Late Ordovician Arabian ice stream: The largest known terrestrial ice stream

Abstract:

Mega-streamlined landforms (MSL) can be attributed to multiple erosional processes. Identifying the forces that shape these landforms could advance our understanding of the earth’s paleoclimate, constrain ice sheet reconstructions, and assist in interpreting extraterrestrial analogues. Field and satellite-based observations support a Late Ordovician glacial origin for streamlined landforms in NW Arabia, previously interpreted as aeolian yardangs and argue against an aeolian origin: (1) the distribution of the MSL is confined to the preglacial rock units and is absent in postglacial units; (2) the morphometric parameters of the MSL are similar to those reported for recent subglacial environments; (3) there is a spatial correlation between the distribution of the MSL and the distribution of reported glacial deposits and tunnel valleys; and (4) the elongation direction of the MSL is orthogonal to the wind direction in the southern part of the study area. The presence of highly attenuated landforms (elongation ratio 10 to >100) suggests that the mega-streamlined glacial features were formed by an ice stream, hereafter referred to as the Arabian Ice Stream (AIS). This suggestion is supported by the following observations that were extracted from the paleo-geomorphological reconstructions: (1) topographic focusing by a high topographic obstacle (>2000m) of the Arabian Shield that impeded the ice advancement south of the AIS; (2) subglacial meltwater routing as indicated by the presence of tunnel valleys along the extension of the AIS; (3) presence of calving margins that are inferred from the reported glaciomarine deposits to the east of the AIS (present day location in W. Iran), which indicates ice advance over the continental shelf for hundreds of kilometers. These lines of evidence suggest that these glacial features are a part of a marine-terminating ice stream (~2000 km continental extent and up to 400 km on the continental shelf). During the LGM, the longest ice stream extended between ~ 1000 to 1300 km (i.e. approximately half the length of the reported AIS). If we were to adopt sedimentary flux estimates from recent ice streams (1000 to 8000 m³ a^-1 per meter of ice stream width), the flux from AIS would range from 0.2 to 2 km³/yr and 2 x10⁵ to 2x10⁶ km³ if the AIS lasted for a million years.