Fig 1.
The study site is located at the Town of Cairo Highway Department quarry.
The study site is also known as the Town of Cairo Highway Department Fossil Site (TCHD). The Town of Cairo is located along the routes NY-23 and NY-32 at the west of the Hudson River in Greene County, New York State, USA.
Fig 2.
An aerial map of the sediment exposure at the TCHD.
The aerial exposure map of the sediment exposures were drawn on a USGS base map. The planar exposure of the sediment deposits and covered areas are represented by different colors. Parallel cross-sections on the map were named alphabetically from south to the north of the quarry. The cross-section A-B located at the east-southeast, and the M-N at the north-northwest of the quarry floor. The Dip-slip fault was marked with a dashed line and the strike-slip fault with arrows.
Fig 3.
The distribution of the fossilized root systems belonging to three different tree clades.
The tree distributions at the TCHD were mapped using Stein’s map as base-map [11]. Stein’s map only covered the exposed fossils around the C-D cross-section (Fig 2). Arch stands for Archaeopteris, Eosp for Eospermatopteris, and Lyc Tree for the lycopsid tree. Note L- shaped distributions of the Eosp trees in the form of the two clusters (one around Eosp 1, and another around Eosp 2). Likewise, note the distribution of the Arch tree from Arch 1 to Arch-5. The linear distribution extends to Arch 6 which is not shown in this map. The colors in the map represent the dominant drainage patterns in the fossilized landscape that were inferred from the redox coloration. The actual surface paleosol colors were light-red, dark-gray, and yellowish-brown indicating the existence of a drainage gradient from well-drained, moderately drained to poorly drained area.
Fig 4.
The main features of the Eospermatopteris 2, 3 and 4.
The main features of the Eospermatopteris root-mold included a central depression, rootlets-paleosol mound that surround the central depression, rootlets, and slickensides. The central depression formed by the bulbous bases of the Eospermatopteris trees. The rootlets-paleosol mound formed by the mantle of rootlets that emanated from the bulbous bases and hugged the paleosol. Slickensides developed by the differential vertic movements as a result of seasonal swell-shrink of the paleosols, and the rootlets-paleosol mound. Note that the Eosp 3 shows multiple concentric slickensides, Eosp 2 strong slickenside at the border between the rootlets-paleosol mound and the host paleosol, and no visible slickensides observable at the boundary of Eosp 4. The bulbous base and the rootlets-paleosol mound acted as a single unit to stabilize trees.
Fig 5.
The variation in the sizes of the pseudoanticlines in rooted and unrooted areas.
Roots trace fossils are shown in green color, the first generation pseudoanticlines in red, and the second generation in yellow colors. PA 1–3 is the maps of the pseudoanticlines in the unrooted areas along section C-D. The PA-4 is the map of the pseudoanticlines in the proximal area of the lycopsid root system. PA-5 is the map of the pseudoanticlines in the proximal area, and PA-6 in the distal area of Arch-5.
Fig 6.
Drill-core extracts from the TCHD.
The core-extracts were selected that possessed the representative features of the subsoil (Fig 6A–6F and 6H) from the well-drained areas as well as hydromorphic paleosol (Fig 6G). (A) Note the reduced surface paleosol in comparison to the more oxic subsoil. (B) Reduced areas are dominant around rhizohalos. The almost vertical rhizohalos indicated that roots didn’t face resistance in the deep soil. (C) Note the branching root-casts (marked by arrow) surrounded by the rhizohalos. (D) The figure shows the end of top-paleosol and the beginning of underlying paleosol. The underlying paleosol has a reduction-zone followed by a desiccation zone (E). (F) The figure shows the rooting zone of the underlying paleosol where the branched root system is observable. (G) A core extract from hydromorphic paleosol: Note the iron-manganese zone, organic-rich zone, and underlying surface hydromorphic paleosol recorded variations in moisture-saturation of the paleosol. (H) A desiccation zone from the well-drained paleo-vertisol: The orientation of the subrounded peds in the reduced matrix, and likewise, the subrounded organic materials are notable.
Fig 7.
Photomicrograph from the fine root areas along the C-D section.
(A) A fine root working as a borderline between oxidized and reduced sediments. (B). The network of dense fine roots. (C) An iron concretion formed around a spherical clay. (D) A Spore along a fine root.
