VOLCANIC AND AUTHIGENIC FABRICS IN TEPHRA FROM THE ‘SES LLUMETES’ SHIPWRECK AND ROMAN MARINE CONCRETES

Underwater investigations of Porto Cristo harbor, Majorca, Spain reveal a merchant vessel shipwrecked in 50-60 CE. ‘Ses Llumetes’ had a heterogeneous cargo; a ~25 cm deposit of vitric-crystal-lithic tephra with armoured lapilli, as well as small fragments of ceramic and construction materials, protected the wood architecture from decay. Major and trace elements of the shipwrecked pumice are identical to pumice pozzolan from Campi Flegrei volcanic district in Roman concrete harbor structures drilled by the ROMACONS project. To understand whether the deposit represents ballast or, alternatively, pozzolan for concretes, the fabrics of the shipwrecked tephra, Campi Flegrei Bacoli Tuff and mortars of the Portus Cosanus, Santa Liberata harbor concretes are described. Tephra component classification of rimmed magma pyroclasts includes: (V) vitric armoured lapillus; fresh glass, (P) pumice armoured lapillus; altered glass, (C) crystal armoured lapillus. Rimmed edifice fragments include (VL) vitric-lithic armoured lapillus; tuff, (LL) lithic armoured lapillus; lava, (CL) crystal fragments; quartz, and (CmL) composite armoured lapillus. Porto Cristo tephra contains P, VL, and CmL with accretionary rim thickness 92-1341 mm. Bacoli Tuff contains V, P, VL, LL, CL, and CmL with rims 80-352 mm. Porto Cosanus mortars contain P, VL, CL, CmL with rims 59-1844 mm. Santa Liberata mortars contain P, VL, and CmL with rims 29-221 mm. Mortars from other ROMACONS drill cores also include armoured lapilli. The fabrics suggest the ‘Ses Llumetes’ deposit could have been destined for concrete construction, albeit with some recycled materials. Synchrotron microdiffraction analyses indicate authigenic analcime and nanocrystalline clay mineral in shipwrecked pyroclasts whereas authigenic phillipsite and poorly-crystalline calcium-aluminum-silicate hydrates occur in mortar pyroclasts. This suggests different solid-fluid interactions in the shipwrecked deposit compared to the massive harbor structures.