Sedimentary recycling, provenance and paleoweathering from chemistry and mineralogy of Mesozoic continental redbed mudrocks, Peloritani mountains, southern Italy

Abstract

The Triassic to Lowermost Jurassic mudrocks from continental redbeds of the Longi-Taormina Unit (Calabria-Peloritani Arc; southern Italy) have been mineralogically, chemically and petrographically analyzed, in order to reveal their complex history, which record an important phase of the geological evolution of the Mediterranean area.The Late Triassic corresponds with a low first-order sea level stand and a time of high continental emergence whereas the Early Jurassic was the time of the initiation of the first-order sea level rise in the mid-Mesozoic, generally marked by a transgressive trend.The mineralogical assemblage, dominated by the occurrence of illite and illite/smectite mixed layers, coupled to the CIA index and to the A-CN-K plot, indicates post-depositional K-enrichments.Palaeoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that they likely record a recycling effect from their metasedimentary basement rocks. A recycling effect is also suggested by the distribution of Al 2 O 3 , TiO 2 , and Zr. In the Zr/Sc vs. the Th/Sc plot the redbeds are not clustered along the primary compositional trend but fall along a trend involving zircon addition and thus sediment recycling. Recycling could significantly affect the weathering indices which likely monitor a cumulative effect including a first cycle of weathering at the source rocks. Weathering occurred under hot, episodically humid climate with a prolonged dry season. Wet-humid conditions favored the formation of stream channels that eroded the soil profiles, whereas the dry season promoted the sedimentation. The climate alternation in the Early Jurassic favored recycling.An additional provenance terrane occurring in the basement, including metavolcanic rocks having mafic composition cannot be excluded, since the Eu anomaly is slightly higher than the PAAS value. Although the effects of recycling on REE distribution are uncertain, the Eu/Eu* should increase, as more feldspar is destroyed during weathering and diagenesis. This involves that the Eu/Eu* ratio could monitor a supply of low Eu/Eu* mafic detritus which compensate for the recycling effect by reducing Eu/Eu*. Eu released during the dissolution of feldspar could be retained by clay minerals contributing to minimize the recycling induced increase of the Eu-anomaly. This may involve that the recycling effect on the Euanomaly was minor and that the low Eu/Eu* mafic detritus supply was also minor. The subordinate importance of a mafic supply is confirmed also by other provenance proxies including the La-Th-Sc plot and the Cr/V and Y/Ni ratios.The proportions of illitic layers in I/S mixed layers coupled with the illite crystallinity values, expressed as Kübler Index (KI), suggesting an estimated temperature experienced by the Longi Units in the range of 100-150°C. Starting from this range the diagenetic/tectonic evolution should correspond to a lithostatic/tectonic loading of about 4-5 km.

Latest Triassic climate humidification and kaolinite formation (Western Carpathians, Tatric Unit of the Tatra Mts)

“…This could be sup ported also by the sam ple set po si tion in Fig ure 16D, E. Th/Sc vs. Zr/Sc di a gram ( Fig. 16D; Mongelli et al, 2006) shows two sets and sug gest Zr (prob a ble as zir con) ac cu mu la tion in grav ity sorted quartz sand-frac tion. A fresh water event at the be gin ning of the ma rine trans gres sion is in dicated by lithological data and by sta ble iso topes (Figs.…”

“…Ti and Al can be used as prox ies of rel a tive chem i cal and me chan i cal weath er ing in ten sity of source rocks in mudstones and car bon ate se quences Mongelli et al, 2006). Ti is fractioned in Ti-ox ides (iden ti fied in XRD pat tern) and clays as in di cated by low but var ied Ti/Al val ues in the mudstones (Ta ble 4).…”

“…The chem i cal com po si tion of the de pos its has been af fected by me chan i cal sort ing and re cy cling (Cullers, 2000;Mongelli et al, 2006;Vïaèný et al, 2013). Be sides vary ing Ti-HFSE dis tribu tions, raised Zr con tent and near-chondrite val ues of Zr/Hf ratio (34-40) in all sam ples (Ta ble 4) in di cate zir con oc cur rence or me chan i cal sort ing in the se quence, re spec tively.…”

“…The in ten sity of weath er ing, the com po si tion of the par ent rocks and the sed i ment prov e nance of the ma te rial can be in dicated by means of chem i cal anal y sis, par tic u larly by ra tios of ma jor el e ments and by trace el e ment dis tri bu tion (Murray et al, 1992;Cullers, 2000;Price and Velbel, 2003;Mongelli et al, 2006;Prochnow et al, 2006;Ohta and Arai, 2007;Shel don and Ta bor, 2009;Galbarczyk-G¹siorowska, 2010). The spe cific distri bu tion of REE known from ter res trial de pos its and palaeosols may act as an an other in di ca tor of cli mate as well as of sed i mentary con di tions (e.g., Nesbit et al, 1990;Condie,1993;Hannigan and Sholkovitz, 2001;Haley et al, 2004;Shields and Webb, 2004;Ounis et al, 2008).…”

Discovery and significance of Quaternary aqueously deposited aeolian sandstones in the Sanhu area, Qaidam Basin, China

“…Dish-shaped and disciform pits with both regular and arcuate edges formed in highly rounded particles indicate high-intensity wind. These pits range 10-30 lm in depth in particles 100 lm in diameter (Mongelli et al 2006;Abdullah and Eswaran 2014;Refaat and Hamdan 2015). Conchoidal fracture of quartz grains is interpreted as evidence of glacial deposition (Mahaney et al 2001;Cowan et al 2008;Deane 2010).…”