basin even after opening the North Atlantic Ocean (Azerêdo et al., 2002a).

FIGURE 1. (A) Chronostratigraphic chart of the Upper Triassic–Jurassic interval from the Central Lusitanian Basin, tectonic events, and plate kinematics associated with North Atlantic–Central Atlantic-Tethys conjugated margin. The studied succession (highlighted in green) is part of the Candeeiros Formation, and the Middle–Upper Jurassic disconformity encompasses a middle Callovian–middle Oxfordian hiatus in this location. Salt diapir, in white, crosses all Jurassic units. Note the GSSP between the Pliensbachian and Toarcian stages. (B) Schematic palaeogeographical reconstruction during early Callovian. The positive topography created by salt domes delimited the occurrence of marine carbonates eastwards. The structural low between salt domes and the Berlengas horst trapped clastic sediments and delivered them southwards to the depocenter. Based on Alves et al. (2002), Tucholke et al. (2007), Azerêdo and Wright (2004), Schettino and Turco (2009), Mateus et al. (2013), Pena dos Reis and Pimentel (2014), and Taylor et al. (2014).

During the Late Triassic rift phase, continental red beds (Silves Formation) filled an extensive area of multiple half-graben basins (Pena dos Reis et al., 2017) that were eventually overlain by evaporites (Dagorda Formation) and a thick carbonate succession (Coimbra Formation, Brenha and Candeeiros groups; Azerêdo, 1998; Leleu et al., 2016; Nirrengarten et al., 2017; Pena dos Reis et al., 2017; Tucholke et al., 2007; Wilson et al., 1989). Most of the Early–Middle Jurassic was a time of relative tectonic quiescence characterising the post-rift stage with the development of a carbonate ramp depositional system (Azerêdo & Wright, 2004; Duarte et al., 2017).

The Middle–Upper Jurassic disconformity marks the end of the Late Triassic–Middle Jurassic rift phase. This event is related to a very prolonged extension episode that created a hyperextended rift and, probably, the oceanic crust between conjugated basin margins that evolved to continental breakup from the Barremian to the Aptian (Alves et al., 2002; Causer et al., 2020; Dinis et al., 2008; Fernandéz, 2019; Manspeizer, 2015; Nirrengarten et al., 2017; Tucholke et al., 2007). This extension created several sub-basins filled with carbonate platform deposits (Cabaços and Montejunto formations), mixed carbonate-clastic, basinal (Abadia Formation) and continental to shallow-marine (Alcobaça Formation) deposits, and carbonate ramp, overlain by continental to coastal strata (Lourinhã and Farta Pão formations; Alves et al., 2002; Dinis et al., 2008; Hill, 1988; Leinfelder & Wilson, 1998; Mateus et al., 2013; Rasmussen et al., 1998; Schneider & Fürsich, 2009; Taylor et al., 2014). During the Late Cretaceous, the Iberian plate was subjected to compressional motion because of the convergence of Africa with Eurasia plates during the Alpine Orogeny. This event triggered the inversion of the Lusitanian Basin and, subsequently, the exposure of a significant part of its rift 1, post-rift, and rift 2 successions (Schettino & Turco, 2009; Terrinha et al., 2019).

Study interval

The study interval comprises the outcropping succession of the Candeeiros Formation between the villages of Consolação and São Bernardino (Portugal), in the southern flank of the Consolação anticline (Figure 2). Strata consist of shallow-marine grey to greenish siltstone, light cream sandstone, and cream carbonate rocks dipping 8° S. This colour pattern contrasts with the light grey sandstone and red to brown siltstone from 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. The study area is located on a faulted anticline in its northern portion, whose axis is situated in the village of Consolação. This normal fault (i.e. Consolação Fault) marks the base of the studied succession, dips towards the north-east and strikes N43W, making part of a fault zone whose traces are observed on the beach ground and in the cliff (Data S2: Figures S2 through S7).

FIGURE 2. (A and B) Location of the study area in the Lusitanian Basin (LB), between Consolação and São Bernardino villages. The Middle Jurassic unit's east boundary has not been defined (The question mark indicates uncertain identification and white area in B). (C) The studied succession crops out along the coastal cliffs at the southern Consolação anticline flank (red line). (D) Overall current tectonic configuration of the Lusitanian Basin. Modified from Taylor et al. (2014) and Pimentel and Pena dos Reis (2016).

METHODS

This study was carried out along a continuously exposed 1.8 km long and 180 m thick succession. Facies analysis (sensu Walker, 1992), macrofossil identification, ichnological and microfossil analysis (ostracods, calcareous nannofossil and palynomorphs), conventional petrography, and VOM were integrated to interpret depositional systems and sequence stratigraphy. Additional information is available in supplementary data.

Facies analysis

A composite sedimentological log (1:40 scale, Data S1) integrates all depositional facies identified in the studied succession. Facies log locations were assigned on orthophotographs to ensure that continuous thicknesses were measured perpendicular to the bed plane. Individual logs and sample positions were georeferenced and included in VOM. Facies analysis considered the lithology, grain size, sedimentary structures, palaeocurrent readings from cross-bedded strata, macrofossil identification, description of trace fossils and Bioturbation Index (BI; Taylor & Goldring, 1993), petrographic aspects, carbonate constituents, matrix and microfossil content (ostracods, calcareous nannofossils and palynomorphs). Ichnofacies analysis was based on a description of ichnogenera and integration with facies analysis (Data S2). Depositional facies classification follows Miall (1996) and Terra et al. (2010) for clastic and carbonate systems respectively. Depositional facies were grouped into facies associations. The VOMs supported the definition of external geometry, lateral extension and contact with adjacent units.

Petrography

Semi-quantitative standard petrographic analysis of 51 thin sections was undertaken to identify constituents from carbonate and sandstone facies (Data S3). Thin sections were stained with Alizarin Red-S and potassium ferricyanide (Tucker, 1988) to identify carbonate minerals.