Fig 8.
Correlations of the north, northwest, and southeast at the TCHD quarry-walls sediment deposits.
The sediment deposits, paleosols, and fossils from the quarry walls, floor and the drill-cores were used to construct the sedimentary profiles. For instance, the information on the depth of the vertisols from the drill-core extracts were included in the profile of the southeast wall. The Northwest wall profile showed more variations as the strike-slip fault made a near 3-D exposure of the wall. Likewise, the quarry floor made it possible to trace the paleosols that made the forest floor as well as the capping sediments from south to north. The fossils included in-situ rooting as well as washed-in fossils such as fish and trees which were helpful in the correlations of the paleosols exposed on the quarry floor. The primary sedimentary structures and the tracing of the sedimentary deposits across the quarry walls made it possible to correlate the sedimentary deposits of the wall. There were four sequences of deposits from base to the top of walls including, trough cross-bedded sandstone, heterolithic bedding, followed by trough cross-bedded sandstone, and paleosols, respectively that varied in their thickness between the walls.
Fig 9.
Interpretation of the depositional environments of the TCHD.
The actual deposits of the TCHD are limited to the two vertical dashed lines shown in the figure. rooted area. The interpretation of the areas between the dashed line are extrapolations based on the thinning or thickening of the sediments at the TCHD: (A) A forest on an abandoned channel on a distant floodplain. (B) Crevasse splays changed the depositional environment from seasonal-pooling to permanent-pooling which resulted in the disappearance of the forest and preservation of the (C) A flood deposited washed-in fishes and young trees. (D) The crevasse splays and flood changed the local landscape by partially filling the local depression. Lateral migration of a local channel scoured part of the local depression and changed the depositional environment to an active channel. (E) Another lateral migration resulted in a channel bank deposit in the form of the heterolithic beds on the northwest side of the TCHD (F) Yet another episode of lateral migration followed by stabilization of the channel-bank at the northwest side of the TCHD that resulted in the development of the paleosols there.
Fig 10.
Interpretation of deposits associated with the lateral migration of a local channel.
TCHD is represented as a rectangular box. The position and possible direction of the lateral migration of the channel is based on extrapolations of the field observation at TCHD. The variations in sedimentary deposits, their thickening and thinning were used to extrapolate possible changes beyond TCHD. (A) A local depression along an abandoned channel that pooled seasonally at a distal part of a floodplain. The environment was stable for long enough time that allowed the establishment of the multi-general forests. (B) A crevasse splay changed the environment from a seasonal pool to a permanent wetland. The forest didn’t survive the change in the depositional environment. (C) The accretion of the clay and silt changed the local landscape which resulted in lateral migration of the local channel. (D) The channel scoured the deposits in the local depression and carved a new channel. (E) Shale deposited on the distal part of the active channel (F) Another lateral change made the bank of the active channel stable as was evident from the development of a paleosol.
Fig 11.
Sedimentary profiles of the cross-sections A-B to M-N.
The sedimentary profiles of the cross-sections A-B to M-N were drawn based on the field observations and drill cores. The profiles are not scaled and are meant to complement the map in Fig 2. The variations in sediment sizes, the thickness of the deposits, and planar exposures are shown from sections A-B to M-N.
Fig 12.
Main features of the A-B section.
(A) A washed-in young Eospermatopteris tree. (B) The displaced stump-like object in the form of an oxidized cast and its trace-mark in the form of a mold. (C) Organic-rich, fossiliferous sandstone underlying the siltstone. (D) Small scale ripple marks. Note that the direction of the displacement of the object is southward, and the Eospermatopteris tree northward. Additionally, the redox features of the siltstone are also notable.
Fig 13.
Some informative features of the paleo-vertisol along the C-D section.
(A) Multiple-steps mudflow at the bank of the preserved abandoned channel. The preserved mudflow was located between Arch-5 and Arch-6. Note yellowish-brown oxidation coloration at the lower end of mud-flow. (B) Pseudoanticline: Note the visible micro-lows around the pseudo-anticlines. Black arrows point to the micro-highs. (C) A polished section from a cut-saw hand-sample from surface paleosol: Fine sand and silt size sediments filled a desiccation crack (fine sand and silt size sediment capped the forest floor and preserved it). (D) Light-olive green rhizohalos-like features in the weak-red paleosol matrix on the exposure of the capping paleosol close to the point-C: Note they have some of the features of the Eospermatopteris rhizohalos such as being equidimensional, non-branching and running in bundles.
