Planktonic foraminifers were generally abundant below 475.9 ft (145.1 m) in the Double Trouble corehole (Tables T3, T4, T5) and were used to assign ages in the lower middle Eocene through Maastrichtian section. Preservation was good in most of the section, but often important marker species were not present, making precise age assignments difficult. Planktonic foraminiferal zones used are those of Berggren and Pearson (2005) with references to the older Berggren et al. (1995) zonation and timescale.
The Double Trouble corehole was barren of planktonic foraminifers above 475.9 ft. The section from 475.9 to 506 ft (145.1 to 154.2 m), in the Toms River Member and uppermost lower Shark River Formation, was assigned to planktonic foraminiferal Zone E10 (lower P12 of Berggren et al., 1995) based on the highest occurrence of Acarinina cuneicamerata at 511 ft (155.8 m), which is not generally found above lower Zone E9. The section from 511 to 571 ft (155.8 to 174.0 m) is assigned to undifferentiated Zones E8–E9 (P10–P11) encompassing the lower part of the lower Shark River Formation. The two zones could not be differentiated because of the near absence of Globigerinatheka in the core (the first occurrence of Globigerinatheka kugleri marks the base of Zone E9). The fauna is typified by the presence of Acarinina mcgowrani, Jenkinsina columbiana, Morozovelloides coronatus, Subbotina corpulenta, and Turborotalia frontosa.
The upper Manasquan Formation (576–614 ft; 175.6–187.1 m) is assigned to Zones E6–E7 (P8–P9). The lower/middle Eocene boundary is difficult to place in the absence of Hantkenina and the delayed first occurrence of Guembelitrioides nuttalli at 521 ft (158.8 m). The Zone E7/E8 boundary (lower/middle Eocene) is placed at the highest occurrence of Acarinina pentacamerata at 576 ft (175.6 m) below the lowest occurrence of T. frontosa at 566 ft (172.5 m). The age of the sample at 571 ft (174.0 m) is not certain.
The lower Manasquan Formation (626–696 ft; 190.8–212.1 m) is assigned to Zones E4–E5 (P6b–P7) based on the first occurrence of Morozovella formosa at 696 ft (212.1 m). Zones E4 and E5 could not be subdivided because Morozovella aragonensis, the marker for the base of Zone E5, is not present in the core. The presence of A. pentacamerata in these samples suggests the section might be all Zone E5.
The two samples from the base of the Manasquan Formation (701 and 706 ft; 213.7 and 215.2 m) are difficult to date. The sediments appear to be conformable with those above but contain a planktonic foraminiferal fauna that is anomalously older than the overlying sediments. The samples do not contain Pseudohastigerina wilcoxensis, the marker species for the base of Zone E2, which is usually common in New Jersey Eocene sediments. A sample at 701 ft (213.7 m) contains a single specimen of Globanomalina pseudomenardii (whose range defines Zone P4 but might be reworked) and Globanomalina imitata that are generally not found above Zone P4. Other species, such as Morozovella occlusa, Morozovella apanthesma, and Morozovella velascoensis (whose highest occurrence defines the top of E2), are not found above Zone E2. This would imply that the sediments at the base of the Manasquan Formation at Double Trouble are Zone E2 or older and that there is an unconformity with a hiatus equal in time to at least Zone E3 between 696 and 701 ft (212.1 and 213.7 m). However, there is no physical expression of an unconformity in the cores (see "Lithostratigraphy and Sequence Stratigraphy"), and this finding is in disagreement with the calcareous nannoplankton biostratigraphy (Zone NP11 [planktonic foraminiferal Zone E4]; see "Calcareous Nannofossils"). Thus, we conclude that the older ages are due to reworking.
The highest occurrence of G. pseudomenardii is at 714.6 ft (217.8 m; i.e., this assumes that the specimen of G. pseudomenardii at 701 ft [213.7 m] is reworked). A sample at 711 ft (216.7 m) is assigned to Paleocene Zone P5, and samples at 714.6–731 ft (226.1–222.8 m) are assigned to Paleocene Zone P4. However, nannofossils indicate that this section is lower Eocene Zones NP9b and NP10a (see "Calcareous Nannofossils") and that the specimens of G. pseudomenardii at both 714.6 ft (217.8 m) and 701 ft (213.7 m) are reworked.
