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| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 19 |
| Value | Definition |
|---|---|
| A1 | Abbreviated symbol for A1 r_cgS where r = rippled, cgS = coarse-grained sand |
| A2 | Abbreviated symbol for A2 i_cgS where i = immobile, cgS = coarse-grained sand |
| C | Abbreviated symbol for C i_cbG where i = immobile, c = cobble, b = boulder, G = gravel |
| E | Abbreviated symbol for E i_cgS where i = immobile, cgS = coarse-grained sand |
| F | Abbreviated symbol for F i_cgS / pcbG where i = immobile, cgS = coarse-grained sand, / = overlying, or partial veneer over, p = pebble, c = cobble, b = boulder, G = gravel |
| G1 | Abbreviated symbol for G1 i_mfgS where i = immobile, m = muddy, fgS = fine-grained sand |
| Y | Abbreviated symbol for Y r_cgS where r = rippled, cgS = coarse-grained sand |
| Z | Abbreviated symbol for Z r_cgS where r = rippled, cgS = coarse-grained sand |
| AB | Abbreviated symbol for AC r_fgS r = rippled, fgS = fine-grained sand |
| AC | Abbreviated symbol for AC r_cgS r = rippled, cgS = coarse-grained sand |
| AG | Abbreviated symbol for AG r_cgS where r = rippled, cgS = coarse-grained sand |
| AI | Abbreviated symbol for AI r_cgS where r = rippled, cgS = coarse-grained sand |
| AJ | Abbreviated symbol for AJ i_cgS where i = immobile, cgS = coarse-grained sand |
| AK | Abbreviated symbol for AK i_cgS / pcbG where i = immobile, cgS = coarse-grained sand, / = overlying, or partial veneer over, p = pebble, c = cobble, b = boulder, G = gravel |
| AL | Abbreviated symbol for AL r_gcgS / i_pcG where r = rippled, g = gravelly, cgS = coarse-grained sand, / = overlying, or partial veneer over, i = immobile, p = pebble, c = cobble, G = gravel |
| AM | Abbreviated symbol for AM r_cgS where r = rippled, cgS = coarse-grained sand |
| AN | Abbreviated symbol for AN r_cgS where r = rippled, cgS = coarse-grained sand |
| AO | Abbreviated symbol for AO r_cgS where r = rippled, cgS = coarse-grained sand |
| AP | Abbreviated symbol for AP r_cgS / i_pcbG where r = rippled, cgS = coarse-grained sand, / = overlying, or partial veneer over, i = immobile, p = pebble, c = cobble, b = boulder, G = gravel |
| AQ | Abbreviated symbol for AQ r_fgS where r = rippled, fgS = fine-grained sand |
| Value | Definition |
|---|---|
| A1 r_cgS | Rippled, coarse-grained sand. Substrate A1 is a mobile, coarse-grained sand deposit that covers the southeastern part of Stellwagen Bank and its flank and the eastern approaches to Race Point Channel. It occupies 74.7 km2 or 40.4 percent of the mapped area of quadrangle 3. Water depth range of the stations is 32 to 59 m and of the mapped substrate 30 to 60 m. Mean weight percents of aggregates and composite grades: mud, <1; sand, 94 (fgS, 2; cgS, 92); gravel, 6 (G1, 6; G2, <1). The substrate extends westward onto the southwestern part of the bank in quadrangle 2 (fig. 1; Valentine and Cross, 2024), and northward onto the eastern flank of the bank in quadrangle 6 (fig. 1; Valentine and Gallea, 2015). Substrate A1 is dominantly coarse-grained sand and is very low in mud and fine-grained sand content. Its surface is smooth as observed in multibeam topographic imagery, but video imagery reveals the substrate’s surface is covered with sand ripples with wavelengths of 0.5 to 1.0 m; the orientation of ripple crests varies from N-S to NW-SE. The ripples are symmetrical and well-shaped (sometimes with narrow, sharply-defined