{"title":"关于“中侏罗统多尺度海侵-海退旋回——以鲁西塔尼亚盆地为例”的讨论,magalh<e:1>等,沉积记录,2023,9(1),174-202","authors":"Ana C. Azerêdo, Vânia F. Correia, Ángela Fraguas","doi":"10.1002/dep2.252","DOIUrl":null,"url":null,"abstract":"<p>The paper by Magalhães et al. (<span>2023</span>) 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., <span>2022</span>; Leinfelder, <span>1986</span>; Manuppella et al., <span>1999</span>; Schneider et al., <span>2009</span>; Werner, <span>1986</span>). 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.</p><p>The Alcobaça Formation, recently formalised by Fürsich et al. (<span>2022</span>), is an important unit of the Upper Jurassic of the LB (Figure 2). Fürsich et al. (<span>2022</span>) 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. (<span>2023</span>). 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., <span>2022</span>; Kullberg & Rocha, <span>2014</span>; Leinfelder, <span>1986</span>; Manuppella et al., <span>1999</span>; Schneider et al., <span>2009</span>; Werner, <span>1986</span>).</p><p>If the part of the section described by Magalhães et al. (<span>2023</span>) 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.</p><p>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, <span>1988</span>, <span>1993</span>; Guéry et al., <span>1986</span>; Ruget-Perrot, <span>1961</span>). Incidentally, Magalhães et al. (<span>2023</span>) cite Azerêdo (<span>1988</span>) 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, <span>1988</span>, <span>1993</span>, <span>1998</span>, <span>2007</span>; Azerêdo et al., <span>2014</span>, <span>2020</span>). Thus, it is highly implausible that a siliciclastic system occurred simultaneously only in that small local section. Magalhães et al. (<span>2023</span>) 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. (<span>2022</span>) 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. (<span>2023</span>) invoke a very local explanation dubiously in middle Jurassic times.</p><p>We do not discuss the sequence stratigraphic approach of Magalhães et al. (<span>2023</span>) 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., <span>2014</span>, <span>2020</span>).</p><p>Magalhães et al. (<span>2023</span>) 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.</p><p>Overall, the conclusions of Magalhães et al. (<span>2023</span>) 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.</p><p>The authors declare no conflict of interest.