Samples between 736.3 and 786 ft (224.4 and 239.6 m) were either barren or had poor preservation. The section from 796 to 816 ft (242.6 to 248.7 m) is assigned to Zone P4 based on the occurrence of G. pseudomenardii. Zone P4 could not be subdivided because of the absence in the core of Acarinina soldadoensis and Parasubbotina variospira. The presence of Morozovella aequa in most of the Zone P4 samples to 811 ft (247.2 m) suggests that interval should be assigned to Zone P4c.
Paleocene sediments (Table T4) below 821 ft (250.2 m) generally contain thin sequences. A sample at 821 ft (250.2 m) is assigned to Zone P3 because of the presence of Morozovella angulata and the absence of G. pseudomenardii. Zone P3 could not be subdivided because of the absence in the core of Igorina albeari. Other species typical of Zone P3 include Acarinina strabocella and Igorina pusilla. Samples at 826, 830, and 831 ft (251.8, 253.0, and 253.3 m) are assigned to Zone P1c because of the presence of Globanomalina compressa and Praemurica inconstans. In addition, the presence of Eoglobigerina eobulloides at 826 ft (251.8 m) suggests the samples are not younger than Zone P1c. Thus, planktonic foraminiferal biostratigraphy suggests an unconformity between 821 and 826 ft (250.2 and 251.8 m) and that Zone P2 is represented by a hiatus, consistent with placement of an unconformity at 822.95 ft (250.8 m; Fig. F6). Samples from 836 and 836.35 ft (254.8 and 254.9 m) are assigned to Zone P1b because of the presence of Subbotina triloculinoides that defines the base of the zone and Praemurica taurica, which does not generally range above Zone P1b. Samples between 836.65 and 838.65 ft (255.0 and 255.6 m) contain few specimens and are assigned to Zones P0 to P1a undifferentiated because they are below the first occurrence of Subbotina triloculinoides. Planktonic foraminiferal biostratigraphy is thus consistent with an unconformity recognized in the cores at 832.65 ft (253.8 m), implying that a portion of Biochron P1c or P1b is not represented.
Samples below 839 ft (839–856 ft; 255.7–260.9 m; Table T5) contain an abundant and diverse assemblage of Upper Cretaceous species, including members of the genera Globotruncana, Heterohelix, Racemiguembelina, and Rugoglobigerina, among others.
A sample (340.6–340.7 ft; 103.83 m) from the Toms River Member of the Shark River Formation was analyzed qualitatively for dinoflagellate cyst biostratigraphy. The dinoflagellate cysts place the sample in the upper part of the middle Eocene and indicate approximate correlation with calcareous nannofossil Zones NP16–N17. Important species include Pentadinium goniferum and Pentadinium polypodum. A sample from 458.4 ft (139.7 m) has dinocysts that also indicate equivalence of nannofossil Zone NP16 or higher.
Samples were examined for biostratigraphic dating by means of calcareous nannofossils in the interval between 470.0 and 841 ft (143.3 and 256.3 m). The resolution was low (up to 20 ft [6 m] between samples) except between 707 and 742 ft (215.5 and 226.2 m), where samples were taken at a 2 ft (0.6 m) interval. The abundance and preservation of nannofossils fluctuate considerably in this upper Paleocene–middle Eocene sedimentary section. In some samples, small coccoliths are abundant, as if recovered from a chalk. Preservation may be exceptionally good at some levels, whereas dissolution hampers confident biozonal assignment at other levels.
A sample at 470.0 ft (143.3 m) was barren. Samples at 481 and 511 ft (146.6 and 155.8 m) are assigned to mid-Zone NP16 based on the co-occurrence of Chiasmolithus solitus, Helio-discoaster distinctus, Reticulofenestra floridana, and Reticulofenestra reticulata. Calcareous nannofossils were abundant and very well preserved in these samples.
Samples at 521 and 541 ft (158.8 and 164.9 m) also yielded abundant and well-preserved coccoliths. They yielded Chiasmolithus solitus, Sphenolithus furcatolithoides, and Reticulofenestra cf. R. samodurovi and are assigned to the NP15–NP16 zonal interval.
A sample at 568 ft (173.1 m) yielded common but poorly preserved nannofossils due to dissolution. Diversity was low, and no marker taxa were found. Because of stratigraphic position it is questionably assigned to Zone NP15.
