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Jurassic Global Stratotype Section and Points (GSSPs)-a potential serial World Heritage Site?

Page K., Melendez G., Henriques M.

Volumina Jurassica

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2008

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Vol. 6, no. 1

155-162

EN

The Operation Guidelines for the UNESCO World Heritage Convention state that proposed areas should: “..be outstanding examples representing major stages of Earth’s history, including the record of life”, “..contain all or most of the key interrelated and interdependent elements in their natural relationships”, “..have a management plan…” and “..have adequate long-term legislative, regulatory, institutional or traditional protection..”. By definition, Global Stratotype Sections and Points (GSSPs) should satisfy all these criteria, although in isolation, the proposal of any single GSSP is unlikely to succeed, however, as an individual site may lack a broader context. Nevertheless, combining a suite of GSSPs sites for a System within a ‘serial’ World Heritage site proposal would satisfy such a concern and could be an ultimate goal for the International Subcommission on Jurassic Stratigraphy.

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Stratigraphic distribution of brachiopods in the Lower Jurassic – Middle Jurassic transition of the Lusitanian Basin (Portugal) and a proposal of biozonation

Andrade B., Joral F., Henriques M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

143-143

EN

A detailed revision of the brachiopods of the Lower-Middle Jurassic transition in the Lusitanian Basin (Andrade 2006) has enabled the establishment of the stratigraphical distribution of this fauna. More than 2,000 specimens were collected at 11 sections throughout the basin, including the Bajocian GSSP in Murtinheira (Cabo Mondego). In all, 24 species, belonging to 14 genera, have been recognized along a stratigraphical interval that includes the Upper Toarcian, the Aalenian, and the Lower Bajocian. The Toarcian associations are characterized by species also recorded in neighbouring basins, such as Stroudithyris stephanoides, Sphaeroidothyris vari, Pseudogibbirhynchia bothenhamptonensis and Soaresirhynchia renzi; as well as species endemic to the Lusitanian Basin, such as Choffatirhynchia alcariensis, Nannirhynchia delgadoi, N. cotteri, Praemonticlarella conimbriguensis, Neozeilleria duartei and Pamirorhynchia(?) jorali. This mixed palaeobiogeographical character persists in the Aalenian, in which the associations include, together with widely distributed species such as Neozeilleria anglica, Pseudogibbirhynchia mutans or Lophrothyris withingtonensis, other species known in neighbouring basins, such as Sphaeroidothyris uretae and Neozeilleria sharpei, and other species recorded only in the basin, such as Soaresirhynchia minor, S. murtinheirensis and Sphaeroidothyris henriquesae. In the Lower Bajocian, excluding Loboidothyris perovalis, only endemic species are present (belonging mainly to endemic genera), such as Lusitanina bituminis, Stroudithyris choffati, Lusothyris atlantica and Mondegia limica. The interpretation of these distributions also enables to propose a brachiopod based biozonation for the studied interval. Three zones have been erected: 1. the Renzi Zone, for the Upper Toarcian, with two subzones: Renzi and Duartei; 2. the Anglica Zone, that ranges from the Aalensis Biochronozone of the Toarcian to the base of the Bajocian. It has been subdivided in 3 subzones: Nuskae, Anglica and Uretae; 3. the Choffati Zone, which comprises the main part of the Discites, Laeviuscula and Sauzei biochronozones, with two subzones: Bituminis and Limica; 4. this proposal of biozonation can be correlated with other established in neighbouring basins, such as the Iberian Range in Spain or the French Basins.

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Jurassic Global Stratotype Section and Points (GSSPs) – a potential serial World Heritage Site?