crests and sometimes with broad crests hosting secondary ripples) when first formed by storm-wave generated currents, but they subsequently are rounded by faunal disturbance and flattened by bottom-tending fishing gear such as dredges and trawls. Those stations that occur in the A1 polygon that are not documented with video imagery or that do not display sand ripples because they have been disturbed by fishing gear are nevertheless characterized as “rippled” by analogy to the many nearby stations in A1 that exhibit ripples in video imagery. Substrate A1 is texturally similar to substrate Z that is recognized as a separate substrate because it lies in deeper water in Race Point Channel south of Stellwagen Bank and contains slightly more fine-grained sand. Substrate A1 is similar in its mud and overall sand content to substrate A3. However, substrate A3 contains more fine-grained sand (13 wt pct). Each sample from A3 generally contains 10 wt pct or more of fine-grained sand, mostly as 3 phi sand, and its surface is covered with smaller ripples. Substrate A3 deposits occur within the areas occupied by substrates A1, Z, and AN and are not mappable as a coherent unit at the present scale. |
| A2 i_cgS | Immobile, coarse-grained sand. Substrate A2 is an immobile, coarse-grained sand deposit that lies along the southeastern flank of Stellwagen Bank and in the deeper eastern approaches to Race Point Channel. It occupies 10.7 km2 or 5.8 percent of the mapped area of quadrangle 3. Water depth range of the stations is 59 to 73 m and of the mapped substrate 55 to 80 m. Mean weight percents of aggregates and composite grades: mud, 1; sand, 98 (fgS, 10; cgS, 88); gravel, 2 (G1, 2; G2, 0). Substrate A2 is dominantly coarse-grained sand and is very low in mud and fine-grained sand content. Its surface is unrippled in contrast to adjacent mobile substrate A1 which lies in shallower depths (30-60 m) to the west and contains less fine-grained sand (2 wt pct). Substrate A2 is bounded in deeper water to the east by substrate E, also an immobile, coarse-grained sand and by substrate G1, a muddy, fine-grained sand. Substrates A2, E, and G1 all extend northward into adjacent quadrangle 6 (fig. 1; Valentine and Gallea, 2015). |
| A3 r_cgS | This is not mappable as a separate polygon but included because of references to the unit elsewhere in the document. Rippled, coarse-grained sand. Substrate A3 is a collection of mobile, coarse-grained sand deposits that lie within the areas occupied by substrates A1, Z, and AN. Water depth range of stations is 42 to 55 m. Mean weight percents of aggregates and composite grades: mud, <1; sand, 98 (fgS, 13; cgS, 85); gravel, 2 (G1, 2; G2 0). It is also present as scattered deposits on the crest and western flank of the bank in adjacent quadrangle 5 to the northwest (fig. 1; Valentine and Cross, 2024). Substrate A3 is similar texturally to substrate A1 in having a very low mud content. It differs from A1 in having more fine-grained sand (each sample generally contains 10 wt pct or more of fine-grained sand, mostly as 3 phi sand), and its surface ripples are much smaller, with wavelengths of 10 to 20 cm. Substrate A3 is also similar to substrate A2. They both contain more fine-grained sand than substrate A1, but A2 has less fine-grained sand than A3, is immobile, and lies at deeper water depths (55-80 m). The scattered deposits identified as substrate A3 occur within areas mapped as substrates A1, Z, and AN and are not mappable as a coherent unit at the present scale. |
