An extremely small but significant exposure of possibly Precambrian or Pre-Deccan Mesozoic plutonic rocks spanning 200 $\times$ 90 m in size with 15 m elevation, remotely located amidst vast salt flats of the Great Rann of Kachchh received attention when it was first reported by Biswas in 1968; however, systematic petrological and petrographical studies remained undone. Therefore, in the present study, we addressed complete geological accounts to establish its possible origin. Our detailed geological study indicates that the complex is made up of nepheline and aegirine bearing alkali feldspar syenite with numerous fine-to-medium grained felsic dykes. It lays two viewpoints: (1) it has affinity with Trans Aravalli Belt anorogenic felsic magmatism, i.e., Precambrian and (2) it is genetically related to the pre-Deccan Mesozoic plutonic intrusives like Nir Wandh in Pachham Island and Mundwara and Sarnu–Dandali complexes in Rajasthan. The nearest felsic magmatic suite is an exposure of gray and pink granites of Nagar Parkar of Neoproterozoic age. Presence of undersaturated minerals and xenoliths of diorites within syenite parent body may suggest partial melting of lower crust probably during Rodinia supercontinent rifting. However, presence of alkali-rich minerals, alkali feldspars, kaersutite, aegirine, apatite and rutile needles and the complex being part of the Kachchh rift basin suggests its genetic resemblance with Pre-Deccan Mesozoic plutonic events. The radiometric age will confirm the age of this plutonic massif.

$\bf{Highlights}$

Based on the field geological and petrographical studies of Meruda Takkar syenitic complex, two viewpoints have been raised:

$\bullet$ The alkali feldspar syenite complex of Meruda has close affinity with the anorogenic felsic igneous suites contemporaneous with Malani Igneous Suite and slightly younger than post-Delhi Erinpura granites, i.e., Neoproterozoic intraplate magmatism chronologically equivalent to the splitting of Rodinia supercontinent,

$\bullet$ The alkali feldspar syenites of Meruda Takkar have genetic and mineralogical resemblance with the pre-Deccan trap Mesozoic plutonic activities allied to what is prevailing at alkaline complexes of Mundwara and Sarnu–Dandali and in the northern Island belt alkaline intrusives of Nir Wandh, Kuran, Kaladungar and Sadhara sills and dykes.

Radiometric age determination and geochemical analysis of the Meruda syenite are needed to establish its age and origin.

The present study summarizes the existing chronometric data of fossil dunes preserved in the southern Thar Desert margin (STM). The objective is to understand the episodes of dune accretion and causes of their spatial and temporal variability along the precipitation gradient. Based on the published ages, the study identifies three major phases of dune accretion. The oldest phase-I is dated between ${\sim}$ 25 and 17 ka (MIS-2); the second short-lived phase-II between ${\sim}$ 15 and 12 ka, whereas the phase-III occurred between 10 and 5 ka. The second phase terminates with the deposition of fluvially reworked aeolian sand which has the presence of microlithic artifacts and corresponds to the early Holocene strengthened Indian Summer Monsoon (ISM). The study suggests that during phase-I and II, the terrain witnessed a significant reduction in the ISM for which a more southerly position of the Inter-Tropical Convergence Zone (ITCZ) is implicated. During phase-III, an oscillating ISM with overall declining trend is attributed to mid-late Holocene minor fluctuations in the ITCZ (probably proximal to modern summer position). A conspicuous absence of dune building in the northern Thar Desert during the Last Glacial Maximum (LGM) is ascribed to the prevalence of hyper-arid conditions in comparison to the relatively moist conditions in the STM due to its proximity to the Arabian Sea. After ${\sim}$ 15 ka, both the STM and the Thar Desert show a broad synchroneity and that coincides with the gradual strengthening of the ISM.