Geochemical evidence for sediment provenance in mudstones and fossil-poor wackestones (Upper Jurassic, Majorca Island) Rute Coimbra and Federico Olo ´ riz Departamento de Estratigrafı´a y Paleontologı´a, Universidad de Granada, Spain Introduction and geological setting The Balearic Archipelago (Fig. 1A) is an extension of the Betic Cordillera (Fontbote´ et al., 1990; but see Olo´riz et al., 2002 and Sabat et al., 2011) showing late Jurassic brown lime- stones in the Sierra Norte of the Majorca Island. These are exceptional deposits on west Tethyan epioceanic swells, otherwise dominated by AR facies. We clarify these unusual depo- sitional conditions and compare them with potentially recent analogous ones. The Cuber and Cala Fornells sec- tions (Fig. 1A–C) crop out in the Sierra Norte, Majorca (Alvaro et al., 1984 and Sabat et al., 2011 for struc- tural interpretation). The Upper Jurassic in the Sierra Norte is domi- nated by AR of the Alfabia and Son Torrelles Fms. (Caracuel and Olo´riz, 1998, 1999 for details). In contrast, the Aumedra´ Fm. is characterized by expanded, well-bedded brownish mudstones and macrofossil-poor wa- ckestones (Figs 1C and 2) with ca. 40 metres of mainly lowermost Tithonian (Hybonotum Zone) strata. This single ammonite biozone comprises 57% of the total thickness and 6% of the time contained in Upper Jurassic deposits (Caracuel and Olo´riz, 1999). The Au- medra´ Fm. deposits are also very homogeneous, macrofossil-poor, show dark brown colour and very fine grain size. New geochemical arguments pro- vided a better understanding of these deposits, atypical for West-Tethyan Upper Jurassic. Methods Hand samples (n = 122) were col- lected from within a precise ammonite biostratigraphy (Olo´riz et al., 2002) from the Cala Fornells and Cuber sections, covering Middle Oxfordian to lower Middle Berriasian deposits (Fig. 1C). Rock slabs were examined for mi- crofacies, geochemistry and cathodo- luminescence (CL), the latter using a hot stage CL (HC4-LM at Ruhr University Bochum, Germany) to evaluate the degree of preservation of the selected carbonate materials. Bulk powder sub-samples were drilled for geochemical analysis of matrix micrite (n = 380), carbonate cements (n = 61) and belemnite ros- tra (n = 16). Stable C and O isotopes and trace element analysis was performed at Ruhr University. A ThermoFinnigan MAT delta-S mass spectrometer was used for isotope analysis, following McCreaÕs (1950) method. Analytical precision (±1r), controlled by NBS19 and internal standards, was better than 0.03 and 0.05& for d 13 C and d 18 O respectively. Precision of dupli- cate runs was better than 0.01& for d 13 C and 0.05& for d 18 O. The stan- dard d-notation in per mil (&) relative to V-PDB is used. Aliquots of samples used for isoto- pic analysis were investigated for Ca, Mg, Mn, Fe and Sr elemental compo- sition using inductively coupled plas- ma-atomic emission spectrometry (ICP-AES). Analytical precision tested on replicate analysis was better than 3%. Results Optical analysis Microfacies analysis commonly re- vealed a low abundance of microf- ossils in these brown carbonates (Fig. 2E, F; Fig. 2D shows AR for comparison). The Alfabia and Son Torrelles Fms. (AR) are mainly com- posed of wackestones (occasionally packstones) showing Conoglobigerin- idae (Alfabia Fm.), radiolaria, Sac- cocoma and thin shelled bivalves. Undetermined benthic foraminifera, gastropods, bivalves, brachiopods, ammonoids and some aptychi, sponge spicules, dinoflagellate cysts, ostrac- ods and tintinids (Son Torrelles Fm.) also occur. The Aumedra´ Fm. pre- sents relatively constant microfacies, mainly mudstones, with scarce Sacco- coma, filaments and radiolarians. Occasionally, undetermined benthic ABSTRACT The notion that diagenetic imprint on ancient carbonates significantly compromises palaeoenvironmental interpreta- tions is revealed as an oversimplification. The enigmatic case at the core of this research is an extended, homogeneous, macrofossil-poor deposit showing distinctive dark brown colour and very fine grain size (Aumedra ´ Fm., Majorca Island). This markedly contrasts with standard ammonitico rosso (AR) facies known from Jurassic epioceanic swells. Geochemical analysis of matrix micrite, carbonate cements and belemnite rostra are used to interpret the Aumedra ´ carbonates. Stable (Carbon and Oxygen) isotopes and elemental abundance are compared with data from under- and overlying deposits, and coeval sections. Conspicuously higher than expected C and O isotope signature, together with strontium enrichment and a typically low iron and manganese concentrations favour a distant, shallower, probably aragonitic sedimentary supply. Modern and ancient examples of carbonate deposition are integrated with possible hydrodynamic conditions justifying transport over the studied area. A potential NE source is envisaged Terra Nova, 24, 437–445, 2012 Correspondence: Rute Coimbra, Departa- mento de Estratigrafı´ a y Paleontologı´a Facultad de Ciencias-Universidad de Grana- daAv. Fuentenueva s ⁄ n, 18071 Granada, Spain. Tel.: +34 665085651; e-mail: rcoimbra@ ugr.es Ó 2012 Blackwell Publishing Ltd 437 doi: 10.1111/j.1365-3121.2012.01082.x