| C i_cbG | Immobile, cobble, boulder gravel. Substrate C is represented by five boulder ridges (piled cobbles and boulders) that occur in four locations in quadrangle 3. They occupy 0.7 km2 or 0.4 percent of the mapped area of the quadrangle and occur in water depths of >25 to 87 m. The shape and relief of the boulder ridges are based on interpretation of multibeam topographic imagery and on the substrate’s high reflectivity in backscatter imagery, typical of boulder ridges mapped in quadrangles 5 (Valentine and Cross, 2024) and 6 (Valentine and Gallea, 2015). A sinuous boulder ridge with an east-west orientation is present in the southern part of Race Point Channel. It is approximately 1.5 km long and 0.1 km wide, lies in water depths of >55 to 58 m, and is surrounded by gravelly substrate AK. A single station lies within the bounds of this boulder ridge. Two adjacent boulder ridges are present on the southern margin of Race Point Channel near the southern limit of the quadrangle 3 mapped area. The westernmost ridge is 0.5 km long and 0.1 km wide and is oriented approximately east-west. The easternmost ridge extends southward past the map boundary and is at least 0.7 km long and 0.2 km wide and is oriented northwest-southeast. They lie in water depths of >25 to <35 m and are surrounded by substrate AO. A single boulder ridge is present on the southern flank of Race Point Channel in water depths of <30 to 36 m. The feature is approximately 500 m long, 200 m wide, and is oriented NE-SW, normal to the trend of the sediment ridges of substrate AP which surrounds it. Another boulder ridge forms a low feature that trends NW-SE along the southwest margin of South Ninety Bank in water depths of 85 to 87 m; it is surrounded by substrate F which occupies the summit of South Ninety Bank. |
| E i_cgS | Immobile, coarse-grained sand. Substrate E is an immobile, coarse-grained sand deposit that lies in a shallow valley between the southeastern flank of Stellwagen Bank and the western flank of South Ninety Bank. It occupies 0.3 km2 or 0.2 percent of the mapped area of quadrangle 3. Water depth range of the substrate is 75 to 80 m. It separates substrate A2 to the west from substrate G1 that lies on the western flank of South Ninety Bank in deeper water to the east. Substrate E is not represented by any samples in quadrangle 3, and it is interpreted to be a short extension (1.5 km) of substrate E mapped in adjacent quadrangle 6 to the north and to be similar texturally (fig. 1; Valentine and Gallea, 2015). |
| F i_cgS / pcbG | Immobile, coarse-grained sand; partial veneer on pebble, cobble, boulder gravel. Substrate F is a layered substrate of immobile, coarse-grained sand that partially veneers pebble, cobble, boulder gravel. It lies on the southern part of the top of South Ninety Bank. It occupies 3.1 km2 or 1.7 percent of the mapped area of quadrangle 3. Water depth range of the stations is 87 to 97 m and of the mapped substrate 85 to 115 m. Mean weight percents of aggregates and composite grades of the two samples from the sediment partial veneer overlying the gravel: mud, 5; sand, 56 (fgS, 40; cgS, 16); gravel, 39 (G1, 15; G2, 24). The high gravel content is interpreted to represent gravel particles inadvertently collected from the gravel substrate located below the partial veneer of sand.
