**4. Variability of Petrographic Composition**

The petrographic composition of morainic structures making up the cliff shore and the shallow foreshore is dominated by fragments of crystalline rocks (about 40–50%), limestone gravels (30–50%) and sandstones with dolomites (10–15%). The remaining gravels contribute less than 10% [59,72–74]. The gravels occurring on the beach eroded from morainic deposits and were rapidly sorted in both petrographic composition and shape. The contribution of mechanically resistant components (mainly crystalline-rock gravels) increases and contents of less resistant gravels (shales, sandstones, limestones) decrease with distance from the source of the initial material.

Table 1 summarizes contributions of initial gravels originating in morainic tills, which make up the cliffs and the gravels collected on the beach. The percentages of beach gravels are shown in relation to the total gravel weight and to the number of gravel grains collected. In individual petrographic groups, there are small differences between the percentages associated with the gravel weight and number of grains. Because the grain shape was measured on each grain, the contribution of individual petrographic groups to the total number of gravels examined is given (Table 1).



The petrographic composition along the shore section showed considerable variability (Figure 4a–c). The mean weight content of crystalline rock gravels was 75.8%, and ranged within 50–90%. The highest contribution of crystalline gravels (over 75%) was found in the Rewal Upland cliff, where glacial tills dominate in the shallow nearshore and are intensively mechanically reworked during stormy weather, creating an additional source of crystalline components. These processes are especially visible between 375.0 and 383.0 km. The lowest proportion of those gravels (below 70%) was revealed in a zone of contact between the cliff area and the sandbar section of the Dziwna Gate (384.0–387.0 km), as well as on the Rewa Gate dune shore sections in the vicinity of the Rewal Upland dune coast (364.5–368.0 km), and the Dziwna Gate (390.0–391.4 km). The contribution of limestone gravels averaged about 15%. The highest proportions of limestone gravels (above 25%) were recorded in the area of active cliffs from Niechorze to Trz ˛esacz (368–373 km) and (about 20%) between Łuk ˛ecin and Dziwnówek (384.0–386.0 km), as well as in the vicinity of the Dziwnów jetty. The lowest contribution (about 10%) of limestone gravels occurred in the cliff area between Pustkowo and Łuk ˛ecin (375.0–384.0 km) and east of the Liwia Łu˙za mouth (365.5 km). The average percentages of sandstone gravels ranged within 5–15%; elevated contributions (10–15%) of sandstones were found only in the dune shore section in Pogorzelica (364.5–365.5 km) and in the zone of contact between the cliff and dunes at Dziwnówek (386.0–366.5 km). The remaining shore sections showed a similar content of sandstone gravels (5–10%).

The ratio between gravels of less resistant rocks (limestones and sandstones) and more resistant rocks (crystalline rocks with quartz) was at its highest (above 0.4) in the area of active cliff and the Liwia Łu˙za mouth between Niechorze and Rewal, somewhat lower ratios (0.3–0.4) were recorded between Łuk ˛ecin (384.0 km) to the cliff–dune contact zone (386.5 km) to the River Dziwna mouth (391.4 km). The lowest ratios, about 0.2 and below 0.2 were found in sandbar areas east of the Liwia Łu ˙za mouth towards Mrze ˙zyno, and at a temporally active cliff at Pobierowo, respectively, as well as at a cliff in a labile developmental phase (371–377 km), except for clearly eroded sections (Figure 4a). The greatest domination of crystalline rock gravels over limestones and sandstones was revealed east of Pogorzelica and between the Pobierowo cliff to Łuk ˛ecin (375–383 km). Similar were the relationships between sandstones and limestones. At the Pobierowo cliff, the sandstone to limestone ratio was the highest, declining east of Rewal (371–364 km) and west of Łuk ˛ecin (381–391 km). Increased ratios were also related to the presence coastal protection structures, which trap less-resistant gravel components and decrease mechanical reworking of the material.

**Figure 4.** Coastal morphodynamics and petrographic composition of gravels between Pogorzelica and Dziwnów (363.0–391.4): (**a**) the seashore morphodynamics with erosion–accumulation tendencies, (**b**) the petrographic composition of beach gravels, and (**c**) the ratio between mechanically less resistant sedimentary rocks and more resistant gravels. The broken lines indicate a lack of gravel along the coast section investigated.