Microfossil identification

Sixty-seven samples were collected for calcareous nannofossil, palynology and ostracod analysis. For the study of calcareous nannofossils, 67 smear slides were prepared following the double slurry method detailed by Watkins and Bergen (2003) and Blair and Watkins (2009). Preparation for palynology followed the standard technique to eliminate mineral constituents (Wood et al., 1996). A semi-quantitative analysis focussed on dinoflagellate cysts following the taxonomy indicated in Williams et al. (2017). Ostracods were recovered only in seven of 33 analysed samples following the standard hydrogen peroxide (10%) method. All ostracods were hand-picked under a stereomicroscope. The microfossil quantitative analysis is presented in Data S3.

Sequence stratigraphy

The elaboration of a high-resolution sequence stratigraphic framework was based on factors that define stacking patterns and stratigraphic surfaces of various hierarchies (Fragoso et al., 2021; Magalhães et al., 2020). Therefore, the following criteria were used to identify multi-scale sequences: 1—the transgressive–regressive internal pattern (sensu Embry, 1993, 1995; Embry & Johannessen, 1992); 2—their vertical occurrence in each considered hierarchy, 3—trends (non-random distribution) of the vertical arrangement of stacking patterns that define systems tracts of immediately higher order sequences and, 4—mapping of stacking patterns. Sequence stratigraphy nomenclature follows Catuneanu (2006) and Catuneanu et al. (2009, 2010).

Virtual outcrop models

The VOMs were built through Structure from Motion–Multi-View Stereo with images acquired with a DJI Phantom 4 Pro Remote Piloted Aerial System. A low-resolution (2 cm/pixel Ground Sampling Distance—GSD) and a high-resolution (0.5 cm/pixel GSD) VOM were georeferenced using coordinates of ground control points collected by Real-Time Kinematic. Both VOMs then generated Digital Surface Models and orthophotographs. All 1D, 2D and 3D data were integrated into the 3D georeferenced space. Sequence stratigraphic surfaces were traced on VOM using Move software. Bedding plane, faults and sequence stratigraphic surfaces were projected in 3D according to their orientation to assist the stratigraphic correlation and build a 3D structural-stratigraphic model.

RESULTS Facies associations

The studied succession consists mainly of siltstone–sandstone alternations, less frequent carbonate, and rare mixed depositional facies (Table 1, Figures 3, 4 and 5). Siliciclastic FAs occur throughout the succession (Figure 6). In contrast, carbonate FAs are limited to the lower part but with discrete occurrences (i.e. from 10 to 107 m). Facies associations consist of genetically related depositional facies that define a particular sedimentary environment (Table 2). The coastal classification used for carbonate follows Burchette and Wright (1992), and the clastic classification scheme is the one of Walker and Plint (1992). A sedimentological log presents all depositional facies and facies associations identified in this study (Figures 7 and 8).

TABLE 1 Representative depositional facies identified in the studied succession.

[Table omitted. See PDF]

FIGURE 3. Sedimentary facies observed in the studied area. (A) Laminated and bioturbated siltstone (Thalassinoides close to the pencil, position on the log: 21 m). (B) Massive siltstone (position on the log: 19 m). (C) Hummocky cross-stratified sandstone (position on the log: 98.5 m). (D) Massive sandstone (position on the log: 32 m). (E) Trough cross-stratified sandstone (position on the log: 63 m). (F) Sandstone with ripple cross-lamination (Sr) overlain by sandstone with horizontal lamination (Sh, position on the log: 83.5 m). All photographs are N (right)—S (left) oriented. See Figure 7 for the photograph position in metres.

FIGURE 4. Sedimentary facies observed in the studied area (continuation). (A) Boundstone formed by Praeexogyra pustulosa oyster (position on the log: 63.4 m), (B) Boundstone formed by Calamophylliopsis flabellate coral (Consolação fort), (C) Rudstone with fine-grained sandstone matrix and oyster fragments (position on the log: 54.8 m). All photographs are N (right)—S (left) oriented. See Figure 7 for the photograph position in metres.

FIGURE 5. Thin sections of carbonate and bioclastic sandstone facies observed in the studied area. (A) Wackestone/Packstone with calcispheres, bivalves and ostracods (polarised light, position on the log: 12 m). (B) Boundstone with oyster fragments (polarised light, position on the log: 63.4 m). (C) Rudstone with oysters, echinoids and fine quartz grains (polarised light, position on the log: 79 m). (D) Packstone with macroforaminifers, gastropods and very fine quartz grains (polarised light, position on the log: 101 m). (E) Floatstone with fragments of bivalves (polarised light, position on the log: 101.6 m). (F) Bioclastic sandstone with fragments of oyster, algae, crinoid and quartz grains (crossed light, position on the log: 47.5 m). See Figure 7 for the photograph position in metres.

FIGURE 6. Facies associations observed in the studied area. (A) Offshore siltstone (OFM, position on the log: 62 m). (B) Lower shoreface hummocky cross-stratified sandstone (LSF) and heterolithic strata at the top. The erosive base truncates offshore siltstone (OFM, position on the log: 107 m). (C) Upper to middle shoreface sandstone (SHF, position on the log: 90 m). (D) Carbonate build-up (CB) (position on the log: 63 m). (E) Carbonate build-up (CB) forming an oyster reef (Praeexogyra pustulosa, 63.4 m) (F) Inner ramp carbonate (IRC) overlying offshore siltstone (OFM, position on the log: 36 m). Stick is 1.2 m long, and each subdivision equals 20 cm. All photographs are N (right)—S (left) oriented. See Figure 7 for the photographs position in metres.

TABLE 2 Facies associations interpreted in the studied succession.