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":1.9000,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.252","citationCount":"1","resultStr":"{\"title\":\"Discussion on ‘Middle Jurassic multi-scale transgressive–regressive cycles: An example from the Lusitanian Basin’, by Magalhães et al., Depositional Record, 2023, 9(1), 174–202\",\"authors\":\"Ana C. Azerêdo, Vânia F. Correia, Ángela Fraguas\",\"doi\":\"10.1002/dep2.252\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>The paper by Magalhães et al. (<span>2023</span>) 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., <span>2022</span>; Leinfelder, <span>1986</span>; Manuppella et al., <span>1999</span>; Schneider et al., <span>2009</span>; Werner, <span>1986</span>). 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.</p><p>The Alcobaça Formation, recently formalised by Fürsich et al. (<span>2022</span>), is an important unit of the Upper Jurassic of the LB (Figure 2). Fürsich et al. (<span>2022</span>) 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. (<span>2023</span>). 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., <span>2022</span>; Kullberg & Rocha, <span>2014</span>; Leinfelder, <span>1986</span>; Manuppella et al., <span>1999</span>; Schneider et al., <span>2009</span>; Werner, <span>1986</span>).</p><p>If the part of the section described by Magalhães et al. (<span>2023</span>) 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.</p><p>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, <span>1988</span>, <span>1993</span>; Guéry et al., <span>1986</span>; Ruget-Perrot, <span>1961</span>). Incidentally, Magalhães et al. (<span>2023</span>) cite Azerêdo (<span>1988</span>) 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, <span>1988</span>, <span>1993</span>, <span>1998</span>, <span>2007</span>; Azerêdo et al., <span>2014</span>, <span>2020</span>). Thus, it is highly implausible that a siliciclastic system occurred simultaneously only in that small local section. Magalhães et al. (<span>2023</span>) 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. (<span>2022</span>) 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. (<span>2023</span>) invoke a very local explanation dubiously in middle Jurassic times.</p><p>We do not discuss the sequence stratigraphic approach of Magalhães et al. (<span>2023</span>) 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., <span>2014</span>, <span>2020</span>).</p><p>Magalhães et al. (<span>2023</span>) 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.</p><p>Overall, the conclusions of Magalhães et al. (<span>2023</span>) 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. 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引用次数: 1
摘要
