{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T01:21:55Z","timestamp":1760059315022,"version":"build-2065373602"},"reference-count":43,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2025,6,3]],"date-time":"2025-06-03T00:00:00Z","timestamp":1748908800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Fossil Studies"],"abstract":"<jats:p>A cast is an object that results from a fossilization process that is considerably rare in nature. For a cast to be produced, secondary diagenetic processes during and after fossilization are normally involved. Natural casts are formed when minerals are deposited within the fossil mold. Here we describe an exceptional example of the natural cast by gypsum of an ammonite presumably preserved as a limestone-made \u201chalf\u201d mold that had previously been transported as an extraclast, deposited and dissolved within Upper Pliocene quartz sandstones of the ancestral Tejo river. Portable X-ray fluorescence was used to analyze and compare the geochemical composition of the ammonite fossil with that of the nodules found within the same bed, reflecting different diagenetic timings. The composition of the ammonite cast reflects the in situ dissolution of limestone and the precipitation of calcium sulfate. High \u03b434S\u2030 and Sr values obtained from the ammonite show that the cast was produced by percolating acidic waters in the vadose zone, under marine influence, during the Late Pliocene or already in the Pleistocene. The waters being rich in sulfur resulted more likely from a marine water-influenced water table. Alternatively, it may have resulted from the weathering concentration of sulfur from the Marco Furado ferricretes overlying Santa Marta sandstone. This is, so far, the only testimony of the enormous temporal discontinuity that occurred during the taphonomic history of an ammonite, with a final preservation in the form of a cast made of gypsum, the most didactic example of this type of fossilization ever found in Portugal.<\/jats:p>","DOI":"10.3390\/fossils3020008","type":"journal-article","created":{"date-parts":[[2025,6,3]],"date-time":"2025-06-03T03:57:18Z","timestamp":1748923038000},"page":"8","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["An Ammonite Preserved in the Upper Pliocene Lower Tejo River Deposits of Quinta Do Conde (Southwest Portugal)"],"prefix":"10.3390","volume":"3","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3365-6626","authenticated-orcid":false,"given":"Carlos","family":"Neto de Carvalho","sequence":"first","affiliation":[{"name":"Geology Office of the Municipality of Idanha-a-Nova, Naturtejo UNESCO Global Geopark, Centro Cultural Raiano, Av. Joaquim Mor\u00e3o, 6060-101 Idanha-a-Nova, Portugal"},{"name":"Instituto Dom Luiz, Faculdade de Ci\u00eancias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal"},{"name":"Centro Portugu\u00eas de Geo-Hist\u00f3ria e Pr\u00e9-Hist\u00f3ria, Campo das Amoreiras Lt 1 \u2013 2.\u00ba O, 1750-021 Lisboa, Portugal"}]},{"given":"Miguel","family":"Barroso","sequence":"additional","affiliation":[{"name":"Meteoric Cipher, Lda\u2014Geological Consultancy and Services Company, Rua Quinta Nossa Senhora do Sameiro, N\u00ba 25, Foros de Amora, 2845-316 Amora, Portugal"}]},{"given":"Sofia","family":"Soares","sequence":"additional","affiliation":[{"name":"LNEG\u2014Laborat\u00f3rio Nacional de Energia e Geologia IP, Estrada da Portela, Bairro do Zambujal, Alfragide, Ap. 7586, 2610-999 Amadora, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,3]]},"reference":[{"unstructured":"Donovan, S.K. (1998). 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