Facies association	Facies	Diagnostic sedimentary structures/constituents	Interpretation
			Ichnofacies	Depositional setting based on Burchette and Wright (1992) and Walker and Plint (1992)
IRC—Inner ramp carbonate	WCK/PCK, FLT, PCK, RUD	Macroforaminifers, bivalves, gastropods, echinoids, green algae, peloids, quartz grains	—	Carbonate deposition in shallow-marine low-energy inner ramp
CB—Carbonate build-up	BND, RUD	Oysters, corals, bivalves	—	Patch reef on semi-consolidated substrate in shallow-marine low-energy inner ramp
SHF—Upper to middle shoreface sandstone	Sh, St, Sr, Sm, Sbc, Gm, Fm, Fl	Upper part: Sharp-based sandstone bodies, horizontal lamination, trough cross-bedding, usually bioturbated at the top. Lower part: Conformable basal contact, horizontal lamination, trough cross-bedding and ripple cross-lamination. Also massive and locally bioclastic, rich in bivalves, oysters, and corals fragments. Usually bioturbated at the top	Skolithos BI: 1–5	Combination of high energy of wave and current in subtidal shoreface environment
LSF—Lower shoreface hummocky cross-stratified sandstone	Shcs, Swr, Sh, St, Fm. Locally He, Sc.	Erosive basal contact, sharp based, concave-down geometry, hummocky cross-stratification, fining-upwards, underlain by erosional surface and gutter casts. Towards the top sandstone is horizontal laminated and bioturbated. Locally convoluted sandstone	Skolithos BI: 1–2 in Sh facies only	Storm-generated sandstone beds and bioturbated facies deposited in lower shoreface
OFM—Offshore siltstone	Fm, Fl, Fb. Discrete Fbc, Sm	Massive and laminated siltstone, bioturbated at the top	Cruziana, Glossifungites BI: 1–5	Mud settling and sand deposition in offshore
ORC—Outer ramp carbonate	WCK/PCK, FLT, PCK, RUD, Sm.	Calcispheres, planktonic foraminifers, red algae, quartz grains, locally massive fine-grained sandstone beds	—	Carbonate deposition in outer ramp.

FIGURE 7. Sedimentological log of the Consolação—São Bernardino succession. Note that carbonate facies associations are progressively less frequent from 0 to 107 m. From 107 to 172 m, clastic facies associations prevail in the outcrop. Letter M stands for micropalaeontological samples.

FIGURE 8. Legend for all figures.

Outer ramp carbonate Description

Outer ramp carbonate consists of rudstone, wackestone/packstone and floatstone interbedded with laminated and bioturbated siltstone beds that only occur between 7 m and 13 m in the studied succession (Figure 7). This facies association forms a 6 m thick tabular rock body that extends laterally over hundreds of metres. The main characteristic of the outer ramp carbonate is the presence of calcispheres (Figure 5A), 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, with 429 individuals from 12 different species (see Data S3).

Interpretation

Skeletal constituents are direct indicators of carbonate production and depositional setting (Wilson, 1975). According to Flügel (2004, p. 97 Box 4.4), abundant pelagic microfossils (planktonic foraminifera, calpionellids, calcispheres and nannofossils) indicate deposition in deep shelf, slope and basinal 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.

Offshore siltstone Description

This facies association predominantly consist of massive, laminated and bioturbated siltstone. Overall, siltstone is micaceous and locally shows coal fragments up to 2 mm. From bottom to top, the observed vertical stacking consists of massive, laminated and bioturbated siltstone. Below 107 m, individual intervals of this facies association are up to 5 m thick and hundreds of metres long, with wedge-shaped external geometry that thins out southwards. In contrast, between 107 m and 172 m, laminated siltstone beds reach 16 m in thickness and extend laterally over hundreds of metres. Siltstone is always overlaid in this interval by shoreface sandstone (Figure 6B).

Massive siltstone locally includes discrete bivalve concentration layers. Rare bioturbation is observed at the top, generally deep Thalassinoides burrows from overlaying bioturbated layers (BI: 2). Massive sandstone occurs interbedded and is usually fine-grained, commonly thin (20–70 cm thick) and locally bioturbated (BI: 1). Laminated and bioturbated siltstone shows gradational to abrupt basal contact overlying massive siltstone (Figure 6A). The upper contact is abrupt without evidence of erosion by overlaying shoreface sandstone or carbonate facies. Siltstone may be entirely bioturbated or presents an upward increase of BI (BI: 1–5), usually with monospecific assemblages of Thalassinoides (Figure 3A) or a moderately diverse assemblage of Thalassinoides, Rhizocorallium commune and Ophiomorpha nodosa. Rhizocorallium jenense (BI: 2–5) is locally recorded. Bioturbated siltstone exhibits networks with extensive burrows (Thalassinoides) that descend from a single surface, penetrating deep into the substrate, unlined, with sharp walls, passively filled with sediment different from the host rock and minor post-depositional compaction. Elsewhere, this facies association rarely exhibits a few Planolites, locally Teichichnus and Cylindrichnus, Cylindrichnus, Thalassinoides and ?Macaronichnus segregatis (The question mark indicates uncertain identification).

Interpretation

Massive siltstone is generally formed as a result of the settling of mud aggregates formed in sea water through three different processes that occur in mud-dominated coasts and shelves: electrochemical coagulation, biogenic aggregation (faecal pellets), and bonding of mineral particles by dissolved organic molecules (Plint, 2010) as a product of intense bioturbation. However, the low bioturbation index (BI: 2) precludes this last hypothesis. Thalassinoides (Cruziana or Glossifungites Ichnofacies) also suggest that siltstone was deposited in the offshore environment (Clifton, 2006; Walker & Plint, 1992).

Laminated and bioturbated siltstone is usually deposited in offshore settings (i.e. below fair-weather and storm wave base levels) and is generally associated with heterolithic and hummocky cross-stratified sandstone (Clifton, 2006; Dashtgard et al., 2021; Plint, 2010). Thalassinoides, Ophiomorpha and R. commune occur in many marginal and marine palaeoenvironments. They are ubiquitous in shoreface to offshore settings belonging to Cruziana Ichnofacies (Knaust, 2017). Rhizocorallium commune is a common constituent of low-energy sediments in carbonate ramps, muddy deposits of outer-ramp and mid-ramp position and protected lagoons (Knaust, 2013). Thalassinoides and Rhizocallium jenense are often associated with firm substrates (Knaust, 2013, 2017), characterising the substrate-controlled Glossifungites Ichnofacies. However, the Cruziana Ichnofacies comprising Teichichnus and Cylindrichnus associated with siltstone to heterolithic strata may represent offshore settings (Knaust, 2017; Pemberton et al., 2012).