magalh<e:1>等人(2023)的论文涉及葡萄牙Lusitanian盆地(LB)中西部的consola<s:1> <s:1> o和s<e:1> o Bernardino海滩之间的侏罗纪海岸露头(图1)。作者使用层序地层学方法,定义了多尺度旋回,并根据纳米化石和鞭毛藻囊(dinocysts)数据,将该剖面重新划分为中侏罗世“Candeeiros组”;以前该剖面被确定为上侏罗统alcobaa组的一部分(即frsich et al., 2022;Leinfelder, 1986;Manuppella et al., 1999;Schneider et al., 2009;维尔纳,1986)。虽然沉积学和层序分析是详细的,但我们认为他们的评估是不正确的,过于简单,例如,包括单元和剖面顶部的指定年龄。此外,新的化石资料讨论过于简单,数据基础有限,对局部/区域地质的讨论很少。最近由f<s:1> rsich等人(2022)正式确定的alcobaa组是LB上侏罗统的一个重要单元(图2)。f<s:1> rsich等人(2022)提供了广泛的文献综述,其中对该地层进行了全面的描述,说明并在盆地(包括consolao剖面)内进行了对比;他们提出了相分析、宏观古生物学和微观古生物学分类和古生态资料以及古地理解释。然而,magalh<e:1>等人(2023)并没有提到这项开创性的工作。alcobaa组是一个混合的硅-塑料-碳酸盐序列;其年龄受到宏观化石和微化石数据以及锶同位素值的限制,尽管已经讨论了其底部和顶部可能存在轻微的年龄延长(f<s:1> rsich et al., 2022;Kullberg,罗查,2014;Leinfelder, 1986;Manuppella et al., 1999;Schneider et al., 2009;维尔纳,1986)。如果magalh<e:1>等人(2023)描述的部分剖面是中侏罗统地层,那么局部演替将是:中侏罗统(Bathonian/Callovian)“Candeeiros组”在consola<e:1> o剖面上的露头,向南由中侏罗统(Bathonian/Callovian)“Candeeiros组”接替,然后由晚得多的上侏罗统Lourinhã组覆盖,局部(令人难以置信的)不存在中间单元。没有考虑到合理的沉积几何或与附近地层的区域相关性来支持所隐含的剧烈序列变化。在向东约9公里的Cesareda带和向西北约7公里的Baleal半岛(图1),出现了中侏罗世碳酸盐岩露头,根据菊石的年代分别为bajoian - Callovian和bajoian /Bathonian (Azerêdo, 1988, 1993;gusamry et al., 1986;Ruget-Perrot, 1961)。顺便说一句,magalh<e:1>等人(2023)引用了Azerêdo(1988),但在参考文献中错误地将其指定为她1993年的论文;前一部作品是对巴勒剖面的原始研究。这些碳酸盐岩序列是在整个中侏罗统盛行的健康碳酸盐岩斜坡沉积体系框架内发育的(Azerêdo, 1988, 1993, 1998, 2007;Azerêdo et al., 2014,2020)。因此,只在那个小的局部区域同时出现一个硅-塑性体系是极不可能的。Magalhaes et al。(2023)地址(22页)的硅质碎屑的从上升Berlengas块向西流入到他们的研究区域,这将是由地形有界东高(底辟相关),因此输入不影响更遥远的碳酸盐沉积硅质碎屑的东部和北部(dos在塞拉Candeeiros-MCE一样,图1)。然而,中侏罗世部分在Baleal也是西部的建议“栅栏”,它只公开海洋碳酸盐岩。f<s:1> rsich等人(2022)提出了一个类似的模型,适用于consola<e:1> o亚盆地的alcobaa组(这些作者称之为alcobao亚盆地),但范围更广,涉及的是基默里吉纪时期LB历史和构造的一个较晚的不同阶段。magalh<e:1>等人(2023)援引了一个非常局部的解释,在中侏罗纪时期令人怀疑。我们没有讨论magalh<e:1>等人(2023)的层序地层学方法,也没有讨论旋回的定义标准,我们认为如果使用正确的时间框架,这可能对理解区域地层学做出积极的新贡献。然而,其层序J的上上限位于Lourinhã组之下,并不代表中、上侏罗统(Callovian/ oxford)不整合;而且,他们所研究的部分确定巴统/加罗纪时代的微古生物学证据并不可靠(下文将详细讨论)。此外,他们没有将他们的序列方案与LB中侏罗统区间的已发表旋回进行比较(Azerêdo et al., 2014, 2020)。magalh<e:1>等。 从客观上讲,认为所研究的<s:1> o Bernardino序列的顶部对应于中、上侏罗统不整合边界的直接说法是不正确的。这意味着magalh<e:1>等人(2023)用来约束研究层段的关键节点之一(与中/上侏罗统不整合相对应的顶部)是无效的。此外,中/上侏罗统盆地广泛的不整合(加里夫世晚期至牛津世早期)是LB的一个非常有约束和记录的事件(即Azerêdo et al., 2002;gusamry et al., 1986;Kullberg & Rocha, 2014;Leinfelder & Wilson, 1998;Ruget-Perrot, 1961)。它是在同一边界上存在于大西洋沿岸盆地上的主要不连续的区域表现(Norris & Hallam, 1995等),具有特定的沉积、构造、上升和气候过程的证据。在LB,它记录了明显的环境变化,覆盖着淡水和咸淡咸水潟湖到边缘海相cabaos组,该组分为海相Montejunto组(图2)。这些单元由不同的晚牛津/ kimimmeridian沉积接替,这些沉积与裂谷的开始和盆地的后续演化有关,即Abadia(南部),alcobaa和Lourinhã组(Kullberg & Rocha, 2014;Leinfelder & Wilson, 1998;Wilson et al., 1989;图2)晚侏罗世记录了向西和向南的硅屑进积的总体趋势,随着序列变得越来越具有大陆特征,如Lourinhã组具有局部侵蚀性(Leinfelder & Wilson, 1998;Manuppella et al., 1999;Mateus et al., 2017)。s<s:1> o Bernardino向Lourinhã组的过渡与盆地历史的更早阶段和中、上侏罗统不整合完全没有关系;并不是任何古地表都可以被认为与这种不整合相关。magalh<e:1>等人(2023)显然没有意识到区域地层学的相关方面。如果magalh<e:1>等人(2023)描述的部分剖面是中侏罗统地层,那么局部演替将是:中侏罗统(Bathonian/Callovian)“Candeeiros组”在consola<e:1> o剖面上的露头,向南由中侏罗统(Bathonian/Callovian)“Candeeiros组”接替,然后由晚得多的上侏罗统Lourinhã组覆盖,局部(令人难以置信的)不存在中间单元。