In a 1923 monograph on Lateglacial varve chronology in Scania, geologist Gerard De Geer’s assistant Ebba Hult De Geer investigated the deposition rates of varved clays to correlate teleconnections across Scandinavian basins. While previous chronologies relied exclusively on visual countings of summer-silt and winter-clay couplets, Hult De Geer incorporated microfossil pollen analysis of *Pinus* and *Betula* grains preserved within the clay layers. She noted that although winter layers consistently exhibited higher fine-particle density than summer layers, the ratio of arboreal to non-arboreal pollen remained unchanged across seasonal laminations within individual annual varves, provided the sediment matrix had not undergone post-depositional bioturbation. However, in varves where cryoturbation had disrupted the primary stratification, non-arboreal pollen predominated exclusively along the deformed upper boundaries. Contrary to contemporary assumptions that pollen assemblage variations reflected immediate microclimatic oscillations, Hult De Geer demonstrated that these anomalies resulted from selective sorting during frost-heaving events rather than shifts in surrounding vegetation density.
According to the passage, Hult De Geer's research established which of the following explicit facts about the ratio of arboreal to non-arboreal pollen in varved clays?
- It remained constant between seasonal laminations within a single annual varve, assuming post-depositional bioturbation had not occurred.Answer
- BIt shifted continuously in response to short-term microclimatic oscillations occurring between summer and winter deposition periods.
- CIt was consistently higher in summer-silt couplets than in winter-clay couplets across all non-bioturbated Scandinavian basins.
- DIt served as the sole quantitative metric used by Gerard De Geer to establish regional teleconnections prior to 1923.
- EIt correlated directly with the fine-particle density of winter-clay layers in varves affected by cryoturbation.