Abstract
AbstractThe Tajik basin archives the orogenic evolution of the Pamir hinterland. Stratigraphic‐sedimentologic observations from Cretaceous‐Pliocene strata along its eastern margin describe the depositional environment and basin‐formation stages in reaction to hinterland exhumation and basin inversion. During the Late Cretaceous‐Eocene (preorogenic stage: ~100–34 Ma), a shallow‐marine to terrestrial basin extended throughout Central Asia. An alluvial plain with influx of conglomerate bodies (Baljuvon Formation) indicates a first pulse of hinterland erosion and foreland‐basin formation in the late Oligocene‐early Miocene (synorogenic stage Ia: ~34–23 Ma). Further hinterland exhumation deposited massive alluvial conglomerates (Khingou Formation) in the early‐middle Miocene (synorogenic stage Ib: ~23–15 Ma). Westward thickening growth strata suggest transformation of the Tajik basin into the Tajik fold‐thrust belt in the middle‐late Miocene (synorogenic stage IIa: ~15–5 Ma). Increased water supply led to the formation of fluvial mega‐fans (Tavildara Formation). Latest Miocene‐Pliocene shortening constructed basin morphology that blocked sediment bypass into the central basin from the east (Karanak Formation), triggering drainage‐system reorganization from transverse to longitudinal sediment transport (synorogenic stage IIb: < ~5 Ma). Accelerated shortening (~27–20 Ma) and foreland‐directed collapse (~23–12 Ma) of Pamir‐plateau crust loaded the foreland and induced synorogenic stages Ia and Ib. Coupling of Indian and Asian cratonic lithospheres and onset of northward and westward delamination/rollback of Asian lithosphere (i.e., lithosphere of the Tajik basin) beneath the Pamir at ~12–11 Ma transformed the Tajik basin into the Tajik fold‐thrust belt (synorogenic stage IIa). The timing of the sedimentologically derived basin reconfiguration matches the thermochronologically derived onset of Tajik‐basin inversion at ~12 Ma.
Highlights
Retro‐foreland Tajik Basin and Possible Foreland‐Hinterland CouplingSedimentologic processes along the margins of continental foreland basins record the progradation of shortening and exhumation in the orogenic hinterland (e.g., DeCelles & Giles, 1996)
The investigated preorogenic stage spans the succession from the Late Cretaceous to the top of the late Eocene Sumsar Fm
An initial stage of synorogenic foreland‐basin formation commenced in the Oligocene Baljuvon Fm; the foreland basin was fully established in the early Miocene Khingou Fm
Summary
Retro‐foreland Tajik Basin and Possible Foreland‐Hinterland CouplingSedimentologic processes along the margins of continental foreland basins record the progradation of shortening and exhumation in the orogenic hinterland (e.g., DeCelles & Giles, 1996). Retro‐foreland Tajik Basin and Possible Foreland‐Hinterland Coupling. The foreland basins fringing the Pamir‐Tibet orogen have served as archives for tracing the India‐Asia collision from its onset at ~50 Ma to Present (e.g., Allen et al, 1991; Bande et al, 2015; DeCelles et al, 1998; Einsele, 1996; Najman et al, 2009; Wang et al, 2013; Xiao et al, 2012; Zheng et al, 2006). One underexplored archive is the Tajik basin in the Afghan‐Tajik depression west of the Pamir salient (Figures 1a to 1c). In particular on the synorogenic foreland‐basin strata, will―together with studies in the hinterland―enable an understanding of the coupling between the evolution of this retro‐foreland basin and its orogenic hinterland—the Pamir
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