The seabed on the northern part of the top of South Ninety Bank lies in adjacent quadrangle 6 and was mapped as substrate F (Valentine and Gallea, 2015). The seabed on the southern part of the bank top lies in quadrangle 3 and is also mapped here as substrate F. The assignment of this area to substrate F requires explanation. On the northern part of the bank, the grain size of sand is variable; coarse-grained sand is dominant on the bank top (3 stations) and fine-grained sand content (2 stations) increases with water depth on the bank’s flank (Valentine and Gallea, 2015). By contrast, on the southern part of the bank top in quadrangle 3, in the two samples collected, the content of fine-grained sand is greater than coarse-grained sand. Nevertheless, this area is identified as substrate F because sediment texture data here are variable and sparse; and it is unlikely that the northern and southern parts of this relatively smooth and flat bank top are occupied by different substrates, as the multibeam sonar bathymetric and backscatter imagery (Valentine, 2005) show the seabed on the bank top to be of similar character in both quadrangles. More sediment sampling is required to verify this interpretation. |
| G1 i_mfgS | Immobile, muddy, fine-grained sand. Substrate G1 is an immobile, muddy, fine-grained sand deposit that lies on the southern flank of South Ninety Bank and in the deeper waters of the basins to the east and south of it. It occupies 17.8 km2 or 9.6 percent of the mapped area of quadrangle 3. This substrate has been mapped in a similar topographic setting on the northern flank of South Ninety Bank and in its adjacent basins in quadrangle 6 to the north (fig. 1; Valentine and Gallea, 2015). Water depth range of the stations is 78 to 126 m and of the mapped substrate 70 to 130 m. Mean weight percents of aggregates and composite grades: mud, 6; sand, 88 (fgS, 69; cgS, 20); gravel, 6 (G1, 3; G2, 3). Substrate G1 in quadrangle 3 contains only 6 mean weight percent mud, which is less than the 10 weight percent required for it to be characterized as a “muddy” sediment (Valentine, 2019). However, because the weight percent mud composition of the 9 samples (range 1-16, mean 6) collected from quadrangle 3 is very similar to the weight percent mud composition of the 39 samples (range 2-18, mean 10) collected from substrate G1 in quadrangle 6 (Valentine and Gallea, 2015), and because of its similar topographic setting, the substrate mapped as G1 in quadrangle 3 is identified as a muddy, fine-grained sand for consistency with its occurrence in adjacent quadrangle 6 to the north. |
| Y r_cgS | Rippled, coarse-grained sand. Substrate Y is a mobile, coarse-grained sand deposit lying in the eastern part of Little Stellwagen Basin. It occupies 2.0 km2 or 1.1 percent of the mapped area of quadrangle 3. Water depth range of the stations is 62 to 63 m and of the mapped substrate 60 to 63 m. Mean weight percents of aggregates and composite grades: mud, 3; sand, 96; (fgS, 36; cgS, 60); gravel, 1 (G1, 1; G2, 0). Substrate Y lies in the southwestern part of quadrangle 3 and extends westward into quadrangle 2 (fig. 1; Valentine and Cross, 2024). It lies to the west of substrate AC, in somewhat deeper water, and contains more fine-grained sand (36 wt pct) than substrate AC (12 wt pct). Substrate Y is bounded to the south by the northern margin of Cape Cod occupied by substrates AG and AQ. |
| Z r_cgS | Rippled, coarse-grained sand. Substrate Z is a mobile, coarse-grained sand deposit. It lies in Race Point Channel at the base of Stellwagen Bank. It occupies 13.5 km2 or 7.3 percent of quadrangle 3. Water depth range of the stations and of the mapped substrate is 43 to 62 m. Mean weight percents of aggregates and composite grades: mud, 1; sand, 97; (fgS, 5; cgS, 91); gravel, 3 (G1, 2; G2, 1). It is bounded to the north by substrate A1 on Stellwagen Bank and is differentiated from it because it lies in somewhat deeper water in Race Point Channel and because it contains more fine-grained sand (5 wt pct) than substrate A1 (2 wt pct). As observed in multibeam topographic imagery, substrate Z has a relatively smooth surface. In Race Point Channel, it is bounded by a range of sand substrates including substrates AI and AN to the east, and AC and AM to the south. Also, to the south it abuts AK, a layered substrate of sand that partially veneers gravel. Substrate Z extends westward from quadrangle 3 into quadrangle 2 (fig. 1; Valentine and Cross, 2024). |
