3. Incidence of Failure Discussed by Type of Depositional Site

In this section, sites are presented by type of archive. In the next section, mechanisms are proposed that may account for the sterility.

Compiled failures comprise 221 sites, which are here organised by depositional/sedimentary types, and information is given about their location, magnitude of the sterility (all samples versus only particular levels/samples), age or presumed chronology, and the name and affiliation of the pollen-analyst/s (Tables 1-7, Fig. 1 and Fig. 2). Open-air archaeological sites (27.2%), caves (22%) and rockshelters (11.6%) represent a majority of the failed case studies (Fig. 2). The proportion of non-saline (10.8%) and saline lacustrine systems (including lagoons, salt pans, playa lakes, salt marshes, and salt lakes) (9.5%) is higher than peat bogs (4.7%). Coprolites (6%) were sterile either individually, or collectively by site (Table 7). Our files also include a few cases with open-air palaeontological sites (2.6%), fluvial terraces (0.9%), slope deposits (2.2%), moraine deposits (0.4%), palaeosols (1.3%), and exposed travertines (0.9%) (Fig. 2, Table 6). Chronologically, 50% of the failed sites are Holocene, 30.6% Upper Pleistocene, 10.8% Lower Pleistocene, and 3.9% Middle Pleistocene. These percentages are likely to be related to the availability of deposits by age. Sites of unknown age average 4.7% of the reported total (Fig. 2).

Complete sterility notoriously affects open-air palaeontological sites (67%), and is also relatively high in coprolites (57%), slope deposits (60%), rockshelters (55%), open-air archaeological sites (41%), caves (37%), and non-saline lakes (36%), mostly in cases of palaeolakes (Table 1). Complete sterility is only 9% in peat bogs (Table 1). The few samples of travertines and moraine deposits reported a total absence of pollen. Complete sterility averaged 19% of conventional (lacustrine and peaty) pollen sites. In contrast, it averaged 50% in archaeological sites, including caves, rockshelters, and open-air archaeological or palaeontological excavation sites. Thus, the potential of success at re-studying failed sites is clearly higher in the open-air group.

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