Lower shoreface hummocky cross-stratified sandstone Description

This facies association consists of hummocky cross-stratified sandstone that only occurs from 99 to 107 m (Figure 3C). Discrete heterolithic facies also occurs, composed of alternating massive fine-grained sandstone and siltstone layers less than 20 cm thick. Hummocky cross-bedded sandstone consists of sharp-based fine-grained sandstone bodies up to 80 cm thick that exhibit lenticular external geometry (Figure 6B). The basal surface is irregular, erosive and asymmetrical in cross-section view, from 0.4 to 1 m deep and up to 3 m wide. This surface is locally enriched with coal fragments of various sizes, generally from 1 to 20 cm. Sandstone can also be massive or horizontally laminated. Locally, some sandstone intervals are overlain by 60 cm thick heterolithic facies composed of symmetrical cross-laminated sandstone and centimetre thick massive siltstone. Simple vertical burrows characterise this massive siltstone and are passively filled with sediment similar to the host rock (Skolithos, Arenicolites) and escape structures, with a low bioturbation index (BI: 1–2).

Interpretation

Storms probably form hummocky cross-stratification and planar lamination in the lower shoreface (Dashtgard et al., 2021; Jelby et al., 2020; Leckie & Walker, 1982; MacEachern et al., 2010; Plint, 2010; Plint & Nummendal, 2000; Walker & Plint, 1992). Horizontal lamination develops in fine to very fine sand due to the high velocity of the flow and immediately above the erosional base of a storm bed (Arnott & Southard, 1990; Cheel, 1991; Plint, 2010). The sharp and erosional bottom of the sandstone bodies suggests episodes of relatively high-energy wave action and erosive currents that scoured a cohesive muddy substrate and created gutter casts during storm events (Myrow, 1992; Pérez-López, 2001; Plint, 1996). The scours filled with hummocky cross-stratified sandstone suggest deposition in the lower shoreface (Dashtgard et al., 2021; Jelby et al., 2020). This sandstone bed can be classified as simple hummocky (Jelby et al., 2020). The return to fair-weather conditions explains the presence of heterolithic and siltstone intervals with local wave ripple cross-lamination and Skolithos Ichnofacies. These characteristics suggest deposition predominantly between the mean fair-weather and storm wave base levels in the lower shoreface setting (Jelby et al., 2020).

Upper to middle shoreface sandstone Description

Upper to middle shoreface sandstone includes laminated and cross-bedded sandstone and discrete siltstone interbedded strata observed between 60 m and 98.5 m and from 108 to 172 m (Figures 3D,E,F and 6C). This facies association is mainly composed of horizontally laminated, trough cross-bedded, ripple cross-laminated, and subordinately massive sandstone. Laminated facies generally occur on top of sandstone bodies. Trace fossils are frequent with low to high intensity (BI: 1–5) and low diversities, usually Skolithos, Ophiomorpha and Arenicolites, and locally Diplocraterion and Cylindrichnus characterising the Skolithos Ichnofacies (MacEachern & Bann, 2020). Monospecific assemblages of Thalassinoides (Cruziana Ichnofacies; BI: 3) are locally observed. Sparse palaeocurrent readings (15 measures) indicate palaeoflow oriented to N180. Local bioclastic and massive sandstone occur between 32 m and 116 m, some associated with carbonate build-up. Bioclastic sandstone presents a mix of fine-grained to coarse-grained quartz, more than 30% of bivalves, oysters, gastropods, corals and coal fragments up to 5 cm. A discrete, 80 cm thick massive conglomeratic bed occurs at 82 m. It shows polymictic composition (quartz and feldspar grains, mud clasts, bivalves) supported by a fine-grained sandy matrix. This conglomerate occurs laterally related to a boundstone bed and exhibits erosive basal contact with bioturbated siltstone and abrupt top contact with overlaying bioturbated sandstone. In the interval between 60 m and 98.5 m, sandstone bedsets show an elongated lenticular geometry (extending laterally over 50 m and up to 8 m thick) that amalgamate each other northwards. Southwards, sandstone bodies up to 2 m thick extend over tens of metres and are typically separated by siltstone beds up to 50 cm thick and pinch out into laminated and bioturbated or massive siltstone. Between 108 m and 172 m, fine-grained to medium-grained sandstone forms sharp-based deposits up to 8 m thick overlying concave upward erosive surfaces truncating siltstone beds.

Interpretation

The predominance of trough cross-stratification and horizontal lamination in sandstone suggests a progressive upward increase in traction processes (Plint, 2010). The dominance of suspension-feeding behaviours (Skolithos Ichnofacies) over a few deposit-feeding ethologies (Cruziana Ichnofacies) associated with those sedimentary structures is suggestive of deposition above the fair-weather wave base in upper to middle shoreface settings (Dashtgard et al., 2021; MacEachern et al., 2010; Pemberton et al., 2012). Bioclastic sandstone and conglomerate suggest the mixing and deposition of terrigenous material and skeletal fragments due to the reworking of coeval carbonate deposits by waves or currents (Chiarella & Longhitano, 2012). Sandstone bodies with elongated lenticular external geometry that amalgamate northwards (i.e. landward) and pinch out southwards (i.e. basinward and coherently with palaeoflow measures) into muddy distal facies indicate a progradational trend. The erosive concave upward basal contact is interpreted as wave scours (Bruun, 1962; Plint, 1988).

Carbonate build-up Description

Carbonate build-up comprises boundstone and rudstone, both fossiliferous facies mainly composed of oysters, corals, bivalves up to 20 cm in size, and less frequent gastropods and red algae (Figures 6E and 4A,B). Oyster content increases upwards in the studied succession at the expense of other constituents. The position on the sedimentological log at 106 m marks the occurrence of the youngest oyster-dominated boundstone deposit (Figure 7). However, some boundstone layers are only formed by corals, particularly at the lowermost portion of the studied interval. The following specimens were recognised by Werner (1986) and Leinfelder et al. (2004): corals (Calamophylliopsis flabellata, Actinastrea furcata, Stylina sp., Ovalastrea caryophylloides, Cyathophora cesaredensis, Ovalastrea michelini; Axosmilia ssp.), oysters (Praeexogyra pustulosa), bivalves (Alaperna polita, Corbulomima suprajurensis, Protocardia sp., Pteria credneriana, Nanogyra nana), and gastropods (Metriomphalus funatus). Coal fragments up to 5 cm in size and encrusting foraminifers are also commonly found. The carbonate build-up crops out as 0.2–1.6 m thick tabular or elongated lens-shaped cemented and prominent beds that extend seawards from the outcrop for hundreds of metres. Carbonate build-up frequently overlies Upper to middle shoreface sandstone or Offshore siltstone facies associations (Figure 6D).

