Donald H. Monteverde

Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary infl uence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences can be correlated throughout the mid-Atlantic region with Sr-isotopic chronology (±0.6 m.y. to ±1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global δ 18 O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifi es that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21‐ 16 Ma. We attribute this enhanced subsidence to local fl exural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a fi rstorder control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local fl exural loading effects, particularly in regions experiencing largescale progradation.

Sequence boundaries are impedance contrasts: Core-seismic-log integration of Oligocene–Miocene sequences, New Jersey shallow shelf

Integrated Ocean Drilling Program Expedition 313 continuously cored uppermost Eocene to Miocene sequences on the New Jersey shallow shelf (Sites M27, M28, and M29). Previously, 15 Miocene (ca. 23–13 Ma) seismic sequence boundaries were recognized on several generations of multichannel seismic profiles using criteria of onlap, downlap, erosional truncation, and toplap. We independently recognize sequence boundaries in the cores and logs based on an integrated study of core surfaces, lithostratigraphy and process sedimentology (grain size, mineralogy, facies, and paleoenvironments), facies successions, stacking patterns, benthic foraminiferal water depths, downhole logs, core gamma logs, and chronostratigraphic ages. We use a velocity-depth function to predict the depths of seismic sequence boundaries that were tested by comparison with major core surfaces, downhole and core logs, and synthetic seismograms. Using sonic velocity (core and downhole), core density, and synthetic seismograms, we show that sequence boundaries correspond with acoustic impedance contrasts, although other stratal surfaces (e.g., maximum flooding and transgressive surfaces) also produce reflections. Core data are sufficient to link seismic sequence boundaries to impedance contrasts in 9 of 12 instances at Site M27, 6 of 11 instances at Site M28, and 8 of 14 instances at Site M29. Oligocene sequences have minimal lithologic and seismic expression due to deep-water locations on clinoform bottomsets. Miocene sequences (ca. 23–13 Ma) were sampled across several unconformity clinothems (prograding units) on topset, foreset, and bottomset locations. Excellent recovery allows core-seismic integration that confirms the hypothesis that unconformities are a primary source of impedance contrasts. Our core-seismic-log correlations predict that key seismic surfaces observed in other subsurface investigations without core and/or well logs are stratal surfaces with sequence stratigraphic significance.

Testing sequence stratigraphic models by drilling Miocene foresets on the New Jersey shallow shelf

We present seismic, core, log, and chronologic data on three early to middle Miocene sequences (m5.8, m5.4, and m5.2; ca. 20–14.6 Ma) sampled across a transect of seismic clinothems (prograding sigmoidal sequences) in topset, foreset, and bottomset locations beneath the New Jersey shallow continental shelf (Integrated Ocean Drilling Program Expedition 313, Sites M27–M29). We recognize stratal surfaces and systems tracts by integrating seismic stratigraphy, lithofacies successions, gamma logs, and foraminiferal paleodepth trends. Our interpretations of systems tracts, particularly in the foresets where the sequences are thickest, allow us to test sequence stratigraphic models. Landward of the clinoform rollover, topsets consist of nearshore deposits above merged transgressive surfaces (TS) and sequence boundaries overlain by deepening- and fining-upward transgressive systems tracts (TST) and coarsening- and shallowing-upward highstand systems tracts (HST). Drilling through the foresets yields thin (

Paleobathymetry and sequence stratigraphic interpretations from benthic foraminifera: Insights on New Jersey shelf architecture, IODP Expedition 313

Integrated Ocean Drilling Program (IODP) Expedition 313 drilled three holes (Sites M27, M28, and M29; 34–36 m present water depth) across a series of prograding clinothems from the inner continental shelf of the New Jersey (USA) margin, a region that is sensitive to sea-level change. We examined 702 late Eocene to Miocene samples for benthic foraminiferal assemblages and planktonic foraminiferal abundances. We integrate our results with lithofacies to reconstruct paleobathymetry. Biofacies at all three sites indicate a long-term shallowing-upward trend as clinothems built seaward and sediment filled accommodation space. Patterns in biofacies and lithofacies indicate shallowing- and deepening-upward successions within individual sequences, providing the basis to recognize systems tracts, and therefore sequence stratigraphic relationships in early to early-middle Miocene sequences (ca. 23–13 Ma). The clinothem bottomsets and the lower portions of the foresets, which contain the thickest parts of clinothems, yield the deepest water biofacies. Shallower bio facies characterize the sequences in the upper portions of the clinothem foresets and on the topsets. Topsets are characterized by transgressive (TST) and highstand systems tracts (HST). Foresets contain lowstand systems tracts (LST), TSTs, and HSTs. Flooding surfaces mark parasequence boundaries within LSTs, TSTs, and HSTs. Superimposed on the long-term trends, short-term variations in paleowater depth are likely linked to global sea-level changes indicated by global oxygen isotopic variations.

