The digital reconstruction of original spit units enabled us to calculate and assign the volumetric value to each layer. This was a crucial point to let us to generate maps of finds frequency and density, based on the different categories of archeological objects described in the final excavation report and associated to the various parcels and units visualized in the original profile drawing. The 3D maps produced were respectively, a map of pottery, harp seal bones, and bone harpoons (Fig. 6).
A review of the results indicate an overall trend of diminishing pottery density towards the lower levels of the Stora Förvar cave sequence—despite occasional peaks of increased density in parcels such as D, E, and F (Fig. 7, Diagrams 2, 3, and 4). Over time however, the levels of pottery density eventually decrease with some of the spit units reaching as low levels as 0.8 to 0.1 fragments per unit of volume (m3). Acting as a deviation to this trend is parcel A (Fig. 7, Diagram 1). According to the original publication from the 1940s, parcel A and B came about as a result of the same parcel being excavated at two separate occasions, and thus it was also divided accordingly. Unfortunately, as it is rather difficult to understand from the original publication as to how this divide was carried out spatially, the strategy was to treat parcel A and B with its artefactual assemblage as one single 3D-reconstructed unit. As such, the results from the density analysis are not entirely reliable as most of the bottom spit units were neglected for analysis, but also because of the necessity to bundle together a majority of the spit units that were labeled A.1-A.4 and A.5-A.6 to name but a few. Another deviant development also occurs in parcel F. The densities of pottery display a somewhat chaotic sequence in which there are two valleys of increase in pottery density throughout the parcel (Fig. 7, Diagram 4). However, what is interesting is the sudden increase that occurs between spit units F.10 and F.13. Ever since spit unit F.4, parcel F had seen a gradual decrease in pottery density that went from almost six fragments per each unit of volume to its very lowest at just half a fragment. However, all of a sudden, the density increases once again. This rather irregular pattern might very well be explained by the notion that parcel F was excavated at two occasions, in which the excavators dug halfway down into the sequence in parcel F after which excavation of the first couple of spit units in neighboring parcel G began. It is in this specific event that the authors recall how masses of soil had been thrown down from the top of parcel G into the previously excavated parcel F (Schnittger and Rydh 1940, p. 45) and it is thus very likely that this sudden increase is a result of excavators having trampled any pottery remain further down into the parcel causing an accidental intrusion of some of the lower levels. To add support to this hypothesis, one only needs to review the development in the neighboring parcel G. Reviewing the parcel in reverse order, up until spit unit G.8, there is no occurrence of pottery. After spit unit G.8, the density of pottery peaks briefly with a dramatic increase, whereas towards to top it resumes its diminish (Fig. 7, Diagram 5). More importantly, results published by Lindqvist and Possnert (1999) introduced the presence of Early to Late Mesolithic remains within this sequence. Thus, if the neighboring bottom spit units of parcel F were to be contemporary with that of the bottom spit units of parcel G, then the density of pottery should either be very low, or absent altogether as pottery makes its introduction into the Baltic region in the Late Mesolithic (Hallgren 2004, p. 123; Glykou 2014, p. 24).
Parcel H displays an overall low density of pottery per spit unit with layer H.3 amounting to marginally more than a pottery fragment per unit of volume contributing to the general trend of low densities of pottery towards the bottom (Fig. 7, Diagram 6). It should be mentioned once again however that bundled spit units have been neglected, and thus any analysis of spit units “H.4-H.5” has yet to be performed. The final parcel at the very end of the cave is parcel I. Providing us with only three spit units, the pattern is still consistent with previous parcels in which the amount of pottery fragments per unit of volume decreases towards the bottom of the sequence (Fig. 7, Diagram 7).
By using indices of varying pottery densities and results from the osteological analysis (Fig. 8), we argue that additional spit units of the Stora Förvar cave sequence may be added to the Early Mesolithic component for further investigation such as radiometric dating and artefactual studies. This inference is built on the idea of groups of hunter-gatherers that either use, or do not use, ceramic technology. For the Early Mesolithic portion, the density of pottery is at a significantly low level that it may very well be ascribed to pioneering groups that precede the Kongemose and Ertebølle cultures. As of yet however, any further analysis as to the cultural affinities of the pottery at Stora Förvar has been made, and so a possibility could be that there is a presence of Ertebølle pottery (or later) in the lowest of levels. Although, this would not be consistent with the numerous AMS-dates from some of the lowest levels of parcel G (Lindqvist and Possnert 1999: Table 2), and thus lends further strength to the idea of intrusion caused by a systematic and arbitrary method of excavation.
