Abstract
The study of the Antalo Limestone in its type-area has shown that the formation is part of a classic depositional sequence, here termed Mekele Sequence, which consists of a number of parasequences (4° or 5° order cycles). These parasequences display systematic vertical changes in thickness and facies through the entire sequence. At the base, during the relative sea-level rise (transgressive systems tract), they form a thickening-upward retrogradational parasequence set, in the middle, during the highstand, they are of similar thickness with the subtidal facies dominating (aggradational parasequence set), and finally in the upper part they present a thinning-upward trend (progradational parasequence set). The Mekele Sequence (Antalo Limestone and Agulà Shale) was deposited on a gently sloping ramp during a second-order sea-level cycle (Oxfordian-Kimmeridgian). The lower boundary, with the Adigrat Sandstone, is diachronous due to ramp geometry, and occurs via a migrating transitional interval (lagoonal, estuarine); the upper boundary, with the Amba Aradam Formation, is the result of a forced regression and coincides with an angular unconformity.
Riassunto
Nella sua area-tipo il Calcare di Antalo (Oxfordiano-Kimmeridgiano) risulta costituito da gruppi di cicli o parasequenze, retrogradanti nella parte inferiore, aggradanti in quella centrale e progradanti in quella superiore. Questa organizzazione stratigrafico-sequenziale è il risultato di un ciclo trasgressi-vo-regressivo che ha portato alla deposizione di una sequenza deposizionale di secondo ordine, costituita dal Calcare di Antalo e dal sovrastante Agulà Shale. Tale sequenza, qui denominata Sequenza di Macallè, si depositò su di una rampa a debolissima pendenza e può essere considerata l’equivalente cratonico della Sequenza di Uarandab, presente in prossimità del margine continentale est-africano.
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Nella seduta del 22 aprile 1995.
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Bosellini, A., Russo, A., Assefa, G. et al. Il Calcare di Antalo nella regione di Macallè (Tigrai, Etiopia settentrionale). Rend. Fis. Acc. Lincei 6, 253–267 (1995). https://doi.org/10.1007/BF03001687
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DOI: https://doi.org/10.1007/BF03001687