Abstract: Climate plays an important role in controlling both the depositional and erosional settings. Tasmania provides spectacular outcrops where the rock record is well preserved and can be utilized to study the role of climate on sedimentation, especially, in the Late Cambrian and Early Ordovician. In this study a synthesis of field observation and mapping coupled with thin section analysis has been carried out to understand the climate control on the deposition of Late Cambrian–Early Ordovician siliciclastics which are exposed along the western and northwestern Tasmania, Australia. These siliciclastic sediments were deposited in syn-rift half grabens formed by Late Cambrian extension. The siliciclastics are mainly comprised of conglomerate, sandstone, and minor mudstone successions. Our analysis and interpretation suggest that these sediments were deposited in range of depositional settings. We have identified five broad facies that include sheet flows, braided fluvial, alluvial fans, intertidal and shallow marine environment. The stratigraphic build-ups of the study area suggest a strong influence of paleoclimate on the depositional processes. Globally, comparable sediments are different in term of depositional styles from their present day depositional analogues. This is principally due to different parameters controlling the overall depositional style, such as vegetation state, global sea level changes and climate conditions.

The Devonian batholiths of western Tasmania represent a diverse assemblage of highly fractionated intrusions (70 to 77 percent SiO 2 ) that are the products of different source materials. The Housetop batholith exhibits compositional affinities to a fluorine-rich I-type magma. The Meredith batholith also has characteristics indicative of I-type source materials. The Heemskirk batholith is composite, and consists of a volatile (F, B, H 2 O)–rich S-type granite underlying an I-type granite. The Three Hummock Island, Interview River, Sandy Cape, and Conical Rocks plutons probably have an S-type source and are grouped together as the Sandy Cape Suite. Rapakivi texture is common in the Housetop, Meredith, and Heemkirk batholiths. Quartz-tourmaline nodules are found in the Conical Rocks pluton and the S-type portion of the Heemskirk batholith. The Conical Rocks and Interview River plutons yield high initial Sr isotopic ratios of 0.74242 and 0.76009, respectively. The Housetop and Meredith batholiths yield the lowest initial Sr isotopic ratios of 0.71041 and 0.71445, respectively. The S-type portion of the Heemskirk batholith has an initial Sr isotopic ratio of 0.76387. The 40 Ar/ 39 Ar release spectrum and Rb/Sr mineral isochron analyses corroborate previously reported Devonian to Carboniferous age estimates for these batholiths. A relatively low-temperature thermal event (<200°C) caused argon loss from the K-feldspars at about 105 Ma. This heating event is probably related to the continental breakup of Australia from Antarctica. Major-element compositions of the western Tasmanian granites are very similar. The highly fractionated Sandy Cape Suite leucogranites exhibit high Ga/Al ratios typical of A-type granites, but not their extreme Zr, Y, or Ce enrichments. A distinctive feature of the Sandy Cape Suite is the increase in P 2 O 5 concentration with fractionation. The increase in P 2 O 5 with fractionation is apparently due to extremely low Ca activity, which precludes the formation of apatite, thus allowing P 2 O 5 to behave incompatibly in the melt. All of the granitoids have LREE–enriched chondrite-normalized rare earth element patterns. REE fractionation within the individual granitoids can be summarized by two trends: those with LREE >> HREE depletion (Housetop, Meredith, and Heemskirk batholiths), and those with LREE = HREE depletion (Sandy Cape Suite). The first trend is caused by the initial undersaturation of accessory mineral assemblage that resulted from high concentrations of volatiles and/or alkali complexes. The second trend is caused by early saturation of accessory phases and/or refractory accessory phases.