A sample at 571 ft (174.0 m) yielded abundant, moderately preserved nannofossils. The assemblage includes Discoaster sublodoensis and Discoaster lodoensis, indicating Subzone NP14a. A sample at 570.3 ft (173.8 m) also yielded these two species (D. sublodoensis being very rare), but coccoliths and discoasters are few and very poorly preserved at this level (reworking cannot be ruled out).
A sample at 574 ft (175.0 m) belongs to the lower part of Zone NP13, as indicated by the occurrence of Discoaster cruciformis. An unconformity likely occurs between this level and 571 ft (174.0 m). Likewise, we note the absence of Subzone NP14b, implying an unconformity between samples at 571 and 570.3 ft (174.0 and 173.8 m) or between the latter and a sample at 568 ft (173.1 m) (additional samples would resolve this uncertainty).
The interval between 574 and 740 ft (175.0 and 228.9 m) consists of lower Eocene sediments extending from lowermost Eocene Subzone NP9b (post-CIE) to upper lower Eocene Zone NP13. A stratigraphic gap including Subzones NP10b–NP10d (as well as the upper part of Subzone NP10a and the lower part of Zone NP11) occurs between 705 and 707 ft (214.9 and 215.5 m). The NP12/NP13 zonal boundary is placed between 574 and 591 ft (175.0 and 180.1 m); the NP11/NP12 zonal boundary is placed between levels 671.6 and 676 ft (204.7 and 206.0 m).
The NP9b/NP10 zonal boundary is extremely difficult to locate because of the scarcity of Tribrachiatus bramlettei in the section. It is provisionally placed between levels 726 and 728 ft (221.3 and 221.9 ft). In general, the lowest occurrence (LO) of T. bramlettei and the highest occurrence (HO) of Fasciculithus spp. are in stratigraphic proximity. This is not the case here, where fasciculiths occur continuously, albeit in low and variable frequency, up to 707 ft (215.5 m). This is interpreted as evidence of reworking, as supported by the rare occurrence of Helio-discoaster araneus at 714 and 742 ft (217.6 and 226.2 m). This also supported by the consistent occurrence of lower Eocene markers such as Chiasmolithus eograndis between 707 and 712 ft (215.5 and 217.0 m).
An unconformity between 740 and 742 ft (228.9 and 226.2 m) is inferred from calcareous nannofossil stratigraphy, and based on the HO of Fasciculithus alanii in a sample at 742 ft (226.2 m) and the LOs of Fasciculithus involutus, H. araneus, Pontosphaera plana, and Rhomboaster calcitrapa. The HO of F. alanii marks the top of Zone NP9a just below the CIE; the LO of P. plana occurs above the CIE (e.g., the Global Stratotype Section and Point for the base of the Eocene; Aubry et al., 2007). H. araneus is sporadic (see above) and R. calcitrapa is rare at 740 ft (228.9 ft) and above, not abundant as in the CIE interval in which the two species form the "Rhomboaster spp.-Discoaster araneus" (RD) assemblage specific to the CIE.
The interval between samples at 786 and 836 ft (239.6 and 254.8 m) is Paleocene. A sample at 786 ft (239.6 m) yielded no discoasters, but the occurrence of F. alanii characterizes Subzone NP9a. Nannofossils were abundant and well preserved in samples at 796 and 801.9 ft (242.6 and 244.4 m), which belong to Zone NP8 (with the marker Heliolithus riedeli exceptionally common and well preserved). A sample at 811 ft (247.2 m) yielded Heliolithus kleinpelli without Discoaster mohleri; it belongs to Zone NP6. A sample at 821 ft (250.2 m) yielded Fasciculithus tympaniformis without H. kleinpelli; it belongs to Zone NP5. A sample at 826 ft (251.8 m) yielded Ellipsolithus macellus, Cruciplacolithus tenuis, Ericsonia subpertusa, and Prinsius minutus. It is assigned to the lower part of Zone NP4. A sample at 836 ft (254.8 m) was barren.
A sample at 846 ft (257.9 m) yielded Cretaceous assemblages. A sample at 843.7 ft (257.2 m) contains Nephrolithus frequens, the marker for upper Maastrichtian Zone CC26.