Interpretation

The bioaccumulation of oysters, corals, bivalves, gastropods and red algae suggests they constitute oyster reef deposits. However, the limited thickness and elongated lens-shaped external geometry indicate they were restricted, forming patch oyster reefs in low-energy shelf settings (Olivier et al., 2004). The unusual association between corals with oysters and bivalves suggests an evolutionary step towards the leading role of these organisms as Tethyan bioconstructors from the Jurassic, which ended up with the dominance of bivalve rudists during the Cretaceous (Wilson, 1975).

Inner ramp carbonate Description

Inner ramp carbonate is restricted between 22 m and 107 m (Figure 7) and encompasses wackestone/packstone, floatstone, packstone and rudstone. The main characteristic of inner ramp carbonate is the massive-cemented aspect and the presence of a matrix. Petrographic analysis shows variability in the nature of the matrix (i.e. peloidal or muddy matrix with fine-grained quartz grains) and skeletal grains (e.g. bivalves, oysters, corals, red and green algae, gastropods, echinoids, ostracods, agglutinated macroforaminifers and miliolids, Figure 5D,E). Occasionally, Girvanella occurs, encrusting bivalve shells. The size of skeletal grains varies from a millimetre scale to 5 cm. Coal fragments up to 2 cm long are often observed in floatstone. Inner ramp carbonate usually occurs as 20 cm to 1 m thick tabular to elongated lens-shaped carbonate beds with a lateral extent up to 100 m. This facies association abruptly overlies laminated and bioturbated siltstone (Figure 6F).

Interpretation

The muddy and peloidal matrix, fine-grained quartz grains, coal fragments, and organisms that typically strive in low-energy settings indicate that inner ramp carbonate represents a lagoon environment (Wilson, 1975). In contrast, bivalve-rich skeletal floatstone may represent a back-reef environment (Tucker & Wright, 1990). The abrupt basal contact with the substrate-controlled Glossifungites Ichnofacies on top of laminated and bioturbated siltstone is evidence of the required lag time for the photozoans to colonise and become viable long-standing carbonate sediment producers (i.e. the establishment of a carbonate factory; Handford & Loucks, 1993; Jones, 2010).

Micropalaeontological analyses and biostratigraphy

Semi-quantitative micropalaeontological analyses were performed to identify and date the fossil content using palynology, calcareous nannofossils and ostracods (Table 3). The degree of preservation, abundance, number of species identified and relative abundance are reported in Data S3.

TABLE 3 Summary of microfossil assemblages identified in the Consolação—São Bernardino succession. The use of sp.1, 2 or 3 indicates different and unidentified generic species. The question mark indicates uncertain identification.

Calcareous nannofossils	Dinoflagellate cysts	Ostracods
Crepidolithus crassus
Crepidolithus crucifer
Cyclagelosphaera lacuna	Amphorulacysta sp.	Cytherella sp. 1
Cyclagelosphaera margerelii	?Bradleyella sp	Cytherella sp. 2
Discorhabdus criotus	Ctenidodinium cornigerum	Cytherella sp. 3
Lotharingius contractus	Ctenitodinium spp.	Cytheropterina spp.
Lotharingius hauffii	Dissiliodinium sp.	Macrodentina sp. 1
Lotharingius sigillatus	Gonyaulacysta jurassica subspecies adecta	Macrodentina sp. 2
Lotharingius velatus	Meiourogonyaulax spp.	Mantelliana sp.
Parhabdolithus liasicus	Mendicodinium scabratum	Praeshuleridea sp.
Schizosphaerella punctulata	Nannoceratopsis sp.	Schuleridea spp.
Similiscutum novum	Pareodinia sp.	Theriosynoecum spp.
Similiscutum sp. 1	Sentusidinium sp.	Virgulacytheridea sp.
Watznaueria barnesiae	Systematophora penicillata	?Alicenula sp.
Watznaueria britannica	Systematophora spp.	?Neurocythere sp.
Watznaueria manivitiae	Wanaea sp.	?Praebythoceratina sp.
Watznaueria sp. 1
Ascidian spicule

The calcareous nannofossil assemblages are not diverse and are usually poorly to moderately preserved. 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).

Terrestrial elements (e.g. spores, pollen grains and phytoclasts) occur throughout the studied succession, but 13 out of 36 samples contained marine components. The most common are organic dinoflagellate cysts with good to moderate preservation, followed by foraminiferal linings, acritarchs, and Prasinophytes algae from the genus Tasmanites. 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 (Borges et al., 2012; Riding, 2005; Riding & Thomas, 1992).

Previous studies have considered a Late Jurassic age for the studied interval, correlating it with the Alcobaça Formation (Leinfelder et al., 2004; Mateus et al., 2013; Schneider & Fürsich, 2009; Werner, 1986). However, the ranges of calcareous nannofossils and dinoflagellate assemblages indicate this interval is Bathonian–early Callovian in age (Figure 9). Hence, it fills the Middle Jurassic stratigraphic record gap observed between the city of Peniche, where the Global Boundary Stratotype Section and Point (GSSP) is placed for the base of the Toarcian Stage (Rocha et al., 2016), and the overlying Kimmeridgian–Tithonian deposits seen in the village of São Bernardino (Taylor et al., 2014).

FIGURE 9. The range of calcareous nannofossils and dinoflagellate assemblages constrained the Bathonian–early Callovian age for the studied succession.

DISCUSSION: PALAEODEPOSITIONAL SETTING AND SEQUENCE STRATIGRAPHY

Since Werner (1986), the Consolação—São Bernardino succession has been interpreted as a regressive siliciclastic interval dominated by clay-rich to silt-rich strata deposited in calm and protected shallow-water environments. On closer examination this succession reveals a more complex stratigraphic record, with high-frequency alternations of sedimentary facies depicting a cyclic stratigraphic pattern. Thus, applying current sequence stratigraphy concepts allows for a rigorous re-evaluation of previous sedimentary interpretations.