Page K., Melendez G., Henriques M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

253-253

EN

The Operation Guidelines for the World Heritage Convention include the following criteria for the selection of natural heritage sites, which states that they should: "…be outstanding examples representing major stages of Earth's history, including the record of life, significant ongoing geological processes in the development of land forms, or significant geomorphic or physiographic features" [Criteria a (i)]; "The sites listed in a (i) should contain all or most of the key interrelated and interdependent elements in their natural relationships…" [Criteria b (i)]; "The site described in paragraph (a) should have a management plan…" [Criteria b (v)]; "A site described in paragraph (a) should have adequate long-term legislative, regulatory, institutional or traditional protection..." [Criteria b (vi)]. Global Stratotype Sections and Points (GSSPs) represent, by definition, the most stratigraphically complete and globally important stage-boundary sections known. They therefore fully satisfy the World Heritage criterion a (i). Crucially, their identification and ratification is regulated globally by the International Union of Geological Sciences (IUGS) which also advises UNESCO on the selection of World Heritage Sites for geological features - such a ratification can be taken as confirmation of global significance in more than just a technical or scientific sense. In addition, as part of the GSSP selection process aspects of the site's conservation status and safeguard for future study are also taken into consideration, Criterion b (vi) and be satisfied, if not b (v) as well. The proposal of any single GSSP in isolation as a World Heritage site is unlikely succeed, however, as individually such sites may lack a broader context. Combining a suite of GSSPs sites in a "serial" World Heritage site proposal - a well established approach in other contexts - is however, conceptually much more likely to succeed. In particular a proposal incorporating all the applicable GSSPs for a single system could certainly satisfy Criterion b (i), especially as all key interrelated and interdependent elements would then be included, i.e. all component stages of that system. Such a proposal could be an ultimately goal for the ISJS, as a celebration of decades of intensive work by many colleagues from many countries. Such a project would require a high degree of international agreement and already five countries are implicated in the process: Portugal, Spain, England, Scotland and France. Nevertheless, the close working relationships between specialists in different nations established through the Working Groups of the Subcommission can offer a marvellous opportunity for such collaboration.

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Ammonites from Lias-Dogger of n’Zala (Central High Atlas, Morocco)

El Hariri K., Henriques M., Chafiki D., Duarte L., Ibouh H.

Volumina Jurassica

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2006

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Vol. 4, no. 1

170-171

EN

This work aims at presenting the n’Zala section as a reference section characterizing the Lias/Dogger interval in the Moroccan Central High Atlas, both from the biostratigraphic point of view and the knowledge of some Ammonitina associations (recorded there). The n’Zala section is situated on the northern side of Jbel Aouja, near n’Zala Village, about thirty kilometers north of the village at the main road n° 21. The marly-limestone succession partly corresponds to the lower part of the Agoudim Formation. The studied interval covers about 60 metres and its major part consists of decimetric to metric thick alternation of micritic limestones and fissile marls. A study of 250 specimens belonging to over 30 taxa of Ammonitina, Lytoceratina and Phylloceratina makes it possible to recognize biostratigraphic units characterizing the Lias-Dogger interval at n’Zala, particularly the Meneghini Biozone (top), the Aalensis Biozone, the Opalinum Biozone (Opalinum and Comptum subzones) and the base of Murchisonae Biozone (Haugi Subzone). The Meneghini Biozone (about 15 m thick) at the base of the section is characterized by abundance of Catulloceras sp. associated with some Vacekia sp. and some Cotteswoldia sp. One can also notice the presence of Hammatoceratinae (particularly notable Hammatoceras aff insigne) associated with Lytoceratina and Phylloceratina. At the base of the Aalensis Biozone (about 12 m thick), we did not record Pleydellia mactra, the species index of the Mactra Biozone, but an abundance of Tmetoceras scissum, associated with Vacekia sp. along with Lytoceratina and P. aalensis, which appear in the lowest levels of the zone. Below, we found representatives of the species index of the Aalensis Subzone, Pleydellia aalensis, associated with Tmetoceras scissum and Vacekia sp. but without P. mactra. Note that Lytoceratina and Phylloceratina are also present there. The base of the Opalinum Biozone is characterized by the first appearance of forms belonging to the Cypholioceras – Leioceras dimorphic couple. The Opalinum Subzone (about 10 m thick) is defined by striated forms of Cypholioceras sp. along with Leioceras sp., Vacekia sp., Phylloceratina and Lytoceratina. The base of the Comptum Subzone (about 8 m thick) is marked by the presence of the costated representatives of Leioceras (Leioceras cf. comptum, Leioceras costusum), which are associated with Tmetoceras (Tmetoceras scissum and Tmetoceras sp.) along with Planammatoceras, Hammatoceras and Lytoceratina. The base of Murchisonae Biozone is defined by the first appearance of Graphoceratidae (Ancolioceras opalinoides, Ludwigia aff. haugi) characterizing the Haugi Subzone (about 30 m thick). The Tmetoceras sp. and Vacekia sp. persist in the biozone along with the Hammatoceratidae, the Phylloceratina and Lytoceratina. In the n’Zala section, the ammonite associations of the Lias-Dogger interval show marked biostratigraphic and paleogeographic changes. In the Aalensis Biozone, the ammonite associations show a clear Tethyan affinities as indicated by common occurrence of taxa belonging to Hammatocerataceae, Lytoceratina and Phylloceratina. The Opalinum and Murchisonae biozones show rather NW European influences, with a predominance of representatives of Leioceratinae and Graphoceratina consequently allowing the recognition of biostratigraphic units at the level of the subzones.