| AB r_fgS | Rippled, fine-grained sand. Substrate AB is a mobile, fine-grained sand deposit that lies in the northern part of Race Point Channel on the southern flank of Stellwagen Bank in 45 to 55 m water depth. The largest portion of AB lies in adjacent quadrangle 2 to the west (Valentine and Cross, 2024). AB extends eastward into quadrangle 3 where it occupies a very small area. No sediment samples were collected from the portion of AB that lies in quadrangle 3. It is bounded to the north in shallower water on Stellwagen Bank by substrate A1 and to the east and south by substrate Z, both of which contain less fine-grained sand. |
| AC r_cgS | Rippled, coarse-grained sand. Substrate AC is a mobile, coarse-grained sand deposit that lies in the southern part of Race Point Channel. It occupies 1.4 km2 or 0.8 percent of quadrangle 3. Water depth of the one station is 59 m and of the mapped substrate 59 to 60 m. Weight percents of aggregates and composite grades of the one sample: mud, 2; sand, 98 (fgS, 12; cgS, 86; gravel, <1 (G1, <1; G2, 0). The substrate’s surface displays bedforms (50-100 m wavelength) observable in multibeam topographic imagery that trend NW-SE, approximately normal to the trend of Race Point Channel. They resemble bedforms present in the northern part of substrate AM to the east. Substrate AC is bounded to the east by substrate AK. It is bounded to the west by substrates Y and Z whose surfaces are smooth as observed in multibeam topographic imagery. Based on the presence of its distinctive bedforms, substrate AC extends westward for a short distance into quadrangle 2 (Valentine and Cross, 2024). |
| AG r_cgS | Rippled, coarse-grained sand. Substrate AG is a mobile, coarse-grained sand deposit that lies on the south flank of Little Stellwagen Basin north of Cape Cod and extends westward into quadrangle 2 (Valentine and Cross, 2024). It occupies 0.3 km2 or 0.2 percent of the mapped area of quadrangle 3. It is not represented by any samples in quadrangle 3, and it is interpreted to be a short extension of substrate AG from adjacent quadrangle 2 to the west (Valentine and Cross, 2024) and to have a similar sediment texture with a mean mud content of <1 weight percent. Its occurrence in quadrangle 3 is based on interpretation of multibeam topographic and backscatter imagery. Water depth range of the mapped substrate is 50 to 60 m. The surface of substrate AG is covered with storm-generated sand ripples. To the east, along the northern slope of Cape Cod, it abuts substrate AQ, a rippled, fine-grained sand. |
| AI r_cgS | Rippled, coarse-grained sand. Substrate AI is a mobile, coarse-grained sand deposit. It lies in the central part of Race Point Channel between Stellwagen Bank to the north and Cape Cod to the south. It occupies 4.4 km2 or 2.4 percent of the mapped area of quadrangle 3. Water depth range of the stations is 43 to 49 m and of the mapped substrate 43 to 55 m. Mean weight percents of aggregates and composite grades: mud, <1; sand, 90; (fgS, 4; cgS, 85); gravel, 10 (G1, 6; G2, 5). Substrate AI is characterized by areas of smooth seabed separated by areas of subparallel ridges aligned dominantly NW-SE as observed in multibeam topographic imagery. Two samples collected from the ridges are gravelly, coarse-grained sand, suggesting that just below the surface substrate the ridges are gravelly and possibly represent partially buried iceberg keel marks (see substrate AP below). Substrate AI is bounded to the north by substrates AL and AN, to the east by substrate A1, to the south by substrate AP, and to the west by substrate Z. |