没有考虑到合理的沉积几何或与附近地层的区域相关性来支持所隐含的剧烈序列变化。在向东约9公里的Cesareda带和向西北约7公里的Baleal半岛(图1),出现了中侏罗世碳酸盐岩露头,根据菊石的年代分别为bajoian - Callovian和bajoian /Bathonian (Azerêdo, 1988, 1993;gusamry et al., 1986;Ruget-Perrot, 1961)。顺便说一句,magalh<e:1>等人(2023)引用了Azerêdo(1988),但在参考文献中错误地将其指定为她1993年的论文;前一部作品是对巴勒剖面的原始研究。这些碳酸盐岩序列是在整个中侏罗统盛行的健康碳酸盐岩斜坡沉积体系框架内发育的(Azerêdo, 1988, 1993, 1998, 2007;Azerêdo et al., 2014,2020)。因此,只在那个小的局部区域同时出现一个硅-塑性体系是极不可能的。Magalhaes et al。(2023)地址(22页)的硅质碎屑的从上升Berlengas块向西流入到他们的研究区域,这将是由地形有界东高(底辟相关),因此输入不影响更遥远的碳酸盐沉积硅质碎屑的东部和北部(dos在塞拉Candeeiros-MCE一样,图1)。然而,中侏罗世部分在Baleal也是西部的建议“栅栏”,它只公开海洋碳酸盐岩。f<s:1> rsich等人(2022)提出了一个类似的模型,适用于consola<e:1> o亚盆地的alcobaa组(这些作者称之为alcobao亚盆地),但范围更广,涉及的是基默里吉纪时期LB历史和构造的一个较晚的不同阶段。magalh<e:1>等人(2023)援引了一个非常局部的解释,在中侏罗纪时期令人怀疑。我们没有讨论magalh<e:1>等人(2023)的层序地层学方法,也没有讨论旋回的定义标准,我们认为如果使用正确的时间框架,这可能对理解区域地层学做出积极的新贡献。然而,其层序J的上上限位于Lourinhã组之下,并不代表中、上侏罗统(Callovian/ oxford)不整合;而且,他们所研究的部分确定巴统/加罗纪时代的微古生物学证据并不可靠(下文将详细讨论)。 此外,他们没有将他们的序列方案与LB中侏罗统区间的已发表旋回进行比较(Azerêdo et al., 2014, 2020)。magalh<e:1>等人(2023)研究了三种微化石类群:介形虫、钙质纳米化石和岩形类。他们没有识别石灰岩中的有孔虫和藻类。来自纳米化石和恐龙囊的证据证明了修改演替日期的合理性。有几个方面值得进一步讨论,我们认为这个年代是非常值得怀疑的。magalh<e:1>等人(2023)报告了介形虫只在少数样本中出现,它们只被列为一般水平,并保留在开放的命名法中;因此,不能从它们中推断出精确的信息。magalh<e:1>等人(2023)没有将介形类用于生物地层学,而只使用古生态学,认为这些介形类主要是海洋生物。他们注意到两个非海相属可能从大陆到海洋沉积环境被改造过,这是他们考虑改造的一个罕见的例子。钙质纳米化石组合不多样,通常保存较差至中等。由barnesiae、W. britannica、W. manivitiae、Cyclagelosphaera margerelii、Lotharingius velatus、L. hauffii、L. contractus和Similiscutum novum组成的组合是bathonian - Callovian早期的典型组合(Bown & Cooper, 1998;Mattioli & Erba, 1999)。magalh<e:1> es et al.(2023)没有提到钙质纳米化石物种的分类鉴定标准。此外,考虑到保存较差到中等程度,以及一些已确定的物种分布范围很长,需要更多的信息和讨论来确定它们的年龄。由于magalh<e:1>等人(2023)混合了北方和特提斯生物地层方案,出现了一些不一致。例如,根据Bown和Cooper(1998)的研究,在许多北方地区,S. novum和L. hauffii的最后出现(LOs)出现在Bathonian/Callovian的边界,W. manitiae的第一次出现(FO)出现在Callovian的底部;然而,在magalh<e:1>等人(2023)的工作中,最后一个事件是在最底层的Bajocian中确定的。在另一个例子中,Mattioli和Erba(1999)记录了S. novum在特提斯阿勒尼期的LO,这与Bown和Cooper(1998)在Bathonian/Callovian边界的Boreal方案中该物种的相同事件非常不同。此外,Mattioli和Erba(1999)还确定了L. sigillatus的LO(在magalh<e:1>等人的表S3和补充数据S2中提到,2023)在阿勒年,在Watznaueria属的许多形式的FO之前,而Bown和Cooper(1998)将这一事件定位在牛津年。因此,magalh<e:1>等人(2023)应该在适当的时间考虑研究区域的古地理位置。此外,在magalh<e:1>等人的图9中,L. hauffii是将其年龄限制在中侏罗世的物种之一,其范围一直延伸到意大利北部和中部以及法国南部的Callovian/Oxfordian边界(Mattioli & Erba, 1999),甚至延伸到意大利南阿尔卑斯山的晚侏罗世(Casellato, 2010)和西班牙东北部(colombi<s:1>等人,2014)。因此,在特提斯领域,该物种并没有像magalhes等人(2023,图9)所指出的那样,在早Callovian时期消失;这与他们的补充表S3中所示的情况形成对比,其中在最上面和最下面的研究样本中都显示了hauffii的标本。因此,这一生物层位不能作为中侏罗世的诊断。magalh<e:1>等人在他们的补充数据S2中引用了一个样本中的早侏罗世物种Parhabdolithus liasicus,他们认为这是经过重新加工的。但对于其余的组合,没有提到在碎屑流入的背景下进行再加工。由cornigum、Gonyaulacysta jurassica亚种adecta、Meiourogonyaulax spp、Pareodinia ceratophora、Sentusidinium spp、Systematophora penicillata和Systematophora spp组成的鞭毛藻组合跨越了bajoian至Callovian早期的地层范围(Riding, 2005;Riding & Thomas, 1992)。