Fig 14.
Representative fossils of roots systems belonging to three Middle Devonian tree clades.
(A) Eospermatopteris stump-molds composed of a central depression surrounded by a raised mound of paleosol-rootlets. The mound is covered with rootlet rhizohalos. Note the slickensides at the boundary between the paleosol-rootlet mound, and the paleosol-matrix. The grid used to map the rooting system is also visible in the picture. (B) The lycopsid root system was composed of Eospermatopteris-like stump mold and Archaeopteris-like branched roots. (C) Proximal roots of Arch-3 and a trapped fossil of fish that was marked with yellow color for the extraction. (D) A pinched root of Archaeopteris between pseudoanticlines. The slickensides and platy peds that developed around the root are notable features of root-paleosol interactions.
Fig 15.
Some main features of paleosol along the E-F section, and surrounding areas.
Figures (A) and (B) show granular peds of similar sizes. Note that in figure (A) weak-red peds make the matrix and in figure (B), the light-olive green peds make the matrix of the paleosol. (C) The area between section E-F and G-H shows a linear distribution of the pseudo-depressions that mark the edge of the local-depression.
Fig 16.
The main features of the paleosol along the G-H section.
Interestingly, the areas along G-H sections have both vertic and hydromorphic features. (A) A slickenside at the paleosol surface (vertic feature, also young paleosol). (B) A pseudo-anticline (vertic feature) with oxidized boundary (hydromorphic features). (C) A fish fossil that helps correlate it with light-olive green siltstone at the C-D section. (D) The sand dunes deposit overlying the hydromorphic paleosol.
Fig 17.
Main features of the paleosol underlying hydromorphic paleosol.
The paleosol underlying hydromorphic-paleosol was exposed by the quarrying at the local-depression. The presence of the fossilized roots, stems, blocky peds, and pseudo-anticlines as well as its stratigraphic position (underlying light-gray hydromorphic paleosol) made it correlatable with paleoforest at the C-D section. (A) Mini-pseudo-anticlines with oxidized microhigh (weak-red) and reduced microlows (light-olive green): Located between sections I-J and K-L. (B) A cast-fossil of a stem: Note the broad-base and the tapering of the stem. (C) Some carbonized impressions of the branched rootlets. (D) Two hydromorphic features, the yellowish-brown coloration of the surface paleosol (as a result of pyrite oxidation) and iron-manganese in the subsurface paleosol. Note that the paleosol features such as pyrite oxidation, iron-manganese nodules, and carbonized rootlets all indicating that ponding happened at this location, as a result of the impervious subsurface soil as were evident from the presence of the iron-oxide coloration of the micro-pseudoanticline in the subsurface paleosol.
Fig 18.
Preserved features of the abandoned-channel along the I-J section.
(A) The wedged-shaped jumbo-desiccation cracks are oriented parallel to each other on a locally preserved mound. Regular desiccation cracks of varying shapes and sizes developed inside the jumbo cracks. (B) Sinuous-crested ripple marks on the channel floor. (C) A preserved terrace on the left bank of the local channel. (D) Paleosols with light-olive green peds on the left bank of the local channel. Note the absence of root fossils of any type.
Fig 19.
Main features of the paleosols along M-N sections.
(A) Pseudoanticlines with slickensided microlows are visible on the surface of the hydromorphic paleosol. The vertic features along the wedged-shaped peds were used as key features to categorize the paleosol as hydromorphic paleosol. (B) The boundary line between hydromorphic paleosol and underlying paleosol. The dotted lines show the transition of the light-olive green peds (subsurface paleosol) into yellowish-brown (surface paleosol) and the overlying light-gray hydromorphic paleosol. (C) Conglomeratic sandstone overlying the light-gray hydromorphic paleosol. The tape measure is at the boundary between the two deposits. (D) The sand-dunes at the N-point of the M-N section. Note the change from conglomeratic sandstone to sand-dunes (the distance is a few meters) in figures (C) and (D).
Table 1.
Demographic distributions of the Eospermatopteris trees at the Gilboa Riverside Quarry (After Stein et al., 2012).