| AJ i_cgS | Immobile, coarse-grained sand. Substrate AJ is an immobile, coarse-grained sand deposit that lies on the top of a small, unnamed bank located southeast of South Ninety Bank. It occupies 0.2 km2 or 0.1percent of the mapped area of quadrangle 3. Water depth of the single sample is 111 m and of the mapped substrate 110 to 111 m. Weight percents of aggregates and composite grades of the single sample: mud, 9; sand, 88; (fgS, 29; cgS, 59); gravel, 3 (G1, 3; G2, 0). It is surrounded in deeper water by substrate G1. |
| AK i_cgS / pcbG | Immobile, coarse-grained sand; partial veneer on pebble, cobble, boulder gravel. Substrate AK is a layered substrate of immobile coarse-grained sand that partially veneers pebble, cobble, boulder gravel. It lies in the southcentral part of Race Point Channel where it occupies 2.7 km2 or 1.4 percent of the mapped area of quadrangle 3. Water depth range of the stations is 57 to 61 m and of the mapped substrate 55 to 61 m. Mean weight percents of aggregates and composite grades of the very thin sediment partial veneer overlying gravel: mud, 4; sand, 82; (fgS, 11; cgS, 71); gravel, 14 (G1, 4; G2, 9). The substrate is interpreted to be immobile because only two of 10 stations with video imagery show ripples, and they are very poorly developed in the thin, patchy sand that veneers the gravel at some stations. The gravel element of the substrate is documented by video imagery. The substrate’s hummocky surface as observed in multibeam topographic imagery exhibits high reflectivity in backscatter imagery, typical of a hard substrate. Multibeam topographic imagery is the basis for the mapped geographic extent of the substrate. Substrate AK surrounds an east-west trending boulder ridge (substrate C). Substrate AK is bounded on all sides by substrates of rippled sand, which include, substrate Z to the north, substrate AM to the east and southeast, substrate AQ to the south, and substrate AC to the west. |
| AL r_gcgS / i_pcG | Rippled, gravelly, coarse-grained sand; partial veneer on pebble, cobble, boulder gravel. Substrate AL is a layered substrate of mobile, gravelly, coarse-grained sand that partially veneers immobile pebble, cobble gravel. It lies in two separate areas on topographic highs in the northeastern part of Race Point Channel south of Stellwagen Bank. It occupies 2.9 km2 or 1.6 percent of the mapped area of quadrangle 3. Water depth range of the stations is 46 to 53 m and of the mapped substrate 45 to 53 m. Mean weight percents of aggregates and composite grades of the sediment partial veneer overlying gravel: mud, <1; sand, 56 (fgS, 17; cgS, 39); gravel, 44 (G1, 5; G2, 39). Pebbles and cobbles are identified based on video imagery. At some stations substrate AL is a gravel pavement with little or no sand veneer. The substrate’s surface exhibits high reflectivity in multibeam backscatter imagery, typical of a hard substrate; and the mapped geographic extent of the substrate is based on backscatter imagery. The western area of substrate AL is surrounded by substrate AN. The eastern area of substrate AL is bounded to the north and west by substrate AN, to the east by substrate A1, and to the south by substrate AI. |
| AM r_cgS | Rippled, coarse-grained sand. Substrate AM is a mobile, coarse-grained sand deposit. It lies in the southern part of Race Point Channel north of Cape Cod. It occupies 8.0 km2 or 4.3 percent of the mapped area of quadrangle 3. Water depth range of the stations is 45 to 64 m and of the mapped substrate 40 to 64 m. Mean weight percents of aggregates and composite grades: mud, 1; sand, 98; (fgS, 4; cgS, 94); gravel, 1 (G1, 1; G2, <1). Multibeam topographic imagery shows the substrate surface displays large bedforms (100-200 m wavelength) in the south and small bedforms (50-100 m wavelength) in the north. The bedforms trend NW-SE, approximately normal to the trend of Race Point Channel. The small bedforms in the northern part are similar in wavelength and orientation to those present in substrate AC to the west. Substrate AM is bounded to the north by substrates Z and AP, to the east by substrate AP, to the south by substrate AO, and to the west by substrate AK. |