The osteological analyses of faunal remains have provided additional clues to the relative chronology of the finds from the cave. Early on, the analyses of Adolf Pira (1926) showed that the occurrence of seal species varied in different layers. Bones from Gray seal (Halichoerus grypus) and ringed seal (Phoca hispida) were most common in the bottom layers of the cave while harp seal (Phoca groenlandica) appeared higher up in the stratigraphy (e.g., G7 and H7), from approximately 1.2 m above the bedrock (Fig. 8).
We now know that the oldest layers of the cave date to approximately 9200 cal BP, i.e., the Mesolithic. The oldest use of the cave spans a period of around 1000 years after which there is a hiatus in the stratigraphy when the cave apparently was more or less abandoned between approximately 8200 cal BP to around 6000 cal BP (Apel and Storå 2017a; Apel et al. 2017; Lindqvist and Possnert 1997, 1999).
For the present study, the presence of bones of harp seal may be used as an important chronological indicator together with the pottery. Pira (1929) identified bones of harp seal in the sections and layers I4, G4, I5, G5, B6, H7, and G7 (Fig. 8). A later analysis has confirmed the presence in these layers and added finds in F9 and E7 (Apel and Storå 2017a).
The deepest—and chronologically oldest—occurrences of the harp seal bones roughly coincide with the appearance of a large number of bone harpoons and also fish hooks. Bones of domesticated animals became more common and even more common than seal bones in the uppermost layers which date the Iron Age and Historical period (Ibid.). However, there are some finds of sheep and other domestic animals as deep as G8. The harp seal entered the Baltic basin around 6000 BP cal, i.e., around the time when the hiatus in the cave ends (Bennike et al. 2008; Storå and Ericson 2004).
The identifications of harp seal bones show that the layers associated with the oldest Mesolithic phase were up to 1- to 1.2-m thick at the entrance of the cave, in sections A, D, E, and F but thinner in sections G, H, and I. At the far end of the cave in section I, harp seal bones appear already at c.30 cm above the cave floor.
The estimations of the volume of the layers in each section provide a possibility to evaluate the Mesolithic depositional patterns of bones and, thus, the use of the cave, both horizontally and vertically (Figs. 9 and 11). It has so far been very difficult to investigate the horizontal use of the different parts of the cave.
We here consider the sections inside of the cave and those that date to the Mesolithic. The small amounts of bone finds in section D may be a result of recovery bias. There are some noteworthy differences in the density of bone finds in different layers and sections (Fig. 10). In section D, the lowest layer 12 contained smaller amounts of bone finds than layer 11, after which, the find density decreases higher up in the stratigraphy. A similar pattern may be seen in sections E and F, although the deposits with higher amounts of finds are thicker in section F. This could reflect a difference in soil cover in the front end of the cave and at the end of the cave. Thus, the bones could have been deposited on an existing soil cover at the entrance of the cave. Section G and also H and I exhibit the highest densities of finds in the layers immediately on top of the bedrock (floor).
Considerably, larger amounts of finds were deposited in the Mesolithic layers in sections G and F compared to sections D and E. Possibly, the areas at the entrance of the cave, which actually had large floor areas, were kept cleaner from refuse of the seals. There is a marked difference in the floor areas between the layers and sections.
Thus, the absolute amounts of bone finds are highest in the central part of the cave, but the density of bone finds is actually higher at the end of the cave, and lowest at the entrance. Indeed, we discern a Mesolithic depositional pattern to deposit the refuse after the hunted seals. Noteworthy in the comparison is also the drop in density of finds in layers 8 in sections F and G. These layers probably belong to the end of the Mesolithic, at the time of the hiatus in the occupation. It seems that the intensity of deposition, as seen in smaller mean amounts of bone per m3, decreased through time, possibly in the period prior to the abandonment of the cave. This change in depositional patterns is also associated to changes in seal hunting patterns (Apel and Storå 2017a, b).
To summarize, some elements are particularly worth of attention as they provide information in terms of relative and absolute chronology, useful to trace and define certain spatial boundaries. In particular:
Density values of pottery and faunal remains act as chronological indicators to define the temporal boundaries of the Mesolithic phase of inhabitation of the cave. Most importantly, they provide a terminus that here can be marked to spatially define the volume of the sequence characterized by Mesolithic and post-Mesolithic events. In this respect, the presence of harp seal, which entered the Baltic basin around 6000 Cal BP, is another good chronological indicator to be considered.
More traces indicate the uppermost boundary of the Mesolithic portion of the sequence and they can be observed in a historical picture of the profile of section G which is recognizable by the dark color of the soil matrix. The possibility of georeferencing the picture let us to put in connection the visible hiatus in turn with the volumetric model of parcel G, the digitized hand-made profile drawing and the 3D model of the cave (Fig. 11).
In terms of absolute chronology, further indication about the spatial pattern related to the Mesolithic phases of the cave is provided by the c14-dated faunal remains from wall concretions, which have been georeferenced and put in spatial connection with the above-mentioned datasets (Fig. 9).