Correlation of offshore seismic profiles with onshore New Jersey Miocene sediments

Abstract The New Jersey passive continental margin records the interaction of sequences and sea-level, although previous studies linking seismically defined sequences, borehole control, and global δ18O records were hindered by a seismic data gap on the inner-shelf. We describe new seismic data from the innermost New Jersey shelf that tie offshore seismic stratigraphy directly to onshore boreholes. These data link the onshore boreholes to existing seismic grids across the outer margin and to boreholes on the continental slope. Surfaces defined by age; facies, and log signature in the onshore boreholes at the base of sequences Kw2b, Kw2a, Kw1c, and Kw0 are now tied to seismic sequence boundaries m5s, m5.2s, m5.4s, and m6s, respectively, defined beneath the inner shelf. Sequence boundaries recognized in onshore boreholes and inner shelf seismic profiles apparently correlate with reflections m5, m5.2, m5.4, and m6, respectively, that were dated at slope boreholes during ODP Leg 150. We now recognize an additional sequence boundary beneath the shelf that we name m5.5s and correlate to the base of the onshore sequence Kw1b. The new seismic data image prograding Oligocene clinoforms beneath the inner shelf, consistent with the results from onshore boreholes. A land-based seismic profile crossing the Island Beach borehole reveals reflector geometries that we tie to Lower Miocene litho- and bio-facies in this borehole. These land-based seismic profiles image well-defined sequence boundaries, onlap and downlap truncations that correlate to Transgressive Systems Tracts (TST) and Highstand Systems Tracts (HST) identified in boreholes. Preliminary analysis of CH0698 data continues these system tract delineations across the inner shelf. The CH0698 seismic profiles tie seismically defined sequence boundaries with sequences identified by lithiologic and paleontologic criteria. Both can now be related to global δ18O increases and attendant glacioeustatic lowerings. This integration of core, log, and seismic character of mid-Tertiary sediments across the width of the New Jersey margin is a major step in the long-standing effort to evaluate the impact of glacioeustasy on siliciclastic sediments of a passive continental margin.

Pleistocene sequence stratigraphy of the shallow continental shelf, offshore New Jersey: Constraints of Integrated Ocean Drilling Program Leg 313 core holes

We used cores and logs from Integrated Ocean Drilling Program (IODP) Expedition 313 to generate biostratigraphic, lithofacies, biofacies, and geochemical data that constrain the ages and paleoenvironments of Pleistocene sequences. We integrate sequence stratigraphy on cores with new seismic stratigraphic data to interpret the Pleistocene history of the Hudson shelf valley and paleoenvironmental and sea-level changes on the inner to middle continental shelf. Improved age control compared to previous studies is provided by integrated calcareous nannofossil biostratigraphy, Sr isotopic stratigraphy, and amino acid racemization. We recognize four upper Pleistocene–Holocene sequences: sequence uP1 is correlated with Marine Isotope Chrons (MIC; “chron” is the correct stratigraphic term for a time unit, not “stage”) 7 or 5e, sequence uP2 with MIC 5c, sequence uP3 with MIC 5a, and sequence uP4 with the latest Pleistocene to Holocene (MIC 1–2). However, within our age resolution it is possible that sequences uP2 and uP3 correlate with MIC 4–3c and 3a, respectively, as suggested by previous studies. Lower Pleistocene sequences lP1 and lP2 likely correlate with peak interglacials (e.g., MIC 31 and MIC 45 or 47, respectively). Thus, we suggest that preservation of sequences occurs only during peak eustatic events (e.g., MIC 45 or 47, MIC 31, and MIC 5), unless they are preserved in eroded valleys. The architecture of the Pleistocene deposits at Sites M27 and M29 is one of thin remnants of highstand and transgressive systems tracts, with lowstand deposits only preserved in the thalwegs of incised valleys. Incised valleys at the bases of sequences uP3 (IODP Site M27) and uP2 (IODP Site M29) document more southward courses of the paleo–Hudson valley, compared to the more southeastward course of the MIC 1–2 paleo–Hudson valley. The patchy distribution of Pleistocene sequences beneath the New Jersey inner-middle continental shelf is due to low accommodation during an interval of large eustatic changes; this predicts that sequences in such settings will be discontinuous, patchy, and difficult to correlate, consistent with previous studies in Virginia and North Carolina.