Based on facies analysis, the examined succession was subdivided into upper and lower parts. The lower part, from 0 to 98.5 m, is recognised by the presence of carbonate facies associations. In contrast, the upper part corresponds to the interval from 98.5 to 172 m in which carbonate facies associations are absent (Figure 7). In both parts, the sedimentary record is organised into cycles across multiple scales. Such cycles were considered from the perspective of sequence stratigraphy.

The north-west/south-east orientation of the studied outcrops (Figure 2) coincides with the depositional dip direction. The lack of outcrops along the depositional strike direction hindered the observation of variations in the depositional systems.

High-frequency cyclicity

Sequences with the highest resolution are characterised as a cycle of changes in sedimentary facies stacking patterns bounded by the recurrence of the same sequence stratigraphic surface in the geological record (Catuneanu, 2019, 2022; Magalhães et al., 2020). In this study, high-resolution sequences that form the multi-scale stratigraphic framework were defined based on two assumptions: (1) the cyclic changes in facies reflect the shoreline trajectory, and (2) the recurrence of these sequences is organised in an ascending trend that composes the stacking pattern of the immediately higher order sequence, revealing short-term modulation by long-term processes in shoreline shifts.

The lower part of the studied succession exhibits a predominance of offshore siltstone and less frequent carbonate and shoreface sandstone facies associations. This combination agrees with a carbonate-influenced low-energy muddy shelf periodically disturbed by the influx of higher-energy shoreface sand-rich sediments. From bottom to top, the observed vertical stacking consists of high-frequency T–R sequences between 1 m and 7 m thick composed of offshore siltstone overlain by shoreface sandstone or inner ramp to carbonate build-up facies (Figure 10). Offshore siltstone represents the high-frequency Transgressive Systems Tract (TST). The frequent occurrence of entirely bioturbated beds on top of this facies association, or the upward increase of bioturbation index, indicates periods of sediment starvation that allowed the development of substrate-controlled Glossifungites Ichnofacies, thus supporting the interpretation of a condensed section topped by a maximum flooding surface (Figure 10).

FIGURE 10. (A) The medium-frequency T–R Sequence E. The photograph in perspective shows the southwards progradation of the regressive systems tract. (B and C) Examples of high-frequency T–R sequences from the carbonate-influenced low-energy shelf setting. The transgressive term consists of offshore siltstone (OFM, blue triangle). The regressive tract (red triangle) comprises (B) inner ramp carbonate (IRC, close view from the interval 35–37 m) or (C) upper to middle shoreface sandstone (SHF, close view from the interval 88.5–91.5 m). Stick is 1.2 m long, and each subdivision equals 20 cm. All photographs are N (right)—S (left) oriented. See Figure 13 for the position of these outcrops. MRS, maximum regressive surface (in blue); MFS, maximum flooding surface; Seq., sequence.

The change to high-frequency Regressive Systems Tracts (RST) is marked by the deposition of upper to middle shoreface sandstone or inner ramp to carbonate build-up facies associations. The increase in terrigenous influx promoted the deposition of laminated and cross-bedded sandstone with Skolithos Ichnofacies, characterising the upper to middle shoreface setting (Figure 11). Carbonate production and deposition probably occurred when terrigenous influx was low, combined with a semi-consolidated substrate (Cruziana or Glossifungites Ichnofacies) and a lag time after transgression (Handford & Loucks, 1993; Jones, 2010). The decrease in sediment supply may have been favoured by autogenic processes that shifted sediment entry points across-strike. In this case, carbonate can thrive when the clastic sediment's entry point is further away. In contrast, when the clastic sediments entry point is close, the succession is dominated by terrigenous siliciclastics (see discussion in Chanvry et al., 2018; Schwarz et al., 2006). The upper contact of high-frequency RST with younger TST is abrupt (Figure 11).

FIGURE 11. Schematic illustrations of the palaeodepositional settings associated with high-frequency sequences in the lower part. (A) Palaeoenvironment at the end of regression, (B) the end of transgression and (C) schematic chronostratigraphic framework in a clastic setting. (D) Palaeoenvironment at the end of regression, (D) end of transgression and (F) chronostratigraphic framework in a carbonate environment. For clarity, carbonate facies associations are only shown in (D). MRS, maximum regressive surface (in blue); CC, correlative conformity (in red); MFS, maximum flooding surface (in green); IRC, inner ramp carbonate, CB, carbonate build-up; ORC, outer ramp carbonate.

The upper part of the studied succession consists of offshore siltstone and less frequent lower shoreface hummocky and upper to middle shoreface sandstones (Figure 7). Lower shoreface hummocky cross-stratified sandstone is restricted to the interval between 98.5 m and 107 m. The predominance of offshore siltstone reinforces the interpretation of a low-energy setting periodically disturbed by storm events, responsible for the deposition of lower shoreface hummocky cross-stratified sandstone, or wave action and a high influx of higher-energy upper to middle shoreface sandstone. From bottom to top, the observed vertical stacking consists of recurrent high-frequency T–R sequences between 3 m and 16 m thick composed of transgressive offshore siltstone scoured by forced-regressive lower shoreface hummocky or upper to middle shoreface sandstone (Figure 12). These shoreface sandstones form sharp-based deposits that exhibit Skolithos Ichnofacies and an erosive base. Such features are compatible with storm action or deposition above the fair-weather base level. Moreover, within this interval, the recurrent upward stacking of erosive sandstone overlaying offshore strata suggests such surfaces represent the regressive surface of marine erosion truncating offshore strata (Figure 12; Bruun, 1962; Dominguez & Wanless, 1991; Myrow, 1992; Plint, 1988, 1991; Plint & Nummendal, 2000). The stacking pattern and trend analyses indicate a regular recurrence of high-frequency TST composed of transgressive low-energy offshore fine-grained background sedimentation scoured by forced-regressive shoreface sandstone deposits.

