Integrated provenance and tectonic implications of the Cretaceous-Palaeocene clastic sequence, Changla Gali, Lesser Himalaya, Pakistan

This study documented the field relationship and integrated provenance of a clastic sequence exposed at the Mesozoic-Cenozoic boundary located in Changla Gali section, Lesser Himalaya, Pakistan, to provide an insight into Cretaceous tectonics of the northern Indian margin. This boundary sequence is represented by the Early Palaeocene Hangu Formation, which consists of shales in the lower part and sandstone in the upper part. The contact relationship of the Early Palaeocene Hangu Formation with the underlying Late Cretaceous Kawagarh Formation is marked by an angular unconformity. The detrital zircons extracted from the shale and sandstone samples shows a major age cluster, which varies between similar to 700 and similar to 1,100 Ma (45%), similar to 1,600 and similar to 1,900 Ma (15%), and similar to 480 and similar to 590 Ma. Additionally, two minor age clusters of the detrital zircons are identified, that is, similar to 2,300-2,500 Ma and similar to 600-700 Ma. The younger detrital zircon grains have ages of 298 +/- 4 Ma, 297 +/- 4 Ma and 116 +/- 3 Ma. This age pattern reflect the major source area as the Indian Plate. The two younger Permian zircon grains may be derived from the Panjal mafic volcanic rocks exposed in the vicinity of the study area. However, a single Cretaceous grain may be attributed to ophiolites, as well as Tethyan Himalayan (TH) volcanic rocks. Similarly, the sandstone petrographic results show that the sandstones are quartz-rich, which show derivation from the craton interior provenance, which is likely the Indian Plate. However, the trace element data suggest a mixed source consisting of felsic and mafic rocks. The contribution of the mafic source is likely associated with the Panjal mafic rocks exposed along the northern Indian margin. The field relationship shows that the underlying Mesozoic sequence is folded prior to the deposition of the Hangu Formation. This folding suggests that the northern Indian margin experienced a regional compression during the Late Cretaceous time, which folded the Mesozoic sequence before the resumption of sedimentation during the Palaeocene. Furthermore, the detrital zircon provenance suggests that the sediments were mainly derived from the Indian Plate. Combining the results, it can be concluded that the compressional event is likely associated with the Late Cretaceous ophiolite obduction onto the leading edge of the Indian Plate. However, the absence of the major ophiolitic age component in the detrital record may suggest that the ophiolites were emplaced over the northern Indian margin but remained submerged during Early Palaeocene time.

Automated summary

This study investigates the provenance and tectonics of a clastic sequence at the Mesozoic-Cenozoic boundary in the Lesser Himalaya, Pakistan. The findings suggest that the sediments mainly originated from the Indian Plate, with potential contributions from Panjal mafic rocks and ophiolites in the region. The study also indicates regional compression during the Late Cretaceous, with evidence of folding in the underlying Mesozoic sequence before the Palaeocene deposition.