Low-grade metamorphosed Cretaceous sedimentary records of forearc basin systems in the eastern part of the Transhimalaya (Gangdese) arc system have not been reported yet, impairing understanding of the Mesozoic-Cenozoic convergent margin processes along the southern margin of Asia. This study incorporates observations from petrography, stratigraphy, sedimentology, and analyses of detrital-zircon geochronology and bulk-rock Sr-Nd isotope for a series of low-grade metamorphosed sedimentary rocks referred to as the Lilong succession in the eastern Yarlung Zangbo suture zone, east of Langxian, in southeastern Tibet, China. Field observations reveal that this unit has three different lithological associations (I, II, and III) including gravel-coarse sandy inner-middle submarine fan facies, sandy-muddy middle-outer submarine fan facies, and silty-muddy outer submarine fan and/or deep sea plain facies moving higher in the succession. Detrital-zircon geochronology indicates a maximum depositional age of ~110 Ma and the absence of younger zircons that are dominant in the Gangdese batholith north of the basin suggests the minimum depositional age ~ 85 Ma, comprising an interval of the Albian-Santonian age. Volcanic and granitic clasts in sandstones/conglomerates, εNd(0) values (−0.09 and 4.6) and 87Sr/86Sr ratios (0.704105–0.704770) of slates, and detrital zircon age spectra (mainly 100–140 Ma) demonstrate provenance from the central-northern and southern Lhasa Terrane. In addition, there is evidence for recycling of cherty beds of the Chongdui Formation. Similarities between provenance, lithofacies, and tectonic setting lead us to interpret that the newly identified remnant unit correlates to the Ngamring Formation in the Xigaze forearc basin. When taking into account the lower Bomi Group and Nyingchi complex, we propose that the Lilong succession and the metamorphosed composite in the eastern Himalayan syntaxis are counterpart remnants of the eastern Xigaze forearc basin system, which are different from the two forearc basin systems in the western Himalaya. •The Albian-Santonian Lilong succession identified near the E Himalaya syntaxis•The Lilong succession deposited in a submarine fan system•The Lilong succession developed in a forearc basin with sources of Lhasa Terrane•Forearc basin system in central and E Himalaya differs from that in W Himalaya