| AN r_cgS | Rippled, coarse-grained sand. Substrate AN is a mobile, coarse-grained sand deposit. It lies along the northern margin of Race Point Channel and the southern margin of Stellwagen Bank. It occupies 7.3 km2 or 3.9 percent of the mapped area of quadrangle 3. Water depth range of the stations is 48 to 50 m and of the mapped substrate 45 to 50 m. Mean weight percents of aggregates and composite grades: mud, <1; sand, 99 (fgS, 32; cgS, 67); gravel, 1 (G1, 1; G2, 0). Substrate AN is similar in mobility and sand content to adjacent substrate A1 to the north and east and to substrate Z to the west, but substrate AN has a much higher fine-grained sand content (32 wt pct) compared to that of A1 (2 wt pct) and Z (5 wt pct). It is likely that the fine-grained sand in substrate AN has been winnowed and transported by storm-wave generated currents from substrate A1 on Stellwagen Bank which abuts AN to the north. Also, the surface of substrate AN displays ridge-like features in multibeam topographic imagery that are interpreted to be partly-buried iceberg keel marks (see substrates AP and AI), whereas the surfaces of substrates A1 and Z are smooth in topographic imagery. To the south, substrate AN abuts the eastern deposit of substrate AL and surrounds the western deposit of substrate AL. |
| AO r_cgS | Rippled, coarse-grained sand. Substrate AO is a mobile, coarse-grained sand deposit lying along the southern margin of Race Point Channel and the northern margin of Cape Cod. It likely represents a sand apron that extends northward from Cape Cod into Race Point Channel. It occupies 5.9 km2 or 3.2 percent of the mapped area of quadrangle 3. Water depth range of the stations is 28 to 49 m and of the mapped substrate 28 to 55 m. Mean weight percents of aggregates and composite grades: mud, 1; sand, 97; (fgS, 3; cgS, 94); gravel, 2 (G1, 2; G2, 1). The surface of substrate AO is smooth as observed in multibeam topographic imagery. By contrast, it is bounded to the north by substrate AM, to the east by substrate AP, and to the west by substrate AQ, all of which are mobile sand substrates that collectively display surfaces of bedforms, ridges, troughs, and hummocks in multibeam topographic imagery. Substrate AO is similar in grain-size composition to other rippled, coarse-grained sand substates (A1, Y, Z) that display a smooth surface in multibeam topographic imagery in quadrangle 3. Two boulder ridges (substrate C) are present within the southern part of substrate AO. |
| AP r_cgS / i_pcbG | Rippled, coarse-grained sand; partial veneer on immobile pebble, cobble, boulder gravel. Substrate AP is a layered substrate of mobile, coarse-grained sand that partially veneers immobile pebble, cobble, boulder gravel in the southeastern part of Race Point Channel. It occupies 27.2 km2 or 14.7 percent of the mapped area of quadrangle 3. Water depth range of the stations is 34 to 51 m and of the mapped substrate 30 to 51 m. Mean weight percents of aggregates and composite grades of the sediment partial veneer overlying gravel: mud, <1; sand, 92 (fgS, 3; cgS, 89); gravel, 8 (G1, 5; G2, 3). Substrate AP exhibits relatively high reflectivity in multibeam backscatter imagery, typical of coarse sediment. Cobbles and boulders are identified based on video imagery. The substrate’s surface topography as observed in multibeam topographic imagery is a series of subparallel, arcuate troughs and ridges that trend northwestward. Both substrate layers are visible on the ridges, but only the upper layer (the rippled, coarse-grained sand) is visible in the troughs. The troughs are <5 m deep and are interpreted to be iceberg keel marks that were formed during the last deglaciation (Valentine, 2019) by the grounding of ice bergs as they drifted westward into the channel from deeper water to the east. The keel marks are present beginning at 45 to 50 m water depth in the east and extend westward in the channel until the water depth deepens to >50 m. Substrate AP surrounds a boulder ridge (substrate C). Substrate AP is bounded to the north and west in Race Point Channel by substrates AO, AM, AI, and A1, all of which are rippled, coarse-grained sand. Substrate AP is bounded to the east, in the open Atlantic Ocean, by substrate A1. |