FIGURE 12. Orthophotograph showing the general aspect of forced-regressive deposits (lower shoreface hummocky cross-stratified sandstone—LSF) scouring transgressive offshore siltstone (OFM) strata from medium-frequency Sequence H. Note the regressive surface of marine erosion (RSME) overlain by lenticular sandstone bodies with hummocky cross-stratification (LSF facies association). No vertical exaggeration. See Figure 13 for the position of this outcrop. MRS, maximum regressive surface (in blue); CC, correlative conformity (in red); RSME, regressive surface of marine erosion (in orange); Seq., Sequence.

Medium-frequency and low-frequency sequences

The lower part of the studied succession comprises the medium-frequency T–R sequences A to G (Table 4, Figure 13). These sequences compose a distinctive pattern (Figure 10). The TST comprises offshore siltstone. In contrast, the RST consists of amalgamated inner ramp carbonate, carbonate build-up and upper to middle shoreface sandstone strata that prograde southwards. Sequence G includes strata deposited during forced regression and contains the lowermost high-frequency regression surface of marine erosion at 98.5 m. Besides, it also incorporates the youngest carbonate build-up represented by a P. pustulosa oyster reef at 101.5 m, overlying an interval of the substrate-controlled Glossifungites Ichnofacies. Hence, Sequence G includes the boundary between the lower and upper parts: the regression surface of marine erosion at 98.5 m. This surface truncates a Cruziana Ichnofacies interval and marks the upward recurrence of strata deposited during forced regression (i.e. lower shoreface hummocky and upper to middle shoreface sandstone; Figure 13).

TABLE 4 Nested architecture of T–R sequences in lower and upper parts of the Consolação—São Bernardino succession.

Position	Sequence hierarchy	Thickness range (m)	Sequence code	Sequence characteristics
Upper part Siliciclastic-dominated shelf setting (98.5–172 m)	Medium frequency	27 –30	H–J, Upper part of G	Sequences comprise transgressive and forced-regressive deposits. The uppermost sequence (J) is truncated by the Middle Jurassic disconformity at the base of continental deposits from the Lourinhã Formation
	High frequency	3–16	—	Ideal complete sequence composed of transgressive (offshore siltstone) and forced-regressive (lower shoreface hummocky and upper to middle shoreface sandstones) systems tracts
Lower part Carbonate-influenced, low-energy ramp setting (0–98.5 m)	Medium frequency	9–21	A–F, Lower part of G	Transgressive systems tracts tend to be thinner whereas regressive systems tracts tend to be thicker upwards. Regressive tracts exhibit prograding SW amalgamated shoreface sandstone and carbonate facies associations
	High frequency	1–7	—	Ideal complete sequence composed of transgressive (offshore siltstone) and regressive (shoreface sandstone, inner-ramp carbonate and carbonate build-up facies associations) systems tracts

Note: Sequence G includes elements of both environments. The observed thicknesses (m) are indicated. However, they do not represent universal criteria related to sequence hierarchies as “there are no standards for the temporal and physical scales of any type of sequence stratigraphic unit, nor for the lowest hierarchical rank that should be expected in a sedimentary basin” (Catuneanu, 2019).

FIGURE 13. Nested sequence architecture of the Consolação—São Bernardino succession. The upward trend of high-frequency (HF) sequences composes medium-frequency (MF) Sequences A to J. This cluster considered the transgressive and regressive trends exhibited by the stacking of facies associations and ichnofacies to define medium-frequency sequence stratigraphic surfaces. Sequences A–G belong to a carbonate-influenced setting (lower part). In contrast, Sequences H, I and J are part of a storm and wave-influenced environment (upper part). Sequence G includes the boundary between the lower and upper parts: the regression surface of marine erosion at 98.5 m. The studied succession is truncated by the Middle–Upper Jurassic disconformity (red wavy line). For legend, see Figure 8. BI—Bioturbation Index; HF—High-frequency sequences; MF—Medium-frequency sequences; Seq.—Medium-frequency sequence code; LF—Low-frequency sequence; ST—Systems Tracts; TST—Transgressive Systems Tract; RST—Regressive Systems Tract; Kim – Kimmeridgian.

The upper part of the studied succession comprises the medium-frequency sequences H, I and J. The RST of these sequences exhibits strata deposited during high-frequency forced regressions. The sequence I contains the uppermost Cruziana Ichnofacies interval at 116 m. Two samples from the offshore siltstone at 161.6 and 164.2 m presented calcareous nannofossils that confirmed its marine palaeodepositional setting (Data S3). Sequence J is limited at the top by the Lourinhã Formation, the base of which represents the Middle-Upper Jurassic disconformity (Figures 13 and 14; Taylor et al., 2014).

FIGURE 14. (A) The red arrow marks the top of the studied succession (Candeeiros Formation) at the lithological contact with the Lourinhã Formation (according to Taylor et al., 2014). This surface corresponds to the Middle–Upper Jurassic disconformity (position on the log: 172 m). (B) Close-up of the Lourinhã Formation deposits, exhibiting (C) palaeosol levels. Seq., Sequence; OFM, offshore siltstone (Candeeiros Formation).

The stacking pattern of medium-frequency T–R sequences A to J forms the low-frequency T–R sequences 1 and 2 (Figure 13). From bottom to top, the thickening-upward of medium-frequency TSTs from sequences A, B and C comprises the low-frequency TST1 (from 0 to 46.5 m). This trend is concomitant with the upward increase of the Bioturbation Index and the occurrence of Cruziana and Glossifungites Ichnofacies, thus supporting the definition of the low-frequency maximum flooding surface at 46.5 m (Figure 13). From this surface upwards, there is a change of stacking pattern. The thickening-upward trend of medium-frequency RSTs and the recurrence of Skolithos Ichnofacies from sequences D, E, F, G and H characterise the low-frequency RST1 (from 46.5 to 115.3 m). Therefore, the low-frequency T–R 1 sequence is interpreted from 0 to 115.3 m. From 115.3 m upwards, there is a predominance of medium-frequency TSTs over RSTs from the medium-frequency sequences I and J that forms the low-frequency TST2 in this interval. The Middle-Upper Jurassic disconformity truncates the top of the low-frequency TST2 at 172 m.