Foreland crustal structure of the New York recess, northeastern United States

A new structural model for the northeast part of the Central Appalachian foreland and fold-and-thrust belt is based on detailed field mapping, geophysical data, and balanced cross-section analysis. The model demonstrates that the region contains a multiply deformed, parautochthonous fold-and-thrust system of Paleozoic age. Our interpretations differ from previous ones in which the entire region north of the Newark basin was considered to be allochthonous. The new interpretation requires a substantial decrease in Paleozoic tectonic shortening northeastward from adjacent parts of the Central Appalachian foreland and illustrates the common occurrence of backthrusting within the region. During early Paleozoic time northern New Jersey consisted of a Taconic orogenic foreland in which cover folds (F1) involved lower Paleozoic carbonate and flysch overlying Middle Proterozoic basement. F1 folds are open and upright in the foreland and more gently inclined to recumbent southeastward toward the trace of the Taconic allochthons. F1 structures were cut and transported by a fold-and-thrust system of the Alleghany orogeny. This thrust system mostly involves synthetic faults originating from a master decollement rooted in Proterozoic basement. Antithetic faults locally modify early synthetic overthrusts and S1 cleavage in lower Paleozoic cover and show out-of-sequence structural development. The synthetic parts of the regional thrust system are bounded in the northwestern foreland by blind antithetic faults interpreted from seismic-reflection data. This antithetic faulting probably represents Paleozoic reactivation of Late Proterozoic basement faults. Tectonic contraction in overlying cover occurred by wedge faulting where synthetic and antithetic components of the foreland fault system overlap. S2 cleavage in the Paleozoic cover stems from Alleghanian shortening and flattening and commonly occurs in the footwall of large overthrust sheets. Paleozoic structures in Proterozoic basement include fault blocks bounded by high-angle faults and low- to moderate-angle shear zones that locally produce overlying cover folds. Broad and open folds in basement probably reflect shear-zone displacement of subhorizontal foliation. Our cross-section interpretations require limited involvement of lower Paleozoic cover folds in the footwalls of major overthrust faults. Palinspastic restoration of F1 folds produces an arched passive-margin sequence. The tectonic contraction for the Valley and Ridge province and southeastern Pocono Plateau is about 25 km, and tectonic wedge angles are 8°–11°.

Fresh-water and salt-water distribution in passive margin sediments: Insights from Integrated Ocean Drilling Program Expedition 313 on the New Jersey Margin

On the New Jersey shelf (offshore North America), the presence of pore water fresher than seawater is known from a series of boreholes completed during the 1970s and 1980s. To account for this fresh water, a fi rst hypothesis involves possible present-day active dynamic connections with onshore aquifers, while a second involves meteoritic and/or sub- ice-sheet waters during periods of lowered sea level. Expedition 313 drilled three boreholes on the middle shelf, offering a unique opportunity for the internal structure of the siliciclastic system to be accessed, at scales ranging from the depositional matrix to the continental margin. This enables the stratigraphic architecture to be correlated with the spatial distribution and salinity of saturating fl uids. Expedition 313 revealed both very low salinities (<3 g/L) at depths exceeding 400 m below the seafl oor and evidence for a multilayered reservoir organization, with freshand/ or brackish-water intervals alternating vertically with salty intervals. In this study we present a revised distribution of the salinity beneath the middle shelf. Our observations suggest that the processes controlling salinity are strongly infl uenced by lithology, porosity, and permeability. Saltier pore waters generally occur in coarse-grained intervals and fresher pore waters occur in fi ne-grained intervals. The transition from fresher to saltier intervals is often marked by cemented horizons that probably act as permeability barriers. In the lowermost parts of two holes, the salinity varies independently of lithology, suggesting different mechanisms and/or sources of salinity. We present an interpretation of the sedimentary facies distribution, derived from core, logs, and seismic profi le analyses, that is used to discuss the marginscale two-dimensional reservoir geometry and permeability distribution. These proposed geometries are of primary importance when considering the possible pathways and emplacement mechanisms for the fresh and salty water below the New Jersey shelf.

Bedding attitudes as a sequence stratigraphy proxy: A case study from borehole images, Integrated Ocean Drilling Program Expedition 313, Site M28

In this study we investigate the relationship between the dips of seismic reflectors, which are used to define sequence boundaries, and the orientation (dip and dip direction) of bedding surfaces at core scales. Sequence boundaries from seismic data and lithostratigraphic boundaries from cores and logs are compared with the bedding orientations measured on borehole images of Miocene siliciclastic sediments at Integrated Ocean Drilling Program Expedition 313 Site M28. It is not surprising that bedding orientations show huge variations at scales that are too small to be detected on seismic profiles. However, changes of orientation defined as rotation between two successive intervals match the depths of approximately half of the seismic sequence boundaries. While they do not match boundaries between lithostratigraphic units, changes of orientation frequently correlate with maxima and minima in the gamma ray signal, suggesting that they are related to changes in depositional processes rather than to changes in lithology. This study suggests for the first time that bedding attitudes can be used as a stratigraphic tool at various scales from bed to bed across depth intervals of tens of meters.