Geochemical constraints on the depositional environment of Upper Devonian radiolarian cherts from Loei, north-eastern Thailand

Abstract

Late Devonian radiolarian chert sequences in the Indochina block of north-eastern Thailand are exposed in a narrow belt located to the east of Loei province. The analyzed radiolarian cherts were collected from Chiang Klom, Sumnoi and Pha Samyod localities. They are characterized by high silica content ( > 90 wt.%), high aluminum content and low iron content (Al 2 O 3 /(Al 2 O 3 + Fe 2 O 3 ): geomeans 0.91, 0.88 and 0.92). The Al/(Al + Fe + Mn) values are high in both cherts and interbedded shales (geomean 0.89). High Si/(Si + Al + Fe) ratios are observed in cherts (geomean 0.97) and slightly low in shales (geomean 0.69), whereas Fe 2 O 3 /TiO 2 values are low (geomean 5.91). For rare earth element (REE) analysis, the cherts exhibit low La abundances (geomean 4.31, 3.59 and 4.22), slightly negative Ce anomalies (Ce/Ce*: geomean 0.81, 0.76 and 0.93), intermediate ratios of North American Shale Composite (NASC) normalized La n /Ce n (geomean 1.33, 1.37 and 1.12) and intermediate La n /Yb n values (0.79, 0.94 and 1.22). In the interbedded shales, REE characteristics are more or less equal to the cherts.The results indicate that these late Devonian radiolarian cherts were deposited in a continental margin environment. High Si/(Si + Al + Fe) values indicate a biogenic origin of the cherts, however, additional silica content in the cherts could be the result of diagenetic alteration. Intermediate positive Eu anomalies (Eu/Eu*: geomean 1.32, 1.25 and 1.44) are interpreted as the result of detrital feldspar contribution corresponding to the distinctive low content of Fe. Geological evidences from the field support volcanic activities during the Late Devonian-Early Carboniferous.Weathered materials and fragments of basalts and andesites would possibly be supplied to the basin during chert sedimentation. These geochemical constraints indicate that, in western portion of Indochina, deep marine basin was closed before Late Devonian which was followed by the incursion of Early Carboniferous orogeny.

Palaeoenvironmental implications of geochemistry and radiolarians from Upper Devonian chert/shale sequences of the Truong Son fold belt, Laos

“…Plot of NASC‐normalized Ce/Ce* against Eu/Eu* of the Upper Devonian chert/siliceous shale sequences in this study (VR, PS) and those reported from South China (SW, BSI and FSI) (Chen et al ., ), NE Thailand (CK, SN and PSY) (Udchachon et al ., ) and N Thailand (CD) (Hara et al ., ).…”

“…The result suggests that most of our samples from Vilabouly show close Ce/Ce* values to those from South China which are interpreted as open–marine conditions. However, they differ in Eu/Eu* values, as South China has high positive Eu anomalies interpreted as hydrothermal and channelled through deep–seated faults (Chen et al ., ), while most of the samples from Ban Phonxai show close Ce/Ce* values to those from N and NE Thailand which are interpreted as oceanic and continental margin environments, respectively (see Hara et al ., ; Udchachon et al ., ). It was suggested that high positive Eu anomaly in cherts and shales from NE Thailand involves weathered feldspar contribution from the contemporaneous volcanisms (Udchachon et al ., ).…”

“…These major elements have been used successfully, together with trace elements and REEs in order to elucidate the origin of cherts (e.g. Kumimaru et al, 1998;Halamić et al, 2001;Kato et al, 2002;Zhu et al, 2006;Chen et al, 2006;Thassanapak et al, 2011;Udchachon et al, 2011). Differences in REE compositions in cherts and shales are generally related to proximity to continental and spreading ridge influences (Murray, 1994).…”

Geochemical characteristics of siliceous rocks of Wufeng Formation in the Late Ordovician, South China: Assessing provenance, depositional environment, and formation model

“…Although siliceous rock may have a uniform texture and a relatively simple mineral composition, the geochemical studies of siliceous rocks have been widely applied to determine their origins, depositional environments, palaeogeographical variations, palaeo‐upwelling zones, primary productivity areas, and sediment provenance indicators (Chen, Qing, Yan, & Li, ; Eker, Sipahi, & Kaygusuz, ; Garbán et al, ; Halamić, Marchig, & Goričan, ; Igor & Kemkina, 2015; Kato, Nakao, & Isozaki, ; Murray, ; Muttoni & Kent, ; Owen, Armstrong, & Floyd, ; Ragueneau et al, ; Ran et al, ; Udchachon, Thassanapak, Feng, & Chonglakmani, ; Yu, Dong, Widom, Chen, & Lin, ). At present, there are many theories about the formation mechanism of the Wufeng siliceous rock.…”

Geochemical Speciation and Batch Mode Simulation in the Carbonate Depositional Environments

“…The first simulations were initially studied for understanding the chemical reactions in aquatic environments in order to solve water pollution hazards. These simulations also assessed the diagenetic processes such as natural formation and alteration of rocks (Lai et al, 2018;Limarino et al, 2017;Crémière et al, 2016;Klunk et al, 2015;Udchachon et al, 2011). It is impossible to reproduce the exact behavior of most geochemical systems in the laboratory due to the complexity and diversity in time scale of the reactions in geological environments (Klunk et al, 2018).…”