| AQ r_fgS | Rippled, fine-grained sand. Substrate AQ in quadrangle 3 is a mobile fine-grained sand deposit. It lies along the southern margin of Little Stellwagen Basin on the slope that separates the basin from Cape Cod to the south. It occupies 1.2 km2 or 0.6 percent of the mapped area of quadrangle 3. Water depth range of the stations is 54 to 61 m and of the mapped substrate 50 to 61 m. Mean weight percents of aggregates and composite grades: mud, 3; sand, 96; (fgS, 62; cgS, 34); gravel, 1 (G1, <1; G2, <1). The surface of substrate AQ is covered with storm-generated sand ripples. It is bounded to the north by substrates Y, AC, and AK, to the east by substrates AM and AO, and to the west by substrate AG. Substrate AQ likely extends southward into an unmapped area of shallowing water depths on the northern margin of Cape Cod. |
| Value | Definition |
|---|---|
| boulder ridges >=1 meter in height | Boulder ridges greater than or equal to 1 meter in height equivalent to substrate C. |
| immobile sediment | Immobile, coarse-grained sand (substrates E, AJ, and AZ); immobile, muddy, fine-grained sand (substrate G); immobile, coarse-grained sand partial veneer on pebble, cobble gravel (substrate AK); immobile, coarse-grained sand partial veneer on pebble, cobble, boulder gravel (substrate F). |
| mobile and immobile sediment | Rippled, coarse-grained sand partial veneer on immobile, cobble, boulder gravel (substrate AP); rippled, gravelly, coarse-grained sand partial veneer on immobile, pebble, cobble gravel (substrate AL). |
| mobile sediment | Rippled coarse-grained sand (substrates A1, Y, Z, AC, AG, AI, AM, AN, and AO); rippled fine-grained sand (substrates AB and AQ). |
| Value | Definition |
|---|---|
| boulder ridges >=1 meter in height | Boulder ridges greater than or equal to 1 meter in height equivalent to substrate C. |
| dominated by coarse-grained sand in the sand fraction | Coarse-grained sand in which coarse-grained sand (0, 1, and 2 phi combined) constitutes the largest portion of the sand fraction; equivalent to substrates A1, E, F, Y, Z, AC, AG, AI, AJ, AK, AL, AM, AN, AO, AP, and AZ. |
| dominated by fine-grained sand in the sand fraction | Fine-grained sand and muddy, fine-grained sand in which fine-grained sand (3 and 4 phi combined) constitutes the largest portion of the sand fraction; equivalent to substrates AB, AQ and G |
| Value | Definition |
|---|---|
| < 1 | Mud content less than 1 mean weight percent; substrates A1, AG, AI, AL, AN, and AP. |
| 1 to <5 | Mud content 1 to less than 5 mean weight percent; equivalent to substrates A2, E, Z, Y, AB, AC, AK, AM, AO, and AQ. |
| 5 to <10 | Mud content 5 to less than 10 mean weight percent, substrates F, G1, and AJ. |
| boulder ridges >=1 meter in height | Boulder ridges were never sampled due to the nature of the ridges, so are not represented by a measured mud weight percent; equivalent to substrate C. |
| Range of values | |
|---|---|
| Minimum: | 0.163012 |
| Maximum: | 74.6615 |
| Units: | square kilometers |
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| Access_Constraints | No access constraints. Please see 'Distribution Information' for details. |
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| Use_Constraints | The interpretation was completed at a map scale of 1:25,000 and may not be appropriate for use at other scales. These data are marked with a Creative Commons CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. |
| Data format: | This zip file contains the shapefile, browse graphic, and associated FGDC CSDGM metadata. Additionally, ArcGIS 10.8.1 layer files are included for each variation of the mapping units. in format Shapefile (version ArcGIS 10.8.1) Size: 0.5 |
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| Network links: |
https://www.sciencebase.gov/catalog/file/get/65d7c931d34ec3e1801d8149 https://www.sciencebase.gov/catalog/item/65d7c931d34ec3e1801d8149 https://doi.org/10.5066/P13PVHRI |