在我们看来,这是一种过于简化的方法:并非所有提到的分类群都是中侏罗世的诊断,丰度也是一个重要方面。根据他们的表S3,恐龙囊的丰度一直很低。木犀草分类群,木犀草亚科。adecta (Gonyaulacysta adecta in Riding et al., 2022)和Pareodinia ceratophora在Bathonian和Callovian更为丰富,但也可能出现在整个上侏罗世,特别是牛津纪(Borges et al., 2011;Correia等人,2019;Feist-Burkhardt & Wille, 1992;Jan du Chêne等,1985;Riding & Thomas, 1992;Riding et al., 2022;Smelror, 2021)。 已经确定的是,Meiourogonyaulax和Sentusidinium出现于Bajocian以后,各种物种跨越了中生代晚期(Riding & Thomas, 1992;Smelror, 2021;Wood et al., 2016)。这些属的存在没有物种水平的识别评估只表明该剖面的年龄不超过巴约西亚。Systematophora的形式出现在Bathonian/Callovian区间,但通常只能在上侏罗统(Borges et al., 2011;Feist-Burkhardt & Wille, 1992;Riding & Thomas, 1992;Smelror, 2021)。青霉Systematophora penicillata的整体模式是牛津晚期的,所以这个物种的存在更能表明晚侏罗世,而不是中侏罗世。此外,表S3列出了囊胞分类群(如Gonyaulacysta adecta, Systematophora penicillata, Nannoceratopsis sp., Pareodinia sp.),而没有参考样本发生情况,因此令人困惑。我们还注意到文本(13个样本,第190页)和S2(19个样本,第35行)中具有海洋地貌的样本数量不一致。综上所述,我们认为magalh<e:1>等人(2023)报道的恐龙囊组合并不明确地属于巴约西亚到早期卡洛瓦时代。magalh<e:1>等人(2023)写道(第6页):“外部斜坡碳酸盐的主要特征是石囊的存在……以及红藻、双壳类、腹足类、介形类和大有孔虫的骨骼颗粒。值得注意的是,钙化只发生在研究演替的这个位置。此外,该相组合还显示出整个演替中最大量的钙质纳米化石……”在下面,说“根据fl<e:1>(2004…),丰富的远洋微化石(浮游有孔虫,calpionellids, calcisphres和纳米化石)表明沉积在深…环境中。”因此,砂砾石的独特赋存和整个演替中钙质纳米化石的最大数量表明该相组合沉积于开阔的海洋环境。这里有几点需要讨论。据报道,石囊只出现在演替的一个层次上,根据它们的S3,明显地,它们不出现在浮游有孔虫中,而是出现在底栖动物中,特别是凝集而不是透明的形式。从文本来看,大孔虫似乎可能与凿孔虫一起出现,尽管这在他们的表S3中并不清楚;但底栖动物的凝集形式在那里显示。大型底栖有孔虫(所谓的大有孔虫)是一个定义明确的类群,具有复杂的内部结构;它们是典型的浅海,温暖的海水条件(即Bassoullet, 1997等),不会出现在更深的海洋环境中。此外,根据S3的数据,在与石囊的水平面以上约1米的地方,存在绿藻,以及大型底栖有孔虫。在我们看来,更有可能的是,作为漂浮的结构,石球是由一个特殊的事件从外部海洋环境中运来的,并重新沉积在一个较浅的内部环境中,这个环境通常是底栖生物居住的。在整个演替过程中,砂丘集中在一个层位,这一事实支持了这一观点。大型底栖有孔虫的丰富代表出现在LB的中、上侏罗统(Azerêdo, 1993;Leinfelder, 1986;Ramalho, 1981)。magalh<e:1>等人(2023)没有在石灰岩中识别有孔虫和藻类分类群。他们的图5D(相对于破碎层的较高层的薄切片照片)显示了具有复杂内部结构的大型底栖岩屑有孔虫的切片。这种和其他种类的同一组在LB的上侏罗统,包括alcobaa和类似的地层,以及晚侏罗世的特提斯地区(Bassoullet, 1997;f<s:1> rsich et al., 2022;Leinfelder, 1986;Ramalho, 1981)。总的来说,magalh<e:1>等人(2023)的结论是:(i)在他们研究的剖面中存在中/上侏罗统不整合;(ii)研究剖面为中侏罗统“Candeeiros组”;(3)所研究的演替填补了Peniche下侏罗统与s<s:1> o Bernardino上侏罗统之间的中侏罗统地层记录空白,但未得到令人信服的支持。我们认为该剖面属于上侏罗统alcobaa组。a.c. Azerêdo感谢funda<s:1> o para a Ciência e tecologia (FCT), I.P./MCTES, National Funds (PIDDAC) -UIDB /50019/2020。作者感谢Robert Fensome博士的有益评论,这些评论大大改进了本文。这是NRCan的捐款编号20230057。作者还感谢TDR主编Peter Swart的编辑指导。作者声明无利益冲突。 数据共享不适用于这篇评论文章,因为没有创建新数据。数据S1请注意:出版商不对作者提供的任何支持信息的内容或功能负责。任何查询(内容缺失除外)都应直接联系文章的通讯作者。
Discussion on ‘Middle Jurassic multi-scale transgressive–regressive cycles: An example from the Lusitanian Basin’, by Magalhães et al., Depositional Record, 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).
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.
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.