The cyclical pattern observed in the studied area is similar to chrono-equivalent stratigraphic records observed in Iberia, Morocco and Europe (Aurell et al., 2003; Duval-Arnould, 2019; Norris & Hallam, 1995; Ramajo & Aurell, 2008). Bathonian–Callovian chrono-equivalent low-frequency regressive clastic deposits were described in the south-western Iberian Basin (Aurell et al., 2019), Essaouira-Agadir Basin, Western Morocco (Duval-Arnould, 2019), and Western European basins (Norris & Hallam, 1995). The low-frequency T–R sequences interpreted in this study correlate with the long-term T–R cycles of north-east Iberia and western Europe (Aurell et al., 2003, 2019; Jacquin et al., 1998; Ramajo & Aurell, 2008).

Implication for mid-Jurassic palaeogeographical reconstruction

The Middle Jurassic record in the Central Lusitanian Basin consists of a conformable succession that resulted from the westwards progradation of inner ramp limestones (Bajocian to Callovian Candeeiros facies in the east) over the mid–outer ramp marls and limestones (Brenha facies in the west; Azerêdo, 1988, 1998). Bajocian to Callovian carbonate successions are well exposed in the Serra do Candeeiros, Pedrógão and Cabo Mondego areas, located further north than the Berlengas high and not influenced by clastic inputs. At these locations, high-energy inner ramp facies (i.e. cross-bedded grainstone) and a falling stage systems tract were interpreted to represent an open shallow-marine ramp setting (Azerêdo et al., 1998, 2002a, 2002b). However, the occurrence of a predominantly fine-grained shallow-marine clastic succession at least 180 m thick in the study area points to a substantial clastic sediment entry point during the Bathonian–early Callovian (Figure 1). This sediment input probably resulted from the influence of the uplifted Berlengas block, known to have been an active source of clastic sediments to the basin in this area from Toarcian (Wright & Wilson, 1984) to Kimmeridgian times (Hill, 1988). The dynamic of this entry point can explain the progressive demise of carbonate factories in these southern basin's sectors, close to the Berlengas high.

Palaeogeographical reconstruction suggests that clastic sediments were probably trapped in structural lows formed between the western side of the Bolhos and Caldas da Rainha salt domes and the Berlengas high (Alves et al., 2003; Kullberg et al., 2014). Moreover, the overall southwards progradation and palaeoflow measures indicate the depocenter southwards direction, which coincides with the axial N–S configuration of this low area in the Middle Jurassic (Figure 1; Kullberg et al., 2014; Pena dos Reis & Pimentel, 2014). The salt domes, clastic input, and the so-called Middle–Upper Jurassic disconformity reflect the tectonic instability and reorganisation in the Lusitanian Basin before the Late Jurassic–Early Cretaceous rift phase. This reorganisation is also proposed to explain the falling stage systems tract and the significant exposure that marks the Middle-Upper Jurassic disconformity within the carbonate succession northwards from the Berlengas high (Azerêdo, 1988, 1998, 2002a, 2002b).

CONCLUSIONS

The outcropping succession between the villages of Consolação and São Bernardino unveiled significant information regarding the depositional and stratigraphic evolution of the Middle Jurassic in the Central Lusitanian Basin. A critical factor in this study was the integrated approach to gathering data acquired from several methods such as micropalaeontology for accurate dating, carbonate petrography, facies and ichnofacies analysis for palaeoecological interpretation, VOMs for structural reconstruction and mapping of sequence stratigraphic surfaces, and high-resolution sequence stratigraphy to establish a chronostratigraphic framework composed of multi-scale sequences.

New data from calcareous nannofossils and dinoflagellate assemblages constrained the Bathonian–Early Callovian age for the studied interval. This age changed the significance, interpretation, correlation, and relationship with adjacent units. It also unveiled the Middle–Upper Jurassic disconformity in this portion of the Lusitanian Basin as the surface placed at the base of Kimmeridgian–Tithonian continental strata that truncate the Bathonian–early Callovian succession. The studied succession fills the Middle Jurassic stratigraphic record gap observed between the Lower Jurassic strata described in Peniche city (Rocha et al., 2016) and the Upper Jurassic deposits seen in São Bernardino village (Leinfelder, 1993; Taylor et al., 2014).

This study documents three hierarchies of T–R sequences. The stacking patterns of high-frequency T–R sequences compose larger clusters that consider the transgressive and regressive trends exhibited by the stacking of facies associations and ichnofacies to define T–R medium-frequency sequences. Likewise, the stacking pattern of medium-frequency T–R sequences forms two Bathonian–early Callovian low-frequency T–R sequences (Figure 13). Therefore, using descriptive criteria to identify sequences based on the T–R cycle anatomy, recurrence and trends, cyclic stratigraphy has enabled the definition of a conceptual model for the deposition of the studied section that is more robust than conventional interpretations. The latter are based on exhaustive sedimentary descriptions that do not value breaks in the stratigraphic record and fail to recognise high-frequency, medium-frequency and low-frequency palaeoenvironmental changes.

The low-frequency Bathonian–Early Callovian RST resulted from a significant clastic sediment entry point in the Central Lusitanian Basin and agreed with chrono-equivalent regressive clastic deposits observed in Western Morocco and Western European basins (Duval-Arnould, 2019; Norris & Hallam, 1995). The low-frequency T–R sequences correlate with the long-term T–R cycles of north-east Iberia and western Europe (Aurell et al., 2003; Jacquin et al., 1998; Ramajo & Aurell, 2008).

ACKNOWLEDGEMENTS

The authors thank the Instituto Tecnológico de Paleoceanografia e Mudanças Climáticas (itt Oceaneon) at Unisinos University, Brazil, for supporting biostratigraphic analyses, and Dr James B. Riding, British Geological Survey, UK, for his indispensable collaboration in discussing the palynological results. We are in debt with ULisboa laboratory facilities. We thank Gustavo Barros for producing all figures. The paper has benefited from thorough review and constructive feedback provided by Dr Romain Vaucher and Dr Valentin Zuchuat.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available in the supplementary material of this article.