A Giant Arctic Continent During the Early Mesozoic: its Climatic, Eustatic, and Biotic Implications

Discovery of abundant lake ice-rafted debris (L‑IRD) coeval with dinosaurs in continental strata of the Late Triassic to middle Jurassic of northwestern China (Junggar Basin) led to reevaluation of paleolatitude for that region (1). The basin was inferred to lie north of the Arctic Circle during the Late Triassic/Early Jurassic, along with much of Northeast Asia, consistent with paleomagnetic reference frame data (2–4). Similarities in facies transitions through the Triassic and Jurassic in both the North and South China blocks, together with recent paleomagnetic interpretations, suggest amalgamation with the Siberian plate by the Late Triassic (5, 6), implying a giant Early Mesozoic Arctic continent dwarfing present-day Antarctica.

The L‑IRD shows that the southern margin of the Arctic had freezing winters despite high pCO₂, consistent with climate models (7), and the outsized Arctic continent would have had an enhanced continental climate with even colder winters. With lowlands freezing in winter in the southern Arctic, there were presumably significant mountain glaciers, perhaps even a small ice cap, as a background condition, consistent with glacioeustatic Triassic–Jurassic sea-level fluctuations (8).

The end-Triassic sea-level drop stands out in particular: a ∼10⁵‑year event on a multimillion-year rise, broadly coincident with the end-Triassic mass extinction (ETE) (9). This sea-level drop is coincident with the onset of the Central Atlantic Magmatic Province (CAMP), but modeling suggests that CAMP-related uplift would have had relatively local effects (10). An increase in glacial ice triggered by CAMP volcanic winters provides a possible mechanism (11). Perhaps enhanced via ice–albedo feedback and a consequent increase in Earth System sensitivity to polar orbital forcing, ice-sheet growth may have triggered a recently identified ~400 kyr switch in tropical orbital pacing from expected precession dominance to obliquity dominance and back (12), a temporary transition resembling the onset of the “40 kyr world” at the mid-Miocene transition, plausibly caused by growth of the Antarctic Ice Sheet to near-modern size (13).

This giant Arctic continent may have primed the Earth System to switch from a hothouse to a transient icehouse world during CAMP volcanic winters, causing an abrupt sea-level drop. The same cold perturbations may also have driven the extinction of all large non-insulated land animals, paving the way for dinosaur ecological dominance, as these insulated reptiles were already living in the freezing Arctic beforehand.

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