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Ammonite horizons at the basal Bathonian zone (Parvum Subzone) in Cabo Mondego, Portugal

Fernandez-Lopez S., Henriques M., Manglod Ch.

Volumina Jurassica

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2006

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Vol. 4, no. 1

161-161

EN

The ammonite succession at the Bajocian/Bathonian boundary in the Cabo Mondego region provides one of the most complete biostratigraphical records so far recognized in the Iberian Plate. Lower Bathonian ammonite fossil assemblages are composed of Submediterranean taxa. Parkinsonids characterizing the Northwest European Province, as well as phylloceratids and lytoceratids characterizing the Mediterranean Province, are very scarce. The basal Bathonian zone (Zigzag Zone) established for NW Europe areas, belonging to the Northwest European Province, can be identified in the Lusitanian Basin. The Lower Bathonian boundary may be established by the lowest occurrence of the dimorphic group Morphoceras (M) + Ebrayiceras (m), although morphoceratids are scarce. The Zigzag Zone can be characterized as composed of two subunits (Parvum and Macrescens subzones) represented in diverse European basins of the Submediterranean Province. The revision of previous collections from the classical section and new field samplings of two other separate sections on Cabo Mondego allow to distinguish the lowest subzone of Bathonian (Parvum Subzone, Zigzag Zone). Along up to ten metres of thickness, over forty successive assemblages have been recognized in the Parvum Subzone. The lowermost subzone of the Bathonian yields common perisphinctids (40%), oppeliids (25%) and hecticoceratids (20%), being the most abundant genera: Planisphinctes (m) + Lobosphictes (M), Oxycerites (M) + Paroecotraustes (m) and Nodiferites (m) + Zeissoceras (M). Ammonite fossil assemblages of the Parvum Subzone may be grouped into two successive biohorizons. The lower biohorizon, beginning with the lowest occurrence of Morphoceras (M) + Ebrayiceras (m), has been characterized by perisphinctids of the dimorphic couple Bigotites gr. diniensis Sturani (M) + “Bigotites” acurvatus (Wetzel) in Torrens (m), although they are scarce. The upper biohorizon, through 1.5-2 m of thickening upwards beds, has been identified in the stratigraphic interval beginning with the lowest occurrence of Zigzagiceras (m) + Procerozigzag (M) and underlying the lowest occurrence of Morphoceras macrescens (Buckman). These two successive ammonite horizons are biochronostratigraphically equivalent to the subdivisions of the Convergens Subzone distinguished on the Digne-Barr˘me area (France). The occurrence of Bigotites gr. diniensis (M+m) in Cabo Mondego in the Parvum Subzone represents a new criterion for chronostratigraphical subdivision and chronocorrelation with the Digne-Barr˘me area, useful in understanding the evolution of the West Tethyan Perisphinctidae during earliest Bathonian.